Abstract

Biogenic carbonates usually differ significantly both in physical and chemical characteristics from those of the same chemical origin, and heavy metal immobilization is prominent among these differences. In this research, a biosynthetic method of high-magnesium calcite (HMC) generated by Bacillus velezensis (B. velezensis) in the presence of humic acid (HA) was developed to ascertain the immobilization characteristics of biogenic high-magnesium calcite (BHM) for Cd²⁺. The study showed that the presence of HA was crucial to the formation of crystalline BHM. The Cd²⁺ immobilization assay results indicated that significant amounts of Cd²⁺ could be adsorbed and the obtained data could fit the Langmuir equation (R² = 0.98, Q_max = 65.36 mg/g), and the adsorption process conformed to the pseudo-second order kinetic model (R² = 0.99). In particular, BHM can maintain the adsorption capacity at above 100 mg/g even under acidic conditions (pH ≥ 3). Further analysis showed that the adsorption was mainly monolayer physical adsorption, and a small amount of chemisorption also occurred. Thermodynamic parameters (ΔG > 0, ΔH > 0, and ΔS < 0) indicated that the adsorption process was a non-spontaneous endothermic reaction. XRD and SEM-EDS analyses demonstrated that the culture precipitate obtained was mainly HMC, with numerous 10-nm pores based on Barrett-Joyner-Halenda theory of surface area. The results of TG-DTG/DTA analysis showed that the BHM contained about 31.31 ± 3.77% organic matter. Amorphous CdCO₃ and the complex or chelate bearing Cd²⁺ formed in adsorption process could ensure low desorption, implying a novel prospect for remediation of heavy metal pollution using BHM.

摘要

生物碳酸盐与同种化学来源的碳酸盐在物理和化学特性上通常存在显着差异，其中重金属固定化作用尤为突出。本研究开发了一种在腐植酸 (HA) 存在下由Bacillus velezensis ( B. velezensis ) 产生的高镁方解石 (HMC) 的生物合成方法，以确定生物源高镁方解石 (BHM) 的固定特性镉²⁺。研究表明，HA 的存在对结晶 BHM 的形成至关重要。Cd ²⁺固定化实验结果表明可以吸附大量的Cd ²⁺并且获得的数据符合Langmuir方程（R ² = 0.98，Q _max = 65.36 mg/g），吸附过程符合准二级动力学模型（R ² = 0.99）。特别是，即使在酸性条件下（pH ≥ 3），BHM 也能将吸附容量保持在 100 mg/g 以上。进一步分析表明，吸附以单层物理吸附为主，也有少量化学吸附。热力学参数（Δ G  > 0、Δ H  > 0 和 Δ S < 0) 表明吸附过程为非自发吸热反应。XRD 和 SEM-EDS 分析表明，获得的培养物沉淀主要是 HMC，具有基于 Barrett-Joyner-Halenda 表面积理论的许多 10 nm 孔。TG-DTG/DTA分析结果表明，BHM含有约31.31±3.77%的有机质。无定形CdCO ₃和吸附过程中形成的带有Cd ²⁺的络合物或螯合物可以确保低解吸，这意味着BHM修复重金属污染的新前景。