NL192450C - Process for preparing basic aluminum chlorosulfates. - Google Patents

Description

1 192450

Process for preparing basic aluminum chlorosulfates

The invention relates to a process for preparing basic aluminum chlorosulphate of the general formula: 5 [Aln (OH) 3 (Vfn_2p Clm (SO4) p] z (I) in which: - (3n-m-2p) / (3n ) is between 0.4 and 0.7 - p is between 0.04 and 0.25 n, and - m / p is between 8 and 35, while z is £ 1.

Such a method is known from Dutch patent 164832. According to this known method, an aqueous solution containing Al3 * and CMones is mixed with an aqueous alkali metal aluminate solution in the presence of SO42 'ions and at a temperature of 40 ° C, until a gel is formed. The mixture is then heated to 50-80 ° C until the gel is dissolved and the desired product is obtained in solution.

This method makes it possible to prepare the desired compounds in an efficient manner, but has the drawback that a non-negligible amount of alkali metal sulphate is also obtained, which causes contamination problems. - ---------------------------- ---------—----------- -------------------------------------- -----

The object of the invention is to provide a process for preparing basic aluminum sulfates without the aforementioned contamination problems occurring. This object is achieved by starting from a solution obtained by reacting basic aluminum chloride with an excess of aluminum hydroxide in the absence of sulfuric acid. The process according to the invention is therefore characterized in that, at a temperature of 80-120 ° C, relative proportions are chosen such that a product of the above formula (I) is obtained, reacting: - a solution obtained by reaction of basic aluminum chloride with an amount of aluminum hydroxide in the absence of sulfuric acid, in a stirred reactor under pressure, at a temperature of 140-165 ° C, with - basic aluminum sulfate.

The basic aluminum salts are generally aqueous solutions with a concentration of 1-35 moles of alumina per liter, but they may also exist in the form of a more or less hydrated solid material containing more than 30% by weight of soluble alumina.

These basic aluminum chlorosulfates can be used in particular for the purification of water.

Incidentally, it has also been proposed to prepare basic aluminum chlorosulfates by acting as follows: a mixture of hydrochloric acid and sulfuric acid is allowed to act on hydrargillite and the neutral chlorosulfate is brought to the desired basicity by partial and imparted neutralization by means of alkali metal carbonate, hydroxide or hydrogen carbonate (French Patent 2,036,685). This process also poses contamination problems. In addition to the desired compounds, an insignificant amount of alkaline earth metal sulfate, for example calcium sulfate, is obtained.

There are still variants of the above-described process, in which the chloride ion is supplied by calcium chloride, not by hydrochloric acid (French patent 2,281,895): the problem of 40 effluents is thereby exacerbated.

Therefore, an attempt has been made to overcome said drawback of the known art by carrying out the basic stage in another way, namely by treating the aluminum chlorosulfate or chloride with aluminum metal powder. This process not only has the economic disadvantage resulting from the use of aluminum powder, but moreover does not lead to the obtaining of basic salts with the desired polymeric structure for the treatment of water.

Finally, a method has been proposed in which basicization is carried out by pressurizing a mixture of aluminum chloride, aluminum hydroxide and sulfuric acid and at a temperature of 170 ° C, optionally with recirculation of the unreacted excess products (French Patent 2,125,337 ). This mode of operation is related to the prior art basicizing technique, in which hydrochloric acid is allowed to act on excess hydrargillite since the latter method is also performed under pressure to accelerate its kinetics (French Patent 2,174,114). This mode of operation requires the addition of sulfuric acid prior to the alkalization phase to obtain a basic chlorosulfate with better efficiency in the treatment of water than a similar salt made basic in the absence of sulfuric acid.

55 Surprisingly, it has now been found that it is possible to prepare a basic aluminum chlorosulfate having equally good water treatment properties by carrying out the basification phase under pressure in the absence of sulfuric acid, contrary to the teachings of de y 192450 2 state of the art Imagine.

It was surprising to find that, after dissolving the aluminum hydroxide in a concentrated solution of aluminum chloride, operating under pressure, the reaction mixture can be stabilized, namely the basic aluminum chloride can be kept in solution, by adding a more dilute solution of slightly basic aluminum sulfate; in order to obtain this stabilization, the following is done: after bringing the supersaturated solution of basic aluminum chloride to its boiling temperature at atmospheric pressure, a freshly prepared solution of basic aluminum sulfate obtained by sulfuric acid at atmospheric pressure is added allow pressure to act on an excess of aluminum hydroxide, the latter solution being at a temperature as close as possible to that of the basic chloride.

