14th Global Slag Conference, Exhibition & Awards 2019
26 - 27 March 2019 Aachen, Germany

View the conference photo gallery here

The 14th Global Slag Conference has successfully taken place in Aachen, Germany, with 140 delegates from 36 countries in attendance. The 15th Global Slag Conference will take place in Vienna in April 2020.

Charles Zeynel started the conference by saying what he has been saying for the last 15 years, that "slag is a good material, it's in great demand, and there is now not enough to go around." Charlie pointed out that 30% of China's steel production is made in EAF mills, meaning that no new blast furnaces will be built. Demand for slag is outpacing supply and the gap will continue to grow: SCM suppliers are steadily 'moving up the value chain.' Steel companies are now making a profit on slag production, but cement companies are now pushing back, particularly where the landed price of slag is higher than the local cost of clinker. Former users of slag products are looking for alternatives. However, there are tens of millions of tonnes of slag products (particularly in China) in stockpiles and hundreds of millions of tonnes of flyash in ash ponds around the world, that could be utilised by cement companies, and which allow a pushback against slag product price rises. On the other hand, there are multiple challenges to suppliers and to supply lines. "All participants must have a balanced view of sharing the benefits in the value chain." Charlie concluded that knowledge of the markets is paramount for reliable slag supply.

Dan Rogers of Smithers Apex next gave a forecast for the development of ferrous and non-ferrous slags to 2029. Dan gave a thorough breakdown of volumes and uses of slag in various regional markets and industries. His message essentially backed-up that of Charles Zeynel, in that there are increasing shortages, particularly regionally, due to increasing global demand and due to variations in regional supply.

Charles Ochola, president of the US National Slag Association, gave the next presentation giving an overview of slag trends in North America. He appealed to delegates to work to promote slag as a product, rather than viewing it as a byproduct, or worse, as a waste. Charles suggested that increasing the value of slag in the eyes of users and regulators will bring advantages to all.

Marc Fixaris of ArcelorMittal next spoke about the development of air-cooled blast furnace slag (BFS) and steel slag in competitive local markets. He stated that 82% of the company's basic oxygen furnace (BOF) slag in Europe was 'valorised' in 2018. Marc stated that stringent efforts need to be undertaken to persuade potential users to use 'artificial aggregates' derived from slag, instead of natural stone. Each steel plant should be used as a showroom of solutions, and there needs to be an open and ongoing discussion with shareholders, politicians, stakeholders, journalists and citizens. Crucially, the producer needs to know their products, in terms of composition and behaviour. Once a buyer has been found, the producer's first priority is to provide quality products for long-term contracts. Marc mentioned just such a contract, to sell 5Mt of slag products from a steel plant in Luxembourg to a local construction company, substituting for natural aggregates.

Andrey Korablin next gave details of business opportunities for slag recycling companies in Russia. Russia produces around 70Mt of steel each year, as well as 20Mt of metallurgical byproducts. Andrey showed a video of Vladimir Putin stating - in Russian, to a Russian audience - that the 300 most polluting industrial plants in Russia, many of them steel and other metallurgical plants, will be required to dramatically improve their environmental performance by 2021 or face forced closure. Andrey pointed out that European and other slag processing companies potentially have a strong future role to play in bringing value to the current and past production of slag-derived materials.

John Yzenas Jn of Edw. C. Levy Co. started the technical sessions of the conference with a presentation on the characteristics of slags. John compared the benefits of XRD and XRF for characterisation. XRD is now widely used as a quantitative approach and the results can be difficult to compare to the Bogue oxide calculations that are derived from XRF results. Many analytical approaches struggle with the variety of compositions and mineralogies that are present in slag products. "All slags are not the same," stated John.

Henning Schliephake of Georgsmarienhütte GmbH next introduced the NoWASTE approach to electric steel making, which produces, you guessed it, ‘no waste.’ The approach has arisen due to the likelihood of the non-availability of any kind of landfill option in the future in Germany. "First of all, you must know what residual materials you are making in your steel plant, and then, make sure to keep it separate! If it is accidentally or carelessly mixed, you have lost value." In the future we will not be able to use unimproved electric arc furnace (EAF) slag as a road-building component, due to high molybdenum and vanadium contents. Henning suggested that EAF slag should be considered as a liquid iron ore. It can be improved by reduction of iron through addition of reducing materials, to a composition closer to clinker.

