pH tunable anionic and cationic heavy metal reduction coupled adsorption by thiol cross-linked composite: Physicochemical interpretations and fixed-bed column mathematical model study

Over the past, extensive works executed to treat anionic and cationic heavy metal ions from wastewater. Although very few adsorbents were developed to adsorb anionic and cationic heavy metal ions from the same system. In this study, we explored the pH tunable complete reduction plus adsorption mechanism of Pb²⁺ and Cr₂O₇²⁻ by dithiocarbamate-based composite. The pH study recommended that; adsorption of Pb²⁺ occurred at pH 5.5, besides Cr₂O₇²⁻ reduction coupled adsorption executed at pH 3. Furthermore, quick adsorption occurred within 60 min with adsorption capacities of 228.69 and 219.75 mg g⁻¹ for Pb²⁺ and Cr₂O₇²⁻, respectively. Adsorption isotherm well described by the Redlich-Peterson model, also adsorption processes were fitted by pseudo-second-order kinetics model. Interestingly, characteristic techniques, a physical monolayer model and thermodynamic models were applied to the experimental results to further understand the adsorption mechanisms. The results indicated that the physical model with two types of interaction energies was more appropriate to interpret the adsorption mechanism. Based on the physical model, three thermodynamic functions were calculated and interpreted to attribute new macroscopic interpretations at the molecular level of the adsorption systems. Inspiringly, the metal-composite system highly effective for 5 regeneration cycles and fixed-bed column could decontaminate 17.2 L of ~10 mg L⁻¹ Pb²⁺ and 7.3 L of ~10 mg L⁻¹ Cr₂O₇²⁻ to the EPA's wastewater discharge limit by 5 g of CSC@SDBC with the yielding of 400 and 346 mL of eluent, respectively. Theoretically, a liter of CSC@SDBC column may efficiently adsorb 145,646 mg of Pb²⁺ and 57,518 mg of Cr₂O₇²⁻ from industrial effluent, these were calculated from the Bohart-Adams model. These collective batch and fixed-bed systems were cost-effective and environmentally tolerable techniques to remove anionic and cationic heavy metal ions from industrial wastewater.