海水条件下Cd-CaCO_3共沉淀过程的动力学表达:文石

Partition behavior of cadmium in seawater-CaCO_3 system: Aragonite

采用稳定加液系统,在海水条件下模拟了Cd随文石(CaCO3)的共沉淀过程,并对这一过程中Cd的分异行为进行了定量评估。实验结果显示,Cd介于文石和海水之间的分异系数(DCd)仅在0.2至0.9范围内变化,Cd表现为一种不相容元素。随着文石沉淀速率的增加,DCd值呈逐渐上升趋势。这些分异行为显著区别于Cd在方解石-海水体系中的分异行为,表明Cd随碳酸钙的共沉淀过程受到相应CaCO3矿物晶体结构的影响。在运用海相CaCO3沉积物中Cd/Ca比值作为古海洋研究指标的时候,应严格区分相关载体(CaCO3)的晶体矿物学差异。

The coprecipitation of cadmium with aragonite in seawater was experimentally investigated via the constant addition system. It was observed that Cd was weakly partitioned into aragonite. Partition coefficients of Cd （Dco） were restricted within the range of 0.2 to 0.9. Cadmium thus could be regarded as an incompatible element to aragonite. The values of Dcd tend to increase with aragonite precipitation rates. The partition behavior of Cd in the arago nite-seawatcr system shows remarkable differences to what observed in the calciteseawater system. It suggests that the coprecipitation of Cd with CaCO3 would be fundamentally affected by the crystal structure of relative minerals. For the application of Cd/Ca ratios in marine calcium carbonates as proxies of paleo-oceanography, it should cautious to dis-tinguish the mineralogy of relative proxy carriers.