复合电解液强化电动修复铀污染土壤

Enhanced Electrokinetic Remediation of Uranium-contaminated Soil Using Composite Electrolytes

  • 摘要: 电动修复是土壤重金属污染修复中较为有效且常用的方法,而传统电动修复存在二次污染、修复效率低、能耗大等问题,为此本文采用一种新型环境友好型电解液(柠檬酸+硝酸铁)结合阳离子交换膜,并采用交换电解液的方法对铀污染土壤进行强化修复实验。首先探索了电解液的最适浓度,结果显示,在1.5 V/cm的电压梯度下修复120 h,0.1 mol/L 柠檬酸+0.05 mol/L 硝酸铁对铀的去除率最高,为71.60%。在此基础上采用交换电解液结合阳离子交换膜的方法进行实验,结果显示,交换频率为60 h时的去除率最高,为92.45%,累积能耗为0.814 kW/h,处理后的土壤浸出毒性由初始的0.193 mg/L下降到0.042 mg/L,对环境的风险大幅降低。铀形态分析和Visual MINTEQ软件模拟发现,土壤中的铀在酸性条件下以U(Ⅳ)和 \mathrmU\mathrmO_2^2+ 为主,而随着pH的升高,铀逐渐开始形成羟基配合物和有机配合物(如柠檬酸根(Citrate))。且用柠檬酸和硝酸铁处理后,土壤中铀的碳酸盐结合态、铁锰氧化物结合态分别以 \mathrmU\left(\mathrmO\mathrmH\right)_2^2+ 和 \mathrmU\mathrmO_2^2+ 、UO2Citrate和 \mathrmU\left(\mathrmO\mathrmH\right)_3^+ 的形式存在,并最终通过电迁移和电渗析的作用去除。

     

    Abstract: Electrokinetic remediation is widely recognized as an effective method for remediating soil contaminated with heavy metals. However, traditional electrokinetic methods face several challenges, such as secondary pollution, low remediation efficiency, and high energy consumption. To address these issues, a new environmentally friendly electrolyte composed of citric acid and iron nitrate, combined with a cation exchange membrane was explored in this paper. Additionally, an alternating electrolyte method was used to enhance the remediation of uranium-contaminated soil. The results show that the uranium removal rates are 15.3% and 6.28% higher, respectively, than using distilled water as the electrolyte. The removal rate of distilled water is 6.83%. The cumulative energy consumption for citric acid and iron nitrate electrolytes is 0.45 kW/h and 0.498 kW/h, with energy utilization rates of 49.18% and 26.33%, respectively. These results indicate that citric acid and iron nitrate electrolytes improve both uranium removal efficiency and energy utilization compared to distilled water. The optimal concentrations of the combined electrolyte were also explored under the same conditions. The results reveal that a combination of 0.1 mol/L citric acid and 0.05 mol/L iron nitrate as the electrolyte, the highest uranium removal rate is 71.60%. The cumulative energy consumption in this case is 0.63 kW/h, and the energy efficiency is 96.10%. These findings suggest that the combination of citric acid and iron nitrate significantly enhances uranium removal efficiency and energy utilization compared to using individual electrolytes. Building on the optimal electrolyte concentrations, further testing was conducted on the alternating electrolyte method combined with a cation exchange membrane for enhanced remediation. The results show that the highest uranium removal rate of 92.45% is achieved with the exchange frequency of 60 h. The cumulative energy consumption under these conditions is 0.814 kW/h, with an energy efficiency of 87.71%. These indicate that combining alternating electrolytes with a cation exchange membrane can significantly improve both the efficiency of uranium removal and the overall energy utilization. Additionally, the treatment reduces the soil’s leaching toxicity from an initial value of 0.193 mg/L to 0.042 mg/L, which greatly lowers the environmental risk associated with the contaminated soil. Uranium speciation analysis and simulations with Visual MINTEQ reveal that uranium in the organic-bound and residual states is difficult to leach. In acidic conditions, uranium mainly exists as U(Ⅳ) and \mathrmU\mathrmO_2^2+ in the soil. As the pH increases, uranium begans to form hydroxy complexes and organic complexes, such as those with citrate. Following treatment with citric acid and ferric nitrate, uranium in carbonate-bound and iron-manganese oxide-bound forms, such as \mathrmU(\mathrmOH)_2^2+ and \mathrmU\mathrmO_2^2+ , UO2Citrate and \mathrmU\left(\mathrmO\mathrmH\right)_3^+ is effectively removed through electro-migration and electro-dialysis. These forms of uranium are then removed through electro-migration and electro-dialysis. This study not only demonstrates the effectiveness of the combined electrolyte and cation exchange membrane method but also provides insights into the speciation of uranium, which is crucial for optimizing the remediation process.

     

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