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

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.