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

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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

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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

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• 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

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• 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

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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

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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

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Results and Discussion (R&D)

A B

MS-13X Before amendment

Al-MS-13X After amendment

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• MS-A, and sodalite had measurable adsorption capacities

R&D: Efficiency

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• 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)

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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

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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

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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

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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

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• 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

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• 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

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• 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

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• 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

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• National Science Foundation (NSF) (CBET-1066425)

• Jessica Johnston for helping in the lab

• Teshome L. Yami and Anisha Nijhawan

Acknowledgement

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QUESTIONS

Thank you

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• 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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