WO2015176166A1

WO2015176166A1 - Processes for decomposing aluminum chloride into alumina

Info

Publication number: WO2015176166A1
Application number: PCT/CA2015/000334
Authority: WO
Inventors: Ebrahim ALIZADEH; Jonathan BOUFFARD; Hubert Dumont
Original assignee: Orbite Technologies Inc
Current assignee: Orbite Technologies Inc
Priority date: 2014-05-21
Filing date: 2015-05-21
Publication date: 2015-11-26
Anticipated expiration: 2016-11-21

Abstract

There are provided processes for decomposing AlCl₃•6H₂O into γ-Al₂O₃ that comprise heating the AlCl₃•6H₂O at a temperature of about 600°C to about 800°C in the presence of steam and optionally at least one gas (for example chosen from air, argon, nitrogen, carbon dioxide, hydrogen and hydrochloric acid), under conditions suitable to obtain the γ-Al₂O₃. For example, the γ-Al₂O₃ obtained can be suitable for use in an aluminum smelting process or optionally for processes for treating the γ-Al₂O₃ to obtain high purity alumina, fused alumina, transition alumina, tabular alumina, calcined alumina, ultra-pure alumina or specialty alumina.

Description

PROCESSES FOR DECOMPOSING ALUMINUM CHLORIDE INTO ALUMINA

[0001] The present application claims priority on US 62/001 ,351 filed on May 21 , 2014, which is hereby incorporated by reference in its entirety.

[0002] The present disclosure relates to improvements in the field of chemistry applied to the production of alumina. For example, it relates to processes for the production of alumina via the decomposition of aluminum chloride.

[0003] Alumina is the raw material used for the production of aluminum metal usually by the Hall-Heroult process. Most commercial alumina is produced through a Bayer type process. That approach mixes the bauxite with a hot concentrated NaOH solution, which dissolves alumina, silica and other impurities. The Bayer process produces gibbsite (AI(OH)₃) that can be thermally converted into alumina. Due to the presence of NaOH in the process, the alumina end product contains a significant amount of Na₂0 (0.3-0.4%wt). Other oxides are also present but in smaller quantities. This level of impurities is not useful for the modern applications of alumina, for example in making synthetic sapphire for use in LED lighting, Li-ion battery separators and display panels for example, for home, electronics and automotive markets.

[0004] An acid based process to extract alumina from rich silica ore is known. A process intermediate product, in the form of a concentrated aluminum chloride solution, is crystallized to produce aluminum chloride hexahydrate (ACH) crystals. The ACH can be thermally decomposed to produce γ-alumina that once calcined is converted into corundum (α-alumina) at a higher temperature (about 1200°C). Here, the transformation stages into γ-alumina and a-alumina are respectively called decomposition and calcination.

[0005] The decomposition reaction is highly endothermic (ΔΗ(28Κ) = +996.03 kJ/mol Al₂0₃) and the calcination reaction is slightly exothermic (ΛΗ298Κ) = -18.28 kJ/mol Al₂0₃. Both reactions occur at high temperatures which means that to maintain the reactor conditions, especially for the decomposition step, a large amount of energy is used.

[0006] The decomposition reaction produces a gaseous mixture of HCI and water. As a result, attention is given to the design of the decomposer. Materials that can resist the high temperature and highly corrosive nature of the generated gas may be used for equipment construction. Such choice of material can, for example, cause a direct increase of the equipment capital cost.

[0007] Incomplete decomposition (presence of residual chlorine (for example in the form of polyaluminum chlorides) in the product leaving the decomposer) results in the generation of water and HCI gas in the calciner (or other subsequent equipment that operates at high temperature). This situation implies that the calciner may be built to resist to the corrosive gas or a second decomposer is used to remove the remaining chlorine before feeding it to the calciner. Complete decomposition of ACH crystals may, for example result in less challenges in material selection for calciner construction.

[0008] The type of gas that occupies the reaction chamber may have an influence on the reaction kinetics. When the reaction is carried out in a direct fired reactor, the environment is occupied with a nitrogen-rich combustion flue gas and minor contents of HCI as well as water that are derived from fuel combustion and the decomposition reaction. When inert gases such as nitrogen are used to sweep the decomposition gases, the chlorine content left in the decomposed material is as high as about 1 .4 to about 3.8 wt% at a temperature of about 600 °C to about 900 °C for a relatively long residence time of two hours. In addition, in directly fired decomposers the hydrogen chloride concentration in the gas phase may be lowered by the addition of the combustion product. Consequently, larger scrubbing equipment is used to recover the hydrogen chloride and to remove heat from the off gas. [0009] It would thus be desirable to be provided with a process for producing alumina that would at least partially solve one of the problems mentioned or that would be an alternative to the known processes for producing alumina.

[0010] Therefore according to an aspect of the present disclosure, there is provided a process for decomposing AICl3*6H₂0 into γ-ΑΙ₂03, the process comprising heating the AICI₃*6H₂0 at a temperature of about 600°C to about 900°C in the presence of steam and optionally at least one gas, under conditions suitable to obtain the γ-ΑΙ₂03.

[001 1 ] Therefore according to another aspect of the present disclosure, there is provided a process for decomposing AICl3*6H₂0 into γ-ΑΙ₂03, the process comprising heating the AICI₃*6H₂0 at a temperature of about 600°C to about 850°C in the presence of steam and optionally at least one gas, under conditions suitable to obtain the γ-ΑΙ₂0₃.

[0012] Therefore according to another aspect of the present disclosure, there is provided a process for decomposing AICl3'6H₂0 into γ-ΑΙ₂0₃, the process comprising heating the AICI₃*6H₂0 at a temperature of about 600°C to about 800°C in the presence of steam and optionally at least one gas, under conditions suitable to obtain the γ-ΑΙ₂0₃.

[0013] Therefore according to another aspect of the present disclosure, there is provided a process for decomposing AiC *6H₂0 into γ-ΑΙ₂0₃, the process comprising heating the AICI₃ ^«6H₂0 at a temperature of about 600°C to about 800°C in the presence of steam and optionally at least one gas chosen from air, argon, nitrogen, carbon dioxide, hydrogen and hydrochloric acid, under conditions suitable to obtain the γ-ΑΙ₂0₃.

