Research on Ca²⁺ adsorption onto the mineral surface is of significant importance with regard to geochemical processes. Sverjensky (Geochim Cosmochim Acta 70(10), 2427–2453, 2006) assumed that alkaline earths form two types of surface species on oxides: tetranuclear (> SOH)₂(> SO⁻)₂_M(OH)⁺ and mononuclear > SO⁻_M(OH)⁺. To look into the above assumption we investigated calcium adsorption on SiO₂ and Al₂O₃ because they are the most widespread minerals in the environment. We have determined the proton surface charge, electrokinetic potential and metal adsorption as a function of pH. The Ca²⁺ uptake and concentration in the system were monitored by the calcium ion-selective electrode (Ca-ISE). The Ca-ISE measurements indicated a similar affinity of Ca²⁺ for both materials despite their differently charged surface, negative for silica and mainly positive for alumina. This may suggest that simple electrostatic interactions are not the primary driving force for calcium adsorption, and that solvation of calcium ions at the surface may be crucial. We have analyzed our experimental data using the 2-pK triple-layer model (2-pK TLM). Three calcium complexes on the mineral surface were reported. Two of them were the same for both oxides, i.e. the tetranuclear (\(>\) SOH)₂(\(>\) SO⁻)₂_Ca²⁺ and mononuclear complexes > SO⁻_CaOH⁺. Additionally, minor contribution from >SOH…Ca²⁺ for silica was assumed. In the case of Al₂O₃ the hydrolyzed tetranuclear complexes (\(>\) SOH)₂(\(>\) SO⁻)₂_CaOH⁺ at pH > 7.5 occurred based on the modeling results. Two types of surface complexes suggested by Sverjensky allowed for the correct description of proton and calcium uptake for alumina. However, the electrokinetic data excluded hydrolyzed tetranuclear surface species for this oxide.

对于地球化学过程，研究Ca ²⁺吸附到矿物表面上具有重要意义。Sverjensky（Geochim Cosmochim ACTA 70（10），2427至2453年，2006年）认为碱土金属形成两种类型的氧化物表面物质：四核（> SOH）₂（> SO ^- ）₂ _M（OH）⁺和单核> SO ⁻ _M（OH）⁺。为了研究上述假设，我们研究了钙在SiO ₂和Al ₂ O ₃上的吸附因为它们是环境中分布最广泛的矿物。我们已经确定了质子表面电荷，电动势和金属吸附随pH的变化。通过钙离子选择电极（Ca-ISE）监控系统中Ca ^2+的吸收和浓度。Ca-ISE测量表明Ca ²⁺具有相似的亲和力对于两种材料，尽管它们的带电表面不同，但对二氧化硅为负，对氧化铝主要为正。这可能表明简单的静电相互作用不是钙吸附的主要驱动力，并且表面上钙离子的溶剂化可能至关重要。我们已经使用2-pK三层模型（2-pK TLM）分析了我们的实验数据。据报道，矿物表面有三种钙配合物。它们中的两个是用于两种氧化物是相同的，即，四核（\（> \）  SOH）₂（\（> \）  SO ^- ）₂ _CA ²⁺和单核配合> SO ^- _CaOH ⁺。此外，> SOH…Ca ^2+的贡献很小假定为二氧化硅。在Al的情况下，₂ Ó ₃水解的四核配合物（\（> \）  SOH）₂（\（> \）  SO ^- ）₂ _CaOH ⁺在pH> 7.5发生基于该模拟结果。Sverjensky建议使用两种类型的表面配合物来正确描述氧化铝的质子和钙吸收。但是，电动数据排除了该氧化物的水解四核表面物质。