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 MadusankaOther group members:Eranga WarsakoonNuwan GunawardeneHasitha KalaheImalka MunaweeraNilwala Kottegoda

IntroductionAbout 1 billion people in the world, mostly in developing countries, have no access to potable water2.6 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

Mild dental fluorosis to crippling skeletal fluorosis

Chronic kidney disease (CKD)

Fluoride removing methods in water

AdsorptionPrecipitation or AdsorptionIon-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 HydroxidesStructure-based on the Brucite ( Mg(OH)2 )structure

General formula: M2 +1-xM

3+ x(OH)2.A

n-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

Isomophous substitution of M2+ of brucite by M3+.

Brucite

brucite like layers

Inter layer region

Charge balancing anions

4.8 nm

LDH

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 lowcost and under ambient conditions.

Applications of Layered Double Hydroxides

Biomedical applications-Drug stabilizer, Antacids,Gene and Drug Delivery

Catalysis- Hydrogenation,Polymerizations

Polymer nanocomposites

Ion Exchanger

Intercalation

LDH as an Ion Exchanger

Research methodology

1) Synthesis of Mg-Al-hydroxide LDH (Mg-Al-OH)

Mg-AlMixed metal solution

50 ml

Anionic solution (Al: OH- =1:10)

50 ml+

co- precipitation reaction

25 oC, pH=10Under 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

SEM Images of LDHs

Results

(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.

PXRD

(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

FTIR

Weight of filter

material/ (g)

LDH Flouride

concentration (mg/l)

Brick powderFlouride

concentration (mg/l)

00.010.050.10.20.51.02.0

8.047.807.576.636.544.571.801.05

8.047.256.756.656.556.5

5.485.08

Flouride ion concentrations after filtering though LDHs and brick powder.

Adsorption isotherm for Mg-Al-OH LDH and brick powder

Ca(OH)2 solution inlet for

regeneration

Outlet for backwash

water outlet

Inlet for Chlorination

Storage

Deflouridation Columns (with LDH)

Sand filter

Bore hole

Water Pump

Treated water

Proposed layout design of the purification plant

ConclusionsLayered 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 economically and environmentally sustainable.

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 MadusankaEranga WarsakoonNuwan GunawardeneHasitha KalaheImalka MunaweeraNilwala Kottegoda