SYSTEM AND PROCESS FOR RECOVERING WASTE FROM ALUMINUM PRODUCTION

Description

1 / 7 SYSTEM AND PROCESS FOR RECOVERING WASTE FROM ALUMINUM PRODUCTION Field of Invention

[001] The present invention belongs to the technical field of metallurgy and industrial waste treatment. More specifically, it refers to a system and a process for utilizing solid waste generated in the production of primary aluminum, known as sub-layer oxide, transforming it into high value-added raw materials. Fundamentals of the Invention

[002] Primary metallic aluminum is produced industrially, almost exclusively, by the Hall-Héroult electrolytic process. This process is conducted in high-temperature reactors, called electrolytic cells, which consist of a steel shell internally lined with refractory materials and carbon blocks that act as cathodes. Anodes, which are large blocks of carbon, are suspended above the cell.

[003] The operation consists of the electrolysis of aluminum oxide (Al2O3), known as alumina, which is dissolved in a bath of molten cryolite (Na3AlF6) at temperatures of approximately 950-970 °C. The passage of a high amperage electric current promotes the reduction of aluminum ions at the cathode, forming liquid metallic aluminum. Simultaneously, oxygen ions react with the carbon anodes to form carbon dioxide.

[004] The process generates different types of waste. At the end of the tank's useful life, typically 5 to 8 years, the cathodic lining and refractory materials are discarded, constituting Spent Pot Lining (SPL), a hazardous waste due to its fluoride and cyanide content.

[005] Additionally, during continuous operation, a second type of waste is generated. Structural materials and raw materials that fall from the furnace structure accumulate in a lower area, commonly called the subroom. This waste, called subroom oxide, is composed mainly of aluminum oxide, but Petition 870250070005, dated 06 / 08 / 2025, page 6 / 25 2 / 7 also contains valuable materials such as metallic aluminum, cryolite, coal coke, and metallic iron. State of the art

[006] Current management of subsurface oxide waste includes disposal in controlled landfills or inertization processes, implying high costs, environmental liabilities, and loss of valuable materials. Existing treatment systems for this waste generally do not achieve the quality required for the full reuse of the recovered material. Conventional treatment only separates the material granulometrically, failing to remove other contaminants such as iron, silicon, and metallic aluminum, a problem that the present invention proposes to solve.

[007] Patent literature reveals several approaches to the treatment of aluminum industry waste and to the purification of the metal, but with scopes, materials and methods distinct from the present invention.

[008] US patent 3,955,969 entitled “PROCESS FOR THE PRODUCTION AND USE OF ACTIVATED ALUMINA” describes a process for producing activated alumina from aluminum dross. The process involves digesting the dross with hot water, preferably under pressure, to decompose nitrides and carbides and dissolve halide salts. After digestion, the metallic aluminum particles and the purified alumina are separated as distinct fractions. Although it treats a residue from aluminum production (dross), this process uses a fundamentally chemical route (digestion in hot water) for purification, unlike the purely physical separation sequence (granulometric, magnetic, Foucault) proposed in the present invention for the subsoil oxide.

[009] US patent 6,375,712 B1 entitled “METHOD OF REMOVAL OF LIGHT METALS FROM ALUMINUM” discloses a method for removing light metals (sodium, lithium, calcium, and magnesium) from virgin aluminum. The method consists of injecting fine particulate aluminum fluoride and / or sodium aluminum tetrafluoride, carried by a gas, into molten aluminum via a rotating impeller. The chemical reaction between the fluorides and the contaminating metals promotes the purification of the aluminum. Petition 870250070005, dated 06 / 08 / 2025, p. 7 / 25 The 3 / 7 process focuses on the chemical purification of liquid metal, aiming at the removal of contaminants at the PPM level, and is not applicable to the treatment of a heterogeneous solid waste such as sub-room oxide for the recovery of its macroscopic components.

[010] US patent 10,513,789 B2, entitled “INTEGRATED GAS TREATMENT,” describes an integrated gas treatment (IGT) system located within the superstructure of each electrolytic cell. The system uses non-fluorinated alumina in a fluidized bed to adsorb gaseous fluoride from process gases, generating fluorinated alumina which is then used as feedstock in the cell itself. The focus of this prior art is the treatment of gaseous emissions at the point of generation, aiming at air purification and fluoride recovery, without addressing the treatment and separation of the components of the sub-cell oxide solid waste.

[011] Document CN 117127041 B entitled “ENVIRONMENT-FRIENDLY TREATMENT METHOD FOR REGENERATED CAST ALUMINUM ALLOY MELT” presents a method for treating recycled cast aluminum wheels scrap. The process includes melting in a double-chamber furnace where paint removal occurs without pretreatment, followed by refining with a specific agent (KCl, MgCl2, CaF2, KAIF4, KBF4), degassing with argon, and slag filtration. This document describes a process involving melting and chemical refining steps of a specific feedstock, diverging from the proposed dry physical separation route for the treatment of sub-room oxide residue.

