Low-cost organic adsorbent usage for removing Ni2+ and Pb2+ from aqueous solution and adsorption mechanisms

This study aimed to investigate Ni2+ and Pb2+ removal by using pistachio, peanut, and almond shells from an aqueous medium. The contact time, pH, and biosorbent dosage effects on the sequestration of nickel and lead were evaluated. Optimum adsorption of metal ions at pH value of 6.0, contact time 45 min at room temperature with 1.0 g adsorbent was found. The sorption process of metal ions was well defined by the pseudo-second-order kinetic model and Freundlich isotherm for nickel and Langmuir isotherm for the lead. The adsorption capacity for nickel and lead was obtained in the order of pistachio shell (72.46 mg g(-1)) > almond shell (71.94 mg g(-1)) > peanut shell (60.97 mg g(-1)), and almond shell (48.14 mg g(-1)) > peanut shell (37.14 mg g(-1)) > pistachio shell (36.73 mg g(-1)), respectively. The FTIR spectra and SEM images were used to characterize the adsorbents. FTIR analysis demonstrates that the surface carboxylic/hydroxyl functional groups of organic residuals are responsible for the adsorption of Ni2+ and Pb2+. Various mechanisms including the electrostatic interaction, ion exchange, metal complexation, physical/chemical adsorption take place in the adsorption process. The results indicate that pistachio, peanut, and almond shell, locally available organic residuals, are efficient and green adsorbent for the reduction of Ni2+ and Pb2+. According to their adsorption capacity, pistachio shell for Ni2 + and almond shell for Pb2 + can be recommended.