RO128290A2 - Process for treating the industrial red mud waste by using process effluents - Google Patents

Abstract

The invention relates to a process for treating the industrial red mud waste in order to reduce the alkalinity at a pH value of 6.7...8.8. According to the invention, the process consists in treating the red mud waste, resulting from various types of bauxite, in continuous flow, at the atmospheric pressure and ambient temperature, in order to reduce the alkalinity to a pH of 6.7...8.8, with residual gaseous fluxes containing 2...20 % COresulting from thermal installations, there being obtained a solid product with improved chemical and superficial characteristics, which is used as absorbent material for treating industrial waste water or as an inorganic matrix for polymeric composites, the water resulting after the separation of the neutralized solid being used for the synthesis of hydrotalcite-type structures.

Description

PROCESS FOR THE PROCESSING OF RED WASHER INDUSTRIAL WASTE WITH

USE OF PROCESS WATERS

Red mud is the main by-product in the process of industrial aluminum production by the Bayer process by which the bauxite ore is treated with concentrated NaOH solutions at 150-230 ° C and under pressure. During the process, the aluminum reacts with NaOH to form sodium aluminate by removing the sludge from the red mud. The amount of red mud generated per tonne of Al depends on the type of bauxite used and can be from 0.3 t to 2.5 t. The main constituents of red mud are Fe ₂ O ₃ (30-60%), A1 ₂ O3 (10-20 %), SiO ₂ (3-50%), Na ₂ O (2-10%), CaO (2-8%), TiO ₂ (trace -10%). Due to the presence of NaOH and Na ₂ CO ₃ (1-6%, commonly expressed as Na ₂ O), red mud waste is a high alkalinity material, whose pH usually varies in the range 10.5-13 u.pH. Although it may be a valuable source of raw materials due to the metal oxides it contains, the presence of sodium hinders their recovery. Usually, the red mud is stored as a suspension (15-40%) in uneven terrain or specially arranged basins. The storage of such material raises a number of environmental problems, mainly due to the possibility of solubilizing the alkaline compounds in the groundwater during the rainy periods and the spreading of very fine particles in the air during the dry periods [Newson, T .; Dyer, T.; Adam, C.; Sharp, SJ Geotech. & Geoenviron. Eng. 2006, 132: 2,143-151].

The safe storage of this material requires technical solutions for collecting leaks to prevent contamination of soil and groundwater. Dust formed on the dry surface of the residue dump containing predominantly Na ₂ CO ₃ can endanger the lives of people and living beings by inhalation. Physical and chemical properties (high pH, small particle size) limit storage efforts but also future use. Neutralization of this type of material requires both the neutralization of the interparticle liquid phase and the mineral phases with alkaline potential.

Neutralizing the red mud alkalinity associated with appropriate treatments to transform it into useful products allows both a problem related to the contamination of the environment and the economic aspects related to the management of raw materials and resources. Neutralization strategies that can be used and have different degrees of efficiency feel:

- addition of mineral acids (usually H2SO4 or HCl) to reduce the pH to 10.5 u.pH

which is safe [US 4,913835] but has the disadvantage that it is an ui option in which a surplus of mineral acid is available;

^ 2 0 1 1 - 0 0 9 6 5 -28 -09- 20J1 Ț

- the use of red mud suspension for the retention of sulfur or nitrogen compounds from industrial emissions [US 4222992/1980],

- adding high quantities of seawater (mass ratio 13/1 water / NR) to reduce the pH from 12.5 to 8.5, (many aluminum factories being close to the sea), or concentrated saline solutions obtained by evaporating the water from high, or by using acidic waters of mine or brines rich in Ca ⁺² or Mg ⁺² that will react with OH ', CO3 ² ', oxalate (COO) ₂ ² 'ions present in the red mud residue [WO02 / 34673 if C. Hanahan, D. McConchie, P. John, R. Creeiman, M. Clark, C. Stocksiek Environ. Eng. Sci. 21, 2004, 125-138]. An analysis of the seawater neutralization process shows that it generates about 20% more CO2 and needs about 44% more electricity than the lime neutralization process [D. Tuazon, GD Corder, Resources, Conservation and Recycling 52, 2008, 1307-1314]

- Treatment with lime in the presence of carbonaceous materials (coke) allows the recovery of the iron ensuring only a superficial neutralization of the particles [US4045537,1977],

- Another way to neutralize red mud is to treat it with CO ₂ [D. Bonenfant, L. Kharoune, S. Sauve, R. Hausler, P. Niquette, M. Mimeault, MKharoune, Ind. Eng. Chem. Res. 47, 2008, 7617-7622; S. Khaitan, DA Dzombak, GV Lowry, J. Environ. Eng. 135 (2009) 433-438].

