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US20130186236A1 - Energy Efficient Salt-Free Recovery Of Metal From Dross - Google Patents

Energy Efficient Salt-Free Recovery Of Metal From Dross Download PDF

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Publication number
US20130186236A1
US20130186236A1 US13/655,204 US201213655204A US2013186236A1 US 20130186236 A1 US20130186236 A1 US 20130186236A1 US 201213655204 A US201213655204 A US 201213655204A US 2013186236 A1 US2013186236 A1 US 2013186236A1
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United States
Prior art keywords
furnace
dross
metal
filling material
recovered
Prior art date
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Abandoned
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US13/655,204
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English (en)
Inventor
Michel G. Drouet
Francois Rivard
Pierre Carabin
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Pyrogenesis Canada Inc
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Pyrogenesis Canada Inc
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Publication date
Application filed by Pyrogenesis Canada Inc filed Critical Pyrogenesis Canada Inc
Priority to US13/655,204 priority Critical patent/US20130186236A1/en
Assigned to PYROGENESIS CANADA, INC. reassignment PYROGENESIS CANADA, INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: CARABIN, PIERRE, DROUET, MICHEL G., RIVARD, Francois
Publication of US20130186236A1 publication Critical patent/US20130186236A1/en
Priority to US15/094,857 priority patent/US20170009319A1/en
Priority to US16/712,810 priority patent/US20200332392A1/en
Priority to US18/096,641 priority patent/US20230357888A1/en
Priority to US18/972,008 priority patent/US20250327150A1/en
Abandoned legal-status Critical Current

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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
    • C22B21/0084—Obtaining aluminium melting and handling molten aluminium
    • C22B21/0092—Remelting scrap, skimmings or any secondary source aluminium
    • 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
    • C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
    • C22B7/001—Dry processes
    • C22B7/003—Dry processes only remelting, e.g. of chips, borings, turnings; apparatus used therefor
    • 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
    • C22B13/00—Obtaining lead
    • C22B13/04—Obtaining lead by wet processes
    • C22B13/045—Recovery from waste materials
    • 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
    • C22B19/00—Obtaining zinc or zinc oxide
    • C22B19/20—Obtaining zinc otherwise than by distilling
    • 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
    • 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
    • C22B21/0038—Obtaining aluminium by other processes
    • C22B21/0069—Obtaining aluminium by other processes from scrap, skimmings or any secondary source aluminium, e.g. recovery of alloy constituents
    • 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
    • C22B21/064—Obtaining aluminium refining using inert or reactive gases
    • 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
    • C22B23/00—Obtaining nickel or cobalt
    • C22B23/04—Obtaining nickel or cobalt by wet processes
    • 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
    • C22B5/00—General methods of reducing to metals
    • 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
    • C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
    • C22B7/04—Working-up slag
    • 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
    • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
    • C22B9/05—Refining by treating with gases, e.g. gas flushing also refining by means of a material generating gas in situ
    • C22B9/055—Refining by treating with gases, e.g. gas flushing also refining by means of a material generating gas in situ while the metal is circulating, e.g. combined with filtration
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B17/00—Furnaces of a kind not covered by any of groups F27B1/00 - F27B15/00
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B7/00—Rotary-drum furnaces, i.e. horizontal or slightly inclined
    • F27B7/06—Rotary-drum furnaces, i.e. horizontal or slightly inclined adapted for treating the charge in vacuum or special atmosphere
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B7/00—Rotary-drum furnaces, i.e. horizontal or slightly inclined
    • F27B7/10—Rotary-drum furnaces, i.e. horizontal or slightly inclined internally heated, e.g. by means of passages in the wall
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B7/00—Rotary-drum furnaces, i.e. horizontal or slightly inclined
    • F27B7/14—Rotary-drum furnaces, i.e. horizontal or slightly inclined with means for agitating or moving the charge
    • F27B7/16—Rotary-drum furnaces, i.e. horizontal or slightly inclined with means for agitating or moving the charge the means being fixed relatively to the drum, e.g. composite means
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B7/00—Rotary-drum furnaces, i.e. horizontal or slightly inclined
    • F27B7/20—Details, accessories or equipment specially adapted for rotary-drum furnaces
    • F27B7/2016—Arrangements of preheating devices for the charge
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D3/00—Charging; Discharging; Manipulation of charge
    • F27D3/16—Introducing a fluid jet or current into the charge
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D3/00—Charging; Discharging; Manipulation of charge
    • F27D3/16—Introducing a fluid jet or current into the charge
    • F27D2003/162—Introducing a fluid jet or current into the charge the fluid being an oxidant or a fuel
    • F27D2003/163—Introducing a fluid jet or current into the charge the fluid being an oxidant or a fuel the fluid being an oxidant
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D3/00—Charging; Discharging; Manipulation of charge
    • F27D3/16—Introducing a fluid jet or current into the charge
    • F27D2003/167—Introducing a fluid jet or current into the charge the fluid being a neutral gas
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/25—Process efficiency

