Adsorption of Cr(VI) from Industrial Wastewater Using a Novel Zeolite-A/Fe₃O₄/Biochar/MOF‑5 Composite

Disposal of Cr­(VI) into environments without adequate pretreatment from various industrial wastes has detrimental effects on human health that range from skin irritation to cancer depending on the dose and the exposure level. Taking this into consideration, a novel Zeolite-A/Fe₃O₄/Biochar/MOF-5 (Z-A/Fe₃O₄/BC/MOF-5) composite was synthesized through the solvothermal method for the adsorption of Cr­(VI) from industrial wastewater. The phase structure, surface area, functional group, surface morphology, and elemental composition of the as-synthesized adsorbent were characterized by using XRD, BET, FT-IR, and SEM-EDX, respectively. The batch adsorption was studied by optimizing the adsorption parameters. The maximum adsorption efficiency (95.12%) and adsorption capacity (47.57 mg/g) were obtained at 15 mg/L of initial concentration, 0.3 g/L of adsorbent dose, 120 min of contact time, and pH = 5, respectively. The adsorption isotherm and kinetic of Z-A/Fe₃O₄/BC/MOF-5 composite were well fitted with the Freundlich and pseudo-second-order models, which suggests that the adsorption occurred through chemosorption on the heterogeneous adsorbent’s surface. Furthermore, the recyclability of the Z-A/Fe₃O₄/BC/MOF-5 adsorbent was conducted for five successive runs and resulted in 95.07, 89.59, 85.69, 71.74, and 64.83% for the first, second, third, fourth, and fifth runs, respectively. The synthesized quaternary adsorbent was finally tested on industrial wastewater with a Cr­(VI) initial concentration of 36.27 mg/L collected from Batu Tannery Industry PLC, Ethiopia. Interestingly, the Z-A/Fe₃O₄/BC/MOF-5 composite shows higher adsorption performance, 92.85% Cr­(VI) removal efficiency, much higher than its pristine MOF-5 (90.57%), binary Z-A/MOF-5 (83.05%), and ternary Z-A/Fe₃O₄/BC (82.83%) composites. This could be due to the synergic effect of the individual materials in the Z-A/Fe₃O₄/BC/MOF-5 composite. Consequently, the quaternary Z-A/Fe₃O₄/BC/MOF-5 composite is promising for the removal of Cr­(VI) from industrial wastewater.