Solidification of Lithium Slag via Microbial-Induced Carbonate Precipitation Mediated by Urease-Producing Bacteria

The rapid development of the new energy industry has led to a sharp increase in the demand for lithium resources, resulting in a substantial accumulation of lithium smelting residue (lithium slag). Conventional disposal methods like landfilling and open-air storage may cause potential environmental concerns, including the migration of soluble components and long-term ecological risks. Microbial-induced carbonate precipitation (MICP) presents an alternative biologically based stabilization strategy for waste stabilization by leveraging biomineralization to convert reactive components into stable precipitates. Herein, the feasibility of solidifying lithium slag (LS) via MICP was investigated using urease-producing bacteria with contrasting enzyme activities, including a laboratory-isolated strain Lysinibacillus sp. WD018 and a commercial strain Sporosarcina pasteurii (S. pasteurii). Due to its superior urease activity (45.25 vs. 2.25 mM/min/OD600), S. pasteurii induced markedly greater carbonate precipitation, resulting in higher CaCO3 production and the formation of more crystalline calcite. Among the tested conditions, a cylindrical flow-through mold, 1 M cementation solution, and seven treatment cycles were favorable for producing intact LS specimens. X-ray diffraction (XRD) indicated calcite formation after MICP treatment, and S. pasteurii yielded more crystalline calcite than WD018. The CaCO3 content was higher in the upper section (51 ± 0.91% for S. pasteurii vs. 32 ± 0.10% for WD018). Untreated LS had permeability coefficients of (1.71 × 10−6)~(1.13 × 10−5) m/s, whereas treated specimens showed no visible water seepage during a 30 min constant-head test. These findings indicated that bacterial urease activity and flow-through treatment configuration are important factors controlling carbonate precipitation and LS stabilization.