9th Global Slag Conference 2013
10 - 11 December, Dubai, UAE

Reviewed by Dr Robert McCaffrey, Global Cement Magazine

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Video of the Global Slag Conference, Exhibition and Awards 2013

Global Slag 2013 - First day

Charles Zeynel of ZAG International started the conference with a global overview of slag trends. He suggested that organisations around the world are coming to the realisation that slag is a useful material, for example as a highway construction material, and that this will bolster the demand for the material. Global cement production is currently at around 3.7bn t and will double in size in the next ten years: there are increasing pressures towards environmental regulation and continued pressure to decrease costs and an increasing recognition that the costs and benefits of the use of supplementary cementitious materials (SCMs) are not currently balanced. Slag availability varies around the world – it is in plentiful supply in Europe, and in short supply in Asia. Mill scale is in very short supply and is being hoarded by the steel industry instead of being made available to the cement industry. Charlie pointed out that the US is a large resilient economy with high productivity and innovation, steady immigration and population growth, increasing energy independence and decreasing feedstock costs and increasing incentives for 'green' buildings. US cement capacity utilisation has grown from a low of 62% in 2010 to the nearly 90% forecast in 2014 – essentially at full capacity. GBFS is globally traded, originating in blast furnaces around the world and economically-transportable half way around the world. Japan is currently producing around 28Mt of GBFS, but no Japanese slag is available on the open market, due to the merger and rationalisation of Sumitomo and NSC, post-tsunami reconstruction and the 2020 Olympics in Japan. Charles concluded with news of ZAG's recent deal with Steag for the marketing of flyash originating in northern Europe.

David Roth of GPS Global Solutions gave a paper on steel slag processing. David pointed out that recycling plants typically crush air-cooled slag down to only <50mm, meaning that a large proportion of metals is not recovered. Given that stainless steel might be valued at $2600/t and even carbon steel might be $650/t, when limestone may be worth only $15 and slag products used as construction materials typically have a price of less than $100, it makes sense to make full recovery of the metals a priority. Aggressive sustainability, in David's mind, involves maximising metal recovery, crushing with controlled dust generation and maximising by-product value. He pointed out that there is as much metal in <50mm product as there is in >50mm product. He sought to defend slag-derived materials as product, stating that 'To be considered as a product, a material has to be used for a specific purpose, there has to be a market or demand for it, it should meet technical requirements and legislative standards and it should not have any deleterious health or environmental effects.' Slag-based products, he said, fulfilled all of these conditions and should be classified as a product. David introduced the Didion rotary tumbler, which can crush large lumps down to 3mm to maximise metal recovery and which can classify and produce materials in up to eight different material sizes in one process step.

Els Nagels next spoke about the use of software to provide a better understanding of slag properties. Els suggested the use of 'slag engineering' to optimise slag product characteristics. The controlling factors for slag characteristics are composition, temperature, and the composition and temperature histories or 'trajectories' of the slag. These factors will control liquidus (when the slag becomes fully liquid) and solidus (when the slag is fully solid) temperatures, equilibrium mineral phases, solid fractions, viscosity, and fluxing behaviour. The Spark software from InsPyro allows the input of a variety of slag properties and compositions and will model/forecast the corresponding output properties. The software is based on thermodynamic calculations involving the minimisation of the Gibbs free energy of the slag system, and also presuming that once solid phases are made in the slag that they do not then change composition – the cooling trajectory of the slag in this case can be important for the final mineralogical composition of the solidified slag. Enthalpy is also taken into account in the calculations, as is the calculated viscosity of the slag and Els said that the combination of physics and thermodynamics gives a good basis for forecasting slag properties. This knowledge and understanding can be used in slag engineering, R&D, process optimisation and daily reporting on slag quality.

At the start of the next session, on molten slag granulation, Kazuma Hagiwara of JFE Steel, Japan, presented the first of two papers on JFE's new slag solidification and heat recovery process, part of a programme to reduce CO₂ emissions from steel blast furnaces. Part of the programme is based on the use of hydrogen for iron ore reduction, with eventual CO₂ capture and storage. The new slag solidification process uses a pair of water-cooled copper rolls rotating at 5 - 10rpm to cool molten slag from 1600°C to less than 300°C to produce 3-20mm-thick slag 'plates' on an apron conveyor, which are then fed into a hot rotary hammer crusher and then into a heat recovery chamber consisting of a packed-bed with forced-air transfer at 50,000Nm³/hr. A conventional Kalina cycle (steam-based) process is used for waste heat recovery. Following heat recovery, fines are collected in a cyclone while the coarser fraction of the solidified slag is sent for further processing.

Yasutaka Ta of JFE Steel gave the second part of the paper, outlining results from the pilot plant. He pointed out that to recover CO² from a CO² absorbent, a large amount of energy is required – energy that is currently wasted in the steel making process, albeit at temperatures too low to be easily used. Mr Ta pointed out that to maximise the heat recovery, the heat transfer area of particles should be maximised by reducing their particle size to less than 5mm in thickness, whereas on the other hand, the slag needs to be coarser if it is eventually to be used as an aggregate. Thinner slag plates can be formed with a faster roll speed and this thinner form can give a heat recovery rate of over 30%.

Horst Kappes of the Paul Wurth company, Luxembourg, next spoke on dry slag granulation at a rate of 2.4t/minute. Historically, slag can be dumped and air-cooled, including high handling costs, sulphurous emissions and no heat recovery. More recently, the INBA slag wet granulation plant can produce a more valuable fine sand, reduced sulphurous emissions but with no energy recovery. Dry granulation, on the other hand, can produce a valuable dry product with the possibility of energy recovery. The discontinuous flow of slag from a blast furnace has to be transformed into a continuous energy output to be useable in a waste heat recovery process, while at the same time dealing with the changeable properties of the molten slag. In the new Paul Wurth process, cold steel balls are mixed with molten slag to create a cooled slag cake at a temperature of around 600°C. The slag is thus cooled rapidly (critically at a rate faster than the 20°C per second required for glass formation), producing a glass content of around 95%. A buffer storage area is used to even-out the process, with the slag cake being broken up rior to heat recovery. The grindability of this slag was found to be within the range of wet-granulated blast furnace slag, and the strength of mortars prepared from wet and dry granulated slags are comparable. Recooling of the steel balls is undertaken separately and is a significant rate-limiting step in the process. A conventional heat exchanger is used to produce steam at 15 bar and 325°C from the process. When used to produce electricity, the payback time is just over four years, and when used to produce direct energy in the form of hot air, the payback is just less than four years. The process has been used for BF, BOF, EAF and FeNi slags on an experimental scale.

A final paper in the session from Ian McDonald of Siemens VAI gave details on the new slag dry granulation process, developed in a joint venture with Voestalpine Stahl, the University of Leoben and the FEhS institute in Germany. He pointed out that air-cooling of molten slag equates to 1.5GJ of wasted energy per tonne of slag, or Euro3.5m of wasted energy based on a 6000t/d hot metal furnace. His company's answer for dry slag granulation is to pour the molten slag onto a rapidly-rotating metal alloy dish: the slag is spun off at high speed forming molten droplets which impact the walls of the granulator and which then fall onto a cooling bed fed with pressurised air – which can then be used for heat exchange and recovery. The produced granulated slag has >98% glass content and a grain size of 1 - 3mm and crucially is delivered in a dry state, with no contaminated water produced and limited emissions to atmosphere. Air is drawn from the granulating chamber at 600°C, either for electricity generation or for thermal preheating of fuel or raw materials. The cost of granulating the slag is lower than with a wet process granulator and the system has a lower capital cost than an equivalent-capacity wet granulation process. The produced particles are rounded, with no open pores and low closed porosity. Ian gave details of a new pilot plant at the Voestalpine Stahl Linz BF plant which will prove the technology on an industrial scale and which will be in operation in late 2014.

Tim Stanfield of Tube City IMS finally revealed 'the true identity' of steel slag – and pointed out that it is no good just changing the name of 'slag' – we have to change the perception of slag as a material. Tim pointed out the differences between recycled materials, by-products, co-products and products and concluded that cooled steel furnace slag is a co-product. Indeed, the USGS considers steel slag as a commodity. On the other hand, in the US regulation of slag typically falls under the aegis of state Bureaus of Waste Management – with the regulatory status of steel slag varying greatly from state to state, ranging from co-product, product, excluded from waste-regulations, or decided on a case-by-case basis. The National Slag Association in the US and steel makers came together starting in 2011, to try to have slag defined country-wide as a product: the ASTM already has standards for slag as a product, and the so-called Slag Coalition has decided to work with the ASTM and the European REACH regulations to promote this standpoint – of basing the specifications for slag as a product on the basis of the combination of mineralogical components and the lengthy history of the successful use of steel slag as a useful industrial material around the world. He concluded that steel slag is a 'product that is a result of the steel manufacturing process and is managed as an item of value in a controlled manner and not as a discarded material.' "Steel and slag companies" stated Tim, "must come together all over the world to promote steel slag as a product."

Global Slag Awards Dinner

Delegates had the opportunity to visit the viewing deck of the world's tallest building, the Burj Khalifa, prior to the Global Slag Awards Dinner at the Armani Hotel. The Global Slag Awards are presented on the basis of online nominations and votes, and registered the greatest number of votes so far for the awards. Global Slag 'plant of the year' went to Harsco's Taiyuan project in China, 'equipment supplier of the year' was awarded to Loesche, 'slag user of the year' went to Holcim and the Global Slag 'personality of the year' was awarded to Nick Jones of Harsco, a long-time supporter of the Global Slag Conference. USG was awarded the 'slag-based product of the year' award for its slag-based insulation, while Calumite LLC was awarded the 'technical innovation of the year' award for its slag-based glass.

