海水中文石溶解、沉淀速率及动力学研究

Research on dissolution and precipitation rates and kinetics of aragonite in artificial seawater

利用free-drift开放反应系统,在恒压力(1×105Pa)、恒温度(25.0℃±0.2℃)环境下,研究人工海水中近溶解、沉淀平衡状态时二氧化碳分压(pCO2)的变化对文石溶解、沉淀速率及其动力学方程的影响。每组实验中通入混合气体的pCO2分别为2300×10-6和320×10-6两种,并保持通入气体的pCO2恒定,通过实验得到了这两种pCO2环境下,文石的溶解和沉淀速率及动力学方程。研究结果表明:(1)文石在近溶解、沉淀平衡附近,溶解速率相对于Ac(碳酸盐碱度值)或?(饱和度)的变化速率要大于沉淀速率相对于Ac或?的变化速率;(2)Ac相同时,pCO2越高,溶解速率越高,沉淀速率越低;?相同时,亦是如此;(3)溶解实验中,在?>0.8的区间内,反应液和混合气体之间pCO2平衡,反应级数n介于9～10之间;沉淀实验中,文石的反应级数介于2.0～3.2之间。

The influence of variations of carbon dioxide partial pressure （pCO2） in seawater on the precipitation rate and kinetics of calcite and aragonite was studied using free-drift open reaction system which was kept at constant pressure （1atm） and temperature （25.0±0.2℃）. In the experiments, two kinds of mixture gas with pCO2≈2300×10-6 and pCO2≈320×10-6 were used respectively. In every experiment, the pCO2 of mixture gas was kept constant. And the dissolution and precipitation rates and reaction equations were achieved under different pCO2. The results show that： （1） Near dissolution and precipitation equilibrium of aragonite, the variation rate of dissolution rate in relative of carbonate alkalinity （Ac） or saturation state （？） is larger than that of precipitation rate in relative of carbonate alkalinity（Ac） or saturation state（？）. （2） The higher the pCO2, the higher the dissolution rate and lower precipitation rate of aragonite with the same Ac or ？. （3） In dissolution experiments, the equilibrium of pCO2 between reaction solution and mixture gas is achieved when ？0.8, and the reaction order is between 9 and 10 for aragonite. And in precipitation experiments, the reaction order is between 2.0 to 3.2 for aragonite.