WO2018115560A1 - Method for producing anionic clays of aluminium and derivatives thereof from saline slags from aluminium recycling processes - Google Patents

Abstract

The invention relates to a method for producing anionic clays of aluminium and derivatives thereof from saline slags from aluminium recycling processes, which allows aluminium extracted from saline slags from aluminium recycling processes, using acid or base solutions, to be used directly in the synthesis of anionic clays with a reduced number of stages, since the solution in which the aluminium is extracted is added warm, drop by drop, onto a solution containing a divalent metal cation, an interlaminar anion and a precipitating agent, the anionic clays being formed therefrom. Inter alia, the method allows anionic clays of aluminium and of Co²⁺, Mg²⁺, Ni²⁺ or Zn²⁺ to be obtained, with carbonate as an interlaminar anion. The materials obtained have a specific area of up to 290 m²/g and a pore volume of up to 0.700 cm³/g.

Description

 Manufacturing procedure for anionic aluminum clays and their derivatives from salt slags from aluminum recycling processes

DESCRIPTION

Object of the invention The object of the invention relates to the manufacture of anionic aluminum clays and their derivatives from salt slags from the aluminum recycling processes. The synthesis process will be carried out, directly and hotly using the solution containing Al ³⁺ , without any conditioning step and applying a new modified coprecipitation method in which pH control is not necessary. Technical Field of the Invention

The present invention relates to the obtaining of anionic aluminum clays and their derivatives, from aluminum residues, for example salt slags from the second melting processes of aluminum. By chemical attack of these residues, it is possible to extract part of the aluminum that is used directly in hot and without further treatment steps for the synthesis of anionic clays and products derived from Co ²⁺ , Mg ²⁺ , Ni ²⁺ , among others.

Background of the invention

Aluminum recycling and salt slag generation:

In recent years, the convenience or not of treating the waste generated in aluminum recycling and how it is carried out has generated a wide debate in the scientific and industrial community. Various types of waste are generated during the recycling process [1], highlighting salt slags among them. Salt slags are produced when salts are used to cover molten material mainly from low-quality aluminum scrap and aluminum-rich slags. The molten salt reduces the melting temperature, prevents oxidation of aluminum and allows metal oxides to be easily separated from metal aluminum [2]. The average composition of salt slags can be summarized as: 3-9% aluminum metal; various oxides 20-50%, Al ₂ 0 ₃ , Na ₂ 0, K ₂ 0, Si0 ₂ and MgO, fraction referred to as non-metallic products; 50-75% fluxes, usually NaCI and KCI; and other compounds in smaller proportion; among them Nal, AI ₄ C ₃ , AI ₂ S ₃ , Si ₃ P ₄ , Na ₂ S0 ₄ , Na ₂ S and cryolite [3]. Some of these components result from the reaction with air and moisture, so that their formation could be minimized by good process control. The amount Salt slags generated in these operations can be between 30 and 60% of the metal produced. Both the amount generated, and the composition of the slags can vary widely depending on the material to be melted, the type of oven used and the mode of operation thereof and the composition of the fluxes used, among others [3-1 1]. Due to its composition and possible reaction with water, salt slags from aluminum recycling processes are classified as hazardous waste, code LER (European Waste List) 100308 [12], and must be deposited in controlled landfills or in security deposits

Several million tons of salt slags are produced every year, and this amount tends to increase due to the demand for recycled aluminum [13]. Around 95% of this waste is taken to landfill, its cost being estimated at 80 million euros, value that would be increased by the management, transport and construction of the landfill itself in the case that it is specific for this material. The best option to reduce this cost would be to reduce the production of salt slag during the recycling process. Some options would be, for example, to use electric arcs or induction furnaces as heat sources to melt aluminum [14]. In both cases, it would be necessary to work in inert atmospheres, also requiring great purity in the raw materials to be used. In these processes no melting salts are used and, therefore, salt slags are not generated either. The disadvantages are, on the one hand, the large consumption of electric energy, when compared with the consumption of natural gas used to reach the melting temperature, and on the other, that only residues with a high content of raw materials could be used aluminum.

The hydrometallurgical processes of treating this residue are complex. Once the aluminum metal has been separated from the material by crushing and screening, the residue is treated with water to separate the soluble fraction from the insoluble. In this way a new residue with lower salt content and a saline solution would be obtained where the salt should be recovered. Although the idea of reusing salt in a subsequent process seems attractive, its recovery implies a significant expenditure on energy to separate the water, obtaining as a counterpart salt of little value and difficult application. Also noteworthy is the emission of gases (H ₂ , NH ₃ , CH ₄ , H ₂ S, among others) that occurs in this wet stage, which should be controlled and treated. The composition of the solid waste is very diverse, depending on the materials that have been used in the recycling treatment. This heterogeneity limits the possible applications and that is chosen for its management in controlled landfill. It is precisely the storage in landfill controlled the other alternative to the management of salt slags once the aluminum metal fraction has been recovered [3].

It is worth mentioning the actions that have been implemented in different companies in order to reduce the generation of these wastes: pretreatment systems for the materials to be melted, such as chip drying systems and deslacado systems applied to beverage containers; optimization of furnace burners to control the atmosphere, oxidizing or reducing, in them; furnace heating systems preventing the combustion of organic compounds: electric heating system, plasma heating systems, electric arc heating systems; new smelting furnaces (rotary tilting furnaces). Despite these improvements, it is not possible to eliminate the formation of these materials since fluxes are necessary to maximize the recovery of aluminum.

An attempt has been made to find alternatives to landfill deposits that value this type of waste, as well as applications for new materials. The use and applications of aluminum residues depend on the chemical composition of the oxides and the chloride content, which can be reduced in the steps before the applicable limits. The main phase detected in this type of waste is alumina, regardless of the origin of the residue [15]. Without any additional treatment, it can be used for direct applications such as inert filler for construction, road paving, mortar components, aluminum salts, inert filler in polymeric composite materials, adsorbents, mineral wool, etc. Aluminum can also be recovered as a high value-added product and used to synthesize materials such as pure alumina, salts and hydroxides [16-18].

