| Microbial mineralization is a common biogeochemical phenomenon in nature.The research on the mechanism of microbial mineralization is of practical significance in many aspects,such as helping to enrich and improve the theory of soil formation,immobilization atmospheric CO2,repair and reinforce dams of stone artifacts and concrete materials.In recent years,researchers have carried out a lot of effective work on microbial mineralization processes and mechanisms,but the current understanding of the mechanism is still superficial.The researchers paid a certain degree of attention to the role of Mg2+ in the formation of calcium carbonate,while little attention has been paid to Sr2+ and Ba2+ of the same main group.In fact,they are similar in chemical properties and can enter the lattice of carbonate minerals by isomorphic replacement or non-lattice substitution.In order to explore the role of Mg2+,Sr22 and Ba2+ in the formation of calcium carbonate,Arthrobacter sp.MF-2 was used to conduct mineralization experiments in the medium containing Ca+Mg,Ca+Sr and Ca+Ba,respectively,and to conduct chemical experiments at the same ion concentration by gas diffusion method.The effects of microorganism and alkaline earth metal ions(Mg2+,Sr2+,Ba2+)on mineral formation were discussed by observing the dynamic changes of solid and liquid phase products under microorganism and inorganic chemistry conditions.The main research results are as follows:(1)Arthrobacter sp.MF-2 can induce the formation of carbonate minerals.In the presence of only Ca2+ without other alkaline earth metal ions,the type of calcium carbonate induced is calcite,and the morphology is rhombohedron,spherical and irregular shape.(2)The addition of Mg2+,Sr2+ and Ba2+ have a great influence on the species and morphology of microbial carbonate minerals.The minerals formed in Ca+Mg medium include amorphous calcium carbonate(ACC),high-magnesium calcite and aragonite.The mineral morphology is spherical,hemispherical,irregular and triangular,and the mineral volume is small.The minerals formed in Ca+Sr medium are calcite and aragonite.In the early and middle stages of the experiment,the minerals are mostly spherical,and in the later stage,the morphology is gradually complicated.The minerals formed in Ca+Ba medium were calcite and rhombohedral.(3)In the Inorganic chemical system,with the participation of Mg2+,the carbonate minerals are high-magnesium calcite and aragonite,the shape is rod-shaped,dumbbell-shaped,spherical,etc.,and the mineral morphology evolution trend is:rod-shaped→dumbbell-shaped→cauliflower shape→spherical;With the participation of Sr2+,Ba2+,the mineral species is calcite,the morphology is mainly rhombohedron and thorn ball.The EDS spectrum shows that Mg2+ and Sr2+ enter the mineral lattice,and Ba2+ does not enter the mineral lattice.(4)In the microbial mineralization system,Organic matter secreted by MF-2 strain was favorable for Mg2+ to enter the carbonate mineral lattice,and promoted the stability of ACC under the combined action of Mg2+.Sr2+ will enter the lattice of carbonate minerals,increasing the space of the crystal surface of calcite(104)(from 3.0355 nm to 3.0374 nm～3.0850 nm).Ba2+ may promote the secretion of an organic substance by MF-2 strain,which combine with metal ions and eventually leads to the transformation of calcite morphology.(5)In the mineralization process,alkaline earth metal ions that are not significantly different from the radius of Ca2+ generally change the types and forms of mineralized products by means of isomorphism replacement.Alkaline earth metal ions(Ba2+)with a radius larger than Ca2+ may affect mineral formation by changing the mineralization system environment.(6)pH value,microorganism and alkaline earth metal ions(Mg2+,Sr2+ and Ba2+)can affect the formation process of carbonate minerals to some extent. |
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