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Preparation, fluoride adsorption, and regeneration of aluminum hydroxide
amended molecular sieves and zeolites
Junyi Du
CEES
WaTER Center
Advisors: Elizabeth C. Butler, David A. Sabatini
1
Introduction
• Worldwide problem of elevated fluoride concentration in drinking water
• Health problems caused by excessive fluoride intake
Dental and skeletal fluorosis, sources (left to right): <http://www.inrem.in/fluorosis/about.html>, <http://www.protectorsystems.com/protectors-in-action.html>, <http://www.fluorideandfluorosis.com/fluorosis/printfluorosis.html>
National Health and Medical Research Council (Australia) 2007
2
Introduction
• Fluoride removal techniques
Filtration
• Fluoride removal materials
Commercial materials
Locally available materials
Novel synthesized materials
Nalgonda Electro coagulation
Filtration Membrane
Activated alumina
Aluminum (hydr)oxide
Activated carbon
Clay
3
• Aluminum (hydr)oxide (AlOOH) amended substrate materials
Advantages
Favorable hydraulic performance
Reduced costs
Introduction
Problems of using AlOOH amended substrate materials in developing world
Limited fluoride adsorption capacity
Most desirable substrate materials not available for developing world
4
• Zeolites (molecular sieves) Widespread minerals in many developing regions
Origins of zeolites close to endemic fluorosis areas
Porous (alumino)silicate
Consisting of hollow cage framework
Large porous space for loading of aluminum (hydr)oxide
Introduction
5
Stilbite
Sodalite
Objectives
To develop locally available and efficient fluoride adsorbents using molecular sieves and natural zeolites
To understand the factors and processes that affect the fluoride adsorption of amended molecular sieves and zeolites
To assess the regeneration ability of aluminum hydroxide amended molecular sieves
Objectives
6
Adsorbent Largest pore
dimension (nm)a pHPZC Al content (%)
MS-3A 0.3 9.4 17.8
MS-4A 0.4 10.1 19.0
MS-5A 0.5 8.0 19.5
MS-13X 1.0 8.2 15.7
MS-Y 1.12 8.4 0.2-15.7
Si-MS3.2 (SiO2) 3.2 5.7 0
Sodalite Not measured NM 16.7
• Materials: Molecular sieve (MS) and zeolite
Methods
Commercial molecular sieves
Molecular sieve 13X
Sodalite
AlOOH amendmentwith AlCl3 at pH 5.3
7
Results and Discussion (R&D)
A B
MS-13X Before amendment
Al-MS-13X After amendment
8
• MS-A, and sodalite had measurable adsorption capacities
R&D: Efficiency
9
• Significant improvement in fluoride adsorption capacity
was observed after amendment (amended versus
unamended).
AlOOH amendment superior to other Al loading methods
R&D: Efficiency
Adsorbent Q1.5 (mg F-/g) Modification method
Al-sodalite 23.7±2.0 AlOOH amendment (this study)
Al exchanged zeolite F-9 4.66 Al exchange (Onyango et al. 2004)
Al loaded natural zeolite 0.92 Immersion in Al salt solution (Samatya et al. 2007)
10
Amendment
• No. of bed volume reaching breakthrough with Al-sodalite: 1360 (Inflow F- concentration: 10 mg/L, pH: 7, flow rate: 0.58 mL/min, EBCT: 6.8 min, media packing height: 5 cm)
R&D: Efficiency
1.5 mg/L
Material
No. of bed volume reaching breakthrough
Reference
Kanuma mud (silica, alumina) 60 Chen et al. 2011
Granular red mud 440 Tor et al. 2009
Fe3+ loaded cellulose 24 Zhao et al. 2008
Laterite 55 Sarkar et al. 2006
11
Breakthrough point
• Normalized Q1.5 of amended molecular sieves and zeolite by the mass fraction of aluminum (hydr)oxide (37.5% by weight) were generally less than the Q1.5 of pure AlOOH.
R&D: Factors and processes
12
Amended molecular
sieves and zeolite
Q1.5 (mg F-/g amended materials)
(Qe when Ce is 1.5 mg/L)
Q1.5 normalized by AlOOH
mass (mg F-/g AlOOH)
Al-MS-3A 7.3±0.7 19.6±1.9
Al-MS-4A 7.7±0.9 20.5±2.4
Al-MS-5A 4.2±0.4 11.1±1.2
Al-MS-13X 11.8±0.6 31.4±1.7
Al-MS-Y 14.5±1.3 38.6±3.5
Al-Si-MS3.2 17.4±1.3 46.3±3.4
Al-Sodalite 23.7±2.0 63.2±5.3
AlOOH 44.6±2.3 44.6±2.3
• The anticipated benefits of AlOOH amendment are more likely to be achieved using molecular sieves with larger pores.
