纳米铁炭微电解去除水中硝酸盐途径及其动力学研究
发布时间：2018-11-25 09:34
【摘要】：纳米铁炭(NZVI/AC)作为一种强还原性材料能够有效去除水中硝酸盐已受到广泛关注,学者多从硝酸盐去除效率及NZVI/AC材料改性出发开展了较多研究,但对NZVI/AC微电解体系去除硝酸盐的反应过程少有报道,需进一步分析探讨纳米铁炭体系去除硝酸盐的反应途径及其动力学为NZVI/AC后续实际应用提供一定理论依据。本文通过研究NZVI/AC、纳米铁(NZVI)、活性炭(AC)对硝酸盐的还原或吸附过程探讨微电解作用,反应前后NZVI/AC变化、氮种类变化、pH变化,以及NO_3~-和Fe~(2+)的相互作用探讨其还原途径,沿用LangmuirHinshelwood建模思路并对准一级反应、准二级反应、n级反应、准一级吸附、准二级吸附等模型加以讨论选出最优模型,参数的计算,使用非线性回归的方法,将假定的数学模型积分,对比不同条件下(NZVI/AC投加量、硝酸盐浓度、溶液初始pH、离子强度)的动力学规律,得到以下主要结论:(1)NZVI/AC的去除效率明显的高于单独的NZVI和AC,且大于两者之和,说明了NZVI/AC之间存在协同作用。(2)探讨了负载量、离子强度和溶液初始pH对微电解体系的影响,发现负载量为0.4 g时具有最优活性,Cl-对于微电解体系同时存在促进(促进电子的传递)和抑制作用(Cl-和NO_3~-存在竞争吸附关系),仅当Cl-在50 mg/L时对体系有促进作用,当Cl~-达到200 mg/L反应主要表现为抑制作用;此外在整个pH=3-11范围内纳米铁炭材料都能有效的去除NO_3~-。(3)在NZVI/AC去除硝酸盐反应过程中NO_3~-首先被吸附在NZVI/AC材料的表面,然后再其表面发生氧化还原反应,并且吸附的速率快于表面反应速率;在反应过程中反应会消耗溶液中的H~+,在较高pH条件下NH_4~+能够形成氨水再随着外部的振荡或搅拌脱离了溶液,所以反应的终产物,主要是NH_4~+,过程中没有N_2生成;NZVI/AC还原硝酸盐过程,NZVI首先被氧化成Fe~(2+)进入溶液,由于该反应会消耗溶液中H~+,所以pH升高产生Fe(OH)_2沉淀,最后在被氧化成Fe_2O_3。(4)无论是在NZVI/AC不足或过量的情况下,准二级吸附动力学模型对于NO_3~-的去除和Langmuir-Hinshelwood模型对于NH_4~+的生成都能提供很好的拟合结果。普遍使用的准一级动力学模型无论是在NO_3~-的去除或NH_4~+的生成,在NZVI/AC投加量不足的条件下不能得到很好的拟合结果。通过L-H模型很好的解释了反应过程中总氮先下降后上升现象,且从动力学上证明了NO_3~-的去除是一个先吸附在反应的过程,所以NZVI/AC将NO_3~-还原为NH_4~+的过程是一个非均相催化反应过程,反应速率常数随着初始条件的变化有着很好的相关性。在高NZVI/AC投加量、低离子强度、低初始pH和低初始硝酸根浓度情况下硝酸根的去除和铵根的生成速率更快,在初始pH=11条件下对反应的抑制作用大于在pH=3时的促进作用,在NZVI/AC表面对于NO_3~-吸附并没有受到OH~-及其形成的Fe(OH)_2沉淀过多的抑制作用,相比于单独的NZVI,NZVI/AC形成的微电解体系具有更广阔的适用范围。
[Abstract]:Nanocrystalline iron carbon (NZVI/AC) can effectively remove nitrate in water as a strong reductive material. Many scholars have carried out many researches on nitrate removal efficiency and modification of NZVI/AC materials. However, there are few reports on the process of nitrate removal in NZVI/AC microelectrolysis system. It is necessary to further analyze and discuss the reaction path and kinetics of nitrate removal by nano-iron-carbon system, which provides a theoretical basis for the practical application of NZVI/AC in the future. In this paper, the reduction or adsorption of nitrate by NZVI/AC, nano-iron (NZVI), activated carbon (AC) was studied. The changes of NZVI/AC, kinds of nitrogen and pH before and after the reaction were discussed. As well as the interaction between NO_3~- and Fe~ (2), the reduction path is discussed and the optimal model is obtained by using the LangmuirHinshelwood modeling method and focusing on the models of first-order reaction, quasi-second-order reaction, n-order reaction, quasi-first-order adsorption and quasi-second-order adsorption. The parameters were calculated by nonlinear regression method and the assumed mathematical model was integrated to compare the kinetic laws under different conditions (NZVI/AC dosage, nitrate concentration, initial pH, ionic strength of solution). The main conclusions are as follows: (1) the removal efficiency of NZVI/AC is significantly higher than that of single NZVI and AC, and the sum of the two shows that there is a synergistic effect between NZVI/AC. (2) the amount of load is discussed. The effects of ionic strength and solution initial pH on the microelectrolysis system showed that the optimum activity was obtained when the loading was 0.4 g. Cl- can promote (promote electron transfer) and inhibit (Cl- and NO_3~- competitive adsorption) at the same time, only when Cl- is 50 mg/L, it can promote the system. When Cl~- reached 200 mg/L, the inhibitory effect was mainly shown. In addition, NO_3~-. (3) can be effectively removed by nano-iron-carbon materials in the whole range of pH=3-11. In the process of NZVI/AC removal of nitrate, NO_3~- is first adsorbed on the surface of NZVI/AC materials. Then the redox reaction takes place on the surface, and the adsorption rate is faster than the surface reaction rate. In the reaction process, the reaction will consume the H ~ in the solution. Under the condition of higher pH, NH_4~ can form ammonia water and leave the solution with external oscillation or agitation. Therefore, the final product of the reaction, mainly NH_4~, does not produce NSP 2 in the process. In the process of NZVI/AC reduction of nitrate, NZVI is first oxidized to Fe~ (2) into the solution. Since this reaction consumes H ~ in the solution, pH increases to produce Fe (OH) _ 2 precipitation. Finally, if it is oxidized to Fe_2O_3. (4), whether it is insufficient or excessive NZVI/AC, The quasi-second-order adsorption kinetic model can provide good fitting results for the removal of NO_3~- and the formation of NH_4~ by Langmuir-Hinshelwood model. No matter the removal of NO_3~- or the generation of NH_4~, the commonly used quasi-first-order kinetic model can not get a good fitting result under the condition of insufficient NZVI/AC dosage. The L-H model is used to explain the first decrease of total nitrogen and then the rise of total nitrogen in the reaction process, and it is proved that the removal of NO_3~- is a process of first adsorption in the reaction. Therefore, the process of NZVI/AC reducing NO_3~- to NH_4~ is a heterogeneous catalytic reaction process, and the reaction rate constant has a good correlation with the change of initial conditions. At high NZVI/AC dosage, low ionic strength, low initial pH and low initial nitrate concentration, the removal of nitrate and the formation rate of ammonium were faster, and the inhibitory effect on the reaction at initial pH=11 was greater than that at pH= 3. The adsorption of NO_3~- on the surface of NZVI/AC is not inhibited by OH~- and its formed Fe (OH) _ 2 precipitate, which is more suitable than the microelectrolysis system formed by NZVI,NZVI/AC alone.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU991.2
