EP0323323A1 - Andalusite beneficiation process - Google Patents

Abstract

A process for beneficiation of andalusite present in a compound containing it, by separation from other silicates by flotation to obtain a concentrate whose andalusite content is higher than 90%. It is characterised in that the process comprises at least the following stages: a) optional grinding and pulping of the said compound containing andalusite b) preconditioning of the said compound containing andalusite by maintaining the pH of the aqueous phase of the pulp at a value below 3.50, the solids content in the pulp being higher than 30% (one significant figure); c) conditioning for at least ten minutes after addition of an alkyl sulphonate; d) optional dilution of the said pulp to bring it to a solids content of between 15 and 30% e) flotation by bubbling small air bubbles calibrated in a manner known per se, the actual flotation lasting not more than ten minutes. <??>Application to the production of refractory raw materials.

Description

The present invention, which was carried out in the laboratories and mobile pilot installations of the company MINEMET RECHERCHE, relates to a process for the enrichment of an industrial mineral, andalusite, which is a particular form of aluminum silicate .

This mineral is often associated with other silicates and sometimes even with some having the same formula.

The separation of the silicates between them is a particularly delicate operation because it would often involve similar flotation mechanisms. The flotation of such minerals often requires long studies and significant know-how because it is common for compounds of the same formula to float very differently. Examples include quartz and chalcedony. This difficulty is also found for other non-silicate minerals: we can cite pyrite and marcasite which, although having an identical formula, because of their different crystal lattice, see, under identical conditions, their selectivity vis -to other metal sulfides reversed during flotation.

The flotation specialist already knows the reagents used to carry out a flotation of silicate compounds. These reagents are generally alkyl sulfonates, primary, secondary, tertiary amines or the salts of quaternary amines. It is also possible to use certain carboxylic acids, in particular those known under the name of fatty acids.

However, in the case of Andalusite, given the low margins of this industrial mineral, a large number of techniques cannot be applied in because of their cost. In addition, this aluminum silicate is generally extremely difficult to separate from its own silicate gangue. Among the minerals constituting this gangue, mention may in particular be made of quartz, plagioclase feldspar, muscovite and biotite. In addition, to obtain commercial quality, the iron content must be extremely low.

A mineral close to andalusite, kyanite (sometimes called disthene), but which has properties distinct from andalusite, has already been studied for enrichment by flotation. However, the authors of this last study came to conclusions different from those of the research which is the subject of the present application and, on the other hand, only concluded that enrichment was possible under particularly expensive and not very selective conditions. vis-à-vis the silicates present when they are applied to the flotation of andalusite.

As a reference for studies on kyanites, we can cite the article by V.A. HAW "Kyanite in Canada" in The Canadian Mining and Metallurgical, Jan. 1954, pages 27-34, in which the author indicates that the best results are obtained in the zone of pH 4.0-4.5 at a temperature of 30 ° C. Practically similar conditions are found in the article by JS BROWNING published in the Transactions of AIME in September 1969 (vol. 244, pages 283-287) under the title "Flotation of Southeastern Kyanite Ore": pH 3.7 to l roughing and 3.9 at rewashing and temperature of 27 ° C during packaging.

This is why one of the aims of the present invention is to provide a method for enriching andalusite by separation of the latter from its gangue and in particular from other natural silicates such as quartz, feldspar plagioclase, muscovite. , biotite.

Another object of the present invention is to provide a process of the above type whose operating costs are as low as possible.

Another object of the present invention is to provide a process which avoids having to work at a temperature above ambient and which therefore allows use of the process under variable climatic conditions and in particular that its economy is not affected by the summer-winter rhythm.

• a) broyage éventuel et mise en pulpe dudit composé conte­nant de l'andalousite
• b) pré-conditionnement dudit composé contenant de l'anda­lousite en maintenant le pH de la phase aqueuse de la pul­pe à une valeur inférieure à 3,50, le taux de solide dans la pulpe étant supérieur à 30 % (un chiffre significa­tif) ;
• c) conditionnement pendant au moins dix minutes après ad­dition d'un alcoyl sulfonate ;
• d) dilution éventuelle de ladite pulpe pour l'amener à un taux de solide compris entre 0,1 et 0,3 ;
• e) flottation par barbotage de bulles d'air calibrées de manière connue en soi, la flottation proprement dite du­rant au plus dix minutes.

