The Study Of The Species And Morphologies Of The Biogenic Carbonate Minerals In Different Mg/Ca Experiments

Carbonate is the indispensable component of sedimentary rocks; it plays an important role in geo-environments. The processes of carbonate formation not only reflect the evolution process of geo-environments, but also display the biogeochemical cycle in the whole geologic settings. Microbes and Mg/Ca ratio are significant factors that affect the formation of carbonate. Therefore, exploring these two elements and studying the interaction between them may help us in understanding the mechanism of mineral formation as well as providing evidence for the microbial activities in the depositional environments.Much attention has been paid to the roles of microbe and Mg/Ca ratio on the mineralization over the past two decades, but little knowledge is available of the dynamic study about mineralization process under different Mg/Ca conditions, and roles of microbe and Mg/Ca ratio in the mineralization also needs further study.In the present paper, two series of experiments are designed to study the influences of microbes and Mg/Ca ratio on the mineralization with the purpose of making up the deficiency of the previous work.:one to study the influence of organisms on the mineralization, including mixted culture experiments where sulphate-reducing bacteria (SRB) is the main constitute of bacteria and pure culture experiments where Clostridium sp. is the only constitute of bacteria, and the other to investigate that of Mg/Ca by preparing various solutions with different Mg/Ca ratios. During the metallogenic process, we can synthetically judge the impact of the two factors on the species and morphologies of carbonate by monitoring the activity of bacteria, the variety of solutions and the characters of minerals under the help of pH、1CP-AES、 HPLC、 XRD、 SEM、 EDS and so on. The mainly results are as follows:(1) Because of the otherness in the constitute of bacteria, there exist diversity in their abilities to promote the formation of minerals. The mineralizing ability of mixed bacteria is stronger than that of pure strain, so the former can promote the generation of Ca-dolomite (55d), and even dolomite (165d).(2) The discrepancy in the kinds of bacteria affects the morphologies and sizes of aggregrates of minerals. The morphologies of aggregrates in pure culture experiments are different from those of precipitations in mixed culture solutions, and the sizes of precipitations occurred in mixed culture experiments are bigger than that occurred in pure culture experiments.(3) Different amount of Mg2+substitutes in the lattice of carbonate in different Mg/Ca solutions. The higher the ratio of Mg/Ca is, the more the amount of Mg2+in the lattice of minerals is, and the less d value of mineral is, too.(4) The differences of Mg/Ca ratios also have impacts on the shapes of aggregrates of minerals. At55d, the morphologies of aggregrates in solutions with lower Mg/Ca ratios(in the1:1and2:1samples) are dumbbell and cauliflower. Increase in the magnesium content of the solution to6:1and8:1yields lamellar aggregrates of minerals in the pure strain experiments and smooth or rough sphere-shaped ones in mixted culture experiments.(5) These two factors of Mg/Ca and organisms are interacting. The differences of Mg/Ca ratios in the medium lead to the discrepancy on the salinity and supersaturation. Organisms produce various metabolites in different environments, which changes the metallogenic environment as well as the Mg/Ca ratios in the solutions.(6) Under the co-action of bacteria and Mg/Ca minerals can form favoringly. In the control experiments, mineralization process undergos slowly, and the forms of aggregrates are in wild disorder.