EP0065854A2 - Elimination des métaux alcalins et alcalino-terreux contenus dans de l'aluminium en fusion - Google Patents

Elimination des métaux alcalins et alcalino-terreux contenus dans de l'aluminium en fusion Download PDF

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Publication number
EP0065854A2
EP0065854A2 EP82302448A EP82302448A EP0065854A2 EP 0065854 A2 EP0065854 A2 EP 0065854A2 EP 82302448 A EP82302448 A EP 82302448A EP 82302448 A EP82302448 A EP 82302448A EP 0065854 A2 EP0065854 A2 EP 0065854A2
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EP
European Patent Office
Prior art keywords
aluminium
molten
impeller
vessel
metal
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Granted
Application number
EP82302448A
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German (de)
English (en)
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EP0065854B1 (fr
EP0065854A3 (en
Inventor
Ghyslain Dubé
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Rio Tinto Alcan International Ltd
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Alcan International Ltd Canada
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Publication of EP0065854A2 publication Critical patent/EP0065854A2/fr
Publication of EP0065854A3 publication Critical patent/EP0065854A3/en
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Publication of EP0065854B1 publication Critical patent/EP0065854B1/fr
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B21/00—Obtaining aluminium
    • C22B21/06—Obtaining aluminium refining
    • C22B21/062—Obtaining aluminium refining using salt or fluxing agents

