Mn²⁺ Removal From Water By Heated Limonite And Its Action Mechanism

Limonite is a widely occurring mineral aggrgate in the earth's crust and its main mineral phase is goethite.The samples in this work were obtained from limonite located in Tongling,Anhui Province,China.The morphological and mineralogical properties of limonite and its calcined product before and after reacting with Mn²⁺ were characterized and analyzed using X-ray diffraction?XRD?,X-Ray Fluorescence?XRF?,transmission electron microscopy?TEM?,and X-ray photoelectron spectroscopy?XPS?.In comparison with limonite,the effects of various parameters,viz.,hrat treatment temperature,initial p H,contact time,initial Mn²⁺ concentration,temperature,and DO concentration: and the performance and mechanisms on Mn²⁺ removal by heated limonite were investigated by batch experiments.The mechanism of action was elucidated through in situ DO comparison experiments,XPS analysis,and data review.The effect of HA on the reaction was studied by static tests.In addition,a dynamic experiment was used to study the material's ability to continuously purify Mn²⁺ in groundwater.The main achievements and understanding of the thesis are as follows:?1?The optimal temperature point for the heat-activated limonite is 300?,which is transformed into nanocrystalline hematite with the largest specific surface area and many active sites.?2?The nanocrystalline hematite has good removal effect on Mn²⁺ in water.The effect of p H reaction is not obvious in the range of p H 5-10,and the removal rate is greater than 95%.The maximum adsorption of low concentration of Mn²⁺ in water under low oxygen conditions is 6.45mg/g.The adsorption kinetics accords with the quasi-second-order kinetics model,nanocrystalline hematite formed by heat treatment of limonite has Mn²⁺ adsorption and catalytic oxidation,and the impurities of manganese oxide have an enhanced effect on Mn²⁺ adsorption and catalytic oxidation.?3?Nanocrystalline hematite catalytic oxidation of heavy metal ions Mn²⁺ mainly depends on the interaction of oxygen vacancies with water/oxygen to form active sites.A series of chemical reactions occur between Mn²⁺ and hematite in the liquid phase,and the O vacancies on the hematite are regarded as active sites.Under conditions with active sites and oxygen,the formation of a low coordination O and hydrogen bonding complex on the surface of hematite causes Mn²⁺ to be easily adsorbed on the surface of hematite and oxidized to Mn4+.?4?HA has a certain complexing effect on Mn²⁺ in water,and in the presence of nanocrystalline hematite,it leads to competitive adsorption of HA and Mn²⁺ in water,resulting in a decrease in the effect of hematite adsorption on Mn²⁺.?5?The treatment effect of heat treated limonite at 300 was significantly better than ?that of untreated samples.The effluent concentration reached the national drinking water standard.The total adsorption of Mn²⁺ was 143.8 mg/g,and the effluent p H was stable between 6-8.It is very feasible for practical continuous treatment of Mn²⁺ in water.