Preparation of potassium niobium sulfide and its selective adsorption properties for Sr2+ and Co2+

A novel metal sulfide: potassium niobium sulfide (KNbS) was prepared by hydrothermal method. The morphology and composition of KNbS were characterized by scanning electron microscopy and X-ray diffraction. It was confirmed that the adsorption process of KNbS was carried out by exchange reaction of K+ with Co2+ and Sr2+. The effects of pH, contact time, coexisting ions and initial concentration of strontium and cobalt on the adsorption of Sr2+ and Co2+ by KNbS were studied by static adsorption experiments. Thus, the optimal adsorption conditions of KNbS for Co2+ and Sr2+ were determined. The results show that KNbS has a greater affinity for Sr2+ and Co2+ than other coexisting ions. In addition, the adsorption mechanism was analyzed by kinetic, Weber–Morris, Boyd and isothermal models. It was revealed that the adsorption of Co2+ and Sr2+ by KNbS was chemical adsorption of monolayer and the intraparticle diffusion was the main rate-control step.