THE PRECIPITATION OF LEAD JAROSITE FROM CHLORIDE MEDIA

Lead jarosite, Pb0.5Fe3(SO4)2(OH)6, was precipitated from concentrated FeCl3-LiCl-PbCl2 media containing Li2SO4 as the independent sulphate source, and the parameters affecting the amount and composition of the precipitate were determined. Lead jarosite is precipitated over the pH range 0.0-0.8 and at temperatures from 80 to 150-degrees-C; higher temperatures result in Fe2O3 formation. High total chloride concentrations are required to prevent the co-precipitation of PbSO4. The amount of product increases with increasing concentrations of PbCl2, FeCl3 and Li2SO4, but the product composition is significantly affected only at Li2SO4 concentrations < 0.15 M. The kinetics of lead jarosite precipitation from chloride media at 98-degrees-C are relatively slow, and approximately 24 h are needed to achieve steady state conditions. Efforts to incorporate silver in the structure of the lead jarosite were not successful; the silver content never exceeded 70 ppm Ag. Likewise, it was not possible to precipitate end-member silver jarosite, and this behaviour is attributed to the strong complexation of silver in concentrated chloride media.