A process for recycling and refining aluminium from metal waste

Abstract

The disclosure describes a process for recycling of aluminium waste into aluminium hydroxide and / or alumina to produce high purity aluminium hydroxide and / or smelter grade alumina. The process comprises dissolving, or partially dissolving, aluminium waste in an alkaline aqueous solution to form a reaction mixture and refining the reaction mixture by extracting one or more sediments enriched in impurities from said reaction mixture. Aluminium hydroxide may then solidify in the reaction mixture and the solidified aluminium hydroxide may be separated from the reaction mixture and extracted and can be converted to alumina which can be electolysed to obtain pure aluminium metal.

Description

[0001] A process for recycling and refining aluminium from metal waste

[0002] TECHNICAL FIELD

[0003] The disclosure relates to the technical field of metal recycling, and more particularly to the recyclingand upgradingof aluminium waste into aluminium hydroxide with increased purity of aluminium.

[0004] BACKGROUND

[0005] Aluminium is frequently touted as being easily and economically recyclable, as remelting aluminium to cast into new items, or roll into sheets, uses much less energy (about 1 / 20th) than making new aluminium via conventional aluminium smelting. However, aluminium is frequently used in various different alloys with different content of non-aluminium components such as iron and silica. It remains challenging to purify the aluminium from melted aluminium scrap and thus the obtained aluminium is typically limited to use in lower quality alloys or other products with less stringent composition specifications. Or, if stringent alloy and impurity specifications need to be met then the only current solution is to bring down impurity levels by mixing in significant amounts of high purity primary aluminium (non-recycled aluminium produced from ore) in the practice called “sweetening”. This sweetening is not compatible with an ever more circular economy with less mining and more recycling.

[0006] The Bayer process is a well-known process for converting bauxite ore to alumina and is part of the conventional production process for making primary aluminium, via the Hall- Heroult smelting process. The Bayer process involves crushing and dissolving bauxite in sodium hydroxide at high temperature and pressures to form sodium aluminate (Na[Al(OH)4]) solution, from which aluminium hydroxide is crystallized, typically by the aid of adding seed crystals. The aluminium hydroxide is subsequently converted to alumina.

[0007] EP3903952A1 discloses a method for recycling aluminium from consumer packaging such as aseptic carton packs, flexible packs, and aluminium powders via alkaline dissolution in Bayer liquor or in NaOH. This step may be followed by subjecting the dissolved mixture to the Bayer process to form alumina or later aluminium. However, such direct application of the Bayer method on consumer packaging is likely to yield recycled aluminium of low purity.

[0008] SUMMARY

[0009] The present invention is specified in the claims as well as in the description below.

[0010] The invention provides an improved process for recycling aluminium scrap or waste which allows purification of the aluminium to obtain aluminium of higher purity than in the scrap or waste used as source material in the process.

[0011] The present invention broadly refers to a process for recycling aluminium scrap or other aluminium, with improved purity of the aluminium comprising product, compared to source material. This is achieved by hydrolysing the scrap or waste, and then refining the dissolved aluminium scrap or waste by separating out at least one solid sediment (a dirty fraction) comprising non-aluminium components from the dissolved reaction mixture before recovering purified (upgraded) aluminium as a component of a purified precipitate.

[0012] The aluminium waste may thus be recycled into an aluminium-containing solid, most typically aluminium hydroxide. In some embodiments, the aluminium hydroxide may further be recycled into alumina, or even further into aluminium.

[0013] An advantage of the present invention is that smelter grade (high purity) alumina may be produced from aluminium waste that comprises one or more non-aluminium components. Typical impurities that can be removed by this invention include unwanted alloy elements from the waste mix, and / or so-called “tramp elements” picked up by the aluminium scrap during its production, use, lifecycle, or recycling collection or processing.

[0014] With this invention the inventors have produced, to the best of their knowledge, the world’s first “upcycled aluminium”, in Reykjavik Iceland. “Upcycled aluminium” refers to the achievement of smelting high purity aluminium from alumina that is 100% derived from waste aluminium. “High purity aluminium” refers to aluminium metal that meets premium alloy specifications. Moreover, with the method disclosed here the recycled aluminium is purer than the aluminium waste it is produced from, and this upcycling is achieved without any sweetening by primary, or “mined”, aluminium. This invention and disclosure encompasses this new recycling process to achieve this “upcycling”, and discloses the combination of methods or steps necessary to achieve smelter grade alumina from the process. Useful features of the invention include specific hydrolysis conditions, specific fractional separation or crystallization conditions, washing or leaching, and non-contamination measures.

[0015] Herein the term “aluminium waste” that can be used in the invention encompasses any pieces / objects containing aluminium which it is desired to recycle in order to re-use the aluminium metal therein, and “aluminium waste” thus can refer broadly to any kind of aluminium scrap, parts and objects no longer in use such as, but not limited to, body parts and engine parts, building materials, electronic components including aluminium used in wind turbines and solar cells, packaging materials and the like. Thus, “aluminium waste” may refer to a chemical mixture comprising elemental aluminium such as, but not limited to, a mixture of aluminium, or an alloy thereof, and other metal components and / or non-metal components. The aluminium may be comprised in a substance such as a metal alloy. In standard applications, the chemical mixture may be a solid-solid mixture comprising two or more components. In some embodiments, aluminium waste may be provided as a waste product or as a by-product from another industrial process. A common example of the latter is dross.

[0016] Herein, the terms “aluminium waste”, “aluminium scrap” and “waste comprising aluminium” may be used interchangeably.

[0017] The present invention is therefore particularly useful for recycling aluminium from industrial and manufacturing waste and / or offcuts from such processes as well as for recycling parts and objects no longer in use. The present invention may be highly advantageous for recycling of metallurgical waste and discontinued products from industries such as, but not limited to, the automotive, maritime, aero, building and electronics and power industry. In an aspect of the present invention, a process for recycling aluminium waste is provided, wherein the process comprises steps of: providing aluminium waste to a chemical reactor, hydrolysing said aluminium waste to form a reaction mixture comprising aluminate, refining (or cleaning) said reaction mixture at least once by separating at least one solid sediment comprising non-aluminium components from said reaction mixture, wherein said sediment may be enriched in non-aluminium components, forming solid aluminium hydroxide in the reaction mixture, separating said aluminium hydroxide from said reaction mixture to obtain solid aluminium hydroxide, to thereby obtain material with a higher grade of aluminium than in the aluminium waste used as source.

[0018] The aluminium waste may comprise elemental aluminium such as, but not limited to, aluminium comprised in pure aluminium, aluminium alloys or substances comprising aluminium. In some embodiments, the aluminium waste may further comprise one or more elements that belong to one or more of the following groups: alkali metals, earth- alkali metals, semi-metals, non-metals, and any combination thereof. In such embodiments, the aluminium waste may further comprise one or more of the following elements: magnesium, manganese, iron, copper, zinc, silicon, titanium, zirconium, chromium, nickel, tin, lithium, gallium, vanadium, sodium, sulphur, any alloy thereof, or any substance thereof, or any combination thereof.

