Patent Publication Number: US-2023138875-A1

Title: Plasma process to convert spent pot lining (spl) to inert slag, aluminum fluoride and energy

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority on U.S. Provisional Application No. 62/993,043, now pending, filed on Mar. 22, 2020, which is herein incorporated by reference. 
    
    
     FIELD 
     The present subject matter relates to the production of inert slag, aluminum fluoride (AlF 3 ) and energy and, more particularly, by converting Spent Pot Lining (SPL). 
     BACKGROUND 
     Problem Statement 
     In core aluminum manufacturing processes, a high-temperature electrolysis cell converts alumina to aluminum metal. The cell, colloquially called pot, is lined with carbon (the cathode) and with multiple layers of refractory bricks ( FIG.  1   ). The electrolyte within the cell dissolves slowly into the cell wall over time. This electrolyte dissolution causes the cell to fail after 5 to 8 years of service 1 . There is no way to fix or recycle back to the smelter a contaminated cell wall (called spent pot lining or SPL). Thus, the contaminated cell wall becomes the largest solid waste stream from any aluminum smelter 2 . 
     An aluminum smelter produces up to 25,000 tons of SPLs per year 3 . All the 270 or so aluminum smelters around the world must handle such waste stream, which amounts to more than 1,500,000 metric tons per year worldwide. The SPL is a hazardous residual material because of its high content of leachable fluorides and cyanides. Moreover, SPL reacts with water to generate explosive gases, such as methane and hydrogen. Hence, transportation, remediation and final storage of SPL is subject to strict regulations. SPL is highly heterogeneous 5 , which complicates any recycling treatment. Still today, due to these considerations, the most common route to treat SPL is to dump it directly into highly secured (and expensive) landfills. 
     Commercial Alternatives to SPL Landfill 
     Many companies have worked to develop processes to decontaminate SPL, to recover or valorize the SPL carbon value and to recover the SPL fluoride value. The process alternatives to landfilling divide into either leaching or thermal destruction. Both alternatives have advantages and disadvantages. The most advanced decontamination processes for each process alternative are described hereinbelow. 
     Leaching: SPL decontamination and carbon recycling via low-caustic leaching and liming (LCL&amp;L) 
     A major current alternative to SPL landfilling (or forever storage) is the low-caustic leaching and liming (LCL&amp;L) process 6 . Rio Tinto currently operates an 80,000-ton/year LCL&amp;L plant in the Saguenay region, Quebec. The process has the uttermost advantage of having already been through a difficult and long scale-up. Nonetheless, the process suffers from its complexity. 
     The following describes some of the process&#39; complexity:
         the process requires several complex equipment, such as a multi-effect evaporator, a pressure reactor and a crystallizer, which are difficult to operate.   the cyanide control is very complex and requires a complete wastewater treatment unit.   grinding the contaminated and dangerous SPL to 300 μm (microns) is tantamount to an efficient leaching process. SPL dust is explosive and thus a stringent dust control is required.   leaching a reduced waste with metallic aluminum and sodium causes a safety concern due to the reaction with humidity to produce hydrogen.   the process generates a high-pH solid residue comprising carbon, silica, alumina and other oxides. The solid residue is difficult to valorize or recycle. For this reason, the residue is discarded in a specialty landfill.   some suggest floating carbon from this solid residue to recover a recyclable carbon powder for cathode manufacturing 7 . The suggestion implies floatation cells and various floatation agents. Nonetheless, recycled carbon from SPL might not comply with composition, morphology and structure specifications for use as carbon material in the aluminum smelter 8 .       

     Thus, the major drawback of the LCL&amp;L process is that it does not reduce the amount of solid wastes (1.17 kg solid by-product per 1 kg SPL), not counting all the liquid wastes. The process literally creates a new type of solid waste with a different decontamination challenge. 
     Thermal destruction: SPL decontamination and carbon valorization via a burner-powered thermal treatment 
     The other major current alternative process to SPL landfilling is the thermal degradation of SPL and the mechanical sorting of the degraded solid residue. The alternative process degrades the cyanides, volatilises the acid components and produces an inert sand from a SPL feedstock. The sand is sorted into carbon and refractories in a subsequent processing step to manufacture valuable by-products for the cement industry. 
