CA2259565A1 - Anode improvements and a process for the manufacture and production of aluminum - Google Patents

Abstract

Anode improvements and a process for the manufacture and production of aluminum of the type defined in claims 1 through 20 of patent No. PI 9800469-7, filed on 04/17/98, wherein the anode used in processes for the electrolytic production of primary aluminum comprises with Brown Sugar, Demerara, VHP, Crystal, Refined or Hard Sugar as the binding agent of the components that constitute same.

Description

"ANODE IMPROVEMENTS AND A PROCESS FOR THE MANUFACTURE AND
PRODUCTION OF ALUMINUM"
The present addition certificate refers to 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 aluminum.
As mentioned in patent application PI 9800469-7, it is a new type of anode, whose composition comprises sugar cane molasses as a binding agent, and is used in pots for electrolytically reducing alumina to primary aluminum.
More specifically, the technology presented in patent application PI 9800469-7, refers to the replacement of the electrolytic pitch frequently used in conventional processes for the manufacture of anodes in the primary aluminum industry, by pure or additive-containing sugar cane molasses.
With a view to improve and diversif y the constructive configuration described and claimed in patent application PI 9800469-7, the anode improvements, for the process of manufacture and production of aluminum now presented as an addition certificate consists of the possibility of replacing the electrolytic pitch used in conventional processes for the manufacture of anodes in the primary aluminum industry, also by Brown Sugar, Demerara, VHP, Crystal, Refined, Hard Sugar or similar.
Thus, the technique of using Brown Sugar, Demerara, VHP, Crystal, Refined, Hard Sugar as binder in the manufacture of the paste and green anodes, object of the present addition certificate, is identical to that of the traditional processes for production of anodes based on electrolytic pitch, which are widely known in the aluminum industry.
Similarly, the Brown Sugar, Demerara, VHP, Crystal, Refined, Hard 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, Brown Sugar, Demerara, VHP, Crystal; Refined, Hard Sugar and additives, and/or the properties required for the anode produced.
Therefore, the anode composition according to the present improvement, comprises about 500-700 of petroleum coke, 150-300 of "butt" and 100-250 of Brown Sugar, Demerara, VHP, Crystal, Refined or Hard Sugar, based in the total weight of the composition.
Preferably, the percentage of Brown Sugar, Demerara, VHP, Crystal, Refined or Hard Sugar used in the anode composition according to the present improvement is about 16o by weight.
The additives, lithium, fluorine, aluminum, alumina, boron and sulfur based substances and the mixtures, thereof, according to the present improvement, may alternatively be included in percentages varying from 0 to about loo by weight.
The process for the manufacture of anodes according to the present improvement comprises, the preparation of a mixture containing petroleum coke, anode wastes from the electrolytic process called "butts" and Brown Sugar, Demerara, VHP, Crystal, Refined or Hard 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 Brown Sugar, Demerara, VHP, Crystal, Refined or Hard Sugar, in continuous or batch mixers, at temperatures ranging from 150°C to 250°C. Preferably, the suitable temperature is around 190°C, 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°C to 1300°C for a time ranging from 70 to 200 hours. Preferably, the baking temperature is about 1100°C.
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 aluminum production.
According to the now certified improvement, the typical composition of the Brown Sugar, Demerara, VHP, Crystal, Refined or Hard 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 0 Pol * 37 - 63 0 Purity * 50 - 75 0 Reducing sugars * 3 -10 0 Conductive ashes 6 -10 0 *

Polarization * * 99 -99.8 Moisture * * <0.3 0 Ashes * * <0.25 IMPURITIES:

Iron 200 max ppm Silicon 250 max ppm Nickel traces Vanadium 150 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 improvement, 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.

TABLE II
PARAMETER RANGE UNIT

Apparent density 0.8 -0.9 g/cm3 Real density 1.9 -2.1 g/cm3 Volatiles 0,1 -0.5 0 Ashes 0,1 -0.6 Moisture 0 -0.3 s IMPURITIES:

Iron 400 max ppm Silicon 300 max ppm Nickel 300 max ppm Vanadium 400 max ppm Sodium 200 max ppm Calcium 300 max ppm Sulfur 3.0 max o ~ ppm = parts per million ~ max = maximum The improvement object of the addition certificate will be described in relation to the same example given in patent application PI 9800469-7, 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 aluminum industry.

