13th Global Slag Conference, Exhibition & Awards 2018
24 - 25 April 20178 Prague, Czech Republic
View the conference photo gallery
The 13th Global Slag Conference and Exhibition has taken place in Prague, with 120 delegates in attendance from 30 different countries. The 14th Global Slag Conference will take place on 3 - 4 April 2019 in Aachen, Germany.
Adam Smith of Kallanish Commodities started the conference by speaking about trends in the global steel industry. Donald Trump's imposition of tariffs on steel and aluminium imports caused a spike in steel prices in North America at the start of 2018, but these have fallen back after most countries were given waivers from the tariffs. However, an ongoing Trump-led crusade on Chinese intellectual property ‘acquisitions’ is still dampening market sentiment. The EU exemption from the tariffs ends on 1 May 2018, and European steel association Eurofer fears that around 13Mt of US-bound global steel exports may soon be diverted to Europe instead. The EU is now considering its own external tariffs as well. Two major mergers are in the pipeline, between Tata Steel Europe and thyssenkrupp, as well as the ArcellorMittal takeover of Itailian producer Ilva. Adam suggested that with the EU's trade defence measures, that the mergers may raise steel consumers' sourcing costs (meaning that steel prices are set to rise). The World Steel Association has published forecasts for 2018-2019, suggesting that there will be a mild economic deceleration in the Chinese economy (leading to a fall in steel demand), and that developing economies will once again lead global growth. Developed nations including the EU will attain steady but moderate growth, while India is readying to be a standout growth region for the coming years.
Doug Haynes of Smithers Apex next gave an executive summary of the Smithers report 'The future of ferrous slag to 2027.' Doug suggested that around 50% of global slag production is used in the cement industry, with 32% used in road construction, 10% used in 'other applications,’ 3% used in embankments and 2% in internal recycling. These figures exclude disposal to landfill. Doug points out that drivers for slag use include construction demand in India, China and Asia, construction market demand, a trend towards sustainability, the technical properties of cement and concrete with slag, environmental pressures on primary rock extraction and the development of processes capable of mitigating Basic Oxygen Furnace (BOF) slag free-lime expansion. However, there are many barriers, including potential decreases in slag production capacity, the financial cost of installing new technology and environmental regulations restricting the use of ferrous slag.
Charles Zeynel of ZAG International next gave an update on granulated blast furnace slag (GBFS), other supplementary cementitious materials (SCMs) and the global cement industry. He started by saying that "after having forecast for years that we are going to run out of slag, the day has finally arrived." He recounted a story of a company that had signed a five-year contract with a Chinese state-owned steel company for significant tonnages of slag: six months later, the price tripled despite the contract terms. “But just try and sue a state-owned company in China - you will not get far.” The value of slag, he concluded, has increased dramatically. The slag producers have concluded that they want a larger share of the value of slag, so that prices have increased. Charlie pointed out that there is a global oversupply of clinker, but that there is a positive overall outlook for the cement industry due to population growth and urbanisation. Countries are starting to stipulate non-clinker components in cement (some of the emirates in the UAE now stipulate at least 60% fly ash or slag in cement). Due to the continuing closure of coal-fired power stations, particularly in the US and EU, flyash supplies are effectively reducing: slag is the next 'go-to' SCM on the list. There is no current global growth in blast furnace slag production, due to the rise of Electric Arc Furnace (EAF) steel production. Only around 75% of globally-produced blast furnace slag (BFS) is granulated, creating around 250Mt of GBFS, albeit with 150Mt in China, 30Mt in Japan and 70Mt in the rest of the world. China is now auctioning slag supplies for export each week, with the 'winner' having to pay cash ‘up-front.’ Now around 25Mt of slag is traded internationally, of which 12Mt is Japanese slag, and around 5-6Mt is Chinese slag. Freight rates are rising from their historic lows, and will eventually become a major factor in slag use and pricing. From being a buyer's market, slag is becoming a seller's market.
