Layered Metal Sulfide NMTS for Rapid Removal of Radioactive Strontium Ions from Aqueous Solution

A one-step hydrothermal method was used to synthesize a quaternary metal sulfide material, NMTS, to remove strontium ions from simulated radioactive wastewater, in which metal tin was replaced by tin and magnesium salts to reduce the cost of the raw materials. The adsorption characteristics and behavior of Sr2+ were studied using batch experiments. NMTS has a layered structure, and the approximate molar ratio of Na:Mg:Sn:S is 4:1:10:23, with an approximate 61% reduction in the raw material cost compared to NaTS. NMTS exhibited ultrafast kinetics for Sr2+ with rapid adsorption of 97.1% in 0.5 min and 99.8% at an equilibrium time of 3 min, followed by the pseudo-second-order model and Langmuir model with a maximum adsorption amount of 52.6 mg/g at 298 K. NMTS had a high affinity for Sr2+ with Kd values of >106 at pH values ranging from 4 to 11. The adsorption of Sr2+ mainly involves ion exchange and surface adsorption. Ion exchange Na+ for Sr2+ was predominant with initial Sr2+ concentrations ranging from 5 to 20 mg/L, and both ion exchange and surface Sr-S bonding interactions occurred with initial Sr2+ concentrations higher than 20 mg/L. Sodium and potassium ions had little effect on the adsorption of Sr2+, whereas the presence of calcium and magnesium ions greatly affected it. In addition, NMTS also exhibited high selectivity for the adsorption of cobalt, nickel, and manganese, followed by Ni2+ > Sr2+ > Mn2+ > Co2+. NMTS is a promising adsorbent for removing Sr ions from aqueous solutions.