Remediation of noxious chromium (VI) utilizing acrylic acid grafted lignocellulosic adsorbent

The chemical modification of Ficus carica fibers with acylic acid using ceric ammonium nitrate (CAN) as initiator was attempted. The chemically modified fiber was used as adsorbent for the removal of Cr(VI) from aqueous system by batch adsorption technique at 30 ± 1 °C. The adsorbent was characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA/DTA), and X-ray diffraction (XRD). Factors influencing the adsorption of Cr(VI) ions from aqueous solution were investigated. The adsorption data was fitted with the isotherms (Langmuir, Freundlich, Tempkin, Harkin's-Jura and Dubinin-Radushkevich), kinetic models (pseudo first order, pseudo second order and intraparticle diffusion models) and thermodynamics. The equilibrium data was best represented by the Langmuir isotherm model, pseudo second order kinetics. The maximum adsorption capacity of Cr(VI) onto adsorbent was found to be 28.90 mg g^{- 1}. The thermodynamic parameters such as enthalpy change (δH°), entropy change (δS°) and free energy change (δG°) observed were - 7.91 kJ mol^{- 1}, 8.89 J mol^{- 1} K^{- 1} and - 10.61 kJ mol^{- 1} respectably at 30 °C that accounted for spontaneous and exothermic process. The removal of Cr(VI) was also studied in the presence of ions such as Na⁺, Mg²⁺, Ca²⁺, SO ₄^2-, HCO₃^- and Cl^-. It was illustrated that the adsorption of Cr(VI) increased in the presence of HCO^3- ions and decreased in the presence of Ca²⁺ and Mg²⁺ ions. Further, desorption studies illustrated that 35.74 % of metal ions was recovered by desorption in the first cycle and adsorbent can be reused.