[0014] The processes of the present disclosure may improve the process of alumina production from thermal decomposition of ACH crystals in comparison to known processes for preparing alumina, for example in that: γ-alumina is obtained at a lower temperature (about 600°C to about 800°C) with steam instead of about 900°C as for conventional alumina processes with an air medium. Having the reactor at a lower temperature may lead to less energy consumption.

[0015] When using the processes of the present disclosure, the content of residual chlorine drops to less than few hundred ppm. Therefore, subsequent equipment may not, for example require a special design regarding construction material when corrosion is taken into account. When a smelter grade alumina is produced for an aluminum metal production purpose, complete decomposition in a single reactor rather than two consectuvie ones may, for example, eliminate the necessity of a second decomposer and therefore decrease the capital cost to design, manufacture and operate the equipment. In a single reactor, the processes can be carried out in a single step or in more than one step. According to another example, the decomposition can be carried out in two different recators or decomposers or in a plurality thereof.

[0016] The off gas mainly contains hydrogen chloride and steam that may, for example be treated easily in the scrubbing plant since both gases are easily condensed/absorbed by water. In traditional approaches, the presence of inert gases or exhaust gas reduces the concentration of hydrogen chloride and steam in the off gas and the efficiency of the absorption process may, for example be decreased due to mass transfer limitations. The presence of a large quantity of exhaust gas may also, for example use more cooling agent in the scrubbing system.

[0017] For example, off gases containing chlorine (for example in the form of HCI) can be condensed/absorbed and reused in the alumina preparation plant either at the leaching/digestion or at ACH precipitation, crystallization, or preparation thereof.

[0018] In the following drawings, which represent by way of example only, various embodiments of the disclosure : [0019] Figure 1 is a plot showing the results of differential scanning calorimetry as a function of temperature for ACH crystals heated under an argon atmosphere at a heating rate of 10°C/min according to another comparative example for the processes of the present disclosure in comparison to ACH crystals heated under a steam atmosphere at a heating rate of 10°C/min according to an example of the processes of the present disclosure;

[0020] Figure 2 is a plot showing the results of thermogravimetric analysis as a function of temperature for ACH crystals heated under an argon atmosphere at a heating rate of 10°C/min according to another comparative example for the processes of the present disclosure in comparison to ACH crystals heated under a steam atmosphere at a heating rate of 10°C/min according to an example of the processes of the present disclosure;

[0021] Figure 3 is a plot showing an enlarged verion of the area indicated with a circle in the results of thermogravimetric analysis shown in Figure 2;

[0022] Figure 4 is a plot showing the chlorine content (wt%) as a function of temperature (°C) for samples of amorphous alumina heated at various temperatures while sweeping with air or nitrogen gas according to another comparative example for the processes of the present disclosure compared to samples of amorphous alumina heated at various temperatures while sweeping with steam or a mixture of steam and air according to another example of the processes of the present disclosure;

[0023] Figure 5 is a plot showing the chlorine content (wt%) and morphology as a function of temperature (°C) for samples of amorphous alumina heated at various temperatures while sweeping with air or nitrogen gas according to another comparative example for the processes of the present disclosure compared to samples of amorphous alumina heated at various temperatures while sweeping with steam according to another example of the processes of the present disclosure; and [0024] Figure 6 is a plot showing the results of differential scanning calorimetry as a function of temperature for ACH crystals heated under an argon atmosphere at a heating rate of 10°C/min according to another comparative example for the processes of the present disclosure in comparison to ACH crystals heated under an environment comprising 6 % of steam in argon at a heating rate of 10°C/min according to an example of the processes of the present disclosure.

[0025] The term "suitable" as used herein means that the selection of the particular conditions would depend on the specific manipulation or operation to be performed, but the selection would be well within the skill of a person trained in the art. All processes described herein are to be conducted under conditions sufficient to provide the desired product quality. A person skilled in the art would understand that all reaction conditions, including, when applicable, for example, reaction time, reaction temperature, reaction pressure, reactant ratio, flow rate, reactant purity, and the type of reactor used can be varied to optimize the yield of the desired product and it is within their skill to do so.

[0026] In understanding the scope of the present disclosure, the term

"comprising" and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, "including", "having" and their derivatives. The term "consisting" and its derivatives, as used herein, are intended to be closed terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The term "consisting essentially of, as used herein, is intended to specify the presence of the stated features, elements, components, groups, integers, and/or steps as well as those that do not materially affect the basic and novel characteristic(s) of features, elements, components, groups, integers, and/or steps. [0027] Terms of degree such as "about" and "approximately" as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms of degree should be construed as including a deviation of ±10% of the modified term if this deviation would not negate the meaning of the word it modifies.

[0028] The terms "smelter grade alumina" or "SGA" as used herein refer to a grade of alumina that may be useful for processes for preparing aluminum metal. Smelter grade alumina typically comprises, for example, α-ΑΙ₂0₃ in an amount of less than about 5 wt%, based on the total weight of the smelter grade alumina. The terms "high purity alumina" or "HPA" as used herein refer to a grade of alumina that comprises alumina in an amount of 99 wt% or greater, based on the total weight of the high purity alumina.

[0029] The expression "transition alumina" as used herein refers to a polymorphic form of alumina other than a-alumina. For example, the transition alumina can be χ-ΑΙ₂0₃, κ-ΑΙ₂0₃, γ-ΑΙ₂0₃, θ-ΑΙ₂0₃, δ-ΑΙ₂0₃, η-ΑΙ₂0₃, ρ-ΑΙ₂0₃ or combinations thereof.

[0030] The expression "amorphous alumina" as used herein refers to a non-crystalline alumina that lacks the long-range order characteristic of a crystal.

[0031] The below presented examples are non-limitative and are used to better exemplify the processes of the present disclosure.

