Mechanism of microbiologically induced calcite precipitation for cadmium mineralization

• Published in: The Science of the total environment 2022-12, Vol.852, p.158465-158465, Article 158465
• Main Authors: Zeng, Yong, Chen, Zezhi, Lyu, Qingyang, Wang, Xiuxiu, Du, Yaling, Huan, Chenchen, Liu, Yang, Yan, Zhiying
• Format: Article
• Language: English
• Subjects: Adsorption model; MICP; Mineralized species; Molar ratio; Urease gene
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2022.158465

Microbiologically induced calcite precipitation (MICP) technology shows potential for remediating heavy metal pollution; however, the underlying mechanism of heavy metal mineralization is not well-understood, limiting the application of this technology. In this study, we targeted Cd contamination (using 15:1, 25:1, and 50:1 Ca2+/Cd2+ molar ratios) and showed that the ureolytic bacteria Sporosarcina ureilytica ML-2 removed >99.7 % Cd2+ with a maximum fixation capacity of 75.61 mg-Cd/g-CaCO3 and maximum precipitation production capacity of 135.99 mg-CaCO3/mg-cells. Quantitative PCR analysis showed that Cd2+ inhibited the expression of urease genes (ureC, ureE, ureF, and ureG) by 70 % in the ML-2 strain. Additionally, the pseudo-first-order kinetics model (R2 = 0.9886), intraparticle diffusion model (R2 = 0.9972), and Temkin isotherm model (R2 = 0.9828) described the immobilization process of Cd2+ by bio calcite in MICP-Cd system. The three Cd2+ mineralization products generated by MICP were attributed to surface precipitation (Cd2+ → Cd(OH)2), direct binding with the CO32−/substitution calcium site of calcite (Cd2+ → CdCO3, otavite), and calcite lattice vacancy anchors (Cd2+ → (CaxCd1-x)CO3). Our findings improve the understanding of the mechanisms by which MICP can achieve in situ stabilization of heavy metals. [Display omitted] •Maximum mineralized capacity reached 75.61 mg-Cd/g-CaCO3 by MICP at 24 h.•Maximum precipitation yield induced by ML-2 strain was 135 mg-CaCO3/mg-cell.•qPCR revealed the effect of Cd2+ on the key genes of urease metabolism.•The adoption kinetics and isotherm models of calcite fixed Cd2+ were verified.•Three chemical species of mineralizing Cd2+ by MICP were demonstrated.