The basic aluminum chloride, which can be used in the present invention, can be obtained in any suitable manner. In particular, it can be obtained in the following manner known per se: hydrochloric acid is allowed to act on alumina in amounts such that after conversion a solution of aluminum chloride is obtained which is substantially supersaturated; the solution is then reacted with aluminum hydroxide in an excess of 10-150% relative to the amount theoretically required for the desired basicity, in a stirred medium for a maximum duration of 5 hours; at a temperature of 140-165 ° C under a pressure of 50-300 kPa.

The basic aluminum sulfate which can be used according to the present invention can be prepared by any method known per se. In particular, it can be prepared in the following manner known per se: to a solution of sulfuric acid, aluminum hydroxide is added in an excess of 10-100% relative to the stoichiometry of the neutral sulfate; the resulting suspension is heated and kept at boiling temperature for 15-30 minutes.

In a more detailed manner, the process, which can be continuous or discontinuous, can be carried out as follows: hydrochloric acid with a weight concentration equal to or greater than 30%, preferably 33%, and aluminum hydroxide (for example hydrargillite) are introduced into a stirred reactor. in amounts such that after the reaction a solution of aluminum chloride is obtained which is close to saturation; the solution, which may contain aluminum hydroxide in suspension, when the previous reaction is carried out with an excess of this reactant, is then transferred to a pressure-resistant reactor in which aluminum hydroxide is also applied, so that an excess of 10- 150% and preferably 70-120% is obtained relative to the amount theoretically required for the desired basicity. The reaction medium, which is stirred, is brought to a temperature of 140-165 ° C and a pressure of 50-300 kPa for a maximum duration of 5 hours, but preferably 2-3 hours according to the fineness of the hydroxide used. ; these operating conditions make it possible to obtain the maximum possible solution of the aluminum hydroxide. The reaction mixture is then brought back to atmospheric pressure, the temperature then being 120-125 ° C according to the initial concentrations of chloride, the degree of solution of the hydroxide and the water content of the latter.

Simultaneously with making the aluminum chloride basic, the basic aluminum sulfate, which is intended to stabilize the basic chloride, is synthesized. To a solution of sulfuric acid, aluminum hydroxide is added in an excess of 10-100%, preferably 30-70% relative to the stoichiometry of the neutral sulfate, and the resulting suspension is heated and then boiled for 15-30 minutes; this duration is variable according to the fineness of the hydroxide used. After dilution with water to fluidize the reaction medium, this slightly basic aluminum sulfate, the temperature of which is then between 70 and 100 ° C, is poured into the basic aluminum chloride, the temperature of which is 120-125 ° C, in amounts such that the chlorosulfate obtained corresponds to the general formula: [Aln (OH) 3rvm.2p Clm (SO4) p] z wherein n, m and p have the meanings indicated previously and z is> 1.

50 To ensure maximum dissolution of the aluminum hydroxide in the solution of aluminum chloride, it is necessary to add an excess of about 100% thereof, one or more times, the granules having a size of less than 30 µm contributing to it , preferably by dissolving, to make the reaction medium basic. The unreacted aluminum hydroxide is recovered on filtration to yield the final solution of basic chlorosulfate; depending on the excess used, the amount thereof may be sufficient to prepare a new solution of aluminum chloride, the complement being provided by fresh hydroxide. This solution is then made basic with fresh hydroxide, which is added in excess in one or three 192450 several times.

That excess can vary between 10 and 150%, preferably between 70 and 120%, depending on the reactivity and the moisture of the hydroxide. After all, a very moist hydroxide which is added in too great an excess leads to a dilution of the aluminum chloride solution and a reduction in its boiling temperature, thus to a reduced reactivity, which in turn must be compensated by an increase in the pressure in the stirred autoclave.

After stabilizing the basic chloride with the sulfate solution, the basic chlorosulfate is diluted, cooled and filtered to remove the excess hydroxide, according to techniques known to those skilled in the art. An additional advantage of the invention is that the reaction between the basic aluminum chloride and the basic aluminum sulfate proceeds quickly. The reaction time is generally between a few minutes and one hour.

