Hydrothermal Synthesis of Analcime from Construction Waste Bricks and Its Adsorption Mechanism for Pb²⁺

Construction waste bricks were used as raw materials to synthesize analcime through a hydrothermal method, and it was employed for the adsorption of simulated wastewater containing Pb²⁺. Firstly, the effects of NaOH concentration, reaction temperature, and time on the synthesis of zeolite were investigated. Then, the impacts of adsorption time, temperature, initial Pb²⁺ concentration, and pH on the adsorption performance were studied. The adsorption kinetics and thermodynamic characteristics were discussed. The results show that the optimal conditions for the hydrothermal synthesis of analcime are NaOH concentration of 2 mol/L, hydrothermal temperature of 160 °C, and reaction time of 6 h. The product has a specific surface area of 25.52 m²/g, a total pore volume of 0.232 cm³/g, an average pore size of 18.22 nm, and a CEC of 114.351 meq/100 g. The adsorption capacity of analcime for Pb²⁺ is positively correlated with the initial Pb²⁺ concentration, temperature, time, and pH. The adsorption of Pb²⁺ by analcime follows two-stage adsorption kinetics equations, and the intraparticle diffusion process is the rate-controlling step but not the sole step. The adsorption behavior includes monolayer adsorption and multilayer adsorption, which is a complex adsorption mechanism involving both chemical adsorption and physical adsorption. The adsorption process was spontaneous and endothermic.