IFM produces ferrochrome from chromite ore located in the Bushveld Igneous complex. The ore body at Buffelsfontein consists of multiple seams and the method employed is a combination of down-dip stoping and breast mining. The two parallel declines at the Lesedi Shaft were developed on seam from surface. One trackless decline is used to handle miners and equipment and the second is fitted with a conveyor installation system for the handling of Run of Mine (ROM) material and waste.
Ore extracted from the mine is crushed to minus 85mm, i.e. smaller than 85mm. This ore is then fed into the Beneficiation Plant where the entrenched waste is separated from the ore. Ore is separated in two sizes. Lump ore of between 10 to 85mm in size is separated from concentrate ore which is sized between 0 and 1mm. Waste is separated by dense medium separation and concentrate material is separated through a spiral centrifugal water process. Fine waste is separated in a thickener and the sludge is pumped to a tailings dam.
The design of the plant caters for the separate treatment and storage of different ore streams by operating in campaigns. The streams are managed independently in order to respond to quality variations, without impacting on stockpiling, plant availability or processing efficiency.
This ultimately allows for products from the two ore bodies at Lesedi to be blended in a controlled way, to achieve optimum processing during pelletising and smelting. The beneficiation plant is designed to produce only two types of product, namely lumpy ore and concentrate, to maximize the recovery of the lumpy fraction for the production of ferrochrome.
Pelletising & Sinter plant
This involves grinding the chromite concentrate in a ball mill, pelletising a mixture of concentrate, coke, fines and bentonite which acts as a binder, then heating the pellets in a steel belt sintering furnace. In sintering, the pellets are heated to form strong bonds between the chromite grains to yield and agglomerate material. The sintered material is sized and then used as feed to the furnace. The world-renowned engineering and technology supply company Outukumpu (Oututec) provided the pelletising and sintering technology; the Outukumpu technology has been proven at a number of sites, including other ferrochrome operations in South Africa. The process is extremely energy-efficient and produces strong, high quality pellets with low binder requirements and high chrome content. Sintering ensures that pre-oxidation takes place. This modifies the crystal structure and makes the pellets more readily reducible in the smelting furnace.
Ferrochrome is then produced using submerged arc furnaces. IFM’s plant consists of two submerged acr closed-top furnaces, each rated at 66 MVA. This technology not only avoids the release of dangerous gases but is also more efficient, using less electricity than open furnaces.
Chromite lump ore, pellets, carbon, quarts and lime stone are mixed in a pre-calculated composition. The material mix is fed into the furnaces where the ferrochrome alloy is produced via a reduction process of the Chromite ore to elemental chrome.
The casted alloy from the furnaces is crushed and screened to different sizes according to customer specification. This alloy is then transported to South Africa's main ports by road or rail for export to stainless steel producers around the world.