By Markus Erwee, PDD
Mintek Pyrometallurgy and Minerals Processing Divisions are currently running a project called “PACMAN” for which the aim is to separate valuable metal and unreacted material from waste during ferrochrome production. This project also draws on the talent from many graduates-in-training that execute smaller projects while on rotation, which has shown great success in 2017.
Ferrochrome, an alloy of iron and chrome, is produced in South Africa by smelting chromite, a chrome containing mineral in electric furnaces. This alloy is used as primary raw material for stainless steel production and hence a very important resource for South Africa. So important it provides over 20 000 jobs.
The aim of the smelting process is to remove oxygen bound to chrome in the ore and to separate the valuable metal from the waste called ‘slag’. The alloy and slag separate due to their difference in density in the furnace.
In the smelting process, approximately 1 ton of slag is produced for every 1 ton of ferrochrome. Roughly 3.5 million tons of waste slag is produced in South African processes.
The smelting process is not 100% efficient, hence the waste slag always contains some partially reacted chromite (PACs) and alloy droplets. This occurs because the slag is sometimes more ‘sticky’ than it should be and the PACs and alloy particles can’t separate effectively.
Industry partners focus only on recovering alloy droplets from slag and then often stockpile it, but some 10% PACs, which still contains a lot of chrome, remains.
Markus Erwee, Chief Engineer said, “The aim is to develop technologies to selectively recover the “PACs” from the waste slag and convert it into useful high-value furnace feeds or direct alloy products, whilst making the remaining slag safer for use by, for example, the cement industry.”
He added, “The ultimate goal is for Mintek to develop technology that could be used by communities around smelters to start up smaller recovery plants that could process waste slag dumps.”