Abstract:

Microbial induced calcium carbonate precipitation (MICP) technology combined with modified jute fiber can effectively cement the uranium tailings and fill the pore between the particles, thus, improve the impermeability of uranium tailings. In this study, the effects of some parameters, such as particle gradation, concentration of cementing solution, as well as the length, mass content and hydrothermal treatment time of modified jute fiber, on the impermeability of uranium tailings cemented by microbe in coordination with modified fiber were studied, and the best values of these parameters were determined. Then, the structure type of calcium carbonate crystal produced by MICP and modified fiber was analyzed using the scanning electron microscope (SEM) and X-ray diffraction (XRD), in order to analyze the impermeability mechanism. The results showed that the modified fibers provided more spots for bacterial adhesion, due to the increased surface roughness by hydrothermal treatment. This promoted the growth, reproduction, migration and fixation of microorganisms in uranium tailings, increased the uniformity of calcium carbonate precipitation, and decreased the permeability coefficient of uranium tailings. In the case of gradation number A3, the permeability coefficient of the cemented tailings decreased sharply. When the fiber length, fiber mass content, hydrothermal treatment time of fiber and the cementing solution concentration were 20 mm, 0.5%, 2 h and 2 mol/L, respectively, the permeability coefficient of uranium tailings decreased by 99% after 11 rounds of bio-grouting, indicating these values are optimal. The calcium carbonate crystal, formed in the cemented uranium tailings by the modified fiber combined with MICP, presented calcite characteristic peaks at diffraction angles 2θ of 23º, 29.4º, 36º, 39.3º, which demonstrated that the crystal is mainly calcite.

Key words: uranium tailings, modified jute fiber, microbial induced calcium carbonate precipitation, permeability coefficient, impermeability