These aims, as well as others which will appear subsequently, are achieved by means of a process for the enrichment of andalusite present in a compound containing it, by separation from other silicates by flotation to obtain a concentrate with an Andalusite content greater than 90%, characterized in that it comprises at least the following stages:

• a) possible grinding and pulping of said compound containing andalusite
• b) preconditioning said compound containing andalusite while maintaining the pH of the aqueous phase of the pulp at a value less than 3.50, the level of solid in the pulp being greater than 30% (a significant figure);
• c) conditioning for at least ten minutes after addition of an alkyl sulfonate;
• d) optional dilution of said pulp to bring it to a solid content of between 0.1 and 0.3;
• e) flotation by bubbling air bubbles calibrated in a manner known per se, the flotation proper lasting at most ten minutes.

When, for various reasons such as basic gangue or addition of basic reagents, the pH rises above the maximum indicated, it is preferable to regulate the pH in steps c), d) and e) to a value less than 4.

The two grinding and pulping operations of step a) can be carried out simultaneously in the case of wet grinding.

It is preferable that the grinding of step a) is carried out so that said compound has a d₈₀ at most equal to 0.5 millimeter (rounded figure according to mathematical use).

Recall that d _x , where x is between 1 and 100, is the smallest mesh allowing x% by weight of the product to pass. Thus, d₈₀ is the smallest mesh allowing 80% of the product to pass through.

To obtain a good flotation yield, it is desirable that said d₈₀ be at most equal to 400 micrometers (a significant figure) and greater than the lower limit of flotation, which is of the order of 10 micrometers (a significant figure) .

To obtain good selectivity vis-à-vis other silicates and gangue in general, the pH plays a very important role; it is advantageously kept at a value less than 3 during step b) as well as in steps c), d) and e).

In the field of selectivity, another parameter plays a non-negligible role: the level of solid, which, during steps b) and c), is preferably brought and maintained at a value at least equal to 50%.

In general, the first flotation carried out is insufficient to bring the content of andalusite to a value substantially greater than 90%. In addition, this content of 90% is a relatively low limit which is insufficient for certain commercial qualities and it is preferable that the content of andalusite is greater than 95%, even 98%. This can be remedied by performing following step e) the following step:
f) rewashing the concentrate obtained in step e).

This rewashing step is relatively classic per se in the enrichment process by flotation. In this specific case, it requires the addition of new quantities of flotation reagents, here the alkyl sulfonic acids and the alkali or ammonium salts. This rewashing of the concentrate can be carried out in several sub-steps and in several flotation cells arranged in cascade.

Furthermore, in an extremely surprising manner, it has been demonstrated, within the framework of the present study, that rewashing is only effective if the flotation step proper e), called by those skilled in the art "roughing flotation "was carried out quickly enough, often to the detriment of weight yield.

A good guide for those skilled in the art to obtain good rewashability of the roughing concentrate is to stop this roughing flotation when only 80 to 95% of the andalusite is mounted in the form of scum.

In general, a duration of about ten minutes (a significant figure), as indicated above, allows good results to be obtained.

The amounts of alkylsulfonate used in step c), and where appropriate in step f), are between 300 to 1,500 grams per tonne of ore processed.

The alkyl sulfonates used can be straight or branched chain and preferably have from 8 to 16 carbon atoms. They have at most two ramifications (three branches). We can use in particular those sold under the trade names of BAYMIN CO 300 and CO 301 from BAYER, SYNACTO 247 from PARAMINS, the Aero-Promoters of the 800 series from CYANAMID, reagent 7723 from GERLAND and R 231 from at FLOAT ORE Ltd.

Advantageously, the pH of the pulp, which may have changed during the addition of alkyl sulfonate, is brought to a value at most equal to 3 by addition of a strong mineral acid, in particular by means of an acid chosen from the group of strong hydrohalic acids (HCl), HBr, HI, sulfuric, nitric and phosphoric.