     This process alternative is the basis of a commercial process that produces specialty carbon bricks and specialty inorganic salts from SPL 9 . The process is being used in Australia since the early 2000s and its major advantage is that it is mostly dry. 
     This process is well established but suffers drawbacks as well:
         the main market for these bricks is cement and brick manufacturing. This bottleneck is a major drawback since these industries tolerate only a small composition window for fluorine (0.25 wt % F max. 10 ). It is an issue since part of the SPL fluorine content is not even volatile (i.e. CaF 2 ).   the by-product bricks from the process must comply with heavy international regulations to be sold as industrial-grade products.   the process requires additive supplies to meet cement and brick manufacturers requirements and to fully neutralize the solid residue.   the SPL feedstock must be fine-crushed to 50 μm-20 mm and sorted to get the right process recipe prior to thermal degradation at 450° C. However, at that temperature, the hot sand tends to partly melt thus agglomerating the fine-crushed SPL into larger chunks.   the hot sand resulting from thermal degradation at 450° C. must be quenched with water to volatilize the acid components, such as hydrogen fluoride (HF) and carbon monoxide (CO).   after that, the wet sand is exposed to air for up to 4 weeks to complete the stabilization before further processing. Such a long stabilization step oxidizes the other SPL volatile compounds, such as methane. A large closed hangar with an air treatment is thus required.   the multi-step process produces various off gases of different compositions and temperatures, which must be fully treated before release to the environment.       

     Here again, the major drawback of this batch-mode process is that it does not lower the amount of solid wastes. 
     Therefore, it would be desirable to provide an apparatus and a process that provide a reliable solution to the above problem afflicting core aluminum manufacturing processes. 
     SUMMARY 
     It would thus be desirable to provide a novel apparatus and process for converting Spent Pot Lining (SPL) into inert slag, aluminum fluoride (AlF 3 ) and energy. 
     The embodiments described herein provide in one aspect a process for converting spent pot linings (SPL), comprising a plasma arc furnace, a dry syngas cleaning train and an aluminum fluoride (AlF 3 ) reactor, 
     a. the plasma arc furnace including an anode and a cathode, wherein: 
     i. the plasma arc furnace is adapted to gasify carbon to syngas; 
     ii. the plasma arc furnace is adapted to convert a mineral fraction to vitrified slag; 
     iii. steam is used to capture an excess energy from a gasification reaction and contributes to raise a syngas hydrogen content; 
     b. a cyclone at an outlet of the plasma arc furnace being adapted to collect dust particles; 
     c. the reactor being adapted to convert hydrogen fluoride (HF) in the syngas to AlF 3 ; 
     d. a waste heat boiler being adapted to cool down the syngas and to be possibly used for energy recovery; 
     e. a baghouse is adapted to recover at least part of the dust particles not recovered by the cyclone, wherein the dry syngas typically has a very low dew point, avoiding condensation 
     Also, the embodiments described herein provide in another aspect a process, wherein a temperature of the plasma arc furnace is between 500° C. and 1800° C. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein a vitrification of inert constituents of the SPL is carried out without requiring adding a slag agent, such as calcium oxide. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein a conversion of HF to AlF 3  is adapted to take place at a temperature higher than 500° C. but below 1000° C. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein a source of Al 2 F 3  to produce AlF 3  is feed material to an aluminum electrolyser, purified Al 2 F 3 , or an intermediary aluminum hydroxide in a Bayer process. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein the reaction heat produced by a neutralisation of HF by Al 2 F 3  is adapted to produce more steam in a heat recovery boiler (for instance HX-0411). 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein any excess heat from the gasification of SPL in the plasma arc furnace is adapted to be used for converting water vapor (steam) or liquid water to hydrogen. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein the water is bled from the condensate-steam loop that flows in the waste heat recovery boiler (HX-0411). 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein an oxidizing medium includes a mixture of air and water. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein a hydrogenation of fluorine volatized from the SPL is achieved via steam reaction. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein the slag can be valorized as a concrete additive. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein the plasma SPL gasification and vitrification furnace is adapted to maintain a certain amount of feed material on top of a molten inorganic bath, ensuring a substantially complete temperature gradient in the plasma arc furnace, thereby allowing for drying, pyrolysis and partial combustion of the SPL. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein a plasma SPL processing system requires only electricity as its energy source, i.e. no fossil fuels. 
