WO2005003041A2

WO2005003041A2 - Stabilised solutions of aluminium polychloride and iron salt for the treatment of effluents

Info

Publication number: WO2005003041A2
Application number: PCT/FR2004/001472
Authority: WO
Inventors: Vincent Favreau; Yvette Pescher
Original assignee: Rhodia Chimie
Priority date: 2003-06-16
Filing date: 2004-06-11
Publication date: 2005-01-13
Also published as: FR2856053A1; WO2005003041A3; FR2856053B1

Abstract

The invention relates to stable liquid compositions comprising, in solution, a mixture of aluminium polychloride and an iron salt, the solution stabilised by the presence of a cationic polyelectrolyte, such as for example, a polymer with quaternary ammonium groups. The invention further relates to a method for production of said compositions and the use thereof for the treatment of aqueous media, in particular, for elimination or reduction of odours from aqueous effluents such as the residual water from sewage plants.

Description

Compositions based on stabilized solutions of aluminum polychloride and iron salt for the treatment of aqueous effluents

The present invention relates to liquid compositions comprising a stabilized mixture of aluminum polychloride and an iron salt, having a low viscosity. These compositions, which can be pumped and which can generally be stored for periods of the order of several months, prove to be particularly advantageous in the field of the treatment of aqueous effluents, in particular for the treatment of waste water from treatment plants, for example for the treatment of unpleasant odors due to the presence of sulfur derivatives in such effluents.

Numerous methods are currently known for treating and purifying aqueous effluents. Most of these methods use a stage of elimination of suspended matter, using agents ensuring flocculation or coagulation and then gravity decantation of the flocculates or coagulates obtained, the supernatant clarified waters then being subjected to filtration.

In this context, it is notably known to use, as coagulating agents, compounds such as aluminum or iron salts. Even if each of these agents is relatively effective in certain fields when used alone, it often proves advantageous to use these agents in combination, in order to benefit from the combined advantages of different agents.

However, it sometimes proves difficult to make two coagulating agents of a different type coexist within the same composition. In particular, mixtures of iron compounds and aluminum compounds are generally found to be unstable. Thus, a mixture of iron salts and aluminum salts generally leads to nucleation and crystallization processes which most often lead to gelation phenomena. (leading to a decrease in the pumpability of the composition) or precipitation (inducing a loss of effectiveness of the composition).

When it is desired to use two separate coagulating agents together, it thus generally proves necessary either to use the two reagents in two successive separate stages, or, at best, to carry out the mixing directly on the treatment site of the aqueous effluent in cases where this proves possible. To remedy this problem, attempts have been made to develop stable compositions which make it possible to use two or more types of coagulating agents together, and in particular a combination of iron and aluminum salts. To do this, the potential implementation of certain specific agents has been described ensuring stabilization of the mixture. In this regard, application EP 626347 describes in particular the use of alkali or alkaline earth halides to stabilize a mixture of poly aluminum chloride and iron salts. The inventors have now unexpectedly found that certain coagulating agents, namely canonical polyelectrolytes (such as, for example, polymers carrying quaternary ammonium groups of the polyamine, polyDADMAC, or polyacrylamide type) can ensure the role of stabilizing agents in a composition comprising in solution a combination of aluminum polychloride and iron salts. Surprisingly, the inventors have thus discovered stable associations based on three types of coagulating agents. Even more unexpectedly, the work of the inventors has made it possible to demonstrate that it is possible to obtain polychloride aluminum / iron salt / cationic polyelectrolyte associations having sufficient concentrations and suitable proportions of the three coagulating agents, giving them properties which are particularly advantageous for the treatment of aqueous effluents, and this in particular with compositions based on ferrous salts. Thus, the stable compositions developed by the inventors most often prove to be particularly effective for the treatment of effluents having an unpleasant odor linked to the presence of sulfur derivatives such as sulphides.

On the basis of these different results, the present invention aims to provide compositions suitable for the treatment of aqueous effluent, in general to reduce or even eliminate their odors, in particular linked to the presence of sulfur derivatives, comprising a combination of several coagulating agents, and stable over a significant period, typically of the order of a few months, making it possible to envisage storing the composition before its use. In this context, the invention aims in particular to provide compositions based on an association of aluminum polychloride and iron salts in which the gelling and precipitation phenomena generally observed with this type of association are sufficiently inhibited so that the composition retains a low viscosity and good effectiveness for the treatment of aqueous effluent over a period of time of the order of a few months.