One of the advantages of the present invention is that, unlike the known methods for neighboring minerals, there is no need to regulate the temperature. The preferred temperature is therefore room temperature whatever the climatic conditions. It is perfectly possible to operate the process in the temperature range 10-30 ° C.

One of the important constraints for the marketing of Andalusites is their iron content which must be as low as possible and preferably not exceed 1.5% expressed as Fe₂O₃.

In the case where there is iron in the form of iron-containing sulfur compounds, there is carried out between steps a) and b) a flotation, or a possible magnetic separation in the case of pyrrhotite, of the latter by techniques known per se. It is understood that, for this flotation to be effective, step a) of grinding should be carried out so as to release at least 60% of the said ferric sulfur compounds, preferably 80 to 95%. A good compromise is often 90%.

During the study which led to the present invention, it was surprisingly shown that in order to achieve a good elimination of sulfur-containing iron compounds, such as pyrite, marcasite, chalcopyrite, pyrrhotite, it is preferable that the duration of the proper flotation of said ferric sulfur compounds is equal to a value greater than the usual value of the sulfide flotation as skilled in the art can determine. As an indication, one chooses between 1.5 and 3 times said usual duration for this kind of compounds, all other things being equal.

It has been surprisingly noticed that in doing so using the conventional sulfide collectors, preferably the xanthates, not only the sulfur-containing sulfur compounds are floated but also the phyllitous iron compounds.

To obtain good selectivity, the presence of fine particles is troublesome and these latter must be eliminated by carrying out a de-flaming before step b).

Deschamming is advantageously carried out by eliminating at least 75%, preferably at least 90%, of solid particles smaller than 50 micrometers, (a significant figure).

However, depending on the classification technique used, preferably an equivalence classification technique, it is preferable that the de-flaming be carried out as efficiently as possible, at the limit of the possibility of its means, which implies for these two techniques elimination of at least 95% of solid particles smaller than 50 micrometers.

One of the surprising and advantageous aspects of the process according to the present invention is that it has been shown that the adsorption of the sulfonate on andalusite is reversible and that it is therefore possible to obtain andalusite without sulfonate by rinsing. in basic medium (greater than or equal to 9) of the flotation concentrate.

• 1. Conditionnement (repulpage) avec avec de la soude (NaOH) (1 kg/t de concentré) pendant 5 mn (taux de solide supérieur à 10 %) ;
• 2. Essorage sur tamis ;
• 3. Conditionnement (repulpage) à l'eau pendant 5 mn ;
• 4. Essorage sur tamis (les opérations 3 et 4 peuvent être renouvellées une ou plusieurs fois suivant le degré d'élimination du sulfonate désiré ;

As an indication, such rinsing can be carried out by the following sequence of operations:

• 1. Conditioning (repulping) with sodium hydroxide (NaOH) (1 kg / t of concentrate) for 5 min (solid content greater than 10%);
• 2. Spin on sieve;
• 3. Conditioning (plumping) with water for 5 min;
• 4. Spinning on a sieve (operations 3 and 4 can be repeated one or more times depending on the degree of elimination of the desired sulfonate;

Standard flotation tests on the plump cake at natural pH (around 9) and at around 20% pulp rate do not cause andalusite in the overflow thus demonstrating the absence of significant residual adsorption of the alkyl sulfonates on the 'andalusite. It should be noted that this flotation technique makes it possible to lower the sulfonate content in the mother liquors and that such a technique can be used to remove part of the alkyl sulfonates.

The filtrate from step 2 can be recycled to step c) of the process, especially if the level of solid in operation 1 is greater than 1/2, preferably 3/4 (rounded figures).

Furthermore, to avoid the risk of siltation of industrial flotation installations, it is desirable to add foaming agents, for example those of the polyglycol type such as that sold under the trade name Aerofroth 65 of American Cyanamid (cf. example 5 ).

The following nonlimiting examples allow those skilled in the art to better understand the different parameters of the process according to the invention.

