Removal of Cu(II), Zn(II) and Cd(II) ions from aqueous solutions by adsorption on walnut shell-Equilibrium and thermodynamic studies: treatment of effluents from electroplating industry

In this work, the efficiency of walnut shell as a low-cost and natural adsorbent for removing metal ions from aqueous solution and electroplating wastewater has been studied. Batch experiments were conducted to study the effect of some parameters such as contact time, initial concentration, solution pH and temperature on the adsorption of Cu(II), Zn(II) and Cd(II) by walnut shell. Langmuir and Freundlich models were employed for the mechanistic analysis of experimental data and the observation reveals that in our system adsorption follows the Langmuir isotherm. The maximum adsorption capacity of Cu(II), Zn(II) and Cd(II) were found to be 14.53, 7.47 and 7.29mg/g, respectively. The pseudo-first-order and pseudo-second-order models were employed for kinetic analysis of adsorption process. It was found that adsorption process follows pseudo-second-order kinetics. The adsorption process was subjected to thermodynamic study revealing that adsorption of these metals on the natural adsorbent was spontaneous and endothermic in nature. According to the experimental investigation, walnut shell seems to be an effective, natural, low-cost and alternative adsorbent for the removal of these metal ions from aqueous solutions. The efficacy of walnut shell in the treatment of effluent from electroplating industry has been explored and the results have been found encouraging.