EP2013145A1

EP2013145A1 - Method of extracting organic and metallic pollutants.

Info

Publication number: EP2013145A1
Application number: EP07728239A
Authority: EP
Inventors: Jean Paul Canselier; Christophe Gourdon; Lindemberg De Jesus Nogueira Duarte; Edouardo Lins Barros Neto; Boumediene Haddou; Catherine Gumila
Original assignee: Institut National Polytechnique de Toulouse INPT
Current assignee: Institut National Polytechnique de Toulouse INPT
Priority date: 2006-04-21
Filing date: 2007-04-18
Publication date: 2009-01-14
Also published as: WO2007122158A1; FR2900145B1; FR2900145A1

Abstract

The present invention relates to a method of treating aqueous effluents that employs an organic-solventless liquid/liquid extraction which allows the organic and metallic pollutants to be extracted by virtue of their solubilization in mixed micelles. These mixed micelles, which are formed of ionic surfactants, are capable of simultaneous extraction of the organic and metallic pollutants. The method according to the invention is simple, quick to implement and economic in terms of energy. The reduction in polluted volumes without production of new pollution is also a very advantageous result. The method makes it possible, moreover, to regenerate the surfactants for subsequent use, and also to recover the compounds extracted, which can be stored directly as ultimate waste or utilized for other purposes. The method may also be carried out as a continuous procedure, on the same site at which the effluents are produced.

Description

PROCESS FOR EXTRACTING ORGANIC POLLUTANTS

AND METALLIC.

The present invention relates to the field of the treatment of polluted waters loaded with organic and metal compounds, based on phase separation extraction techniques.

It relates to an aqueous effluent treatment process, using a liquid / liquid extraction without organic solvent, for extracting organic and metal compounds through their solubilization in mixed micelles.

Industrial activities generate various types of pollution that can create significant environmental nuisances. Water is a subject of particular attention since it is involved in the production chains of the majority of industrial activities, which generates significant quantities of effluents, a portion of which is released into the surrounding environment after having contributed to the production , cleaning, transport or cooling in different processes. Increasingly stringent regulation has been adopted over the years, which forces manufacturers to control their daily discharges, but also to treat the waste generated on the production site to the stage of ultimate waste. It has, moreover, been found that it may be economically advantageous to recover certain compounds present in the effluents, whether or not they are considered as waste and / or of a nature that is harmful to the environment.

Hazardous pollutants are those with the characteristics of toxicity, bioaccumulation and persistence. These are mainly organic pollutants and heavy metals.

Organic pollution, resulting from natural biological reactions and agricultural, industrial or domestic activities, is characterized by its insidious appearance and complexity. It is generally in dissolved form, can be more or less biodegradable, and has a great diversity, including phenolic derivatives especially from the chemical and pharmaceutical industries, pesticides and related products such as plasticizers, lubricants, hydraulic fluids, etc. or the hydroxyl and amine compounds which are widely used in the manufacture of varnishes, paints, inks, or in the perfume and aroma industry. Toxic phenomena induced are extremely variable from one substance to another and are related to the stability of the product, its ability to accumulate, etc.

Metallic pollutants, often called "heavy metals", or more frequently now "trace elements", are in turn present in water in the form of electrolytes. They are well targeted by regulation: they are essentially mercury, cadmium, lead, silver, copper, chromium, nickel and zinc, coming from the rejections of various industrial activities, such as surface, electroplating, hydro metallurgy, mining, chemical, petrochemical, pharmaceutical, etc. They are particularly harmful because they are not biodegradable and accumulate in the tissues as one moves up the food chain. Their toxic effects may include the nervous system, blood or bone marrow, and they are usually carcinogenic.

For the treatment of organic pollutants, there are at present a number of techniques such as physico-chemical treatments of flocculation-decantation-flotation type, adsorption on activated carbon, as well as oxidative techniques and electrochemical processes. . All these techniques have disadvantages. They are often expensive in energy, require the use of expensive reagents whose recycling raises difficulties in turn, these problems being amplified by the fact that many industrial processes generate large amounts of waste water.

Other techniques are based on the principle of liquid / liquid extraction using a solvent. They are more and more used in place of precipitation and filtration techniques, especially for the recovery of organic acids from aqueous effluents. They have the advantage of being applied to the separation of organic compounds, often unstable or thermosensitive. They do not require significant energy input and have the merit of being inexpensive. However, if at the end of the treatment, the effiuent is rid of polluting organic compounds, the problem of removing the solvent remains intact. Indeed organic solvents are also considered as pollutants, because they are mostly flammable and / or toxic. National and European regulations now make it necessary to limit their use on a large scale. However, extraction with organic solvent leads to a significant dilution factor, producing waste volumes whose reprocessing leads to high costs.

More recently, an alternative method has been proposed allowing the separation and concentration of organic pollutants from aqueous industrial discharges, through the use of nonionic surfactants. This method takes advantage of the properties association of surfactants aggregates (or micelles) that trap substances poorly soluble in the medium and increase their apparent solubility (solubilization), and secondly the ability of nonionic surfactants to form two distinct phases above a certain temperature, called "cloud point". One of the phases has a concentration of surfactant close to the Critical Micellar Concentration (this is the diluted phase), while the other phase has a much higher concentration (it is the coacervate) and plays the role of an extraction solvent. The increase of the temperature above the cloud point of the solution therefore allows the concentration in the coacervate of a hydrophobic or amphiphilic substance solubilized by the surfactant. The two-phase separation - the concentrated extract and the raffinate - is carried out by decantation.