Example 1 : Description of the enrichment process at the pilot stage

Reference will be made to FIG. 1 constituting the rheogram of the process tested.

In a ball mill (A), the ore to be treated (1) and water (2) are introduced in an amount necessary to be at a mass concentration of solids of 30%. The ball load, stepped from 10 to 40 millimeters, is calculated so as to deliver at the outlet of the mill a pulp (3) whose particle size is for 80% by weight less than 240 micrometers. The pulp (3) is then introduced into a double-blade reactor (B), brought to a solids concentration of 20 to 25% by the addition of water (4) and conditioned for 3 minutes in the presence of sulfuric acid in quantity sufficient to maintain a pH value of 5 and a dose of 100 grams per tonne of sulfide collector ore of the xanthat family. The pulp (5) is then conveyed to the flotation cells intended to collect the iron-bearing sulphides. This flotation step, lasting 10 minutes, is carried out in several banks of MINEMET H 300 cells with 2 or 3 turbines (C) operating in series. Each turbine delivers 3.3 m³ / h of air. The number of turbines is advantageously brought to a value at least equal to 5. The introduction of 20 grams per tonne of surfactant (Methyl-isobutyl carbinol) at the start of the flotation makes it possible to recover in the form of foam the carrier sulfides iron and some ferric phyllitic minerals (6). In this example, the floated product represents 2 to 3% of the weight of the food. The rejection from this stage is pumped to a double-step screw classifier (or a cyclone) (D) in which the cut between the finest particles (less than 40 micrometers) which constitute the diluted rejection is effected by equivalence ( 8) and particles larger than 40 micrometers (9) which constitute the supply for the Andalusite flotation. This also thickens the pulp. (9) at a mass concentration value of solids of 70%.

The pulp (9) which contains 91.5% of the weight of ore is then introduced into two double blade conditioners (E) operating in series.

During the first conditioning, lasting 6 minutes, water is added (10) so as to obtain a solids concentration of 50% and an addition of sulfuric acid in an amount sufficient to maintain a pH value. if possible equal to 2.8 and in all cases less than 3. The second step is intended to condition for ten minutes the sulfonate introduced at the rate of 570 grams per tonne of general ore. The pulp (11) emerging from this second packaging is pumped to the flotation cells (F) which consist of a bank of two MINEMET cells of the H 450 type followed by two banks of three MINEMET cells of the H 300 type. Rejection rewash (16) also feeds the cells (F), which leads to a solids concentration close to 30%. This flotation lasts 9 minutes. All of the turbines deliver 40 m³ of air per hour. During roughing flotation it is necessary to keep the pH below 3 and to introduce a dose of 570 grams per ton of sulfonate. Uncollected products (12), which represent 26.5% of the initial weight, constitute the rejection of Andalusite flotation. Andalusite is collected in the form of a scum (13) which feeds the rewashing stage (G). This last step, lasting 9 minutes, is carried out at a mass concentration of 20%, which involves the addition of water (14). The pH is also maintained at a value at most equal to 3 by the addition of sulfuric acid and 200 grams per tonne of general sulphonate ore are added to the top of the two banks of triple MINEMET H 300 cells.

The collected product (15) constitutes the final andalusite concentrate, while the solids which have not floated (16) return to the top of the draft flotation. ge (F).

Under these operating conditions, and for a feed ore (1) containing 45.4% of alumina and 1.15% of iron expressed as Fe₂O₃, a purified product is obtained which titers 59.2% of alumina and less 0.6% Fe₂O₃ while recovering more than 88% of the andalusite contained (see table below). Product Weight% Content% Recoveries% Andal. Al₂O₃ Fe₂O₃ Andal Al₂O₃ Fe₂O₃ Food 100 65.5 45.4 1.15 100 100 100 Pyrite flotation rejection 97.5 66.8 46.5 0.65 99.5 99.9 55.5 Schlamms 6.0 28.4 22.7 1.80 2.6 3.0 9.4 Andalusite flotation supply 91.5 69.4 48.1 0.58 96.9 96.9 46.1 Andalusite concentrate 65.0 89.2 59.2 0.59 88.5 84.8 33.3

This example also illustrates the positive influence of de-flaming on the iron content of the product since this operation makes it possible to reduce the iron content of the product by 10%. This results from the use of the screw classifier (or a cyclone) (D) which allows the elimination by elutriation of ferric phyllitous minerals.