Definitions

  • This invention relates to the removal of contaminant quantities of alkali metals and alkaline earth metals from molten aluminium by reaction with aluminium fluoride.
  • Molten aluminium withdrawn from electrolytic reduction cells contains small amounts of alkali metals such as lithium and sodium and alkaline earth metals such as magnesium and calcium. The presence of these contaminant alkali metals and alkaline earth metals is deleterious for various uses to which the primary metal may be put.
  • sodium in amounts of approximately 2 p.p.m. or more can cause "hot shortness" or edge cracking during hot rolling.
  • the presence of trace quantities of lithium and/or sodium increases the rate of oxidation of molten aluminium. This increases the melt loss and generates a thick dross layer which can block casting machine nozzles and diminish metal fluidity. Therefore, economic and technical considerations require that these elements be removed as soon as possible after withdrawal of primary aluminium from the reduction cells to reduce the time period during which lithium- and/or sodium-containing molten aluminium is exposed to the atmosphere.
  • Magnesium in small quantities is detrimental to electrical conductivity and should be removed from primary aluminium which is to be used for products in which this property is important.
  • aluminium fluoride aluminium fluoride
  • the treatment material may consist essentially of aluminium fluoride, or may be composed wholly or in part of alkali metal fluoaluminates which are solid at the temperature of the molten metal.
  • An example of the latter type of material (useful for removal of lithium, magnesium, and calcium) is particulate sodium cryolite or lithium-free reduction cell electrolyte having a low ratio by weight of sodium fluoride to aluminium fluoride so as to contain aluminium fluoride in excess of the stoichiometric requirements of Na 3 AlF 6 with a composition such that a major proportion remains solid at the treatment temperature, as is usually the case provided the aforementioned ratio remains within the range of 1.3 - 1.5. Indeed, it is not essential that the addition remain in solid form; a low (approximately 725°C) melting- temperature compound containing a large excess of AlF 3 (e.g..).
  • the active fluoride material may also contain inert material such as aluminium oxide, in a proportion even as high as 50% by weight, although 7 - 20% is the more usual aluminium oxide content of commercial aluminium fluoride.
  • Treatments with aluminium fluoride are considered advantageous for removal of alkali metals and alkaline earth metals, as compared with fluxing with chlorine gas or chlorine/inert gas mixtures, because the gas fluxing operations yield deleterious gaseous byproducts and are otherwise inconvenient.
  • a substantial proportion of the products of reaction of the alkali metal (Li, Na, Mg) with aluminium fluoride remains trapped on or within the reactive bed or associated filter material to cause premature plugging; electrolyte from the reduction cell, sludge and/or other solid or liquid impurities carried over with the molten metal from the electrolytic cell have the same effects.
  • a preferential metal path or "channel" can appear within the reactive bed and seriously reduce the alkali metal removal efficiency.
  • the aluminium fluoridc material is consumed during the treatment of molten metal and consequently the performance of a reactive bed is not constant during its service life.
  • aluminium fluoride powder is not easily wetted by molten aluminium, and is thermally very stable, i.e. it does not melt under atmospheric pressure, and it has a sublimation temperature of approximately 1,270°C, so that reaction between liquid- liquid or gas-liquid phases is impossible at the treatment temperature of molten aluminium (660 C - 900°C).
  • aluminium fluoride powder It is also possible to make a large addition of aluminium fluoride powder to the bottom of an empty crucible before metal addition.
  • the aluminium fluoride powder reacts preferentially with the cell electrolyte (which is invariably siphoned from the reduction cell along with the molten Al metal) to form a solid mass which remains attached to the crucible lining.
  • the cell electrolyte which is invariably siphoned from the reduction cell along with the molten Al metal
  • the method of the invention requires the addition of an appropriate charge of the treatment material (AIF 3 or A1F 3 -containing material) to the molten Al metal under conditions which involve re-circulation of the treatment material within the molten metal while avoiding excessive disturbance of the molten metal surface, to hold down oxidation of the metal.
  • the treatment material is entrained in the molten aluminium by supplying the treatment material to a vortex generated in a body of the molten metal held within a container.
  • the vortex generator also serves to generate upwardly spiralling currents in the molten metal in the region of the boundaries of the container to maintain prolonged contact of the particles of the treatment material with the molten metal.
  • the circulation of the molten metal by vortex generation is continued for a sufficient length of time to reduce the alkali metal and alkaline earth metal content of the molten metal to a desired low value, after which the circulation is discontinued.
  • Some of the reaction products, which are admixed with residual treatment material, will rise to the surface as a dross, from which the molten metal can be separated by dross skimming or metal siphoning or other conventional means.
