Synthesis And Arsenic Removal On Ferruginous Manganese Composite Oxides

Arsenic is a kind of toxic element which belongs to one of the water pollutants. With the excessive exploitation of mineral resources, the arsenic pollution is increasingly threatening the health of human being. It has become a hot topic for environmental scholars to investigate that removing arsenic pollution in the water and the preparation of efficient adsorption material has also been a kind of important technical methods to the treatment of arsenic wastewater. This article is using the iron and manganese ion that leaching from the natural iron manganese ore with sulfuric acid. Choose the appropriate iron and manganese salt as raw material, change the iron manganese molar mass ratio of solution and then synthetize the best Fe-Mn oxides after precipitation, filtering, drying and roasting process. Investigate its mechanism of arsenate adsorption by using X-ray fluorescence, X-ray diffraction, energy dispersive spectroscopy, fourier transform infrared spectroscop and scanning electron microscope to characterize material. This study does a comprehensive research in the arsenate uptake ability of the Fe-Mn oxides, the saturated adsorption amount and the influence factors of arsenic removal efficiency. Finally, desorption, regeneration, stabilization of the compound and solidification research of acid leaching residues are done to prevent the secondary pollution.Research shows that when the concentration of the sulfuric acid is2.1mol/L, the response time is3.5h, reaction temperature is90℃and solid-to-liquid ratio is1:4, the leaching rate of iron will be reach66%, the leaching rate of manganese will be93%and the Fe/Mn in the filtrate will be1:2.4. Determined by the experimental results, NaCO3has been chosen as precipitation agent. At the best calcining temperature (400℃), Fe/Mn will have the best remove ability to As(III) and As(V) when the ratio respectively is12:1and4:1.Characterizing the Fe-Mn oxides with XRF, XRD, EDS, FTIR and SEM, a conclusion is drawn that the material is mainly composed of Fe and Mn. Then the Al is in the third place. Fe is existed as artificial hematite (a-Fe2O3), magnetic hematite (y-Fe2O3) and goethite (a-FeOOH). Mn is existed as hydroxyl compounds and amorphous form of MnO2. Mn in complex can oxidize As(III) to As(V). After the adsorption, FeAsO4is detected on the surface of these two kinds of the solid. Scanned by SEM, the Fe-Mn oxides seem to be composed of loose spherical particle with a good uniformity.Studies suggest that the mechanism of arsenic removal by Fe-Mn including oxidation, precipitation reaction and adsorption. Material surface hydroxyl complexation is given priority to the effect of adsorption.The adsorption isotherm could be well described by using the Langmuir model and R2>0.99.The maximum adsorption of As(III) and As(V) is181.82mg/g and161.29mg/g for these two compounds. The relationship between adsorption quantity and time can be suitably described with the Lagergren second level rate equation. Additionally, the rise of temperature can enhance the adsorption. pH expresses a significant influence on the arsenic removel as well. On the whole, there is a tendency that removal rate increases with pH value rising in the interval of pH3-9. Ca2+and Mg2+can promote the adsorption of arsenic while HCO3-has a negative influence. It seems that SO42-doesn’t play an important role so that it can be ignored. In this study, the desorption solution is concentrated alkali immersion method. When the concentration of NaOH is0.5mol/L, the resolution rate can be90%or more. Manganese composite oxide could reduce the arsenic efficiently after regeneration. The concentration of arsenic is0.00237mg/L in the arsenic residue after curing, which is below5mg/LThe feature of this research is that we use the natural iron manganese ore as materials to prepare a new type of Fe-Mn oxides which are efficient to remove arsenic from the water and also could be economic saving. In addition, this paper comprehensively discusses the performance of the compound and uses several methods to characterize the material so that to explain the mechanism of arsenic removel by Fe-Mn oxides. It provides the theoretical basis for the engineering practice. Finally the methods like desorption, regeneration and recycling, which have been used in the experiment, have significance for protecting the environment.