Patent Publication Number: US-2013233130-A1

Title: Process for extracting aluminum from aluminous ores

Description:
TECHNICAL FIELD 
     The present disclosure relates to improvements in the field of chemistry applied to extraction of aluminum from aluminous ores. For example, such processes are useful for extracting aluminum from aluminous ores comprising various types of metals such as Fe, K, Mg, Na, Ca, Mn, Ba, Zn, Li, Sr, V, Ni, Cr, Pb, Cu, Co, Sb, As, B, Sn, Be, Mo, or mixtures thereof. 
     BACKGROUND OF THE DISCLOSURE 
     More than 96% of the alumina which is produced worldwide is obtained from bauxite, which is a mineral that is particularly rich in alumina (40-60%) and whose main suppliers are from Jamaica, Australia, Brazil, Africa and Russia. In certain areas of the world there are large quantities of aluminous ores, which are aluminosilicates (for example argillite, nepheline, etc.) that are relatively rich in alumina (20-28%). However such areas have received little attention up to now because the production costs for extracting aluminum from such ores remained too high. In these aluminous materials, and contrary to bauxite, aluminum oxide is associated with silicated or sulfated phases. Thus, the Bayer process cannot be used, which means that alternative treatments for the production of alumina must be used or developed. Various processes have been proposed so far in order to extract aluminum from such aluminous ores comprising aluminosilicates but there is still room for improvement or for alternative routes. 
     SUMMARY OF THE DISCLOSURE 
     According to one aspect, there is provided a process for extracting aluminum ions from argillite, the process comprising:
         leaching the argilite with HCl;   at least partially removing iron from the argillite by substantially selectively precipitating at least a portion of the iron ions by reacting the iron ions with a base so as to obtain an Al-rich composition or by substantially complexing the iron ions with an extracting agent; and   optionally purifying said Al-rich composition by:
           substantially selectively precipitating said aluminum ions;   by means of a hollow fiber membrane; or   by means of a liquid-liquid extraction.   
               

     According to another aspect, there is provided a process for extracting aluminum ions from argillite, the process comprising:
         leaching the argillite with HCl so as to obtain a composition comprising the aluminum ions and iron ions;   at least partially removing the iron ions from the composition by substantially selectively precipitating at least a portion of the iron ions by reacting the composition with a base and at least partially removing the precipitated iron ions so as to obtain an Al-rich composition; and   optionally purifying said Al-rich composition by:
           substantially selectively precipitating said aluminum ions;   by means of a hollow fiber membrane; or   by means of a liquid-liquid extraction.   
               

     According to another aspect, there is provided a process for extracting aluminum ions from an aluminous ore, the process comprising:
         leaching the aluminous ore with HCl;   at least partially removing iron from the aluminous ore by substantially selectively precipitating at least a portion of the iron ions by reacting the iron ions with a base so as to obtain an Al-rich composition or by substantially complexing the iron ions with an extracting agent; and   optionally purifying said Al-rich composition by:
           substantially selectively precipitating said aluminum ions;   by means of a hollow fiber membrane; or   by means of a liquid-liquid extraction.   
               

     According to another aspect, there is provided a process for extracting aluminum ions from an aluminous ore, the process comprising:
         leaching the aluminous ore with an acid so as to obtain a composition comprising the aluminum ions and iron ions;   at least partially removing the iron ions from the composition by substantially selectively precipitating at least a portion of the iron ions by reacting the composition with a base and at least partially removing the precipitated iron ions so as to obtain an Al-rich composition; and optionally purifying said Al-rich composition by:
           substantially selectively precipitating said aluminum ions;   by means of a hollow fiber membrane; or   by means of a liquid-liquid extraction.   
               

     According another aspect, there is provided a process for extracting aluminum ions from a mixture comprising iron ions and the aluminum ions. The process comprises recovering the aluminum ions from a composition comprising the aluminum ions, the iron ions, an organic solvent and an extracting agent adapted to form an organometallic complex substantially selectively with the iron ions or with the aluminum ions which is soluble in the organic solvent. 
     It was found that the processes of the present disclosure are effective for extracting aluminum from various aluminous ores. More particularly, it was found that such processes were efficient for extracting aluminum from ores having a considerable amount of iron such as argillite. Such processes were thus found to be an interesting alternative to the Bayer process. In fact, the Bayer process was found not to be efficient for extracting aluminum from certain ores such as ores having a high iron content (for example argillite). 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       In the following drawings, which represent by way of example only, various embodiments of the disclosure: 
         FIG. 1  shows a bloc diagram of a process according to one embodiment of a process for extracting aluminum from an aluminous ore. 
     
    
    
     DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS 
     The acid used for leaching the aluminous ore can be HCl, H 2 SO 4 , HNO 3  or mixtures thereof. More than one acid can be used as a mixture or separately. Solutions made with these acids can be used at various concentration. For example, concentrated solutions can be used. For example, 6 M or 12 M HCl can be used. For example, up to 100% wt H 2 SO 4  can be used. 
     The processes of the present disclosure can be effective for treating various aluminous ores or aluminum-bearing ores. For example, clays, argillite, mudstone, beryl, cryolite, garnet, spinel, bauxite, or mixtures thereof can be used as starting material. 
     The leaching can be carried out under pressure into an autoclave. For example, it can be carried out at a pressure of about 5 KPa to about 850 KPa, about 50 KPa to about 800 KPa, about 100 KPa to about 750 KPa, about 150 KPa to about 700 KPa, about 200 KPa to about 600 KPa, or about 250 KPa to about 500 KPa. The leaching can be carried out at a temperature of at least 80° C., at least 90° C., or about 100° C. to about 110° C. In certain cases, it can be done at higher temperatures. 
     The leaching can also be carried out under pressure. For example, the pressure can be about 100 to about 300 or about 150 to about 200 psig. The leaching can be carried out for about 30 minutes to about 5 hours. It can be carried out at a temperature of about 60° C. to about 200° C. 
     According to one embodiment, the process can comprise:
         leaching the argillite with HCl so as to obtain a leachate comprising the aluminum ions and the iron ions, and a solid residue;   separating the leachate from the solid residue;   at least partially removing the iron ions from the leachate by substantially selectively precipitating at least a portion of the iron ions by reacting the base with the leachate and removing a so-formed precipitate, so as to obtain an Al-rich aqueous composition; and   purifying the Al-rich aqueous composition by substantially selectively precipitating the aluminum ions by reacting the composition with an acid or base, and by recovering the precipitated aluminum ions.       

     According to another embodiment, the process can comprise:
         leaching the argillite with HCl so as to obtain a leachate comprising the aluminum ions and the iron ions, and a solid residue;   separating the leachate from the solid residue;   at least partially removing the iron ions from the leachate by substantially selectively precipitating at least a portion of the iron ions by reacting the base with the leachate and removing a so-formed precipitate, so as to obtain the Al-rich aqueous composition; and   purifying the Al-rich aqueous composition by means of a hollow fiber membrane, or by a liquid-liquid extraction.       

     According to another embodiment the process can comprise:
         leaching the argillite with HCl so as to obtain a leachate comprising the aluminum ions and the iron ions, and a solid residue;   separating the leachate from the solid residue;   at least partially removing the iron ions from the leachate by substantially selectively precipitating at least a portion of the iron ions by reacting the base with the leachate and removing a so-formed precipitate, so as to obtain the Al-rich aqueous composition; and   purifying the Al-rich aqueous composition by substantially selectively precipitating the aluminum ions and recovering the precipitated aluminum ions.       

     For example, the Al-rich aqueous composition can be purified by complexing the aluminum ions with an extracting agent so as to obtain a complex, separating the complex form the composition and precipitating the aluminum ions. For example, the extracting agent can be bis(2,4,4-trimethylpentyl)phosphinic acid. 
     For example, the Al-rich aqueous composition can be purified by complexing impurities contained in Al-rich aqueous composition with an extracting agent, at least partially removing the complexed impurities from the composition and precipitating the aluminum ions. For example, the extracting agent can be chosen from di-2-ethylhexyl phosphoric acid (HDEHP), bis(2,4,4-trimethylpentyl)phosphinic acid and 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester. 
     The base that can be used for substantially selectively precipitating the iron ions can be KOH, NaOH, or a mixture thereof. 
     The base that can be used for substantially selectively precipitating the aluminum ions can be KOH, NaOH, or a mixture thereof. 
     For example, in an acidic medium, the precipitation of iron ions can be carried out at a pH of about 3 to about 6, about 3.0 to about 5.5, about 3 to about 5, about 3 to about 4, about 3.0 to about 3.5, about 3.5 to about 4.0, about 4.0 to about 5.0, about 4.0 to about 4.5, or about 4.5 to about 5.0. 
     For example, the Al-rich composition can be purified by reacting the Al-rich composition with a base for substantially selectively precipitating the aluminum ions at a pH of about 5 to about 6, about 5.0 to about 5.5, or about 5.5 to about 6.0. 
     According to another aspect, there is provided a process for producing alumina comprising:
         obtaining aluminum ions by means of a process as defined in the present disclosure; and   converting the aluminum ions into alumina.       

     For example, the aluminum ions can be converted into alumina by heating Al(OH) 3  at a temperature of about 800° C. to about 1200° C. 
     According to another aspect, there is provided a process for producing alumina comprising:
         converting the alumina into aluminum.       

     According to another aspect, there is provided a process for producing aluminum comprising:
         obtaining alumina by means of a process as defined in the present disclosure; and   converting the alumina into aluminum.       

     According to another aspect, there is provided a process for extracting aluminum from an aluminous ore, the process comprising:
         leaching the aluminous ore with an acid so as to obtain a leachate and a solid residue;   removing at least a portion of iron ions contained in the leachate by:
           (i) substantially selectively precipitating the at least portion of the iron ions in basic conditions in which the pH is of at least 10, so as to obtain an aluminum enriched composition; or   (ii) substantially selectively complexing the at least portion of the iron ions with an extracting agent adapted to form an organometallic complex substantially selectively with the iron ions so as to obtain an aluminum enriched composition.   
               

     In the processes of the present disclosure, the acid can be HCl. The aluminuous ore can be leached with HCl at a temperature of at least 80° C., at least 90° C., or about 100° C. to about 110° C. HCl can have a concentration of about 6 M. The alunimuous ore/acid ratio can be about 1/10 in weight by volume. 
     For example, the removal of the at least portion of iron ions can be carried out by precipitating the iron ions from a basic aqueous composition. The composition can comprise comprising NaOH or KOH. 
     For example, the removal of the at least portion of iron ions can be carried out by reacting the leachate with a base in order to obtain a pH of at least 10 and precipitating the iron ions. 
     For example, the precipitated iron ions can be separated from the rest of the leachate by carrying out a filtration, a decantation, a centrifugation, or mixtures thereof. 
     The processes can further comprise rinsing the obtained precipitated iron ions with a basic solution. The basic solution can have a concentration of about 0.01 M to about 0.02 M. The pH can be at least 11, at least 12, about 10.8 to about 11.2, or about 11.5 to about 12.5. The process can further comprise purifying the precipitated iron ions by means of a hollow fiber membrane. 
     The removal of the at least portion of iron ions can be carried out by reacting the leachate, under acidic conditions, with the extracting agent and an organic solvent in order to obtain a composition comprising an acidic aqueous phase comprising aluminum ions and an organic phase comprising iron ions complexed with the extracting agent. The aluminum enriched composition can be obtained by separating the aqueous phase from the organic phase. The aqueous phase can have a pH of about 1 to about 2.5, or about 2. The extracting agent can be chosen from di-2-ethylhexyl phosphoric acid (HDEHP), bis(2,4,4-trimethylpentyl)phosphinic acid and 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester). The extracting agent can have a concentration of about 0.5 M to about 1.5 M in the organic phase or about 1 M in the organic phase. 
     For example, the organic solvent can be chosen from C 5 -C 12  alkanes and mixtures thereof. The organic solvent can be heptane. The composition can have a volumic ratio organic phase:aqueous phase of about 1:1. The organic phase and the aqueous phase can be separated by means of a filtration membrane. The membrane can be a hollow fiber membrane. The membrane can comprise polypropylene, polyvinylidene difluoride, or a mixture thereof. 
     After passing the composition through the membrane, the aqueous phase can separated from the organic phase. The aluminum ions can be recovered in the aqueous phase and the aqueous phase is treated with a base (such as NaOH or KOH). The aqueous phase can be treated with the base so as to obtain a pH of at least about 4. The process can further comprise a separation by filtration to obtain Al(OH) 3 , which can be eventually washed. 
     For example, the aluminous ore can be crushed and roasted before being leached. 
     For example, before removal of the iron ions, the leachate is treated with a base. 
     For example, before removal of the iron ions, the leachate can be distilled so as to reduce its volume. 
     For example, the process can further comprise at least partially recovering the aluminum ions present in the aluminum enriched composition. 
     For example, the aluminum enriched composition can be treated with an extracting agent adapted to form an organometallic complex substantially selectively with the aluminum ions in the presence of an organic solvent and an acid solution in order to form a composition comprising an acidic aqueous phase comprising impurities and an organic phase comprising aluminum ions complexed with the extracting agent. The aluminum ions can be recovered by separating the aqueous phase from the organic phase. For example, the aqueous phase can have a pH of about 2.5 to about 3.5. The extracting agent can be a phosphinic acid or a derivative thereof. The extracting agent can be bis(2,4,4-trimethylpentyl)phosphinic acid. The extracting agent can have a concentration of about 10% to about 25% v/v or about 20% v/v with respect to the organic solvent. The organic solvent can be chosen from C 5 -C 12  alkanes and mixtures thereof. The organic solvent can be heptane. The composition can have a volumic ratio aqueous phase:organic phase of about 1:1 to about 1:3. The organic phase and the aqueous phase can be separated by means of a membrane (for example a hollow fiber membrane). The membrane can comprise polypropylene, polyvinylidene difluoride, or a mixture thereof. The composition can be at a temperature of about 30° C. to about 50° C., or about 35° C. to about 45° C. After passing the composition through the membrane, the aqueous phase can be separated from the organic phase. The complexed aluminum ions can be recovered in the organic phase. The organic phase can then be treated with HCl so as to obtain an aqueous composition comprising the aluminum ions. The aluminum ions can be converted into Al(OH) 3  by contacting it with a base. Al(OH) 3  can then be converted into Al 2 O 3 . Such a conversion of Al(OH) 3  into Al 2 O 3  can be carried out at a temperature of about 800° C. to about 1200° C. 
     According to one embodiment, the composition can comprise an acidic aqueous phase comprising aluminum ions and an organic phase comprising iron ions complexed with the extracting agent and wherein the aluminum ions are recovered by separating the aqueous phase from the organic phase. The aqueous phase can have a pH of about 1 to about 2.5 or of about 2. The extracting agent can be chosen from phosphoric acids and derivatives thereof, and phosphinic acids and derivatives thereof. For example, the extracting agent can be chosen from di-2-ethylhexyl phosphoric acid (HDEHP), bis(2,4,4-trimethylpentyl)phosphinic acid and 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester. The extracting agent can have a concentration of about 0.5 M to about 1.5 M in the organic phase or of about 1 M in the organic phase. The composition can have a volumic ratio organic phase:aqueous phase of about 1:1. After extraction (passing the composition through the membrane), the aqueous phase can be separated from the organic phase, and the aluminum ions can recovered in the aqueous phase and the aqueous phase can be treated with a base (for example NaOH, KOH, or a mixture thereof). The aqueous phase can be treated with the base so as to obtain a pH of at least about 4. The process can further comprise treating the organic phase with HCl and isolating the iron ions in the form of Fe 3+ . 
     According to another embodiment, the composition can comprise an acidic aqueous phase comprising iron ions and an organic phase comprising aluminum ions complexed with the extracting agent, and wherein the aluminum ions are recovered by separating the aqueous phase from the organic phase. The aqueous phase can have a pH of about 2.5 to about 3.5. The extracting agent can be a phosphinic acid or a derivative thereof. For example, the extracting agent can be bis(2,4,4-trimethylpentyl)phosphinic acid. The extracting agent can have a concentration of about 10% to about 25% v/v with respect to the organic solvent or of about 20% v/v with respect to the organic solvent. The composition can have a volumic ratio aqueous phase:organic phase of about 1:1 to about 1:3. During the process, the composition can be at a temperature of about 30° C. to about 50° C. or at a temperature of about 35° C. to about 45° C. After extraction through the membrane, the aqueous phase can be separated from the organic phase. The complexed aluminum ions can be recovered in the organic phase. The organic phase can then be treated with HCl so as to obtain an aqueous composition comprising the aluminum ions. 
     For example, the organic solvent can be chosen from hydrocarbons. For example, the organic solvent can be chosen from C 5 -C 12  alkanes and mixtures thereof. The organic solvent can also be hexane or heptane. The organic phase and the aqueous phase can be separated by means of a filtration membrane, for example a hollow fiber membrane. Such membrane can comprise polypropylene, polyvinylidene difluoride, or a mixture thereof. The aqueous phase can be treated with the base so as to obtain a pH of at least about 4. The process can also further comprise a separation by filtration so as to obtain Al(OH) 3 . The process can also comprise washing the Al(OH) 3 . The process can also comprise converting Al(OH) 3  into Al 2 O 3 . Conversion of Al(OH) 3  into Al 2 O 3  can be carried out at a temperature of about 800° C. to about 1200° C. 
     According to another aspect there is provided a composition comprising aluminum ions, iron ions, an organic solvent and an extracting agent adapted to form an organometallic complex substantially selectively with the iron ions or with the aluminum ions which is soluble in the organic solvent. 
     According to another aspect, there is provided a composition comprising an acidic aqueous phase comprising aluminum ions and an organic phase comprising iron ions complexed with an extracting agent. 
     According to another aspect, there is provided a composition comprising an acidic aqueous phase comprising iron ions and an organic phase comprising aluminum ions complexed with an extracting agent. 
     According to another aspect, there is provided a process for at least partially separating aluminum ions from iron ions comprised in a composition, the process comprising substantially selectively precipitating at least a portion of the iron ions in basic conditions in which the pH is of at least 10. The iron ions can be precipitated from a basic aqueous composition comprising NaOH or KOH. For example, the base can be reacted with the composition so as to obtain a mixture in which the pH is of at least 10, and then, the at least portion of precipitated iron ions can be separated from the rest of the mixture. For example, the precipitated iron ions can be separated from the rest of the mixture by carrying out a filtration, a decantation, a centrifugation, or combinations thereof. The process can further comprise rinsing the obtained precipitated iron ions with a basic solution. The basic solution can have a concentration of about 0.01 M to about 0.02 M. The pH can be at least 11, at least 12, about 10.8 to about 11.2, or about 11.5 to about 12.5. The process can further comprise purifying the precipitated iron ions by means of a hollow fiber membrane. 
     The various parameters, embodiments and examples previously described concerning the processes can also be applied, when possible, to these compositions. 
     Further features and advantages will become more readily apparent from the following description of various embodiments as illustrated by way of examples only in the appended drawings wherein: 
     As it can be seen from  FIG. 1 , such a process can comprise various steps, and each of these steps can eventually be individually considered has being a process. 
     Preparation of Argillite Sample 
     Argillite can be finely crushed in order to help along during the following steps. For example, micronization can shorten the reaction time by few hours (about 2 to 3 hours). In order to remove most of the iron, a leaching step at room temperature is optionally carried out between the crushing step and the roasting step (see option 1). This operation is, for ex ample, carried out with hydrochloric acid HCl (12 M) and an argillite/acid ratio (weight/volume) of 1:5 is used. Depending on experimental conditions (sizes of the particles, time of treatment, agitation system), about 65% to about 93% of the iron can then be removed. However, this leaching step can also bring in a certain percentage of the aluminum (0-5%). The last step of the preparation of argillite comprises roasting the pretreated argillite. This can be accomplished at a temperature greater than 550° C. for a period of about 1 to 2 hours. For example, a heat treatment makes it possible to increase the quantity of extracted aluminum by about 30% to about 40% for the same period of time. In others words, the quantity of extracted aluminum is doubled. When leaching at room temperature is carried out, a phase separation before roasting can be made in order to recover the acid and reduce heating costs. 
     Acid Leaching 
     Acid leaching comprises reacting the crushed and roasted argillite with a hydrochloric acid solution at elevated temperature during a given period of time. For example, the argillite/acid ratio can be of about of 1:10 (weight/volume), the HCl concentration can be of about 6 M, the temperature can be of about 100° C. to about 110° C., and the reaction time can be of about 5 to about 7 hours. Under such conditions, more than about 90% of the aluminum and about 100% of the iron can be extracted in addition to impurities. 
     During the second half of such a treatment (for example the last 2 or 3 hours), a portion of the acid can be recovered by condensation. Once the extraction is terminated, the solid (argillite impoverished in metals) can be separated from the liquid by decantation or by filtration, after which it is washed. The residual leachate and the washing water may be completely evaporated. The corresponding residue can thereafter be washed many times with water so as to decrease acidity and to lower the quantities of sodium hydroxide (NaOH) that are required to adjust the pH during iron removal. Final volume accounts for 10% to 20% of initial volume. The acid recovered will can be re-utilized after having adjusted its titer either by adding gaseous HCl, or by adding concentrated HCl (12 M). After the reaction, the titer of the acid can vary from about 4 M to about 6 M depending on experimental conditions. With respect to the solid, it represents about 65% to about 75% of the initial mass of argillite, it can be valorized and be used again either as an ion exchange resin, or as an adsorbent. 
     Removal of Iron 
     Removal of iron can be carried out by precipitation of the iron ions in (i) basic medium or (ii) an acidic medium. For example, in a basic medium, precipitation can be carried out at a pH of at least 10 or at a pH of about 11.5 to about 12.5. For example, in an acidic medium, the precipitation can be carried out at a pH of about 3 to about 6, about 3 to about 5, about 3 to about 4, about 3.0 to about 3.5, about 3.5 to about 4.0, about 4.0 to about 5.0, about 4.0 to about 4.5, or about 4.5 to about 5.0, by adding the base. Such a step under basic or acidic conditions can be made by adding NaOH or KOH for example at a concentration of about 0.1 M to about 18 M. For examples, a concentration of 0.1 M, 1 M, 6 M or 10 M can be used. Then, all that is required is to separate the solid portion from the liquid portion by filtration, decantation or centrifugation and to rinse the solid by means of a diluted base, such as a solution of NaOH (for example NaOH at a concentration of 0.01 M to 0.02 M). Then, the solid is washed with distilled water. The liquid portion comprises aluminum and alkaline-earths A substantially complete removal of the iron and of nearly all the impurities (other metals) can thus be achieved. Optionally, it is possible to recover iron by using a refining step by liquid-liquid extraction through a hollow fiber membrane (see option 2). 
     Alternatively (see option 3), removal of iron can be carried out by using an extracting agent and a hollow fiber membrane. Various extracting agents that could substantially selectively complex iron ions over aluminum ions (or aluminum ions over iron ions) could be used in such a step depending an Al/Fe ratio. For example, extraction can be carried out by using HDEHP (diethylhexylphosphoric acid) as an extracting agent adapted to complex iron ions. A concentration of about 1 M of HDEHP can be used in an organic solvent, such as heptane or any hydrocarbon solvent. Such an extraction can require relatively short contact times (few minutes). For example, the pH of the order of 2 can be used and aqueous phase/organic phase ratio can be of about 1:1. It was observed that is possible to extract from 86% to 98% iron under such conditions. It will be understood that in the present case, iron is trapped in the organic phase. To recover iron in an aqueous phase, a reverse extraction with hydrochloric acid (2 M or 6 M) and organic phase/acidic phase ratio of about 1:0.5 can then be carried out. In such a case, the resulting aqueous phase is rich in Fe 3+  ions. 
     Aluminum Recovery 
     The solution obtained from the previous step using either the precipitation or the extraction technique is relatively clean and mainly contains aluminum for example about 90% to 95% (without the alkaline-earths in the case of precipitation). Recovery of the latter can be carried out by liquid-liquid extraction for example by using a same hollow fiber membrane and an extracting agent that is adapted to complex at least substantially selectively aluminum over other metals or residues. 
     For example, bis(2,4,4-trimethylpentyl)phosphinic acid (such as the one sold under the name Cyanex™ 272) can be used as an extracting agent specific to aluminum. For example, this extracting agent can be used at a concentration of about 20% v/v in an organic solvent such as heptane. The ratios between the aqueous phase and the organic phase can be of about 1:1 to about 1:3. For example, the extraction temperatures can be of about 40° C. and the pH can be maintained at about 2.5 to about 3.5. It was observed that such a technique makes it possible to extract more than 70-90% of the aluminum. 
     After the aluminum has been trapped in the organic phase, it can be recovered in the form of a concentrate of Al 3+  ions by using a back extraction. For example, the reverse extraction can be carried out at a temperature of about 40° C. with hydrochloric acid (for example at a concentration of 6 M). Under this condition, more than 90% of aluminum can be recovered. Then, Al 3+  can be converted into aluminum hydroxide Al(OH) 3  by addition of NaOH. Finally, Al(OH) 3  can be converted into alumina (alumina Al 2 O 3 ) by roasting Al(OH) 3  for example at a temperature of about 800° C. to 1200° C. 
     The following non-limiting examples further illustrate the disclosure. 
     EXAMPLES 
     Example 1 
     Preparation of Argillite Sample 
     Crushing of mudstone: The resulting micronization average employed for the tests ranges between 10 and 50 microns. 
     Roasting: Crushed mudstone was roasted at least during 1 hour at a temperature of 600° C. Its average composition was: 
     
