Claims:1] A method for treating aluminum dross for recovery of residual metal and other components, comprising-
a) selecting aluminum dross to be processed;
b) in a preheated vessel of a gas-fired rotary furnace, charging the aluminum dross using the charging skip of said rotary furnace;
c) closing the lid of the rotary furnace to create an airtight environment containing the aluminum dross charged;
d) in the airtight environment, blowing argon over the aluminum dross charged inside the gas-fired rotary furnace via an inflow valve provided in rotary furnace to thereby prevent thermiting of said aluminum dross during processing;
e) in parallel, rotating the rotary furnace at a speed ranging between 30 to 300 RPM and subjecting the aluminum dross being processed to vibration at a frequency of 500 to 3000 vibrations per minute using the vibration plate, to create concomitant centrifugal motion and vibrational force to thereby extract and recover oxide-free molten aluminium which is separated from non-metallic residue;
f) after a holding time of 5 minutes to 45 minutes, tilting the gas-fired rotary furnace with help of the hydraulics for discharge of oxide-free molten aluminium into a launder;
g) pouring the discharged oxide-free molten aluminium metal into ingot molds to obtain ingots;
h) straightening the gas-fired rotary furnace with help of the hydraulics to blow oxygen into the furnace to kill nitrides and result in a white colored heated admixture of Alumina and aluminum;
i) tilting the gas-fired rotary furnace with help of the hydraulics to discharge the white colored heated admixture into a ladle of a ladle furnace, said discharge being through a stainless steel strainer of mesh size 325 B.S.S., to thereby collect oxide-free molten aluminium into said ladle;
j) blowing of oxygen using a porous plug from below to thermite the micro fine aluminum, and thereby result in molten alumina, and release heat which is used to drive the instant process without requiring any extrinsic supply of heat; and
k) casting the molten alumina into a pit from the ladle to result in a grey colored mass of low alpha alumina that can be returned back to the cast house for use.

2] The method for treating aluminum dross for recovery of residual metal and other components as claimed in claim 1, wherein the gas-fired rotary furnace is selected as one having a charging skip for feeding aluminum dross into the vessel, gas-burner for heating the vessel, inflow valves traversing the shell of said vessel for infusing argon and oxygen, a thermocouple fitted onto said vessel for monitoring of temperatures, hydraulics for tilting the vessel, and a motor-powered vibration plate for vibrating said vessel.

3] The method for treating aluminum dross for recovery of residual metal and other components as claimed in claim 1, including further that the aluminum dross to be processed can be preheated, using the gas burner of the rotary furnace, to a temperature selected between 300oC to 700oC in the event said aluminum dross selected is cold dross.

4] The method for treating aluminum dross for recovery of residual metal and other components as claimed in claim 1, including further that the aluminum dross to be processed is transferred to the rotary furnace in an enclosed ladle from the cast house to avoid thermiting during transfer, in the event said aluminum dross selected is hot dross.

5] The method for treating aluminum dross for recovery of residual metal and other components as claimed in claim 1, wherein gas-fired rotary furnace to a temperature ranging between 1000 to 1500oC is achieved by using the gas-fired burner exclusively for the first operative run, and achieved by self-sustaining exothermic reaction occurring during the preceding operative run

6] The method for treating aluminum dross for recovery of residual metal and other components as claimed in claim 1, wherein the inflow of argon for avoiding thermiting and maintained at a flowrate of 1 to 5 Kg/Min until stage of aluminium extraction.

7] The method for treating aluminum dross for recovery of residual metal and other components as claimed in claim 1, wherein the inflow of oxygen to break AlN is maintained at a flowrate of 20 to 40Kg per minute.

8] The method for treating aluminum dross for recovery of residual metal and other components as claimed in claim 1, further including raising the temperature of the furnace to convert the low alpha alumina to high Alpha alumina for refractory, in the event the AlN is high.

