CONCENTRATESJena, Das and co-workers described the treatment of manganese nodules by ammoniacal leaching with ferrous sulfate as a reductant,44 aqueous 802 solutions,45 sulfuric acid leaching with oxygen,46 dilute hydrochloric acid,47.48 and by sulfation roasting49 or dry chlorination 50 at moderate temperatures, followed by water leaching of the resulting salts. Turker et al. compared HCI-alcohol and HCI-Hp systems for leaching ilmenite, developing a theoretical model for the leaching capability.51 Majima and coworkers studied the leaching kinetics of columbite and tantalite in various acidic fluoride-containing solutions. 52 Cho reported the leaching kinetics of scheelite in sodium carbonate. 53 Graydon and Kirk studied the formation of refractory zinc ferrite during sphalerite roasting. 54 Lu and Muir determined the effect of oxidant and reductant species in solution on the dissolution rates of copper, zinc and nickel ferrites, along with hematite, magnetite and nickel oxide in HCI, correlating this behavior with cyclic voltammograms for each oxide in a carbon paste electrode. 55Kocakerim and Alkan determined that the dissolution of colemanite, a calcium borate mineral, in 802 saturated water is chemically controlled, and follows shrinking sphere kinetics. 56 Crawford and colleagues modeled the dissolution kinetics of alumina in acidic sulfate solutions. 57 Hodgson and Dudeneyinvestigated the physico-chemical processes affecting the hydrothermal alteration of kimberlite in acid media, which would be an alternative to comminution as a means of liberating diamonds. 58Crundwell summarized the energy level model of semiconductor electrochemistry and used this to interpret the literature on the leaching and anodic electrochemistry of base-metal sulfides, stressing the importance of the electronic structure of the solid and solution in determining behavior. 59 This model was exemplified by an analysis of the effect ofiron impurities on the dissolution rate of sphalerite concentrates. 60 Tozawa and Piao examined the effect of iron content on the pressure leaching of zinc sulfide concentrates. 61 Kobayashi and Kametani related the dielectric properties of particulate sphalerite samples and zinc
