Regulation of Klebsiella-induced calcium carbonate precipitation with xanthan gum for the solidification of uranium tailings

Microbially induced calcium carbonate precipitation (MICP) is a promising and environmentally friendly biocementation technique for geotechnical applications. However, its engineering effectiveness is often constrained by the bacterial strain, solidification process and environmental conditions. This study used Klebsiella as the mineralizing bacterium and introduced xanthan gum (XG) as a functional additive to systematically investigate the regulatory effects of XG on the Klebsiella -induced MICP process and the resulting solidification of uranium tailings under two treatment strategies. The results demonstrate that XG effectively regulates CaCO 3 precipitation characteristics and significantly enhances mechanical strength. At an XG dosage of 1.4%, the unconfined compressive strength (UCS) of the 7 rounds synchronous group and the 14 rounds asynchronous group reached 1486.7 kPa and 1498.0 kPa, respectively, representing an approximately 16-fold increase compared with that of the MICP-treated group. The CaCO 3 precipitation yields increased significantly to 3.15 g and 3.36 g, corresponding to 2.06% and 2.19% of specimen mass, respectively, with particle sizes notably reduced to 3.18–6.25 μm and a more uniform spatial distribution of precipitates throughout the specimens. The precipitates exhibited a balanced calcite/vaterite ratio (approximately 50% each). Specimen porosity decreased from 34.5% (untreated) to 15.3%, accompanied by a reduction in average pore radius from 163.2 μm to 137.5 μm and a decrease in average coordination number from 8.4 to 4.6, indicating a denser and less connected pore structure. This study provides a theoretical basis for the customized regulation of MICP microscopic characteristics and the synergistic enhancement of macroscopic mechanical properties, offering novel insights for the development of efficient, controllable and environmentally friendly solidification technologies.