It is known that CO ₂ emissions contribute to the global phenomenon of global warming and acidification of water stretches. CO ₂ is a by-product of combustion processes and creates operational, economic and environmental problems. The risk reduction for the occurrence of climate and environmental changes can be achieved by retaining atmospheric CO ₂ with the help of industrial waste: fly ash (fine) coal, heavy ash, slag from steel making, ash from blast furnaces, broken cement. , cement dust from lime kilns, thus achieving their greening [US 2005/007694 or W02005 / 086843],]. Waste gases from different industrial processes (plants for the production of electricity through the combustion of methane gas, coal, oil, natural gas liquefaction plants, cement industry, steelworks) with various CO ₂ contents [US2011 / 0030957 Al] are environmentally friendly. by sequestering CO ₂ in aqueous suspensions (about 30% solid) in which there are Ca ²⁺ and Mg ²⁺ cations. Depending on the nature of the CO ₂ storage resource the quantities retained vary within the limits of 0.012-

CV 2 Ο 1 1.- 0 0 9 6 5 -2 8 “09“ 2011

A variant of reducing the CO2 content of the gases emitted in the atmosphere is the carbonation of the liquid flows (from the Bayer process of obtaining aluminum) at 40-100 ° C, following the recovery of the dawssonite of Na, NaAROIThCCU from these flows [US 1977 / 4036931].

One way to reduce the alkalinity of previously washed red mud is to use CO2 from the flue gas stream from the Bayer process [WO 1993/16003] at pressures of 40 atm. The process allows a recovery of the soda initially introduced, and of the desilication products (DSP) introduced in the Bayer process of obtaining aluminum.

The invention relates to obtaining an oxide material with reduced alkalinity by processing the red mud waste from different types of bauxite, using process waters in the synthesis of hydrotalcite type structures.

The hydrotalcite-type structures can be described by the general formula Mg _x . _y M ⁿ yAli. uM ^ra u (OH) 2 (x + i) A _z ^y '.wH2O, wherein M ⁿ may be a bivalent cation such as Ca ²⁺ , Sr ²⁺ , Co ²⁺ , Cu ²⁺ , Fe ²⁺ , Ni ²⁺ , Zn ²⁺ ; M ^ra is a trivalent cation (Fe ³⁺ , Cr ³⁴ , V ³⁴ ), A _z ^y_ is an inorganic anion (OFT, CF, NO3 ·, CO3 ² 3 or organic (carboxylate, dodecylsulfonate, etc.), with charge y and the molar fraction z or a combination of different anions having the same charge or different charges, x can have different values between 1.6-8, y can have values between 0 and 8, u can have values between 0 and 1 , w can have values between 0.5 and 4. [F. Cavani, F. Trifîro, A. Vaccari, "Hydrotalcite-type anionic clays: preparation, properties and application" Catalysis Today 11 (1991) 173-301] Compounds of this class has basic and anion exchange properties, being used for different purposes such as: acidity moderators in pharmaceuticals, adsorbents, ion exchangers, basic catalysts, stabilizers for polymers, etc. since their spread in the natural form is reduced , in the last years different modalities have been used summary types such as:

- Variable pH precipitation method (pH increase method);

- Method of precipitation at constant pH (under low or high supersaturation conditions; also called coprecipitation method to indicate that all cations precipitate simultaneously);

- Deposition method (by precipitation reactions, hydrothermal synthesis, hydrolysis reactions, anion exchange, structural reconstruction, electrochemical methods).

