LU86040A1 - PROCESS FOR THE MANUFACTURE OF THIOXOTROPIC DETERGENT COMPOSITIONS - Google Patents

Description

An aspect of the present invention is an aqueous thixotropic detergent for an automatic dishwashing machine, comprising a liquid phase which is water containing, in solution, tri-05 polyphosphate, silicate and alkali metal and, in dispersion, a thickener of the non-swelling clay type (preferably of the attapulgite type), and a solid phase which consists mainly of sodium tripolyphos-phate. The composition also contains preferential 10-chlorine bleach (preferably in the form of dissolved sodium hypochlorite) and an anionic surfactant resistant to the bleach. It also preferably contains an alkali metal carbonate. United States Patent Application No. 497,615 filed May 24, 1983 describes certain compositions of this type.

It has now been discovered that greatly improved results are achieved by including a limited proportion of a hydrosoluble potassium compound, for example a potassium salt (or KOH), in the composition, to obtain a weight ratio. K: Na gui is in the range of about 0.04 to 0.5 / preferably about 0.07 to 0.4, for example about 0.08 to about 0.15. The resulting product is much more stable in the sense that it has less tendency to thicken unfavorably or separate on aging, in particular at 38 ° C. Similarly, the replacement of part of the sodium salt by the same weight of the corresponding potassium salt results in a considerable decrease in viscosity (for example as measured using a Brookfield HATD viscometer at 25 ° C at 20 rpm using a pin No. 4), greater stability against separation upon aging (e.g., at room temperature), and inhibition of relatively large crystal growth upon aging. The reduction in viscosity facilitates handling in the installation of! ! Ί *., »· Ί.ητ ff I \ mmwmn - κ t>» 2 v »production, distribution in service, and helps the consumer to destroy the thixotropic structure of the product (by shaking the container in which it is contained ), so that it can be easily poured into the detergent compartment (s) of an automatic household machine for washing dishes.

In the formulation of the product, the proportions and the ingredients indicated in the aforementioned United States Patent Application No. 497,615 can be used. In this application, a series of ranges of proportions is approximately, by weight î (a) 8 to 35% of alkali metal tripolyphosphate, (b) 2.5 to 20% of sodium silicate, (c) 0 to 9% of alkali metal carbonate, 15 (d) 0.1 to 5 î an active ingredient of the organic deter gent type dispersible in water and stable vis-à-vis a chlorine bleach, (e) 0 to 5% of foam depressant stable vis-à-vis a chlorine bleach, (f) a chlorine compound as a bleach, in a proportion which can provide about 0.2 to "4% of available chlorine, and (g) a thixotropic thickener in a sufficient proportion to give the composition a thixotropy index of about 2.5 to 10.

Preferably, in the compositions described here, the proportion of sodium tripolyphosphate '30 is greater than 15% (better still in the range of about 20 to 25 or 30%), the proportion of sodium silicate is at least about 4% (for example in the range of about 5 to 10 or 15%), the proportion of alkali metal carbonate is about 2 to 6 or 35%, the proportion of chlorine bleach is such that it provides more than 0.5% of available chlorine (for example approximately 1 to 2% of available Cl), 1/3 • the proportion of active detergent material is in the range from 0.1 to 0 , 5%. Calculated as SiO2, a preferred range of proportions of sodium silicate is about 3.5 to 7% SiO2 in the com-1 05 position.

The proportion of water in the compositions (measured using a Cenco humidity analyzer (in which the sample is heated by an infrared lamp, until it reaches a cons-10 weight ), is preferably in the range of about 40 to 50%, more preferably about 43 to 48%, for example about 44 or 46%.

The compositions described here generally have a pH much higher than 11 or 12. In a preferred type of formulation, the composition, when diluted with water to a concentration of 0.75%, exhibits a pH in the range of about 10.7 to 11.3.

The compositions described here are preferably formulated so as to have viscosities (measured with a Brookfield HATD viscometer at 25 ° C. at 20 rpm using a pin No. 4) of less than approximately 8000 mPa.s , and better still in the range of about 20Ö0 or 3000 to 7000 irtPa.S, for example about 4000 to 6000 mPa.s. Viscosity, and other properties, are preferably measured a few days (for example a week) after the composition has been prepared; an advantageous practice is to shake the sample before measuring its viscosity and to let the viscometer run for about 90 seconds before taking the reading.

