Abstract Dolomite is a widespread carbonate mineral that has been investigated extensively over the past two centuries. Despite the high level of investigation, aspects of the environmental conditions of crystallization, diagenesis and dissolution remain elusive and the transformation of dolomite into other value-added products is still challenging. This work shows a novel, cleaner method to dissolve dolomite by taking advantage of the acidity from the hydrolysis of Lewis acid AlCl3 and as such the mineral can be efficiently converted into Ca-Mg-Al layered double hydroxide (LDH). The dolomite and the resulting Ca-Mg-Al LDH samples were characterized by powder X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), thermogravimetric analysis (TG), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The composition of the products was measured by energy dispersive spectrometer-mapping (EDS-mapping), X-ray fluorescence (XRF) and atomic absorption spectroscopy (AAS). Particle sizes of the products were measured by a dynamic light scattering method. It is documented, for the first time, that dissolution of dolomite in AlCl3 aqueous solution is facilitated by hydrothermal treatment. Well-crystallized Ca-Mg-Al LDH crystals are achieved under (Ca + Mg): Al molar ratio = 1:1, pH = 10.5 via a simple co-precipitation method. The maximum utilization efficiencies of Ca2+, Mg2+ from dolomite to LDH are 36.3% and 95.5%, respectively. The possible mechanisms of LDH formation were: 1) the dolomite dissolved in the strong acid solution due to the hydrolysis of AlCl3 and thus provided Ca2+ and Mg2+; 2) with addition of NaOH, Al3+ cations precipitated to form Al(OH)3 (at 8.3 ≤ pH ≤ 9.3) and then part of the Al(OH)3 reacted with Ca2+ and Mg2+ to form the Ca-Mg-Al LDH; 3) at pH = 10.5, the Al(OH)3 was transformed as [AlO(OH)] and meanwhile Ca2+, Mg2+ and Al3+ took part in the formation of Ca-Mg-Al LDH; 4) when pH = 10.6, [AlO(OH)] reacted with NaOH to dissolve into [Al(OH)4]− and the [Al(OH)4]− finally co-precipitated with Ca2+ and Mg2+ to form the Ca-Mg-Al LDH during heating for drying.

中文翻译：

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白云石向Ca-Mg-Al层状双氢氧化物的跟踪变化

摘要 白云石是一种分布广泛的碳酸盐矿物，在过去的两个世纪中得到了广泛的研究。尽管进行了高水平的调查，结晶、成岩和溶解等环境条件仍然难以捉摸，白云石向其他增值产品的转化仍然具有挑战性。这项工作展示了一种新的、更清洁的方法，通过利用路易斯酸 AlCl3 水解产生的酸性来溶解白云石，因此可以有效地将矿物转化为 Ca-Mg-Al 层状双氢氧化物 (LDH)。通过粉末 X 射线衍射 (XRD)、傅里叶变换红外光谱 (FT-IR)、热重分析 (TG)、扫描电子显微镜 (SEM) 和透射电子显微镜对白云石和所得 Ca-Mg-Al LDH 样品进行表征(TEM)。通过能量色散光谱仪-映射（EDS-mapping）、X射线荧光（XRF）和原子吸收光谱（AAS）测量产物的组成。产品的粒度通过动态光散射法测量。首次证明水热处理促进了白云石在 AlCl3 水溶液中的溶解。在 (Ca + Mg): Al 摩尔比 = 1:1、pH = 10.5 下，通过简单的共沉淀方法获得结晶良好的 Ca-Mg-Al LDH 晶体。Ca2+、Mg2+从白云石到LDH的最大利用效率分别为36.3%和95.5%。LDH形成的可能机制有：1）白云石溶解在强酸溶液中，由于AlCl3水解，提供Ca2+和Mg2+；2) 加入氢氧化钠，Al3+阳离子沉淀形成Al(OH)3(8.3≤pH≤9.3)，部分Al(OH)3与Ca2+和Mg2+反应形成Ca-Mg-Al LDH；3) pH=10.5时，Al(OH)3转化为[AlO(OH)]，同时Ca2+、Mg2+和Al3+参与形成Ca-Mg-Al LDH；4) 当 pH = 10.6 时，[AlO(OH)] 与 NaOH 反应溶解成 [Al(OH)4]-，[Al(OH)4]- 最终与 Ca2+ 和 Mg2+ 共沉淀形成 Ca-加热干燥过程中的 Mg-Al LDH。