Co-precipitation is the most commonly used method for the preparation of large quantities of hydrotalcite-type compounds, allowing higher crystallinity, particles with specific surface areas greater than when precipitation is performed on co-precipitation at high supersaturation and constant pH. with ions of M (II) and M (III) are added very rapidly over

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the solution containing NaHCO ₃ and NaOH. Less crystalline solids are obtained due to the large number of crystallization germs [F. Cavani, F. Trifiro, A. Vaccari, "Hydrotalcite-type anionic clays: preparation, properties and application" Catalysis Today 11 (1991) 173-301)]

The solutions of Μ (Π) and M (III) ions can be prepared from nitrates, chlorides or sulphates of these metals. For a typical preparation by co-precipitation under low supersaturation conditions, a solution is prepared in which the concentration of metal ions (Π (+) + Μ (ΙΠ) is 1.5M and the molar ratio M (II) / M (III) in the range 4/1 -1.8 / 1 called solution A and a solution called solution B containing a concentration of 4.4M M ^(I '- alkali metal) and IM CO3 ² ions, prepared from M ⁽ⁱ⁾ OH and M®2CO3 (M® molar ratio) 0H / M®2CO ₃ = 2.5 / 1).

A problem to be solved by the present invention is the association of the improvement of the chemical and morphological characteristics of the red mud waste destined for the different uses with the use of the water resulting from the treatment process in the synthesis of hydrotalcite type compounds.

By applying the treatment to reduce the alkalinity and to homogenize the morphological structure, it increases the possibility of using this waste in different fields (environmental applications, obtaining polymeric composites, conductive polymers) and implicitly reducing the volume of waste deposited near the aluminum producers.

Another problem solved by this invention is the use as a reducing agent of the red mud alkalinity of residual gaseous fluxes with different CO2 contents from installations where thermal processes take place, which determines the reduction of the amount of greenhouse gases emitted. in the atmosphere as well as the effects of using other types of neutralizing agents that can lead to the appearance of by-products with influence on the life cycle of the neutralized red mud product.

An economic and ecological advantage of the invention is that the neutralization process is carried out at a temperature of 20-25 ° C and atmospheric pressure, without additional input of thermal energy and energy to achieve high pressures.

Another advantage of the invention is the fact that it allows both the processing of the waste stored in time and the slurry suspension in the muma solution, taken from the industrial flow to obtain the aluminum before being sent as waste to the landfill.

Unlike [WO 1993/16003], the process proposed in this invention does not require an initial washing phase of the red mud waste.

According to the invention, the process for treating the red mud waste with waste gases with reeds that may come from the power plants for the production of electricity through methane, coal, oil, natural gas liquefaction installations,

J υ ι j - u u a D J - 2 8 -09- 2011 cement industry, steelworks, incineration plants of different wastes takes place in 3 stages of

reaction separated by two steps of defining ionic equilibrium. Each reaction step consisted of passing a gas stream containing CO ₂ with a flow rate of 250-325ml / min preferably 283 ml / min through an aqueous suspension of red mud, in which the solid / liquid ratio is in the range 1 / 10-1 / 2, obtained either directly from the slurry taken from the industrial flow to obtain the aluminum, or by suspending in the waste water taken from the industrial dump. The neutralization process takes place at ambient temperature (25 ° C) and atmospheric pressure. Each step is considered to be completed when the pH of the suspension is in the range 6-7 u.pH, depending on the quantity and characteristics of the red mud waste introduced into the neutralization reactor. The neutralization stages are separated by stages of defining the ionic equilibrium, which can last between 1 and 4 hours, preferably 2 hours. After each of the two stages of defining the ionic equilibrium the pH value registers an increase of

1.5-1.9u.pH versus the limit value of the completion of each reaction step. After the neutralization process, the solid is separated by filtration from the processed aqueous suspension. Depending on the destination of the neutralized oxide material, the wet paste either dries in air flow 90-110 ° C, for 2-4 hours, or is subjected to a molding operation with the addition of additives.

According to the invention, the waters resulting from the separation operation of the neutralized red mud solid are used for the synthesis of hydrotalcite solids with ratios Μ (Π) / Μ (ΠΙ) in the range 8 / 1-1.5 / 1 (preferably 4 / 1-1.8 / 1). Depending on the chemical composition of the waters resulting from the separation operation of the red mud solid, the quantities of salts of the bivalent and trivalent metals (which can be nitrogen, chlorides or sulphates) needed to prepare solution A (characterized by the concentration Μ ( ΙΙ) + Μ (ΙΠ) of 1.5M and the molar ratio M (II) / M (III) included in the range 8 / 1-1.5 / 1) and respectively the amounts of M®OH and M ^ CCfi respectively necessary for the preparation of solution B (characterized by a concentration of 4.4M alkaline metal ions and an IM concentration of CC ions> 3 ² ', prepared from M®OH (M® = alkali metal) and M®2CC> 3 (molar ratio M ^(I) OH / M®2CO3 = 2.5 / 1).

