Over 140 delegates from nearly 40 countries assembled in Brussels at the end of November for the 5th Global Slag conference and exhibition. As ever, the delegates represented the world’s largest slag producers, as well as the main slag users, including cement and concrete groups from around the world. The 6th Global Slag Conference will take place in Sydney, Australia, at the invitation of the Australasian (Iron and Steel) Slag Association, in November 2010.

The 5th Global Slag Conference took place in the shadows cast by the global recession. Iron and Steel companies world-wide have cut their production by 50%, so that slag production has also fallen by a half. However, this has given rise to a new dynamic in relations between the slag producers and slag users. Cement demand has typically not fallen by as much as slag production, so demand for slag (compared to how much is available) has increased. Given that CO2 emissions permits may increase in cost in the next couple of years, the cement producers are also scrambling to try to secure long-term supplies of (non-CO2-emitting) slag. Such was the intruiging background to the conference. The first speaker was Charlie Zeynel of ZAG Industries. He stated that in his experience, the total volume of slag traded around the world has dropped. However, slag supply has become very tight, and slag prices have doubled. Slag is now even being shipped from Japan as far as France and Belgium (after the closure of a European steel works situated next to a slag-grinding plant). Japan has started to increase its production of steel and slag due to an increase in demand from China, although overall slag demand has dropped due to the fall in cement demand (which has led to widespread clinker grinding overcapacity).

Charlie pointed out that around 25-30% of pig iron tonnage is composed of slag, and that an increasing percentage of slag is granulated - increasing from 48% woldwide to 68% worldwide in 2010, or 292Mt of the 450Mt of blast furnace slag produced worldwide. However, the proportion granulated varies from country to country. In the US, only 35% of BFS is granulated, 48% in China, 73% in the EU and 79% in Japan, while in India fully 83% of BFS is granulated.
Cement demand in Japan is forecast to have dropped by 20% through 2009, as big infrastructure projects have been cancelled, with the effect that a greater proportion of the locally-produced slag and GGBFS is now available for export. As Charlie said, “Slag supply from China is likely to dramatically increase, but the quality is suspect.” He started and finished his presentation with a call for the iron and steel industries, the power companies (and their ash-producing units) and for the shipping companies to come together to engage in some ‘joined-up thinking.’

Stuart Reynolds of globalsteelconsultants.com backed-up Charlie’s remarks on slag trends, and mentioned that a new report on slag markets worldwide is now available.

Hendrik van Oss, a specialist on cement, ferrous slags and coal combustion products at the US Geological Survey, spoke on the environmental issues affecting the use of slag and similar materials in the US construction sector. Hendrik mentioned that new regulations on fly-ash suggest that it should be classified as ‘hazardous’ if it is stored, but that it would be ‘non-hazardous’ if used ‘beneficially.’ However, Hendrik suggested that power plants may cease to make fly-ash available for third-party use for fear of incurring product liabilities.

Heather Booysen of Samancor Chrome then gave a summary of the situation for slag in South Africa. In 2006 the government decided to de-list ferrochrome slag as a hazardous material, to try to ensure that the material was used in a more productive manner. Samancor managed to have its materials passed for use, before the ‘door of opportunity’ closed to other producers. The material is now classified on the basis of its most hazardous constituent, and this has allowed it to be used in bricks, concrete products and road building, although Heather says that it is a big job to change perceptions of the materials. A new waste management act is now promoting the re-use of waste, and this is expected to increase the proportion of slag used in South Africa. Renaat van Geel of Thermo Fisher Scientific started the technical sessions at the conference with an overview of how slag may be analysed using the ARL 9900 integrated XRF-XRD workstation. The machine can analyse pressed powdered pellets, directly moulded pellets and even in-situ slag. As always, longer counting times provide higher accuracies and lower detection limits.

Daneel Geysen of the University of Leuven next spoke on the link between slag chemistry and valorisation. The composition of hot slag can be controlled by variation of the raw materials, the furnace type, additions, the targets that the furnace is set, slag foaming and even by the personnel operating the equipment. The control of the composition of cooling slag can be controlled by the mixing of slags, through control of the cooling rate (either in the slag yard or via box cooling), via water spraying, slag layer thickness and of course through the operation of any granulating device. Magnesium is normally added to the slag to stop the dissolution of magnesium from slag pot refractories - the slag must be saturated in Mg but not oversaturated. The transition from beta-C2S to gamma-C2S can be prevented by adding boron to the slag, although this will reportedly soon be banned. The CaO/SiO2 target for the slag needs to be optimised, as does the cooling profile for the slag. Cr(VI) leaching potential can be reduced by increasing the development of crystalline spinel formation. Daneel also stated that reducing the slag pH will tend to reduce the leachability of minor constituents.

