近平衡状态海水中方解石溶解-沉淀速率及动力学研究

本文利用free-drift开放反应系统,在恒压力(1atm)、恒温度(25.0±0.2℃)环境下,研究海水中近溶解、沉淀平衡状态时二氧化碳分压(pCO2)的变化对方解石溶解、沉淀速率及其动力学方程的影响。研究结果表明:溶解速率相对于碳酸盐碱度(Ac)或饱和度(Ω)变化的敏感度要高于沉淀速率;Ac或Ω相同时,pCO2越高,溶解速率越高,而沉淀速率越低;方解石的溶解过程可分为pCO2欠平衡、平衡两个阶段,当Ω>0.8时反应液pCO2平衡,方解石的溶解反应级数介于8～9之间;沉淀反应级数介于2.4～2.6之间,且反应液pCO2的改变对沉淀反应级数的影响不明显。

Research on Dissolution and Precipitation Rates and Kinetics of Calcite in Seawater near Equilibrium

The influence of variation of carbon dioxide partial pressure (pCO_2) in seawater on the dissolution and precipitation rates and kinetics of calcite were studied using the free-drift open reaction system which was kept at constant pressure(latm)and temperature(25.0+0.2℃). In every experiment, the pCO_2 of mixture gas of CO_2/N_2 was kept constant, and dissolution and precipitation rates and reaction equations of calcite under different pCO_2 were established. The results showed that: (1) Near dissolution and precipitation equilibrium, the variation of dissolution rate related to carbonate alkalinity(A_c) or saturation state(Ω) was larger than that of precipitation rate related to carbonate alkalinity(A_c) or saturation state(Ω). (2) The higher the pCO_2, the higher the dissolution rate and the lower precipitation rate of calcite with the same A_c. (3) The higher the pCO_2, the higher the dissolution rate with the same Ω. (4) In dissolution experiments, when pCO_2 of reaction solution was constant, the reaction order(n) was between 8 and 9 which is obviously larger than that obtained by earlier researchers. The reaction order was between 2.4 and 2. 6 in the precipitation experiments, which means that the influence of variation of pCO_2 in seawater on the reaction order of calcite precipitation rate was small.