原位固化黑荆树皮对Cr(Ⅵ)吸附性能的研究

Adsorption of Cr (VI) by in-situ immobilized black wattle bark

通过甲醛的交联作用使单宁分子在黑荆树树皮内形成相互交联的大分子,低成本地制成原位固化黑荆树皮,用于吸附溶液中的Cr(VI)。结果表明,原位固化黑荆树皮对Cr(VI)的吸附量随体系pH值的增加而减小,随Cr(VI)初始浓度和温度的升高而增加。在284K、吸附4h条件下,pH=1.96时原位固化黑荆树皮对Cr(VI)的吸附容量是pH=5.10时的2.7倍;pH=2.0时,Cr(VI)初始质量浓度从30mg/L升高到120mg/L,吸附容量由30.0mg/g增大到100.1mg/g;溶液温度从284K升高到298K,吸附容量由76.2mg/g增大到94.2mg/g。原位固化黑荆树皮对Cr(VI)的吸附动力学可以用拟二级速度方程来描述。吸附前后的原位固化黑荆树皮红外谱图表明,Cr(VI)可能先被还原成Cr(Ⅲ),再与原位固化黑荆树皮中酚羟基螯合而被吸附。

This article intends to study the adsorption behavior of the modified bark to Cr（Ⅵ ） ions in aqueous solution. For this purpose, we have investigated the tannins in the bark by cross-linking reaction of formaldehyde so as to make the so-called initu immobilized black wattle bark. The results of our investigation indicate that such black wattle bark can be made into a fine agent for adsorbing Cr（Ⅵ） ions. Its actual adsorption capacity tested was 56.8 mg/L under the condition of 30.5 mg/L of the initial concentration of Cr（ Ⅵ ）, with the pH value of 1.96 and adsorption time of 4 h at 284 K. Further experi- ments prove that the amount of Cr （Ⅵ） ions adsorbed by the bark tends to decrease with the increase of pH, but tends to increase with the increase of initial concentration of Cr（ Ⅵ ）. Moreover, it was proven that its adsorption capacity to Cr（ Ⅵ） at the pH value of 1.96 would increase by 1.7 time as compared to that at the pH value of 5.10 under the condition of 284 K and the adsorption time of 4 h. Since the amount of Cr（Ⅵ ） adsorbed by the bark tends to increase with the increase of temperature. And, when the adsorption of the bark to Cr（ Ⅵ ） under the experimental conditions can also be taken as a chemical adsorption mechanism. Moreover, the data of the adsorption rate proves well fitted by the pseudo-second-order rate model. Thus, the IR spectra of the bark before and after the above said adsorption may suggest that Cr（ Ⅵ ） ions may first of all reduce to Cr （ Ⅲ）, and then be absorbed by the hydroxyl groups in the bark.