Title of Invention	"AN ELECTROCHEMICAL PROCESS FOR THE RECOVERY OF CERIUM (IV) HYDROXIDE/OXIDE FROM RARE EARTH CHLORIDES."
Abstract	The present invention relates to an electrochemical process for the recovery of cerium (IV) hydroxide/ oxide from rare earth chlorides. The invention provides an electrochemical process for the recovery of the rare earth chloride solution obtained while processing cerium (IV) hydroxide from monazite sand containing rare earth elements from Lanthanum to Yittrium. The process eliminates the addition of sodium chloride., The process employs a rotating cathode which avoids the deposition of the cerium (IV) hydroxide onto the cathode thus resulting in high performance efficiencies. The process also employs metal oxides coated titanium anodes to reduce the electrical energy.

Title of Invention

"AN ELECTROCHEMICAL PROCESS FOR THE RECOVERY OF CERIUM (IV) HYDROXIDE/OXIDE FROM RARE EARTH CHLORIDES."

Abstract

The present invention relates to an electrochemical process for the recovery of cerium (IV) hydroxide/ oxide from rare earth chlorides. The invention provides an electrochemical process for the recovery of the rare earth chloride solution obtained while processing cerium (IV) hydroxide from monazite sand containing rare earth elements from Lanthanum to Yittrium. The process eliminates the addition of sodium chloride., The process employs a rotating cathode which avoids the deposition of the cerium (IV) hydroxide onto the cathode thus resulting in high performance efficiencies. The process also employs metal oxides coated titanium anodes to reduce the electrical energy.

