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)
