DESC:*** Complete Specification ***

“Method of processing Aluminium dross residue to obtain non-hazardous products therefrom”

Cross references to related applications: This complete specification is filed further to patent application No. 202331056639 filed on 24/02/2024 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 belongs to the aluminum industry and therein relates generally to methodologies for treatment of Aluminium dross residue. A yet-preferred embodiment of the present invention disclosed hereunder particularly outlines an inventive method for treatment of hazardous Aluminium dross residue, which is otherwise waste, to bulk products.

Background of the invention
Aluminum dross is a waste by-product generated during the smelting and processing of aluminum. The hazardous non-metallic fraction of aluminum dross, especially the fine fraction with particle size less than 1 mm, poses significant disposal and environmental challenges.

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 aluminum smelted, as smelter works in highly reducing conditions.

Aluminium dross 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 is extremely burdening in financial and procedural aspects. Aluminium dross 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.

Aluminium dross, which in principle can be assigned to new scrap, consists of up to 10 to 60% 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 Aluminium dross is important for environmental protection as well as an economic point of view. However, prior art, to the limited extent presently surveyed, does not list a single effective solution embracing all considerations mentioned hereinabove, thus preserving an acute necessity-to-invent.

Description of related art
The treatment and management of aluminum dross present several technical challenges, including:
(a) High Reactivity & Environmental Concerns: When exposed to air or moisture, aluminum dross can oxidize and generate heat, potentially leading to spontaneous combustion. Also, the presence of nitrides and carbides in dross can react with moisture to release toxic gases such as ammonia (NH3) and hydrogen (H2). Secondary aluminum dross, in particular, is often classified as hazardous waste due to the presence of reactive compounds like aluminum nitride (AlN) and aluminum carbide (Al4C3). These compounds can react with moisture to release harmful gases like ammonia (NH3) and methane (CH4), posing environmental and safety risks.
(b) Composition complexity / variability: Dross is a complex mixture of metallic aluminum, aluminum oxides, other metal oxides, salts (especially in secondary dross), nitrides, and carbides. This varied composition makes it difficult to apply a single treatment method effectively.
(c) Metal Recovery Challenges: Inadequate processing leads to significant metal loss as aluminum is trapped in the oxides and slags.
(d) Incomplete Decomposition: Hydrolysis, a common method for treating dross to neutralize reactive compounds, can suffer from incomplete decomposition of AlN. This is because the reaction can form a layer of hydrated aluminum oxide on the AlN particles, hindering further reaction.
(e) Gas Management: The hydrolysis process generates gases like ammonia, hydrogen, and methane, which are flammable and potentially explosive. Managing these gases safely, including their collection, treatment, or utilization, is a significant technical challenge.
(f) Salt Content: Secondary dross often contains high levels of salts, primarily chlorides. These salts can leach into the environment if the dross is not treated properly, causing soil and water contamination. Removing and managing these salts is a crucial technical aspect of dross treatment.
(g) Economic Viability: The cost-effectiveness of dross treatment methods is a significant consideration. Balancing the need for environmentally sound practices with the economic realities of the aluminum industry is an ongoing challenge.

Existing treatment methodologies either fail to extract substantial value from this residue or result in the release of undesirable by-products such as ammonia.

Prior art, to the extent surveyed, lists some scattered attempts to address the issues mentioned hereinabove. For example, JP7076736B2 (Filed 2019; Assigned to Tohoku University NUC) teaches a method and equipment for Aluminum dross treatment. The system includes a gas supply device that introduces an oxidizing gas, preferably ozone, into the slurry. This oxidizing gas reacts with and neutralizes the ammonia produced by the reaction of aluminum nitride with water. The treatment method involves contacting the dross and aqueous medium with the oxidizing gas to oxidize the ammonia in the water slurry, effectively mitigating the hazardous byproducts of aluminum dross processing.