Definitions

  • the present invention relates to the salt-free recovery of non-ferrous metals, such as aluminum, from dross, without the use of any external heat source.
  • Dross is a material which forms on the surface of molten non-ferrous metals, such as aluminum or zinc, during remelting, metal holding and handling operations when the molten metal is in contact with a reactive atmosphere.
  • Dross normally consists of metal oxides entraining a considerable quantity of molten free (unreacted) metal, and for economic reasons it is desirable to extract the free metal before discarding the residue.
  • Recovery can be carried out by treating the dross in a furnace at a high temperature.
  • several furnaces have been devised and are presently being used; such furnaces are normally heated with an external heat source, such as fuel- or gas-operated burners, plasma torches, or electric arcs.
  • the dross which normally contains about 50% aluminum metal, is skimmed off from the surface of the molten metal in a smelting or similar furnace and is usually loaded into special containers or pans where it is cooled and then it is stored, before being processed in a dross treating furnace which, as mentioned above, is heated with an external heat source.
  • the dross In the case of zinc dross, the dross, once cold, is crushed in a ball mill followed by separation of the metallic particles from the oxide powder by sieving. That process leads to a very poor metal recovery and, in addition, an important amount of the separated metal is lost when dumped into the holding furnace as it oxidizes on the surface of the melt.
  • the reintroduction of the recovered metal also negatively affects the control of the holding furnace. In that case, it is large metal ingots which are fed into the holding furnace; the ingots, being cold, negatively affect the temperature control of the holding furnace.
  • a process for treating dross containing a recoverable metal, in order to recover said metal comprising:
  • an apparatus for recovering metal, such as aluminum, contained in a dross comprising:
  • a rotary or oscillatory furnace adapted for high temperature treatment of drosses, said furnace having a chamber partially filled with a filling material capable of accumulating and conducting heat provided by an exothermic reaction within said chamber, said filling material also being capable of storing a high density of heat suitable for heating a charge of dross above the melting point of the metal to be recovered, said furnace also having an opening through which dross may be charged into the chamber and dross residue discharged from said chamber, as well as a door for hermetically closing said opening during treatment of the dross, and said furnace further having a tap hole for tapping recovered molten metal:
  • (g) means for pouring the recovered molten metal into the holding furnace.
  • an apparatus for recovering metal, such as aluminum, contained in a dross comprising:
  • a rotary or oscillatory furnace adapted for high temperature treatment of drosses, said furnace having a chamber adapted to be partially filled with a filling material capable of accumulating and conducting heat provided by an exothermic reaction within said chamber, said filling material also being capable of storing a high density of heat suitable for heating a charge of dross above the melting point of the metal to be recovered, said furnace also having an opening through which dross may be charged into the chamber and dross residue discharged from said chamber, as well as a door for closing said opening during treatment of the dross, and said furnace further having a tap hole for tapping recovered molten metal:
  • a suitable container such as an insulating refractory lined ladle for transporting the recovered molten metal and for pouring it into the plant molten metal holding furnace.
  • an apparatus for recovering metal, such as aluminum, contained in a dross comprising:
  • a rotary or oscillatory furnace adapted for high temperature treatment of drosses, said furnace having a chamber partially filled with a filling material capable of accumulating and conducting heat provided by an exothermic reaction within said chamber, said filling material also being capable of storing heat suitable for heating a charge of dross above the melting point of the metal to be recovered, said furnace also having an opening through which dross may be charged into the chamber and dross residue discharged from said chamber, as well as a door for hermetically closing said opening during treatment of the dross, and said furnace further having a tap hole for tapping recovered molten metal:
  • an apparatus for recovering metal, such as aluminum, contained in a dross comprising:
  • a rotary or oscillatory furnace adapted for high temperature treatment of drosses, said furnace having a chamber adapted to be partially filled with a filling material capable of accumulating and conducting heat provided by an exothermic reaction within said chamber, said filling material also being capable of storing heat suitable for heating a charge of dross above the melting point of the metal to be recovered, said furnace also having an opening through which dross may be charged into the chamber and dross residue discharged from said chamber, as well as a door for closing said opening during treatment of the dross, and said furnace further having a tap hole for tapping recovered molten metal:
  • a suitable container such as an insulating refractory lined ladle for transporting the recovered molten metal and for pouring it into the plant molten metal holding furnace.