Second day

Nick Jones of Harsco started the second day of the conference, looking at metal recovery from slag, specifically at a case study with Tisco Taiyuan Iron and Steel, 250km west of Beijing, the largest stainless steel producer in the world. Nick mentioned the 'Harsco Zero Waste Vision,' aiming to reuse or recycle all by-products wherever commercially viable. At the Taiyuan plant, the preexisting steel scrap recovery system did not recover all of the scrap in slag, and the slag was difficult to market since it still contained stainless steel. In addition, Tisco's on-site landfill became full and there was no option for off-site landfill. To solve the problem, Tisco and Harsco have entered into a 25 year JV to process steel and carbon steel slags to recover Fe, Ni and Cr and to produce valuable by-product fertiliser, cement and aggregate. The new recovery plant will process 1Mt of stainless steel slag and 400,000t of carbon steel slag each year and will eliminate landfill at the site. The recovery plant is situated on a large plot where stainless steel slag is wet-ground in ball mills, down to <1mm for maximum steel recovery. The stainless steel slag fertiliser was originally introduced for soil remediation, but with the addition of micronutrients it can be sold as a higher value product. The fertiliser has a high level of soluble silica, providing plants with resistance to heat stress and disease and also conferring increased insect resistance. The plant also manufactures 'Superfines' which is a cement additive manufactured from BOS steel slag, enhanced by fine grinding. Superfines-enhanced cement can be used in bridge construction, underground and marine applications and can be used in both common and higher performance concretes. Fineness is around 4000 - 5000Blaine, with metallic steel magnetically separated from the materials at various stages in the process. Superfines is capable of replacing up to 50% of GGBFS in blended cements, with no loss of strength and has a lower heat of hydration than GGBFS with less microcracking. The Tisco plant also makes a fully-recycled base for concrete or asphalt roads, composed of a steel slag aggregate bound with granulated steel slag and GGBFS, to make a slow-curing roadbase.

Fernando Duenas of Cemengal then introduced the Plug'n'Grind modular grinding plant concept for slag grinding. The components of the grinding plant can be transported anywhere in the world in only eight 40-foot shipping containers, allowing producers to follow and supply cement demand wherever it occurs. The time between order and delivery can be as short as eight months, and the installed plant – with simple civil works – can be operated with as few as four employees per shift. The Plug'n'Grind plant can produce ground slag at 7.5t/hr at 4000Blaine (78kWh/t total power), using its 500kW two-chamber ball mill. The integrated manual packing unit can produce 200 x 50kg bags per hour. For slag grinding, moisture content must be less than 1.5% which can be achieved with outside drying in the Middle East or with an external dryer. Increased production can be achieved with a grinding aid, at a rate up to around 9t/hr. Fernando gave some details of a slag grinding Plug'n'Grind installation for slag in Saudi Arabia.

Caroline Woywadt of Gebr. Pfeiffer next spoke about Vertical Roller Mill (VRM) grinding of granulated blast furnace slag. The company will celebrate its 150th birthday in 2014, having been founded in 1864. In 2011 the company sold the MVR 6700 C-6 mill, the largest-capacity cement and slag grinding mill in the world, with six 1920kW MultiDrives. Gebr. Pfeiffer's MVR mills are an improved version of its MPS VRM mills, with an increased number of rollers, use of roller suspension, a flat table, cylindrical rollers and a parallel grinding gap, the use of the MultiDrive concept with variable speed drives and built-in active redundancy. The mill is capable of drying, grinding and separating in one machine and also features a metal removal system. Caroline usefully pointed out that Blaine fineness systematically varies by around 10% according to whether it has been measured using ASTM or EN standards. For example 4500Blaine 'European' equates to around 3900Blaine 'American.'

Stefan Baaken of Loesche went on to speak about slag powder valorisation, specifically the conversion of steel slag into a highly reactive cementitious product. Loesche takes a slightly different approach to vertical roller mill technology from its competitors, using a smaller support roller to precompact the grinding bed, to allow the main roller to apply its full grinding force to the material bed. The company has installed 119 mills worldwide for GBFS grinding, many in China where steelworks will typically grind their own slag. As revealed at the Global Slag Conference in Las Vegas in 2012, Loesche is also in the process of building a steel slag grinding and carbonisation plant based on the SlagRec process – with more details to come soon. Loesche's newly-announced process for conversion of steel slag into a reactive cementitious product involves taking slag from the Linz-Donawitz process, and placing it into a converter for heat treatment: a recovered metal product is tapped-off and the remaining low-metal calcareous slag with higher alite and reduced belite content carefully cooled to produce a modified steel slag that can be ground in a Loesche VRM to produce a high-quality metal fraction and a reactive cementitious material. The modified slag, at a proportion of 30% with OPC, has a lower early strength but at 28 days has a higher compressive strength than 100% OPC. The company has so far conducted tests on a laboratory scale, and has now entered into an agreement with Siemens VAI of Linz, Austria to proceed to a pilot-scale plant.

Christoph Pichler of the University of Leoben, Austria, spoke about the use of slags remaining from metals recovery processes, both ferrous and non-ferrous slags. Christoph pointed out that electric arc furnaces produce around 9Mt/y of EAF dust, the majority of which is currently landfilled. However, this dust has a zinc content of around 20%, alongside a lead content of 2 - 7% and an iron content of 18 - 35%. A Waelz kiln can be used to oxidise zinc in the dust, leaving behind a recycling slag with zinc content of 5-9% and FeO content of 35 - 40%. This recycling slag can then be further reacted in a rotary slag smelting furnace or a metal bath process, where a reducing agent such as coke or charcoal is added to reduce Fe and Zn to recoverable oxides. The process produces an iron scrap, a zinc-rich filter dust and a residual slag that could possibly be used as a clinker raw meal replacement material due to its high CaO content.

In the penultimate session of the conference, on the use of granulated slag as a cement additive, Manish Wani of UltraTech Cement India spoke on the use of quadruple blends (cement, flyash, slag and ultra-fine slag) to produce mass concrete for high rise buildings. In mass concrete, it is important to dissipate or reduce the exothermic heat of hydration, which may otherwise lead to thermal stresses and cracking, with reduced compressive strength. For high-strength concrete, this cracking must be avoided, potentially through careful mix design. At the same time, concrete flowability and pumpability must not be adversely affected, while maintaining high compressive strengths and sufficient early strengths. Knowing the characteristics of the individual components in the mix goes some way to allowing the forecast of the final mix performance, but components can also interact in the final mix in unexpected ways. Careful testing of final mixes must be undertaken to ensure performance in place.

Anil Parashar of the Binani Cement Factory, Dubai, next spoke about NanoFine, a slag-based high performance cementitious binder. Binani Cement in Dubai is based in the Jebel Ali free port and is the largest clinker grinding plant in the UEA, with a capacity of 2Mt/yr using three ball mills. NanoFine, despite its name, actually occupies a niche between the nano- and micro-scales, and is based on GBFS, with addition of around 10% of a mix of other materials. The material has a fineness of 8 - 9000Blaine, or 30% below 1micron, with a reactive phase of above 90%. Addition of NanoFine to OPC actually increases the compressive strength at all testing stages by around 60%, partly through the mechanism of efficient particle packing and densification of concrete.

David Ball of the David Ball Group plc spoke about 'the beauty' of no-cement concrete. David introduced 'Cemfree,' ultra-low carbon concrete and cementitious materials containing no OPC. Cemfree is a composite material composed of GGBFS and pulverised fly ash (PFA) activated by a patented proprietary activator. Use of Cemfree leads to low heat of hydration, acid and sulphate resistance, low water permeability, low water demand and a light-coloured concrete. As an example of high-slag cement use, David mentioned the continuous pour of the 5600m³ 3m-thick foundation high-slag concrete slab of the UK's tallest building, the Shard, which had a temperature rise of only 7°C.

In the final session on slag product applications, ^{Pouyan Naseri of the Pasargad Steel Complex} in Iran spoke about the use of EAF slag to control acid mine drainage. Acid mine drainage forms where sulphide minerals such as pyrite and Marcasite are placed in oxidising surroundings. AMD is characterised by acidity, raised levels of sulphides and elevated concentrations of dissolved metals. The selection of the most effective AMD control system depends on the initial pH level, effluent water composition, available resources and budgets, and it is sometimes required to combine active and passive control systems. Steel slag yields hundreds of times more alkalinity than limestone, and the neutralisation potential of steel slags exceeds both lime and hydrated lime and for longer periods of time. Pouyan outlined an experiment to demonstrate the effectiveness of Pasargad steel slag for acid mine drainage remediation, using a down-flowing circulation of acid liquids through a column of slag with measurement of pH levels over 60 days. It was found that precipitation of iron, aluminium and manganese hydroxides can lead to the clogging of surface pores of the slag and reduction of slag activity. During the experiment, the ability of the slag to reduce acidity decreased as fine slag particles were dissolved: the ability of the slag to retain its activity depended on a continuing fresh supply of active surfaces and particles, which can be provided by having a wide range of particle sizes in the slag.

At the end of the presentation programme, delegates split into four discussion groups to further examine trading opportunities, slag optimisation, grinding technologies and slag applications. This 'Global Slag Exchange' session was greatly enjoyed and valued by the delegates.

