FR2786206A1 - Anode for use in electrolytic aluminum manufacture contains natural or refined sugar as binder instead of pitch - Google Patents

Abstract

An anode comprising a natural or refined sugar binder is new. Independent claims are also included for the following: (i) production of the above anode by mixing ground and sieved petroleum coke and residual anode butts with sugar at 150-250 deg C; and (ii) aluminum manufacture using the above anode. Preferred Features: The sugar is brown sugar, VHP sugar, granulated sugar, candy sugar or refined sugar. The anode contains 50-70 wt.% petroleum coke, 15-30 wt.% butts and 10-25 wt.% sugar.

Description

ANODE FOR PRODUCING ALUMINUM, PROCESS FOR

  MANUFACTURE OF SUCH ANODE, MANUFACTURING METHOD

  OF ALUMINUM USING SUCH ANODE

  The present application relates to improvements obtained during the study and verification relating to the product for the manufacture of the anodes used in the

  electrolytic manufacturing processes for basic (or primary) aluminum.

  As indicated in patent application FR-A-9807579, it is a new type of anode, the composition of which comprises cane sugar molasses as a bonding agent and which is used in pots or crucibles for the electrolytic reduction of alumina to primary aluminum. More particularly, the technology presented in patent application FR-A-9807579 relates to the replacement of the electrolytic pitch often used in the conventional processes for manufacturing anodes in the primary aluminum industry, by molasses

  cane sugar, pure or containing an additive.

  In order to improve and diversify the construction configuration which has been claimed in patent application FR-A-9807579, improvements to the anode, intended for the process of manufacturing and producing aluminum, consist of possibility of replacing the electrolyte pitches used in the conventional processes for manufacturing anodes in the basic aluminum industry also with natural sugar (brown, whole, hard brown, candy, crystallized) or refined sugar, in particular sugar brown, brown sugar, VHP sugar,

  very high purity, granulated sugar, refined sugar and Candy sugar or similar.

  Therefore, the technique of using brown sugar, brown sugar, VHP sugar, refined sugar and Candy sugar as a binder in the manufacture of raw dough and anodes, which is the subject of the present application, is identical to the technique of conventional anode manufacturing processes, based on electrolytic pitch, which are widely

  widespread in the aluminum industry.

  Likewise, the content of brown sugar, brown sugar, VIIP sugar, granulated sugar, refined sugar and Candy sugar is also in coke and butts, as well as the operating conditions such as the temperature of the mixture, the cooking temperature. and the duration, represent parameters which can vary according to the types of coke, brown sugar, brown sugar, VHP sugar, granulated sugar, refined sugar

  and Candy sugar and the required additives and / or properties and the final anode.

  Consequently, the anode composition, according to the present improvement, comprises approximately 50% to 70% of petroleum coke, 15% to 30% by weight of ends ("butts") and 10 to 25% of brown sugar, brown sugar, VHP sugar, granulated sugar, sugar

  refined or Candy sugar, expressed relative to the total weight of the composition.

  Preferably, the percentage of brown sugar, brown sugar, VHP sugar, granulated sugar, refined sugar or Candy sugar used in the composition

  anode according to the present improvement is about 16% by weight.

  Additives, substances based on lithium, fluorine, aluminum, alumina, boron and sulfur as well as their mixtures, according to the present invention, can

  optionally present in an amount of 0 to about 10% by weight.

  The anode according to the present invention, for example has a maximum content of impurities such as iron, silicon, nickel, vanadium, sodium and

calcium, about 400 ppm.

  The anode according to the invention is characterized, for example, in that petroleum coke has a maximum content of impurities such as iron, silicon, nickel, vanadium, sodium and calcium, of approximately 500 ppm , and a content of

sulfur of about 3.0%.

  The process for manufacturing the anodes according to the present invention comprises the preparation of a mixture containing petroleum coke, anode waste from an electrolytic operation called "butts" (or "abouts") and brown sugar, brown sugar, V11P sugar, granulated sugar, refined sugar or Candy sugar. Petroleum coke and anode waste are crushed, sieved and classified into fractions of appropriate size. Then, these fractions are heated and mixed with brown sugar, brown sugar, VHP sugar, granulated sugar, refined sugar or Candy sugar, in mixers, continuously or batchwise, at temperatures between 150 C and 250 C. Preferably, the suitable temperature is of the order of 190 C, and the duration of the mixing depends on the nature and the capacity of

  mixing equipment used in the process.

  The paste resulting from this kneading can be used directly in pots or crucibles of electrolytic reduction or be compressed or packed or vibro-packed in suitable presses or in compressing machines, with or without vacuum, to

form raw anodes.