The principle of extraction of organic compounds by coacervate is well known. This technique is for example one of the steps of separation of dissolved organic compounds implemented in US Patent 4,948,512. Laboratory work has established the concentration / temperature equilibrium diagrams of various ternary water / organic compound / nonionic surfactant mixtures (demixing curves). Indeed, it is known that the cloud temperature of such mixtures varies depending on the nature of the nonionic surfactant, its concentration, but also other physicochemical characteristics of the mixture, including the nature of the organic compound to be extracted.

Heavy metals can be removed from aqueous effluents by coagulation, sand filtration, activated carbon or ion exchange, electrodialysis, or reverse osmosis techniques. At present, the most widely used method for the treatment of heavy metal effiuents is, as for organic pollutants, liquid / liquid separation using a solvent. However, most often, the solvent must be accompanied by a complexing agent of the metal to be extracted, which increases the cost. Of course, as for the extraction of organic, the problem arises of the subsequent evolution of the solvent and the complexing agent, their recycling or their elimination.

In some cases, the extraction of the metals is carried out using a nonionic surfactant by phase separation at cloud point. Nevertheless, the solubilization of the metals in the surfactant micelles can only be done with the aid of lipophilic complexing agents (such as Lix®, Kelex®) whose price is extremely high and which are rarely recyclable. This explains that this technique is mainly used for the recovery of uranium and plutonium in the waters of the nuclear industry. It is obviously impossible to apply it to the treatment of large volumes of effluents produced by more ordinary industrial activities. The present invention provides a solution to this problem by providing a simple and inexpensive aqueous effluent treatment process, using a liquid / liquid extraction without organic solvent metal pollutants, through their solubilization in mixed micelles consisting of surfactants associated nonionic and ionic

These mixed micelles formed of two types of surfactants are used for the first time in an industrial application of extraction of metal pollutants. They fulfill several functions related to the combined properties of nonionic and ionic surfactants.

First of all, it is known that the surfactant molecules are capable of self-associating into aggregates (among which micelles), in which molecules of variable polarity interacting with the hydrophilic or hydrophobic solubilization sites of said aggregates can be trapped. .

On the other hand, it is known that nonionic surfactants have the property of causing separation of their aqueous solutions in two phases, one of reduced volume fraction containing most of the nonionic surfactant in the form of micellar aggregates ( concentrated phase or coacervate), and the other diluted in surfactant relative to the initial solution. This phenomenon however occurs under certain conditions of surfactant concentration and temperature, the medium may also play a role. So called "cloud temperature" or "cloud point", the temperature above which the phase separation is carried out. The ternary system consisting of a solute dissolved in water in the presence of a nonionic surfactant at equilibrium can be characterized by a temperature / concentration phase diagram. The diagram of a given system has a demixing curve indicating for each composition, the corresponding cloud temperature Tc.

When nonionic and ionic surfactants coexist in a medium, these two species can interact, this interaction being reflected in most cases by a specific association and the formation of these original structures that are mixed micelles (K. Ogino and M. Abe, 1993, Surf Sci. Series, Volume 46, Marcel Dekker, New York).

Mixed micelles appeared to have excellent electrolyte extraction capabilities in solution, the ionic surfactant acting as a complexing agent for metal ions. If it appeared possible to remove the metallic pollutants from the aqueous effluents using mixed micelles, the various tests carried out have also shown quite surprisingly, that can be extracted by the method according to the invention, concomitantly, the metallic and organic pollutants of the aqueous effluents. In particular it has been found that the presence of ionic surfactant molecules in the mixed micelles does not alter their properties vis-à-vis organic compounds. Thus, not only do the mixed micelles exhibit excellent electrolyte extraction capabilities of the solution, but they are as effective as the nonionic micelles alone for the simultaneous extraction of organic compounds.

No technique has so far made it possible to achieve such a result despite recent developments in liquid / liquid solvent extraction. The work carried out has sought to improve the effectiveness of the treatments with respect to one or the other without ever proposing a technique capable of eliminating by a single treatment both the organic compounds and the metal ions. It was therefore necessary to treat the effluents in several stages, each addressing a different family of pollutants, which represents high cumulative costs, especially since the pollutants are numerous and the volumes of water to be treated often enormous. .

It is therefore a particularly advantageous characteristic of the process according to the invention to provide the possibility of simultaneously extracting organic and metallic pollutants by simultaneous solubilization in mixed micelles.

The subject of the invention is thus a method for treating aqueous effluents using a liquid / liquid extraction without organic solvent, for extracting the metal pollutants alone or simultaneously with the organic pollutants, thanks to their solubilization in mixed micelles consisting of associated nonionic and ionic surfactants. This extraction makes it possible to eliminate the two pollutants at the same time, if they are present together in the effluent. Of course, it can also be used if one of the pollutants (singularly a metallic pollutant) is only present in the effluent.

