Pagnanelli Francesca, Bornoroni Lorena, Toro Luigi
Department of Chemistry, University of Rome La Sapienza, Ple A Moro, 5, 00185 Rome, Italy.
Environ Sci Technol. 2004 Oct 15;38(20):5443-9. doi: 10.1021/es049760q.
In this paper a methodological approach is proposed to validate mechanistic modeling for proton binding onto active sites of mineral and soil samples by reducing the uncertainty and arbitrariness of model schematization. This approach is based on the quantitative formulation (X-ray calibration method) of a simulating mineral mixture (SMM) accounting for the main mineral phases in the soil (quartz, goethite, hematite, muscovite, clinochlore). Mineral and organic contributions were separated by comparing titration curves of river sediment and SMM. Specific mineral contributions to the acid properties of SMM were separated by comparing titration models of SMM and single minerals. Different nonelectrostatic models were used for titrations of SMM and single minerals: two-site/three-KH models (one amphoteric plus one monoprotic site) for clay minerals and SMM; one-site/two-KH models (one amphoteric site) for goethite and hematite; and a one-site/one-KH model (one monoprotic site) for quartz. Crossed-comparisons of titration models allow for identifying and quantifying the specific contributions of the distinct edge hydroxyl groups of iron oxides, clay minerals, and quartz in the different pH ranges. In particularthe amphoteric sites of aluminosilicates mainly contribute in the acid-neutral pH range, the amphoteric sites of iron oxides take part in the neutral-basic range, and finally the monoprotic edge hydroxyl groups of quartz react in the upper basic region of pH. The good simulation of the acid-base properties of SMM (according to single mineral titration models and quantitative composition by X-ray) confirms both model schematization and SMM formulation. Speciation diagrams of the active sites of the different mineral components (aluminosilicates, iron oxides, and quartz) were obtained by implementing the database of a dedicated software with the apparent equilibrium constants regressed by titration modeling of single minerals.
本文提出了一种方法，通过减少模型构建的不确定性和随意性，来验证质子与矿物和土壤样品活性位点结合的机理模型。该方法基于一种模拟矿物混合物（SMM）的定量公式（X射线校准法），该混合物考虑了土壤中的主要矿物相（石英、针铁矿、赤铁矿、白云母、绿泥石）。通过比较河流沉积物和SMM的滴定曲线来分离矿物和有机成分。通过比较SMM和单一矿物的滴定模型来分离特定矿物对SMM酸性性质的贡献。SMM和单一矿物的滴定使用了不同的非静电模型：粘土矿物和SMM使用双位点/三KH模型（一个两性位点加一个单质子位点）；针铁矿和赤铁矿使用单位点/双KH模型（一个两性位点）；石英使用单位点/单KH模型（一个单质子位点）。滴定模型的交叉比较允许识别和量化不同pH范围内铁氧化物、粘土矿物和石英不同边缘羟基的特定贡献。特别是，铝硅酸盐的两性位点主要在酸性至中性pH范围内起作用，铁氧化物的两性位点在中性至碱性范围内起作用，最后石英的单质子边缘羟基在较高的碱性pH区域发生反应。SMM酸碱性质的良好模拟（根据单一矿物滴定模型和X射线定量组成）证实了模型构建和SMM公式。通过使用专用软件的数据库，并结合通过单一矿物质滴定建模回归得到的表观平衡常数，获得了不同矿物成分（铝硅酸盐、铁氧化物和石英）活性位点的形态图。
