Evaluation of a platinum group metal flotation re-cleaner stage performance and possible improvement

South Africa has massive Platinum Group Metal (PGM) deposits found in Bushveld Igneous Complex (BIC). Due to depletion of Merensky reef, many companies are now treating UG2 reef which has a high chromite content which has negative impact in the smelting process of the platinum concentrates. Generally, PGMs are processed by rougher followed by cleaner and re-cleaner flotation banks and the final concentrate must contain less than 3% chromite. The effect of residence time and depressant dosage on PGM recovery and chromite entrainment on the recleaner stage was investigated by floating the feed to the re-cleaner banks using Dow froth 200, Cu2SO₄, sodium isobutyl xanthate and carboxymethyl cellulose in a 3l Denver cell. It was found that extra 30g/t of depressant dosage (carboxymethyl cellulose) from standard conditions reduces the chromite content to 2.11% from 8.63% and only 37.54% of PGMs are lost to the recleaner tailings which are recirculated to the cleaner feed. The residence time was reduced by 15minutes from the normal residence time. The Malvern particle size analyzer results indicated that the increase in depressant dosage and decrease in residence time the finer the concentrate. By controlling the depressant dosage, amount of chromite content in the final concentrate can effectively be reduced to meet the required standards.