Valorisation of stainless steel slag

Valorisation of stainless steel slag by selective Cr recovery and carbonation of the matrix material

The Flemish Institute for Technological Research (VITO), Centre Terre et Pierre (CTP) and the University of Duisburg Essen (UDE) researched and developed processes to selectively recover chromium (Cr) from historic stainless steel slags.

Currently 50 per cent of slags are still disposed of in landfills because they contain hazardous metals and 50 per cent are used in low-grade applications, such as road aggregate.

VITO developed an alkaline oxidative pressure leaching (APL) process to remove Cr from the slag material, without dissolving matrix materials, while UDE investigated if Cr could be removed and recovered from the slag material by using an aerobic biological process, known as biological leaching.

While the bioleaching did not lead to the release of heavy metals from the slag materials, the milling of the slag material, by VITO and CTP, led to a dramatic increase in the removal of Cr during the APL process and in fact, the milling caused a “mechanochemical activation” (MA) of the material.

Overall results showed that after Cr leaching by APL, assisted by MA and a subsequent washing step, the left over matrix material can be used for building materials through a carbonation step. This results in a complete recycling of the slag material, fulfilling the zero waste principle.

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