Investigation of regeneration of OAC-Mn and OAC-Fe material after arsenic adsorption was carried out by NaOH solution with concentration of 0.1 – 0.5 Ma. The liquid phase was then d[r]
Trang 1MINISTRY OF EDUCATION AND
TRAINING
VIETNAM ACADEMY
OF SCIENCE AND TECHNOLOGY
GRADUATE UNIVERSITY SCIENCE AND TECHNOLOGY
-
Pham Thi Hai Thinh
INVESTIGATION OF ACTIVATED CARBON DENATURATION IN ORDER
TO CREATE MATERIAL FOR TREATMENT OF SEVERAL HAZARD IONS IN
Trang 2The thesis was accomplished at Institute of Science and Technology, Vietnam Academy of Science and Technology
The science advisor 1: Assoc Prof Dr Tran Hong Con
The science advisor 2: Dr Phuong Thao
The Thesis could by search in:
- The Science and Technology Library
- The Vietnam National Library
Trang 3INTRODUCTION
1 The urgency of the thesis
The pollution of ammonia, arsenic and heavy metal in supplied and drinking water in Vietnam was not strictly treated yet; even deferent solutions were applied, such as biological treatment, aeration at high pH, oxidation by chlorine, adsorption…Adsorption methods using materials such as zeolite, silica, polymers or activated carbon were recognized as a simple application technics to remove pollution substances Activated carbon is material having more advantages than others, such as low cost, available, easy to use, stable in acidic and basic environment, high mechanic stability and regeneration possibility
Activated carbon has relatively hydrophobic surface, therefore it can
be very good used for treatment of non polar or less polar organic substances [2], but it is less effective in treatment of compounds in ionic forms [3], [4] Activated carbon, as its nature, has reductive groups in its surface, so it can be oxidized to transform to different functional groups such as carboxylic acids and other weak or very weak acids For that reason, we have had ideal to oxidize activated carbon in order to denaturate it’s surface to form a new cationic exchange material, which has high ion exchange capacity and safe for environment, and can be safely to use in drinking water treatment The new material avoids releasing monomers and other hazard by products (from synthetic ion exchange resins) into treated water Denaturation of activated carbon beside the forming new ion exchange material, it also transformed the hydrophobic surface of activated carbon into hydrophilic one This action enhanced adsorption possibility and capacity of the material for ammonium, arsenic and other metals ions in water environment Therefore, this investigation opens a new promising research orientation in water treatment, particularly drinking water treatment technology
At present time, in the domestic as well as international markets, there are many activated carbon types However, activated carbon, domestic product of Tra Bac Company, Ltd, which has highest market share in Vietnam The Tra Bac activated carbon was produced from coconut shell, one of waste during exploiting coconut products It is low cost, available and stable source; therefore the Tra Bac granule activated carbon was chosen for all investigations in the thesis
Trang 42 The research goals of the thesis
(1) Preparation and characterization of activated carbon products denaturated by surface oxidation technics (2) Determination of cation exchange capacity of the materials (3) Investigation of Mn and Fe linking
on surface of prepared materials to form a new adsorption material for effective removing hazard anions in water environment
3 The main contents of the thesis
- Oxidation of activated carbon by different oxidative reagents and based on the research results to evaluate the reduction ability (electrons exchange ability) and forming characters of different acidic functional groups containing oxygen on the activated carbon surface
- Study of physico-chemical characters and properties of the materials by SEM, EDX, IR, BRT methods, Boehm titration and pHPZC
determination
- Evaluation of ion exchange ability of denaturated activated carbon with several cations
- Investigation of regeneration ability of the ion exchange materials
- Linking of Fe and Mn ions on oxidized activated carbon and evaluation of arsenic removal from ground water
- Investigation and application of oxidized activated carbon in ammonia treatment for supplied and drinking water
- Investigation and application of activated carbon for oxidative
substances treatment in water such as Cr(VI)
Chapter 1 THE GENERAL VIEW
1.1 The actual situation of the ammonia, arsenic and heavy metals pollution in groundwater, and the investigation, application for ammonia, arsenic treatment in water
1.1.1 The actual situation of ammonia and arsenic pollution in groundwater
There appeared the situation of local pollution of groundwater in whole country of Vietnam In which, ammonia is one of uncovered parameters with the value higher than allowable value listed in the national technical norm for groundwater and drinking water In Hanoi and Ho Chi Ming City, the measured ammonia concentration in groundwater is many
