| 摘要: | 近年來，由於工業快速成長，發生工業廢水及廢料之濫排等事件，導致重金屬、有機物及酸鹼度等污染滲入土壤中。重金屬堆積於土壤後，再藉由河水和雨水持續灌溉，使土壤中重金屬隨著土壤孔隙水被農作物根部吸收進入農作物內部，累積於食物鏈或是向下滲透至地下水區域，擴大污染範圍。
本研究使用牡蠣殼作為土壤中重金屬之吸附劑。牡蠣殼為牡蠣養殖所產生之副產物，為台灣西部沿海地區常見的廢棄物，不僅影響海岸線生態、產生惡臭，還會滋生蚊蟲和造成公衛上等問題。本研究將牡蠣殼進行前處理及表面改質，先利用NaOH鹼洗牡蠣殼，再使用KMnO4進行表面改質。藉由土壤管柱實驗評估牡蠣殼、鹼洗牡蠣殼和錳改質牡蠣殼對鎘和銅去除的能力與時效性。另外，三種牡蠣殼施放於受污染土壤中進行土壤培育實驗，使土壤孔隙水中的重金屬離子與牡蠣殼進行接觸後，將其固定於牡蠣殼上，探討是否能有效降低重金屬的遷移率，減少向下滲透至地下水區域及被植物吸收的可能性。
由三種牡蠣殼對鎘和銅之等溫吸附實驗與吸附動力實驗結果顯示，三種牡蠣殼皆對重金屬銅之吸附行為符合Freundlich等溫吸附模式及擬二階吸附動力模式，其等溫吸附常數n值皆大於 1，屬於有利之吸附反應；三種牡蠣殼皆對重金屬鎘之吸附行為符合Langmuir等溫吸附模式及擬二階吸附動力模式。
土壤管柱實驗結果顯示，三種牡蠣殼對鎘或銅去除能力皆為錳改質牡蠣殼>鹼洗牡蠣殼>牡蠣殼。三種牡蠣殼對去除銅的時效性(去除率>95%)皆可長達180小時；固定鎘的時效性為：錳改質牡蠣殼(108小時) >鹼洗牡蠣殼(36小時) >牡蠣殼(24小時)。在土壤培育實驗中，經過15天實驗結果顯示，土壤孔隙水中銅、鎘的濃度皆有所下降，牡蠣殼對銅和鎘的最佳去除率分別為：銅81.04%、鎘46.44%；鹼洗牡蠣殼對銅和鎘的最佳去除率分別為：銅83.21%、鎘60.2%；錳改質牡蠣殼對銅和鎘的最佳去除率分別為：銅86.51%、鎘83.17%。綜合本研究結果顯示，牡蠣殼、鹼洗牡蠣殼及錳改質牡蠣殼皆有固定土壤中鎘和銅的能力，而又以錳改質牡蠣殼的效果最佳。
;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. |