The compositions described herein have flow indices much greater than 20.0 Pa and are preferably formulated to exhibit flow indices less than about 110.0 Pa and greater than about 30.0 Pa, more preferably less than about 90.0 Pa, e.g., about 40.0 to 60.0 Pa.

k "14 • The flow index is an indication of the shear rate at which the thixotropic structure collapses. It is measured with a Haake RV 12 or RV 100 viscometer using an MVIP 05 spindle at 25 ° C with a speed of shear which increases linearly in 5 minutes (after a rest period of 5 minutes) from zero to 20 seconds "*. In the Haake viscometer, a thin layer of the material is sheared between a rotating cylinder and the cy-10 lindric wall closely adjacent to the container surrounding it Figures 1-3 are graphs obtained with such a test on the products of the three Examples shown, the crests Y showing the flow indices.

Another factor measured with the aforementioned Haake viscometer is the degree to which the composition recovers its thixotropic structure. In a measurement technique after the aforementioned 5 minute increase in shear speed, the rotation is decelerated to zero in 5 minutes, then after a 30 second rest period the rotation is still accelerated, to increase the shear speed linearly in minutes from zero to 22.6 seconds “1. This gives a second flow index, that is to say Yr in FIG. 1. Preferably, this second flow index (recovered) is at least 20.0 Pa, for example 50%, 75% or more of the flow index initially measured.

FIG. 4 is a photomicrograph 30 (taken to the scale indicated in this figure) of the composition of Example 4.

The following nonlimiting examples are given by way of illustration of the invention.

In these Examples, Attagel No. 50 is powdered attapulgite clay (from Engelhard Minerais & Chemicals, the literature of which 51e indicates that, as produced, it contains 5 '1. approximately 12% by weight of free moisture, as measured by heating δ 104® C, and has a BET specific surface area of approximately 210 mVg calculated on a moisture-free basis); Graphtol green is 05 a coloring agent; LPKN 158 is an anti-foaming agent from American House (Knapsack) comprising a 2: 1 mixture of mono- and dialkyl esters of C ^ gC ^ g of phosphoric acid, sodium silicate has a Na20: SiO2 ratio of 1: 2.4; Dowfax 3B2 is a 45% aqueous solution of sodium salts of monodecyl- / didecyl-diphenyl-oxide-disulfonates, an anionic surfactant resistant to bleaching agents .; STPP is sodium tripolyphosphate. Unless indicated; on the contrary, STPP is added in the form of the finely pulverized anhydrous commercial material, the water content of which is approximately 0.5%; in this material, generally about 4.5 to 6.5% of the material is present as pyrophosphate. The water used is deionized water, unless otherwise indicated.

20 EXAMPLE 1

The following ingredients are introduced into a container, in the order indicated below, while mixing using a conventional laboratory stirrer of the paddle type. The temperatures and the mixing times at the various stages are also indicated below:

Mass Temperature (g) _ (° c) 30 Graphtol Green at 10% (dye) 5

54.4® water C 1746 LPKN 158 melted (defoamer) 8

Dowfax 3B2 (surfactant) 40 52.2 (2 min) 35 9: 1 mixture of Attagel N® 50 and Ti02 as white pepper 180 fa *

V I

6. 50fΟ (1 min) 48.9 (3 min)

Anhydrous sodium carbonate 275 K, CO, 75. .

2 3 56.7 (1 mm) 05 56.6 (3 min) STPP hexahydrate fine powder ---- - - 750 ------- 52.8 (1 min) 51.7 (3 min) 10 51 , 1 (5 min)

47.5% aqueous solution of 421 sodium silicate previously mixed with

a 50% aqueous solution of 150 15 NaOH

47.8 (3 min)

13% aqueous solution of NaOCl 500 42.2 (3 min) STPP hexahydrate in fine powder 750 42.2 (1 min) 20

Total 5000 g 41.7 (5 min)

The viscosity of the mixture, measured as indicated above, is approximately 5000 mPa.s, after 3 weeks aging at 38 ° C, and approximately 4800 mPa ^ s after 3 months aging at 38 ° C .

In this Example, the STPP hexahydrate has the following approximate distribution of dimensions: Rest on a 5 mesh screen of 30 (mm) (%) 2.00 0 0.42 0 0.149 25.4 35 0.074 31.5 0.044 16, 5 7 * 'ti

Passes through a 0.044 mm thimble sieve · 25.9 EXAMPLE 2 05 The following formulations are prepared and their properties are measured, as indicated below:

The ingredients are mixed in the following order: water, dye, clay, half of phosphate, antifoam, hypochlorite, sodium carbonate, potassium carbonate, NaOH, silicate, the second half phosphate, the surfactant.

