A computer modeling study of the competitive adsorption of water and organic surfactants at surfaces of the mineral scheelite.
A computer modeling study of the competitive adsorption of water and organic surfactants at surfaces of the mineral scheelite.
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DOI：
10.1021/la049796w
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发表时间：
2004-04
期刊：
影响因子：
--
通讯作者：
T. G. Cooper;N. D. de Leeuw
中科院分区：
文献类型：
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作者：
T. G. Cooper;N. D. de Leeuw
采用原子计算机模拟技术研究了一系列有机表面活性剂分子与白钨矿表面的相互作用。吸附物主要通过其氧（或氮）原子与表面钙离子之间的相互作用与表面配位，然后通过与表面氧离子的氢键相互作用与表面配位。两个表面钙离子之间的桥接是优选的吸附模式，但两个吸附质氧离子对同一表面钙离子的双齿相互作用也是稳定的构型，并且表面和吸附质分子之间的多重相互作用导致最大的吸附能。所有含有羰基和羟基的吸附物与表面强烈相互作用，释放约80 - 170 kJ mol（-1）的能量，但仅含有-NH 2官能团的甲胺吸附到表面的程度要小得多（55-86 kJ mol（-1））。羟基甲酰胺和羟基乙醛都以重叠构象吸附在某些表面上，这是这些官能团的必要条件。吸附的有机材料通过更换预吸附水在不同的表面功能计算为主要是放热的甲酸，但较少的羟基甲酰胺和羟基乙醛分子，而甲胺不会取代预吸附水在白钨矿表面。因此，计算出表面活性剂分子的功效为羧酸>烷基异羟肟酸酯>羟基醛>烷基胺。从这项研究的结果表明，计算机模拟可以提供一种途径，以识别，甚至设计特定的有机表面活性剂用于矿物分离过程。
Atomistic computer simulation techniques were employed to investigate the interaction of a selection of organic surfactant molecules with a range of scheelite surfaces. The adsorbates coordinate mainly to the surfaces through interaction between their oxygen (or nitrogen) atoms to surface calcium ions, followed by hydrogen-bonded interactions to surface oxygen ions. Bridging between two surface calcium ions is the preferred mode of adsorption, but a bidentate interaction by two adsorbate oxygen ions to the same surface calcium ion is also a stable configuration and multiple interactions between surfaces and adsorbate molecules lead to the largest adsorption energies. All adsorbates containing carbonyl and hydroxy groups interact strongly with the surfaces, releasing energies between approximately 80 and 170 kJ mol(-1), but methylamine containing only the -NH2 functional group adsorbs to the surfaces to a much lesser extent (55-86 kJ mol(-1)). Both hydroxymethanamide and hydroxyethanal adsorb to some surfaces in an eclipsed conformation, which is a requisite for these functional groups. Sorption of the organic material by replacement of preadsorbed water at different surface features is calculated to be mainly exothermic for methanoic acid, but less so for the hydroxymethanamide and hydroxyethanal molecules, whereas methylamine would not replace preadsorbed water at the scheelite surfaces. The efficacy of the surfactant molecules is hence calculated to be carboxylic acids > alkyl hydroxamates > hydroxyaldehydes > alkylamines. The results from this study suggest that computer simulations may provide a route to the identification or even design of particular organic surfactants for use in mineral separation processes.