LU84743A1 - PROCESS FOR PRODUCING ZEOLITE A AND PRODUCTS OBTAINED - Google Patents

Description

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PROCESS FOR PRODUCING ZEOLITE A AND PRODUCTS OBTAINED

Zeolite A is a compound with ion exchanger characteristics, which is incorporated in particular in washing powder formulations.

It is well known to prepare zeolite A by reaction in an adequate stoichiometric ratio of sodium silicate and sodium aluminate. This zeolite A must meet certain physical criteria, among which mention may be made, in particular, of the whiteness or reflectance, the particle size and the sequestering power.

In order for a production process to be profitable on an industrial scale, the operating parameters, in particular the separability of the by-products and of the products sought after, must also be easily controllable.

Zeolite A is currently produced by relatively expensive processes, starting from expensive raw materials. The present invention aims to produce a zeolite A of good quality, in particular for everyday use, namely as an ingredient in washing powders.

The process of the invention is based on the use of less expensive reagents than those usually used, namely on the one hand on the use of residual sulfuric acid, in particular as it is produced by the manufacture of carbon dioxide. titanium according to the "sulphate" process, which has generally so far been discharged into the sea and, on the other hand, on the recovery of aluminum solutions, especially produced during the surface treatment (anodization) of the aluminum .

- · The main characteristic of the invention is the fact that the basic silica pulp 5 which is used comes from the treatment of blast furnace slag using residual acid of the aforementioned type j 35 and / or that the aluminate sodium comes from a residual solution of sodium aluminate obtained during the surface treatment of aluminum and / or bare aluminum obtained during the dissolution of the slag.

*> 2 d The Applicant has observed that the transposition into practice of the use of the indicated raw materials with a view to the production of a zeolite A which meets industrial requirements made it necessary, however, to resort to a series of specific techniques which will be described in more detail below and which constitute as many inventive characteristics.

According to the invention, it is in particular intended to use a sequence of simple operations to use the aforementioned reagents, in order to arrive at the desired result, i.e. a reduced cost price for a zeolite Has good quality.

It is known that granulated slag, obtained by rapid cooling of the molten slag when it leaves the blast furnace, constitutes an interesting source of silica. There are also various sources of residual sulfuric acid, in particular that resulting from the manufacture of titanium dioxide or that containing residual sulfuric acid consisting for example of spent pickling acids.

The residual acid compositions originating from the manufacture of titanium dioxide depend in particular on the composition of the leached titanium ore. The average concentration of sulfuric acid varies between 10 25 and 20%, the major impurity being ferrous sulfate, the content of which can reach 20 gr‘de iron per liter.

The acid contains other minor impurities, - * such as Al, Mg, Cr, V, Ti, Mn.

The pickling acid residues are also characterized by a high iron content.

Iron however constitutes a particularly annoying pollutant because it tends to finally color the zeolite A produced.

On the other hand, it has been found that the conditions for dissolving the slag must be chosen to maintain the silicic acid in a stable state with little polymerization.

jl The reaction of the slag which is a basic reagent.

i 3 that with the acid takes place according to the following equation: ^ (CaOSiO20.2 Al2O30f35 Mg 0) + 1.95 H2SC> 4 +1.05 H2O -► dairy i H2Si O3 + 0.2 Al2 (S04) 3 + 0.6 Mg S04 + Ca S04. 2 H20 5 The neutralization of the slag is homogeneous, the dissolution of the various constituents taking place at the same speed. The reaction products are soluble in water, except the gypsum which precipitates., · The dissolution is exothermic.

In practice, however, it can be seen that easy separation of the gypsum by filtration is only possible on condition that the particle size of the treated slag is less than 0.4 mm, preferably 0.2 mm. An operating condition of the process of the invention therefore generally consists in grinding the granulated slag to the particle size indicated.

The slag is dissolved at constant pH (1.5) by feeding the reactor simultaneously with slag pulp (50% solid) and the re-siduary acid, at appropriate flow rates. The temperature of the dissolution medium can vary between 60 and 70 ° C.

