载铁活性炭对水中草甘膦吸附性能研究

通过浸渍-焙烧法制备载铁活性炭,并用SEM电镜分析了载铁活性炭表面形态,研究了载铁活性炭(Fe-AC)对草甘膦溶液的吸附等温线和吸附动力学,并分析了各种影响因素对载铁活性炭吸附性能的影响.实验表明,Freundlich方程可以对Fe-AC草甘膦吸附等温线进行很好拟合,最大吸附量约为5.8mmol/g;其吸附动力学过程用Lagergren方程拟合,吸附速率常数在0.088min-1左右,且随着温度的升高逐渐减小.根据Kannan & Sundaram颗粒内扩散模型拟合,颗粒内扩散速率常数kp大于10mg·min-1/2/g,并随着起始温度的升高而减小.由于草甘膦的存在形态和Fe-AC材料表面性质的变化,AC-Fe对草甘膦的吸附能力随水溶液的pH升高而降低.NaCl的存在产生拮抗效应使得Fe-AC对草甘膦的吸附容量大大下降,随着NaCl浓度增加至4g/L后,盐析效应开始占主导地位,使得Fe-AC的吸附容量略有增加;由于草甘膦分子的空间位阻效应和亚磷酸根与载铁活性炭表面形成较强的络合物,使得随亚磷酸根浓度的升高Fe-AC对草甘膦的吸附量持续下降.

Glyphosate adsorption by ferric supported active carbon

Ferric supported active carbon was prepared by impregnation-calcination method and the characteristics of its surface were investigated by scanning electron magnification (SEM), and both adsorption isotherm and adsorption kinetics of Fe-AC were studied. The effects of different factors on the adsorption process were also studied. Freundlich equation fitted well to supported ferric active carbon adsorption isotherm, the maximum adsorption capacity was 5.8mmol/g; and the adsorption kinetics was fitted well by Lagergren equation, so adsorption rate constant can be calculated out 0.088min-1 that can decrease with the temperature increase. According to Kannan & Sundaram internal diffusion model, the internal diffusion constant was higher than 10mg·min-1/2/g, which decreased with the temperature increase. Due to the ionization form of glyphosate and the change of Fe-AC surface characteristics, the adsorption capacity of glyphosate decreased when the pH of solution increased. Antagonistic effect caused the adsorption capacity decrease of Fe-AC due to the existence of NaCl, and when the concentration of NaCl reached 4g/L, salting-out effect became dominant, which increased the adsorption capacity slightly. Because of the steric hindrance of glyphosate and the complex formation between phosphate and supported ferric active carbon surface, the Fe-AC adsorption capacity decreased continuously while the concentration of phosphate increase.