湘江衡阳段沉积物对硝态氮的吸附特性研究

Characteristics of adsorption of nitrate nitrogen for the sediment substances in Hengyang section of Xiang River

为探究沉积物对水体中硝态氮的吸附特性,以湘江衡阳段上游沉积物为研究对象,通过室内模拟吸附试验,探讨沉积物吸附硝态氮的影响因素、动力学规律及吸附等温线特征,并且利用SEM、FTIR等表征手段揭示吸附机理。结果表明,环境因素的改变会对硝态氮的吸附产生一定影响,泥水比的增大使沉积物的固体浓度效应明显,吸附量减小;硝态氮初始质量浓度越高,吸附量越大;温度越低越有利于沉积物对硝态氮的吸附;扰动速率偏高和偏低都会使吸附量减小。吸附过程在60 min后逐渐达到稳定,其吸附过程符合准二级动力学模型方程和Langmuir等温吸附方程,以化学吸附和单分子层吸附为主。SEM表征分析表明,沉积物呈粗糙多孔的片层结构,具有较多的吸附位点;FTIR表征分析表明,沉积物对硝态氮有一定的吸附作用,沉积物中含有羟基、酰基等多种基团,与硝态氮反应的机理主要表现为置换和吸附作用。

This essay attempts to present its study results on the adsorption characteristics of sediments on the nitrate nitrogen in water,with the sediments in the upper reaches of the Hengyang section of Xiang River as a case study sample. In the paper,the essay has done the investigation and determination of the influential factors,the kinetic laws and the adsorption isotherm characteristics of the sediment absorption of the nitrate nitrogen through the room-in simulated adsorption experiments so as to disclose its adsorption mechanism by means of SEM and FTIR. The results of our investigation and simulated experiments demonstrate that the change of the environmental factors may influence the adsorption of nitrate nitrogen to some extent. For example,with the increase of the sediment-water ratio,the solid content concentration rate would become more and more obvious while the adsorption capacity may tend to decrease. The higher the initial concentration of the nitrate nitrogen exists,the greater the adsorption capacity would be. On the contrary,the lower the temperature of the room is,the more favorable it will be for the sediment absorption of the nitrate nitrogen. Even if the disturbance rate can be too high or too low,the sediment adsorption capacity of nitrate nitrogen tends to get reduced. On the condition when the process of adsorption of the nitrate nitrogen by the sediment has been sped up,the rapid adsorption can be shortened to mere 10 min.,and,it would be possible for the stability of absorption to reach gradually merely in60 min. What is more,the aforementioned adsorption process tends to be done in line with the quasi-second order kinetic model equation and that of the Langmuir isotherm,which gives the priority to the chemical and monolayer adsorption. Thus,the SEM analysis shows that the surface layer of the sediment is rough and porous,whereas its lamellar structure is endowed with lots of adsorption sites,which is favorable for its adsorption. Further FTIR analysis demonstrates that the sediments may have a certain adsorption effect on the nitrate nitrogen in lots of functional groups,such as the hydroxyl group and the acyl group. Therefore,it can be concluded that the reaction mechanism between the functional groups and the nitrate nitrogen is mainly manifested in the reaction of substitution and adsorption.