Reduction of Bromate and Perchlorate in Water by Modified Nano Zero-Valent Iron = 개질된 나노영가철에 의한 물속의 브로메이트와 퍼클로레이트의 제거

다국어 초록 (Multilingual Abstract)

Nano zero valent iron (NZVI) is often used to treat various pollutants in groundwater and soil, such as chlorinated organic compounds, heavy metal ions, antibiotics and dye wastewater. NZVI has the advantages of high reactivity and large specific surface area. However, due to the magnetism among the NZVI particles, it is easy to agglomerate，and its high reactivity makes it easy to oxidize in contact with oxygen. In order to make NZVI technology more practical, researchers try to improve the agglomeration and oxidation of ZVI particles by loading or adding dispersants. In this study, the liquid-phase reduction method for preparing nano iron by traditional chemical method is improved. Poly vinyl pyrrolidone (PVP), carboxy methyl cellulose (CMC) and starch (starch) are selected as three stabilizers of nano iron and NZVI. The NZVI iron and its materials not only have good dispersion in aqueous solution, but also have good antioxidant capacity. It has been successfully applied to the manufacture of novel modified NZVI under aerobic conditions.
The natural water containing bromine ion is oxidized by ozone to form bromate. Bromate is identified as 2B potential carcinogen by the International Agency for Cancer (IARC). The natural perchlorate mainly comes from the cost of raw materials and the artificial synthesis mainly comes from rockets, fireworks and so on. They are recognized as universal, potential and persistent harmful substance. Therefore, the development of bromate and perchlorate removal technology is particularly urgent.
The removal ability and kinetic mechanism of bromate and perchlorate are also investigated. The results are as follows:
In this study, the modified NZVI is prepared by liquid phase reduction method. That newly modified process has better dispersion and stability. The effects of three surfactants, PVP, starch and CMC regarding the preparation and the dispersibility of modified NZVI are studied. The effects of surfactant type, ultrasonic time, surfactant dosage, ethanol concentration and pH value on the preparation process are discussed as well. The results show that the dispersion stability of NZVI firstly increases and then decreases with the extension of ultrasonic time and each surfactant have the best ultrasonic time and concentration. The dispersion effects of different surfactants from high to low is PVP>starch>CMC. The results of SEM, XPS, BET and XRD show that NZVI prepared by 0.2wt% PVP have the best dispersibility, the particles size is the smallest, with an average of 18nm, the specific surface area is 32.152 m 2 /g, the percentage of ZVI increases and the diffraction peak of Fe0 appear sat 44.8° with high crystallinity and no obvious oxidation phenomenon. The optimum dispersion process factors of NZVI prepare in aerobic environment are as follows: 10 min ultrasonic time, 0.2wt%PVP concentration (mass fraction), 60% ethanol concentration.
In the process of removing bromate and perchlorate with modified NZVI, the factors affecting the experimental conditions are: the amount of nano particles, the initial concentration of bromate and perchlorate and the initial value of solution. Increasing the amount of new modified NZVI can increase the specific surface area of nano iron, thus increasing the contact between nano iron and bromate and perchlorate. The removal experiments of pollutants were carried out. When pH=5 and PVP-NZVI dosage is 25mg/L, the removal rate of bromate with initial concentration of 5mg/L can reach more than 90% within 60min; when pH=4 and PVP-NZVI dosage is 25mg/L, the removal rate of perchlorate with initial concentration of 0.5mg/L can reach more than 90% within 60min. The experimental results show that the new modified NZVI has high removal effect on bromate and perchlorate.
By fitting the experimental data of the removal of bromate and perchlorate by PVP-NZVI, it is found that the removal process conforms to the second-order reaction kinetics. The reaction rate increases with the increase of PVP-NZVI dosage, but decreases with the increase of initial concentration and pH value.
The following research is the removal of bromate and perchlorate by NZVI in continuous flow experiment. The research will be also nvestigate whether the removal effect of NZVI decreases after storage for a certain time.
The regeneration and reuse performance of NZVI will be studied as well.

