Flotation selectivity, process modelling and simulation for a complex sulphide ore

University dissertation from Luleå : Luleå tekniska universitet

Abstract: This thesis covers research with different methods on the same fine-grained complex sulphide ore - Petiknäs - from the Skellefte Field in Northern Sweden. Mineralogical research results demonstrate that the degree of liberation of galena, rather than the chemical factors under the current flotation conditions, is the dominant factor affecting Pb grade and recovery, since galena has the same flotation as chalcopyrite if having the same degree of liberation. A novel approach for liberation pattern recognition is proposed based on multivariate statistical modelling and a four-parameter liberation model developed in this study. This approach opens up the possibility to use automatic pattern recognition and identification, and provides us with a quicker and more illustrative way to visualise mineral liberation characteristics. It is found that the effect of oxidising and reducing gases is only significant if the ore has been ground in a mild steel environment. The combination of mild steel grinding and prolonged aeration produces a slightly better selectivity between the copper minerals and zinc or iron sulphides compared with stainless steel grinding. However, this is at the expence of a slower flotation kinetics. For mild steel grinding, it is found that the copper flotation shows a marked potential dependence with a flotation "edge" at approx. +75mV (SHE). The pulp chemistry data show that mild steel grinding increases the surface oxidation of sulphide minerals, mobilising more sulphur into the pulp liquid. A combination of a galvanic interaction mechanism and a ferric leaching effect is probably responsible for the increased oxidation of sulphides after mild steel grinding. Also, theoretical calculations support that the hydrophobic entity responsible for chalcopyrite flotation with dithiophosphate is probably a surface percipate similar to the stoichiometric copper-collector compound. In batch flotation experiments, the first-order kinetic model with rectangular distribution of floatability is best fitted to the test data after stainless steel grinding only. For mild steel grinding, no traditional kinetic models are applicable. Redox potential has a profound effect on the flotation kinetics of chalcopyrite. In research on industrial kinetics, a similar phenomenon to mild steel grinding in batch tests is observed, i.e., there is no traditional kinetic model suitable to the full-scale kinetic data. Instead, the first-order classical kinetic model modified with a zero- time factor is found to give a simpler form and the best fit to the industrial data.

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