The recovery of platinum group metals from low-grade concentrates to an iron alloy using silicon carbide as reductant
W Malan, G Akdogan, S Bradshaw, GA Bezuidenhout
The purpose of the study was to investigate the feasibility of SiC reduction
of low-grade concentrates from Lonmin’s Rowland and Easterns
operations with respect to metal fall and PGM recovery. These concentrates
are rich in SiO2 and MgO with low concentrations of chalcopyrite
and Cr2O3. Pd is the most abundant of the PGMs. SiC reduction of samples
was conducted at 1600? with 2.5–3.5 kg SiC per 100 kg concentrate.
PGM recoveries for Easterns concentrate were better than for Rowland.
More than 85% of the Ir and Pd and almost 60% of the Pt were recovered
with 3.5 kg SiC per 100 kg concentrate. SEM of slag samples showed little
entrainment of metallic prills compared to Rowland samples. This was
attributed to the relatively higher melt viscosities of the Rowland
concentrate. In order to decrease slag viscosity and to enhance PGM
recovery, the FeO content of the Easterns concentrate was increased with
the addition of 10 kg converter slag per 100 kg concentrate. Ir and Pd
recoveries were increased to about 95%, while Pt recovery was around
70%. On the basis of these results an optimum feed ratio between
Easterns and Rowland concentrates and converter slag is proposed.
Carbothermic reduction of the optimum charge was also compared to SiC
reduction. Carbothermic reduction yielded a marginally higher metal fall;
however, the calculated gas emissions and energy requirements were
higher than for SiC reduction.
Keywords: SiC reduction, PGM recovery, LG concentrates, FactSage modelling.