Mechanism Of Catalytic Oxidation Of Mn²⁺ In Groundwater By Active Filter Membranes

In the northern area of China, mostly small and middle-sized cities usegroundwater as drinking water sources. However, the monitoring records of thegroundwater qualities showed that the over standard rate of manganese indicator is high,which is the important urgent problem to be solved. At present, the catalytic oxidationprocess is widely used in drinking water treatment process to remove manganese inChina. In this paper, the physical and chemical properties of the co-oxides activemembrane on the surface of filter materials were studied in the pilot scale filter system,by which the groundwater high in iron and manganese of the city of A was treated. Theadsorption kinetics of active filter membranes for Mn²⁺and DO were studied and themechanism of catalytic oxidation of manganese was studied. This research will providecertain theoretic backgrounds for catalytic oxidation of manganese. The main results areas follows:（1） As the active membrane formed, the filter layer removal of Mn²⁺graduallyenhanced and the specific surface area, the average pore diameters are increased thatenlarged the numbers of adsorption sites on the surface, and improved the adsorption ofMn²⁺and DO.（2） As the active membrane formed, the adsorption rate and capacity of active filtermembranes for Mn²⁺were gradually improved. The adsorption processes meet theLangmuir equation, i.e., meet the monolayer chemical adsorption model;（3） Positive linear correlation was found between the initial concentration ofMn²⁺and its equilibrium adsorption capacity. In the range of Manganese concentrationfrom0to5mg·L-1, the adsorption capacity for Manganese with active membrane could be calculated by the relationship of Se（mg·g-1）=0.02781C0（mg·L-1）+0.02712.（4） The adsorption sites of Mn²⁺on the less grown filter membranes surface are theoxygen atoms in FeOOH, and the main adsorption activity sites of DO are the ferrumatoms in FeOOH and FeO. In addition, the adsorption sites of Mn²⁺on the grown filtermembranes coated sands surface are the oxygen atoms in Mn-O and Fe-O, the mainadsorption activity sites of DO are the ferrum atoms in FeOOH and FeO and themanganese atoms in MnO2, Mn2O3and MnFeO4.（5） The analysis results of the adsorption sites show that Mn²⁺on the surface of themembrane filter was adsorbed in the oxygen atoms in Mn-O and Fe-O, which wasoxidized by dissolved oxygen, and then catalytic oxidation of manganese was finishedon the surface of the active membrane.