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”)当溶液通过粘土等具有渗透性的材料时就会发生。溶质的同位素以相同的速度向膜平流，但由于单个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集层。对于像氯化钠这样的双同位素溶质，开发的超滤模型预测，砂质和/或碳酸盐物质的孔隙水应该发生显著的分馏(相对于Smoc，每毫升5个)，靠近粘土透镜或页岩的提升侧。检验该模型的最简单方法是对其最具体的预测进行实验研究：d37Cl最小值。该模型的这一方面很容易测试，因为10-5到10-7cm.sec-1的溶液流量很容易在实验室中复制。计算表明，d37Cl极小值出现在发达的浓差极化层(从膜的高压界面向外测量)长度的10左右。对于中等(20%)理想的粘土膜，预测的最低d37Cl值可以达到-5/mil。该项目的独特之处在于直接从CPL现场采样溶液。到目前为止，这一点既没有做过，也没有考虑过。拟议的实验将明确表明，存在(或不存在)最低限度。如果实验不能证实这一理论，那么超滤对水体系中溶质同位素的分馏没有任何意义。然而，如果实验数据支持这一模型，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对他们的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.