CH660724A5 - PROCESS FOR THE MANUFACTURE OF BASIC ALUMINUM CHLOROSULFATES. - Google Patents

Description

The present invention relates to a process for the preparation of basic aluminum salts corresponding to the general formula:

[Aln (OH) 3n_m_2p Clm (S04) p] 2 (I)

where the basicity of aluminum chlorosulfate, defined by the ratio

3n — m — 2p 3n is between 40 and 70%.

These products are generally aqueous solutions with a concentration of 1 to 35 moles of alumina per liter, but they can also be provided in a more or less hydrated solid form, containing more than 30% by weight of soluble aluminum.

These basic aluminum chlorosulfates find an application, in particular for water purification.

It has been proposed to prepare basic aluminum chlorosulfates, by operating as follows: the hydrargillite is attacked by a mixture of hydrochloric acid and sulfuric acid and the neutral chlorosulfate is brought to the desired basicity by partial neutralization and consolidated with means of alkaline carbonate, hydroxide or bicarbonate (FR 2 036 685); this type of process effectively makes it possible to prepare the most suitable compounds, but has the drawback of underproducing a non-negligible amount of alkali-no-earth sulphate, calcium for example, which poses pollution problems.

There are other variants of the above process, where the chloride ion is brought in by calcium chloride and not in the form of hydrochloric acid (FR 2 282 895): the problem of effluents is further amplified.

This is why it has been attempted to overcome this defect of the prior art by carrying out the basification step in a different way: the aluminum chlorosulfate or chloride is treated with metallic aluminum powder. This process, in addition to the economic handicap resulting from the use of aluminum powder, does not make it possible to obtain the basic salts having the desired polymer structure for water treatment.

Finally, a process has been proposed which performs basification by bringing under pressure and at a temperature of 170 ° C. a mixture of aluminum chloride, aluminum hydroxide and sulfuric acid, optionally recycling the excess products n 'having not reacted (FR 2125 337). This way of operating is similar to the already known basification technique of attacking an excess of hydrargillite with hydrochloric acid, this reaction also taking place under pressure to accelerate its kinetics (FR

2174114). This procedure requires adding sulfuric acid before the basification phase to obtain a basic chlorosulfate having better efficiency in water treatment compared to a similar salt basified in the absence of sulfuric acid. 20 However, it has been discovered quite unexpectedly in the licensee's laboratories that it is possible to prepare a basic aluminum chlorosulfate having also good characteristics for water treatment by carrying out the basification phase under pressure. in the absence of sulfuric acid, contrary to what let 25 know from the data of the prior art.

It was surprising to note that after having dissolved the aluminum hydroxide in a concentrated solution of aluminum chloride by operating under pressure, the reaction mixture can be stabilized, that is to say keep the chloride in solution. basic aluminum, by addition of a more dilute solution of slightly basic aluminum sulfate; to achieve this stabilization, the procedure is as follows: after bringing the supersaturated solution of basic aluminum chloride back to its boiling point at atmospheric pressure, a freshly prepared solution of basic aluminum sulphate obtained is added by attacking an excess of aluminum hydroxide with sulfuric acid at atmospheric pressure, the latter solution being at a temperature as close as possible to that of basic chloride.

The present invention therefore provides a process for the manufacture of basic aluminum chlorosulfate corresponding to the general formula:

[Al „(OH) 3„ _m_2p Clm (S04) p] z (I)

in which:

43 3n — m — 2p. not . . _

is between 0.4 and 0.7

3n

- p is between 0.04 and 0.25 n and

- m / p is between 8 and 35, z being> 1

50 consisting in reacting basic aluminum chloride with basic aluminum sulphate, heated beforehand, at a temperature between 80 and 120 ° C. The reaction is rapid: the reaction time is usually between a few minutes and an hour.

The relative proportions of the constituents are determined so as to obtain a product having the formula (I) above.

The basic aluminum chloride which can be used according to the present invention can be obtained by any suitable means. It can in particular be obtained in the following manner known per se: 60 hydrochloric acid is reacted with alumina in proportions such that, after reaction, an aluminum chloride solution close to supersaturation is obtained, then react this solution with aluminum hydroxide in excess of 10 to 150% relative to the theoretical quantity necessary for the desired basicity, in an agitated medium, 65 for a maximum duration of 5 hours, at a temperature of 140- 165 ° C under a pressure of 0.5 to 3 bar.

