Effective, rapid and selective adsorption of radioactive Sr2+ from aqueous solution by a novel metal sulfide adsorbent

Abstract

A novel metal sulfide (KZTS) adsorbent has been synthesized using a simple one-step hydrothermal method for radioactive Sr2+ removal from aqueous solutions. XRD and TG analyses indicated that KZTS was chemically and thermally stable. SEM-EDS and TEM images showed that KZTS possessed both flake-like and polyhedral structure with the formula of K1.67Zn0.67Sn2.17S6.00 and K5.84Zn3.47Sn5.04S16.99, respectively. The average formula was determined to be K1.87ZnSn1.68S5.30 using ICP-OES. The adsorption ability of KZTS for Sr2+ was evaluated in detail by batch experiments. The kinetics studies showed that Sr2+ was rapidly removed from the aqueous solution within the equilibrium time of 10 min. According to Langmuir isotherm, the maximum adsorption capacity of KZTS was 19.3 mg/g at 298 K and the high value of the Langmuir constant indicated the high affinity of KZTS for Sr2+. The adsorption mechanisms involved ion exchange and surface Sr–S bonding interactions, with the former dominating. High adsorption performance was observed over a broad pH range of 3–11, although it could be inhibited by co-existing ions, especially Ca2+ and Mg2+. The adsorbent showed a high distribution coefficient (Kd = 1.26 × 106 mL/g) and negligible adsorbate leaching at low Sr2+ concentrations, indicating the strong and irreversible adsorption of Sr2+ on KZTS. Further, KZTS exhibited high selectivity for Sr2+ in alkaline and tap water. These remarkable features suggest that KZTS is a highly desirable adsorbent to remove radioactive strontium from radioactive wastewater.