Trang 5times higher than allowable limit [1] Beside that one, the ammonia concentration in groundwater of several provinces in midland, Northern Delta and Southern Delta showed many times higher than allowable limit Except ammonia pollution spreading out in almost whole country, the groundwater in several areas were still polluted by arsenic and/or heavy metals, such as Pb, Mn…Following the statistics of Health Ministry in
2017 [6], in whole country, there were about 17 million persons (approximately 21.5% population) used water contaminated by arsenic for daily life due to water exploited from drilled wells was not or non completely treated and their health was threaten
1.1.2 The investigation and application for ammonia, arsenic treatment
in water
In the last years, the investigation of ammonia and arsenic treatment has got more interesting of scientists Present technologies can effectively treat ammonia and arsenic in groundwater; however, the application of these technologies in the reality meets problems with economic condition, operating and maintenance regulations and also the effectiveness of the technology Particularly for small scale such as household, many technologies are very difficult to apply and deploy With the present living level of Vietnamese people, so high spending for water or waste water treatment, they could not pay, particularly people in the suburban or rural areas The application of solutions with low expenses, sustainable and out spreading application possibility is recognized as the priority approach The investigations about ammonia adsorption material with low cost and available were limited up to now The discovered materials have not high enough adsorptive capacity, therefore, research to find out the material with high ammonia adsorption capacity, low cost and available to be necessary in present situation
1.2 The over view for activated carbon
1.2.1 The general concept of activated carbon and its potential application in the environment
1.2.2 The general characters of activated carbon
1.2.2.1 The porous construction of activated carbon
Activated carbon has porous construction due to random arrangement
of carbon micro crystals and the stable cross linking between them The porous construction was established during carbonization and developed
Trang 6during activation process The size of the pores of activated carbon depends on production technics
1.2.2.2 The chemical construction of the activated carbon surface
The chemical construction of the activated carbon surface was taken form due to uncompleted carbonization or/and during activation process the chemical bonds between carbon – carbon and carbon with other atoms
The carbon – oxygen groups on the activated carbon are most important one to influence on the character and property of activated carbon surface (such as hydrophilic, acidic, polarization, electrical conductivity, catalytic possibility and chemical reactive ability)
1.2.3 Modification of activated carbon surface
Before modifying, the source, the surface construction and other factors influencing on activated carbon properties need to be good recognized and understood The modification of activated carbon could be classified to chemical modification and physical modification The modification action can modify one or some surface characters; but stronger actions make deeper change on the activated carbon until total denaturation of activated carbon surface The unexpected products of denaturation process, however, can be avoided by carefully chosen method and close control
1.2.4 Domestic and international researches about activated carbon denaturation by different oxidative reagents
1.3 The over view of adsorption and ion exchange
1.3.1 The over view of adsorption
- Classification of adsorption isotherm curves
- The adsorption technics
1.3.2 The over view of ion exchange
- The basic theory of ion exchange process
- The basic principal of ion exchange reaction
Chapter 2 THE RESEARCH METHODS
2.1 The research objectives
- Activated carbon: Activated carbon used for studies of the thesis is activated carbon made from coconut shell of Tra Bac Company Ltd Some physico-chemical characters of Tra Bac activated carbon are: Density at
25oC and 1 atm: 0.45 g/cm3, Humidity: 3.3%, Ash: 2.5%, Grain size: 0.5 –
Trang 72.2 Chemicals, devices and equipments for experiments
All chemicals used for research have purity for analysis The devices
and equipments have precision and accuracy satisfying requirement for
experiments of a doctoral thesis
2.3 Experimental methods
2.3.1 Methods for activated carbon oxidation
2.3.1.1.Oxidation of activated carbon by nitric acid
The activated carbon modification process was carried out as follow: Step 1 Sieve raw activated carbon in order to take the portion with the size of 0.5 – 1.0 mm
