Chemical dissolution of sulfide minerals

Chemical dissolution treatments involving the use of aqua regia, 4 N HNO₃, H₂O₂-ascorbic acid, oxalic acid, KClO₃+HCl, and KClO₃+HCl followed by 4 N HNO₃ were applied to specimens of nine common sulfide minerals (galena, chalcopyrite, cinnabar, molybdenite, orpiment, pyrite, stibnite, sphalerite, and tetrahedrite) mixed individually with a clay loam soil. The resultant decrease in the total sulfur content of the mixture, as determined by using the Leco induction furnace, was used to evaluate the effectiveness of each chemical treatment. A combination of KClO₃+HCl followed by 4 N HNO₃ boiling gently for 20 min has been shown to be very effective in dissolving all the sulfide minerals. This treatment is recommended to dissolve metals residing in sulfide minerals admixed with secondary weathering products, as one step in a fractionation scheme whereby metals in soluble and adsorbed forms, and those associated with organic materials and secondary oxides, are first removed by other chemical extractants.