Title of Invention	A PROCESS FOR THE PREPARATION OF CARBON REFRACTORIES FROM SPENT CATHODES OF ALUMINIUM SMELTING PLANT
Abstract	The present invention relates to a process for the preparation of carbon-refractories from spent cathodes of aluminum smelting plant. The process steps comprises : mixing graphite powder with a dry refractory mix of china clay, ball clay, feldspar and quartz powder to obtain mixture of equal volume of the said graphite powder and refractory mix, diluting the mixture with water to obtain a dough, the cast was allowed to dry and fired in inert gas atmosphere first at 600 deg C and then at 1200 deg C to obtain the desired carbon-refractory brick.

Title of Invention

A PROCESS FOR THE PREPARATION OF CARBON REFRACTORIES FROM SPENT CATHODES OF ALUMINIUM SMELTING PLANT

Abstract

The present invention relates to a process for the preparation of carbon-refractories from spent cathodes of aluminum smelting plant. The process steps comprises : mixing graphite powder with a dry refractory mix of china clay, ball clay, feldspar and quartz powder to obtain mixture of equal volume of the said graphite powder and refractory mix, diluting the mixture with water to obtain a dough, the cast was allowed to dry and fired in inert gas atmosphere first at 600 deg C and then at 1200 deg C to obtain the desired carbon-refractory brick.