It is precisely the obtaining of aluminum-based materials from this residue one of the objectives set forth in this invention. Both the method of synthesis of these materials and the applications in which they can be used, may allow the recovery of this waste to make economic sense, not only because of the limited application of salt, but also because the materials that can be obtained Have your own importance. Valorization of salt slags:

The potential use of the non-metallic fraction of salt slags as a clay replacement material in obtaining blocks with industrial and building applications has been studied by Shinzato e Hypolito [19], Miqueleiz et al. [20], Hsieh et al. [21] and Gómez de Salazar et al. [22]. Shinzato and Hypolito [19] explain that the Aluminum recycling companies in the metropolitan area of Sao Paulo (Brazil) operate using a simple method for the treatment of slags. The slag is initially crushed to release the metal part trapped in the residue. The remaining material is leached with water and the recovered material is sorted by size. Particles larger than 20 mesh (that is, particles that do not pass through a mesh with a nominal aperture of 0.841 mm), mainly from Al, are sent to the secondary foundry industries. Particles smaller than 20 mesh (diameter less than 0.841 mm) are sold to steel manufacturers as a refractory product. Liquid waste, which is rich in soluble salts, is transferred to the settling tanks to separate the solid fraction. This fraction has a low Al content and is finally disposed in landfills. Alternatively, this type of material is also used to obtain blocks by adding two parts of the residue to one part of cement and four parts of sand. The blocks thus produced have a low compressive strength. López et al. [6] analyze the possibility of producing a mixture of alumina and spinel by sintering the residues produced after leaching of salt slags. Although the treatment seems simple, several stages of separation are necessary, so the overall process has a relatively high technical complexity and economic cost. The process initially involves grinding the slag and carrying out the grain screening, which leads to the recovery of most of the aluminum metal found in the original material. The process continues with leaching with water of the non-metallic part of the slag once it has been ground to a grain diameter of less than 500 μηι. The fraction which is not soluble in water is granulated and then calcined at 1500 ^and C in an oxidizing atmosphere to produce a mixture of a-AI ₂ 0 _3, MgOAI ₂ 0 _3, Si0 ₂ and CaOAI ₂ 0 ₃ * 2Si0 _2. Finally, the authors propose that sintered materials can be applied in cement and glass smelters, such as refractory materials, mineral wool, abrasives and ceramic fibers. Yoshimura et al. [23] have proposed directly using aluminum slag to replace raw material in obtaining refractories. The use of the non-metallic fraction in the production of mineral wool has been reported by O'Driscoll [24].

Mineral wool is an insulation product that plays an important role in the conservation of energy in residential and industrial buildings. These products absorb sound, are not flammable and do not allow the growth of mold or bacteria. All these properties are derived from its structure. In general, mineral wool is manufactured by melting natural rocks (basalt, diabasa, amphibolite) and adding certain fine-tuning materials (limestone, dolomite, as well as olivine) and alumina. The typical chemical composition of mineral wool is in the range of 45-48% Si0 ₂ ; 18% Al ₂ 0 ₃ , 10% Fe ₂ 0 ₃ , 10% CaO and 10% MgO. The main source of alumina is bauxite. However, taking into account the alumina content of the non-metallic fraction, this type of material can be considered as an alternative source of alumina. In recent years, Portland cement industries have begun to use certain amounts of alumina for cement production. As the aluminum oxide requirement is around 5%, many producers in the US they use aluminum slag oxide to reach this content [7.25]. Pereira et al. [7] have observed that up to 10% of scum washed can be used in the cement formulation, so scum washing is a necessary step in this procedure, without observing appreciable changes in the properties of the mortars obtained.

The alumina recovered from aluminum slags can be a good alternative as a raw material in those formulations of materials that use natural alumina [26]. This is the case of materials from the treatment of salt slags that are marketed under several names. Oxiton® (BUS, Germany) is used as raw material for refractory materials. The mineralogical components of this material are a-AI ₂ 0 ₃ and MgO (64-75%), with the following physical properties: a specific density 2.95 g / cm ³ ; particle size between 10 and 20 μηι and a melting point greater than 1680 ^e C. Given its composition and properties, the areas that can be applied include ceramics, refractories, cement, glass, mineral wool, ceramic fibers, cast iron steel and mixtures and abrasives. Oxiton® can replace up to 25% of the alumina used in cement formulations. Valoxy® (RVA, La Vignette, Les Islettes, France), a solid with a chloride content of less than 0.5%, has been used in the synthesis of a borosilicate glass composite material that can be used in a wide range of applications [27]. Valoxy® is an aluminum oxide-based material marketed by the company RVA [28] that contains about 70% alumina and is offered as a substitute for bauxite / alumina in non-metallurgical applications such as cement production, binders, bricks, aluminates and refractories. This material is classified by the French environmental authorities as not dangerous. Paval® (Befesa, Sevilla, Spain) has been used as raw material for the manufacture of cement, refractory material and ceramics [29]. It is a solid that contains alumina and halite, and that can be combined with calcium hydroxide to produce a stable and insoluble compound known as Friedel salt (ΰ3 ₄ ΑΙ ₂ ΰΙ ₂ Ο ₆ · 10Η ₂ Ο). The material resulting from the cement / waste mixture shows lower mechanical strength and greater total porosity.

In the valuation of salt slags or aluminum residues in which there is some kind of chemical reaction or transformation, the synthesis of calcium aluminate carried out by López-Delgado et al. [30-32]. Such materials are extremely useful in many fields of metallurgy as additives that reduce the sulfur content of steel and, in general, as refractory materials, as described in US Pat. US5716426 and US6238633 [33,34]. The ternary formulation CaO-AI ₂ 0 ₃ -Si0 ₂ was used by the authors where the amount of Al ₂ 0 ₃ is incorporated from the aluminum residue. Up to 75% of the waste can be immobilized using this procedure to obtain a homogeneous and stable glass. The hardness and toughness properties obtained for this type of materials are comparable to those presented by calcium aluminosilicate synthesized from pure reagents. The authors point out that these characteristics could confer an advantage for possible applications of Al ₂ 0 ₃ as a raw material in the glass industry.

The synthesis of mixtures of cement and calcium aluminate from this type of waste has been studied by Ewais et al. [35]. The authors selected cement mixtures manufactured from 45-50% aluminum slags, with a content of 12.50 to 13.75% alumina, as well as the optimal ratios for the manufacture of calcium aluminate cement since they meet the requirements of the international standard specifications for cementation and refractory properties.

Bajare et al. [36] have produced light aggregates of expanded clay from a clay with a high carbonate content and varying proportions of non-metallic fraction (from 0 to 37.5%). These aggregates were treated at a temperature between 1 150 and 1270 ^e C to remove impurities and to produce a material rich in Al ₂ 0 ₃ and spinel. The authors observed an important effect of the composition and heat treatment on the properties of the material such as density and porous structure. The results indicate that the bulk density of aggregates at the maximum expansion temperature is between 0.4 and 0.6 g / cm ³ . Valorization of aluminum present in salt slags:

The treatment of aluminum residues with solutions of acids or bases allows to extract part of the aluminum, to later synthesize high purity alumina. Thus, for example, aluminum slag treated with H ₂ S0 ₄ allows recovering a high percentage of aluminum that can be used in the production of γ-ΑΙ ₂ 0 ₃ [37]. The authors of this work indicates that the aluminum hydroxide of great value that is obtained, can be used as adsorbent or catalytic support, after a heat treatment at 900 ^e C. In another work, Pickens and Waite, in US Pat. US61 10434 [38], treat the non-metallic fraction at various pHs so that alumina and magnesia can be selectively separated. In an initial treatment at acidic pH, the magnesium aluminate is dissolved without dissolving by filtration. The pH of the solution is raised between 9.5 and 12 to precipitate the magnesium oxide, which is also filtered off. As the pH of the remaining liquid approaches neutrality, alumina trihydrate precipitates, resulting in a pure product. It is worth highlighting the large number of stages that have this type of treatment, which implies a certain technical complexity and could be an inconvenience from the point of view of its industrialization.

