Project: Characterisation of the impact, boron addition has on the physical and smelting properties of chromite slag
| Acronym | BOFLUX |
| Project Topic | The slag liquidus temperature in most pyrometallurgical processes is controlled by the addition of fluxes such as silica, lime and dolomite. High-melting point materials, like chromite ores (the only commercial source of chromium metal), in particular utilises the flux principle. Boron containing fluxes are widely used for glass production since they lower the melting temperature of silica by a significant extent. The purpose of this study is to evaluate the potential use of boron containing minerals in chromite smelting process to achieve improved energy and operating efficiencies. |
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Project Results (after finalisation) |
BOFLUX, funded via ERA-MIN, is a joint project between Mintek, EtiProducts, and Siyanda Chrome Company which aimed to explore the potential benefits of using colemanite as an alternative fluxing agent for chromite smelting. This report is presents at a high level the main outcomes and conclusions of the work. Laboratory-scale smelting tests were conducted at Mintek over the course of two years. The work included evaluation of a variety of boron-containing materials to replace or partly replace conventional fluxes. The laboratory test results indicated that colemanite had the best outcomes. The tests confirmed that addition of boron lowers the liquidus of the slag and smelting can be done at 1650°C, lower than conventional smelting temperatures. The grade of the final product improved by approximately 1 to 2.5 % Cr units, depending on the grade of the ore smelted. The test work was supplemented by modelling work through which various flowsheets were developed and evaluated for suitability. The study focused on South African chromite concentrates, assessing the impact of using various grades of colemanite, analyses and samples provided by EtiProducts. 7 Project BOFLUX Characterisation of the impact, boron addition has on the physical and smelting properties of chromite slag EtiProducts can supply a wide range of grades and part of the objective was to establish whether any significant benefits can be demonstrated for a one type of colemanite over any other. The mainconclusions from the study can be summarised as follows: • Nosignificant benefits were demonstrated between the various types of colemanite ores which EtiProducts can supply. Colemanite products that would be suitable for chromite smelting of South African chromite ores would need at least 30% B2O3 and 25% CaO with a maximum SiO2 content of 8% (on an uncalcined basis). Most products in the EtiProducts range meet these requirements. • Replacing conventional fluxes with colemanite appears to offer an opportunity for process intensification (increased chrome production for the same power input). The benefits are marginal for smelting process without pre-treatment of the colemanite (calcining). Pre-heating of the ore and colemanite is thus highly recommended. • Tests with lower grade chromite concentrates resulted in only marginal metallurgical improvements. Modelling work and mass and energy balance calculations showed the same trends as the test work. Benefits are most significant South African metallurgical grade chromite. • The flowsheetscenario with the most potential for process intensification includes provision for pre-heating feed and calcination of colemanite; here the benefits when compared to conventional processing is significantly higher than any other scenario evaluated. Pre-heating of chromite ore is not a direct benefit of BOFLUX. The benefits presented by addition of colemanite must always be weighed against the cost of replacing conventional fluxes with colemanite. The BOFLUX results highlighted that the cost of the colemanite will need to be similar to that of conventional fluxes. • Some of the BOFLUX benefits may not be directly measurable through a test work based study that focused on the metallurgical impact. However, it is worth highlighting that lower operating temperatures can lead to increased longevity of refractories and tap-holes, which can improve cost and efficiency of a commercial smelter significantly. Reduction of maintenance downtime, even relatively small reductions, could outweigh any process intensification benefits associated with the increased throughput for example. This may ultimately be the primary selling point for colemanite, especially for chromite smelter that is currently operating with smelting temperature in excess of 1800°C The BOFLUX project demonstrated successfully that process intensification appears to be possible by replacing conventional fluxes (quartzite and/or limestone) with colemanite, however further technoeconomic and sensitivitystudies should be undertaken to evaluate the cost of replacing conventional fluxes with an imported product. The technicaloutcomes of the work conducted under the BOFLUX project added to the scientific knowledge and directly resulted in additional research beyond the original scope of the project. |
| Network | ERA-MIN |
| Call | ERA-MIN 2nd Joint Call on Sustainable Supply of Raw Materials in Europe |
Project partner
| Number | Name | Role | Country |
|---|---|---|---|
| 1 | Mintek | Coordinator | South Africa |
| 2 | Ab Etiproducts Oy | Partner | Finland |
| 3 | Siyanda Chrome Smelting Company Pty Ltd | Partner | South Africa |