本試驗是以淨水廠產出之鐵錳污泥所改質之石英砂(Fe-Mn sludge sand, FMSS)作為吸附劑，探討FMSS在不同克數、不同pH及水公司實場地下水原水中對As(V)的吸附作用。在不同克數及不同pH之試驗使用人工配製原水，砷濃度約為500ppb上下進行試驗。結果顯示隨吸附劑量增加，對砷之去除率隨之提升，但吸附劑對砷之單位吸附量卻隨吸附劑量之增加而減少。此外，在低pH的環境下有助於去除水體中的As(V)，pH為12之試驗顯示砷之去除率極低，主要因FMSS在高pH下因高於其等電位點，導致表面帶負電性。而高pH下存在水中砷之物種亦帶負電荷，電性斥力導致砷不易被吸附。在實場含砷地下水之試驗部分，次氯酸鈉的添加可以加速對砷之吸附，並較未加氯者有較高之砷去除率。評估Freundlich及Langmuir等溫吸附模式後，發現單層吸附之Langmuir模式較為符合FMSS對砷之吸附作用；另外吸附動力學之評估，顯示本吸附較符合擬二階動力吸附，屬化學性吸附。 In this study, the adsorptive removal of arsenate from aqueous solution using iron-manganese coated sand (FMSS) derived from drinking water treatment sludge was investigated. Under a constant initial concentration of 500 ppb, the effect of mass of FMSS (0.125 to 0.4 g), contact time (1 to 23 h) and initial pH (pH 4 to 12) on the % removal and adsorption capacity of As(V) was examined. Results showed that as the mass of FMSS was increased, the adsorption capacity decreases and % As(V) removal were observed to increase as well. Meanwhile, the adsorption capacity and % As(V) removal would both increase due to increase in contact time and as the initial pH becomes more acidic. The removal of As(V) was observed to decrease as the pH becomes more basic. This is due to the negative surface charge of FMSS at pH 12, which is above its isoelectric point. Under a basic pH, the existing forms of As(V) are HAsO42- and AsO43-, which is also negatively charged. The approaching ions of As(V) will exert a repulsive form towards the surface of FMSS, therefore lower removal and adsorption capacity were obtained. The equilibrium data was analyzed using the Langmuir and Freundlich isotherm, where the Langmuir model correlated well with the experimental data. This implies that the adsorption of As(V) onto FMSS could be described as a monolayer adsorption onto binding sites with the same energy levels. Kinetic equations such as pseudo-first order and pseudo-second order equation were used to evaluate the kinetics data. The experimental data agreed well with pseudo-second order equation, which implies that chemisorption is the rate controlling step. This indicates the formation of a covalent bond between As(V) and binding sites of FMSS by sharing a pair of electrons. The removal of As(V) from real groundwater samples were studied, where a higher % removal could be achieved by application of a pre-treatment method, which is oxidation using NaOCl.
