Formation of saponite by hydrothermal alteration of metal oxides: implication for the rarity of hydrotalcite
Formation of saponite by hydrothermal alteration of metal oxides: implication for the rarity of hydrotalcite
复制标题
金属氧化物的热液蚀变形成皂石：对水滑石稀有性的影响
DOI：
10.2138/am-2019-7043
复制
发表时间：
2019
影响因子：
3.1
通讯作者：
Komarneni Sridhar
中科院分区：
文献类型：
--
作者：
Tao Qi;Zeng Qingjin;Chen Manyou;He Hongping;Komarneni Sridhar
通过金属氧化物的水热碱蚀变，观察到水滑石（Ht）向皂石的转化。转化过程为水化-溶解-沉淀的过程。它涉及几个关键步骤，包括从金属氧化物中构建Ht，从Ht中溶解Al 3+，偏硅酸盐阴离子与Ht缩合，最后结晶皂石。Ht的相对低的Mg/Al比率、沿着环境中高浓度的Al 3+和硅酸盐低聚物有利于缩合，从而产生高度结晶的皂石。后者的转换大大加快了同晶取代的Al 3+的Si 4+在硅酸盐低聚物。取代产生额外的负电荷，并导致上述与Ht表面的缩合，从而促进皂石TOT层的形成。在这个过程中，二氧化碳是不可或缺的成分。最初作为CO 32-插入形成Ht，随后从固相中消除CO2，当层电荷反转时形成皂石。因此，本研究提出了一种新的形成机制的皂石从金属氧化物通过水滑石，并有助于更好地理解的结晶，化学稳定性，和转化的Ht的皂石。这些结果也与评估地球表面的金属可用性和碳循环有关。
Conversion of hydrotalcite (Ht) to saponite was observed by hydrothermal alkaline alteration of metal oxides. The conversion was through a pathway of hydration-dissolution-precipitation. It involved several critical steps, including the construction of Ht from metal oxides, dissolution of Al3+ from Ht, condensation of metasilicate anions with Ht, and finally crystallization of saponite. The condensation was favored by relatively low Mg/Al ratios of Ht, along with high concentrations of Al3+ and silicate oligomers in the environment, resulting in highly crystalline saponite. The latter conversion was greatly accelerated by the isomorphous substitution of Al3+ for Si4+ in silicate oligomers. The substitution generated the extra negative charge and led to the aforementioned condensation with Ht surface, thereby promoting the formation of saponite TOT layers. During the process, CO2 is an indispensable component. Initially intercalated as CO32− to form Ht, CO2 was subsequently eliminated from the solid phase, and saponite formed when the layer charge was reversed. Thus, this study presents a novel formation mechanism of saponite from metal oxides via hydrotalcite and contributes to a better understanding of the crystallization, chemical stability, and transformation of Ht to saponite. The results are also relevant to evaluating metal availability and carbon cycling on the surface of the Earth.