     Furthermore, the embodiments described herein provide in another aspect a process for converting spent pot linings (SPL) into inert slag, aluminum fluoride (AlF 3 ) and energy in the form of steam and syngas. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein the inert slag can be valorized as a concrete additive. 
     Furthermore, the embodiments described herein provide in another aspect a process for converting spent pot linings (SPL), comprising a plasma arc furnace, a dry syngas cleaning train and an aluminum fluoride (AlF 3 ) reactor, 
     a. the plasma arc furnace including an anode and a cathode, wherein: 
     i. the plasma arc furnace is adapted to gasify carbon to syngas; 
     ii. the plasma arc furnace is adapted to convert a mineral fraction to vitrified slag; 
     iii. steam is used to capture an excess energy from a gasification reaction and contributes to raise a syngas hydrogen content; 
     b. a cyclone at an outlet of the plasma arc furnace being adapted to collect dust particles; 
     c. the reactor being adapted to convert hydrogen fluoride (HF) in the syngas to AlF 3 ; 
     d. a waste heat boiler being adapted to cool down the syngas; and 
     e. a baghouse is adapted to recover at least part of the dust particles not recovered by the cyclone. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein a temperature of the plasma arc furnace is between 500° C. and 1800° C. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein a vitrification of inert constituents of the SPL is carried out without requiring adding a slag agent, such as calcium oxide. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein a conversion of HF to AlF 3  is adapted to take place at a temperature higher than 500° C. but below 1000° C. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein a source of Al 2 F 3  to produce AlF 3  is feed material to an aluminum electrolyser, purified Al 2 F 3 , or an intermediary aluminum hydroxide in a Bayer process. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein reaction heat produced by a neutralisation of HF by Al 2 F 3  is adapted to produce more steam in a heat recovery boiler (for instance HX-0411). 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein any excess heat from the gasification of SPL in the plasma arc furnace is adapted to be used for converting water vapor (steam) or liquid water to hydrogen. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein water is bled from a condensate-steam loop that flows in a waste heat recovery boiler (HX-0411). 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein an oxidizing medium includes a mixture of air and water. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein a hydrogenation of fluorine volatized from the SPL is achieved via steam reaction. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein the slag can be valorized as a concrete additive. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein the plasma SPL gasification and vitrification furnace is adapted to maintain a certain amount of feed material on top of a molten inorganic bath, ensuring a substantially complete temperature gradient in the plasma arc furnace, thereby allowing for drying, pyrolysis and partial combustion of the SPL. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein the process requires only electricity as its energy source, i.e. no fossil fuels. 
     Furthermore, the embodiments described herein provide in another aspect a process for converting spent pot linings (SPL), comprising a plasma arc furnace that includes an anode and a cathode, the plasma arc furnace being adapted to gasify carbon to syngas and to convert a mineral fraction to vitrified slag, steam being provided to capture an excess energy from a gasification reaction and contributes to raise a syngas hydrogen content. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein a cyclone provided at an outlet of the plasma arc furnace is adapted to collect dust particles. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein a AlF 3  reactor is adapted to convert hydrogen fluoride (HF) in the syngas to AlF 3 . 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein a waste heat boiler is provided for cooling down the syngas. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein a baghouse is provided for recovering at least part of the dust particles not recovered by the cyclone. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein a temperature of the plasma arc furnace is between 500° C. and 1800° C. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein a vitrification of inert constituents of the SPL is carried out without requiring adding a slag agent, such as calcium oxide. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein a conversion of HF to AlF 3  is adapted to take place at a temperature higher than 500° C. but below 1000° C. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein a source of Al 2 F 3  to produce AlF 3  is feed material to an aluminum electrolyser, purified Al 2 F 3 , or an intermediary aluminum hydroxide in a Bayer process. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein reaction heat produced by a neutralisation of HF by Al 2 F 3  is adapted to produce more steam in a heat recovery boiler (for instance HX-0411). 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein any excess heat from the gasification of SPL in the plasma arc furnace is adapted to be used for converting water vapor (steam) or liquid water to hydrogen. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein water is bled from a condensate-steam loop that flows in a waste heat recovery boiler (HX-0411). 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein an oxidizing medium includes a mixture of air and water. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein a hydrogenation of fluorine volatized from the SPL is achieved via steam reaction. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein the slag can be valorized as a concrete additive. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein the plasma SPL gasification and vitrification furnace is adapted to maintain a certain amount of feed material on top of a molten inorganic bath, ensuring a substantially complete temperature gradient in the plasma arc furnace, thereby allowing for drying, pyrolysis and partial combustion of the SPL. 