Another example, EP2838868A1 (Filed 2019; Current Assignee Cast Aluminium Industries) teaches a method for creating a fast-hardening, inorganic foam involves mixing a solid reactive powder with a liquid alkali metal silicate (water glass). The powder, with particles mostly smaller than 1mm, consists of 45-65% alumina, 10-20% aluminum nitride, and 5-15% metallic aluminum. Mixing these components in a 0.5-2:1 powder-to-liquid ratio creates a paste that exothermically reacts within 10 minutes to form a foam with a density below 0.7 g/cm³. The process can be done at room temperature with minimal mixing time. The preferred alkali metal silicate has a silica-to-metal-oxide molar ratio of 1.0-2.2. The reactive powder preferably has a high aluminum nitride to metallic aluminum ratio and a low BET surface area. The reactive powder can be derived from aluminum dross. This foam, especially when made from dross, is suitable for lightweight, thermally insulating, and fire-resistant building materials, including prefabricated parts like insulating panels.

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 applicant/s hereof, 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 an effective method for treatment of Aluminium dross residue.

It is another objective further to the aforesaid objective(s) that said method results in valuable / value-added bulk products.

It is another objective further to the aforesaid objective(s) that said method optimizes a dross treatment process for maximum aluminium recovery, minimize waste generation, and reduce environmental impact.

It is another objective further to the aforesaid objective(s) that said method is safe and easy to implement, without undue requirement of capital, time or skilled resources.

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 an illustration, according to a first embodiment, of the process flow / logic of the present invention.

FIGURE 2 is an illustration, according to a second embodiment, of the process flow / logic 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.

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
The present invention provides a method for treating non-metallic aluminum dross residue with an average particle size of less than 1 mm through a systematic sequence of thermal processing steps to obtain three distinct valuable products: Calcined Alumina, Tabular Alumina, and Fused Alumina. The process ensures a single-pass treatment without ammonia liberation, thus offering industrial applicability and environmental safety.

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 present invention aims to overcome the deficiencies of prior art by providing a novel, efficient, and environmentally friendly method to process hazardous aluminum dross residue into commercially valuable products. A multidisciplinary approach involving materials science, chemical engineering, environmental engineering, and process optimization is thus adopted by the applicant named herein for successful achievement of said aims.

A preferred embodiment of the invention is described in the implementation of the following sequence of steps:

Step 1. Selection of Aluminum Dross Residue:
The non-metallic aluminum dross residue is identified and separated for treatment. Said identification and separation may be undertaken by using any of the common art mechanical methods (such as Screening & Sieving, Magnetic Separation (if iron contamination is present), Density Separation (Air Classifiers or Water Separation), Eddy Current Separation etc.), chemical methods (such as Leaching (if salt-based dross is involved), or thermal treatment (Rotary Kiln or Plasma Processing).

Step 2. Grinding and Screening:
The aluminum dross residue is subjected to grinding (by using common art equipment such as ball / roller mills or pulverizers) and screening (via common art means such as vibrating meshes, screens, cyclone separator, drum separator, rotary sieve, air classifier or their equivalents) to obtain two fractions:
(a) Particles greater than 1 mm, which are sent for re-melting.
(b) Particles less than 1 mm, which are classified as hazardous waste and selected for further processing.

Step 3. Preheating in a Cyclone Preheater:
The < 1 mm fraction is fed into a cyclone preheater using an elevator. The material undergoes heat treatment and oxidation through a counter-current mechanism, where heat is generated by a primary rotary kiln and oxygen is supplied by a mechanical blower. The process oxidizes the NMP and following reaction takes place in the Cyclone pre heaters and oxidation kiln.

Oxidation reactions occur as follows:
2AlN + 3O2 ? Al2O3 + N2 ……………….. (1)

4Al + 3O2 ? 2Al2O3 ……………….. (2)

From the above-mentioned reaction white colored Alumina is obtained.

Step 4. Primary Rotary Kiln Processing:
The oxidized alumina is passed through a primary rotary kiln operating at approximately 1050°C to obtain Calcined Alumina. At this point volume stabilization is done

Step 5. Secondary Rotary Kiln Processing:
The Calcined Alumina is subjected to further heating in a secondary rotary kiln at a temperature exceeding 1450°C, causing nodulization / clinkerization. This step decreases apparent porosity, increases bulk density, and induces grain formation to produce high-alpha Tabular Alumina.
Step 6. Arc Furnace Processing (First Alternative):
The Calcined Alumina obtained in Step 5 is subjected to an arc furnace treatment at temperatures ranging between 1400°C and 1900°C in the presence of oxygen to obtain Fused Alumina.