Vlad Popovici of Bredero Shaw, Canada, then went on to speak about the possibilities for valorisation of Electric Arc Filter (EAF) dust. Most recycling options for EAF dust produce varying amounts of zinc oxide as a valuable by-product, due to the variability of the composition of the original dusts, as well as further EAF dust recycling slag. Vlad forecast that EAF dust recycling slag tonnage will increase from the current level of 1.5Mt/year to around 4.5Mt/year within 10 years.

New building material
Mieke Quaghebeur of the Flemish Institute for Technologicial Research (VITO) gave details of an innovative new product ‘Carbstone,’ which uses fine-grained steel slags treated at high pressure with CO2 to form a high-strength building material. The carbonated materials “can compete with concrete products and have excellent environmental and technical properties, as well as the advantage of sequestering 180-200kg CO2/t of slag.” The process can use different waste materials, including LD slags, stainless steel slag and furnace bottom ash, although the final mix needs to have the correct composition, the right suite of reactive minerals and the correct grain size profile. The ingredients are mixed with water, shaped in a mould and cured with CO2, with carbonation increasing (intriguingly) from the centre outwards. A pilot installation for 10,000t/year of slag use is currently planned for 2010.
The next paper, by co-authors from Recmix Belgium, was also on the valorisation of stainless steel slags. Evelyne Nguyen pointed out that beta-C2S-rich fines can best be used as a filler in self-compacting concrete, while gamma-C2S-rich fines are best used as artificial aggregates for road construction, or recycled as slag foaming agents.

Professor Roberto Roberti and co-authors from Italy and Austria then spoke about the Slag-Rec project for direct dry granulation of EAF slag, using a new machine. The presentation was met with lively questioning.

Gala dinner and Global Slag Awards The conference social evening took place at the stunning Brussels Atomium, on the site of the 1958 World Fair. Following an hour or so of roulette and blackjack (delegates had been issued with 300 ‘slag dollars’) attendees sat down to local dishes as the globular room swayed slightly in the wind (the ‘globes’ of the Atomium represent an iron crystal - appropriately - magnified 165 billion times). It transpired that Mari Kurttio of Tapojärvi Oy (lower right) had won the most (possibly with the help of her colleagues) at the tables, and was awarded the ‘best gambler’ award.

During the dinner, the Global Slag Awards were presented. Cloos S.A. was awarded the ‘company of the year’ award, after gaining five new contracts in a tough year. Ecotrade was the popular winner of the ‘slag supplier of the year’ award (see right), while ArcelorMittal Stainless Steels’ Chatelet plant in Belgium was awarded the ‘plant of the year’ title. Slag product of the year was awarded to Carbstone, see above, while the Global Slag ‘personality of the year’ went to Nigel Cooke of Lafarge Cement UK, for his previous work (and future work, in the same vein as Obama and the Nobel Peace Prize) on ash and slag use in cementitious products.

Second day
The second day concentrated on slag grinding and handling and on slag applications. Gérard Marchal summarised a lifetime’s work in only 25 minutes with his presentation, ‘What I have learned in a lifetime in comminution’ - an independent assessment of the options now available for slag grinding. Stefan Baaken from Loesche next gave an overview of slag grinding using the Loesche 2+2/3+3 vertical roller mill, and was treated to an extended questioning session, such was the level of interest in the possibilities of his equipment. Conference stalwart York Reichart of Gebr. Pfeiffer rounded-off the session with an overview of operational data from the MPS vertical roller mill for producing slag powder and slag cement.

Davide Gambarotta of Italian-international bulk materials handling company Gambarotta-Gschwendt srl gave a thought-provoking presentation on state-of-the-art handling for slag, and Ben Laenen, on behalf of colleagues from VITO, spoke about an integrated evaluation strategy for the recyling of metallurgical slags, particularly with regards to Belgian slags.

The final presentation at the conference was given by Erki Unn of Estonian company Silteh W2P, on thermal decomposition and valorisation of waste using a molten slag bath. The original technology was developed by the Gintsvetmet Institute in Russia and uses a a sparked molten slag bath at a temperature of 1250-1600°C to thermally decompose industrial, municipal and even hazardous wastes, with slag/cement, steam, electricity, metals, gases and potable water as some of the by-products. Once again, the fascinating presentation was rewarded with intense questioning from the assembled delegates.

Awards and prizes At the conference farewell reception, a number of awards were presented. Loesche won the ‘best exhibition stand’ award. Following voting by delegates, Heather Booysen of Samancor Chrome was the valiant fourth-placed presenter, while late replacement Erki Unn of Silteh W2P was third. In second place with his very interesting presentation on trends in the global slag markets was Charlie Zeynel of ZAG International, but Mieke Quaghebeur (left) of VITO, the Flemish Institue for Technological Research was awarded the ‘best presentation’ award.

At the invitation of the Australasian (Iron and Steel) Slag Association, the 6th Global Slag Conference and Exhibition will take place in Sydney, Australia, on 22-23 November 2010. We hope to see you there!