     Furthermore, the embodiments described herein provide in another aspect a process, wherein the process requires only electricity as its energy source, i.e. no fossil fuels. 
     Furthermore, the embodiments described herein provide in another aspect an apparatus for converting spent pot linings (SPL), comprising a plasma arc furnace, an anode, a cathode, a crucible in the plasma arc furnace for receiving the SPL, the plasma arc furnace being adapted to generate an electric arc traveling from the anode to the cathode and within the SPL. 
     Furthermore, the embodiments described herein provide in another aspect an apparatus, wherein the plasma arc furnace is adapted to gasify carbon to syngas and to convert a mineral fraction to vitrified slag, steam being provided to capture an excess energy from a gasification reaction and contributes to raise a syngas hydrogen content. 
     Furthermore, the embodiments described herein provide in another aspect an apparatus, wherein a cyclone provided at an outlet of the plasma arc furnace is adapted to collect dust particles. 
     Furthermore, the embodiments described herein provide in another aspect an apparatus, wherein a AlF 3  reactor is adapted to convert hydrogen fluoride (HF) in the syngas to AlF 3 . 
     Furthermore, the embodiments described herein provide in another aspect an apparatus, wherein a waste heat boiler is provided for cooling down the syngas. 
     Furthermore, the embodiments described herein provide in another aspect an apparatus, wherein a baghouse is provided for recovering at least part of the dust particles not recovered by the cyclone. 
     Furthermore, the embodiments described herein provide in another aspect an apparatus, wherein a temperature of the plasma arc furnace is between 500° C. and 1800° C. 
     Furthermore, the embodiments described herein provide in another aspect an apparatus, wherein a vitrification of inert constituents of the SPL is carried out without requiring adding a slag agent, such as calcium oxide. 
     Furthermore, the embodiments described herein provide in another aspect an apparatus, wherein a conversion of HF to AlF 3  is adapted to take place at a temperature higher than 500° C. but below 1000° C. 
     Furthermore, the embodiments described herein provide in another aspect an apparatus, wherein a source of Al 2 F 3  to produce AlF 3  is feed material to an aluminum electrolyser, purified Al 2 F 3 , or an intermediary aluminum hydroxide in a Bayer process. 
     Furthermore, the embodiments described herein provide in another aspect an apparatus, wherein reaction heat produced by a neutralisation of HF by Al 2 F 3  is adapted to produce more steam in a heat recovery boiler (for instance HX-0411). 
     Furthermore, the embodiments described herein provide in another aspect an apparatus, wherein any excess heat from the gasification of SPL in the plasma arc furnace is adapted to be used for converting water vapor (steam) or liquid water to hydrogen. 
     Furthermore, the embodiments described herein provide in another aspect an apparatus, wherein water is bled from a condensate-steam loop that flows in a waste heat recovery boiler (HX-0411). 
     Furthermore, the embodiments described herein provide in another aspect an apparatus, wherein an oxidizing medium includes a mixture of air and water. 
     Furthermore, the embodiments described herein provide in another aspect an apparatus, wherein a hydrogenation of fluorine volatized from the SPL is achieved via steam reaction. 
     Furthermore, the embodiments described herein provide in another aspect an apparatus, wherein the slag can be valorized as a concrete additive. 
     Furthermore, the embodiments described herein provide in another aspect an apparatus, wherein the plasma SPL gasification and vitrification furnace is adapted to maintain a certain amount of feed material on top of a molten inorganic bath, ensuring a substantially complete temperature gradient in the plasma arc furnace, thereby allowing for drying, pyrolysis and partial combustion of the SPL. 
     Furthermore, the embodiments described herein provide in another aspect an apparatus, wherein the apparatus requires only electricity as its energy source, i.e. no fossil fuels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the embodiments described herein and to show more clearly how they may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, which show at least one exemplary embodiment, and in which: 
         FIG.  1    is a schematic representation of an aluminum production electrolytic cell, wherein a cell wall becomes a cumbersome waste stream that piles up to 25,000 tons of SPLs (Spent Pot Lining) per year per aluminum smelter 3 ; 
         FIG.  2    is a schematic representation of an apparatus in accordance with an exemplary embodiment, which apparatus includes a plasma arc furnace; and 
         FIG.  3    is a schematic representation of an integration of the present apparatus and the plasma arc furnace thereof into a dry SPL decontamination process, in accordance with an exemplary embodiment. 
     
    
    
     DESCRIPTION OF VARIOUS EMBODIMENTS 
     The new plasma technology described herein and using plasma provides a reliable solution to a problem afflicting the core aluminum manufacturing process. 
     The above overview of the two current alternative processes to landfilling stresses out what should be an optimal SPL treatment process. An optimal SPL treatment process would respond to four (4) major criteria. 
     These criteria are the following: 
     1. to generate a harmless solid by-product that can be easily discarded in any landfill. 
     2. to valorize the SPL carbon on-site for its energy content and thus to reduce the purchase of natural gas or other procured fuel. 
     3. to recover the SPL fluoride value for reuse on-site, without the need to comply with external regulations and without the need to buy a reagent to capture fluoride (such as calcium oxide). 
     4. to be a continuous process occupying a small footprint on the smelter site. 
     The fluorine recovery, as a valuable by-product reusable on-site, is key in the optimal SPL treatment process. Not all plasma technologies would deliver on fluorine recovery. For instance, some technologies trap the fluorine in their residual solid by-product via reaction with the reagent calcium oxide 11 . This approach requires the mixing of SPL with neutralisation and fluxing reagents as a first step to their process. The ratio of added reagents to SPL can be as high as 50%. 
     The thermal destruction of waste via plasma described herein responds to these four (4) criteria and does not need outsourced fluxing agents nor neutralisation reagents. 
     Therefore, as shown in  FIG.  2   , an apparatus A is provided for converting Spent Pot Lining (SPL) into inert slag, aluminum fluoride (AlF 3 ) and energy. The apparatus A includes a plasma arc furnace F such that the destruction of SPL occurs in this plasma arc furnace F. The furnace F uses electricity to generate an electric arc  30  (see  FIG.  3   ) within the waste. The arc  30  travels from an anode  10  to a cathode  12  and destroys the waste due to the arc&#39;s extreme local temperature (5,000° C.). The extreme temperature that exists locally around the arc  30  converts the mineral fraction of SPL  14  into vitrified inert slag  16  lying within a crucible  17 , which SPL  14  is fed via a feed bin  18 . The slag  16  is very similar to obsidian, a natural-occurring mineral. 
     The furnace F gasifies the carbon content of the SPL  14  and produces a well-balanced syngas  20 . The gasification takes place due to the controlled intake of air  22  and steam  24  to the furnace F. Gasification is the process of converting carbonaceous matter into a gaseous mixture of carbon monoxide (CO) and hydrogen (H 2 ). The gasification reaction liberates a significant amount of energy. Steam captures this excess energy, provides part of the oxygen requirement for gasification and contributes to raise the syngas H 2  content. Steam also contributes to the conversion of some SPL fluorides (NaF and Al 2 F 3 ) into hydrogen fluoride. 
     The plasma process operates either in a continuous mode or in a semi-continuous mode. SPL  14  feeds into the furnace F continuously and syngas  20  continuously evolves from the furnace F. The slag  16 , on the other hand, does not need to be poured out of the furnace continuously. The pouring of the slag  16  out of the furnace F can occur at a predetermined frequency, during which the feeding (of SPL  14 , steam  24  and air  22 ) to the furnace F is idle. 
