针铁矿/水界面反应性的实验研究

选择针铁矿对Pb2+、Cu2+、Cd2+等3种重金属离子的吸附实验,开展矿物/水界面反应性研究.金属离子(M2+)在矿物-水溶液间分配有多种表面反应机制,这些表面反应发生作用的条件主要取决于吸附质水化学性质和矿物表面荷电性,因此,溶液pH值是影响矿物/水界面反应性的关键因素.在不同pH值条件下, 表面羟基可通过发生质子化或去质子化反应而使得矿物表面产生荷电性并发生改变,而金属离子的水解则可显著加快金属羟基配合物的形成,从而进一步增强了矿物/水界面反应.本实验条件下针铁矿表面对重金属离子的吸着量随pH值升高而升高,在一个较窄的pH值范围内吸附率急剧升高,呈S形分布.针铁矿对3种不同的重金属离子的吸附能力的强弱顺序是Cu2+＞Pb2+＞Cd2+.无论是Langmuir方程还是Freundlich方程,都能较好拟合针铁矿对重金属离子的等温吸附过程.Freundlich方程的n值均在0.1～0.5之间,说明重金属离子在针铁矿表面的吸附并不能简单地归结为单配位或双配位模式,可能存在着多种吸附结合形态.表观吸附常数KM值的变化规律,说明重金属离子与针铁矿表面反应模式及其表面吸附形态发生了变化,具体的吸附形态还有待谱学研究进一步证实.

An experimental study of goethite-water interface reaction

In this paper the authors studied the sorption of heavy metal ions Pb2+, Cu2+, Cd2+ on goethite as a case study of the mineral-water interface reaction. The prerequisite for the multi-reaction of heavy metal ions distributed on the mineral-water interface mainly depends on the hydrolyzation of the adsorbates and the electric charge of the sorbent. Thus the pH value becomes a key factor affecting the reaction of mineral-water interface. Under different pH conditions, the electric charges of the mineral surface varied when the ≡FeOH protonated or deprotonated and meanwhile, the metallic hydrolysis could greatly develop the formation of metal hydroxocomplexes and change the mineral-water interface reaction. Under the condition of this study, metal affinity for the goethite surface was examined as a function of pH. Typical S-shaped adsorption edges could be observed for all metals; with the increasing pH, adsorption increased from zero to almost 100% over a narrow pH range. The metal capacity followed the trend of Cu>Pb>Cd. The heavy metal ions sorption isotherms could be fitted well by Langmuir and Freundlich equations with correlation coefficients R＞0.91. The constants of Freundlich equations (n values) are between 0.1 and 0.5, indicating that the surface complexes are very complicated but not monodentate. The change of constant KM also indicates the existence of a variety of surface complexes on goethite surface with the increasing of the pH value.