Ingredients Proportions a b c d 15 Clay (Attagel 50) 3,285 3,285 3,285 3,285 3,285 STPP 23.0 23.0 17.01 16.5 23.0

Potassium tripolyphosphate - - - 6.5 20 Pyrophosphate

potassium - - 5.99 - O

Sodium carbonate 5.0 ”* - 5.0 5.0 2.5

25 potassium carbonate - 5.0 - - 2.5

Sodium hypochlorite <12%) 9.375 9.375 ^, 375 9.375 9.375

Sodium hydroxide (50%) 2.05 2.05 2.05 2.05 2.05 30 Sodium silicate (47.5%) 10.53 10.53 10.53 10.53 10.53

Surfactant (Dowfax 3B-2) 0.80 0.80 0.80 0.80 0.80

Antifoam 35 (Knapsak LPKN) 0.16 0.16 0.16 0.16 0.16

Dye 0.381 0.381 0.381 0.381 0.381

Water The rest.

18

Properties ·

Capillary flow time (min) 8.2 12.1 10.9 11.4 11.2

05 Viscosity (mPa.s) after aging at 38 ° C

1 week 9080 3100 2900 5120 5400 2 weeks 9200 3480 2820 6340 5240 10 3 weeks 9300 3600 3040 6700 6560

The capillary flow time is a conventional test, in which a circle with a diameter of 6.8 cm is drawn on a sheet of 15 cm in diameter 15 of Whatman filter paper of dimension 41, a ring of plastic material ( internal diameter of 3.5 cm, external diameter of 4.2 cm, height of 6.0 cm) is placed vertically, concentric to the circle, on the filter paper, and the ring is filled with the composition 20 to be tested . The liquid from the composition is thus absorbed on the filter paper and spreads slowly towards the traced circle. The time which elapses until the liquid comes into contact with the circle is measured at three predetermined points and an average value is calculated.

EXAMPLE 3 '

The following formulations are prepared, mixing the ingredients in the order indicated.

The compositions are then centrifuged at 275 g, until there is no further increase in the volume of the clear (continuous) separated liquid phase. and the resulting liquid is analyzed ï a b c d 35 Deionized water 27,106 ------- *

Dye 0.016 -—--

Sodium carbonate 6 4 2. 0 9 "1" i Potassium carbonate 0246 STPP · 21.106 --------

Deionized water 14,184 __ ^

Attagel N ° 50 4.00 v 05 Ti02 0.444 ->

50% solution of NaOH 2.5 ---

47.5% sodium silicate solution 13.684 ^

Antifoam 0.16 ---- 10 13% NaOCl solution 10.0 ------------

45% solution of active surface 0.8 -; ——- 100.00 15

Thus, the compositions are identical, except for their K: Na ratios.

Properties - of Product 20 a b c d

Viscosity (mPa.s) - After 1 day at room temperature ”8320 5520 4200 2120 - After 3 weeks 25 at room temperature 8550 6200 4500 2420 - After aging at 38 ° C for 7 weeks 9400 8000 5600 3400

Density 1.37 1.37 1.40 1.39 30

Properties of the liquid obtained by centrifugation a b c d

Viscosity at 25 ° C compared to water at 1 mPa.s 4.4 4.4 4.8 6.3 r “..". • -, Λ-ν ιΙΙ ", * Γ '' 10: .% soluble silicate I (calculated at a molar ratio Na20: SiO2 of 1: 2.4) 7.5 7.3 7.3 7.1 105% carbonate '(calculated as Na ^ CO ^) 8.8 8.5 7.4 6.6% phosphate (calculated as Na ^ P ^ O ^) 1.7 2.5 3.7 6.1

Density 1,257 1,262 1,276 1,30 10

The viscosities of the product of this Example are measured with a Brookfield RVT viscometer, pin N? 5, at 26.7 ° C.