More generally, the invention is also intended to provide stable compositions based on a combination of coagulating agents, in which the presence of agents other than coagulating agents useful for the treatment of aqueous effluents n is not required. Thus, according to a first aspect, the subject of the present invention is a composition, suitable in particular for the treatment of aqueous effluents such as waste water from a purification station, comprising, in solution (most often in aqueous solution, or optionally in hydro-alcoholic solution), a mixture of: (a) at least one weakly basic poly aluminum chloride; and

(b) at least one iron salt, where the solution comprising the mixture of compounds (a) and (b) further contains:

(c) at least one water-soluble cationic polyelectrolyte, acting as a stabilizing agent, inhibiting gelling and precipitation phenomena. As a general rule, a composition according to the invention is in the form of an aqueous solution of compounds (a), (b) and (c). This aqueous solution most often contains only a mixture of weakly basic aluminum polychloride, one or more ferrous and / or ferric salts, and one or more cationic polyelectrolytes soluble in water. The presence of additional compounds is certainly not excluded, but it is not required. Thus, it is in particular to emphasize that the stability of a composition according to the invention can be obtained by using only a cationic polyelectrolyte, without having to use another stabilizing agent, such as, for example, an alkali or alkaline halide - earth as described in application EP 626 347.

A composition according to the invention has a low viscosity, generally less than or equal to 500 cp (that is to say 500 mPa.s) at 20 ° C, preferably less than or equal to 150 cp at 20 ° C. Thus, this viscosity is typically between 5 and 100 cp at 20 ° C. The viscosity to which reference is made here is the viscosity as measured according to the method described in particular by using a BROOKFIELD DV II device, at a rotation speed of 60 revolutions per minute and by using the mobile No. 2. This low viscosity in particular gives the composition high pumpability and workability. This low viscosity is generally maintained even after storage of the composition for a few months. Thus, the inventors have demonstrated that, in a composition according to the invention, the gelling phenomena of the aluminum / iron system are sufficiently inhibited so that, in the general case, the composition retains its low viscosity at least 4 months after its preparation, in general at least 6 months after its preparation, and most often at least 9 months after its preparation, under normal storage conditions. Thus, after 4 months of storage, it is generally found that the viscosity of the solution comprising the compounds (a), (b) and (c) remains less than or equal to 200 cp at 20 ° C, most often less than or equal 150 cp at 20 ° C, and most often less than or equal to 100 cp at 20 ° C, the viscosity of the solution generally not exceeding these values even after storage for 6 months, or even after longer storage.

Thus, in most cases, a low viscosity, typically less than 150 cp at 20 ° C, or even 100 cp at 20 ° C is maintained for a storage period of

9 months. Furthermore, a composition according to the invention also appears to be stabilized "with respect to precipitation phenomena of iron hydroxides or of mixed species based on aluminum and iron which are generally observed when coexisting of iron and aluminum salts within the same composition. Thus, no appearance of precipitate is generally observed after storage of the composition for 4 months. Most often, no formation of precipitate is observable. after a storage of 6 months, and generally even after a storage of 9 months. Thus, one notes, as a general rule, that after a storage of a duration of 4 months, at least 95% in mass, generally at least 99% by mass, and most often at least 99.9% by mass (or even at least 99.99% by mass) of the compounds (a) and (b) remain in solution. In general, it is found that at least 99% after 6 months of storage, or even after 9 months, and in most cases at least ins 99.9% of compounds (a) and (b) remain in solution.

The term "aluminum polychloride ¹ 'denotes, within the meaning of the present description, a compound corresponding to the following formula (I): - [Al _n (OH) _m Cl _3n - _m - _2k (Sθ4) k] [ H ₂ 0] z (I), in which: n, m, are positive numbers (whole or not); k is a positive or zero number (whole or not), less than or equal to 0.4 times the value of n, i.e. a positive number between 0 and 0.4n; (3n-m-2k) denotes a positive number (whole or not); and z is a positive whole number at least equal to 1. Polychlorides aluminum in which the coefficient k is not zero are generally designated by the term "aluminum polychlorosulfate". The use of such aluminum polychlorosulphates can be envisaged according to the invention, however, aluminum sulphate-free polychlorides are generally preferred, ie in which the coefficient k is zero. Thus, according to a preferred embodiment, the poly aluminum chloride (a) of a composition according to the invention corresponds to the following formula (la): - [Aln (OH) _m Cl _3n ] [H ₂ 0] _z (la), in which: n, m are positive numbers (whole or not); (3n-m) denotes a positive number (integer or not); and z is a positive integer at least equal to 1.

Aluminum polychlorides are compounds well known to those skilled in the art, as is their mode of synthesis. Thus, these compounds are in particular the subject of US patent 3,929,666, or also applications FR 2,534,897, FR 2,584,699.