Farewell and prize-giving

At the farewell party on the last evening of the conference, a number of awards were presented after delegates voted for their favourite presentations. Stefan Baaken of Loesche was in third place for his paper on steel slag processing to produce a cementitious product, while Ian McDonald's paper on Siemens VAI's dry slag granulation process was in second place. The winner of the best presentation award, however, was David Ball of the David Ball Group, for his eloquent paper on 'no-cement concrete.'

Delegates rated the conference very highly in all categories, and agreed that it had been one of the best-ever Global Slag Conferences:

• 'I loved the breakout at the end – very informative.'

• 'The discussion in small groups is very useful.'

• 'Good conference!'

• 'Good mix of steel producers, cement producers and suppliers.'

• 'The Global Slag Exchange was interesting and should be built upon at future events.'

It was announced at the event that the next Global Slag Conference – the 10th – will take place in Aachen, Germany, on 8 - 9 December 2014. We look forward to seeing you there!

10th Global Slag Conference, Exhibition & Awards 2014
8 - 9 December, Aachen, Germany

Reviewed by Dr Robert McCaffrey, Global Cement Magazine

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The 10th Global Slag Conference, Exhibition and Awards 2014 have successfully taken place in Aachen, Germany, attracting 170 delegates from 35 countries to attend 16 presentations and more than 12 hours of networking and business opportunities, including 12 exhibitors. The 11th Global Slag Conference will take place in November 2015 in Bangkok, Thailand.

Welcome!

On the evening before the conference, the 10th Global Slag Conference started off with a convivial welcome party in the event's exhibition area, which was graced with 12 slag industry supplier-exhibitors.

Conference first day

After a welcome to the conference from the event convenor Robert McCaffrey, the first speaker, Charlie Zeynel of ZAG International, started the conference by saying that we are just entering into a major boom in the cement industry. Charlie pointed out that the global cement scene has changed a great deal since the first Global Slag Conference in Düsseldorf in 2005. Chinese companies have burst into the global top ten cement producers, while the European cement companies have been fighting back through mergers and acquisitions. Slag supply and demand have shifted over the decade and now slag products are in increased demand. Charlie suggested that the US will become the largest importer of raw materials over the next decade. Indeed, imports are set to resume in 2015, mostly into the Gulf Coast, with 10Mt set to be landed in 2015, and 20Mt/year expected by 2020 (possibly more if environmental regulations lead to plant shutdowns in the US). Other supplementary cementitious materials (SCMs) such as flyash, are set to be sucked in at the same time.

Africa's population is set to double over the next couple of decades and will be a 'great place to be,' in terms of business and trade, according to Charlie. At the same time, China has a huge 'overhang' of production capacity, equal perhaps to 1.6t of cement production capacity per person per year, compared to a long term average demand in developed countries of around 500kg per person. Along with Europe, we could see a 'Japan-like' rationalisation of production capacity, with capacity being cut by around 50% over as little as a decade. Charlie reminded delegates that ten countries control 96% of blast furnace iron production worldwide, with a total of around 361Mt of slag produced, but with only 273Mt of slag being granulated. Blast furnace production capacity expansion is slowing, as mini-mills replace integrated blast furnace complexes. The reactivity of granulated blast furnace slag (GBFS) varies around the world, according to the source. Charlie underlined the fact that the global supply of slag products and of fly ash is insufficient to meet global demand.

Next, Michael Connolly of Tube City IMS showed delegates a video extolling the virtues of slag products. He said that Nebraska had legislated so that slag which is not 'discarded' is now regarded as a product rather than as a waste. Tennessee and Iowa have both followed along the same regulatory path, with additional states being targeted for similar legislation including South Carolina, Indiana and Texas. The regulatory trend in the US seems to be to try to ensure that cooled-slag and slag products are classified as products rather than as by-products or as waste, and also to specify product characteristics and performance to ensure that slag products can compete with other building materials. Ohio has stipulated that, in essence, if a material is treated like a waste, then it is a waste; If, on the other hand, it is treated as a valuable resource, and is managed as such, then it can be classified as a co-product. Michael concluded that the treatment of cooled-slag or slag products varies from state to state, but that the best way forward is to work with state legislators to ensure that slag products are classified as products rather than as waste. Manganese has come into the sights of legislators and the slag products industry is fighting legislation on this on a number of fronts.

Winnie Matthes of Holcim Technology spoke about Holcim's long history of the use of slag products in the cement industry. In 1995 Holcim had a clinker factor of over 80%, but this is now lower than 70%, partly thanks to increasing use of slag but also due to the use of other SCMs. The company makes a variety of products with varying amounts of slag substitution, from low-slag with elevated early strengths, to higher slag contents with improved workability, lower heat of hydration, increased late strength, improved ASR and chemical resistance and a lighter colour but with lower early strengths. Robusto (slag and burnt oil shale), Opticeo (cement, slag and silica fume - Opticeo is a CEM II/A-S (slag composite cement) - offered as an alternative to the conventional solution of OPC + silica fume) and Spinor (slag-based finely-ground micro-cements for oilwell cementing and ground rehabilitation) are just three of the new slag-containing products from Holcim. Winnie pointed out that the higher the content of GBFS in the product, the higher the effect on performance of the quality of the GBFS.

Slag from different regions in the world varies in general composition, with slag from Asia being high in alumina, slag from North America being low alumina and Russian and Eastern European slags tending to have low alumina and with C/S being medium to high. With increasing C/S ratio, the strength of the final product tends to increase. Elevated levels of titanium, Winnie said, should be considered as deleterious to cement strength, so that Ti concentration should be reduced to as low a level as possible in the GBFS, also given that higher Ti levels lead to lower grindability of the granulated slag. Glass content, chloride content, bulk density, moisture content, loss on ignition and the state of prehydration are all important factors influencing granulated slag quality. Lower granulated slag quality tends to increase cement production cost, through adjustment of cement composition, blending, the use of additives and possible pre-treatment of the GBFS before use.

SK Khoo of ZAG International spoke about short and long term drivers of freight rates influencing the costs of international SCM trade. He pointed out that China is rapidly reaching a crisis point in its economy, including an ongoing collapse in house prices, which may lead to a rapid reduction in the amount of freight capacity that is required to service the country. India is having to import more coal, due to the inefficiency and bureaucracy of its own coal industry. SK told delegates that a large number of new ships is on order, and that they are going to be larger ships than in the past. The average age of a ship when it is scrapped is also coming down, due to the oversupply in the freight market. In the 20 years to 2008, shipowners added 200Mt of shipping capacity, whereas 200Mt was added to the global freight fleet in just four years, in the period 2008-2012. A reduction in slow steaming (due to the fall in fuel prices) has also effectively added to the availability of freight capacity. This imbalance in supply and demand has led to a near-collapse in the profitability of freight operators, but on the other hand the cost of shipping materials over considerable distances has reduced for producers, shippers and users.

Sander Arnout of InsPyro, a Belgian university spin off, spoke about the feasibility of re-melting for the recovery of metal and to upgrade slag. Sander spoke about his company's thermodynamic approach to process modelling, which is not just based on theory, but which also includes 'real-world' lessons from practical process technology. The slag melting and crystallisation model can take input compositions and can then predict - with a given cooling profile - compositions and mineralogy of the resultant cooled slag. The validation of the models using real-world slag sampling is crucial.

Stefan Baaken spoke about the latest Loesche technologies for processing by-products from the steel industry. Stefan spoke about a new installation at the Charleroi plant in Belgium which takes pre-crushed stainless steel slag and grinds it in a specially-modified Loesche mill, to liberate even fine particles of stainless steel enclosed by slag. The mill produces a fine slag-based mineral filler product and a very high purity metal recovery fraction. The plant has a capacity of 20t/hr, with a feedstock of 3-15% stainless steel, and it produces a stainless steel raw material product with a metal content of 90%. The fine filler is mixed with water and additives, moulded into the appropriate form such as blocks or kerb stones, and is then processed in an autoclave to create high specification 'CarbStone' building materials.

In the second part of his presentation, Stefan spoke about the co-grinding of GBFS and concrete rubble in a Loesche mill, the aim being to disaggregate the inputs to create aggregates at least equal in quality to natural aggregates. The waste material needs to be pre-crushed and the rebar removed, along with other contaminants. The material is ground in a specially-adapted Loesche mill, which effectively separates out the cement component to produce a dry powder of 4500-5000 Blaine. Gravel and sand are produced as a 'reject' fraction, which after classification can be used as products or fed back into the mill for further processing. The recycled aggregate lends a higher strength to produced concretes compared to the use of natural aggregate, possibly due to crystallisation promotion through a fine coating of cement minerals of the recycled gravels. The finely-ground cement filler powder produced by the mill can be used as a filler for concrete.

In the third part of his presentation, Stefan spoke about the processing of LD steel slag to a highly reactive cement component and recovery of metal. Three steps are used to optimise the final product: a thermal phase is used to react the remaining metal in the hot slag to a more useable phase, which at the same time optimises the composition of the slag towards a more reactive set of phases akin to the composition of clinker - with alite increasing and belite, C4AF and amorphous phases decreasing. A dry granulation process is used to optimise the crystal structure of the product and to allow energy recovery, and finally the milling process increases the reactive surface area of the product and allows a final fine separation of metal content. Mortar tests show that the new clinker replacement material provides equivalent or higher strengths compared to OPC, particularly when the clinker replacement material is finely ground. Stefan concluded by stating that the next step is to find a parent for a prototype installation.

