FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
1. Title of the invention
A METHOD OF REMOVING FLUORIDE FROM WATER
2. Applicant(s)
Name Nationality Address
TATA CHEMICALS LIMITED INDIA BOMBAY HOUSE, 24 HOMI MOD! STREET, MUMBAI -
400001, INDIA
3. Preamble to the description
COMPLETE SPECIFICA TION
The following specification particularly describes the invention and the manner in which it is
to be performed.

The present disclosure provides a method of removing fluoride from water. Particularly, a method of removing fluoride from water using a water purification composition is disclosed.
BACKGROUND
Generally, water available from natural sources, such as groundwater or surface water, contains impurities and is not safe for human consumption. The impurities may include chemical impurities, such as fluoride, bromide, phosphate, arsenic etc. These impurities can thus cause acute and chronic illnesses.
Excessive exposure to fluoride can give rise to a number of adverse effects. These effects range from mild dental fluorosis to crippling skeletal fluorosis as the level and period of exposure increases. Various health organizations have prescribed safe limits for fluoride concentration in drinking water. For example, the World Health Organization prescribes a limit of 0.5-1.5 parts-per-million (ppm) as the safe limit for fluoride concentration in drinking water.
The prescribed safe limits for fluoride concentration often tend to be difficult to achieve. A large population across the world, especially those in developing and underdeveloped countries, directly consumes contaminated water containing fluoride. Defluoridation plants may be set up for providing purified water for the population but such plants usually get abandoned due to lack of proper maintenance. Point-of-use or household defluoridation devices, including reverse osmosis units and ion exchange based systems, that are available in the market are expensive and involve regular maintenance, which puts them beyond the reach of many households.
The prior art processes are able to remove fluoride from aqueous streams by using large amounts of expensive chemical additives. Therefore, there remains a need for an

inexpensive and easy to perform method of removing fluoride from water. Further, there is a need for a method of removing fluoride from water that removes fluoride to an acceptably low level for drinking purposes.
SUMMARY
A method of removing fluoride from water is disclosed. The method comprises of adding lime to the water to precipitate phosphate, bromide, silicate, sulphate and /or metal hydroxides; removing the precipitate from the water, adding alum and a flocculent to the water obtained after removing the precipitate, to further precipitate fluoride and facilitate formation of flocs thereof. The method further comprises of passing the water with flocs through a water purification composition capable of removing flocs, the water purification composition comprising quartz particles having iron hydroxide and aluminum salt coated thereon, wherein the iron hydroxide and aluminum salt are formed in-situ by reacting an iron salt with aluminum hydroxide, the coated quartz particles heat stabilized by calcination and collecting water with reduced fluoride levels from the water purification composition.
DETAILED DESCRIPTION
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the disclosed process, and such further applications of the principles of the invention therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.
Reference throughout this specification to "one embodiment" "an embodiment" or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrase "in one embodiment*', "in an embodiment" and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
The present disclosure provides a method of removing fluoride from water. The method comprises of adding lime to the water to precipitate phosphate, bromide, silicate, sulphate and /or metal hydroxides, removing the precipitate from the water. The method further comprises of adding alum and a flocculent to the water obtained after removing the precipitate, to further precipitate fluoride and facilitate formation of flocs thereof, passing the water with flocs through a water purification composition capable of removing flocs, the water purification composition comprising quartz particles having iron hydroxide and aluminum salt coated thereon, wherein the iron hydroxide and aluminum salt are formed in-situ by reacting an iron salt with aluminum hydroxide, the coated quartz particles are heat stabilized by calcination; and collecting water with reduced fluoride levels from the water purification composition.
In accordance with an embodiment, the method further comprises of passing the water collected from the water purification composition through another water purification composition capable of removing remaining flocs, the water purification composition comprising quartz particles having iron hydroxide and aluminum salt coated thereon,

wherein the iron hydroxide and aluminum salt are formed in-situ by reacting an iron salt with aluminum hydroxide, the coated quartz particles are heat stabilized by calcination.
In accordance with an embodiment, further passing of water collected from the water purification composition through another water purification composition facilitates further reduction in fluoride levels. This also reduces the time required to obtain water having acceptably low levels of fluoride for drinking purposes. Further, this also helps in achieving equivalent retention time required to obtain water having acceptably low levels of fluoride for drinking purposes.
In accordance with an embodiment, iron salt is selected from ferrous sulphate, ferric chloride or ferric nitrate.
In accordance with an embodiment, iron salt and aluminum hydroxide are reacted in stoichiometric amounts.
In accordance with an embodiment, the water purification composition adsorbs fluoride present in water. By way of example, fluoride present in water reacts with the water purification composition in accordance with the following reaction(s) depending on iron salt used:
A1(N03)3 + 3 NaF --------→ A1F3 + 3 NaN03
AlCl3 + 3 NaF --------→ A1F3 + 3 NaCl
A12(S04)3 + 6 NaF -------→ A1F3 + 3 Na2S04
In accordance with an embodiment, quantity of lime added to the water is sufficient to increase pH of water to at least 8.5. By way of example, quantity of lime added to the water is such that the pH of water is in a range of 8.5 to 12. In accordance with an embodiment, increase in pH of water facilitates precipitation of phosphate, bromide,