[0032] In the processes of the present disclosure, the AICI₃*6H₂0 may be heated optionally in the presence of air. For example, the air may be delivered to a reaction chamber in which the AICI₃ ^«6H₂0 is heated via an air stream. It will be appreciated by a person skilled in the art that AICI₃ ^»6H₂0 crystals may contain organics, for example, organics derived from an ore used to prepare the AICI₃'6H₂0 crystals. The optional air may be useful to oxidize such organic molecules. The optional air may also be used to dilute the steam concentration and thereby may inhibit or prevent the condensation of steam at an inlet and/or an outlet of the reactor. The relative concentration of air and steam may, for example, alter other conditions useful for the decomposition reaction. For example, a process wherein higher amounts of air are used to dilute the steam will typically use higher temperatures and/or longer residence times.

[0033] For example, the at least one gas can be chosen from air, argon, nitrogen, carbon dioxide, hydrogen and hydrochloric acid.

[0034] For example, the steam can be present in an amount that is at least a catalytic amount. For example, the steam can be present in an amount of at least about 5 wt%. For example, the steam can be present in an amount of at least about 6 wt%. For example, the steam can be present in an amount of at least about 10 wt%. For example, the steam can be present in an amount of at least about 15 wt%. For example, the steam can be present in an amount of at least about 25 wt%. For example, the steam can be present in an amount of at least about 35 wt%. For example, the steam can be present in an amount of at least about 45 wt%. For example, the steam can be present in an amount of at least about 55 wt%. For example, the steam can be present in an amount of at least about 65 wt%. For example, the steam can be present in an amount of at least about 70 wt%. For example, the steam can be present in an amount of at least about 75 wt%. For example, the steam can be present in an amount of at least about 80 wt%. For example, the steam can be present in an amount of at least about 85 wt%. For example, the steam can be present in an amount of at least about 90 wt%. For example, the steam can be present in an amount of at least about 95 wt%. For example, the steam can be present in an amount of about 5 wt% to about 95 %.

[0035] For example, the AICI₃ ^»6H₂0 can be heated in the presence of steam and the at least one gas. For example, the steam can be present in an amount of about 80 wt% to about 90 wt% and the at least one gas can be present in an amount of about 10 wt% to about 20 wt%, based on the total weight of the steam and the at the least one gas . For example, the steam can be present in an amount of about 82 wt% to about 88 wt% and the at least one gas can be present in an amount of about 12 wt% to about 18 wt%, based on the total weight of the steam and the at least one gas . For example, the steam can be present in an amount of about 85 wt% and the at least one gas can be present in an amount of about 15 wt%, based on the total weight of the at least one gas .

[0036] In the studies of the present disclosure, it was observed that decomposition of AICI₃ ^»6H₂0 into γ-ΑΙ₂0₃ in the presence of steam and optionally air in a single step reactor may be achieved at temperatures as low as about 600°C. At a temperature of about 600°C, the reaction takes a longer time to reach completion than when the AICI₃*6H₂0 is heated at higher temperatures. For example, it is possible to heat the AICI₃*6H₂0 at a temperature of at least about 700°C. It will be appreciated by a person skilled in the art that heating the AICI₃*6H₂0 at elevated temperatures, for example above about 800°C, will typically use more energy than heating at lower temperatures.

[0037] Accordingly, for example, the AICI₃ ^»6H₂0 can be heated at a temperature of about 650°C to about 800°C. For example, the AICI₃ ^«6H₂0 can be heated at a temperature of about 700°C to about 800°C. For example, the AICI₃ ^«6H₂0 can be heated at a temperature of about 700°C to about 750°C. For example, the AICI₃'6H₂0 can be heated at a temperature of about 700°C.

[0038] For example, the AICI₃ ^«6H₂0 can be heated at the temperature for a time of less than about 5 hours. For example, the Α ₃·6Η₂0 can be heated at the temperature for a time of less than about 4 hours. For example, the AICI₃'6H₂0 can be heated at the temperature for a time of less than about 3 hours. For example, the AICI₃*6H₂0 can be heated at the temperature for a time of less than about 2 hours. For example, the AICI₃ ^«6H₂0 can be heated at the temperature for a time of less than about 1 hour. For example, the AICI₃ ^«6H₂0 can be heated at the temperature for a time of less than about 45 minutes. For example, the AICI₃ ^«6H₂0 can be heated at the temperature for a time of less than about 40 minutes. For example, the AICI₃ ^«6H₂0 can be heated at the temperature for a time of less than about 30 minutes. [0039] For example, the steam can be provided at a rate of from about

0.0001 grams to about 2 grams of steam per gram of AICI₃ ^«6H₂0, per minute. For example, the steam can be provided at a rate of from about 0.001 grams to about 2 grams of steam per gram of AICI₃'6H₂0, per minute. For example, the steam can be provided at a rate of from about 0.01 grams to about 2 grams of steam per gram of AICI₃*6H₂0, per minute. For example, the steam can be provided at a rate of from about 0.05 grams to about 1 gram of steam per gram of AICI₃*6H₂0, per minute. For example, the steam can be provided at a rate of from about 0.05 grams to about 0.5 grams of steam per gram of AICI₃*6H₂0, per minute.

[0040] For example, the steam can be introduced at a ratio of mass of steam introduced to mass of γ-ΑΙ₂0₃ obtained of about 0.001 :1 to about 100:1. For example, the steam can be introduced at a ratio of mass of steam introduced to mass of γ-ΑΙ₂0₃ obtained of about 0.01 :1 to about 100:1. For example, the steam can be introduced at a ratio of mass of steam introduced to mass of γ-ΑΙ₂0₃ obtained of about 0.1 :1 to about 100:1. For example, the steam can be introduced at a ratio of mass of steam introduced to mass of γ-ΑΙ₂0₃ obtained of about 1 :1 to about 50:1. For example, the steam can be introduced at a ratio of mass of steam introduced to mass of γ-ΑΙ₂0₃ obtained of about 10:1 to about 50:1. For example, the steam can be introduced at a ratio of mass of steam introduced to mass of γ- Al₂0₃ obtained of about 10:1 to about 30:1 .

[0041] Alternatively, for example, the heating of the AICI₃ ^«6H₂0 at the temperature can be carried out in a chamber in the presence of the steam and optionally the at least one gas, and the steam and optionally the at least one gascan be released from the chamber after the γ-ΑΙ₂0₃ is obtained. For example, the heating of the AICI₃ ^«6H₂0 at the temperature can be carried out in a chamber, the steam and optionally the at least one gas can be introduced into the chamber prior to the heating at the temperature, and the steam and optionally the at least one gas can be released from the chamber after the γ-ΑΙ₂0₃ is obtained.

