| In this paper, nature walnut shell(named P-W) and modified walnut shell(named NC-W) were the adsorbent to remove Cd2+ or Pb2+ in wastewater. Mainly affecting factors, such as dosage of adsorbent, solution p H, initial concentration of mental ions(Cd2+ or Pb2+), adsorption time and reaction temperature, and adsorption property for adsorption process of mental ions(Cd2+ or Pb2+) on P-W and NC-W have been studied. The kinetic processes were described by Lagergren pseudo-second kinetic model and intra-particle diffusion kinetic model and the thermodynamic processes were fitted by Langmuir isotherm model and Freundlich isotherm model to conduct its thermodynamic parameters research and analysis.In this study, sodium hydroxide(Na OH 0.05mol/L) and calcium chloride(Cacl2 0.05mol/L) were selected as chemical modification reagents respectively for two stages under the whole processes to produce adsorbents. Results showed that the surface area and porosity of nature walnut shell(named P-W) were increased and the capabiliies of mental ions(Cd2+ or Pb2+) were improved after modified. Under the same conditions, the capabiliies for removing mental ions(Cd2+ or Pb2+) on NC-W were 10.7 and 9.6 times to P-W. That is to say, NC-W is better than P-W.Dosage of adsorbent, solution p H, initial concentration of mental ions(Cd2+ or Pb2+) and adsorption time were the mainly affecting factors on P-W and NC-W. Optimum p H was 5~6. The adsorption capacity of P-W or NC-W was increased with the increasing of solution p H, initial concentration of mental ions(Cd2+ or Pb2+), reaction temperature or adsorption time, while it was decreased with the increasing of P-W or NC-W amounts. When the initial concentration was low, the adsorption efficiency to remobve Cd2+ or Pb2+ was better on both P-W and NC-W. When the reaction temperature was 298 K, the adsorption capabilities of Cd2+ or Pb2+ were 1.27 or 7.16mg/g on P-W and 13.62 or 68.70mg/g on NC-W. Therefore, adsorption capacity of walnut shell has been greatly improve after chemical modification.The adsorption equilibrium time on P-W and NC-W to adsorbed Cd2+ or Pb2+ has no direct relationship with sorbent dosage, p H value, initial ion concentrations and reaction temperatures. The speed was rapid at 5 min, and the adsorption equilibrium was reached in the 20 min. The kinetics of the former adsorption process was found to follow the Lagergren pseudo-second order much better than intra-particle diffusion kinetic model.The adsorption of Cd2+ or Pb2+ on P-W and NC-W were both found to follow the Langmuir isotherm model(R2 were greater than 0.99) very well, indicating that the adsorption processes were both single molecular adsorption mode and the adsorption behavior of Cd2+ or Pb2+ on NC-W was happen more easily than P-W.The entropy was increased with the adsorption process of Cd2+ or Pb2+ on the P-W and NC-W, and the physical adsorption was the mainly processes during the adsorption. It can be seen the adsorption reactions were spontaneous endothermic process. With the increasing of reaction temperature, the adsorption equilibrium capacity on P-W increased from 14.60 mg/g to 15.20mg/g for removing Cd2+ and incrreasd from 36.90 mg/g to 38.02mg/g for removing Pb2+, while the adsorption equilibrium capacity on NC-W increased from 29.61 mg/g to 36.72mg/g for removing Cd2+ and incrreasd from 78.0 mg/g to 92.64 mg/g for removing Pb2+. It can be seen from the equilibrium adsorption amount, the adsorption capacity of NC-W was higher than P-W, and from the rate of increasing, the impact from changes of reaction temperature was not great for adsorption on P-W and NC-W. Therefore, the impact of reaction temperature can be ignored to remove mental ions in wastewater from the practical engineering applications. That is to say, we can use this adsorbent directly for the treatment of sewage and wastewater at room temperature. |
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