The effect of sulphate ions and temperature on the leaching of pyrite. III. Bioleaching

Abstract

The effect of the total sulphate concentration on the rate of pyrite dissolution was investigated in batch, bioleach tests on a high-grade concentrate at 35°C, 50°C and 65°C.Good microbial activity was achieved for concentrations up to 42 g/L sulphate.However, higher concentrations resulted in decreased ferrous oxidation kinetics, with the solution potential profiles showing "lag periods" at the highest sulphate concentration.The bioleach results showed that the rate of pyrite dissolution decreased markedly above an average sulphate concentration of 55 g/L for all three temperatures, with the adverse effect on the dissolution kinetics being more pronounced at 50°C and 65°C.As a result of this, increased temperature has no beneficial effect on the rate of dissolution at concentrations of sulphate above 55 g/L.High extents of pyrite dissolution (90% to 98%) were achieved at all three temperatures irrespective of sulphate concentration, with almost identical extents of sulphide oxidation.Rates of pyrite dissolution under bioleaching conditions agree well with those derived under similar conditions from abiotic dissolution experiments and electrochemical measurements. This important observation confirms the so-called indirect mechanism A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPTfor the bioleaching process in the case of pyrite and also that the mixed potential model can be used to quantitatively describe both abiotic and biotic dissolution of pyrite in acidic solutions.

Study of the kinetics of pyrite oxidation under controlled redox potential

“…However, adsorbed molecular oxygen acts as a pyrite oxidant and is incorporated into the produced sulfate in anaerobic and low oxygen experiments with low ferric iron/surface ratios (Heidel and Tichomirowa, 2011). The rate of pyrite dissolution decreases with increased sulfate concentration and ferrous concentration, as verified by an electrochemical method (M.J. Nicol et al, 2013).…”

“…The indirect oxidation mechanism of pyrite bioleaching has been confirmed by many researchers (Sand et al, 2001;Tributsch, 2001;Heidel and Tichomirowa, 2011;Basson et al, 2013). The process of pyrite bioleaching involves two rate-controlling sub-processes: chemical leaching of pyrite by ferric ion and bacterial oxidation of ferrous ion to regenerate ferric ion (Boon et al, 1998).…”

“…However, few investigations of pyrite oxidation have been conducted under controlled redox potential. M. Nicol et al (2013) performed pyrite oxidation by controlling solution potential with potassium permanganate, showing that the rate of dissolution is significantly higher at a potential of 850 mV than it is at 800 mV (throughout this paper potentials are quoted with reference to the standard hydrogen electrode, SHE). Leaching studies (Chandra and Gerson, 2011a) have shown that the rate of pyrite dissolution is faster at a solution Eh of 900 mV than at 700 mV controlled by 15 wt.% hydrogen peroxide (H 2 O 2 ) solution at pH 1 in the leach media of HCl, H 2 SO 4 and HClO 4 .…”

Responses of zinc recovery to temperature and mineral composition during sphalerite bioleaching process

“…Secondly, the process of sulfide dissolution was also interfered by other physicochemical parameters, other than temperature. The rate of pyrite dissolution was affected by the concentration of sulfate at temperature gradients (Basson et al 2013 ). With additional low concentration of sulfate (3.94 g/L), the dissolution rate was high at high temperature (65 °C), while with additional moderate concentration of sulfate (42.1 and 78.5 g/L sulfate), it was high at 50 °C, and with additional high concentration of sulfate (119 g/L), it was high at 35 °C.…”

“…Studies (Basson et al 2013 ; Mousavi et al 2008 ; Shiers et al 2014 ) found that, to some extent, energy resources (sulfur, iron or organic matter) could also enhance metal recovery. Mineral, which comprises sulfur and/or iron, is one kind of energy resource.…”