[012] From the analysis of the state of the art, it is concluded that a gap persists for a technological solution that treats sub-room oxide residue in an integrated and systematic way by predominantly physical and mechanical means. None of the prior art describes the specific sequence of granulometric, magnetic separation with mixed magnets and by eddy currents, configured to recover the multiple valuable components of sub-room oxide with the purity necessary for their direct reintegration into the production cycle. The present invention aims to fill this gap. Objectives of the invention Petition 870250070005, dated 06 / 08 / 2025, page 8 / 25 4 / 7

[013] The main objective of the present invention is to provide a system and a process for the treatment and valorization of sub-layer oxide residue generated in the production of primary aluminum. Specific objectives are: • to systematically and efficiently separate the main components of the waste, such as aluminum oxide, cryolite, metallic iron, and metallic aluminum; • To obtain recovered products with a degree of purity similar to that of virgin raw material, allowing their direct reuse in the metallic aluminum production process without the need for changes in the production process; • Overcoming the limitations of conventional systems by implementing a multi-purpose process that effectively removes contaminants; • to introduce a technical innovation in the magnetic separation stage, through a separator with mixed ferrite and neodymium magnets, optimized for the specific characteristics of the sub-layer oxide; • To offer an environmentally advantageous and economically viable solution that transforms an environmental liability into an economic asset, promoting the circular economy, reducing the need for mineral extraction, the consumption of inputs, and the costs of waste disposal. Summary of the invention

[014] The present invention achieves the proposed objectives through a system and a recovery process from sub-room oxide residue. The process is based on a flowchart of physical separation steps, which treats the different particle size fractions of the residue distinctly to maximize the recovery efficiency of each component. The process begins with a particle size separation step, which divides the material into a coarser fraction and a finer fraction. The coarse fraction is directed to a magnetic separation step and, subsequently, to an eddy current separator to segregate iron and metallic aluminum. The fine fraction undergoes a further screening step and a high-efficiency magnetic separator to purify the aluminum oxide. The main innovation of the process lies in the design of a modified magnetic separator, which uses a combination of magnets Petition 870250070005, dated 06 / 08 / 2025, page 9 / 25 5 / 7 ferrite and neodymium to ensure highly efficient separation of ferrous particles. Description of the figures

[015] The invention will be better understood with reference to the accompanying figures, which illustrate a preferred and not limiting embodiment: Figure 1: Detailed flowchart of the process for recovering waste from aluminum production, showing the different stages and the products generated; Figure 2: Schematic view of the operating principle of a roller-type magnetic separator; Figure 3: Schematic view of the operating principle of an eddy current separator; Figure 4: Schematic cross-section of an electrolytic cell for aluminum production. Detailed description of the invention

[016] The SYSTEM AND PROCESS FOR RECOVERING WASTE FROM ALUMINUM PRODUCTION, the subject of this patent application, consists of a process characterized by a sequence of physical separation steps, beginning with the classification of the waste in a deck sieve (5) into coarse (A) and fine (B) fractions. The coarse fraction (A) is purified in a magnetic separator (6) and by eddy current (7). The fine fraction (B) is processed in a circular sieve (12) and in a high-efficiency magnetic separation module (13). The inventive feature lies in the said module (13), which uses a combination of ferrite (F) and neodymium (N) magnets to optimize the removal of iron dust (14), generating recovered aluminum oxide (18) of high purity.

[017] The present invention relates to an integrated system and a sequential process for the recovery and valorization of aluminum production waste. The treated waste, called sub-room oxide (X), originates from the operation of electrolytic cells (1), whose basic structure is shown in Figure 4, where components such as the anode (2), the cryolite bath (3) and the cathodic paste (4) can be observed. The accumulation of materials released from this structure in the lower area, the sub-room, generates the heterogeneous waste. A Petition 870250070005, dated 06 / 08 / 2025, page 10 / 25 The invention proposes the systematic separation of its valuable components, as detailed in the flowchart in Figure 1.