Full Text	The present invention relates to an electrochemical process for the recovery of cerium (IV) hydroxide / oxide from rare earth chlorides. The cerium (IV) oxide finds application in [i] polishing of optical and ophthalmic glasses, [ii] glass decolouring, [iii] making shells of TV tubes, [iv] stabiliser for glass used for TV tubes, windows for nuclear industry and glass used in UV sterilisation and [v] in glass to cover solar battery cells in satellites. Usually, the Rare Earths refers to a group of 14 elements from Lanthanum to Yittrium. These are present in the Monazite sand from which the individual components are separated by appropriate techniques. The rare earth solution is obtained during the processing of minerals such as monazite sand. The rare earth chlorides so obtained has the following composition: Samarium 2 to 3%. Praseodymium 5 to 6%, Neodymium 19 to 22%, Lanthanum 22 to 24%, Cerium at least 45%, Yittrium and others 0.5 to 1%. As can be seen Cerium is the major constituent constituting about 45-48% (as Ce02). Hitherto it has been the practice to recover eerie hydroxide by chemical reaction between the rare earth chlorides and sodium hypochlorite. [Ref: Yost, D. M, et.al (ed) The Rare Earth Elements and their Compounds, John Wiley Inc, New York, 1947 P.44]. The process has the following disadvantages: In the chemical process, sodium chloride, a low value byproduct is obtained. The preparation of sodium hypochlorite, involves transport and storage of chlorine which may lead to environmental hazard. Further a separate unit operation for the preparation of hypochlorite is required. The main object of the present invention is to provide an electrochemical process for the recovery of the rare earth chloride solution obtained while processing cerium (IV) hydroxide from monazite sand containing rare earth elements from Lanthanum to Yittrium, which obviates the drawbacks as detailed above. Another object of the present invention is to provide the hypochlorite necessary for the oxidation of cerium (III) 'in situ1 by the electrolysis of rare earth chloride solution containing cerous chloride without the addition of sodium chloride. Still another object of the present invention is to employ the metal oxides coated titanium anodes to reduce the electrical energy involved in the process, as well as to avoid the problems associated with the dissolution of the anode material normally encountered with graphite anode in chloride electrolytes. Yet another object of the present invention is to employ a rotating cathode which avoids the deposition of the cerium (IV) hydroxide onto the cathode thus resulting in high performance efficiencies. Accordingly, the present invention provides an electrochemical process for the recovery of cerium (IV) hydroxide / oxide from rare earth chlorides which comprises; electrolysing rare earth chloride solution used as electrolyte containing cerium (III) chloride 100-180 g/1 in an electrochemical cell having coated titanium anode and rotating cathode such as herein described concentrically placed inside the anode and the said rare earth chlorides as electrolyte at 10 to 30°C, anode current density of 1 - 5 A. dm-2, recovering precipitated cerium (IV) hydroxide by filtration, heating in a conventional manner to get cerium oxide. The anode is of titanium substrate coated with mixed oxides of noble metals and non-noble metals like ruthenium, iridium, palladium, titanium, tin and antimony such that RuO2/TiO2 (30:70), RuO2/TiO2/SnO2 (30:58:12), RuO2/IrO2/Ti02 (15:15:70) etc and is in the form of strips positioned in a circular arrangement or perforated cylindrical structure or expanded mesh type. The cathode being a cylindrical rod positioned at the centre surrounded by the anode (s), with an interelectrode distance of 0.5 to 1.5cm and connected through a shaft to a motor, the electrical connection being given through the shaft. The electrochemical cell is fitted with one or more anodes and cathodes. Rare earth chloride solution containing 100 - 180 g/1 of chloride at a p in the range of 5.0 to 7.0 is used as electrolyte. Cathode rotation being maintained at a peripheral velocity between 50 to 100 m.min-1, when the cerium (III) is oxidised to cerium (IV) and precipitated as cerium (IV) hydroxide, at a current efficiency of 55 - 60% with a product purity of about 91%. In an embodiment of the present invention, rare earth chloride solution containing 125 g/1 chloride is used as the electrolyte at a pH 6.0 and maintained at a temperature of 20°C. In yet another embodiment of the present invention, the anode current density is 2.5 A.dm-2 and the cathode current density is 4.5A.dm-2 and the cathode rotation is maintained at a peripheral velocity of 98m.min-1. The elctrochemical process operated under the above conditions provides the oxidation of cerium (III) to cerium (IV) which precipitates as cerium (IV) hydroxide at a current efficiency of 55 to 60% with a product purity of about 91%. The oxidation of cerium (III) to cerium (IV) and separation of cerium as cerium (IV) hydroxide effected by the present invention provides a novel process than the conventional method, in that the present process does not require addition of sodium hypochlorite from an external source. Further the present process avoides the addition of sodium ions to the process stream, containing mainly rare earth ions thus eliminating the downstreams process for the separation of sodium chloride from the rare earth salt solutions. The following typical examples are given to illustrate the invention and should not be construed to limit the scope of this invention: EXAMPLES (Table Removed) * Rare Earth Chloride containing Cerium (III) Chloride. The main advantages of the present invention are: 1. The novelty of the process is the utilisation of the rare earth chlorides themselves to generate required hypochlorite. Thus the addition of sodium hypochlorite from external source is avoided. 2. The rotating cathode prevents the formation of a coating on the cathode surface by the hydroxide to a large extent resulting in high current efficiencies and .•* smooth operation. 3. The rotating cathode provides an efficient stirring of the electrolyte enhancing the formation of hypo chlorite for the oxidation of cerium (III) to cerium (IV) . 4. The method provides a better process for the recov ery of cerium (IV) hydroxide, from rare earth chlo rides, of reasonable purity. We Claim: 1. An electrochemical process for the recovery of cerium (IV) hydroxide / oxide from rare earth chlorides which comprises; electrolysing rare earth chloride solution used as electrolyte containing cerium (III) chloride 100-180 g/1 in an electrochemical cell having coated titanium anode and rotating cathode such as herein described concentrically placed inside the anode and the said rare earth chlorides as electrolyte at 10 to 30°C, anode current density of 1 - 5 A. dm-2, recovering precipitated cerium (IV) hydroxide by filtration, heating in a conventional manner to get cerium oxide. 2. An electrochemical process as claimed in claims 1 wherein coated titanium anode used is the one having high catalytic activity for chlorine evolution and is selected from titanium coated with oxides of noble and non-noble metals like ruthenium, iridium, platinum, tin, antimony such as RuO2/IrO2/TiO2 (15:15:70). 3. An electrochemical process as claimed in claims 1 & 2 wherein anode used is in the form of strips positioned in a circular arrangement or perforated cylindrical structure of expanded mesh type. 4. An electrochemical process as claimed in claims 1 to 3 wherein cathode used is selected from stainless steel and mild steel. 5. An electrochemical process as claimed in claims 1 to 4 wherein cathode is cylindrical and interelectrode distance is 0.5 to 1.5cm. 6. An electrochemical process as claimed in claims 1 to 5 wherein rare earth chloride solution used as electrolyte is preferably 125 g/1. 7. An electrochemical process as claimed in claims 1 to 6 wherein the pH of the electrolyte is maintained between 5.0 to 7.0, preferably 6.0 , 8. An electrochemical process as claimed in claims 1 to 7 wherein the electrolysis is effected below 30°C. 9. An electrochemical process as claimed in claims 1 to 8 wherein an anode current density used is 2.5 A.dm-2 and cathode current density used is 4.5 A. dm-'2 10. An electrochemical process as claimed in claims 1 to 9 wherein the cathode rotation is maintained at a peripheral velocity of 98 m./min. 11. An electrochemical process for the recovery of cerium (IV) hydroxide / oxide from rare earth chlorides substantially as herein described with reference to the examples.

