IE43542B1 - Aluminium hydroxychlorides - Google Patents

Abstract

1525082 Aluminium hydroxychlorides; water purification RHONE POULENC INDUSTRIES 8 July 1976 [10 July 1975] 28491/76 Headings C1A and C1C A method of preparing stable solutions of aluminium hydroxychlorides, suitable for the treatment of water and aqueous effluents by flocculation, wherein the aluminium hydroxychlorides have the general formula in which Y' is a univalent anion, Y" is a bivalent anion, Y111is a tervalent anion, M is at least one ammonium or alkali metal cation, M' is at least one alkaline-earth metal cation, a, b, c, d, e, f and g represent numbers of chemical equivalents such that comprises reacting one or more soluble basic compounds of cations M and/or M' with an initial stable solution of aluminium chloride and/or aluminium hydroxychlorides of general formula in which and c, d, e,f, g, Y', Y", Y111, M and M1 are as defined above, at a temperature below 50‹ C, and except when c‹+f‹+g‹ = c+f+g, adding, after the reac tion of the basic soluble compounds, a complementary quantity of anions Y, Y" and/or Y111in order to arrive at the desired total quantity of equivalents of such anions in the product. In the above formulae, b and b‹ are determined by subtraction. The anion specified is sulphate.

Description

The invention concerns the preparation of aluminium hydroxychlorides in the form of stable solutions, more particularly intended for treating water and aqueous effluents. > Aluminium hydroxychlorides are more or less basic aluminium chlorides. They have been known for a long time and a large number of processes has been proposed for their preparation. General formulae may be adopted for them, such as Al (0Η)χcl3_x Where x, LO which expresses the degree of basicity of the compounds, is less than 3. However, it has been found that the behaviour of various hydroxychlorides very similar in general formula may vary greatly, particularly when they are put to different uses. The L5 differences in behaviour appear to be related to the processes of preparation, which suggests that there may be various polycondensed ions of complex structures in solution and that these may vary according to the processes of preparation.

The various applications of these aluminium hydroxychlorides include manufacture Of cosmetics, manufacture of catalyst carriers made of alumina, and treatment of waters and aqueous effluent. As far as the last application is concerned,'aluminium hydroxychlorides are tending to replace other products such as iron salts and aluminium sulphate, owing to their greater capacity for coagulating and flocculating the impurities present. This capacity may be increased by the synergistic effect resulting from the addition of sulphate (SO^ ) anions, a fact which has been known for quite a long time.

Whereas aluminium sulphate, which was used in the past, is very stable, the same cannot be said of solutions of aluminium hydroxychlorides. Their stability decreases as the concentration and basicity increase and also decreases when polyvalent anions such as sulphate are present. The proportion of sulphate anions suitable for these water-treatment and effluent-treatment applications is approximately 0.3 mole per atom of aluminium at the maximum, and under these conditions the concentration of these solutions of hydroxychlorides cannot exceed 15% by weight of alumina A12O3· More particularly, with regard to aluminium hydroxychlorides containing polyvalent anions such as sulphate, several processes of preparation have been proposed, seeking to obtain effective, stable products.

One such known process, for example, comprises adding calcium carbonate, for purposes of partial neutralization, to the result of reacting mixtures of hydrochloric and sulphuric acids with natural products supplying the aluminium; the solutions obtained may be matured after the calcium sulphate precipitate formed has been removed, taking with it the excess of sulphate anions. Another known process comprises reacting an alkaline aluminate on sodium sulphate and aluminium chloride in the desired proportions and at temperatures close to normal, so as to obtain a gel, then moderately heating the whole reaction medium so as to liquefy the gel; this gives the required solution of hydroxychlorides containing the sulphate anion. Thus the first of these processes 10 C1b Y'c Y f/2 '’g/3 Md M e/2 in which Y' is univalent anion, Y*' is a bivalent anion, Y''' tervalent anion, M is at least one ammonium or - 4 involves filtration, with its attendant disadvantages, and the second involves gel-formation, with its attendant disadvantages, which may include the need to filter and also necessitates heating the product, which has an effect on its properties.