[0042] For example, the decomposition of the AICI₃ ^«6H₂0 into the γ-ΑΙ₂0₃ can be carried out in the presence of superheated steam. For example, the steam can be introduced into the process as saturated steam, water or a mixture thereof.

[0043] In the processes of the present disclosure, heating the reactor indirectly will typically lead to higher concentrations of HCI in the off gas and may therefore reduce contamination of the product γ-ΑΙ₂03. However, it is also useful to heat the reactor directly, for example, where it is not as important that the product γ-ΑΙ₂0₃ has low amounts of contamination.

[0044] Accordingly, for example, the AICI₃*6H₂0 can be heated indirectly. Alternatively, for example, the AICI₃*6H₂0 can be heated directly.

[0045] In the processes of the present disclosure, the decomposition of AICI₃'6H₂0 into γ-ΑΙ₂0₃ can be carried out in a single heating step in a single reactor. This may, for example, decrease capital cost for design and manufacture.

[0046] Accordingly, for example, the decomposition of the AICI₃ ^«6H₂0 to the γ-ΑΙ₂0₃ can be carried out in a single step.

[0047] In the processes of the present disclosure, the thermal decomposition of AICI₃ ^«6H₂0 to obtain γ-ΑΙ₂0₃ can be carried out in any type of reactor that can provide suitable conditions for heating the AICI₃ ^«6H₂0 at a desired temperature, for example a temperature of about 600°C to about 800°C, in the presence of steam and optionally the at least one gas to obtain the γ- Al₂0₃. A variety of known reactors can provide suitable conditions, the selection of which for a particular process can be made by a person skilled in the art.

[0048] For example, the process can be carried out in a fluidized bed reactor. For example, the process can be carried out in a rotary kiln reactor. For example, the process can be carried out in a pendulum kiln reactor. For example, the process can be carried out in a tubular oven.

[0049] The selection of a suitable source of Α ₃·6Η₂0 for the process of the present disclosure can be made by a person skilled in the art.

[0050] For example, the AICI₃'6H₂0 can be derived from an aluminum- containing-material.

[0051] For example, the aluminum-containing-material can be SGA, ACH, aluminum, red mud, fly ashes etc.

[0052] For example, the AICI₃ ^«6H₂0 can be derived from an aluminum- containing ore.

[0053] For example, the aluminum-containing ore can be a silica-rich, aluminum-containing ore. For example, the aluminum-containing ore can be an aluminosilicate ore. For example, the AICI₃'6H₂0 can be derived from the aluminum-containing ore by an acid-based process. For example, the AICI₃ ^«6H₂0 can be obtained by dissolving of aluminum, alumina or aluminum hydoxide in HCI. For example, the AICl3*6H₂0 can have a particle size distribution D50 of about 100 μιτι to about 1000 pm or of about 100 pm to about 5000 μητι. For example, the AICl3'6H₂0 can have a particle size distribution D50 of about 200 μιη to about 800 pm. For example, the AICI₃ ^»6H₂0 can have a particle size distribution D50 of about 300 pm to about 700 pm.ln the studies of the present disclosure, heating AICI₃*6H₂0 at temperatures of about 600°C to about 800°C in the presence of steam and optionally the at least one gas was found to result in the production of γ-ΑΙ₂0₃ having a significantly lower residual chlorine content than the γ-ΑΙ₂0₃ obtained by heating AICI₃*6H₂0 at this temperature range in the presence of the at least one gas (without addition of steam) or nitrogen. γ-ΑΙ₂0₃ having a lower level of impurities may be useful in processes for producing smelter grade alumina and processes for producing high purity alumina, as well as fused aluminas and specialty aluminas. [0054] For example, the γ-ΑΙ₂0₃ can contain less than about 1500 ppm by weight chlorine. For example, the γ-ΑΙ₂0₃ can contain less than about 1000 ppm by weight chlorine. For example, the γ-ΑΙ₂0₃ can contain less than about 750 ppm by weight chlorine. For example, the γ-ΑΙ₂0₃ can contain less than about 500 ppm by weight chlorine. For example, the γ-ΑΙ₂0₃ can contain less than about 400 ppm by weight chlorine. For example, the γ-ΑΙ₂0₃ can contain less than about 200 ppm by weight chlorine. For example, the γ-ΑΙ₂0₃ can contain less than about 100 ppm by weight chlorine. For example, the γ-ΑΙ₂0₃ can contain less than 50 ppm by weight chlorine.

[0055] It will be appreciated by a person skilled in the art that the γ-ΑΙ₂0₃ obtained from the processes of the present disclosure may be suitable for various uses, for example, uses wherein a low residual chlorine content is useful. For example, the γ-ΑΙ₂03 can be suitable for use in a process for preparing smelter grade alumina (SGA). For example, the γ-ΑΙ₂0₃ can be smelter grade alumina (SGA). For example, the γ-ΑΙ₂0₃ can be suitable for use in a process for calcining the γ-ΑΙ₂0₃ to obtain high purity alumina (HPA). For example, the γ-ΑΙ₂0₃ can also be suitable for use in a process for converting the γ-ΑΙ₂0₃ to obtain speciality aluminas or fused aluminas.

[0056] The off gases released by the processes of the present disclosure mainly comprise hydrogen chloride and steam.

[0057] For example, the off gases can be recycled and reused in the aluminum chlorides extraction process and/or the AICI₃.6H₂0 crystals extraction and purification process. For example, off gases containing chlorine (for example in the form of HCI) can be condensed/absorbed and reused in the alumina preparation plant either at the leaching/digestion or at ACH precipitation, crysrtallization, or preparation thereof.