By applying the present invention the following advantages are obtained:

- it is used as a neutralizing agent residual gas from the power plants for the production of electricity through the combustion of methane gas, coal, oil, natural gas liquefaction plants, cement industry, steelworks, incineration plants of the various oxide erial that fall into the norms EN 12457-2 regarding the sanding in the pH of the aqueous suspension S / L = l / 10 which allows the use either as waste;

c <- 2 Ο 1 1—00965-2 8 "09/2011 adsorbent material intended for the treatment of industrial waste water, either as an inorganic matrix for obtaining polymeric composites with different destinations (building materials, wood replacement);

- through the use of process water, the raw materials needed to obtain hydrotalcite type structures are saved, while water consumption is reduced;

- by obtaining a material with chemical and morphological characteristics corresponding to the various uses, the degree of use of the waste deposited in the dump increases with the diminishing effects on the process of solubilization / drainage with implications on the environment and groundwater.

In the following, without considering them limiting, examples of embodiment of the invention are presented (in relation to fig 1 and tables 1 and 2).

Table 1. Characteristics of the initial and final suspensions corresponding to the initial moment and

end of each neutralization step, referring to examples 1-3

Example Neutralization pHi u.pH pH _f u.pH Conductivity, pS / cm. Conductivityf, pS / cm. Stage Duration, min 1 I 60 10.620 7273 3260 2765 II 50 9040 6078 2768 2498 III 40 8478 6987 2501 2380 2 I 150 11.839 7776 16253 9200 II 95 9227 7728 9123 8360 III 50 8340 7717 8369 8450 3 I 93 10.620 7030 3260 2675 II 78 9125 7321 2678 2390 III 65 8657 7169 2393 2150

EXAMPLE 1 In a glass reactor with a capacity of 2 1 provided with a double pallet agitation system (100 rpm), with a system for supplying and evacuating the gas flow and controlling the pH and the conductivity, 300g is introduced. of waste red mud taken from the dump and dried at 60 ° C for 1 hour to 3 hours, preferably 2 hours, which disperses in water (conductivity 240-300.pS/cm) in the reactor (suspension 1). The suspension 1 is characterized by a solid / liquid ratio 1 / 3.5. The red sludge introduced into the reactor comes from a mixture of residues resulting from the processing of several types of bauxite (Al = 10.5% (mineralogical phases: gypsum 11%, diaspora 9%, Boemite 3%}; Fe = 27%), has a content of monovalent and bivalent metals in the ratio ΣΜεΎΣΜο * ⁺ = 1,059, and a ganulometric distribution

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2-38µτη 71.8%, 38-80pm 7.9%. Suspension 1 has a ρΗ = 10.785u.pH, and ο a conductivity of 3260 pS / cm.

In the reaction vessel in which the suspension 1 is located, it is introduced with a flow of 283ml / min, a mixture of gases containing CO2 (10%, v / v). The treatment of suspension 1 with the gas mixture is done at room temperature (25 ° C) and at atmospheric pressure in three neutralization stages separated by two stages of defining the ionic equilibrium of 2 hours each. Each neutralization step is considered to be completed when the pH value remains constant for five minutes. Table 1 gives the values of the pH and conductivity of the suspension 1 corresponding to the initial and final moment of each reaction step.

The amount of CO2 used to neutralize suspension 1 was 131.7mmol / kg of the dry solid substance. The material resulting after filtering and drying at 105 ° C for 2 hours has a continuum of monovalent and bivalent metals in the ratio ΣΜο '/ ΣΜε ^ Μλϊόδ, a trimodal particle size distribution with the following volumetric distribution of particle sizes: 0.4-2pm 19.7 %, 2-38pm 66.6%, 38-80pm 13.7%. whereas by dispersing the neutralized material in deionized water at a ratio S / L = l / 10, an aqueous suspension characterized by a pH of 8.4 u.pH and a conductivity of 423pS / cm is obtained, as a result adsorbent for environmental applications