The basicity of a polychloride of aluminum is reflected by the ratio

(expressed in molar%) of the number of groups (OH) divided by 3 times the number of aluminum atoms, i.e. by the ratio (m / 3n) xl00 in formulas (I) and (la) above. This ratio is generally between 10 and 80% in a poly aluminum chloride. The aluminum polychloride which can be used in a composition according to the invention is a "weakly basic" aluminum polychloride. By this term is meant a polychloride of aluminum corresponding to one of the above formulas (I) or (la), characterized by a ratio (m / 3n) xl00 of at most 60%, and preferably less than or equal to 50%. In a polychloride (a) of low basicity which can be used according to the invention, the ratio (m / 3n) xl00 is generally between 10 and 60%, this ratio preferably being between 10 and 50%. Advantageously, this ratio is between 15 and 45%. Thus, this ratio (m / 3n) xl00 is typically between 20% and 43%. As weakly basic aluminum polychloride (a) which can be used in a composition according to the invention, mention may especially be made of aluminum polychlorides of the type of those sold by Rhodia under the trade names.

AQUARHONE18 or AQUARHONE18D. Whatever the exact nature of the aluminum polychloride (a), it is preferred that its content in the solution comprising the mixture of the compounds (a), (b) and (c) is at most 22% by mass , and preferably less than or equal to 20% by mass expressed in Al ₂ θ3 equivalent. This content is generally between 5 and 22% by mass, this content advantageously being greater than or equal to 10% by mass, and preferably greater than or equal to 12% by mass. Thus, this content is typically between 10 and 20% by mass, advantageously between 12 and 17% by mass, and, in a particularly preferred manner, of the order of 15% by mass, the various percentages by mass indicated above. for the poly aluminum chloride contents being expressed in Al θ3 equivalent. Furthermore, a composition according to the invention typically comprises an iron salt (b). This iron salt is generally an iron (II) or iron (III) salt, preferably chosen from an iron (II) or iron (III) chloride, an iron (II) or iron ( III), an iron (III) chlorosulf ate, or a mixture of these compounds. Particularly advantageously, it is ferrous chloride FeCh or ferric chloride FeC, the salt (b) preferably being a ferrous chloride FeCl ₂ . As will be described below, the properties of a composition according to the invention, as well as its method of preparation, are notably influenced by the exact nature of the iron salt used. Nevertheless, a stabilization of the composition according to the invention, with a water-soluble cationic polyelectrolyte, is obtained whatever the nature of the iron salt used.

The cationic polyelectrolyte (c) present in a composition according to the invention is itself a water-soluble polymer, linear or branched, optionally cyclic or partially cyclized, carrying positively charged groups. Preferably, the water-soluble cationic polyelectrolyte (c) is a polymer having a molecular weight of less than 1,000,000 g / mol, preferably less than 800,000 g / mol. Thus, its molecular mass is advantageously between 50,000 and 1,000,000 g / mol, and even more preferably between 100,000 and 500,000 g / mol. Preferably, the water-soluble cationic polyelectrolyte (c) is a polymer consisting of a repetition of monomer units carrying a positively charged group, these groups being, for example, advantageously, quaternary ammonium groups. Thus, the water-soluble cationic polyelectrolyte (c) is advantageously a polymer carrying quaternary ammonium groups or quaternizable amino groups, in particular chosen from polyamines, polyacrylamides, polydadmacs, gums of natural origin carrying quaternary ammonium groups or quaternizable amino groups, polysaccharides carrying quaternary ammonium groups or quaternizable amino groups, and mixtures of these compounds, polyamines, polyacrylamides, polydmacs, and mixtures of these compounds being generally preferred. According to a particularly advantageous mode, the water-soluble cationic polyelectrolyte (c) is a polyamine, preferably a polyamine comprising a chain of units - [- CH ₂ -CHOH-CH ₂ -N ⁺ (-CH3) ₂ -] - (and advantageously essentially consisting of a series of such units). Thus, it can typically be a polymer resulting from the polycondensation of molecules of epichlorohydrin and ethylene diamine. Thus, as particularly interesting polyamines, mention may be made of the polyamines marketed by the company Rhodia under the name of EQUALIS OPALE or LAZULI, or by the company SNF under the name of FL 1840.

Two main embodiments of the invention can be distinguished, depending on the nature of the iron salt used in the composition. Thus, according to a first major embodiment, which is generally the most advantageous, a composition according to the invention comprises, as iron salt

(b), an iron (II) salt. Where appropriate, the salt (b) is preferably ferrous chloride

Feck. According to this first variant, the Fe ²⁺ / Al ³⁺ molar ratio within the mixture of compounds (a), (b) and (c) is preferably between 1% and 10%, this ratio being generally lower or equal to 7%, and preferably remaining greater than or equal to 3%, and advantageously at least 4%. Thus, this ratio is advantageously between 4 and 10%, preferably between 4.5% and 7%, and it is typically of the order of 5.5%. Furthermore, when the salt (b) is an iron salt (II), it is generally preferable for the content of water-soluble cationic polyelectrolyte (c) in the solution of the compounds (a), (b) and (c ) is between 0.5 and 2% by mass of polyelectrolyte relative to the total mass of the solution, this polyelectrolyte content advantageously being greater than or equal to 0.7% by mass, and preferably greater than or equal to 1% en masse. It is moreover preferred that this content remains less than or equal to 1.7% by mass of polyelectrolyte, and preferably less than or equal to 1.5% by mass. Thus, this content can advantageously be between 1 and 2.5% of polyelectrolyte relative to the total mass of the solution.

Thus, when the salt (b) is an iron salt (II), a composition according to the invention is thus advantageously an aqueous solution comprising: - a weakly basic polychloride of aluminum at a rate of 10 to 20% (and preferably at a rate of 15%) by mass relative to the total mass of the composition (percentages expressed in AI2O3 equivalent); - a ferrous salt, preferably a ferrous chloride, in an amount such that the Fe ²⁺ / Al ³⁺ molar ratio within the composition is between 4 and 7 (typically of the order of 5.5), or , in general, at a Fe ²⁺ concentration of 0.1 to 0.25 mol / L (typically 0.118 to 0.237 mol / L) in the solution a water-soluble cationic polyelectrolyte, preferably of the polyamine type, at a content of 1 and 1.5% by mass of polyelectrolyte relative to the total mass of the solution.

The compositions according to the invention comprising an iron salt (II) as an iron salt (b) prove to be particularly advantageous for the treatment of aqueous effluents. In this regard, the work of the inventors has in particular made it possible to demonstrate that this type of composition proves to be particularly effective for the treatment of odors linked to the presence of sulfur compounds such as sulphides. In this context, it has been discovered that a composition according to the invention comprising an iron (II) salt proves to be more advantageous for the treatment of odors than a solution of ferric chloride used at the same concentration.

In addition, the compositions according to the invention comprising an iron salt (II) as the iron salt (b) have many other advantages over the ferric chloride solution. Thus, it is in particular to emphasize that they do not lead to the coloring and corrosivity problems encountered with the iron III salts. In addition, in particular due to the additional presence of compounds (a) and (c), which are good flocculating and / or coagulating agents, the compositions according to the invention have much more marked coagulation properties of suspended matter, than those of iron (III) salt solutions.

According to the other major possible embodiment, a composition according to the invention comprises, as the iron salt (b), an iron salt (III). If appropriate, the salt (b) is preferably ferric chloride FeCb. According to this second embodiment, the molar ratio Fe ³⁺ / Al ³⁺ within the mixture of compounds (a), (b) and (c) is preferably between 0.5% and 1.5%, this ratio preferably being between 0.8% and 1.2%, and it is typically of the order of 1%. Furthermore, when the salt (b) is an iron (III) salt, it is generally preferable for the content of water-soluble cationic polyelectrolyte (c) in the solution of compounds (a), (b) and (c ) is between 0.05 and 0.2% by mass of polyelectrolyte relative to the total mass of the solution, this polyelectrolyte content advantageously being between 0.10 and 0.14% by mass

(typically about 0.12% by mass).

According to another aspect, the present invention relates to a process for the preparation of the compositions defined above. In general, a composition according to the invention can be obtained by implementing a process comprising the steps consisting in:

- mix a solution of weakly basic aluminum polychloride (a) and the water-soluble cationic polyelectrolyte (c), then