Step 2 Wash out recovered activated carbon sample by distilled water, then dry for 24 h at 105oC (the sample is signed as AC)
Step 3 Oxidize AC by HNO3 with concentration in the range of 3 –
14 M for 2, 4 and 6 h at 100oC The portion of AC and HNO3 solution was 1:3 In order to avoid loss of HNO3 during oxidation process, the oxidation device was equipped with back flow system The oxidation temperature was kept at 100 ± 5oC by thermal control system
Step 4 After oxidation, the liquid phase was decanted out The solid phase was washed by distilled water until pH of effluence meets constant
Step 7 After neutralization, the liquid phase was decanted out The solid phase was washed out by distilled water until pH was constant (about
Trang 8The oxidation process was carried out at room temperature by KMnO4 0.01M solution in H2SO4 6M as follow:
Step 1 KMnO4 solution was dripped into accurate quantity of AC in erlenmeyer flask and continuously stirred at 150 r/min until solution appeared violet color stable for 5 min Note the spent volume of KMnO4
for further calculation
Step 2 Pour liquid phase out and wash out the solid phase by distilled water
Step 3 Dry solid portion at 105oC for 24 h (the product was signed
as OACKMnO4)
2.3.1.3 Oxidation of activated carbon by K 2 Cr 2 O 7 solution
The oxidation process was carried out at room temperature by
K2Cr2O7 0.1M solution in H2SO4 1.5M The experiment steps were the same as oxidation by KMnO4 Except the equilibrium point was determined by dimethylcarbaside indicator The product was signed as OACK2Cr2O7
2.3.2 Investigation of adsorption/ion exchange in static model
Investigation of adsorption/ion exchange in static condition was carried out with constant portion of solid phase and liquid phase at the same temperature and pressure (atmospheric pressure) By the way of the change of pH solution, contact time of the phases and initial ions concentration to determinate the optimal pH, the time for equilibrium establishment and isotherm adsorption/ion exchange curves From isotherm curves, the maximum adsorption/ion exchange of investigation ion was determined
2.3.3 Investigation of adsorption/ion exchange in dynamic model
Investigation of adsorption/ion exchange in dynamic condition was carried out on the PVC transparent column with internal diameter of 13
mm and height of investigation material about 50 - 60 mm Adsorbate solution with optimal pH and ions concentration was flowed though the column with designed rate Ions concentration of effluent fractions was determined All important factors were determined
2.3.4 Investigation of regeneration possibility of the used material
Investigation of regeneration of OACNa material after ammonia adsorption was carried out by HCl solution with concentration of 1; 2 and
Trang 93 M; then neutralization by NaOH with concentration of 0.3; 0.5; 0.7 and 1.0 M
Investigation of regeneration of OAC-Mn and OAC-Fe material after arsenic adsorption was carried out by NaOH solution with concentration of 0.1 – 0.5 M
2.3.5 Attaching of Mn 2+ and Fe 3+ on OAC Na
b Attaching of Fe 3+
The initial step of linking of Fe3+ on OACNa was carried out by the same way as for Mn2+; but the pH of the mixture was adjusted to 3 by HCl 0.1 M and concentrations of Fe3+ were 3; 5; and 8.1% The solid phase was neutralized by NaOH 0.1 M until pH of the effluent solution meet 9; then washed by distilled water until clean of Cl- ions and dried at 70oC for 24h
2.3.6 The methods for surface characters determination
The SEM, EDX, IR, BRT methods, Boehm titration and pHPZC test were used for determination of the material surface characters
2.5 Analytical methods
2.6 Methods for calculation
Chapter 3 RESULTS AND DISCUSSION
3.1 The results of AC oxidation by different oxidative reagents
3.1.1 The materials achieved by oxidation and surface treatment
36 materials were achieved after oxidation of AC by HNO3 and surface treatment by NaOH, and 4 materials after oxidation of AC by KMnO4 and K2Cr2O7 (ACKMnO4, ACKMnO4-Na, ACK2Cr2O7 và ACK2Cr2O7-Na)
3.1.2 The surface characters of the materials before and after oxidation
3.1.2.1 The morphology and elemental composition of the AC and OAC surface
The SEM image of original AC showed that is has fibrillary form with dimension in the range of nanometers, porous and fold each on the
Trang 10other In the SEM image of OAC, there is no remarkable difference in
comparison with the SEM image of AC
EDX analysis showed that, the percentage of carbon in OAC is reduced in comparison with original AC; but that of oxygen is increased and appeared Na component in OACNa This phenomenon demonstrate that carbon in AC was oxidized and formed more oxygen containing functional groups and Na atoms were bound (see also at table 3.2)
Table 3.2 The composition of the AC and OACNa
