Study On The Formation Of Manganese Oxide And Manganese Cutan Coated On The Surface Of Quartz Sand And The Influential Factors

Manganese minerals, which are a kind of important compositions in the soil, have great effects on the physicochemical and biochemical properties of the soil. As the existing form of manganese minerals in soil interface, manganese cutans widely exist in subtropical areas in China. Compared with iron, manganese element has higher reaction activities and shows greater impacts on the soil, which leads to wide attention on manganese cutans studies. Manganese minerals were synthetized by the redox reaction between bivalent manganese salt and KMnO4in the research. The impacts of some synthesis conditions such as manganese mole ratio R (Mn2+/Mn7+), temperature and anion types on the synthesis process were studied, and the reaction mechanism was discussed. Manganese cutans were synthetized afterward by coating manganese minerals on the surface of quartz sand media under simulated condition in laboratory. And the influences of different synthesis conditions on the synthesis process were researched as well. The new synthetized manganese cutans were utilized as adsorbents in Pb2+adsorption experiment, and the adsorption effect and influencing factors were discussed. Conclusions can be drawn as follows after a series of experiments:1. In the SO42-system, when R was1:1, the synthetized minerals under different synthesis temperatures were pure cryptomelane; Scanning Electronic Microscope (SEM) images showed that the crystal morphology of the productions was acicular and both crystalline and average oxidation state of manganese (AOSMn) of the production increased as the temperature rose. When R was1:2, the productions under different synthesis temperatures were mixtures of cryptomelane and birnessite, and as the temperature increased, the proportion of birnessite in the mixture built up; SEM images indicated that the crystal morphology was acicular mixed with granular, and AOSMn of the minerals increased as temperature rose. When R was1:3or1:4, the synthesis production under different temperature were pure birnessite; SEM images showed that the crystal morphology was granular, and with the rising of the temperature, the size of the crystal particles grew and both crystalline and AOSMn increased gradully.2. Under the synthesis temperature of110℃, when R was1:1, the synthetized productions by the reduction of MnCl2and MnSO4were pure cryptomelane, and the crystalline of the latter production was higher than the former one; SEM images showed the crystal morphology was mainly acicular. While when Mn(NO3)2was used as reductant, the synthetized production was a mixture of cryptomelane and ramsdellite; SEM images showed that the crystal morphology was acicular mixed with fusiform. When R was1:2, the production only showed characteristic diffraction peaks of birnessite by X-Ray Diffraction (XRD) analysis, and the crystalline of the production in the MnCl2system was the highest; SEM images showed that the crystal morphology of the production was acicular in MnSO4system, granular in MnCl2system, and mainly granular mixed small amount of acicular or fusiform. When R was1:3, the synthetized productions of all the anion reaction systems were granular birnessite; and in different systems, the crystalline of the productions decreased in the consequence of Mn(NO3)2system, MnCl2system and MnS04system.3. Under the synthesis temperature of30℃, when R was1:1, synthetized manganese cutan was a mixture of granular birnessite and acicular cryptomelane; when R was1:2,1:3, and1:4, manganese cutans were all granular birnessite, but with the decrease of R, the crystalline of the cutans increased while the mineral content on the surface of the cutans declined.4. When R was1:3, synthesis temperature had few influence on the mineral type of the synthetized cutans, but with the synthesis temperature rising, the crystalline of the mineral increased and the mineral content on the surface of the cutans slightly reduced.5. Aging time hardly had any impact on the mineral type of the synthetized cutans, and its influence on the mineral content on the cutan was slight; stirring wouldn’t affect the mineral type, but the mineral content grew as the stirring time lengthened.6. Addition of quartz sand would reduce the crystalline of the syngthetised minerals, but had no impact on the mineral type; as the quartz amount added increased, the crystalline of the minerals declined, and the mineral content on the surface of the cutan appeared to reduce first and then rise with the increase of the temperature.7. Under the synthesis conditions of temperature30℃, R1:3, quartz sand added amount40g, and aging time48h, the zero point charge (PZC) of the synthetized manganese cutan was2.17, between the PZC of pure birnessite (1.21) and quartz sand (2.62); the manganese cutan synthetized under above condition had favourable effect on the adsorption of Pb2+in the water, and achieved maximum adsorption quantities under the condition of ionic strength0.01mol/L and pH range of4-6.