The isotherm and kinetic study of Nickel and Chromium adsorption by pumice powder from aqueous environments

Nickel and chromium are toxic heavy metals that have serious adverse effects on human health and the environment. The removal efficiency of nickel and chromium from aqueous solution was evaluated using pumice powder as an adsorbent. After preparing pumice powder, batch experiments were performed at different times and adsorbent dosages (pH=7, heavy metals concentrations = 50 mg/L, and stirring/minute= 200rpm). Obtained products were adsorbed using Langmuir and Freundlich isotherms, pseudo-first order and second-order models, intra-particle diffusion, and Elovich kinetics. Results indicate that nickel adsorbs more than chromium and adsorption of both nickel and chromium follows the Freundlich model. Correlation coefficients obtained from Freundlich model and pseudo-second order kinetic are R2=0.995, R2=0.996 and R2=0.999, respectively, which shows that the Freundlich expression and the kinetics of pseudo-second order provided a better fit to the experimental data of pumice powder. Also, the removal efficiency was increased significantly by increasing the adsorbent dose and contact time (R2<0.001). According to the obtained value (0 – 1) for dimensionless constant separation term of Langmuir model (RL) and adsorption intensity (1/n), pumice is a proper adsorbent for the removal of nickel and chromium from aqueous environments.