Colloidal iron oxide slime coatings and galena particle flotation

Microflotation was used to investigate the influence of colloidal iron oxide “slimes” on galena (PbS) particle flotation. Complementary particle adsorption (heteroaggregation) studies were undertaken to investigate the formation of iron oxide slime coatings and to develop methods for their removal. Trace quantities of hematite (Fe2O3) colloids have a significant depressant action on both the collector-induced and collectorless flotation of galena particles. For example, slime particle surface coverage as low as 10% of an equivalent close-packed particle monolayer decreased the flotation rate constant of galena by an order of magnitude. In the pH range 4 to 7, high affinity Fe2O3 particle adsorption was observed on PbS and the surface coverage approached that of an equivalent particle monolayer. In contrast, in mildly alkaline solutions, particle adsorption isotherms were of low affinity, with plateau surface coverages significantly less than an equivalent particle monolayer. These observations are discussed in terms of the surface chemistry of galena and slime coating mechanisms. The use of shear, sonication, pH control and chemical reagent addition to quantitatively remove iron oxide slime coatings is also reported. A combination of physical and chemical methods is most effective at iron oxide particle removal and synergistic effects have been observed.