Remediation mechanism of Sporosarcina pasteurii XL-1 for removal of Cr(VI) and Cr(III) by induced carbonate precipitation

In this study, a strain capable of inducing carbonate precipitation was screened and obtained from the polluted soil near the chromium slag dump; A chromium ion tolerance domestication test was conducted to determine the bacterial identification (optical density (OD₆₀₀), pH, electrical conductivity (EC), urease activity(UA), NH₄⁺ ); Reduction and mineralisation kinetics, combined with scanning electron microscope (SEM), energy dispersive spectrometer (EDS), fourier transform infrared spectroscopy (FTIR), and X-Ray diffraction (XRD) were used to analyse the removal mechanism of Cr(III) and Cr(VI). The strain was identified as Sporosarcina pasteurii XL-1; with maximum tolerance level of 1200 mg/L for Cr(III) and 500 mg/L for Cr(VI). Reduction kinetics indicated that Cr(VI) reduction was primarily by extracellular enzymes; Mineralisation kinetics indicate that the bacterial solution could regulate the crystal morphology, leading to gradual aggregation and bonding that resulted in a denser mineral structure favorable for the encapsulation and removal of heavy metals such as chromium; Microscopic analysis showed Cr(III) removal mechanism included bio-induced carbonate precipitation and abiotic precipitation of Cr(OH)₃; Cr(VI) removal mechanism was mainly bioreduction, supplemented by bio-induced carbonate precipitation and abiotic Cr(OH)₃ precipitation. Finally, a process model was proposed to describe the mineralisation and immobilisation of Cr(VI) and Cr(III) via MICP, offering theoretical guidance for the subsequent remediation of chromium-contaminated water.