The aluminum hydroxide used in carrying out the method according to the invention can be of different origins. Namely, it may be a freshly prepared hydroxide, but for economic reasons it is preferred to use hydrargillite obtained by the Bayer extraction process of aluminum oxide from bauxite, in a moist form (water content on the order of 35%) or in a dry form. According to the acceptable levels of impurities, it is also possible to make direct use of an - alumina mineral, for example bauxite, as such or after prior calcination .-------------------- - - ______

The invention is further illustrated by the following examples, which, however, have no limiting meaning.

20

Example I

In a stirred reactor, 550 g of 40% hydrochloric acid (density 1.198) were poured onto 162 g of moist hydrated alumina with a content of 62.8% of Al2 O3. After the reaction was slowed down using a suitable heating-cooling system to keep the temperature at 40-60 ° C, heating was gradually made at 150 ° C, after which 324 g of moist hydrated alumina was added.

By continuing the heating, the boiling temperature of 123 ° C was reached at atmospheric pressure.

The reactor was then brought under an air pressure of 120 kPa, while the boiling point was again heated when the temperature of the reactor was 147 ° C. The heating was then moderate to maintain an initial cooking for 3 hours. Despite the excess hydrated alumina employed, no thickening of the slurry, which would be due to precipitation of basic chloride, occurred. The heating was stopped and the pressure was allowed to slowly rise to atmospheric pressure. With continued stirring, a warm solution (about 80-90 ° C) of basic sulfate was added, which was prepared as follows: 91 g of 70% sulfuric acid were poured onto 55 g of hydrated alumina. It was brought to the boiling temperature for 15 minutes, with stirring, 35 g of cold water was added, then 220 g of warm dilution water.

The contents of the 1 liter reactor were transferred to a 2 liter vessel which was stirred. 700 g of water at 40 ° C were then added, the mixture was stirred for 15 minutes to cool at 40 ° C and the suspension was filtered. In less than 12 minutes, 1895 g of a solution with a density of 1.225 was recovered at 20 ° C, which was diluted with 136 g of water to bring the density to 1.206. The solid residue had a weight of 40 207 g and a content of 57% Al 2 O 3 and 2.0% chloride ion. It consisted mainly of excess alumina and adhering solution.

The solution had a density of 1.206 and a content of 10.0% chloride ion, 10.5% alumina and 3.0% total sulfate ion.

45 Example II

184 g of the previous residue to prepare the aluminum chloride solution was poured into 550 g of 40% hydrochloric acid and basified in the manner previously described with 324 g of moist hydrated alumina by boiling for 3 hours hold at 146 ° C under a pressure of 120 kPa.

The basic sulfate was otherwise prepared with the remainder of the residue, to which 43 g of hydrated alumina were added. After boiling, diluting with 30 g of cold water and 220 g of water at 90 ° C, this suspension was poured into the basic chloride solution, which was then diluted with 830 g of water at 40 ° C. Filtration gave 200 g of a residue with 57.7% Al2 O3 and 1.93% chloride ion, as well as 2050 g of a solution with a density of 1.213, which was brought to a density of 1.206 with 58 g of water. The 2108 g of the final solution had a content of 9.95% chlorideone, 10.6% Al2 O3 and 3.0% SO4 ion.

As can be seen, the entire spent alumina benefits the manufacture of

Claims (1)

192450 4 the solutions of basic aluminum chlorosulfate, while in certain processes for neutralizing with lime or calcium carbonate, the portion which is not converted at 105 ° C in an acid medium formed by hydrochloric and sulfuric acids is lost with the significant gypsum residue that is formed . A process for the preparation of basic aluminum chlorosulfate of the general formula: [Al „(OH) 3tvm_2p Clm (SO4) p] z (I) 10 in which: - (3n-m-2p) / (3n) is between 0, 4 and 0.7 - p is between 0.04 and 0.25 n, and - m / p is between 8 and 35, while z is> 1, characterized in that at a temperature of 80- 120 ° C, selected in relative amounts to give a product of the formula (I) shown above, react: - a solution obtained by reacting basic aluminum chloride with an excess of aluminum hydroxide in the absence of sulfuric acid, in a stirred reactor under pressure, at a temperature of 140-165 ° C, with - basic aluminum sulfate. \