METHOD FOR TREATING AN EFFLUENT COMPRISING A SALT AND A METAL WITH AN ALUMINA-BASED SOLID.

Abstract

The present invention relates to a method for treating an aqueous effluent, said effluent comprising: - a metal chosen from the list consisting of copper, zinc, nickel, chromium, tin, aluminum, iron, cobalt, silver, gold, palladium and rhodium, alone or in combination, - a salt comprising an anion chosen from the list consisting of sulfate, chloride, nitrate, fluoride, sulfamate, acetate, carbonate, citrate, cyanide, hydroxide, nitrite, oxide and phosphate alone or in combination, and a cation chosen from the list consisting of calcium, sodium, potassium, ammonium, quaternary ammonium, iron, magnesium, pyridinium and lithium alone or in combination, the method comprising a step a) of bringing said effluent into contact with at least one alumina-based solid, said solid being obtained by a method comprising the following steps: i) abruptly dehydrating by flashing an aluminum hydroxide or an oxyhydroxide aluminum,to obtain an active alumina powder; ii) the active alumina powder obtained in step i) is shaped so as to obtain a solid in the form of a ball or extrudate; iii) the solid obtained in step ii) is heat treated; iv) the heat-treated solid obtained in step iii) is hydrothermally treated; v) the treated solid obtained in step iv) is calcined.,

Description

Title of the invention: METHOD FOR TREATING AN EFFLUENT COMPRISING A SALT AND A METAL WITH AN ALUMINA-BASED SOLID. Technical field

[0001] The present invention is in the field of adsorbents and methods for treating industrial effluents, in particular from surface treatment industries. Prior art

[0002] The problem of industrial aqueous discharges is regaining importance in the context of global warming, which involves recurring periods of drought, leading to both a shortage of water resources and increasingly stringent regulatory constraints in terms of discharges. For example, the continuous decline in low-water flows of rivers, used as a reference in French regulations for the protection of the receiving environment of industrial discharges, imposes more restrictive thresholds in terms of maximum concentration of pollutants in discharges from ICPE installations. Among the pollutants monitored and harmful to the environment, metals are among the species present in many types of discharges and for which the regulatory thresholds are increasingly restrictive.

[0003] The mechanical engineering and surface treatment and coating industry is particularly concerned by the presence of metals in its waste, particularly due to wet treatments. In these workshops, successive treatments of dipping mechanical parts in baths (electrolytic, chemical deposition, immersion in molten metal, etc.) take place, to give these parts the desired properties in terms of hardness, conductivity, mechanical resistance, wear resistance, corrosion resistance, but also to improve the aesthetics and degree of finishing of the parts.

[0004] A surface treatment chain generally includes the following activities: degreasing, pickling, demetallization, neutralization, deposition and conversion. Controlling bath discharges is therefore complex, with flows of diverse nature and numerous species that can interact with each other.

[0005] Liquid discharges from these industries can be loaded with different substances such as: organic matter (oils, greases, solvents, wetting agents, brighteners, etc.), organohalogenated compounds (chlorinated oils, degreasing solvents and paint solvents, etc.), suspended matter (metal hydroxides, carbonates, dust), metals (chromium, zinc, copper, nickel, aluminum, iron, cadmium, tin, etc.), cyanides, phosphorus-containing materials, nitrogen-containing materials, fluorides, various salts (chloride, sulfate, potassium, sodium, etc.), organohalogenated COHV compounds (such as chloromethane and perchloroethylene), or even BTEX (benzene, toluene, ethylbenzene, xylenes, etc.).

[0006] It is the complex and diverse nature of these discharges (rich in metals but also in salts, surfactants, complexing agents, etc.) with numerous physicochemical interactions between pollutants and also with the treatment systems, which makes these discharges particularly difficult to treat, in addition to past and future tightening of regulations. Indeed, in France, the discharge flow rate must be less than 10% of the QMNA5 low water flow (minimum flow rate which is likely to be found every 5 years). This flow limitation, associated with the NQE standard in the environment, generates very low emission limit values ​​(ELVs). Depending on the regions and the type of receiving environment, the ELVs can be around 0.5 mg / 1 for each metal, with a trend towards 0.2 mg / 1 or even below 0.1 mg / 1 in the future. This leads to high risks of non-compliance and exposes manufacturers to sanctions that could go as far as site closure.