EXAMPLE 2 In a glass reactor with a capacity of 2 L equipped with a double pallet agitation system (100 rpm), with a system for supplying and evacuating the gas flow and controlling the pH and conductivity, 300 is introduced. g of red sludge directly from the slurry taken from the industrial flow to obtain the aluminum to which the channel water (conductivity 240-300.pS/cm) is added to reach the solid / liquid ratio (1 / 3.5) ( suspension 2). The suspension of red mud taken from the industrial flow of aluminum comes from the processing of a bauxite with high gypsum continuum (Al = 8.2% {mineralogical phases: gypsum 31%}; Fe = 31%,), and is characterized by a continuous of monovalent and bivalent metals in the ratio ZMe ⁺ / EMe ⁺⁺ = 1.537 and a bimodal ganulometric distribution with the following volumetric distribution of particle sizes: 0.4-2pm 23.3%, 2-60pm 76.7%. The pH and conductivity values of suspension 2 are: pH = 11,839 u.pH, conductivity = 16253 pS / cm.

In the reaction vessel where the suspension 2 is located, a gas mixture containing CO2 (10%, v / v) is introduced, with a flow rate of 283ml / min. The treatment of suspension 2 in the reaction vessel with the gas mixture is carried out at room temperature (25 ^l 'C) and under pressure atmpsțisrKăT'n' ^ rei neutralization stages separated by two stages of defining ic '^ for 2 hours. every. Each neutralization step is considered completed

Bucharest υ 1; 1 - 0 U 9 6 5 - 28 -09 “2011

when the pH value remains constant for five minutes. Table 1 gives the values of the pH and the conductivity of the suspension 2 corresponding to the initial and final moment of each reaction step.

The amount of CO2 used to neutralize the suspension 2 of red mud was 400.5 mmol / kg of the dry solid substance. The material resulting after filtration has a content of mono-valence and bivalent metals in the ratio ΣΜε ⁺ / ΣΜε ^{++ =} 1.233, and a bimodal ganulometric distribution with the following volumetric distribution of the particle sizes: 0.4-2pm 35.3%, 2-60pm 64 , 7%. whereas by dispersing the neutralized material in deionized water at a ratio S / L = 1 / 1O, an aqueous suspension characterized by a pH of 8.6 u.pH and a conductivity of 719pS / cm is obtained, as a result adsorbent for environmental applications.

Example 3 The suspension 1 is introduced into the reaction vessel used in Examples 1 and 2 and is supplied with a flow rate of 288ml / min, a mixture of gases containing CO2 (5.5%, v / v). The treatment is carried out under the same conditions of temperature, pressure, succession of the neutralization and finalization stages of the ionic equilibrium as those presented in example 1. Table 1 gives the values of the pH and the conductivity of the suspension corresponding to the initial and final moment of each stage of reaction.

The amount of CO2 used to neutralize the suspension of 3 red mud was 142.7mmol / kg of the dry solid substance. The material obtained after filtering and drying at 105 ° C for 2 hours has a continuum of monovalent and bivalent metals in the ratio ΣΜε ⁺ / ΣΜε ⁺⁺ = 0.775, a trimodal particle size distribution with the following volumetric distribution of particle sizes: 0.4-2pml8, 4%, 2-38pm 66.7%, 38-80μιη 14.9%. whereas by dispersing the neutralized material in deionized water at a ratio S / L = l / 10, an aqueous suspension characterized by a pH of 8.3 u.pH and a conductivity of 396 pS / cm is obtained, it can be used as an adsorbent for environmental applications.

EXAMPLE 4 Neutralized red sludge according to the procedure described in Example 2 in powder form with granulation below 40 pm in the amount of 142g is introduced into a mechanical mixer provided with pallets where it is mixed with 10 g of natural zeolite with clinoptilolite - (Ca, Fe , K, Mg, Na) 3 ^ Si30AleO72.24H2O, 7g natural magnesium silicate in the form of serpentinite / (Mg, Fe, Ca) 3 (Si, Al) 2O5 (OH) 4 or any other similar magnesium silicate, 24 g aluminum silicate in the form of A12SÎ2O ₅ (OH) 4 kaolin and / or montmorilonite (Na, K, Ca)) 4θιο (ΟΗ) 2 · ηΗ2θ added to improve the plasticity of the mixture, aqueous solution with 30% concentration added as a binder, 4 g MC (methyl cellulose), type A porous olein and porosity and water residue,