Thus, the experiments have been performed in "Bench Scale" equipment supplied by R.D.C., 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.
TTDTT TTT
PARAMETER BROWN SUGAR HARD SUGAR CRYSTAL SUGAR

Polarization (S) 83,3 63,2 99,8 Conductive Ashes(o) 2,16 1,31 0,04 Calcium ( ppm) 1280 1400 100 Sodium (ppm) 100 300 < 0, O1 The features of the process that showed the best results were:
~ Concentration of with Brown Sugar, Hard Sugar or Crystal, = 16%-200;
~ Mixing temperature of mixture = 135°C- 170°C~
~ Baking temperature = 1100°C.
The anodes of the present improvement were also compared to conventional anodes that use electrolytic pitch as the binding agent.
The results are given below in Table IV.

TABLE IV
INVENTION BROWN I(ARD CRYSTAL CON

(MOLASSES) SUGAR SUGAR SUCAR V' (Pitt 11) PROPERTIES I8%l8% 20% 15% 20%15% 20% 16%I8% 14,5 Oh TILE ANODC ST=4ST=2ST=20ST=2ST=20S'f=3S'f=3ST=3ST=3ST=2 h Oh h Oh h Oh Oh Oh Oh Oh APARENT DENSITY1,5831,6071,6101,5841,5221,5911,5821,6271,6301,577 (GA); S/cm3 APARENT DENSITY1,4421,4461,4711,4401,3481,4601,4631,4761,4471,530 ~ ~ ~ ~ ~ ~
(BA) g/cm3 REAL DENSITY;2,0932,0892,0902,0892,0922,0912,0932,0852,0792,125 g/cm3 STRENGHT.:
kgf/cm2 RESISTIVITY.;

uOhm.cm AIRPERMLABILITY;1,5631,5821,4011,2920,5621,1960,5840,7961,0501,982 2 0 nPm THERMAL 2,122,162,102,481,842,402,511,882,042,1 CONDUCTIVITY, w/mk AIRREACTIVIY55,769,568,966,064,964,473,660,161,671,6 RESIDUE;%

C02 REACTIVIY58,257,565,470,669,881,880,167,971,681,5 RESIDUE, ST="saking time" at baking temperature; in hours;
30 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 improvement are equivalent to conventional anodes containing pitch. However, improvements are necessary and after these all the public health and work environment problems previously described related to the use of pitch will be eliminated.

Claims (4)

1- Anode improvements and a process for the manufacture and production of aluminum of the type defined in claims of 1 through 20 of patent No. PI 9800469-7, filed on 04/1798, characterized by the fact that the anode used in processes for the electrolytic production of primary aluminum comprises natural (brown, whole sugar, hard brown, crystal) or refined sugar as the binding agent of the components that constitute same.

2- Anode improvements and a process for the manufacture and production of aluminum of the type defined in claims 1 through 20 of patent No. PI 9800469-7, filed on 04/17/98, characterized by the fact that the process for the manufacture of the anode comprises the preparation of a mixture containing petroleum coke, anode wastes from reductions or "butts" and natural (brown, whole sugar, hard brown, crystal) or refined sugar, crushing, screening and classification of the petroleum coke and "butts", heating of the fractions above in mixture with with Brown Sugar, Demerara, VHP, Crystal, Refined or Hard Sugar at temperatures ranging from 150°C to 250°C.

3- Anode improvements and a process for the manufacture and production of aluminum of the type defined in claims 1 through 20 of patent No. PI 9800469-7, filed on 04/17/98, characterized by the fact that the process for producing aluminum uses, as the anode in electrolytic reduction pots, one anodes as defined in claim 1.

4- Anode improvements and a process for the manufacture and production of aluminum of the type defined in claims 1 through 20 of patent No. PI 9800469-7, filed on 04/17/98, characterized by the fact that the process for producing aluminum uses, as the anode in electrolytic reduction pots, anodes manufactured according the process defined in claim 2.