Gerhard Auer of Ferro Duo GmbH next spoke about an ingenious approach to removing some heavy metals, particularly lead and zinc, from materials such as blast furnace sludge and EAF dust. The materials can be reacted with chlorine-rich 'solvents' such as a FeCl2 solution from steel pickling or waste chlorides from the TiO2 industry or widely-available HCl solutions. The heavy metals react to become ZnCl2 and PbCl2, which have relatively low boiling points. During indirect heating in a rotary kiln the compounds are selectively volatilised and can be removed in the process gas for condensation and recovery. A 'mineral compound' is left behind with near to zero heavy metal content, composed of FeO, CaO, carbon and SiO2. This material can be recycled back into either steelmaking or cement manufacture, as a raw material or as a fuel, since it has a carbon content of 40%.

"Is it possible to correlate granulated slag analytical results with reactivity?" was the question posed by Andreas Ehrenberg of the FEhS, with his answer being “No, or at least, not easily.” This is because there are many factors in slag product reactivity, including blast furnace processes, slag viscosity, slag composition, glass formation, storage conditions, the granulation technology used and the specific granulation conditions in each case. GBS may even vary from heat-to-heat. However, laboratory-scale granulation test and mortar tests are a good start towards predicting slag reactivity.

Yusuke Kato of JFE Steel of Japan next spoke about research that involved oxygen injection into molten slag to promote the exothermic oxidation and increased dissolution of MgO in Fe2O3-rich BOF slag. This process eliminates MgO from the cooled slag, so that hydration and volume expansion can be avoided.

Ryan Hyatt of Edw. C. levy Co. next spoke about the use of drone-based photogrammetry to measure slag product stockpiles, showing delegates some impressive photo-realistic 3D images of slag product stockyards, which can allow an accurate calculation of stockpile volumes.

Global Slag Awards Dinner

The Global Slag Awards dinner took place at the Tonnengewölbe in the Ratskeller Aachen (barrel-vaulted cellars of Aachen’s town hall), featuring the presentation of the Global Slag Awards 2019. Global Slag Company of the Year was Tata Steel Ltd, while slag user of the year was LafargeHolcim. Slag Plant of the year was awarded to the Steelphalt plants of Harsco in the UK, while the slag product of the year was awarded to Koranel synthetic minerals, produced by Metallo Belgium N.V. The technology supplier of the year went to Loesche, and the Global Slag Technical Innovation Award went to Tapojärvi Oy of Finland, for its slag-based geopolymer. The Global Slag Personality of the Year went to Michael Connolly of TMS International LLC.

Second day

The first speaker on the second day of the conference, Dr Winfried Ruhkamp, spoke with co-authors Holger Wulfert and Horst Ludwig on a Loesche separation plant for the production of ultra-fine granulated blastfurnace slag. Due to low reactivity, only the smallest slag particles (<2µm) contribute to early strength in slag cement, whereas large particles >60µm) make virtually no contribution to final strength development. Winfried gave some details of an approach to deliver ultra-fine slag grinding, using an additional cyclone separator group. Approximately 13% of the normal ground granulated BFS that is produced from a Loesche mill can be separated as an ultra-fine product. Using such ultra-fine slag may allow a clinker factor down to 30%, as well as applications in shotcrete, providing low heat of hydration and high early strength. Ultra-fine GGBFS can also be used to produce ultra-high-performance concrete with strength of beyond 150MPa compressive strength, at a lower cost than when using silica fume, partly due to the complete filling of all voids in the concrete.

York Reichardt of KHD next spoke about the energy consumption and total cost of grinding of three different designs of grinding plants: a vertical roller mill, a roller press with finish grinding, and a ball mill, each grinding slag of the same grindability and at the same throughout rate and Blaine fineness. York showed calculations suggesting that the roller press with finish grinding had the lowest total costs.

Dirk Schmidt of KIMA Process Control next spoke about Smartmill 'electronic ears' and Millmaster (software) approaches to grinding optimisation. Dirk pointed out that having a measurement of the fill level of first and second chambers of a ball mill gives an indication of the grindability of the clinker being fed, and allows control over grinding. It also allows the discovery of problems such as blockages or even a hole in the diaphragm between the chambers. Temperature measurements in the chambers also give useful information and the possibility to take control action, for example with additional moisture input. Millmaster software ensures stable operating conditions in the mill, in combination with data from the Smartmill 'ears.'

