Adsorptive performance of an amine-functionalized poly(hydroxyethylmethacrylate)-grafted tamarind fruit shell for vanadium(V) removal from aqueous solutions

A novel adsorbent (PGTFS–NH3+Cl−) bearing –NH3+Cl− functional moiety was prepared from tamarind fruit shell (TFS) through graft copolymerization of hydroxyethylmethacrylate onto TFS in the presence of N,N′-methylenebisacrylamide as a cross linking agent using K2S2O8/Na2S2O3 initiator system, followed by transmidation and hydrochloric acid treatment. The applicability of PGTFS–NH3+Cl− for the effective removal of vanadium(V) ions from aqueous solutions was investigated. The maximum adsorption was observed in the pH range 3.0–6.0. The adsorption was fond to be concentration dependent and exothermic, and the equilibrium was established within 4 h. The adsorption follows reversible second-order kinetics and the low Ea (−4.06 kJ/mol) indicated a diffusion controlled process. Equilibrium studies demonstrated that the adsorption process obeys Langmuir isotherm model and the maximum adsorption capacity of PGTFS–NH3+Cl− towards V(V) was 45.86 mg/g at 30 °C. The values of change in entropy (ΔS0) and heat of adsorption (ΔH0) for V(V) adsorption on PGTFS–NH3+Cl− were estimated as −47.20 J/mol K and −15.64 kJ/mol, respectively. The values of isosteric heat of adsorption (ΔHi) were also calculated at different surface coverages. The results indicate that PGTFS–NH3+Cl− used possessed nearly homogeneous surface sites. The PGTFS–NH3+Cl− was evaluated for its efficiency in V(V) recovery from simulated groundwater. The spent PGTFS–NH3+Cl− was regenerated using 0.2 M NaOH, with up to 96% recovery and the adsorbent was reused in four adsorption–desorption cycles without any substantial loss in adsorption capacity.