25 - 26 June 2025, Vienna, Austria

The 17th Global Slag Conference has successfully taken place in Vienna, with 140 delegates from 36 countries, 20 presentations, the presentation of eight Global Slag Awards, over two days of intense networking. The 18th Global Slag Conference will take place in Istanbul on 15 - 16 April 2026.

First Day

Volkert Feldrappe of the FEhS kicked off the conference with an overview of the slag situation in Europe. The European iron and steel industry is making extensive and expensive plans to convert to 'greener' steel-making, but this will produce less GBFS. Approximately 73Mt of slag will be needed by the European cement industry by 2050. Large quantities of EAF slags and direct reduced iron (DRI) slags will become available, and work is ongoing to make these materials more reactive (and more valuable). Early attempts to increase EAF slag reactivity increased viscosity to unusable levels, while treatment with quartz sand was more successful, producing a cementitious  material, albeit with low early strength. The ‘Sabine’ project used non-reduced, water-granulated sand-treated slag, but early strengths were ‘muted.’ The 'WAGEOS2SHS’ (water-granulated EAF slag transformed into black GBS) project will continue to 2027, with a pilot plant at an EAF plant. The latest research suggests that DRI slags can be treated to give latent hydraulic properties, with concrete durability yet to be fully proven.

The conference then convened a well-received panel discussion, with representatives from north and south America, South Africa, northwest Africa, Europe, India and Asia discussing the difficulties of using slag and slag products in their respective jurisdictions. The consensus was that success starts with regarding slag as a co-product, by-product or even as a product - not as anything less valuable!
 
Sun In Hong, Hyundai Steel, next explained that once processed into aggregate, 50.3% of slag in South Korea heads to landfill, with the remainder used for road stabilisation (46.3%) and concrete (3.3%). To increase the use of steel slags in construction, the company undertook a series of long-term structural trials, starting in 2013. Individual panels were made from different blends containing granulated blast furnace slag (GBFS), BOF slag (BOFS) and electric arc furnace slag (EAFS) aggregates and sand. All panels exceeded South Korean compressive strength standards. Concrete containing GBFS was better than OPC at resisting chloride, which could be assessed due to the buildings’ proximity to the sea. Initiation time of steel corrosion was three times longer than for OPC concrete for some of the BFS combinations, due to the dense pore structure in the interfacial transition zone (ITZ). At 13 years and 4 months, the BOFS-containing structure exhibited a poor surface due to the volumetric expansion of free lime in the BOFS. In contrast, concrete made with GBFS aggregates exhibited no defects 12 years after construction.

Following on from his colleague, Hydundai Steel’s Jeshin Lee said expansion issues with BOFS can be eliminated by fine grinding. The company ground BOFS for 120 minutes using a ball mill. The product was added at different particle sizes at 10% and 20% substitution for sand and cured at 20°C and 90°C. At 20% BOFS at 90°C, mortars containing slag larger than 2.4mm were destroyed by free-CaO expansion within five days. No problems were observed at a particle size of 150μm. At 20°C no expansion was observed over 90 days for any sample. With 10% BOFS, concrete blocks exhibited a slight reduction in compressive strength compared to a blend containing 15% GBFS and 10% fly ash. The BOFS blocks exhibited a higher compressive strength than concrete made with OPC. The presenter asserted that the low embodied emissions of BOFS (82kg of CO₂ per tonne) enable producers to reduce CO₂ emissions substantially with a BOFS substitution rate of just 10%. A concrete blend that contained 10% BOFS and 10% gypsum led to higher compressive strength. Lee hypothesised that this was due to the BOFS containing 6% mayenite which led to the formation of ettringite.

Giulia Bragaggia, University of Padova, spoke about the use of sleelmaking slag as a filler for polymetric matrices with polystyrene (PS), polymethylmethacrylate (PMMA), polypropylene (PP) and grafted PP.  Samples were made using a plastograph, which melts the polymer and combines it with the slag using a screw. Samples were made using electric arc furnace slag (EAFS) at 5%, 15%, 30% and 40% by weight. With PS the Youngs Modulus was increased from 3863MPa (no EAFS) to 6296MPa at 40%, with similar results for PMMA. PP is more elastic, with its Youngs Modulus increasing from 38MPa at 0% EAFS to 254MPa at 40% EAFS. Grafting maleic anhydride onto PPC at 8% by weight caused a further slight increase due to the oxygen of the maleic moiety chemically bonding to the metal oxides in the EAFS. Partial activation of the EAFS by activation with a monomer followed by free-radical polymerisation achieved a similar result.

