We investigated the dissolution of a natural Fe-containing dolomite [Ca_1.003Mg_0.972Fe_0.024Mn_0.002(CO₃)₂] under acidic conditions (pH 3–5.5) with atomic force microscopy (AFM) at 20 °C and with batch dissolution experiments at 80 °C. Dolomite dissolution proceeded by two identified mechanisms: removal of dolomite layers through spreading and coalescence of etch pits nucleated at defect points, and stepped retreat from surface edges. The dolomite dissolution rate increased when pH decreased (from 0.410 nm s^–1 at pH 3 to 0.035 nm s^–1 at pH 5). Rates calculated from edge retreat (v_edges) and from etch-pit spreading rates (v_sum) were consistent; the etch-pit digging rate was almost 10 times slower than its spreading rate. Nanocrystalline secondary phases precipitated in the course of dolomite dissolution at pH 3 and 80 °C were identified as (nano)hematite, ferrihydrite, and an ankerite like mineral using X-ray diffraction, transmission electron microscopy, MicroRaman and X-ray photoelectron spectrometry. In addition, Mg enrichment of the surface layer was observed at 80 °C. The characterizations performed at a nanocrystalline scale highlighted the role played by impurities in the dolomite dissolution/precipitation scheme and evidenced that the preponderant mechanism explaining the incongruent dolomite dissolution is secondary phase precipitation from major and minor elements initially present in the pristine dolomite.

中文翻译：

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含铁白云石在不同温度下的溶解研究：在白云石表面形成次生纳米晶富铁相的证据

我们在20°C的原子力显微镜（AFM）和分批溶解的条件下，研究了在酸性条件下（pH 3–5.5）溶解天然的含铁白云石[Ca _1.003 Mg _0.972 Fe _0.024 Mn _0.002（CO ₃）₂ ]在80°C下进行实验。白云石的溶解通过两种确定的机制进行：通过在缺陷点成核的腐蚀坑的扩散和合并去除白云石层，以及从表面边缘逐步退缩。当pH降低时，白云石溶解速率增加（从pH 3的0.410 nm s ^–1到pH 5的0.035 nm s ^–1）。从边缘后退计算的速率（v个_边缘）和蚀刻坑扩展率（v _sum）是一致的；蚀刻坑的挖掘速度几乎比其扩散速度慢10倍。在X射线衍射，透射电子显微镜，MicroRaman和X射线光电子能谱法下，在白云石溶解于pH 3和80°C的过程中沉淀的纳米晶次生相被鉴定为（纳米）赤铁矿，三水铁矿和像金属一样的铁长石。另外，在80℃下观察到表层的Mg富集。在纳米晶尺度上进行的表征突出了杂质在白云石溶解/沉淀方案中所起的作用，并证明了解释不相容白云石溶解的主要机理是来自原始原始白云石中主要和次要元素的次生相沉淀。