EXAMPLE 2 Influence of the Solid Concentration of the Pulp During Conditioning Prior to Andalusite Flotation

The influence of the pulp solids concentration during the conditioning which precedes the Andalusite flotation on the result of this flotation is clearly highlighted by the comparison of two pilot tests carried out, one with a mass percentage of solids of 25%. , the other 50%.

The scheme of these two tests is fairly similar close to that of the previous example. We will therefore refer to the rheogram of Figure 1 for the steps between A and E and to the rheogram of Figure 2 for the following steps (F, G and H).

In this example, steps A, B, C and D are identical to those described in Example 1. However, there are differences in the following operations. The addition of water (10) is obviously variable for the two tests described here: the solid concentrations of the pulp during conditioning are 25% or 50%. Aside from this variation, step E is identical to that of the previous example. Before the andalusite roughing flotation step (F), water (12) is added so as to obtain a mass solids concentration of 25% in both cases. The progress of step F is modeled on that of Example 1. The floated product (13) is again collected during the rewashing step (G) after addition of water (15) making it possible to obtain a concentration close to 20%. Sulfuric acid is introduced during this step to maintain the pH at a value of 3. The flotation time and the material used are those of Example 1 for this same step. The rejection of this flotation (17) is not recycled while the concentrate (16) undergoes a second rewashing (H) after a new addition of water (18) to maintain a solids concentration of 20%. Sufficient sulfuric acid is also used to maintain the pH at 3 and 250 grams per tonne of sulfonate feed ore. The circuit is identical to that of the first rewash and allows the final Andalusite concentrate (19) to be collected and to eliminate a rejection from the second rewash (20).

Tables 2.1 and 2.2 make it possible to compare the balances obtained for the two concentrations of the conditioning (the calculations are carried out with respect to the product (11). It can be seen that the mode of conditioning has little influence on the Andalusite roughing flotation. On the other hand, diluted packaging results in ineffective washes (little gain in content for a significant loss of Andalusite yield). Table 2.1 Content% Recoveries% Andalusite Al₂O₃ Andalusite Al₂O₃ Andalusian food. 72.2 48.0 100.0 100.0 Concent. roughing 75.4 49.5 94.4 97.4 Rewash Concentrate 1 79.4 51.5 69.7 74.9 Rewash Concentrate 2 81.1 52.2 64.4 70.1 Partial balance of the Andalusite pilot flotation in the case of concentrated packaging (25% solids) Content% Recoveries% Andalusite Al₂O₃ Andalusite Al₂O₃ Andalusian food. 67.7 47.4 100.0 100.0 Concent. roughing 75.6 51.7 99.0 96.7 Rewash Concentrate 1 86.2 58.8 82.9 80.7 Rewash Concentrate 2 87.4 59.6 78.0 75.9 Partial balance of the Andalusite pilot flotation in the case of diluted packaging (50% solids)

Example 3 Influence of the pH on the Result of the Andalusite Flotation

Reference is made to FIG. 3 constituting the rheogram of the process tested.

In a porcelain ball mill A loaded with 50 balls, 1 kg of ore (1) is ground in the presence of water (2) at 70% by weight of solid matter for 50 minutes. nutes. The pulp obtained (3), the d₈₀ of which is 250 micrometers, is sieved in the presence of water (4) on a sieve (B) with a 63 micrometer mesh. The rejection of sieving (5) is introduced into a flotation cell (C) of the MINEMET brand with 2.5 liters capacity in the presence of water (6), which brings the concentration to 40% by weight of solids. The sieving pass (6) is considered as rejection.

