Study On The Crystallization Mechanism Of Calcium Carbonate Caused By Sulfate Reducing Bacteria On The Surface Of Materials

The irrational development and exploitation of the ocean has led to serious environmental problems such as marine water pollution and marine ecological damage.Pollutants will become part of the food chain with the migration and transformation,which ultimately endangers human health.Therefore,a large number of marine buoy-type water quality online detectors,marine high-precision monitoring sensors and on-site water quality detectors have been deployed on the coastline to monitor the marine environment.However,a layer of inorganic salt crystals well be produced on the surface if the instrument were exposured in the marine environment for long.Along with various microbial and marine life activities,it will produce micro-scale fouling and corrosion on the surface of the instrument,which will significantly reduce its performance and life.Surface crystallization not only affects the reliability of data acquisition,but also brings huge and incalculable economic losses.We collected the crystals attached on the bottom of a freight ship from Lianyungang coastal.XRD analysis（S1,S2）indicated that the main components of the scale were calcite,acid salt and small amount of iron oxide.At present,scholars have done a large amount of work on the corrosion behavior of metals in seawater and the biological fouling of marine materials has also been studied in depth.Therefore,we isolated the different components of（Sulfate reducing bacteria,SRB）,and studied the effects of different components and the effect of（Soluble microbial products,SMP）concentrations on the surface crystallization of calcium carbonate.Finally,we studied the effects of calcium carbonate scale on the surface of copper T2 at different pH,and the reasons for the effects were analyzed yet.The specific research contents and conclusions are as follows:（1）The crystallization process of calcium carbonate was simulated by gas diffusion method,and SRB was used as the representative marine microorganisms.The characteristics and properties of calcium carbonate crystals in the presence of（soluble microbial products,SMP）,dead cells and（Extracellular Polymeric Substances,EPS）were investigated.Analysis results showed that microorganisms accelerated the growth of calcium carbonate from amorphous crystals to calcite and influences of morphology by different microbial components were significantly related to the groups and structures of organic components.Calcium ions can be effectively adsorbed or chelated by organic components,which leads to partial supersaturation near the microbial composition and the Ca²⁺concentration of solution decreases.Ultimately,microbial compositions promoted the formation of single crystal calcite.（2）We investigated the effects of three concentrations（8.95 mg/L,17.90 mg/L,44.76 mg/L）of SMP secreted on CaCO₃ crystallization by monitoring crystallization rates,crystal polymorph and morphology.At the concentration of 8.95 mg/L,the most mass of crystals mixed with vaterite and calcite formed in the initial stage of crystallization,but it quickly turned into pure phase calcite as nucleation and growth goes on.It is partly for the large amount of SMP complexation with Ca²⁺,which provides a nucleation site for calcite.Simultaneously,crystallization by particle attachment promotes an increase in the crystallization mass density.As the concentration increased to 17.90 mg/L,more ratio of vaterite was obtained and stabilized throughout the experiment.In contrast,further increase in concentration（44.76 mg/L）didn`t promote a greater proportion of vaterite,with only elongated calcite formed and crystallization rate decreased further.Therefore,SMP as the main component of DOM exhibits a good inhabitation on surface crystallization.（3）Finally,the effect of calcium carbonate scale on the surface of T2 copper was studied at pH=7.5 and pH=8.5.The results indicate that the presence of SMP promotes the formation of stacked calcite.At pH=8.5,the scale product was still dominated by stacked morphology,but a small amount of globular calcite appeared.This result may be caused by the adsorption of Ca²⁺by SMP,hindered the growth of calcite at the SMP-Ca attachment point and leaded to the formation of irregular spheroids.At the same time,the dissolution and recrystallization of a large mount of vaterite enables OH^-ions to pass through the protective layer of calcium carbonate scale,accelerating the corrosion process of T2 copper.Our result not only riches the theory of biomineralization but also counributes to the understanding of the mechanism of microbial influence on calcium carbonate crystallization.At the same time,it provides theoretical support for the surface protection of marine economic development and marine monitoring equipment.