[0058] Accordingly, for example, the process can release an off gas comprising hydrogen chloride and steam. For example, the composition of the off gas can be substantially hydrogen chloride and steam. It will be appreciated by a person skilled in the art that hydrogen chloride gas and steam are easily condensed and/or absorbed by water. Accordingly, for example, the process can further comprise treating the off gas in a scrubbing unit, wherein in the scrubbing unit, the hydrogen chloride and steam are condensed and/or absorbed by water and/or recycling and reusing the off gas in the aluminum chloride extraction process and/or the AICI3.6H2O crystals extraction and purification process. For example, off gases containing chlorine (for example in the form of HCI) can be condensed/absorbed and reused in the alumina preparation plant either at the leaching/digestion or at ACH precipitation, crysrtallization, or preparation thereof.

[0059] For example, the processes of the present disclosure can be useful for preparing SGA.

[0060] For example, the processes of the present disclosure can further comprise treating the γ-ΑΙ₂0₃ in order to obtain HPA, fused alumina, transition alumina, tabular alumina, calcined alumina, ultra-pure alumina or specialty alumina. Such treatments can comprise, for example, heating (such as calcination, plasma torch treatment), forming (such as pressure, compacting, rolling, grinding, compressing, spheronization, peptization, densification).

[0061] For example, such fused alumina and and specialty alumina can be used for various applications.

[0062] The following examples are non-limitative and are used to better exemplify the processes of the present disclosure:

EXAMPLES

Example 1

I. Methods and Results

[0063] Several experiments have been carried out at the bench scale. Decomposition was carried out inside a tube furnace under nitrogen, air, steam and a mixture of air and steam environments. The residual chlorine content was measured and the crystalline structure was investigated (Table 1 ). [0064] The tools to run the experiments were two tube furnaces, a rotary kiln, a scrubbing unit, a nitrogen cylinder, a compressed air cylinder, a pH meter, and a steam generator.

[0065] The tools/techniques used to analyze the samples were inductively coupled plasma mass spectrometry (ICP-MS).

[0066] The residence time at the above temperatures depended on the temperature. In each of the trials, over an about 10 hour period, the samples were heated at a rate of 240°C/hour until the desired temperature was reached, the temperature was substantially maintained at this temperature for the relevant time then cooled at a rate of 180°C/hour until room temperature was reached. For example, residence time at 500°C was about 6 hours, residence time at 600°C was about 5.5 hours, residence time at 700°C was about 5 hours, and residence time at 800°C was about 4 hours. As can be seen from the results in Table 1 , the reaction temperature can be decreased as low as 600°C. The reaction at 600°C takes a long time and, therefore, it is useful to carry out the process at >700°C. The content of residual chlorine in the alumina produced in the process with a steam environment is significantly smaller than the residual chlorine content of the alumina produced in the processes with an air or nitrogen environment.

II. Discussion

[0067] The operation of the decomposer at high temperatures and the content of unreacted ACH are two concerns in the known methods for the production of transition alumina or alumina from ACH crystals. [0068] Processes comprising the thermal decomposition of ACH crystals in a steam or steam and air environment at a reduced temperature are disclosed herein. The complete decomposition of ACH crystals occurs in a single reactor at a lower temperature than for other types of atmospheric media. Another advantage of the processes of the present disclosure is that the off gas contains a negligible amount of inert gas which may simplify the design of a scrubbing section associated to the decomposer or allow for the off gas to be recycled and reused in the aluminum chloride extraction process and/or the AICI₃.6H₂0 crystals extraction and purification process. For example, off gases containing chlorine (for example in the form of HCI) can be condensed/absorbed and reused in the alumina preparation plant either at the leaching/digestion or at ACH precipitation, crystallization, or preparation thereof.

[0069] The complete decomposition occurs at reduced temperatures (as low as 600°C compared to 900°C typically) and unreacted ACH content decreases to less than a few hundred ppm. As the chlorine content drops to a very small level, it may, for example, reduce the potential corrosion which may occur in subsequent equipment.

[0070] Instead of reaction in the steam environment, known processes for the preparation of alumina may comprise the decomposition of ACH crystals carried out in the presence of other gases such as air, hydrogen or nitrogen. The use of hydrogen may, for example increase the operational cost due to consumption of hydrogen as well as treatment of the off gas. Its usage is also, for example associated with stricter codes and standards for the process and equipment design which may, for example increase the capital cost and/or the potential safety issues. The decomposition reaction in an environment of air or nitrogen occurs at higher temperatures (at least about 800°C) and the content of residual chlorine in the product may, for example be relatively higher than the chlorine content in alumina which is produced in the presence of steam. To produce alumina which contains a low content of residual chlorine, in an air environment, the reaction uses very high temperatures (about 900-1000°C). A high level of residual chlorine content may, for example result in corrosion inside the subsequent equipment over a long time period if the process is operated at high temperatures (for example inside a calciner to obtain corundum). Residual chlorine is also problematic, for example when the alumina is used in the Hall process for aluminum metal production. In addition, a low chlorine content may, for example be desired for high quality alumina refractories, fused alumina or other such uses of alumina.

Example 2

[0071] ACH crystals were analyzed by thermogravimetric analysis (TGA) and by differential scanning calorimetry (DSC) under an argon atmosphere, heated at a rate of 10.0°C per minute as compared to a steam environment under the same conditions. As can be seen from Figure 1 , the temperature for the transition to both γ-ΑΙ₂0₃ and α-ΑΙ₂0₃ occurs at a lower temperature for the ACH crystals heated under a steam atmosphere (γ-ΑΙ₂0₃. peak at 771 °C; u-AI₂0₃: peak at 1 188°C) in comparison to the ACH crystals heated under an argon atmosphere (γ-ΑΙ₂0₃: peak at 862°C; α-ΑΙ₂0₃: peak at 1243°C) at the same heating rate.

[0072] ACH crystals were also analyzed by TGA under a steam atmosphere, heating at a rate of 10°C/minute. Figure 2 shows a comparison between the TGA curves for ACH crystals heated under the steam atmosphere to ACH crystals heated under an argon atmosphere under similar conditions. Figure 35 shows an enlarged version of the area indicated with a circle in Figure 2.