In US patents US7906097B2 and US7651676, aluminum chloride is obtained by treatment of Nova ^M aluminum waste (Alean Internationl Limited, Montreal, Canada) and Serox® (Befesa, Lunen, Germany) with H ₂ S0 ₄ and HCI [ 39]. These aluminum residues are formed by a mixture of alumina, aluminum metal, aluminum nitrate, spinel (MgAI ₂ 0 ₄ ), and gibbsite (AI (OH) ₃ ), as well as other oxides such as NaAI Oiy, Na ₃ AIF ₆ , etc. As a previous step, once the aluminum has been extracted, the authors of this patent obtain the aluminum precursors, AICI ₃ and AI ₂ (S0 ₄ ) ₃ . The process from there is, therefore, very similar to that which can be used if the aluminum salts are used directly, regardless of their origin. The heat treatment at 1050 ^e C allows to obtain a high purity alumina.

By an acid leaching treatment of the non-metallic fraction at low temperature David and Kopac [40] were able to extract the aluminum and synthesized alumina with a high degree of purity (99.28%). The authors indicate that several stages are necessary as treatment with acid, purification, precipitation and calcination until the final product is obtained. It was also indicated that aluminum sulfate can be used directly as a coagulant for wastewater treatment, as reflected in Spanish Patents ES2176064 and ES2277556 [41, 42]. In a similar way, Park et al.

[43] have leached a residue with NaOH to extract aluminum as sodium aluminate and precipitate it in the form of aluminum hydroxide. The oxide, once calcined, is used to make moldable refractories by mixing with aggregates and alumina cement. El- Katatny et al. [44] describe a process in which aluminum is recovered from the slag by precipitation with aluminum hydroxide. The powder obtained is activated at 600 ^e C to obtain γ-ΑΙ ₂ 0 ₃ . The process involves several stages: extraction with sodium hydroxide and transformation into sodium aluminate, precipitation, filtration, washing, drying and calcination. Anionic clays and their synthesis:

Natural clays are components of sedimentary rocks of the earth's crust that are essentially composed of hydrated aluminum / magnesium silicates, laminar or fibrous structure, which may contain other elements such as iron, calcium, sodium, potassium or others. Its great adsorption capacity and its applications in catalytic processes, such as the Houdry process, has been a cause of interest on the part of the industry, which has been developing variants of natural clays. They have advantageous properties such as low cost, versatility of use, simple handling, among others, which make them useful materials to be key parts in environmentally friendly processes. Clays are used for the manufacture of cements, they are used for the degreasing of fabrics and skins, for the discoloration of fats and oils, for oil refining and as a base for paints and rubbers. They have a great importance in agriculture, since many soils contain high amounts of clay materials, which characterizes the key properties of the soil: structure, texture, water retention, etc.

Anionic clays are also known as double laminar hydroxides, mixed metal hydroxides or hydrotalcite-type compounds, because the diffraction patterns of many anionic clays are similar to those of the latter mineral. They are laminar materials of similar structure to that of brucite (mineral magnesium hydroxide), in which part of the Mg ²⁺ cations have been replaced by trivalent Al ³⁺ cations, which generates an excess load that must be compensated by the incorporation of anions and water in the interlaminar space. In general, interlaminar anions are usually carbonates, but others are also possible, such as N0 ₃ ^" , OH ^" , CI ^" , Br ^" , Γ, S0 ₄ ^{2 "} , Si0 ₃ ^2" , Cr0 ₄ ^{2 "} , B0 ₃ ^{2 "} , MnO ⁴ -, HGa0 ₃ ^2" , HV0 ₄ ^{2 "} , CI0 ₃ ^~ CI0 ₄ ^~ I0 ₃ ^~ S ₂ 0 ₃ ² -, W0 ₄ ^2" , [Fe (CN) ₆ ] ^{3 "} , [Fe (CN) ₆ ] ^{4 "} , (PMo ₁₂ O ₄₀ ) ³ -, (PW ₁₂ O ₄₀ ) ³ -, V ₁₀ O ₂₆ ⁶ -, Mo ₇ 0 ₂₄ ^6" , etc. The Mg ²⁺ cation can be substituted, in part or in its entirety, by other divalent cations, such as: Cu ²⁺ , Ni ²⁺ , Zn ²⁺ , Co ²⁺ and Ca ²⁺ , resulting in derivatives of the anionic clays.

In particular, they are hydroxides of formula [Me (ll) ₁ - _x Me (lll) _x (OH) ₂ (A ^{n "} ) _{x / n} ] -mH ₂ 0, where

M (ll) is a divalent cation (Me ²⁺ ), M (lll) is a trivalent cation (Me ³⁺ ),

A is a charge anion n, x is a rational number between 0.2 and 4, determines the charge density in each layer and the anion exchange capacity, n represents the negative electronic charge of the interlaminar anion and is an integer that can vary between -1 to -8, m represents the water molecules present as hydration water or as water present in the interlaminar region and is a rational number between 0 and 10, where A, x, n and m are such that the formula meets the rule of neutrality of its total charge.

Anionic clays exhibit the ability of anion adsorption and diffusion properties and ion exchange, together with a basic surface that makes them important materials for many current applications, including clinical applications related to controlled drug delivery.

Several procedures for the synthesis of anionic clays have been described, coprecipitation being the most commonly used.

Coprecipitation involves the addition of two solutions. One of them contains cationic precursors, that is, the divalent Me ²⁺ cations (such as Mg ²⁺ ) together with the trivalent Me ³⁺ cations (generally Al ³⁺ ); and the other solution contains the precipitating agent (usually sodium hydroxide) together with a compound containing the interlaminar anion. Usually, it is attempted to maintain the pH at basic values, often close to 10. The ratio divalent cation to trivalent cation (Me ² 7Me ³⁺ ) has a great influence on the properties of the solid, given that instead of the double hydroxide structure the mixture of simple hydroxides can be obtained. Different documents can be found where examples of application of this procedure or variants thereof are given.

U.S. Pat. US4454244, refers to synthetic minerals formed by expanded layers that are the product of anion exchange reactions between certain layered minerals and polyanions, as well as the methods for the production of said minerals. Example 3 of said document describes a process in which two solutions are prepared, a first solution containing the divalent cations Mg ²⁺ and Zn ²⁺ and the anion N0 ₃ ^" , and a second alkaline solution (NaOH) acting as The two solutions are mixed by adding them dropwise simultaneously to a container while maintaining the pH at approximately 10. A solid is obtained which after its separation, washing and drying is said to correspond to a material whose formula is indicated as Zn _x Al _y (OH) 2x- ₊ 3y-nz-z (N0 ₃ ) .tH ₂ 0, and whose structure is hydrotalcite type. U.S. patent application Published under US2005261381 A1 refers to compositions of nanoparticles of anionic clays, stable colloidal dispersions of nanoparticles of anionic clays and methods for preparing the latter. The possibility of mixing saline solutions of metal cations with a base in the high shear mixing zone is considered. Preference is shown that the solutions of the metal salts and the solution with the base are brought into contact in a particle precipitation vessel by introducing the feed streams of said components into a highly agitated area of the precipitation vessel. Among the specific examples of preparation, comparative Examples 4 to 6 stand out, which correspond to the preparation of anionic clays with larger particle size and which describe three ways of mixing the precursors of the anionic clay to obtain said particles. In both Example 4 and 5, the mixed solution containing the metal salts (Mg (N0 ₃ ) ₂ and AI (N0 ₃ ) ₃ ) is initially added to the particle formation vessel and subsequently added dropwise. drop the basic solution of NaOH, with vigorous stirring, until the pH becomes 10, continuing with stirring and then let stand. In Example 6, which is described herein as coprecipitation synthesis, the addition to the vessel of the mixed solution with the metal salts and the addition of the NaOH precipitating solution are performed simultaneously and dropwise; The NaOH solution is added in sufficient proportion to keep the pH near 10.

Some authors have proposed the synthesis of anionic clays from aluminum residues. Galindo and collaborators [45] have proposed a process for the preparation of hydrotalcite-like materials in which waste from the aluminum tertiary industry is started, specifically fine dust dispersions from the bag filters used in management of the gaseous effluent that is produced in the milling of aluminum slags. The authors prepare stable solutions of Al ³⁺ from said dispersions and undergo their conventional coprecipitation process at pH 10 with magnesium chloride hexahydrate. The structure of the materials obtained is generally of low crystallinity, with the presence of small spherical agglomerates due to the synthesis carried out, their properties depend on the presence of iron, as well as on the carbonate and chloride content. In subsequent publications of the same group [46], differences in the properties of the synthesized compounds are discussed when Al ³⁺ solutions obtained by moderate acid treatment of waste from the tertiary aluminum industry are coprecipitated with dilute sodium hydroxide with the help of ammonium or triethanolamine, keeping the pH at 10. It would therefore be interesting to have processes that facilitate the valorization of salt slags from processes of second fusion of aluminum and give rise to products of industrial interest, such as anionic clays. Preferably, the designed process should be as simple as possible, reducing as much as possible the high number of stages that aluminum recovery processes usually entail, to facilitate their industrial application.

The present invention provides a solution to that problem.

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Summary of the invention

The present invention is based on a process of preparing anionic clays of divalent cations, Me ²⁺ , and containing Al ³⁺ as a trivalent cation, by a modified coprecipitation process. The proposed method is based on an aqueous solution containing aluminum that comes from the attack, with acid or basic solutions, of salt slags generated in the recycling of scrap and aluminum by-products. The process of the invention is a modified coprecipitation process in which a solution containing the divalent cation Me ²⁺ is prepared separately together with the precipitating agent and the anion intended to compensate for the laminar load. Is this the solution that is reacted to cause precipitation, adding on it, drop by drop and hot, the aqueous solution containing Al as it has been obtained from the salt slag, without subjecting it to any intermediate preparation step. This method has the advantage that it requires a reduced number of stages, because no intermediate step of preparing the solution containing Al ³⁺ obtained from the salt slag is necessary; In addition, it has the additional advantage that it is not necessary to control the pH of the reaction, unlike the methods reported to date.

Thus, in a first aspect, the invention relates to a method for the preparation of anionic clays from salt slags from aluminum recycling processes comprising the steps of: a) contacting the salt slag with an aqueous solution acidic or basic; b) let the solution react with the salt slag; c) separating the salt slag from the aqueous solution with resulting Al ³⁺ ; d) add the aqueous solution of step c), dropwise and hot, onto a solution containing divalent cations together with a precipitating agent and the anions intended to occupy the interlaminar zone; e) Allow to react at least until the solution is finished adding with the aluminum and for a maximum of 6 hours.

Preferably, the method comprises the additional steps of: f) separating the solid formed in e) from the supernatant; g) subject the solid obtained in f) to heat treatment.

In a second aspect, the invention relates to an anionic clay obtained by the above method.

Brief description of the figures

Fig. 1: N ₂ adsorption-desorption isotherms of Ni: AI anionic clays with a 2: 1 molar ratio, treated at various heating temperatures, 200, 300 and 400 ^e C. Curves: o: anionic clay of Ni: AI treated at 200 ^e C for 24 hours; x: Ni anionic clay: AI treated at 300 ^e C for 24 hours; +: Ni anionic clay: AI treated at 400 ^e C for 24 hours. Fig. 2: Difractog X-ray branches representative of the anionic clays of Ni: AI and Co: AI synthesized with a 2: 1 molar ratio.

Fig. 3: Adsorption-desorption isotherms of N ₂ of the anionic clays of Co: AI with a 2: 1 molar ratio, treated at various heating temperatures, 200, 300 and 400 ^e C. Curves: o: anionic clay of Co: AI treated at 200 ^e C for 24 hours; x: Co: AI anionic clay treated at 300 ^e C for 24 hours; +: Co anionic clay: AI treated at 400 ^e C for 24 hours.

Description of the invention

The present invention comprises a new method of synthesis of anionic clays that directly and hotly uses the aqueous solution from the extraction of Al ³⁺ from a salt slag. The starting material (saline slag) is treated with solutions of acids or bases to extract aluminum, taking into account the time and temperature of treatment as variables. This first stage of treatment of the starting material was already described in a previous patent, specifically the Spanish Patent ES2350435 [47], directed to the use of the salt slag once treated. In that patent, said treatment conditions were used to activate a residue from the aluminum industry, specifically a salt slag from a second fusion process of aluminum, and use it as an adsorbent. In the present invention, the aluminum extracted in this activation process is used for use in the synthesis of other products, using the solution obtained as supernatant directly and hot in the process of activating the residue.

The conventional method of coprecipitation, by which an anionic clay can be obtained from an aluminum solution, is not applicable in this case. In said conventional method, the solution containing the aluminum also contains the divalent cation together with the anion intended to compensate for the laminar load, while the precipitating agent (generally sodium hydroxide) is supplied from another solution. Under the conditions of the present invention, the incorporation of the divalent cation into the supernatant containing Al ^{3+ would} lead to its precipitation, which prevents the formation of the anionic clay, producing the formation of simple oxides independently. To solve this difficulty, the invention requires a modification of the coprecipitation method, according to which the solution containing the divalent cation together with the precipitating agent and the anion intended to compensate for the laminar load is prepared separately. It is this solution that is reacted by adding on it drop by drop, hot, the supernatant containing Al ³⁺ as it has been obtained from the salt slag, without any intermediate preparation step, with the additional advantage that it is not necessary to control the pH of the reaction, unlike previously established methods.

This procedure allows to reduce the number of stages necessary for the synthesis of the hydroxide, since all the methods known in the state of the art require one or more intermediate stages in which the aluminum is separated from the solution containing it, in the form of some salt, before it can be used in the synthesis of hydroxide. In addition, it does not require pH control during mixing and resting of the coprecipitating solutions. The aluminum extraction process, as already mentioned, was described in Spanish patent ES2350435 and consists in contacting an aluminum salt slag with an aqueous, acidic or alkaline solution. The conditions under which this stage of contact with the slag or extraction of aluminum can be carried out can be any, as long as they give rise to the extraction of aluminum. The temperature of the contact process is generally the ambient temperature, but it can be in the range between 20 ^e C and the reflux temperature, which will be about 100 ^e C at a pressure of 101, 33 kPa (1 atmosphere). The pressure at which this stage is carried out may be atmospheric pressure, but it can also be carried out at higher pressures. The contact time depends largely on the reaction temperature, but is generally in the range of 0 to 2 hours. Preferably, this extraction stage a) is carried out in a container with stirring although, optionally and / or after a first stirring step, it can be carried out under reflux conditions.

As in the Spanish patent ES2350435, it is preferred that the salt slag be a slag from a second melting process of aluminum, with special preference for slags coming from a rotary kiln of fixed axis, and especially when they have an equal size or less than 1 mm. But the process of the present invention can also be applied to salt slags from other processes related to aluminum, these other alternatives being included within the scope of the invention.

As for the relationship between the reagents, the ratio between the amount of saline slag and the volume of acidic or basic aqueous solution with which it is contacted in step a) may be between 10 g / liter and 100 g / liter. It is considered appropriate to contact, for example, 2 g of saline slag with 0.2 liters of aqueous, acidic or basic solution, as in the Examples of the present application. Of all the variables of the aluminum extraction process, the most important are the pH of the activation solution, the concentration of the chemical agents, the time and the contact temperature.

It is preferred that the pH of the extraction solution is less than 2 or greater than 10, although it depends on the concentration of the acid or base. Specifically, the concentration of acids and bases used in this work varied between 0 and 2 mol / liter, obtaining that a greater amount of extracted aluminum is obtained when concentrations of 2 mol / liter are used.

Regarding the concentration of the acidic or alkaline aqueous solution, concentrations of 2 mol / liter or less are preferred. Thus, in said aqueous solution one or more acidic compounds or one or more basic compounds may be present at concentrations, preferably between 0 and 2 mol / liter. The acids can be organic or mineral origin, such as nitric (HN0 ₃ ), sulfuric (H ₂ S0 ₄ ) or hydrochloric (HCI) acids. Among the possible basic compounds that can be added to achieve alkaline solutions, sodium hydroxide (NaOH) stands out, but others, such as sodium bicarbonate (NaHC0 ₃ ), can also be used, which results in alkaline pH closer to neutrality. , about 8.

As for the extraction temperature, it may be between room temperature and reflux temperature, but the latter is preferable since the amount of aluminum extracted is greater.

Once the contact time that has been considered adequate has elapsed, the salt slag is removed from the solution with which the aluminum has been extracted in the form of Al ³⁺ cations. In order to carry out the salt slag separation step, any separation technique, such as filtration, centrifugation, supernatant decantation can be used after resting the salt slag mixture and dissolution and the like. In the present invention, the use of filtration is preferred.

The extracted aluminum is used in step c) of the process of the invention for the synthesis of anionic clays. Said synthesis is carried out according to this invention, using directly and hotly the solution in which the aluminum has been extracted, without any conditioning step, this new method being the main object of the invention, as explained above. The temperature range in step c) in which this process could be used without additional heating of the solution containing the extracted Al ³⁺ would be between 40 and 60 ^e C. The solution containing Al ³⁺ is reacts with a solution of a divalent metal that also contains a precipitating agent and an anion intended to compensate for the laminar charge. In the case of using a lower extraction temperature, the amount of aluminum extracted will be much lower. In this situation, the amount of anionic clay that can be synthesized will also be smaller or it will be necessary to increase the volume of the equipment since the volume of the solutions to maintain the yields will also be greater. In this second case, the volume of water to be managed will increase. It should also be noted that an additional heating step of the solution containing Al ³⁺ , up to at least 40-60 ^e C, will be necessary, since the reaction for obtaining the anionic clay must be hot. Therefore, the temperature of the solution containing the divalent metal, the precipitating agent and the anion should also be at least 40-60 ^e C when Al ³⁺ is added and must be maintained at least at that temperature during the time of reaction between Al ³⁺ and the other reagents that give rise to anionic clay.

According to the method of the present invention, this reaction consists in adding dropwise, and preferably under stirring, the solution containing Al ³⁺ on a solution containing the divalent metal cation (Me ²⁺ ) together with the agent precipitant and the anion. The precipitating agent is preferably sodium hydroxide, although others may be used, including ammonium hydroxide and triethanolamine; the anion is preferably carbonate (C0 ₃ ²⁺ ), although they may be others, such as those that are usually involved in the composition of materials called anionic clays, double lamellar hydroxides, mixed metal hydroxides or hydrotalcite-type compounds, such as they can be: N0 ₃ ^" , OH ^" , CI ^" , Br, Γ, S0 ₄ ^2" , Si0 ₃ ^{2 "} , Cr0 ₄ ^2" , B0 ₃ ^{2 "} , MnO ^4" , HGa0 ₃ ^{2 "} , HVC ^2" , CI0 ₃ ^" CI0 ₄ ^" I0 ₃ ^" S ₂ 0 ₃ ^2" , W0 ₄ ^{2 "} , [Fe (CN) ₆ ] ^3" , [Fe (CN) ₆ ] ⁴ - (PMoi ₂ O ₄₀ ) ^{3 "} , ( PW ₁₂ O ₄₀ ) ^{3 "} , V ₁₀ O ₂₆ ^6" , Mo ₇ 0 ₂₄ ^{6 "} , etc. As for the divalent metal cation, it is preferred that it be selected from the group of Co ²⁺ , Ni ²⁺ , Mg ²⁺ or Zn ²⁺ , although it can also be Cu ²⁺ , Mn ²⁺ , Ba ²⁺ , Fe ²⁺ , Ca ²⁺ or other divalent metal cations.

The solution containing the divalent metal, together with the precipitating agent and the anion, is preferably prepared once the concentration of aluminum in the extraction solution is known, by choosing the concentration of the salt of the metal cation in order to obtain solid with the desired Me ² 7AI ³⁺ ratios. Preference is given to the range of ratios used in the Examples of the present invention, that is, Me ² 7AI ³⁺ molar ratios between 2: 1 and 4: 1, both values included.

The reaction time between the solutions may vary, although it is considered appropriate that it is comprised between at least until the solution has been added with the solution. aluminum and up to a maximum of 6 hours, preferably between 1 and 6, as in the examples of the present application. The reaction is carried out under stirring, it being recommended that the stirring speed be in the range between 100 and 700 rpm. As a result an anionic clay is generated, which precipitates. To obtain the clay as such, dried and separated from the reaction mixture from which it has precipitated, it is preferred that the method of the invention include further steps in which the clay is separated from the supernatant and subjected to heat treatment. The separation of the anionic clay from the supernatant can be carried out by filtration, centrifugation or decantation with filtration being preferred. And the subsequent heat treatment preferably consists in subjecting it to a temperature between 50 and 400 ^e C, preferably in the range of 200 ^e C to 400 ^e C, for a time between 0.1 and 100 hours, the most usual between 0.5 and 48 hours.

The present invention also relates to the anionic clays obtained by the method of the present invention. Said clays respond to the formula [Me (ll) ₁ - _x Me (lll) _x (OH) ₂ (A ^{n "} ) _{x /} n] -mH ₂ 0, where

M (ll) is a divalent cation (Me ²⁺ ),

M (lll) is Al ³⁺ ,

A is a charge anion n, x is a rational number between 0.2 and 4, determines the charge density in each layer and the anion exchange capacity, n represents the negative electronic charge of the interlaminar anion and is an integer which can vary between -1 and -8, m represents the water molecules present as hydration water or as water present in the interlaminar region and is a rational number between 0 and 10, where A, x, n and m are in such a way that the formula meets the rule of neutrality of its total load.

As mentioned before, these are anionic clays that comprise Al ³⁺ cations and divalent metal cations, and anions and water in the interlaminar space. In the Examples presented below, the synthesis of anionic clays in which the divalent metal cation is selected from the group of Co ^{2+ is described} and Ni, the anion is C0 ₃ and the metal cation / Al ratio varies between 2: 1 and 4: 1. Experiments show that its specific surface area varies between 19 and 281 m ² / g and its total pore volume is between 0.045 and 0.685 cm ³ / g. This degree of porosity makes them suitable for use in catalytic and adsorption processes.

The tests shown in the Examples section, performed with Co ²⁺ and Ni ²⁺ , and with C0 ₃ ²⁺ are representative cases of the applicability of the method of the invention. According to previous knowledge about the synthesis of anionic clays and derivatives thereof, the method is considered applicable and suitable for any other divalent cation and any other anion, especially those that have been previously used or known to be valid. for the preparation of anionic clays, hydrotalcite type compounds, double lamellar hydroxides or mixed metal hydroxides, under usual conditions of preparation of these compounds, as previously stated. The method of synthesis of the anionic clays and their properties will now be explained in more detail by means of the Examples and the Figures included below.

Examples

Example 1 .- Obtaining anionic clays of Ni In the present Example, a salt slag from a rotary kiln with a fixed axis and of a size smaller than 1 mm was used for the extraction of aluminum by chemical agents.

Chemical extraction was carried out using aqueous solutions of NaHC0 ₃ (99.7%, Sigma-Aldrich), HCI (65%, Panreac), H ₂ S0 ₄ (98%, Panreac) and NaOH (Panreac) in various concentrations . Specifically, concentrations between 0 and 2 mol / liter. The reaction time with each of these solutions was also a parameter studied, being between 0 and 2 hours. Briefly, at each activation 2 g of saline slag are contacted with 200 cm ³ of chemical reagent solution. The stirring speed of the suspensions was 500 rpm. After the reaction time elapsed, the suspensions were filtered to separate the slag from the solution. The amount of aluminum extracted was analyzed by ICP-radial and is between 3 and 1609 mg _A | / liter depending on the reaction time, chemical reagent concentration and temperature conditions (see Table 1). Table 1 . Aluminum extracted (mg / liter) depending on the chemical reagent, for a concentration of the chemical reagent of 2 mol / liter and under thermal reflux conditions. NaHC0 ₃ time, NaOH HCI, H ₂ S0 ₄ ,

(min) reflux Reflux (TT reflux reflux

0 3 1007 (18) 987 1246

20 5 1352 (152) 1249 1391

60 30 1385 (417) 1296 1494

120 86 1514 (342) 1418 1609

^* Between parénl is the aluminum extracted at room temperature (T ^a ). Ni anionic clays were prepared from aqueous solutions of Ni (N0 ₃ ) ₂ -6H ₂ 0 (PA, Panreac) and Na ₂ C0 ₃ (Sigma-Aldrich) in order to obtain solids with molar ratios Ni ² 7AI ^{3 +} between 2: 1 and 4: 1 (see Table 2). The solution with extracted aluminum was added dropwise and under stirring at 500 rpm, to the solution resulting from dissolving nickel nitrate and sodium carbonate. The temperature and reaction time were 60 ^e C and 1 h.

Table 2. Concentrations of the reagents used in the synthesis of Ni anionic clays.

Sample Ni ² 7AI ³⁺ Al ^{3+ *} Ni (N0 ₃ ) ₂ NaOH Na ₂ C0 ₃ ^**

Ni: AI_2: 1 2: 1 6495 mg / liter 12990 mg / liter 0.8 mol / liter 0.19 mol / liter Ni: AI_4: 1 4: 1 6564 mg / liter 26256 mg / liter 0.8 mol / liter 0.19 mol / liter

^* Aluminum extracted by treating 2 g of salt slag with 200 cm ³ of NaOH 2 mol / liter for 2 hours.

 "Concentration in the final volume.

After the reaction time, the suspensions were filtered to separate the solid from the solution. To dry the product, we proceeded to heating at 60 C ^and at atmospheric pressure for 48 hours. The textural properties of the solids obtained were determined by adsorption of N ₂ (Air Liquide, 99.999%) at -196 ^e C in a commercial static volumetric equipment (ASAP 2010 of the Micromeritics commercial house). The solids were previously degassed for 24 h and at a pressure below 0.1 Pa. The amount of solid used in the experiment was 0.2 g.