In order that the silicic acid is kept in a polymerization state as weak as possible, care will be taken to respect the following operating parameters: 25 - the pH of the reaction must be adjusted so that the medium remains clearly acid, the stability of the silicic acid being · maximum at pH 1.5; above pH 2, the silica polymerizes quickly; the concentration of silicic acid is advantageously adjusted to be close to the optimum concentration of 25 g Si C> 2 per liter. This may involve a dilution of the residual acid which is a function of the H2SC content> 4. In general, the dilution is close to the 1/1 ratio in the case of concentrated residual acid from the production of Ti O 2 and the rate of polymerization of silicic acid increasing with temperature, because the synthesis of ß silica gel is carried out at 40 ° C, it is generally i * 4 necessary to cool the dissolution medium.

It is observed that the kinetic curve of dissolution of the slag is characterized by a fast step and a slow step. Almost equilibrium is reached after 30 5 minutes of contact and the dissolution yield corresponds to 85%. Advantageously, the retention time is fixed at 30 minutes and the dissolution system consists of two tanks., The material passing through 10 minutes in the first (rapid stage) while it remains 1 10 20 minutes in the second (stage slow).

Agitation of the tanks keeps the slag in suspension in order to achieve a high dissolution rate (> 85%). As will be indicated below, it is advantageous that the gypsum suspensions obtained by flotation during the separation of the gel-gypsum mixtures are recycled at the dissolution level, this recycling promoting the formation of larger crystals and reducing the number of filtrations.

The dissolving slurry is filtered to separate the gypsum from the silicic acid solution; the gypsum cake is washed to collect all the filtrate.

The filterability of the gypsum is characterized by the value of the S.C.F.T. (standard cake formation time); this parameter is defined as the time required to form a cake 1 cm thick under a differential pressure of one atmosphere. The value S.C.F.T. gypsum average is 20 + 5 seconds, this value diagnoses the very good filterability of the gypsum.

The gypsum cake is washed with an amount of water corresponding to the filling of the pore volume and total recovery of the filtrate is obtained. The gypsum produced is well suited for recycling in the cement industry provided that it has a high dryness (85-90%). In order to achieve this objective, the separation of the gypsum can be carried out in two stages: the slurry being filtered on a thickening filter under pressure and the gypsum cake then being dehydrated on a filter press.

Æ The silicic acid resulting from the dissolution

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5: slag, after separation by filtration of the gypsum formed during this dissolution, is then precipitated, with concomitant precipitation of a new quantity of gypsum, using calcium carbonate, according to the equation: n Si ( 0H) 4 + Al3 + + 1.5 SC> 4 + 1.5 Ca CC> 3 -► "((HO), Si 0) Al (OH) _ + 1.5 Ca S0„ .2 H, 0 + 1 , 5 C0_ J nz 4 z z + (n - 3) H20

r "It appeared that obtaining a zeolite A

10 of permissible whiteness is subject to the use of a calcium carbonate whose content by weight of Fe 2 O 3 is less than 0.1% and which is preferably 0.02% or less.

In order to be able to easily filter the insoluble silica gel and gypsum, according to a characteristic of the invention, alumina is incorporated into the silica during precipitation, in a weight content of between 0.1 and 10%. , preferably between 3 and 4%, and very particularly of the order of 3.5%. It is found that as the alumina content decreases, the solution becomes more and more difficult to filter. For contents greater than 10%, the gel cannot be used for the preparation of a zeolite A formulation, in fact, the characteristics of the zeolite derived therefrom do not meet commercial requirements.

The precipitation of the silica gel is carried out between pH 2; 8 and 4, preferably at pH 3.2 by simultaneous addition of the solution of silicic acid and calcium carbonate. The correct dosage of the incorporation of aluminum-30 silica is obtained by careful adjustment of the precipitation pH. Below pH 2.8, the precipitation of silica is incomplete; the gel obtained is infiltra-ble. Above pH 4, too much α- lumine is incorporated into the silica. The gel is precipitated 35 at 40 ° C without calorific contribution. The silica sol must: be cooled because a reaction temperature above f) at 40 ° C. would cause the precipitation of iron oxide.

