Mechanistic Study Of Microbially Induced Calcite Precipitation For Solidification Of Red Loose Pisha Sandstone

In Inner Mongolia Ordos region,arsenic sandstone is widely distributed and the degree of rock formation is low,which is highly susceptible to damage by wind,water and gravity erosion,producing a large amount of weathered loose arsenic sandstone.Due to the low organic matter content of the weathered arsenic sandstone,it is difficult to manage,resulting in serious soil erosion on the Ordos Plateau and becoming an important source of sediment for the Yellow River.The current microbial induced calcium carbonate precipitation as an anti-erosion bio-consolidation technology with soil improvement potential is expected to provide an efficient and green treatment method for ecological restoration of arsenic sandstone areas.In this paper,Sporosarcina pasteurii induced calcite precipitation was used to reinforce red loose arsenic sandstone.The macro-mechanical properties and microstructure of the cured soil columns under different working conditions were monitored with the aid of unconfined compressive strength tests,ultra-field depth three-dimensional microscopy,X-ray diffraction spectroscopy,scanning electron microscopy,Fourier infrared spectroscopy and thermogravimetric analysis to investigate the microbial induced calcium carbonate deposition on the curing mechanism of loose arsenic sandstone.The main conclusions are as follows.（1）For mineralisation characteristics of Sporosarcina pasteurii the growth retardation period of the bacteria can be reduced by preferential selection of the medium.In the range of OD₆₀₀=0.4～0.7,as the concentration of bacterium solution increased,the rate of urea hydrolysis also increased accordingly,and the amount of calcium carbonate production increased.Calcium carbonate production rate increased rapidly in the early stage and increased slowly in the later stage when the concentration of Ca²⁺was 1.0 mol/L.The bacterial urease activity was maintained at a high level in the p H range of 7.0～9.0.（2）In single-phase injection,the minimum curing depth and curing volume decrease as the amount of additional solvent injected increases,and only local curing of the arsenic sand column can be achieved.After mineralisation by self-adsorption biphasic injection,the overall curing of the sand column is significant due to the more uniform spatial distribution of the bacterially induced calcium carbonate production.（3）On the one hand,the strong adsorption of montmorillonite in the arsenic sandstone can have a colonising effect on bacteria,while in the chemical environment of the biomineralisation treatment,the montmorillonite and part of the quartz are then dissolved,prompting the transformation of the montmorillonite phase to the illite phase,thus eliminating the swelling properties of the arsenic sandstone in water.（4）The calcium carbonate crystals wrap around the loose arsenic sandstone particles to form agglomerates,increasing the roughness between particles,while the gaps between particles are filled with calcium carbonate precipitation,forming effective cementation points and improving the bonding of the arsenic sandstone soil particles.（5）The molecular structure and pyrolysis analysis revealed the presence of extracellular polymers in the biogenic calcium carbonate and that the chemical environment of Si atoms,C-O bonding and Si-O bonding electron cloud density in the arsenic sandstone particles were altered by the modulation of the extracellular polymers,resulting in intermolecular hydrogen bonding,making the calcite precipitation strongly electrostatic and the crystal structure more stable.