Dissolution of well and poorly crystallized kaolinites: Al speciation and effects of surface characteristics
Dissolution of well and poorly crystallized kaolinites: Al speciation and effects of surface characteristics
复制标题
良好和不良结晶高岭石的溶解：铝形态和表面特性的影响
DOI：
10.2138/am-1999-0415
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发表时间：
1999
影响因子：
3.1
通讯作者：
Qunhui Zhou
中科院分区：
文献类型：
--
作者：
S. Sutheimer;P. Maurice;Qunhui Zhou
摘要本研究比较了结晶良好(KGa-1b)和结晶不良(KGa-2)高岭石标准样品的表面特征和溶解行为。原子力显微镜(AFM)显示，KGa-1b颗粒一般具有良好的六方微观形貌和结晶可控的微形貌特征。KGa-2的颗粒也是六方的，但其微观形态趋向于更圆。基面表面往往更加不规则，具有更少的明显的结晶控制特征。KGa-1b颗粒往往比KGa-2颗粒直径大、厚度大。微观形态测量表明，KGa-1b和KGa-2都有大约0.1(平均值~0.2)的模式边缘与总表面积之比，尽管这些测量没有包括潜在的大的基面台阶边缘的贡献(额外的20%或更多)。在pH 3，22°C，I=0.01M的条件下，在草酸和无机酸中进行了溶出实验。KGa-2在1 mM草酸中的溶解速度(以硅释放衡量)大约是KGa-1b的两倍(2.27比0.96nmol/m2·h)。KGa-2和KGa-1b在硝酸溶液中的反应速率相似(分别为0.86和1.16nmol/m2·h)。Wieland和Stumm(1992)研究的这两种沉积高岭石和一种热液高岭石的可比速率表明，高岭石的基本结构而不是特定的表面细节对溶解动力学的影响最大。用高效阳离子交换色层(HP-CEC)测定了高岭石溶解过程中单体铝形态的分布。对于在1 mM草酸盐中的溶解，观察到几乎完全与平衡形态计算结果一致的草酸铝。对于在HNO_3中的溶解，如计算所预测的那样，代表未络合Al物种的峰Alf占优势，但不是唯一的。具有+2电荷物种保留时间特征的峰可能是Alosi(OH)32+物种的证据，值得进一步研究。
Abstract This study compared surface characteristics and dissolution behavior of well-crystallized (KGa-1b) and poorly crystallized (KGa-2) kaolinite standards. Atomic force microscopy (AFM) revealed that particles of KGa-1b generally have nicely hexagonal micromorphology and crystallographically controlled microtopographic features. Particles of KGa-2 are also hexagonal, but their micromorphology tends to be more rounded. Basal-plane surfaces tend to be more irregular with fewer clearly crystallographically controlled features. KGa-1b particles tend to be larger in diameter and thicker than KGa-2 particles. Micromorphologic measurements showed that both KGa-1b and KGa-2 have modal edge- to total surface-area ratios of approximately 0.1 (mean ~ 0.2), although these measurements did not include the potentially large contribution of basal-plane step edges (additional 20% or more). Dissolution experiments were conducted in oxalic acid and inorganic acids at pH 3, 22 °C, I = 0.01 M, under batch dissolution conditions. Dissolution rates (measured as Si release) in 1 mM oxalic acid were approximately twice as fast for KGa-2 as for KGa-1b (2.27 vs. 0.96 nmol/m2·h). Rates for KGa- 2 and KGa-1b were similar in HNO3 (0.86 and 1.16 nmol/m2·h, respectively). The comparable rates for these two sedimentary kaolinites and for a hydrothermal kaolinite studied by Wieland and Stumm (1992) suggests that the fundamental structure of kaolinite, rather than specific surface details, exerts the greatest influence on dissolution kinetics. High-performance cation exchange chromatography (HP-CEC) was used to determine the distributions of monomeric Al species over the course of kaolinite dissolution. For dissolution in 1 mM oxalate, Al-oxalates were observed almost exclusively in agreement with results of equilibrium speciation calculations. For dissolution in HNO3, the peak representing uncomplexed Al species, Alf, was predominant but not exclusive, as predicted by calculations. A peak having a retention time characteristic of species with +2 charge may be evidence for an AlOSi(OH)32+ species, and warrant further investigation.