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.

Keywords: Coordination; Membrane separation; Plant polyphenols; Radionuclide tolerance mechanism; Ultraselective enrichment.