The negative effect of carbonate on the rate and extent of bioreduction of aqueous U(VI) has been commonly reported. The solution pH is a key chemical factor controlling U(VI)_aq species and the Gibbs free energy of reaction. Therefore, it is interesting to study whether the negative effect can be diminished under specific pH conditions. Experiments were conducted using Shewanella putrefaciens under anaerobic conditions with varying pH values (4–9) and bicarbonate concentrations (${\left[{\text{CO}}_3^{2-}\right]}_{\text{T}}$, 0–50 mmol/L). The results showed a clear correlation between the pH-bioreduction edges of U(VI)_aq and the ${\left[{\text{CO}}_3^{2-}\right]}_{\text{T}}$. The specific pH at which the maximum bioreduction occurred (pH_mbr) shifted from slightly basic to acidic pH (∼7.5–∼6.0) as the ${\left[{\text{CO}}_3^{2-}\right]}_{\text{T}}$ increased (2–50 mmol/L). At ${\left[{\text{CO}}_3^{2-}\right]}_{\text{T}}$ = 0, however, no pH_mbr was observed in terms of increasing bioreduction with pH (∼100%, pH > 7). In the presence of ${\left[{\text{CO}}_3^{2-}\right]}_{\text{T}}$, significant bioreduction was observed at pH_mbr (∼100% at 2–30 mmol/L ${\left[{\text{CO}}_3^{2-}\right]}_{\text{T}}$, 93.7% at 50 mmol/L ${\left[{\text{CO}}_3^{2-}\right]}_{\text{T}}$), which is in contrast to the previously reported infeasibility of bioreduction at high ${\left[{\text{CO}}_3^{2-}\right]}_{\text{T}}$. The pH-bioreduction edges were almost comparable to the pH-biosorption edges of U(VI)_aq on heat-killed cells, revealing that biosorption is favorable for bioreduction. The end product of U(VI)_aq bioreduction was characterized as insoluble nanobiogenic uraninite by HRTEM. The redox potentials of the master complex species of U(VI)_aq, such as ${\left({\text{UO}}_2\right)}_4{\left(\text{OH}\right)}_7^{+}$, ${\left({\text{UO}}_2\right)}_2{\text{CO}}_3{\left(\text{OH}\right)}_3^{-}$, and ${\text{UO}}_2{\left({\text{CO}}_3\right)}_3^{4-}$, were calculated to obtain insights into the thermodynamic reduction mechanism. The observed dynamic role of pH in bioreduction suggests the potential for bioremediation of uranium-contaminated groundwater containing high carbonate concentrations.

碳酸盐对U（VI）水溶液生物还原的速率和程度的负面影响已被普遍报道。溶液的pH值是控制U（VI）_水溶液种类和反应的吉布斯自由能的关键化学因子。因此，研究在特定pH条件下是否可以减轻负面影响是很有趣的。实验使用进行腐败希瓦氏菌在厌氧条件下具有不同的pH值（4-9）和碳酸氢盐的浓度（${\left[{\text{一氧化碳}}_3^{\mathrm{2个}-}\right]}_{\text{Ť}}$，0–50 mmol / L）。结果表明：U（VI）的pH生物还原边缘之间的明显的相关性_水溶液和${\left[{\text{一氧化碳}}_3^{\mathrm{2个}-}\right]}_{\text{Ť}}$。发生最大生物还原的特定pH（pH _mbr）从弱碱性变为酸性pH（〜7.5-〜6.0）。${\left[{\text{一氧化碳}}_3^{\mathrm{2个}-}\right]}_{\text{Ť}}$增加（2–50 mmol / L）。在${\left[{\text{一氧化碳}}_3^{\mathrm{2个}-}\right]}_{\text{Ť}}$= 0，然而，无pH _MBR与pH增加生物还原而言，观察到（〜100％，pH值> 7）。在......的存在下${\left[{\text{一氧化碳}}_3^{\mathrm{2个}-}\right]}_{\text{Ť}}$，在pH _mbr下观察到明显的生物还原作用（在2–30 mmol / L时约为100％${\left[{\text{一氧化碳}}_3^{\mathrm{2个}-}\right]}_{\text{Ť}}$50 mmol / L时为93.7％ ${\left[{\text{一氧化碳}}_3^{\mathrm{2个}-}\right]}_{\text{Ť}}$），这与先前报道的在高温度下进行生物还原的不可行性形成对比 ${\left[{\text{一氧化碳}}_3^{\mathrm{2个}-}\right]}_{\text{Ť}}$。pH值生物还原边缘几乎可以与热灭活细胞上U（VI）_水溶液的pH值生物吸附边缘相媲美，这表明生物吸附有利于生物还原。U的终产物（VI）_水溶液生物还原被表征为通过HRTEM不溶nanobiogenic沥青铀矿。U（VI）_aq的主要复杂物种的氧化还原电势，例如${（{\text{O}}_{\mathrm{2个}}）}_4{（\text{哦}）}_7^{+}$， ${（{\text{O}}_{\mathrm{2个}}）}_{\mathrm{2个}}{\text{一氧化碳}}_3{（\text{哦}）}_3^{-}$， 和 ${\text{O}}_{\mathrm{2个}}{（{\text{一氧化碳}}_3）}_3^{4-}$被计算以获得对热力学还原机理的见解。观察到的pH在生物还原中的动态作用表明了对碳酸盐浓度较高的铀污染地下水进行生物修复的潜力。