Use of Laponite as Adsorbents for Ni(II) Removal from Aqueous Solution

Silicate-bearing hectorites (laponite) were synthesized by hydrothermal method, and the laponite sample was characterized by Fourier transform infrared (FTIR) spectroscopy, Xray diffraction (XRD), zeta potential, Brunauer-Emmett-Teller (BET) surface area, and pore size analyses. The adsorption of Ni(II) from aqueous solution on laponite as a function of contact time, pH, ionic strength, laponite dosage, and temperature was studied via batch technique. The maximum removal of 99% (approx) could be achieved at the optimum adsorbent dosage of 2.5 g L-1 and near-neutral pH. Adsorption of Ni(II) on laponite is strongly dependent on pH but independent on ionic strength. At low pH, the adsorption of Ni(II) was dominated by ion exchange with Li+ on laponite surfaces, whereas inner-sphere surface complexation and surface precipitation were the main adsorption mechanisms at near-neutral pH and alkaline environment, respectively. The adsorption kinetic data of Ni(II) on laponite were well described by the pseudo-second-order kinetics model. The intraparticle diffusion was involved in the adsorption process but was not the only rate-controlling step. The adsorption isotherms of Ni(II) on laponite can be described well by the Langmuir model and the maximum Ni(II) adsorption capacity of laponite obtained from Langmuir model was 65.79 mg g(-1). The thermodynamic studies indicated that the adsorption of Ni(II) on laponite was endothermic and spontaneous. The laponite exhibited excellent adsorption properties for Ni(II) uptake compared with various adsorbents, indicating that it is a suitable material as an adsorbent for preconcentration and immobilization of Ni(II) from aqueous solution. (C) 2017 American Institute of Chemical Engineers