DESC:*** Complete Specification ***

“Method for recovery of pure Alumina and ammonia from Aluminum dross”

Cross references to related applications: This complete specification is filed further to patent application No. 202231075453 filed on 26/12/2022 titled “Method for recovery of pure Alumina and ammonia from Aluminum dross residue” and the entire content of the provisional specification filed therewith is incorporated herein in its entirety by way of reference.

Field of the invention
This invention relates generally to pyrometallurgical techniques for recycling of Aluminum dross residue. A yet-preferred embodiment of the present invention disclosed hereunder particularly outlines an inventive method, and its implementing system, for recovery of Alumina and Ammonia by agitating, Aluminium Nitride component of Aluminum dross residue in water, by further processing to beneficiation.

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. The following definitions shall hold for the instant document-
(a) “Dross” typically refers to a byproduct formed during the production of non-ferrous metals, particularly Aluminium. It is generated when Aluminium or other non-ferrous metals are melted, and impurities or oxides separate from the molten metal. The composition of dross can vary depending on the specific metal production process and the raw materials used. The term "dross" is commonly associated with Aluminium production, but similar byproducts exist in the production of other non-ferrous metals.
(b) “Dross residue” refers to dross plus impurities.
(c) “NMP” refers to Non-metallic particles.
(d) "SiC heaters" refers to heaters that use silicon carbide (SiC) as the heating element.
(e) “MS” refers to Mild Steel.
(f) “PID” refers to Proportional–integral–derivative.

Background of the invention
Aluminium makes up about 8% by weight of the earth’s solid surface, and never occurs as a free element in nature (P.E. Tsakiridis, J. Hazard. Mater. 217, 1. (2012)). The world over, Aluminium is extracted from its ore, bauxite, typically by either Bayer process followed by the Hall–Heroult electrolysis, or recycling Aluminium from process scrap and used Aluminium products.

During the manufacturing processes of Aluminium, especially during the processes of melting and alloying, oxidation occurs at the surface where molten Aluminium meets the oxidizing atmosphere, leading to the formation of a semisolid mass, known as dross. This dross comprises Aluminium oxide, metallic Aluminium, magnesium spinel, periclase, quartz and other salts with small traces of Aluminium carbides and nitrides (S.O. Adeosun, O.I. Sekunowo, O.O. Taiwo, W.A. Ayoola, and A. Machado, Adv. Mater. 3, 6. (2014)).

Dross formed as a by-product during production of Aluminium and its alloys contains residual Aluminium which, if unrecovered, would be a valuable loss. White dross / primary dross, formed during the primary production of Aluminium, contains a high percentage of elemental Aluminium and Aluminium oxides (S.K. Verma, V.K. Dwivedi and S.P. Dwivedi, Mater. Today Proc. (2021)). Black dross on the other hand, which is formed at the time of the secondary Aluminium refining processes, is a mix of Aluminium oxides and slag and, in comparison to White dross, contains a smaller amount of elemental Aluminium (O. Manfredi, W. Wuth, and I. Bohlinger, JOM 49, 48. (1997); D.B. Masson, and M.M. Taghiei, Mater. Trans. 30, 411. (1989); B. Lucheva, T. Tsonev, and R. Petkov, J. Univ. Chem. Technol. Metallurgy 40, 335. (2005)).

Non-metallic particles of dross residue mainly consist of Aluminium micro fines, Alumina, Aluminium Nitride and some carryover fluxes like bath material. The non-metallic particles cannot be charged back to the smelter because Aluminium Nitride breaks in oxidizing condition but not in reducing conditions and hence will become an inclusion in the Aluminium smelted, as smelter works in highly reducing conditions.

Aluminum dross residue is also toxic and poses a grave environmental hazard if untreated as it contaminates surface and ground water, which further leads to production of hazardous gases such as phosphine and ammonia which pollute the atmosphere. Aluminium Nitride present in dross is hazardous in nature. On contact with moisture, it turns to Aluminium hydrate and releases ammonia. The carryover materials (fluxes for smelting alumina) make it inconsistent for use in refractories. Thus, the safe disposal of Aluminum dross residue is extremely burdening in financial and procedural aspects. Aluminum dross residue arising from the Aluminium smelting industry has been in fact categorized in India under the hazardous category as per the Hazardous and Other Wastes (Management and Transboundary) Movement Rules 2016.

Aluminum dross residue, which in principle can be assigned to new scrap, consists of up to 80% of metallic Al, Aluminium oxides in various forms (a and ?), and Aluminium Nitride (Aluminium Nitride). In addition, silicon, iron, calcium, and magnesium oxides (as well as other Al compounds such as carbides, chlorides, and fluorides).