[0073] As can be seen in Figure 3, the ACH crystals heated under an argon atmosphere show additional weight loss (about 3-4 wt%) in a temperature region wherein the ACH crystals heated under a steam atmosphere do not show weight loss. While not wishing to be limited by theory, the weight loss in this region of the ACH crystals heated under an argon atmosphere is chlorine which was present before loss from the sample in the form of polyaluminum chlorides. The end of the decomposition for the ACH crystals heated under a steam atmosphere was at about 750°C whereas the end of the decomposition for the ACH crystals heated under an argon atmosphere was at about 1200°C. The experiments also showed that under a steam atmosphere the "drastic loss of mass" during the transition from the γ-ΑΙ₂0₃ phase is not observed (see the loss of residual chlorine when decomposition is carried out under an argon atmosphere).

Example 3

[0074] About 20 grams of amorphous alumina was heated in a crucible in a furnace at various temperatures. Figure 4 shows various results obatined while sweeping with nitrogen gas, air, steam or a combination of steam and air. Steam has been introduced at a rate of 3.62 ± 0.45 grams/minute.

[0075] Figure 4 shows the results for the experiments with nitrogen gas. As can be seen in Figure 4, the amorphous alumina used had a chlorine content of about 3.8 wt%. After the amorphous alumina was heated for the high residence time used for the temperature of 500°C there was still between 3-4 wt% chlorine present in the sample. As the temperature increased, the chlorine content after heating decreased but was still significant for the temperature of 900°C. Proper granular flow may help to increase the capacity but not the chlorine content.

[0076] Figure 4 also shows the results for the experiments with air compared to the results of the experiments with nitrogen gas. As can be seen in Figure 4, the amorphous alumina for the experiments with air had a chlorine content of about 3.5 wt%. In comparison to the experiments conducted with nitrogen, the samples heated with air had a lower chlorine content. After heating the amorphous alumina at a temperature of 800°C while sweeping with air, the chlorine content was 2000 ppm by weight (0.2 wt%). After heating the amorphous alumina at a temperature of 1200°C while sweeping with air, the chlorine content was less than 150 ppm by weight. Figure 4 also shows the results for the experiments with steam compared to the results of the experiments with air and nitrogen gas. As can be seen in Figure 4, the amorphous alumina for the experiments with air had a chlorine content of about 3.2 wt%. In comparison to the experiments conducted with nitrogen or air, the samples heated with steam had a lower chlorine content. For example, the presence of steam decreases the chlorine content to 500 ppm by weight (0.05 wt%) after heating at a temperature of 600°C.

[0077] Figure 4 shows the results for the experiments with steam and air (air: 15 ± 1 wt%) compared to the results of the experiments with air, nitrogen gas and steam (without air). In comparison to the experiments conducted with nitrogen or air, the samples heated with steam and air had a lower chlorine content. For example, the presence of steam and air decreases the chlorine content to 300 ppm by weight (0.03 wt%) after heating at a temperature of 600°C.

[0078] Figure 5 shows the results for the above-described experiments with steam compared to the results for the above-described experiments with air and nitrogen, labeled to indicate the results of crystalline structure analysis (XRD). As can be seen from Figure 5, for the experiments with nitrogen, the sample remained amorphous after heating at 700°C but after heating at 800°C and 900°C, γ-ΑΙ 0₃ was obtained. For the experiments with air, the sample remained amorphous after heating at 700°C but after heating at 750°C, γ-ΑΙ₂0₃ was obtained. For the experiments with steam, the sample remained amorphous after heating at 500°C but after heating at 600°C, γ-ΑΙ₂0₃ was obtained and after heating at 1200°C, sharp peaks corresponding to α-ΑΙ₂0₃ were observed.

Example 4

[0079] ACH crystals were analyzed by differential scanning calorimetry (DSC) as described in Example 2, with the exception that the comparison was made between conditions under an argon atmosphere and conditions under an environement comprising argon and 6 % of steam. As can be seen from Figure 6, the temperature for the transition to both γ-ΑΙ₂0₃ and α-ΑΙ 0₃ occurs at a lower temperature for the ACH crystals heated under an environment comprising 6 % os team and argon (γ-ΑΙ₂0₃: peak at 776.5°C; α-ΑΙ₂0₃: peak at 1169.5°C) in comparison to the ACH crystals heated under an argon atmosphere (γ-ΑΙ₂0₃: peak at 862.3°C; α-ΑΙ₂0₃: peak at 1243°C) at the same heating rate.

[0080] While a description was made with particular reference to the specific embodiments, it will be understood that numerous modifications thereto will appear to those skilled in the art. Accordingly, the above description and accompanying drawings should be taken as specific examples and not in a limiting sense.

[0081] All publications, patents and patent applications are herein incorporated by reference in their entirety to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference in its entirety. Where a term in the present disclosure is found to be defined differently in a document incorporated herein by reference, the definition provided herein is to serve as the definition for the term.

Claims

WHAT IS CLAIMED IS:

1. A process for decomposing AICI₃*6H₂0 into γ-ΑΙ₂0₃, said process comprising heating said ΑΙΟΙ₃·6Η₂0 at a temperature of about 600°C to about 800°C in the presence of steam and optionally at least one gas chosen from air, argon, nitrogen, carbon dioxide, hydrogen and hydrochloric acid, under conditions suitable to obtain said γ-ΑΙ₂0₃.

2. The process of claim 1 , wherein said AICI₃'6H₂0 has a particle size distribution D50 of about 100 pm to about 5000 pm.

3. The process of claim 1 , wherein said AICI₃'6H₂0 has a particle size distribution D50 of about 100 pm to about 1000 pm.

4. The process of claim 1 , wherein said AICI₃*6H₂0 has a particle size distribution D50 of about 200 pm to about 800 pm.

5. The process of claim 1 , wherein said AICI₃ ^«6H₂0 has a particle size distribution D50 of about 300 pm to about 700 pm.

6. The process of any one of claims 1 to 5, wherein said AICI₃ ^«6H₂0 is heated at a temperature of about 650°C to about 800°C.

7. The process of any one of claims 1 to 5, wherein said AICl3*6H₂0 is heated at a temperature of about 700°C to about 800°C.

8. The process of any one of claims 1 to 5, wherein said AICI₃'6H₂0 is heated at a temperature of about 700°C to about 750°C.

