浸矿微生物氟抑制机理及铁的竞争络合作用

Mechanism of fluoride inhibition on bioleaching bacteria and competitive complexation of ferric ions

  • 摘要: 含氟矿石中生物浸出技术推广应用存在瓶颈,究其原因在于伴随含氟脉石矿物溶解,氟对浸矿微生物有较强的抑制作用.本研究利用氟的水化学特性,通过添加可形成稳定络合物的物质来转换F离子存在形态,进而使浸矿微生物可以耐受高氟环境.本文系统研究了氟对细菌的抑制机理,明确了氟的真实毒性形态HF,发现了氟对细菌存在跨膜抑制作用,氟胁迫条件下,干细胞内氟离子质量分数明显高于无氟对照组达到18%以上.选择在生物冶金体系中常见Fe3+做为研究对象,研究了Fe3+对F-的络合解毒作用,热力学分析结果可知,Fe3+可以与HF发生一级竞争络合反应,破坏HF络合结构.在铁离子存在条件下,细菌最高可以耐受F-质量浓度1.0 g·L-1的环境下生长.铁氟络合形态分析可知,只有当培养基中Fe3+质量浓度5倍过量于F-质量浓度,细菌才能正常生长,对应的FeF2+在氟化物中质量分数达45%时,而游离氟离子浓度为2.87×10-5 mol·L-1.络合机理实验结果表明,根据配位化学原理,随着F-/Fe3+浓度比的减小,配体浓度相对较低,氟与铁的络合物向低配位方向移动,可以通过调整培养基中的氟铁浓度比来调整氟铁络合产物,使细菌在高氟环境中生长成为可能.

     

    Abstract: A bottleneck occurs in the application of bioleaching technology to fluoride-containing ore. The reason for this is that fluorine has a strong inhibitory effect on leaching bacteria with the dissolution of fluorine-containing gangue minerals. In this study, we use the chemical properties of fluorine to convert F ions by adding substances that can form stable complexes with F-, which enables the leaching bacteria to tolerate high fluoride environments. In this research, we studied the inhibition mechanism of fluorine on bacteria, and identified its true toxic form (HF). We found that fluoride exhibited a transmembrane inhibitory effect on bacteria. Under fluoride stress conditions, the concentration of intracellular fluoride was significantly higher than that of a non-fluorinated control group, which was about 18% dry cell. We selected common Fe3+ ions in the bioleaching system, and studied the competitive complex detoxification of Fe3+ to F-. Our thermodynamic analysis results show that Fe3+ can compete with HF in first-order competitive complexation reactions whereby the HF complex structure is converted to FeFn3-n. In the presence of ferric ions, we found that the bacteria could tolerate F-concentrations up to 1.0 g·L-1. Our analysis of the Fe and F complex species indicates that bacteria could grow normally when the concentration of Fe3+ ions was five times greater than that of F- ions. Correspondingly, the proportion of FeF2+ components in the solution was ≥ 45%, and the concentration of free fluoride was 2.87×10-5 mol·L-1. The complexation mechanism shows that as the ratio of F--Fe3+ decreases, the concentration of the ligand is relatively lower. Based on the coordination chemistry, the complex of fluoride and iron moves in a lower coordination direction, and the Fe and F complex species can be controlled by adjusting the concentration ratio of F- and Fe3+ in the medium, therefore making it possible for bacteria to grow in a high-fluorine environment.

     

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