Martina Messuti, Tenova, presented three examples of her company’s work with granulated slags. The core part of her talk covered a CFD study looking at the design of a dry granulation process for 100% direct reduced iron (DRI) slag as part of the InSGeP (Investigations of Slags from Next Generation Steel Making Processes) project. A large fan and specially-designed nozzle was used to blow a falling stream of molten slag into droplets. The initial layout was altered by adding a ‘slag tundish’ to control the flow rate of the falling slag close to the fan. This allowed for average droplet diameters close (2.03mm) to that of the previous laboratory scale pilot (1.86mm). Messuti further discussed results from tests using granulated electric arc furnace (EAF) slag in a mortar sample in place of sand and a report on an industrial-scale installation of a ladle furnace (LF) slag dry granulation unit at Ferriere Nord steel plant in Italy.

Nie Wenhai, Sinoma-Tianjin, was unable to attend the conference in person so he supplied a video recording of his presentation on the ultrafine grinding of slag. He first set the scene in China revealing that 256Mt of granulated blast furnace slag (GBFS) and 136Mt of steel slag were produced in 2024. Wenhai explored the grinding technology required to grind granulated blast furnace slag (GBFS) to a high fineness of 6000cm2/kg or finer. As the fineness increases the performance of the resulting product improves. Notably, as the fineness of a slag powder grows the sphericity of the particles tops out at 0.884, its activity continuously increases and the fluidity ratio gradually decreases. The company is testing a TSM dry stirred mill - composed of motor, cylinder, agitator and fine ceramic ball grinding media – to reach higher levels of fineness with GBFS slag.

Chen Xialoing, Sinoma-CDI, next looked at the utilisation of steel slag at scale. Challenges include high content of f-CaO, f-Mg and iron. The first two issues can cause problems with volume stability (expansion) and cementitious properties. Xialoing emphasised that the three main ways to activate steel slag are by physical activation, reformulation at high temperature and chemical activation with mechanical grinding (physical) being the preferred approach. Xialoing provided a number of reference projects including the Wuan Xinfeng Lvneng Waste Solid Disposal Project that was built in 2020 and 2021. This site has a capacity of 9Mt/yr of blast furnace slag and 4Mt/yr of steel slag. It has eight VRMs. The speaker said it was the largest steel slag grinding site in the world.

Ehab Tara of the Montanuniversität Leoben then spoke about the characterisation and utilisation of slags from zinc recycling. Europe annually uses around 2.6Mt of zinc each year, with only 27% produced in the EU. Byproducts from the steel, lead and zinc industries contain large amounts of recoverable zinc, and lead slag or steel mill dust are primary sources. In Ehab’s experimental setup, firstly these materials would be dried, and would then proceed to a pyrometallurgical reduction step (using bio-char as the reducing agent) followed by adjustment of basicity (using CaO/SiO2) and tapping of the modified slag. It would then be granulated and crushed if required. He then carefully studied the resulting slags using a variety of instruments, and hopes that his research leads to an industrial-scale slag processing plant that will provide a valuable zinc product.

Michael Wyrsta of Karbonetiq gave the final presentation at the end of the first day, outlining a carbon dioxide removal (CDR) process, by using steel slag as an absorbent for CO₂, working with Harsco Environmental. Mike said that 400Mt of steel slag is generated annually, mostly stockpiled or used as low-value aggregate and he suggested that it has under-leveraged chemical potential. The voluntary carbon market is active and has premium pricing of around $150-200/t of CO₂ removed. The slag is crushed to less than 5mm, loaded into a modular high-surface area Karbonator system, which allows carbon dioxide to be passively absorbed from the air over 7-14 days through the carbonation of free lime to form larnite. The carbon removal is certified, and the audit-ready credit sold. The system removes around 100 - 300kg of CO₂/t of slag used. Measurement, reporting and verification (MRV) is critical to the validation of the process. EAF, BOF, LF and LKD can all be used in the process. The processed slag can be used in a variety of applications.