! The precipitation of the silica gel is very rapid, but it is advantageous to keep the reagents in the reactor for one hour in order to ensure complete dissolution of the calcium carbonate.

The agitation system must allow homogenization of the reaction medium to prevent the sedimentation of calcium carbonate in the bottom of the reactor. Under such conditions, the yield of the precipitation of silica reaches 100%.

The gel-gypsum mixture is then separated from the mother liquor by vacuum filtration; the filtrate is kept because it contains recoverable alumina, the recovery of which will be described below. The cake is washed on the filter with water at pH 2 in order to reduce the iron content as much as possible. A sequence of at least three washes is preferable, the volume of water of each wash corresponds to the pore volume of the cake. The process water, after purification and acidification, can be used for washing.

We observe a filterability of the cake of the melan-20 ge gel-gypsum corresponding to a value S.C.F.T. on the order of 40 seconds. Given the quality required for washing, a belt filter (vacuum) is suitable.

The two constituents of the mixture are separated by flotation of the gypsum. This operation is carried out on a pulp whose solid content reaches 120 g / l and whose pH is between 3.0 and 3.5, preferably.

The technique of separating gypsum and silica gel by flotation is an elegant and efficient way of separating the components under conditions which, at first sight, may seem to cause significant difficulties as a result of the presence of the silica gel.

The Applicant has observed in this regard that the use as a collecting agent for dodecylamine (laurylamine) alone or in admixture with other amines with a fatty hydrocarbon chain (for example in C ^ g) gives II separation results which other compounds, also - I »% 7 ment used in other circumstances as a collector do not allow to obtain.

By way of illustration, it may be mentioned that "the use of a mixture of tallow and coconut amines can be provided as a collector of gypsum, at a dosage which depends on the amount of gypsum produced. The - gypsum separation yield is excellent (99%); the loss of silica gel caused by gypsum is low (8%). The dry matter content of the 10 gel pulp reaches 10%.

r - At the operative level, the thickened pulp is kept as it is. The gypsum pulp is recycled in the slag dissolving step.

Under the aforementioned working conditions, the 15 ---- synthesis solution of the silica gel contains upgradeable aluminum at a content of the order of 6.3 g / l.

This aluminum carried by the mother solution of silica gel is therefore selectively precipitated by the addition of calcium carbonate. The overall precipitation reaction is represented by the equation: - [Al (OH) "* - n S04" ~] + n Ca C03 (n + 1.5) H20- * A1 (OH) 3+ n Ca SO . 2H, 0 + n CO ,.

2 4 ά 2 Δ

A gypsum precipitate is therefore formed at the same time as the alumina gel.

It has appeared, according to a characteristic of the invention, that the subsequent separation of the gypsum by flotation is facilitated if, before the precipitation of the alumina, a certain amount of soluble silicic acid is added to the solution containing aluminum. The addition of a small amount of soluble silicic acid corresponding approximately to the molar ratio Si 0.35 --- 0 · 1 ’

Al2 ° 3 gives the gel surface properties which allow the gypsum to be separated by flotation.

Various techniques can be used to

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8 precipitation of alumina in the gel state.

Advantageously, this precipitation is carried out in two stages. In a first stage, which takes place at a constant pH of the order of 3.9, a solution of aluminum and calcium carbonate is added simultaneously (reaction time of the order of 2 hours). The requirements with regard to the purity of the calcium carbonate used are less stringent than when precipitating the silica gel. It has appeared in particular that a content of Fe 2 O 4 which can reach values of the order of 0.08% does not cause any serious disadvantage.

The precipitation is then completed (in thirty minutes) in a second stage at a pH of the order of 4.6 by adding caustic soda contained in the mother solution of zeolite A. This technique ensures good reactivity of the calcium carbonate and makes it possible to purge the crystallization circuit of zeolite A, the volume consumed of mother solution of the solution A consumed is equivalent to the purge required to balance the material balance (water and impurities) of the system.