  • FIG. 1 is a side elevation view of a rotary furnace in accordance with the present invention, and shown in a run/tapping mode thereof;
  • FIG. 2 is a front elevation view of the furnace in the run/tapping mode
  • FIG. 3 is a side elevation view of the furnace in an emptying mode thereof;
  • FIG. 4 is a front elevation view of the furnace in the emptying mode.
  • FIGS. 5 a to 5 e are six (6) schematic representations of successive steps of the present process.
  • Reintroduction of the recovered metal into the holding furnace will be made in such a way as to avoid (i) oxidation of metal, (ii) perturbation of the holding furnace operation and (iii) the loss of heat.
  • the present process for treating dross containing a recoverable metal, such as aluminum, in order to recover this metal comprises the following steps, which are also represented in the illustration below:
  • an oxidizing gas such as oxygen
  • the oxidizing gas can be injected through a super alloy or ceramic tube protruding through the refractory shell or furnace door.
  • a small amount of the filling material, placed in the furnace is ignited with an external heat source; once that small amount is burning, oxidizing gas is injected and the combustion propagates rapidly to the rest of the filling material leading to its complete heating at the temperature required to treat the first batch of dross, with all subsequent overheating of the filling material being done, without any external source, but simply through the oxidation reaction with oxidizing gas injection.
  • the controlled amount of oxidizing gas injected to carry out the exothermic oxidation reaction is normally introduced into the reactor at a controlled rate to heat the filling material at a predetermined rate and to a predetermined temperature.
  • the thermitting rate is controlled by monitoring the temperature and adjusting the oxidizing gas flow rate. Any runaway reaction is prevented by completely stopping the oxidizing gas injection and initiating inert gas injection.
  • the novel process may be carried out in a closable rotary refractory lined furnace, the rotation frequency of the furnace being adjusted to promote tumbling of the charge in the furnace barrel in order to maximize mixing of the cold dross charge with the hot filling material.
  • the rotation may be carried out in a continuous or intermittent manner.
  • U.S. Pat. No. 4,952,237 also considers the injection of oxygen into a dross treatment furnace after discharge of the metal. However, the objective of such operation is not to provide processing energy as is the present case and it is, therefore, totally different. Furthermore, the energy produced by the process disclosed in U.S. Pat. No. 4,952,237 is not sufficient to treat the cold dross being treated by that process.
  • the complete processing of the dross is carried out under inert atmosphere in order to prevent oxidation of the recoverable metal; the injection of oxidizing gas to induce exothermic reaction in the filling material is only allowed once the tapping of the recoverable metal has been achieved and part of the dross residue has been discharged.
  • inert gas such as argon
  • FIGS. 5 a to 5 e provide schematic illustrations of successive steps of the present process, wherein FIG. 5 a shows dross charging; FIG. 5 b shows dross heating; FIG. 5 c (i) shows metal discharging through the door; FIG. 5 c (ii) shows metal discharging through the tap hole; FIG. 5 d shows residue discharging; and FIG. 5 e shows filling material heating.
  • a furnace 10 suitable for the purposes of the present application is shown in the run/tapping mode in FIGS. 1 and 2 and similarly in the emptying mode in FIGS. 3 and 4 .
  • a framework 15 in FIGS. 1 and 3 is drawn.
  • the furnace 10 comprises a hollow steel cylinder 11 having its interior lined with a high temperature resistant refractory wall 12 .
  • As wall 12 one may use a high alumina castable refractory, for example.
  • One end of the cylinder 11 is closed by an end wall 11 a while the other end has an opening 13 (see FIG. 3 ) which is closable by a door mechanism shown generally as 14 .
  • the above structure forms an enclosed furnace chamber 27 for treatment of dross when the door mechanism 14 closes the opening 13 .
  • the cylinder 11 is rotatable and tiltable, supported by the framework 15 .
  • the framework 15 allows the cylinder 11 to rotate on its longitudinal axis on rollers and trunnions 16 or a gear ring rigidly connected to the cylinder 11 and a chain which passes around the gear ring.
  • the rotation is driven by a motor capable of rotating the cylinder 11 either intermittently or continuously in either direction at speeds of up to 20 R.P.M.
  • the arrangement of the rotating system is conventional and is not shown in the drawings.
  • the framework 15 also permits the cylinder 11 to tilt about pivot 17 . Tilting may be effected by a hydraulic piston which moves a cradle 18 within the framework 15 .
  • the door mechanism 14 is supported by a framework 19 which can be tilted about pivots 20 with respect to the main framework 15 .
  • the door mechanism comprises a door mount 21 used to support a circular refractory lined door 22 so that the door can sit properly in the opening 13 of the cylinder 11 when the furnace 10 is in the run mode.
  • the door 22 has a hole 23 which acts as a gas vent to permit escape of furnace gases to the exterior.
  • the vent is covered by an exhaust conduit 24 enclosed within the door mount 21 .
