海水条件下Cd-CaCO_3共沉淀过程的动力学表达:方解石

Partition behavior of cadmium in seawater-CaCO_3 system:Ⅰ. calcite

采用稳定加液系统对海水中方解石(CaCO3)沉淀形成时镉元素(Cd)的共沉淀现象进行了实验模拟,并对Cd-Ca-CO3共沉淀过程中Cd的分异行为进行了定量评估。实验结果显示:Cd在共沉淀过程中发生了明显的分异,基于方解石沉淀和海水溶液各自Cd/Ca比值计算得出的分异系数分别为33.0～61.8(5℃)、31.8～55.0(15℃)和17.4～31.8(25℃)。在各个温度下,DCd值都随着方解石沉淀速率的增加而有规律的下降。进一步分析表明温度和碳酸根浓度是影响Cd分异行为的根本因素。这一实验结果对于Cd/Ca古海洋指标的应用具有重要的参考价值。

Using the constant addition system,the co-precipitation of cadmium（Cd） with calcite in seawater was simulated at 5,15,and 25℃.Our results show that Cd was remarkably partitioned between calcite overgrowths and seawater.Its partition coefficients（DCd） were respectively determined to be 33.0~61.8 at 5℃,31.8~55.0 at 15℃,and 17.4~31.8 at 25℃.At each temperature,DCd values were decrease with the increase of calcite precipitation rate.The co-precipitation of Cd was apparently under the kinetic control of calcite precipitation,while further analyses suggest that temperature and carbonate concentrations are the fundamental impact factors to the partition behavior of Cd.Such a conclusion is of considerable theoretical importance to the application of Cd/Ca proxies.