Stellerite-seeded facile synthesis of zeolite X with excellent aqueous Cd2+ and Ni2+ adsorption performance

Abstract

• Stellerite zeolite was converted to zeolite X by a two-step hydrothermal method. • Adsorption capacities at 298 K were 173.553 (Cd 2+ ) and 75.897 mg·g - 1 (Ni 2+ ). • Main Ni 2+ removal mechanism by zeolite X was ion exchange. • Main Cd 2+ removal mechanism by zeolite X were ion exchange and precipitation. • The synthesized zeolite X is an effective tool to remove Cd 2+ /Ni 2+ from wastewater. Zeolite X was synthesized by a two-step hydrothermal method using natural stellerite zeolite as the silicon seed, and its adsorption performance for Cd 2+ and Ni 2+ ions was experimentally and comprehensively investigated. The effects of pH, zeolite X dosage, contact time, and temperature on adsorption performance for Cd 2+ and Ni 2+ ions over were studied. The adsorption process was endothermic and spontaneous, and followed the pseudo-second-order kinetic and the Langmuir isotherm models. The maximum adsorption capacitiesfor Cd 2+ and Ni 2+ ions at 298 K were 173.553 and 75.897 mg·g −1 , respectively. Ion exchange and precipitation were the principal mechanisms for the removal of Cd 2+ ions from aqueous solutions by zeolite X, followed by electrostatic adsorption. Ion exchange was the principal mechanisms for the removal of Ni 2+ ions from aqueous solutions by zeolite X, followed by electrostatic adsorption and precipitation. The zeolite X converted from stellerite zeolite has a low n (Si/Al), abundant hydroxyl groups, and high crystallinity and purity, imparting a good adsorption performance for Cd 2+ and Ni 2+ ions. This study suggests that zeolite X converted from stellerite zeolite could be a useful environmentally-friendly and effective tool for the removal of Cd 2+ and Ni 2+ ions from aqueous solutions.