The effect of grinding environment on flotation of sulphide poor PGE ores

The effects of grinding media and pulp chemistry may have significant effects on floatability of sulphide ores. Grinding in mild steel mill is suggested to cause reducing environment, galvanic interactions and formation of surface hydroxides which suppress sulphide flotation. In this study the influence of grinding environment on floatability of two Finnish PGE ores with low sulphur content has been studied. Variables in the study were grinding atmosphere (CO2, N-2 and air) and grinding media. The effect of addition of lime into mill was tested as a reference. It was found that CO2 atmosphere in grinding clearly improved both PGM grade and recovery in flotation of the ore with lower sulphide content. Platinum selectivity was improved also with the other ore but recovery was similar to the other tests. Grinding in CO2 atmosphere seems to diminish the oxidation which assists upgrading of platinum group minerals. It is also proposed that impact of CO2 may result from formation of hydrophilic carbonates on mineral surfaces. (C) 2010 Elsevier Ltd. All rights reserved.