Full Text	The present invention relates to a process for the preparation of carbon-refractories from spent cathodes of aluminum smelting plant In aluminum extraction cell, cathode carbon forms intercalated compounds with sodium present in the electrolyte at the operating temperature, and this intercalation leads to improved wetting of the cathode carbon block and crystal growth of the electrolyte in the carbon. This phenomenon ultimately, in some cathodes, leads to failure and ultimate rejection. Spent cathodes also contains fluoride and cyanide compounds as contaminants, and storage as well as ultimate disposal of such wastes possess environment risk created by the plant. Accordingly, this invention provides a means for safe disposal and utilization of the treated products to a high value item such as carbon refractories. Carbon refractors are used in metallurgical industries where reducing atmosphere prevails in the operating atmosphere. One such example is the lower bearth (bosch) region of the blast furnace. The main objective of this invention has been to prepare the above carbon refractories from the spent cathode blocks. Yet another objective of the in mention has been to decontam9nate these spent cathode blocks and absorb the toxic elements in dilute alkali for safe disposal. An internet search indicate that the above carbon refractories has been attempted to from spent cathode blocks of aluminium industries. Accordingly the present invention provides a process for the preparation of carbon-refractories from spent cathodes of aluminum smelting plant which comprises a) mixing the graphite powder with a refractory binders composition comprising bentonite clay, china clay, feldspar and quartz powder in a ratio ranging from 1.2: 1.0: 1.0: 1.2 to 1.7: 1.0: 1.0: 1.7 so as to obtain the graphite powder to refractory binder mixture in range of 1:1 to 1:2, b) diluting the above said mixture with water to obtain a tight dough, c) curing the above said dough by pouring it into a cardboard tray for extruding a desired shape for about 24 hrs, d) pressing the above cast brick by a weight of 20 to 35kg followed by first firing at a temperature ranging between 500-600°C for 6 hours and then at 1300°C for 12 hours in an inert atmosphere to obtain the desired carbon-refractory brick. In an embodiment of the present invention the carbon-refractory brick obtain has a transverse breaking strength of about 300 kg/cm. The said process first converts the cathode powder (2 mm to dust size) to free flowing graphite powder by treatment of chromic acid. The said cathode powder is taken in a conical flask fitted with stirrer and thermometer and placed on a tray with arrangement for circulating cold water around it. The whole assembly is placed in a small fume cupboard, exhaust of which is passed through a dilute sodium-hydroxide solution. The said carbon powder then slowly mixed with chromic acid with constant stirring and the temperature is maintained 130-140°C by controlling the addition rate of the acid and flow rate of water around the flask. The reaction is vigorous and generally the reaction is complete in about 15 minutes time. Addition of acid is stopped as soon as the reaction is over. The reaction mixture is then cooled and diluted with distilled water and filtered. Washing is continued till the filtrate get neutralized to pH-paper. The treated mass is then dried in an air oven at about 80°C for 2 hours. After completion of drying the carbonaceous mass is heated at about 950°C for 2-3 minutes to convert the mass to a free flowing fine graphite powder. MALVBERN particle size analysis indicates average size of these graphites crystallites to be around 20 micro-meters. F" And CN" concentration came down from 15% and 0.3% (respectively) to nil after the above treatment. A process for the preparation of graphite powder from waste cathode blocks generated by aluminium extraction plant has been disclosed in our co-pending application no. 0999/ del/2001. The said graphite powder is then mixed with a dry mix consisting following ingredients : china clay, ball clay, feldspar and quartz powder all below -125 microns. China clay had all particles below 5 micron and iron impurity below 0.1%, while ball clay was screened in 300 micron mesh with 80% below 2 micron. Equal volume of the said graphite powder and above refractory mix was mixed thoroughly well in a ball mill, and then mixed with little distilled water to make a tight dough which was then moulded into the desired shape in a thin cardboard mould. The cast was left to dry for 24 hours in a shaded area and then hand pressed to compact the said cast. In this case, the cast was in the shape of a small brick. The said cast brick was covered with carbon powder in a high alumina crucible and fired in inert gas atmosphere first at 600°C for 6 hours and then at 1300°C for 12 hours. The fired brick was slowly cooled to room temperature and the carbon-refractory was found to have transverse strength of about 300 kg/cm. The following examples are given by the way of illustration and should not construed to limit the scope of the invention. EXAMPLE 1 This example pertains to a process for the preparation of graphite powder from waste / cathode blocks generated by aluminium extraction plant. The said process has been disclosed in our co-pending application no. NF 371-2000. 50 gm of the said waste cathode material of size 2-3 mm was reacted with 50 ml of chromic acid in about 20 minutes time and washed with distilled water untill neutral and then dried in an oven at 100°C for 2 hours and then inserted into a heated furnace at 950°C to generate free flowing graphite crystallite with average particle size of 20 micrometer. The resultant graphite powder was suspended in silicone oil as shown in Table-1 below with as mentioned loading rate to obtain a satisfactory colloidal-graphite solution. EXAMPLE 2 6 gm of bentonite clay was mixed with 4 gm of china clay, 6 gm of feldspar powder and 4 gm of quartz powder all passing through -125 micron mesh. This refractory mix was mixed with 20 gm of graphite powder derived from the waste cathode material as described above. This mixture was mixed with little distilled water to make a tight dough which was poured into a 1 inch x 1 inch x 1/2 inch cardboard tray and kept for 24 hours ina shaded area for curing. The cast brick then was pressed by a weight of about 20 kg to compact the same. The cast brick then carefully taken out and heated slowly upto 600°C at about 50°C/hr incremental rate and kept at 600°C for 6 hours. The cast brick was covered with carbon powder and placed in a high alumina crucible before firing and heated in inert gas atmosphere. The temperature of firing then slowly increased to 1300°C and kept at that temperature for about 12 hours. The furnace was then cooled slowly to room temperature and the cast brick taken out. This carbon refractory showed transverse breaking strength of 280 kg/cm. EXAMPLE-3 3 gm of bentonite clay was mixed with 2 gm of china clay, 3 gm of feldspar and 2 gm of quartz powder (all passing through -125 micron mesh), and the mixture was then mixed with 10 gm of graphite powder derived from spent cathode carbon as mentioned above. The mixture was diluted with about 15 ml of distilled water and cast into a thin cardboard mould and left in shade area for 24 hours for curing. The cured mould was then pressed with a weight of about 30 kg weight to compact the cast, and then the cast was placed in an oven to dry slowly at 80°C for 2-3 hours. The dried cast was taken out of the cardboard mould and placed in a high alumina crucible covered with carbon powder and fired at 600°C in an inert atmosphere in a furnace for 6 hours, and then at 1300°C for 12 hours. The furnace was allowed to cool slowly to room temperature and the carbon refractory cast was then taken out. This carbon-refractory brick showed a transverse breaking strength of 300 kg/cm. ADVANTAGES OF THE PRESENT INVENTION : 1. The process provides a means for safe disposal of the waste cathode blocks from aluminium smelting plant and converting them to a high value product. 2. The process treats the contaminated cathode blocks in an environmentally safe manner. 3. Decontamination step of the process of the spent cathode blocks, provides raw material for subsequent conversion to carbon-refractories. 4. The process is simple and all raw materials are available in this country in plenty. 5. The process does not require any special equipment for preparation of the said carbon-refractories. 6. The initial concentration of fluoride in the cathode block was 15% and that of the cyanide 0.3%, which after chemical treatment came to nil. We Claim: 1. A process for the preparation of carbon-refractories from spent cathodes of aluminum smelting plant which comprises: a) mixing the graphite powder with a refractory binders composition comprising bentonite clay, china clay, feldspar and quartz powder in a ratio ranging from 1.2: 1.0: 1.0: 1.2 to 1.7: 1.0: 1.0: 1.7 so as to obtain the graphite powder to refractory binder mixture in range of 1:1 to 1:2, b) diluting the above said mixture with water to obtain a tight dough, c) curing the above said dough by pouring it into a cardboard tray for extruding a desired shape for about 24 hrs, d) pressing the above cast brick by a weight of 20 to 35kg followed by first firing at a temperature ranging between 500-600°C for 6 hours and then at 1300°C for 12 hours in an inert atmosphere to obtain the desired carbon-refractory brick. 2. A process as claimed in claim 1, wherein the carbon-refractory brick obtain has a transverse breaking strength of 300 kg/cm. 3. A process for the preparation of carbon-refractories from spent cathodes of aluminum smelting plant substantially as herein described with reference to the examples.

