Properties of electrolyte solutions relevant to high concentration chloride leaching/III. Solubility of pertinent solids and iron(III)/iron(II) redox potential measured in concentrated magnesium chloride solutions

摘要

Results of solubility measurements of nickel chloride, manganese chloride, iron(II) chloride, hematite and akaganeite in aqueous solutions of MgCl_2 (0.5-3.5 mol L~(-1)) at temperatures of 60 and 90 deg C are reported. Solubilities of metal(II) chlorides decrease almost linearly with MgCl_2 concentration due to the common ion effect. Nickel chloride and iron(ll) chloride solubilities are very similar, while manganese chloride is about 30 percent more soluble. Hematite is more stable (i.e. less soluble) than akaganeite under all conditions investigated in this study, while ferrihydrite is considerably less stable. In other words, there is no change in the relative stabilities of these phases effected by the presence of high magnesium chloride concentrations. The solubility of all of these phases decreases with temperature and, for each temperature, the solubility constants increase linearly with the MgCl_2 concentration. The present results allow the prediction of the iron concentration as a function of the H~+ and MgCl_2 molality at equilibrium with hematite or akaganeite. The Fe(III)/Fe(II) redox behaviour has been characterized in concentrated aqueous solutions of MgCl_2 (1.5-3.5 mol L~(-1)) at a temperature of 25 deg C. Standard redox potentials are ca. 100 mV lower than at infinite dilution and change linearly by only 13 mV in the range 2-4 mol L~(-1) MgCl_2