In the first of a pair of presentations both on the topic of dry slag granulation, Ian McDonald of Siemens VAI Metals Technologies spoke about his company's project to recoup the 1.5Gj of heat energy in each tonne of hot blast furnace slag. The solution is to pour molten slag onto a spinning cup, with the air in the chamber heated to 600°C by the cooling slag and then subject to heat exchange for steam generation and power production. The slag cools quickly in the cooling chamber and the aim is to produce at least 98% glass phase, with granulate size of 1-3mm and in a dry state. Ian pointed out the cost reduction in dry slag granulation compared to wet slag granulation. He also described a 'eureka moment' of realisation that the molten slag droplets in the cooler could still be allowed to be molten when they hit the water-cooled wall of the cooling vessels: The impacting droplets would be distorted but would reform as droplets due to surface tension, while still not being hot enough to agglomerate and instead to form a granular material of mostly between 1-3mm. The technology will be proven in a pilot plant at the VoestalpineStahl Linz blast furnace, which is currently under construction and which is due to come into operation in late 2015.

In the second paper on dry granulation, Daniel Michels of Paul Wurth spoke about his own company's unique approach to dry slag granulation. The company's INBA slag granulation plant, common around the world, uses water for granulation and has no energy recovery. Dry slag granulation saves the 700kg of water per cooled tonne of slag, but is also able to recover energy from the slag and at the same time reduce sulphurous emissions. Dry slag granulation saves on transportation costs owing to the dry product, involves no drying at the cement factory, the dry granules do not freeze in winter thanks to low water content and the granulated slag has a higher bulk density (1.3-1.4t/m3) than water-cooled granulated slag (1.0-1.1t/m3). All blast furnace dry slag granulation technologies must cope with surges in slag volumes and the new technology from Paul Wurth is able to do this. In the Paul Wurth technology, cold steel balls are tipped into the molten slag which is contained in large moulds, which leads to a fast cooling of the slag, down to 650°C within 30 seconds. The mixed balls and hot but not molten slag are placed into a buffer vessel which is used to heat air for heat exchange. The mix is then crushed and the slag balls separated out using magnets, with the steel balls then reused. Grindability of the produced granulated slag is akin to water-cooled slag, the glass content is generally above 95% and the compression strength of BF slag cements produced with the dry granulated slag is the same as cements made with water-cooled slags.

The first phase of a pilot plant was built at Dillinger Hütte BF 4, coming into operation in November 2013, but excluding the waste heat recovery phase. Daniel showed an impressive video of the plant in operation and mentioned that the process is appropriate for BF, BOF, EAF and FeNi slags. At the moment the vitrification rate from the process is still too low at around 90%, partly due to heat losses in the 35m-long slag runner. Once these issues have been addressed, the waste heat recovery phase of the pilot project will be undertaken.

Gala Dinner and Global Slag Awards

In the evening of the first day of the conference, delegates were transported by coach to Chateau Neercanne, literally right on the border between Belgium and Netherlands, to enjoy an evening of music, networking, fine wines, business and superb cuisine. During the evening, the Global Slag Awards were presented, after a two-stage on-line nomination and voting process which was open to all participants in the global slag industry. Slag company of the year was Tata Steel; Slag user of the year was Holcim; Equipment supplier of the year was Loesche; Slag plant of the year was the Calvert, Alabama, plant of Tube City IMS; Slag product of the year was heavily-bound EAF steel slag ER-MB20 road-base from SCE Materials and Recycling in Australia; the technical innovation of the year was the dry slag granulation and energy recovery process from Paul Wurth and finally the Global Slag personality of the year was a surprised and delighted David Ball, chairman of the David Ball Group, Cambridge. Slag discussions continued late into the night back at the hotel bar.

Second day

On the second day of the conference, Anil Parashar of Binani Cement in Dubai spoke about his company's management of slag. Binani Cement was the first company to grind slag in the UAE, back in 1999, as a contract grinder. Now the company grinds and markets GGBFS in the UAE and it accounts for around 30% of the market volume. Binani's production is expected to amount to 500,000t of GGBFS product within the next two or three years. The plant in Dubai operates three ball mills with a combined grinding capacity of 2Mt per year. The company faces a number of challenges, including slag storage, increasing slag prices and competitive pressures. Anil pointed out that the ball mills produce practically half the tonnage when grinding slag when compared to grinding OPC clinker. The factory has a constrained area for slag storage, particularly after a portion of the factory's land was appropriated by the Dubai municipality. Slag prices have increased by approximately 30% over the last two years, particularly for quality slag from Japan. Anil stated that the construction materials market in the UAE totally collapsed after 2008, but that it is coming back slowly, starting in 2012. The company has switched its production to its largest ball mill to achieve economies of scale and sufficient production tonnage. The company now also blends Japanese, Indian and Chinese slags, although the Japanese slags form the basis of the mix, with a maximum of 25% of other GBF slags. Some Indian slags were approaching Japanese slags in terms of reactivity. The plant had found that the use of a hot air generator was costing the equivalent of $7/t of slag ground, so that since 2012, the use of the generator was banned: the plant has coped nonetheless, albeit at lower production capacity.

Anil concluded that a variety of infrastructure projects in the Gulf States will continue to boost cement demand. In order to cope with future expected increases in demand, the Binani Cement Factory is considering the installation of a roller press for pre-grinding, with an investment of around US$8m and a payback time of 48 months. Anil repeatedly lamented the fact that the company had bought ball mills instead of vertical roller mills, but he shrugged and concluded, "We are where we are."

Rudolf Schulze of technical representative company Schulze & Partner spoke about the use of ACT's EcoSafe fire-resistant HFDU hydraulic fluid for slag and steel mill equipment. EcoSafe is a fully-synthetic fluid on a butol base, with lubricity over a wide temperature range, from -45°C to around 150°C, which can be used for slag-handling vehicles.

Caroline Woywadt of Gebr. Pfeiffer then spoke about her company's solutions for slag grinding. The grindability of a slag is controlled by many factors, including the mineralogy of the slag, the glass content and the weathering extent of the slag. The company still needs to undertake trial grinds of large (1000kg) samples to characterise the materials before proposing a design for a vertical roller mill. The company uses smaller scale mills for its tests, which require the test samples to be pre-crushed 'to scale'. The test mill can determine the throughput, the friction factor, the absorbed power and specific power consumption, the wear rate, dust load at the classifier and the range of fineness for all materials. The test results from the small test mills are continuously compared to results from full scale mills in order to validate the scaling of results. Caroline showed the construction of a major cement and slag grinding mill in Australia, with a guaranteed throughout of 190t/h at residual moisture of 0.5% and Blaine4200.

Franz Muschaweck of Dalog pointed out that every third VRM gearbox of above 2000kW is currently destined to fail, but that condition monitoring can avoid early gearbox failure and also allow production optimisation through the diagnosis of a variety of equipment anomalies such as a cracked table liner.

Emad Ewais of the Refractory and Ceramic Materials Division of the Central Metallurgical Research and Development Institute of Egypt next spoke about the conversion of slag into a ceramic foam as a new feedstock for industry, through a simple rapid quenching technique. He pointed out that some slags accord to the composition of highly valuable calcium aluminate cements, and with higher levels of manganese they trend towards highly valuable ceramic materials. Emad has created a brittle low-density amorphous foam-like ceramic material from slag, with many possible industrial applications, including as a raw material for insulating bricks or as monolithic castables.

The next presentation came from Muhammad Kalimur Rahman of the King Fahd University of Petroleum and Minerals from Dhahran, Saudi Arabia, who spoke on the use of slag cement in mass concrete blocks subject to marine environments. He pointed out that the development of microcracks in the young concrete - due to volume changes caused by hydration - create pathways for chloride and sulphate ingress and eventual reinforcement failure. Seawater in the Gulf has very high salinity, and temperatures are extreme, leading to short durability of reinforced concrete structures, partly due to corrosion of rebar. The King Abdullah Cultural Centre is to be built on reclaimed land, and concrete for the project is required to be highly sulphate- and chloride-resistant. Of course, slag cement, microsilica, flyash and corrosion inhibiting additives can all be used to mitigate this harsh environment. In one model, the use of 65% BFS compared to a zero BFS cement, the service life of the concrete jumped from a calculated three years to 22 years, due to reduction in microcracking, partly due to a lower heat of hydration, and subsequent chemical ingress and corrosion. Mohammad said that it was important to insulate the top and sides of castings to prevent the formation of cracking due to thermal gradient formation.

David Ball of the David Ball Group, Cambridge, spoke about using slag to reduce concrete's carbon legacy in the built environment. David's company manufactures CemFree binder through the blending of GGBFS and/or PFA with a lime-based proprietary patented activator. The CemFree binder can be used as a replacement for the OPC in structural concrete mix designs. The new binder has a number of advantages over OPC, according to David, including having negligible associated CO2 emission, enhanced long-term durability of concrete structures, a reduced requirement for steel reinforcement, low water demand, a reduced number of required joints in large areas and high volume jobs, and increased thermal mass due to higher density of concrete, all the time making use of existing concrete industry infrastructure and practices.

