Adsorptive Removal of Pb(II), Ni(II), and Co(II) from Simulated Wastewater Using Delonix Regia Seed: Equilibrium and Kinetic Studies

The development of low-cost biosorbents from agricultural biomass offers a sustainable approach for the remediation of heavy metal-contaminated wastewater. In this study, Delonix regia seed (DRS) was evaluated as a natural biosorbent for the removal of Pb(II), Ni(II), and Co(II) ions from simulated wastewater. The adsorbent was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FTIR), revealing an amorphous surface enriched with hydroxyl and carbonyl functional groups that participate in metal ion binding. Batch adsorption experiments were conducted to investigate the effects of solution pH, adsorbent dosage, initial metal ion concentration, contact time, and temperature. Maximum removal efficiencies exceeding 90% were achieved under optimized conditions. Equilibrium data were best described by the Langmuir isotherm, with maximum monolayer adsorption capacities of 62.57 mg g⁻ 1 for Pb(II), 59.26 mg g⁻ 1 for Co(II), and 73.59 mg g⁻ 1 for Ni(II), indicating favorable monolayer adsorption on a homogeneous surface. Kinetic analysis showed that the adsorption process followed the pseudo-second-order model, suggesting that chemisorption is the dominant rate-controlling mechanism. The combined characterization and adsorption results demonstrate that Delonix regia seed is an abundant, inexpensive, and environmentally sustainable biosorbent with considerable potential for heavy metal removal in wastewater treatment applications.