- add the iron salt (b) to the mixture of compounds (a) and (c) previously produced. As a general rule, the first stage of mixing of the compounds (a) and (c) is carried out by mixing an aqueous solution of the aluminum polychloride (a) and an aqueous solution of the cationic polyelectrolyte (c), with stirring, preferably with agitation corresponding to an energy delivered in the middle of 300 to 800 W / m ³ , and typically of the order of 600 W / m ² (for example between 500 and 700 W / m ³ ) which can in particular be obtained by carrying out the mixing by means of a paddle stirrer, in particular with a dilaceralcircuited paddle (deflocculator) with a diameter of the order of 0.5 m, at a stirring speed of 400 to 500 revolutions per minute. In the most general case, the first step of mixing the compounds (a) and (c) is advantageously carried out by mixing an aqueous solution of poly aluminum chloride (a) having a content of compound (a) of 10 to 20%. > by mass (expressed in AI2O3 equivalent, and an aqueous solution of cationic polyelectrolyte (c) having a content of compound (c) of 20 to 60% by mass of polyelectrolyte, and typically of the order of 40% by mass. Generally, the mixture of compounds (a) and (c) is carried out by leaving the mixture of the two solutions with stirring for a period of between 10 minutes and 30 minutes, and typically for 20 minutes. In the most general case, the step of adding the iron salt (b) to the mixture of the compounds (a) and (c) is advantageously carried out while maintaining the medium with stirring, and preferably by adding the salt of iron as quickly as possible, namely generally in a period of less than 2 minutes, this addition being preferably carried out in less than a minute, advantageously in less than 40 seconds, and preferably in less than 30 seconds. The iron salt can be added in dry form, or preferably in the form of an aqueous solution. Most often, following the addition of the iron salt (b), the method further comprises a stage of maturing of the medium, consisting in leaving the mixture with stirring, for a period of 5 to 30 minutes, and typically for a period of in the range of 10 to 15 minutes.

With regard more specifically to the preparation of a composition according to the invention comprising an iron salt (II) as salt (b), the preparation process generally comprises the steps consisting in:

- Mixing a solution of weakly basic aluminum polychloride (a) and the water-soluble cationic polyelectrolyte (c), preferably at a temperature between 40 ° C and 70 ° C; then

add the iron salt (b) (II) to the mixture of the compounds (a) and (c) previously produced, the salt being preferably introduced in the form of an aqueous solution, having an iron concentration advantageously between 100 and 200 g / L, and typically between 140 and 180 g / L, this iron (II) salt solution preferably having an initial temperature of between 10 and 30 ° C, for example between 15 and 25 ° C, at the time of its introduction into the mixture of compounds (a) and

(vs)- Thus, when the salt (b) is an iron salt (II), it is preferable that the first step of mixing the compounds (a) and (b) be carried out at a temperature higher than room temperature, so as to obtain , at the end of the mixture, a medium having a temperature advantageously between 40 and 70 ° C, and preferably between 50 and 65 ° C, and even more advantageously between 52 and 62 ° C, into which the solution is then added iron salt at room temperature. According to a conceivable mode, the hot medium of the first mixing step can be obtained by mixing the compounds (a) and (c), then by raising the temperature of the mixture. However, preferably, it turns out to be rather advantageous to carry out the first step by adding a solution of poly aluminum chloride, (a) preheated to a temperature of 40 to 70 ° C (and preferably between 50 and 65 ° C) in a solution of the polyelectrolyte (c) at room temperature (typically 10 to 30 ° C, for example between 15 to 25 ° C).

The process for preparing a composition according to the invention in which the salt (b) is an iron (III) salt preferably comprises the steps consisting in:

- Mixing a solution of the weakly basic aluminum polychloride (a) and the water-soluble cationic polyelectrolyte (c) at a temperature between 10 to 30 ° C, and preferably 15 to 25 ° C; then

- Add the iron salt (b) (III), generally in the form of a solution having an iron concentration between 30 and 150 g / L, to the mixture of the compounds (a) and (c) previously produced.

As previously emphasized, the compositions according to the invention, in particular. compositions based on iron (II) salts are particularly advantageous for the treatment of aqueous effluents, and in particular for the purification of waste water. In this context, the compositions according to the invention can in particular be used to produce coagulation and / or flocculation suspended elements (generally negatively charged) these coagulated or flocculated elements which can then be separated by gravitation and filtration. The compositions according to the invention also prove to be advantageous for carrying out the phosphate removal of effluents rich in phosphate ions, such as for example certain urban waste waters, or else effluents from the food industry, such as waste water from dairies or slaughterhouses. Finally and above all, the compositions according to the invention are particularly useful for eliminating sulfur-containing compounds of the sulphide type responsible for unpleasant odors within an aqueous medium such as effluents from treatment plants. More generally, the compositions according to the invention are particularly useful for limiting or eliminating odors in an aqueous effluent, in particular odors linked to the presence of sulfur derivatives. The compositions according to the invention, based on iron (II) salts are particularly advantageous for this type of anti-odor application. The different aforementioned uses of the compositions previously defined constitute another specific object of the present invention.

Various advantages and characteristics of the invention will emerge even more clearly in the light of the illustrative examples given below.