Marc Fixaris of ArcelorMittal finished the speaker programme at the conference by speaking about the use of converter and secondary metallurgical slags as liming agents for the control of soil pH, and as the supplier of silica and micronutrients for agricultural applications. Basic Oxygen Furnace steel slag is already used as a soil improvement agent, for example in the UK, to aggregate fine soil particles, to help nitrogen-fixation, to increase crop fungal resistance and to increase yields through phosphorous absorption. Marc reminded delegates that the chemistry of the slag is important to determine its efficacy as a soil improver. To use the slags as a soil improver, a very finely-ground material must be used, typically after screening and grinding with a roller press, for example in France to 96% below 630µm and 75% less than 160µm. A number of countries have been identified with market development potential, including Spain, Ukraine, Romania, Kazakhstan, South Africa and Brazil.

Farewell and prizes

At the conference farewell party a number of prizes were awarded the first of which went to Sennebogen for the best exhibition stand. David Ball came third in the best presentation awards, with Winnie Matthes of Holcim the runner-up. However, the first prize went to Charlie Zeynel for his update and overview on the global slag industry.

What the delegates said in 2014

• The organisation and time schedule was perfect - well done.
• Well done! A great event.
• Great team. Thanks a lot. Merci beaucoup.
• All good - format very balanced. Keep up the good work.
• Great conference!!!
• Very good quality of the conference overall.
• Good job.
• Good show.
• This is a must-attend for a cement company, I need to attend it all the time.
• Networking opportunities were directed perfectly, with meet the delegates and speed dating session, lunches, gala dinner, etc.
• Thank you. Overall, it was a very productive and focussed conference.
• Very friendly 'family' atmosphere.

11th Global Slag Conference, Exhibition & Awards 2016
24 - 25 May 2016, London, UK

Reviewed by Dr Robert McCaffrey, Global Cement Magazine

Image gallery for the 10th Global Slag Conference 2016 (large gallery - may take time to load)

The 11th Global Slag Conference has successfully taken place in London, with 110 delegates from 24 countries in attendance. Sixteen presentations were given over two days, and the next Global Slag Conference will take place in Duesseldorf in May 2017.

Paul Mullins of Kallanish Commodities opened the 11th Global Slag Conference in London with an overview of trends in the global steel industry. Global steel production peaked in 2014 at 1.6bn tonnes, with Asia producing around 60% of the total: China produced 800Mt of this total. Japan, India, the USA, South Korea and Russia are also top producers. Demand is currently depressed in China, the USA, Russia and Brazil, but forecasts suggest that demand will increase through to 2017. Paul suggested that the ASEAN nations will see 5 - 7% per year growth over the next few years. China is still growing, officially at 6.5 - 7% per year, but steel demand is expected to fall by 3% in 2016 and 4% in 2017, due to the fact that the steel intensity of infrastructure development is falling. In addition, many cities around China have massive overstocks of housing supply, meaning that construction will slump, leading to further weakening in demand. Lower prices and weaker domestic demand has meant that a tide of Chinese steel has swept out of the country and onto the export markets. Beijing is now committed to reducing steel production capacity by up to 150Mt by 2020, although excess capacity is already currently estimated at 325 - 400Mt. A controlled stream of managed closures is not expected to impact the national economy, since much of the excess capacity is already effectively mothballed. Having said that, central edicts do not always work in China: "The mountains are high and the Emperor is far away," commented Paul. China's real aim it to build bigger, more efficient and less polluting steel production, not only to supply its own demands, but also to go out and conquer the rest of world. China is likely to export over 110Mt of steel each year, more steel than Japan produces overall. Paul suggested that NAFTA markets will be robust in the next couple of years, with construction enjoying low but steady growth. Falling oil prices have hit the Middle East, with both steel- and cement-intensive infrastructure weakening, but there has been a recovery in a number of other industries. Paul is extremely bullish on prospects for Iran. Trade and anti-dumping tariffs around the world have increased dramatically in the last few years, but end-user resentment means that there is also pressure against tariffs.

The second speaker at the conference, Charles Zeynel of ZAG International, started by saying that the 1.6bn tonnes of iron and steel production worldwide produces around 250Mt of slag. Charlie contrasted the outlook from the last Global Slag Conference in December 2014, when things were looking rosy in terms of both supply and demand, with the situation today. The fact is that the Chinese 'overhang' has depressed prices around the world and has led to widespread steel company losses. Demand for cementitious materials is still strong, even though cement demand growth has slowed to perhaps 1 - 2% per year. Charlie dated the moment of Chinese oversupply hitting the world markets to October 2015, causing the traded price of cement to drop by around $10/t to $40/t. Freight rates have dropped to incomprehensibly low levels, but a correction in shipbuilding is now taking place, so that the bottom is 'surely here.' Charlie concluded that the time of SCMs is here, including GBFS, flyash and FGD gypsum. The supply of blast furnace slag is actually reducing, as blast furnaces around the world are closed, and as the world converts to mini-mills and electric arc furnaces for smaller scale steel production and for steel recycling. The supply of GBFS is not expected to grow significantly: "There is not enough slag to go around and that's why cement companies have been busy locking in supplies over the last ten years." Japanese slag is of very high quality, but is now only available on allocation, and prices are rising. "I would not touch 95% of the slag that comes out of China, due to its variable quality, particularly from state-owned companies, while pricing policies can change practically from day to day," concluded Charlie Zeynel.

Sunghee Han, a senior manager at POSCO of South Korea, next gave an overview of slag markets in Korea. The country is the fifth largest steel producer in the world, with three integrated steelworks with a total of 71Mt of crude steel capacity, with the both the largest and second largest single-site steel plants in the world. Cement consumption is expected to decrease from current levels by about 10% by 2020, while GBFS supply is expected to increase due to increases in steel production. Housing construction is a major driver of cement demand, but this has been driven in the recent past by government policies rather than by market demand. In fact, 86% of Korean slag is granulated, with only 14% being air-cooled. A total of 13.9Mt of GBFS is produced in Korea each year, with 2.9% used for rice cultivation as a calcium silicate fertiliser, while the rest is used in the cement and concrete industry. There are four companies that are 'pure' GBFS players, that take the raw materials, grind it and then sell it on to cement companies. Grade I GBFS for use in concrete in Korea has Blaine of up to 8000, with lower grades ranging down to 4000 Blaine.  POSCO expects a surplus of slag in the near future and is interested to find new applications for slag products. The climate of Korea presents challenges for slag use, being hot in the summer and very cold in the winter. The addition of activators to slag cement may improve early-strength gain and reduce cracking: Posment is an alkali-activator primarily made from a byproduct of the steel-making process that addresses these current weaknesses in slag-based cements. Posment is currently being used for concrete for the construction of high-rise towers in Korea.

The next speaker was Rajan Ramaswamy of OCL India, who gave an overview of slag supply and demand in India. The country produces 16Mt of slag each year, but does not currently use all of this material, the rest being either exports or 'sent to stockpile.' Rajan suggested that the Indian economy has a huge potential for growth. The Dalmia Bharat Group of which OCL is a part, is concentrated on the east coast of the country and has more than 25Mt of cement production capacity. The company has a target to reduce its clinker factor to a minimum through the use of flyash and slag. There is a trend towards the use of a higher proportion of LD  and BOF slags.

Anil Parashar of Cem Consult next spoke about the growth of slag in the GCC region. The region is currently looking at an oversupply of around 30Mt of cement per year. The consumption of silica fume and flyash  in the region has dropped, but GGBS consumption has grown. For example, the consumption of GBFS in the UAE has grown from just over 1Mt in 2012, to reach 3Mt in 2016, while the number of grinding plants has risen from 7 to 12. There are no blast furnaces in the GCC, so that all slag is imported. Japan has previously been the major source, but this is progressively changing over to Chinese slag. Regulatory changes are partly driving slag demand: The Dubai municipality has stipulated that concrete used in local infrastructure must contain significant quantities of SCMs. In addition, concrete with SCMs tends to have improved field performance in the countries of the GCC due to the challenging climate. Challenges to the increased use of slag in the GCC include the current design of grinding systems installed in the area, since grinding slag typically decreases the throughput rate of a mill previously used only for cement. Anil suggested that the addition of a roller grinder as a pre-grinding circuit can sufficiently increase capacity. At the same time, pre-drying of the slag may also be required, even in the GCC. The grinding capacity of the UAE is large enough to cater for the demand for the whole GCC, although there is currently a lack of adequate terminals for the material. There is also a trend towards the concept of 'captive production,' when ready-mixed producers own their own slag grinding units. Anil concluded that mega-projects like the Dubai Expo 2020 and the World Cup in Qatar will boost cement and slag demand in the GCC in the next few years.

In the second session of the conference, on slag and slag technology, Ian McDonald of Primetals Technologies Ltd spoke about dry slag granulation with waste heat recovery. Ian pointed out that each tonne of slag dumped for air-cooling represents 1.5GJ of wasted unrecovered energy, equal to around Euro3.5m for a 6000t/d furnace. Ian gave details of a process whereby molten slag falls onto a spinning cup and is spun out to impinge on a water-cooled receptacle wall: the granulated slag bed is then aerated, and the heated air can be used for heat recovery. The produced granulated slag has zero moisture, but due to its low porosity it has a low tendency to take onboard additional moisture, up to a maximum of around 2%. A pilot plant at the University of Leoben showed a glass content of 98%, with granules of 1 - 3mm, with particle size controlled by the speed of rotation of the spinning cup. An industrial-sized pilot plant is under construction at the VoestAlpineStahl Linz blast furnace, fed directly from a slag runner, and is expected to be commissioned in January 2017. The unit will finally accept full slag flow of 2t/min, with a maximum of 6t/minute.