The method according to the invention has multiple technical advantages and meets a number of current regulatory and economic constraints. Industrialists concerned by the problem of the elimination of toxic discharges will now have a suitable, efficient and economical technique, applicable on a large scale to the depollution of their aqueous effluents, and allowing them to respect all the regulatory texts of more in more strict. The process according to the invention is applicable to aqueous mixtures containing very diverse pollutants. It is thus adapted to the treatment of waste water from various industrial activities, consisting of homogeneous aqueous fluids or loaded with droplets of immiscible liquid and / or solid material. It can therefore be used to treat dispersed pollutants and soluble pollutants present in complex mixtures of contaminants.

It is simple and quick to implement, extraction and concentration being performed simultaneously. It is a virtually instantaneous process when it is performed at a given temperature. The temperature remains generally below 50 ⁰ C during the entire operation, so little energy is consumed.

The reduction of polluted volumes without producing a new pollution is a very interesting result of the claimed process. The water consumption is in fact minimal or even zero, and the final volume is not significantly increased. Purified water also represents a high fraction of the final volume, while a small fraction concentrated in pollutants remains to be reprocessed. Since only surfactant compounds are added, there is no problem of solvent reprocessing. The diversity of existing surfactants makes it possible to choose the least toxic and preferably also biodegradable.

Another advantage of the process according to the invention is that, in certain cases (when the pollutant has an acidic or basic character), the surfactants can be regenerated for later use from the coacervates (low volumes, concentrated in pollutants), but also to be able to recover extracted compounds that can be directly stored as ultimate waste, or better, recovered in other uses if the objective is their reuse.

Finally, a decisive advantage of the process according to the invention is that it is possible to achieve it in a continuous process, at the production site itself, which avoids having to transport the effluents. It does not require heavy equipment and easily adapts to the particular conditions that may vary from one industrial site to another. In particular, the nonionic surfactant may be chosen as a function of the initial temperature of the effluent to be treated, so that no heating is required to reach the minimum temperature required for phase separation.

More specifically, the subject of the present invention is a method for treating an aqueous effluent containing metal pollutants alone or in combination with organic pollutants, essentially comprising the steps of: a) - preparing a solution consisting of an ionic surfactant and at least one nonionic surfactant, b) - contacting the effluent with said solution, c) - stirring the mixture, and if necessary heating to a temperature greater than minus 1 ° C at the cloud point of said mixture, d) - decant until separation into two aqueous phases, one being the concentrated phase of metal pollutants and possibly organic pollutants, and the other being the dilute phase, e) - recover the two phases separately.

When the effluent is relatively cold, it may be that the mixture obtained in b) has a temperature below the cloud temperature, in which case a homogeneous mixture is obtained, which must be heated during step c) to reach the cloud point and cause phase separation.

According to a preferred characteristic of the invention, the mixture obtained in step b) has a temperature at least greater than 10 ^° C. above the cloud temperature of said mixture. Indeed, in this case no heat input is necessary to reach a temperature slightly above the cloud point of the mixture, the latter then dividing spontaneously into two phases. This advantageous situation is encountered when the industrial processes lead to the discharge of rather hot effluents (that is, when the cloud temperature of the mixture is lower than the temperature of the effluent), since it is the temperature of the effluent which contributes mainly to the temperature of the mixture. Indeed, as will be explained in detail below, the effluent volume is generally much greater than the volume of surfactant solution entering the mixture.

One way of obtaining an effluent / surfactant solution mixture at a temperature above the cloud point, even when the effluent to be treated is relatively cold, is to choose a nonionic surfactant having a fairly weak cloud point, which is that is several degrees Celsius lower than the temperature of the effluent. In this way, it gives the mixture a cloud temperature lower than the working temperature after mixing, avoiding here also having to heat it. In general, the addition of the ionic surfactant increasing the cloud point, the choice of the nonionic surfactant giving the mixture the lowest possible cloud temperature will allow to have an operating temperature for the extraction without having to heat.

The cloud point value measured under standard conditions (pure 1% compound in water) is available for many known surfactants. However, because of the presence of the solute to be extracted and the ionic surfactant, the cloud temperature of the nonionic surfactant mixed with an industrial effluent can be clearly different from its standard value. Also, the choice of the nonionic surfactant must take into account this shift towards generally higher temperatures. The inventors have established that the difference ΔTc between these two values is most often less than 5 ° C, and can go up to 10 ⁰ C under certain particular conditions. This observation makes it possible to quickly define the specific conditions for carrying out the process according to the invention for a given effluent.

Thus, in the process according to the invention, the nonionic surfactant may advantageously be chosen from compounds having a cloud point, measured as a 1% solution in water, which is at least 5 ° C., preferably less than 5 ° C. at least 10 ⁰ C, at the initial temperature of the effluent.

According to a particular mode of implementation of the method according to the invention, the nonionic surfactant is chosen as a function of the initial temperature of the effluent, among the compounds conferring on the mixture obtained in step b) a lower cloud temperature at least 1 ° C at the temperature of said mixture.

