Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400085, India.
J Phys Chem B. 2010 Apr 8;114(13):4471-6. doi: 10.1021/jp910580f.
Studies on isotopic and ion-exchange kinetics of mercury ions in Nafion-117 membrane have been carried out with (203)Hg radiotracer in the presence of Cl(-) and NO(3)(-) in solution. The results of isotopic-exchange kinetics indicate that mercury ions diffuse into the membrane as monovalent cation from HgCl(2) solution while as divalent ion from Hg(NO(3))(2) solution. The studies on the kinetics of ion exchange of Hg(2+) with Na(+) follow the prediction of the Nernst-Planck equation when NaNO(3) is used as an external salt solution. The Nernst-Planck equation fails to predict the kinetics when NaCl is used as an external salt solution, indicating that the complexation of Cl(-) with Hg(2+) in the membrane influences the kinetics. Permeation studies using (203)Hg and (36)Cl radiotracer between two HgCl(2) solutions show that the permeability coefficients of mercury and chloride ions are the same, indicating the cotransport of mercury and chloride ions through the membrane. Ion-exchange equilibrium studies using a mixture of HgCl(2) and HNO(3) solution were carried out to ascertain the species transporting through the membrane. The equilibrium sorption of mercury in the membrane shows the uptake of an ionic species, presumably HgCl(+), not a neutral salt. The speciation diagrams, calculated as a function of pH, show wide divergence of species present in HgCl(2) and Hg(NO(3))(2) solution and explain the difference in membrane transport behavior for HgCl(2) and Hg(NO(3))(2) solution. The results show that any ion-exchange-membrane-based separation of Hg(2+) needs careful consideration regarding the anions present in the solution, as it influences the speciation of mercury and hence its transport behavior through the membrane.
已使用 (203)Hg 放射性示踪剂在溶液中存在 Cl(-) 和 NO(3)(-) 的情况下，对 Nafion-117 膜中汞离子的同位素和离子交换动力学进行了研究。同位素交换动力学的结果表明，汞离子从 HgCl(2)溶液中作为单价阳离子扩散到膜中，而从 Hg(NO(3))(2)溶液中作为二价离子扩散到膜中。当使用 NaNO(3)作为外部盐溶液时，Hg(2+)与 Na(+)的离子交换动力学符合 Nernst-Planck 方程的预测。当使用 NaCl 作为外部盐溶液时，Nernst-Planck 方程无法预测动力学，表明膜中 Cl(-)与 Hg(2+)的络合影响动力学。使用 (203)Hg 和 (36)Cl 放射性示踪剂在两个 HgCl(2)溶液之间进行的渗透研究表明，汞和氯离子的渗透系数相同，表明汞和氯离子通过膜共传输。使用 HgCl(2)和 HNO(3)溶液的混合物进行离子交换平衡研究，以确定通过膜传输的物种。膜中汞的离子交换平衡吸附表明，吸收的是离子物种，可能是 HgCl(+)，而不是中性盐。根据 pH 计算的形态图显示了 HgCl(2)和 Hg(NO(3))(2)溶液中存在的物种的广泛差异，并解释了 HgCl(2)和 Hg(NO(3))(2)溶液通过膜的传输行为的差异。结果表明，任何基于离子交换膜的 Hg(2+)分离都需要仔细考虑溶液中存在的阴离子，因为它会影响汞的形态，从而影响其通过膜的传输行为。
