Efficient Co-Adsorption and Highly Selective Separation of Cs+ and Sr2+ with a K+-Activated Niobium Germanate by the pH Control

Cs-137 and Sr-90 are hazardous to ecological environment and human health due to their strong radioactivity, long half-life, and high mobility. However, effective adsorption and separation of Cs+ and Sr2+ from acidic radioactive wastewater is challenging due to stability issues of material and the strong competition of protons. Herein, a K+-activated niobium germanate (K-NGH-1) presents efficient Cs+/Sr2+ coadsorption and highly selective Cs+/Sr2+ separation, respectively, under different acidity conditions. In neutral solution, K-NGH-1 exhibits ultrafast adsorption kinetics and high adsorption capacity for both Cs+ and Sr2+ (q(m)(Cs) = 182.91 mg g(-1); q(m)(Sr) = 41.62 mg g(-1)). In 1 M HNO3 solution, K-NGH-1 still possesses q(m)(Cs) of 91.40 mg g(-1) for Cs+ but almost no adsorption for Sr2+. Moreover, K-NGH-1 can effectively separate Cs+ from 1 M HNO3 solutions with excess competing Sr2+ and M-n(+) (M-n(+) = Na+, Ca2+, Mg2+) ions. Thus, efficient separation of Cs+ and Sr2+ is realized under acidic conditions. Besides, K-NGH-1 shows excellent acid and radiation resistance and recyclability. All the merits above endow K-NGH-1 with the first example of niobium germanates for radionuclides remediation. This work highlights the facile pH control approach towards bifunctional ion exchangers for efficient Cs+/Sr2+ coadsorption and selective separation.