Digestion kinetics of arsenic removal from enargite–tennantite concentrates

• Arsenic and antimony in the minerals are removed rapidly by NaHS–NaOH digestion.
• The copper in the minerals remains in the solid phase as digenite (Cu9S5).
• The digestion rate is controlled by diffusion through a digenite product layer.

Copper sulfide concentrates with high contents of deleterious impurities such as arsenic and antimony must be pretreated before conventional smelting to prevent atmospheric pollution with toxic compounds. In this work, the selective removal of arsenic and antimony from enargite–tennantite concentrates by a hydrometallurgical process was studied. The process consists of an alkaline digestion using a small volume of concentrated NaHS–NaOH solutions to obtain soluble arsenic and antimony compounds and insoluble copper sulfides. The soluble arsenic and antimony is separated from the copper sulfide by water leaching of the digested material. The experiments were carried out using a copper–arsenic concentrate with 15.1% As and 1.42% Sb. The results showed that the digestion temperature and the concentrations of NaHS and NaOH were the most important variables affecting the rate of arsenic and antimony removal. The rate of the digestion reaction was analyzed by using the unreacted shrinking core model controlled by the diffusion of S2− ions through the layer of the product copper sulfide. An experimental activation energy value of 57 kJ/mol was determined for the arsenic removal in the range of temperature of 60–90 °C.