Hence, reutilization of Aluminum dross residue is important for environmental protection as well as an economic point of view and, as the reader shall appreciate, the recovery of Aluminium content in the process would be a much desired advantage.

Description of related art
Processes for recovery of Aluminium from Aluminum dross residue are known in the art. JP6828036B2 (filed by Byung Doo) which teaches recovery of alumina from black dross. Another reference is KR20190112527A (filed by Ahn Byung-doo) teaches a Aluminium black dross recycling system for recycling black dross generated when dissolving Aluminium scrap in a flux-treated Aluminium melt.

Processes for recovery of Aluminium from Aluminum dross residue are known in the art. Common methods for recycling Aluminum dross residue include-

(a) Salt Recovery Process: This involves treating the dross with salt to recover the metallic Aluminium. The salt reacts with the Aluminium oxide, forming salt cake, which is then processed to extract the Aluminium.

(b) Mechanical Processing: This involves crushing and screening the dross to separate the metal from the non-metallic components. This process can recover a significant amount of Aluminium, and the remaining material can be used in construction or other applications.

(c) Pyrometallurgical Methods: These involve heating the dross to high temperatures to separate the metal from the oxide components. This can include processes like rotary salt fluxing and plasma processing. Dross can be processed to recover Aluminium metal through various methods such as rotary furnaces or reverberatory furnaces. The recovered metal can then be reintroduced into the Aluminium production process

(d) Leaching Process: This involves treating the dross with a solution that dissolves the Aluminium oxide, leaving behind the metallic Aluminium. This can be done using acids or alkaline solutions.

(e) Thermal Reduction: This involves dross being heated in the presence of reducing agents to extract the metal.

(f) Bayer Process: The Bayer process is a well-known method for extracting alumina from bauxite ore, but it can also be adapted for recovering alumina from certain types of dross. The process involves digestion of the dross with sodium hydroxide (NaOH), followed by precipitation of alumina and further purification steps.

(g) Hydrothermal Treatment: This involves subjecting the dross to high-temperature and high-pressure conditions in the presence of a solvent. This process can selectively dissolve alumina, allowing for its recovery.

(h) Smelting: This can be employed to recover alumina from dross. The dross is melted, and impurities are removed, leaving behind molten alumina. This requires careful control of temperature and other process parameters.

Among patent prior art, examples of approaches for recycling Aluminum dross residue include JP6828036B2 (filed by Byung Doo) which teaches recovery of alumina from black dross. Another reference is KR20190112527A (filed by Ahn Byung-doo) teaches a Aluminium black dross recycling system for recycling black dross generated when dissolving Aluminium scrap in a flux-treated Aluminium melt.

However, all the approaches in prior art, without exception, are not able to find true applicability in the art due to various lacunae and process inefficiencies that persist in them.

Technical issues to be resolved
As stated above, the state of art, as it exists today, is inundated with lacunae and process inefficiencies, particularly being-
(a) Low efficiency in recovery of Aluminium
(b) Stringency for reagents / chemicals.
(c) Inability to effectively adjust to varying dross compositions.
(d) Ineffective Separation of Metal and Oxides, leading to lower recovery rates.
(e) Dependency on pre-treatment of dross before the recovery process, leading to lower recovery rates if pretreatment is not effective.
(f) High stringency of temperature and other process parameter control.
(g) High costs associated with apparatuses, chemicals, process implementation.
(h) Indispensability of skilled labor.
(i) Indispensability of high fuel requirements and consequent burden on operational budgets.
(j) Smell of ammonia.

Prior 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.

As the aforesaid lacunae and process inefficiencies remain to be addressed, the need for further research in this domain is preserved. The Applicant has therefore undertaken targeted research in this direction, and consequently come up with novel solutions for resolving all needs of the art once and for all.

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 an efficient and sustainable process for the recovery of Alumina from Aluminum dross residue.

It is another objective further to the aforesaid objective(s) that the process so provisioned is effective in removal of Ammonia from dross, and make it smell free.

It is another objective further to the aforesaid objective(s) that the process so provisioned is effective in removal of water-soluble salts and bath inclusions from dross.

It is another objective further to the aforesaid objective(s) that the process so provisioned is cost-effective to implement.

It is another objective further to the aforesaid objective(s) that the process so provisioned does not mandate the involvement of skilled personnel.

It is another objective further to the aforesaid objective(s) that the process so provisioned has high throughput of recovered Alumina.

It is another objective further to the aforesaid objective(s) that the process so provisioned is unaffected by the technical issues outlined earlier in this document.

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:

FIGURE 1 is a schematic illustration of the setup for pre-processing, by water-treatment, of Aluminum dross residue as per the present invention.