9] The method for treating aluminum dross for recovery of residual metal and other components as claimed in claim 1, further including blowing of further oxygen from top and bottom of the ladle to melt the alumina for making fused alumina abrasive grade, in the event the AlN is high. , Description:-: Complete Specification :-

“Method and system for treating aluminum dross for recovery of residual metal and other components”

Field of the invention
This invention relates generally to methods and systems applicable for processing aluminum dross to recover reusable materials from the same. More particularly, the present invention outlines a method which takes an input of aluminum dross and gives an output of extracted aluminum metal, low alpha smelter grade alumina and also fused alumina characteristically without the need of any external heat source and leaving behind zero waste.

Definitions and interpretations
Before undertaking the detailed description of the invention below, it may be advantageous to set forth definitions of certain words or phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect, with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “NMP” refers non-metallic product; “Cast-house” refers a reservoir to maintain a buffer of liquid Aluminum for various forward integration needs;

Background of the invention and description of related art
In a cast-house, the top layer of the liquid pool gets in contact with oxygen and nitrogen to form dross comprising of Al2O3 and AlN. This spongy layer entraps some liquid metal with it. During skimming of this top layer, which is identified as dross, some cryolite and aluminum fluoride also come to this pool via siphon to ladle.

As can be appreciated, dross contains a number of valuable components, including but not limited to aluminum, thus making recovery of said materials, to the best extent possible, to be extremely desirable. Otherwise, such a rich source of valuable components is wasted by traditional practices for disposal via landfilling operations which are not only expensive, but also deleterious to the environment and more importantly, are undertaken without any attempt to recover contained reusable components therein. Therefore, it would be advantageous to have some means of treating dross, for recovery of said valuable components, which would be useful of course for realization of value of said components, but also amortize the volumes and / or costs of the traditional disposal methodologies.

Prior art, to the extent surveyed, lists some scattered solutions proposed and utilized for treating aluminum dross. For example, one commonly observed technique involves crushing and concentrating the dross in a suitable impact mill and melting the fragmented concentrate in a furnace, to thereby allow separation of aluminum as a molten fraction from the residual dross. An alternative iteration of this technique involves crushing the dross and leaching the fragmented material on a continuous basis to recapture the fluxing salts contained therein, the insoluble balance of the material being sent to the furnace.

Among patent prior at, US5102453A (Assigned to Aluminum Waste Technology Inc) is notable, in which a method for recovering reusable materials from aluminum dross is disclosed comprising crushing the dross and extracting solubles therefrom with water in a digester. The brine so obtained is processed in a crystallizer to obtain fluxing materials contained therein, and the insolubles are furnaced to separate the free aluminum metal therefrom. pH is used as a controlling parameter to prevent undesirable reactions from occurring in the digester, which are mainly to blame for production of hazardous and noxious products.

Another notable example is US4039173A (Assigned to Alumax Mill Products Inc) which discloses a treatment of active metal dross, slags and skimmings to recover metallic values. In this method, cooling and breaking up of larger pieces of aluminum dross is prescribed while retaining entrained aluminum metal to give an improved recovery of metal values.

Typical to methodologies involving cooling of dross, the cooling is uncontrolled as it is left to ambient conditions which wastes aluminum component therein due to thermiting loss. To an extent, dross presses resolve this issue, however not without mandating re-heating / re-melting which is nothing but a waste of fuel for re-heating and an added operation, besides not ameliorating recovery losses, salt contamination in the NMPs.

As shall be further appreciated, methodologies involving shaking of the hot dross and squeezing out of the metal are largely inefficient as they use atmospheric oxygen to thermite and to keep the dross in hot condition till the extraction was carried out. A further drawback is that the squeezed out metal out of this process has oxides inclusions.

