Crystal Facets Regulation And Interfacial Interaction Mechanism Of Hematite

Ferromanganese minerals are widely distributed in nature and have a wide variety of species(such as hematite,goethite,ferrihydrite and rhodochrosite,pyrolusite,black manganese,etc.).Because of the similar radius of manganese and iron ions,the degrees of substitution phenomenon of iron and manganese are common in ferromanganese minerals.Iron and manganese minerals are the most active mineral types in the supergene geochemical process.They are deeply involved in environmental processes such as the fixation of heavy metals,the degradation of organic pollutants,and the weathering of microorganisms.In these processes,the mineral crystal face is the place for contact and reaction with environmental substances.Its type and properties determine the apparent reactivity of the mineral.The influence of isomorphic substitution on the reactivity of the mineral crystal face is also very worthy of attention.Therefore,revealing the nature of mineral crystal faces and the micro-mechanism of the interface process,has great significance for understanding the geochemical effects of iron-manganese minerals in the supergenetic process and the potential for environmental engineering applications.This paper focuses on the surface and interface reactivity of the iron-manganese mineral crystal surface,and conducts in-depth research on the catalytic effect of the mineral crystal surface and the microbial redox mechanism.Taking hematite as the starting point,controling hematite crystal faces and the synthesis of manganese-containing hematite,studing the physical and chemical properties and surface catalytic effects of different crystal faces of hematite.Deeply discussing the micro-mechanism of the mineral-microbe interface reaction through the research of process studies of microbial oxidation of rhodochrosite(104),and the reducing manganese-bearing hematites(001)and(012)by microbes.These reaserches obtained three new understandings.The synthesis and morphological control of nano-sheet-shaped hematite and manganese-substituted hematite have been realized,and the formation mechanism of nano-sheet-shaped hematite has been revealed.By changing the p H of the reaction system,the concentration of ethanol,the addition ratio of Fe³⁺and sodium acetate,the precise adjustment range of the diameter of the lamellar hematite is 120 nm to 12?m,and the thickness is 17 to 900 nm;all the exposed crystal faces of the lamellar hematite are uniform.The exposure ratio of(001)and(012)plane ranges from 8:1 to 1:1.The growth path of hematite is Fe ions-dilinear ferrihydrite-hematite.The influence of manganese instead of nano-sheet-like hematite morphology is obvious.When the manganese content is less than7 mol%,hematite can still maintain a good sheet-like morphology.When the manganese content is higher than 7 mol%,the hematite starts to transform into polyhedrons.But it has little effect on micron hematite sheets,and it can still maintain a good flake morphology when the Mn content is close to 10 mol%.Comparative experiments found that the crystal face type of nano-sheet-shaped hematite and the substitution of manganese for Mn significantly affect its photocatalytic effect.Two types of hematite nanosheets with(001)and(012)surface exposure ratios of 7.6 and 1.8and similar specific surface areas were selected to compare and analyze the photocatalytic degradation effects of the two types of hematite on methylene blue.The experimental results show that:the capacity of iron ore(001)surface to adsorb methylene blue is 3 times that of(012)surface,and the photocatalytic rate is 15 times that of(012)surface.The comparative experiment of nano-flaky hematite and manganese-containing hematite of the same size shows that the photocatalytic degradation efficiency of manganese-containing hematite for methylene blue is more than 5 times that of pure hematite,which can be compared with manganese instead of hematite.The photocatalytic process provides more electrons and is related to the electron shuttle.Founding the microbial adhesion and reductive erosion on the surface of hematite have crystal plane selectivity,but the manganese substitution of hematite significantly reduces this crystal plane selectivity and presents the element selectivity that manganese preferentially dissolves.The results of experiments on the reduction of micro-hematite and manganese-bearing hematite by Shewanella oneida MR-1,the results show that MR-1 will preferentially attach to hematite when interacting with pure hematite(001)surface.And the surface erosion pit starts from the local position of the(001)surface and gradually expands to the entire(001)surface.While the dissolution phenomenon of the(012)surface is weak.However,the adhesion and reductive erosion of MR-1 on the surface of manganese-bearing hematite do not show crystal plane selectivity,but it shows a certain element selectivity.That is,preferential reduction and dissolution of element Mn,which is like Mn-in hematite.O is related to the structural stability of Fe-O and the redox potential of iron and manganese.Mn doping changes the surface energy of micron flake hematite and changes the reduction method and path of microorganisms.In summary,this thesis experimentally studies the crystal face regulation and crystal face reactivity of hematite,and initially reveals the phenomenon and causes of crystal face selectivity in the process of microbial-mineral interactions.These findings are for in-depth understanding of mineral surface reactions.The dynamic mechanism of sex and microbial-mineral interaction provides new data and new understanding.