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 halforder for the concentration of the oxidant. This is in agreement with the experimental evidence.