Calcine, its use in EZ's new selective zinc precipitation process for impurity and water balance control

CIM Bulletin, Vol. 81, No. 913, 1988

O.M.G. NEWMAN, D.J. PALMER and J.R. WELSH, Electrolytic Zinc Company of Australasia Limited, Risdon, Tasmania, Australia

The use of calcine for selective zinc precipitation requires specialist knowledge to achieve satisfactory flowsheet design. Calcine from the bed of a fluid roaster is preferred, and factors such as the size distribution of ground calcine, the stoichio-metric ratio of the calcine precipitant to the initial dissolved zinc concentration and the moisture content of the resultant filter cake are parameters which require critical attention. Extensive testing in a fully-integrated electrolytic zinc plant pilot plant has demonstrated that properly designed selective zinc precipitation plants using calcine as the precipitant are reliable operating units. The advantages of using calcine instead of limestone for selective zinc precipitation include a decreased cost of reagents, as well as avoiding the formation of by-product gypsum. Process simulation modelling has demonstrated that the use of calcine in this context has widespread application in the design of zinc plants with superior impurity and water balance control characteristics. A particularly powerful approach involves closed circuit washing. In this mode, filtrate from the selective zinc precipitation step is used to wash a zinc plant residue such asjarosite, and the resulting filtrate is returned to the selective zinc precipitation section.

Mots Clés: Calcine, Precipitation process, Zinc, Selective Zinc Precipitation, (SZP) Process, Washing, Hydrometallurgy, Impurity control