Michael Connolly of TMS International next gave an update on the regulatory approach to slag and slag products in the USA. In the US around 20Mt of iron and steel slag is produced and marketed each year. Eleven states have now decided that slag is a product rather than a waste, 'if it is not discarded and is distributed for use in commerce.' Industry and the US National Slag Association are busy trying to persuade the remaining states to adopt the same approach to slag. Steel slag is actually the preferred aggregate in high-demand road surface applications, due to its higher coefficient of friction, high resistance to rutting and its high compressive strength, leading to superior skidding resistance. This has led to its use as the track surface for the Indianapolis Motor Speedway, home of the Indy 500. “When properly segregated from ladle slag, steel slag is an excellent high-density aggregate ideal for use in concrete. The only drawback is its high density, but when mixes are properly designed using a mix of natural aggregates and slag, a high efficiency mix can be achieved. These mixes usually have a slightly higher strength and durability than mixes with just natural aggregate stone." Steel slag has also been used as an SCM, while TMS also supplies EAF slag to several cement companies as a cement raw feed.
Andrey Korablin of Russian company SmartScrap Ltd, celebrated his birthday by giving an overview of the Russian steel and slag markets. Russia is the fifth largest steel producer in the world, just behind the US, producing around 70Mt, concentrated in the ‘Central Federal District,' around Moscow, in the south west and also around the Urals. The largest producers are Evraz, NLMK, MMK and Severstal. Many slag producers process their own slag, but others use either subsidiary companies or independent processors. Only around 50% of metallurgical waste is recycled. Federal laws are being tightened on waste dumping, while the goal of the Ministry of Industry is to bring the level of municipal solid waste recycling to 80% by 2030, while there are also potential tax breaks for slag use. Road construction and use in the cement industry are the areas, Andrey concluded, with the most potential for increased slag use in Russia.
At the start of the second session, on slag beneficiation, Victoria Masaguer Torres of ArcelorMittal Spain spoke about the use of steelmaking slag in the passive neutralisation of mine waters. The project started a decade ago when a highway construction project allowed the interaction between groundwater and pyritic materials that caused an acid water problem. A laboratory-scale anoxic trial using steel-making slag was used to prove the efficacy of the slag as a neutralisation agent: calcium content of the slag was reduced during the trial, while the pH of the acidic waters was reduced. In a pilot scale trial, 50t of ladle slag was used in one pit, while limestone was used in a control pit. It was found that limestone achieve an acidity reduction of around 90%, compared to around 80% for slag. The slag has a half-life of around two years, and following the exhaustion of the slag as a neutralising material, the pit would be closed and left in place.
Patrick Lecherf of Euragglo next spoke about the agglomeration and briquetting of steel-plant byproducts. Particles are briquetted by first squeezing out the air between particles. Then, if the particles are not self-compacting, by using a binder (such as molasses and lime in the case of steel plant byproducts), the materials are formed into briquettes by being squeezed between patterned rollers. Other binders can be used, such as bentonite, sodium silicate, lignosulfonate, polymers and hardeners, starch and cement. The abrasiveness of the material to be briquetted will determine the frequency of maintenance of the forming rollers.
Amir Shakurov of Ecoslag Recycling of Russia then gave details of molten slag beneficiation using an innovative drum crystalliser. Amir pointed out that a number of different slags have similar viscosity, melting points and enthalpy over a similar temperature range (1500-1800°C). The Ecoslag solution is the accelerated cooling and solidification of molten slag (including carbon, stainless, ferro alloys, copper and nickel slags) using a continuously-rotating drum crystalliser to stabilise dicalcium silicate into a stable form. Amir suggested that the slag crystalliser is built of heat-resistant materials that can withstand the wear-and-tear of 100,000 melts. The Ecoslag drum crystalliser has been successfully installed by the Vyksa steel plant in Russia. Amir mentioned a previous Russian invention for slag cooling and granulation in a rotary drum with steel balls and water sprays, which he claimed has been copied by Chinese firms and has now been re-exported around the world.
Jitka Halamová and Jiří Pyš of ArcelorMittal Ostrava, a company that will soon become an independent unit, next spoke on the efficient use of slag resources. Starting in 2012, the company commenced a series of small steps towards improving the recycling rates of its slag materials. Better internal communication, benchmarking, cross-exchange of ideas from other units, logistics optimisation, and some equipment upgrades allowed the beneficiation and significant addition of value to slag.
