Mechanism of fluoride inhibition on bioleaching bacteria and competitive complexation of ferric ions
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摘要: 含氟礦石中生物浸出技術推廣應用存在瓶頸,究其原因在于伴隨含氟脈石礦物溶解,氟對浸礦微生物有較強的抑制作用.本研究利用氟的水化學特性,通過添加可形成穩定絡合物的物質來轉換F離子存在形態,進而使浸礦微生物可以耐受高氟環境.本文系統研究了氟對細菌的抑制機理,明確了氟的真實毒性形態HF,發現了氟對細菌存在跨膜抑制作用,氟脅迫條件下,干細胞內氟離子質量分數明顯高于無氟對照組達到18%以上.選擇在生物冶金體系中常見Fe3+做為研究對象,研究了Fe3+對F-的絡合解毒作用,熱力學分析結果可知,Fe3+可以與HF發生一級競爭絡合反應,破壞HF絡合結構.在鐵離子存在條件下,細菌最高可以耐受F-質量濃度1.0 g·L-1的環境下生長.鐵氟絡合形態分析可知,只有當培養基中Fe3+質量濃度5倍過量于F-質量濃度,細菌才能正常生長,對應的FeF2+在氟化物中質量分數達45%時,而游離氟離子濃度為2.87×10-5 mol·L-1.絡合機理實驗結果表明,根據配位化學原理,隨著F-/Fe3+濃度比的減小,配體濃度相對較低,氟與鐵的絡合物向低配位方向移動,可以通過調整培養基中的氟鐵濃度比來調整氟鐵絡合產物,使細菌在高氟環境中生長成為可能.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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參考文獻
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