The basic aluminum sulphate usable according to the present invention can be prepared by any suitable means. It can in particular

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be prepared in the following manner known per se: aluminum hydroxide in excess of 10 to 100% relative to the stoichiometry of neutral sulfate is added to a sulfuric acid solution, the suspension obtained is heated and keeps it boiling for 15 to 30 minutes.

In a more detailed manner, the implementation of the process, which can be continuous or discontinuous, can be carried out as follows: hydrochloric acid having a weight concentration equal to or greater than 30% is introduced into a stirred reactor , and preferably 33%, as well as aluminum hydroxide (hydrargillite for example) in proportions such that after reaction, an aluminum chloride solution is obtained which is close to saturation; the solution, which may contain aluminum hydroxide in suspension if the previous reaction was carried out with an excess of this reagent, is then transferred to a pressure-resistant reactor into which aluminum hydroxide is also introduced so as to have an excess of 10 to 150% and preferably 70 to 120% relative to the theoretical quantity necessary for the desired basicity. The reaction medium, subjected to stirring, is brought for a maximum duration of 5 hours, but preferably 2 to 3 hours depending on the fineness of the hydroxide used, at a temperature of 140-165 ° C and under pressure from 0.5 to 5 bar; these operating conditions make it possible to obtain the maximum dissolution of the aluminum hydroxide. The reaction mixture is then brought back to atmospheric pressure, the temperature then being 120-125 ° C. depending on the initial concentrations of chloride, the degree of dissolution of the hydroxide and the water content of the latter.

Simultaneously with the basification of aluminum chloride, the basic aluminum sulphate, intended to stabilize the basic chloride, is synthesized. To a sulfuric acid solution is added aluminum hydroxide in excess of 10 to 100% and preferably 30 to 70% relative to the stoichiometry of neutral sulfate and the suspension obtained is heated and then kept at boil for 15 to 30 minutes; this duration is variable depending on the fineness of the hydroxide used. After dilution with water to make the reaction medium more fluid, this slightly basic aluminum sulphate, the temperature of which is then between 70 and 100 ° C., is poured into basic aluminum chloride, the temperature of which is 120-125 ° C, in proportions such that the chlorosulfate obtained corresponds to the general formula:

[Aln (OH) 3n_m_2P Cl "(S04) p] z (I)

where n, m and p have the above meanings and z is> 1.

In order to ensure maximum dissolution of the aluminum hydroxide in the aluminum chloride solution, it is necessary to add an excess of about 100%, in one or more times, the grains of size less than 30 microns preferably contributing by dissolving to basify the reaction medium. The unreacted aluminum hydroxide is recovered during filtration which delivers the final solution of basic chlorosulfate; depending on the excess used, its quantity may be sufficient to make a new solution of aluminum chloride, the complement being provided by new hydroxide. This solution is then made basic by new hydroxide added in excess, in one or more times.

This excess amount can vary between 10 and 150% and preferably 70 and 120% depending on the reactivity and the humidity of the hydroxide. Indeed, a very wet hydroxide added in too large excess amounts to dilute the aluminum chloride solution and to reduce its boiling temperature, therefore of attack, which must then be compensated by an increase in pressure of the agitated autoclave.

After stabilization of the basic chloride by the sulfate solution, the basic chlorosulfate is diluted, cooled, filtered to remove the excess hydroxide according to techniques known to those skilled in the art.

The aluminum hydroxide used in the process according to the invention can have different origins, it can be a freshly prepared hydroxide, but hydrargillite from the Bayer process will preferably be used for economic reasons. alumina extraction from bauxite, in wet form (water content of the order of 35%) or in dry form. Depending on the acceptable content of impurities, it is also possible to directly use an alumina ore, bauxite for example, as it is or after prior calcination.

