Parameters influencing the concentration of aqueous tin in acidic sulphate solutions containing Fe(III
Master Thesis
2008
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University of Cape Town
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This thesis investigates parameters influencing the concentration of aqueous tin in acidic sulphate solutions containing Fe(III/II) as they arise in the Reduction Releach process at Teck Cominco Trail Operations (TCML). This study documents the impact of initial sulphuric acid and As(V) concentrations, temperature, and lead concentrate reductant amount on tin solubility in acidic Fe(III/II) sulphate solutions as they arise in an intermediate leaching step at TCML. Supporting test work examined the speciation of commercial tin bearing residues involved in the processing of indium and germanium. Analysis of these residues determined the oxidation state of crystalline tin in ZnO fume, Ge Preconcentrate, and Releach residue to be primarily Sn(IV), and associated with zinc, lead, and iron oxides; in addition to lead, iron, and aluminum silicates, and minor amounts of Sn(II) as SnO or SnSO₄. Experimental validation of Sn(II) solubility values in 100 g/L H2SO4, between 30 to 90 °C, compared well with literature and theoretical tin solubility values. Measured tin solubility values ranged between 95 g/L Sn and 99 g/L Sn concentration. The aqueous tin concentration decreased slightly (4 g/L Sn) when the temperature was increased from 30 to 90°C. Measured aqueous tin values for both thesis benchscale test work and commercial Reduction Releach process were all less than 1 g/L Sn. The oxidation rate of Sn(II) between 300 mg/L and 700 mg/L in 100 g/L H₂SO₄ at 20 °C, was first order kinetics with a rate constant ranging between 0.0002 and 0.0003 mg Sn/L∙s, and the REDOX potential (Eh) varied between 550 and 650 mV. The low rate constants may have been due to poor mass transfer. Iodometry could not be used for aqueous tin analysis with other divalent and trivalent cations present in solution and, therefore, inductive coupled plasma analysis was used.
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Includes bibliographical references (leaves 118-123).
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Kuhn, J. 2008. Parameters influencing the concentration of aqueous tin in acidic sulphate solutions containing Fe(III. University of Cape Town.