The rate of dissolution of sphalerite is shown to be directly proportional to the concentration of substitutional iron impurity in the solid. This is attributed to the formation of a narrow impurity band within the forbidden band gap of the sphalerite. The impurity band is of iron d-orbital origin. The transfer of electrons between this d-orbital band and the oxidant is energetically more favorable than the transfer of electrons between the valence band and the oxidant. A fundamental model combining the electronic structure of sphalerite and semiconductor electro- chemistry is presented. An equation is derived that describes the rate of dissolution as being first order for the concentration of iron in the solid and half-order for the concentration of the oxidant. This is in agreement with the experimental evidence.