Chlorite dissolution in the acid pH-range:: A combined microscopic and macroscopic approach
Chlorite dissolution in the acid pH-range:: A combined microscopic and macroscopic approach
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DOI：
10.1016/s0016-7037(02)01293-0
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发表时间：
2003-04-01
影响因子：
5
通讯作者：
Bernhard, G
中科院分区：
文献类型：
--
作者：
Brandt, F;Bosbach, D;Bernhard, G
通过混流实验对中等铁含量的亚氯酸盐的溶解进行了宏观研究，并通过原子力显微镜（AFM）进行了微观研究。 25 ℃、pH 2 至 5 时，BET 表面积归一化稳态溶解速率在 10(-12) 和 10(-13) mol/m(2.)s 之间变化。计算出溶解反应相对于质子的级数约为0.29。当 pH 值为 2 至 4 时，发现亚氯酸盐以非化学计量方式溶解，并优先释放八面体配位阳离子。八面体配位阳离子的额外释放可能是由于亚氯酸盐从颗粒边缘向内转变为层间亚氯酸盐/蛭石。对已在 pH 2 下预处理数月的亚氯酸盐样品的基面进行原位原子力显微镜检查，表明存在缺陷控制的溶解机制。具有高度差的分子台阶对应于亚氯酸盐的不同亚基，例如TOT片和水镁石状层，起源于表面缺陷，例如成分不均匀或裂纹，这可能是由于绿泥石样品的变形历史造成的。与其他片状硅酸盐相比，在 pH 2 时，纳米级蚀刻坑出现在由 TOT 片终止的平坦平台内以及水镁石状层内的亚氯酸盐基底表面上。绿泥石基面逐层溶解，因为大多数表面缺陷仅通过单个TOT或类水镁石层表达。与晶粒边缘的溶解相比，缺陷控制的溶解机制有利于基底表面上分子台阶的溶解。在 pH 2 时，亚氯酸盐基面的溶解主要由 14 A 步的后退决定，代表一个亚氯酸盐晶胞。宏观和微观亚氯酸盐溶解速率可通过 AFM 识别的反应表面积联系起来。与溶解相关的反应表面积仅占 BET 表面积的 0.2%。当标准化到反应表面积时，通过 pH 2 下的宏观和微观溶解实验计算出 2.5 x 10(-9) mol/m(2)S 的溶解速率。版权所有 (C) 2003 爱思唯尔科学有限公司
The dissolution of chlorite with intermediate Fe-content was studied macroscopically via mixed flow experiments as well as microscopically via atomic force microscopy (AFM). BET surface area normalized steady state dissolution rates at 25 degreesC for pH 2 to 5 vary between 10(-12) and 10(-13) mol/m(2.)s. The order of the dissolution reaction with respect to protons was calculated to be about 0.29. For pH 2 to 4, chlorite was found to dissolve non-stoichiometrically, with a preferred release of the octahedrally coordinated cations. The additional release of octahedrally coordinated cations may be due to the transformation of chlorite to interstratified chlorite/vermiculite from the grain edges inward.In-situ atomic force microscopy performed on the basal surfaces of a chlorite sample, which has been preconditioned at pH 2 for several months, indicated a defect controlled dissolution mechanism. Molecular steps with height differences which correspond to the different subunits of chlorite, e.g. TOT sheet and brucite like layer, originated at surface defects such or compositional inhomogenities or cracks, which may be due to the deformation history of the chlorite sample. In contrast to other sheet silicates, at pH 2 nanoscale etch pits occur on the chlorite basal surfaces within flat terraces terminated by a TOT-sheet as well as within the brucite like layer. The chlorite basal surface dissolves layer by layer, because most of the surface defects are only expressed through single TOT or brucite-like layers. The defect controlled dissolution mechanism favours dissolution of molecular steps on the basal surfaces compared to dissolution of the grain edges. At pH 2 the dissolution of the chlorite basal surface is dominated by the retreat of 14 A steps, representing one chlorite unit cell.The macroscopic and microscopic chlorite dissolution rates can be linked via the reactive surface area as identified by AFM. The reactive surface area with respect to dissolution consists of only 0.2% of the BET-surface area. A dissolution rate of 2.5 x 10(-9) mol/m(2)S was calculated from macroscopic and microscopic dissolution experiments at pH 2, when normalized to the reactive surface area. Copyright (C) 2003 Elsevier Science Ltd.