Global Slag Awards Dinner

Delegates then enjoyed an evening at the Schloss Schönbrunn, culminating in the presentation of the Global Slag Awards 2025. 'Company of the Year' (as a slag-product producer) was Swecem, and suppler of the year was Paul Wurth S.A. Slag plant of the year went to Ecocem's Dunqerque unit, with Conor O'Riain of Ecocem also named as one of two 'Global Slag personalities of the year,' alongside Swecem's Ludwig Zetterström. The Global Slag 'product of the year' was awarded to AgroSilício from Harsco, Titan scooped the award for slag user of the year, and the technical innovation award went to Karbonetiq.

Second Day

Gulvira Shaimerdenova started the conference’s second day, with a presentation on the slag sectors of Central Asia, for which reliable statistics are particularly hard to find. Uzbekistan, Turkmenistan, Kyrgyzstan, Tajikistan and others are still developing, with slag used locally in small quantities, generally in the construction industry. On the other hand, Gulvira pointed out that Kazakhstan, the ninth largest country in the world, largest uranium producer and a major steel producer, is a major industrial power. The country produced 4.2Mt of steel in 2023, with an iron and steel slag production total of around 1.5Mt, with significant quantities of copper and aluminium slag as well. Gulvira stated that the country is in the process of aligning its regulations - including those concerned with slag and slag products - with those of the European Union. Large quantities of ferrous slag exist in stockpiles in the country and are available for sale and use.

Seolji Nam of South Korea’s RIST institute next spoke about a novel continuous multi-stage magnetic sorting process for slag, using weak magnets. The elegant process enables the identification of the optimal separation conditions, based on slag characteristics, allowing recovery of various grades of high-ferrous and low-ferrous slags, which can be used for steel-making raw materials, clinker production or for aggregates.

Matt Kennedy-Good, president of Neocrete, outlined new activation approaches for steel slag. The company has an inorganic fine dry powder activator, which when dosed into GGBFS at 3-7% accelerates development of early strength, and improves workability. Neocrete also activates other SCMs, including ash and calcined clays. The activator can be dosed into the cement, or can be added to fresh concrete.

Charles Zeynel of ZAG - in his last-ever presentation before retirement - spoke about risks, rewards and routes for GGBFS. Around 1.9Bnt of steel is produced each year, while around 1000t of concrete is poured worldwide each second. The World Steel Association reports that blast furnace operations, which generate GBFS as a byproduct, represented 71% of global steel production in 2024, down from 74% in 2022 as electric arc furnace methods gain market share. Maritime constraints are increasing due to geopolitical factors. Charles suggested that the global GGBFS market will increase to a value of $32Bn by 2031, growing from 408Mt in 2022 to 498Mt in 2035. Asia is a leader in slag production, but the US is still an attractive market for slag, given attractive margins. AI-driven quality control, nano-grinding technology and new alkali-activation systems are all innovations coming down the tracks towards the slag industry. Charlie has been quietly shouting about the benefits of the use of slag for many years - since at least the first Global Slag Conference - and his persistence has finally come to fruition, with slag now widely valued, and his own trading company going from strength to strength under the guidance of his son, Christopher.

Andreas Weber, Founder and CEO of Ferrum Technologies, spoke about the conversion of electric arc furnace slag (EAFS) into a material more akin to granulated blast furnace slag (GBFS). EAFS is available in large quantities but is not practical as an SCM, whereas GBFS is in high demand but supplies are in decline. EAFS can be converted into a ‘GBFS-type material' in the company’s proprietary Ferrum Melter. It is also possible to use low-quality iron ore in the EAF, which leads to new slag chemistry that can also be further processed in the Ferrum Melter. Ferrum’s process was validated at the laboratory scale in 2023 in collaboration with FehS. In 2024 it was validated at MFL, a small steel producer in Austria. The company is currently searching for a partner to test at full industrial scale in 2025 and 2026.  
 