It will be ensured that the pH of the second stage does not exceed 4.6, under penalty of also precipitating an iron oxide. Precipitation does not require a calorific contribution; the temperature of the reaction medium reaches a maximum of 40 ° C., temperature of the mother liquor of the silica gel. Agitation should be sufficient to maintain the solid phase in suspension. The yield of precipitation of alumina reaches 100% under the conditions indicated.

The alumina-gypsum gel mixture is filtered and washed. The gypsum pulp, collected at the end of the flotation, is preferably recycled when the slag dissolves.

The alumina gel pulp is characterized by filterability having an S.C.F.T. can vary between 1 and 3 minutes. Pressure filtration on a thickening filter is suitable, given the low solids content (5%) in the solids. The cake is »· 9 t; washed to remove soluble salts, washing being carried out on the pressure filter.

The two components of the mixture are then separated by flotation of the gypsum. The operation is carried out on a pulp whose solid content is fixed at 120 g / l and whose pH is between 4.5 and 5. The process water after purification is used for pulping.

_ "Advantageously, the mixture of tallow amine and? 10 of coconut is used as a gypsum collector, at a dosage which depends on the amount of gypsum produced.

As a variant of the technique described, a second mode of precipitation of the alumina gel is possible.

To do this, the metals of the residual solution are precipitated at constant pH 10 by residual aluminate and then the aluminum is selectively precipitated at a pH of approximately 4.3 constant by means of the suspension obtained in step former. The gel obtained also has good filterability.

The synthesis of zeolite A is then carried out in three stages: conditioning of the reagents; - formation of the reaction mixture; I- crystallization of zeolite A, filtration and conditioning thereof.

In known manner, zeolite A is crystallized from an alkaline suspension consisting of silica gel, sodium aluminate and caustic soda.

The formulation of the mixture is fixed by the following molecular ratios:

If 0_ Na? O H, O

- = 1.7; --- = 1.8 and —- = 33 AI2 C> 2 Si C> 2 Na2Ü

It has been found that the sequence of addition of the reactants in the formation of zeolite A is important in order to obtain good results.

The conditioning of the reagents consists in neutralizing the silica and alumina gels precipitated in • · 10 acid medium, with caustic soda and then causing an attack in the caustic soda.

The silica and alumina pulps (100 g gel / 1) obtained at the end of the gypsum flotation steps are first neutralized to pH 10, respectively by means of a fresh brine of caustic soda and residual aluminate solutions from anodizing workshops. Neutralization is carried out at room temperature until pH = 10. Neutralization of the alumina gel causes precipitation of the aluminum. conveyed by residual aluminate solutions; the recovery of this aluminum is complete. The neutral pulps are dehydrated on a press filter in order to obtain a dryness at least equal to 35%. To balance the water balance, the hydration volume of the filter cakes is replaced by an equivalent volume of synthesis solution of zeolite A.

The silica gel is attacked at room temperature in a caustic soda solution consisting of synthetic water enriched with soda. The amount of sodium hydroxide used corresponds to the molar ratio:

Na „0 '—— = 0.8

SiO 2 25 The attack on the gel is rapid (3 minutes) but incomplete and an insoluble residue of silica remains.

The alumina gel is dissolved at room temperature in a caustic soda solution, consisting of the stock solution enriched in soda. Enrichment.

30 corresponds to the soda consumed by the purge. The gel dissolves in 15 minutes. Iron and silica associated with alumina gel are very poorly soluble in alkaline medium; they form a precipitate polluting the solution of sodium aluminate.

This residue is filtered under pressure and washed. The dissolution yield is 90%; the composition of the solution obtained is characterized by the molar fl ratio: • m \\

Na O - ~ - = 2 ^ 2 ^ 3

The formation of the reaction mixture involves mixing the reactants and a predigestion.