     As to the integration of the apparatus A and the plasma arc furnace F thereof into a complete SPL treatment process, the present apparatus A and its plasma arc furnace F greatly simplify the process of SPL decontamination, energy recovery, contaminant control and process integration within an aluminum smelter (see  FIG.  3   ). The only downstream equipment to the furnace F that the process requires is that needed for the treatment of the syngas  20 . The process assumes the cleaned syngas displaces natural gas in the anode baking area—a major energy consumer in any aluminum smelter. 
     Regarding the treatment of the syngas  20 , in order to maintain robust and simple operations, the syngas treatment process is entirely dry from the feed inlet to the clean syngas delivery to the smelter. The major process units are an aluminum fluoride (ALF 3 ) reactor  32 , a syngas cooler  34  and a baghouse  36 . 
     The following describes these three (3) major process units: 
     The AlF 3  reactor  32  converts the hydrogen fluoride (HF) in the syngas  20  into a highly valuable by-product aluminum fluoride  38 . The AlF 3  reactor  32  uses alumina (Al 2 O 3 ) as reagent, which is the raw material to any aluminum smelter. Such reactors are available commercially to produce AlF 3 . 
     The waste heat boiler (syngas cooler)  34  cools down the temperature of the syngas  20  from about 850° C. to 150° C. and by doing so, produces steam  42 . The steam  42  is used for energy recovery and, for instance, to vaporize process water into the furnace F. Alternatively, the steam  42  can also feed a non-condensing steam turbine to generate electricity. 
     The baghouse  36  recovers any dust particles that neither a cyclone  44  at the outlet of the furnace F nor the AlF 3  reactor  32  could capture. The baghouse uses regular particle bags to capture the dust. The dry syngas has a very low dew point. Thus, the syngas flowing through the baghouse is not prone to condensation. 
     It is noted that the flowsheet of  FIG.  3    assumes that the smelter is already equipped with a flue gas treatment plant to capture any remaining HF traces. HF traces do not pose any problem in the anode baking process. 
     While the above description provides examples of the embodiments, it will be appreciated that some features and/or functions of the described embodiments are susceptible to modification without departing from the spirit and principles of operation of the described embodiments. Accordingly, what has been described above has been intended to be illustrative of the embodiments and non-limiting, and it will be understood by persons skilled in the art that other variants and modifications may be made without departing from the scope of the embodiments as defined in the claims appended hereto. 
     REFERENCES 
     
         
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         [2] Ullmann Encyclopedia (2009), chapter “Aluminum”, section 6.3, p. 30. 
         [3] Assuming 25 kg SPL per metric ton of primary aluminum and a maximum aluminum smelter capacity of 1,000,000 metric tons per year. Web site: https://gulfbusiness.com/top-10-largest-aluminium-smelters-in-the-world/, accessed 2020-03-04. 
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         [5] Birry, L., Leclerc, S. and Poirier, S. (2016). The LCL&amp;L Process: A Sustainable Solution for the Treatment and Recycling of Spent Potlining. In Light Metals 2016, E. Williams (Ed.). doi:10.1002/9781119274780.ch77. 
         [6] Burry, L., Leclerc, S. and Poirier, S. (2016). “The LCL&amp;L Process: A Sustainable Solution for the Treatment and Recycling of Spent Potlining”. In Light Metals 2016, E. Williams (Ed.). doi:10.1002/9781119274780.ch77. 
         [7] Pawlek R. P. (2018) “SPL: An Update”. In: Martin 0. (eds) Light Metals 2018. TMS 2018. The Minerals, Metals &amp; Materials Series. Springer, p. 671. 
         [8] Pawlek R. P. (2012) “Spent Potlining: an Update”. In: Suarez C. E. (eds) Light Metals 2012. Springer, p. 1313. 
         [9] Cooper B. J., et al. (2009), Regain Technologies Pty Ltd. U.S. Pat. No. 7,594,952 B2, “Treatment of Smelting By-Products”. 
         [10] Pawlek R. P. (2018) “SPL: An Update”. In: Martin 0. (eds) Light Metals 2018. TMS 2018. The Minerals, Metals &amp; Materials Series. Springer, p. 671. 
         [11] Chapman C., et al. (2010), Tetronics Limited. US Patent Publication No. US2010/0137671 A1, “Method for Treating Spent Pot Liner”.