Study On The Formation Of The Calcium Carbonate Induced By The Soil Bacteria Arthrobacter Sp.MF-2 Strain And Its Characteristic Secrets

Microbially induced calcite precipitation is one of the most important study of geological microbiology.An in-depth understanding of the behavior of microbially induced calcite precipitation is instructive for understanding microbial activity during geological periods and its potential applications in geological storage of carbon dioxide.In recent years,microbially induced calcite precipitation has played an increasingly important role in soil solidification.At present,it is generally believed that biological or organic molecules affect the phase,morphology,structure and distribution of trace elements in calcium carbonate.However,there are still many problems that have not been solved for the regulation of specific organic molecules in the process of biomineralization.Therefore,in this paper,four series of mineralization experiments were carried out with Arthrobacter sp.MF-2 and its main characteristic secretions,and a control experiment was also set up.The mineral composition,surface morphology and elemental composition of the experimental solid phase products were observed and determined by X-ray diffractometer,fourier transform infrared spectroscopy and electron microscopy.At the same time,we determined the number of bacteria,pH value,conductivity,and extracellular polysaccharide,CA,sediment weight,and Ca2+concentration.The main purpose of this paper is to analysis the effects and mechanisms of organic factors such as bacterial and their characteristic components on calcium carbonate deposition process and sedimentary products by studying the types and forms of calcium carbonate minerals formed by bacterial and its characteristic secretions.Thus gain insight into the processes and mechanisms of microbial induced calcite mineralization.The main findings are as follows:(1)The minerals formed by the MF-2 strain are calcite with polyhedral and spherical shape and quadrilateral pyramid with a depression in the centre.The mechanism of mineral formation under the participation of the bacteria include heterogeneous nucleation with bacterial secretions(such as extracellular polymeric substances-EPS)as a nucleation template,and homogeneous nucleation under the control of physico-chemical environment.(2)The presence of carboxylate could inhibit the precipitation of calcium carbonate mineral to a certain extent,and the degree of inhibition increases with the increase of the number of carboxyl groups,and the influence on the crystal morphology development would be more and more.The form of calcium carbonate mineral formed under the sodium lactate system is only rhombohedral;the mineral formed under sodium oxalate system is mainly rhombohedral,and also has disc-shaped and spherical shape;the sodium citrate system has few rhombohedral shapes,mainly irregular shape.(3)The extracellular polymeric substances of bacteria have an effect on the mineral type and morphology.The formation of calcite and vaterite is induced by EPS,and the mineral forms are mainly spherical,twin-shaped and rhombohedral.EPS mainly acts on the early(8 h)growth of minerals,which may be related to the formation of amorphous calcium carbonate(ACC)and the accumulation of a large number of small spherical minerals in the early stage of the experiment.(4)The CA secreted by bacteria not only accelerates the precipitation rate of calcium carbonate minerals by catalyzing the hydration reaction of CO2,but also affect the formation of calcium carbonate minerals via some certain specific amino acid components it contains,which resulted in special morphology such as hollow spheres and dumbbells.(5)Bacterial mineralization mechanism of calcium carbonate.By the action of alkali production and the secretion of carbonic anhydrase(CA),the bacteria can adjust the pH value and HCO3-concentration of the culture solution to create a favorable physical and chemical environment for the formation of calcium carbonate.Carboxyl group-containing organic substance such as a carboxylic acid can be used to modulate the supersaturation of calcium carbonate in the solution by its own ionization hydrolysis and adsorption of the carboxyl group to Ca2+,thereby regulating the growth of calcium carbonate crystals.EPS secreted by bacteria can act as heterogeneous nucleation sites to affect the crystal style and morphology of the mineral.