DESC:*** Complete Specification ***

“Process to manufacture refractory aggregate using dross or residue of dross with reduced oxides as a byproduct”

Cross related applications: This complete specification is filed further to patent application No. 202331064732 filed with provisional specification on 26/09/2023. The contents of this provisional specification are incorporated herein in their entirety, by way of reference.

Field of the invention
This invention belongs to the field of metallurgy and relates generally to methodologies directed toward the effective management of dross in the aluminum industry. More specifically, the present invention is directed to a process for using dross or residue of dross to manufacture a refractory aggregate product, therein realizing reduced oxides as a byproduct.

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 certain definitions are set forth for this document, as follows: -
(a) “Dross” refers to a waste byproduct that forms on the surface of molten metals, particularly aluminum, during the smelting or casting processes.
(b) “White Dross” refers to a byproduct formed during the melting of aluminum with exposed to air, primarily consisting of aluminum oxide and other metal oxides. It is characterized by its lighter color and higher aluminum content compared to black dross. White dross typically contains 30-70% aluminum, with the remainder being aluminum oxide and other impurities.
(c) “Black Dross” is dross generated during melting of scrap aluminum. The impurities in this dross is normally higher due to dust and contamination coming with the scrap. Black dross is characterized by its darker color and lower aluminum content compared to white dross. Black dross typically contains a lower percentage of aluminum (around 5-20%) and higher amounts of impurities, including various metal oxides and non-metallic materials.
(d) “Residue of dross” refers to the remaining material or waste that is left behind after the primary separation of metal particles.
(e) “Refractory aggregates” refer to materials capable of withstanding high temperatures and thermal shock.
(f) “Thermiting” shall refer to a highly exothermic reaction between metal oxides and aluminum powder. The reaction involves aluminum reducing a metal oxide and process parameters as followed conventionally in the art.

Background of the invention
Copious amounts of waste materials are generated during the smelting / casting / refining of aluminum, generally termed as “dross”, which consist of impurities, aluminum oxides, and other non-metallic substances that are skimmed off the surface of the molten aluminum.

Dross forms as aluminum is melted, typically when impurities react with oxygen. The oxidation process leads to the creation of aluminum oxide and other metal oxides. Dross is hazardous for several reasons, including-
(a) Solidified dross contains sharp fragments that pose a risk of cuts or injuries during handling.
(b) Dross often contains heavy metals, such as lead, cadmium, or arsenic which pose health risks if inhaled or ingested by flora and fauna.
(c) Certain components in dross can react with moisture or acids, potentially leading to the release of harmful gases or creating hazardous waste.
(d) If improperly disposed of, toxic components in dross can leach into soil and groundwater, leading to environmental contamination.
(e) During processing, especially if burned or heated, dross can release harmful fumes and particulates, affecting air quality.

Due to the aforesaid reasons, dross resulting from the manufacturing of aluminum is classified as hazardous waste by environmental regulatory authorities the world over who therefore prescribe stringent norms for the special handling, transportation, and disposal procedures for dross. Thus, there is a global pressing need for some effective means for proper management of dross and thereby improve safety and environmental sustainability of the underlying manufacturing processes.

In another perspective, Aluminum dross can contain several valuable materials that can be salvaged and recycled, such as-
(a) Aluminum metal: A significant portion of aluminum can often be recovered. White dross typically contains a higher aluminum content compared to black dross.
(b) Alumina: Recovered aluminum oxide (i.e., alumina) can be used in various applications, such as abrasives, ceramics, and as a feedstock for producing aluminum.
(c) Metal oxides: Dross may contain other metal oxides, such as magnesium oxide, which can be processed for use in construction materials or chemical applications.
(d) Non-metallic residues: These residues can sometimes be repurposed in construction, such as in concrete production or as aggregates.
(e) Fines and dusts: Fine particles from dross can be collected and processed to recover additional aluminum or other useful materials.

Recovering materials from aluminum dross not only reduces waste but also provides economic benefits by reclaiming valuable resources that can be reused in production. This recycling process also minimizes the environmental impact associated with aluminum production, making it more sustainable.

Thus, the reader shall appreciate that there is an acute need for effective dross management and recovery practices the world over, for ensuring sustainable manufacturing processes without or minimal, if at all, harm to the environment.

Description of related art
Prior art, to the extent surveyed, lists some scattered attempts to address the issues mentioned hereinabove. For treatment of dross, a variety of techniques have been documented in theory, including the ones listed in Table 1 below.