The present invention, at least in its preferred aspects, involves neither filtartion nor gel-formation. In accordance with the present invention, solutions of aluminium hydroxychlorides of general formula Al (0H)a a is a alkali metal cation, M* is at least one alkaline-earth metal cation, a, b, c, d, e, -f and 3 represent numbers of chemical equivalents such that 1.2 < a < 1.7 ί c < 0.6 < d < 1.7 < e < 1.7 0 < f « 0.6 4 2 -S 0.6 0.2 < d + e < 1.7 < c + f + 3 5 4 2 - 5 Al (0H)ao cy Yy γ·y/2 y-<2o/2 m£o m-£o/2 a° <: 1.1 c° < c d° < d e° < e f° < f 2° < 2 a° + b° + c° + f° + 2° = 3 + d° + e° and c, d, e, f, £, Y1, Y, Y', M and M' are as defined above, at a temperature below 50°C, and preferably not more than 1°C above the freezing point of the reaction medium, for the purpose of partial neutralization and, except when c° + f0 + g° = c + f + £, adding, after the reaction of the basic soluble compounds, a complementary quantity of anions Υ', Y'' and/or Y''' in order to arrive at the desired total quantity of equivalents of anions Y', Y'1 and/or Y1'1 in the product. In the above formulae, b and b° are determined by subtraction.

It has been found that, when one proceeds to lowtemperature neutralization of such initial solutions with a basicity, expressed by a' of a maximum of 1.1, the solutions of aluminium hydroxychloride obtained contain polycondensed ions which appear to have a special character, which does not depend on the process used to obtain the initial solutions; in particular, the initial solutions may be obtained equally well from any starting product and under any temperature conditions. However, subsequent heating of solutions of aluminium hydroxychlorides obtained by the present process will irreversibly change the special character of the polycondensed ions. Their special character is revealed by - 6 the differences found in the results of treating water, the aluminium hydroxychlorides obtained at low temperature giving large flocculates, which are favourable to satisfactory decantation and satisfactory filtration.

From the point of view of the economy of the process however, and from the point of view of obtaining products that contain a small proportion of cations M and M', it is obviously particularly advantageous that the Initial solutions should be sufficiently basic. In particular, suitable initial soultions may be obtained by the method described and claimed in Patent Specification No. 40245.

Furthermore the initial solutions, as shown by their formula, need not necessarily contain the cation M or M', which may come from the starting products or from partial neutralization with basic compounds of M or M'.

The preferred cations in the preceding formulae are ammonium and those of alkali metals, and they are most appropriately derived from the corresponding bases and the carbonate, bicarbonates and sulphides. In working practice partial neutralization is advantageously effected by carbonates and particularly well by bicarbonates of alkali metals, since these enable the reaction temperature to be substantially lowered, thus helping to retain the character of the most active polycondensed ions. However, compounds of alkalineearth metals may also be used, although there is a danger that precipitates may appear, which is precisely what the present process seeks to avoid.

The anion used is preferably sulphate i.e. Υ'r is sulphate and c and £ are 0.

Various examples will now be given of the preparation of aluminium hydroxychlorides, and the j results obtained in treating water with these aluminium - 7 hydroxychlorides. The Examples are illustrative and include comparative data, as well as a series of tests showing how the character of the poly-condensed ions develops according to the temperature to which the solutions are heated and whether they are more or less basic in composition.

EXAMPLE 1 240 kg of aluminium chloride AlCl^ 6¾0 is dissolved in 600 litres of water at a temperature close to boiling and with agitation. The solution is allowed to cool. Then, when its temperature is near ambient, 126 kg of sodium bicarbonate NaHCO^ is added gradually during the course of one hour. Once the evolution of carbon dioxide has ceased, 32 kg of sodium sulphate Na2S04.10 HjO is added. This gives 930 kg of a solution of an aluminium hydroxychloride of empirical formula Al (OH). , „ Cl, „ SO. 1.48 3.0 4q>10 .5% by weight of alumina A^Oj.

Comparative Test The product obtained in this accordance with the invention. Its general formula is the same as that of the product in Example 1 and it is prepared with the same substance in the same proportions. Preparation differs from that in Example 1 in that the initial solution of aluminium chloride is kept at approximately 100°C throughout the addition of the sodium bicarbonate and is not cooled until after the evolution of carbon dioxide has ceased. 1.68 test is not in - 8 EXAMPLE 2 145 kg of a partially hydrated alumina with 95% of alumina AlgO^ (obtained by taking trihydrated alumina obtained by the Bayer process and heating it rapidly in a current of hot gas) is fed gradually into an agitated reactor containing 350 kg of 35% hydrochloric acid, 37 kg of 96% sulphuric acid and 450 litres of water, the temperature being kept at 107°C for 3 hours. After decantation 914 kg of a solution of a complex hydroxychloride of empirical formula Al (ΟΗ)θ Cl^ SO. , which contains 11.2% by weight of alumina 40.18 Al2O3, is obtained. When this solution has cooled completely to normal temperature, 75 kg of sodium bicarbonate HaHCO^ is added to it gradually. When the evolution of carbon dioxide gas has completely ceased 950 kg of a basic aluminium hydroxychloride is obtained, of empirical formula Al (OH) 42 Cl^ SO^ NaQ 45· 0.18 EXAMPLE 3 845 kg of alumina trihydrate obtained by the 0 Bayer process is fed gradually into a reactor containing 800 litres of 35% hydrochloric acid, with agitation.

