Commissariat à l'Énergie Atomique, CE Saclay, CEA/DEN/DANS/DPC/SECR, Laboratoire de Spéciation des Radionucléides et des Molécules, Bâtiment 391 PC 33, F-91191 Gif-sur-Yvette Cedex, France.
Water Res. 2012 Mar 1;46(3):731-40. doi: 10.1016/j.watres.2011.11.042. Epub 2011 Nov 22.
Adsorption of purified Aldrich humic acid (PAHA) onto α-Al(2)O(3) is studied by batch experiments at different pH, ionic strength and coverage ratios R (mg of PAHA by m(2) of mineral surface). After equilibration, samples are centrifuged and the concentration of PAHA in the supernatants is measured. The amount of adsorbed PAHA per m(2) of mineral surface is decreasing with increasing pH. At constant pH value, the amount of adsorbed PAHA increases with initial PAHA concentration until a pH-dependent constant value is reached. UV/Visible specific parameters such as specific absorbance SUVA(254), ratio of absorbance values E(2)/E(3) and width of the electron-transfer absorbance band Δ(ET) are calculated for supernatant PAHA fractions of adsorption experiments at pH 6.8, to have an insight on the evolution of PAHA characteristics with varying coverage ratio. No modification is observed compared to original compound for R ≥ 20 mg(PAHA)/g(α)(-)(A)1₂(O)₃. Below this ratio, aromaticity decreases with initial PAHA concentration. Size-exclusion chromatography - organic carbon detection measurements on these supernatants also show a preferential adsorption of more aromatic and higher-sized fractions. Spectrophotometric titrations were done to estimate changes of reactivity of supernatants from adsorption experiments made at pH ≈6.8 and different PAHA concentrations. Evolutions of UV/Visible spectra with varying pH were treated to obtain titration curves that are interpreted within the NICA-Donnan framework. Protonation parameters of non-sorbed PAHA fractions are compared to those obtained for the PAHA before contact with the oxide. The amount of low proton-affinity type of sites and the value of their median affinity constant decrease after adsorption. From PAHA concentration in the supernatant and mass balance calculations, "titration curves" are experimentally proposed for the adsorbed fractions for the first time. These changes in reactivity to our opinion could explain the difficulty to model the behavior of ternary systems composed of pollutants/HS/mineral since additivity is not respected.
用批实验法研究了在不同 pH 值、离子强度和覆盖率比 R（矿物表面每平方米毫克的 PAHA）下，纯化的 Aldrich 腐殖酸（PAHA）在α-Al(2)O(3)上的吸附。达到平衡后，将样品离心，测量上清液中 PAHA 的浓度。单位矿物表面积上吸附的 PAHA 量随 pH 值的增加而减少。在恒定 pH 值下，随着初始 PAHA 浓度的增加，吸附的 PAHA 量增加，直到达到依赖于 pH 值的恒定值。在 pH 值为 6.8 的吸附实验中，对上清液的 PAHA 分数进行 UV/Visible 特定参数（如比吸光度 SUVA(254)、吸光度值 E(2)/E(3)的比值和电子转移吸光度带的宽度Δ(ET)）的计算，以了解随覆盖率比变化时 PAHA 特性的演变。对于 R≥20mg(PAHA)/g(α)(-)(A)1₂(O)₃，与原始化合物相比，没有观察到任何修饰。在该比值以下，芳香度随初始 PAHA 浓度的增加而降低。对这些上清液进行的尺寸排阻色谱-有机碳检测测量也表明，更芳香和更高尺寸的分数优先吸附。分光光度滴定法用于估计在 pH≈6.8 和不同 PAHA 浓度下进行的吸附实验后上清液的反应性变化。通过处理随 pH 值变化的 UV/Visible 光谱的演变来获得滴定曲线，这些滴定曲线在 NICA-Donnan 框架内进行解释。未吸附 PAHA 分数的质子化参数与与氧化物接触前获得的参数进行比较。吸附后，低质子亲和型位点的数量和它们的中值亲和力常数的值减少。根据上清液中的 PAHA 浓度和质量平衡计算，首次实验提出了吸附分数的“滴定曲线”。我们认为，这种反应性的变化可以解释为什么在组成污染物/HS/矿物的三元系统中很难对行为进行建模，因为不遵守加和性。
