納米鐵炭微電解去除水中硝酸鹽途徑及其動力學研究
發(fā)布時間：2018-11-25 09:34
【摘要】：納米鐵炭(NZVI/AC)作為一種強還原性材料能夠有效去除水中硝酸鹽已受到廣泛關(guān)注,學者多從硝酸鹽去除效率及NZVI/AC材料改性出發(fā)開展了較多研究,但對NZVI/AC微電解體系去除硝酸鹽的反應(yīng)過程少有報道,需進一步分析探討納米鐵炭體系去除硝酸鹽的反應(yīng)途徑及其動力學為NZVI/AC后續(xù)實際應(yīng)用提供一定理論依據(jù)。本文通過研究NZVI/AC、納米鐵(NZVI)、活性炭(AC)對硝酸鹽的還原或吸附過程探討微電解作用,反應(yīng)前后NZVI/AC變化、氮種類變化、pH變化,以及NO_3~-和Fe~(2+)的相互作用探討其還原途徑,沿用LangmuirHinshelwood建模思路并對準一級反應(yīng)、準二級反應(yīng)、n級反應(yīng)、準一級吸附、準二級吸附等模型加以討論選出最優(yōu)模型,參數(shù)的計算,使用非線性回歸的方法,將假定的數(shù)學模型積分,對比不同條件下(NZVI/AC投加量、硝酸鹽濃度、溶液初始pH、離子強度)的動力學規(guī)律,得到以下主要結(jié)論:(1)NZVI/AC的去除效率明顯的高于單獨的NZVI和AC,且大于兩者之和,說明了NZVI/AC之間存在協(xié)同作用。(2)探討了負載量、離子強度和溶液初始pH對微電解體系的影響,發(fā)現(xiàn)負載量為0.4 g時具有最優(yōu)活性,Cl-對于微電解體系同時存在促進(促進電子的傳遞)和抑制作用(Cl-和NO_3~-存在競爭吸附關(guān)系),僅當Cl-在50 mg/L時對體系有促進作用,當Cl~-達到200 mg/L反應(yīng)主要表現(xiàn)為抑制作用;此外在整個pH=3-11范圍內(nèi)納米鐵炭材料都能有效的去除NO_3~-。(3)在NZVI/AC去除硝酸鹽反應(yīng)過程中NO_3~-首先被吸附在NZVI/AC材料的表面,然后再其表面發(fā)生氧化還原反應(yīng),并且吸附的速率快于表面反應(yīng)速率;在反應(yīng)過程中反應(yīng)會消耗溶液中的H~+,在較高pH條件下NH_4~+能夠形成氨水再隨著外部的振蕩或攪拌脫離了溶液,所以反應(yīng)的終產(chǎn)物,主要是NH_4~+,過程中沒有N_2生成;NZVI/AC還原硝酸鹽過程,NZVI首先被氧化成Fe~(2+)進入溶液,由于該反應(yīng)會消耗溶液中H~+,所以pH升高產(chǎn)生Fe(OH)_2沉淀,最后在被氧化成Fe_2O_3。(4)無論是在NZVI/AC不足或過量的情況下,準二級吸附動力學模型對于NO_3~-的去除和Langmuir-Hinshelwood模型對于NH_4~+的生成都能提供很好的擬合結(jié)果。普遍使用的準一級動力學模型無論是在NO_3~-的去除或NH_4~+的生成,在NZVI/AC投加量不足的條件下不能得到很好的擬合結(jié)果。通過L-H模型很好的解釋了反應(yīng)過程中總氮先下降后上升現(xiàn)象,且從動力學上證明了NO_3~-的去除是一個先吸附在反應(yīng)的過程,所以NZVI/AC將NO_3~-還原為NH_4~+的過程是一個非均相催化反應(yīng)過程,反應(yīng)速率常數(shù)隨著初始條件的變化有著很好的相關(guān)性。在高NZVI/AC投加量、低離子強度、低初始pH和低初始硝酸根濃度情況下硝酸根的去除和銨根的生成速率更快,在初始pH=11條件下對反應(yīng)的抑制作用大于在pH=3時的促進作用,在NZVI/AC表面對于NO_3~-吸附并沒有受到OH~-及其形成的Fe(OH)_2沉淀過多的抑制作用,相比于單獨的NZVI,NZVI/AC形成的微電解體系具有更廣闊的適用范圍。
[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.
【學位授予單位】：成都理工大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：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.
【學位授予單位】：成都理工大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TU991.2
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