Examples 4 to 6, below, illustrate a novel and useful process for the manufacture of the products described above (containing limited amounts of potassium). It can also be used to manufacture other products of the type indicated in the aforementioned United States patent application 20 Np 497 615 (for example in which the potassium compound is absent), as well as d other detergent suspensions comprising fine particles of water-soluble mineral detergency builder salts dispersed in water containing salt solution 25. detergency builder, clay or other colloidal thickener, and surfactant. In these Examples (in which the particles of the detergency builder salt contained in the product consist largely of STPP hexahydrate plus sodium carbonate hydrate), a very viscous mixture is formed (for example with a viscosity of 20,000 at 60,000 mPa.s) of a limited amount of water, a highly alkaline saturated solution of detergency builder salts and, as the dominant constituent, undissolved particles of the water-soluble detergency builder salt. This viscous mixture is subjected to grinding of the non-dispersed particles, using a dispersing apparatus at 11.

*; high speed, after which the solid particles of the clay thickener are added and the clay is mechanically disaggregated; then, the rest of the ingredients of the formula (for example, the other liquids or materials which dissolve or disperse easily in the liquid phase with a high electrolyte content) can be mixed there. The mixture can then be subjected to another mechanical action of high shear to further deagglomerate the clay. It has been found that with this process, the prior dispersion of the clay in an aqueous medium is not necessary. Solid clay particles are easily dispersed, even if the medium is strongly alkaline. The grinding of salt particles adjuvanted without undissolved detergency is carried out much more efficiently and quickly in the almost total absence of clay.

In the process illustrated by Examples 4 to 6, the adjuvant detergency which constitutes the dominant part of the undissolved particles is preferably added to an aqueous solution which already contains a concentration of other adjuvant detergency salts dissolved such that this addition results in the detergency builder salt being released from the solution (eg, by a common ion effect), and thus recrystallized as tiny crystals.

Another important feature of the mixing process illustrated in Examples 4-6 is the fact that it makes it possible to manufacture repeated batches with reproducible properties using the whole "heel" of the batch previously formed as an ingredient in each successive batch.

As indicated above, the use of the process illustrated in Examples 4 to 6 is not limited to the manufacture of compositions containing potassium salts. Although he has so far found his

The greatest utility in the manufacture of formulations in which the clay is attapulgite. It can also be used for compositions in which all or part of the clay is of the swelling type; for example a smectite type clay such as bentonite (for example Gelwhite GP) * or hectorite.

EXAMPLE 4 In 32.0 parts of deionized water mixed with a small amount of a pigment (that is to say 0.028 part of Graphtol green, an aqueous paste containing 28% of pigment), 2 is completely dissolved. , 0 parts of K2CO3 i ^ have water solubility 15 is more than 100 parts per 100 parts of water even at 0 ° C and 5.0 parts of granular sodium carbonate (whose water solubility is about 45 games for 100 to 35th C). The solution has a temperature of approximately 32.2 ° C. 23.116 parts of powdered STPP containing approximately 0.5% water of hydration are then added, while continuing to subject the mixture to the action of a high speed disperser. The amount of STPP is much greater than that which is soluble in the amount of water present; its solubility in water is approximately 20 g per 100 ml at 25 ° C. In this example, STPP is a product of Olin Corp. having a phase I content of about 50%, a sodium sulfate content of about 2%, and a very small particle size .; it is a mixture of anhydrous STPP powder made by the known "wet process" and STPP hexahydra-ty powder. When STPP is added to the solution, it hydrates rapidly, forming hard crystalline lumps comprising STPP hexahydrate. (Note that 23 parts of STPP can "absorb up to about 7 parts of water by formation of the hexahydrate).

