The Study On Adsorption Of As (Ⅲ) From Aqueous Solution By Iron Oxide And Manganese Oxide Coated Zeolite

Arsenic contamination in drinking water brings great harm to human health. Filtration is a simple and effective water treatment method for the treatment of arsenic contamination. This paper was to prepare iron and manganese oxide modified zeolite as filter material to adsorb and remove As (Ⅲ) in water. Iron-coated modified zeolite filter material (ADZ),Iron-coated modified zeolite filter material (HEZ) and manganese-coated modified zeolite filter material (MZ) were prepared respectively by the method of alkalization-depositing, heat-evaporating and depositing,the characterization of the modified zeolite filter material was analyzed by scanning electron microscope (SEM), X-ray diffraction spectroscopy (XRD), and FT-IR, as well as the physical stability test; The effects of influencing factors including contact time, dosing quantity of modified zeolite, initial arsenic concentration, the pH of initial solution and temperature were tested in removing As(Ⅲ) from water by all kinds of modified zeolite filter material in batch experiments. The processes of adsorption kinetics and thermodynamic of different filter material were discussed. Dynamic adsorption column of As(Ⅲ) solution was tested with HEZ (particle size 0.3～0.9 mm), the breakthrough curves of As(Ⅲ) in the dynamic adsorption column were obtained by changing the empty bed contact time (EBCT), as well as the pH and concentration of solution. The adsorbing saturated filter material was regenerated and recycled by use of three different regenerant; at last, the mechanism of adsorbing As(Ⅲ) onto iron and manganese oxide modified zeolite filter material was discussed. The main conclusions were summarizedas followed:(1) Comparison on the characterization of the natural zeolite and the modified zeolite showed that there is hydroxides magnetite (mixture of Fe3O4) on the material on ADZ's surface, ferric hydroxide and hematite (mixture of Fe2O3) on HEZ's surface, and manganese dioxide on MZ's surface. The surface area of modified zeolite filter material was larger, and its micropore was more and uniform. These features make it easier to adsorb As(Ⅲ); The surface of modified zeolite filter material was obviously hydroxyl ions telescopic vibration and M-OH swing vibration, and physical stability was very good.(2) The modified zeolite with small particle size was more efficient in removing As(Ⅲ) than big one; With longer contact time, higher temperature or larger dosages, the removal rate of As(Ⅲ) appeared to be a fast raise in initial phase and then became gentle gradually. Moreover, the efficiency increases in rank of MZ material, ADZ material and HEZ material. The removal rate of 0.3 mg/L As (Ⅲ) waste in neutral or acidic can reach 92.93% with lOg/L of SHEZ, under the conditions of 30℃and oscillation 30min, in the same condition, the removal rate of removing As(Ⅲ) used nature zeolite was 10.9%.(3) The adsorption of As (Ⅲ) in water by using coating of iron and manganese on the surface of zeolite were fitted using Langmuir isotherm and Freundlich isotherm model. It is more appropriate to describe for coated iron modified zeolite to adsorb As (Ⅲ) at low temperatures by Langmuir isotherm equation, but it is more appropriate to describe for coated manganese modified zeolite at high temperatures by Freundlich isotherm equation, and it is more appropriate to describe by using coated Mn zeolite to adsorb As (Ⅲ) at high or low temperatures with the Freundlich adsorption isotherm equations; Meanwhile, the adsorption of As(Ⅲ) by all modified zeolite filter material is a spontaneous exothermal process, in which physical adsorption is the main course, together with chemical adsorption. The sorption kinetics can be well described by the second-order kinetics (R2>0.99), which can predict the influence of time on adsorption.(4) Dynamic adsorption equipment shown that:the amount of treatment water have increased as the EBCT increases, the pH of solution had minor impact on the production of water in dynamic method. The high concentrations of solution increased the load of column adsorption and reduced the production of water. The regeneration experiment of adsorbing HEZ was researched by using distilled water, HCl solution and NaOH solution respectively, the result showed that NaOH was the best, and the volume of water production was 3.3 times than HC1 solution which was as regenerant in reuse test, while distilled water had no any effect.(5) Comparison the FT-IR spectra of iron and manganese oxide and iron and manganese oxide adsorbed As(Ⅲ), it was found that the structure of metal oxides did not change, OH and As(Ⅲ) were adsorbed at the same time. It was speculated that the adsorption As (Ⅲ) with the iron and manganese oxides modified zeolite was in the ionic form.