Simultaneous partitioning of divalent metal ions between alabandite and 1 mol/l (Ni, Mg, Co, Zn, Fe)Cl₂ aqueous solutions under supercritical conditions

To clarify the element partitioning behavior between minerals and aqueous chloride solutions, we conducted experiments to investigate simultaneous partitioning of Ni2⁺, Mg2⁺, Co2⁺, Zn2^+, Fe2⁺, and Mn2⁺ions between alabandite (MnS) and 1 mol/L (Ni, Mg, Co, Zn, Fe)Cl2 aqueous solutions at 500–800^◦C and 100 MPa. The bulk partition coefficients calculated using the following equation were in the order of Fe2⁺ > Co2⁺ > Ni2⁺ ≈ Zn2⁺ > Mn2⁺ >> Mg2⁺; KPN = (xMeS/mMeaq)/(xMnS/mMnaq). A partition coefficient-ionic radius (PC-IR) curve was plotted with the logarithmic value of the partition coefficient on the y-axis and the ionic radius at the six-fold coordinated site on the x-axis. The peak of this curve was located near the ionic radius of Fe2+ and not near the ionic radius of Mn2⁺. Zn2⁺ showed a slight negative partitioning anomaly, which increased in the order of sulfide minerals < arsenic sulfide minerals < arsenide minerals as the covalent bond became stronger. Ni2⁺ showed a positive partitioning anomaly, which indicated that it preferred an octahedral structure. The width of the PC-IR curve decreased in the order of sulfide minerals > arsenic sulfide minerals > arsenide minerals as the covalent bond became stronger, that is, the ion selectivity became stronger.