Abdilla Bektur, Lee Sang Soo, Fenter Paul, Sturchio Neil C
Department of Earth Sciences, University of Delaware, Newark, Delaware 19716, United States.
Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States.
Environ Sci Technol. 2024 Sep 17;58(37):16525-16534. doi: 10.1021/acs.est.4c03567. Epub 2024 Sep 5.
The reaction of dissolved Pb with calcite surfaces at near-equilibrium conditions involves adsorption of Pb and precipitation of secondary heteroepitaxial Pb-carbonate minerals. A more complex behavior is observed under far-from-equilibrium conditions, including strong inhibition of calcite dissolution, development of microtopography, and near-surface incorporation of multiple monolayers (ML) of Pb without precipitation of secondary phases [where 1 ML ≡ 1 Ca/20.2 Å, the crystallographic site density of the calcite (104) lattice plane]. However, the mechanistic controls governing far-from-equilibrium reactivity are not well understood. Here, we observe the interfacial incorporation of dissolved Pb during the dissolution of calcite (104) surfaces at pH ∼ 3.7 in a flow-through reaction cell, revealing the formation of a ∼1 nm thick Pb-rich calcite layer with a total Pb coverage of ∼1.4 ML. These observations of the sorbed Pb distribution used resonant anomalous X-ray reflectivity, X-ray fluorescence, and nanoinfrared atomic force microscopy. We propose that this altered surface layer represents a novel sorption mode that is stabilized by conditions of sustained disequilibrium. This behavior may significantly impact the transport of dissolved metals during disequilibrium processes occurring in acid mine drainage and subsurface CO injection and, if appropriately accounted for, could improve the predictive capability of geochemical reactive-transport models.
在接近平衡条件下，溶解态铅与方解石表面的反应涉及铅的吸附以及次生异质外延碳酸铅矿物的沉淀。在远离平衡条件下会观察到更复杂的行为，包括对方解石溶解的强烈抑制、微地形的形成以及在不形成次生相的情况下近表面多层（ML）铅的掺入[其中1 ML ≡ 1 Ca/20.2 Å，即方解石（104）晶格平面的晶体学位点密度]。然而，控制远离平衡反应性的机制尚未得到很好的理解。在此，我们在流动反应池中观察到在pH约为3.7时方解石（104）表面溶解过程中溶解态铅的界面掺入，揭示了形成了一个约1纳米厚的富含铅的方解石层，铅的总覆盖量约为1.4 ML。这些关于吸附铅分布的观察使用了共振反常X射线反射率、X射线荧光和纳米红外原子力显微镜。我们提出这种改变的表层代表了一种由持续不平衡条件稳定的新型吸附模式。这种行为可能会显著影响酸性矿山排水和地下二氧化碳注入过程中发生的不平衡过程中溶解态金属的迁移，如果能适当考虑，可能会提高地球化学反应传输模型的预测能力。