  These raw anodes can be baked in special ovens at temperatures

  between 800 C and 1300 C for a period between 70 and 200 hours.

  Preferably, the cooking temperature is of the order of I 1 00 C.

  The above paste can be used directly in the Soderberg process, while the raw anodes, after being baked, can be used in the process

  "precooking". These Soderberg and precooking processes are used for the manufacture-

  tion of basic aluminum. According to the invention, the typical composition of brown sugar, brown sugar, VHP sugar, granulated sugar, refined sugar or candy sugar which can be used in the anode composition has the characteristics listed in the

  Table 1, which can be met alone or simultaneously.

TABLE I

UNIT FORK PARAMETER

  Brix Refractometric 75-83% Pol * 37-63% Purity * 50-75% Reducing sugars * 3-10 Conductive ash * 6-10 Polarization * * 99-99.8 humidity ** <0.3% Ash * * < 0.25

IMPURITIES

  Iron 200 max 1ppm Silicon 250 max ppmi Nickel traces Vanadium 150 max pp Calciuml 200 max plpm Sodium 200 max liplp *: À Composition dc molasses base ** 'Sugar base composition ppmi part per million max: mlaximumll pol / polarization: content in sucrose

  According to the present improvement, the typical composition of petroleum coke used

  sand in the anodc composition preferably has the given characteristics

  in the table above, which can meet alone or simultaneously.

1 -

TABLE II

UNIT FORK PARAMETER

  Bulk density 0.8-0.9 g / cm3 True density 1.9-2.1 g / cm3 Volati Is 0.1-0.5% Ash 0.1-0.6% Humidity 0-0.3%

IMPURITIES

  Iron 400 max ppn Silicon 300 max ppm Nickel 300 max ppm Vanadium 400 max ppm Sodium 200 max ppm Calcium 300 max ppm Sulfur 3.0 max% ppm = parts per million max = maximumii The invention will now be described in relation to the same example which appears in patent application FR-A9807579, and similarly, this example should not be considered as limiting the scope and conditions of the present application. O Comparative tests were carried out in the laboratory by varying the conditions of composition of the anode and its manufacturing process, in order to obtain the best possible parameters which can serve as a reference for the process.

  manufacturer of precooked anode in the basic aluminum industry.

  So we did the experiments in a laboratory scale equipment

  l 5 roof supplied by R.D.C., making it possible to obtain 5 kg of dough for 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 the

table III.

TABLE III

  RED SUGAR PARAMETER SUGAR CANDY SUGAR

CRYSTALLIZED

  Polarization (S) 83.3 63.2 99.8 Ash 2.16 1.31 0.04 conductive (%) Calciumi (ppm) 1280 1400 100 Sodium (ppm) 100 300 <0.01 The characteristics of the process which have leads to the best results are: - concentration of brown sugar, candy sugar or granulated sugar: 16-20 O; - mixing temperature 1 35-170; - baking temperature: 1100 ° C. The anodes according to the invention are also compared with conventional anodes I 0 which use electrolytic pitch (or pitch) as binding agent. The results are

given in Table IV.

TABLE IV

  RED SUGAR MELASSES SUGAR CANDY SUGAR CONVEN-

TIONAL CRYSTALLIZATION

WITH PIT

  PROPERTIES 18% 18% 20% 15% 20% 15% 20% 16% 18% 14.5%

  DE st = st = st = st = st = st = st = st = st = st = L'ANODE 4h 20h 20h 20h 20h 30h 30h 30h 30h 20h

  DENSITY 1,583 1,607 1,610 1,584 1,522 1,591 1,582 1,627 1,630 1,577

RELATED

(GA); g / cm3

  DENSITY 1,442 1,446 1,471 1,440 1,348 1,460 1,463 1,476 1,447 1,530

RELATED

  (BA); g / cm- '-, 4 CD o O'} TABLE IV (continued) TRUE DENSITY g / cm3 2,093 2,089 2,090 2,089 2,092 2,091 2,093 2,085 2,079 2,125

  RESISTANCE AT 318 224 209 235 205 181 201 260 209 263

CRUSHING: kg / cm2

  RESISTIBILITY 8,583 8,738 7,541 7,815 7,819 1,054 9,640 8,987 8,181 7,995

ELECTRIC;! TOhm.cm. 5

  PERMEABILITY OF 1,563 1,582 1,401 1,292 0,562 1,196 0,584 0.796 1,050 1,982

AIR: nPmrn

  CONDUCTIVITY 2.12 2.16 2.10 2.48 1.84 2.40 2.51 1.88 2.04 2.1

THERMAL, w / m k

  AIR REACTIVITY 55.7 69.5 68.9 66.0 64.9 64.4 73.6 60.1 61.6 71.6

RESIDUAL% ___ _

  REACTIVITY AT 58.2 57.5 65.4 70.6 69.8 81.8 80.1 67.9 71.6 81.5

RESIDUAL CO%.

