An investigation into chemical factors that affect the behaviour of Gangue minerals in the flotation of PGM ores

Word processed copy.Bibliography: leaves 80-85.Flotation is one of the key steps in the beneficiation of Platinum Group Elements (PGE) from the Bushveld Complex in South Africa. This process aims to optimise the recovery of valuable PGE and sulphide minerals and the rejection of unwanted gangue minerals. The major reefs are exploited in South Africa i.e. Merensky reef and UG-2 reef. Gangue minerals, pyroxene and feldspar constitute more than 80% of the Merensky reef and chrornite up to 60% of the UG-2 reef. Although these minerals are considered to be hydrophilic and thus not floatable, these gangue minerals are known to report to the concentrate in large quantities during froth flotation. This results in lower grades and increased difficulties in downstream processing. Some Platinum Group Mineral (PGM) concentrators report that 2/3 of the gangue collected on the concentrate is by true flotation and only 1/3 by entrainment [Malysiak et ai, 2001]. This also suggests that mechanisms other than entrainment are responsible for this phenomenon. The behaviour of these minerals is selected for investigation in this thesis. During flotation of PGM ores, reagents such as copper sulphate and sodium isobutyl xanthate (SIBX) are added to enhance the recovery of valuable minerals. Copper sulphate, although added as an activator for valuable minerals, as the conditions used has been shown to also activate gangue minerals, thus its activation is non-selective [Shackleton, 2003 and Wesseldijk et ai, 1999]. Wesseldijk et ai, (1999), showed that copper sulphate could activate chromite and the subsequent addition of collector resulted in high recoveries of chromite in contrast to the low recoveries obtained in the absence of copper sulphate