[0019] Once the aluminium scrap or waste is provided to the chemical reactor and the hydrolysing reaction is initiated, the reaction may occur both rapidly and exothermically (releasing heat). Therefore, it may be dangerous to attempt to remove at least one solid sedimentfrom the mixture, especially with the additional build-up of pressure (inside the chemical reactor) and the formation of H2. To the best of the applicants’ knowledge, no one has attempted (or reported conceiving of) removing at least one solid sediment from the reaction mixture at this early stage in order to refine the reaction mixture. The reason may likely be attributed to the dangerous conditions associated with the reaction, and difficulty of removing what may be a small amount of the aforementioned at least one solid sedimentfrom the reaction mixture quickly. Also, in prior research and applications of the hydrolysis of aluminium and aluminium waste, derivatives and variations of this reaction, emphasis has typically been placed on harvesting hydrogen and heat from the reaction, instead of purification.

[0020] The step of hydrolysing said aluminium waste to form a reaction mixture comprises forming a solution of aluminate, e.g., a solution of sodium aluminate (Na[Al(OH)4]) or potassium aluminate (K[Al(OH)4]).

[0021] The precise timing of the hydrolysis reaction may be heavily dependent upon and may be defined by the reaction conditions such as, but not limited to, the concentration of the aluminium waste and the molarity of the solution.

[0022] In some embodiments, the step of hydrolysing may be conducted in an aqueous solution. In some such embodiments, the aqueous solution may be an aqueous solution of a base, i.e., an alkaline solution. In some embodiments, the base may be a hydroxide of an alkali metal (group 1 ) or earth-alkali metal (group 2) or a combination of two or more such hydroxides. In such embodiments, the base may comprise one or more of the following: lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, caesium hydroxide, calcium hydroxide, strontium hydroxide and barium hydroxide. In preferred embodiments, the base comprises sodium hydroxide and / or potassium hydroxide.

[0023] In some embodiments, said aqueous solution may provide a hydroxide concentration in the range of about 0.001 M to about 6 M, preferably in the range from about 0.0125 to about 1 M, wherein M is the molarity of the hydroxide, and more preferably in a range from about 0.02M, orfrom about 0.05M orfrom about O.I M, orfrom about 0.2M orfrom about 0.3M, orfrom about 0.4M, to about 5M, orto about 4M, orto about 3M, orto about 2M, or to about 1 M, or to about 0.8M, or to about 0.6M, such as about 0.1 M, about 0.2M, about 0.3M, about 0.4M, about 0.5M, about 0.6M, about 0.7M, about 0.8M, about 0.9M, or about 1 .0M. For comparison, the standard Bayer process typically provides an aqueous alkaline solution with a hydroxide concentration in the range of about 5 to about 10 M.

[0024] Once the hydrolysis reaction is initiated, e.g., by providing aluminium waste into an alkaline solution in a chemical reactor, hydrogen may evolve from the hydrolysis reaction, accordingly, the method may comprise a step of extracting said formed hydrogen. In some embodiments, the extracted hydrogen may be directly used and / or stored, e.g. in fuel cells.

[0025] Yet another advantage of the present invention is that it offers an energy efficient process for recycling aluminium waste. In some embodiments, the process may be operated at a temperature in the range from about 20°C to about 90°C, preferably in the range from about 65°C to about 75°C, more preferably in the range from about 70°C to about 75°C. In some embodiments, the process may be operated at a temperature in a range from about 55°C, or from about 60°C, or from about 65°C, to about 90°C, or to about 85°C, or to about 80°C, or to about 75°C or to about 70°C, such as at a temperature of about 70°C, or about 72°C or about 75°C or about 80°C. Moreover, the process may be operated at substantially ambient pressure, e.g., in the range of about 0.8 atm or from about 0.9 atm, or from about 0.95 atm or from about 1 .0 atm, to about 1 .2 atm, or to about 1 .1 atm or to about 1 .05 atm; preferably in the range of 0.9 atm to 1 .1 atm, more preferably in the range of 0.95 to 1.05 atm. The pressure may vary slightly based on the produced hydrogen during the reaction and its take-off. However, in typical applications of the process, the hydrogen may be extracted from the reactor vessel. For comparison, the Bayer process for refining bauxite is typically operated at a temperature of 170-200°C and at a pressure in the range of about 4.5 atm to about 15 atm.

[0026] Accordingly, the process of the present invention for refining aluminium waste into aluminium hydroxide may be significantly more energy efficient than the Bayer process for converting bauxite into alumina with the exothermic hydrolysis reaction producing significant amounts of energy in the form of hydrogen and heat that can both be extracted and utilized.

[0027] In some embodiments the aluminium waste is provided in small particle or fine grain form. Thus, in some embodiments the process further comprises shredding or comminuting the aluminium waste material. The small particle or fine grain form may comprise material e.g. in grain, flake or shave form, in some embodiments comprising material with average grain size of less than 10 mm and preferably less than 5 mm such as less than 3 mm. In some embodiments, the use of a base may be avoided. In such an embodiment, the hydrolysis reaction may be initiated by providing aluminium powder. Accordingly, in some embodiments the method may comprise the step of milling the aluminium waste, preferably, aggressive milling to obtain fine aluminium waste powder, i.e., aluminium waste powder with a small grain size, such as but not limited to a grain size of less than about 50 pm including less than about 20 pm or less than about 5 pm. In such embodiments, the aluminium hydrolysis reaction (with hydrogen evolution) may also be initiated at lower pH than that resulting from e.g. 0.1 M NaOH, including neutral pH or below. Although this low base, or base-free, embodiment may also achieve some of the refinement disclosed here, the skilled person will anticipate that the relative solubility of aluminium compared to the solubility of impurities would likely become closer, compared to the larger solubility difference present at higher pH. A smaller gap between the solubility (and also precipitation kinetics) of impurity elements to be separated out at short time, and of the purer aluminium hydroxide to be extracted or “harvested” at relatively longer time, may result in a lower yield of purified aluminium hydroxide and / or less pure aluminium hydroxide for embodiments using no or less base. Hence, although the “base-free” embodiment of the process, discussed herein, for aluminium waste refinement may have the benefit of avoiding base consumption, it typically will suffer from poorer performance in terms of purification and therefore it often may not be the optimal, or preferred, embodiment in any application where a higher degree of purification is important.

[0028] In some embodiments, the step of hydrolysing the aluminium waste may be initiated by using high temperature conditions, wherein such high temperature conditions may refer to a temperature in a range with a lower bound of 75°C, or 100°C and an upper bound of 200°C, or 250°C, or 300°C, or 350°C, or 400°C, or 450°C, or 500°C, or 570°C. At a temperature in a given range of e.g. 100°C-300°C, the hydrolysis of aluminium may produce dissolved aluminate in the form of aluminium hydroxide (Al(OH)3), hence similar ionic species that may be dominant at low temperature hydrolysis. These observations suggest that refinement aluminium by the method disclosed herein is possible up to an upper bound range of 300°C. For higher temperature range spanning e.g., 200°C to 570°C it is known in the art that the main dissolved aluminate species produced by the hydrolysis reaction is aluminium hydroxide oxide (AIO(OH)). Hence, in this temperature regime refinement of the waste as reported here may also still be possible, but clearly the relative dissolution and precipitation timing may be quite different since the ionic species and dominant precipitate changes along with the accelerated kinetics of high temperature. It is reported that at temperatures above 570°C the aluminium hydrolyses directly to stable oxide Al2O3, and therefore the purification mechanism this invention exploit is likely not applicable in the ultra-high temperature range (> 570°C).

[0029] In some embodiments, the process, or parts thereof, may be operated at substantially thermally isolated conditions. In some embodiments, said chemical reactor may be configured to operate at the conditions described above.

