Karlsruhe Institute of Technology (KIT) Institut für Nukleare Entsorgung, INE Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
Karlsruhe Institute of Technology (KIT) Institute of Meteorology and Climate Research - Atmospheric Aerosol Research - (IMKAAF), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
Geochem Trans. 2014 Jun 19;15:9. doi: 10.1186/1467-4866-15-9. eCollection 2014.
We have studied the impact of dissolved aluminum on interfacial properties of two aluminum bearing minerals, corundum and kaolinite. The effect of intentionally adding dissolved aluminum on electrokinetic potential of basal plane surfaces of sapphire was studied by streaming potential measurements as a function of pH and was complemented by a second harmonic generation (SHG) study at pH 6. The electrokinetic data show a similar trend as the SHG data, suggesting that the SHG electric field correlates to zeta-potential. A comparable study was carried out on kaolinite particles. In this case electrophoretic mobility was measured as a function of pH. In both systems the addition of dissolved aluminum caused significant changes in the charging behavior. The isoelectric point consistently shifted to higher pH values, the extent of the shift depending on the amount of aluminum present or added. The experimental results imply that published isoelectric points of clay minerals may have been affected by this phenomenon. The presence of dissolved aluminum in experimental studies may be caused by particular pre-treatment methods (such as washing in acids and subsequent adsorption of dissolved aluminum) or even simply by starting a series of measurements from extreme pH (causing dissolution), and subsequently varying the pH in the very same batch. This results in interactions of dissolved aluminum with the target surface. A possible interpretation of the experimental results could be that at low aluminum concentrations adatoms of aluminum (we will refer to adsorbed mineral constituents as adatoms) can form at the sapphire basal plane, which can be rather easily removed. Simultaneously, once the surface has been exposed to sufficiently high aluminum concentration, a visible change of the surface is seen by AFM which is attributed to a surface precipitate that cannot be removed under the conditions employed in the current study. In conclusion, whenever pre-treatment or the starting point of an experiment favor the dissolution of aluminum, dissolved Al may remain in the experimental system and interact with the target surfaces. The systems are then no longer pristine and points of zero charge or sorption data are those of aluminum-bearing systems.
我们研究了溶解态铝对两种含铝矿物刚玉和高岭石界面性质的影响。通过流动电势测量研究了有意添加溶解态铝对蓝宝石基面电动电势的影响，该研究还补充了 pH 值为 6 时的二次谐波产生 (SHG) 研究。电动数据显示出与 SHG 数据相似的趋势，表明 SHG 电场与 ζ 电位相关。对高岭石颗粒进行了类似的研究。在这种情况下，测量了电泳迁移率随 pH 值的变化。在这两种体系中，添加溶解态铝都会导致荷电行为发生显著变化。等电点始终向更高的 pH 值移动，移动的程度取决于存在或添加的铝量。实验结果表明，已发表的粘土矿物等电点可能受到了这一现象的影响。实验研究中溶解态铝的存在可能是由于特定的预处理方法（例如在酸中洗涤和随后吸附溶解态铝）造成的，甚至可能只是由于从极端 pH 值开始进行一系列测量（导致溶解），然后在同一系列中改变 pH 值。这会导致溶解态铝与目标表面发生相互作用。对实验结果的一种可能解释是，在低铝浓度下，铝的吸附原子（我们将吸附的矿物成分称为吸附原子）可以在蓝宝石基面形成，并且很容易被去除。同时，一旦表面暴露于足够高的铝浓度，原子力显微镜就会看到表面发生明显变化，这归因于在当前研究中采用的条件下无法去除的表面沉淀物。总之，只要预处理或实验的起始点有利于铝的溶解，那么溶解的 Al 可能会留在实验系统中并与目标表面相互作用。这样，系统就不再是原始状态，零电荷点或吸附数据就是含铝系统的零电荷点或吸附数据。
