Title of Invention

A PROCESS FOR THE REMOVAL OF OXALATES AND OTHER HUMIC BODIES FROM BAYER'S LIQUOR.

Abstract A process for the removal of oxalates and coloured humic bodies from Bayer's liquor by contacting the impure alkali aluminate Bayer's liquor with activated carbon, maintaining the intimate contact between the liquor and the activated carbon for a time period ranging from 0.5 to 2 hrs to effect the sorption of oxalates and coloured humic bodies followed by separation of the liquor from the absorbents for recycling.
Full Text The present invention relates to a process for the removal of oxalates and other humic bodies from Bayer's liquor.
Bayer's process liquors obtained from digestion of bauxites in presence of caustic solutions contains organic impurities such as humates and oxalate carbon in it. During the processing of the said liquor for production of aluminium hydrate and alumina, coprecipitation of sodium oxalate with fine hydrate crystals (the needle crystals of oxalate) act as secondary nucleation sites, reduction in agglomeration efficiency, difficulties in particle size classification imparting brittleness to crystals and thus fragmentation of particles during calcination [ J.A. Chartouni (1988), VI Int. Congress of ISCOBA May 11-22, 1988; P.J. The and J.F. Bush, 1987, Light Metals, p.5; L.A.D. Chin, Light Metals 1988, pp 49-33]. Hence removal of oxalate from the Bayer's liquor helps in improving the above factors.
Reference may be made for oxalate removal / reduction in Bayer's liquor which is broadly comprises chemical reaction, removal based on physical properties and chemical reaction with physical separation [U.S. Patent 3, 337, 305 ; US Patent 3, 649, 185 ; US Patent 3, 899, 571 ; US Patent 3, 457, 032. Other ..
related references are application of Hydrocyclone in alumina refining process [S.K. Patnaik and R. Brahma, "Bauxal-96, Feb 20=21, 1996,p.l57-164] and use of special chemicals [US Patent 4578255].
In India, wet oxidation technology is the only method employed in the HINDALCO Plant for removal of oxalates from Bayer's liquor.
The main object of the present invention is to develop a process for removal/reduction of oxalates and coloured humic materials from Bayer's liquor using adsorption techniques and adsorbents such as activated carbon . It involves adsorption of oxalate and coloring matter onto the carbon surfaces. In this process the liquor is either slurried with the adsorbents such as powdered activated carbon or it is passed through the activated carbon column.

Another object of the present invention is to utilize the Bayer's liquor containing dispersed therein solids generated by the Bayer's process such as oxaltes and alumina hydrates.
Still another object of the present invention is to utilize the purified liquor for production of aluminium based roducts such as aluminium hydrate, alumina and zeolite.
Novelty of this process is that it is capable of being continuously applied as a process steps without interfering the major Bayer process thus removing the oxalates and coloring matters by contacting the impure alkali aluminate bayer liquor with adsorbents such as activated carbon in both powdered as well as granulated form for a time sufficient to effect the sorption of the same followed by separating the liquor from the adsorbents for recycling, thereby improving the product purity and production rate of aluminium based compound such as aluminium hydrate alumina and zeolite.
Accordingly, the present invention provides a process for the removal of oxalates and coloured humic bodies from Bayer's liquor which comprises contacting the impure alkali aluminate Bayer's liquor with activated carbon characterized in that the activated carbon used is either selected from powdered or granulated form , maintaining the intimate contact between the liquor and the activated carbon for a time period ranging from 0.5 to 2 hrs to effect the sorption of oxalates and coloured humic bodies followed by separation of the liquor from the absorbents for recycling.
In an embodiment of the present invention, the activated carbon used is selected from powdered form and granulated form of activated carbon.

In an embodiment of the present invention, the impure alkali aluminate used comprises alumina in the form of Al2O3 in the range of 49-155 g/1, caustic as Na2CO3 in the range of 158 - 170 g/1 and oxalate carbon along with coloured humic materials in the range of 0.4 - 0.5 g/1.
In still another embodiment the present invention, the oxidant carbon and coloured humic bodies removed from Bayor's liquors are in the range of 50-70% and 60-80% preferably in the rangeof 20-60% and 60-70% respectively.
In yet another embodiment of the present invention, the Bayor's liquor obtained after removal of oxidants and coloured humic bodies is useful when mixed with fresh Bayor's liquor for the precipitation of aluminium based materials such as aluminium hydrate, alumina and zeolite.
The following examples are given by way of illustration how the invention is carried out in actual practice and should not be construed to limit the scope of the invention.
Example 1.
To 300 ml of Bayer's liquor ( Density - 1.25 gpl ) containing oxalate carbon ( 0.5 gpl ), 3 gms of powdered carbon ( -325 mesh) was slurried and mixed under stirring condition for 30 minutes. Then the liquor was filtered and the process was repeated thrice to obtain the liquor with removal/reduction of oxalate carbon from 0.5 gpl to 0.072 gpl with 60-70% color removal.