EXAMPLE 1 Preparation of a Composition Based on a Polyaluminum Chloride / FeCl Polyamine Mixture 95.1 ml (or 108.42 g) of a 41% by weight polyamine solution were introduced into a mixer. polyamine. The polyamine used is the EQUALIS OPALE polyamine marketed by RHODIA, which is a polyamine with an average molecular weight equal to 400,000 g / mol. The introduction of the polyamine solution into the mixer was carried out at room temperature (20 ° C). Then added to the mixer 2.651 liters (or 3613.9 g) of a poly aluminum chloride solution having a poly alumium chloride content of 16.3% by mass expressed in AI2O3 equivalent, and a basicity of 37 , 7% (this basicity corresponds to the molar ratio expressed as a percentage of the number of groups (OH) divided by 3 times the number of aluminum atoms, as defined previously in the description). The aluminum polychloride used is AQUARHONE 18 sold by the company RHODIA. Before its introduction into the mixer, the polychloride solution was brought to a temperature of 57 ° C.

Following the introduction of poly aluminum chloride at 57 ° C, agitation was started, with a power transmitted per unit volume of 614 W / m ³ (which corresponds to an agitation speed of 800 revolutions / minute in the mixer used). The system was allowed to evolve in an external medium at room temperature (20 ° C), with stirring, and without temperature control, for 18 minutes. We then introduced into the mixer, over a period of 30 seconds,

208 mL (i.e. 277.7 g) of a ferrous chloride (FeCk) solution, previously filtered, with a total iron content of 173 g / L including an iron (II) content of 171 g / L. Following this addition, the medium was thus left to mature, with stirring for a period of 13 minutes.

There was thus obtained, by emptying the mixer, 4 kg of a composition denoted (Cl).

EXAMPLE 2 preparation of a composition based on a polychloride of aluminum / FeCl2 / polyamine mixture In a mixer, 4.75 L (or 5.42 kg) of a 41% by weight polyamine solution were introduced polyamine. The polyamine used is the same as in Example 1. The introduction of the polyamine solution into the mixer was carried out at room temperature (20 ° C). Then added to the mixer 133 liters (or 180.7 kg) of a poly aluminum chloride solution having a poly aluminum chloride content of 16.3% by mass expressed in Al ₂ θ3 equivalent, and a basicity 37.7% (molar ratio of the number of groups (OH) divided by 3 times the number of aluminum atoms). The poly aluminum chloride used is the same as in Example 1. Prior to its introduction into the mixer, the poly aluminum chloride solution was brought to a temperature of 58 ° C.

Following the introduction of poly aluminum chloride at 58 ° C, agitation was started, with a power transmitted per unit volume of 241

W / m ³ , which corresponds to a stirring speed of 393 revolutions / minute in the mixer used. The system was allowed to evolve at room temperature (20 ° C), with stirring and without temperature control, for 20 minutes. Was then introduced into the mixer, over a period of 50 seconds, 10L (or 13.8 kg) of a ferrous chloride solution (FeCl ₂ ), previously filtered, having a total iron content of 173 g / L, including an iron (II) content of 171 g / L. Following this addition, the medium was left to mature with stirring, for a period of 11 minutes. 200 kg of a noted composition were obtained by emptying the mixer

(C2).

EXAMPLE 3 Preparation of a Composition Based on a Polyaluminum chloride / FeCl- / pplyamine Mixture

2.63 mL (or 3.0 g) of a 41% by weight polyamine polyamine solution was introduced into a mixer. The polyamine used is the same as in Example 1. The introduction of the polyamine solution into the mixer was carried out at room temperature (20 ° C).

Then added to the mixer 67.2 mL (or 93.4 g) of a poly aluminum chloride solution having a poly aluminum chloride content of 16.3% by mass expressed in Al ₂ θ3 equivalent, and a basicity of 37.7% (molar ratio of the number of groups (OH) divided by 3 times the number of aluminum atoms). The poly aluminum chloride used is the same as in Example 1. Prior to its introduction into the mixer, the poly aluminum chloride solution was brought to a temperature of 58 ° C.

Following the introduction of poly aluminum chloride at 58 ° C., agitation was started, with a power transmitted per unit volume of 600 W / m ³ , which corresponds to an agitation speed of 240 revolutions / minute in the mixer used. The system was allowed to evolve at room temperature (20 ° C), with stirring and without temperature control, for 20 minutes.

Was then introduced into the mixer, over a period of 5 seconds, 3.6 g of a ferrous chloride powder (76% FeCh powder). Following this addition, the medium was left to mature with stirring, for a period of 11 minutes.