Derek Schussele of Dust Control Technology, Inc. spoke about atomized mist dust-suppression for steel torching and slag generation plants. Spraying water onto dust sources increases its weight and cohesion and suppresses dust, but too much water can be destructive. Fine droplets sprayed into the air can entrap dust particles, and may be used with surfactants and foams to improve performance. Water droplets that are much larger than dust particles will tend to cause dust to pass around them in a slipstream effect, whereas the best dust capture will occur when the droplet size is the same as the dust size, such as atomised water droplets. Dust Boss offers a ducted fan solution that has a 'throw' of up to 100m with low water puddling. The cool down time of refractory bricks can be reduced with the use of a Dust Boss atomised water ducted fan.

Mark Tilley of Lixivia Inc. next told delegates about the use of stabilised BOF and ladle slag for use as fillers in cement. Lixivia's offering is the separation and purification of calcium from lime in slag using the 'Selex' closed-loop ion-exchange chemical leaching approach, which generates a more stable aggregate material, as well as producing valuable purified calcium products such as precipitated calcium carbonate, magnesium oxide and rare earths and at the same time sequestering carbon dioxide. The company is currently at the laboratory scale, but is preparing for a scale-up stage.

The final presentation of the day was given by Frank Dardemann of Loesche, who spoke about the mobilisation of hydraulically active phases in slag by producing ultra fine materials. Frank stated that the huge amounts of steel slag around the world are essentially unreactive. LD Linz-Donawitz slags are essentially the same as BOF slag, and the basis of the research was the realisation that there was a high proportion of potentially reactive mineral phases, principally belite, in the solidified slags. Frank gave details of an experiment where LD slags were ground at the Loesche research unit to high fineness, but he said that at the highest fineness beyond around 7000 Blaine that typical laser particle size determination becomes somewhat unreliable. It was found that the finer that the LD slag was ground, the closer the mix would come in 56-day strength to OPC mixes, despite having rather low early strengths. Heat of hydration of ultra-fine LD-based cement blends was lower than OPC blends, with peak exothermic reaction coming later than OPC. "The genesis of slag influences not only the chemical and mineralogical composition of the slag but also the grindability." Frank concluded that ultra fine grinding is extremely energy intensive, but that with further investigations, the optimum fineness and particle size distribution may be elucidated.

The Global Slag Awards Gala Dinner took place in the stunning surroundings of Stoke Park Country Club. The Global Slag 'product of the year' was awarded to Harsco Steelstop; Plant of the year went to Lafarge's Duquesne plant; the Global Slag 'innovation of the year' went to JFE Steel's rooler cooling of slag with waste heat recovery; the Global Slag equipment supplier of the year was Loesche; HeidelbergCement was awarded the Global Slag 'user of the year;' TMS International (the old Tube City IMS) was awarded the Global Slag 'producer of the year;' and finally, Ian Cottam of Cemex was awarded the coveted 'Global Slag Personality of Year.'

Luigi Cattini of the University of Leoben started the second day of the conference with a presentation on recycling of slag which is produced from the desulphurisation of pig iron. In Austria the land filling of any materials will soon b completely banned, so that it is imperative to recycle this problematic slag. The largest particles of the slag contain the largest amount of iron, which can be recovered, whereas the smallest particles of slag with low iron content and high sulphur tend to be sent to landfill. Through a series of experiments, Luigi and his research group discovered that the slag may be roasted in a rotary converter at high temperature (1400 - 1450C) to liberate sulphur, and with addition of calcium from lime the slag may then be reused in the blast furnace. The sulphur liberated is delivered to a sulphuric acid plant. The patents process is soon to be installed on a blast furnace at Linz, Austria.

Stefan Seemann of Humboldt Wedag next spoke about the use of high pressure grinding rolls (HPGR) for slag grinding. When slag particles pass through the gap between the grinding rolls many micro-cracks are created, which make the slag more grindable, reducing the energy requirement from 53kWh/t for grinding to 4000Blaine to as low as 13kWh/t slag. Stefan noted that the energy bonus increases with greater grinding fineness. The KHD Comflex circuit uses a Sepmaster third generation high-efficiency dynamic classifier, the HPGR roller press and beneath it a static V-separator. Stefan mentioned the world's largest slag grinding plant, with a capacity of 195t/h slag at 4500Blaine, built for a steel company in India, of which a pair was built for a total capacity of 390t/h. Energy consumption for the use of HPGRs is around 16 - 35kWh/t, depending on slag grindability and final product fineness. As a final case study Stefan gave details of the JUGPK Novotroizk cement plant in Russia which uses 30% blast furnace slag as a raw material source, which uses a HPGR for raw material grinding, leading to the world's lowest specific energy consumption for clinkerisation, of around 600kCal/kg.

The Global Slag conference featured a session on non-ferrous slags for the first time and Christoph Pichler of the University of Leoben started the session with a paper on the recycling potential of these important slags.  Worldwide, total production of non-ferrous metals amount to the following: copper 23Mt (copper metals is worth approximately $4700/t; zinc 14Mt/t ($1900/t); lead 11Mt ($1700/t); aluminum 60Mt/y. All of these metals produce slags of various kinds during smelting and recycling. Christoph mentioned a number of research projects looking at recycling processes for zinc, lead and copper slags. As an example, Christoph mentioned the high content of zinc in filter dust from BOF and EAF which may then be treated in the Waelz furnace process: the slag generated form this process may then be further processed using reducing agents, either in solid cooled state or in a molten liquid state. Alternatively a new 2sDR process may be used to avoid the Waelz process, a two stage process involving pelletisation, clinkering (to liberate chlorine and fluorine), with the hot clinker n then immersed Ina hot metal bath. In another case the normal method of zinc production gives rise to large quantities of jarosite, potentially containing commercial quantities of lead, silver and rare metals. A special roasting step for sulphur is a prerequisite prior to a reducing process for the liberation of the commercial metals.

Next Gernot Roesler, also from the University of Leoben, spoke about utilisation possibilities for dumped lead slag. A huge amount of lead slag has been dumped over the last 150 years, derived from the lead blast furnace process, with the slag typically also containing zinc, silver, indium and germanium and gallium. Treatment options were often not applied, particularly 'in the early days,' even though the reducing processes are known to work well and are relatively easy to apply. Decontamination of dump sites means that the slag should now be reprocessed, with the valuable metals being separated and the inert residues becoming available for example for the construction industry. Around 1t of glassy slag is produced for each tonne of lead produced, with silicon, calcium and magnesium predominating in the slags, alongside lead, iron and other heavy metals. Hydrometallurgical processing seems to b inefficient since the zinc yield is too low, so that pyro metallurgical processing is preferred. Electrical slag cleaning furnaces, the top-blown rotary converter, the Waelz rotary kiln process or other (Ausment/IsaSmelt) technologies can be used for lead slag processing. Gernot suggest that the addition of lead slags to Electric Arc Furcnace Dust in the Waelz process may result in higher value 'Waelz oxide' byproducts from lead slag processing.

Nikolaos Katsiotis and co-authors from the University of Athens presented a life cycle assessment of OPC and blended cements with ferro-nickel electric arc furnace slag. Nikolaos referenced the lateritic nickel Laryma project of Greek company Larco, which has one of the highest costs of production in the world, which is a significant challenge in today's world of low commodity prices. Electric arc furnace slag from the ferro-nickel industry was previously widely used in the cement industry in Greece, despite its high chromium content of over 2%, but changes in European standards caused the practice to cease. A life cycle analysis suggests that the use of ferro-nickel slag at a rate of 5% reduces the CO₂ emission from a tonne of Cem I 52.5 cement from 839kg/t to 797 - 827kg/t, depending on the classification of the slag as either a byproduct or as a waste and hence whether the environmental impact of the slag is 'carried' with the by-product or 'left behind' with the ferry-nickel process if the slag is considered as a waste.

Nick Jones of Harsco Metals and Minerals next asked (and answered) his own question, 'Is steel slag asphalt really that good?' Steel-slag-based asphalt lasts longer than natural aggregates, with less rutting, no stripping and less wear, with good skid resistance which is maintained throughout its service life, since it does not tend to take a polish like natural aggregates. The UK's Transport Research Laboratory undertook a study of Harsco's SteelPhalt steel-slag-based asphalt and found that the road surfaces did indeed perform better than equivalent natural aggregate asphalt surfaces. A new surfacing called Steelflow offers great potential for eve higher performance. The answer to Nick's own question seems to be an emphatic "Yes."