9. The process of any one of claims 1 to 5, wherein said AICI₃ ^«6H₂0 is heated at a temperature of about 700°C.

10. The process of any one of claims 1 to 9, wherein said AICI₃ ^»6H₂0 is heated at said temperature for a time of less than about 5 hours.

1 1 . The process of any one of claims 1 to 9, wherein said AICI₃*6H₂0 is heated at said temperature for a time of less than about 4 hours.

12. The process of any one of claims 1 to 9, wherein said AICI₃ ^»6H₂0 is heated at said temperature for a time of less than about 3 hours.

13. The process of any one of claims 1 to 9, wherein said AICI₃ ^«6H₂0 is heated at said temperature for a time of less than about 2 hours.

14. The process of any one of claims 1 to 9, wherein said AICI₃ ^«6H₂0 is heated at said temperature for a time of less than about 1 hour.

15. The process of any one of claims 1 to 9, wherein said AICI₃*6H₂0 is heated at said temperature for a time of less than about 45 minutes.

16. The process of any one of claims 1 to 9, wherein said AICI₃ ^«6H₂0 is heated at said temperature for a time of less than about 40 minutes.

17. The process of any one of claims 1 to 9, wherein said AICI₃*6H₂0 is heated at said temperature for a time of less than about 30 minutes.

18. The process of any one of claims 1 to 17, wherein said steam is provided at a rate of from about 0.0001 grams to about 2 grams of steam per gram of AICI₃ ^«6H₂0, per minute.

19. The process of any one of claims 1 to 17, wherein said steam is provided at a rate of from about 0.001 grams to about 2 grams of steam per gram of AICI₃'6H₂0, per minute.

20. The process of any one of claims 1 to 17, wherein said steam is provided at a rate of from about 0.01 grams to about 2 grams of steam per gram of AICI₃*6H₂0, per minute.

21 . The process of any one of claims 1 to 17, wherein said steam is provided at a rate of from about 0.05 grams to about 1 gram of steam per gram of AICI₃*6H₂0, per minute.

22. The process of any one of claims 1 to 17, wherein said steam is provided at a rate of from about 0.05 grams to about 0.5 grams of steam per gram of AICI₃ ^»6H₂0, per minute.

23. The process of any one of claims 1 to 17, wherein said steam is introduced at a ratio of mass of steam introduced to mass of γ-ΑΙ₂0₃ obtained of about 0.001 : 1 to about 00: 1 .

24. The process of any one of claims 1 to 17, wherein said steam is introduced at a ratio of mass of steam introduced to mass of γ-ΑΙ₂0₃ obtained of about 0.01 :1 to about 100:1.

25. The process of any one of claims 1 to 17, wherein said steam is introduced at a ratio of mass of steam introduced to mass of γ-ΑΙ₂0₃ obtained of about 0.1 :1 to about 100:1.

26. The process of any one of claims 1 to 17, wherein said steam is introduced at a ratio of mass of steam introduced to mass of γ-ΑΙ₂0₃ obtained of about 1 : 1 to about 50: 1 .

27. The process of any one of claims 1 to 17, wherein said steam is introduced at a ratio of mass of steam introduced to mass of γ-ΑΙ₂0₃ obtained of about 10:1 to about 50: 1 .

28. The process of any one of claims 1 to 17, wherein said steam is introduced at a ratio of mass of steam introduced to mass of γ-ΑΙ₂0₃ obtained of about 10:1 to about 30:1.

29. The process of any one of claims 1 to 28, wherein said heating of said AICI₃ ^»6H₂0 at said temperature is carried out in a chamber in the presence of said steam and optionally said at least one gas chosen from air, argon, nitrogen, carbon dioxide, hydrogen and hydrochloric acid , and said steam and optionally said at least one gas chosen from air, argon, nitrogen, carbon dioxide, hydrogen and hydrochloric acid are released from said chamber after said γ-ΑΙ₂0₃ is obtained.

30. The process of any one of claims 1 to 28, wherein said heating of said AICI₃*6H₂0 at said temperature is carried out in a chamber, said steam and optionally said at least one gas chosen from air, argon, nitrogen, carbon dioxide, hydrogen and hydrochloric acid are introduced into said chamber prior to said heating at said temperature, and said steam and optionally said at least one gas chosen from air, argon, nitrogen, carbon dioxide, hydrogen and hydrochloric acid are released from said chamber after said γ-ΑΙ₂0₃ is obtained.

31 . The process of any one of claims 1 to 30, wherein said steam is present in at least a catalytic amount.

32. The process of any one of claims 1 to 30, wherein said steam is present in an amount of at least about 5 wt%.

33. The process of any one of claims 1 to 30, wherein said steam is present in an amount of at least about 15 wt%.

34. The process of any one of claims 1 to 30, wherein said steam is present in an amount of at least about 25 wt%.

35. The process of any one of claims 1 to 30, wherein said steam is present in an amount of at least about 35 wt%.

36. The process of any one of claims 1 to 30, wherein said steam is present in an amount of at least about 45 wt%.

37. The process of any one of claims 1 to 30, wherein said steam is present in an amount of at least about 55 wt%.

38. The process of any one of claims 1 to 30, wherein said steam is present in an amount of at least about 60 wt%.

39. The process of any one of claims 1 to 30, wherein said steam is present in an amount of at least about 65 wt%.

40. The process of any one of claims 1 to 30, wherein said steam is present in an amount of at least about 70 wt%.

41. The process of any one of claims 1 to 30, wherein said steam is present in an amount of at least about 75 wt%.

42. The process of any one of claims 1 to 30, wherein said steam is present in an amount of at least about 80 wt%.

43. The process of any one of claims 1 to 30, wherein said steam is present in an amount of at least about 85 wt%.

44. The process of any one of claims 1 to 43, wherein said AICl3*6H₂0 is heated in the presence of steam and said at least one gas chosen from air, argon, nitrogen, carbon dioxide, hydrogen and hydrochloric acid.

45. The process of claim 44, wherein said steam is present in an amount of about 80 wt% to about 90 wt% and said at least one gas chosen from air, argon, nitrogen, carbon dioxide, hydrogen and hydrochloric acid is present in an amount of about 10 wt% to about 20 wt%, based on the total weight of said steam and said at least one gas chosen from air, argon, nitrogen, carbon dioxide, hydrogen and hydrochloric acid .

46. The process of claim 44, wherein said steam is present in an amount of about 82 wt% to about 88 wt% and said at least one gas chosen from air, argon, nitrogen, carbon dioxide, hydrogen and hydrochloric acid is present in an amount of about 12 wt% to about 18 wt%, based on the total weight of said steam and said at least one gas chosen from air, argon, nitrogen, carbon dioxide, hydrogen and hydrochloric acid .

47. The process of claim 44, wherein said steam is present in an amount of about 85 wt% and said air is present in an amount of about 15 wt%, based on the total weight of said steam and said at least one gas chosen from air, argon, nitrogen, carbon dioxide, hydrogen and hydrochloric acid .

48. The process of any one of claims 1 to 47, wherein said process is carried out in a fluidized bed reactor.

49. The process of any one of claims 1 to 47, wherein said process is carried out in a rotary kiln reactor.

50. The process of any one of claims 1 to 47, wherein said process is carried out in a pendulum kiln reactor.

51 . The process of any one of claims 1 to 47, wherein said process is carried out in a tubular oven.

52. The process of any one of claims 1 to 51 , wherein said AICI₃'6H₂0 is heated indirectly.

53. The process of any one of claims 1 to 51 , wherein said AICI₃ ^«6H₂0 is heated directly.

54. The process of any one of claims 1 to 53, wherein said decomposition of said AICI₃ ^»6H₂0 into said γ-ΑΙ₂0₃ is carried out in a single step or multiple steps.

55. The process of any one of claims 1 to 54, wherein said decomposition of said AICI₃*6H₂0 into said γ-ΑΙ₂0₃ is carried out in the presence of superheated steam.

56. The process of any one of claims 1 to 55, wherein said steam is introduced into said process as saturated steam or water.

57. The process of any one of claims 1 to 56, wherein said AICI₃ ^«6H 0 is derived from an aluminum-containing ore or an aluminum-containing material.

58. The process of claim 57, wherein said aluminum-containing ore is a silica- rich, aluminum-containing ore.

59. The process of claim 58, wherein said aluminum-containing ore is an aluminosilicate ore.

60. The process of any one of claims 57 to 59, wherein said AICI₃ ^«6H₂0 is derived from said aluminum-containing ore by an acid-based process.

61 . The process of claim 57, wherein wherein AICI₃ ^«6H₂0 is derived from an aluminum-containing material that is ACH or SGA.

62. The process of any one of claims 1 to 60, wherein said AICI₃ ^«6H₂0 is obtained by dissolving aluminum, alumina and/or aluminum hydroxide into HCI.

63. The process of any one of claims 1 to 62, wherein said γ-ΑΙ₂0₃ contains less than about 1500 ppm by weight chlorine.

64. The process of any one of claims 1 to 62, wherein said γ-ΑΙ₂0₃ contains less than about 1000 ppm by weight chlorine.

65. The process of any one of claims 1 to 62, wherein said γ-ΑΙ₂0₃ contains less than about 750 ppm by weight chlorine.

66. The process of any one of claims 1 to 62, wherein said γ-ΑΙ₂0₃ contains less than about 500 ppm by weight chlorine.

67. The process of any one of claims 1 to 62, wherein said γ-ΑΙ₂0₃ contains less than about 400 ppm by weight chlorine.

68. The process of any one of claims 1 to 62, wherein said γ-ΑΙ₂0₃ contains less than about 200 ppm by weight chlorine.

69. The process of any one of claims 1 to 62, wherein said γ-ΑΙ₂0₃ contains less than about 100 ppm by weight chlorine.

70. The process of any one of claims 1 to 62, wherein said γ-ΑΙ₂0₃ contains less than about 50 ppm by weight chlorine.

71 . The process of any one of claims 1 to 70, wherein said γ-ΑΙ₂0₃ is suitable for use in a process for preparing smelter grade alumina (SGA).

72. The process of any one of claims 1 to 70, wherein said γ-ΑΙ₂03 is smelter grade alumina (SGA).

73. The process of any one of claims 1 to 70, wherein said γ-ΑΙ₂0₃ is suitable for use in a process for calcining said γ-ΑΙ₂0₃ to obtain high purity alumina (HPA).

74. The process of any one of claims 1 to 70, wherein said γ-ΑΙ₂0₃ is suitable for use in the manufacture of specialty alumina or fused alumina for raw material in refractories, ceramics shapes, grinding wheels, sandpaper, blasting media, metal preparation, laminates, coatings, lapping, polishing or grinding.

75. The process of any one of claims 1 to 70, wherein the process further comprises treating γ-ΑΙ₂0₃ in order to obtain HPA, fused alumina, transition alumina, tabular alumina, calcined alumina, ultra-pure alumina or specialty alumina.

76. The process of any one of claims 1 to 70, wherein the process further comprises treating γ-ΑΙ₂0₃ in order to obtain HPA, fused alumina, transition alumina, tabular alumina, calcined alumina, ultra-pure alumina or specialty alumina, and wherein said treating comprises heating (such as calcination, plasma torch treatment), or forming (such as pressure, compacting, rolling, grinding, compressing, spheronization, peptization, densification).

77. The process of any one of claims 1 to 76, wherein said process releases an off gas comprising hydrogen chloride and steam.

78. The process of claim 77, wherein said process further comprises treating said off gas in a scrubbing unit, wherein in said scrubbing unit, said hydrogen chloride and said steam are condensed and/or absorbed by water.

79. The process of claim 77, wherein off gases containing chlorine are condensed/absorbed and reused.

80. The process of claim 79, wherein said off gases are reused for leaching/digestion or for ACH precipitation, crystallization, or preparation thereof.

81. The process of any one of claims 77 to 80, wherein said process further comprises recycling hydrogen chloride so-produced.

82. The process of claim 77, wherein said process further comprises recycling hydrogen chloride so-produced and reusing it for the production of aluminum chloride.

83. The process of claim 77, wherein said hydrogen chloride is used for leaching a material and/or precipitating aluminum chloride.