  ST = Impregnation time at baking temperature in hours GA = Raw anode BA = Cooked anode OD o 0 'Fold CD According to the indications in Table IV above, it can be seen that the properties of the anodes on the scale of laboratory manufactured according to this

  improvement, are equivalent to conventional anodes containing pitch. However, the invention makes it possible to avoid all the public health and environmental problems of the premises previously encountered relating to the use of pitch.

m rs

Claims (14)

  1.- An anode to be used in the production of primary aluimliniuim, characterized in that the anode comprises natural sugar (brown, whole sugar, hard brown sugar, crystallized) or refined sugar, as an agent connecting components which constitute this anode.   2. An anode according to claim 1, in which the sugar is chosen from brown sugar, brown sugar, VHP sugar, crystallized sugar, candy sugar and sugar. I (0 refined.   3.- An anode according to claim I or 2, characterized in that it comprises a composition consisting of approximately 50 to 70% by weight of coke   petroleum, from 15 to 30% by weight of ends, and from 10 to 25% by weight of sugar.   4. An anode according to claim 3, characterized in that it comprises   preferably about 16% O by weight of sugar.   5. An anode according to any one of the preceding claims,   0 characterized in that it comprises additives based on lithium, fluorine, aluminum,   alumina, boron, sulfur or their mixtures.   6.- An anode according to claim 5, characterized in that the proportion   of additive is about 0 to 10% by weight.   7.- An anode according to any one of claims I to 6. characterized in   that the sugar has a refractometric Brix index of approximately 75 to 83%, a Pol index of approximately 37 to 63 / O, a purity of approximately 50 to 75%, a reducing sugar content - of approximately 3 to 10% /, and a conductive ash content of about 6 to 0 10%.   8.- An anode according to any one of claims I to 7. characterized in   that sugar cane molasses has a maximum content of impurities such as iron, silicon, nickel, vanadium, sodium and calcium, of about 400 ippm.   9.- An anode according to one of claims 2 to S. characterized in   that petroleum coke has an apparent density of about 0.8 to 0.9 g / cm3, an actual density of about 1.9 to 2.1 g / cm3, a content of Shoot-   volatile matter of approximately 0.1 to 0.5%, an ash content of approximately 0.1 to 0.6%,   and a moisture content of about 0 to 0.3%.   10.- JUne anode according to any one of claims 2 to 8, characterized in   that petroleum coke has a maximum content of impurities such as iron, silicon, nickel, vanadium, sodium and calcium, of about 500 ppim, and a sulfur content of about 3.0% I 1. - A process for the manufacture of an anode according to any one of   I) claims I to I 0, characterized in that this method comprises   preparing a mixture containing petroleum coke. residual reduction anodes or abouLts, and sugar; grinding. sieving and sorting petroleum coke and butts; heating the sorted fractions in a mixture with sugar to a temperature in the range from 150 ° C. to 250 ° C., the sugar being chosen from brown sugar, brown sugar, VIIP sugar, crystallized sugar, candy sugar and refined sugar. 12. A process for the manufacture of an anode according to claim 11I1,   0 () characterized in that the heating temperature of the mixture is approximately 190 C.   13.- A process for the manufacture of an anode according to claim II or 1 2, characterized in that the product of said heated mixture is a bhoue which can be directly used in electrolytic reduction tanks or which can be] 5 compressed or compacted or vibro-impacted in presses or compactors   suitable, with or without vacuum, to produce raw anodes.   14.- A process for the manufacture of an anode according to claim 13, characterized in that said raw anodes are subjected to firing in   () special ovens at a temperature in the range of 800 C to 1,300 C.   15.- A process for the manufacture of an anode according to claim 13 or 14, characterized in that said raw anodes are cooked for a period of time ranging from 70 to 20 () 0 hours.   16. A process for the manufacture of an anode according to claim 13, characterized in that the cooking temperature of the raw anodes is approximately 1 1 00 C.   ii w F l l 17.- A process for the manufacture of aluminum, characterized in that a   anode as defined in one of claims I to I10 is used in   electrolytic reduction tanks.   D5 18.- A process for the production of alumlinium, characterized in that a   anode manufactured according to the process defined in one of claims I1 to 16 is   used as an anode in electrolytic reduction tanks.   19.- A process for the manufacture of aluminum according to claim 17 or I () 18, characterized in that the anode is in the form of a mud or is compressed   or compacted or vibro-compacted in the form of raw anodes.