silicate, sulphate and metal hydroxides. Phosphate, bromide, silicate, sulphate and metal ions present in water compete with fluoride for adsorption by the water purification composition.
In accordance with an embodiment, the precipitate is removed by passing the water through a water purification composition, the water purification composition comprising quartz particles having iron hydroxide and aluminum salt coated thereon, wherein the iron hydroxide and aluminum salt are formed in-situ by reacting an iron salt with aluminum hydroxide, the coated quartz particles are heat stabilized by calcination.
In accordance with an aspect, quantity of alum added to the water is sufficient to decrease pH of water to at least 5.5. By way of example, quantity of alum added to the water is such that the pH of water is in a range of 5.5 to 7.5. Decrease in pH of water facilitates precipitation of fluoride. In accordance with an embodiment, alum is ferric alum.
In accordance with an aspect, flocculent is added to facilitate formation of fluoride containing floes.
In accordance with an embodiment, flocculent is non-ionic polyacrylamide. By way of example, flocculent having a non-ionic group which is effective in a pH range of 2-10 including polyethylene-imines, polyamides-amines, polyamines, polyethylene oxide, sulfonated compounds can be used.
In accordance with an embodiment, the water purification composition is prepared by a method comprising coating quartz particles with iron hydroxide and aluminum salt, wherein the iron hydroxide and aluminum salt are formed in-situ by reacting an iron salt with aluminum hydroxide. The method further comprises of drying and calcining the coated quartz particles to obtain heat stabilized coated quartz particles.

In accordance with an embodiment, the iron salt is selected from ferrous sulphate, ferric chloride or ferric nitrate.
In accordance with an embodiment, the iron salt and aluminum hydroxide are reacted in stoichiometric amounts. By way of example, 495 gm of ferric nitrate is reacted with 95.5 gm of aluminum hydroxide.
In accordance with an embodiment, the iron salt and aluminum hydroxide are reacted in distilled water to facilitate in-situ formation of iron hydroxide and aluminum salt. By way of example following reaction(s) result in in-situ formation of iron hydroxide and aluminum salt, depending on iron salt used:
FeCI3 + AI{OH)3 --------→ Fe(OH)3 + AICI3
Ferric chloride Aluminum hydroxide Ferric hydroxide Aluminum chloride
3 Fe(SO)4.7H2O + 2 AI(OH)3 --------→ 3 Fe{OH)3 + A!2(S04)3
Ferrous sulphate Aluminum hydroxide Ferric hydroxide Aluminum sulphate
Fe(N03)39H20 + AI(OH)3 --------→ Fe(OH)3 + AI(N03)3
Ferric nitrate Aluminum hydroxide Ferric hydroxide Aluminum nitrate
In accordance with an embodiment, drying is carried out at a temperature of 130°C.
In accordance with an embodiment, drying is carried out for a time period of 2 hours.
In accordance with an embodiment, calcining is carried out at a temperature of 550°C.
In accordance with an embodiment, calcining is carried out for a time period of 5 hours.

In accordance with an aspect, calcining of the coated quartz particles facilitates heat stabilization of the coated quartz particles, such that the heat stabilized coated quartz particles exhibits no or reduced leaching of iron hydroxide or aluminum salt when water is passed there through. Calcining facilitates densification and pore size reduction of the coated quartz particles due to increase in compaction and decrease in porosity. Calcining also provides structural strength and stability to the coated quartz particles. By way of example, passing of approximately 1500 litres of water through a column packed with 50 grams of the water purification composition results in no leaching of iron hydroxide and aluminum salt.
In accordance with an aspect, in-situ formation of iron hydroxide and aluminum salt facilitates adsorption of fluoride from water in an efficient manner thereby resulting in reduction in fluoride levels to acceptable limits. In-situ formed iron hydroxide in nascent is very active and has higher affinity for fluoride and like ions.
In accordance with an aspect, the water purification composition is capable of removing arsenic, fluoride, phosphate, bromide, silicate, sulphate and heavy metals from water.
In accordance with an aspect, the water purification composition is capable of being used in a pH range of 5-12 of input water.
The following example(s) of results obtained by using the method of removing fluoride from water and method of making the water purification composition are exemplary and should not be understood to be in any way limiting.
Example 1:
A suitable quantity of water purification composition was loaded in a column bed to impart adequate contact time. The contaminated water covered reasonable range of fluoride concentration. In an experiment, contaminated water having 20 mg of NaF is