For the final presentation at the conference, Sebastian Teir of the VTT Tchnical Rsearch Centre of Finland spoke about the production of filler and coating materials in the form of ground synthetic and precipitated calcium carbonate from steel making slags. Pic is produced by calcining high quality lime won't,e adding lime with water and adding CO₂ to precipitate the fine mineral. The Mina's are used as fillers and coatings for paper making and around 74Mt/ is used worldwide. Sebastian used an ammonium salt solution to extract around 50% of the calcium from a finely ground steel slag to produce a slurry, from which a calcium-rich solvent can be derived: the addition of CO₂ leads to precipitation of calcium carbonate and as part of the process the ammonium solution is partially regenerated. A laboratory-scale pilot plant at the University of Aalto in Finaldn has been able to produce PCC of high purity and brightness with potential for use as a paper filler. Sebastian mentioned a techno-economic assessment case study for a pair of industrial facilities: The Tornio stainless steel plant in Finalnd produces 280,000t/y of argon oxygen decurburisation and ladle slag, while nearby the Veitsiluoto paper mill annually uses 60,000t of PCC. The Slag2PCC technology has shown that in this case there is only weak extraction of calcium from blast furnace and ladle slag, and the production of scalenohedral PCC was possible but expensive. However, it was possible to economically produce rhombohedral calcite and aragonite of a coarser size, which can then be ground to the required size. The process would be economic if the input cost of the slag into the process was zero, while it would be yet more profitable with a significant CO₂ price, since the process acts as a carbon sink, reducing emissions by 0.3t CO₂ per tonne of PCC produced. A residual slag byproduct with moisture content of around 10% is also produced,which also contains a remnant of the ammonium solvents. The slag residues could be used in concrete, for mine filling purposes and as a geopolymer. The UK company Carbon8 has produced artificial aggregates from AOD slag residues and this is a potential use for the slag residues from the current study. Briefly he mentioned that he has also been working on the use of slags as a raw material for the capture and sequestration of CO₂.

At the end of the end of the conference, a number of prizes were presented at the farewell party. In the best presentation awards, Juha Koskinen of Tapojärvi Oy was given an 'honourable mention,' Christoph Pichler of the Montanuniversitaet Leoben was thrid, Ian McDonald of Primetals Technologies Ltd was second and the winner was Nick Jones of Harsco Metals and Minerals.

Delegates strongly commended the event for its convivial and collegiate atmosphere, and for its smooth and punctual organisation. Delegates were unanimous in the approval of the destination for the next, 12th, Global Slag Conference and Exhibition, and agreed to meet on 18-19 May 2017 in Düsseldorf, Germany.

12th Global Slag Conference, Exhibition & Awards 2017
18 - 19 May 2017, Düsseldorf, Germany

Image gallery for the 12th Global Slag Conference 2017 (large galery - it may take time to load)

The 12th Global Slag Conference 2017 has successfully taken place in Düsseldorf, Germany, attracting 130 delegates from 29 countries to listen to 19 presentations over two days, alongside an exhibition of slag-related services and equipment. 

Charlie Zeynel of ZAG International started the conference with a stark statement: "Demand is exceeding supply: we are running out of slag. There is 'way too much' clinker production capacity in the world right now, and people ought to be thinking about building grinding stations rather than new clinker production capacity." Most of the iron and steel producers have sold out their slag and pricing has changed dramatically. The US cement market is now growing at '5-8%/year for the next ten or 15 years,' but freight rates have leapt from historic lows and are now once again a major factor in delivered costs, having increased by around 35% from 2016 to 2017. Imports into the US may be problematic in the coming years. Charlie pointed out that the question of the ownership of the slag is critical, since the owner has the power to decide on pricing and allocation. However, the ownership of the slag is not always clear. Blast furnaces are no longer being built, so that the supply of blast furnace slag will not increase. China dominates in this area, as in so many others: it produces 60% of the global total of pig iron each year and an equally large proportion of the global total of slag. Around 360Mt of blast furnace slag (BFS) is produced worldwide each year, with 75% of this being granulated to produce around 250Mt of granulated BFS. China produces 170Mt of this GBFS, Japan 30Mt and the rest of the world produces the remainder - 50Mt. Japan uses the majority of its own GBFS, with only around 10Mt made available for export. Slag product prices are inexorably moving upwards - that's if you can find the product to buy.

Michael Connolly of TMS International LLC next gave details of the status of slag and slag products in the USA. He pointed out that Mr Trump has told his administration to do what it can to 'oil the wheels' of industry, and has mandated his officials to repeal 75% of Federal regulations. However, it is the states that regulate non-hazardous materials including slag products. A number of states have recognised that slag is not a waste but is a product, provided that it is not discarded. Michael went through some of the regulations of the different states, pointing out that the use of slag products in some states require extremely onerous stipulations (for example in Illinois, where written notice is required to be given to adjacent landowners that industrial byproducts are being used in any project). In general, regulations vary wildly from state to state, from almost outright bans to widespread use. Through diligent advocacy work, US companies and other organisations  - notably the National Slag Association - are gradually persuading regulators that slag products are 'a good idea.'

Christian Kohl of Kallanish Commodities next spoke about trends in steel supply. Christian pointed out that there has been a recovery in prices for steel products in the last 18 months, starting in spring 2016 and with a strong 'kick' in autumn 2016. He suggested that prices started to rise once some particular large buyers entered the market, causing a stampede, but steel prices were also backed by iron ore price increases. European efforts to stem a tide of imports of steel products from Asia also helped to boost steel prices in Europe, although these tariffs have not been universally popular with steel buyers. Global crude steel production was 1.6bnt in 2016, with China producing 800Mt - which, if true, is well beyond what was needed. The Chinese government now plans to reduce its capacity to a more sensible total of around 150Mt by 2020.

Tony Murray presented on behalf of Smithers Pira on key market trends for slag and non-ferrous slags, to 2027. Tony suggested the key trend will be that the global supply of BFS will reduce over the next decade due to the closure of Chinese blast furnaces.

Frank Dardemann of Loesche next introduced a new process for the production of cement clinker from steelmaking slag. Frank pointed out that other uses of slag have much lower value compared to using slag products to substitute for cement clinker, so that using steel slag as a supplementary cementitious material makes a lot of sense - if it can be done. Alite (C3S) is the main active component of clinker, and the new process is designed to optimise the cooling and composition of the slag to create a high proportion of alite in the final steel slag. The ratio of SiO2 and CaO must be optimised to form alite, while MnO content must be between 1-5% and the MgO content must be below 5%. The cooling time of the slag should be on the scale of seconds to minutes. The beneficiation of the slag starts when it is still molten, through the reduction of iron oxides in the slag through the introduction of coal as a reducing agent, during electrical heating and bottom stirring. The reduction of the iron oxides in the slag to iron metal allows high recovery of remaining metal in the molten slag. The subsequent dry solidification of the molten slag generates the crystal structure, while also allowing energy recovery from the cooling of the molten slag. The solidification can be accomplished by thin-film open dumping, with BSSF, or with dry granulation using a rotating disc. Finally, Frank said that the grinding step increases surface area and hydraulic activity, while at the same allowing further recovery of metal from the treated slag. Frank pointed out that the economics of the process are positive. At the same time, by using the steelmaking slag as an alternative steel slag clinker (or 'slinker' as it was dubbed) rather than using a normal clinker reduces the CO2 output of the final cement by 589kg.

Janice Bolen of Canadian company Hatch next spoke about recent developments in the Ecomaister-Hatch dry slag atomisation process. Janice suggested that water granulation of slag involves complex system design, high use of water, has explosion potential and pollution potential. Dry slag granulation avoids many of these downsides, through using high pressure air to atomise the molten slag. This creates a different product from water granulation, the so-called 'slag balls,' which can be used for abrasive blasting, road pavements, concrete materials and as a sand replacement. The Ecomaister system allows heat recovery of the post-atomisation heated air. Lab scale testing has been undertaken on a wide variety of slags from around the world, and the company has also developed mobile suitcase-size and shipping container-sized test rigs. Stainless steel AOD slags are notorious dust-producers, from free lime generation and hydration and from the dicalcium silicate beta to gamma transition which causes volume expansion and crystal disintegration. By rapidly cooling the slag through the 490C phase transition temperature through slag atomisation, the crystal disintegration can be avoided. The process is used in a number of steelworks in Korea and India.

At the start of the next special session on the slag research of the FEhS institute for building materials, the director of the institute, Thomas Reiche, introduced the organisation. The FEhS provides research, consultancy and advocacy for slags and by-products, with 37 member companies from the steel, cement and slag processing industries. Over 20 research projects are currently running on building materials, based in its six laboratories.

Henning Schliephake of EAF steel-maker Georgsmarienhütte GmbH spoke about the company's NoWaste strategy. He pointed out that a change in German environmental regulations would mean that if the company's slag disposal strategy was continued, then it would be hit with a bill of over Euro2.5m each year. Business as usual is not an option, since in the future landfill will not be economic. Chrome, manganese and vanadium oxides are all present in EAF slag and can be a challenge for further use of the slag. Boron and phosphorous addition to LF slag can bring problems if any portion of the slag is returned to the steel-making process. Dry solidification can be used, with the EAF slag being reused as a slag former instead of limestone. The company pioneered the use of inclined copper plates for rapid cooling of EAF slag. Henning Schliephake pointed out that viscosity of a slag will increase as metal is recovered, meaning that to retain the same viscosity the slag will need to be heated. EAF slag will also need to be dephosphorised. However, if the EAF slag can be reduced in the direction of the composition of BFS, then it can be more readily used. He pointed out that the reduced EAF slag cannot be reused in the EAF, but can be used in other metallurgical processes, since it essentially already has the composition of a steel alloy. He concluded, "Steel workers do not only produce steel meeting the highest requirements of their customers but also byproducts with an intrinsic value of which they are often not aware."

Volkert Feldrappe of the FEhS underlined the importance of the industry and pointed out that the volume of raw materials used in cement production in Germany each year would fill up the Pyramid of Cheops, twice. Volkert pointed out that the vast majority of possible compositions of 'cement' have not been standardised. However, there is now a recognised European procedure underway to try to standardise the composition and properties of these possible compositions, which are combinations of OPC clinker, flyash, GBFS, pozzolans, silica fume and limestone. On the basis of just a ternary mix of clinker, ash and slag, mathematical models of mortar strength development can be shown to be highly accurate, when other strength-influencing factors such as particle size and reactivity are carefully controlled.