[0030] In embodiments where high temperature heat or steam extraction is desired the reactor can also be pressurized with the result that operating temperatures in the range 100°C to 570°C may be used. In such embodiments the selective removal of impurities (sediment), and subsequent collection of purified aluminium hydroxide(s), can in principle occur at optimal temperatures as the reactor effluent (aluminate solution resulting from hydrolysis) is cooled allowing for precipitation of first the impurity rich precipitate, and later the purified aluminium hydroxide.

[0031] Herein, the term “sediment” may refer to a solid substance, or a mixture of solid substances, that are solidified and removed from the chemical reaction mixture, i.e., the aluminate solution. Accordingly, the sediment may comprise one or more nonaluminium elemental components such as, but not limited to, magnesium, iron, copper, zinc, manganese, nickel, tin, lithium, gallium, vanadium, silicon, titanium, zirconium, chromium, sodium, sulphur. The sediment is preferably rich in said one or more nonaluminium components. Typically, the non-aluminium components are more concentrated in the sediment compared to the reaction mixture. The sediment may also comprise elemental aluminium, but preferably in small to trace amounts.

[0032] In the present context, the step of separating at least one solid sediment comprising nonaluminium components from the reaction mixture may further encompass separating and removing / extracting at least one solid sediment from the reaction mixture. In some embodiments, the step of separating said reaction mixture may be carried out through known solid-liquid separation processes such as, but not limited to, filtering, and / or sedimentation, decanting, centrifugation, or any combination thereof.

[0033] In the preferred embodiments, said step of refining the reaction mixture (separating solid sediment) may be carried out shortly after cessation of the hydrolysis reaction, and / or duringthe hydrolysingstep itself. In some embodiments, the step is carried out preferably prior to considerable amount of Al(OH)3is formed and precipitated. As an example, the time frame used for at least the first impure sediment removal from the reaction mixture may be in the range from 10 minutes to 300 minutes, such as the range from 30 minutes to 300 minutes, preferably in the range 60 minutes to 240 minutes, after initiation of the hydrolysis reaction. In some embodiments the first refining (separating) step is initiated after a time period in the range from about 10 minutes or from about 20 minutes or from about 30 minutes or from about 40 minutes or from about 60 minutes, to about 300 minutes or to about 240 minutes or to about 200 minutes or to about 180 minutes or to about 150 minutes or to about 120 minutes. In some embodiments, the aforementioned time frame, including the above or other suitable time ranges, for removing a sediment from the reaction mixture, may be adjusted accordingto the amount of aluminium waste and the molarity of the solution. As a non-limiting example, at a pH level around 13, and at an aluminium charge to the reactor at approximately 90 g / L solution, the timing of said step of refining the reaction mixture may preferably be carried out within a time interval of 60 to 120 minutes from initiation of hydrolysis. As another non-limiting example, at a pH level around 13 and aluminium charge of approximately 20 g / L, the timing of said step of refining said reaction mixture may preferably be carried out within a time range of 10- 180 minutes.

[0034] In some embodiments, the pH of the reaction mixture may be tuned to optimize the degree of separation prior to sediment removal. In such embodiments, the pH of the reaction mixture may be adjusted by adding a base, an acid, or a buffer, or any combination thereof.

[0035] Accordingly, the time frame of the step of refining said reaction mixture may be a function of the pH and be adjusted according to the pH of the reaction mixture. In some embodiments, said step of refining said reaction mixture may be repeated to obtain two or more solid sediments comprising non-aluminium components. Accordingly, in some embodiments, the step of refining the reaction mixture may be repeated, sequentially, one time, ortwo times, orthree times, orfourtimes, orfive times, or 10 times, or a number of times in a range therebetween.

[0036] In some embodiments, there may be significant time lag between two or more subsequent formation and / or removal of solid sediment(s). The optimal selected time lag may be a function of the reaction conditions. As a non-limiting example, the time lag may comprise a lower bound from 0.2 hours, or from 0.25 hours, or from 0.5 hours, or from 1 hour, or from 2 hours, or from 3 hours, or from 4 hours, or from 5 hours. The time lag may comprise an upper bound to 1 hour, or to 2 hours, or to 3 hours, or to 4 hours, or to 5 hours, or to 6 hours, or to 7 hours, or to 8 hours, or to 9 hours, or to 10 hours, or to 12 hours or 72 hours.

[0037] In some embodiments, the step of refining said reaction mixture may comprise adding more base to the reaction mixture, that is, after an initial period of hydrolysis.

[0038] In some embodiments, the step of refining said reaction mixture may comprise adding more elemental aluminium to the reaction mixture. The addition of elemental aluminium may be in the form of pure aluminium, or in the form of an aluminium alloy or more aluminium waste.

[0039] The step of forming solid aluminium hydroxide in the reaction mixture may comprise inherent and / or facilitated formation and precipitation of solid aluminium hydroxide (inherent referring to crystallization without crystallization enhancing / initiating additive, whereas facilitated crystallization refers addition seed crystals or other additive for enhancing crystallization, such as those further discussed below).

[0040] In some preferred embodiments, the step of forming solid aluminium hydroxide may comprise waiting for a period of time after the sediment has been removed, allowing aluminium hydroxide to crystallize / precipitate out of the refined aluminate solution. In such embodiments, the step may further comprise sealing the reaction mixture e.g., to prevent contamination and / or to reduce evaporation. As a non-limiting example, the period of time may be in a range from about 2 hours to about a week, preferably in a range from about 12 hours to about 5 days, more preferably in a range from about 24 hours to about 72 hours. In some embodiments the waiting time period is in the range from about 2 hours, or from about 4 hours, or from about 8 hours, or from about 12 hours, to about one week, or to about 5 days, or to about 96 hours, or to about 72 hours, or to about 48 hours, or to about 24 hours.

[0041] Advantageously, the step of forming solid aluminium hydroxide may comprise utilising fractional crystallisation and stepwise extraction of obtained fractions at different timepoints. In this way, desired increased purity levels can be achieved. The stepwise extraction may comprise any solid-liquid separation process such as but not limited to one or more of filtration, sedimentation, decanting or centrifugation. Fractional crystallization is beneficial in the invention to achieve maximum levels of removal of alloy element, tramp element, and all other impurity removal, in the obtained aluminium hydroxide fraction(s). In a typical embodiment this fractional crystallization utilizes the timing of the extraction of crystal fractions. Optimal fractional crystallization can be particularly important to remove elements that may co-precipitate with the product aluminium hydroxide. An example of an element that, if present in the aluminium waste fed to the process, requires fractional crystallization to meet SGA is silicon. As an example, dilution can be applied to further delay the co-precipitation of specific impurities that precipitate at various rates with aluminium hydroxide, such as silicon.

[0042] In some embodiments the step of forming solid aluminium hydroxide involves controlling the temperature of the solution, such as by temperature programming (adjusting temperature to desired level at specific timepoints).

[0043] In some embodiments, the step of forming solid aluminium hydroxide may be assisted, or promoted, or accelerated, by commonly known methods that could promote or accelerate precipitation and crystallization. Examples of such commonly known strategies for promoting or speeding up precipitation which may be applicable in the present invention are cooling, addition of certain ions or chemicals that promote or effect crystallization or precipitation, such as but not limited to adding surfactant or salts, the addition of crystal seeds or any other particles than can act as seeds or catalysts for crystallization, agitation, sonication, bubbling of gasses that promote precipitation or crystallization such as, but not limited to, CO2, altering pH of the solution and alteringthe concentration of the solution such as by evaporation, dilution or TFF (tangential flow filtration). In some embodiments, the step of forming solid aluminium hydroxide may comprise adding acid to said reaction mixture to facilitate crystallization of the aluminium hydroxide from the reaction mixture. The quantity and type of acid may be selected to neutralize the solution and precipitate aluminium hydroxide, i.e., to obtain a pH in vicinity to pH 7. In some embodiments, the acid may be but is not limited to sulfuric acid. In some embodiments, the step of forming solid aluminium hydroxide may comprise adding seed crystals to the reactor such as seed crystals comprising aluminium hydroxide.

[0044] In some embodiments, the step of forming solid aluminium hydroxide may also yield formation of other solid aluminium substances such as, but not limited to, solid aluminium sulphate. As a non-limiting example, the precipitate comprising solid aluminium hydroxide may further comprise aluminium sulphate when sulphuric acid is used to facilitate the crystallization of aluminium hydroxide.

[0045] In some embodiments the step of forming solid aluminium hydroxide may include limiting exposure to atmosphere and, in particular, to CO2, to prevent CO2adsorption or absorption on the aluminium hydroxide, that may affect its surface area. Thus, the step may include to us a sealed reaction vessel and other measures to limit exposure to CO2during the formation and / or separation, such as in-feeding CO2-free or CO2-limited gas.

[0046] The step of separating aluminium hydroxide from the reaction mixture may comprise filtering the solution and extracting the filtered aluminium hydroxide. In other embodiments, other suitable methods of separating and extracting the solid aluminium hydroxide from the liquid solution may be used as would be recognized by the person skilled in the art.

[0047] After, or during, the separation of said solid aluminium hydroxide from the reaction mixture, the method may comprise the step of washing the obtained solid aluminium hydroxide. The step of washing may be repeated one or several times. The washing may be carried out with any suitable solvent such as, but not limited to, distilled water. The washing can affect the composition and surface area of purified material. Optimal washing, or leaching separation, from the solid hydroxide product can be critical to remove impurity elements like Na and K down to SGA levels, but also alloy and tramp elements such as, but not limited to, Mg.

[0048] In some embodiments, the process may further comprise the step of drying the solid aluminium hydroxide. In some embodiments, the drying may comprise a step of heating the solid aluminium hydroxide. In such embodiments, the step of heating may comprise but is not limited to heating said solid aluminium hydroxide to a temperature of about 70°C, or of about 80°C, or of about 90°C, or of about 100°C.

[0049] An advantage of the present invention is that the relative ratio of elemental aluminium to targeted alloy or tramp element impurities in the “purified” solid aluminium hydroxide is preferably higher than the relative ratio of aluminium to targeted alloy or tramp element impurities in the aluminium waste. The relative content of elemental aluminium in the solid precipitate comprising aluminium hydroxide may be above 85% of the metals in the aluminium hydroxide precipitate by weight, more preferably above 90% of the metals in the precipitate by weight, yet more preferably above 95% of the metals in the precipitate by weight. The relative content of elemental aluminium in the solid aluminium hydroxide precipitate may be determined or effected by, or be a function of, the number of repetitions, or timing and duration, degree of separation and hence the reaction conditions, of the step of washing and refining the reaction mixture one or more times by separating at least one solid sediment.

[0050] An advantage of the present invention is that the solid aluminium hydroxide (and aluminium sulphate) may be further recycled into alumina and / or substantially pure aluminium. Accordingly, in some embodiments, the process may further comprise the step of calcinating, e.g., by a calciner or a rotary kiln, the obtained solid aluminium hydroxide to produce alumina, wherein said step of calcinating comprises heating the solid aluminium hydroxide to a temperature in the range of about 700°C to about 1000°C, to oxidize the aluminium hydroxide and / orto remove volatile compounds such as, but not limited to, sulphur containing compounds. Advantageously, the process of the invention allows for control of the specific surface area (e.g. as determined by BET surface area) of the obtained alumina, by control of the process conditions, allowing for the production of both high and low BET surface area alumina, including alumina with a BET surface area below 10 m2 / g, suitable for applications such as abrasives, ceramics, refractories, or inert fillers. Thus, with the invention, particle size and phase composition of the formed alumina can be tuned during calcination to match desired target specifications for industrial electrolysis performance.

[0051] In some embodiments, the process may further comprise the step of converting obtained alumina to substantially pure aluminium, e.g., by the as such well-known Hall-Heroult process for smelting aluminium.

[0052] Among process conditions that affect material properties of obtained aluminium hydroxide and / or obtained alumina, is to take care to limit organic or carbon contamination during some or all steps of the process, including absorption or adsorption of CO2 and other organics from the atmosphere in particular, one or more of the aluminium hydroxide formation step, aluminium hydroxide separation step, hydrolysis step, refining step, and calcination step. That is, using low carbon or extra pure caustic, and using reactor and separation vessels sealed from the atmosphere. In some embodiments, this may as well include feeding CO2-free or CO2-limited atmosphere / gas to the reaction and separation vessels used. It is disclosed that carbon contamination can critically determine the surface area, crystalline phase and morphology of the aluminium hydroxide obtained, and / or alumina obtained with calcination step. Specific surface area, and crystalline phase composition, of the alumina are key product parameters that preferably need to be within SGA specifications if the goal is recycling to aluminium and this can be achieved in preferred embodiments of the present invention.

[0053] In another aspect, the disclosure provides a process for producing aluminium metal, comprising steps of: a) obtaining alumina by calcining aluminium hydroxide produced from recycled aluminium waste usingthe method as disclosed herein; b) introducing the obtained alumina into an aluminium electrolysis cell; c) operating the electrolysis cell under conditions suitable for aluminium metal product to electrolyse the alumina and obtain aluminium metal.

[0054] It follows that the aluminium metal produced by electrolysis in accordance with the disclosure can be re-used in manufacturing, forming a recycling system or loop, which essentially can be a closed-loop system, from aluminium waste to new aluminium products. Advantageously, this process allows for a closed-loop recycling system from aluminium waste to new aluminium products is operated without the use of primary bauxite-derived material.

[0055] The process can advantageously be applied in an electrolysis cell with vertical inert electrodes, this is in fact demonstrated in the accompanying example 7. The process can equally be applied using conventional electrolysis cells with carbon anode(s).

[0056] BRIEF DESCRIPTION OF FIGURES

[0057] The foregoing and other aspects, features and advantages of the invention will be apparent from the following more particular description of particular embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

[0058] Figure 1 shows a flowchart illustrating a process for recycling aluminium waste in accordance with an embodiment of the present invention.

[0059] Figure 2 shows a flowchart illustrating some of the various embodiments in accordance with an embodiment of the present invention.

[0060] Figure s shows a schematic drawing illustrating the hydrolysis reaction in a chemical reactor using a base in accordance with an embodiment.

[0061] Figure 4 shows flowchart illustrating how aluminium hydroxide may be further refined into alumina and / or aluminium in accordance with an embodiment of the present invention. Figure 5 shows an example of an exemplary chemical reactor in accordance with one embodiment of the present invention. Figure 5(a) shows a front view of the chemical reactor. Figure 5(b) shows a cross-sectional view of the chemical reactor, through the cross-section H-H. Figure 5(c) shows a topview of the chemical reactor.

[0062] Figure 6 a flowchart illustrating an embodiment of the present invention outlined in Example 2

[0063] Figure 7 a flowchart illustrating an embodiment of the present invention outlined in Example 3.

[0064] Figure 8 a flowchart illustrating an embodiment of the present invention outlined in Example 4.

[0065] Figure 9 aluminium object produced as described in Example 7, from recycled aluminum obtained by the invention.

[0066] DETAILED DESCRIPTION

[0067] Figure 1 shows a process in accordance with the present invention for recycling aluminium waste into aluminium hydroxide, Al(OH)3. Advantageously, the method may produce aluminium hydroxide of sufficient purity which may later be used to obtain smelter grade aluminium, e.g., through calcination of the aluminium hydroxide into alumina and later conversion of alumina into substantially pure aluminium, as would be recognized by the person skilled in the art.

[0068] The process comprises the steps of providing aluminium waste (10) to a chemical reactor, hydrolysing the provided aluminium waste (20) forming a chemical mixture comprising aluminate, refining the reaction mixture (30) by separating a solid sediment (31) (i.e., separation and extraction of the solid phase forming in the reaction mixture) from the aluminate reaction mixture to obtain a refined reaction mixture. The solid sediment (31 ) may comprise concentrated non-aluminium components such as, but not limited to, other metallic components. In some embodiments, it may be beneficial to remove two or more solid sediments (steps 31 a, 31 b, 31 c...) from the reaction mixture, meaning that an initial sediment is removed, and hydrolysis is continued, then a second sediment is removed, and this may be further repeated (illustrated by a dashed line, which indicates one or more than one cycle of refinement).

[0069] This is followed by an inherent step of the process (not shown), wherein aluminium hydroxide is formed and subsequently precipitated out of the reaction mixture. The aluminium hydroxide may crystallize e.g. in the form of gibbsite and / or bayerite.

[0070] The removal of the one or more solid sediments (31 ) should preferably be carried out shortly after the start of or any time during the hydrolysis or after the cessation of the hydrolysis reaction, preferably, prior to the formation and / or crystallization of aluminium hydroxide. The optimal time for the removal and optional subsequent removals of solid sediment(s) is strongly correlated with the reaction conditions such as, but not limited to, quantity of aluminium to volume of solution. In some embodiments, hydrogen gas evolves from the reaction mixture. The hydrogen gas may be extracted from the chemical reactorforfurther use, e.g., in augmenting fuelfor combustion engines. Furthermore, the evolution of the hydrogen gas may be monitored to aid in determining the time for a removal of sediment, e.g., when hydrogen gas is no longer being formed.

[0071] The crystallized aluminium hydroxide is then separated (50) from the liquid phase of the refined reaction mixture to yield solid aluminium hydroxide (60).

[0072] Referring to Figure 2, the aluminium waste may be provided (10) into a reaction vessel comprising a liquid solution such as an aqueous solution. In the various embodiments, the hydrolysis may be initiated by using an aqueous alkaline solution (10c), wherein base such as alkali or earth alkali metal hydroxide is mixed with water. In useful embodiments, the base may be selected as sodium hydroxide or potassium hydroxide. Additionally, or alternatively, the aluminium waste may be aggressively milled (10a) into a suitably small grain size prior to being provided to said reaction vessel, such as but not limited to a grain size in the range from 0.0001 mm to 5.00 mm, such as in the range 1-5 mm. In some embodiments, the hydrolysis reaction may be initiated by heating (10b) the reaction vessel and / or aluminium waste to a temperature in the range of 100-570°C, preferably to a temperature in the range of 100°-300°C. In some embodiments, the method may combine two or more of the steps (10a), (1 Ob) and (1 Oc).

[0073] Once hydrolysis is started it may begin to form a reaction mixture comprising aluminate (21). A solid sediment (31) may begin to form and settle from the reaction mixture (21). The sediment may be separated and extracted from the reaction mixture using known separation techniques for separation solids from liquids such as, but not limited to, decantation, or filtration to obtain a refined reaction mixture (35). As discussed above, this process may be repeated and the time between two subsequent refinement steps may heavily depend upon the reaction conditions.

[0074] In some embodiments, additional aluminium waste may be added to the reaction mixture prior to the removal of said solid sediment, or in between one or more subsequent steps of sediment removal (not shown). In some embodiments, additional substantially pure aluminium may be added instead of aluminium waste. In some embodiments, additional base may added to the reaction mixture prior to, in between two subsequent sediment removal steps, or after the removal of sediment (not shown).

[0075] Aluminium hydroxide may begin to crystallize from the refined reaction mixture (35). The induction time of crystallization may often be hours or even days and hence requires the step of waiting (41 ). In some embodiments, the induction time may be reduced by adding ions and / or chemicals (42a) to the reaction mixture that promote crystallization and / or by adding seed crystals (42b) such as, but not limited to, aluminium hydroxide seed crystals and / or by bubbling of gases (42c), preferably inert gases, through the reaction mixture and / or by adding a chemical catalyst (42d) capable of catalysing the crystallization of aluminium hydroxide, i.e., the catalyst will serve to reduce the barrier of crystallization and hence enhance the crystallization rate and / or by adding acid (42e) to neutralize the reaction mixture, i.e., to yield a pH in the range of 6 to 8, preferably to be about pH = 7. In embodiments, wherein acid is added to the reaction mixture other substances comprising aluminium may be obtained in the final aluminium substance to be extracted, see Example 2 as a non-limiting example, wherein sulphuric acid was added to neutralize the solution and the product to be separated from the reaction mixture comprised both aluminium hydroxide and aluminium sulphate. In some embodiments, any of the methods discussed above, i.e., 8(a)-8(e), or any combination thereof, may be used to reduce the induction time and promote crystallization or precipitation of aluminium.

[0076] The crystallized aluminium hydroxide may be separated (50a) from refined reaction mixture through any known separation technique for separation solids from liquids such as, but not limited to, filtration (50a). The filtrated aluminium hydroxide (and / or aluminium sulphate) may then be washed (51) to remove impurities from filtrate and subsequently dried (51 ) to obtain aluminium hydroxide (60). In some embodiments, the drying may be carried out at a temperature in the range of 70°-100°C, preferably at around 90°C.

[0077] Figure 3 shows an exemplary chemical reactor (80) for a process in accordance with the present invention. In this embodiment, aluminium waste may be reacted with aqueous solution of sodium hydroxideto obtain hydrogen (26) and sodium aluminate as described by the overall chemical equation (1 ) depicted in Figure 3 as an inset and below:

[0078] 2 Al + 6 H2O + 2 Na++ 2OH- - 2 Na+2 Al(OH)4+ 3H2(1)

[0079] The hydrogen may be sufficiently pure for use in fuel cells for electricity / heat production.

[0080] The reaction rate may depend on various factors, such as the concentration of hydroxide ions in the aqueous solution, the temperature, particle size of the aluminium used and alloying elements in the aluminium waste. If the ratio of OH- to Al is high enough, and the temperature is sufficiently high and / or aluminium particle size sufficiently small, it is possible to get up to 100% yield of the produced hydrogen. In some embodiments, the aluminium waste may be reacted with aqueous solutions of potassium hydroxide, or other suitable strong bases as would be recognized by the skilled person in the art.

[0081] At sufficiently high OH- concentrations most of the aluminium will go into solution as the ionic species Al(OH)4_with Na+as the counter ion, resulting in a supersaturated sodium aluminate solution. Sodium aluminate may be written as Na+[Al(OH)4]_or NaAlO2. However, many of the alloying elements in the aluminium of the aluminium waste, and many of the impurities, either will not go into solution when treated with sodium hydroxide solution, or will have much lower solubility relative to aluminium hydroxide hence forming a sediment.

[0082] Supersaturated sodium aluminate solutions are metastable and after some time crystallization of Al(OH)3, possibly in the form of gibbsite and / or bayerite, may begin. The Al(OH)3may then be extracted.

[0083] Referring to Figure 4, the Al(OH)3(60) may then be processed further, in accordance with an embodiment of the present invention, to produce substantially pure aluminium. In such an embodiment, the aluminium hydroxide (and / or other aluminium substances such as aluminium sulphate) is calcinated (100) to produce alumina (Al2O3(s)) (101 ). The calcination may be carried out by placing the aluminium hydroxide (60) in a calcinator at a temperature in the range of 700°C-1000°C. The alumina (101 ) may then be processed, by smelting (Hall-Heroult process) (102) to form substantially pure, or smelter grade, aluminium (103).

[0084] An advantage of the present invention is that substantially pure aluminium may be produced from aluminium waste without the need to use known techniques such as sweetening.

[0085] Figure 5 shows a schematic of a chemical reactor (80) capable of carrying out the process in accordance with an embodiment of the present invention. The one of ordinary skill in the art is well aware of that other designs of a reaction chamber may equivalently be used to carry out the process of the present invention such as, but not limited to, batch-type reactors or continuous flow reactors.

[0086] Referring to Figure 5(a) which illustrates a front view of the chemical reactor. The chemical reactor (80) comprising a reactor body (81), or a housing, with a hollow interior providing volume to keep reactants and solvent, e.g., the aqueous solution, aluminium waste and base. The chemical reactor may be sealed with a bottom lid (83) and top lid (84) forming a closed reaction vessel with the chemical reactor (80) comprising two reactor flanges (82) to provide a secure connection, i.e., sealing the hollow interior, to the lid parts. Referring to Figure 5(b), which illustrates a cross-sectional view through the H- H plane illustrated in Figure 5(a), a temperature probe housing (86) is shown inside the chemical reactor (80), the temperature probe housing (86) may be used to host a thermostat or the-like which may be used to monitor, preferably, continuously the temperature of the interior hollow and / or the reaction mixture. The chemical reactor may be equipped with heating elements (not shown) configured to heat, i.e., increase the temperature, inside the chemical reactor. In some embodiments, the temperature may be (automatically) controlled through an external control unit. In some embodiments, the housing may be equipped with a barometer (not shown) for measuring the pressure inside the chemical reactor (80). Referring to Figure 5(c), which shows a top-view of the chemical reactor, during the hydrolysis reaction, gases may evolve such as hydrogen which in turn build up pressure inside the sealed chemical reactor. The hydrogen may be extracted through one or more gas outlet pipe(s) (85) to alleviate the pressure build up and for further use. Additionally, in some embodiments in particular embodiments involving high temperatures and / or embodiments involving aluminium waste comprising volatile elements, other substances may evaporate from the reaction mixture, such evaporated species may also be extracted using the gas outlet pipes (85).

[0087] The chemical reactor (80) further comprises a fill pipe (87). The fill pipe is configured to supply liquids such as an aqueous solution or an alkaline aqueous solution to the chemical reactor (80).

[0088] EXAMPLES

[0089] In the following exemplary embodiments of the invention are described. These embodiments are provided to provide further understanding of the invention, without limiting its scope.

[0090] Example 1

[0091] Table 1 shows the elemental composition of a sample of a prototypical aluminium waste and the relative content of each element. The data was obtained through inductively coupled plasma optical emission spectroscopy (ICP-OES) experiment and analysis on the sample. The aluminium waste sample comprises high abundance of aluminium and small amounts (or trace amounts) of magnesium, iron, copper, zinc, silicon, titanium, zirconium, chromium, sodium and sulphur.

[0092] The prototypical aluminium waste is used as a starting material in Examples 2 and 3.

[0093] Table 1. Elemental composition of exemplary aluminium waste.

[0094] Example 2

[0095] An embodiment of the process of the invention was applied to 5g sample of the prototypical aluminium waste described in Example 1. The process applied in the example, is outlined in Figure 6. The aluminium waste was treated with 500 ml of 0.5 M NaOH solution in a chemical reactor. After, and / or during, the reaction of sodium hydroxide (NaOH) with the aluminium waste to form sodium aluminate solution, sediment was obtained in the reaction. The solution was filtered from the sediment. The sediment weighed 2.7 g, elemental composition was analysed by ICP-OES, see second column of Table 2. Sulphuric acid (H2SO4) was then added to the filtered sodium aluminate solution to neutralize the solution (i.e., to pH 7), followed by separating (by filtration) the acid precipitate from the solution. The acid precipitate weighted 13.2 g, after washing and drying and elemental composition analysed by ICP-OES, see third column in Table 2.

[0096] Table 2. Elemental composition of a sediment (extracted from the aluminate solution during refinement of the solution) and precipitate after addition of acid (during neutralizing of the solution) in Example 2.

[0097] Comparison of the composition of the aluminium waste in Table 1 and the composition of the sediment and acid precipitate in Table 2 shows that most of the alloying elements and impurities in the aluminium are concentrated in the sediment except for Si which is only partially concentrated in the sediment.

[0098] The high content of Na and S in the acid precipitate are resides from NaOH being used and H2SO4. The content of Na and S might be lowered with a more thorough washing of the acid precipitate. In this example, the aluminium waste is recycled into an acid precipitate that may comprise aluminium hydroxide. However, due to the use of sulphuric acid, the acid precipitate may additionally, or alternatively, comprise aluminium sulphate.

[0099] Furthermore, X-Ray diffraction analysis (XRD) showed that the acid precipitate was very poorly crystallized. If the precipitation process would yield more crystallized material, the removal of sodium (or ions thereof) and sulphate (or ions thereof) by washing would be likely to be facilitated.

[0100] The calcination of the acid precipitate at elevated temperatures (in the range 700°C- 1000°C) will yield Al2O3(alumina) with some impurities. The composition of alumina after calcination of the obtained precipitate was computed and is shown in Table 3. Sulphur, or compounds thereof, is omitted from the results since this element, or compounds thereof, are likely to be eliminated in the calcination process. It is also assumed that sodium, or compounds thereof, are removed to the same level as in the commercial alumina from the Bayer process. Table 3. Shows computed elemental composition of a sample after calcination of the acid precipitate comprising aluminium hydroxide, in Example 2.

[0101] Example 3

[0102] In this example, an embodiment of the process was applied to 5g sample of aluminium waste (sample material described in Example 1 ). The process of the example, or parts of the process, are outlined in Figure 7.

[0103] First, sodium aluminate solution was obtained from the aluminium waste using 5g of aluminium waste in a 500 ml of 0.5 M NaOH solution. The time before separating, e.g., by filtering of, the sediment was in the range of 2 to 3 hours. The mass of the sediment was measured to be 0.42g. Then, 5g of aluminium were added to the filtered solution to react more with the electrolyte and generate more hydrogen for an additional reaction period, which was in the range of 4 to 4.5 hours. The sediment was then filtered from the solution, washed, and filtered to yield 4.4g of sediment.

[0104] The filtered sodium aluminate solution was then left in a covered beaker for several days to allow for time for crystallisation of aluminium hydroxide without using any additives such as acid. The precipitate was then filtered, washed with distilled water and dried at 90°C.

[0105] The mass of the dried product was measured to be 10.1 g.

[0106] Without being bound by theory, it may be noted that the upper bound of the mass of aluminium hydroxide produced, from 5 g of pure Aluminium, is 14.5 g of aluminium hydroxide. In reality, the yield will be lower because of the solubility of aluminium hydroxide in sodium hydroxide. Furthermore, it should be noted that according to equation 1 , at least one mole of sodium hydroxide is needed to bring one mole of Al into solution, and that in the first step of the experiment, the molar ratio of NaOH to Al is 1 .35, so unreacted aluminium may be expected in the second step of the experiment, i.e., there is not sufficient NaOH in the second step for dissolution of the aluminium. In fact, the second sediment was found to comprise unreacted aluminium.

[0107] The dried product was analysed by ICP-OES, see Table 4. In comparison to the results of first experiment presented in Example 1 , the chemical analysis yields the same low concentration of most elements, except for Si and Na. The Si content is lower than in the acid precipitate obtained in Example 2.

[0108] Table 4. Elemental composition of the aluminium hydroxide precipitate from the process described in Example 3. Example 4

[0109] An embodiment of the present invention with single step of fractional crystallization. Prototypical aluminium waste sample of 5 g was used (sample as described in Example 1). Process flowchart is shown in Figure 8.

[0110] First, sodium aluminate solution was obtained from the aluminium waste using 5g of aluminium waste in a 500 ml of 0.5 NaOH solution. The reaction time and hydrogen evacuation is selected to be 1 .5-3 hours before filtering of the dirty cut with large sieve. Then sediment is filtered usingfilter paper. Filtered by-product is washed and let to dry in 60 to 70 °C. Collected aluminate solution is set aside, closed and left to settle for 72 hours. During settling fractional crystallization of aluminium hydroxide proceeds, then the precipitate is filtered from the solution, and washed. Both the first small particle sediment and the crystallization precipitate from the aluminate solution were analysed using ICP-OES as seen in the Table 5.

[0111] Table 5. Elemental composition of small particle sediment and crystallization precipitate (aluminate) from the aluminate solution Example 5

[0112] This example illustrates the influence of washing on the content of tramp elements. A 5g sample of a prototypical aluminium waste was utilized, as described in Example 1 .

[0113] A sodium aluminate solution was obtained by mixing aluminium waste with 500 mL of 0.5 M NaOH solution, allowing the hydrolysis reaction to proceed for 72 hours. Upon completion, the resulting sediment was separated via filtration. The sediment was then subjected to two different washing protocols: in one case, it was washed with pure water (initial washing) and then dried; in the second, it underwent substantially more extensive washing (additional washing) followed by drying. The elemental composition of both washed samples was analyzed using ICP-MS. The results are presented in Table 6. As shown, additional washing led to a noticeable reduction in the content of certain tramp elements, notably magnesium (Mg) and sodium (Na), thereby demonstrating the effectiveness of enhanced washing procedures.

[0114] Table 6. Effect of washing on elemental composition of the sediment.

[0115] Example 6

[0116] This example illustrates the influence of carbon dioxide (CO2) contamination on the BET surface area of aluminium hydroxide [Al(OH)3(s)] precipitated via hydrolysis in accordance with the invention. The experiment was conducted using aluminium waste and NaOH solutions of varying molarity (0.24 M, 0.50 M, and 1 .00 M), with a fixed liquid volume of 500 mL and a solid input of 5 g aluminium per test, as outlined in Examples 1 through 3.

[0117] Each NaOH solution was prepared with either properly dried or undried NaOH. The hydrolysis reactions were performed at six temperatures (20°C to 70°C) for each concentration. To minimize CO2ingress, selected reactions were conducted in sealed vessels with CO2-free water and reagents, while other samples were exposed to ambient air. After a 72-hour reaction time, the Al(OH)3(s) precipitates were separated via filtration, dried, and subjected to BET surface area analysis. The BET results are summarized in Table 7. The results clearly show that the highest BET surface areas were obtained at 30- 40°C using 0.24 M NaOH under CO2-free conditions with properly dried NaOH. In contrast, higher NaOH concentrations and elevated temperatures resulted in substantially reduced surface area, likely due to rapid precipitation and carbonation effects.

[0118] Table 6. BET Surface Area (m2 / g) of Al(OH)3(s). All samples with low BET showed contamination with CO2 except the two samples with high BET surface area of 247 m2 / g and 193 m2 / g. Notably, a BET surface area of 247 m2 / g and 193 m2 / g were achieved at 30°C and 40°C respectively with 0.24 M NaOH, demonstrating the potential of this method to produce high-surface-area Al(OH)3(s), a critical requirement for Smelter Grade Alumina (SGA) production. These findings underscore the importance of optimizing both reagent purity and reaction conditions to meet industrial standards.

[0119] Example 7

[0120] This embodiment of the invention illustrates the conversion of aluminium hydroxide obtained from aluminium waste into alumina, and its subsequent use in aluminium electrolysis.

[0121] Aluminium hydroxide [Al(OH)3] was produced in accordance with the process steps disclosed in Examples 1 through 6. The Al(OH)3was calcinated at a temperature of 900°C to obtain alumina (Al2O3). The calcined alumina was then processed through crushing and sieving to achieve a grain size distribution suitable for dissolution in a molten electrolyte and effective use in electrolysis.

[0122] The resulting alumina was fed into an aluminium electrolysis cell equipped with vertical inert electrodes. A total of 142.82 grams of alumina was consumed during the course of the electrolysis. The electrolysis process was carried out continuously for 9 hours and 32 minutes.

[0123] The average cell voltage was measured at 3.66 V, with a standard deviation of 0.04 V, indicating a low and stable operating voltage throughout the experiment. Bath temperature was monitored using two thermocouples, one connected to the power system and the other to a data logger. Minor deviations between the sensors were attributed to suboptimal placement of the data logger thermocouple.

[0124] The following operational outcomes were observed: The solubility of the recycled alumina in the electrolyte was stable over the duration of the electrolysis.

[0125] Approximately 74.22 grams of aluminium metal was produced.

[0126] The purity of the aluminium obtained was found to be comparable to aluminium produced from conventional commercial alumina as seen in Table 7.

[0127] Table 7.

[0128] No significant operational deviations were observed, confirming compatibility of the recycled alumina with the inert-electrode electrolysis process.

[0129] These results confirm that alumina derived from aluminium waste, using the methods disclosed herein, is capable of supporting commercial-grade aluminium production with performance and product purity comparable to alumina sourced from traditional Bayer- processed bauxite.

[0130] Figure 9 shows a photograph of the aluminium metal product obtained by electrolysis of recycled alumina derived from aluminium hydroxide produced according to the method of the present invention. The aluminium was collected after 9 hours and 32 minutes of electrolysis using vertical inert electrodes. The product exhibits visual and morphological characteristics consistent with high-purity aluminium, comparable to that obtained using commercial smelter grade alumina. In the foregoing description, a series of steps may be described. The skilled person will appreciate that unless required by the context, the order of steps is not critical for the resulting configuration and its effect. Further, it will be apparentto the skilled person that irrespective of the order of steps, the presence or absence of time delay between steps, can be present between some or all of the described steps.

