Search

Microbial-induced calcium carbonate precipitation (MICP) technology is a new green reinforcing technology in soil stabilization. Targeting on the problem that seepage is the main factor of causing the instability of a tailings dam, a comparative experiment is conducted, which includes the MICP technology on reinforcing tailings with or without the effect of a seepage field. The results of the comparative experiment are as follow: the mercury penetration test indicates that, under the function of a seepage field, the total pore in the tailing is relatively decreased; SEM shows that under the function of a seepage field, the intergranular pore increases; the direct shear test shows that under the function of a seepage field, the tailings' shear strength decreases; the determination of calcium ion content shows that the distribution of calcium carbonate in the tailings under the action of a seepage field is more uneven. [ABSTRACT FROM AUTHOR]

Particle flow numerical simulation software (PFC3D) was utilized to establish the consolidated-undrained triaxial compression test numerical models of mine tailings with different dry densities to deeply investigate the macroscopic and microscopic characteristics of mine tailings in a tailing pond in Hunan Province. Comparing the results of the simulation and the laboratory experiment, the mesoscopic parameters of the particle flow numerical simulation were obtained through continuously adjusting the mesoscopic parameter with the higher degree of agreement between the stress-strain curve, the peak strength, and the elastic modulus as the determining standard. The macroscopic and microscopic characteristics of mine tailings were studied from the perspectives of stress-strain, axial strain-volume strain, coordination number, particle velocity vector, and contact force between particles. After numerous numerical tests, it was found that the PFC3D simulation results are consistent with experiment results of the dry density tailing samples under different confining pressures; compared with the high confining pressure, the simulation test results at lower confining pressures were more with that of the laboratory tests; low density and high confining pressure both have inhibitory effect on the dilatancy characteristics of triaxial samples; with the same confining pressure, the dilatancy tendency of low dry density samples is suppressed comparing with the high dry density samples. The initial coordination number of the numerical model is large, which proves that the contact degree of the model is good to some extent. [ABSTRACT FROM AUTHOR]

The precipitation rate and cementation strength of calcium carbonate crystals during the process of microorganism-induced calcium carbonate precipitation (MICP) are key factors that affect the application effect of this technology. In order to improve the quality of calcium carbonate formation in the MICP process, egg white protein with a volume fraction of 20%, bovine serum albumin with a mass fraction of 0.3%, sucrose with a mass fraction of 5%, bamboo leaves with a mass concentration of 25 g/L, and bamboo leaf-magnesium chloride (M g 2 + / C a 2 + = 4 : 1) were added during the experiment of different groups of MICP solutions. The results of the solution test study showed that there was no obvious lag period for bacterial growth under the action of organic matrix. The concentration of bacteria in the reaction solution was higher under the action of sucrose and egg white. The conversion rate of Ca2+ under the action of egg white was the fastest, which was about 2.5 times higher than that of the control group. After 14 days of grouting reaction, it was found that the proportion of calcite-type calcium carbonate produced under the action of egg white was the highest, and the Ca element accounted for 66.24% in the solidified material. Sucrose was second; bovine serum albumin was the lowest. The calcium carbonate crystals generated by the control of each organic matrix had a high degree of pore size matching with the tailings under a dry-wet cycle. The structural characteristics of the calcium carbonate crystals, such as crystal form, morphology, and particle size, were mainly due to the interaction between the organic matrix and the calcium carbonate crystals. This study proves that the addition of the organic matrix can improve the formation rate and crystal structure of calcium carbonate during MICP, thus providing a new reference for the development of MICP technology. [ABSTRACT FROM AUTHOR]