The above solutions, though shown to be reduced to practice, do not form a final closure as the following issues remain to be address in their entirety-
a) Waste of fuel to re-melt dross for recovery of aluminum
b) Technical complexities and added operations while recovery of aluminum from dross
c) Non-attention to other valuable materials besides aluminum that can be recovered from dross
d) Loss of aluminum content due to thermiting because of contact with atmospheric oxygen.
e) Resultant aluminum is not free from oxide inclusions
f) Traditionally used rotary salt furnaces leave behind hazardous waste
g) Resultant non-metallic fraction yet contains a substantial amount of impure metal thus making the process inefficient.
h) Lack of safe and efficient process of aluminum extraction from dross results in waste of valuable aluminum content.
i) Current processes are unable to utilize non-metallic particles in dross. This resultant nonmetallic particles usually end up getting land filled

State-of-art therefore, does not list a single effective solution embracing all considerations mentioned hereinabove, thus preserving an acute necessity-to-invent for the present inventor/s who, as result of focused research, has come up with novel solutions for resolving all needs once and for all. Work of the presently named inventor/s, specifically directed against the technical problems recited hereinabove and currently part of the public domain including earlier filed patent applications, is neither expressly nor impliedly admitted as prior art against the present disclosures.

A better understanding of the objects, advantages, features, properties and relationships of the present invention will be obtained from the following detailed description which sets forth an illustrative yet-preferred embodiment.

Objectives of the present invention
The present invention is identified in addressing at least all major deficiencies of art discussed in the foregoing section by effectively addressing the objectives stated under, of which:

It is a primary objective to provide a method for efficient treatment of dross that allows substantial recovery of valuable fractions therein.

It is another objective of this invention to provide the architecture of equipment capable of hosting the aforementioned method for efficient treatment of dross that allows substantial recovery of valuable fractions therein.

It is another objective of this invention to minimize unwanted side reactions that are observed in conventional dross treatment methods.

It is another objective of this invention to eliminate the thermiting losses incidental to aluminum recovery from dross.

It is another objective of this invention to eliminate the salt contamination in the NMPs observed in conventional dross treatment methods.

It is another objective of this invention to eliminate or at least minimize the amount of material remaining from dross recovery that must be disposed of via conventional routes.

It is another objective of this invention to eliminate the hazardous components especially if toxic, flammable and explosive, in the material remaining from dross recovery, thus reducing risk at workplace and also to the environment.

It is another objective of this invention to eliminate the heating time and thus fuel requirements for heating otherwise inherent to dross recovery.

It is another objective of this invention to minimize the technical complexities and costs incidental to treatment / salvaging of valuable fractions from aluminium dross.

The manner in which the above objectives are achieved, together with other objects and advantages which will become subsequently apparent, reside in the detailed description set forth below in reference to the accompanying drawings and furthermore specifically outlined in the independent claims. Other advantageous embodiments of the invention are specified in the dependent claims.

Brief description of drawings
The present invention is explained herein under with reference to the following drawings, in which:

FIG. 1 is a front view of the gas-fired rotary furnace system for dross treatment as per the present invention.

FIG. 2 is a right side view of the system shown in FIG. 1.

FIG. 3 is a left side view of the system shown in FIG. 1.

FIG. 4 is a side view of the ladle furnace used in the present invention.

FIG. 5 is a front view of the ladle furnace shown in FIG. 4.

FIG. 6 is a schematic illustration to showcase the manner of mass transfer between the rotary furnace and the ladle furnace.

FIG. 6 is a schematic representation of the relative placement of the rotary furnace and ladle furnace with respect to each other in the execution environment of the present invention.

The above drawings are illustrative of particular examples of the present invention but are not intended to limit the scope thereof. The drawings are not to scale (unless so stated) and are intended for use solely in conjunction with their explanations in the following detailed description. In above drawings, wherever possible, the same references and symbols have been used throughout to refer to the same or similar parts, as under-
(01) - Gas-fired rotary furnace
(02) - Lid of (01)
(03) - Vibrating base plate
(04) - Vibration Motor
(05) - Base for gas cylinders and burner fuel
(06) - Strainer
(07) - Thermocouple
(08) - Oxygen gas inflow valve
(09) - Burner
(10) - Argon gas inflow valve
(11) - Charging skip
(12) - High tension spring (16 mm coil spring)
(13) - Gas cylinders with flow meters
(14) - Furnace gear
(15) - Motors for furnace rotation
(16) - Probe for gas outflow
(17) - Electric panel with SCADA enabled PLC
(18) - Hydraulics for furnace inclination

Though numbering has been introduced to demarcate reference to specific components in relation to such references being made in different sections of this specification, all components are not shown or numbered in each drawing to avoid obscuring the invention proposed.