Full Text

The present invention relates to a process for the preparation of carbon-refractories from spent cathodes of aluminum smelting plant
In aluminum extraction cell, cathode carbon forms intercalated compounds with sodium present in the electrolyte at the operating temperature, and this intercalation leads to improved wetting of the cathode carbon block and crystal growth of the electrolyte in the carbon. This phenomenon ultimately, in some cathodes, leads to failure and ultimate rejection. Spent cathodes also contains fluoride and cyanide compounds as contaminants, and storage as well as ultimate disposal of such wastes possess environment risk created by the plant. Accordingly, this invention provides a means for safe disposal and utilization of the treated products to a high value item such as carbon refractories.
Carbon refractors are used in metallurgical industries where reducing atmosphere prevails in the operating atmosphere. One such example is the lower bearth (bosch) region of the blast furnace.
The main objective of this invention has been to prepare the above carbon refractories from the spent cathode blocks. Yet another objective of the in mention has been to decontam9nate these spent cathode blocks and absorb the toxic elements in dilute alkali for safe disposal. An internet search indicate that the above carbon refractories has been attempted to from spent cathode blocks of aluminium industries.
Accordingly the present invention provides a process for the preparation of carbon-refractories from spent cathodes of aluminum smelting plant which comprises
a) mixing the graphite powder with a refractory binders composition comprising bentonite clay, china clay, feldspar and quartz powder in a ratio ranging from 1.2: 1.0: 1.0: 1.2 to 1.7: 1.0: 1.0: 1.7 so as to obtain the graphite powder to refractory binder mixture in range of 1:1 to 1:2,

