Physics of Geological Processes, University of Oslo, 0316 Oslo, Norway.
Environ Sci Technol. 2012 May 1;46(9):5253-60. doi: 10.1021/es300403n. Epub 2012 Apr 20.
The dissolution and carbonation of brucite on (001) cleavage surfaces was investigated in a series of in situ and ex situ atomic force microscopy (AFM) experiments at varying pH (2-12), temperature (23-40 °C), aqueous NaHCO(3) concentration (10(-5)-1 M), and PCO(2) (0-1 atm). Dissolution rates increased with decreasing pH and increasing NaHCO(3) concentration. Simultaneously with dissolution of brucite, the growth of a Mg-carbonate phase (probably dypingite) was directly observed. In NaHCO(3) solutions (pH 7.2-9.3,), precipitation of Mg-carbonates was limited. Enhanced precipitation was, however, observed in acidified NaHCO(3) solutions (pH 5, DIC ≈ 25.5 mM) and in solutions that were equilibrated under a CO(2) atmosphere (pH 4, DIC ≈ 25.2 mM). Nucleation predominantly occurred in areas of high dissolution such as deep step edges suggesting that the carbonation reaction is locally diffusion-transport controlled. More extensive particle growth was also observed after ex situ experiments lasting for several hours. This AFM study contributes to an improved understanding of the mechanism of aqueous brucite carbonation at low temperature and pressure conditions and has implications for carbonation reactions in general.
在一系列不同 pH 值（2-12）、温度（23-40°C）、水合碳酸氢钠浓度（10^(-5)-1 M）和 PCO₂（0-1 大气压）的原位和异位原子力显微镜（AFM）实验中，研究了水镁石在（001）解理表面上的溶解和碳化。溶解速率随 pH 值降低和碳酸氢钠浓度增加而增加。与水镁石的溶解同时，直接观察到 Mg-碳酸盐相（可能是 dypingite）的生长。在碳酸氢钠溶液中（pH 7.2-9.3），Mg-碳酸盐的沉淀受到限制。然而，在酸化的碳酸氢钠溶液（pH 5，DIC ≈ 25.5 mM）和在 CO₂气氛下平衡的溶液中观察到增强的沉淀（pH 4，DIC ≈ 25.2 mM）。成核主要发生在溶解程度较高的区域，如深阶边缘，表明碳化反应是局部扩散-传输控制的。在持续数小时的异位实验后，也观察到更广泛的颗粒生长。这项 AFM 研究有助于更好地理解低温低压下水镁石碳化的机制，并对一般的碳化反应具有启示意义。
