Radionuclide tolerance mechanism of plants for ultraselective enrichment of low content of thorium with exceptional selectivity coefficient

Abstract

Selective enriching low content of radionuclides from radioactive wastewater is a critical issue for environmentally benign utilization of nuclear power. Inspired by the tolerance mechanism of plants to radionuclides, we developed a pH-triggered ultraselective coordinative adsorption (CA) membrane. The as-prepared CA membrane featured the advantages of both coordinative adsorption and membrane separation, including ultrahigh selectivity coefficient of 1242, large capacity (80 L m−2) and short mass transfer distance. The adsorption isotherms of Th4+ on the CA membrane were well described by the Freundlich model (R2 > 0.99), and the adsorption kinetics have a good fitting by using the pseudo-second-order kinetic model (R2 > 0.99). In a continuous separation under gravity, the CA membrane was able to selectively enrich the low content of Th4+ (0.05 mmol L-1) in the presence of 700 folds (35 mmol L−1) of co-existing ions (Na+, Mg2+, K+, Ca2+, Sr2+, Cs+ and Ba2+). The exceptional extraction efficiency to Th4+ was 100%, superior to that (3.7%) of all co-existing ions. Notably, the Th4+ enriched on the CA membrane was facilely eluted by diluted HNO3 (0.1 mol L−1). The Th4+ in the eluents was enriched by up to 54 folds. The eluted CA membrane was further reused for selective enrichment of Th4+, which showed no obvious loss of selectivity and enrichment capability. Our strategy might open up a new strategy for realizing ultraselective and recyclable enrichment of low content of irradiation contaminants from wastewater.