Experimental Verification of a Chlorine-37 Minimum in Concentration Polarization Layer Profiles as Predicted by a Hyperfiltration Model

Fritz - 0001054超滤(又名；“反渗透”)发生时，溶液平流通过透选择性材料，如粘土。溶质的同位素以相同的速度向膜平流；然而，由于各同位素的水扩散系数不同，它们以不同的速率扩散回高压储层。对于像NaCl这样的双同位素溶质，开发的超滤模型预测，在粘土透镜体或页岩的上斜侧附近的砂质和/或碳酸盐物质的孔隙水中，应该会发生显著的分馏（相对于SMOC而言，5 / mil）。测试该模型最简单的方法是实验研究它最具体的预测：d37Cl最小值。模型的这一方面很容易测试，因为10-5至10-7 cm.sec-1的溶液通量很容易在实验室中复制。计算表明，d37Cl的最小值出现在形成的浓度极化层长度的10倍左右（从膜的高压界面向外测量）。对于中等（20%）理想的粘土膜，预测的d37Cl最小值可达到-5 / mil。这个项目的独特之处在于直接从cpld中对解决方案进行现场采样。到目前为止，这还没有被做过，甚至没有被考虑过。拟议中的实验将明确表明，存在（或不存在）最小值。如果实验不能证实理论，那么超滤对水体系中溶质同位素的分馏没有意义。然而，如果实验数据支持该模型，那么如果他们的地下水样本流经膜功能单元，同位素地球化学家可能不得不重新评估其溶质同位素数据的解释。

Fritz - 0001054Hyperfiltration (a.k.a. "reverse osmosis") occurs when solution advects through permselective material like clays. Isotopes of solutes are advected toward the membrane of the same velocity; however, they diffuse back into the high-pressure reservoir of different rates owing to differences of individual isotope's aqueous diffusion coefficients. For a two-isotope solute like NaCl, the developed hyperfiltration model predicts that signfiicant fractionation (5 per mil relative to SMOC) should occur in pore water of arenaceous and/or carbonate material adjacent to the upgradient side of a clay lens or shale.The easiest way to test the model is to experimentally investigate its most specific prediction: the d37Cl minimum. This aspect of the model is easily testable because solution fluxes of 10-5 to 10-7 cm.sec-1 are easy to replicate in a laboratory. Calculations show that the position of the d37Cl minimum occurs at about 10 of the length of the developed concentration polarization layer (as measured outward from the membrane's high-pressure interface). The predicted magnitude of the d37Cl minimum can attain -5 per mil for a clay membrane of moderate (20%) ideality. The unique aspect of this project is in situ sampling of solutions directly from a CPL. Until now, this has neither been done nor even considered. The proposed experiments will yield show unequivocally that a minimum does (or does not) exist. Should the experiments fail to confirm the theory, then hyperfiltration plays no meaningful role in fractionation of solute isotopes in aqueous systems. If, however, the experimental data support the model, then isotope geochemists may have to reevaluate interpretations of their solute isotope data if their groundwater samples flowed through membrane-functioning units.