Fundamental Studies Of Calcium Carbonate Mineralization Induced By Microbiologically In Stone Materials Surface Protection

The essence of deposition of the microorganism-induced calcium carbonate is that the secretion of enzyme was naturally achieved during the process of the metabolism of microorganism, and that special enzymatic effect happened consecutively. Produced by various vital organic matrix proteins with micro-scale, the controlling consequence on mineralization was a principal orientation of the research and utilization of bio-mineralization mechanism in recent years. This research is supported by the key technology R&D program of china (NO.2007BAB18B01). The research was conduced on the breeding and training of the bacteria of carbonate mineralization. The mineralization experiment of calcium carbonate is tested by its enzymatic peculiarity, and the basic study of its effect on laminating of stone materials surface, to inspect the mineralization film via modern analytical techniques, such as its acid-resistance, heat-resistance, adhesion and breathability, with the purpose of the preparing research on the protection of stone materials utilizing microbial techniques.(1)The research results of cultivating feature of bacillus pasteurii demonstrated that the optimal formulation were mannitol 40g/L, soybean peptone 25g/L, ammonium chloride 8g/L and NaCl 5g/L at pH of 8.0. The optimal cultivation temperature is 30℃. Rotating speed of cradle is 225r/min. Inoculated-pathogen quantities is 4.0% (V/V), Liquid level is 75mL/250mL. Cultivation period of 24h reached the peak of mycelium concentration. The quantity of the optimized living bacterium was 1.71 times of that of ordinary LB, and 1.55 times of that of beef extract peptone under the same conditions.(2) The research results of deposition experiment for calcium carbonate induced by bacillus pasteurii and of analyses for its mechanism had revealed that the sedimented calcium carbonate particles were dispersed, with spheroid, petaling and random nubbly shapes and particle size of 1～15μm. The crystal form was mixture of calcite and vaterite with a small amount of organics. Mycelium contributed to the formation of calcium carbonate crystal. Urease was the most essential factor in the sedimentation procedure of calcium carbonate crystal induced by Bacillus pasteurii, since bacillus pasteurii excreted urease under the induction of carbamide, decomposed urea and generated CO₃2-. Calcium carbonate crystal was generated with the existence of Ca²⁺.(3) The mechanism of calcium carbonate crystal formation induced by bacillus pasteurii was studied. The results indicated:①According to SEM photographs, calcium carbonate crystal formed in pure water was in calcite-shaped and multi-layered nubbly oblique parallelepiped structure. And when the strain solution and metabolite were calcium carbonate crystals, different sizes of spherical or globular aggregates and regular rhombohedron in certain scales were formed. When concentration of strain rises, the regulation to calcium carbonate crystal became more obvious. Mycelium had little influence on crystal features, forming density porous layercrystal structure.②XRD analysis showed that calcium carbonate crystals prepared by strain solution were all calcites, while the ones induced by metabolite had vaterite crystals in addition to the most stable calcite crystals.③The electric conductivity measuring and FT-IR analysis showed that organic polarity base, along with Ca²⁺, generating franklinism, coordination and other interactions to regulate the growth of crystal.(4)The cultivation base of calcium carbonate deposition and the optimization experiment of its cultivation were conduced. It had pointed out that the optimal formulation were glucose 30g/L, soybean peptone 10g/L, urea 50m/L, the concentration of calcium nitrate 0.5 mol/L, the concentration of tween 80 for 0.05%(V/V) and chlorination nickel 250μmol/L. The optimal cultivation condition was at pH range from 8 to 9, temperature of 30℃, rotating speed of 175r/min, inoculum for 6%(V/V). Analyzing sediment via SEM, IR and XRD, it could be seen that the sedimentary calcium carbonate whose surface was rough with irregular aggregates and distribution desultorily, had a particle size range of 20～100μm. Crystal ball is calcite and aragonite mixed matter with bacteria involved in the formation of calcium carbonate crystals. Through the TG/DSC and Raman analysis, it could be noticed that calcium carbonate contained a small amount of organic precipitate.(5) The test on the laminating of stone materials sample via the immersion method and coating method, and various performances testing about mineralization membrane was conduced. It could be concluded that the immersion method was more efficient, though the latter being also able to generate a layer of particle size in the range of 1～10μm of tiny calcium carbonate particles on gravel and marble surface, forming a layer of dense mineralization membrane of calcium carbonate of 50～100μm. The former calcium carbonate crystal formed on sample surface was calcite and aragonite mixed crystal ball, whereas the latter only formed calcite type. Mineralization membrane and the grassroots had strong cohesion, while the acid-resistance degrees of mineralized membrane was less than 2, which could effectively resist the corrosion of acid rain. It also obtained excellent heat resistance, anti-freeze as well as the light and aging resistance, effectively restraining the damage to the stone artifacts caused by weather changes. What is more it maintained the original breathability, and anti-permeability was significantly improved. Via the research of the basic application characteristics of the microbial bionic mineralization protection materials, their excellent effect on surface protection, marvelous performance on surface reinforcing with convenience of manufacture craft, had been displayed perfectly. This achievement could be regarded as an excellent reference to develop new stone protection material in this area, and some bases could be provided in the study to widen the research area of bio-mineralized material.