passed through a column bed supported by sieve mesh with pore size 250 μ, with a flow rate of 6 Litre / minute (approx). For two stage column bed studies (Table 2), each column bed is packed with 50 g of coated quartz particles. The output water thus obtained has fluoride levels reduced to acceptable limits for drinking purposes. Further, batch experiments are conducted by adding 50 gm of coated quartz to a stainless steel cylindrical vessel having 40 Litre of fluoride contaminated water and treated water was intermittently withdrawn. Such samples of treated water have fluoride levels as illustrated in Table 1:
Table 1: Batch experiment results for fluoride removal, [fluoride in input water = 10 mg / litre]

Sample collected after Fluoride input Fluoride outpul
0.0 hr 10 mg / Litre -
0.5 hr 10 mg / Litre 2.42 mg/Litre
l.Ohr 10 mg / Litre 1.53 mg/Litre
2.0hr 10 mg / Litre 1.415 mg/Litre
3.0 hr 10 mg / Litre 0.898 mg/Litre
4.0 hr 10 mg / Litre 0.393 mg/Litre
Table 2: Two Stage Column bed studies for fluoride removal from contaminated water

S.No. Filter bed Flow Cumulative Fluoride Fluoride
rate L/hr volume water input output
passed (Lit) .

1. Fl 2.6 96 5 mg / Litre 3 mg /Litre

F2 2.8 96 Fl output water 1.08 mg/Litre
2. FS1 2.6 33 5 mg / Litre 3.66 mg/ Litre

FS2 2.9 33 FS1 output water 0.783 mg /Litre
3. FN1 2.4 33 5 mg / Litre 1.29mg/Litre

FN2 2.8 33 FN1 output water 1.10 mg/Litre
Wherein:
Fl indicates filter bed packed with 50gm of the water purification composition obtained by reacting ferric chloride and aluminum hydroxide.
F2 indicates filter bed packed with 50gm of the water purification composition obtained by reacting ferric chloride and aluminum hydroxide.
FS1 indicates filter bed packed with 50gm of the water purification composition obtained by reacting ferrous sulphate and aluminum hydroxide.
FS2 indicates filter bed packed with 50gm of the water purification composition obtained by reacting ferrous sulphate and aluminum hydroxide.
FN1 indicates filter bed packed with 50gm of the water purification composition obtained by reacting ferric nitrate and aluminum hydroxide.
FN2 indicates filter bed packed with 50gm of the water purification composition obtained by reacting ferric nitrate and aluminum hydroxide.

Example 2:
Lime is added to 1 liter of contaminated water having 20 mg / Litre of fluoride ( as NaF ) and pH around 7, to raise pH of water above 8.5 which facilitates precipitation of base metal compounds as hydroxides and further at pH between 11-12 phosphates are eliminated. Further, ferric alum is added to reduce pH to 6 -7 which is suitable for getting rid of fluoride. A non-ionic flocculent (polyacryl amide) is added within a couple of minutes of adding alum to facilitate formation of fluoride containing larger floes, in a quantity of about 20-25 ppm. Chemical consumption in a typical fluoride removal method:
Lime requirement for adjusting pH = 11.72 = 2 g / Litre
Ferric alum added to adjust pH = 6.5 - 6 g / Litre
Poly acryl amide = 25 mg / Litre
Example 3:
495 grams of ferric nitrate is added to 400 ml distilled water to obtain a solution. Followed by addition of 95.5 grams of aluminum hydroxide to facilitate in-siiu formation of ferric hydroxide and aluminum nitrate. 500 grams of quartz particles are then added and mixed with the mixture obtained in the preceding step. Thus obtained mixture is then dried in a hot air oven at a temperature of 120 °C for a time period of 2 hours to remove moisture. The dried mixture is then subjected to calcination in a furnace at a temperature of 550 °C for a time period of 5 hours to obtain heat stabilized coated quartz particles.
SPECIFIC EMBODIMENTS ARE DESCRIBED BELOW
A method of removing fluoride from water comprising adding lime to the water to precipitate phosphate, bromide, silicate, sulphate and /or metal hydroxides; removing the

