On the effect of aqueous Ca on magnesite growth - Insight into trace element inhibition of carbonate mineral precipitation
On the effect of aqueous Ca on magnesite growth - Insight into trace element inhibition of carbonate mineral precipitation
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DOI：
10.1016/j.gca.2016.01.019
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发表时间：
2016-04-01
影响因子：
5
通讯作者：
Oelkers, Eric H.
中科院分区：
文献类型：
--
作者：
Berninger, Ulf-Niklas;Jordan, Guntram;Oelkers, Eric H.
出于对方解石生长速率的强烈影响，本研究使用水热原子力显微镜（HAFM）和水热混流反应器（HMFR）实验，以探讨在100摄氏度和pH值类似于7.7的菱镁矿生长动力学的影响，水溶液钙。在流体饱和状态下，菱镁矿生长过程中（104）表面上的钝阶速度测量为4 ± 3 nm/s，等于离子活度商除以菱镁矿水解反应的平衡常数86-117。当Ca水溶液浓度达到3 × 10（-3）mol/kg时，这些速率不发生系统性变化。通过HAFM测定的菱镁矿生长速率发现，在这些饱和状态下，含水Ca的存在对菱镁矿生长速率的影响可以忽略不计，并且与Saldi等人（2009）和Gautier等人（2015）先前在含水无Ca系统中报告的菱镁矿生长速率基本一致。同样，菱镁矿生长速率测定HMFR表现出水溶液中的Ca浓度没有系统的变化。然而，在这项研究中的速率，被扩展到更高程度的流体过饱和度相对于菱镁矿比以前的研究。考虑到螺旋生长和二维成核/生长机制的综合影响，所有测量的HMFR速率都可以准确地描述。尽管缺乏一个明确的效果，水溶液中的钙菱镁矿的生长速率，拉曼光谱证实了高达8摩尔%的Ca 2+的掺入到不断增长的菱镁矿结构。(C)2016爱思唯尔有限公司版权所有
Motivated by the strong effect of aqueous Mg on calcite growth rates, this study used hydrothermal atomic force microscopy (HAFM) and hydrothermal mixed-flow reactor (HMFR) experiments to explore the effect of aqueous Ca on magnesite growth kinetics at 100 degrees C and pH similar to 7.7. Obtuse step velocities on (104) surfaces during magnesite growth were measured to be 4 + 3 nm/s at fluid saturation states, equal to the ion activity quotient divided by the equilibrium constant for the magnesite hydrolysis reaction, of 86-117. These rates do not vary systematically with aqueous Ca concentration up to 3 x 10(-3) mol/kg. Magnesite growth rates determined by HAFM are found to be negligibly affected by the presence of aqueous Ca at these saturation states and are largely consistent with those previously reported in aqueous Ca-free systems by Saldi et al. (2009) and Gautier et al. (2015). Similarly, magnesite growth rates measured by HMFR exhibit no systematic variation on aqueous Ca concentrations. Rates in this study, however, were extended to higher degrees of fluid supersaturation with respect to magnesite than previous studies. All measured HMFR rates can be accurately described taking account the combined effects of both the spiral growth and two dimensional nucleation/growth mechanisms. Despite the lack of a clear effect of aqueous Ca on magnesite growth rates, Raman spectroscopy confirmed the incorporation of up to 8 mol percent of Ca2+ into the growing magnesite structure. (C) 2016 Elsevier Ltd. All rights reserved.