Hartley–Crank Equations for Coupled Diffusion in Concentrated Mixed Electrolyte Solutions. The CaCl₂ + HCl + H₂O System

详细信息

下载全文

推荐本文 |

• 作者：Leaist ; Derek G. ; Curtis ; Nicolette
• 关键词：Activity coefficients ; aqueous CaCl2 + HCl solutions ; coupled diffusion ; Hartley– ; Crank theory ; hydration ; ionic mobilities ; mixed electrolyte diffusion ; Nernst— ; Planck equations ; Pitzer equations ; ternary diffusion ; viscosity
• 刊名：Journal of Solution Chemistry
• 出版时间：1999
• 出版年：1999
• 期刊代码：24_00959782
• 类别：en
• 卷：28
• 期：4
• 页码：341-366
• 数据来源：sp

摘要

Nernst–Planck equations and ionic conductivities are used to calculate accurate limiting interdiffusion coefficients $D\{\backslash rm\; ^o\_\{ik\}\}$ for mixed electrolyte solutions. The electrostatic mechanism for coupled electrolyte diffusion is investigated by calculating the electrostatic contribution to each $D\{\backslash rm\; ^o\_\{ik\}\}$ coefficient to give the flux of each electrolyte driven by the electric field, which is generated by the migration of ions of different mobilities. Ternary diffusion coefficients are measured for dilute aqueous K₂SO₄ + KOH and Li₂SO₄ + LiOH solutions. Because of the different mobilities of K⁺ and Li⁺ ions relative to $\{\backslash rm\; SO\}^\{2-\}\_4$ ions, diffusing K₂SO₄ drives cocurrent flows of KOH, but diffusing Li₂SO₄ drives counterflows of LiOH. To describe coupled diffusion in concentrated mixed electrolyte solutions, the Hartley–Crank theory is used to correct the limiting $D\{\backslash rm\; ^o\_\{ik\}\}$ coefficients for nonideal solution behavior, viscosity changes, ionic hydration, and the zero-volume flow constraint. Diffusion coefficients predicted for concentrated aqueous CaCl₂ + HCl solutions are compared with recently reported data. The large amount of HCl cotransported by the diffusing CaCl₂ is attributed to the “salting out” of HCl by CaCl₂ and to the migration of H⁺ ions in the diffusion-induced electric field, which slows down the Cl⁻ ions and speeds up the less-mobile Ca²⁺ ions to maintain electroneutrality along the CaCl₂ gradient.