The pros and cons of reductive matte smelting for PGMs

Platinum group metals (PGMs) are traditionally smelted in electric furnaces where the valuable metals are collected in a base-metal sulphide matte. An alternative to this process is the ConRoast process that uses reductive alloy smelting in a DC arc furnace to collect the valuable metals in an iron-rich alloy. Reductive smelting of feed materials containing PGMs, using carbon as a reducing agent, can be used to obtain high PGM and base-metal recoveries and to ensure the solubility of chromium in slags.Based on work carried out in Mintek’s 3 MW DC arc furnace at throughputs of over 1000 tons per month, it was found that PGMs could be collected effectively, and that the chromium problem could be managed. However, if matte is present in the furnace, there remains a significant risk of furnace failure. Furthermore, the PGM ‘lockup’ (inventory inside the furnace) in a process that used reductive matte smelting of UG2 concentrates was much greater than that of reductive alloy smelting. Further differences exist in the better working environment and lower emissions of SO2 in the case of the ConRoast process.

► Reductive matte smelting in a DC arc furnace was tested.
► Carbon as reductant solubilises chromium oxide in slag.
► Matte smelting has containment problems relative to alloy smelting.
► Reductive alloy smelting in a DC arc furnace is better than reductive matte smelting.
► - UG2 concentrates should be roasted then treated by reductive alloy smelting.