In cell (C), the pulp is conditioned in the presence of sulfuric acid in sufficient quantity to obtain a pH value of 5. 60 grams are also introduced per tonne of andalusite of sulfide collector (Amyl-xanthante of potassium: AXK). After two minutes, air is introduced to carry out the flotation after having put 8 grams per ton of a surfactant (Methyl-isobutyl carbinol: MIBC). During the 10-minute sulfide flotation, 40 g / t of AXK and 15 g / t of MIBC are introduced in several doses. The concentrate obtained (7) consists of a pulp of sulphides.

The rejection of this flotation (8) is again screened (D) at 63 micrometers in the presence of water (9). The sieving pass is a rejection (10). The rejection of sieving (11) is introduced into a flotation cell (E) previously described in (C) as well as water (12), which brings the concentration to 60% of solids. A 10-minute conditioning is then carried out in the presence of sufficient sulfuric acid to obtain a pH value of between 2 and 5 according to the tests and of an alkyl-sulfonate type collector at the rate of 350 grams per ton. Air is then introduced for 7 minutes so as to ensure the collection of andalusite and its overflow in the form of pulp (13). During flotation, the pH is maintained at the desired value by a measurement / regulation system by servo pump.

Two other equal doses of sulfonate are also introduced, representing a total of 700 grams per tonne of ore. After the flotation, the cell is emptied of the rest of the pulp (14) containing the product which has not fleet.

The characteristics of the andalusite concentrate, obtained after 7 minutes of flotation, are given in the following table for four different pH values. In this table, the weight yield is equal to the ratio of the weight of solid in the concentrate (3) to the weight of initial solid (1) expressed as a percentage. The Andalusite contents are those of the concentrate. Andalusite yields are the ratios of the Andalusite weight of the concentrate to that contained in the feed of the Andalusite flotation (11). pH Weight yield% Andalusite content% Andalusite yield% 2 66.6 90.1 97.7 3 68.6 85.2 99.5 4 85.3 69.4 99.7 5 82.8 69.8 98.9

There is a marked decrease in selectivity when the pH of the Andalusite flotation is increased. In particular, for the pH value commonly used for kyanite, the selectivity is insufficient.

Example 4 Influence of rough Andalusite on the efficiency of the first rewash

The rheogram of the process is identical to that of Example 3 with regard to operations A, B, C and D. The principle of step E of flotation for roughing Andalusite is also invariant. The only differences concerning roughing are the collector dose here equal to 1200 grams per tonne of ore in four additions, the flotation time (3.5 minutes for one test, 6 minutes for the other) and the dose d sulfuric acid introduced in sufficient quantity throughout the flotation to maintain a pH value of 3. It will also be noted that the ore (1) is different from that of Example 3.

Following this flotation, the concentrate (13) is introduced into a flotation cell (F) together with water (15), which brings the solid concentration to 30%. A conditioning is then carried out in the presence of sulfuric acid intended to maintain a pH value equal to 3. Air is then introduced for 5 minutes to collect the andalusite by overflow (16). During this flotation are added, in two doses, 100 grams per tonne of ore coming from the collector of the alkyl sulfonate type as well as sulfuric acid in sufficient quantity to maintain the pH at the value of 3. At the end of this operation, the product which has not been collected is collected at the bottom of the cell (17).

The results of the two tests relating to the influence of the roughing flotation time on the efficiency of rewashing are given in the following table. Roughing concentrate Washed concentrate % weight % Al₂O₃ Yard * Al₂O₃ % weight % Al₂O₃ Yard * Al₂O₃ Roughing 3,5 mn 62.9 58.2 90.3 60.9 59.3 90.2 Roughing 6 mins 75.2 53.4 98.4 70.4 53.6 92.4 * Yield = yield

It can be seen that with short roughing, rewashing allows a gain in content without loss of yield. Conversely, when roughing lasts 6 minutes, rewashing hardly allows any gain in content despite a significant loss of yield.

Example showing that during industrial flotation, it is best to add at the start of the roughing flotation of Andalusite 1/20 to 1/10 kg / t (rounded figures) of a polyglycol type foaming agent (for example Aerofroth 65 from American Cyanamid) to avoid sanding phenomena.

Similarly, roughing flotation for pulp solid concentrations of less than 25 or even 20% also plays a role in the fight against the phenomena of silting up.

