The behaviour of the rare earths during the precipitation of sodium, potassium and lead jarosites

The behaviour of the rare earths during the precipitation of sodium, potassium and lead jarosites from both sulphate and chloride media was investigated. Efforts to synthesize the end-member rare earth analogues of sodium jarosite and potassium jarosite were unsuccessful. The precipitation of sodium jarosite or potassium jarosite in the presence of various concentrations of the rare earths resulted in the incorporation of < 0.3 wt.% of the rare earths in the jarosite structure. Comparable levels of rare earth incorporation were noted in both sodium jarosite and potassium jarosite. Increasing solution pH or increasing ferric ion concentration resulted in higher precipitate yields, but had only a minimal effect on the structural incorporation of the rare earths in the jarosite. Sodium jarosite and potassium jarosite precipitated from predominantly chloride media had levels of rare earth incorporation comparable to those of the jarosites made from sulphate solutions. Lead jarosite precipitated from rare earth-containing solutions incorporated < 0.2 wt.% of the rare earths. SEM studies showed that the presence of the rare earths had little effect on the morphology of the precipitated sodium, potassium and lead jarosites. Clearly, the trivalent rare earth (RE) elements do not substitute extensively for trivalent iron in the jarosite structure, and this behaviour likely reflects the larger size, different co-ordination and the significantly lower hydrolyzability of the trivalent rare earth ions relative to ferric ions. (C) 2004 Elsevier B.V. All rights reserved.