Observations and modelling of the reactions of 10 metals with goethite:: adsorption and diffusion processes
Observations and modelling of the reactions of 10 metals with goethite:: adsorption and diffusion processes
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DOI：
10.1111/j.1365-2389.2007.00924.x
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发表时间：
2007-12-01
影响因子：
4.2
通讯作者：
Barrow, N. J.
中科院分区：
文献类型：
--
作者：
Fischer, L.;Bruemmer, G. W.;Barrow, N. J.
针铁矿的样品混合的时间范围从2小时到8周的稀硝酸盐的铅，汞，镉，锌，铜，镍，钴，锰，铬和铝的溶液。每个时期后的吸附量进行了测量为每个金属的适当的pH值范围。的吸附行为的特点是通过使用的吸附曲线，如pH值的一半的添加的金属被吸附（pH值（50）），并通过拟合的模型，其中吸附主要是由亲和常数和扩散常数的特点。初始吸附，无论是由pH值（50）或亲和常数的特点，是密切相关的适当的金属的解离常数。金属对氢氧根离子的亲和力越大，它们对针铁矿表面的亲和力就越大。这些金属继续与针铁矿反应的速率不同。铅的持续反应最慢，钴最快。持续的反应是由于扩散到颗粒中。其特征在于拟合的扩散常数和随时间的变化的pH值（50）。对于八种二价金属中的七种，这些与金属的离子半径相关：半径越大，反应越慢。对于Al和Cr，速率比从离子半径预期的要慢，我们认为这表明这些离子作为较大的M（OH）（2+）离子反应。Ni的行为与表面物种的氧化和Ni（OH）（2+）离子的扩散一致。这种持续的反应与金属离子与土壤反应时所观察到的相似，表明它们与铁氧化物的反应在土壤中很重要。研究结果还表明，在吸附测量仅在一个阶段的反应是不完整的，平衡模型的应用，这样的结果是误导。
A sample of goethite was mixed for periods which ranged from 2 hours to 8 weeks with solutions of dilute nitrate salts of Pb, Hg, Cd, Zn, Cu, Ni, Co, Mn, Cr and Al. The amount of sorption after each period was measured for an appropriate pH range for each metal. The sorption behaviour was characterized both by using characteristics of the sorption curves such as the pH at which half of the added metal was sorbed (pH(50)) and by fitting a model in which sorption was mainly characterized by an affinity constant and by a diffusion constant. Initial sorption, whether characterized by the pH(50) or by the affinity constant, was closely correlated with the appropriate dissociation constants of the metals. The greater the affinity of the metals for hydroxide ions, the greater their affinity for the goethite surface. The metals differed in the rate at which they continued to react with the goethite. Lead had the slowest continuing reaction, cobalt the fastest. The continuing reaction was due to diffusion into the particles. It was characterized by the fitted diffusion constant and by the change with time in the pH(50). For seven of the eight divalent metals, these were correlated with the ionic radius of the metals: the larger the radius, the slower the reaction. For Al and Cr, rates were slower than would be expected from the ionic radii and we suggest this shows that these ions react as the larger M(OH)(2+) ions. The behaviour of Ni was consistent with oxidation of the surface species and diffusion of Ni(OH)(2+) ions. The continuing reaction was similar to that observed when metal ions react with soils and suggests that their reaction with iron oxides is important in soils. The results also show that studies in which sorption is measured at only one period of reaction are incomplete and the application of equilibrium models to such results is misleading.