Example 5 : Comparison of the results of industrial roughing flotation with and without the addition of foaming agent.

The roughing flotation was carried out as in Example 1, with however a concentration of solid matter of approximately 20% and in cells of size clearly greater than that of the pilot since they had a capacity of approximately 4 m³ , each cell being equipped with four turbines.

The first results showed a phenomenon of silting that it was possible to alleviate using systems known per se of automatic sand removal and somewhat complicated upstream recycling. This sanding phenomenon, linked to a problem of change of scale, was resolved by adding a foaming agent of the polyglycol type (Aerofroth 65 from American Cyanamid).

The results are summarized in the table below: Industrial roughing concentrate Mass % Al₂O₃% content Al₂O₃% recovery Conventional roughing flotation 59.4 58.3 71 Draft flotation with 80 g / t of foaming agent 73.2 58.4 85

Claims (18)

1. Process for the enrichment of andalusite present in a compound containing it by separation from other silicates by flotation to obtain a concentrate whose Andalusite content is greater than 90%, characterized in that it comprises at least the following steps: a) possible grinding and pulping of said compound containing andalusite b) preconditioning said compound containing andalusite while maintaining the pH of the aqueous phase of the pulp at a value less than 3.50, the level of solid in the pulp being greater than 30% (a significant figure); c) conditioning for at least ten minutes after addition of an alkyl sulfonate; d) possible dilution of said pulp to bring it to a solid content of between 15 and 30%. e) flotation by bubbling air bubbles calibrated in a manner known per se, the flotation proper lasting at most ten minutes. 2. Method according to claim 1, characterized in that step a) of grinding is carried out so that said compound has a d₈₀ at most equal to 0.5 millimeter. 3. Method according to claims 1 and 2 taken separately, characterized in that the pH is regulated during steps c), d) and e) at the same numerical value as during step b). 4. Method according to claims 1 to 3, taken separately, characterized in that during step b) the pH is maintained at a value less than 3. 5. Method according to claims 1 to 4, taken separately, characterized in that the solid content during steps b) and c) is maintained at a value at least equal to 50%. 6. Method according to claims 1 to 5, taken separately, characterized in that it comprises, after step e) the following step:
f) rewashing the concentrate obtained in step e). 7. Method according to claims 1 to 6, taken separately, characterized in that the amount of alkyl sulfonate used during step c) is between 300 to 1500 grams per ton of andalusite contained in said compound. 8. Method according to claims 1 to 7, taken separately, characterized in that during step c) the pH is maintained at a value less than 3. 9. Method according to claims 1 to 8, taken separately, characterized in that one uses to fix the pH a strong mineral acid chosen from the group of sulfuric, nitric and phosphoric acids. 10. Method according to claims 1 to 9, taken separately, characterized in that the temperature is room temperature. 11. Method according to claims 1 to 10, taken separately, characterized in that one carries out between steps a) and b) a flotation of the sulfur-containing iron compounds by techniques known per se and by the fact that the step a) grinding is carried out so as to liberate at least 60% of said ferric sulfur compounds. 12. Method according to claim 11, characterized in that the duration of the actual flotation of the sulfur-containing sulfur compounds is equal to 1.1 to 1.5 times the usual duration for this type of compound. 13. Method according to claims 1 to 12, taken separately, characterized in that one carries out a deschlammage before step b). 14. Method according to claim 13, characterized in that the de-flaming is carried out by the elimination of at least 90% of the solid particles smaller than 50 micrometers. 15. Method according to claim 14, characterized in that the déschlammage is carried out by the elimination tion of at least 95% of solid particles smaller than 50 micrometers. 16. Method according to claims 13 and 14 taken separately, characterized in that the de-flaming is carried out by means of sieves or hydrocyclones. 17. Method according to claims 1 to 16 taken separately, characterized in that it further comprises step g) washing of the Andalusite concentrate by means of a basic aqueous solution. 18. Method according to claims 1 to 17 taken separately, characterized in that one adds in one of steps c) or d) a foaming agent at a concentration between 1/20 and 1/10 kg / t Andalusite.

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