  • Controlled amount of inert gas, such as argon, or oxidizing gas, such as oxygen, may be injected in the furnace using piping (not shown) mounted in the wall of the exhaust conduit 24 (see FIGS. 2 and 4 ) and a nozzle (not shown) located in the hole 23 of the door 22 .
  • the refractory-lined door 22 When the furnace 10 is in the run mode, the refractory-lined door 22 can be lowered and allowed to sit on the cylinder 11 . In the run mode, the refractory-lined door 22 rotates with the cylinder 11 . Escape of gases between the periphery of the opening 13 and the door 22 is prevented by a gasket 25 made of compressible material capable of withstanding high temperatures, like ceramic fiber rope. In the run mode, the door 22 is normally held closed simply by the pressure due to its own weight; however, a latch (not shown) may also be provided to further compress the gasket 25 .
  • the filling material content of the furnace 10 in the run position as illustrated in FIG. 1 has been preheated as a result of the exothermic oxidation of the non-recoverable metal remaining in the filling material of the previous batch. This is done by injection of an oxidizing gas, such as oxygen, at a controlled rate into the inert gas filled furnace 10 until a desired temperature is reached.
  • the door 22 is seated on the cylinder 11 to prevent the energy stored in the filling material to escape to the exterior.
  • the filling material may be preheated using, for example, a gas burner, a plasma torch or an electric arc.
  • a hot dross charge is prepared in a charging device (not shown) adapted to allow charging of the furnace chamber 27 when the cylinder 11 is tilted upwardly as shown in FIGS. 1 and 2 . Then, the door 22 is opened and the charge of hot dross is dropped into the inert gas filled furnace chamber 27 ; in order to avoid damaging the refractory wall or lining 12 it may be desirable to tilt the furnace 10 horizontally as shown in FIGS. 3 and 4 , in order to allow the charge to be pushed inside the furnace chamber 27 using a tool similar to an ember rake instead of being dropped in.
  • the total dross charge, including the filling material is such that it occupies about one quarter to one third of the total interior volume of the furnace chamber 27 .
  • the furnace cylinder 11 being in the run mode position (tilted upwardly), the door 22 is lowered to close tightly, compressing the gasket 25 .
  • the tilting angle of the cylinder 11 is such that maximum use is made of the volume of the furnace chamber 27 without affecting the tumbling effect of the charge which is normally needed for maximum recovery of metal contained in the dross by mixing and heat transfer with the overheated filling material followed by agglomeration of the metal droplets contained in the dross.
  • the cylinder 11 of the furnace 10 is then either rotated or preferably oscillated in the case when large blocks of dross were charged, low amplitude oscillation being preferred in that case to prevent damage to the refractory lining 12 which could result from the tumbling of the heavy dross blocks within the furnace 10 .
  • the tumbling noise produced by the large blocks of dross may be monitored using a sound monitor mounted in the gas exhaust conduit 24 and full rotation of the furnace would only be allowed to proceed once the tumbling noise signal is below a predetermined level. As the furnace is rotated, heat transfer occurs between the dross charge and the filling material.
  • thermocouples mounted in the gas exhaust conduit 24 and several thermocouples mounted inside the refractory wall 12 .
  • RF radio frequency
  • the thermocouples can be used on the rotating furnace.
  • the separated molten metal is tapped off into a suitable crucible. Tapping is carried out through a taphole 26 located at the lowest point in the cylinder 11 of the furnace 10 when in the upward tilt position ( FIG. 1 ).
  • the taphole plug is lined with refractory material that is replaced after each tap. While tapping the furnace 10 , the door 22 remains sealed and the atmosphere in the furnace 10 is an inert gas such as argon. If preferred, tapping could also be made through the door opening 13 .
  • the tapped metal can then be kept molten in a suitable container such as a refractory lined ladle, returned to the molten metal holding furnace and is poured into the melt of that holding furnace, thus avoiding loss of heat, metal oxidation and cooling of the holding furnace melt as would have occurred if the recovered metal was left to cool down before being reintroduced in the plant production line.
  • a suitable container such as a refractory lined ladle
  • the furnace 10 After the metal has been tapped, it is desirable to rotate the furnace 10 again for a certain period of time because repeated tests have shown that the solid residue floating on the molten metal bath remain wetted with appreciable amount of metal; in one example, following a first tapping of aluminum, the furnace 10 was rotated for a further five minutes, allowing a second tapping of an amount of metal corresponding to more than 20% of the first tapping.
  • the taphole 26 is closed, in the case where tapping was made using a tap hole.
  • the furnace door 22 is then lifted, the furnace cylinder 11 is tilted forward as shown in FIG. 3 and the residue is discharged while rotating the furnace 10 , leaving a fraction of the residue inside the furnace 10 which will act as the filling material for the next batch.
  • the rotation is stopped, the furnace cylinder 11 is placed in the run position illustrated by FIG. 1 , and the furnace door 22 is closed to prevent heat loss by radiation.
