Pagnanelli Francesca, Bornoroni Lorena, Moscardini Emanuela, Toro Luigi
Department of Chemistry, University of Rome La Sapienza, P.le A. Moro 5, 00185 Rome, Italy.
Chemosphere. 2006 May;63(7):1063-73. doi: 10.1016/j.chemosphere.2005.09.017. Epub 2005 Nov 8.
Potentiometric titrations and lead sorption tests were conducted using muscovite, clinochlore, hematite, goethite, quartz, and a mixture of these same minerals. Mechanistic models were developed to represent and interpret these data. The aim was isolating the specific contribution of each mineral in proton and lead binding. Acid-base properties of each single mineral as well as their mixture were represented by discrete models, which consider the dissociation of n monoprotic sites (n-site/n-K(H) models). A one-site/one-K(H) model (logK(H1) = 10.69) was chosen for quartz (dissociation of SiOH edge hydroxyl groups). Goethite and hematite (FeOH groups) were represented by the same one-site/one-K(H) model (logK(H1) = 10.35). Three-site/three-K(H) models were used for muscovite (logK(H1) = 4.18; logK(H2) = 6.65; logK(H3) = 9.67) and clinochlore (logK(H1) = 3.84; logK(H2) = 6.57; logK(H3) = 9.71) assuming that SiOH and AlOH of the aluminosilicate matrix dissociate in the acid-neutral pH range while SiOH groups of quartz inclusions dissociate in the basic range. Similarly, the mixture of these minerals was represented by a three-site/three-K(H) model (logK(H1) = 3.39; logK(H2) = 6.72; logK(H3) = 10.82). According to crossed comparisons with single minerals, the first two sites of the mixture were associated with the aluminosilicate matrix (SiOH and AlOH respectively) and the third site with iron oxides (FeOH) and quartz groups. Additivity of proton binding in the mixture was demonstrated by simulating the mixture's titration curve. A unified model for the entire set of titration curves (single minerals and mixture) was also developed introducing a three-peak distribution function for proton affinity constants. Experimental data for lead sorption onto the mixture and individual minerals in 3-5 pH range denoted the competition between protons and metallic ions. The entire set of lead isotherms (individual mineral and mixture data) was represented adequately by a unified model taking into account both monodentate and bidentate complexes with the three active sites (additivity of lead binding). Experimental data of metal distribution in solid and liquid phases were successfully simulated by implementing the protonation and the surface complexation constants into the database of a dedicated software for chemical equilibria.
使用白云母、斜绿泥石、赤铁矿、针铁矿、石英以及这些相同矿物的混合物进行了电位滴定和铅吸附试验。开发了机理模型来表示和解释这些数据。目的是分离出每种矿物在质子和铅结合中的特定贡献。每种单一矿物及其混合物的酸碱性质由离散模型表示，该模型考虑了n个单质子位点的解离（n位点/n-K(H)模型）。为石英（SiOH边缘羟基的解离）选择了单一位点/单一K(H)模型（logK(H1)=10.69）。针铁矿和赤铁矿（FeOH基团）由相同的单一位点/单一K(H)模型表示（logK(H1)=10.35）。假设铝硅酸盐基质的SiOH和AlOH在酸中性pH范围内解离，而石英包裹体的SiOH基团在碱性范围内解离，则为白云母（logK(H1)=4.18；logK(H2)=6.65；logK(H3)=9.67）和斜绿泥石（logK(H1)=3.84；logK(H2)=6.57；logK(H3)=9.71）使用了三位点/三个K(H)模型。同样，这些矿物的混合物由三位点/三个K(H)模型表示（logK(H1)=3.39；logK(H2)=6.72；logK(H3)=10.82）。根据与单一矿物的交叉比较，混合物的前两个位点分别与铝硅酸盐基质（SiOH和AlOH）相关，第三个位点与铁氧化物（FeOH）和石英基团相关。通过模拟混合物的滴定曲线证明了混合物中质子结合的加和性。还开发了一套完整滴定曲线（单一矿物和混合物）的统一模型，引入了质子亲和常数的三峰分布函数。在3-5 pH范围内铅吸附到混合物和单个矿物上的实验数据表明了质子和金属离子之间的竞争。考虑到与三个活性位点的单齿和双齿络合物（铅结合的加和性），一套完整的铅等温线（单个矿物和混合物数据）由一个统一模型充分表示。通过将质子化和表面络合常数应用于专用化学平衡软件的数据库中，成功模拟了固液相中金属分布的实验数据。
