An investigation of froth effects in scavenging flotation of platinum from UG-2 ore.

Abstract

South Africa is the largest supplier of platinum group metals (PGMs), which are mined from three reefs in the Bushveld Igneous Complex. About 60% of the world’s mined PGMs come from a single reef, the UG-2 reef (Mudd, 2010). Flotation is the primary method used to concentrate the PGMs. There are currently two major problems which are experienced during the flotation of UG-2 ore. Firstly, mineralogical studies have shown that the platinum losses in flotation plants are currently in excess of 10% and secondly the high chromite content in the flotation concentrate leads to downstream smelting problems. This project was aimed at improving the recovery of platinum and reducing the amount of chromite in the feed to the smelter. Platinum concentrators in South Africa normally consist of two stages of grinding and flotation and this investigation was focussed on the second stage, where platinum-containing particles tend to float slowly and the fine grinding leads to entrainment of chromite. Tests were performed on a low-grade UG-2 ore sample, obtained from a plant (the feed to the secondary grinding mill). Sub-samples of the ore were ground to a size at which 80% passed 75 μm. Subsequent flotation tests were done in two stages, the rougher and scavenger stages. Focus of this project will be on optimising the scavenger stage as it has the potential to recover most of the ‘lost’ platinum. The objective of the research was to improve PGM recovery and reduce the chromite recovery in the scavenger. This was to be achieved by varying different parameters, which included froth washing, froth depth, the use of a baffle (an innovative technique, in which two baffle lengths were used), and the replacement of the standard frother dosage with: a mixture of diesel and frother; a mixture of paraffin and frother; a reduced frother dosage and no frother dosage. Flotation concentrates were obtained from the experiments and sent for PGM and chromite analysis to an external laboratory where the fire assay analysis was done to determine the PGM content and an inductively coupled plasma- mass spectroscopy analysis was used to determine the % chromite. Base case experiments showed that the overall recovery of platinum in the secondary rougher/scavenger, using standard hand scraping, was 71%, with a cumulative chromite content of 6.33%. The wet mass of concentrate was controlled, by weighing the concentrate. Promising results were obtained for tests with a nearly horizontal longer baffle and the diesel and frother replacement for the standard frother. This combination had an overall PGM recovery of 82 % and the chromite content was reduced to 4.18%. The reduced frother dosage (10 g/ton as compared to the standard 20 g/ton dosage) showed promising results with a 77.5% PGM recovery and 4.10% chromite content. Tracer tests showed that froth washing had potential, but the desired reduction of chromite did not take place, due to dilution of the froth.