Geochemical and metallurgical analysis company Mintek is currently conducting a project called Pacman for which the aim is to separate valuable metal and unreacted material from waste during ferrochrome production. The project is run by Mintek’s pyrometallurgy and minerals processing divisions.
This project draws on the talent of many graduates in training that execute smaller projects while on rotation, and showed great success last year.
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 is therefore an important resource for the country – 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, about 1 t of slag is produced for every 1 t of ferrochrome. About 3.5-million tons of waste slag is produced in South African processes.
The smelting process is not 100% efficient, consequently 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 not 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.
“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, while making the remaining slag safer for use by, for example, the cement industry,” says Mintek chief engineer Markus Erwee.
“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,” he concludes.