AU742528B2 - Anode improvements and a process for the manufacture and production of aluminium - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT *w a..

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Applicant: ALBRAS ALUM4TNIO BRASILEIRO S.A.

Invention Title: ANODE IMPROVEMENTS AND A PROCESS FOR THE MANUFACTURE AND PRODUCTION OF ALUMINIUJM The following statement is a full description of this invention, including the best method of performing it known to me/us: 2- "ANODE IMPROVEMENTS AND A PROCESS FOR THE MANUFACTURE AND PRODUCTION OF ALUMINIUM" The present application for a Patent of Addition is directed to an improvement in, or modification of, the invention disclosed in Australian patent application 73110/98.

The present application concerns improvements attained in the studies and verifications related to the material for the manufacture of anodes used in processes for the electrolytic production of primary aluminium.

Australian patent application AU 73110/98 is directed to a new type of anode, having a composition including sugar cane molasses as a binding agent, that is O* suitable for use in pots or vats for electrolytically reducing alumina to primary aluminium. More specifically, the invention disclosed in patent application AU 73110/98, concerns the replacement of pitch frequently used in conventional processes for the manufacture of anodes in the primary aluminium industry, with pure or additivecontaining sugar cane molasses.

o, S 0 With a view to improve and diversify the constructive configuration described and claimed in patent application AU 73110/98, the present application is directed to the possibility of replacing the pitch used in conventional processes for the manufacture of anodes in the primary aluminium industry, with natural (brown, whole, hardbrown, crystal) or refined sugar.

The technique of using natural (brown, whole, hard brown, crystal) or refined sugar as binder in the manufacture of the paste and green anodes is analogous to that of the traditional processes for production of anodes H:\Priyanka\Keep\speci\14729.99bdoc 21/09/99 3 based on pitch, which are known in the aluminium industry.

Similarly, the natural (brown, whole, hard brown, crystal) or refined sugar contents and also coke and "butts" contents, as well as the process conditions such as the temperature of the mixture, the baking temperature and time, represent parameters that can be altered depending on the types of coke, natural (brown, whole, hard brown, crystal) or refined sugar and additives, and/or the properties required for the anode produced.

Therefore, the anode composition according to the present invention preferably includes about 50%-70% of petroleum coke, 15%-30% of "butt" and 10%-25% of natural (brown, whole, hard brown, crystal) or refined sugar, based in the total weight of the composition.

Preferably, the percentage of natural (brown, whole, hard brown, crystal) or refined sugar used in the anode composition according to the present improvement is about 16% by weight.

*o ;The additives, lithium, fluorine, aluminium, alumina, boron and sulfur based substances and the mixtures 0. thereof, according to the present improvement, may be included in percentages varying from 0 to about 10% by weight.

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The process for the manufacture of anodes according to the present invention includes the preparation of a mixture containing petroleum coke, anode wastes from the electrolytic process called "butts" and natural (brown, whole, hard brown, crystal) or refined sugar. The petroleum coke and the anode wastes are crushed, screened and classified into appropriate sized fractions. Next, such fractions are heated and mixed with natural (brown, whole, hard brown, crystal) or refined sugar, in continuous H:\Pr~iyanka\Keep\speci\14729.99.doc 21/09/99 4 or batch mixers, at temperatures ranging from 150 C to 250 C. Preferably, the suitable temperature is around 1902C, and the mixing time depends on the type and capacity of the mixing equipment used in the process.

The paste resulting from this mixing can be directly used in electrolytic reduction pots or be pressed or compacted or vibro-compacted in suitable presses or compacting machines, with or without vacuum, to form green anodes.

These green anodes can be baked in special furnaces at temperatures ranging from 800 2 C to 13002C for a time ranging from 70 to 200 hours. Preferably, the baking temperature is about 11002C.

The above paste can be directly used in the Soderberg process, while the green anodes, after being baked, can be used in the "prebaked" process. Both the Soderberg and Prebaked processes are used for primary aluminium production.

According to the present invention, the typical composition of the natural (brown, whole, hard brown, crystal) or refined sugar to be used in the anode composition shows the features given in Table I, which can occur individually or simultaneously.