The mixture is first of all a diluted suspension of 5 ja · ** “- ·· - '·· - · --- I 13 I - STPP not dissolved in a liquid which is a supersaturated solution I. The temperature rises, due to the hydration reaction, reaching a maximum of about 60 ° C. In about 3 to 4 minutes, the mixture becomes much more viscous; its viscosity rises to I over 20,000 mPa.s (for example around 40,000 - I 50,000 mPa.s, as measured at the temperature of the suspension, for example with a Brook-I field RVT viscometer, pin N® 6, at 10 rpm). It is believed that, during the process, the sodium carbonate separates I from the solution phase by crystallization (in the form of very fine crystals), due to the effect I of common ions (sodium of STPP). When the mixture has become viscous, the high-speed dispersing apparatus acts to grind the particles (for example hydrated STPP) to a size of fine particles; the grinding action is indicated, I. on the one hand, by the increased energy consumption of the dispersing apparatus, and, on the other hand, by an additional rise in temperature (for example I up to 65.6 ° C., this which causes an increased dissolution of the detergency builder salts; these, in turn, recrystallize in the form of fine crystals by cooling). This grinding is continued for approximately 5 minutes, after the initial thickening of the suspension; during grinding, the visible lumps of material disappear and the particle size of the undissolved particles I is reduced, so that almost all of the particles are assumed to have diameters less than 40 microns. Then, another 9.367 parts of water are added, lowering the viscosity to less than I 10,000 mPa.s (for example in the vicinity of 5,000 mPa.s, I measured as indicated above), after which, add- I. 35 te 3.3 parts of Attagel N ° 50 and 0.732 parts of I Ti02 k ^ anc (anatase) as a pigment with a highly alkaline mixture (whose pH is well above 9, for example 114 of 10 , 5), however that the mixture is continuously subjected to the action of the high-speed dispersing apparatus, which disperses (deagglomerates) the clay to a great extent, so that the thick mixture 05 becomes homogeneous and smooth appearance. Then added 2.70 parts of aqueous solution at 50% NaOH, 0.16 part 3 'antifoam (Knapsack ΧιΡΚΝ 158), 10.53 parts of aqueous solution at 47.5% sodium silicate (including the Na20 ratio : Si02 is 1: 2.4), 10.0 10 parts of a 12% aqueous solution of sodium hypochlorite and 0.8 part of a 45% aqueous solution of a resistant anonic active surf 3 1 · bleaching agent (Dowfax 3B2); these additions can be made under any desired mixing conditions, for example, by simple stirring (although it may be convenient to continue the high shear dispersing action for such mixing). The mixture is then subjected to a grinding action, for example by passing it through a continuous mill such as "Dispax Reactor" from Tekmar (which operates at a top speed of 22 meters per second) which subjects mixing at a high shear rate for a relatively short time (for example, the "residence time" in the mill can be as little as two seconds or less). The main effect of this is to further disagglomerate the clay particles, as indicated by a marked increase in the flow index, for example by raising the flow index of the mixture by about 33%.

The resulting mixture is thixotropic. It is believed that the particle size of the dispersed solid particles it contains is so small that about 80% by weight, or more, has particle sizes of less than 10 microns. The melan-35 ge is at a temperature close to 49-54.5 ° C (at this temperature, its viscosity is higher than that, for example, at 21.1 ° C). It is discharged from the mixing container (for example by a lower valve, when the container has a conical bottom, or by a lower side valve of a mixing container with a substantially flat bottom). About 10 S of the mixture res-05 tent as "heel" in the container; due to its flow characteristics, it is difficult to remove the entire composition of the container.

The procedure described above is then repeated in its entirety many times in the same mixing container, without ever removing the heel.

The high speed dispersing apparatus may comprise a circular horizontal plate having circumferential teeth alternating up and down, which plate is mounted (on; a vertical shaft directed downwards) so as to rotate quickly enough to the circumferential speed (of the teeth) is greater than about 22.86 m / s (for example 24.5 m / s). For laboratory scale operation, a Cowles high speed dispersing apparatus is suitable; for larger scale operation, a Myers Model 800 high speed disperser can be used. These high speed dispersers 25 reduce particles by grinding, impact, toothed plate and laminar shear force exerted on the mixture. Shear generates heat in the load, in addition to the heat generated by dissolution, hydration, etc. At the resulting relatively high temperature, the ingredients are more soluble and, after crystallization on cooling, give relatively small particles which dissolve only slowly, if not at all. The high-speed dispersing apparatus causes a "rolling" of the mixture, that is, the path of the movement of the mixture descends in the center of the container, outward along the rotating plate. ve, up along the side walls of the container, and inward to. the upper surface of the mixture. During this movement, a desirable deaeration occurs, that is, the air (which is always introduced when the powders are added) leaves the mixture during its inward journey. ”~

Apparently, after processing the composition described above, a growth of rate-cries appears giving many crystals of larger, relatively uniform size (as indicated by the photomicrographs). Thus, Figure 4 indicates the presence of crystals with a diameter of about 80 micrometers. These crystals appear to contain polyphosphate, but have not, however, been whole. rely identified.

EXAMPLE 5

Example -4 is repeated, with the difference that the STPP powder is an anhydrous STPP from Monsanto manufactured by the known "dry process" and comprises anhydrous STPP humidified as long as its water content of hydration is 0.5% (or 'slightly more, for example' 1.5%). Its phase I content is approximately 20%. This STPP 25 is also used in Example 3.