  • the greater part tends to adhere to the crucible lining during the stirring process, whence it can be removed when the crucible is empty.
  • the vortex is preferably generated and maintained by using a rotating stirrer having a multi- bladed rotor immersed within a body of molten metal contained in a crucible and rotated about a vertical axis, with the blades pitched so that each blade has a major surface facing downwardly at an acute angle to the vertical.
  • the impeller rotor is preferably arranged in the crucible eccentrically with respect to the vertical centre line of the crucible.
  • Electromagnetic induction stirring may also be employed to generate a vortex.
  • Appropriately arranged induction coils may be disposed externally of a crucible or other vessel containing the molten metal.
  • the invention also provides apparatus for mixing particulate AlF 3 treatment material with molten aluminium, including a crucible for the molten metal, and an impeller or rotor having pitched blades and disposed eccentrically of the vertical centre line of the crucible, with various dimensional and positional relationships maintained within specified ranges or limits described below.
  • a cylindrical crucible 10 contains a body of molten aluminium 11.
  • a separate lid 12 supports an eccentrically mounted impeller 14, driven by a motor 16.
  • the impeller 14 has a shaft 18 which carries blades 20 for immersion in the molten aluminium body 11.
  • the lid 12 also includes a duct 22 for supply of treatment material to the crucible; and an exhaust conduit 24 for exhausting fumes from the crucible.
  • the crucible comprises a steel shell, with a refractory lining inert to molten aluminiu.
  • the lid 12 and associated items comprise a vortex generator assembly which may be transferred to permit the same stirring apparatus to be used to stir batches of molten metal contained in a series of different mobile crucibles.
  • the crucible 10 For removal of contaminant alkali metals and/ or alkaline earth metals from molten aluminium, the crucible 10 is charged with an appropriate quantity of molten Al metal. The lid 12 is then placed on the- crucible to immerse the bladed portion of the impeller 14. Particulate treatment material comprising or consisting of aluminium fluoride (AIF 3 ), which is solid at the temperature of molten aluminium, is then fed by gravity through the duct 22. Rotation of the impeller should preferably be commenced before introduction of the treatment material (but may be commenced after such introduction) and maintains a stable vortex (indicated at 26 in Fig. 2) in the molten body 11.
  • AIF 3 aluminium fluoride
  • Rotation of the impeller is continued, with maintenance of the vortex 26 and recirculation of the aluminium fluoride particles until there has been sufficient reaction between the aluminium fluoride and the dissolved contaminant alkali metals and/or alkaline earth metals to reduce the content of these contaminants in the melt to a desired low value.
  • the time required to achieve this result is no more than about ten minutes, and Indeed often substantially less than ten minutes.
  • cryolithionite compounds produced by reaction of the contaminant alkali metals and - alkaline earth metals with the aluminium fluoride, float on the surface of the molten body, and may be readily removed by skimming or other means when the rotation of the impeller is ended and the lid is lifted away from the crucible. The decontaminated molten metal may then be poured or otherwise withdrawn from the crucible.
  • the impeller may comprise a plurality of equiangularly spaced, pitched blades 20 each having a major surface 20a that faces downwardly at an acute angle to the vertical.
  • the axis of the impeller shaft is disposed eccentrically of the geometric axis of the crucible, and the direction of impeller rotation is such that the blade surfaces 20a are the leading surfaces of the blades, exerting a force having a downward component on the molten aluminium.
  • 9 designates the pitch angle of the blade surfaces 20a
  • d designates the overall diameter of the bladed portion of the impeller
  • h designates the height of the impeller blades
  • x designates the eccentricity of the impeller shaft
  • y designates the vertical distance from the bottom of the crucible interior to the midpoint of the impeller blades
  • H designates the vertical distance from the bottom of the crucible interior to the quiescent level of molten metal in the crucible
  • D is the internal diameter of the crucible
  • the arrow R represents the direction of impeller rotation.
  • the eccentricity, x, of the impeller shaft is usually in the range of 0.1 - 0.25D and more preferably in the range of 0.25 - 0.7 d. It is especially preferred to utilize three blades spaced 120 apart with a pitch angle of 30 - 35 , and a ratio d/D of about 0.25.
  • the impeller eccentricity, x is most preferably 0.5 d.
  • the described impeller arrangement is advantageous in creating a stable vortex without use of vertical baffles, which would be impracticable in interchangeable transfer crucibles.
  • the function of conventional baffles in generating vortices by maintaining a high rate of relative rotation between the impeller and the liquid is achieved with the present impeller arrangement by the combination of radial and axial flow components produced by the impeller.
  • blade pitch angles 8 as large as 45° or more tend to cause splashing and surface waves, it is preferred to use a smaller pitch angle, such as 30 - 35 to force the metal downwardly to drag the fluoride powder into the molten aluminium.
  • the requisite axial component of molten metal flow can be achieved, even with a vertical-bladed impeller, by locating the impeller eccentrically with respect to the geometric axis of the crucible.