Example 2.
To 1 litre of Bayer's liquor containing 0.4 gpl of oxalate carbon, 50 gms of powdered activated carbon (-325 mesh) was added and stirred for one hour. Then the liquor was filtered to remove the oxalates and small amount of color bodies therefrom.. Liquor with 50% removal of oxalate and 70% color removal was obtained. Example 3:
This example illustrates the operation of a column of paniculate activated carbon.
A column 5 cm (2" dia) and 180cm (6 ft) high was packed with granular activated carbon (0.4 -5 mm, Indian standard), a specific surface area ~ 1200 m2 /g and to a height of 120 cm (4 ft). Clarified Bayer's liquor containing 0.401 gpl oxalate carbon was passed through the column by a peristaltic pump at a flow rate 2 ml/min. The column was continuously run upto the breakthrough point. The liquor with 50% removal of oxalates and 70% color removal was obtained. This liquor as such can be mixed with fresh liquor in the precipitation chamber for further removal of oxalates from the same or it can be used for precipitation of aluminium based materials such as aluminium hydrate, alumina and zeolite.
The main advantages of the present invention are of the followings l)This process step of purification of liquor can be added before the process of precipitation of aluminium hydrate stage or before the removal of sodium

carbonate from the spent liquor in the Bayer's process.
2. Purified liquor with different percentages of removal of oxalates and humic
matter can be produced and can be used for further helping of the oxalates
precipitation from the liquor left after the aluminium hydrate precipitation.
3. The process uses granulated carbon for easy removal of the same for
regeneration and the process can be continuous.
4. The process uses simple adsorption techniques with use of adsorbents such as
activated carbon.
5. The purified liquor can be used for preparation of special grade aluminium
hydrate, aluminium and zeolite.



We claim:
1. A process for the removal of oxalates and coloured humic bodies from Bayer's
liquor which comprises contacting the impure alkali aluminates Bayer's liquor
with activated carbon characterized in that the activated carbon used is either
selected from powdered or granulated form, maintaining the intimate contact
between the liquor and the activated carbon for a time period ranging from 0.5 to
2 hrs to effect the sorption of oxalates and coloured humic bodies followed by
separation of the liquor from the absorbents for recycling.
2. A process as claimed in claim 1-2 wherein the impure alkali aluminates used
comprises alumina in the form of Al2O3 in the range of 49-155 g/1, caustic as
Na2CO3 in the range of 158-170 g/1 and oxalate carbon along with coloured
humic materials in the range of 0.4-0.5 g/1.
3. A process as claimed in claims 1-3 wherein the Bayer's liquor obtained after
removal of oxidants and coloured humic bodies is useful when mixed with fresh
Bayer's liquor for the precipitation of aluminum based materials selected from
aluminum hydrate, alumina or zeolite.
4. A process for the removal of oxalates and coloured humic bodies from Bayer's
liquor substantially as herein described with reference to the examples.

Documents:

1213-del-2000-abstract.pdf

1213-del-2000-claims.pdf

1213-del-2000-correspondence-others.pdf

1213-del-2000-correspondence-po.pdf

1213-del-2000-description (complete).pdf

1213-del-2000-form-1.pdf

1213-del-2000-form-19.pdf

1213-del-2000-form-2.pdf


Patent Number 244026
Indian Patent Application Number 1213/DEL/2000
PG Journal Number 47/2010
Publication Date 19-Nov-2010
Grant Date 15-Nov-2010
Date of Filing 26-Dec-2000
Name of Patentee COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH
Applicant Address RAFI MARG, NEW DELHI-110001, INDIA.
Inventors:
# Inventor's Name Inventor's Address
1 PRATIMA MISHRA SCIENTIST C, RRL, BHUBANESWAR-751013, ORISSA.
2 KADAMBINI SARANGI SCIENTIST C, RRL, BHUBANESWAR-751013, ORISSA.
3 RADHANATH PRASAD DAS SCIENTIST G, RRL, BHUBANESWAR-751013, ORISSA.
PCT International Classification Number NA
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA