极低饱和度和近饱和状态下海水中方解石和文石溶解动力学研究

Research on dissolution kinetics of calcite and aragonite in seawater with very low saturation state and near saturation

利用free-drift开放反应系统,在恒压力(101.325 kPa)和恒温度(25.0±0.2)℃环境条件下,研究人工海水中二氧化碳分压(pCO2)的变化对方解石和文石的溶解速率及反应级数的影响。研究结果表明:如果溶解实验中pCO2未达到完全平衡,计算得出的反应级数偏小,且反应液pCO2不平衡是造成不同反应阶段反应级数不同的主要原因。pCO2平衡时,文石和方解石反应级数n都介于8.0～9.5之间,其中方解石在pCO2为2 600×10-6和320×10-6条件下溶解反应级数分别为8.1和9.0;文石在pCO2为2 300×10-6和320×10-6条件下的溶解反应级数分别为9.5和9.0。当反应液pCO2平衡、Ω小于0.75时,文石的溶解速率大于方解石;当反应液pCO2平衡、Ω大于0.8时,文石的溶解速率小于方解石。

The influence of variations of carbon doxide partial pressure（pCO2） in seawater on the dissolution rate and kinetics of calcite and aragonite was studied using free-drift open reaction system which was kept at constant temperature（25.0±0.2）℃ and pCO2（101.325 kPa）.The results show that： If the pCO2 between mixture gas and reaction solution is out of balance,the deserved dissolution reaction order is smller than the actual one.The imbalance of pCO2 is the main reason for different reaction orders at different stage.In pCO2 balance stage,the reaction order of aragonite and calcite is between 8.0 and 9.5.The reaction orders of calcite are 8.1 and 9.0 respectively with pCO2 of 2 600×10-6 and 320×10-6,while for aragonite they are 9.5 and 9.0 respectively with pCO2 of 2 600×10-6 and 320×10-6.When pCO2 reached a balance between the mixture gas and reaction solution,if Ω0.75,the dissolution rate of aragonite is larger than that of calcite and if Ω0.8 the dissolution rate of aragonite is smaller than that of calcite with the same temperature,Ω and pCO2.