Indeed, when it is desired to further specify the optimum conditions of the process, for example choose surfactants (ionic and nonionic) giving a maximum extraction rate and have a cloud point of the mixture with the effluent that allows the setting In the process without heat input, it may be interesting to refer not to the cloud point of the surfactant under standard conditions, but to rely on the actual values of the cloud point of the effluent / solution mixture of surfactants obtained with solution of surfactants of given composition and an effluent of given composition and temperature.

In this case, before carrying out the process according to the invention, it is necessary to carry out tests on samples, in order to determine the actual cloud temperature Tc (m) of an effluent / solution mixture of surfactants. The initial temperature T (e) of the effluent being known, it is also possible to determine the temperature T (m) of the mixture. The nonionic surfactant is then chosen so that under the conditions selected, the cloud point Tc (m) of the mixture is lower than the temperature T (m), even if only one degree Celsius.

In practice, the cloud point of the effluent to be treated / surfactant solution mixture is determined on test mixtures of the effluent and surfactant solutions. Then The values obtained are compared with those of a model equilibrium diagram, established from ternary mixtures of water / pollutant / surfactant. It is of course advantageous to have a data bank comprising the phase diagrams of many ternary water / pollutant / surfactant mixtures. These diagrams, when they are not available, can be made by measurement on some ternary mixtures.

At this stage a remark must be made concerning the possibility of using two (or more) nonionic surfactants in the solution of surfactants (also including the ionic surfactant). If it is decided to use two nonionic surfactants, each of them is chosen as indicated in the present description. In general, the present description of the process according to the invention is written for a single nonionic surfactant. It is expressly stated, however, that the invention also relates to the case where two nonionic surfactants are used in the surfactant solution, the preferred characteristics applying to the mixture of the two compounds, knowing that the cloud temperature of a mixture of surfactants Nonionic varies linearly depending on its composition.

The nonionic surfactant is a compound having one or, preferably, several unfilled functional groups containing heteroatoms such as nitrogen or oxygen, for example alcohol, ether, ester, amide groups. There may be mentioned in particular polyethers in alkoxylated surfactants and polyols in surfactants derived from sugars.

According to one characteristic of the invention, the nonionic surfactant is advantageously chosen from polyethoxylated compounds having a hydrocarbon chain of length

C ₁₀ to C ₁₆ , preferably from polyethoxylated alcohols, pure or in mixtures. A number of carbon atoms between 10 and 16 leads to good properties of detergency, adsorption, wetting and solubilization. When a mixture of polyethoxylated alcohols is used, the structural variations of the different alcohols in this mixture play either on the length of the hydrophobic chain, on its degree of branching, or on the degree of ethoxylation of the mixture. hydrophilic part. In general, commercial surfactants, non-specific synthetic products, are almost always mixtures of compounds: the hydrophobic parts are most often hydrocarbon chains of different lengths. In the case of polyethoxylated surfactants, the hydrophilic parts have a variable number of ethylene oxide units distributed in a Gaussian or lognormal distribution. Formula of a linear polyethoxylated pure alcohol: n-CiH _{21 + 1} (OCH ₂ CH ₂ ) _j OH, abbreviated n-QE ,, with according to the invention 10 <i <16 and 3 <j <10.

According to a particular embodiment of the process according to the invention, the nonionic surfactant is an ethoxylated alcohol obtained by fixing the ethylene oxide on a fatty alcohol or oxo in the presence of an alkaline catalyst. It is preferably freed of the residual polyols by washing. An oxo alcohol is obtained by the process of the same name allowing the hydroformylation of olefins. It provides a mixture of linear and branched alcohols.

Ethylene oxide reacts with the various alcohols, without it being possible to obtain a very precise, pure molecule. Hydrophilic parts consisting of mixtures with a normal log distribution of the number of ethoxy units, designated by the formula of the middle alcohol, are finally obtained.

Formula of a polyethoxylated alcohol oxo: OXO-C ₁ H _{21 + I} (OCH ₂ CH ₂ ) _J OH, abbreviated to OXO-C ₁ E _j , with according to the invention 10 <i <16 and 3 <j <10 .

It will be noted with interest that the preferred surfactants, especially polyethoxylated alcohols, are those of lower toxicity, especially since their concentration at the end of the extraction is very low (around the CMC, less than 100 ppm). They are indeed at the same time efficient in small dose and biodegradable, they do not induce carcinogenic, mutagenic or teratogenic effect (Ho Tan Ho Tan, 1999, Dunod, Paris). In addition they are also cheap.

In addition to the nonionic surfactant, the surfactant solution used in the present process also includes an ionic surfactant. The latter, used alone, plays no direct role in the phase separation process, but in a mixture, it participates in the micellar structure, inserting itself between the molecules of the nonionic surfactant, so that the metal ions are attracted enough to be fixed and concentrated in the coacervate. Its presence also induces a change in the cloud point of the mixture. It must be emphasized that such micelles, known as "mixed micelles" have never been used for the extraction of dissolved metals in effluents.

It may be noted in this regard that the present process can very well be implemented for the depollution of media containing only metal pollutants. In this case, the ionic surfactants act as complexing agents for the metal ions, whereas the nonionic surfactants make it possible to obtain two phases.

