Abstract Recent increases in industrial activity have resulted in elevated chromium (Cr) pollution in the natural environment, from the degradation of concrete and the leakage of water from landfills or mine waste. The release of toxic chromate ions into the environment could have harmful consequences. Methods for Cr removal are therefore becoming increasingly important to control the release of this highly toxic metal into the environment. This study examines how chromate (CrO42−) can be incorporated into a new, stable solid phase at a dissolving calcite surface. To study the relationship between solutions containing chromate and calcite, we performed two series of time-lapse atomic force microscopy (AFM) experiments to identify calcite dissolution and growth rates in the presence of chromate. In addition, we conducted complementary experiments in a stirred flow-through reactor to determine the amount of Cr removal from solution. All experiments were performed at room temperature and under a constant initial pH in the range 6–12. During the AFM experiments, we observed calcite dissolution via etch pit formation and propagation. In the presence of chromate, nanoparticles of a new phase nucleated and grew at the calcite surface by a coupled dissolution-precipitation process. In experiments with concentrations above 10 ppm Cr or at pH 10 and higher, we observed many nanoparticle precipitates, while precipitates were rarely observed at lower concentrations of Cr. At pH 10.5, the precipitates covered the calcite surface. This partly passivated further calcite dissolution, an observation confirmed by the low amounts of Cr removal measured in the flow-through experiments. Scanning electron microscopy analysis demonstrated that Cr was associated with the precipitates, indicating that Cr could be captured from solution and trapped in solid nanoparticles in the presence of calcite. However, the passivation of the calcite surface by a new precipitate may eventually slow down Cr sequestration.

中文翻译：

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暴露于富铬流体的方解石耦合溶解-沉淀和生长过程的直接成像

摘要 最近工业活动的增加导致了自然环境中铬 (Cr) 污染的增加，这是由于混凝土的降解以及垃圾填埋场或矿山废物中的水泄漏。有毒的铬酸盐离子释放到环境中可能会产生有害的后果。因此，去除 Cr 的方法对于控制这种剧毒金属释放到环境中变得越来越重要。这项研究检查了铬酸盐 (CrO42−) 如何在溶解的方解石表面结合到新的稳定固相中。为了研究含有铬酸盐和方解石的溶液之间的关系，我们进行了两个系列的延时原子力显微镜 (AFM) 实验，以确定在铬酸盐存在下方解石的溶解和生长速率。此外，我们在搅拌流通式反应器中进行了补充实验，以确定从溶液中去除 Cr 的量。所有实验均在室温和 6-12 范围内的恒定初始 pH 值下进行。在 AFM 实验期间，我们通过蚀刻坑的形成和传播观察到方解石溶解。在铬酸盐存在下，新相的纳米颗粒通过溶解-沉淀耦合过程在方解石表面成核和生长。在 Cr 浓度高于 10 ppm 或 pH 值为 10 或更高的实验中，我们观察到许多纳米颗粒沉淀物，而在较低 Cr 浓度下很少观察到沉淀物。在 pH 10.5 时，沉淀物覆盖方解石表面。这部分钝化了方解石的进一步溶解，在流通实验中测得的少量 Cr 去除证实了这一观察结果。扫描电子显微镜分析表明，Cr 与沉淀物相关，表明在方解石存在的情况下，Cr 可以从溶液中捕获并捕获在固体纳米颗粒中。然而，新沉淀物钝化方解石表面可能最终减缓 Cr 螯合。