Step 6. Arc Furnace Processing (Second Alternative):
The Tabular Alumina obtained in Step 5 is subjected to an arc furnace treatment at temperatures between 1400°C and 1900°C in the presence of oxygen to obtain Fused Alumina.

As the reader can therefore appreciate, this invention provides several advantages over conventional methods, including but not limited to:
(a) Single-pass treatment process without requiring additional processing stages.
(b) No liberation of ammonia, ensuring environmental safety.
(c) Efficient conversion of hazardous waste into three distinct and commercially valuable products: Calcined Alumina, Tabular Alumina, and Fused Alumina.

Industrial Applicability
The method described herein is highly suitable for industrial-scale applications in the aluminum processing and refractory industries, therein offering at least the following advantages-
(a) Single pass treatment
(b) No liberation of Ammonia
(c) Three valuable products can be obtained namely, Calcined Alumina, Tabular Alumina, Fused Alumina.
(d) The process defined herein is particularly advantageous for waste management in aluminum production plants, offering a sustainable and profitable solution for dross treatment.

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 method for treating hazardous aluminum dross residue comprising:
(a) Selecting non-metallic aluminum dross residue;
(b) Grinding and screening the residue to obtain a fraction with particles less than 1 mm and therein sending particles greater than 1 mm for re-melting;
(c) Feeding, with help of an elevator, the fraction with particles less than 1 mm into a cyclone preheater with heat and oxygen exposure to induce oxidation;
(d) Subjecting the oxidized alumina to a primary rotary kiln at approximately 1050°C to obtain Calcined Alumina;
(e) Processing the Calcined Alumina in a secondary rotary kiln at temperatures exceeding 1450°C to produce Tabular Alumina;
(f) Optionally treating the Calcined Alumina or Tabular Alumina in an arc furnace at temperatures between 1400°C and 1900°C in the presence of oxygen to obtain Fused Alumina.

2] The method for treating hazardous aluminum dross residue as claimed in claim 1, wherein the step of selecting non-metallic aluminum dross residue is undertaken by either among-
(a) mechanical methods selected from among screening, sieving, magnetic separation, Density Separation, Eddy Current Separation, their equivalents and their combinations.
(b) chemical methods including leaching, its equivalents and their combinations; or
(c) thermal treatment using rotary kiln or plasma processing, their equivalents and their combinations.

3] The method for treating hazardous aluminum dross residue as claimed in claim 1, wherein the step of grinding the residue of step (a) is undertaken using equipment chosen among ball mills, roller mills, pulverizers, their equivalents and their combinations.

4] The method for treating hazardous aluminum dross residue as claimed in claim 1, wherein the step of screening the residue of step (a) is undertaken using equipment chosen among vibrating meshes, screens, cyclone separator, drum separator, rotary sieve, air classifier, their equivalents and their combinations.
5] The method for treating hazardous aluminum dross residue as claimed in claim 1, wherein oxidation reactions include:
(a) 2AlN + 3O2 ? Al2O3 + N2
(b) 4Al + 3O2 ? 2Al2O3

6] The method for treating hazardous aluminum dross residue as claimed in claim 1, wherein the cyclone preheater operates with a counter-current mechanism to enhance oxidation efficiency.

7] The method for treating hazardous aluminum dross residue as claimed in claim 1, wherein the process is free from ammonia liberation, making it environmentally sustainable.

8] The method for treating hazardous aluminum dross residue as claimed in claim 1, wherein the final products include:
(a) Calcined Alumina;
(b) Tabular Alumina;
(c) Fused Alumina

9] The method for treating hazardous aluminum dross residue as claimed in claim 1, wherein the process enables a single-pass treatment without requiring additional purification or separation steps.

10] The method for treating hazardous aluminum dross residue as claimed in claim 1, wherein the processed materials exhibit improved bulk density, reduced porosity, and enhanced grain formation for industrial applications.