       
         
           
               
               
               
             
               
                   
               
             
            
               
                   
                 Al 2 O 3   
                 21.0% 
               
               
                   
                 Fe 2 O 3   
                  8.0% 
               
               
                   
                 K 2 O 
                  1.5% 
               
               
                   
                 Na 2 O 
                  0.9% 
               
               
                   
                 TiO 2   
                  0.9% 
               
               
                   
                 CaO 
                 0.08% 
               
               
                   
                 ZnO 
                 0.06% 
               
               
                   
                 SiO 2   
                 51.0% 
               
               
                   
               
            
           
         
       
     
     Acid Leaching 
     500 g of argillite crushed and roasted were added to 5 liters of hydrochloric acid 6 M. The mixture was then heated at 100° C.-110° C. during 7 hours. 
     After reaction, the liquid part was separated from the solid part by filtration. The solid was washed with distilled water which was added to the liquid portion. This washing makes it possible to recover part of the aluminum trapped in the solid. This solid had a dry mass of 345 ±-5 g, which corresponds to a loss of about 30% -32%. 
     The remaining liquid part, containing aluminum, iron and a great part of the impurities initially present in mudstone, was reduced by evaporation at a temperature of 100° C. to 90% of its initial volume. Residual volume was then 50 mL. The liquid compositions before and after evaporation were: 
     
       
         
           
               
               
               
             
               
                   
               
               
                   
                   
                 Evaporated leaching 
               
               
                   
                 Leaching solution 
                 solution 
               
               
                   
                 Composition (%) 
                 Composition (%) 
               
               
                   
                 [concentration (mg/L)] 
                 [concentration (mg/L)] 
               
               
                   
               
             
            
               
                 Aluminum 
                 47.63 
                 47.86 
               
               
                   
                 [9 250] 
                 [59 500] 
               
               
                 Iron 
                 31.54 
                 31.07 
               
               
                   
                 [6 125] 
                 [38 625] 
               
               
                 Alkaline-earths 
                 19.30 
                 19.53 
               
               
                 (Na, Mg, K, Ca) 
                 [3 749] 
                 [24 277] 
               
               
                 Other metals 
                 1.53  
                 1.54  
               
               
                   
                 [297.3] 
                  [1 920] 
               
               
                   
               
            
           
         
       
     
     All the ions species seem to remain soluble. 
     Removal of Iron 
     The residual volume was slightly diluted (+25%) and concentrated hydroxide sodium (10 M) was added until a pH higher than 11.5 was reached. The formed precipitate was separated from the solution by standard filtration and was washed several times with NaOH diluted and hot ultra-pure water. The precipitate contained all the iron and the majority of the metal impurities. The filtrate contained in addition to ions Al 3+  mainly alkaline-earths and some following impurities: 
     
       
         
           
               
               
             
               
                   
               
               
                   
                 Major filtrate impurities 
               
               
                   
                 (%) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Iron 
                 0.14 
               
               
                   
                 Sodium 
                 94.13 
               
               
                   
                 Alkaline-earths 
                 5.71 
               
               
                   
                 (Mg, K, Ca) 
                   
               
               
                   
                 Other metals 
                 0.02 
               
               
                   
               
            
           
         
       
     
     Na+ came from soda and was also the Al(OH) 4   −  counter-ion. 
     Other tests have been made for precipitating iron ions under acidic conditions and more particularly at a pH of about 4.5 to about 5.0 with 0.1 M, 1 M and 6M (twice) of NaOH and it was observed that such an embodiment was efficient. In fact, it was found that around a pH of about 4.6 to about 4.8, almost all the iron was precipitated. 
     Aluminum Recovery 
     The filtrate is adjusted at a pH of 2.5 to 3.5 by addition of HCl 6 M. The resulting solution is extracted by means of the complexing agent, Cyanex 272, at a concentration of 20% volume/volume in an organic solvent with a volumetric ratio of 1:1. The extraction is carried out at a temperature of 40° C. in a membrane contactor with hollow fibers. In less than about 30 to 60 min, more than 85% of aluminum is extracted. The pH adjustment is performed by a regulation loop controling the NaOH (10 M) addition. Complexed Al 3+  in Cyanex are then recovered by carrying out a back extraction with HCl (6 M) at 40° C. and an organic phase/acid phase volumetric ratio of 1:0.5. After the back extraction, the composition of the recovered acid phase is: 
     
       
         
           
               
               
             
               
                   
               
               
                   
                 Composition (%) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Aluminum 
                 92.81 
               
               
                   
                 Iron 
                 0 
               
               
                   
                 Alkaline-earths 
                 7.14 
               
               
                   
                 (Na, Mg, K, Ca) 
                   
               
               
                   
                 Other metals 
                 0.05 
               
               
                   
               
            
           
         
       
     
     To increase the percentage of purity, the Al 3+  ions are precipitated in the form of Al(OH) 3  hydroxide, then washed several times with ultra-pure water. The composition of the hydroxide becomes: 
     
       
         
           
               
               
             
               
                   
               
               
                   
                 Composition (%) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Aluminum 
                 99.09 
               
               
                   
                 Iron 
                 0 
               
               
                   
                 Alkaline-earths 
                 0.88 
               
               
                   
                 (Na, Mg, K, Ca) 
                   
               
               
                   
                 Other metals 
                 0.03 
               
               
                   
               
            
           
         
       
     
     Further purification can be performed by recrystallization 
     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.