Bucharest

<V2 O 1.1 -00965-2 8 -09- 2011 that the liquid fraction of the cheek should be in the range 23-28% of weight calculated as a ratio of the whole mass of solids, after which the raw mixture obtained as a malleable paste is modeled by passing through a round section die with a diameter of 1.5 mm, in the form of cylindrical extrudates with lengths up to 50 mm, which were left to air dry for about 24 hours, after which the extrudates arranged in the form of a bed with a thickness of up to 8 mm is subjected to a second drying operation, more advanced, in the electric oven, in the air, at 105 ° C for 3 hours, after which the dried extrudates are calcined in an electric oven with resistances at 650 ° C a sufficient time of about 2-4 hours for the removal of the residual liquid phase and the removal of the organic additives used for extrusion. Cylindrical extrudates with a round section of about 1.5 mm diameter are obtained, porous, with an open porosity of up to 5560% with interconnected pores, characterized by good adsorption capacity, especially for aqueous liquid media.

Example 5. Synthesis of a hydrotalcite-type compound with a ratio of Μ (ΙΙ) / Μ (ΠΙ) = 3/1 using as a raw material the waters resulting from the operation of separating the neutralized red mud solid according to the methods described in Examples 1 and 2, whose characteristics and composition are presented in Table 2.

Table 2. Composition and characteristics of the waters resulting from the separation operation of the neutralized red mud solid according to the methods described in examples 1 and 2

Example 1 Composition mg / L pH (u-pH) Conductivity (mS / cm) the 10.7 9.62 2.38 Fe 0026 N / A 10 K 660 That 15 HCO3- 1510 Example 2 Composition mg / L pH (u.pH) conductivity (MS / cm) the 0.5 9.25 8.45 Fe 0 N / A 16 K 2600 That 20 mg 0.12 HCO3- 4980

Taking into account the composition of the waters resulting from the separation operation of the neutralized red mud solid according to the methods described in examples 1 and 2, it is calculated what amount of salts (Π), and trivalent metal Μ (ΙΠ) and what amount of I and M®, respectively 2CO ₃

C \ -2 O 1 1, -0 0 9 6 5 2 8 -09- 2011

should be used to obtain solutions A and B respectively used for the synthesis of hydrotalcite solids to meet the conditions imposed by the preparation recipe.

Taking into account the basic pH of the waters whose characteristics are presented in table 2, they will not be able to be used in the synthesis of hydrotalcites as solution A. However, considering that both their bivalent metals are included in their composition ( As, Mg) as well as trivalent metals (Al, Fe), in the preparation of solution A it will be necessary to take into account their existence so that in the reaction mixture the molar ratio characteristic for the hydrotalcite type compound to be prepared must be maintained , respectively Μ (Π) / Μ (ΠΓ) = 3. Solution A must have the concentration Μ (Π) + Μ (ΙΠ) of 1.5M and the molar ratio Μ (Π) / Μ (ΙΙΓ) = 3/1). In 720 mL solution A must therefore be found 1.08 moles Μ (Π) + Μ (ΙΠ).

If 720 mL of water resulting from the separation of the neutralized red mud solid is used for preparation, according to the method described in Example 1, it contains 0.0003 moles Μ (ΠΓ) as Α1 (ΙΠ) and Fe (IH) and 0.0003 moles Μ (Π) in the form of Ca (II), thus summing 0.0006 moles M (II) + M (III). To meet the required composition of solution A, add 1.08-0.0006 = 1.0794 moles Μ (Π) + Μ (ΙΠ). For preparation, choose M (1I) = Mg and Μ (ΠΙ) = Al as nitrogen. Calculate how many moles of salt of Al and Mg respectively are needed for the 720 mL of solution according to the formula:

Moles Α1 (ΙΠ) = (1.0794 / 4) - 0.0003 = 0.26955

Mg Mg (II) = 0.26955 * 3-0.0006 = 0.80805

Check the ratio Μ (ΙΙ) / Μ (ΙΠ) = (0.80805 + 0.0003) / (0.26955 + 0.0003) = 2.995

