高盐溶液蒸发过程的分子动力学模拟与分析

Molecular dynamic simulation and analysis on evaporation of high-salt solution

随着膜浓缩工艺产生的高盐废水急剧增加,热蒸发技术在减量化处理高盐废水工程当中得到广泛应用。采用分子动力学模拟方法,从微观角度研究了含KCl和CaCl_(2)的高浓度溶液在铜表面的非稳态蒸发过程。研究结果表明:盐溶液蒸发过程中的蒸发水分子主要来源于远离离子的自由水分子,而离子配位水分子对蒸发水分子贡献不大,在相同加热温度下2种盐溶液的蒸发速率都比纯水低,并且加热温度越低,差距越大;同时,由于Ca^(2+)和水分子的作用强于K^(+)和水分子的作用,相同摩尔浓度的KCl溶液蒸发速率大于CaCl_(2)溶液。由于界面离子的存在改变了其周围水分子的取向,有利于界面水分子与碰撞水分子间氢键的形成,使得两种溶液蒸发系数都低于纯水。

Since evaporation has become an important method to treat high-salt wastewater,research on saline water evaporation from the microscopic perspective has attracted more and more attention.The non-equilibrium evaporation of KCl and CaCl_(2)aqueous solution on the copper surface was studied by molecular dynamics simulation.The results showed that the evaporation rate of the two solutions was lower than that of pure water and the difference increased with the decrease of temperature.KCl solution evaporation rate was larger than that of CaCl_(2)solution with the same molar concentration.During the evaporation of saline solution,the evaporated water molecules mainly came from the free water molecules far away from ions,while the contribution of ionic coordination water molecules is small.The evaporation coefficient of the two saline solutions was less than that of pure water,because the existence of interface ions changed the orientation of water molecules around them,which was conducive to the formation of hydrogen bonds between interface water molecules and colliding water molecules.