EXAMPLE 6

Example 4 is repeated, with the difference that the initial proportion of water is 28.0 parts, the second proportion of water is 13.637 parts, and before the addition of the attapuigite clay, we add 1.11 part of aqueous solution at 45% of sodium polyacrylate (Acrysol LMW-45N, having a molecular weight of approximately 4.500). The quantity of KjCO ^ is / here / of 3 parts and 35. the amount of Na ^ CO ^ is 4 parts.

It was found that the products of Examples 4 to 6 had the following characteristics: ΜΒΡχν. · "- - 17. . Example 4 5 6

Viscosity (mPa.s) 4000 6000 4400

Flow index (Pa) 450 600 450 05 Capillary flow time (min) 8.2 5.6. 6.1 Separation by centrifugation (%) 16 26.3 12

Thixotropy index 5 4/3 4.1 10

"Separation by centrifugation" is measured by centrifugation at 275 g, as described in Example 3, above, and by measuring the volume of the transparent liquid phase relative to the total volume.

The "thixotropy index" is the ratio of the viscosity at 30 rpm to that at 3 rpm, measured at room temperature with a Brookfield HADT viscometer, pin Ne 4, as described in ~ 20 'said request No. 497,615.

In Example 6, a soluble polymer resistant to chlorine bleaches is present. The presence of the polymer has been found to improve the resistance to separation of the product at rest or by centrifugation, without imparting a proportionally greater increase than the viscosity of the product. Note that the polymer is present here in a very highly concentrated (saturated) electrolyte solution. It is also found that the presence of the polymer results in better protection of the glaze layer of the dishes (fine porcelain).

In fact, so far, these effects have been observed with polyacrylic acid salts which have been shown to be fully compatible with the chlorinated bleaching agents and with the clay of this system; for example the content of active chlorine is maintained, as well as the viscosity. It is possible to use polymers o I 18 I of different molecular weights; for example, the polymer may have a molecular weight of less than 10,000, or a molecular weight of 100,000 or more.

I The proportions of polymer can be from 0.01 to 3%, I 05 the lower proportions being more appropriate I for polymers of high molecular weight (for example I 0.06% for a polymer of molecular weight I of 300,000). Other polymers resistant to bleaching agents can be used.

In the present application, all the proportions are expressed by weight, unless otherwise indicated. In the Examples, the atmospheric pressure is used, unless otherwise specified.

I It goes without saying that the invention is not li ~ I * 15 limited to the embodiments described and that I r is susceptible to various variants without departing from I. its frame.

H

Claims (7)

19 Λ 1 ·. Process for the manufacture of a thixotropic detergent suspension, characterized in that it consists in forming a suspension of solid particles of 05 adjuvant salt of alkaline detergency * water-soluble in a liquid which is water saturated with an adjuvant salt of alkaline detergency water-soluble, the proportion of said solid particles being sufficient for the suspension to have a viscosity of approximately 10 20,000 to 60,000 mPa.s, to subject the viscous suspension to the action of a high-speed dispersing device operating at a top speed of at least about 22.5 m / second to effect wet grinding of the solid particles, then to add water, to lower the viscosity of the suspension,, and of the clay powder, and to deagglomerate the clay in the suspension by mechanical action in the presence of solid particles of adjuvant salt of soluble detergency. 2. Method according to claim 1, charac terized in that said particles are, at least for the most part, sodium tripolyphosphate and the air - "" gile is clay of the attapulgite type. 3. Method according to claim 1, carac-tërisê in that a water-soluble anionic surfactant is then added to the resulting mixture. 4. Method according to claim 1, characterized in that the viscous suspension is formed by the addition of substantially anhydrous sodium tripolyphosphate to a solution of alkali metal carbonate in water. 5. Method according to claim 4, characterized in that the concentration of alkali metal carbonate in the solution is sufficiently high that the presence of added sodium tripolyphosphate causes the crystallization of sodium carbonate from said solution. ,. ja · "- *" 20 6. Method according to claim 1, characterized in that it is implemented in a mixing container and comprises the stage consisting in removing from the container most of the suspension 05 containing the resulting deagglomerated clay, while leaving a substantial heel of suspension in the container, then repeating the process in the presence of said heel, this heel constituting approximately 5 to 20% of the mixture during this repetition. 7. The method of claim 2, charac terized in that the proportion of clay is about 1 to 5%. ΙΊ% 0