炭化小麦秸秆对水中氨氮吸附性能的研究

用直接炭化法制备了小麦秸秆吸附剂,并通过静态吸附试验研究了炭化小麦秸秆对氨氮的吸附性能和影响因素。结果表明:直接炭化法制备小麦秸秆吸附剂的最佳炭化温度为300℃;在试验的pH值范围内,pH=9时炭化小麦秸秆对氨氮的吸附去除最好;300℃时炭化小麦秸秆吸附不同质量浓度(ρ=30 mg/L、50 mg/L、100 mg/L)氨氮的动力学曲线符合准二级动力学模型,吸附常数k2分别为0.681 8g/(mg.min)、0.747 4 g/(mg.min)、1.025 0 g/(mg.min);直接炭化小麦秸秆吸附剂对氨氮吸附去除的最佳温度是30℃;不同温度下的吸附等温线可用Freundlich吸附等温方程进行拟合;由吸附热力学方程计算得到的等量吸附焓变ΔH>0,吸附自由能变ΔG<0,吸附熵变ΔS>0,表明炭化小麦秸秆对氨氮的吸附为吸热的和熵增加的自发过程,且属于物理吸附。

Study on the absorption of ammonia nitrogen by using carbonized wheat straw

The present article is aimed at the study of the sewage treatment efficiency by using carbonized wheat straw,For this purpose,first of all,the article tested three important factors that may affect the absorption process,including the choice of the carbonization temperature,adsorption temperature,and the pH value.Secondly,we have worked out all the kinetic data respectively by means of pseudo-first-order equation,pseudo-second-order equation,Elovich equation and the intra-particle diffusion model.Thirdly,we have analyzed the equilibrium isotherms by using the Langmuir and the Freundlich.And,finally,calculation was done to race the free energy changes ΔG,the enthalpy changes ΔH and enthalpy changes ΔS via the thermodynamics equation.The experimental results indicate that the optimal temperature for direct carbonization proves to be 300 ℃. Within the scope of the pH value,the optimal pH value for the ammonia nitrogen adsorption tends to be 9,whereas the carbonized wheat straw can adsorb different mass concentration(ρ=30 mg/L,50 mg/L,100 mg/L) of the ammonia nitrogen,which may follow the pseudo-second-order kinetics and the adsorption constant k2 (0.681 8 g/(mg·min),0.747 4 g/(mg·min),1.025 g/(mg·min)),but the intra-particle diffusion would not be the main rate-controlling step for the ammonia nitrogen adsorption onto the carbonized wheat straw.At the same time,the result of the given study also indicates that the higher the temperature,the better the absorption would be.The adsorption temperature of ammonia nitrogen on the adsorbent,the carbonized wheat straw,is 30 ℃.Therefore,all the above methods prove to be helpful for enhancing the capacity to remove ammonia nitrogen from the sewage to a great extent.In addition,the equilibrium data tends to fit well with the model Freundlich at 15 ℃,25 ℃and 35 ℃ respectively.In addition,the enthalpy changes(ΔH) and the entropy changes(ΔS) are positive,while the free energy changes(ΔG) are negative.Thus,the thermodynamic study proves that the adsorption process is a spontaneously endothermic process,implying that ammonia nitrogen adsorption by carbonized wheat straw might be of physisorption by nature.The results reveal that the potential of wheat straw,a waste material,can be used as a low-cost sorbent for removing ammonia nitrogen.