b) diluting the above said mixture with water to obtain a tight dough,
c) curing the above said dough by pouring it into a cardboard tray for extruding a
desired shape for about 24 hrs,
d) pressing the above cast brick by a weight of 20 to 35kg followed by first firing at
a temperature ranging between 500-600°C for 6 hours and then at 1300°C for 12
hours in an inert atmosphere to obtain the desired carbon-refractory brick.
In an embodiment of the present invention the carbon-refractory brick obtain has a transverse breaking strength of about 300 kg/cm.
The said process first converts the cathode powder (2 mm to dust size) to free flowing graphite powder by treatment of chromic acid. The said cathode powder is taken in a conical flask fitted with stirrer and thermometer and placed on a tray with arrangement for circulating cold water around it. The whole assembly is placed in a small fume cupboard, exhaust of which is passed through a dilute sodium-hydroxide solution. The said carbon powder then slowly mixed with chromic acid with constant stirring and the temperature is maintained 130-140°C by controlling the addition rate of the acid and flow rate of water around the flask. The reaction is vigorous and generally the reaction is complete in about 15 minutes time. Addition of acid is stopped as soon as the reaction is over. The reaction mixture is then cooled and diluted with distilled water and filtered. Washing is continued till the filtrate get neutralized to pH-paper. The treated mass is then dried in an air oven at about 80°C for 2 hours. After completion of drying the carbonaceous mass is heated at about 950°C for 2-3 minutes to convert the mass to a free flowing fine graphite powder. MALVBERN particle size analysis indicates average size of these graphites crystallites to be around 20 micro-meters. F" And CN" concentration came down from 15% and 0.3% (respectively) to nil after the above treatment.
A process for the preparation of graphite powder from waste cathode blocks generated by aluminium extraction plant has been disclosed in our co-pending application no. 0999/ del/2001.

The said graphite powder is then mixed with a dry mix consisting following ingredients : china clay, ball clay, feldspar and quartz powder all below -125 microns. China clay had all particles below 5 micron and iron impurity below 0.1%, while ball clay was screened in 300 micron mesh with 80% below 2 micron. Equal volume of the said graphite powder and above refractory mix was mixed thoroughly well in a ball mill, and then mixed with little distilled water to make a tight dough which was then moulded into the desired shape in a thin cardboard mould. The cast was left to dry for 24 hours in a shaded area and then hand pressed to compact the said cast. In this case, the cast was in the shape of a small brick.
The said cast brick was covered with carbon powder in a high alumina crucible and fired in inert gas atmosphere first at 600°C for 6 hours and then at 1300°C for 12 hours. The fired brick was slowly cooled to room temperature and the carbon-refractory was found to have transverse strength of about 300 kg/cm.
The following examples are given by the way of illustration and should not construed to limit the scope of the invention.
EXAMPLE 1

This example pertains to a process for the preparation of graphite powder from waste /
cathode blocks generated by aluminium extraction plant. The said process has been disclosed in our co-pending application no. NF 371-2000.
50 gm of the said waste cathode material of size 2-3 mm was reacted with 50 ml of chromic acid in about 20 minutes time and washed with distilled water untill neutral and then dried in an oven at 100°C for 2 hours and then inserted into a heated furnace at 950°C to generate free flowing graphite crystallite with average particle size of 20 micrometer. The resultant graphite powder was suspended in silicone oil as shown in Table-1 below with as mentioned loading rate to obtain a satisfactory colloidal-graphite solution.