  • eccentric location of the impeller permits the crucible to be filled to a greater extent without risk of splashing during the stirring of metal in transfer crucibles of large size.
  • the eccentric location of the impeller constitutes an important feature of a preferred arrangement in accordance with the invention since it permits the treatment of a substantially larger batch of metal in a crucible of given size.
  • the minimum rate of rotation, for a given impeller, is that which will generate and maintain a stable vortex, while the maximum rotation rate is that above which air is ingested into the molten body being stirred. These values are determined by the impeller diameter d.
  • the optimum rotation rate is that which produces a good vortex without causing excessive metal splashing and loss or being responsible for erosion of either the crucible refractory or impeller construction material. Referring to an impeller providing a d/D ratio within the preferred range of 0.15 - 0.40, it is at present preferred to operate such an impeller at a rotation rate of about 100 to about 300 r.p.m. However, rates of rotation outside this range may also be used, so long as they produce the desired vortex without excessive splashing.
  • alkali and alkaline earth metals react with AlF 3 to form mixed alkali cryolithionite compounds, e . g . Na 5 Al 3 F 14 , N a 2 L iA1 F 6 , and Li 3 Na 3 Al 2 F 12 .
  • These compounds having a relatively low melting point, can easily be agglomerated or stick to the crucible walls or float to the melt surface where they react with metal oxide or particles of cell electrolyte always present after the siphoning of electrolytic cells. During subsequent metal transfer by siphoning, most of these compounds will remain inside the crucible and are thus separated from the molten Al.
  • the impeller diameter, d was 12.5 cms and the impeller was a four-bladed impeller having a blade height of 8.8 cms, with the blades inclined at an angle of 35°.
  • the diameter of the crucible was 50 cms and the values of H and x were respectively 37.5 cms and d/2.
  • a pitched-bladed impeller having a blade height of 28 cms and diameter of 45 cms was immersed in the molten aluminium with an eccentricity of 20-30 cms (preferably 22.5 cms) with the centre of the impeller blades 37.5 cms above the crucible bottom, such that the top edges of the blades were located halfway between the top of the melt and the crucible bottom (the blades thus being disposed entirely within the lower half of the molten metal body); the impeller was rotated, in each case, for 10 minutes at a rate of between about 130 and about 135 r.p.m. to create and maintain a stable vortex.
  • the mode of addition of AlF 3 particles, and the molten metal temperature were varied from test to test. Results of twenty successive tests were as follows:
  • the aluminium fluoride powder used (92% A1F 3 , about 8% Al 2 O 3 by weight) had a bulk density of 1.5 - 1.7 g/cm and a particle size distribution as follows: 25% larger than 100 microns, 50% larger than 80 microns, 75% larger than 65 microns.
  • the crucibles contained approximately 3,500 kg. of molten aluminium each.
  • a three-bladed impeller having a blade pitch (angle ⁇ ) of 35 0 , diameter (d) of 46 cm., and blade height (h) of 25 cm.
  • Series 1 illustrates-the removal of alkali metals due to the aluminium stirring effect only.
  • the greater sodium removal after 3 and 6 minutes (61% and 72%) compared to the lower lithium removal efficiency (15% and 19%) is attributable to the much lower vapour pressure of lithium than sodium.
  • sodium has a boiling point at atmospheric pressure of 882°C compared with 1,329°C for lithium.
  • Series 5 is identical to series 3 except for an increased r.p.m. from 100 to 150. This increased the sodium and lithium removal efficiency from 89% to 92% and from 74% to 85%, respectively.
  • Series 6 illustrates, for 7 transfer crucibles, the influence of a sequential addition of AIF 3 powder on the removal rate of alkali metals. It can be seen that this also helps in increasing the removal rate, probably by increasing the interfacial area between the powder and the aluminium (the addition of a large quantity of AlF3 in one "shot” can cause powder agglomeration and decrease the effective contact with the aluminium).
  • a synthetic mixture containing 50% each (by weight) of cryolite (Na 3 AlF 6 ) and AlF 3 (weight ratio of NaF/AlF 3 0.43) was prepared by fusion of the two compounds, ground to -35 mesh particle size, and employed for treatment of molten aluminium in accordance with the present method. Two 150 kg.
  • the high efficiency of the AlF 3 /Na 3 AlF 6 mixture is possibily attributable to the formation of low melting point (about 700°C) phases. It therefore melts after contact with the liquid aluminium providing a liquid- liquid reaction rather than the solid-liquid reaction with the AlF 3 powder which compensates for the aluminium fluoride dilution.
  • aluminium fluoride powder in mixtures of a wide range of particle size distribution have been used, with the average particle size dimension varying between 1 and 0.05 mm.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Manufacture And Refinement Of Metals (AREA)
  • Battery Electrode And Active Subsutance (AREA)
  • Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
EP82302448A 1981-05-19 1982-05-13 Elimination des métaux alcalins et alcalino-terreux contenus dans de l'aluminium en fusion Expired EP0065854B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US26525481A 1981-05-19 1981-05-19
US265254 1981-05-19

