Partitioning of In, Ga, and Sc between aqueous phase and secondary ferric minerals

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Acid and neutral mine drainage (MD) systems accompany the mining wastes worldwide and precipitate often copious amounts of secondary ferric minerals. Because of crystal chemical similarities between Fe3+ and the trivalent cations of the critical metals In, Sc and Ga, it is reasonable to assume that these elements enter the structure of the ferric minerals and remain there in solid solutions. In this work, I am proposing to quantify the partitioning of Fe, In, Sc and Ga between aqueous solutions and minerals common in MD systems. This goal will be achieved by calorimetric measurements and thermodynamic calculations for end-members and solid solutions that involve these metals. The systems to be investigated include, but are not limited to alpha-FeOOH – InOOH, alpha-FeOOH – ScOOH, alpha-FeOOH – GaOOH, FeAsO4·2H2O – InAsO4·2H2O, and (H5O2)Fe2(SO4)·H2O – (H5O2)In2(SO4)·H2O. Using solution and relaxation calorimetry, the enthalpies of formation and entropies will be determined for the end-members. With the same techniques, the thermodynamic mixing parameters will be calculated for the solid solution, and the partitioning of the elements will be quantified. Synthesis protocols for common MD minerals will be carried out with In, Sc and Ga and the resulting phases will be characterized. If they should be isostructural or similar to the common ferric MD minerals, their thermodynamic properties will be measured as well. The data obtained in this work could serve to identify the phase(s) which concentrate the critical metals In, Sc and Ga strongly and thus could be used for economic extraction of these metals from mining waste.