“Save a megawatt, save an industry.”
Mintek’s Pyrometallurgy Division has partnered with Ab Etiproducts Oy and Siyanda Chrome Smelting Company Pty Ltd to investigate the potential benefits of using boron-containing minerals in ferrochrome smelting.
The May 2014 updated Report on Critical Raw Materials for the EU includes chromium on the list of 20 such materials. Chromium is the second-least substitutable material (after phosphate), an estimated 80% of remaining world resources is located in South Africa and about 80% of the EU imports are derived from South Africa. These statistics evidence the extent of EU reliance on South Africa as a long-term source for this critical, relatively irreplaceable metal, essential for steelmaking.
South Africa exports chromium in the form of either chromite ore or ferrochromium alloy. Most EU imports are in the form of ferrochromium. Cost competitive ferrochromium production is dependent on relatively low electricity costs. South Africa has suffered from sharp increases in electricity costs over the past few years and the ferrochromium industry has come under significant pressure due to not only these increased costs but also restrictions on the quantity of electricity allocated to it. Any improvement in the cost of ferrochromium production is thus to the mutual benefit of South Africa and the EU.
The slag liquidus (melting temperature) in most pyrometallurgical processes is controlled by the addition of fluxes such as silica, lime and dolomite. Boron-containing fluxes are widely used for glass production because they lower the melting temperature of silica by a significant extent. Several boron-containing minerals have been identified as having a potential use as flux where lowering the slag liquidus is a process requirement.
The proposition of BOFLUX is that the addition of relatively small amounts of boron to the flux will decrease the liquidus, thereby decreasing energy consumption and increasing overall chromium recovery.
The smelting of alloys such as ferrochromium, ferromanganese and titania-containing slags could therefore benefit from the addition of minor amounts of boron-containing fluxes.
These potential benefits include the following:
- Lower natural resource requirement to produce chromium-containing alloys;
- Lower energy consumption and flux requirements;
- Potential to increase metal recovery;
- Decrease in slag formation, and thus less by-product slag to handle and dispose of;
- Less chromium entrainment in the discard slag, which reduces the adverse environmental impact;
- Improved physical properties of the slag (lower slag viscosity);
Turkey is the world’s largest exporter of boron products and is enthusiastic to increase its export markets. Interestingly, we thus have a single opportunity involving two critical materials – the one used to increase the recovery of the second! It is thus essential to keep this aspect in mind when investigating this opportunity. The optimum point should be identified where the recovery of chromium is maximised with the minimum consumption of boron.
The BOFLUX project includes both theoretical modelling studies and medium-scale testwork. While the primary focus will be boron addition to ferrochromium slags, the developed know-how and data can be extended in the future to other commodities. The theoretical studies will include theoretical modelling, thermodynamic evaluations, phase diagram development and measurements. Slag properties are of utmost importance when defining a pyrometallurgical process flowsheet and the experimental phase will evaluate the impact of boron addition on the slag systems associated with ferrochromium production in terms of slag liquidus, viscosity and conductivity. Experimentally-verified data will serve as a basis to design industrial-scale furnaces based on including the optimum amount of boron flux in the feed materials.
The results of this project will not be restricted to the smelting of South African ores. The studies and experimentation will also include samples of chromite ore from EU sources and those smelted in the EU – Turkey and Finland. There are two producers of ferrochromium in Europe: Finland and Sweden (both ERA-MIN member countries). The results of the project will also be made available to these producers.
Scientific objectives and the relationship to the ERA-MIN call
The text of the 2nd ERA-MIN Joint Call for the Sustainable Supply of Raw Materials in Europe (2014) includes the statement: “The scope of the Call is needs-driven research on non-energy raw materials, addressing one or several areas of the value chain”. The BOFLUX proposal is directly matched to this call:
- “needs-driven” – the subject matter of the proposal is related to chromium and borate minerals, two of the 20 recently-identified critical raw materials. The EU thus needs chromium and the South African ferrochromium industry needs ways to reduce their energy cost.
- “research” – BOFLUX includes strong elements of both theoretical and experimental research into a novel area of technology.
- “non-energy raw materials” – chromium and borates both fall into this category.
- “addressing (an) area of the value chain” – BOFLUX falls into Sub-topic 1D (metallurgy) of the stipulated areas for research for ERA-MIN.
The International Chromium Development Association (ICDA) is currently based in Paris, but was founded In South Africa at Mintek. Chromium has recently been added to the list of Europe’s strategic metals, as an essential, irreplaceable component in stainless steel. The EU is amongst the world’s leading stainless steel producers.
The EU and South Africa thus have a long history of collaboration in ferrochromium alloy smelting and this inter-dependence is still very strong. BOFLUX will reinforce and extend this interaction.
The scientific objectives include the following:
- Improved understanding of the dissolution of chromium oxides into slag systems that result from the unreduced and partly reduced components from the chromium spinel (namely Al2O3 and MgO and FeO, Fe2O3 and Cr2O3 respectively).
- Addition to the scientific knowledge of the more traditional slag forming additions, namely SiO2 and CaO, with the characterisation of slag behaviour based on the addition of boron.
- Quantification of the relationships between the slag composition at various basicity ratios over a range of boron levels on the efficiency of extraction during the smelting of ferrochromium.
- Experimental data to support the use of models of these slag systems and to enable mass and energy balances to be calculated using relevant thermodynamic data.
- Application of this data, using the necessary models, to improve the smelting efficiency of smelting chromite ores from a wider supply base, both within the EU and external to the EU. This improved scientific base will support EU efforts to secure a sustainable supply of chromium.
- The technology addressed in this proposal is also applicable to secondary recycling. Chromium has been shown to be very difficult to replace by substitution but is very suitable for recycling and in fact needs to be recycled to avoid any potential negative environmental impact.
About The Consortium
The consortium undertaking the work as proposed is deliberately small and well-focused. The three partners collectively possess all the expertise, facilities and resources necessary for successful completion of the prosed scope, and industrial implementation of the outcomes.
Mintek has the smelting know-how, experience and facilities to undertake the testwork. The BOFLUX project is also complimentary to Mintek’s expertise in modelling and measurement of slag properties.
Etiproducts is the world’s largest producer of boron products and would supply the samples for the project testwork and would ultimately be the commercial boron supplier.
Siyanda Chrome Smelting Company is a South African mining company, producing and exporting chromium to the EU, who would implement the use of boron in their ferrochromium production.
Need more information on the project?
We are aiming to present the first results of the work at the Molten 2016 conference.
Please contact us for more information:
Manager: Mintek Pyrometallurgy Division