The use of a surface complexation model to describe the kinetics of ligand-promoted dissolution of anorthite
The use of a surface complexation model to describe the kinetics of ligand-promoted dissolution of anorthite
复制标题
DOI：
10.1016/0016-7037(88)90146-9
复制
发表时间：
1988-12
影响因子：
5
通讯作者：
C. Amrhein;D. Suarez
中科院分区：
文献类型：
--
作者：
C. Amrhein;D. Suarez
在控制pH和co2的条件下，研究了氟和草酸存在下钙长石（CaAl2Si208）的溶解。在pH 5 ~ 9之间，钙长石在无配体的情况下的溶解几乎与pH无关。形成络合物的配体的存在导致溶解速率随溶液ph的降低而线性增加。溶解数据采用反应速率与活化位点的表面浓度成正比的理论进行建模。表面活化位点是由质子和络合配体的吸附形成的。在钙长石上，质子促进的活化位点可能以Si为中心，而配体促进的活化位点可能以Al为中心。为了描述整个反应，将两个表面化学模型结合起来。在pH值小于4.2时，质子促进溶解的速率与toΓ4成线性比例，其中Γ为吸附质子的表面浓度。发现配体促进的溶解速率与吸附配体的表面浓度成线性关系。这些发现表明，对于大多数自然体系，pH和络合配体对长石溶解具有协同作用。自然界观察到富钙斜长石比富钠长石耐风化性差，这可归因于有机配体对富钙长石的反应性增强。反应性的提高是由于钙长石中Al含量的增加。
The dissolution of anorthite (CaAl2Si208) in the presence of fluoride and oxalate was studied under controlled pH and CO2conditions. The dissolution of anorthite in the absence of complex-forming ligands was nearly pH independent between pH 5 and 9. The presence of complex-forming ligands resulted in a dissolution rate that increased linearly with decreasing solution pH. The dissolution data were modeled using the theory that the reaction rate is proportional to the surface concentration of activated sites. Surface activated sites are formed by the adsorption of protons and complexing ligands. On anorthite, the proton-promoted activated sites are probably Si centered and the ligand-promoted activated sites Al centered. Two surface chemistry models were combined in order to describe the overall reaction. At pH values less than 4.2, the rate of the proton-promoted dissolution was linearly proportional toΓ4, where Γ is the surface concentration of adsorbed protons. The rate of the ligand-promoted dissolution was found to be linearly related to the surface concentration of adsorbed ligand.These findings suggest that for most natural systems, pH and complexing ligands have a synergistic effect on feldspar dissolution. The observation in nature that Ca-rich plagioclase feldspars are less resistant to weathering than Na-rich feldspars can be attributed to the increased reactivity of organic ligands towards Ca-rich feldspars. The increased reactivity is attributed to the higher proportion of Al in the Ca-feldspars.