It has appeared that two modes of addition of the reagents are possible.

In the case of a batch process, it is useful for the sequence of addition of the reactants for the formulation of zeolite A to be: b- a. sodium aluminate solution; b; basic silica pulp ..

The mixing of the reactants can also be carried out in a continuous regime. The alkaline silica pulp and the sodium aluminate solution are fed simultaneously, in this case, to the mixing tank and the reagent flow rates are adjusted in order to achieve and maintain the formulation of the mixture constant.

In both cases, the agitation is adjusted so as to allow rapid homogenization of the reagents because the operation generates a thick gel.

The reaction mixture is directed to a digestion tank where it remains for 12 hours at room temperature.

Finally, zeolite A is crystallized by heating the reaction mixture to 85 ° C for 2 hours; good stirring ensures the homogenization of the medium, the solid content of which is 16% dyed. The crystallization yield is 100%.

The crystalline solid is separated from the mother liquor by filtration, the filterability of the zeolite pulp being characterized by an S.C.F.T. 2 minutes. The solid is filtered and washed with deionized water until the pH of the pulp is 10.5. The humidity of the vacuum filtered cake 35 can reach 58%.

Zeolite can be delivered in two different! J forms: i • Ί I. 12 different: - either in suspension, a mixture of sodium polyacrylate (fluidization agent for atomization) and phosphate, preferably sodium polyphosphate being added at a rate of 0.3% to the pulp filtered in order to obtain a fluid suspension at 40% of dry matter 9 „- either in powder form, the zeolite paste being dried so as to obtain a powder which is well dispersed after drying.

9 _ * The invention will be described in more detail with reference to the appended example which is intended to illustrate 9 - the invention, without limitation.

9 EXAMPLE

9 1. DISSOLUTION OF THE DAIRY.

9 The granulated slag is dissolved in a residual acid 9 from the production of titanium dioxide; the composition of these two reagents is given below:

Granulated slag Residual acid 20 Constituent Proportion,% Constituent Content, g / 1

Si 02 34.13 H2 S04 184.4

Al2 03 12.63 Pe2 + 19.16

Mg 0 8.39 Al 4.17 25 Ca O 34.86 Mg 5.13

Fe2 03 0.96 Na 0.84 Μη O 0.54 V 0.96 K 1.37 Cr 0.26

Na 0.94 Ti ° 2 3.61 30 Ti ° 2 0.78

A pulp of crushed slag (0 0.2 mm) is used while the residual acid is diluted prior to dissolving. The gypsum suspensions obtained after their separation from silica and alumina gels are added to the pulp of ground slag.

i ““ · '"' · ''” 13 me continuous, in a system consisting of two reactors (15 and 28 liters) each equipped with 3 baffles and agitated so as to keep the solid matter in suspension The reagents are introduced into the first tank with 5 peristaltic pumps.

The supply of slag is constant while that of the acid is subjected to the measurement of pH. The contents of the first tank overflowed in the second, the system being adjusted in order to achieve an average stay of 30 10 minutes in the reactors. These conditions make it possible to obtain a dissolution yield of 85%.

The hourly consumption of the reagents is as follows: - slag pulp comprising: 6.65 kg of ground slag, 15 4.38 kg of gypsum and 11.03 1 of water.

- acid solution comprising: 37.8 1 of acid and 28.33 1 of dilution water.

The hourly production of silicon acid pulp is 77.16 1; the dry matter content is 20 15.5%.

The acid pulp is filtered and washed on a vacuum filter (vacuum = 0.3 bar) at a rate of 1.3 1 2 per m per second; under these conditions, the thickness of the cake measures 10.5 mm. The composition of the silicic acid separated from the gypsum is shown below.

Constituent Content, g / 1

If 02 25 30 Al 7.03

Fe2 + 10.55

Mg 6.53

Ti O 1.85

Cr 0.14 35 V 0.49 * Na 0.99 JL K_0.86! 1 14

2. PRECIPITATION OF SILICA GEL

The precipitation of the silica gel is carried out at pH 3.2 by adding calcium carbonate to the solution of silicic acid. The calcium carbonate is used in the form of a 25% suspension; the preferred particle size is less than 55 microns while the iron oxide content does not exceed 0.02%.