When the reaction slows down the reaction medium is heated under reflux for 6 hours. Xt is then allowed to cool and decant for 5 hours, and then the clear liquid at the top is siphoned off. The second and subsequent operations comprise adding to the residual unreacted alumina from each operation 420 kg of the same trihydrate of alumina and 800 litres of hydrochloric acid and then, in the same way as in the first operation, carrying out the reaction and recovering the clear liquid at the top. This represents semi-continuous manufacture of a solution of an aluminium hydroxychloride of empirical formula Al(OH)^ 05cly 95 containing 245 g/litre of alumina A12O3· 43543 - 9 3 m of this solution is then placed in an agitated tank and 0.7 m of a 170 g/litre solution of sodium carbonate Na2C03 is added slowly at ambient temperature. The speed at which it is introduced is governed by the loss of C02, and the solution takes about one hour to add. Finally 230 kg of coarsely ground sodium sulphate Na^O^ .1011.,0 is added and the mixture is agitated for 3 hours.

This gives 2250 kg of a solution of a complex hydroxychloride of empirical formula Al (OH) Cl^ g,SO. Na which contains 10.9% by weight of 40.15 1 alumina Al20g.

EXAMPLE 4 m of the non-basic solution of a hydroxychloride of formula Al (OH)^ Cl^ gg, obtained by the semicontinuous operation described at the beginning of Example 3, is placed in an agitated reactor. 0.5 m of an aqueous solution of ammonia containing 20% by weight of NH^OH is then added slowly at ambient temperature.

The mixture is agitated for one hour, then 230 kg of sodium sulphate Na2SO^.lOH2O is added and agitation is continued. 2080 kg of a solution of a complex aluminium hydroxychloride of empirical formula Al (OH)^ g2 Cl^ gg SO. NH, Nan is thus recovered. This contains 40.15 40.57 °·30 11.8% by weight of alumina A12Q3 and in accordance with the invention.

EXAMPLE 5 o m of the same non-basic solution as that used in the previous Example is placed in an agitated reactor. 0.6 rn3 of an aqueous solution of sodium 43543 - 10 sulphide Na2S.9 H20 is then added slowly. When the hydrogen sulphide has been given off, 150 kg of sodium sulphate Na^O^.lO HjO is added and the mixture is agitated for 3 hours. Some impurities are eliminated j and the product recovered is 2270 kg of a solution of an aluminium hydroxychloride of empirical formula Al (°H)qo42 C11.95 S°4 Nao 57' product contains 10.8% by weight of alumina A12O3 and is also in accordance with the invention. .0 EXAMPLE 6 This Example is given to pinpoint the effect of temperature. It concerns a series of preparation methods similar to those in Examples 1 and 2, carried out with the same initial substances but at different .5 temperatures: 5°C and 40°C, which are in accordance with the present invention, and 70°C and 105°C, which are not. The various products obtained have substantially the same empirical formula Al (OH)^ Cl3 θ δΟΔ Na^ gg as the products of Example 1 the comparative test forming part of that Example. The various preparation methods comprise reacting sodium bicarbonate, in solution, with aluminium chloride A1C13 at the various temperatures indicated above (these being maintained for one hour) and in proportions of 1.5 mole of sodium bicarbonate per mole of aluminium chloride and then adding 0.1 mole of sodium sulphate to each of the preparations to give the products of the above-mentioned composition.

In order to show the differences obtained in purifying water with the products prepared in accordance with the various Examples, coagulation tests are carried out by the conventional method known as the jar test. The method comprises taking a synthetic charged 3 5 4 2 - 11 water, obtained by adding 100 mg/litre of powdered kaolin to a 30° TH water (French hydrotimetric value, 1° TH corresponding to 10 mg (Ca + Mg) expressed as CaCOj/litre), and treating it with a dose of each product corresponding to 5 mg of AljO^/litre of water.