Technique Process Description
(a) Mechanical Separation Skimming During the melting process, dross is skimmed off the surface of molten aluminum. This method is simple but may not recover all aluminum.
Vibratory Screens These are used to separate aluminum particles from the dross, enhancing recovery rates.
(b) Thermal Processing Re-melting Dross can be re-melted to separate aluminum from the oxides. This process often requires careful temperature control to minimize further oxidation.
Rotary kilns These are used to process dross at high temperatures, allowing for the separation of aluminum and oxides.
Direct heating Directly heating dross in a controlled environment can help volatilize certain components, allowing for the recovery of aluminum.
Controlled processes This involves conducting thermal processing in an inert atmosphere can reduce oxidation and improve aluminum recovery.
(c) Chemical Processing Hydrometallurgical Methods These involve using chemicals, such as sodium hydroxide, to dissolve aluminum oxide and recover aluminum. This method can be effective but may generate hazardous waste.
Salt fluxing This involves adding flux materials to molten aluminum to help separate aluminum from dross, improving recovery rates.
(d) Biological Methods Bioremediation This involves using specific microorganisms that can help degrade hazardous components in dross.
(e) Modern methods Plasma treatment This involves incorporation of plasma technology to treat dross, allowing for high-temperature processing that can effectively separate aluminum and other materials.
Electrolysis This involves utilizing electrolysis techniques to recover aluminum from dross efficiently.

Table 1

Other than those mentioned in Table 1, landfills remain the only option for residues that cannot be recycled or processed effectively. Uncontrolled disposal can lead to contamination of soil and water, which is a concern in regions with a significant aluminum industry presence, hence the industry is subject to mandatory compliance with stringent statutory norms and regulations.

It is thus increasingly becoming implausible to assure proper disposal methods, adherence to hazardous waste management regulations and effectively preventing environmental impact/s.

Technical issues
Solutions referenced in prior art have not been an ideal solution for the persistence of the following technical issues-
(a) Lack of processivity
(b) High infrastructural and operative costs
(c) Inability to address the persisting non-retrievable metallic and non-metallic components which are left in the aluminum dross residue.

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.

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 process for effectively salvaging dross or residue of dross.

It is another objective further to the aforesaid objective(s) that the process so provided lends favorably to industrial scale implementation in an economically viable, or preferably, profitable manner

It is another objective further to the aforesaid objective(s) that the process so provided is not unduly complex, expensive or mandates the inclusion of highly skilled manpower.

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.

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 / Statement of the invention
This invention is focused on processing and recycling of dross or residue of dross to obtain products of value, namely fused refractory aggregates, and moreover obtaining reduced oxides as a byproduct, thus encouraging sustainability and resource conservation in the value chain of aluminum manufacturing industry.

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 a process for using dross or residue of dross to manufacture a refractory aggregate product, therein realizing reduced oxides as a byproduct.

Composition of the residue of dross can include various materials, such as unreacted or partially reacted metal, non-metallic compounds, and other impurities. In the case of aluminum dross, the residue may contain-
(a) Aluminum Oxide: The primary component, often in the form of alumina (Al2O3).
(b) Metal Oxides: Includes oxides of other metals present in the aluminum feedstock, such as magnesium oxide, iron oxide, and silicon dioxide.
(c) Impurities: May contain various contaminants from the original aluminum source, including heavy metals and non-metallic elements.

Preferred mode of implementing the present invention:
Though 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, reference is now made to a non-limiting illustrious manner in which the present invention is intended to be practiced.

Implementation of the present invention is via the following steps-
(a) Collection and separation of waste of aluminum production processes (dross / residue of dross): Aluminum dross and / or residue of dross is collected and separated from the molten aluminum during aluminum manufacturing process. Conventional techniques such as screening or sieving or magnetic separation may be employed for this purpose.
(b) Thermal processing: Metered quantum of dross / residue of dross and other oxides are charged, in a predefined stochiometric ratio at least 0.01%, to an electric arc furnace to thereby obtain refractory aggregates. Mill scale (thermite starter) is charged to initiate reaction which can be mill scale with or without other oxides to be reduced.

According to a related aspect, the waste of aluminum production processes (dross / residue of dross) generally conforms to the chemical makeup reflected in Table 2 below.

Waste type Ingredient % w/w
Dross Aluminum oxide 30% to 70%
unoxidized aluminum 30% to 50%
Metal oxides including magnesium oxide, silicon dioxide, and iron oxide Trace
Impurities including sodium, potassium, and calcium Trace
Residue of Dross Aluminum oxide Minor
Aluminum particulates Minor
Oxidized aluminum Minor
Metal oxides including magnesium oxide, silicon dioxide, and iron oxide Trace
impurities including sodium, potassium, and calcium Trace

Table 2.

The present invention owes its novelty to its unique and non-obvious chemistry, wherein the aforesaid raw materials, that is the metered quantum of dross or residue of dross and other oxides, are made to undergo the following chemical reactions-

2AlN + 3FeO / other oxides ? Al2O3 (Slags of refractory)
+ 3Fe (Reduced oxides)
+ N2 (Gas that will escape the furnace)
…….. (A)
(Thermiting)
2Al + 3FeO ? Al2O3 (Part of slag)
+ 3Fe (Part of metal or reduced oxides)
…….. (B)

In reaction (A) above, it shall be understood that the “other oxides” refer to Manganese oxides, Chrome oxides etcetera. if dross is used and not only the residue of dross is used.

In reaction (B) above, it shall be understood that Al from the AlN is reduced or thermited to liberate energy. Nitrogen, and not NOx, is formed due to the calculated oxygen of weak other oxides used. Herein, oxidation losses are minimised as the reaction happens very fast and mostly uses the chemical oxygen of the oxides instead of air.

