ES2919251B2 - Pillared clays with improved textural properties, their preparation from salt slag from aluminum recycling processes and their use - Google Patents

Description

DESCRIPTION

Pillared clays with improved textural properties, their preparation from saline slags from aluminum recycling processes and their use

Technical field of the invention

The present invention is within the field of industrial chemistry. Specifically, it refers to the obtaining of pillared clays and their derivatives, from aluminum waste, for example, salt slag from the second aluminum smelting processes.

BACKGROUND OF THE INVENTION

Aluminum recycling and salt slag generation:

Whether or not to treat the waste generated in aluminum recycling and how it is carried out has generated a wide debate in the scientific and industrial community. During the aluminum recycling process, various types of waste are generated [1]. Salt slags are produced when salts are used to cover molten material mainly from low-quality aluminum scrap and aluminum-rich slags [2]. The average composition of the saline slags can be summarized as: aluminum metal 3-9%; various oxides 20-50%, AbO3, Na2O, K2O, SiO2 and MgO, fraction referred to as non-metallic products; 50-75% fluxes, usually NaCl and KCl; and other compounds in smaller proportion; among them Nal, A L C A^S3, Si3P4, Na2SO4, Na2S and cryolite [3]. Due to its composition and possible reaction with water, salt slag from aluminum recycling processes is classified as hazardous waste, code LER (European Waste List) 100308 according to the Agency's "European Waste Catalog and Hazardous Waste List". of Environmental Protection [4], and must be managed through controlled dumping or in security deposits.

Once the aluminum metal has been separated from the residue by screening, the material produced is treated with water to separate the soluble from the insoluble fraction. In this way, a new residue with a lower salt content and a saline solution would be obtained. Where should the salt be recovered from? The composition of this new waste limits the possible applications and makes it possible to opt for its management in controlled dumping. Controlled landfill storage is precisely the other alternative to the management of saline slag once the metal aluminum fraction has been recovered [3]. This option is not the most desirable, so an attempt has been made to find alternatives to dumping that value this type of waste, as well as applications for the new materials. The use and applications of aluminum waste depend on the chemical composition of the oxides. The main phase detected in this type of waste is aluminum oxide [5]. Without any additional treatment, it can be used for direct applications as inert filler for construction, road paving, mortar components, aluminum salts, inert filler in polymeric composite materials, adsorbents, mineral wool, etc. WO9109978, US5132246 and WO9412434 describe that aluminum can also be recovered as a high added value product and used to synthesize materials such as pure alumina, salts and hydroxides [6-8].

Recovery of aluminum present in salt slags:

The aluminum present in salt slags can be extracted by treatment with solutions of acids or bases to be used later in the synthesis of other materials. This has been the objective of a very limited number of works in which these residues have been used as a source of aluminum. Thus, for example, aluminum slag treated with H2SO4 allows the recovery of a high percentage of aluminum that can be used in the production of y-AbO3 [9]. In this work the authors propose that the synthesized material can be used as an adsorbent or catalytic support, after a treatment at 900 °C to stabilize the synthesized oxide phase. In US6110434 [10], the non-metallic fraction at various pH is described to selectively separate alumina and magnesia. Several authors [11-13] extract aluminum by acid leaching treatment of the non-metallic fraction at low temperature and synthesize alumina with a high degree of purity (99.28%). Aluminum sulfate can also be used directly as a coagulant for wastewater treatment, as reflected in ES2176064 and ES2277556 [14,15]. Using a procedure similar to that described above, Park et al. [16] leached a residue with NaOH to extract the aluminum as sodium aluminate and precipitate it as aluminum hydroxide. The authors use the calcined oxide to make castable refractories by mixing with aggregates and alumina cement. El-Katatny et al. [17] describe a process in which aluminum is recovered from the slag by precipitation with aluminum hydroxide. The obtained powder is activated at 600 °C to obtain Y-AI2O3. A similar procedure is described by Jung and Mishra [18]. Recently Meshram et al. [19] propose the synthesis of tamarugite, an aluminum sulfate (NaAI(SO4)-6H2O) by adding NaOH and H2SO4 solutions to salt slag. This salt can be used as a coagulant. Zhang et al. [20] synthesize MgAlO4 spinel from aluminum slag by physical mixing with MgO, 25 MPa pressure, and heat treatment between 1100 and 1500 °C for 3 h. The authors also study how the density of the material obtained by adding Eu2O3, La2O3, Y2O3 and CeO2 increases. The results obtained are explained by the formation of oxides of the YAlO3, Al2Ca0,5La0,5 type. Using a similar procedure, other authors synthesize a (Mg,Si)Al2O4 spinel, which is also used as a refractory material [21]. Murayama et al. [22] and Kim et al. [23] synthesized microporous aluminophosphate molecular sieves (AlPO4-5 and CrAlPO4-5). The synthesis of materials from this type of waste has been recently reviewed by Meshram and Singh [24].

In ES267037 B1 [25] the authors propose a method for revaluing the fines from the grinding of aluminum slags by transforming them into zeolites. Zeolites are crystalline aluminosilicates with a structure based on a three-dimensional network of AlO4 and SiO4 tetrahedra that share their oxygen atoms. Zeolites have been used in processes such as catalysis, gas separation, water purification, among others [26]. In recent years, zeolites have been synthesized from a wide variety of residues used as low-cost precursors [27]. The invention arises through a hydrothermal synthesis method in which the residue from the grinding of the slag is added to a reactor with NaOH and sodium silicate solutions. The reaction is carried out at a temperature of up to 200 °C and under pressure. The zeolites obtained are of the NaP1 type, analcima (ANA) and sodalite (SOD), materials that presented a low specific surface area of up to 15.5 m2/g. The synthesis of zeolite X (NaX), zeolite A (LTA) and sodalite (SOD) from a saline slag from aluminum recycling has been developed by Yoldi et al. [28]. The procedure used requires two stages. In the first, the aluminum is extracted from the slag by treatment with a NaOH solution, to later carry out a hydrothermal treatment with an external source of silicon. The zeolites obtained presented specific surfaces of up to 450 m2/g.

ES2673587 B2 [29] proposes the use of the aluminum cation, Al3+, extracted from salt slags for the synthesis of so-called anionic clays, hydrotalcite-type compounds or mixed metal hydroxides of the formula [Me(II)1-xMe(III) x(OH)2(An-)x/n].mH2O (where M(II) is a divalent cation (Me2+), M(III) is a trivalent cation (Me3+), A is a charge anion n, and x is a rational number between 0.2 and 4, which determines the charge density in each layer and the ionic exchange capacity). These compounds are lamellar double hydroxides that incorporate anions and water in the lamellar space. The document shows the obtaining of hydrotalcites with divalent cations such as Co2+, Mg2+ and Ni2+, from cationic aluminum (Al3+) extracted from salt slag, by means of modified coprecipitation in a single step, which is achieved thanks to the fact that the aluminum extracted from The salt slag is added dropwise and hot to a solution containing both the precipitating agent and the divalent metal cation and interlaminar anion. Among others, the method has the advantage that it is not necessary to control the pH of the reaction.

Pillared clays and their synthesis:

One of the families of materials that has been studied with greater intensity and depth in the last 50 years has been intercalated clays, materials that offer commercial advantages as being cheap, stable and easy to prepare. Clay minerals are present in the earth's crust as major components of rocks. They are mainly made up of hydrated aluminum/magnesium silicates, with a lamellar or fibrous crystalline structure, in which there may also be other elements such as Fe3+, Ca2+, Na+, K+, among others. These materials are made up of SiO4 tetrahedrons joined together to form continuous tetrahedral layers, while the octahedral groups of AlO6 or MgO6 form continuous octahedral layers. When two tetrahedral layers with an intervening octahedral layer are joined, a 2:1 sheet is obtained. The smectites belong to this family of clays, which include the clay minerals montmorillonite, beidellite, saponite, hectorite, among others. Between the 2:1 sheets of the idealized structure are interlamellar hydrated cations that balance the sheet charge.

The idealized structure of a smectite consists of a succession of 2:1 sheets, each formed by two tetrahedral layers and a central octahedral layer joined together by oxygen common to the layers. The sheets grow in a plane and are stacked, in some order or not, along the axis perpendicular to that plane. Between the 2:1 sheets are hydrated interlamellar cations that balance the charge. Smectites have been the most commonly used clays for the preparation of stable intercalated clays and, among them, montmorillonite, whose theoretical formula is:

Mg+(Si8)IV(Al4-xMgx)VIO2o(OH)4

where M+ is the exchangeable cation and x is the charge on the sheet (0.6 < x < 1.2).

The synthesis of interbedded clays has provided new opportunities in the applications of clay-based solids [30]. These materials, initially developed in the 1970s as an alternative to zeolites in catalytic hydrocracking, are synthesized by exchanging metal cations that offset the interlaminar negative charge with metal polyhydroxycations. When the intercalated clays are thermally treated, the inserted polycations produce stable rigid oxides, which allow the clay sheets to be separated in a stable manner and act as pillars inserted between one sheet and the other that stabilize the structure. For this reason, the clays thus generated are called pillared clays and are often referred to by the abbreviation PILC, from the English term Pillared InterLayered Clay.

Pillared clays are characterized by having an interesting microporous structure formed by the spaces found between the clay sheets and between the rigid structures of the intercalated metal oxides. The distances that define these spaces, as well as some of the physicochemical properties of the pillared solids, related to their texture, are controlled by adjusting variables of their synthesis process, which gives rise to variations in their adsorption capacity and storage.

The flexibility in pore size variation is one of the main advantages of pillared clays, compared to other materials such as zeolites or carbon-based materials. Its structure can undergo other modifications, aimed at increasing its adsorption capacity.

A wide variety of polycations have been used in the synthesis of pillared clays. Among aluminum-based intercalating reagents, one of the most widely used as intercalating solution is a hydrolyzed base/AlCh solution, prepared at OH/Al molar ratios between 1.0 and 2.5. The intercalating species with which the expansion of the interlaminar gap is related is the aluminum polyhydroxycation known as the Keggin ion, [Al13O4(OH)24(H2O)12]7+. During calcination, the intercalating precursor is converted into rigid pillars of alumina and protons are released, which migrate to the octahedral layer of the sheets and become inaccessible for cation exchange.

Montmorillonite is one of the most widely used clay minerals to obtain pillared clays and, in particular, intercalating it with an aluminum polyhydroxycation and calcining it. The adsorption capacity of this type of material is known, although attempts have been made to modify it by including other additional compounds in the pillared clay.

US4757040 describes the intercalation of a rectorite with a solution of aluminum chlorohydroxide synthesized from AlCl3 and NaOH with a 1:1 molar ratio and aged for 6 days at room temperature. The synthesis ratio used by the authors is 3.29 mgAl/heron, 0.5 h of reaction and a pH between 4 and 6. After filtration and washing, the solid obtained is treated for 2h at 650 °C. The basal spacing is between 0.6 and 1.0 nm with a specific surface area value of 174 m2/g. Along the same lines, we can cite US3887454, US4176090 and US4216188,

US5214012 describes a procedure to obtain an intercalated smectite by adding an oligomeric cationic hydroxide to the aqueous suspension containing the clay. Basal spacing can be controlled by adjusting the amount of oligomeric cation added. Although they indicate that the smectite can be any clay mineral and do not indicate that it must be laminar with ionic exchange capacity, in the patent examples they are developed with a hectorite. The Al oligomer to be used in the intercalation is prepared from Ab(OH)5Cl-2.4H20. Thus, in the first example of the patent, in addition to the hectorite and the Al precursor, PVA (polyvinyl alcohol) is added to the aqueous suspension, which will allow the clay to expand and intercalation to take place. After calcination at 500 °C, the basal spacing that they obtain can be up to 2.44 nm, but they do not indicate if it is due only to the presence of the Al oligomer or if the presence of PVA plays a fundamental role. Likewise, they do not indicate the accessibility, based on the specific surface, of these materials. In US5087598, the authors propose a simplified procedure to the one previously presented in which they do not include PVA as an agent to aid the intercalation. They propose a commercial aluminum chlorohydroxide solution as a source of the Al polycation, obtaining materials with a specific surface area of up to 267 m2/g and a basal spacing of 0.84 nm.

US5360775 refers to a layered clay with ion exchange properties which is mixed with a solution containing a metal hydroxo polycation, a hydroxide or charged fine particles and which can be exchanged with the clay surface. The Clay is heat treated to generate a porous interlayered clay. In the case of the aluminum exchange cation, it is obtained from the reaction of the commercial salt AlCl3-6H2O with NaOH. The basal spacing that is generated is 0.85 nm with a specific surface area of 250 m2/g.

US5486499 refers to the synthesis of an adsorbent suitable for use in the purification of edible oils such as soybean oil comprising the treatment of a laminar clay mineral with a solution of a material such as an aluminum cation suitable to generate a pillar in the clay mineral. The process is characterized by the removal of at least some structural aluminum from the clay mineral by acid treatment prior to contact with the intercalation material. The clay used by the authors is a smectite supplied by Laporte Industries Limited and the intercalating agent is an aluminum chlorohydrate solution aged preferably at 40 °C and with a pH of 6.

A commercial aluminum polycation with an approximate chemical structure of Al2(OH)5Cl-2H2O, sold under the name Chlorhydrol® by the Reheis Chemical Company, has been used in several patents. Thus, for example, in US4637991. The polycation marketed in this way is used directly for the intercalation of clay to obtain specific surfaces between 97 and 235 m2/g. These materials have been used to separate mixtures of O2/N2, H2/N2, CH4, C2H6, among other hydrocarbon mixtures. Another commercial product that has been used in the intercalation of clays are Al2O3 particles, a commercial product protected by US6342153 B1 where a rectorite is included as a material to be intercalated, reaching a specific surface area of 137 m2/g. This material is used as a catalyst for the catalytic pyrolysis of hydrocarbons.

In line with ES2350435 B2 and ES2673587 B2, it is interesting to have processes that facilitate the recovery of saline slags from secondary aluminum smelting processes and that give rise to products of industrial interest, as is the case of pillared clays that giving industrial waste value as a raw material and using a natural material to produce others with added value. Preferably, the designed process should be as simple as possible, thus reducing the preparation steps of the intercalating agent and the volume of water required, but achieving a product that presents high textural properties, to facilitate its industrial application, particularly as an adsorbent. The contribution of new and alternative procedures to obtain the intercalation precursors could also provide new avenues of synthesis to explore on which to make modifications with a view to obtaining improvements in the interspersed and pillared materials.

The present invention provides a solution using only commercial sources for the synthesis of the intercalating agent for layered clays. Several routes are proposed to achieve the intercalation and, therefore, the pillared material that allows obtaining a useful material as an adsorbent.

Bibliographic references

1. G. Drossel, S. Friedrich, W. Huppatz, C. Kammer, W. Lehnert, O. Liesenberg, M. Paul, K. Schemme, Aluminum Handbook, Vol. 2. Forming, Casting, Surface Treatment, Tecycling and ecology. Ed. Aluminum-Verlag Marketing and Communication GMBH, (2003).

2. J.A.S. Tenorio, D.C.R. Espinosa, Effect of salt/oxide interaction on the process of aluminum recycling, Journal of Light Metals, 2, (2002), 89-93.

3. A. Gil, Management of the salt cake from secondary aluminum fusion processes, Industrial & Engineering Chemistry Research, 44, (2005), 8852-8857.

4. European Waste Catalog and Hazardous Waste List, Environmental Protection Agency, Ireland, valid from 1 January 2002.

5. J.N. Hryn, E.J. Daniels, T.B. Gurganus, K.M. Tomaswick, Products from salt cake residue oxide, Third International Symposium on Recycling of Metals and Engineering Materials, P.B. Queneau and R.D. Peterson, Eds. The Minerals, Metals & Materials Society, 905-916 (1995).

6. G. Chauvette, F.M. Kimmerle, R. Roussel. Process for converting dross residues to useful products. WO 91/09978 (1991).

7. C. Brisson, G. Chauvette, F.M. Kimmerle, R. Roussel, Process for using dross residues to produce refractory products. United States Patent: 5,132,246 (1992).

8. L. Parent, S. Tremblay. Process for converting waste aluminum dross residue into useful products. WO 94/12434 (1994).

9.B.R. Das, B. Dash, B.C. Tripathy, I.N. Bhattacharya, S.C. Das, Production of y-alumina from waste aluminum dross, Minerals Engineering, 20, (2007), 252-258.

10. JW Pickens, MD White, Recovery of products from non-metallic products derived from aluminum dross. US Patent 6,110,434 (2000).

11. E. David, J. Kopac, Aluminum recovery as a product with high added value using aluminum hazardous waste. Journal of Hazardous Materials, 261, (2013), 316-324.

12. M. Mahinroosta, A. Allahverdi, Enhanced alumina recovery from secondary aluminum dross for high purity nanostructured g-alumina powder production: Kinetic study. Journal of Environmental Management, 212, (2018), 278-291.

13. M. Mahinroosta, A. Allahverdi, A promising green process for synthesis of high purity activated-alumina nanopowder from secondary aluminum dross. Journal of Cleaner Production, 179, (2018), 93-102.

14. C. Iranzo. Manufacturing procedure for aluminum sulfate and its derivatives from aluminum hydroxide sludge from anodizing plants. Spanish Patent: 2,176,064 (2003)

15. C. Iranzo, N. Lopez. Manufacturing procedure for basic aluminum salts and their derivatives from aluminous waste and applications. Spanish Patent: 2,277,556 (2008).

16. H. Park, H. Lee, J. Kim, A processing for recycling of the domestic aluminum dross, Global Symposium on Recycling, Waste Treatments and Clean technology, Vol. II. REWAS, San Sebastian, Spain, p. 995.

17. E.A. El-Katatny, S.A. Halany, M.A. Mohamed, M.I. Zaki, Surface composition, charge and texture of active alumina powders recovered from aluminum dross tailings chemical waste, Powder Technology, 132, (2003), 137-144.

18. M. Jung, B. Mishra, Recovery of gibbsite from secondary aluminum production dust by caustic leaching, Minerals Engineering, 127, (2018), 122-124.

19. A. Meshram, A. Jain, D. Gautam, K.K. Singh, Synthesis and characterization of tamarugite from aluminum dross: Part I, Journal of Environmental Management, 232, (2019), 978-984.

20. Y. Zhang, Z. Guo, Z. Han, X. Xiao, Effect of rare earth oxides doping on MgA^O4 spinel obtained by sintering of secondary aluminum dross. Journal of Alloys and Compounds, 735, (2018), 2597-2603.

21. T. Hashishin, Y. Kodera, T. Yamamoto, M. Ohyanagi. Synthesis of (Mg,Si)A^O4 spinel from aluminum dross. Journal of the American Ceramic Society, 87, (2004), 496-499.

22. N. Murayama, N. Okajima, S. Yamaoka, H. Yamamoto, J. Shibata. Hydrothermal synthesis of AlPO4-5 type zeolitic materials by using aluminum dross as a raw material. Journal of the European Ceramic Society, 26, (2006), 459-462.

23. J. Kim, K. Biswas, K.-W. Jhon, S.-Y. Jeong, W.-S. Ahn, Synthesis of AIPO4-5 and CrAPO-5 using aluminum dross. Journal of Hazardous Materials, 169, (2009), 919-925.

24. A. Meshram, S.K. Singh. Recovery of valuable products from hazardous aluminum dross: a review. Resources, Conservation & Recycling, 130, (2018), 95-108.

25. A. López Delgado, I. Padilla Rodríguez, R. Sánchez Hernández, O. Rodríguez Largo, S. López Andrés, Procedure for the revaluation of a residue from the grinding of aluminum slag. IS 2,617,037 B1 (2018).

26. H.M. Auerbach, K.A. Carrado, P.K. Dutta (Eds.), Handbook of Zeolite, Science and Technology, Marcel Dekker, Inc. (2003).

27. M. Yoldi, E.G. Fuentes-Ordoñez, S.A. Korili, A. Gil, Zeolite synthesis from industrial wastes, Microporous Mesoporous Materials, 287, (2019), 183-191.

28. M. Yoldi, E.G. Fuentes-Ordoñez, S.A. Korili, A. Gil, Zeolite synthesis from aluminum saline slag waste, Powder Technology, 366, (2020), 175-184.

29. A. Gil Bravo, S.A. Korili, E. Arrieta Chango, Procedure for manufacturing anionic aluminum clays and their derivatives from saline slags from aluminum recycling processes. IS 2,673,587 B2 (2018).

30. A. Gil, M.A. Vicente, Progress and perspectives on pillared clays applied in energetic and environmental remediation processes, Current Opinion in Green and Sustainable Chemistry, 21, (2020), 56-63.

patents

D.R. Battiste, J.R. Harris, Pillared interlayered clays. US 4,637,991 (1987).

C. Brisson, G. Chauvette, F.M. Kimmerle, R. Roussel, Process for using dross residues to produce refractory products. United States Patent: 5,132,246 (1992).

G. Chauvette, F.M. Kimmerle, R. Roussel. Process for converting dross residues to useful products. WO 91/09978 (1991).

I. Davis, M.E. Whittle, W. Jones, R. Mokaya. Pillared clays. United States Patent:

5,486,499 (1996).

A. Gil, SA Korili. Modification of saline slags from the second aluminum smelting processes and use as adsorbents of the products obtained. IS 2,350,435 B2 (2011).

A. Gil Bravo, S.A. Korili, E. Arrieta Chango, Procedure for manufacturing anionic aluminum clays and their derivatives from saline slags from aluminum recycling processes. IS 2,673,587 B2 (2018).

J. Guan, E. Min, Z. Yu, Class of pillared interlayered clay molecular sieve products with regularly interstratified mineral structure. US 4,757,040 (1988).

J. Guan, X. Wang, Z. Yu, Z. Chen, Q. Liu, Y. Liao, Pillared clay catalysts for heavy oil catalytic pyrolysis process and the preparation method thereof. US 6,342,153 B1 (2002).

GIVES. Hickson, Layered clay minerals and processes for using. US 3,887,454 (1975).

C. Iranzo. Manufacturing procedure for aluminum sulfate and its derivatives from aluminum hydroxide sludge from anodizing plants. Spanish Patent: 2,176,064 (2003).

C. Iranzo, N. Lopez. Manufacturing procedure for basic aluminum salts and their derivatives from aluminous waste and applications. Spanish Patent: 2,277,556 (2008).

A. López Delgado, I. Padilla Rodríguez, R. Sánchez Hernández, O. Rodríguez Largo, S.

López Andrés, Procedure for the revaluation of a residue from the grinding of aluminum slag. IS 2,617,037 B1 (2018).

L. Parent, S. Tremblay. Process for converting waste aluminum dross residue into useful products. WO 94/12434 (1994).

J.W. Pickens, M.D. White, Recovery of products from non-metallic products derived from aluminum dross. US Patent 6,110,434 (2000).

J. Shabria, N. Lahari, Cross-linked montmorillonite molecular sieves. US Patent 4,216,188 (1980).

M. Suda, K. Ohtsuka, Porous clay intercalation compound and its production method. US Patent 5,360,775 (1994).

K. Suzuki, T. Mori, Method for production of pillared clay. US Patent 5,087,598 (1992).

K. Suzuki, M. Horio, H. Masuda, T. Mori, Method for production of silicate interlayer crosslinked-smectite. US Patent 5,214,012 (1993).

DEW Vaughan, RJ Lussier, JS Magee Jr., Pillared interlayered clay materials useful as catalysts and sorbents, US Patent 4,176,090 (1979).

SUMMARY OF THE INVENTION

The present invention is based on a process for preparing pillared clays where the aluminum polyhydroxycationic intercalating reagent is obtained from aluminum extracted from a salt slag. The proposed method is based on an aqueous solution that contains aluminum that comes from the chemical treatment, with acid or basic solutions, of saline slag generated in the recycling of scrap metal and aluminum by-products.

The process of the invention is an ion exchange process in which a solution containing the intercalating agent is separately prepared. To this solution, preferably, the clay is added, although the solution can also be added to the clay. This method has the advantage that it can valorize both the aluminum that has been extracted with acidic and basic solutions and allows obtaining microprose adsorbents with improved properties compared to those of the materials obtained by intercalation with aluminum polyhydroxycations synthesized with commercial salts, and its application as an adsorbent for organic pollutants. The general method for preparing pillared clays of the present invention covers several alternatives for obtaining the intercalating precursor and how to bring this solution into contact with the clay. These alternatives are due precisely to the particular aluminum extraction conditions that determine the contact between the intercalating solution and the clay.

Therefore, in a first aspect, the present invention refers to a method for the preparation of pillared clays, where the aluminum polyhydroxycationic intercalating agent is obtained from salt slag from aluminum recycling processes, which comprises steps of:

a) obtain a solution containing Al3+ from a saline slag by means of the substages of

i) contacting the saline slag with an acidic or basic aqueous solution, ii) allowing the solution to react with the saline slag,

iii) separating the salt slag from the aqueous phase containing Al3+ in solution;

b) obtaining the intercalating agent by means of the substeps of

iv) rectify the pH of the aqueous solution containing Al3+ to the intercalation pH between 3.5 and 5, where the value of the OH/Al molar ratio is between 0.5 and 2.5,

v) heating the rectified solution at a temperature between 25 and 90 °C, between 0.5 and 2 h;

c) obtain the intercalated material by adding the clay to the previous solution, to obtain a suspension with a ratio of between 2 -20 mmol Al/g clay and allowing the mixture to react for a maximum of 22 h;

d) eliminating the excess of non-intercalated aluminum polyhydroxycation by means of the substeps of

vi) washing with water, and

vii) separation of the suspension.

Preferably, the method comprises the following additional steps:

vi) separating the solid formed in d) from the supernatant by filtration, centrifugation, dialysis or another technique;

vii) subjecting the solid obtained in e) to calcination heat treatment at a temperature between 25 and 500 °C.

It is most especially preferred that the clay is sodium montmorillonite.

Following this method, in stage b) the solution of the intercalating agent is obtained, once the Al3+ has been extracted from the saline slag, rectifying the pH value by adding HCl, in the case of the Al3+ extracted in a basic medium, and NaOH, in the case of Al3+ extracted in an acid medium. The OH/Al molar ratio will be between 0.5 and 2.5. The solution is preferably subjected to a heat treatment, which is usually called maturation or ageing, at a temperature between 25 and 90 °C so that the intercalating agent [A li3O4 (OH) 24 (H2O ) i2 ] is formed. 7+.

Another aspect of the present invention is the use of the pillared clays obtained by the method of the present invention as adsorbents for emerging organic pollutants such as 2,6-dichlorophenol.

In these pillared clays, the specific surface is between 10 and 284 m2/g and the total pore volume is between 0.0001 and 0.210 cm3/g. Preferably, the specific surface is greater than 45 m2/g,

DESCRIPTION OF THE FIGURES

Fig. 1: X-ray diffractogram (basal reflection (001)) of natural montmorillonite and natural montmorillonite intercalated with polycations synthesized from Al3+ that is extracted from a saline slag with a 2 mol/liter HCl or NaOH solution in reflux conditions and the pH is rectified with NaOH (Method3(acid)-2-10) or with HCl (Method3(basic)-2-15-25°C/pH=3.87). For comparison, the diffractogram obtained for the natural monmorillonite intercalated with polycations synthesized by the traditional procedure in which the intercalating agent is synthesized from AlCh-6H2O salt (Simulated3(acid)-2-10) is included.

Fig. 2: Adsorption capacity ( qt) of the synthesized montmorillonite and pillared clays over time, for the removal of 2,6-dichlorophenol from aqueous solutions. Pillared clays: Method3(acid)-2-10, Method3(basic)-2-15-25°C/pH=3.87 and Simulated3(acid)-2-10 treated for 4 h at 500 °C. Adsorption conditions: 50 mg of adsorbent, 250 cm3 of aqueous solution and 25, 50 and 75 pmol/dm3 of organic adsorbate. Where qt = V ( Co-Ct)/M. ( q t, adsorption capacity in pmol/g; V, solution volume in dm3; C0,t, adsorbate concentration in pmol/dm3 and M weight of adsorbent in g).

DETAILED DESCRIPTION OF THE INVENTION

The present invention is based on the manufacture of pillared clays from salt slag from aluminum recycling processes, on the pillared clays obtained by said procedure and on their use as adsorbents.

The synthesis process is carried out using the solution that contains Al3+ applying new procedures to obtain the clay intercalation precursors. These new procedures, specifically, are two alternative methods of extraction of Al3+ from salt slag, either by treatment with HCl or with NaOH, with approximately similar results: they are the procedures that are called in this document the acid method, and the basic method. Next, the pH of the extraction solutions obtained is rectified by adding NaOH or HCl, to reach the desired OH/Al molar ratio, preferably at a value of 2.0, and a heat treatment of the solution at a temperature between 25 and 90 °C, in which the intercalation precursors are obtained. In the state of the art, commercial Al precursors are commonly used AlCh-6 H2O, aluminum chlorohydroxide solutions and Al2(OH)5Cl-2 H2O to obtain the intercalating agent, so the method presented is a technical advantage. important with respect to the commonly known methods since it recovers the Al present in an industrial residue. In addition, the pillared clays object of the present invention have specific surface areas generally between 10 and 284 m2/g, that is to say, considerably higher in some cases than those obtained by many of the methods known in the state of the art and, in any case, case, suitable for use as adsorbents.

The synthesized pillared clays can be used as adsorbents, for example in the removal of emerging contaminants present in polluted water streams such as 2,6-dichlorophenol.

The present invention includes new methods for the synthesis of pillared clays that allow the use of the aqueous solution from the extraction of Al3+ from a saline slag. For this, the starting material (salt slag) is treated with solutions of acids or bases to extract aluminum, taking into account treatment time and temperature as variables. The conditions in which this stage of contact with the slag or extraction of the aluminum is carried out can be any, as long as they lead to the extraction of aluminum. The temperature of the contacting process is generally room temperature, but can be in the range of 20°C to reflux temperature, which will be approximately 90°C, at a pressure of 101.33 kPa (1 atm). The pressure at which this stage is carried out can be atmospheric pressure, but it can also be carried out at higher pressures. The contact time is highly dependent on the reaction temperature, but is generally in the range of 0.5 to 2 h. Preferably, this extraction stage a) is carried out in a stirred vessel although, optionally and/or after a first stirring step, it can be carried out under reflux conditions.

In the present invention, aluminum extracted from salt slag is used following the method described in ES2350435 B2, using the solution obtained as a supernatant in the waste activation process (salt slag). But in the present invention, said solution with the extracted aluminum is used for the synthesis of different products, not mentioned in said Spanish patent and which have a different structure and peculiar, and different from the structure of anionic or hydrotalcite clays: pillared cationic clays. And the direct use of the solution containing the Al3+ extracted from the saline slag, in combination with the addition to said solution of another NaOH (or HCl) drop by drop so that the structure of the Al intercalating agent is formed. Once the intercalating agent is formed, the clay is added, facilitating the ionic exchange of the intercalating agent and the surface cations contained in the layered clay. The methods used are compatible with the extraction of Al3+ by acid and basic means, which allows obtaining the intercalating agent and generating the pillared clays, as they appear in Examples 1 and 2, in addition, they present specific surface values that make them suitable for use as adsorbents.

It is preferred that the salt slag be a slag from a second aluminum smelting process, with special preference for slag from a fixed-axis rotary kiln, and especially when they have a size equal to or less than 1 mm. But the process of the present invention can also be applied to dross from other processes related to aluminum, these other alternatives being included within the scope of the invention. In no case are previous washing stages of the saline slag carried out before treatment with acids or with bases to extract aluminum, thus reducing the number of previous treatment stages.

Regarding the ratio between the reactants, it is considered preferable that the ratio between the amount of salt slag and the volume of acidic or basic aqueous solution with which it is contacted in step a) is between 50 and 70 g of slag per L of acid or basic solution. More specifically, contacting, for example, 2 g of salt slag with 0.2 liters of aqueous, acidic or basic solution, as in the Examples of the present application.

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 the base. Specifically, the concentration of acids and bases used in this work varied between 0.1 and 2 mol/liter, observing 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 comprised between 0.1 and 2 mol/liter. Acids can be of organic or mineral origin, such as nitric (HNO3), sulfuric (H2SO4) or hydrochloric (HCl) acids. Among the possible basic compounds that can be added to achieve alkaline solutions, sodium hydroxide (NaOH) stands out, but others can also be used, such as sodium bicarbonate (NaHCO3), which gives rise to alkaline pH closer to neutrality, of about 8.

As for the extraction temperature, it can be between room temperature and reflux temperature (approximately 60°C), but the latter is preferable since the amount of aluminum extracted is greater. Preferably, the pressure is atmospheric or higher.

Once the contact time that has been considered adequate has elapsed, preferably between 0.1 and 2h, the saline slag is separated from the solution with which the aluminum has been extracted in the form of Al3+ cations. To carry out the step of separating the salt slag, any separation technique can be used, such as filtration, centrifugation, decantation of the supernatant after leaving the mixture of salt slag and solution to stand, and the like. In the present invention, the use of filtration is preferred.

The sub-stages just described, which lead to obtaining the solution containing Al3+ from salt slag, are included in the procedure described in ES2673587 B2, although it did not mention that the use of said solution could have some interest or some advantage for the preparation of other solid structures of which the Al3+ cation is a part other than anionic clays, not mentioning in said patent a possible application for the preparation of compounds with a structure like the one presented by pillared clays, which are the object of the present invention. The stages that are detailed below are already specifically destined to the synthesis of the intercalating agent and designed for it to obtain it, as well as the pillared clays.

The aluminum in cationic form present in the aqueous solution resulting from step a) of the method of the present invention is used for the synthesis of pillared clays. Said synthesis is carried out according to this invention, starting from the procedure described in b) where the OH/Al molar ratio is adjusted depending on whether the Al has been extracted with an acid, specifically HCl, or a base, preferably NaOH, all of which had not been described so far in none of the methods of the state of the art for the preparation of pillared clays. The method of preparing pillared clays of the present invention is the main object of the invention, as explained above. The solution containing Al3+ is subjected to a rectification of the pH value and heating to temperatures between 25 and 90 °C that allows the formation of the Keggin ion structure [A li3O4(OH)24(H2O )i2]7+ to obtain a precursor of the intercalating agent, which can be achieved, according to the method of the present invention, by at least two different procedures, which have been called acid and basic, depending on the means of extraction of Al3+ from the salt slag Following. Depending on the specific procedure for obtaining the precursor, the synthesis of the intercalating agent can likewise be obtained by various procedures. Thus, in the case of acid extraction, this solution can be cooled, heated or evaporated before adding NaOH to rectify the pH and adjust the OH/Al value to the required value. In the case of the basic extraction, the same procedure of rectifying the pH and adjusting the values of OH/Al and Al/clay was carried out. Next, the clay will be added for the ion exchange reaction to take place.

The preparation of the intercalation precursor by means of the acid procedure that forms part of the method of the present invention, requires the preparation of two solutions. In the first, as already mentioned, it starts with an aqueous solution containing Al3+ that comes from the attack, with an acid solution, of saline slag generated in the recycling of scrap metal and aluminum by-products. This solution is subjected to an additional intermediate heat treatment preparation step which may involve complete evaporation of water from the solution. Additionally, a NaOH solution with a concentration of preferably 2 mol/litre is added dropwise, and preferably under stirring, until reaching the desired OH/Al molar ratio, in the range between 0.5 and 2.5. This second solution can be reheated to between 25 and 90 °C.

The maturation/aging time of the Al3+ solutions can vary, although it is considered adequate that it be between at least until the NaOH solution is finished and up to a maximum of 4 h, preferring that it be between 1 and 2, as in Example 1 of the present application, in which the acid procedure is used. The reaction is carried out under stirring, it being recommended that the stirring speed be in the range between 100 and 700 rpm.

The solid clay is then added in an Al/clay ratio in the range between 2 and 20 mmolAl/heron, the value of 10 being preferred, as in Example 1 of the present application. The solution/clay contact time can vary, although it is considered adequate that it be between at least until the clay is finished being added and up to a maximum of 24 h, preferably between 4 and 22 h, as in Example 1. of the present application, in which the acid process is used. The reaction is carried out under stirring, it being recommended that the stirring speed be in the range between 100 and 700 r.p.m.

Preferably, the intercalated clay is separated from the suspension before being subjected to the calcination heat treatment, by means of a technique selected, for example, from the group of filtration (as in Example 1), centrifugation, decantation or direct evaporation of the solvent. . In order to eliminate the excess of non-intercalated aluminum polyhydroxycation, it is necessary to include several stages of washing with water and separation of the suspension, as in the previous step. It is also preferred that it be subjected to a drying heat treatment, optionally (but also preferably) after being separated from the liquid medium (supernatant) in which it has been formed, a drying treatment that can occur in an oven at atmospheric pressure, or at empty. When drying occurs in an oven, it is preferred that it last between 4 and 24 h, and more preferably, that it occurs at 100 °C for 12 h.

The method of the present invention for the preparation of pillared clays from saline slags from aluminum recycling processes, in which the intercalation solution is obtained by means of the procedures just described, can thus also be defined as a method that includes the stages of:

ai) contacting the saline slag with an acidic or basic aqueous solution; aii) allowing the solution to react with the salt slag under agitation;

aiii) separating the saline slag from the aqueous phase containing the Al3+ in solution; b) rectify the pH and heat the aqueous solution that has Al3+ up to the intercalation pH; c) let the clay react with the intercalation solution for a maximum of 22 h.

d) washing and separation of the suspension.

The method for obtaining pillared clays includes the additional stages of: e) separating the solid formed in d) from the supernatant;

f) subjecting the solid obtained in e) to initial heat treatment (which can be in an oven or under vacuum) and subsequently subjecting the solid obtained to final heat treatment, at a temperature preferably between 200 and 500 °C, preferably 500 °C.

It is worth noting that none of the state-of-the-art methods for preparing pillared clays includes, proposes or suggests the synthesis of the intercalating agent from industrial waste, as is the case with the present procedure, therefore the method of the invention in the one using Al3+ extracted from a saline slag constitutes a new and inventive alternative to the usual procedures.

In the Examples that follow, the synthesis of pillared clays from intercalating agents obtained by acid and basic extraction is described. The experiments carried out show that its specific surface varies between 10 and 284 m2/g, in which there is intercalation of montmorillonite cases between 142 and 284 m2/g, and its total pore volume is between 0.001 and 0.250 cm3/ g, being more specifically 0.210 cm3/g one of the higher values obtained. This degree of porosity makes them suitable for use in adsorption processes. The pillared clays obtained by the methods of the present invention can be considered new and inventive, due to the particularities of their structure, for which they are also an aspect of the present invention, particularly those whose preparation is described in the Examples herein.

The tests shown in the Examples section, Example 3, are representative cases of the applicability of the methods of the invention. The methods are considered applicable and suitable for synthesizing adsorbents that can retain organic pollutants, especially those considered as priority or emerging ones present in aqueous liquid effluents. The tests carried out in Example 3 with the selected pillared clays already included in Examples 1 and 2 demonstrate that they can be used as useful adsorbents in the removal of 2,6-dichlorophenol, although other contaminants can also be used. The results show that the pillared clays synthesized from aluminum extracted from salt slags can be used as adsorbents and that this capacity is superior to that of the starting montmorillonite, as well as the pillared clay that can be obtained from a precursor. commercial intercalation.

examples

Example 1. Obtaining pillared clays, acid method.

In the present Example, a saline slag from a fixed axis rotary kiln with a size of less than 1 mm was used for the extraction of aluminum by means of chemical agents.

The clay used is a commercial sodium montmorillonite, from the Tsukinuno region, Japan, provided by The Clay Science Society of Japan, to be intercalated by the solutions synthesized in this Example.

Chemical extraction was carried out using a 2 mol/litre aqueous HCl (65%) solution. The reaction time was 2 h. Briefly, 50 g of salt slag is brought into contact with 750 cm3 of HCl solution. The stirring speed of the suspensions was 600 r.p.m. After the reaction time has elapsed, the suspension is filtered to separate the dregs from the solution. The amount of aluminum extracted was analyzed by ICP-radial and is between 6.75 and 8.96 gAl/dm3 (see patent ES2673587 B2).

The pH of the Al3+ solution, 10 cm3, was rectified by adding NaOH with a concentration of 0.09 mol/litre until an OH/Al molar ratio = 2.0 and pH = 4.0. The extraction solution was previously heated between 25 and 90 °C (Method 1 (acid)) to rectify the pH, once rectified (Method 2 (acid)) or it was brought to evaporation and subsequently rectified (Method 3 (acid )), shaking at 700 r.p.m. for 1 hr. Next, a quantity of clay was added to the previously prepared solutions, with an Al/clay ratio between 2 and 10 mmolAl/heron, stirring at 700 rpm for 22 h. The volume of the final suspension varied between 60 and 85 cm3.

After the reaction time had elapsed, the suspensions were centrifuged to separate the solid from the solution. The process was repeated several times, each time replacing the intercalation solution with deionized water in order to wash the intercalated clay from the intercalation solution. To dry the product, it was heated in an oven at 100 °C at atmospheric pressure for 12 h. Finally, the solids were treated in a programmable electric oven for 4 h at 500 °C. The samples were named as "MethodX(acid)-OH/Al-Al/clay-Theating solution ^ai ".

The basal spacings of the solids obtained were determined by X-ray diffraction. The textural properties, specific surface area, and total pore volume of the solids obtained were determined by N2 adsorption at -196 °C in commercial static volumetric equipment. The solids were previously degassed for 24 h and at a pressure lower than 0.1 Pa. The amount of solid used in the experiment was 0.2 g.

The results referring to the basal spacings and the textural properties obtained for the pillared clays from the extraction of aluminum with HCl of concentration 2 mol/liter are shown below in Table 1. Information on the Simulated sample obtained from of the same synthesis conditions, but with commercial AlCl3-6H2Ü as source of Al3+ instead of Al3+ extracted from the salt slag. This Al3+ solution is initially prepared in a 2 mol/liter HCl solution, to later follow the same procedure as the extraction solutions.

These materials were also characterized by X-ray diffraction. A representative example is presented in Fig. 1 , where the intensity data are represented, in arbitrary units, as a function of the diffraction angle (2 theta), as is usual in the X-ray diffractograms. These results confirm that the basal spacing of montmorillonite, which characterizes the distance between two sheets, increases from 1.0 nm to 1.85 nm in the case of interbedded clays. This increase in basal spacing demonstrates clay intercalation. In the case of the textural results included in Table 1 , the method presented in this invention allows obtaining pillared clays with high values of specific surface area and pore volume, solids that will be suitable for application as adsorbents. These properties are included in Example 3 of this invention.

Table 1. Basal spacing and textural properties derived from N2 adsorption at -196 °C. Acid extraction methods.

d(001)a Sb V pT otalc Sample

(nm) (m2/gd) (cm3/gd) Method1(acid)-2-10-25°C 1.37 45 0.066 Method1(acid)-2-5-25°C 1.22 40 0.099 Method1(acid )-2-2-25°C 1.14 28 0.051 Method1(acid)-2-10-60°C 1.73 142 0.098 Method1(acid)-2-5-60°C 1.44 51 0.082 Method1( acid)-2-2-60°C 1.17 42 0.067 Method1(acid)-2-10-90°C 1.80 197 0.174 Method1(acid)-2-5-90°C 1.69 70 0.073 Method1 (acid)-2-2-90°C 1.24 44 0.101 Method2(acid)-2-10-25°C 1.39 61 0.072 Method2(acid)-2-10-60°C 1.80 218 0.163 Method2(acid)-2-10-90°C 1.83 199 0.182 Method3(acid)-2-10 1.85 284 0.210 Simulated3(acid)-2-10 1.82 207 0.158 Montmorillonite 1.0 10 0.048 a Basal spacing;

b Specific surface area;

c Total pore volume;

d grams of degassed sample

Example 2. Obtaining pillared clays, basic method.

In the present Example, a saline slag from a fixed axis rotary kiln with a size of less than 1 mm was used for the extraction of aluminum by means of chemical agents.

The clay used is a commercial sodium montmorillonite, from the Tsukinuno region, Japan, provided by The Clay Science Society of Japan, to be intercalated by the solutions synthesized in this Example.

Chemical extraction was carried out using a 2 mol/litre aqueous NaOH solution. The reaction time was 2 h. Briefly, 50 g of salt slag is brought into contact with 750 cm3 of NaOH solution. The stirring speed of the suspensions was 600 r.p.m. After the reaction time has elapsed, the suspension is filtered to separate the dregs from the solution. The amount of aluminum extracted was analyzed by ICP-radial and is between 6.75 and 8.96 gAl/dm3 (see patent ES2673587 B2).

The pH of the Al3+ solution, 30 cm3, was rectified by adding HCl with a concentration of 0.5 mol/liter up to OH/Al molar ratios between 0.5 and 2.0, as well as Al/clay ratios between 5 and 20 mmolAl/heron (Method 1(basic)). For a fixed value of OH/Al = 2 and Al/clay = 10 mmolAl/heron, the pH of the intercalation solution changed between 3.50 and 4.50 (Method 2(basic)), and even for a ratio Al/clay = 15 mmolAl/heron (Method 3(basic)). This solution was previously heated between 25 and 90 °C. In all cases, the solutions were shaken at 700 r.p.m. for 1 hr. Next, a quantity of clay was added to the previously prepared solutions, according to the Al/clay ratio, stirring at 700 rpm for 22 h. The volume of the final suspension varied between 60 and 85 cm3.

After the reaction time had elapsed, the suspensions were centrifuged to separate the solid from the solution. The process was repeated several times, each time replacing the intercalation solution with deionized water in order to wash the intercalated clay from the intercalation solution. To dry the product, it was heated in an oven at 100 °C at atmospheric pressure for 12 h. Finally, the solids were treated in a programmable electric oven for 4 h at 500 °C. The samples were named as “MethodX(basic)-OH/Al-Al/clay-Theating solution ^ai ”.

The basal spacings of the solids obtained were determined by X-ray diffraction. The textural properties, specific surface area, and total pore volume of the solids obtained were determined by N2 adsorption at -196 °C in commercial static volumetric equipment. The solids were previously degassed for 24 h and at a pressure lower than 0.1 Pa. The amount of solid used in the experiment was 0.2 g.

The results referring to the basal spacings and the textural properties obtained for the pillared clays from the extraction of aluminum with NaOH of a concentration of 2 mol/liter are shown below in Table 2 .

These materials were also characterized by X-ray diffraction. A representative example is presented in Fig. 2 , where the intensity data is represented, in arbitrary units, as a function of the diffraction angle (2 theta), as is usual in the X-ray diffractograms. These results confirm that the basal spacing of the clay intercalated with an Al solution extracted with a NaOH solution, the basal spacing value obtained is 1.71 nm. In the case of the textural results included in Table 2 , the method presented in this invention allows obtaining pillared clays with high values of specific surface area and pore volume, solids that will be suitable for application as adsorbents. These properties are included in Example 3 of this invention.

Table 2. Basal spacing and derived textural properties.

of N2 adsorption at -196 °C. Basic extraction methods.

d(001)a Sb V pT otalc Sample

(nm) (m2/gd) (cm3/gd)

Method1 (basic)-0.5-10-25°C 1.43 --

Method1 (basic)-1.0-10-25°C 1.42 --

Method1 (basic)-1.5-10-25°C 1.42 --

Method1 (basic)-2.0-10-25°C 1.45 10 0.028

Method2(basic)-2-10-25°C/pH=3.50 1.39

Method2(basic)-2-10-25°C/pH=3.70 1.39 --

Method2(basic)-2-10-25°C/pH=3.75 1.57 --

Method2(basic)-2-10-25°C/pH=3.80 1.58 13 0.032

Method2(basic)-2-10-25°C/pH=3.85 1.61 17 0.031

Method2(basic)-2-10-25°C/pH=3.87 1.63 17 0.031

Method2(basic)-2-10-25°C/pH=3.90 1.56 13 0.028

Method2(basic)-2-10-25°C/pH=3.95 1.50

Method2(basic)-2-10-25°C/pH=4.00 1.46

Method2(basic)-2-10-25°C/pH=4.30 1.46

Method2(basic)-2-10-25°C/pH=4.50 1.44

Method3(basic)-2-15-25°C/pH=3.80 1.61

Method3(basic)-2-15-25°C/pH=3.85 1.69 78 0.15

Method3(basic)-2-15-25°C/pH=3.87 1.71 100 0.12

Method3(basic)-2-15-25°C/pH=3.90 1.57 83 0.08

Simulated3(basic)-2-15-25°C/pH=3.87 1.77 141 0.11

Montmorillonite 1.0 10 0.048

a Basal spacing;

b Specific surface area;

c Total pore volume;

d grams of degassed sample

Example 3. Adsorption capacity of organic molecules.

Next, the retention capacity of organic molecules (2,6-dichlorophenol) of the pillared clays obtained described in Examples 1 and 2 was evaluated. The studies were carried out in a discontinuous regime, with 50 mg of adsorbent in each experiment and an initial concentration of 25, 50 and 75 pmol/dm3. The selected adsorbents were those that presented the greatest textural properties and were called as Method3(acid)-2-10 and Method3(basic)-2-15-25°C/pH=3.87. To compare the adsorption capacity of these materials, the starting montmorillonite and the Simulated 3(acid)-2-10 sample were also included. The experiment intends to study the effect of time on the adsorption capacity of clays and to determine from which moment the adsorption remains constant and has reached equilibrium. To obtain this evolution, from time to time a sample of the solution was taken, separating the adsorbent present by means of filtration. The amount of adsorbate present in the solution is determined by UV-visible analysis (A = 279 nm).

The amount of organic molecule retained by the clays is represented as: q ^t = V ( C ^o -C ^t )/M, where q ^t , adsorption capacity in pmol/g; V, volume of solution in dm3; C0,t, initial adsorbate concentration and at time t in pmol/dm3 and M weight of adsorbent in g. The evolution over time of the adsorbed amounts of the four studied adsorbates is included in Fig. 2 .

If the results obtained are compared, it is observed that the amount adsorbed increases as the adsorption time elapses. Two adsorption maxima can be observed, at about 50 min and at 900 min of contact time between the adsorbent and the adsorbate, which may correspond to the initial filling of the interlaminar structure and the filling of the entire outer surface. Pillared clays with aluminum extracted from the slag are the adsorbents that retain the highest organic molecule capacity, when compared to both montmorillonite and pillared clay using commercial precursors. Compared to montmorillonite, the new adsorbents retain between 72 to 197% more contaminant, and compared to pillared clay synthesized from commercial precursors, between 28 to 33% more adsorbent capacity. Therefore, the pillaring of the clay with a solution of aluminum extracted from the saline slag considerably increases the adsorption capacity.

Claims (16)

1. A method for the preparation of cationic pillared clays, where the aluminum polyhydroxycationic intercalating agent comes from saline slags from aluminum recycling processes, which comprises the steps of: a) obtain a solution containing Al3+ from the saline slag by means of the substages of i) contacting the saline slag with an acidic or basic aqueous solution, ii) allowing the solution to react with the saline slag under agitation, iii) separating the saline slag from the aqueous phase containing Al3+ in solution, b) obtaining the intercalating agent by means of the substeps of iv) rectify the pH of the solution containing Al3+ up to the intercalation pH between 3.5 and 5, where the value of the OH/Al molar ratio is between 0.5 and 2.5, v) heating the rectified solution at a temperature between 25 and 90 °C, between 0.5 and 2 h; c) obtaining the intercalated material by adding the clay to the previous solution to obtain a suspension with a ratio of between 2-20 mmol Al/g clay, and allowing it to react under stirring for 4 to 22 h; d) eliminating the excess of non-intercalated aluminum polyhydroxycation by means of the substeps of vi) washing with water, and vii) separation of the suspension. The method according to claim 1, comprising the additional steps: e) separating the solid formed in d) from the supernatant by means of filtration, centrifugation, dialysis or another technique; f) submitting the solid obtained in e) to calcination heat treatment at a temperature between 200 and 500 °C. 3. The method according to claim 1, wherein the salt slag from step a) comes from a second aluminum smelting process. The method according to any one of the preceding claims, wherein: - the relationship between the quantity of saline slag and the volume of acidic or basic aqueous solution with which it is brought into contact in stage a) is between 50 and 70 g of slag per L of acidic or basic solution; - the saline slag and the aqueous solution are brought into contact in stage i) and are left in stage ii) at a temperature between room temperature and 60 °C, and at atmospheric pressure or higher; - the contact time between the slag and the aqueous solution in stage ii) is in the range of 0.1 to 2 h. 5. The method according to any of the preceding claims, wherein the aqueous solution from step i) has a pH of less than 2 or greater than 10. 6. The method according to any of the preceding claims, wherein the aqueous solution of step i) is prepared by adding one or more acidic compounds, preferably HCl, or one or more basic compounds, preferably NaOH, at concentrations between 0, 1 and 2 mol/liter. 7. The method according to any of the preceding claims, wherein step iii) of separating the saline slag from the aqueous extraction solution is carried out by filtration, centrifugation or decantation of the supernatant after leaving the slag mixture to rest. saline and aqueous solution. 8. The method according to any of the preceding claims, for the preparation of a pillared smectite clay comprising the following steps: a') contacting a smectite with an intercalating aqueous solution containing an aluminum polyhydroxycation prepared by step b) according to claim 1, so that the relationship between the concentration of Al3+ contained in the intercalating solution and the grams of clay that come into contact with it is comprised in the range of 2 to 20 mmolAl/heron; b') separating the intercalated clay obtained in the previous stage from the aqueous solution by means of filtration, centrifugation, dialysis or another technique; c') heating the intercalated clay obtained in the previous stage in conditions that allow stabilizing the porous structure generated by dehydroxylation processes that allow the formation of Al2O3. The method according to claim 8, wherein the smectite is sodium montmorillonite. 10. The method according to any of claims 8 or 9, wherein the contact temperature between the smectite and the intercalation solution is carried out at a temperature between 25 and 90 °C and the contact time ranges from 4 and 10 p.m. The method according to any of claims 8 to 10, wherein the contacting step is carried out in a stirred vessel. 12. The method according to any of claims 8 to 11, wherein step b') of separating the smectite from the intercalation solution is carried out by filtration, centrifugation or decantation of the supernatant after leaving the mixture at rest. smectite and intercalation solution. 13. A method according to any of claims 8 to 12, in which the clay obtained in stage b') is calcined at a temperature between 200 and 500 °C, at atmospheric pressure. 14. A pillared clay obtained according to the process of any of claims 1 to 13, and characterized by having a specific surface area of between 10 and 284 m2/g and a total pore volume of between 0.001 and 0.250 cm3/g. 15. Use of a pillared clay according to claim 14, for the adsorption of organic contaminants present in liquid streams. 16. Use according to claim 15, for the adsorption of 2,6-diclophenol.