Perhaps fluoride could access the AlOOH amended larger pores
R&D: Factors and processes
13
Amended molecular
sieves and zeolite
Q1.5 (mg F-/g amended materials)
(Qe when Ce is 1.5 mg/L)
Q1.5 normalized by AlOOH
mass (mg F-/g AlOOH)
Al-MS-3A 7.3±0.7 19.6±1.9
Al-MS-4A 7.7±0.9 20.5±2.4
Al-MS-5A 4.2±0.4 11.1±1.2
Al-MS-13X 11.8±0.6 31.4±1.7
Al-MS-Y 14.5±1.3 38.6±3.5
Al-Si-MS3.2 17.4±1.3 46.3±3.4
Al-Sodalite 23.7±2.0 63.2±5.3
AlOOH 44.6±2.3 44.6±2.3
Adsorbent Largest pore
dimension (nm)
MS-3A 0.3
MS-4A 0.4
MS-5A 0.5
MS-13X 1.0
MS-Y 1.12
Si-MS3.2 (SiO2) 3.2
Sodalite Not measured
• Experimental Q1.5 was larger than the calculated Qmax considering only surface adsorption based on the surface area.
Taking Al-MS-13X as an example
Surface area of Al-MS-13X: 40.1 m2/g
Diameter of hydrated fluoride ion: 0.52 nm
The maximum fluoride adsorption capacity assuming full monolayer coverage: 6 mg/g
6 mg/g < 11.8 mg/g
Amended molecular
sieves and zeolite
Q1.5 (mg F-/g amended materials)
(Qe when Ce is 1.5 mg/L)
Al-MS-13X 11.8±0.6
R&D: Factors and processes
14
• Measured fluorine content after adsorption (6% wt.) was greater than the calculated maximum fluorine content (0.56% wt.) due to surface adsorption alone based on surface area.
Al-MS-13X before adsorption
Al-MS-13X after adsorption
Elemental compositions (wt.%)
Additional processes contributing to fluoride removal
Co-precipitation of minerals containing fluoride
Exchange of chloride by fluoride
R&D: Factors and processes
15
• Use of 0.1 M sodium hydroxide led to poor fluoride removal in subsequent adsorption tests
Due to dissolution and loss of molecular sieves at high pH
• 60-80% of the original fluoride removal efficiency was recovered after regeneration when using 10-4 M (pH 9.6) or 10-6 M (pH 6.8) NaOH
R&D: Regeneration
16
• Decreased Q1.5 after each regeneration cycle for Al-MS-13X using 10-4 M NaOH
Due to loss of Al content over multiple regenerations
Fluoride adsorption to Al-MS-13X before and after regeneration with Freundlich isotherm fits
• Acceptable Q1.5 (2.21±0.11 mg/g) after two regeneration cycles
Al-MS-13X Al-MS-13X after four regeneration cycles
R&D: Regeneration
17
• Promising performance of amended materials in both batch and column experiments based on locally available zeolites (and molecular sieves)
• Substrates of large pores favorable for amendment; and processes in addition to surface adsorption contributing to the fluoride removal
• Ability to be regenerated and to partially recover fluoride adsorption capacity
Conclusions
18
• National Science Foundation (NSF) (CBET-1066425)
• Jessica Johnston for helping in the lab
• Teshome L. Yami and Anisha Nijhawan
Acknowledgement
19
QUESTIONS
Thank you
20
• Chen, N., Zhang, Z., Feng, C., Li, M., Chen, R. and Sugiura, N. (2011). “Investigations on the batch and fixed-bed column performance of fluoride adsorption by Kanuma mud.” Desallination, 268, 76-82.
• Onyango, M. S., Kojima, Y., Aoyi, O., Bernardo, E. C. and Matsuda, H. (2004). "Adsorption equilibrium modeling and solution chemistry dependence of fluoride removal from water by trivalent-cation-exchanged zeolite F-9." J. Colloid Interf. Sci., 279(2), 341-350.
• Samatya, S., Yüksel, Ü., Yüksel, M. and Kabay, N. (2007). "Removal of Fluoride from Water by Metal Ions (Al3+, La3+ and ZrO2+) Loaded Natural Zeolite." Sep. Sci. Technol., 42(9), 2033-2047.
• Sarkar, M., Banerjee, A., Pramanick, P. P. and Sarkar, A. R. (2006). “Use of laterite for the removal of fluoride from contaminated drinking water.” J. Colloid Interf. Sci., 302, 432-441.
• Tor, A., Danaoglu, N., Arslan, G. and Cengeloglu, Y. (2009). “Removal of fluoride from water by using granular red mud: Batch and column studies.” J. Hazard. Mater., 164, 271-278.
• Zhao, Y., Li, X., Liu, L. and Chen, F. (2008). “Fluoride removal by Fe(III)-loaded ligand exchange cotton cellulose adsorbent from drinking water.” Carbohydr. Polym., 72, 144-150.
References
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