Recovery of rare earths from industrial wastewater using extraction-precipitation strategy for resource and environmental concerns

Abstract Unlike the classic separation technologies, an extraction-precipitation strategy has been developed for the recovery of rare earth (RE) and from industrial wastewater using a novel phenoxycarboxylic acid of 2-(4-butoxyphenoxy) acetic acid (BPAA). Compared with 4-(4-butoxyphenoxy) butanoic acid (BPBA) and 2-(4-(benzyloxy) phenoxy) acetic acid (BZAA), BPAA enabled minimal reagent/equipment/energy uses in each step of the sustainable process. It was successfully used to enrich REEs with the concentration of 159 mg/L, and the enrichment factor of 189 times was reached. The formed precipitate sizes were bigger than the REEs precipitates from industrial precipitants, i.e., oxalic acid, ammonium hydrogencarbonate, CaO and MgO, which could be settled quickly within 1 min. Compared with COD value of 432 mg/L and 725 mg/L in traditional liquid-liquid extraction using P507 and NA, the COD value of 45 mg/L from BPAA using extraction-precipitation strategy were much lower. It is worthwhile mentioning that BPAA has revealed some advantages in the extraction-precipitation process, i.e., higher efficiency, larger processing capacity, lower energy consumption and simple process. The extraction-precipitation strategy may be suitable for large-scale applications.