FIGURE 2 is a flow chart to illustrate the value chain for utilization of Aluminium grade non-metallic dross particles as per the present invention.

FIGURE 3 is a flow chart to illustrate the value chain for utilization of alloy-grade non-metallic dross particles as per 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.

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.

Statement / Summary of the invention
This invention is identified in establishment of an able process for recovery of-Alumina and Ammonia by agitating, Aluminium Nitride component of Aluminum dross residue in water, by further processing to beneficiation.

Detailed description
Principally, general purpose of the present invention is to assess disabilities and shortcomings inherent to known systems comprising state of the art and develop new systems incorporating all available advantages of known art and none of its disadvantages. Accordingly, the disclosures herein are directed towards an inventive method, and its implementing system, for recovery of Alumina and Ammonia by agitating, Aluminium Nitride component of Aluminum dross residue in water, by further processing to beneficiation.

This invention is about utilization of the nonmetallic particles of Aluminum dross residue from two major sources -
a) Aluminium grade dross
b) Alloy grade dross

The method developed by us for the above-mentioned cause is fundamentally based on following objectives-
a) Removal of Ammonia from dross, and make it smell free. This will also reduce one component of hazardous characteristics from dross i.e., AlN. Ammonia released can be collected and sold or can be flared up or used as fuel.
b) Removal of salts and bath inclusions, which are soluble in water.
c) Beneficiation and recovery of Alumina.
d) Segregation / recovery of Aluminium rich particles.
e) To recover fine Aluminium and utilize it as a reducer in other industries.

Dross is the input material, which is first crushed using Jaw Crusher and pulverizers. This material is then screened using a 2mm screen. All material that is above 2mm size has high Aluminium content as Aluminium metal cannot be crushed beyond a certain size. >1mm material high in Aluminium content is melted and casted into Aluminium ingots for sales. The <1mm material is called Non-metallic particles (NMP).

Non-metallic particles of dross residue mainly consist of Aluminium micro fines, Alumina, AlN and some carryover fluxes like bath material.

Accordingly, the method of this invention is intended to be practiced via treatment with water followed by heat treatment. The material is charged into a specially designed system shown in FIGURE 1. The system has a surge storage with a bell cone to control the discharge flow of the input material into the system. Water treatment is given to the residue dross. The non-metallic particles readily react with water in a closed vessel and agitated with help of an agitator, so as to release Aluminium hydrate and ammonia as per reaction (1), among which the latter can be captured as Ammonium Hydroxide (Liquor Ammonia) and stored for alternative commercial applications or compressed to be either disposed off by flaring.

AlN + 3H2O ? Al(OH)3 + NH3 ……………………………..……. (1)

Ammonia generated in the process is captured in a Water bath as Ammonium Hydroxide (Liquor Ammonia) and sold or flared up. The agitator helps in ensuring the material fed into the system is mixed and moved around well so the entire batch receives proper treatment. The dead material Al2O3+Metallic microfine Al+Aluminium hydrate is discharged from the equipment.

Accordingly, the resultant residue is charged in heating equipment, so as to burn the leftover microfine Al and break Aluminium Hydrate to Alumina and Water vapor, as per reaction (2).

2Al(OH)3 ? Al2O3 + 3H2O ……………………………..……. (2)

Similarly to the prior embodiment, the high grade alumina (Al203) is smelter grade alumina that can be again used as raw material input for Aluminium smelters. The poor grade residue will be granulated in small sizes and fired along with lime to make calcium aluminate cement.

The heating step is intended to be carried out in equipment selected among suspended calciners, rotary kilns, fluidized bed boilers, tunnel kilns, vertical shaft kilns and the like. The temperature range required for the above-mentioned reaction to occur is in the range of 700°C to 1300 °C.

Furthermore, the residue from the aforementioned process (Al2O3 and few impurities) and (Al2O3, Al(OH)3), few impurities or washed NMP ((Al2O3, Al(OH)3) can be used to manufacture calcium aluminate cement and synthetic slag for use in refractory and steel.

Non-metallic particles (NMP), procured as per the foregoing narration, are subjected to fine grinding, sieving, and segregation by air classifier, respectively, to obtain metal rich particles and Alumina rich particles. As shown in FIGURE 2, the metal particles having size >20 BSS are utilized in the manufacturing of following Briquettes-
a) Metal Briquettes: For Remelting
b) Composite Briquette: Briquettes including Alkali rich minerals and to be utilized as Slag, reducers and conditioners for Steel Industry.
c) Compressed Agglomerate: For the purpose of reducing surface area.
d) Powder: For Thermit process eg. Low Carbon Ferro Manganese.
e) The metal particles having size <500 BSS will be utilized in the manufacturing of Calcined Alumina.
Calcined Alumina: The residues of size <500 BSS, left behind after the above-mentioned process is calcined in Fluidized Bed Furnace, which leads to the manufacturing of Calcined Alumina.

