Solid material comminution or disintegration – Processes – With application of fluid or lubricant material
Reexamination Certificate
1999-06-30
2001-03-13
Rosenbaum, Mark (Department: 3725)
Solid material comminution or disintegration
Processes
With application of fluid or lubricant material
C241S024130
Reexamination Certificate
active
06199779
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the recovery of metal or metal concentrate from a metal-containing thermal processing by-product or dross.
BACKGROUND OF THE INVENTION
Used aluminum beverage cans and other products made from aluminum are often recycled to recover the aluminum they contain for use in other products. Typically, aluminum scrap is recycled in reverberatory furnaces. Flux is used in these furnaces to promote the melting of the aluminum. This flux, together with oxides, dirt, and other materials, forms a viscous mass of dross, which floats on top of the molten aluminum. This dross impedes the assimilation of additional metal to the molten aluminum, and therefore must be skimmed off of the liquid aluminum before additional solid material may be melted in the furnace. The dross solidifies after cooling into a mass that typically contains about 65% aluminum metal.
Methods to recover aluminum from furnace dross include grinding and screening the metallic dross. Grinding achieves some separation of the metal from the portions having a high salt and oxide content because the waste products are more friable than the portions having a relatively high metal content. Therefore, after grinding, the portions of the dross constituting waste are reduced to fine particles, while those portions having a higher aluminum content tend to resist reduction by the mill. Accordingly, a screening operation can achieve some separation between metal enriched and waste products. However, previous methods for recovering aluminum values from dross that rely on grinding processes either do not produce a high enough grade product because efficient separation of aluminum from waste is not effected or have poor recoveries if sufficient size reduction is conducted because aluminum fines are produced which are lost with waste product.
Another method for directly recovering metal from metal-containing dross, used alone or in combination with grinding, is the melting of metal-containing dross in a rotary furnace. According to such a method, the dross is fed into a rotary furnace, together with a large amount of salt flux. The flux is necessary to enable the release of the aluminum metal from the other constituents. This salt flux reports to salt cake upon cooling, which must be landfilled. Therefore, such methods have associated drawbacks, such as environmental concerns.
An additional method for recovering metal from dross, disclosed in U.S. Pat. No. 5,192,359, involves the separation and classification of dross particles based on the electrical conductivity of each particle. According to this method, size separation is conducted and large particles are processed in a furnace and small particles are subjected to a linear electromagnetic force field provided by an inclined linear induction motor. Particles that are dropped generally along the length of the inclined linear motor are levitated if they are conductive. A separator then allows the conductive, metal-containing particles to be collected separately from the waste particles.
Accordingly, there is a need for an economical process that is capable of recovering high grade metal from metal-containing dross, and which is capable of processing large amounts of dross. Furthermore, there is a need for a process that reduces the amount of waste material remaining after the metal has been removed from the metal-containing dross.
SUMMARY OF THE INVENTION
The present invention includes a method to recover metal from a metal-containing dross material. In preferred embodiments, the metal in the metal-containing dross can include aluminum, magnesium, nickel, tin, copper, brass, zinc, gold, silver, and platinum. In a further preferred embodiment, the metal is aluminum.
The method includes comminuting the dross in a comminution device. A salt enriched small size fraction is removed from the comminuted dross on a size separation basis. A metal-enriched, large size fraction is removed from the comminuted dross on a size separation basis. Metal from the metal enriched fraction of material is recovered using a method selected from the group consisting of eddy current separation, magnetic separation, electromagnetic separation, density separation, electrostatic separation, electrodynamic separation, size separation, shape separation and color separation to form a metal product and a recycle product. The metal product from this separation is preferably of high grade. Thus, the separation is made so that the recycle product contains particles which are substantially mixed quality. Therefore, the recycle product contains particles having significant amounts of metal, in addition to particles which are of substantially only waste material. Typically, the recycle product comprises between about 30% and about 75% by weight metal. The method further includes conducting the recycle product to the comminution device for further processing. In this manner, the mixed quality particles can be further comminuted to liberate the metal portions of the particles for separation as a high quality metal product.
In a preferred embodiment, the comminution device is a mill, and in a further preferred embodiment, the comminution device is a semi-autogenous mill. According to one embodiment, the step of removing a salt enriched small size fraction from the comminuted dross material comprises removing that fraction using an air sweep.
The metal in the metal-containing dross material can be of any type. According to one embodiment of the invention, the metal is selected from the group consisting of aluminum, magnesium, nickel, tin, copper, brass, zinc, gold, silver, and platinum. Further, the metal-containing dross material may be an aluminum dross, a copper slag, or a brass dross. According to one embodiment, the metal-containing dross material comprises between about 50% and about 65% metal.
In a further preferred embodiment, the described method is conducted continuously. In an additional preferred embodiment, the step of recovering metal from the metal enriched large size fraction comprises eddy current separation. In yet another preferred embodiment, the metal enriched fraction comprises greater than about 65% by weight aluminum. In a more preferred embodiment, the recovered metal comprises greater than about 70% by weight aluminum.
In another preferred embodiment, the salt enriched small size fraction is processed by a vertical vortex classifier. Larger and/or heavier particles from a vertical vortex classifier can be returned to the comminution device for further processing. In yet another preferred embodiment, the salt enriched small size fraction is additionally processed by cyclone classifiers. The heavier fraction from the cyclone classifiers can be screened to produce a metal concentrate and a waste product.
According to an additional embodiment of the present invention, the method for recovering metal from a metal-containing dross material comprises comminuting the dross in a semi-autogenous mill having a peripheral port. A salt enriched fraction is continuously removed from the comminuted dross material using an air sweep. A metal enriched fraction comprising greater than about 65% by weight metal is continuously removed from the comminuted dross through the peripheral port of the semi-autogenous mill. An enriched product, comprising greater than about 70% by weight metal, and a recycle product comprising between about 30% by weight and about 75% by weight metal, are formed by conducting eddy current separation on the metal enriched fraction. The recycle product is then conducted to the comminution device.
According to a further embodiment of the present invention, a method for recovering aluminum from an aluminum-containing dross is provided. According to this method, a continuous flow of aluminum-containing dross is provided to a semi-autogenous mill having at least one peripheral port. The particle size of this dross is less than about 150 mm and comprises between about 50% and about 65% by weight aluminum. The size of the aluminum-containin
Alcoa Inc.
Lavine Edward L.
Rosenbaum Mark
Sheridan & Ross P.C.
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