The Reduction of Chrome in UG-2 Flotation Concentrate by Hydrometallurgical Means

The South African platinum industry has advanced into an era of predominantly mining and processing Upper Group Two (UG-2) ore to extract Platinum Group Metals (PGMs). Flotation concentrates derived from processing UG-2 ore are typically characterized by high chrome contents (>3 wt.%) which are not amenable to conventional PGM smelters. The net effect of high chrome, inter alia, includes increased smelting energy requirements and the reduction of effective furnace capacity. Various interventions ranging from the redesign and modification of existing physical and pyrometallurgical operations have been introduced and these have yielded no sustainable solutions. In this study, a hydrometallurgical process was investigated as an alternative route to reduce chrome in UG-2 concentrates. The parameters initially considered for investigation were acid concentration, leaching time, temperature and oxygen flowrate while keeping solid to liquid ratio and agitation rate constant. Results showed that oxygen flowrate and an interaction of temperature, time and acid concentration had a positive but minimal effect on Cr extraction. The highest Cr extraction obtained was 7.0%. Further test work entailed exploring the effect of solid to liquid ratio using optimized conditions. The results showed a substantial increase of Cr extraction of up to 37%. This represents 1.33% decrease in chrome content, from 3.63% to 2.30%, in UG-2 concentrate.