The precipitation installation consists of two tanks, the useful volume of which is 40 liters; they are internally equipped with 3 baffles and a heating resistance allowing precipitation to be carried out at 40 ° C. Agitation of the tanks completes the suspension of the solid phase. The reagents are introduced simultaneously into the first tank by pumps; the synthesis mixture then overflows into the second tank. Reactive flow rates are set to! maintain the gel for one hour in the synthesis medium. An electrode system measures the precipitation pH and controls the servo regulating the flow of calcium carbonate.

Hourly consumption of reagents amounts to 77.16 l of silicic acid and 0.698 kg of calcium carbonate. The silica gel and gypsum pulp produced has a dry matter content of 5%. The mineral mixture is filtered and washed with acidified water (pH 2) on a vacuum filter; washing continues until the iron is completely eliminated.

This solid-liquid separation is carried out at a rate of 0.37 1 of pulp per m per second; the vacuum of the filter is 0.3 bar. In these conditions, . the thickness of the cake is 11 mm.

The separation by flotation of silica gel and gypsum is carried out on a pulp containing 120 g of solid per liter, the separation requires roughing and finishing. A mixture of tallow amine (C16) and coconut (C12) is used as a collector at a rate of 150. and 600 g per tonne of product to be separated respectively; js pine oil is the foaming agent.

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Taking into account the efficiency of the separation, the hourly masses of the separated products are as follows: t - silica gel 2.33 kg.

5 - gypsum 2.33 kg.

The volume of stock solution containing aluminum * is 77.16 l.

The compositions of silica gel and water. mother are given below: 10 ____

Silica gel Mother liquor

Constituent Proportion,% Constituent Content g / 1

Si 02 78.1 Al 6.3 Ï5 Al2 o3 3.81 Fe2 + 10.55

Loss on ignition 8.7 Mg 6.53

Cr2o3 0.17 Mn 0.30

Fe3 o3 0.08 K 0.86

Ti 02 8.85 Na 0.99 20 v2 ° 5 ° '34 3. PRECIPITATION OF ALUMINA GEL.

Prior to the precipitation of the alumina gel, a solution of silicic acid is added to the mother solution containing aluminum, in order to achieve the molar ratio Si 0? -i = 0.1! * Al2 ° 3

Precipitation is carried out in two stages in an installation similar to that used to precipitate silica gel.

In a first stage, the pH rose to 3.9 by adding a suspension of 25% calcium carbonate · the particle size of the carbonate is less than 55 mi-35 crons. The residence time of the reactants in the reactors is two hours, the temperature reaches 40 ° C. In a λ second stage, the pH is raised to 4.6 by addition of caustic J7 sodium hydroxide from the synthesis water of zeolite A.

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Hourly consumption of reagents amounts to 77.16 1 of aluminum solution to which 2.16 1 of a solution of silicic acid (25 g / l>, 1.247 kg of calcium carbonate and 0 , 3 kg of caustic soda.

5 The pulp of alumina gel and gypsum produced

has a dry matter content of 5.2%; the mineral mixture * is filtered and washed with acidified water (pH

4,6) on a vacuum filter. Filtration, followed by; , 2 washing is carried out at the rate of 0.53 1 of pulp per m 10 and per second; the vacuum of the filter is 0.3 bar. Under these conditions, the thickness of the cake measures 8 mm.

Separation by flotation of silica gel! and gypsum is made on a pulp containing 120 g i of solid per liter; separation requires roughing 15 and two finishing operations.

A Wedag machine, model MN 935/4, equipped with a 6-liter cell is used for the flotation.

A mixture of tallow amine and coconut is used as a collector at the rate of 450 g of mixture, per ton of solid to be separated; pine oil is the foaming agent.