Global Slag Awards Dinner
At the end of the first day of the conference, delegates gathered on the dining yacht Grand Bohemia for a cruise along the Vltava River, among the fabulous sights of historic Prague. During the cruise the Global Slag Awards 2018 were presented. Global Slag company of the year (slag/slag product producer) was Harsco Metals and Minerals, and the slag user of the year was CRH Group. The ’supplier of the year’ for technology, equipment or services was Loesche. The Recoval Dria unit in Belgium was named as the Global Slag plant of the year, and, fittingly, Carbstone blocks (from the same company) were named as the slag product of the year. The Global Slag ‘technical innovation’ award went to Loesche for its process for steelmaking slag beneficiation. In a popular decision, Dr York Richard was named the ‘Global Slag Personality of the Year.’ Finally, it was announced that the Global Slag Conference will return on 3-4 April 2019 to the location where it has most recently (2014) achieved the greatest number of delegates - to a location in the very heart of the ‘slag universe:’ the charming and well-located German town of Aachen.
Conference second day
On the second day of the conference, Phillip Hemple of Gebr. Pfeiffer SE spoke about the MVR vertical slag grinding mill, with MultiDrive. The mill can grind up to 600t/hr of OPC, with total drive power up to 18,000kW. The MultiDrive concept is essentially the substitution of a conventional drive with planetary gear and axial thrust bearing, with up to six decentralised drive units with girth gears and radial thrust bearings. Phillip showed that the vertical roller mill has the lowest long-term maintenance cost. The MVR mill has a parallel grinding gap, leading to symmetrical wear and the ability to turn the rollers. Cement Australia grinds GBFS at Port Kembla with a MVR 6000 C-6 mill, with 5500kW, to 4000-5000 Blaine.
Taking a different view, Dr York Reichardt of KHD Humboldt Wedag spoke about operating results using a roller press for grinding blast furnace slag. York suggested that a strong point of recommendation for the roller press is the roller surface of tungsten carbide studs, which has a guaranteed lifetime of 17,000hr without refurbishment. He also pointed out that the entire plant needs to be wear-resistant, since there is no point in having a roller that lasts 20,000hr but with chutes that wear out after 2000hr: all parts of the plant need to be designed to last when handling an abrasive material like slag. A new series of even larger KHD roller presses will grind up to 280t/hr of OPC and up to 180t/hr slag (to 4200cm2/g Blaine).
Andreas Jungmann next gave a presentation on behalf of Loesche on steel and steel-alloy slag processing. A Loesche vertical roller mill can be used for slag comminution, and Andreas also gave details of a dry density-separation step based on a fluidised bed approach. Such a process has been installed at the Orbix (Recoval/Recmix) stainless steel slag processing plant at Farciennes in Belgium, driven in large part by the economics of metal recovery. Another approach is to modify the molten LD slag (using technology such as from Primetals and FIB), so that the slag has a much lower metal content, making it much more similar in composition to clinker. Ultra-fine grinding can then activate the ‘cryptocrystalline’ belite phases (which are actually crystals smaller than 1µm), to give a 28-day strength similar to OPC.
Fernando Dueñas of Cemengal then gave details of the Plug&Grind modular grinding system, featuring an OK VRM from FLSmidth. The Plug&Grind modular mill concept has previously been based on ball mills, and has focused on small to medium capacities, from 60,000t/y up to 400,000t/y ('Plug&Grind Xtreme'). The new vertical roller mill concept uses a three-roller VRM with 1600kW that can grind slag at 4000 Blaine at 60t/hr or 450,000t/y. Such a unit, grinding cement at 500,000t/y and using 1300kW motors, has just been sold to CRH at its cement plant in Dunbar, Scotland.
Andreas Ehrenberg of the FEhS - the Institut für Baustoff-Forschung e.V. - next spoke about the grindability and reactivity of stored granulated blastfurnace slag. Andreas pointed out that a GBFS stored outside in moist conditions will react and will harden. After initial ‘proof-of-concept’ laboratory tests, a 3000t test pile was formed and was sampled over 55 months. It was found that, without grinding or activation, the material at the bottom of the slag pile became rock-hard, through the hydration and carbonation of the surface of the slag granules. Material at the top of the pile was not so strongly altered. No significant crystallisation of the granules had occurred during storage: hardening was due to superficial surface hydration, forming calcium-silicate-hydroxide (CSH) reaction products. It was found that the grindability of the slag increased with storage time, requiring only 50% of the specific grinding energy for the same fineness after storage for 55 months. However, this was due to the increased grindability of the reacted surface layer, rather than that of the unreacted interior of the granules. In further tests, it was found that for samples ground to the same Blaine fineness, the particle size distribution was actually coarser, due to the preferential grinding of the softer surface layers of the hydrated granules. Prehydration products are located at the surface of the slag particles, so that the majority of the slag is unaffected by hydration. Andreas concluded that when GBFS is ground to the same particle size distribution, then there is no significant loss of strength despite increasing length of storage time - even for decades.
