The behaviour of zinc, cadmium, thallium, tin and selenium during ferrihydrite precipitation from sulphate media.

CIM Bulletin, Vol. 91, No. 1019, 1998

J.M. Zinck and J.E. Dutrizac, Mining and Mineral Sciences Laboratories, CANMET, Natural Resources Canada, Ottawa, Ontario

Ferrihydrite is often the initial precipitate resulting from the rapid neutralization of Fe(III) sulphate solutions, and it seems to be a major constituent of zinc plant neutral leach residues. The most important parameters affecting ferrihydrite precipitaton are temperature, solution pH and the neutralization rate. Low temperatures and rapid neutralization rates yield poorly filterable ferrihydrite, whereas higher temperatures and slower neutralization rates produce readily filterable precipitates; in all instances, however, the precipitates are two-line ferrihydrite. Significant amounts of Zn are incorporated in the ferrihydrite precipitates, and the Zn contents increase with increasing Zn concentration, pH or temperature. Generally, the sulphate contents of the precipitates decrease as the Zn contents increase, and this may indicate that the Zn is adsorbed on the ferrihydrite. Discrete Zn phases were not detected. Neither Cd nor Tl is precipitated with ferrihydrite, although thallium jarosite co-precipitates with ferrihydrite at high Tl concentrations and elevated temperatures. Virtually all

Mots Clés: Environment, Ferrihydrate, Zinc, Cadmium, Thallium, Tin, Selenium.