Study of the potential of composite material based on zeolite and geopolymer as an adsorbent of toxic metals

The increasing generation of metallic effluents by the electroplating industry poses significant environmental challenges due to the toxicity and persistence of these contaminants. The present study evaluated a geopolymer-zeolite A composite adsorbent, synthesized from fly ash of steel mill furnaces, for the removal of Cu ²⁺ , Ni ²⁺ , and Zn ²⁺ ions from aqueous solutions. The synthesis yielded a material exhibiting the structural and morphological characteristics of both components, as confirmed by physicochemical characterization techniques. Batch adsorption experiments were conducted using a synthetic solution that represented electroplating effluents. In the kinetic studies, Cu ²⁺ demonstrated the highest initial adsorption rate, Zn ²⁺ exhibited the highest equilibrium capacity, and Ni ²⁺ performed poorly in both. The Sips model demonstrated the optimal compatibility with the isotherm data, thereby reflecting the heterogeneity of the adsorptive surface. Saturation of the sites was observed at approximately 150 mg·L ^− 1 , with maximum capacities of 162.393 mg·g ^− 1 (Zn ²⁺ ), 99.801 mg·g ^− 1 (Cu ²⁺ ) and 63.266 mg·g ^− 1 (Ni ²⁺ ). The initial concentration exerted a significant influence on the kinetics and removal efficiency, particularly in the case of Cu ²⁺ , which demonstrated a heightened sensitivity to the availability of ions. The highest removal percentages were achieved at the lowest initial concentration (0.8 mmol·L⁻¹): 34.7% (Cu ²⁺ ), 32.67% (Zn ²⁺ ), and 17.12% (Ni ²⁺ ). Ion exchange was identified as one of the primary mechanisms, as evidenced by the increase in Na⁺ concentration in the solution from 800 mg·L ^− 1 to 1,112 mg·L ^− 1 , indicating the release of this cation by the matrix in exchange for the metal ions. The findings suggest that the developed composite is a promising and sustainable alternative for treating metallic effluents.