David Algermissen of the FEhS gave the final presentation on the first day, on the metallurgical conversion of EAF slag to form a beneficial material for the cement industry, as part of the Klinkeos project. In the future, German regulations will place EAF slags into three categories, with only 15% in class 1 which will not be considered a waste. Classes 2 and 3 will be considered waste and will not be allowed for use. David spoke about the reduction of EAF slag using carbon and/or FeSi additives, but initial experiments created 'falling' slags that disintegrated with the C2S beta- to gamma mineral phase transition. Addition of too much lime to the EAF avoided the problem of falling slags, but led to highly viscous slags with free lime. Careful attention of the amount of lime addition was critical to creating a slag that was useable as a clinker replacement in the cement industry. Another option was to add silica, to create a material with the composition of GBFS. Although this is indeed possible, the process has a high energy demand, requires conditioning chemicals such as lime and produces a poor quality metal, while at the same time being sensitive to the reducing/conditioning times. Further work on this promising area of research is required.

Global Slag Awards
The Global Slag Awards Dinner took place at the Classic Remise classic car centre in Düsseldorf, featuring a locally-sourced menu, German beers and classic jazz. The Global Slag Awards were presented at the dinner, with the Global Slag ‘company of the year’ award going to Harsco Metals & Minerals. Slag equipment supplier of the year was awarded to Loesche GmbH, ‘plant of the year’ went to Phoenix Services’ Burns Harbor slag handling plant near Chicago, ‘product of the year’ went to Umicore’s battery recycling slag, ‘slag user of the year’ was awarded to Cemex and the ‘technical innovation’ prize was awarded to the FEhS in recognition of its work on slag research. The Global Slag ‘personality of the year’ award - equivalent to induction into a kind-of Global Slag ‘hall of fame’ - went to well-known slag grinding expert Caroline Woywadt, of Gebr. Pfeiffer.

Second day
On the second day, Caroline Woywadt of Gebr. Pfeiffer started the session on slag grinding advances with a case study of slag grinding in the world's largest cement mill at Barroso in Brazil. Caroline pointed out that without knowledge of the grindability of the slag, the output of the vertical roller mill cannot be calculated. Extensive testing of the slag must take place to enable effective engineering and design of the mill. The Barroso plant chose an MVR 6700 C6 mill from Gebr. Pfeiffer, on the basis of its lowest capex. The grinding table is 6.7m wide, with six rollers, each with 2.7m diameter. There are six 1950kW drives in a 'MultiDrive' setup. The mill can produce up to 450t/h of 34% slag cement at 4420 Blaine. The mill has the possibility of operating with fewer than six rollers, and with fewer than six drives.

Winfried Ruhkamp of Loesche next gave a paper on the mobilisation of hydraulically active phases in steel (LD) slags through the production of ultra-fine material. Winfried pointed out that there are huge quantities of steel slags worldwide with low technological and economic value, while at the same time the demand for cement is ever-increasing. In a study, LD slags were shown to contain clinker-like mineral phases such as alite and belite, but also significant quantities of unusual phases such as srebrodolskite, Ca2Fe2O5. An XRD study of LD slags suggested that the amorphous phase was in fact a 'crypto-crystalline' belite phase. Additionally, belite is often overgrown with inactive phases such as magnetite and wustite. These otherwise non-reactive phases could be activated through ultra-fine grinding. The highest-fineness LD slag sample demonstrates strength nearly as high as CEM I. Winfried Ruhkamp pointed out that the particular grinding mode in a VRM means that a different pattern of cracking of crystals allows a higher strength development compared to grinding in ball mills. In some cases, a coarser fraction of the VRM-milled slag demonstrated a higher strength development. This was found to be because the coarser fraction was enriched in the belite mineral phase, whereas the amorphous crypto-crystalline belite phase was enriched in the finer fraction. It was found that the LD slag with the slowest cooling had the lowest content of crypto crystalline belite, and this slag had the highest strength development response to fine grinding.

Bunpei Suzue of Kawasaki Heavy Industries (KHI) of Japan introduced delegates to the CK vertical roller mill, which is already in use for cement and slag grinding in plants around the world. The second generation CK mill features a modular design of rollers and roller arms to reduce construction costs, a low-vibration concrete pedestal (contrasting with the steel pedestal of the first generation mills) and hard-facing on the tyres and table. KHI has a manufacturing facility in Wuhu, China, capable of producing 18 CK mills each year. Bunpei Suzue pointed out that two CK 450 mills have the same output as a CK 610 six roller mill, using 50% less equipment and nearly 20% lower overall cost. Finally, he gave some details of a counter-weighted movable material bed stabiliser used to de-aerate the material bed before the rollers, which led to some improvement in production rate or reduction in specific energy consumption compared to a fixed bed stabiliser.

Next Stefan Seemann of Humboldt Wedag gave a comparison of high pressure roller presses and VRMs for slag grinding. In a roller press, one roller is fixed while the other is mobile and is pressed using an hydraulic system to provide the grinding force. The roller press can be combined with static and/or dynamic separators to achieve high recovery of pig iron in slag grinding, while at the same time providing high grinding fineness. Stefan suggests that roller presses use around 3-5kWh/t less compared to a VRM to grind slag to the same fineness, or, using the same specific energy consumption can grind to a much higher fineness. Both systems have the same heat consumption. However, there is a very large difference in service life, with the stud lining of the roller press having a lifetime of 25-40,000 hours, compared to perhaps a tenth of this lifetime for wear surfaces in a VRM. Civil costs are also around 10% lower with a roller press, according to Stefan Seemann.

Adam Reid of Yara next gave a presentation on the impact of calcium nitrate (CN) on the setting behaviour and strength development of OPC and slag-based blended cements. CN has traditionally been used as a set accelerator for concrete setting in cold weather, as well as an accelerator for the precast industry to increase production. Blended cements featuring slag (and flyash) typically suffer from retarded strength development. Adam showed that addition of CN to flyash blends accelerated hydration and decreased the heat of hydration, while compressive strength was not significantly affected. In the same way, setting times were reduced with GBFS dosed with CN. The effect was greater at higher ambient temperatures (20°C) compared to lower temperatures (5°C). Beyond 4% dosage some deleterious effects were seen on compressive strength development.

Patrick Ullrich of MAPEI GmbH spoke about performance improvement of BFS blended cements. The most suitable slag for use in cement plants is that with the most hydraulic reactivity, which is controlled by its basicity ((CaO+MgO)/SiO2 - higher is better) and a high glass content. Three categories of cement additives may be employed to improve the performance of slag cements: pure grinding additives, grinding additives which also have a chemical effect on strength and performance enhancers which allow the reduction of the clinker factor. In some ball mills, the balls may become coated which decreases grinding efficiency, while agglomeration of fine particles reduces the efficiency of the classifier. Through the reduction of charges on the particles, agglomeration can be reduced with concomitant increases in grinding efficiency. Additives can also be used to improve 'dry flow,’ for example to avoid problems in transport from mill to silo and allowing faster loading from the silo to the truck. Performance enhancers can be used to increase the production of a grinding unit or to provide the same strength development at a coarser level of grinding.

Els Nagels gave the final presentation at the conference, on how to produce quality products from non-ferrous slags. Previously the approach might have been 'what is the composition of the feed materials and what strength will we thus achieve in the final product?' However, recently a different approach has been pioneered, on the basis of 'what strength do we require and hence what composition of feed materials do we need to choose to achieve this?' Els pointed out that practically every characteristic of the final slag can be calculated in advance, including its viscosity, the expected minerals in the slag after cooling and the hydraulicity and activation possibilities. Non-ferrous slag-forming processes typically have lower temperatures and iron must be thought of as the primary reactive ingredient that reacts with contaminants to form a slag. Els pointed out that if the metallurgical industry wants to sell solidified slag as a product then it needs to be treated as a product and if the construction industry wants to use slags as a raw material, then it needs to define the specifications of the slag product inputs. However, Els suggested that Portland cement-like chemistry can never be achieved from non-ferrous slags. Slag engineering is possible, with chemical slag stabilisation and with ‘cleaning’ of slags through the removal of Pb, Zn and Cu. The mineralogy can also be controlled by altering the cooling profile. Spark software can be used to forecast cooled slag mineralogy and final mechanical properties. Slag can also be used as a base ingredient (with soluble sodium silicate (‘water glass’) and sand/rock) to form an inorganic polymer which has respectable compressive and flexural strength. Els concluded that slag engineering can be accomplished if the will exists.

Farewell and prizes
At the end of the conference, a number of prizes were awarded. Ralf Perret of thyssenkrupp Industrial Services was voted to have taken the best photo submitted in the Global Slag Photo Competition 2017, while Loesche was awarded the prize for the best exhibition stand. In the best presentation awards, Winfried Ruhkamp of Loesche was third for his paper on the mobilisation of active phases via ultra-fine grinding; Stefan Seemann of Humboldt Wedag was second for his paper on a comparison between roller presses and VRMs; and Els Nagels of InsPyro was the winner of the best presentation award for her in-depth paper on slag engineering and design - the conference had obviously saved ‘the best until last.’

The conference was highly praised by delegates for its mix of networking and technical content. 

Global Slag Conference field trip to Dyckerhoff's Lengerich cement plant - Wednesday 17 May 2017

Photos courtesy Peter und Lochner, Aerzener Maschinenfabrik