FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
"A Method of Effluent Treatment And An Effluent Treatment Plant Thereof."
Tata Chemicals Limited, an Indian company of Bombay House, 24 Homi Mody Street, Mumbai -1
The following specification particularly describes the invention and the manner in which it is to be performed.

The invention refers to the treatment of plant effluent and the extraction of useful elements from plant effluent. More particularly, the invention relates to a method and system of utilizing effluent from a plant for the production of magnesium carbonate.
Background of the Invention
5 Chemical plants use various ingredients for the manufacture of desired
compounds and generate large quantities of effluent. A plant for the manufacture of soda ash is one such example.
Sodium carbonate, soda ash or washing soda finds wide use in industry including the manufacture of glass, pulp and paper, detergents, chemicals such as sodium silicates 10 and sodium phosphates and often as an alkaline agent in many chemical industries.
Soda ash is synthetically produced in large quantities from sodium chloride generally from a process referred to in the industry as the Solvay process. The Solvay process describes the conversion of sodium chloride to sodium carbonate using ammonia and limestone. A typical soda ash plant generates large quantities of effluent and as an 15 example the assignees plant generates approximately 23,000 Kilolitres effluent per day. The soda ash plant effluent is typically disposed off to the sea after necessary treatment as required for compliance with environment norms.
This effluent comprises of elements that are capable of being utilized in different industries. As an example the plant effluent comprises of substantial quantities of 20 magnesium hydroxide.
There is an increasing demand that useful elements are extracted from the effluent so as to work towards a sustainable environment and economies of production be achieved.
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Magnesium carbonate is a white solid that is used to produce magnesium metal,
refractory bricks, and also in flooring, fireproofing, cosmetics, dusting powder and
toothpaste, amongst other uses. Magnesium carbonate also finds use as a filler material,
smoke suppressant in plastics, re-enforcing agent in neoprene rubber, drying agent,
5 laxative, and color retention. High purity magnesium carbonate is used as antacid and as
an additive in table salt. Magnesium carbonate also finds use as a drying agent for hands in rock climbing, gymnastics and weight lifting. Not all applications of magnesium carbonate require high purity of the compound.
Magnesium carbonate is produced from magnesium rich bittern and lime as a raw 10 material or from Magnasite ore in conventional processes.
Summary of the Invention
The invention provides for a method of effluent treatment comprising the steps of converting magnesium hydroxide in effluent to magnesium bicarbonate, filtering effluent
15 to remove insolubles, and converting magnesium bicarbonate to magnesium carbonate. The invention also provides for an effluent treatment plant comprising: a carbonator for converting magnesium hydroxide to magnesium bicarbonate, a primary filter for filtering out insolubles from effluent, and a decarbonator for converting magnesium bicarbonate to magnesium carbonate.
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Brief Description of Accompanying Drawings:
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The accompanying drawings illustrate the preferred embodiments of the invention and together with the following detailed description serve to explain the principles of the invention.
5 FIG. 1 is a schematic illustration of an effluent treatment plant for the production
of magnesium carbonate in accordance with an embodiment of the invention.
Detailed Description of Invention
To promote an understanding of the principles of the invention, reference will be 10 made to the embodiment illustrated in the drawing 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 illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the
15 invention relates.
The invention describes a method of treating effluent from a plant to produce magnesium carbonate. The invention also describes a system for extracting magnesium carbonate from plant effluent.
Plant effluent usually in liquid or sludge form has dissolved and un-dissolved
20 elements in it. Magnesium present in the effluent is largely in the form of magnesium
hydroxide. The effluent is carbonated that results in the conversion of magnesium
hydroxide to magnesium bicarbonate that is soluble in the effluent. This carbonated
effluent is filtered to remove insolubles and solids. Filtrate obtained includes dissolved
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magnesium bicarbonate that undergoes de-carbonation causing bicarbonate in the solution to precipitate out as magnesium carbonate.
In order to increase the solid concentration the plant effluent is preferably
thickened before carbonation. The effluent is also preferably washed with water to reduce
5 chloride content before carbonation. In accordance with an embodiment of the invention
the end products from the de-carbonation stage are preferably filtered and washed to
provide magnesium carbonate.
In accordance with an embodiment the invention provides for an effluent treatment plant for the extraction of magnesium carbonate from plant effluent. The
10 effluent treatment plant comprises of a carbonation section, a filtration section and a de-carbonation section. The carbonation section of the plant is for conversion of magnesium hydroxide to magnesium bicarbonate in the effluent. The filtration section filters out all solids and insolubles from the carbonated effluent. The de-carbonation section precipitates out magnesium carbonate from the filtrate.
15 In accordance with an embodiment of the invention the effluent treatment plant is
preferably provided with a thickener. The thickener receives effluent from plant and increases the solid concentration.
