Removal of copper(II) ions from aqueous solutions by walnut-, hazelnut- and almond-shells

The batch removal of Cu(II) ions from aqueous solution using low-cost adsorbents such as walnut (WNS) (Juglans regia), hazelnut (HNS) (Corylus avellana), and almond (AS) (Prunus dulcis) shell under different experimental conditions was investigated in this study. The main parameters influencing Cu(II) ion sorption on WNS, HNS, and AS were: initial metal ion concentration, amount of adsorbent, contact time, and the pH value of the solution. The influences of initial Cu(II) ion concentration (0.005-0.05 mmol/mL), pH (2 - 9), contact time (10 - 240 min), and adsorbent amount (0.1 - 1.0 g) have been reported. WNS presented the highest adsorption capacities for the Cu(H) ion. Each of WNS, HNS, and AS as sorbents for the removal of Cu(II) ions showed that the sorption process was pH dependent. The greatest increase in the rate of adsorption of metal ion on the shells was observed for pH changes from 5.5 - 7.0. For WNS, HNS, and AS, the optimum pH value was 6 and the equilibrium time was 120 min. The metal ion sorption obeyed both the Langmuir and Freundlich isotherms. The sorption process conformed to the Langmuir isotherm with maximum Cu(II) ion sorption capacities of 6.74, 6.65, and 3.62 mg/g for WNS, HNS, and AS, respectively. The experimental results demonstrated that chelation and ion exchange is one of the major adsorption mechanisms for binding metal ions to the sorbents. The percentage removal Cu(II) ion was maximum at 10(-3) mol/L solution concentration and initial pH of 6.0 (80.3, 75.6, and 75.0% by WNS, HNS, and AS, respectively).