In the process according to the invention, the ionic surfactant may be an anionic surfactant. It is then preferably chosen from alkylbenzenesulphonates and alkane sulphonates. alpha-olefin sulphonates, petroleum sulphonates, or alkyl sulphates. Advantageously, the ionic surfactant is sodium dodecyl sulphate of formula C12H25OSO3 ^" Na ⁺ , or sodium dodecylbenzenesulphonate, a mixture containing, for example, the species of formula CgHi ₉ -CH (C ₂ H ₅ ) -C eH ₄ SO ₃ ^" Na ⁺ . The use of an anionic surfactant will lead to the formation of negatively charged mixed micellar structures which will complex the metal cations by electrostatic interactions.

Alternatively, the ionic surfactant used in the process according to the invention may be a cationic surfactant. It is then preferably chosen from alkyltrimethylammonium halides, benzethonium halides and cationic derivatives of nitrogenous heterocycles. Advantageously, the cationic surfactant is hexadecyltrimethylammonium bromide of the empirical formula CH ₃ (CH ₂₎ _IS N ⁺ (CH _S) ₃ Br. ^"The use of a cationic surfactant will lead to the formation of mixed micellar structures positively charged which will complex the metal anions by electrostatic interactions.

Both types of surfactants (ionic and nonionic) are used together, in solution in water or even pure. It is therefore a mixed solution of nonionic surfactant / ionic surfactant which is introduced into the effluent. The surfactants constitute mixed micelles, the ionic molecules being inserted into the nonionic micellar structure. For micelles to form, the concentration of nonionic and ionic surfactants must be greater than the Critical Micellar Concentration (CMC) of the mixture. On the other hand a certain proportion of ionic surfactant relative to the nonionic surfactant will allow the optimal formation of mixed micelles.

This is why, preferably, the two types of surfactants must be in concentrations such that the solution of surfactants gives to the mixture, in mass per unit volume of the mixture:

from 1% to 10%, preferably from 2% to 5%, of nonionic surfactant, and from 0.1% to 1%, preferably from 0.4% to 0.6%, of ionic surfactant.

More preferably, the nonionic surfactant NI and the ionic surfactant I are in an NI / I mass ratio of between 2 and 12.

As already indicated, an advantage of the process according to the invention lies in the minimal increase of the liquid volumes. According to a preferred embodiment, the effluent E and the solution of surfactants S are mixed in a ratio by volume S / E as low as possible, generally between 0.01 and 0.1. According to a particular embodiment of the process according to the invention, steps a) to e) are repeated at least once to treat the diluted phase recovered in step e). Since the distribution of pollutants is based on the same distribution coefficient during each cycle, we obtain raffinates that are increasingly diluted in pollutants. It is therefore possible to take up the dilute phase (the raffinate) until a satisfactory reduction of the pollutants. Knowing the pollutant content in the effluent and the rate of extraction by the chosen system during each cycle, we can predict the number of treatment cycles to be performed to lower the concentration of a given pollutant below a given pollutant. certain value, for example that of the legal standard.

According to another particular embodiment of the method, when repeating step a), a solution of different surfactants is used. Indeed, it may be interesting to treat the effluent by different surfactants, having a different affinity for the various polluting substances. This is obviously the case for anions and metal cations, which can be extracted in successive cycles of treatment, thanks to the use of cationic and anionic surfactants, respectively.

Whether the raffinate obtained in step e) is reprocessed or not, it is possible, in certain cases, to recycle the concentrated surfactants in the coacervate, which makes it possible in particular to make the extraction process according to the invention profitable, economically but also ecologically. Indeed, when the pollutant has an acidic or basic character, a method has been developed consisting of the addition of an acid / base pair, which makes it possible to dissociate the pollutant from the coacervate, and then to regenerate the non-surfactant. ionic surfactant (the ionic surfactant remains complexed with the extracted metal). This recycling has the double advantage of ensuring a more thorough depollution and to allow the recycling of useful compounds. The term "pollutant" will therefore designate here as well compounds for which the effluent must be disposed of for ecological reasons, as compounds that it is desired to recover in order to enhance them, the two purposes being sometimes confused.

In a first step, the surfactants and the pollutant compounds of the concentrated phase obtained in step e) are separated by acid-base de-extraction according to the following procedure. The weak acidic pollutant (or weak base) is displaced by the addition of a strong base (or a strong acid). The dissociated species no longer interact with the micelle, the complex with the surfactant breaks and the pollutant dissolves preferentially in the water. After passing at a temperature above the cloud point of the medium, two phases are formed, one containing the concentrated surfactant, the other containing the pollutant (as well as diluted surfactant). The pollutant can then be either destroyed or recovered. In a second step, the nonionic surfactant concentrated in the coacervate is regenerated by neutralization-precipitation. Indeed, at basic pH (or acid), it contains hydroxyl ions (or hydroniums) in high concentration which are ineffective for effiuent treatment. To restore its effectiveness, it is necessary to reduce the pH to a neutral value and also to precipitate the added base (or acid) in the form of salt to eliminate it. The coacervate is thus regenerated and, if necessary, constitutes a solution of surfactants according to the invention, active for a new treatment cycle.