Publications (3)

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EP0065854A2 true EP0065854A2 (fr) 1982-12-01
EP0065854A3 EP0065854A3 (en) 1983-01-26
EP0065854B1 EP0065854B1 (fr) 1985-08-28

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EP82302448A Expired EP0065854B1 (fr) 1981-05-19 1982-05-13 Elimination des métaux alcalins et alcalino-terreux contenus dans de l'aluminium en fusion

Country Status (9)

Country Link
EP (1) EP0065854B1 (fr)
JP (1) JPS6017009B2 (fr)
AU (1) AU553304B2 (fr)
CA (1) CA1188107A (fr)
CH (1) CH651320A5 (fr)
DE (1) DE3265793D1 (fr)
ES (2) ES512288A0 (fr)
FR (1) FR2506333B1 (fr)
NO (1) NO160663C (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0620285A1 (fr) * 1993-04-14 1994-10-19 Norsk Hydro A/S Dispositif pour introduire
NO20210630A1 (en) * 2021-05-21 2022-11-22 Norsk Hydro As Na removal from pot-room Al metal with under-pressure and forced convection

Families Citing this family (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA1188107A (fr) * 1981-05-19 1985-06-04 Ghyslain Dube Separations des metaux alcalins et de terre alcaline de l'aluminium en fusion
DE3276823D1 (en) * 1982-11-09 1987-08-27 Alcan Int Ltd Removal of alkali metals and alkaline earth metals from molten aluminium
EP0112024B1 (fr) * 1982-11-16 1986-10-22 Alcan International Limited Elimination d'impuretés à partir d'aluminium en fusion
GB8622458D0 (en) * 1986-09-18 1986-10-22 Alcan Int Ltd Alloying aluminium
US4822412A (en) * 1986-11-17 1989-04-18 The Boeing Company Method of removing lithium from aluminum-lithium alloys
US4832740A (en) * 1987-03-30 1989-05-23 Swiss Aluminium Ltd. Process for removing alkali and alkaline earth elements from aluminum melts
DE4029396A1 (de) * 1990-09-17 1992-03-19 Vaw Ver Aluminium Werke Ag Vorrichtung zum reinigen von ne-metallschmelzen, insbesondere aluminiumschmelzen
US5080715A (en) * 1990-11-05 1992-01-14 Alcan International Limited Recovering clean metal and particulates from metal matrix composites
JPH059007U (ja) * 1991-07-08 1993-02-05 株式会社村田製作所 結合線路素子
US6602318B2 (en) 2001-01-22 2003-08-05 Alcan International Limited Process and apparatus for cleaning and purifying molten aluminum
CN116354572B (zh) * 2023-04-27 2024-05-17 上海开鸿环保科技有限公司 基于重金属组分回收的危废污泥高温熔融处理方法