In accordance with an embodiment of the invention the effluent treatment plant is preferably provided with a washer or re-pulper. The washer or repulper washes the
20 effluent to reduce chlorine content. It is preferred that the washing or re-pulping is carried out after the thickening.
With reference to the accompanying figures and initially to figure 1 an effluent treatment plant (10) in accordance with an embodiment of the invention is schematically
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illustrated. As preferred, effluent from plant is sent to a thickener (1). A thickener is essentially equipment used to concentrate suspended solids by gravity settling so that steady state material balance is achieved. As also preferred, underflow from the thickener is sent to a repulper (2) which is an agitated vessel used for mixing of underflow solids 5 with water. The thickened effluent is washed with water at repulper (2) to reduce chloride content. Effluent from repulper is sent to a carbonation section (3).
Carbonation is carried out using a stream of C02 gas. Carbon dioxide is bubbled through the effluent in the carbonating tank (3). An agitator is preferably provided to enhance the proper dispersion of the gas in to the effluent and also ensure that the mass of 10 the effluent is not allowed to settle down. Passing of carbon dioxide through effluent causes magnesium hydroxide present in effluent to be converted to magnesium bicarbonate. Magnesium bicarbonate is soluble and dissolves in the effluent.
The reaction for the above step is:
4Mg(OH)2 + 8C02 ► 4 Mg(HC03)2
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In accordance with an embodiment the carbon dioxide for the carbonation section may be obtained from the plant itself without requiring any additional arrangements.
The carbonated effluent from the carbonator (3) is sent to a primary filter (4) where any insolubles or solids such as Si02, R3O3 etc, or unconverted magnesium 20 hydroxide are filtered out and effluent in the form of filtrate of magnesium bicarbonate, free of solids, is obtained. This filtrate is then sent for decarbonation to the decarbonator (5). In the decarbonator (5) steam is bubbled through the filtrate. The magnesium bicarbonate in the filtrate precipitates out as magnesium carbonate in the decarbonator.
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The reaction for the above step is
4Mg(HC03)2 Hot Air ^ 3 MgC03.Mg(OH)2 .3H20 + C02
The resultant solution comprising the precipitated magnesium carbonate from the 5 decarbonation section is preferably sent to a second filter where the precipitated magnesium carbonate is filtered out and washed. This Magnesium Carbonate is then sent for drying and packaging.
In accordance with an embodiment, filtrate from second filter may be utilized as part of the water required for repulping or washing the effluent. This also assists in an 10 enhanced utilization of elements present in effluent.
In accordance with an embodiment the solids and insolubles filtered out at the primary filter may be used in some industry, after suitable treatment or modification, as may be necessary.
It will readily be appreciated by those skilled in the art that the present invention 15 is not limited to the specific embodiments herein shown. Thus variations may be made within the scope and spirit of the accompanying claims without sacrificing the principal advantages of the invention.
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We Claim:
1. A method of effluent treatment comprising the steps of;
i. converting magnesium hydroxide in effluent to magnesium
bicarbonate, ii. filtering effluent to remove insolubles, and iii. converting magnesium bicarbonate to magnesium carbonate.
2. A method of effluent treatment as claimed in claim 1 wherein the magnesium hydroxide is converted to magnesium bicarbonate by carbonation.
3. A method of effluent treatment as claimed in claim 1 or 2 wherein the effluent is thickened before the magnesium hydroxide is converted to magnesium bicarbonate.
4. A method of effluent treatment as claimed in claim 1 or 2 wherein the effluent is repulped before magnesium hydroxide is converted to magnesium bicarbonate.
5. A method of effluent treatment as claimed in claim 1 wherein the effluent comprising converted magnesium carbonate is filtered.
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A method of effluent treatment as claimed in claim 1 wherein the magnesium carbonate obtained is washed.
An effluent treatment plant comprising:
a. a carbonator for converting magnesium hydroxide to
magnesium bicarbonate,
b. a primary filter for filtering out insolubles from effluent,
and
c. a decarbonator for converting magnesium bicarbonate to
magnesium carbonate.
An effluent treatment plant as claimed in claim 1 comprising a thickener for increasing solid concentration of the effluent.
An effluent treatment plant as claimed in claim 1 comprising a repulper for washing effluent with water to reduce chloride content.
An effluent treatment plant as claimed in claim 1 comprising a filter located after the decarbonator for filtering out magnesium carbonate from effluent.
A method of effluent treatment substantially as herein described with reference to and as illustrated by the accompanying drawings.
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12. An effluent treatment plant substantially as herein described with
reference to and as illustrated by the accompanying drawings.
5 Dated this f day of March 2007
Of Anand and Anand Agent for Applicant Essenese Obhan 10
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ABSTRACT
The invention provides for a method of treatment of plant effluent and the extraction of useful elements from plant effluent. More specifically, the invention
5 provides for a method and system of utilizing effluent from a plant for the production of magnesium carbonate.
Figure 1
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