乳化液膜萃取Cr(Ⅲ)的内相反萃步骤动力学研究

Stripping reaction at internal phase of extracting Cr( Ⅲ) by emulsion liquid membranes

文章采用恒界面法对乳化液膜分离Cr(Ⅲ)的液膜内相反萃步骤进行了研究,考察了搅拌速度、温度、界面面积、水相p H值、DEHPA[二(2-乙基己基)磷酸]浓度和络合物浓度对反萃速率的影响,得到反萃反应的动力学与热力学数据,并推导出反萃的反应机理。实验结果表明:搅拌速度大于0.45 m/s时出现与搅拌强度无关的化学反应控制"坪区",且反萃速率与界面面积成正比,此时反应属于扩散和化学反应共同控制,并且反应主要发生在相界面上;由温度与反萃速率的关系得知,该反萃反应是一个放热反应,反应的活化能Ea=24.25 k J/mol,焓变ΔH=-55.85 k J/mol,熵变ΔS=-566.37 J/mol,在T=308 K时ΔG=118.59 k J/mol;在控制步骤反应式中,DEHPA反应级数为0,络合物浓度和水相氢离子的反应级数为1,并推导出反萃反应的控制步骤的方程式为r=k0[Cr(OH)2HL2(o)][H+(w)]。

The stripping reaction of internal phase of emulsion liquid membranes in process of extracting Cr （ Ⅲ） was studied using a constant interfacial method, and the mechanism and reaction kinetics were derived based on some influential factors such as stirring speed, temperature, specific interfacial area, pH, reactant concentrations and the stripping velocity of Cr （ Ⅲ）. The results show that the stripping velocity of Cr （ Ⅲ ） is independent of the stirring speed when it is greater than 0.45 m/s. The velocity of stripping is directly proportional to the interracial area, which indicates that the stripping velocity is jointly controlled by diffusion and the chemical reaction, and the stripping reaction occurs mainly in the interface between the oil and the aqueous phase; the values of the apparent activation energy （Ea = 24.25 kJ/mol）, enthalpy change （ AH = - 55.85 kJ/mol） and entropy change （ AS = -566.37 J/mol） are from the experimental results of the temperature dependence of the extraction velocity; the