Multiply the number of moles Α1 (ΙΠ) by the molecular mass of Al (NO3) 3x9H2O and the number of moles of Mg (II) as the molecular mass of Mg (NO3) 2x6H2O, resulting in 101.0759 g Al (NO3) 3x9H2O and 207.1032 g Mg respectively. (N03) 2x6H2O

If 720 mL of water resulting from the separation of the neutralized red mud solid is used for preparation, according to the method described in Example 2, it contains 0.00001 moles Μ (ΙΠ) as A1 (IH) and 0.00036 moles 36 (Π) as of Ca (II), thus summing 0.00037 moles M (II) + M (HI). To meet the required composition of solution A, add 1.08-0.00037 = 1.07963 moles Μ (Π) + Μ (ΙΠ). For preparation, M (H) = Mg and Μ (ΙΠ) = Al are chosen as nitrogen. Calculate how many moles of salt of Al and Mg respectively are needed for the 720 mL of solution according to the formula:

Mole A (HT) = (1.07963 / 4) - 0.00001 = 0.2699

7 = 0.2699 * 3-0.00037 = 0.80933 ^ Μ (Π) / Μ (ΠΙ) = (0.80933 + 0.00037) / (0.2699 + 0.00001) = 2.999

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Multiply the number of moles Al (III) by the molecular mass of Al (NO3) 3x9H2O and the number of moles of Mg (II) as the molecular mass of Mg (NO3) 2x6H2O, resulting in 101.2062 g Al (NO3) 3x9H2O and 207.4313 g Mg respectively. (NO3) 2x6H2O

Taking into account the pH and composition of the waters whose characteristics are presented in Table 2, they will be used in the synthesis for the preparation of solution B, characterized in that it has a concentration of alc® 4.4M alkaline metal ions and an IM ion concentration. CO3 ² .

Under this condition, in solution 720 mL B there should be 3,168 moles of M® alkaline metal and 0.72 moles of CO3 ² · ions.

In 720 mL of water from experiment 1 there are 0.012 mol M® and 0.009 mol CO ² ions. To obtain solution B, add 0.72-0.009 = 0.711 moles of CO3 ² 'ions as

Na 2 CC> 3 anhydrous (0.711 moles = 79.632 g)

Considering that 79,632 g of Na 2 CC> 3 anhydrous contains 1,422 moles of M® alkaline metal and 0.012 moles of M® are already present in the solution, to reach the M4 concentration of 4.4M, a further 720 mL solution must be added: 3.168-0.012-1.422 = 1.734 mol M® as NaOH (1.734 mol = 69.36 g).

In 720 mL of water from Experiment 2 there are 0.048 moles of M® and 0.059 moles of CO3 ² '. To obtain solution B, add 0.72-0.059 = 0.661 moles of CO ₃ 'ions as

Na 2 CC> 3 anhydrous (0.0661 moles = 74,032 g)

Considering that 74,032 g of Na 2 CC> 3 anhydrous contains 1,322 moles of M® alkaline metal and 0.048 moles of M® are already present in the solution, to reach the M4 concentration of 4.4M, a further 720 mL of solution must be added: 3.168 - 0.048 - 1.322 = 1.798 mol M® as NaOH (1.798 mol = 71.92 g).

In a glass reactor with a capacity of 2 L equipped with a magnetic stirring system (600 rpm), with a system of feeding liquid reagents and controlling pH and conductivity, 200 ml of distilled water is introduced whose pH is corrects to 10 u.pH by adding a quantity of solution to B. Then, at the same time, solutions A and B are added simultaneously with two microdosing pumps. After precipitation, the gel was left to mature at 60 ° C for 18h under stirring. After that, the precipitate is separated by vacuum filtration, washed with distilled water until the coductivity of the washing water drops below 0.3mS / cm, is dried at 90 ° C for 24 hours, resulting in the hydrotalcite solid by calcining it at 460 ° C for 18h results in Mg-Al mixed oxides with Mg / Al ratio = 3/1. After drying from the water of Example 1, 42 g of HT-type compound was obtained, and from the water of example 2, 81,633 g of compound were obtained. X-ray diffractograms were obtained for the HT-type compounds obtained from the treatments presented in Example 1. and example 2 compared to

Ct-2 011-.0 0965-28 -09- 2011 diffractogram of a compound type HT prepared by the standard method of coprecipitation. Miller diffraction peaks and indices are shown in Figure 1 and correspond to a hexagonal network with R3m rhombohedral symmetry typical of the hydrotalcite lamellar structure (JCPDF file 70-2151 [PDF4 + -JCPDF files (2009), International Center for Diffraction Data (ICDD), Newtown Square, PA, USA]) with an interlamellar distance that depends on the anionic composition first and which is around 3 Å for Mg ²⁺ and Al ³⁺ hydrotalcts and with anionic groups of CO3 'and OH'.

