Adsorption of Zn(II), Pb(II), and Cu(II) by Residual Soil-Derived Zeolite in Single-Component and Competitive Systems

Using construction residual soil (RS) as the raw material, RS-derived zeolite (RSDZ) was prepared through a fusion-hydrothermal process. The adsorption performance and mechanisms of RSDZ for Pb2+, Zn2+, and Cu2+ were investigated in single-component and competitive systems. The strong RSDZ X-ray diffraction peaks at 2θ = 12.47, 17.73, 21.65, 28.18, and 33.44°, together with the results of scanning electron microscopy and Fourier transform-infrared spectroscopy (FT-IR) indicated that NaP1 zeolite (Na6Al6SiO32∙12H2O) was successfully synthesised. The Brunauer–Emmett–Teller surface area, average pore size, and cation exchange capacity increased from 9.03 m2∙g−1, 18.85 nm, and 0.12 meq∙g−1 to 47.77 m2∙g−1, 41.60 nm, and 0.61 meq∙g−1, respectively, after the fusion-hydrothermal process. The maximum Langmuir adsorption capacity of RSDZ for Zn2+, Pb2+, and Cu2+ in the unary systems was 0.37, 0.38, and 0.40 mmol·g−1, respectively. Increasing the initial solution pH facilitated the adsorption reaction, and the adsorption performance was stable when pH > 3. The distribution coefficients in the binary and ternary systems indicated that RSDZ had greater affinity for Pb2+ and Zn2+ than for Cu2+ due to the larger ionic radius and relative atomic weight of the former two cations. The relative affinity to Pb2+ and Zn2+ was related to their concentration, with more competitive adsorption of Pb2+ at concentrations higher than 0.4 mmol·L−1 in binary systems and 0.25 mmol·L−1 in ternary systems. X-ray photoelectron spectroscopy and FT-IR analyses indicated that ion exchange was the main mechanism involved in the adsorption of heavy metal ions by RSDZ, accompanied by ligand exchange.