International Conference on Sustainable Built Environment
NANCO AND UNIVERSITY OF MELBOURNE JOINT RESEARCH SESSION ON
NANOTECHNOLOGY AND SUSTAINABLE BUILT ENVIRONMENT
13-14 December, 2010 at Earls Regency, Kandy, Sri Lanka
DEFLOURINATION OF DRINKING WATER USING
LAYERED DOUBLE HYDROXIDES
Presented by: Nadeesh Madusanka
Other group members:
Eranga Warsakoon
Nuwan Gunawardene
Hasitha Kalahe
Imalka Munaweera
Nilwala Kottegoda
Introduction
About 1 billion people in the world, mostly in
developing countries, have no access to potable
water
2.6 billion people lacking access to adequate
sanitation.
Sri Lanka currently faces a number of water
related problems.
70 % of the Sri Lankan population satisfies their
water needs from dug wells, deep wells, reservoirs
and rivers.
One of the pertaining water related problem in the
dry zone of Sri Lanka
Levels fluoride ion
concentrations in ground water
> 10 ppm
WHO recommended
fluoride ion concentration
1 ppm
Adverse effects due to the excessive
exposure to fluoride in drinking-water
Chronic kidney disease (CKD)
Mild dental fluorosis to
crippling skeletal fluorosis
Fluoride removing methods in water
Adsorption
Precipitation or Adsorption
Ion-exchange
Electro dialysis
Electrochemical Processes
The most common approach to remove
fluoride in the dry zone
of Sri Lanka
•Use of brick filters -low efficiency.
•Combination of alum (or aluminium chloride)
and lime (or sodium aluminate), together with
bleaching powder, are added to high-fluoride
water, stirred and left to settle.
•Flocculation, sedimentation and filtration.
Currently, nanotechnology has not left any field
Untouched.
This new technology can be harnessed to
provide sustainable solutions to water related
problems prevailing in Sri Lanka particularly to
remove fluoride ions from drinking water.
Possible Nanomaterials
Layered Double Hydroxide
Nano TiO2
Nano Magenetite
Layered Double Hydroxides
Structure-based on the Brucite ( Mg(OH)2 )structure
brucite like
layers
4.8 nm
Inter layer region
Isomophous
substitution of M2+ of
brucite by M3+.
Charge balancing
anions
Brucite
LDH
2+
3+
n-
General formula: M 1-xM x(OH)2.A x/n-.mH2O
M2+ is a divalent metal ion, such as Mg2+, Ca2+, Zn2+
M3+ is a trivalent metal ion, such as Al3+, Cr3+, Fe3+
An− is any anion
Characteristics of Layered Double Hydroxides
Thermally stable.
A range of trivalent and
divalent cationic combinations
are available.
The cationic ratio can be
modified within a wide range.
Large anion exchange
capacity.
Can be synthesized as bulk
quantities with relatively low
cost and under ambient
conditions.
Applications of Layered Double Hydroxides
Biomedical applications-Drug
stabilizer, Antacids,Gene and Drug
Delivery
CatalysisHydrogenation,Polymerizations
Polymer nanocomposites
Ion Exchanger
LDH as an Ion Exchanger
Intercalation
Research methodology
1) Synthesis of Mg-Al-hydroxide LDH (Mg-Al-OH)
Mg-Al
Mixed metal solution +
50 ml
25 oC,
pH=10
Anionic solution
(Al: OH- =1:10)
50 ml
co- precipitation
reaction
Under N2
atmosphere
MgAl-OH- LDH
Ref. Hibino and Jones , 2001 J. Mater. Chem 11 1321
2) Flouride removal from drinking water
using Mg-Al-OH-LDH
Different weights of LDH were added to water
samples containing fluoride ions (8.2 ppm ,100 ml)
and kept it for 24 hours on the magnetic stirrer.
Final concentration of the fluoride solution was
tested using an ion selective electrode.
The efficiency of the LDH material was compared
with that of the conventional method where brick
powder is used as the ion exchange medium.
3) Regeneration of the material
Exhausted LDH powder was calcined at 400 oC for
three hours.
Then the resulting mixed oxide was characterized
by PXRD and FTIR.
Then it was exposed to 1 M NaOH solution for 24
hours with mechanical stirring and the resulting
product was characterized using PXRD and FTIR.
The fluoride gas coming out was allowed to absorb
into 1 M calcium hydroxide solution.
4) Characterization
Scanning Electron Microscopy
Powder X-ray Diffraction
Fourier Transform Infra Red Spectroscopy
Chemical Analysis
Results
SEM Images of LDHs
PXRD
(a) Mg-Al-OH LDH
(b) Mg-Al-F LDH
(c) mixed oxide received after
calcination of the
Mg-Al-F LDH at 450 0C
(d) regenerated mixed oxide
in the presence of OH ions.
FTIR
(a) Mg-Al-OH LDH
(b) Mg-Al-F LDH
(c) mixed oxide received after
calcinations of the Mg-Al-F
LDH at 450 0C
Flouride ion concentrations after filtering
though LDHs and brick powder.
Weight of
LDH
Brick powder
filter
Flouride
Flouride
material/ (g) concentration concentration
(mg/l)
(mg/l)
0
8.04
8.04
0.01
7.80
7.25
0.05
7.57
6.75
0.1
6.63
6.65
0.2
6.54
6.55
0.5
4.57
6.5
1.0
1.80
5.48
2.0
1.05
5.08
Adsorption isotherm for Mg-Al-OH LDH
and brick powder
Proposed layout design of the purification
plant
Deflouridation Columns (with LDH)
Sand filter
Water Pump
Bore hole
Storage
Ca(OH)2 solution Outlet for
backwash
inlet for
water
regeneration
outlet
Inlet for
Chlorination
Treated
water
Conclusions
Layered double hydroxides have displayed high
efficiency in removing fluoride ions from drinking water
compared to the basic methods currently used.
LDHs can be used in either regional water
purification units or domestic house hold filters.
Product is
sustainable.
economically
and
environmentally
An added advantage of using LDHs would be its
superior capability of removing other anions such as
carbonate, sulfates etc
Acknowledgement
D.S. Senanayake College, Colombo 07.
Sri Lanka Institute of Nanotechnology
DEFLOURINATION OF DRINKING WATER
USING LAYERED DOUBLE HYDROXIDES
Research Group:
Nadeesh Madusanka
Eranga Warsakoon
Nuwan Gunawardene
Hasitha Kalahe
Imalka Munaweera
Nilwala Kottegoda