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.