To illustrate the principle of this operation, there may be mentioned by way of example the desextraction of phenol which is a weak acid. The non-dissociated species (PhOH) is more easily extracted than the ionic species, since it is less hydrophilic. It is therefore the molecular form PhOH which is preferentially retained in the coacervate. The acid / base pair used for the desextraction may be oxalic acid / calcium hydroxide.

De-extraction consists of dissociating the phenol from the nonionic surfactant. Since the ionic form PhO ^" does not interact with the surfactant head, increasing the pH by adding a base to the surfactant / PhOH complex separates the surfactant from the phenolate. extinguished), to raise the pH sufficiently (by at least two units above the pKa of phenol) to release the phenolate ion which dissolves most of the time in the water. The dilute phase is neutralized with oxalic acid to precipitate its calcium salt, for example phenol, solubilized by the surfactant known as the phenolate. Triton X-114 ^® denomination, then desextracted as indicated above, could thus be recovered with a level of 80% phenol.

Thus, according to an advantageous embodiment of the process according to the invention, it comprises a step f) for recycling the surfactants in which:

i) the surfactants and pollutant compounds of the concentrated phase obtained in step e) are separated by acid-base de-extraction, and

ii) the surfactants are regenerated by neutralization-precipitation.

According to an interesting characteristic, the surfactants regenerated in step f) of the process are used in step a) of a new treatment cycle.

The present method can be implemented for a very wide range of effiuents to be treated. The effluent can be stored in a tank, then treated with a solution of surfactants as described above, after which the two phases are recovered separately. According to a particularly interesting embodiment, the treatment is carried out as and when the effluent production, the different stages of the process taking place in different tanks. Thus according to a preferred embodiment of the invention, the steps a) to d) are carried out in separate compartments, according to a continuous process.

As explained above, the present process is particularly designed to be applied to the extraction of metal ions, alone or simultaneously with organic compounds contained in aqueous effluents. Such effluents may for example be from industrial activities of manufacturing, cleaning, transport or cooling, including the following industrial activities: metallurgy, mechanics, surface treatment, screen printing, fine chemicals, pharmaceuticals, textile, dyeing, wood.

Other features and advantages of the invention will appear on reading the following examples given for illustrative purposes without in any way limiting the scope.

EXAMPLE 1

Extraction of phenol and lead by nonionic surfactant OXO-C ₁₀ E ₃ and SDS

A solution Sl, containing 2 g / l of phenol and 1.5 g / l of lead was treated with a solution of surfactants S (TA) according to the following protocol.

• Surfactant solution

- Ionic surfactant: sodium dodecyl sulfate (SDS), 288.38 g / mol (Sigma-Aldrich). It contains in its hydrophobic chain 12 carbon atoms.

- Nonionic surfactant: OXO-C ₁₀ E ₃ ; The nonionic surfactant OXO-C10E3 used herein (Simulsol T150CT, SEPPIC, Castres) is an ethoxylated alcohol obtained by fixing the ethylene oxide on an oxo alcohol (linear-branched mixture) in the presence of an alkaline catalyst. The presence in the sample of residual polyols that can affect the properties of the surfactant, the latter is preferably washed out. To do this, 25% of water and 75% of the surfactant to be washed are mixed and then heated to 95 ° C. Two phases are then obtained, one rich in surfactant (of the order of 98-99%) and the other rich in polyols. The coacervate of surfactant OXO-C ₁₀ E ₃ is used directly for extraction. Its standard cloud temperature, measured before washing according to the NFT 1890D standard (10% of surfactant in 75% water + 25% butyldiglycol), is 54-58 ° C. This surfactant is virtually insoluble in water at all temperatures.

The surfactant solution S (TA) is obtained by mixing 1 g of surfactant OXO-C ₁₀ E ₃ and 0.095 g of SDS, ie a solution of ratio NI / I = 1 / 0.095 = 10.53.

• Extraction

The S (TA) solution is introduced into 25 ml of pollutant-loaded solution S1, so that the surfactant OXO-C10E3 is added to the mixture at a concentration of 4% by weight and SDS at a concentration of 0.38% by weight. This mixture is stirred at 800 rpm for 10 minutes. Its initial temperature is 20 ⁰ C (room temperature). The mixture is then heated at 45 ° C. for at least 15 minutes, which allows good phase separation. The volume fraction of the coacervate (light phase) is of the order of 0.18.

• Performance

A control of the extraction efficiency has been realized. The efficiency of the extraction E% of a solute is expressed by the percentage of solute initially dissolved extracted by the coacervate.

E% = (m _s (i _N ) - HIs (D) / m _{s (} iN)) x 100 with Hi ₈ (DVf) and Hi ₈ (D) representing the solute masses respectively in the initial solution and in the phase diluted after extraction.

Lead was assayed in the diluted phase by Induced Plasma Atomic Emission Spectroscopy (ICP). There is a lead extraction rate of 81%. The phenol content in the diluted phase was measured by reverse phase high performance liquid chromatography (HPLC). A phenol extraction rate of 72% is found.

EXAMPLE 2 Extraction of Phenol and Lead by Nonionic Surfactant OXO-C ₁₀ E ₃ and SDBS

The same solution S1 as in Example 1, containing 2 g / l of phenol and 1.5 g / l of lead was treated with a solution of surfactants S '(TA) according to the following protocol .