The mixture is agitated for one minute by an agitator turning at 120 revs/minute; then the speed of the agitator is reduced to 40 revs/minute and kept at that value for 20 minutes. The time when floe begins to appear after the speed has been changed to 40 revs/ minute is noted. The dimensions of the floccules are assessed on the following scale ranging from 0. to 10: - no floe - floe hardly visible 4 - small dots - flocculate of average dimensions 8 - coarse flocculate - very coarse flocculate The various results obtained are set out in the following table: Products Time when floccules appear (in seconds) Dimensions of floccules Example 1 40 10 Comparative test 300 6 Example 2 35 10 Example 3 30 10 Example 4 30 10 Example 5 30 10 Example 6 (i) prepared at + 5° 30 10 (ii) prepared at + 40° 40 10 (iii) prepared at + 70° 180 8 (comparative) (iv) prepared at + 1050 300 6 (comparative) A certain number of comparisons can be drawn from this table.

A. If the results obtained with the product from the comparative test 2 are compared with the products from each of Examples 1 to 5, it will be seen that the product obtained hot gives less good results than those obtained cold (Example 1). However, it is sufficient for neutralisation to be carried out cold beyond a value of about 1.1 for OH (Examples 2 to 5).

B. The effect of temperature is pinpointed by the results obtained with the different products in Example 6. It will be found that the shortest times for the appearance of the floccules and the floccules 3 5 4 3 with the largest dimensions are obtained with products that have not exceeded a temperature between 40°C and 70°C, which can be estimated at say 50°C.

C. Comparison of the results obtained with the products from Examples 1, 2 and 3 shows that the initial product is immaterial and that it may equally well be aluminium chloride as hydroxychlorides obtained in various ways with the value of OH below 1.1.

D. Comparison of the results obtained with the products from Examples 2, 3, 4 and 5 shows that the use of different basic products for neutralization does not produce any changes in the results, since sodium carbonate, sodium bicarbonate, ammonia and sodium sulphide are substantially equivalent.

E. If the results obtained with the product from Example 2 are compared with those obtained with the product from Example 3, It will be seen that the compound providing the sulphate ions may be added at any stage of the preparation process.

F. Finally, if the results obtained with the product from Example 1 are compared with those for the product from Example 2, it will be seen that the nature of the compound providing the sulphate ions is immaterial.

Claims (11)

1. A method of preparing solutions of aluminium hydroxychlorides of general formula Al (0H) a Cl^ Y' Y' ’ f / 2 Y ' ' 'g/g m <2 M ' e /2 in whicl1 Y' is a univalent ~ anion, Y' 1 is a bivaTent anion, γ' 1 ' is a tervalent anion, M is at least one ammonium or alkali metal cation. M' is at least one alkaline-earth metal cation, a, b, c, d, e, f and 2 represent numbers of chemical equivalents such that 1.2 < a < 1.7 0 < c -4 0.6 0 < d < 1.7 0 < e < 1.7 0 < f 0.6 0 ·$ 2 < °· 6 0.2 < d + e < 1.7 0 < £ + ί. + 2 < °· 6 a + b + c + f + 2 = 3+d + e that comprises reacting one or more soluble basic compounds of cations M and/or M' with an initial stable solution of aluminium chloride and/or aluminium hydroxychlorides of general formula Al (0H) a o Cl^o Y’ £ o Υ'· £ ο /2 Y' a O /2 M^o Μ'θο /2 in which o a d e c 4 3 5 4 8 f° < f o a < a a° + b° + c° + f° + 2° = 3 + d° + e° and c, d, e, f, g, Υ', Υ 11 , Υ' 1 ', M and M' are as defined above, at a temperature below 50°C, and except when £° + f° + £° = c + f + £, adding, after the reaction of the basic soluble compounds, a complementary quantity of anions Υ', Y'' and/or γ 11 ' in order to arrive at the desired total quantity of equivalents of such anions in the product.

2. A method as claimed in Claim 1, in which the temperature is not more than 1°C, above the freezing point of the reaction medium.

3. A method as claimed in any preceding claim, in which the anion Y'' is sulphate and c and £ are both 0.

4. A method as claimed in any preceding claim, in which M is the cation of an alkali metal and e = 0.

5. A method as claimed in Claim 4, in which M is the sodium cation.

6. A method as claimed in Claim 5, in which the sodium cation is provided by sodium carbonate.

7. A method as claimed in Claim 5, in which the sodium cation is provided by sodium bicarbonate.

8. A method as claimed in any one of Claims 1 to 3, in which M is the ammonium cation and e = 0. 9 *

9. A method of preparing solutions of aluminium hydroxychlorides substantially as hereinbefore 4 3 S 4 3 - 16 described in any one of Examples 1 to 5, 6 (i) and 6 (ii)

10. Aluminium hydroxychlorides when prepared by a method as claimed in any one of Claims 1 to 9.

11. Treatment of water and aqueous effluent by aluminium hydroxychlorides as claimed in Claim 10.