Next Nick Jones of Harsco and Mark Tilley of Lixivia gave a co-authored paper on a pilot-scale project for the extraction of valuable high-purity calcium products from steel slag. Nick reminded delegates that steel slag is currently used as construction aggregate, for agriculture, for drainage materials and as a feed material for construction and insulation, but he said that Harsco is always looking for approaches to add further value to steel slag. New ideas go through a process at Harsco, from discovery and development to final commercial deployment. Such an idea is Lixivia's Selex process, which is a patented water-based hydrometallurgical process using a recoverable lixiviant (a liquid used to selectively extract a metal from a solid ore) that can selectively separate the complex mixture of minerals and metals that are found in steel slag, which can then be sold onwards. The pilot-scale project concentrated on the production of high-purity precipitated calcium carbonate. Full results will be presented in a future edition of the Global Slag Conference.
The penultimate presentation at the 13th Global Slag Conference was given by David Algemissen of the FEhS, sharing details of the ProInnoLDS project, which was to find new markets for Basic Oxygen Furnace BOF-slag-based products, through the creation of a low-phosphorus hot metal that could be recycled in the steelworks. The problem is an acute one, since 3.1Mt of BOF slag is made each year in Germany, and 10.7Mt each year in Europe. Reducing the basicity of the BOF slag results in a dramatic increase in viscosity, to levels where the reduced slag cannot be poured. Adding 10% sand at 1650°C improved the pour ability of the slag, which was further improved by heating to 1750°C, but not to finally acceptable levels, and also without producing minerals that would add cementitious properties. Increasing levels of sand addition and adding Al2O3 decreased the basicity, giving a product of low viscosity, high glass content and with adequate cementitious mineralogy, essentially through modifying the chemical composition of the BOF slag to become nearly identical to that of blast furnace slag. The economics of the chemical modification of the slag and reheating required are currently ‘marginal,’ but may change with the evolving cost of carbon emissions (from the cement industry) over the coming years, to give a economical replacement material for Portland clinker.
The final presentation was given by Jürgen Haunstetter of the German Aerospace Centre (DLR), on the use of slag as a thermal energy storage medium in a concentrated solar power (CSP) unit, as part of the EU-financed research project 'REslag.' Molten salt is commonly used, up to 450°C, but regenerator-type storage can be heated using hot air, up to 1300°C and slag is being considered as the heat storage medium. Hot air would be passed downwards through a chamber containing the material, heating it through the day, until the sun sets. At this point cool air would be passed up through the medium in the chamber to heat the air before it was sent to the boiler. Ceramic bricks and ceramic honeycombs, refractory materials and packed beds (for example containing slag) can all be used as the thermal storage medium. However, during heating and cooling thermomechanical stresses arise in and between the particles and also between the particles and the walls of the containers. The project was to determine the stresses in slag materials and in the slag containers. After 500 compression cycles at 600°C in an experimental rig, no significant damage was found to the slag, suggesting that it could be stable in industrial usage. It was found that perlite refractory bricks were too fragile to be used as an insulating medium at the bottom of such a chamber, but that super-duty firebricks were robust enough for potential use.
Conference prizes
At the end of the conference, a number of prizes were awarded. Following a vote by delegates, Nick Jones of Harsco and Mark Tilley of Lixivia won third prize for their paper on a new process to extract valuable minerals from stainless steel slag, while David Algemissen of the FEhS won second prize for his paper on BOF slag modification. However, completing a good day for his organisation, Andreas Ehrenberg won the prize for the best presentation for his paper on grindability and reactivity of slag after prolonged storage. Delegates agreed to meeting again soon, in Aachen in April 2019.
Selected presentations