- Ionic surfactant: sodium dodecylbenzenesulphonate (SDBS), 348.25 g / mol (Rhodacal DS-10, Rhodia France). - Nonionic surfactant: OXO-C ₁₀ E ₃ , as in Example 1. The surfactant solution S '(TA) is obtained by mixing 1 g of surfactant OXO-C ₁₀ E ₃ and 0.15 g of SDBS, ie a solution of ratio NI / I = 1 / 0.15 = 6, 67.

Extraction It is introduced into 25 ml of solution Sl, so that the surfactant OXO-C10E3 is added to the mixture at a rate of 4% by weight and SDBS at a rate of 0.6% by mass. The procedure is as in Example 1. The initial temperature of Sl is 20 ^° C. The mixture is heated at 45 ° C. for at least 15 minutes, which allows a good separation. The volume fraction of the coacervate is of the order of 0.15.

• Performance

A control of the efficiency of the extraction was carried out as previously. There is a lead extraction rate of 80% and a phenol extraction rate of 71.5%.

EXAMPLE 3

Extraction of lead and 2,4-dimethylaniline by nonionic surfactant OXO-C ₁₀ E ₃ and SDS.

A solution S2 containing 1.3 g / l of 2,4-dimethylaniline (DMA) and 1.5 g / l of lead was treated with a surfactant solution according to the following protocol.

- Nonionic surfactant: oxo-CioE ₃

- Ionic surfactant: sodium dodecyl sulphate (SDS).

The preceding operating procedure is repeated with 1 g of oxo-CioEβ and 0.095 g of SDS, ie a solution of ratio NI / I = 1 / 0.095 = 10.53%.

It is introduced into 25 ml of solution Sl, so that the surfactant OXO-C10E3 is added to the mixture at 4% by weight and the SDS at 0.38% by weight.

• Extraction

The procedure is as in Example 1. The initial temperature of S2 is 20 ⁰ C, the mixture is heated to 45 ° C for at least 15 minutes, which allows good phase separation. The volume fraction of the coacervate is of the order of 0.25.

• Performance

A control of the efficiency of the extraction was carried out as previously. A lead extraction rate of 80.8% and a DMA extraction rate of 78.5% are found. EXAMPLE 4

Extraction of metal cations Pb ²⁺ , Cd ²⁺ , Ni ²⁺ , Cr ³⁺

25 ml model solutions containing a metal cation at 1.5 g / l were treated with the following pairs of surfactants.

1) Non-ionic TA: OXO-C ₁₀ E ₃ , 0.5 g is a mixture of 2%, and ionic TA: SDS 0.1 g or a mixture of 0.4%, with NI / I = 5

2) Nonionic TA: OXO-C ₁₀ E ₃ 0.5 g is a mixture of 2%, and ionic TA: SDBS 0.2 g or a mixture of 0.8%, with NI / I = 2.5.

We proceed as already indicated. For each solution extraction is carried out at 45 ° C with each pair of surfactants. The volume fractions of coacervate are all between 0.1 and 0.3. The results obtained with regard to the maximum extraction rate are shown in Table 1.

TABLE 1

Metal ion extraction rate at 45 ° C (%) Ion ^TPA Pb ²⁺ Cd ²⁺ Ni ²⁺ Cr ³⁺

SDS 86.0 68.0 55.0 49.0

SDBS 90.0 70.0 59.0 51.0

From these results, it can be seen that the process according to the invention makes it possible to significantly reduce the content of the main cations encountered in the effluents.

EXAMPLE 5

Extraction of molybdenum in the form of molybdate

A solution containing 1.5 g / l of molybdenum in the form of molybdate (MoO ₄ ^" ) was treated with the following two pairs of surfactants: 1) nonionic TA: OXO-C ₁₀ E ₃ and

Cationic TA: benzethonium chloride. 2) Nonionic TA: OXO-C ₁₀ E ₃ and

Cationic TA: hexadecyltrimethylammonium bromide or CTABr. Various tests have been carried out with varying contents of cationic surfactants. The nonionic surfactant is provided in all tests at a rate of 0.625 g, or 2.5% by weight, based on the working volume of 25 ml. The operating procedure is identical to that described in Example 1. The initial temperature of Sl is 20 ^° C. The mixture is maintained at 50 ^° C. for at least 15 minutes.

The volume fractions and the extraction rates obtained for the two pairs of surfactants 1) and 2) are presented in Tables 2 and 3 respectively. The ratios of nonionic surfactant / ionic surfactant (NI / I) are also indicated.

