School of Environmental Science and Engineering, Sun Yat-Sen University, 135 Xingang Road West, Guangzhou 510275, China.
Chemosphere. 2011 Apr;83(3):302-10. doi: 10.1016/j.chemosphere.2010.12.056. Epub 2011 Jan 12.
Phenanthrene is commonly present together with heavy metals at many contaminated sites. This study investigated the influence of coexisting lead (Pb(2+)) or cadmium (Cd(2+)) on phenanthrene adsorption on soils. Batch experiments were conducted under different geochemical conditions including pH, mineral structure, organic matter content, and varying amounts of heavy metals. The results showed that the presence of heavy metals in solution at a fixed pH of 5.8±0.1 enhanced phenanthrene adsorption, the extent of which was closely related to the concentrations and the electro-negativity of the metals. The enhancement on phenanthrene adsorption was positively correlated to the amount of adsorbed metals. Although Cd(2+) is a softer Lewis acid, Pb(2+) displayed a more significant effect as it was adsorbed to a greater extent on the soil surfaces. Thus, density of cation accumulation appears to be more influential than metal softness in enhancing phenanthrene adsorption. Moreover, with a portion of organic matter removed by heating at 550°C, there was a stronger enhancement of phenanthrene adsorption by coexisting Pb(2+), indicating an increasingly dominant mechanisms associated with Pb(2+) at a lower organic matter content. Similar enhancement phenomenon was observed on bentonite and kaolinite, probably resulting from the cation-π bonding between the adsorbed soft metal cations and the aromatic ring of phenanthrene in solution. The desorption experiments further suggested that the bonding of phenanthrene adsorption was strengthened in the presence of Pb(2+) and that a larger proportion of adsorbed phenanthrene remained on the soils (residual fraction) even after sequential methanol extractions. Further spectroscopic analyses and surface characterization are required to provide direct evidence of the formation and relative significance of cation-π bond for phenanthrene adsorption.
菲是许多污染场所中普遍与重金属共存的物质。本研究调查了共存的铅（Pb(2+)）或镉（Cd(2+)）对土壤中菲吸附的影响。在不同地球化学条件下进行了批实验，包括 pH 值、矿物质结构、有机质含量和不同量的重金属。结果表明，在固定 pH 值为 5.8±0.1 的溶液中存在重金属会增强菲的吸附，其程度与金属的浓度和电负性密切相关。重金属的吸附量与吸附增强程度呈正相关。尽管 Cd(2+)是一种较软的路易斯酸，但 Pb(2+)的影响更为显著，因为它在土壤表面的吸附量更大。因此，阳离子堆积密度似乎比金属软度更能增强菲的吸附。此外，通过在 550°C 下加热去除一部分有机质，共存的 Pb(2+)会更强地增强菲的吸附，这表明在较低有机质含量下，与 Pb(2+)相关的机制变得越来越重要。在膨润土和高岭土上也观察到类似的增强现象，这可能是由于吸附的软金属阳离子与溶液中菲的芳香环之间存在阳离子-π 键。解吸实验进一步表明，在 Pb(2+)存在下，菲吸附的键合被增强，即使经过连续的甲醇提取，仍有较大比例的吸附菲留在土壤中（残留部分）。需要进一步的光谱分析和表面表征，以提供阳离子-π 键形成和相对重要性的直接证据，用于解释菲的吸附。