Next up was Jürgen Haunstetter of the German Aerospace Centre, who introduced the REslag project to find higher value uses for steel slags, including as refractory materials, and, the theme of his presentation, as a solar-thermal energy storage medium. Jürgen said that sintered slag is first pelletised to optimise packing. Expansion of the slag during the heating phase of the solar-thermal system can lead to stresses on the pellets and on the thermal energy storage vessel and its internal insulation. Endurance tests were undertaken in a pilot plant to discover if the slag pellets could survive repeated heating and cooling and the stresses involved. Damage was limited to below 10% by weight and the slag pellets were deemed as being suitable for thermal energy storage. A 12m height vessel would use 30,000t of sintered slag and the pellets would have a lifetime of approximately 20 years.

Dave Roth of GPS-Global Solutions next spoke on means to upgrade different sizes of solidified ladle slag through the use of Didion rotary impact crushers. The primary objective was to increase metal recovery, while controlling the production of fines, particularly metals fines (which leads to metal loss). Larger lumps can be broken using an internal lump-breaker, while smaller particles can be broken open in an autogenous grinding process, using internal lifting plates in the rotary grinding machine.

Victoria Masaguer Torres of ArcelorMittal next gave an update on the neutralisation of acid drainage waters with passive treatments using slag-based byproducts. Acid mine drainage, containing high concentrations of sulphide minerals, is a worldwide problem. BOF slags can be used as an ion exchange system to decrease the acidity of mine drainage water, which can cause the precipitation of contaminants. Slag-based water purification systems have a specific lifespan, after which time they are generally retired from use and the water treatment cell is closed. The company's byproduct roadmap involves a variety of approaches including reduction, retention (internal recycling), recycling (external), reprocessing and ’regulation’ (landfilling). As previously mentioned, 82% of the company's BOF slag was valorised in 2018.

Thomas Fenzl, speaking for Primetals as part of a team of co-authors, next gave details of developments in dry slag granulation technology, with energy recovery. Molten BF slag contains 1.3GJ of heat energy per tonne, so the energy recovery factor is worth some effort to address. VoestAlpine has built a pilot plant (commissioned in 2017) capable of processing up to 2t/minute of blast furnace slag at 1450°C, albeit with no energy recovery. Slag is drained onto a spinning rotating cup and the cooling slag is projected onto the water-cooled wall of the vessel. The granulated slag then falls into a fluidised bed where energy could theoretically be recovered. The next phase of installation will be a full-sized industrial unit, which will aim to maximise the off-gas temperature up to 500°C and to increase reliability of longer runs. Grindability of wet- and the dry-granulated slags from the process has been measured to be nearly identical. Glass content in dry granulated slag is around 95%, compared to 98% for wet granulated slag. There is no significant variation in strength development between dry and wet slag granulation, nor in final compressive strength or in heat of hydration.

Kelly Cook of Edward C. Levy Co. next spoke about slag characterisation, including pH, XRF, XRD, ICP (for total metals), TCLP (toxicity characteristic leaching procedure), calcium carbonate equivalency (for agricultural applications), free lime and quantitative mineralogy. Physical properties that are characterised include particle size and shape, density, surface area and porosity. Volumetric stability when exposed to moisture is among the most crucial of values, particularly with regard to future suitability of applications of the material.

Eramet Norway has three manganese alloy plants in Norway and a group plant in Dunkirk, France, and Leif Hunsbedt gave some information on the silico-manganese and FeMn slags that are produced by the process. The slags can be air- or water-granulated, with the resultant slag products having slightly different properties. The slag products have been used for construction materials, as well as a raw material for clinker production. There is also the possibility of using the slags to cover polluted sediments at the bottom of the Norwegian fjords. SiMn slag has low leaching properties and no toxic effects, Leif concluded.

Prizes and farewells

At the conference farewell party, a number of prizes were awarded. Pewag/Rockworx won the prize for best exhibition stand. In the best presentation awards, Thomas Fenzl and co-authors were in third place for their paper on dry-granulation of slag at VoestAlpine, while Winfried Ruhkamp of Loesche was second for his co-authored paper on ultra-fine grinding of blast furnace slag. Ryan Hyatt of Edw. C. Levy Co. was awarded first prize for his impressive presentation on drone-based photogrammetry of slag product stockpiles.

The 15th Global Slag Conference will take place in Vienna on 6-7 May 2020.

Selected videos from the 14th Global Slag Conference 2019 (hosted on YouTube)

Drones and photogrammetry of slag product stockpiles. Ryan Hyatt, Edw C. Levy Company, and Stockpile Reports.

