A Novel Process for Recovering Rare Earth from Weathered Black Earth

A novel process for recovering rare-earth (RE) elements from weatheredblack-earth slime is developed. This process involves the initial removal of Mn by reduction leaching using SO2 followed by ammonium chloride roasting of the residual solids from the leaching process. The controlled roasting selectively converts RE oxides to water-soluble RE chlorides. The roasted materials are then dispersed in warm water (75°C) to extract RE, while water-insoluble iron oxides remain in gangue sludge, minimizing iron impurities in final RE products and hence simplifying the purification process. Lead-chloride precipitates are obtained by cooling the leachate to -10°C, and RE is recovered using oxalic acid precipitation. With this new process, a product of 92 pct purity at a RE recovery greater than 65 pct is obtained. In addition, Mn and Pb are recovered as byproducts, with a recovery of 64 and 54 pct, respectively. The effect of operating variables on RE recovery is examined and the process chemistry described.