The mechanism of dissolution of minerals in acidic and alkaline solutions: Part III. Application to oxide, hydroxide and sulfide minerals

The reactions of oxide and sulfide minerals with acids are among the most straight-forward of chemical reactions. Despite this, there are still aspects which are not fully understood or explained. The rate of dissolution of these minerals is remarkable, in the sense that their orders of reaction with respect to H+ are most often either 0.5 or 1. In addition, the rate of dissolution is strongly dependent on the metal-oxide bond strength. It is proposed that the breaking of the metal–oxygen or metal-sulfur bond under the influence of the interfacial potential difference determines the rate of dissolution. Both metal atoms and oxygen or sulfur atoms at the surface react independently with species in the solution. The rates of these independent processes are coupled by the potential difference across the Helmholtz layer. The mechanism of dissolution proposed here correctly predicts the observed orders of reaction.