Dry granulated BF sand: a groundbreaking and sustainable Innovation – production process, product grinding and building materials investigations. Alexander Fleischanderl, Thomas Fenzl (speaker); Primetals; Holger Wulfert, Winfried Ruhkamp; Loesche; Horst Michael Ludwig; Bauhaus Universität Weimar, F. A. Finger-Institut für Baustoffkunde.

Pilot-scale extraction of valuable high-purity calcium salts from steel slag, Mark Tilley, Lixivia Inc. & Nick Jones, Harsco

15th Global Slag Conference, Exhibition & Awards 2023
6 - 7 June 2023 Düsseldorf, Germany

The 15th Global Slag Conference, Exhibition and Awards has successfully taken place in Düsseldorf - after a Covid delay of three years - with 160 delegates from 36 countries in attendance.

View the conference photo gallery here

Following a trip to Holcim’s Schwelgern slag grinding plant in Duisburg the day before the conference (pictured above), Joe Harder of OneStone Consulting started off the event by saying that in 2021, 1912Mt of crude steel was produced worldwide, with China responsible for 52% of production. The steel industry is currently undergoing a structural change, with EAF (electric arc furnace) production increasing rapidly, to 37% of steel production in 2030, and to 53% by 2050. An additional 560Mt of EAF production will be needed by 2050. Pig iron production from blast furnaces will also increase to 2050, but more slowly, from 1350Mt in 2021, to 1403Mt in 2030. With declining iron ore quality in the future, slag production rates will increase slightly, from 0.308t slag/t pig iron in 2017, to 0.317/t in 2030. GBFS (granulated blast furnace slag) production will increase from 331Mt in 2021, to more than 450Mt in 2030, with reductions in North America and Europe, and increases in all other areas. Global granulation rates will increase from 86% in 2021, to 93.5% in 2030, with China granulating all of its blast furnace (BF) slag by 2025, and North American granulating only 45%, even in 2030. Slag and slag/cement mill orders have been strongly concentrated in South Asia, in India in particular, and in Southeast Asia and the Middle East for the last half decade. Global slag trade will increase from around 27Mt in 2021, to around 38Mt in 2030.

Yuri Mytko of CarbiCrete spoke about the use of steel slag and carbon dioxide for the production of building materials. In the CarbiCrete process, EAF, BOF (basic oxygen furnace) and ladle slag are all usable. The slag is first finely ground, then mixed with aggregate and water and is then put into a block-making machine. The block is put into a curing chamber where CO₂ is injected to react with the steel slag to form calcium silicates hydrates and and calcium carbonates. Concrete masonry units (CMUs), pavers and retaining walls can all be made, with comparable performance to cement-based materials. For each 18kg CMU, up to 1kg of CO₂ can be sequestered, as well as avoiding 2kg of CO₂ emissions through not using OPC-based cement. CarbiCrete is already producing 2500 CMUs each day, and is busy signing contracts to roll out its technology worldwide.

Andrey Korablin of SmartScrap spoke about how to maximise profit through the use of slag. The value of the slag depends on its iron content, its chemical composition, and also its size. For example, large ‘skulls’ from the bottom of slag pots have a high value, but sludge has a negative price. Slag aggregates, EAF dust and mill scale all have different values. The iron content in a skull must be measured, or calculated, and the presence of deleterious elements determined, to come to a fair price. Andrey mentioned that skulls can be used effectively as a source of iron in an electric arc furnace, although electricity use may be increased if the EAF is not set up correctly.

Charlie Zeynel of ZAG International gave an overview of SCM trade worldwide, pre- and post-Covid. Charlie started by saying “If everyone was to switch to using slag and ash today, in the same proportion that the Japanese use them, then we would run out in six hours!” The supply is finite, and demand is increasing post-Covid. “The industry has finally woken up to the possibilities of slag, since it is the lowest-hanging fruit for the cement industry to reduce its carbon footprint.” China has enough GBFS to flood the world market, but has not chosen, yet, to export in bulk.  Japanese slag is considered the ‘gold standard’ for GBFS, and this material is not now available to new customers. “For the US, there’s not enough slag and it’s the wrong place.” Imports are the only way for the US to grow its slag markets. “Equilibrium in the markets for SCMs is essentially unobtainable.” The value of SCMs has increased dramatically, but so has the price of cement, so that there is still room for an increase in the value of slags.