Claims (3)

1. Process for treating red mud waste with CO2-containing waste gas (in the 2-20% volume concentration range) and which may come from power plants for the production of electricity through the combustion of methane gas, coal, oil, natural gas liquefaction plants, cement industry, steelworks, incineration plants of different wastes and which takes place in 3 reaction stages separated by two stages of defining the ionic equilibrium. Each reaction step consisted in the passage, with a flow rate of 250-325ml / min, of a gas stream containing CO2 through an aqueous suspension of red mud, in which the solid / liquid ratio is in the range 1 / 10-1 / 2 and which is obtained either by suspending in the water the red mud waste taken from the industrial dump, or from the red mud suspension taken from the industrial flow to obtain the aluminum to which the water is added to reach the solid / liquid ratio in the range 1 / 10-1 / 2. The neutralization process takes place at ambient temperature (25 ° C) and atmospheric pressure. Each step is considered to be completed when the pH of the suspension is in the range 6-7 u.pH, depending on the quantity and characteristics of the red mud waste introduced into the neutralization reactor. The neutralization stages are separated by stages of defining the ionic equilibrium, which can last between 1 and 4 hours. After each of the two stages of defining the ionic equilibrium, the pH value increases by 1.5-1.9 u.pH compared to the limit value of the completion of each reaction step. After the neutralization process, the solid is separated by filtration from the processed aqueous suspension. 2. The second claim relates to the production of composites having the characteristics required to be molded by extrusion in the form of monoliths with constant section, porous, with an open porosity of up to 40-60%, based on neutralized red mud according to claim 1. mixed with natural magnesium silicate in the form of coil / (Mg, Fe, Ca) 3 (Si, Al) 2O5 (OH) 4 or any other similar magnesium silicate, aluminum silicate in the form of A12SI2O ₅ (OH) 4 kaolin and / or montmorilonite (Na, K, Ca) (Al, Mg, Fe,) 2 (Si, Al) 40io (OH) 2-nH ₂ 0 added to improve the plasticity of the mixture, Na2SiO3 as aqueous solution with concentration 30 % added as binder, MC 2% aqueous solution (methyl cellulose), olein type A porosity and water residue, so that the liquid fraction of the cheek is in the range 23-28% of weight calculated as a ratio of the whole mass of solids . The molding is re-cast.ase in the form of cylindrical extrudates with lengths up to 50 mm, which air in about 24 hours, after which the extrudates arranged in the form of a bed with a ^ "2 0 1 1 - 0 0 9 6 5 -2 8 -09- 2011 thickness of up to 8 mm are subjected to a second drying operation, more advanced, in the electric oven, in the air, at 105 ° C for 3 hours after which the dried extrudates are calcined in an electric oven with resistances at 650 ° C a sufficient time of about 2-4 hours for the removal of the residual liquid phase and the removal of the organic additives used for extrusion. The use of the waters resulting from the separation operation of the neutralized red mud solid according to claim 1, for the synthesis of hydrotalcite solids with ratios Μ (Π) / Μ (ΙΠ) in the range 8 / 1-1.5 / 1. Depending on the chemical composition of the waters resulting from the separation operation of the red mud solid, the quantities of salts of the bivalent and trivalent metals (which can be nitrogen, chlorides or sulphates) needed to prepare solution A (characterized by the concentration Μ ( Π) + Μ (ΙΠ) of 1.5M and the molar ratio M (II) / M (IU) included in the range 8 / 1-1.5 / 1) and the quantities of M®OH and M® ₂ CO3 respectively required for the preparation of the solution B (characterized by a concentration of 4.4M alkaline metal ions and an IM concentration of CO3 ² · ions, prepared from M®OH (M® = alkali metal) and M® ₂ CO3 (molar ratio M®OH / M® ₂ CC > 3 - 2.5 / 1).