Mixtures of collectors have been widely used for many years in sulphide flotation, and a range of performance benefits have been reported for many different systems, Norm Lotter of Xstrata Process Support (XPS) and Dee Bradshaw from JKMRC explain. “The combinations of collector types used have varied, as have the ratios that have been used. Synergistic effects have been obtained and in some cases the mechanisms of this improved behaviour have been identified. The benefits have been attributed to increased carrying capacity of the froth phase, faster kinetics, and more successful recovery of middling or coarse particles. It is the interaction between the various components of the mixed collector system, rather than the individual main effects, that dominate the performance benefits.”
The process benefits include increased paymetal recoveries and grades – as well as increased rates of recovery, whilst using lower dosages of reagents. Various mechanisms have been reported and are discussed in the paper presented at MEI’s Flotation ’09 conference in Cape Town, November 2009. These have been shown to affect different composition/liberation classes and sizes of mineral particles.
In recent years, automated quantitative mineralogy and surface analysis technology such as ToF-SIMS have enabled the development of better information, to establish what aspect of the process has been affected.
Candidate selection for the mixed collector suite is presently based on experience and knowledge of the mineralogy and flotation conditions. Optimum combinations can be identified experimentally at laboratory scale prior to any plant trial. Such laboratory work should be performed using a factorial design with replicates and quality controls, such as may be delivered from High-Confidence Flotation Testing.
Xstrata Alloys’ Eland Platinum mine in South Africa recently completed a successful plant trial to demonstrate the flotation performance gains to be delivered from an optimised mixed collector suite. The mixed collector suite was developed at XPS using samples of Eland’s normal ore.
Mixed collector suites are synergistic mixtures of conventional collectors. Mineralogy, the electrochemistry and organic chemistry involved and finally, High-Confidence Flotation Tests showed that a tailored mixture of conventional collectors would increase PGE recoveries by 2% over those produced by their standard single xanthate collector.
The plant trial was designed by XPS and performed by the Eland operations staff, in conjunction with reagent supplier Senmin. Senmin manufactured and supplied the trial reagent batches to XPS specification to meet the plant schedule between August and November 2009. The trial demonstrated that, for normal ore, a PGE recovery gain of 2.5% has been sustained, together with a concentrate grade gain of 16% relative. Additionally the chrome grade in final concentrate dropped from 2 to 1.6%. All of these gains were proven to be statistically significant.