100 g of a composition denoted (C3) were obtained by draining the mixer. EXAMPLE 4 Preparation of a Composition Based on a Polyunnurnum Chloride / FeCl- / Polyamine Mixture 2.63 mL (or 3.0 g) of a 41% polyamine solution was introduced into a mixer. - polyamine mass. The polyamine used is the AQUALIS OPALE of Example 1. The introduction of the polyamine solution into the mixer was carried out at room temperature (20 ° C). 68.9 mL (i.e. 95.7 g) of a poly aluminum chloride solution having a poly aluminum chloride content of 16.3% by mass, expressed as equivalent Al ₂ θ3, and a basicity of 37.7% (this basicity corresponds to the molar ratio expressed as a percentage of the number of groups (OH) divided by 3 times the number of aluminum atoms, as defined previously in the description ). The aluminum polychloride used is Aquarhone 18 sold by the company RHODIA. The aluminum polychloride solution was introduced at a temperature of 20 ° C. Following the introduction of the aluminum polychloride, stirring was started, with a power transmitted per unit volume of 600 W / m ³ which corresponds to a stirring speed of 240 revolutions / minute in the mixer used. The system was allowed to evolve at room temperature (20 ° C) for 10 minutes. Was then introduced into the mixer, over a period of 30 seconds, 0.95 ml (or 1.3 g) of a ferric chloride solution (FeCk) (previously filtered) having a FeCl3 content of 41% and a iron (III) content of 141.3 g / L. Following this addition, the medium was left to mature with stirring for a period of 10 minutes. There was thus obtained, by draining the mixer, 100 g of a composition denoted (C4). EXAMPLE 5 stability of compositions C1, C2, C3, C4.

Each of compositions C1, C2, C3 and C4 was subjected to an accelerated aging test simulating storage of the composition for four months at room temperature. This test consisted in subjecting each of the samples to five successive temperature cycles, each consisting in leaving the composition for 24 hours at 4 ° C., then for 24 hours at 45 ° C.

For each of the compositions tested, no deposit of precipitate was observed at the end of the aging tests carried out.

EXAMPLE 6 treatment of aqueous effluents with compositions Cl, C2, C3 and C4

In order to evaluate the effectiveness of compositions C1, C2, C3 and C4 for the treatment of waste water, these compositions were used to treat an aqueous composition containing suspended matter (inducing an initial turbidity of the composition of 307 NTU ), organic matter (corresponding to an initial COD of the composition of 728 mg / L), phosphates (at the rate of an initial content of 75 mg / L) and sulphides (at the rate of an initial content 2, 5 mg / L).

In each of the tests carried out, variable amounts of the various compositions C1, C2, C3 or C4 were added to 1000 ml of the aqueous medium tested. The results obtained (produced at the end of the synthesis and after 4 months of storage at room temperature) with the different amounts of compositions C1, C2 and C3, are reported in Table 1 below. Some tests were carried out with freshly prepared solutions, others with solutions stored for a few months. The storage time (t) is indicated in brackets (t = 0: freshly prepared solution) TABLE 1: treatment of a standard waste water by compositions (Cl), (C2), (C3) and (C4)

The above results clearly demonstrate the effectiveness of the compositions according to the invention. It also appears from the above examples that this efficiency remains unchanged even after a long storage period.

Other tests were used to produce compositions under the conditions of Examples 1 to 4, but using as polyamine the polyamine marketed by the company S.N.F instead of the Equalis Opale polyamine marketed by RHODIA. These tests led to obtaining results similar to the results set out above. Furthermore, tests carried out with solutions stored for periods longer than 4 months show that the compositions of the invention retain their effectiveness over long periods of time, generally at least for 6 months, and most often for 9 months. , see more.

Claims

1. Composition comprising, in solution, a mixture of:

(a) at least one weakly basic polychloride of aluminum; and

(b) at least one iron salt, the solution comprising the mixture of compounds (a) and (b) additionally containing:

(c) at least one water-soluble cationic polyelectrolyte, ensuring a role of stabilizing agent inhibiting gelling and precipitation phenomena.

2. Composition according to claim 1, characterized in that it is in the form of an aqueous solution of compounds (a), (b) and (c).

3. Composition according to claim 1 or according to claim 2, characterized in that the solution comprising the compounds (a), (b) and (c) has a viscosity less than or equal to 500 cp at 20 ° C.

4. Composition according to any one of the preceding claims, characterized in that the solution comprising the compounds (a) and (b) is such that after four months of storage, more than 95% by mass, preferably more than 99%, of the compounds (a) and (b) remain in solution, and in that said solution additionally retains a viscosity less than or equal to 150 cp at 20 ° C, and preferably less than or equal to 100 cp at 20 ° vs.