Priyapratim Patra then presented three slag valourisation projects currently being undertaken by JSW Cement. In the first, BOF and LF slag was used as a raw material for clinker as a partial substitute for regular alumina sources. Tests with three different clinkers produced concrete with compressive strengths similar to those of standard concrete. The second project showed that EAF Slag can be used as an SCM in conjunction with GBFS at up to 10%. The third project involved the modification of BOF slag into a ‘sulpho-SCM’ by fine grinding and reaction with sulphuric acid to generate gypsum. Again, compressive strengths were in line with regular blends.

Wilbert Mtangi, Chinhoyi University of Technology, Zimbabwe presented a literature review on developing pozzolanic cements from steel slags. He set the scene in Zimbabwe as a country with a large mining industry creating plenty of byproducts available for exploitation. In summary, pozzolanic cements minimise bleeding in concrete since they act as micro-fillers and lubricants. However, there is a need to monitor the quantities of free-CaO and free-MgO in the artificial pozzolanic materials as they result in volume expansion and instability, which causes internal tensions leading to cracking and degradation.

Anna Gobetti, University of Brescia, discussed her research of using EAF and LF slags as a filler in rubber compounds. Using slags as fillers has previously been discounted due to the risk of leaching of heavy metals. In her team’s research, the slag compounds exhibited a higher average particle size than a commercial CaCO3 based filler. During testing a shielding effect from leaching due to the polymer matrix was confirmed and comparable mechanical properties were observed. Compression tests before and after 24 hour immersion in water were similar for CaCO3 and EAF slag but LF performed worse after immersion. Notably, Gobetti’s life cycle assessment on a rubber component made using an EAF slag instead of CaCO3 performed significantly better with a marked reduction in potential to cause cancers in humans. She then showed some examples of rubber components such as o-rings, oil cups and gears made using slags as fillers. Gobetti noted the size of fillers market at over 15Mt/yr, with a value of €12.5 billion in 2023 and disparities in the geographic availability of conventional fillers.

Lukas Paul of Beumer next spoke about the use of pipe conveyors to transport slag in difficult sites. Existing buildings, roads, railways, and even rivers may form obstacles to traditional conveyor belts, but a pipe conveyor, “which is just like a normal conveyor, only closed and more flexible!,” said Lukas, allows conveyance around curves and bends. The conveyor belt is turned over on itself, protecting the product from dust and spillage and from interaction with the atmosphere, and also allowing transport at high inclinations, up to 30°. The conveyors can be engineered to carry up to 6000t/h, and have been built up to 8km long.

The final presentation at the conference was given by Zak van der Westhuizen of Metix (Pty) Ltd, which is part of the SMS Group, as is leading granulator supplier Paul Wurth and tapping measurement technology supplier TMT. Zak gave the business case for including a patented pyrometallurgical slag valorisation furnace (SVF) into new or existing iron and steel facilities. The SVF can take iron and steel slags and refining slags, as well as scales, sludges and dusts, and add value to them through conditioning in the furnace through the reduction of metal oxides to the metal phase and settling and collection of metals entrained in the feed, while also using the sensible heat from the upstream process. There is also the possibility to combine with a waste heat recovery unit, and the use of carbon monoxide gas from other parts of the process as a fuel. The SVF may be circular or rectangular, depending on local conditions, and typically offers payback periods of less than three years. 

Prizes and farewells

After the conclusion of the technical programme, delegates gathered for farewells and prizes. Martina Messuti of Tenova was in third place of the 'best presentation' prizes, followed by Zak van der Westhuizen of Metix (both presentations being on high-temperature beneficiation of slag). However, Charles Zeynel won the prize for best presentation, with his talk on the future prospects for slag - the last-ever of his career. We will miss him!

The day after the conference, delegates had the opportunity to visit the voestalpine Leoben steelworks, two hours south of Vienna. Participants were treated to a live steel tapping, and were able to see slag granulation in action. The steelworks had its annual families' day celebration the same day, and delegates were able to see the impressive efforts that the company goes to to make its workers feel valued, while throwing open its doors to the local community.

Delegates strongly praised the event for its slick organisation, collegiate and friendly atmosphere, for its strict adherence to its timetable, for its global outlook and for its excellent networking opportunities.

The next Global Slag Conference will take place on 15 - 16 April 2026, in Istanbul. See you there!

Below: Delegates at voestalpine Leoben.