[Abstract]:Nanocrystalline iron carbon (NZVI/AC) can effectively remove nitrate in water as a strong reductive material. Many scholars have carried out many researches on nitrate removal efficiency and modification of NZVI/AC materials. However, there are few reports on the process of nitrate removal in NZVI/AC microelectrolysis system. It is necessary to further analyze and discuss the reaction path and kinetics of nitrate removal by nano-iron-carbon system, which provides a theoretical basis for the practical application of NZVI/AC in the future. In this paper, the reduction or adsorption of nitrate by NZVI/AC, nano-iron (NZVI), activated carbon (AC) was studied. The changes of NZVI/AC, kinds of nitrogen and pH before and after the reaction were discussed. As well as the interaction between NO_3~- and Fe~ (2), the reduction path is discussed and the optimal model is obtained by using the LangmuirHinshelwood modeling method and focusing on the models of first-order reaction, quasi-second-order reaction, n-order reaction, quasi-first-order adsorption and quasi-second-order adsorption. The parameters were calculated by nonlinear regression method and the assumed mathematical model was integrated to compare the kinetic laws under different conditions (NZVI/AC dosage, nitrate concentration, initial pH, ionic strength of solution). The main conclusions are as follows: (1) the removal efficiency of NZVI/AC is significantly higher than that of single NZVI and AC, and the sum of the two shows that there is a synergistic effect between NZVI/AC. (2) the amount of load is discussed. The effects of ionic strength and solution initial pH on the microelectrolysis system showed that the optimum activity was obtained when the loading was 0.4 g. Cl- can promote (promote electron transfer) and inhibit (Cl- and NO_3~- competitive adsorption) at the same time, only when Cl- is 50 mg/L, it can promote the system. When Cl~- reached 200 mg/L, the inhibitory effect was mainly shown. In addition, NO_3~-. (3) can be effectively removed by nano-iron-carbon materials in the whole range of pH=3-11. In the process of NZVI/AC removal of nitrate, NO_3~- is first adsorbed on the surface of NZVI/AC materials. Then the redox reaction takes place on the surface, and the adsorption rate is faster than the surface reaction rate. In the reaction process, the reaction will consume the H ~ in the solution. Under the condition of higher pH, NH_4~ can form ammonia water and leave the solution with external oscillation or agitation. Therefore, the final product of the reaction, mainly NH_4~, does not produce NSP 2 in the process. In the process of NZVI/AC reduction of nitrate, NZVI is first oxidized to Fe~ (2) into the solution. Since this reaction consumes H ~ in the solution, pH increases to produce Fe (OH) _ 2 precipitation. Finally, if it is oxidized to Fe_2O_3. (4), whether it is insufficient or excessive NZVI/AC, The quasi-second-order adsorption kinetic model can provide good fitting results for the removal of NO_3~- and the formation of NH_4~ by Langmuir-Hinshelwood model. No matter the removal of NO_3~- or the generation of NH_4~, the commonly used quasi-first-order kinetic model can not get a good fitting result under the condition of insufficient NZVI/AC dosage. The L-H model is used to explain the first decrease of total nitrogen and then the rise of total nitrogen in the reaction process, and it is proved that the removal of NO_3~- is a process of first adsorption in the reaction. Therefore, the process of NZVI/AC reducing NO_3~- to NH_4~ is a heterogeneous catalytic reaction process, and the reaction rate constant has a good correlation with the change of initial conditions. At high NZVI/AC dosage, low ionic strength, low initial pH and low initial nitrate concentration, the removal of nitrate and the formation rate of ammonium were faster, and the inhibitory effect on the reaction at initial pH=11 was greater than that at pH= 3. The adsorption of NO_3~- on the surface of NZVI/AC is not inhibited by OH~- and its formed Fe (OH) _ 2 precipitate, which is more suitable than the microelectrolysis system formed by NZVI,NZVI/AC alone.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU991.2
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