The adsorption of N ₂ provides a series of quantitative properties such as surface area and pore volume. The surface area can be calculated by applying the BET equation [48]: plp ° 1

 H p I p

(l - p / p °) ^~ V _m - CV _m - C

siendo S el área superficial, V_m el volumen de monocapa, a el área ocupada por una molécula de N₂ adsorbido sobre la superficie de la arcilla (16,2 Á²/molec), N_A el número de Avogadro (6,023- 10²³ molec/mol) y V el volumen ocupado por un mol de N₂ a 25^eC y 1 atmósfera (22.386 cm³/mol). Los volúmenes de poros totales (Vp_Totai) se estiman a partir de los volúmenes de N₂ adsorbidos a un valor de presión relativa de 0,99 [48], asumiendo que la densidad del nitrógeno en los poros es igual a la del nitrógeno líquido a -196^eC (0,81 g/cm³) [48]. p / p ^Q \ being at relative pressure, V e \ volume of N ₂ adsorbed in equilibrium by the sample at the relative pressure p / p ^e , V _m the volume of monolayer and C a constant. The linear adjustment of the BET equation in the relative pressure range between 0.05 and 0.20, allows to ensure the formation of a monolayer and calculate the volume of monolayer. With the volume of monolayer the surface area of the slag can be calculated using the equation:

S being the surface area, V _m the monolayer volume, to the area occupied by a molecule of N ₂ adsorbed on the clay surface (16.2 Á ² / molec), N _A Avogadro's number (6.023-10 ²³ molec / mol) and V the volume occupied by one mole of N ₂ at 25 ^e C and 1 atmosphere (22,386 cm ³ / mol). Total pore volumes (Vp _To tai) are estimated from the volumes of N ₂ adsorbed at a relative pressure value of 0.99 [48], assuming that the density of nitrogen in the pores is equal to that of nitrogen liquid at -196 ^e C (0.81 g / cm ³ ) [48].

The results regarding the textural properties obtained for the double laminar hydroxide synthesized from the extraction of aluminum with a solution of NaOH of concentration 2 mol / liter and with a molar ratio of Ni ² 7AI ³⁺ of 2: 1 are shown at continued in Table 3. The adsorption-desorption isotherms of the materials obtained by this preparation at various treatment temperatures are shown in Fig. 1.

Table 3. Textural properties derived from the adsorption of N ₂ to -196 ^e C.

Sample S ⁵ Vp _™

(m ² ^ (cm ³ ^

Ni: AI_2: 1_200 ^and C 19 0.045

Ni: AI_2: 1_300 ^and C 244 0.185

Ni: AI_2: 1_400 ^and C 281 0.214 a Specific surface;

 b Total pore volume;

⁰ grams of degassed sample

These materials were also characterized by X-ray diffraction using a SIEMENS diffractometer, model D5000. A representative example is presented in Fig. 2.

The X-ray diffraction results included in Fig. 2 confirm the obtaining of Ni anionic clays. Therefore, the method presented in this invention makes it possible to obtain anionic clays from aluminum extracted from residues from the aluminum industry. In the case of the textural results included in Table 3, the method presented in this invention also allows to obtain solids with high values of specific surface area and pore volume, solids that will be suitable for application as adsorbents and as catalysts. Example 2.- Obtaining anionic clays of Co

In the present Example, a salt slag from a rotary kiln with a fixed axis and smaller than 1 mm was used for the extraction of aluminum by chemical agents.

The anionic clays of Co were prepared from aqueous solutions of Co (N0 ₃ ) ₂ -6H ₂ 0 (99%, Sigma-Aldrich) and Na ₂ C0 ₃ (Sigma-Aldrich) in order to obtain solids with Co molar ratios ² 7AI ³⁺ between 2: 1 and 4: 1 (see Table 4). The solution with extracted aluminum is added dropwise and under stirring, to the solution resulting from dissolve nickel nitrate and sodium carbonate. The temperature and reaction time were 60 ^e C and 1 h.

Table 4. Concentrations of the reagents used in the synthesis of anionic clays from Co.

Sample Co ² 7AI ³⁺ Al ^{3+ *} Co (N0 ₃ ) ₂ NaOH Na ₂ C0 ₃ ^**

Co: AI_2: 1 2: 1 6322 mg / liter 12644 mg / liter 0.8 mol / liter 0.19 mol / liter Co: AI_4: 1 4: 1 6584 mg / liter 26336 mg / liter 0.8 mol / liter 0.19 mol / liter

^* Aluminum extracted by treating 2 g of salt slag with 200 cm ³ of NaOH 2 mol / liter for 2 hours.

 "Concentration in the final volume.

The results referring to the textural properties obtained for the double laminar hydroxide synthesized from the extraction of aluminum with a solution of NaOH of 2 mol / liter concentration and with a molar ratio of Co ² 7AI ³⁺ of 2: 1 are shown at then in Table 5. The adsorption-desorption isotherms of the materials obtained by this preparation at various treatment temperatures are shown in Fig. 3.

Table 5. Textural properties derived from the adsorption of N ₂ to -196 ^e C.

Sample S ⁵ Vp ™ ^"

(m ² ^ (cm ³ ^

Co: AI_2: 1_200 ^and C 97 0.541

Co: AI_2: 1_300 ^e C 186 0.677

Co: AI_2: 1_400 ^and C 189 0.685 a Specific surface;

 b Total pore volume;

 0 grams of degassed sample

These materials were also characterized by X-ray diffraction using a SIEMENS diffractometer, model D5000. A representative example is presented in Fig. 2. The X-ray diffraction results included in Fig. 2 confirm the obtaining of Ni anionic clays. Therefore, the method presented in this invention makes it possible to obtain anionic clays from aluminum extracted from residues from the aluminum industry. In the case of the textural results included in Table 5, the method presented in this invention also allows to obtain solids with high values of specific surface area and pore volume, solids that will be suitable for application as adsorbents and as catalysts.

Claims

one . A method for the preparation of anionic clays from salt slags from aluminum recycling processes, comprising the steps of: a. contacting the salt slag with an acidic or basic aqueous solution; b. let the solution react with the salt slag c. separate the salt slag from the aqueous phase with resulting Al ³⁺ ; d. add the aqueous solution resulting from step c), dropwise and hot, onto a solution containing divalent metal cations together with a precipitating agent and with the anions intended to occupy the interlaminar zone; and. allow to react at least until the solution is finished adding with the aluminum and for a maximum of 6 hours. 2. The method according to claim 1, comprising the additional steps of: f. separating the solid formed in e) from the supernatant; g. subject the solid obtained in f) to heat treatment. 3. The method according to any one of claims 1 or 2, wherein the salt slag of step a) is derived from a second melting process of aluminum which has taken place in rotary furnaces with a fixed axis. 4. The method according to any one of the preceding claims, wherein: i) the relationship between the amount of saline slag and the volume of acidic or basic aqueous solution with which it is contacted in step a) is comprised between 10 g / liter and 100 g / liter; ii) the salt slag and the aqueous solution are contacted in step a) and left in step b) at a temperature between room temperature and reflux temperature, and at atmospheric pressure or higher; iii) the contact time between the salt slag and the aqueous solution in step b) is in the range of 0 to 2 hours. 5. The method according to any one of the preceding claims, wherein the aqueous solution of step a) has a pH of less than 2 or greater than 10. 6. The method according to any one of the preceding claims, wherein in the aqueous solution of step a) it is prepared by adding one or more acidic compounds or one or more basic compounds at concentrations between 0 and 2 mol / liter. 7. The method according to any one of the preceding claims, wherein the aqueous solution of step a) is prepared i) by adding an acid selected from nitric acid (HN0 ₃ ), sulfuric acid (H ₂ S0 ₄ ) or hydrochloric acid (HCI), or ii) adding to water a base selected from sodium hydroxide (NaOH) or sodium bicarbonate (NaHC0 ₃ ). 8. The method according to any one of the preceding claims, wherein step c) of separating the salt slag from the resulting aqueous extraction solution is carried out by filtration, centrifugation or decantation of the supernatant after leaving the mixture at rest. of salt slag and aqueous solution. 9. The method according to any one of the preceding claims, wherein the divalent metal cations of the solution onto which the solution resulting from step c) is poured dropwise are selected from the group of Co ²⁺ , Ni ²⁺ , Mg ²⁺ , Zn ²⁺ , Cu ²⁺ , Mn ²⁺ , Ba ²⁺ , Fe ²⁺ and Ca ²⁺ . 10. The method according to claim 9, wherein the divalent metal cations are Co ²⁺ cations or Ni ²⁺ cations. eleven . The method according to any one of the preceding claims, wherein the anion intended to occupy the interlaminar area of the clay and present in the solution onto which the solution resulting from step c) is poured dropwise is selected from the group of C0 ₃ ²⁺ , N0 ₃ ^" , OH ^" , CI ^" , Br, Γ, S0 ₄ ^2" , Si0 ₃ ^{2 "} , Cr0 ₄ ^2" , B0 ₃ ^{2 "} , MnO ^4" , HGa0 ₃ ^{2 "} , HV0 ₄ ² -, CI0 ₃ -, CIO ₄ -, I0 ₃ -, S ₂ 0 ₃ ^{2 "} , W0 ₄ ² -, [Fe (CN) ₆ ] ^3" , [Fe (CN) ₆ ] ^{4 "} , (PMo ₁₂ O ₄₀ ) ^{3 "} , (PW ₁₂ O ₄₀ ) ^3" , V ₁₀ O ₂₆ ^{6 "} , Mo ₇ 0 ₂₄ ^6" . 12. The method according to any one of the preceding claims, wherein the precipitating agent present in the solution onto which the aqueous solution resulting from step c) is poured dropwise is NaOH. 13. The method according to any one of the preceding claims, which includes an additional intermediate step in which the concentration of Al ³⁺ present in the aqueous solution resulting from step c) is determined before preparing the solution containing divalent metal cations together with a precipitating agent and with the anions intended to occupy the interlaminar zone and which is used in step d). 14. The method according to any one of the preceding claims, wherein the solution of step d) containing divalent metal cations together with an agent 5 precipitant and with the anions intended to occupy the interlaminar zone is prepared prior to step d) so that the divalent metal cation / Al ³⁺ molar ratio has a value of 2: 1 to 4: 1. 15. The method according to any one of the preceding claims, wherein the aqueous solution with Al ³⁺ resulting from step c) is at a minimum temperature of 10 40-60 ^e C when added in step d) to the solution containing divalent metal cations together with a precipitating agent and the anions intended to occupy the interlaminar zone. 16. The method according to any one of the preceding claims, wherein the reaction temperature in step e) is maintained at a value of at least 40-60 ^e C. The method according to any one of the preceding claims, wherein the reaction time in step e) is comprised between 1 and 6 hours and the reaction takes place with stirring at a speed of 100 to 700 rpm. 18. The method according to any one of the preceding claims, wherein steps f) and g) claimed in claim 2 are carried out. The method according to claim 18, wherein i) step f) is carried out by separating the solid formed in step e) from the supernatant by filtration, and ii) step g) is carried out by subjecting the solid obtained in step f) at a heat treatment at a temperature between 50 ^e C and 400 ^e C and for a time 25 between 0.1 and 100 hours. 20. The method according to claim 2, wherein: in step a), 2 g of salt slag from second-melting processes of aluminum are contacted with 0.2 liters of an aqueous NaOH solution of concentration of 2 mol / liter, in step b), the salt slag and the aqueous solution are allowed to react for a reaction time of 2 hours, at a stirring speed of 500 r, pm, under thermal reflux conditions, in step c) the salt slag it is separated from the aqueous phase with resulting Al ³⁺ 5 by filtration, before performing stage d), the concentration of Al ³⁺ present in the aqueous solution resulting from stage c) is determined, stage d) is carried out with a solution containing divalent metal cations together with a precipitating agent and with the anions intended to occupy the interlaminar zone 10, a solution that is prepared before performing step d) so that the ratio divalent metal cations / Al ³⁺ , after adding all Al ³⁺ in step d), has a value of 2: 1 or 4: 1, the metal cation is selected from Co ²⁺ and Ni ²⁺ , the precipitating agent is NaOH and the anions are C0 ₃ anions ²⁺ , in step e), the reaction time is 1 hour and the reaction temperature is 15 of 60 ^e C, in step f) the solid formed in step e) is separated from the supernatant by filtration, in step g), the solid obtained in step f) is subjected to a heat treatment at a temperature of 60 ^e C for a period of 1 hour. 20 21. An anionic clay obtained by the process of any one of claims 1 to 20. 22. Anionic clay according to claim 21, which responds to the formula: [Me (ll) i- _x Me (lll) _x (OH) ₂ (A ⁿ ) _{x / n} ] -mH ₂ 0, wherein M (ll) it is a divalent cation (Me ²⁺ ), 25 M (lll) is a trivalent cation (Al ³⁺ ), A is a charge anion n, x is a rational number between 0.2 and 4, determines the charge density in each layer and the anion exchange capacity, n represents the negative electronic charge of the interlaminar anion and is a number 30 integer that can vary between -1 and -8, m represents the water molecules present as hydration water or as water present in the interlaminar region and is a rational number between 0 and 10, where A, x, n and m are such that the formula meets the neutrality rule of its total load 23. Anionic clay according to claim 21 or 22, comprising in its sheets Al ³⁺ cations and divalent metal cations, and anions and water in the interlaminar space. 24. Anionic clay according to claim 23, wherein the divalent metal cations is selected from the group of Co ²⁺ and Ni ²⁺ , the anion is C0 ₃ ²⁺ and the metal cation / Al ³⁺ ratio varies between 2: 1 and 4: 1. 25. Anionic clay according to claim 23 or 24, whose specific surface area varies between 19 and 281 m ² / g and whose total pore volume between 0.045 and 0.685 cm ³ / g.