The Interface Reactions between Divalent Manganese Ion and Manganese-Coated Sand

本研究利用錳砂為吸附劑，除了分析其特性外，更進一步探討錳離子在其表面之吸附、脫附作用及自媒催化情形，並利用不同水質條件測試其對錳離子吸附效果之影響。 人造錳砂特性分析方面，在X光繞射分析結果顯示人造錳砂上之錳氧化物並非單一物種，其物種包括三氧化二錳(Mn2O3)、氧化錳(MnO2)及氫氧化錳(Mn(OH)4)，而在顯微結構分析中，可觀察到人造錳砂表面為一粗糙不平及佈滿大小顆粒狀之錳氧化物及許多孔隙之濾料。另外，由SEM/EDS分析結果中，可知人造錳砂上之錳氧化物與石英砂間之界面型態為機械界面層，並且也觀察到錳離子有擴散至石英砂內部，導致披覆在人造錳砂上之錳氧化物為一薄層，但也間接強化錳氧化物覆膜在石英砂表面之強度。批次實驗方面，在無錳砂之溶氧實驗中，顯示系統pH<9時，二價錳之氧化速率非常緩慢；吸附動力試驗結果，錳離子在初期吸附非常快速，吸附反應2小時已有85%以上之吸附率，並且在4小時後吸附反應已達平衡，總吸附量約在96.7%；吸附邊緣曲線試驗則顯示錳吸附量隨pH值上升而增加，而且在pH=2.75時，錳吸附量仍有50%，係因人造錳砂之pHzpc為1.26所致；恆溫吸附曲線之研究結果中，錳離子在人造錳砂表面呈現多層吸附型態，推測為錳離子之自媒催化反應(autocatalysis)，且經迴歸模擬後，遵循非線性之多層模式。另外，在溫度影響下，其多層吸附量隨溫度上升而增加；由競爭吸附結果，可知亞鐵離子確實與二價錳離子產生競爭，且亞鐵離子濃度愈高，競爭效果愈顯著；最後在脫附實驗中，可得到初期錳離子脫附非常快速，但在30分鐘後脫附速率已趨於平緩，總脫附率約在88%，而在不同吸附接觸時間之影響方面，則顯示吸附時間愈長，錳總脫附量愈少。&quot;Manganese-coated sand&quot; is a type of coated silica medium with manganese oxides, which formed from the sorption of manganese oxides during long-term filtration via the process of rapid sand filtration, followed by aeration in water treatment plant. Locally available manganese-coated sand, both of packing and byproduct of filtration process for water treatment plants in Taiwan, was found to be a low-cost and promising adsorbent for removal of Mn2+ from raw water. This study was conducted to build the basic data for coating hydrated manganese oxide on the sand surface to utilize adsorbent properties of the coating and filtration properties of sand. In this study, gas adsorption porosimetry and scanning electron microscope (SEM) analyses were used to investigate the surface properties of the coated layer. An energy dispersive X-ray (EDAX) technique of analysis was used for characterizing metal adsorption sites on a manganese-coated sand surface. Results indicated manganese-coated sand had more micropores and higher specific surface area, owing to attachment of manganese sand. Manganese ions penetration into the micropores and mesopores of manganese oxide on a sandy surface; regeneration of manganese-coated sand could be achieved by soaking with pH