EXAMPLE 2
6 gm of bentonite clay was mixed with 4 gm of china clay, 6 gm of feldspar powder and 4 gm of quartz powder all passing through -125 micron mesh. This refractory mix was mixed with 20 gm of graphite powder derived from the waste cathode material as described above. This mixture was mixed with little distilled water to make a tight dough which was poured into a 1 inch x 1 inch x 1/2 inch cardboard tray and kept for 24 hours ina shaded area for curing. The cast brick then was pressed by a weight of about 20 kg to compact the same. The cast brick then carefully taken out and heated slowly upto 600°C at about 50°C/hr incremental rate and kept at 600°C for 6 hours. The cast brick was covered with carbon powder and placed in a high alumina crucible before firing and heated in inert gas atmosphere. The temperature of firing then slowly increased to 1300°C and kept at that temperature for about 12 hours. The furnace was then cooled slowly to room temperature and the cast brick taken out. This carbon refractory showed transverse breaking strength of 280 kg/cm.
EXAMPLE-3
3 gm of bentonite clay was mixed with 2 gm of china clay, 3 gm of feldspar and 2 gm of quartz powder (all passing through -125 micron mesh), and the mixture was then mixed with 10 gm of graphite powder derived from spent cathode carbon as mentioned above. The mixture was diluted with about 15 ml of distilled water and cast into a thin cardboard mould and left in shade area for 24 hours for curing. The cured mould was then pressed with a weight of about 30 kg weight to compact the cast, and then the cast was placed in an oven to dry slowly at 80°C for 2-3 hours. The dried cast was taken out of the cardboard mould and placed in a high alumina crucible covered with carbon powder and fired at 600°C in an inert atmosphere in a furnace for 6 hours, and then at 1300°C for 12 hours. The furnace was allowed to cool slowly to room temperature and the carbon refractory cast was then taken out. This carbon-refractory brick showed a transverse breaking strength of 300 kg/cm.

ADVANTAGES OF THE PRESENT INVENTION :
1. The process provides a means for safe disposal of the waste cathode blocks from
aluminium smelting plant and converting them to a high value product.
2. The process treats the contaminated cathode blocks in an environmentally safe
manner.
3. Decontamination step of the process of the spent cathode blocks, provides raw
material for subsequent conversion to carbon-refractories.
4. The process is simple and all raw materials are available in this country in plenty.
5. The process does not require any special equipment for preparation of the said
carbon-refractories.
6. The initial concentration of fluoride in the cathode block was 15% and that of the
cyanide 0.3%, which after chemical treatment came to nil.

We Claim:
1. A process for the preparation of carbon-refractories from spent cathodes of
aluminum smelting plant which comprises:
a) mixing the graphite powder with a refractory binders composition comprising
bentonite clay, china clay, feldspar and quartz powder in a ratio ranging from 1.2:
1.0: 1.0: 1.2 to 1.7: 1.0: 1.0: 1.7 so as to obtain the graphite powder to refractory
binder mixture in range of 1:1 to 1:2,
b) diluting the above said mixture with water to obtain a tight dough,
c) curing the above said dough by pouring it into a cardboard tray for extruding a
desired shape for about 24 hrs,
d) pressing the above cast brick by a weight of 20 to 35kg followed by first firing at
a temperature ranging between 500-600°C for 6 hours and then at 1300°C for 12
hours in an inert atmosphere to obtain the desired carbon-refractory brick.

2. A process as claimed in claim 1, wherein the carbon-refractory brick obtain has a
transverse breaking strength of 300 kg/cm.
3. A process for the preparation of carbon-refractories from spent cathodes of
aluminum smelting plant substantially as herein described with reference to the
examples.

Documents:

1011-del-2001-abstract.pdf

1011-del-2001-claims.pdf

1011-del-2001-correspondence-others.pdf

1011-del-2001-correspondence-po.pdf

1011-del-2001-description (complete).pdf

1011-del-2001-form-1.pdf

1011-del-2001-form-18.pdf

1011-del-2001-form-2.pdf

1011-del-2001-form-3.pdf

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Patent Number

218351

Indian Patent Application Number

1011/DEL/2001

PG Journal Number

19/2008

Publication Date

09-May-2008

Grant Date

31-Mar-2008

Date of Filing

28-Sep-2001

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	BIMANRAJAN MAZUMDER	SAINETST RGIONAL RESEARCH LEBRATY BHONESVAR, INDIA.

PCT International Classification Number

C01B 31/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA