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    • 专利摘要:
    Procedure for the revaluation of a residue from the grinding of aluminum slags. The object of the invention is a process for the revaluation of hazardous waste from the grinding of aluminum slags through their transformation into zeolites. The use as raw material of fines with a granulometry of less than 200 μm obtained in the aluminum slag milling process, recovered both by granulometric separation and by collection systems is contemplated. Through the process object of the present invention it is possible to transform a hazardous waste into a commercial product such as zeolites, also allowing the recovery of released gases such as ammonia and hydrogen, which can be used for other purposes, as well as recovery of the salts obtained by evaporation of the washing waters. The process has been optimized by recirculating the resulting mother liquor after the separation of the zeolites. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2617037A1
    申请号:ES201531811
    申请日:2015-12-15
    公开日:2017-06-15
    发明作者:Aurora López Delgado；Isabel PADILLA RODRÍGUEZ；Ruth SÁNCHEZ HERNÁNDEZ；Olga RODRIGUEZ LARGO；Sol LÓPEZ ANDRÉS
    申请人:Consejo Superior de Investigaciones Cientificas CSIC；Universidad Complutense de Madrid；
    IPC主号:
    专利说明:

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    PROCEDURE FOR REVALUATION OF A WASTE FROM THE GRINDING OF ALUMINUM ESCORIES
    DESCRIPTION SECTOR AND OBJECT OF THE INVENTION
    The invention is part of the sector of waste utilization of the metallurgical industry.
    Specifically, the invention relates to a process of revaluation of hazardous waste from the milling of aluminum slags by transformation into zeolites. The use of fine granulometry of less than 200 µm obtained in the grinding process of aluminum slags, recovered by both granulometric separation and collection systems such as sleeve filters, is contemplated as raw material.
    By means of the process object of the present invention, a hazardous waste, whose destination is the safety landfill, is transformed into a commercial product such as zeolites, also allowing the recovery of the released gases such as ammonia and hydrogen, which can be destined to other uses, as well as, the recovery of the salts obtained by evaporation of the washing waters. STATE OF THE TECHNIQUE
    One of the most effective waste management strategies of the metallurgical industries is the recovery of metals, since not only the need for landfill space is reduced, but also the conservation of natural resources is acted upon.
    At present, aluminum is one of the metals in greatest demand for a large number of sectors such as transport, construction, packaging, etc., due to its excellent physical-chemical properties. This metal is obtained from bauxite in primary metallurgy, and from materials that have reached the end of their useful life (scrap metal) in secondary metallurgy. In both industries slags are generated that are recycled in the tertiary industry for different uses. Thus, the latter industry, and through different procedures, including the grinding of slags, recovers the residual metallic aluminum contained therein, which is subsequently marketed for other uses, such as in the steel industry to reduce the temperature of the broth.
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    The fines produced in the slag milling process, mainly composed of aluminum, silicon oxides and different salts, are considered hazardous waste according to the European Waste Catalog (group 10 03 21). The negative impact of this residue is mainly due to its high reactivity in the presence of water, as a result of its fine granulometry and its heterogeneous chemical composition, which involves dangerous compounds (metallic aluminum, aluminum nitride, aluminum carbide and aluminum sulfide). Toxic and / or dangerous gases such as hydrogen, ammonia, methane and hydrogen sulfide, can be released in the presence of ambient humidity by spontaneous and exothermic reaction of the residue with water.
    In previous studies, different processes have been developed in which the waste is used as raw material for obtaining aluminas and hydrotalcites of Mg-Al. Basically, the processes consist of a first stage of hydrolysis in an acid medium in which the soluble aluminum compounds contained in the residue are extracted, and a later stage of precipitation of the products by alkalization and aging [R. Galindo, A. López-Delgado, I. Padilla, M. Yates, “Hydrotalcite-like compounds: A way to recover a hazardous waste in the aluminum tertiary industry”, Appl. Clay Sci. 95 (2014) 4149]. However, in these procedures only the soluble fraction of aluminum contained in the residue is recovered, obtaining at the same time, a by-product containing all the non-soluble compounds of aluminum, silicon, and the rest of the components of the residue. The total transformation of the residue into a value-added material, such as zeolites, without generating any other solid waste, is conceived as the best procedure for complete recovery.
    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 the common characteristic of being regular and uniform porous structures. Many of its properties are explained by the presence of channels and holes that allow adsorption and diffusion of different ions and molecules. The substitution of Si (IV) by Al (III) in the tetrahedra induces negative charges in the structure that is compensated by cations such as Na +, K +, Ca2 +, etc. Zeolites have been widely studied and used in catalysis, gas separation, water purification and other industrial applications [M. Moliner, C. Martínez, A. Corma, "Synthesis Strategies for Preparing Useful Small Pore Zeolites and Zeotypes for Gas Separations and Catalysis", Chem. Mater. 26 (2013) 246258]. Zeolites can be natural or synthetic, the latter are obtained from a wide variety of sources of Si and Al. In recent decades, and motivated, mainly, by the need to minimize the disposal of waste in landfills and its consequent impact Environmentally, zeolites have been synthesized from various residues that have been used as low-cost precursors. These include the fly ash of coal combustion and waste incineration plants, rice husk residues, etc., which have been widely used to synthesize different zeolites. The zeolites NaP1, analcime (ANA) and sodalite (SOD) are of great interest due to their cation exchange and adsorption properties.
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    The NaP1 zeolite is characterized by a gismondin type structure, with two types of channels and its high exchange capacity, which gives it potential applications for water decontamination.
    The ANA zeolite, with a structure formed by irregular channels consisting of rings formed by 4, 6 and 8 highly distorted tetrahedra and small opening pores, is used in heterogeneous catalysis and selective adsorption.
    The cubic network of the SOD is based on truncated octahedral regular boxes, with a small opening of pores and characterized by its high stability in basic solutions. SOD is used for the preparation of membranes used in separation processes of small molecules such as He and H2.
    A wide variety of zeolite synthesis methods are described in the literature following conventional and unconventional hydrothermal routes (using microwave or ultrasound radiation synthesis). In general, these procedures involve previous steps of reagent activation before the actual synthesis process. For example, in G.G. Hollman, G. Steenbruggen, M. Janssen-Jurkovičová, “A two-step process for the synthesis of zeolites from coal fly ash”, Fuel 78 (1999) 1225-1230, a two-stage synthesis procedure is carried out the zeolites NaP1, NaX and NaA from fly ash. In the first stage an alkaline treatment of the precursor (90 ° C for 6 h) is carried out, obtaining a Si-rich filtrate and an ash residue. The Si / Al molar ratio in the filtrate is adjusted by adding an aluminate solution and then the synthesis of the zeolites is carried out by heating for 48 h at 90 ° C. In this stage a new filtrate is obtained which is mixed with the residue of the first stage for 24 h at 90 ° C to obtain a residue of fly ash with high content of zeolitic material. As a result, 50, 75 and 85 g of the NaP1, NaX and NaA zeolites are obtained per kg of fly ash, respectively. In A.Y. Atta, B.Y. Jibril, B.O. Aderemi, S.S. Adefila, "Preparation of analcime from local kaolin and rice husk ash", Appl. Clay Sci. 61 (2012) 8-13, ANA zeolite is synthesized from a mixture of rice husk ashes, metacaolin and a sodium hydroxide solution in relation (Na2O / Al2O3 = 2.6). Prior to the synthesis, the rice husk and kaolin were calcined at 800 and 900 ° C, respectively, for 3 h. After calcination, the metacaolin obtained is dissolved in a 4M solution of NaOH at 90 ° C. Subsequently, an aging stage is performed for 3 days followed by a hydrothermal process at 180 ° C for 24 h. In S. Bohra, D. Kundu, M.K. Naskar, "One-pot synthesis of NaA and NaP zeolite powders using agro-waste material and other low cost organic-free precursors", Ceram. Int. 40 (2014) 1229-1234, the use of rice husk ashes (obtained by calcination at 700 ° C for 6 h), aluminum foil and NaOH (Na2O / Al2O3 = 2.1) is also studied for obtaining of the NaA and NaP zeolites. First, the reagents are subjected to strong stirring for 15 h, to continue with the hydrothermal synthesis at 100 ° C for 15 h for NaA, and 72 h for NaP. In M. Król, W. Mozgawa, J. Morawska, W. Pichór, "Spectroscopic investigation of hydrothermally synthesized zeolites from expanded perlite", Microporous Mesoporous Mater. 196 (2014) 216-222, the effect of temperature (30-90 ° C), NaOH concentration (0.5-5 M) and time (24-72 h) on the synthesis of zeolites is studied from of a byproduct of the manufacture of expanded perlite, with SOD and NaP1 (with traces of zeolite X) predominant phases at 90 ° C for 24 h with 5 and 3 M NaOH, respectively.
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    In recent studies [A. López-Delgado et al. “Industrial aluminum hazardous waste as a new raw material for zeolite synthesis”, Seventh International Conference on Waste Management and the Environment, 2014 and R. Sánchez-Hernández et al. “Synthesis of zeolite NaP1 from industrial waste”, XXIV Meeting of the Crystallography and Crystal Growth Specialized Group, 2014] describes the preparation of zeolites as NaP1 or ANA, from an unconventional raw material such as the residue of the aluminum industry The synthesis is carried out by hydrothermal treatment.
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    However, it is considered that said processes are susceptible to improvement, introducing stages prior to hydrothermal treatment and improving their efficiency through the previous washing of the waste, the recovery of salts from the washing waters and the recycling of the washing waters, the capture of synthesis gases and recycling of mother liquors, as well as extending the process to other types of zeolite, such as SOD. EXPLANATION OF THE INVENTION
    In a first aspect, an object of the present invention constitutes a method of revaluation of a residue from the milling of aluminum slags, by means of its transformation into zeolites by a hydrothermal synthesis process comprising the following steps: -addition to the reactor of the residue from the milling of aluminum slags, a solution of NaOH with a concentration between 1 M and 5 M and a solution of 11 M sodium silicate, so that the liquid / solid ratio in the reactor load is between 7 and 30 l / kg and an initial Si / Al molar ratio of 2.0 -reaction of the mixture formed in the previous stage, by heating at a temperature between 90 ° C and 200 ° C, for a period of time between 3 and 24 h and under conditions of agitation at speeds between 600 and 1200 rpm - separation of the zeolites obtained from their mother liquors, by vacuum filtration or pr Exion and subsequent drying at a temperature below 100 ° C. What differentiates the procedure from that reflected in the state of the art is that it additionally includes: -a stage prior to the addition of the load to the reactor, in which the residue from the grinding of aluminum slags is washed with water, the washing waters being separated by decantation or filtration before loading into the reactor - the recovery of the salts contained in the washing waters by concentration and evaporation - the recycling of the resulting washing waters of the recovery of salts -the recovery of the gases generated in the hydrothermal synthesis by dragging with an inert gas once the heating stage is finished and -the recycling of the resulting mother liquors after the separation of the zeolites for use in the stage of addition to the reactor, adjusting the alkalinity of the mother liquors with a fresh solution of NaOH so that the concentration is comp rendered between 1 M and 5 M.
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    In a preferred embodiment, the fine granulometry of less than 200 µm obtained in the aluminum slag grinding process is used as raw material.
    Preferably, the solid / liquid ratio in the wash stage prior to the addition of the charge to the reactor is 1:10 and the liquid / solid ratio in the reactor charge is 15 l / kg and the reaction stage has a duration of 6 h.
    In particular embodiments of the process object of the invention, the washing waters are concentrated by evaporation to dryness recovering 0.08 kg of salts per kg of residue with a composition of 95% NaCl and 5% KCl and obtaining waters that are recirculated in subsequent washings.
    In other particular embodiments of the process object of the invention, the reaction step is carried out at the autogenous pressure of the system between 100 and 1000 kPa or is carried out under an inert nitrogen atmosphere.
    The gases generated in the hydrothermal synthesis are mostly NH3 and H2, which are carried with an inert gas, preferably N2, after the end of the reaction stage. The separation of NH3 from the entrainment stream is carried out by capturing it in a solution of 50% by weight tartaric acid and subsequent recovery by heating in the gas phase, reaching up to 75% of the content, determined from the AlN content of the residue.
    In the recycling of the resulting mother liquors after the separation of the zeolites for use in the stage of addition to the reactor, the volume of fresh NaOH solution added to adjust the alkalinity is increased by 5% in the successive cycles of recirculation.
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    In a particular embodiment to obtain NaP1 zeolites: -the concentration of the NaOH solution added to the reactor is 1M -the temperature in the reaction step is between 90 ° C and 120 ° C and -the concentration of NaOH in the mother water recirculation current is set to 1
    M.
    In a particular embodiment to obtain ANA zeolites: -the concentration of the NaOH solution added to the reactor is 1M -the temperature in the reaction stage is between 160 ° C and 200 ° C and -the concentration of NaOH in the mother water recirculation current is set to 1
    M.
    In a particular embodiment to obtain SOD zeolites: -the concentration of the NaOH solution added to the reactor is 5M -the temperature in the reaction stage is 120 ° C and -the concentration of NaOH in the water recirculation stream mothers fits 5
    M.
    In a second aspect, an object of the present invention is also a NaP1 zeolite obtained by means of the described process that has an adsorption efficiency of Hg in water of 60% in 2 h working with a ratio of 0.01 g of zeolite per ml of dissolution of Hg of concentration 0.2 mg / l and an adsorption efficiency of Cd in water of 99% in 10 min working with 0.005 g of zeolite per ml of solution of Cd of concentration 20 mg / l.
    In a third aspect, an object of the present invention is also an ANA zeolite obtained by means of the described procedure which has an adsorption efficiency of Cd in water of 94% in 10 min working with 0.005 g of zeolite per ml of Cd solution of concentration 20 mg / l.
    DESCRIPTION OF THE FIGURES
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    Figure 1: DRX diagram of the residue from the milling of aluminum slags (A = Al; C = Al2O3; Q = SiO2; N = AlN; H = NaCl; K = KCl; E = MgAl2O4).
    Figure 2: Scheme of the process used for hydrothermal synthesis of zeolites from the residue from the milling of aluminum slags in which:
    (one)  waste washing stage
    (2) hydrothermal synthesis stage
    (3) stage of separation of the zeolites obtained from their mother liquors by filtration
    (4)  drying stage of the zeolites
    (5)  gas capture stage
    (6) NH3 separation and recovery stage
    Figure 3: DRX diagrams of samples obtained at 120 ° C with 1 M NaOH at 3 h without stirring (S1), and with stirring 3 h (S2), 6 h (S3) and 24 h (S4). (P1 = NaP1 and A = ANA).
    Figure 4: DRX diagrams of samples prepared at 120 ° C for 6 h with different concentrations of NaOH: 1 M (S3), 3 M (S5), 4 M (S6) and 5 M (S7). (P1 = NaP1 and S = SOD).
    Figure 5: DRX diagrams of samples prepared with 1 M NaOH for 6 h at different temperatures 80 C (S8), 90 C (S9), 100 C (S10), 120 C (S3), 140 C (S11 ), 160 C (S12) and 200 C (S13). (P1 = NaP1, A = ANA and Q = quartz).
    Figure 6: SEM images of the three zeolites at different magnifications: (a-c) NaP1 (S3), (d-f) SOD (S7), and (g-i) ANA (S13).
    Figure 7: FTIR spectra of the three zeolites: S3 = NaP1, S7 = SOD and S13 = ANA.
    Figure 8: TG-ATD curves of the three zeolites: S3 = NaP1, S7 = SOD and S13 = ANA.
    Figure 9: Particle size distribution of the three zeolites: S3 = NaP1, S7 = SOD and S13 = ANA.
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    Figure 10: DRX diagrams of the NaP1 zeolites obtained at 120 ° C and 6 h in the first and second recycling of mother liquors (S14 and S15, respectively), without adding NaOH solution in the reactor loading stage. Figure 11: DRX diagrams of the NaP1 zeolites obtained at 120 ° C and 6 h in the first, second and third recycling of mother liquors (S16, S17 and S18, respectively), with the addition of fresh NaOH solution in the loading stage at reactor. EMBODIMENT OF THE INVENTION
    Experimental parameters that are involved in the process object of the invention such as stirring, reaction time, temperature, concentration of the NaOH solution have been studied to determine the optimal conditions for obtaining high quality zeolites. The products obtained were characterized by techniques such as X-ray diffraction (DRX), scanning electron microscopy (MEB), Fourier transform infrared spectrometry (FTIR) and thermogravimetry-differential thermal analysis (TG-ATD). The physicochemical characterization was completed with the determination of the specific surface area (SBET), zeta potential (PZ), particle size distribution, polydispersity index (IP) and cation exchange capacity (CIC). materials
    The solid waste used in this work comes from the sleeve filters of the suction system used in the grinding process of aluminum slags. One of the main problems to be solved when these wastes are used in some process as raw material is the obtaining of a homogeneous sample. In order to obtain a representative sample of the residue, nine samples of residues from different Spanish industries were mixed and homogenized by successive quarters. The material thus obtained, a powdery solid, is mainly constituted (> 50%) by particles with a size smaller than 23 µm in diameter, with a content of 65.9% of Al2O3 and 5.3% of SiO2 (Table 1 ) which implies an Al2O3 / SiO2 ratio of 12.4.
    Table 1
    Chemical composition (expressed in% by weight) of the aluminum residue.
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    FRX MkEAA
    Al2O3 SiO2MgOTiO2CaONa2OFe2O3SO3Cl-OthersAlnaAlb
    65.93 5.344.803.463.443.801.111.268.090.9413.0612.84
    aDetermined by the Kjeldhal (MK) method. bDetermined by atomic absorption spectroscopy (EAA).
    Aluminum is distributed in different crystalline phases (Figure 1), such as: corundum (Al2O3), aluminum nitride (AlN), metallic aluminum (Al), and spinel (MgAl2O4). In addition, other phases are observed such as quartz (SiO2), halite (NaCl) and silvite (KCl). The high background noise of the DRX diagram also indicates the presence of non-crystalline or amorphous phases in which metal oxides, such as iron oxide, etc. could be included.
    For the synthesis of the zeolites, the low SiO2 / Al2O3 molar ratio of the residue was increased to 4, adding an 11 M solution of neutral sodium silicate (Na2SiO3, Panreac). As the alkalizing agent, a solution of sodium hydroxide in different concentrations (1-5 M), prepared by dissolving NaOH in lentils (98% NaOH, Panreac) in distilled water, is used. Direct synthesis of zeolites
    The synthesis of the zeolites is carried out by means of a conventional hydrothermal process, without previous activation stage, in the basic Na2O-Al2O3-SiO2-H2O system and in the absence of structure directing agents. The reagents, the solid residue (10 g), the 11 M solution of Na2SiO3 (to adjust the Si / Al ratio) and the NaOH solution are charged in an autoclave with a Teflon vessel (Parr, 1 L capacity). All tests are performed with a Si / Al molar ratio of 2.0 and with continuous stirring under an inert nitrogen atmosphere (to maintain the same pressure in the reactor, 1000 kPa). Different tests are carried out varying the experimental conditions of reaction time, temperature and alkali concentration. Thus, by setting the temperature at 120 ° C, tests are carried out at different times of 3, 6 and 24 h; setting the time to 6 h, tests are carried out by varying the temperature at 80, 90, 100, 120, 140, 160 and 200 ° C. In these experiments a 1 M solution of NaOH is used. To study the effect of alkali concentration, tests are carried out keeping the time fixed at 6 h and the temperature at 120 ºC and using different NaOH solutions (1, 3, 4 and 5 M). Since the formation and crystallization of zeolites is very sensitive to agitation, a test is carried out without agitation. After completion of the reaction, the solid products are separated from the mother liquor by pressure filtration (500 kPa, 0.22 μm Millipore GTTP filter). The mother liquors are analyzed to determine the sodium, aluminum and silicon content, the pH and the ionic conductivity (IC) in order to reuse them in recycling tests due to their high degree of alkalinity.
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    image27 Pre-wash the aluminum residue
    Before performing the zeolite synthesis, the aluminum residue is washed with distilled water using a ratio of 10 ml / g, at room temperature and pressure and under stirring for 30 min in order to remove the salt content (mainly NaCl and KCl). This washing is intended to further favor the formation, growth and development of zeolites. After washing, the water is filtered or decanted. The washed residue, and without drying, is used directly as the main source of Al and Si in the synthesis of zeolites. On the other hand, the washing waters are subjected to concentration and evaporation for the recovery of the salts contained therein (obtaining 0.08 kg of salts per kg of residue with a composition of 95% NaCl and 5% KCl) and clear waters that are reused in subsequent washing of the residue, keeping its pH and ionic conductivity virtually unchanged for at least 5 consecutive washing cycles. Capture of synthesis gases
    Synthesis tests are carried out according to the conventional hydrothermal process allowing the total and direct conversion of the residue into zeolite. At the end of the synthesis, the gases generated, specifically NH3 and H2, are captured by dragging with an inert gas (N2). The separation of NH3 from the gas stream is carried out by capture on a 50% weight tartaric acid solution in which crystalline ammonium tartrate is formed, which is subsequently recovered by gas phase heating. Depending on the experimental synthesis conditions, a recovery of up to 75% has been achieved in the recovery of this gas, in relation to the theoretical content (calculated from the AlN content of the residue). Once the NH3 is separated, the gas stream formed by the entrainment gas, H2 and other unidentified gases (from the hydrolysis of the residue) is recovered and can be used as fuel for itself or other processes.
    image28 Recycling of the alkaline effluent (mother liquor)
    In general, the synthesis of zeolites both from chemical reagents and from residues, results in obtaining a solid product (the zeolitic material itself) and mother liquors (alkaline effluents). The mother liquors can be recycled in the synthesis process, in order to reduce the consumption of water and alkalizing agent, and therefore reduce the environmental impact of the process. In the tests carried out to study the recycling of mother liquors, the corresponding NaOH solution is replaced in its entirety by an equivalent volume of mother liquor. Three consecutive recirculation tests are performed. In the first two tests a zeolite of similar characteristics to the initial one is obtained (obtained without recycling of mother liquors). But in the third trial, and due to the decrease in water alkalinity, a certain amount of unreacted residue is obtained together with the zeolite. In addition, in order to increase the alkalinity of the mother liquors and thus optimize the recycling process, tests are carried out in which 5% fresh NaOH solution is added to the mother liquor, to compensate for the content of Na + ions. In this case, three tests of successive recirculations are carried out, verifying that even in the third recycling, both the crystalline, morphological and textural properties of the zeolites obtained, as well as the reaction yield, do not show variations compared to the initial sample.
    The process scheme used for the hydrothermal synthesis of zeolites from the residue from the milling of aluminum slags is shown in Figure 2 in which:
    (one)  waste washing stage
    (2)  hydrothermal synthesis stage
    (3)  stage of separation of the zeolites obtained from their mother liquors by filtration
    (4)  drying stage of the zeolites
    (5)  gas capture stage
    (6)  NH3 separation and recovery stage
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    image31 Characterization of the residue and zeolite samples obtained
    The chemical composition of the residue was determined by X-ray fluorescence (FRX, X-ray fluorescence spectrometer by Bruker wavelength dispersion, Tiger S8). AlN content was quantified using the Kjehdal method. The mineralogical composition of the samples was determined by X-ray diffraction (DRX) with CuKα radiation, (Bruker D8 Advance diffractometer). The semi-quantitative analysis of the samples was determined by the reference intensity ratio (RIR) method using DRX data and EVA software. Ignition mass loss (LOI) was calculated by heating the sample at 1000 ° C for 1 h in a Pt crucible. The morphology of the zeolites was examined by scanning electron microscopy (MEB, Hitachi S4800 microscope). The Fourier transform infrared spectrum (FTIR) was recorded, using KBr pads, between 400-4000 cm-1 (Nicolet Nexus 670-870). Thermogravimetric analysis (TG) and differential thermal analysis (ATD) were performed at heating rate of 10 ° C / min, in platinum crucible and N2 atmosphere (flow of 100 ml / min) up to 1000 ° C, in a thermoanalyzer Model SDT-Q600, TA Instruments. The specific surface area (SBET) was determined using the BET nitrogen adsorption / desorption method at 77 K (Micromeritics ASAP 2010).
    The particle size distribution (d10, d50, and d90) was measured using aqueous sample suspensions (0.001 g / ml, Mastersize 2000 laser diffraction size analyzer, Malvern). The polydispersity index (PI) was calculated according to Naranjo et al. [M. Naranjo, M.A. Castro, A. Cota, E. Pavón, M.C. Pazos, M.D. Alba, "A new route of synthesis of Na-Mica-4 from sodalite", Microporous Mesoporous Mater. 186 (2014) 176-180)]. The zeta potential (PZ) was determined by laser doppler eletrophoresis (ZetaSizer Nano, Malvern) on aqueous dispersions (0.00005 g / ml) at 25 ° C. The cation exchange capacity (CIC) of the zeolites was determined by the NH4 + ion exchange method with a solution of 1M NH4Cl (pH ~ 7). The composition of the mother liquors (AM) was analyzed by means of an optical emission spectrometer with inductive coupling plasma source, ICP-OES (Spectro Arcos). PH values and ionic conductivity
    (CI) were measured in a multimeter (MM41, Crison).
    Results
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    The different experimental conditions of the tests performed to obtain the zeolites from the aluminum residue are shown in Table 2, together with the crystalline phase identified in each test and the reaction yield expressed in kg of zeolite per kg of residue. Table 2
    Experimental conditions used in the synthesis of zeolites from the aluminum residue, type of zeolite obtained and reaction yield.
    Sample NaOH concentration, (mol / l)t (h)T (C)Zeolitic phaseYield (kg zeolite / kg residue)
    S1a one3120NaP1 + Amorphous Phase2.25
    S2 one3120NaP12.46
    S3 one6120NaP12.47
    S4 one24120NaP12.35
    S5 36120NaP1, SOD2.15
    S6 46120NaP1, SOD2.13
    S7 56120SOD2.17
    S8 one680Amorphous phase1.80
    S9 one690NaP11.86
    S10 one6100NaP12.24
    S11 one6140NaP1, ANA2.38
    S12 one6160ANA2.34
    S13 one6200ANA2.39
    10 a Test performed without agitation. Most of the experimental conditions tested are favorable for obtaining the zeolites due to the high solubility in the alkaline medium used of the different aluminum compounds, especially metallic aluminum and aluminum nitride, as well.
    15 as to the presence of silicon in solution. Given that the initial Si / Al molar ratio was the same for all experiments, it can be said that the formation of the different zeolites depends on the rest of the experimental parameters such as time, temperature and concentration of alkalizing agent.
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    image37 X-ray diffraction data
    Figure 3 shows the DRX diagrams of the samples obtained at 120 ° C, with a concentration of 1 M NaOH, for 3, 6 and 24 h. In all samples, the NaP1 type zeolite was identified as the only phase. Well-defined DRX profiles were obtained, except for the S1 sample prepared without stirring, as a result of incomplete dissolution of the residue. This means that agitation has a great positive effect on the formation and development of zeolites from aluminum residues. The crystallinity of the samples increased with the reaction time, as seen in the diffraction profiles: The most crystalline NaP1 was obtained when the reaction time was 24 h (S4).
    The amount of zeolite NaP1 obtained per kg of residue (Table 2) is about 2.4-2.5 kg for the different times tested (3, 6 and 24 h). For sample S1 (without stirring) a lower value is obtained due to an incomplete zeolitization process.
    Since a reaction time of 6 h is considered adequate to obtain a well crystallized product, it was selected to carry out the following experiments in order to study the influence of other experimental parameters (alkali concentration, temperature and mother liquor recycling ).
    Figure 4 shows the DRX graphs of the samples prepared at 120 ° C for 6 h with different concentrations of NaOH (S3, S5, S6 and S7). When the concentration of alkali increases from 1 to 5 M, both the intensity of the peaks and the size of the crystallites corresponding to the NaP1 phase gradually decrease due to the formation of the sodalite phase (SOD) in alkali concentration greater than 1 M For samples S5 and S6, when the concentration of NaOH increases from 3 to 4 M, the percentage of NaP1 decreases from 43 to 30%. SOD was obtained as a single crystalline phase in the S7 sample, for the highest concentration of NaOH (5 M).
    The amount of SOD obtained per kg of waste is 2.2 kg.
    Figure 5 shows the DRX diagrams of the samples obtained for 6 h, using 1 M NaOH, and temperatures between 80 and 200 ° C. Samples S9, S10 and S3
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    obtained at 90, 100 and 120 ° C, respectively, have DRX profiles characteristic of NaP1, in which an increase in crystallinity with temperature is observed.
    The amount of zeolite NaP1 per kg of residue also increases with temperature, obtaining values greater than 2.0 kg at temperatures above 100 ° C. For the tests carried out at 160 and 200 ° C, the profiles of the DRX diagrams (samples S12 and S13) are characteristic of very crystalline samples, indicating the formation of ANA as a single zeolitic phase.
    With the process of the invention, the ANA zeolite is obtained directly from the transformation of the aluminum slag grinding residue in a single stage, shorter than in the prior art processes.
    For the temperature of 80 ºC, (sample S8), the DRX profile is characteristic of amorphous materials, only being identified as the crystalline phase quartz; and for the temperature of 140 ° C, a mixture of NaP1 and ANA is obtained. The yield obtained for the ANA is 2.4 kg per kg of waste. As in the case of the other zeolites, the reaction yield is very high, and all the residue is transformed into zeolitic material.
    According to the bibliographic data, when these zeolites are obtained from fly ash, in general, a previous activation stage is required and, normally, the yield (85-250 g of zeolite per kg of fly ash) is much lower than obtained using the aluminum residue.
    A complete characterization of the zeolites obtained, NaP1, SOD and ANA (samples S3, S7 and S13) has been performed. Scanning electron microscopy images
    Figure 6 shows the MEB images of the three zeolites obtained at different magnifications. The NaP1 zeolite (sample S3) exhibits a homogeneous "cauliflower-like" morphology consisting of primary aggregates of 15-45 µm (Figures 6a and 6b). These aggregates in turn are formed by smaller secondary aggregates with an average diameter of about 4 µm, formed by nanometric cubic crystals with well-defined edges and anisotropic crystalline growth (Figure 6c), characteristic of gismondin-like structures such as NaP1.
    image39
    The images corresponding to SOD (sample S7) have a morphology characterized by small “blackberry” agglomerates, very densified and with an average diameter of 1.5 µm (Figures 6d and 6e), and in some of which it can be seen that It is hollow balls. At higher magnification (Figure 6f), an intercreation of distorted hexagonal tabular crystals with edges ranging in the range of 40-350 nm is observed.
    The morphology of ANA (sample S13) (Figures 6g and 6h) consists of agglomerates of spherical particles with size between 4 and 8 µm. At higher magnification (Figure 6i), there are ehedral crystals that form trapezohedra with very faceted faces and well defined edges, most of the crystals exhibit intergrowth. Fourier transform infrared spectroscopy data
    The FTIR spectra of 400 to 1200 cm -1 of the NaP1, ANA and SOD zeolites are shown in Figure 7. All spectra show the bands corresponding to aluminosilicates, observing a broad and very strong band around 1000 cm-1 that is assigned to the asymmetric tensions of the internal tetrahedron of Si-O or Al-O. For the S3 sample, the FTIR spectrum obtained is characteristic of NaP1: the three bands centered at 743, 679 and 604 cm-1 are attributed to the vibration of the symmetric tension of the internal tetrahedron, and the band at 433 cm-1 is assigned to the bending vibration of the tetrahedron and are similar to the spectra found in the literature for the NaP1 zeolite obtained from pure chemical reagents. This indicates the high purity of the zeolite synthesized from the aluminum residue.
    In the case of the S7 sample, the characteristic triplet of the SOD zeolite in the region of the "fingerprint" (symmetric tension) at 732, 704 and 669 cm-1 and the two bands corresponding to the flexion of the octahedron at 461 stand out and 433 cm -1. The spectrum of the sample S13, fits well with the results previously published in the literature for the ANA zeolite, in which the band corresponding to the asymmetric tension of the tetrahedron appears at 1014 cm1, the bands corresponding to the symmetric vibrations at 872, 700 and 591 cm-1, and finally the flexure band at 448 cm-1.
    image40
    image41
    image42 Thermogravimetry data and differential thermal analysis
    Figure 8 shows the TG-ATD analysis of the three zeolites. The total loss of mass for
    5 NaP1 is 13.9%, practically similar to that obtained in the LOI (13.3%), which corresponds to the release of 10 water molecules, which takes place at different stages, observing the highest percentage of loss of water at 115 ° C. For SOD, the total loss of mass is 10.9%, a value very similar to that obtained in the LOI (10.2%) and corresponding to 5 water molecules. The lowest total mass loss (7.9%) is obtained
    10 for the ANA, whose value is also very similar to that determined in the LOI (8.2%) and corresponds to a water molecule. Other features: textural, particle size distribution, polydispersity index, zeta potential.