[0131] As used herein, including in the claims, singular forms of terms are to be construed as also including the plural form and vice versa, unless the context indicates otherwise. Thus, it should be noted that as used herein, the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise.

[0132] Throughout the description and claims, the terms “comprise”, “including”, “having”, and “contain” and their variations should be understood as meaning “including but not limited to” and are not intended to exclude other components.

[0133] The present invention also covers the exact terms, features, values, and ranges etc. are used in conjunction with terms such as about, around, generally, substantially, essentially, at least etc. (i.e., "about 3" shall also cover exactly 3 or "substantially constant" shall also cover exactly constant).

[0134] The term “at least one” should be understood as meaning “one or more”, and therefore includes both embodiments that include one or multiple components. Furthermore, dependent claims that refer to independent claims that describe features with “at least one” have the same meaning, both when the feature is referred to as “the” and “the at least one”.

[0135] It will be appreciated that variations to the foregoing embodiments of the invention can be made while still falling within the scope of the invention. Features disclosed in the specification, unless stated otherwise, can be replaced by alternative features serving the same, equivalent, or similar purpose. Thus, unless stated otherwise, each feature disclosed represents one example of a generic series of equivalent or similar features.

[0136] Use of exemplary language, such as “for instance”, “such as”, “for example” and the like, is merely intended to better illustrate the invention and does not indicate a limitation on the scope of the invention unless so claimed. Any steps described in the specification may be performed in any order or simultaneously unless the context clearly indicates otherwise.

[0137] All of the features and / or steps disclosed in the specification can be combined in any combination, except for combinations where at least some of the features and / or steps are mutually exclusive. Preferred features of the invention are applicable to all aspects of the invention and may be used in any combination.

Claims

CLAIMS1 . A process for recycling and upgrading aluminium scrap or waste, comprising steps of: a. providing aluminium waste to a chemical reactor, b. hydrolysing said aluminium waste to form a reaction mixture comprising aluminate, c. refining said reaction mixture at least once by separating at least one solid sediment comprising non-aluminium components from said reaction mixture, d. forming solid aluminium hydroxide in said reaction mixture, and e. separating the solid aluminium hydroxide from said reaction mixture to obtain solid aluminium hydroxide, with a higher grade of aluminium than in the source aluminium scrap or waste.

2. The process according to claim 1 , wherein the aluminium waste is selected from one or more of the following: dross, coated scrap, multi-material composites, electronic waste, or automotive components.

3. The process according to claim 1 , wherein said step (c) is carried out shortly after the cessation of and / or during the hydrolysing step, preferably, prior to substantial formation of solid aluminium hydroxide.

4. The process according to claim 1 , wherein step (c) is repeated to obtain two or more solid sediments comprising non-aluminium components.

5. The process according to any of the preceding claims, wherein at least a portion of said hydrogen and / or heat, is extracted from the chemical reactor.

6. The process according to any of the preceding claims, wherein said step of hydrolysing is initiated, sustained or enhanced by feeding an aqueous solution to said chemical reactor.

7. The process according to claim 6, wherein said aqueous solution is an aqueous solution of a base.

8. The process according to the preceding claim wherein said base is a strong base selected from one or more of a group consisting of: lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, caesium hydroxide, calcium hydroxide, strontium hydroxide and barium hydroxide, preferably sodium hydroxide or potassium hydroxide.

9. The process according to any of the preceding claims, wherein the step of hydrolysing comprises providing the aluminium waste in small particle or fine grain form to said chemical reactor.

10. The process according to any of the preceding claims, wherein the step of forming solid aluminium hydroxide in said reaction mixture comprises adding acid to said reaction mixture to facilitate solidification of the aluminium hydroxide from said reaction mixture.11 . The process according to any one of claims 1 -9, wherein the step of forming solid aluminium hydroxide in said reaction mixture comprises a step of waiting for a period of time after the refinement step.

12. The process according to any of the preceding claims, wherein the reactor is kept sealed for at least part of the step of forming solid aluminium hydroxide, to reduce CO2contamination and affect surface area of formed aluminium hydroxide.

13. The process accordingto any of the preceding claims, wherein the step of forming solid aluminium hydroxide comprises utilizing fractional crystallization and stepwise extraction of obtained fractions at different timepoints.

14. The process according to claim 13, wherein said stepwise extraction comprises one or more of filtration, sedimentation, decanting or centrifugation.

15. The process according to any of the preceding claims, wherein the step of forming solid aluminium hydroxide comprises controlling the temperature during the forming step.

16. The process according to any of any of the preceding claims, wherein the step of forming solid aluminium hydroxide comprises one or more of: agitation, sonication, adding one or more additives, altering pH of the solution, and altering concentration of the solution.

17. The process according to any of the preceding claims, wherein the step of forming solid aluminium hydroxide in said reaction mixture comprises one or more of the following: adding seeds to said reaction mixture, adding catalyst to said reaction mixture, bubbling reactive or inert gas into said reaction mixture and cooling said reaction mixture.

18. The process according to any of the preceding claims, wherein said process further comprises the step of extracting formed solid aluminium hydroxide.

19. The process according to any of the preceding claims, wherein said process further comprises the step of drying formed solid aluminium hydroxide.

20. The process according to any of the preceding claims, wherein said process further comprises the step of washing formed solid aluminium hydroxide.

21. The process according to any of the preceding claims, wherein said chemical reactor is operated in step (a) at a temperature in the range from about 20° to about 80° C, preferably in the range from about 65°C to about 75°C, more preferably in the range from about 70°C to about 75°C.

22. The process according to any of the preceding claims, wherein said chemical reactor is operated at ambient pressure.

23. The process according to any of claims 7 or 8, wherein said aqueous base solution provides a hydroxide concentration in the range of about 0.001 to about 6M, preferably in the range from about 0.0125 to about 1 M.

24. The process according to any of the preceding claims, wherein said process further comprises the step of calcinating said solid aluminium hydroxide to form alumina.

25. The process according to claim 24, wherein the specific surface area of the alumina obtained by calcination of the aluminium hydroxide is controlled with process conditions, allowing for the production of both high and low BET surface area alumina, including alumina with a BET surface area below 10 m2 / g, suitable for applications such as abrasives, ceramics, refractories, or inert fillers.

26. The process according to claim 24 or 25, wherein particle size and phase composition of the formed alumina are tuned during calcination to match desired target specifications for industrial electrolysis performance.

27. The process according to any of claim 24 to 26, further comprising the step of using the alumina obtained by calcination of the aluminium hydroxide as a feedstock in an aluminium electrolysis cell to produce aluminium metal.

28. The process according to claim 27, wherein the aluminium produced exhibits a purity level comparable to aluminium obtained using commercial smelter grade alumina.

29. A process for producing aluminium metal, comprising: a) obtaining alumina by calcining aluminium hydroxide produced from recycled aluminium waste usingthe process of any of claims 1-23; b) introducing said alumina into an electrolysis cell; c) operating the electrolysis cell under conditions suitable for aluminium metal product to electrolyse the alumina and obtain aluminium metal.

30. The process according to claim 29, wherein the aluminium metal produced by electrolysis is re-used in manufacturing, forming a closed-loop recycling system from aluminium waste to new aluminium products.

31. The process according to claim 30, wherein said closed-loop recycling system from aluminium waste to new aluminium products is operated without the use of primary bauxite-derived material.

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