A hydrometallurgical process for extraction of lanthanum, yttrium and gadolinium from spent optical glass

A hydrometallurgical process is developed to recover rare earth (RE) metals from spent optical glass containing 43.12 wt.% lanthanum oxide, 9.37 wt.% yttrium oxide and 4.60 wt.% gadolinium oxide. The process involves the initial conversion of RE from a borosilicate phase to the hydroxide form using sodium hydroxide followed by hydrochloric acid leaching of the residual solids from the conversion. The investigation of the effects of process parameters shows that increase in NaOH concentration, conversion temperature, liquid-to-solid ratio and conversion time accelerates the RE leachability. Also, increase in HCl concentration, leaching temperature, liquid-to-solid ratio and leaching time improves RE extraction rate. By converting RE in a 55 wt.% NaOH aqueous solution and a liquid-to-solid ratio of 2 at 413 K for 60 min followed by leaching the residual solids in 6 M HCl and a liquid-to-solid ratio of 4 at 368 K for 30 min, an aqueous mixture of RE chlorides containing 36.54 g/L La, 7.38 g/L Y and 3.93 g/L Gd at a corresponding recovery of 99.4%, 100% and 100% is obtained from the glass.