5. Composition according to any one of the preceding claims, characterized in that the weakly basic polychloride of aluminum (a) is a compound corresponding to the formula of formula (I) below: - [Aln (OH) _m Cl _3n . m-2k (Sθ4) k] [H ₂ 0] z (I), in which: n, m, are positive numbers; k is a positive or zero number between 0 and 0.4n, k being preferably zero; (3n-m-2k) denotes a positive number; and z is a positive integer at least equal to 1, and where the ratio (m / 3n) xl00 is less than or equal to 60%.

6. Composition according to claim 5, characterized in that the ratio (m / 3n) xl00 is between 10 and 50%, and preferably between 15 and 45%.

7. Composition according to claim 5 or according to claim 6, characterized in that the solution comprising the mixture of the compounds (a), (b) and (c) with a poly aluminum chloride content of between 5 and 22% by mass, expressed in Al ₂ θ3 equivalent.

8. Composition according to any one of the preceding claims, characterized in that the iron salt (b) is an iron (II) or iron (III) salt, preferably chosen from an iron (II) chloride or iron (III), iron (II) or iron (III) sulfate, iron (III) chlorosulfate, or a mixture of these compounds.

9. Composition according to any one of the preceding claims, characterized in that the cationic polyelectrolyte (c) is a polymer having a molecular mass of less than 1,000,000 g / mol.

10. Composition according to any one of the preceding claims, characterized in that the cationic polyelectrolyte (c) is a polymer carrying quaternary ammonium groups or quaternizable amino groups, chosen from polyamines, polyacrylamides, polydmacs, and mixtures of these compounds.

11. Composition according to claim 10, characterized in that the water-soluble cationic polyelectrolyte (c) is a polyamine.

12. Composition according to any one of the preceding claims, characterized in that it comprises an iron salt (II), preferably FeCl ₂ , as the iron salt (b).

13. Composition according to claim 12, characterized in that the molar ratio Fe ²⁺ / Al ³⁺ within the mixture of the compounds (a), (b) and (c) is between 1 and 10%, and preferably between 3 and 7%.

14. Composition according to claim 12 or according to claim 13, characterized in that the content of cationic polyelectrolyte (c) in the solution of compounds (a), (b) and (c) is between 0.5 and 2% by mass of polyelectrolyte relative to the total mass of the solution.

15. Composition according to any one of claims 1 to 11, characterized - in this comprises an iron salt (III), preferably FeCb, as the iron salt (b).

16. Composition according to Claim 15, characterized in that the molar ratio Fe ³⁺ / Al ³⁺ within the mixture of the compounds (a), (b) and (c) is between 0.5 and 1.5% .

17. Composition according to claim 15 or according to claim 16, characterized in that the content of cationic polyelectrolyte (c) in the solution of compounds (a), (b) and (c) is between 0.05 and 0.2% by mass of polyelectrolyte relative to the total mass of the solution.

18. A method of preparing a composition according to any one of the preceding claims, characterized in that it comprises the steps consisting in: - mixing a solution of the weakly basic polychloride of aluminum (a) and of the water-soluble cationic polyelectrolyte (c); then - add the iron salt (b) to the mixture of compounds (a) and (c) previously produced.

19. A method of preparing a composition according to any one of claims 12 to 14, characterized in that it comprises the steps consisting in: - carrying out a mixing of a solution of the weakly basic polychloride of aluminum (a) and water-soluble cationic polyelectrolyte (c), at a temperature between 40 ° C and 70 ° C; then - add the iron salt (b) (II) to the mixture of the compounds (a) and (c) previously produced, in the form of an aqueous solution having an initial temperature between 10 to 30 ° C, at the time of its introduction into the mixture.

20. A method of preparing a composition according to any one of claims 15 to 17, characterized in that it comprises the steps consisting in:

- Mixing a solution of the weakly basic aluminum polychloride (a) and the water-soluble cationic polyelectrolyte (c), at a temperature between 10 to 30 ° C; then

- add the iron salt (b) (III) to the mixture of compounds (a) and (c) previously produced.

21. Process according to any one of claims 18 to 20, in which the addition of the iron salt (b) to the mixture of the compounds (a) and (b) is carried out in a period of less than 2 minutes, and preferably in less than a minute.

22. Method according to any one of claims 18 to 21, comprising, following the addition of the iron salt (b) in the mixture of compounds (a) and (b), a ripening step, consisting in leaving the mixture with stirring, for a period of 5 to 30 minutes.

23. Use of a composition according to any one of claims 1 to 18, for the treatment of an aqueous effluent, in particular for purifying waste water.

24. Use according to claim 23, characterized in that the composition is used to limit or eliminate odors in an aqueous effluent, in particular odors linked to the presence of sulfur derivatives.

25. Use according to claim 24, in which the composition used is a composition according to any one of claims 12 to 14.