appeared peak of C-H bond in aromatic rings On OAC surface, there appeared a sorption peak at 1727 cm-1, due to double binding of C=O in carboxylic group At wave number of 1627 cm-1 are bonds of C=C in the aromatic rings and bonds of C=O in ketone, lactone and aldehyde groups
At wave number 1380 cm-1 appeared peak of C-O bonds in phenol and alcohol groups Particularly, when AC oxidized by HNO3, appeared peak
at 1126 cm-1, it could be the bonds of C-N in aromatic ring and N-O in long chains [60[, [107], [108] For OACNa, all the peaks were appeared in the same wave number corresponding to bonds on the OAC, but the bonds
of O-H and C=O in OACNa have intensity lower than on OAC The reason could be effect of Na binding with oxygen containing groups
3.1.2.3 Specific surface area analysis
The original AC has average BET specific surface area (SBET) 785
m2/g After oxidation, the SBET and total capillary volume (Vtot) of the materials in generally were decreased in comparison with AC, however, OAC oxidized by HNO3 has most decrease The decrease of SBET and Vtot
of OAC10-4, OACKMnO4 and OACK2Cr2O7 were 3,0; 9,1; 17,5% and 7,25; 8,77; 18,87 % respectively
3.1.2.4 The results of Boehm titration and pH pzc determination
- Oxidation by HNO3
Trang 11Results of acidic and basic group concentration on material surface determined by Boehm titration are listed in table 3.6
Table 3.6 Boehm titration results
There was the trend of increase of acidic groups when increase HNO3
concentration The acidic group of OAC oxidized by HNO3 10 M for 4 h was 4.75 mmol/g, while oxidized by HNO3 3 M for the same time was only 1.02 mmol/g When OAC was treated by NaOH, the acidic groups decreased significantly The total basic groups almost ware not been effected by oxidative reagents
The total basic groups were almost uninfluenced by oxidative reagents
Trang 123.1.2.5 Quantification of reductive capacity of the AC by KMnO 4 and
K 2 Cr 2 O 7
The electron exchange capacity of AC determined by titration with KMnO4 and K2Cr2O7 were 8.9 and 3.0 mmol/g respectively Based on the results of this survey, there appeared idea that AC could be used for treatment of oxidative components in water environment
3.2 The NH 4 + ion exchange capacity of OAC oxidized by HNO 3 , KMnO 4 and K 2 Cr 2 O 7
3.2.1 The NH 4 + ion exchange capacity of OAC oxidized by HNO 3
From investigation results, the material oxidized by HNO3 10 M for
4 h has highest NH4+ ion exchange capacity
3.2.1.1 The NH 4 + ion exchange capacity of OAC 10-4 and OAC 10-4Na
The NH4+ ion exchange capacity of OAC10-4 and OAC10-4Na was investigated The results were demonstrated in table 3.9 The ion exchange process was according to Langmuir adsorption isotherm (R2 = 0.979) The maximum adsorption capacity of ammonium ion on OAC10-4Na was significantly higher than that of OAC10-4 (20.41 mg/g and 1.53 mg/g respectively) This phenomenon could be explained by different state of acidic groups on the material surface Before neutralization, almost acidic groups exist in the weak and very weak acidic form; the H+ ion did not dissociate, those resulting to limit ion exchange of ammonium with materials surface After neutralization, almost acidic groups transformed into Na salts Ion Na+ is easy to dissociate in water solution, therefore the
NH4+ exchange capacity increased obviously
Table 3.9 The parameters of Langmuir isotherm adsorption function for
NH4+ on OAC10-4 and OAC10-4Na
Material
Langmuir Isotherm adsorp
3.2.2 The NH 4 + ion exchange capacity of OAC oxidized by KMnO 4
Trang 13The NH4+ ion exchange with OAC oxidized by KMnO4 also according to Langmuir adsorption isotherm (see figure 3.9) with R2 at 0.996 for ACKMnO4 and 0.994 for ACKMnO4-Na Ion exchange capacity of
ACKMnO4 was 3.88 mg/g and that of ACKMnO4-Na was 14.29 mg/g The ion exchange capacity of material after neutralization was higher than before This phenomenon has the same reason mentioned above for OAC oxidized
by HNO3; but the increased value of ACKMnO4-Na was lower in comparison with that of OAC10-4Na It possibly means: oxidation by KMnO4 in strong acidic solution, the porous system was deeply changed than that by HNO3
and total carboxylic group onACKMnO4 lower than that on OAC10-4Na
Figure 3.9 The adsorption isotherm curves of NH4+ on AC oxidized by
KMnO4
3.2.3 The NH 4 + ion exchange capacity of OAC oxidized by K 2 Cr 2 O 7
The ion exchange capacity of NH4+ on AC oxidized by K2Cr2O7 was 7.30 mg/g, higher than AC oxidized by KMnO4 but lower than AC oxidized by HNO3
3.3 The ion exchange ability in static model of ammonium and 2 and 3 valence ions on AC oxidized by HNO 3
3.3.1 The contact time
a For ammonium
Adsorption capacity of ammonium on AC original or OACHNO3 was very low and the contact time reaching equilibrium state was about 40 min However, on the OACHNO3 neutralized by NaOH, the adsorption capacity was very high and the time for reaching equilibrium increased to
60 min
b For Ca 2+
y = 0.260x + 14.09 R² = 0.996
y = 0.070x + 3.397 R² = 0.994
0 20 40 60 80 100
C e /q e
ACKMnO4 ACKMnO4-Na