국문 초록 (Abstract)

브롬을 포함하고 있는 자연수는 오존처리에 의해 브롬산염으로 산화된다. 브롬산염은 국제암학 회에서 잠재적인 발암물질인 2B로 규정되어 있다. 과염소산염은 자연적으로 발생하기도 하지만 주로 로켓,폭죽 등 주로 인위적으로 발생한다. 이 오염물질들은 전세계적, 잠재성, 지속성을 지닌 위해성 물질이다. 그러므로 브롬산염과 과염소산염의 제거 기술개발은 시급성을 지니고 있다.
나노영가철(NZVI)은 높은 반응성과 비표면적이 큰 장점을 가지고 있다. 그래서 지하수와 토양의 다양한 오염물질들(유기염소화합물, 중금속 이온, 항생물질, 염색폐수등)의 제거를 위해 사용되고 있다. 그러나 나노영가철의 자성으로 인해 쉽게 뭉쳐지고, 산소접촉하에 높은 반응성으로 인해 산화 되기 쉽다. 실용적으로 나노영가철을 제조하기 위해서, 연구자들은 다양한 분산제의 첨가에 의해나 노영가철의 응집과 산화를 억제하기 위해 노력하였다 .이 논문은 나노영가철 제조를 위해 수용액 상태 환원법을 이용하였고PVP, CMC, 전분이 나노영가철의 안정제로서 사용되었다. 이렇게 제조된 나노영가철은 수용액에서 높은 분산성을 유지하고 아울러 높은 산화방지 성능을 가졌다. 호기성 상태의 나노영가철 제조공정에 성공적으로 적용할 수 있을 것이다.
개질된 나노영가철에 의한 브롬산염과 과염소산염의 제거능력과 역학적 메커니즘을 조사하였고 이러한 연구 결과는 아래와 같다.
본 연구는 액상환원법에 의해 개질된 나노영가철을 제조하였다. 개질된 나노영가철은 더 나은 분산성과 안정성을 가졌다. PVP, CMC, 전분과 같은 세가지 계면활성제를 사용하여 제조와 분산성 능에 미치는 영향을 연구하였다. 계면활성제 종류, 초음파노출시간, 계면활성제 농도, 에탄올 농도, 그리고 pH 변화가 나노영가철 제조과정에 미치는 영향을 조사하였다. 그 결과 초음파 노출시간이 길어질수록 나노영가철의 분산 안정성이 먼저 높아지고 점차 낮아짐을 관찰하였고 각각의 계면활성 제의 최적의 초음파 노출시간과 농도를 확인하였다. 분산효과는PVP >전분 >CMC의 순서로 나타 났다. SEM, XPS, BET, XRD 분석결과에 의하면 0.2wt% PVP로 제도한 나노영가철이 분산성이 가장 우수하고 입자의 직경이 가장 작았으며 평균 직경은 18nm 이었다. 비표면적은 32.152m 2 /g 이며 영가철 이온함유량이 증가되고 FeO 의회절 피크는44.8로 나타나고 뚜렷한 산화현상이 없다. 호기성상태의 나노영가철 제조를 위한 최적의 공정 조건은 초음파 노출시간 10 분, 0.2wt% PVP (질량분율), 에탄올 농도 60% 이다.
개질된 나노영가철을 이용한 브롬산염과과염소산염 제거공정에서 실험조건은나노입자의 용량, 초기 브롬산염과과염소산염 농도이다. PVP-NZVI의 양을 증가시키면 나노철의 비표면적을 증가시킬 수 있으며 이는 나노철과브롬산염, 과염소산염과의 접촉을 증가시킬 수 있다. pH 5 이고
25mg/L PVP-NZVI 일때초기농도가5mg/L브롬산염의 제거율은 60분이내 90% 이상을 보였다.
pH 4 이고 25mg/L PVP-NZVI 일때초기농도가0.5mg/L 과염소산염의 제거율은 60분이내 90% 이상을 보였다.
PVP-NZVI에 의한 브롬산염과 과염소산염의 제거에 관한 실험데이터 피팅 결과는 2차반응식에 잘 부합하는 것으로 나타났다. 반응속도는 PVP-NZVI 용량이 증가함에 따라 증가하였다.