[018] The system object of the invention is a physical processing plant, composed of interconnected physical separation modules. The modular configuration allows the specific treatment of each fraction of the residue, maximizing recovery efficiency. The system comprises at least four modules. A first primary particle size separation module consisting of a deck screen (5), a vibratory and inclined classification equipment, equipped with multiple levels or grids, designed to process large volumes of raw material. A second coarse fraction purification module composed of two in-line equipment: a magnetic roller separator (6), whose principle is schematized in Figure 2, and an eddy current separator (7), schematized in Figure 3.The magnetic roller separator (6) uses a magnetic roller (8) to remove ferrous contamination (9), while the eddy current separator (7) uses a high-speed magnetic rotor (10) to repel and separate conductive non-ferrous metals (11). A third secondary particle size separation module consisting of a vibrating circular sieve (12), equipped with fine mesh screens (between 50 and 120 mesh) is used for precise classification. A fourth high-efficiency magnetic separation module consists of a grid magnetic separator (13) and constitutes the main technical difference of the invention. The inventive feature of this high-efficiency grid magnetic separation module (13) lies in its mixed magnetic system, which combines ferrite magnets and neodymium magnets in its bars. The synergistic and unexpected technical effect of this combination is what allows for high efficiency in the purification of fine aluminum oxide.Individually, ferrite (F) magnets have a long-range field but low strength to hold particles against the material flow. On the other hand, neodymium (N) magnets have very high strength but a short-range field. The inventive combination uses the long field of the ferrite to attract the iron powder particles (14) dispersed in the material flow, and the superior strength of the neodymium to firmly fix them to the grid, preventing them from being dragged away. This arrangement solves the... Petition 870250070005, dated 06 / 08 / 2025, page 11 / 25 7 / 7 technical deficiency of each type of magnet, resulting in a cleaning capacity superior to the sum of its parts.

[019] The process, illustrated in Figure 1, describes the sequential and synergistic operation of the system modules. The process begins (I) with the feeding of the residual sub-room oxide into the deck screen (5). In the first classification stage (E1), the material is separated into a coarse fraction (A) (> 3mm) and a fine fraction (B) (< 3mm). The coarse fraction (A) (> 3mm) is processed in the purification module. First, it passes through the magnetic roller separator (6), where the larger-sized ferrous contamination is extracted as iron scrap / ferrous contamination (9). Then, in the eddy current separator (7), the aluminum metal (15) / non-ferrous conductive metals (11) are segregated. The final product of this circuit is the clean bath (16), rich in cryolite and ready for reuse. In parallel, the fine fraction (B) goes to the vibrating circular screen (12) for precision classification.The material retained on the screens is classified as contaminated bath (17) material rich in cryolite, coke, silica and other minor contaminants. The passing material, rich in aluminum oxide and iron powder, is directed to the final purification stage. In the final purification stage, the fine material is processed by the magnetic grid separator (13). It is here that the technical effect of the mixed magnets, ferrite (F) and Neodymium (N), manifests itself: the iron powder particles (14) are attracted and firmly retained, ensuring a deep cleaning that results in the high-value final product, recovered aluminum oxide (18). The purity achieved is such that the material can be reintroduced as raw material in the aluminum industry, closing the production cycle and promoting the circular economy. The process also includes an optional stage, indicated by the dashed line in Figure 1, where the Recovered Aluminum Oxide (18) can be subjected to a process in a calciner.The objective of this auxiliary step is the purification of recovered aluminum oxide through the burning of coal coke, generating a higher-value product for specific applications. Petition 870250070005, dated 06 / 08 / 2025, page 12 / 25

Claims

1 / 2 CLAIMS 1) PROCESS FOR RECOVERING WASTE FROM ALUMINUM PRODUCTION, wherein the waste is sub-layer oxide (X), characterized by comprising the steps of: a) subjecting the waste to a primary particle size separation to divide it into a coarse fraction (A) and a fine fraction (B); b) purifying the coarse fraction (A) through magnetic separation and eddy current separation to remove ferrous material (9) and metallic aluminum (15); c) subjecting the fine fraction (B) to a secondary particle size separation to isolate a passing material fraction rich in aluminum oxide; d) purifying the passing material fraction in a high-efficiency magnetic separation step, carried out in a grid magnetic separation module (13) whose magnetic elements are composed of a combination of ferrite magnets (F) and neodymium magnets (N), to obtain the recovered aluminum oxide product (18). 2) PROCESS FOR RECOVERING WASTE FROM ALUMINUM PRODUCTION, according to claim 1, characterized by a grid magnetic separation module (13), ferrite magnets (F) acting to attract iron powder particles (14) from within the material flow and neodymium magnets (N) acting to firmly fix said particles to the magnetic element. 3) PROCESS FOR RECOVERING WASTE FROM ALUMINUM PRODUCTION, according to claim 1, characterized by additionally comprising an optional calcination step to purify coke-containing fractions, such as recovered aluminum oxide (18). 4) SYSTEM FOR RECOVERING WASTE FROM ALUMINUM PRODUCTION, characterized by comprising: a) a primary (5) and secondary (12) particle size separation module; b) a purification module for the coarse fraction, comprising a roller-type magnetic separator (6) and an eddy current separator (7); Petition 870250070005, dated 06 / 08 / 2025, page 13 / 25 2 / 2 and c) a grid magnetic separation module (13) for the fine fraction, having magnetic elements composed of a combination of ferrite magnets (F) and neodymium magnets (N). 5) SYSTEM AND PROCESS FOR RECOVERING ALUMINUM PRODUCTION WASTE, according to claim 4, characterized in that the primary particle size separation module is a deck screen (5) and the secondary particle size separation module is a vibrating circular screen (12). Petition 870250070005, dated 06 / 08 / 2025, page 14 / 25

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