As an alternative to traditional treatment of complex zinc-containing sulphide ores, application of bio-hydrometallurgical routes can be a possible and economical alternative. When the bio-leaching of such ores or concentrates takes place, dilute acidic leachates are produced, which in addition to valuable metals as zinc and copper, also contain high concentrations of impurities such as iron and arsenic. The aim of the present study has been to develop a new process for recovery of zinc and other base metal values from such leachates. In this process, iron and arsenic are precipitated from the leachate with limestone at pH 3. After a solid/liquid separation step the pH is further increased by lime addition whereby zinc, copper and cadmium are precipitated. The hydroxides formed are after a solid/liquid separation step dissolved with sulphuric acid generated by electrowinning of zinc. As a result a solution concentrated in zinc is produced, which after solid/liquid separation and purification, is fed to the tank house for electrolytic production of zinc metal. The results showed that the proposed process is capable of recovering metal values from leachates of variable compositions. Furthermore, the process can handle solutions which contain chloride, thus giving the method an advantage over conventional zinc electrowinning processes. Raw materials and neutralising agents which contain fluoride and to a lesser extent magnesium must, however, be avoided.
Godkänd; 1996; 20080415 (cira)