Full Text

The present invention relates to an electrochemical process for the recovery of cerium (IV) hydroxide / oxide from rare earth chlorides.
The cerium (IV) oxide finds application in [i] polishing of optical and ophthalmic glasses, [ii] glass decolouring, [iii] making shells of TV tubes, [iv] stabiliser for glass used for TV tubes, windows for nuclear industry and glass used in UV sterilisation and [v] in glass to cover solar battery cells in satellites.
Usually, the Rare Earths refers to a group of 14 elements from Lanthanum to Yittrium. These are present in the Monazite sand from which the individual components are separated by appropriate techniques. The rare earth solution is obtained during the processing of minerals such as monazite sand. The rare earth chlorides so obtained has the following composition: Samarium 2 to 3%. Praseodymium 5 to 6%, Neodymium 19 to 22%, Lanthanum 22 to 24%, Cerium at least 45%, Yittrium and others 0.5 to 1%. As can be seen Cerium is the major constituent constituting about 45-48% (as Ce02).
Hitherto it has been the practice to recover eerie hydroxide by chemical reaction between the rare earth chlorides and sodium hypochlorite. [Ref: Yost, D. M, et.al (ed) The Rare Earth Elements and their Compounds, John Wiley Inc, New York, 1947 P.44]. The process has the following disadvantages:
In the chemical process, sodium chloride, a low value byproduct is obtained. The preparation of sodium

hypochlorite, involves transport and storage of chlorine which may lead to environmental hazard. Further a separate unit operation for the preparation of hypochlorite is required.
The main object of the present invention is to provide an electrochemical process for the recovery of the rare earth chloride solution obtained while processing cerium (IV) hydroxide from monazite sand containing rare earth elements from Lanthanum to Yittrium, which obviates the drawbacks as detailed above.
Another object of the present invention is to provide the hypochlorite necessary for the oxidation of cerium (III) 'in situ1 by the electrolysis of rare earth chloride solution containing cerous chloride without the addition of sodium chloride.
Still another object of the present invention is to employ the metal oxides coated titanium anodes to reduce the electrical energy involved in the process, as well as to avoid the problems associated with the dissolution of the anode material normally encountered with graphite anode in chloride electrolytes.
Yet another object of the present invention is to employ a rotating cathode which avoids the deposition of the cerium (IV) hydroxide onto the cathode thus resulting in high performance efficiencies.
Accordingly, the present invention provides an electrochemical process for the recovery of cerium (IV)

hydroxide / oxide from rare earth chlorides which comprises; electrolysing rare earth chloride solution used as electrolyte containing cerium (III) chloride 100-180 g/1 in an electrochemical cell having coated titanium anode and rotating cathode such as herein described concentrically placed inside the anode and the said rare earth chlorides as electrolyte at 10 to 30°C, anode current density of 1 - 5 A. dm-2, recovering precipitated cerium (IV) hydroxide by filtration, heating in a conventional manner to get cerium oxide.
The anode is of titanium substrate coated with mixed oxides of noble metals and non-noble metals like ruthenium, iridium, palladium, titanium, tin and antimony such that RuO2/TiO2 (30:70), RuO2/TiO2/SnO2 (30:58:12), RuO2/IrO2/Ti02 (15:15:70) etc and is in the form of strips positioned in a circular arrangement or perforated cylindrical structure or expanded mesh type. The cathode being a cylindrical rod positioned at the centre surrounded by the anode (s), with an interelectrode distance of 0.5 to 1.5cm and connected through a shaft to a motor, the electrical connection being given through the shaft. The electrochemical cell is fitted with one or more anodes and cathodes. Rare earth chloride solution containing 100 - 180 g/1 of chloride at a p in the range of 5.0 to 7.0 is used as electrolyte. Cathode rotation being maintained at a peripheral velocity between 50 to 100 m.min-1, when the cerium (III) is oxidised to cerium (IV) and precipitated as cerium (IV) hydroxide, at a current efficiency of

55 - 60% with a product purity of about 91%.
In an embodiment of the present invention, rare earth chloride solution containing 125 g/1 chloride is used as the electrolyte at a pH 6.0 and maintained at a temperature of 20°C.
In yet another embodiment of the present invention,
the anode current density is 2.5 A.dm-2 and the cathode

current density is 4.5A.dm-2 and the cathode rotation is
maintained at a peripheral velocity of 98m.min-1.
The elctrochemical process operated under the above conditions provides the oxidation of cerium (III) to cerium (IV) which precipitates as cerium (IV) hydroxide at a current efficiency of 55 to 60% with a product purity of about 91%.
The oxidation of cerium (III) to cerium (IV) and separation of cerium as cerium (IV) hydroxide effected by the present invention provides a novel process than the conventional method, in that the present process does not require addition of sodium hypochlorite from an external source. Further the present process avoides the addition of sodium ions to the process stream, containing mainly rare earth ions thus eliminating the downstreams process for the separation of sodium chloride from the rare earth salt solutions.
The following typical examples are given to illustrate the invention and should not be construed to limit the scope of this invention:

EXAMPLES

(Table Removed)
* Rare Earth Chloride containing Cerium (III) Chloride.
The main advantages of the present invention are:
1. The novelty of the process is the utilisation of the
rare earth chlorides themselves to generate required
hypochlorite. Thus the addition of sodium hypochlorite
from external source is avoided.
2. The rotating cathode prevents the formation of a
coating on the cathode surface by the hydroxide to a
large extent resulting in high current efficiencies and
.•*
smooth operation.
3. The rotating cathode provides an efficient stirring
of the electrolyte enhancing the formation of hypo
chlorite for the oxidation of cerium (III) to cerium
(IV) .
4. The method provides a better process for the recov
ery of cerium (IV) hydroxide, from rare earth chlo
rides, of reasonable purity.

We Claim:
1. An electrochemical process for the recovery of cerium (IV) hydroxide / oxide
from rare earth chlorides which comprises; electrolysing rare earth chloride
solution used as electrolyte containing cerium (III) chloride 100-180 g/1 in an
electrochemical cell having coated titanium anode and rotating cathode such as
herein described concentrically placed inside the anode and the said rare earth
chlorides as electrolyte at 10 to 30°C, anode current density of 1 - 5 A. dm-2,
recovering precipitated cerium (IV) hydroxide by filtration, heating in a
conventional manner to get cerium oxide.
2. An electrochemical process as claimed in claims 1 wherein coated titanium
anode used is the one having high catalytic activity for chlorine evolution and is
selected from titanium coated with oxides of noble and non-noble metals like
ruthenium, iridium, platinum, tin, antimony such as RuO2/IrO2/TiO2 (15:15:70).
3. An electrochemical process as claimed in claims 1 & 2 wherein anode used is in
the form of strips positioned in a circular arrangement or perforated cylindrical
structure of expanded mesh type.
4. An electrochemical process as claimed in claims 1 to 3 wherein cathode used is
selected from stainless steel and mild steel.

5. An electrochemical process as claimed in claims 1 to 4 wherein cathode is
cylindrical and interelectrode distance is 0.5 to 1.5cm.
6. An electrochemical process as claimed in claims 1 to 5 wherein rare earth
chloride solution used as electrolyte is preferably 125 g/1.
7. An electrochemical process as claimed in claims 1 to 6 wherein the pH of the
electrolyte is maintained between 5.0 to 7.0, preferably 6.0 ,
8. An electrochemical process as claimed in claims 1 to 7 wherein the electrolysis
is effected below 30°C.
9. An electrochemical process as claimed in claims 1 to 8 wherein an anode
current density used is 2.5 A.dm-2 and cathode current density used is 4.5 A.
dm-'2
10. An electrochemical process as claimed in claims 1 to 9 wherein the cathode
rotation is maintained at a peripheral velocity of 98 m./min.
11. An electrochemical process for the recovery of cerium (IV) hydroxide / oxide
from rare earth chlorides substantially as herein described with reference to the
examples.

Documents:

3159-del-1998-abstract.pdf

3159-del-1998-claims.pdf

3159-del-1998-correspondence-others.pdf

3159-del-1998-correspondence-po.pdf

3159-del-1998-description (complete).pdf

3159-del-1998-form-1.pdf

3159-del-1998-form-19.pdf

3159-del-1998-form-2.pdf

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Patent Number

215263

Indian Patent Application Number

3159/DEL/1998

PG Journal Number

10/2008

Publication Date

07-Mar-2008

Grant Date

22-Feb-2008

Date of Filing

28-Oct-1998

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI- 110 001, INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	SUBRAMANIAN PUSHPAVANAM	SCIENTIST, C.E.C.R.I., RESEARCH ASSOCIATE, KARAIKUDI, INDIA
2	GANAPATHY SOZHAN	SCIENTIST, C.E.C.R.I., RESEARCH ASSOICATE, KARAIKUDI, INDIA
3	SWAMINATHAN MOHAN	SCIENTIST, C.E.C.R.I., RESEARCH ASSOICATE, KARAIKUDI, INDIA
4	SUBRAMANIAN VASUDAVAN	RESEARCH ASSOCIATE, C.E.C.R.I., RESEARCH ASSOICATE, KARAIKUDI, INDIA
5	VENKATESWARAN RENGARAJAN	SCIENTIST, C.E.C.R.I., RESEARCH ASSOICATE, KARAIKUDI, INDIA

PCT International Classification Number

C01F 17/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA