AN INVESTIGATION OF FROTH EFFECTS IN SCAVENGING FLOTATION OF PLATINUM FROM UG-2 ORE Deepika .I. Bennie This MSc. in Chemical Engineering Dissertation is submitted in fulfilment of the requirements for the MSc. (Engineering) in Chemical Engineering Degree, Faculty of Engineering at the University of KwaZulu-Natal. Supervisor: Prof. B.K. Loveday Co-supervisor: Dr L. Maharaj Date of Submission: 21 January 2013 i ACKNOWLEDGEMENTS I take this opportunity to acknowledge and thank the following who have contributed to the success of this work: . My supervisors, Professor B.K. Loveday and Doctor L. Maharaj for their expert knowledge and guidance. University of KwaZulu-Natal for their financial assistance. The technical staff consisting of Mr Dudley Naidoo, Mr Sadha Naidoo and Mrs Rekha Maharaj. The workshop staff consisting of Mr Gerald Addieah and Mr Patrick Mlambo. And finally my greatest thanks to my wonderful parents and sister for their unflinching support during my studies. ii 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. iii TABLE OF CONTENTS ACKNOWLEDGEMENTS ........................................................................................................................................................ ii ABSTRACT .................................................................................................................................................................................... iii TABLE OF CONTENTS ............................................................................................................................................................ iv LIST OF FIGURES .................................................................................................................................................................... viii LIST OF TABLES ....................................................................................................................................................................... xii NOMENCLATURE ................................................................................................................................................................... xiv CHAPTER 1: INTRODUCTION ............................................................................................................................................. 1 1.1. Background to study .............................................................................................................................................................. 1 1.2. Dissertation objectives .......................................................................................................................................................... 2 CHAPTER 2: LITERATURE REVIEW ................................................................................................................................ 3 2.1. Overview ................................................................................................................................................................................ 3 2.2. The Bushveld Igneous Complex ..................................................................................................................................... 5 2.2.1. Geology of the ore body ........................................................................................................................................ 6 2.2.2. Importance of platinum ....................................................................................................................................... 10 2.2.3. Extraction of PGE’s from the ore ..................................................................................................................... 11 2.3. Process of precious metal extraction ........................................................................................................................... 13 2.4. Background of flotation of UG-2 ore .......................................................................................................................... 14 2.5. Flotation in general ........................................................................................................................................................... 20 2.5.1. True flotation and Entrainment ......................................................................................................................... 22 2.5.2. Froth phase .............................................................................................................................................................. 23 2.5.2.1. Froth Structure ........................................................................................................................................ 24 2.5.2.2. Particle motion in the froth ................................................................................................................. 27 2.5.2.3. Froth movement ..................................................................................................................................... 28 2.5.2.4. Importance of bubble size ................................................................................................................... 29 2.5.3. Solids drainage ....................................................................................................................................................... 30 2.5.4. Froth effects - Means of reducing gangue ..................................................................................................... 30 2.5.4.1. Froth washing .......................................................................................................................................... 30 2.5.4.2. Baffles in flotation ................................................................................................................................. 30 2.5.5. Surface chemistry .................................................................................................................................................. 31 2.5.5.1. Collectors.................................................................................................................................................. 31 2.5.5.2. Frother ....................................................................................................................................................... 32 2.5.5.3. Depressants .............................................................................................................................................. 33 2.5.5.4. Activators ................................................................................................................................................