Wenhai Nie of Sinoma next spoke about energy-saving technology for slag grinding. Wenhai stated that GGBFS (ground GBFS) production in China reached 110Mt in 2022. To date, Sinoma has commissioned 240 VRMs (vertical roller mills) in China, and designed capacity exceeds 100Mt. The company can now supply single mills with 2Mt/year capacity, and with specific electrical consumption (SEC) of 32kWh/t. A new ‘grinding zone structure’ in the mill, and new designs in the separator have made the system more efficient, while heat consumption has also been reduced. Through modular and standardised designs, the table diameter can range up to 6.6m, for a capacity up to 300t/hour at 4200 Blaine. By 2022, 15 mills with a table diameter of more than 6m had been sold, all in China. Wenhai Nie mentioned that LD slag can be crushed and ground and then treated with steam to cause its mineralogical collapse and consolidation, to improve its physical characteristics and metal recovery rates. Sinoma/TCDRI has already developed a 7m diameter grinding table VRM, with SEC of lower than 30kWh/t.

Arusha Khan from the Cemcoa-Shun Shing Group next spoke about the transformation of Bangladesh from an OPC-using country to one that uses 95% blended cements. The transformation came after a switch from British standards to EU standards in 2003, which freed concrete producers to use cements with a lower clinker factor. Bangladesh has only two integrated plants, but has 31 grinding plants. The country has 81Mt of production capacity, with another 14Mt of capacity coming on steam in the near future, all from Loesche VRMs. Cement demand is around 38Mt/year, with around 20Mt of clinker imported each year. Bangladesh is unusual in that it has a population of 170 million people, but has no raw materials for cement production. Cemcoa has started to import LD slag into Bangladesh from India. Many major infrastructure projects are underway in the country, including a nuclear power plant (90% financed by Russia), wind power projects, a submarine base and major dam projects. Cement demand in Bangladesh has grown around 10% per year for the last few years, leading to an increase in demand of around 1.5Mt of additional SCMs each year - the mix of materials depending on availability, logistics and price. A shortage of US dollars and a devaluation of the Bangladeshi Taka has curtailed imports, while political instability due to an upcoming election and a looming recession have also hit business.

Friedrich Fries-Henrich of Circulania then spoke about the industrial circular economy in the European slag market. Friedrich pointed out that diversity in supply chains will become more important in the future. One single slag market in Europe is not currently possible, due to the variation in regulations from country to country, particularly in terms of rules on road construction and agricultural applications. Many local markets exist, depending on availability and demand. He suggested that the true cost of emitting CO₂ is already around Euro200/t, and that the price of emissions certificates may approach this level in due course. Abating the remaining emissions from many industries will involve progressively higher costs, which may slow progress towards net-zero.

Marion Nicco, a mineral processing engineer from Eramet, next spoke about the production of ferromanganese (FeMn) alloy and the optimisation of FeMn slag production. Current FeMn slag has an FeMn content of around 50%, but is currently not saleable. One slag stockpile in a Norwegian plant consisted of around 800t of material. Marion mentioned a project where the metal content needed to be upgraded to around 80%, using a dry process, and usable on a discontinuous basis, ideally with mobile equipment for use on multiple plants. Magnetic separation attempts were unsuccessful. Automatic optical separation is possible, upgrading up to around 70% metal content, although this can be expensive. FeMn has a density of around 8, and the slag around 4, so a density separation should be possible. Using an experimental wet jig, a metal grade of above 95% was achieved, with recovery of up to 86%. The Allgaier GSort6 dry separator was used in a further experiment, which showed that particle sizes would need to be optimised to achieve the same results as the wet jig, but with grades past 86%, and recovery past 80%.

After a popular ‘meet the delegates’ networking session, Marcel Wettring from Allgaier Process Technology spoke about his company’s capabilities in washing, crushing, screening, sorting, cooling and drying, all of which can be put to use to increase the profitability of slag. Direct and indirectly-heated and cooled drum dryers and coolers are available from the company.

Philip Jarvis of Coomtech next spoke about how to make substantial energy savings when processing slag, with a patented non-thermal drying technology. ‘Air knives’ of turbulent air are used to shear the surface moisture of particles passing through a series of drying cartridges, with no moving parts. The turbulent air heats up and can thus bear significantly higher levels of moisture, while also simultaneously deagglomerating a variety of materials.

