Purification of spent electrolyte by sequential precipitation method and its on-line monitoring

In order to recover salt and minimize waste volume, a sequential precipitation method was proposed to remove rare earth (RE = La, Sm, Nd, Dy), Cs, Sr, and Ba from spent electrolyte in the form of phosphate and carbonate precipitation, respectively. The thermodynamic calculation confirmed the feasibility of the process. The precipitation results indicated that RE 3+ and Cs + could be converted to insoluble phosphates using Na 3 PO 4 , whereas Sr 2+ and Ba 2+ to insoluble carbonates by adding K 2 CO 3 . Meanwhile, the phosphate precipitation process was monitored online by square wave voltammetry, and the results showed that with the addition of Na 3 PO 4 , the peak current densities corresponding to the reduction of RE 3+ decreased gradually. The molten salt containing La 3+ , Sm 3+ , Nd 3+ , Dy 3+ , Cs + , Sr 2+ , and Ba 2+ was used to simulate the waste electrolyte for sequential precipitation; the removal rates of RE, Sr, and Ba were found to be over 95.00%, except for Cs 79.17%. Graphical abstract In order to recover the molten salt, the sequential precipitation method was proposed to remove rare earth (RE = La, Sm, Nd, Dy), Cs, Sr, and Ba from spent electrolyte. RE and Cs were separated using Na 3 PO 4 and Sr and Ba using K 2 CO 3 . The removal rates estimated by ICP-OES were found to be over 95.00%, except for Cs.