The examples below illustrate the invention without limiting it. Example 1

In a stirred reactor, 550 g of 40% hydrochloric acid (density 1.198) were poured onto 162 g of moist hydrated alumina titrating 62.8% Al 2 O 3. After braking the runaway reaction using a suitable heating-cooling means to maintain the temperature at 40-60 ° C, it was gradually heated to 105 ° C, then poured 324 g of moist hydrated alumina. By continuing to heat, we reach a boiling point at 1231 C at atmospheric pressure: the reactor is then put under an air pressure equal to 1.2 bar, while the boiling point is restored when the temperature of the reactor reaches 147 ° C. The heating is moderated to maintain the boiling beginning for 3 hours. Despite the excess hydrated alumina used, no thickening of the suspension occurs which would be due to precipitation of basic chloride. The heating is stopped, the pressure is reduced slowly to atmospheric pressure and poured while stirring a hot solution (approximately 80-90 ° C) of basic sulphate prepared as follows: 91 g of 70% sulfuric acid are poured on 55 g of hydrated alumina. Bring to the boil for 15 minutes while stirring, pour 30 g of cold water, then 220 g of hot dilution water.

The contents of the 1 liter reactor are transferred to a stirred 2 liter container. 700 g of water are then poured at 40: C, stirred for 15 minutes to cool to 40 ° C and filter the suspension. In less than 12 minutes, 1805 g of solution with density 1.225 to 20: C are collected and diluted with 136 g of water to reduce the density to 1.206. The solid residue weighs 207 g, title 57% Al203 and 2.0% chlorine ion. It mainly consists of excess alumina and imbibition solution.

The solution of density 1.206 has 10.0% of chlorine ion, 10.5% of alumina and 3.0% of total sulfate ion.

Example 2

Into 550 g of 40% hydrochloric acid, 184 g of the preceding residue are poured to make the aluminum chloride solution, then basified as before with 324 g of wet aluminum while maintaining for 3 hours at boiling point at 146 ° C. under 1 , 2 bar.

Furthermore, the basic sulfate is prepared with the rest of the residue to which 43 g of hydrated alumina are added. After boiling, dilution with 30 g of cold water and 220 g of water brought to 90 ° C., this suspension is poured into the basic chloride solution which is then diluted with 810 g of water at 40 ° C. Filtration produces 220 g of residue containing 57.7% of Al203 with 1.93% of chlorine ion and 2050 g of solution with density 1.213 which is reduced to a density equal to 1.206 with 58 g of water. The 2108 g of final solution titrate 9.95% of chlorine ion, 10.6% of Al203 and 3.0% of SO4 ion. As can be seen, we arrive at a complete consumption of alumina while manufacturing solutions of basic alumina chlorosulfate, while in certain neutralization processes with lime or calcium carbonate, the unaffected portion to 105 = C in hydrochloric + sulfuric acid medium is lost with the bulky gypsum residue formed.

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Claims (3)

660724 1. Process for the production of basic aluminum chlorosulfate corresponding to the general formula: [Al „(0H) 3n_m_2pClm (S04) p] z. (I) in which: 3n — m — 2p. n n „ - is between 0.4 and 0.7 3n - p is between 0.04 and 0.25 n and - m / p is between 8 and 35, z being> 1 consisting in reacting basic aluminum chloride on basic aluminum sulphate, brought to heat beforehand, at a temperature between 80 and 120 ° C., the relative proportions of the constituents being chosen so as to obtain a product corresponding to the formula (I) above. 2. Application of the method according to claim 1 to a basic aluminum chloride obtained by reaction of hydrochloric acid on alumina in proportions such that after reaction a solution of substantially oversaturated aluminum chloride is obtained, followed by reaction of this aluminum chloride solution with aluminum hydroxide in excess of 10 to 150% relative to the theoretical quantity necessary for the desired basicity, in an agitated medium, for a maximum duration of 5 hours, at a temperature of 140 to 165 ° C under a pressure of 0.5 to 3 bar. 2 3. Application of the method according to claim 1 to a basic aluminum sulphate obtained by reaction of sulfuric acid on aluminum hydroxide in excess of 10 to 100% relative to the stoichiometry of the neutral sulphate, the solution being heated and then kept boiling for 15 to 30 minutes.