Attention of the reader is now requested to the detailed description to follow which narrates a preferred embodiment of the present invention and such other ways in which principles of the invention may be employed without parting from the essence of the invention claimed herein.

Summary of the present invention
The present invention is directed to a method which takes an input of aluminum dross and gives an output of extracted aluminum metal, low alpha smelter grade alumina and also fused alumina, in which characteristically–
a) Using centrifugal force to extract aluminium metal from dross;
b) Using vibration to separate metal from oxides without use of salt;
c) Using oxygen infusion as a source to convert AlN to smelter grade alumina or high alpha alumina or fused alumina ; depending on the content of AlN;
d) Using intrinsic heat generated via reaction in equipment to eliminate the need of external fuel source from the second cycle onwards.

Detailed description
As conventionally known, dross is a byproduct of the aluminum smelting process which is otherwise discarded, however from which recovery of residual aluminum metal is possible. Composition of dross usually includes oxides, nitrides, chlorides and fluorides of metals such as sodium, potassium and magnesium besides the component of prime interest - aluminum.

Construction of the system / reactor proposed herein is intended to encompass various embodiments, among which a few are explained below with reference to certain examples that illustrate generically the manner in which principles of the present invention may be employed.

The accompanying FIG. 1, FIG. 2, and FIG. 3 are various views of the gas-fired rotary furnace for the first phase of implementation of the present invention. As seen in these drawings, the vessel has three regular heat resistant probes (16) for burner exhaust, thermocouple, argon / oxygen. Burner (09) is of oil type. Refractory of this vessel has good mass, typically a minimum of 6 inches of refractory lining to retain heat. Material of the refractory lining is chosen from ones used conventionally in the art. After metal extraction the residual is reacted with oxygen by infusing oxygen via the oxygen probe so that AlN breaks to Alumina and Nitrogen escapes from the exhaust probe. This exothermic reaction produces a product white in color, at the same time it will heat the mass of the kiln so that the temperature is around 900oC. The temperature is kept in such a way that it can produce smelter grade alumina, as required. Here, the thermocouple (07) enables monitoring of the temperature thus enabling us to control the heat loss. In exceptional scenarios where temperature falls below desired the burner will be used to increase temperature) that it can produce low alpha smelter grade alumina that can be returned to the cast house.

Working / Operational cycle
Dross skimmed from the cast-house is received for processing at the gas-fired rotary furnace. The hot dross is transferred in an enclosed ladle to avoid thermiting of the dross, and then charged into the furnace using the charging skip (11). Once the charging is complete, the lid (02) is closed creating an airtight furnace.

Once the lid (02) is closed, argon gas from gas cylinders is infused at a flowrate of 1 to 5 Kg/Min using the inflow valve (10) which prevents thermiting of the dross as it is being processed.

The furnace, is lined with thick refractory, rotates between 30 to 300 RPM to process the hot dross. This rotation creates centrifugal motion, which extracts the maximum molten aluminium.

Once the material is charged into the furnace, the vibration plate (03) creates vibration using a 10 HP 2880 RPM motor (04). Here, the vibration frequency is set to between 500 to 3000 vibrations per minute. This vibration coupled with the centrifugal motion of the furnace results in class leading solution for aluminium recovery from hot dross. The vibration enables this dross recovery system to be salt free, thereby eliminating generation of hazardous waste from the process. Additionally, the vibration results in oxide free metal recovery.

