| dc.description.abstract | In recent years, illegal discharges of industrial wastewater have led to the infiltration of heavy metals, organic matters and other pollutants into the soil due to the rapid development of industries. When the heavy metals deposit in the soil, they are absorbed by the crop roots via the soil pore water, accumulated in the food chain, infiltrated into the groundwater, and expanded the pollution areas.
In the earlier research, oyster shells have been used as adsorbents to adsorb heavy metals in soil. Oyster shells are by-products produced by oyster farms and they are common wastes in the western coastal areas of Taiwan. They not only affect the coastline ecology, produce odors, breed mosquitoes, but also cause public health problems. In this study, oyster shells were cleaned by NaOH, and conducted surface modification by KMnO4 to form manganese oxides around the oyster shells. Isothermal adsorption and adsorption kinetic experiments were conducted to investigate the adsorption mechanisms of granular oyster shell (GOS), NaOH-cleaned granular oyster shell (NaGOS) and manganese oxide coated granular oyster shell (MOCGOS). Immobilization ability of cadmium and copper as a function of time by GOS, NaGOS and MOCGOS were evaluated by soil column experiments. In addition, three types of oyster shells were conducted soil incubation experiments to evaluate the immobilization of cadmium and copper in the real contaminated soil.
The results of isothermal adsorption and adsorption kinetic experiments of three types of granular oyster shell for cadmium and copper showed that the adsorption behavior of three types of granular oyster shells to copper was conformed to Freundlich isotherm model and pseudo-second-order kinetics mode. The isotherm adsorption constant n is greater than 1, which is a favorable adsorption reaction. Three types of granular oyster shells to cadmium fit to Langmuir isotherm model and pseudo-second-order kinetics mode.
According to the soil column experiment results, the adsorption capacity of three types of oyster shells toward cadmium or copper were in the order of MOCGOS＞NaGOS＞GOS. The three granular oyster shells still had removal ability for copper at the 180th hour. On the other hand, the effective time (removal＞95%) to remove cadmium was in the order of MOCGOS (108 hours)＞NaGOS (36 hours)＞GOS (24 hours). In the soil incubation experiments, the concentrations of copper and cadmium in soil pore water were all significantly decreased. The best removal efficiency of copper and cadmium for GOS were: 81.04% for copper and 46.44% for cadmium; for NaGOS were: 83.21% for copper, 60.2% for cadmium; for MOCGOS were: 86.51% for copper, 83.17% for cadmium. To sum up, GOS, NaGOS and MOCGOS all have the ability to immobilize cadmium and copper in the soil, and the MOCGOS have the best immobilization ability for cadmium and copper in the soil. | en_US |