In the present study, a new understanding of the application of biosurfactant, saponin, has been explored, over nitric and citric acids, as an electrolyte for the remediation of chromium from tannery sludge using the electrokinetic process. The interaction effects of independent variables [such as electrolyte molarity (M) and applied voltage (V)] and the output responses were studied using the statistical tool, response surface methodology. A significant correlation has been established between responses such as chromium removal, electrolytes consumption and power consumption for the selected independent variables. In terms of total chromium removal, saponin showed maximum effectiveness of 80.01% as compared to 72.37% of citric acid and 67.06% of nitric acid removal efficiency with lowest electrolyte consumption. The proposed mechanistic strategy for maximum removal efficiency with saponin over selected electrolytes can be attributed to the synchronized effects of micelles formation and sequential complexation along with adsorption of chromium ions during electromigration process. Also, the results derived from the sequential extraction analysis revealed that the saponin-treated electrokinetic process successfully increases the transformation rate of labile speciation (i.e., exchangeable and reducible fractions) to stable speciation (i.e., oxidizable and residual fractions) of chromium. This affirmed its lower risk of recontamination during its disposal. Thus, the removal efficiency and transformation of active metal fraction into a non-reactive fraction by saponin have been highly commended.

Graphic abstract

中文翻译：

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制革污泥中铬通过电动过程的传输机理：电解质的作用和运行条件

在本研究中，已经探索了对生物表面活性剂皂苷的应用的新认识，它比硝酸和柠檬酸更适合作为电解质，用于利用电动过程从制革厂污泥中修复铬。使用统计工具，响应面方法研究了自变量（例如电解质摩尔浓度（M）和施加电压（V））与输出响应之间的相互作用。对于选定的独立变量，在诸如铬去除，电解质消耗和功率消耗的响应之间已经建立了显着的相关性。就总铬去除率而言，皂苷显示出最大的功效，为80.01％，而柠檬酸的去除效率为72.37％，硝酸的去除率为67.06％，电解质消耗最低。所提出的用皂素在选定的电解质上实现最大去除效率的机械策略可归因于胶束形成和顺序络合以及电迁移过程中铬离子的吸附的同步效应。同样，从顺序提取分析得出的结果表明，皂苷处理的电动过程成功地提高了不稳定形态（即可交换和可还原的馏分）向稳定铬形态（即可氧化和残留的馏分）的转化率。这肯定了其在处置过程中再次污染的风险较低。因此，已经高度推荐了皂苷的去除效率和活性金属组分转化为非活性组分的方法。

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