The Solution Interaction of Tetrathionate Ions and Sodium Isobutyl Xanthate and Its Effect on the Flotation of Galena and Chalcopyrite

Ngoni Mhonde,Nóra Schreithofer,Kirsten Corin,Leena Pitkänen

doi:10.3390/min11020204

Abstract

Tetrathionates have been found in significantly high concentrations in recycled process waters from massive sulphide ore processing plants. These polythionates react with xanthate added to flotation pulps thus reducing xanthate dosages in solution potentially affecting flotation performance. The current study focused on the effect of the tetrathionate-xanthate reaction on sulphide mineral recoveries. Ore dissolution studies confirmed the generation of tetrathionates by copper-lead-zinc ores. In 20 min, the tetrathionates consumed more than half of the xanthate in solution at pH 7. Rest potential measurements and Fourier transform infrared spectroscopy (FTIR) showed that the degree of collector-mineral interactions of xanthate and both galena and chalcopyrite was greatly reduced in the presence of a 2000 mg/L tetrathionate solution. Microflotation tests showed that chalcopyrite recovery was less sensitive to tetrathionates as indicated by small changes in mineral recoveries. Galena was sensitive to the action of tetrathionates on the mineral surface as the galena recovery significantly declined when floated with xanthate as a collector in both a 500 mg/L tetrathionate solution and a 2000 mg/L tetrathionate solution. These fundamental results lay a sound base on which more discussion into the significance and the effect of tetrathionates on flotation performance of sulphide ores can be developed.

Highlights

The oxidation and dissolution of sulphide ores in flotation process water leads to the formation of thiosalts
Residual xanthate concentrations in the presence of tetrathionate solutions were measured over 1 h at pH 3, 5, 7, 9 and 11
This study has successfully shown that xanthate is degraded in the presence of tetrathionates with significant impacts on the flotation recovery of sulphide minerals

Summary

Introduction

The oxidation and dissolution of sulphide ores in flotation process water leads to the formation of thiosalts. S2 O3 2− (thiosulphates), S4 O6 2− (tetrathionates), S3 O6 2− (trithionates), and S5 O6 2− (pentathionates), where the three latter compounds are collectively known as polythionates. The production of these polythionates has been described as a catalytic oxidation of thiosulphate primarily by pyrite (and other sulphide minerals) in the presence of oxygen [1,2,3]. The proposed mechanism involves the alteration of the elemental sulphur inherently oxidising thiosulphate ions to tetrathionate sulphates [7]. The thermodynamically favoured end product of sulphide oxidation is sulphate, in plant process water and plant water effluents, mass transfer and kinetics limitations result in the production of partially oxidised thiosalts or polythionates [8]

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Conclusion