Mechanisms controlling albite dissolution/precipitation kinetics as a function of chemical affinity: New insights from experiments in 29Si spiked solutions at 150 and 180 °C
Mechanisms controlling albite dissolution/precipitation kinetics as a function of chemical affinity: New insights from experiments in 29Si spiked solutions at 150 and 180 °C
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控制钠长石溶解/沉淀动力学作为化学亲和力函数的机制：来自 150 和 180°C 29Si 加标溶液实验的新见解
DOI：
10.1016/j.gca.2024.03.023
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发表时间：
2024
影响因子：
5
通讯作者：
Chen, Kaiyun
中科院分区：
文献类型：
--
作者：
Schott, Jacques;Saldi, Giuseppe D.;Zhu, Chen;Gong, Lei;Chen, Kaiyun
了解接近平衡的造岩矿物的溶解速率及其对ΔGr（吉布斯反应自由能）的依赖，对于描述涉及固/流相互作用的许多环境和工程过程的时空演化至关重要。在本研究中，我们使用同位素掺杂方法来量化钠长石的正向和净溶解速率。在接近平衡和平衡条件（-25≤ΔGr≤+ 8.2 kJ/mol）的29si加标溶液中，在150°C、180°C和pH = 9下进行了批量实验。与初始BET表面积归一化的正向溶解速率随着时间和ΔGr的增加而连续单调下降，化学平衡时的溶解速率比远离平衡值的初始溶解速率低1.3 ~ 2.4个数量级，在固流比最高时，溶解速率下降幅度最大。这些速率下降伴随着BET比表面积的增加，这与广泛溶解特征的形成有关。在远离平衡条件下（ΔGr≤- 65 kJ/mol），钠长石正向溶解速率随反应时间的增加而减小，BET表面积随反应时间的增加而增大。这些观察结果与随着时间的推移而持续减少和ΔGrof钠长石有效表面积的增加相一致，这与非反应性负晶面的形成有关，此外，蚀刻坑在超过ΔGr临界值时停止成核。因此，观测到的钠长石溶解速率在接近平衡时的下降，主要不是与反向反应贡献的增加有关，而是与正向反应速率的降低以及矿物表面反应位点密度的降低有关。研究结果表明，有效表面积的表征及其随反应时间和化学亲和力的演变对于获得长石等结晶良好的矿物的稳定溶解速率至关重要。不同历史、有效表面积和表面形貌特征的样品在29si加标溶液中的溶解实验有助于更好地量化控制硅酸盐矿物风化的速率规律。
Knowledge of the rates of dissolution of rock-forming minerals close to equilibrium and their dependence on ΔGr, the Gibbs free energy of reaction, is essential for describing the temporal and spatial evolution of many environmental and engineering processes involving solid/fluid interactions. In the present study we used the isotope-doping method to quantify albite forward and net dissolution rates. Batch experiments were performed at 150, 180 °C and pH = 9 at near equilibrium and equilibrium conditions (-25 ≤ ΔGr≤ + 8.2 kJ/mol) in29Si spiked solutions which were undersaturated with the secondary Al-Si solid phases likely to precipitate.The forward dissolution rates normalized to the initial BET surface area were found to decrease continuously and monotonically with increasing time and ΔGr, achieving values 1.3 to 2.4 orders of magnitude lower at chemical equilibrium than initial far from equilibrium values, with the highest rate decrease for the highest solid to fluid ratio. These rate drops were accompanied by an increase in BET specific surface areas associated with the formation of widespread dissolution features. A decrease of albite forward dissolution rate together with an increase of its BET surface area was also observed as a function of reaction time at far from equilibrium conditions (ΔGr≤ − 65 kJ/mol). These observations are consistent with a continuous decrease with time and increasing ΔGrof albite effective surface area linked to the formation of unreactive negative crystal facets, in addition to etch pits stopping nucleating above a critical value of ΔGr. Thus, the observed decrease in albite dissolution rate as equilibrium is approached is not linked primarily to the increase in the contribution of the backward reaction but rather to the decrease of the forward reaction rate in conjunction with the decrease in the density of reactive sites at the mineral surface.The results of this study show that the characterization of the effective surface area and its evolution with reaction time and chemical affinity is crucial to deriving robust dissolution rates of well-crystallized minerals like feldspars. Dissolution experiments in29Si spiked solutions of samples with different history and well-characterized effective surface area and surface morphology should help to better quantify the rate laws controlling silicate minerals weathering.
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