溶液化学环境对给水厂废弃铁铝泥吸附草甘膦的影响

Effects of solution chemistry on glyphosate adsorption by Fe/Al drinking water treatment residuals

考察了给水厂废弃铁铝泥(ferric and alum water treatment residuals,FARs)对有机磷农药草甘膦的吸附特征,探究了溶液初始p H、阳离子种类及其离子强度、磷酸盐和小分子有机酸浓度等对FARs吸附草甘膦的影响。研究结果表明:FARs对草甘膦的吸附较符合伪二级动力学模型(R2=0.942),Freundlich方程能较好地描述FARs对草甘膦的等温吸附过程(R2=0.994),其草甘膦吸附容量KF值达10.35,是已报道铝泥的2倍。溶液化学环境对FARs吸附草甘膦影响较大,随着溶液p H的增加,FARs对草甘膦的吸附量显著降低。与K+相比,Ca2+的存在能显著提高草甘膦的吸附量。此外,溶液中小分子有机酸(苹果酸和柠檬酸)对FARs吸附草甘膦存在明显的抑制作用,且抑制作用随着有机酸浓度的升高而增强。解吸实验结果进一步表明FARs吸附的草甘膦能稳定存在,不易被溶液中的磷酸盐所取代。

In this study, the characteristics of glyphosate sorption by ferric and alum water treatment resid- uals （FARs） were investigated. Additionally, the effects of the solution pH, ionic strength, and background e- lectrolyte, phosphate, and low molecular-weight organic acids （LMWOAs） concentrations were evaluated to elu- cidate the effects of solution chemistry on glyphosate sorption by FARs. The results showed that the kinetics data fitted well with the pseudo-second order model （R2 = 0. 942） , and the equilibrium data can be described by the Freundlich isotherm model （R2 = 0. 994）. Further analysis indicated that the adsorption capacity of FARs for glyphosate （KF = 10.35） is twice that reported for dewatered alum sludge. Moreover, the adsorption behavior of glyphosate on FARs is significantly affected by the solution chemistry： as the solution pH increased, the amount of glyphosate adsorbed drastically decreased. In contrast to K ＋, the presence of Ca2＋ promoted glyphosate ad- sorption. Additionally, LMWOAs （i. e., malic acid and critic acid） inhibited the adsorption of glyphosate on FARs, with a linear decrease in adsorption with increasing LMWOA concentration. Desorption experiment results further showed that glyphosate adsorbed by FARs was very stable and not easily replaced by the phosphate in so- lution.