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Process

 

Some 83% of the world economically mineable ore reserves are located in the Bushveld Igneous Complex (BIC), a saurcer-shaped deposit in the northern part of South Africa. Chromite ore is mined along the eastern and western rims of the complex. Chromite is the only source of chromium and is predominantly used for the production of ferro-alloys and chemicals. World production of chromite ore is around 14 million tons with the South African market share accounting for around 39%.

 

Although there are a number of chrome seams in the BIC, only two are currently considered to be economically viable. These seams are remarkable consistent throughout the BIC in both physical and chemical nature. The lower of the two seams is known as the LG6 (lower group 6) seam and is approximately 1,1 to 1,3 metres thick. The MG1 (middle group 1) seam is located above the LG6 seam and is approximately 1,6 to 1,8 metres thick.  The chrome content of the LG6 seam is higher than that of the MG1 seam at between 43 to 47% Cr2O3 compared to the 42% Cr2O3 of the MG1 seam.

 

Only the LG6 seam, dipping between 16° and 9° is mined at Dilokong Chrome Mine. Conventional scraper mining methods are employed. The ore is drilled and blasted before being scraped mechanically to loading points from where it is transported to the shaft tips in locomotive pulled hoppers. The ore is then hoisted to surface by conveyor belts installed in the incline shaft.

 

Run of mine ore is further beneficiated on surface through a series of size classification and density separation steps that allows for efficient separation and removal of pyroxenite waste from the chromite. Foundry sand produced during the on surface beneficiation is stockpiled separately for supply to international customers while lumpy chromite and metallurgical concentrates are transported to the on site smelter for further beneficiation.

 

At the smelter, charge chrome is produced through a single stage process by smelting a mix of chromite, reductant and fluxes at temperatures in excess of 2000°C. Electrical energy, required for the chemical reactions to occur, is supplied to the submerged arc furnaces, through Söderberg electrodes. The molten waste slag and metallic charge chrome are continually (every 2 to 3 hours) drained from the smelting furnaces and separated in skimmers.

 

The metal ingots are allowed to cool down before a final crushing and screening beneficiation step is performed that allows for the production of sized charge chrome. The stockpiled charge chrome is then supplied to international stainless steel manufactures.