    15 Table 3 shows the textural characteristics of the three zeolites obtained from the aluminum residue together with other physicochemical properties such as particle size distribution, polydispersity index (IP) and zeta potential (PZ).
    20 Table 3 BET specific surface area (SBET), particle size distribution, polydispersity index (IP), and zeta potential (PZ) of zeolites synthesized from the residue.
    Sample PhaseSBET (m2 / g)Particle Diameter (µm)IPPZ (mV)
    d10 d50d90
    S3 NaP114.21.510.622.61.99-55.9
    S7 SOD15.52.015.838.22.29-65.9
    S13 ANA4.60.49.018.11.97-29.5
    25 The crystallite size NaP1 and SOD zeolites much smaller than the ANA zeolite have superior surface areas. The particle size distribution curves (Figure 9) show that in the case of ANA (S13) the distribution is bimodal with two maximums centered at 0.3 and 12 µm, while for NaP1 (S3) and SOD (S7) ), the
    19
    image43
    image44
    image45
    distribution is quasi-monomodal with maximum 17 and 40 µm, respectively. SOD has a narrower distribution curve than the other two zeolites because the increase in alkalinity in the synthesis favors the speed of nucleation and polymerization between silicate and aluminate ions, and as a consequence a more homogeneous particle size distribution. All zeolites have negative PZ values, characteristic of these materials, based on a three-dimensional structure of AlO4 and SiO4 tetrahedra with a negative surface charge. These results indicate that the three zeolites can be used in metal adsorption processes, the electrostatic attraction being between positive charges and the superior active sites for NaP1 and SOD. Cation Exchange Capacity
    In relation to the CIC, the NaP1 zeolite has the highest value (2.73 meq NH4 + / g) as corresponds to high CIC zeolites obtained at low temperature and low alkaline concentration, while SOD and ANA with CIC values of 0 , 71 and 0.57 meq NH4 + / g can be considered as low CIC zeolites. Effect of alkaline effluent recycling on zeolites
    Figure 10 shows the DRX diagrams of the samples obtained (S14 and S15) in two successive tests of mother liquor recirculation without the addition of NaOH. In both cases NaP1 is obtained as the only crystalline phase, with diffraction profiles similar to those obtained in the initial test without recirculation (sample S3). In the profile of the sample S15 corresponding to the second recycling, a widening of the peak at 33.3 ° (2θ) is observed, which could be attributed to the presence of other stabilizing cations of the network such as K +. In a third test of mother liquor recycling, the incomplete reaction of the aluminum residue was observed, due to a deficit of Na + cations, or what is the minimum due to an insufficient alkalinity that does not allow the transformation of the residue to be completed. The amount of zeolite obtained per kg of residue, in the first recirculation was similar to that obtained in the test performed without recirculation, while in the second it was slightly lower.
    Figure 11 shows the DRX diagrams of the samples obtained in three successive tests of recirculation of the mother liquors with the addition of 5% fresh NaOH solution. It is verified that in the three tests (samples S16, S17 and S18) the diffraction profiles obtained correspond to the NaP1 zeolite, checking that even in the third recycling, both the crystalline, morphological and textural properties of the zeolites obtained, such as the reaction yield, they do not show variations in relation to the initial synthesis test (sample S3).
    image46
    image47
    image48
    5 Table 4 shows the contents in Na, Si and Al, the pH and the ionic conductivity (CI) of the mother liquors obtained in the recycling tests without addition of NaOH solution (samples AMS14 and AMS15) and with addition of solution NaOH (samples AMS16, AMS17 and AMS18).
    10 Table 4
    Chemical composition, pH and ionic conductivity (CI) of the mother liquor obtained in the synthesis of NaP1 in two recycled without addition of NaOH (samples AMS14 and AMS15) and in three successive recycled with addition of NaOH to adjust the alkalinity of the medium of
    15 reaction (samples AMS16, AMS17 and AMS18).
    Sample Chemical composition (g / ml)pHCI (mS / cm)
    Na YesTo the
    Recycling of mother liquors without alkalinity adjustment
    AMS14 1700010486513.0136
    AMS15 1370032614513.6106
    Recycling of mother liquors with alkalinity adjustment
    AMS16 24327886twenty13.7126
    AMS17 247876362513.7127
    AMS18 291664034113.6132
    With the inventive process of mother water recycling with successive addition of 5% NaOH solution, it is possible to reduce the consumption of water and alkalizing agent, and consequently reduce the economic and environmental costs of the zeolite production process from the aluminum residue.
