Process development for selective precipitation of valuable metals and simultaneous synthesis of single-phase spinel ferrites from saprolite-limonite laterite leach liquors

To comprehensively utilize the laterite resources, the present study focused on the selective recovery of valuable metals Ni, Co or Al, Cr, and concurrent synthesis of spinel ferrites from saprolite-limonite laterite leach liquors by a one-step selective precipitation method. The precipitation behaviors were investigated in detail, as were factors such as precipitant reagent, pH value, precipitation method, and initial metal ion concentration. In optimal conditions, about 93.0% Ni and 92.0% Co could be enriched in the filtrate by using ammonia (aqueous NH3) solution as precipitant reagent while the recoveries of Al and Cr were 92.0% and 90.0% by using sodium hydroxide (NaOH) solution. After the separation and selective precipitation processes, the precipitates were utilized to synthesize spinel ferrites and the effects of saprolite to limonite laterite mass ratio (MS/L) and calcination temperature on the product purity are discussed. Single phase multi-metal doped magnesium ferrites with high purity could be synthesized when the precipitates were obtained using MS/L ratio of 9:1 and 7:3 by using aqueous NH3 and NaOH solutions as precipitant reagents, and then calcined at 1000 °C for 2 h, respectively. The overall metal recoveries from laterite blends using aqueous NH3 and NaOH precipitant reagents were 89.2% and 85.4%, respectively.