  • the mostly aluminum oxide residue can be recycled as a cover for the aluminum electrolytic cell, as it is not contaminated by salt.
  • the mostly zinc oxide residue can be recycled as a cover for the zinc leaching step.
  • the high temperature treatment step acts as a means of volatilizing contaminants, such as chlorides, sulphur, ammonia, and volatile metals, such as thallium.
  • contaminants such as chlorides, sulphur, ammonia, and volatile metals, such as thallium.
  • the contaminants having been eliminated during the high temperature processing of the dross in the furnace, the residue is a fine powdery product consisting of mostly zinc oxide, which can be marketed, for example, as an activator for rubber vulcanization or as an additive or filler to plastics, ceramics, glass and cement.
  • a controlled amount of oxidizing gas is injected into chamber 27 of the inert gas filled furnace 10 through the nozzle located inside the hole 23 of the door 22 . Controlled oxidation of the non-recoverable metal contained in the filling material is thereby produced; the temperature of the filling material is monitored using the thermocouples previously mentioned. The furnace is rotated while the metal contained in the filling material is reacting with the injected oxidizing gas in order to evenly transfer the energy produced in the reaction to the filling material. Once the predetermined amount of oxidizing gas has been injected, or if the temperature monitored by the thermocouples indicates a temperature value at or above a predetermined level, the injection of oxidizing gas is stopped and the furnace 10 remains filled with inert gas.
  • Preheating of the cold furnace 10 is carried out using a fuel or gas burner or plasma torch or electric arc mounted on a support installed in front of the furnace with the door 22 opened.
  • the preheating is completed, the external heat source is removed and the operating cycle described above can be initiated.
  • Preheating of the cold furnace 10 can also be achieved by first charging a batch of hot dross into the chamber 27 , followed by the injection of an oxidizing gas into the chamber 27 . Controlled oxidation of the metal contained in the dross will occur, resulting in an increase in the temperature in furnace 10 , which will be monitored using the thermocouples previously mentioned. The furnace is rotated while the exothermic reaction is occurring in order to evenly distribute the heat to the dross charge in the furnace 10 . Once the predetermined amount of oxidizing gas has been injected, or once the temperature monitored by the thermocouples indicates a temperature value at or above a predetermined level, the injection of oxidizing gas is stopped and the furnace 10 remains filled with inert gas.
  • the hot aluminum dross formed at the surface of the molten aluminum bath of the molten aluminum holding furnace is skimmed into containers before being transferred to the dross house for treatment in a DROSRITE furnace.
  • the dross in contact with air, continues to oxidize and therefore its temperature does not decrease. In fact, measurements have shown that the temperature of the dross remains high for several hours because of the heat generated by this oxidation.
  • Alcan is marketing a dross cooler where argon is injected in the dross container to prevent contact of the dross with ambient air (c.f.
  • Cooling the dross under inert atmosphere such as argon, is of interest as it prevents a loss of metal which could otherwise be recovered by a subsequent treatment; however the energy contained in the hot dross is lost during cooling in the Alcan cooling box.
  • the energy content of the hot dross is not lost as it is charged right away in a preheated furnace which also contained the amount of preheated filling material required to treat that dross charge.
  • a preheated furnace which also contained the amount of preheated filling material required to treat that dross charge.
  • the mean temperature of the dross charge is assumed to be 400° C., although measurements in industry have shown the temperature to be much higher, of the order of 600° C.
  • the objective is to transfer energy from the overheated filling material into the hot dross charge to bring the total furnace content to 700° C. Once that objective is reached, both the metal and a portion of the dross residue will be discharged at the “low” temperature of 700° C., leaving inside the furnace the 10 metric tons of residues/filling material required for the treatment of the next batch of hot dross. Then, a controlled amount of oxygen is injected into the furnace to bring the filling material back to the original temperature of 1000° C. by burning sufficient non-recoverable metal within the filling material to evenly heat and store in the filling material sufficient energy for treating the next batch of hot dross.
  • This residual metal is part of the non-recoverable metal which remains in any of the various processes which are in operation for the recovery of metal from dross. Measurements have shown that the amount of such residual metal in the residue after treatment is higher than 5%.
  • 3 180 MJ is therefore used to bring the filling material from 700° C. to 1000° C.
  • the remainder is used to maintain the refractory inside surface at the same temperature as the filling material in spite of heat conduction through that same refractory; that energy is also lost as it is transferred to the outside through the furnace wall.

