Meng Qing-Jun, Zhang Yan, Feng Qi-Yan, Zhang Shuang-Sheng
Jiangsu Key Laboratory of Resources and Environmental Information Engineering, China University of Mining and Technology, Xuzhou 221116, China.
Huan Jing Ke Xue. 2011 Nov;32(11):3357-64.
Isothermal adsorption experiment was used to study the adsorbing process of NH4(+) -N in quartz sands under the conditions with and without humic acid; the Langmuir and Freundlich equations were used to fit the absorption result and the maximum adsorption capacity of NH4(+) -N by quarts sands was calculated. Through the soil column experiments, the concentration of NH4(+) -N, NO3(-) -N and NO2(-) -N in effluent water in the tested soil column was investigated, and the effect of humic acid on migration and transformation of NH4(+) -N in saturated aquifer was analyzed, and Pseudo-second-order Kinetics Equation and Two-step Adsorption Kinetics Rate Equation were applied to fit the kinetic processes. The results showed that both Langmuir and Freundlich models can well describe the isothermal adsorption process of NH4(+) -N on the surface of quartz sands, which means that NH4(+) -N adsorbed by the quartz sand was mainly in the form of monolayer adsorption. The humic acid could increase the adsorption capacity of NH4(+) -N on quartz sand, and the saturated adsorption capacity was 0.354 mg x g(-1) under the condition with humic acid and 0.205 mg x g(-1) with the absence of humic acid. The experiment indicated that humic acid increased the adsorption capacity of NH4(+) -N on the surface of quartz sand by increasing adsorption space in the initial stage. After saturation, humic acid influenced the migration and transformation of NH4(+) -N to NO3(-) -N and NO2(-) -N probably through providing carbon source and energy for microorganisms such as nitrifying bacteria and then resulting in lower NH4(+) -N concentration in effluent water. Both Pseudo-second-order Kinetics Equation and Two-step Adsorption Kinetics Rate Equations can well describe the process of NH4(+) -N adsorption kinetics on quartz sand (R2 = 0.997 7 and R2 = 0.998 1 with humic acid; R2 = 0.992 3 and R2 = 0.994 4 without humic acid), indicating that this process was chemical adsorption. By comparing the adsorption rate coefficient of Two-step Adsorption Kinetics Rate Equation k3 (0.247 and 0.143, respectively) and k4 (0.006 27 and 0.001 7) between the treatments with and without humic acid, it can be referred that NH4(+) -N was non-orientated adsorption on active points of the quartz sand at the initial stage, and the humic acid could increase the equilibrium adsorption quantity(q(e)) of NH4(+) -N on quartz sands.
采用等温吸附实验研究了有无腐殖酸条件下石英砂对NH4(+) -N的吸附过程；利用Langmuir和Freundlich方程对吸附结果进行拟合，并计算了石英砂对NH4(+) -N的最大吸附量。通过土柱实验，考察了受试土柱中出水的NH4(+) -N、NO3(-) -N和NO2(-) -N浓度，分析了腐殖酸对饱和含水层中NH4(+) -N迁移转化的影响，并应用准二级动力学方程和两步吸附动力学速率方程对动力学过程进行拟合。结果表明，Langmuir模型和Freundlich模型均能很好地描述NH4(+) -N在石英砂表面的等温吸附过程，即石英砂对NH4(+) -N的吸附主要为单分子层吸附形式。腐殖酸可提高石英砂对NH4(+) -N的吸附量，有腐殖酸条件下的饱和吸附量为0.354 mg x g(-1)，无腐殖酸条件下为0.205 mg x g(-1)。实验表明，腐殖酸在初始阶段通过增加吸附空间提高了石英砂表面对NH4(+) -N的吸附量。饱和后，腐殖酸可能通过为硝化细菌等微生物提供碳源和能量，进而影响NH4(+) -N向NO3(-) -N和NO2(-) -N的迁移转化，导致出水中NH4(+) -N浓度降低。准二级动力学方程和两步吸附动力学速率方程均能很好地描述石英砂对NH4(+) -N的吸附动力学过程（有腐殖酸时R2 = 0.997 7和R2 = 0.998 1；无腐殖酸时R2 = 0.992 3和R2 = 0.994 4），表明该过程为化学吸附。通过比较有无腐殖酸处理的两步吸附动力学速率方程的吸附速率系数k3（分别为0.247和0.143）和k4（分别为0.006 27和0.001 7），可以推断出NH4(+) -N在初始阶段在石英砂活性位点上为非定向吸附，且腐殖酸可提高石英砂对NH4(+) -N的平衡吸附量(q(e))。