precipitate from the water; adding alum and a flocculent to the water obtained after removing the precipitate, to further precipitate fluoride and facilitate formation of flocs thereof; passing the water with flocs through a water purification composition capable of removing flocs, the water purification composition comprising quartz particles having iron hydroxide and aluminum salt coated thereon, wherein the iron hydroxide and aluminum salt are formed in-situ by reacting an iron salt with aluminum hydroxide, the coated quartz particles heat stabilized by calcination; and collecting water with reduced fluoride levels from the water purification composition.
Such method(s), further comprising passing the water collected from the water purification composition through another water purification composition capable of removing remaining floes, the water purification composition comprising quartz particles having iron hydroxide and aluminum salt coated thereon, wherein the iron hydroxide and aluminum salt are formed in-situ by reacting an iron salt with aluminum hydroxide, the coated quartz particles heat stabilized by calcination.
Such method(s), wherein quantity of lime added is sufficient to increase pH of water to at least 8.5.
Such method(s), wherein quantity of alum added is sufficient to decrease pH of water to at least 5.5.
Such method(s), wherein alum is ferric alum.
Such method(s), wherein the flocculent is non-ionic polyacrylamide
Such method(s), wherein the iron salt is selected from ferrous sulphate, ferric chloride or ferric nitrate.
Such method(s), wherein the iron salt and aluminum hydroxide are reacted in stoichiometric amounts.

Such method(s). wherein the precipitate obtained by addition of lime in water is removed by passing the water through a water purification composition, the water purification composition comprising quartz particles having iron hydroxide and aluminum salt coated thereon, wherein the iron hydroxide and aluminum salt are formed in-situ by reacting an iron salt with aluminum hydroxide, the coated quartz particles heat stabilized by calcination.
INDUSTRIAL APPLICATION
The method of removing fluoride from water as described above is easy to perform and economical as there is no requirement of electricity. The method disclosed is capable of removing fluoride from water in a lesser duration of time as compared to conventionally available methods. The method can be easily scaled down to meet individual household requirements or scaled up to meet community requirements. Additionally, the method disclosed is also capable of removing phosphate, bromide, silicate, sulphate and heavy metals from water. The water purification composition used in the disclosed method exhibits no leaching of iron hydroxide or aluminum salt when water is passed there through. Additionally, the exhausted water purification composition through which further removal of fluoride cannot be carried out, can be used as a flux in rotary kiln of a cement mill or brick manufacturing industry.

WE CLAIM:
1. A method of removing fluoride from water comprising:
adding lime to the water to precipitate phosphate, bromide, silicate, sulphate and /or metal hydroxides;
removing the precipitate from the water;
adding alum and a flocculent to the water obtained after removing the precipitate, to further precipitate fluoride and facilitate formation of floes thereof;
passing the water with floes through a water purification composition capable of removing floes, the water purification composition comprising quartz particles having iron hydroxide and aluminum salt coated thereon, wherein the iron hydroxide and aluminum salt are formed in-situ by reacting an iron salt with aluminum hydroxide, the coated quartz particles heat stabilized by calcination; and
collecting water with reduced fluoride levels from the water purification composition.
2. A method of removing fluoride from water as claimed in claim 1, further comprising passing the water collected from the water purification composition through another water purification composition capable of removing remaining floes, the water purification composition comprising quartz particles having iron hydroxide and aluminum salt coated thereon, wherein the iron hydroxide and aluminum salt are formed in-situ by reacting an iron salt with aluminum hydroxide, the coated quartz particles heat stabilized by calcination.
3. A method of removing fluoride from water as claimed in claim 1, wherein quantity of lime added is sufficient to increase pH of water to at least 8.5.

4. A method of removing fluoride from water as claimed in claim 1, wherein quantity of alum added is sufficient to decrease pH of water to at least 5.5.
5. A method of removing fluoride from water as claimed in claim 1, wherein alum is ferric alum.
6. A method of removing fluoride from water as claimed in claim 1, wherein the flocculent is non-ionic polyacrylamide
7. A method of removing fluoride from water as claimed in claim 1, wherein the iron salt is selected from ferrous sulphate, ferric chloride or ferric nitrate.
8. A method of removing fluoride from water as claimed in claim 1, wherein the iron salt and aluminum hydroxide are reacted in stoichiometric amounts.
9. A method of removing fluoride from water as claimed in claim 1, wherein the precipitate obtained by addition of lime in water is removed by passing the water through a water purification composition, the water purification composition comprising quartz particles having iron hydroxide and aluminum salt coated thereon, wherein the iron hydroxide and aluminum salt are formed in-situ by reacting an iron salt with aluminum hydroxide, the coated quartz particles heat stabilized by calcination.