Citations (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3305351A (en) * 1964-02-24 1967-02-21 Reynolds Metals Co Treatment of aluminum with aluminum fluoride particles
US3436212A (en) * 1966-11-22 1969-04-01 Aluminum Co Of America Flux for treating aluminum
US3459536A (en) * 1964-11-06 1969-08-05 Interlake Steel Corp Method for mixing molten metal
US3528801A (en) * 1966-08-24 1970-09-15 Reynolds Metals Co Method of treating aluminous metal with carbon and aluminum fluoride
US3620716A (en) * 1969-05-27 1971-11-16 Aluminum Co Of America Magnesium removal from aluminum alloy scrap
US3767382A (en) * 1971-11-04 1973-10-23 Aluminum Co Of America Treatment of molten aluminum with an impeller
GB1367069A (en) * 1970-10-22 1974-09-18 British Aluminium Co Ltd Removal of non-metallic constituents from liquid metal
US3849119A (en) * 1971-11-04 1974-11-19 Aluminum Co Of America Treatment of molten aluminum with an impeller
US3871872A (en) * 1973-05-30 1975-03-18 Union Carbide Corp Method for promoting metallurgical reactions in molten metal
US3902893A (en) * 1973-01-04 1975-09-02 Ostberg Jan Erik Method for moving and stirring of heavy metallurgical melts
US4058394A (en) * 1976-02-23 1977-11-15 Kennecott Copper Corporation Pyrometallurgical system for solid-liquid contacting
US4138246A (en) * 1976-03-26 1979-02-06 Swiss Aluminium Ltd. Process for lowering the concentration of sodium in aluminum melts
GB2030597A (en) * 1978-08-23 1980-04-10 Alcan Res & Dev Filtering Aluminium

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA1188107A (fr) * 1981-05-19 1985-06-04 Ghyslain Dube Separations des metaux alcalins et de terre alcaline de l'aluminium en fusion

Patent Citations (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3305351A (en) * 1964-02-24 1967-02-21 Reynolds Metals Co Treatment of aluminum with aluminum fluoride particles
US3459536A (en) * 1964-11-06 1969-08-05 Interlake Steel Corp Method for mixing molten metal
US3528801A (en) * 1966-08-24 1970-09-15 Reynolds Metals Co Method of treating aluminous metal with carbon and aluminum fluoride
US3436212A (en) * 1966-11-22 1969-04-01 Aluminum Co Of America Flux for treating aluminum
US3620716A (en) * 1969-05-27 1971-11-16 Aluminum Co Of America Magnesium removal from aluminum alloy scrap
GB1367069A (en) * 1970-10-22 1974-09-18 British Aluminium Co Ltd Removal of non-metallic constituents from liquid metal
US3767382A (en) * 1971-11-04 1973-10-23 Aluminum Co Of America Treatment of molten aluminum with an impeller
US3849119A (en) * 1971-11-04 1974-11-19 Aluminum Co Of America Treatment of molten aluminum with an impeller
US3902893A (en) * 1973-01-04 1975-09-02 Ostberg Jan Erik Method for moving and stirring of heavy metallurgical melts
US3871872A (en) * 1973-05-30 1975-03-18 Union Carbide Corp Method for promoting metallurgical reactions in molten metal
US4058394A (en) * 1976-02-23 1977-11-15 Kennecott Copper Corporation Pyrometallurgical system for solid-liquid contacting
US4138246A (en) * 1976-03-26 1979-02-06 Swiss Aluminium Ltd. Process for lowering the concentration of sodium in aluminum melts
GB2030597A (en) * 1978-08-23 1980-04-10 Alcan Res & Dev Filtering Aluminium

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0620285A1 (fr) * 1993-04-14 1994-10-19 Norsk Hydro A/S Dispositif pour introduire
NO20210630A1 (en) * 2021-05-21 2022-11-22 Norsk Hydro As Na removal from pot-room Al metal with under-pressure and forced convection

Also Published As

Publication number Publication date
ES8403169A1 (es) 1984-03-01
FR2506333B1 (fr) 1990-12-07
AU8378082A (en) 1982-11-25
CH651320A5 (de) 1985-09-13
NO821659L (no) 1982-11-22
EP0065854B1 (fr) 1985-08-28
CA1188107A (fr) 1985-06-04
ES8400501A1 (es) 1983-10-16
ES512288A0 (es) 1983-10-16
JPS6017009B2 (ja) 1985-04-30
JPS57198226A (en) 1982-12-04
DE3265793D1 (en) 1985-10-03
AU553304B2 (en) 1986-07-10
NO160663B (no) 1989-02-06
ES519264A0 (es) 1984-03-01
FR2506333A1 (fr) 1982-11-26
NO160663C (no) 1989-05-16
EP0065854A3 (en) 1983-01-26

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