Air classifier is used in the above-mentioned process, for density air separation of particles by cyclone. Extraction of Ammonia, Alkali Rich minerals, Alumina Rich Al(OH)3, and Aluminium rich particles done from Alloy grade (NMP), shall now be described in further detail hereunder with reference to FIGURE 3.

Nonmetallic particles (NMP) procured from the above-mentioned source are subjected to fine grinding. NMP – fines are then charged to gasification cum beneficiation, Closed batch system.

When the NMP – fines are charged in the gasification unit, the AIN present in NMP – fines react with the water and releases Ammonia gas. Ammonia gas released in the process is captured in a Water bath as Ammonium Hydroxide (Liquor Ammonia) and sold/ flare up/ used as fuel.

Gasification chamber is equipped with the impeller, scrapper, water recirculating unit, external sedimentation tank. This unit acts for beneficiation process, based on forth flotation working principle.

Automated impellers rotate within the chamber, and provides ease for NMP – fines to settle down as per the hydrophobic behavior of different components present within NMP – Fines. As a result Aluminium Rich particles settles down on the bottom layer, subsequently Alumina Rich Al(OH)3 settles down above Aluminium Rich particles. Scrapper is used to remove Aluminium Rich particles from the bottom, subsequently Alumina Rich Al(OH)3 is also removed from the chamber. Salts present within NMP – fines are recycled to the sedimentation tank, where the minerals settles down as Alkali rich minerals.

Aluminium Rich particles is subjected to wet screening. Particles of size >100 BSS, will be added in manufacturing of Metal Briquette for remelting, as described in processing of Aluminium grade – NMP. Alumina Rich Al(OH)3 is transferred and passed through filter press. The mineral obtained undergoes cake calcination in a rotary kiln or Vertical Shaft Kiln, which leads to the manufacturing of Calcined Alumina.

Calcium Aluminate Cement, can be manufactured by adding hydrated lime/ quick lime/ Limestone to the Calcined Alumina or to the Cake. Alkali Rich minerals derived from sedimentation tank, will be used in the manufacturing of Composite Briquette, to be used as Slag, reducer and conditioner in Steel Industry. Water retained from filter press and wet screening as mentioned in the process is recycled to the sedimentation tank.

As will be realized further, the present invention is capable of various other embodiments and that its several components and related details are capable of various alterations, all without departing from the basic concept of the present invention. Accordingly, 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. ,CLAIMS:1] A process for recovery of Alumina and ammonia from Aluminum dross residue, comprising-
(a) Preconditioning, using Jaw Crusher and pulverizers, the Aluminum dross residue input to a non-metallic particle format having an average particle size of less than 1mm consisting mainly of Aluminium micro fines, Alumina, Aluminium Nitride and carryover fluxes, bath material in particular.

(b) Subjecting the non-metallic particle format obtained in step (a) to treatment with water in a closed vessel and agitated with help of an agitator, so as to release Aluminium hydrate and ammonia, the reaction represented as-
AlN + 3H2O ? Al(OH)3 + NH3

(c) Capturing the ammonia generated in step (b), for either one consequence among-
? Being flared up for disposal;
? Received in a water bath to form Ammonium Hydroxide;
? Stored for use as a fuel.

(d) Subjecting the Aluminium hydrate generated in step (b) to heat treatment to result in alumina and water vapor, the reaction represented as-
2Al(OH)3 ? Al2O3 + 3H2O

(e) Charging the high grade Alumina obtained in step (d) to Aluminium smelters to thus achieve recovery of pure Aluminium from input Aluminium dross residue, with poor grade residue as a byproduct.

(f) Finely granulating and firing the poor grade residue obtained in step (e) along with lime to obtain calcium aluminate cement.

2] The process for recovery of Alumina and ammonia from Aluminum dross residue as claimed in claim 1, wherein the step (a) is characterized in that the non-metallic particle format has an average particle size of less than 1mm.

3] The process for recovery of Alumina and ammonia from Aluminum dross residue as claimed in claim 1, wherein the steps (a) and (b) are undertaken in a specially designed system shown in FIGURE 1, characterized in having a surge storage with a bell cone to control the discharge flow of the input material into the system.

4] The process for recovery of Alumina and ammonia from Aluminum dross residue as claimed in claim 1, wherein the high grade Alumina outputted has from 75% to 99% of Aluminium content.