As the material is being processed, a thermocouple (07) enables the monitoring of the temperature within the furnace. Said thermocouple (07) is selected among conventional varieties known to serve in like functions in the art, however for the sake of specification, characterized in being one capable of monitoring temperatures between the range between 500oC to 1200 oC.

After the batch time (holding time of 5 minutes to 45 minutes), the aluminium is separated from the non-metallic residue. At this point, the strainer (06) is lowered and then the furnace is inclined using the hydraulics (18). Once the furnace is inclined the molten aluminium is strained out of the furnace into a ladle. A stainless steel mesh of mesh size ranging between 300 to 500 B.S.S. is used for said straining to eliminate oxide contamination with pure aluminium metal. This molten aluminium is then taken to an ingot casting station to be cast into ingots to be returned to the cast house.

Once the molten aluminium is poured from the furnace, the lid (02) closes again and oxygen is charged into said furnace, at a flowrate of 15 to 40 Kg per min, using the inflow valve as shown in 8. The oxygen charging is such that AlN breaks to alumina and nitrogen escape from the probe as shown in 16. This exothermic reaction produces a product white in colour, at the same time heats the mass of the kiln so that the temperature is around 900oC. The temperature is thus kept in such a way that it can produce low alpha alumina that can be returned back to the cast house for use.

If AlN is significantly high (this can be visible from rising temperature), the red hot powdery mass is poured in a ladle of a ladle furnace as shown in FIG. 6. This ladle furnace directly below the furnace so the powdery mass can be directly transferred to the ladle by pouring. Further oxygen can be blown from top and bottom to melt the alumina for making fused alumina abrasive grade. This bottom blow also ensures better density and lower porosity. In case the AlN is slightly insufficient to melt the charge, external power via 3 electrodes is used to achieve the melting.

Advancement over prior art
Conventionally hot dross skimmed from the cast house is left in the open which results in thermiting leading to loss of aluminum content. The resultant cold aluminum dross still is hazardous in nature due to AlN and Fluoride content. The other commonly used technique is the use of salt treatment in a rotary furnace which creates hazardous salt cakes. Characteristic aspects which help the present invention to score above teachings of art include the gas charging, no requirement of external heat (for second and subsequent batch runs of the present invention using cold dross, and even for first batch and all subsequent batches for hot dross), loop back, application of both centrifugal force and vibrational force for extraction of metal as explained in the foregoing narrative. Thus the process methodology of the present invention is a significant advancement over the same, as it is designed to be set up inside the aluminum smelter so that it can process the hot aluminum dross straight from the cast house.

Reduction to practice / Industrial applicability
While the methodology of this invention is designed for hot dross treatment, it can also process cold dross.

In this trial, 1.5 tons of cold dross was pre-heated at 300 to 700oC. Gas-fired rotary furnace was pre-heated to a temperature of 1000 to 1500oC. The cold dross was charged inside the gas-fired rotary furnace. Argon was blown using industrial cylinder. The rotary furnace was then tilted for discharge after 5 to 45 minutes. 700 to 800 kg of metal that came out in the launder was poured into ingots. The rotary furnace was then put back straight again. Oxygen was blown at a flowrate of 20 to 40Kg per minute using industrial cylinder to kill nitrides. The rotary furnace was then tilted like concrete mixer on opposite side to pour the white hot material (Alumina with some aluminum) into a ladle. Oxygen was blown using porous plug from below to thermite the micro fine aluminum. Molten alumina was casted in a pit from the ladle. The weight of grey fused alumina was 850 to 950 Kg which undeniably implied a process gain, thus corroborating as a proof of concept underlining the true industrial applicability of the present invention.

Process for hot dross is same, except with variation that the hot dross needs to be transferred in an enclosed ladle to avoid thermiting, as well as that there is no need to preheat the dross.

The foregoing description will be regarded as illustrative in nature and not as restrictive in any form whatsoever. Modifications and variations of the system and apparatus described herein will be obvious to those skilled in the art. Such modifications and variations are intended to come within ambit of the present invention, which is limited only by the appended claims.