TABLE 2

TA IONIC 1) Fraction% extraction quantity supply to NI / I by volume at 50 ⁰ C added mixture

0.0625 g 0.25% 10.00 0.07 25.5

0.0750 g 0.30% 8.33 0.10 31.7

0.1000 g 0.40% 6.25 0.15 44.7

0, H25 g 0.45% 5.56 0.23 52.6

TABLE 3

TA IONIC 2) Fraction% of extraction quantity supply to NI / I by volume at 50 ⁰ C added mixture

0.0625 g 0.25% 10.00 0.15 34.0 0.0750 g 0.3% 8.33 0.27 47.0

EXAMPLE 6

Regeneration of the modified (E) -propoxylated (P) ethoxylated surfactant OXO-C10E3P4E2 (Simulsol NW 342, SEPPIC, France) after extraction of 2,4-dimethylaniline. An extraction system containing 8% by weight of surfactant and 0.13% by weight of solute was prepared. The extraction was carried out at a temperature of 42 ° C. When equilibrium is reached, after phase separation, the coacervate is carefully separated from the diluted phase. A sample of the latter was taken and the surfactant and solute concentrations determined. As expected, the concentration of OXO-C10E3P4E2 is of the order of CMC (1.11 × 10 ^-3 M at 15 ° C.) Furthermore, the extraction rate of 2,4-dimethylaniline is 88%.

The desextraction was conducted on the coacervate as follows. The acid / base pair used for the desextraction is here oxalic acid / calcium hydroxide. The coacervate was taken up and the oxalic acid added to pH 2 and then heated to 50 ⁰ C to remove the maximum of water hydration molecules. A new separation is then observed in two phases: one rich in solute (new diluted phase), the other rich in surfactant

(new coacervate acid). The amount of water in this coacervate is very small, which avoids dissolution of dissociated solute in this water, which would reduce the performance of the removal. This gives a desulfurization rate of 2,4-dimethylaniline of 86% in a single step.

To recycle the concentrated surfactant in the coacervate, it returns to pH 7.0. For this purpose, lime is added to the coacervate until a precipitate of calcium oxalate (in small quantity due to the small amount of water) is formed.

Claims

A liquid / liquid extraction treatment process of an aqueous effluent containing metal pollutants alone or in combination with organic pollutants, characterized in that it essentially comprises the steps of: a) - preparing a solution consisting of an ionic surfactant and at least one nonionic surfactant, b) - contacting the effluent with said solution, c) - stirring the mixture, and if necessary heating to a temperature at least 1 ° C above the cloud point of said mixture, d) - decant until separation into two aqueous phases, one being the concentrated phase of metal pollutants and possibly organic pollutants, and the other being the dilute phase, e) - recover separately the two phases.

2- Process according to claim 1 characterized in that the mixture obtained in step b) has a temperature at least 1 ° C higher than the cloud temperature of said mixture.

3. Process according to claim 1 or 2, characterized in that the nonionic surfactant is chosen from compounds having a cloud point, measured as a 1% solution in water, which is at least 5 ° C., preferably less than at least 10 ⁰ C, at the initial temperature of the effluent.

4. Method according to one of the preceding claims, characterized in that the nonionic surfactant is chosen as a function of the initial temperature of the effluent, among the compounds conferring on the mixture obtained in step b) a lower cloud temperature of at least 1 ° C at the temperature of said mixture.

5. Method according to one of the preceding claims, characterized in that the nonionic surfactant is chosen from polyethoxylated compounds having a hydrocarbon chain of length C ₁₀ to C ₁₆ , preferably from polyethoxylated alcohols, pure or in mixtures.

6. Process according to the preceding claim characterized in that the nonionic surfactant is an ethoxylated alcohol obtained by fixing the ethylene oxide on a fatty alcohol or oxo in the presence of an alkaline catalyst. 7- Method according to one of the preceding claims characterized in that the ionic surfactant is an anionic surfactant selected from alkylbenzenesulfonates, secondary alkanesulfonates, alpha-olefinsulfonates, petroleum sulfonates or alkylsulfates.

8- Method according to the preceding claim characterized in that the ionic surfactant is sodium dodecyl sulphate or sodium dodecylbenzenesulphonate.

9- Method according to one of claims 1 to 6 characterized in that the ionic surfactant is a cationic surfactant selected from alkyltrimethylammonium halides, benzethonium halides or cationic derivatives of nitrogenous heterocycles.

10- Method according to the preceding claim characterized in that the ionic surfactant is hexadecyltrimethylammonium bromide.

11- Method according to one of the preceding claims characterized in that the solution of surfactants provides the mixture, by mass per unit volume:

12- Method according to the preceding claim characterized in that the nonionic surfactant NI and the ionic surfactant I are in an NI / I mass ratio of between 2 and 12.

13- Method according to one of the preceding claims characterized in that the effluent (E) and the surfactant solution (S) are mixed in an S / E ratio between 0.01 and 0.1.

14- Method according to one of the preceding claims characterized in that steps a) to e) are repeated at least once to treat the diluted phase recovered in step e).

15- Method according to the preceding claim characterized in that when repeating step a), a solution of different surfactants is used.

16- Method according to any one of the preceding claims, characterized in that it comprises a step f) for recycling the surfactants in which: i) the surfactants and pollutant compounds of the concentrated phase obtained in step e) are separated by acid-base de-extraction, and

ii) the surfactants are regenerated by neutralization-precipitation.

17- Method according to the preceding claim characterized in that the surfactants regenerated in step f) are used in step a) of a new treatment cycle.

18- Method according to one of the preceding claims characterized in that the steps a) to d) are performed in separate compartments, according to a continuous process.

19- A method according to one of the preceding claims applied to the extraction of metal ions alone or simultaneously with organic compounds, from aqueous effluents from industrial manufacturing, cleaning, transport or cooling.