TABLE I PARAMETER RANGE

UNIT

Refractometric Brix 75 83 Pol 37 63 Purity 50 75 Reducing sugars 3 -10 H:\Priyanka\Keep\speci\14729.99,dc 21/09/99 5 Conductive ashes 6 -10 1 Polarization 99 -99.8 Moisture <0.3 Ashes <0.25

IMPURITIES:

Iron 200 max ppm Silicon 250 max ppm Nickel traces Vanadium 1:i50 max ppm Calcium 200 max ppm Sodium 100 max ppm Basic composition of molasses Basic Composition of sugar ppm parts per million; max maximum; Pol Polarization sacarose contents According to the present invention, the typical composition of the petroleum coke to be used in the anode composition shows preferably the features given in Table II below, which can occur individually or simultaneously.

0.0.0 TABLE II PARAMETER RANGE

UNIT

Apparent density 0.8 -0.9 g/cm 3 Real density 1.9 -2.1 g/cm 3 Volatiles 0,1 -0.5 Ashes 0,1 -0.6 Moisture 0 -0.3

IMPURITIES:

Iron 400 max ppm Silicon 300 max ppm Nickel 300 max ppm Vanadium 400 max ppm Sodium 200 max ppm H:\Susan\Keep\speci\JANELLE\ANODE IMPROVEMENTS AND A PROCESS .doc 3/02/99 6 o6°o o o* *oo o *oo *oo Calcium 300 max ppm Sulfur 3.0 max ppm parts per million max maximum The improvement of the present application will be described in relation to the same example given in patent application AU 73110/98, and in a similar way, such example shall not be considered as limiting the scope and conditions of the addition certificate in question.

Comparative tests were conducted in the laboratory by varying the conditions of the anode composition and the process for the manufacture thereof, to attain the best possible parameters, which could serve as a reference for the industrial process for the production of pre-baked anodes in the primary aluminium industry.

Thus, the experiments have been performed in "Bench Scale" equipment supplied by whereby 5 kg of paste were obtained in each test, which is equivalent to the production of 14 anodes of 340 g each.

The composition of the sugars used in the experiments is shown in table III.

TABLE III PARAMETER BROWN SUGAR HARD SUGAR CRYSTAL SUGAR Polarization (2S) 83,3 63,2 99,8 Conductive Ashes(%) 2,16 1,31 0,04 Calcium ppm) 1280 1400 100 Sodium (ppm) 100 300 0,01 The features of the process that showed the best results were: H:\Susan\Keep\speci\JANELLE\ANODE IMPROVEMENTS AND A PROCESS .doc 3/02/99 7 Concentration of with Brown Sugar, Hard Sugar or Crystal, 16% Mixing temperature of mixture 1359C- 1702C; Baking temperature 1100 2

C.

The anodes of the present improvement were also compared to conventional anodes that use pitch as the binding agent.

The results are given below in Table IV.

TABLE IV *00* *0 0 g

S

S.

AU 73110/98

(MOLASSES)

BROWN SUGAR HARD SUGAR CRYSTAL

SUGAR

CONV.

(PITCH)

PROPERTIES OF 18% 18% 20% 15% 20% 15% 20% 16% 18% 14,5% THE ANODE ST=4h ST=20h ST=20h ST-20h ST=20h ST-30h ST-30h ST-30h ST=30h APARENT DENSITY 1,583 1,607 1,610 1,584 1,522 1,591 1,582 1,627 1,630 1,577 g/cm3 APARENT DENSITY 1,442 1,446 1,471 1,440 1,348 1,460 1,463 1,476 1,447 1,530 (BA) g/cm3 REAL DENSITY; 2,093 2,089 2,090 2, 089 2,092 2,091 2,093 2,085 2,079 2,125 g/cm3 CRUSHING 318 224 209 235 205 181 201 260 209 263

STRENGTH.:

kgf/cm2 ELECTRIC 8583 8738 7541 7815 7819 10545 9640 8987 8181 7995

RESISTIVITY.;

.Ohm. cm AIR 1,563 1,582 1,401 1,292 0,562 1,196 0,584 0,796 1,050 1,982

PERMEABILITY;

nPm THERMAL 2,12 2,16 2,10 2,48 1,84 2,40 2,51 1,88 2,04 2,1

CONDUCTIVITY,

w/m'k H:\Priyanka\Keep\speci\14729.99.doc 20/09/99 8 AIR REACTIVITY 55,7 69,5 68,9 66,0 64,9 64,4 73,6 60,1 61,6 71,6 RESIDU; E C02 REACTIVITY 58,2 57,5 65,4 70,6 69,8 81,8 80,1 67,9 71,6 81,5 RESIDUE, ST "soaking time" at baking temperature; in hours; GA green anode; BA baked anode.

According to the data above in table IV, it can be seen that the properties of laboratory scale anodes made according to the present application are equivalent to conventional anodes containing pitch. However, the anodes S* of the present application have the advantage that certain public health and work environment problems associated with S* the use of pitch are avoided.