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US13/655,204 2011-10-18 2012-10-18 Energy Efficient Salt-Free Recovery Of Metal From Dross Abandoned US20130186236A1 (en)

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US13/655,204 US20130186236A1 (en) 2011-10-18 2012-10-18 Energy Efficient Salt-Free Recovery Of Metal From Dross
US15/094,857 US20170009319A1 (en) 2011-10-18 2016-04-08 Energy efficient salt-free recovery of metal from dross
US16/712,810 US20200332392A1 (en) 2011-10-18 2019-12-12 Energy efficient salt-free recovery of metal from dross
US18/096,641 US20230357888A1 (en) 2011-10-18 2023-01-13 Energy efficient salt-free recovery of metal from dross
US18/972,008 US20250327150A1 (en) 2011-10-18 2024-12-06 Energy efficient salt-free recovery of metal from dross

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US16/712,810 Abandoned US20200332392A1 (en) 2011-10-18 2019-12-12 Energy efficient salt-free recovery of metal from dross
US18/096,641 Abandoned US20230357888A1 (en) 2011-10-18 2023-01-13 Energy efficient salt-free recovery of metal from dross
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US18/096,641 Abandoned US20230357888A1 (en) 2011-10-18 2023-01-13 Energy efficient salt-free recovery of metal from dross
US18/972,008 Pending US20250327150A1 (en) 2011-10-18 2024-12-06 Energy efficient salt-free recovery of metal from dross

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US10996113B2 (en) * 2017-09-29 2021-05-04 Foreman Instrumentation & Controls, Inc. Thermowell with expansion joint
CN119860664A (zh) * 2025-03-24 2025-04-22 中色科技股份有限公司 一种金属冶炼扒渣过程气体保护系统及方法

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BE1030126B1 (nl) 2021-12-27 2023-07-24 Reazn Belgium Verbeterde werkwijze voor het recycleren van zink (Zn)

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US4401531A (en) * 1981-07-24 1983-08-30 Daniel Martin San Lorenzo Process for the production of electrolytic zinc or high purity zinc salts from secondary zinc raw-materials
US4983216A (en) * 1990-02-12 1991-01-08 Aluminum Company Of America Aluminum scrap melting
US20110203413A1 (en) * 2004-07-19 2011-08-25 Fundacao De Amparo A Pesquisa Do Estado De Sao Paulo - Fapesp Process and equipment for the treatment of loads or residues of non-ferrous metals and their alloys

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10996113B2 (en) * 2017-09-29 2021-05-04 Foreman Instrumentation & Controls, Inc. Thermowell with expansion joint
CN119860664A (zh) * 2025-03-24 2025-04-22 中色科技股份有限公司 一种金属冶炼扒渣过程气体保护系统及方法

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US20170009319A1 (en) 2017-01-12
US20200332392A1 (en) 2020-10-22
US20230357888A1 (en) 2023-11-09
WO2013056348A1 (fr) 2013-04-25
US20250327150A1 (en) 2025-10-23
EP2768991A1 (fr) 2014-08-27
EP2768991A4 (fr) 2015-06-17
WO2013056348A4 (fr) 2013-06-13

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