David Algermissen of the FEhS next spoke about how the decarbonisation of the steel industry will affect the slag value chain. Around 1900kg of CO₂ is emitted per tonne of crude steel produced, so that decarbonisation is critical. New processes for hot metal production are being investigated, including direct reduction, the HIsarna process, and plasma melting. Using the direct reduction route, iron ore and a reduction gas will be used to create a direct-reduced iron (DRI), with no liquid phase, operating at around 900C, and producing no slag. The DRI will need to be melted so that it can be used, either in a reducing atmosphere in a supplementary arc furnace (SAF), or with the addition of scrap in an EAF. An SAF is new technology for the iron and steel industry, but would allow for flexibility in use of ores, albeit with a likely higher concentration of minor elements in the slag finally produced. Lime needs to be added to reduce the viscosity of the slag, but not to the level that would mirror the chemistry of today’s GBFS, and higher alkaline concentrations would also be present. The gangue from DRI will lead to around 50kg of slag/t of hot metal, and with lime addition is likely to produce around 130kg/t of hot metal. On the other hand, the DRI can be heated in an EAF, with the addition of scrap. In this case, basicity will be slightly higher, there will be slightly higher Fe₂O₃ content, higher TiO₂ and MgO, and lower chromium content. There will be a higher EAF slag amount compared to today. To achieve a composition similar to GBFS, a secondary slag metallurgy can be undertaken, albeit with further costs in terms of additives, in order to allow easy use of a granulator and hence recovery of metal. Another approach would be to add a reducing agent into the slag pot using an injection lance, but this would limit the range of changes that can be undertaken and be more challenging for granulation. However, this has already been tested on a pilot scale, and can more easily be implemented at a steel works. A third way would be to use a treating agent during tapping of the EAF slag, for example addition of sand for SiO2, but this has some operational challenges, and no possibility for metal recovery. The regulatory approach to these new possible slags is yet to be defined. According to currently-announced plans, by 2045, both thyssenkrupp and Salzgitter will have closed all their blast furnaces in Germany and will have transitioned to DRI. Chromium content of the slags may be a limiting factor in the possible use of these slags in the cement and concrete industry. The new slags will be ‘SAF slag’ and ‘DRI-based EAF slag,’ both with chemistries currently unknown to slag users. David’s presentation generated significant discussion.

Global Slag Awards Dinner

At the end of the first day of the conference, delegates enjoyed a meal and liquid refreshments at the Brauerei Schümacher in the old town of Düsseldorf, and the presentation of the Global Slag Awards 2023. Slag-producing company of the year was ArcelorMittal, slag user of the year was CRH, the award for technical innovation went to the FlashPhos project, equipment supplier of the year was awarded to granulator company Paul Wurth, plant of the year went to Ecocem’s Dunkirk plant, and slag-based product of the year also went to Ecocem, for its CEM IIIC product. Four Global Slag ‘personalities of the year’ were announced, clearing a Covid-backlog, namely Joe Harder of OneStone Consulting, Thomas Reich from the FEhS, Miroslav Müller from Holcim (Deutschland), and Satish Pandey from India’s CRRI.

Second day

On the second day of the conference, Professor Andrew Barron of the Energy Safety Research Institute at Swansea University gave some details on how BOF dust, slag and sludge, and EAF slag can be used to make carbon-negative hydrogen. By passing CO₂ through a layered stockpile, a reaction takes place that produces gaseous hydrogen. A million tonne stockpile of slag could be expected to produce 4 million litres of H2 per day, while simultaneously capturing CO₂.

Amit Ahsan of Secopta Analytics GmbH spoke about Laser-Induced Breakdown Spectroscopy (LIBS), where a laser is used to create a plasma on the surface of a sample, which is then analysed using a spectrometer at a rate of up to 1000 times per second. Amit stated that the sampling process amounts to around 80% of measurement uncertainty, compared to around 15% for the sample preparation and only 5% for the measurement process. A 30 second crushing process to produce particles of 2mm is used prior to LIBS, which then takes around 50 seconds for sample analysis, meaning that the data can be used for near real-time process control. Additionally, the system can be used to check the quality of incoming deliveries of materials, and can also be used to check the composition of materials moving on conveyor belts.

Next, Andreas Kunkel of Quantolux GmbH told delegates that he had asked ChatGPT how to add value to slag, and the AI answered at length, stating that the composition of the slag is critical, and that the presence of heavy elements may have negative effects on potential products. Andreas concluded that accurate and fast analysis is crucial to adding value to slag, and he suggested that optical emission spectroscopy (OES) is the answer to the problem. In Spark-OES a spark is used for conductive (metal-based) samples, but in Laser-OES a laser is used and can analyse non-conductive samples, including slags. Andreas suggested that the Quantolux QLX9 L-OES analyser can be used to add value to slag.

Next Bernhard Haslinger from the Montanuniversity of Leoben spoke about the potential recovery of chromium from BOF Slag. In his experiments, iron crucibles were used, rather than refractory-based crucibles which interact with the slag. In an untreated slag, Cr enriches in the iron phase. However, with 10% addition of TiO₂ and Al₂O₃, Cr enriches in a CaTi phase which forms into dendritic crystal structures that would make Cr recovery difficult. Vitally, the degree of interaction of the slag melt with the iron crucible has not been determined.

Xuerun Li of BASF Construction Additives GmbH spoke about C-S-H seeding to optimise slag performance. Li pointed out that the ultimate clinker factor goal will be 20% or less, but this level will only be achievable with SCMs and the use of additives. Xuerun tested a variety of cement blends, including OPC, LC3, LC3+(LC3 plus slag or ash or other SCMs, or additional Ca(OH)₂), with varying C-S-H dosage. Higher early strength can be achieved with C-S-H seeding, even with low levels of clinker, down to 20%. The C-S-H seeding helps to make the solidified paste extremely dense due to the increase in the number of nucleation sites during hydration.

Wilfred Dünnwald of Scrapetec then suggested that the audience should make friends with their conveyor belts. Wilfred showed a rogues’ gallery of dust-generating conveyor belts, with a variety of materials, which showed not only economic losses but also health and safety hazards. The Airscrape conveyor side-skirting uses steel vanes to create a Venturi effect that sucks in air and dust, thus avoiding dust escape. Additionally, the Dustscrape is a filter-cloth-based tunnel over the conveyor, from which dust cannot escape. Finally, the PrimeTracker is a conveyor belt centering device, the latest iteration of which - the ePrimeTracker - can report back on the roller’s condition and operation.

Volkert Feldrappe of the FEhS gave the penultimate presentation at the conference, on the use of steel slag as a concrete aggregate. Volkert pointed out that in Germany, concrete producers have faced a lack of aggregates which has led to delivery delays. BOF and EAF slags have not yet been used for construction applications due to technical and environmental regulations, largely on account of the free lime and free MgO content and absence of standards and standardised testing regimes. Steel slag aggregates can contain free lime/MgO which increases in volume on reaction with water, leading to instability. A new test method has therefore been developed to measure potential dimensional instability of steel slags. EAF slag and copper slag normally have a sufficient soundness to be used, but BOF slag should be treated to minimise free lime content. In all cases, heavy metals are mineralogically-bound and no significant subsequent release can take place. “In various European markets there is no environmental problem with using steel slags as a concrete aggregate, only a problem with the regulations.”

Niklas Tornkvist of Finnish company Magsort Ltd gave the final presentation at the conference, and began by pointing out that there are literally billions of tonnes of slag in piles around the world. His company is in the process of crushing, screening and cleaning this material to gain profit. A patented vertical impact crusher is used to crush the slag to below 1.5mm particle size, at which point a further metal recovery is made. Following subsequent screening steps, one fraction can be used as a pre-decarbonised kiln feed, and since there is no loss on ignition, it can increase clinker production by around 18%. The finest fraction of the ground slag can be used as an SCM, at up to 30% clinker replacement (or up to 50% replacement of GGBFS in slag cement). Another fraction can be used as an aggregate. Yet another can be used as a Cr⁶⁺ -reducing agent. Again, very significant discussion was generated by the presentation.

Conclusions and farewell

At the end of the programme, delegates were able to vote for their favourite presentations. In third place was Niklas Tornkvist of Magsort Ltd, and in second place was Charlie Zeynel of ZAG International. However, in first place was David Algermissen of the FEhS for his paradigm-shifting presentation of the decarbonisation of the steel industry.

Delegates strongly praised the organisation, timekeeping and friendly atmosphere of the event, as well as the many opportunities for networking and business.

Image gallery for the 6th Global Slag Conference which took place in Sydney, Australia on 22-23 November 2010.

Image gallery for the 7th Global Slag Conference which took place in Helsinki, Finland on 17 - 18 November 2011.