0* *6 So S S 0 H:\Priyanka\Keep\speci\14 7 29.99.doc 20/09/99

Claims (14)

1. An anode suitable for use in the electrolytic production of primary aluminium wherein natural or refined sugar or a mixture thereof is used as the binding agent of the components that constitute the anode.

2. An anode according to claim 1 wherein the natural sugar is selected from the rgroup consisting-of brown sugar, whole sugar, hard brown sugar, and crystal sugar.

3. An anode according to claim 1 including a composition of approximately 50 to 70% by weight of petroleum coke, 15 to 30% by weight of butt, and 15 to by weight of natural or refined sugar.

4. An anode according to claim 3 including, approximately 16 to 20% by weight of natural or refined S* sugar. An anode according to any one of the preceding claims including additives based on lithium, fluorine, aluminium, alumina, boron, sulfur or the mixtures thereof.

6. An anode according to claim 5 wherein the additive content is approximately 0 to 10% by weight.

7. An anode according to any one of claims 1 to 4 Swherein the natural or refined sugar shows a refractometric brix of about 75 to 83%, a Pol of about 37 to 63%, a purity of about 50 to 75%, reducing sugars level of about 3 to and conductive ash level of about 6 to

8. An anode according to any of claims 1 to 4 wherein the natural or refined sugar shows a maximum content of impurities such as iron, silicon, nickel, H:\Priyanka\Keep\speci\14729.99.doc 20/09/99 'J 10 vanadium, sodium, and calcium of about 400 ppm.

9. An anode according to any one of claims 1 to 4 wherein the petroleum coke has an apparent density of about 0.8 to 0.9 g/cm 3 a real density of about 1.9 to 2.1 g/cm 3 a volatiles content of about 0.1 to an ashes content of about 0.1 to and a humidity content of about 0 to 0.3%. An anode according to any one of claims 1 to 4 wherein the petroleum coke shows a maximum.content of impurities such as iron, silicon, nickel, vanadium, sodium, and calcium of about 500 ppm, and a sulfur content of about

11. An anode according to any one of claims-1 to 4 wherein said characteristics may occur individually or simultaneously. °12. A process for the manufacture of anode according to any one of claims 1 through to 11 which process includes: preparing a mixture containing petroleum coke, anode wastes from reductions or butts and natural or refined sugar or a mixture thereof; crushing, sieving and classifying of petroleum coke and butts; heating of classified fractions in a mixture with natural or refined sugar or mixtures thereof at temperature ranging from 150 0 C to 2500C.

13. A process for the manufacturing of anode according to claim 12 wherein the mixture heating temperature is from 135 0 C to 170 0 C. H:\Susaf\Keep\speci\JANELLE\NODE IMPROVEMENTS AND A PROCESS .doc 3/02/99 11

14. A process for the manufacturing of anode according to claim 12 or 13 wherein the product of said heated mixture is a slurry which may be directly used in electrolytic reduction vats or may be pressed or compacted or vibrocompacted in proper presses or compactors, with or without vacuum, in order to produce green anodes. A process for the manufacturing of anode according to claim 14 wherein said green anodes are. submitted to baking in special furnaces at temperature ranging from 800 0 C to 1300 0 C.

16. A process for the manufacturing of anode according to claim 14 or 15 wherein said green anodes are baked for a time ranging from 70 to 200 hours. e 17. A process for the manufacturing of anode according to claim 14 wherein the baking temperature of the green anodes is about 1100 0 C.

18. A process for the production of aluminium wherein an anode as defined in one of claims 1 through 11 is used in electrolytic reduction vats or pots. o.

19. A process for the production of aluminium wherein an anode manufactured according to the process defined in one of claims 12 through 17 is used as anode in electrolytic reduction vats or pots. H:\Susan\Keep\speci\JANELLE\ANODE IMPROVEMENTS AND A PROCESS .doc 3/02/99 -12 A process for the manufacturing of aluminium according to claim 18 or 19 wherein the anode is either in the form of a slurry or pressed or compacted or vibrocompacted as green anodes. Dated this 3rd day of February 1999 ALERAS ALUMINIO BRASILEIRO S.A. By their Patent Attorneys GRIFFITH HACK Fellows Institute of Patent and Trade Mark Att-orneys of Australia C 0000 :6.00 00 0000 H:\Susan\Keep\speci\JAELLE\ANODE IMPROVEMENTS ANDC A PROCESS .doc 3/02/99