As(Ⅲ)和As(Ⅴ)在骨炭中迁移行为的对流扩散模型研究

Study on the migration behaviors of As(Ⅲ)and As(Ⅴ) in the bone char using the onedimensional convection-dispersion equation

采用一维对流扩散模型对比分析了As（Ⅲ）和As（Ⅴ）在骨炭中的迁移行为，并开展解吸试验。结果表明，1）Langmuir等温吸附模型能够很好地描述批试验吸附数据，As（Ⅲ）和As（Ⅴ）的最大吸附量（q max ）分别为0.827 mg/g和0.337 mg/g。2）骨炭对As（Ⅲ）和As（Ⅴ）的滞留能力随循环次数增加而降低，用对流扩散模型拟合试验数据获得的滞留因子表明As（Ⅴ）的滞留能力是As（Ⅲ）的1.38-2.20倍。3）共存阳离子在骨炭表面能够形成包覆层，从而增强了骨炭对As（Ⅲ）和As（Ⅴ）的滞留能力，其中Mn^2＋ 强于Al^3＋ ；共存阴离子会降低As（Ⅲ）和As（Ⅴ）的滞留能力，其SiO 2- 3 和PO 3- 4 分别对As（Ⅲ）和As（Ⅴ）影响最强。4）0.1 mol/L的NaOH解吸能力要强于蒸馏水，As（Ⅴ）的解吸程度高于As（Ⅲ），3次累计解吸平均值分别为0.59和0.41。

The article is aimed to introduce our One-Dimensional Convection-Dispersion Equation for analyzing the migration behaviors of As（Ⅲ） and As（Ⅴ） in the bone char and the corresponding desorption experiments we have performed. The results of our investigation and experiments show that： （1） It is possible for Langmuir model to be used to describe the batch experimental data appropriately and achieve the corresponding correlation coefficients R ^2 are 0.98 for As（Ⅲ） and 0.97 for As（Ⅴ）. The obtained maximum adsorption capacities q max of As（Ⅲ） and As（Ⅴ） turned out to be 0.827 and 0.337 mg/g, respectively. （2） The result of the adsorption cycle experiments for single As（Ⅲ） and As（Ⅴ） shows that the capacity for retarding the bone char on As（Ⅲ） and As（Ⅴ） tends to decrease with the increase of the adsorption cycles. And the retardation factors of As（Ⅴ） worked out by the convection-dispersion equation model for the three continuous times are equal to 50.62, 45.99 and 31.51, that is, 1.38-2.20 times as high as that of As（Ⅲ）. （3） The experiments with Mn^ 2＋ and Al^ 3＋ coexisting cations show that it is possible for the coexisting cations to improve the capacities of retardation of bone char on As（Ⅲ） and As（Ⅴ）, with Mn ^2＋ presenting stronger effects than Al ^3＋ , and the capacities of retardation of bone char on As（Ⅴ） being stronger than As（Ⅲ）. At the same time, we have done careful observation of the ＂concave＂ zone in the breakthrough curves of experiments of As（Ⅴ） due to the ＂secondary adsorption＂. Thus, it has been found that the concave zone of breakthrough curves for experiments of Al ^3＋ coexisting cations tends to come out earlier than Mn^2＋ . In addition, the effects of anions on the breakthrough curves can obviously be different from cations, for the coexisting anions would act competitively with As（Ⅲ） and As（Ⅴ） due to their similar molecular structure and electrostatic adsorption feature, especially, those of PO4^3- . （4） The re-adsorptive ability of bone char filling column decreases from^21.28 mg to 13.09 mg and 21.90 mg to 13.62 mg for As（Ⅲ） and As（Ⅴ） with adsorption times, respectively. Therefore, the desorption of 0.1 mol/L NaOH solution proves to be much better than the distilled water. In addition, the mean cumulative desorption degrees should be 0.59 and 0.41 for As（Ⅴ） and As（Ⅲ）, respectively.