목차 (Table of Contents)

• CHAPTER 1：INTRODUCTION ············································· ··· １
• 1.1 Background ·································································· ··· １
• 1.2 Research objectives ························································· ··· ３
• 1.3 Research significance······················································· ··· ３
• 1.4 Research approach ·························································· ··· ５
• 1.5 Innovative methods ························································· ··· ７
• 1.6 Organization of thesis ······················································ ··· ８
• CHAPTER 2：LITERATURE REVIEW ···································· ··· 11
• 2.1 Pollutants (bromate and perchlorate) ····································· ··· 11
• 2.2 Research status of NZVI and its modification ·························· ··· 13
• 2.2.1 Nanometer materials ··················································· 13
• 2.2.2 Technology and characteristics of NZVI ···························· 14
• 2.2.3 Surface modification and modification of NZVI··················· 17
• 2.2.4 Preparation of NZVI ··················································· 21
• CHAPTER 3：MATERIALS AND METHODS ··························· ··· 24
• 3.1 Chemical ····································································· ··· 24
• 3.2 Laboratory instruments ····················································· ··· 25
• 3.3 Experimental device and methods ········································ ··· 26
• 3.3.1 Preparation of different types of modified NZVI ·················· 27
• 3.3.2 Preparation procedure of NZVI under aerobic condition ········· 27
• 3.3.3 Preparation procedure of NZVI under anaerobic condition ······ 30
• 3.4 Experimental analysis method ············································ ··· 32
• 3.4.1 Determination of reaction parameters ······························· 32
• 3.4.2 Characterization of NZVI ············································· 35
• CHAPTER 4 ： FATE OF MODIFIED NZVI:MODIFIED NZVI PREPARED UNDER DIFFERENT CONDITIONS AND COMPARISON OF ITS PROPERTIES ............................................................................... ··· 41
• 4.1 Introduction ·································································· ··· 41
• 4.2 Effects of preparation conditions on reaction activity of NZVI ······ ··· 41
• 4.2.1 Preparation of PVP-NZVI with different weight ratios ··········· 43
• 4.2.2 Preparation of CMC-NZVI with different weight ratios ·········· 45
• 4.2.3 Preparation of Starch-NZVI with different weight ratios ········· 47
• 4.2.4 Investigation of different ratios of ethanol ·························· 54
• 4.2.5 Investigation of different pH ·········································· 56
• 4.3 Characterization ····························································· ··· 56
• 4.3.1 Stability ·································································· 5
• 4.3.2 Analysis of SEM ························································ 59
• 4.3.3 Analysis of BET ························································ 64
• 4.3.4 Analysis of XRD ························································ 65
• 4.3.5 Analysis of XPS ························································· 71
• CHAPTER 5 ： LAB-SCALE SIMULATION OF ADSORPTION AND REMOVAL OF BROMATE AND PERCHLORATE BY MODIFIED NZVI ....................................................................................................................... ··· 82
• 5.1 Introduction ·································································· ··· 82
• 5.2 Results and discussion ······················································ ··· 82
• 5.2.1 Experimental study on removal of bromated ······················· 82
• 5.2.2 Experimental study on removal of perchlorate ····················· 89
• CHAPTER 6：KINETIC ANALYSIS AND REMOVAL MECHANISM · 96
• 6.1 Introduction ·································································· ··· 96
• 6.2 Kinetics of the removal of BrO 3
• 6.3 Kinetics of removal of ClO 4
• - ·············································· · 105
• CHAPTER 7：CONCLUSIONS ··············································· ·· 112
• CHAPTER 8：FUTURE STUDY ············································· ·· 116