Taking into account the separation efficiency, the hourly masses of the separated products are as follows: - alumina gel 1.75 kg - gypsum '2.14 kg

The volume of the residual solution is 77.16 1. The composition of the alumina gel produced is given below:

Constituent Proportion,%

Al2 03 57.71 35 Fe2 ° 3 2.45 SO 3 5.72 fl Loss on ignition 30.65

Insoluble_1,54_ * "* i î 4 i Î17

4. SYNTHESIS OF 2E0LITE A

1. Conditioning of the reagents, a. Neutralization of gels.

The silica and alumina pulps (10% of dry matter) are neutralized to pH 10, using caustic soda. Neutralization is carried out under continuous conditions, at room temperature. The characteristics of the neutralization reaction are given below.

10 _ gel If gel A ^ 0.3 mass treated 2.33 kg 1.94 kg pH of the front pulp.

neutralization 3-3.5 4.5-5 neutralizing agent Na OH, brine Na OH aluminate 355.8 g / 1 residual (80 g

Na OH / 1 and 160 g Al203 / 1) 2q consumption, g / mole δ, 77 40.8

The neutralized gels are filtered, the water impregnating the cakes is exchanged with the mother solution of zeolite A.

The mother liquor consumptions are respectively 4.33 1, and 3.6 1 for the silica and aluminum gel.

b. Attack of gels.

'The neutralized gels are attacked in a discontinuous regime, at room temperature in caustic soda-30 only according to the conditions listed below: λ 35 d 18 Φ m.

gel Si 02 gel Al ^ 0 ^ Reagent Brine Na OH, stock solution 5 365.8 g / 1 zeolite

enriched Na OH

Consumption 4.14 1 20.33 1 + 514 g

Na OH

^ Na solution composition ~ 0 Na ^ O

- —— = 0.8 —-— = 2 10 S1 ° 2 S12 ° 3

Clarification of the solution - +

The sodium aluminate solution is clarified ^ 5 to remove insoluble impurities (iron oxide and silica).

2. Mixing of reagents and predigestion.

The two liquids obtained by attacking the gels are pumped simultaneously into a tank equipped with 3 baffles and agitated in order to produce a homogeneous mixture of the two streams. The reagent flow rates are balanced in order to keep the formulation of the mixture which is represented by the molar ratios constant.

If 07 Na O ..H O

- £ = 1.7: —-— = 1.8 and —— = 33 25 A12 ° 3 Si ° 2 Na2 °

The reaction mixture is matured overnight at room temperature.

3. Crystallization.

The reaction mixture is heated to 85 ° C for 2 hours; the reactor is agitated in order to maintain the solid phase in suspension.

The solid is separated from the mother liquor by vacuum filtration; the crystals are washed with deionized water until the pH of the paste is 10.5.

I I The product obtained identified by diffraction of! i_ * * “i 19 X-rays is zeolite A; its chemical composition is given below:

Constituent Proportion,% i

If 0, '32.31 5 ù

Al2 03 31.05

Na2 0 18.03 H2 0 12.90

Ti 02 4.30 - '10 Fe2 ° 3 ° 05

The main characteristics are given below: Reflectance: 91 Hunter coordinates

Odor: without

Particle size less than 10 μ: 94% 6 μ: 82% 5 μ: 50% pH (1% anhydrous in aqueous suspension): 10.4 20 weight loss after 50 minutes at 800 ° C: 21% sequestering power at 25 ° C per g of anhydrous zeolite after 15 minutes: 150 mg Ca 0

The zeolite A obtained can be used as a calcium sequestering agent in a washing powder formulation.