Likewise, the reactions below are intended to be achieved in analogy to the aforesaid chemistry-
2Al + 3MnO ? Al2O3 + 3Mn …….. (C)

2Al + Cr2O3 ? Al2O3 + 2Cr …….. (D)

The refractory aggregates resulting from the above process are typified in having a chemical composition depending on contents of the dross / residue of dross used. Typical composition of these aggregates and role of each ingredient in final utility of said product is provided in Table 3 below.

Constituent of aggregate Presence in final product Attribute to final product
Alumina (Al2O3) From 30% to 70% w/w High thermal stability and resistance to thermal shock.
Aluminum Silicate (formed from the interaction of aluminum oxides with silica in the dross) Variable, as per raw material used
Silica (SiO2) From 10% to 30% Bonding and mechanical properties of the aggregates.
Magnesium Oxide (MgO) Present if waste used contains magnesium alloys Refractory properties and resistance
Iron Oxides (Fe2O3) Minor Thermal and mechanical performance.
Calcium oxide (CaO) Trace ---
sodium oxide (Na2O)

Table 3.
Thus, the Refractory aggregates made from aluminum dross / residue of dross as per the foregoing narrative can effectively utilize waste materials of the aluminum industry while providing valuable products for applications in construction, furnace linings, and other high-heat environments. The specific compositions of the aggregates will depend on the dross source and processing techniques, but the aggregates generally combine alumina, silica, and various metal oxides to achieve desired refractory characteristics.

Key end-products of the process propounded herein include refractory aggregates containing Corundum, Mullite, and Spinel etcetera. Metal or alloys like iron, ferro aluminium, ferro Manganese etcetera additionally form the byproducts of said process, which are characterised in having at least the following properties:
(a) High Thermal Stability: Maintenance of strength and structural integrity at elevated temperatures.
(b) Low Thermal Conductivity: Provision of insulation / energy efficiency in industrial applications.
(c) High Chemical Resistance: Withstanding corrosion from molten metals and slags.

It shall be appreciated that variations of the above process are possible, but intended to be covered in the present invention, wherein the exact process, exact quantums, exact process conditions etcetera may be varied depending on factors including the specific composition of the input raw materials and the requirements of the intended application of the resultant products.

Industrial applicability
The present invention has been reduced to practice and scalable to industrial proportions, therein qualifying as a zero waste process generating valuable products and by products at the same time destroying the hazardous dross / residue of dross.

The refractory aggregate products outputted by the present invention have been validated to have definitively promising specifications, including temperature resistance, thermal shock resistance, and chemical stability and shall hence find ready markets in industries wherever extreme temperatures and harsh conditions are common, for example, steelmaking, glass manufacturing, cement production, and petrochemical processing, etcetera.

In independent experimental trials undertaken by the applicant, the Refractory Aggregates outputted by the inventive process of the present invention were found to exhibit excellent resistance to thermal shock and corrosion.

the Refractory Aggregates outputted by the inventive process of the present invention can therefore can be used for preparing bricks / linings of furnaces, ladles, and kilns to therefore ensure sustainable high-temperature industrial processes, enhancing safety, efficiency, and longevity of equipment. Key industries of application of said Refractory Aggregates include those for the manufacturing of:
(a) Steel
(b) Iron
(c) Cement
(d) Lime
(e) Petrochemicals
(f) Production of low carbon steel or Ferro alloys

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:We claim,
1) A process for obtaining valuable products from the waste of aluminum production, comprising-
(a) Collecting the waste material;
(b) Charging the collected waste material to a furnace for undergoing a controlled thermal process to thereby result in valuable products being refractory aggregates and metal oxides.

2) The process for obtaining valuable products from the waste of aluminum production as claimed in claim 1, wherein the furnace used is an electric arc furnace.

3) The process for obtaining valuable products from the waste of aluminum production as claimed in claim 1, wherein the controlled thermal process is thermiting in presence of mill scale as a thermiting initiator.

4) The process for obtaining valuable products from the waste of aluminum production as claimed in claim 1, wherein the waste is dross, typically consisting of-
(a) From 30% to 70% w/w of aluminum oxide;
(b) From 30% to 50% w/w of unoxidized aluminum;
(c) Metal oxides including magnesium oxide, silicon dioxide, and iron oxide; and
(d) Minor impurities including sodium, potassium, and calcium.

5) The process for obtaining valuable products from the waste of aluminum production as claimed in claim 1, wherein the waste is residue of dross, typically consisting of-
(a) Aluminum oxide;
(b) Aluminum particulates
(c) Oxidized aluminum;
(d) Metal oxides including magnesium oxide, silicon dioxide, and iron oxide; and
(e) Minor impurities including sodium, potassium, and calcium.
6) A refractory aggregate product resulting from the process of claim 1, being characterized in having –
(a) A chemical makeup consisting of Alumina, Aluminum Silicate, Silica, oxides of magnesium, iron, and chrome –
(b) High Thermal Stability;
(c) Low Thermal Conductivity;
(d) High Chemical Resistance