    权利要求:
    Claims (16)
    [1]
    image 1
    image2
    image3
    1. Procedure of revaluation of a residue from the milling of aluminum slags by means of its transformation into zeolites by a hydrothermal synthesis process comprising the following steps: -addition to the reactor of the residue from the milling of aluminum slags, a NaOH solution with a concentration between 1 M and 5 M and a solution of 11 M sodium silicate, so that the liquid / solid ratio in the reactor load is between 7 and 30 l / kg and an initial molar ratio Si / Al of 2.0 -reaction of the mixture formed in the previous stage by heating at a temperature between 90 ° C and 200 ° C, for a period of time between 3 and 24 h and under stirring conditions at speeds between 600 and 1200 rpm -separation of the zeolites obtained from their mother liquors by vacuum or pressure filtration and subsequent drying at a temperature below 100 ° C, character hoisted because the process additionally includes: -a stage prior to the addition of the load to the reactor, in which the residue from the milling of aluminum slags is washed with water, the washing waters being separated by decantation or filtration before load to the reactor -the recovery of the salts contained in the wash waters by concentration and evaporation -the recycling of the wash waters resulting from the recovery of salts -the recovery of the gases generated in the hydrothermal synthesis by dragging with an inert gas once the heating stage is finished - the recycling of the resulting mother liquors, after the separation of the zeolites, for use in the stage of addition to the reactor, adjusting the alkalinity of the mother liquors with fresh NaOH solution so that the concentration is between 1 M and 5
    M.
    [2]
    2. Procedure for revaluation of a residue from the milling of aluminum slags according to claim 1, characterized in that the fine grains of granulometry of less than 200 µm obtained in the milling process of aluminum slags are used as raw material.
    image4
    image5
    image6
    [3]
    3. Procedure for revaluation of a residue from the milling of aluminum slags according to claims 1 or 2, characterized in that the solid / liquid ratio in the washing stage, prior to the addition of the load to the reactor, is 1: 10 and the liquid / solid ratio in the reactor load is 15 l / kg
    [4]
    4. Procedure for revaluation of a residue from the milling of aluminum slags according to claims 1 to 3, characterized in that the washing waters are concentrated by evaporation to dryness recovering 0.08 kg of salts per kg of residue with a composition 95% NaCl and 5% KCl and obtaining waters that are recirculated in subsequent washes.
    [5]
    5. Process of revaluation of a residue from the milling of aluminum slags according to any one of claims 1 to 4, characterized in that the reaction stage has a duration of 6 h.
    [6]
    6. Procedure for revaluation of a residue from the milling of aluminum slags according to any one of claims 1 to 5, characterized in that the reaction step is carried out at the autogenous system pressure between 100 and 1000 kPa.
    [7]
    7. Method of revaluation of a residue from the milling of aluminum slags according to any one of claims 1 to 5, characterized in that the reaction step is carried out under an inert atmosphere of nitrogen.
    [8]
    8. Method of revaluation of a residue from the milling of aluminum slags according to any one of claims 1 to 7, characterized in that the gases generated in the hydrothermal synthesis are NH3 and H2, which are entrained with an inert gas. Once the reaction stage is over.
    [9]
    9. Method of revaluation of a residue from the milling of aluminum slags according to claim 8, characterized in that the inert gas is N2.
    [10]
    10. Method of revaluation of a residue from the milling of aluminum slags according to claims 8 or 9, characterized in that the separation of the NH3 from the entrainment stream is carried out by means of its capture in a 50% tartaric acid solution in weight and subsequent recovery by heating in the gas phase, reaching up to 75% of the content, determined from the AlN content of the residue.
    image7
    image8
    image9
    [11]
    11. Method of revaluation of a residue from the milling of aluminum slags according to any one of claims 1 to 10, characterized in that in the recycling of the resulting mother liquor after separation of the zeolites for use in the addition stage To the reactor, the volume of fresh NaOH solution that is added to adjust the alkalinity is increased by 5% in successive recirculation cycles.
    [12]
    12. Method of revaluation of a residue from the milling of aluminum slags according to any one of claims 1 to 11, characterized in that to obtain NaP1 zeolites: -the concentration of the NaOH solution added to the reactor is 1M -the temperature in the reaction stage is between 90 ° C and 120 ° C - the concentration of NaOH in the mother liquor recirculation stream is set to 1
    M.
    [13]
    13.-Method of revaluation of a residue from the milling of aluminum slags according to any one of claims 1 to 11, characterized in that to obtain ANA zeolites: -the concentration of the NaOH solution added to the reactor is 1M -the Temperature in the reaction stage is between 160 ° C and 200 ° C. -The concentration of NaOH in the mother water recirculation stream is set to 1
    M.
    [14]
    14. Method of revaluation of a residue from the milling of aluminum slags according to any one of claims 1 to 11, characterized in that to obtain SOD zeolites: -the concentration of the NaOH solution added to the reactor is 5M -the temperature in the reaction stage is 120 ° C and -the concentration of NaOH in the mother liquor recirculation stream is adjusted to 5
    M.
    image10
    image11
    image12
    [15]
    15.-Zeolite NaP1 obtained by a process as defined in claim 12 which has an adsorption efficiency of Hg in water of 60% in 2 h working with a ratio of 0.01 g of zeolite per ml of Hg solution of concentration 0.2 mg / l and an adsorption efficiency of Cd in water of 99% in 10 min working with 0.005 g of zeolite
    5 per ml of Cd solution of concentration 20 mg / l.
    [16]
    16.-Zeolite ANA obtained by a process as defined in claim 13 which has an adsorption efficiency of Cd in water of 94% in 10 min working with 0.005 g of zeolite per ml of Cd solution of concentration 20 mg / l .
    10
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    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    JP2002179423A|2000-12-11|2002-06-26|Etsuro Sakagami|Method of manufacturing artificial zeolite composition using aluminum dross as starting raw material|
    JP2002193613A|2000-12-26|2002-07-10|Etsuro Sakagami|Containing method and equipment for continuously producing white artificial zeolite composition with heated reaction tube and apparatus using the same|
    CN101428816A|2008-11-27|2009-05-13|中国日用化学工业研究院|Process and equipment for synthesis of sub-micron 4A zeolite with continuous crystallization|
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