30 * 35

Claims (21)

1. Process for the manufacture of zeolite A by reaction in an aqueous medium of a solution of sodium aluminate and of a basic pulp of silica in an adequate stoichiometric ratio characterized in that the basic pulp of sodium silicate comes from the treatment blast furnace slag using residual acid and / or that the sodium aluminate comes from a solution. sodium aluminate siduary obtained during the surface treatment of aluminum and / or aluminum obtained during the dissolution of the slag. 2. Method according to claim 1 characterized 'in that the slag ground to a particle size less than 0.4 mm and preferably less than 0.2 mm is dissolved 15. pH between 0 and 2, preferably order of 1.5 and in that the gypsum formed is separated by filtration from the solution. 3. Process according to claim 1 or 2, characterized in that the precipitation of a silica gel is caused by the addition of a calcium carbonate present. as a weight content of Fe2 ° 3 of the order of 0.1%, preferably of the order of 0.02% or less. 4. Method according to any one of claims 1 to 3 characterized in that the silica gel and the gypsum, precipitated by addition of sodium carbonate; are separated by filtration after incorporating into the gel! of silica during precipitation, of alumina in a weight content expressed relative to the silica present of between 0.1 and 10%, preferably between 3 and 30 4% and very particularly 3.5%. 5. Method according to any one of claims 1 to 4 characterized in that the precipitation of the silica gel is carried out at a pH between 2.8 and 4, preferably of the order of 3.2. ; 35 6. Method according to any one of claims 1 to 5 characterized in that the gypsum is separated I n from the mixture of silica gel and gypsum by flotation, j the gypsum being collected in the foam. 4 * - i 4 η 21 7. Method according to claim 6 characterized in that the flotation separation operation of the gypsum is carried out on a pulp whose solid content reaches 120 mg / 1 and the pH is between 3.0 and 3.5. 8. The method of claim 6 or 7 charac terized in that one uses as a collecting agent gypsum, dodecylamine, alone or in admixture with other amines with fatty hydrocarbon chain. 9. The method of claim 8 characterized 10 in that a mixture of tallow amine and. coconut. 10. Method according to any one of claims 5 to 9 characterized in that the separated gypsum pulp is recycled at the level of the dissolution of the slag 15 11. Method according to any one of the claims 1 to 10, characterized in that the aluminum contained in the mother liquors of the synthesis of silica gel is precipitated, in the presence of a silica content. soluble such that the molar ratio 20 if 02 - is of the order of 0.1, Al? 0! 12. The method of claim 11 characterized in that the separation of the mixture of alumina gel and gypsum is carried out by flotation, the gypsum being collected in the foam. 13. The method of claim 12 characterized in that the operation of separation by flotation of the gypsum from the mixture of alumina gel and gypsum is carried out on a pulp whose solid content is of the order of 120 g / l and the pH is between 4.5 and 5. 14. The method of claim 12 or 13 characterized in that one uses as gypsum collecting agent, dodecylamine, alone or in admixture with other amines with fatty hydrocarbon chain. 15. The method of claim i4caractéri-. dried in that we use a mixture of tallow amine and coconut 16. The method of claim 14 or 15 ca- <0 'I * jj \ 22 characterized in that the separated gypsum pulp is recycled at the level of the slag dissolution. 17. Method according to any one of claims 1 to 16 characterized in that the precipitation of the alumina gel is carried out by addition of calcium carbonate in two successive stages, the first consisting, at constant pH of the order of 3.9 by the simultaneous addition of a solution of aluminum and calcium carbonate and 'the second, taking place at constant pH of the order of 10 4.6 being carried out by addition of caustic soda pro from stock solution of zeolite A. 18. Method according to any one of claims 1 to 16 characterized in that the precipitation of the alumina gel is carried out by precipitating at pH 10 the 15 metals of the residual solution with a caustic soda solution which may contain aluminate waste and then selectively precipitating the aluminum to pH 4.3 by means of the suspension obtained in the first step. 20 19- A method according to any one of claims 1 to 18 characterized in that the aluminate solution is added to the basic silica pulp is discontinuous according to the addition sequence a) sodium aluminate solution B) basic silica pulp is continuous by simultaneously mixing these two reagents in the mixing tank. , 20. Products obtained by the process of any one of claims 1 to 19. 21. Products according to claim 20 characterized in that it is zeolite A. fj