[0007] Liquid discharges generated in surface treatment workshops are treated in industrial wastewater treatment facilities located in-situ or ex-situ depending on the size of the workshop. Two main treatment families are implemented: physico-chemical treatments and finishing treatments.

[0008] Physicochemical treatments consist of precipitating and flocculating pollutants and then separating the liquid-solid phases. They include the steps of precipitation, neutralization, coagulation / flocculation and solid / liquid separation. Sometimes, specific oxidation-reduction treatments are applied before physicochemical treatment. Physicochemical treatments are rustic but robust and can reduce approximately 90% of the pollution. In particular, they reduce the content of metals, cyanide, hexavalent chromium, nitrites, phosphorus and fluoride but have no effect on the salt concentration.

[0009] However, the presence of these high concentrations of salts has a strong impact on the second family of treatments (finishing treatments).

[0010] Finishing treatments are often necessary to achieve the emission limit values ​​after physicochemical treatment (below 0.5 mg / l). The finishing treatments known to those skilled in the art are: final neutralization for pH adjustment, sand filtration for retention of suspended matter, activated carbon to retain residual organic matter (COD or Chemical Oxygen Demand) and ion exchange resins to lower residual metal contents.

[0011] Ion exchange resin is the reference solution for finishing treatment in the surface treatment industry. This type of treatment makes it possible to achieve concentration levels of 0.5 mg / l for certain metals, but has limits for going below this threshold. Another disadvantage of this type of solution is its very high cost both in terms of investment expenditure (if regeneration on site in particular) and operating expenditure (cost of resins, regeneration products, etc.).

[0012] Sources: CITRA website Center for Engineering in Advanced Surface Treatments and Coatings - Wet Surface Treatment; Surface Treatment Guide Water Purification, 5th edition, Union of Surface Technology Industries (UITS) and Water Agencies.

[0013] There is therefore a need on the part of manufacturers in the mechanical engineering and surface treatment and coating sector for selective finishing solutions that allow compliance with the ELVs of numerous metals (for example: Cu, Ni, Zn, Cr and Sn).

[0014] The applicant has surprisingly demonstrated that the use in a process for treating an effluent typical of surface industries comprising salts and metals, of an alumina-based solid having particular characteristics and / or being obtained by a particular process, makes it possible to obtain ELVs for the metals close to or lower than the recommended threshold. Summary of the invention

[0015] The present invention relates to a method for treating an aqueous effluent, said effluent comprising:

[0016] - a metal chosen from the list consisting of copper, zinc, nickel, chromium, tin, aluminium, iron, cobalt, silver, gold, palladium and rhodium, alone or in combination, the metal concentration in the effluent being between 2 and 50 mg / L, preferably between 8 and 20 mg / l,

[0017] - a salt comprising an anion chosen from the list consisting of sulfate, chloride, nitrate, fluoride, sulfamate, acetate, carbonate, citrate, cyanide, hydroxide, nitrite, oxide and phosphate alone or in combination, and a cation chosen from the list consisting of calcium, sodium, potassium, ammonium, quaternary ammonium, iron, magnesium, pyridinium and lithium alone or in combination, the salt concentration in the effluent being between 1 and 50 g / L, preferably between 2 and 20 g / L,

[0018] the process comprising a step a) of bringing said effluent into contact with at least one alumina-based solid, said solid being obtained by a process comprising the following steps:

[0019] i) an aluminum hydroxide or an aluminum oxyhydroxide is abruptly dehydrated by flashing, to obtain an active alumina powder;

[0020] ii) the active alumina powder obtained in step i) is shaped so as to obtain a solid in the form of a ball or extrudate, preferably in ball shape, with a raw filling density of between 500 and 1100 kg / cm3, preferably between 600 and 950 kg / cm3;

[0021] iii) a heat treatment is carried out on the solid obtained in step ii) so as to provide it with a specific surface area of ​​between 50 and 450 m2 / g, preferably between 150 and 400 m2 / g, more preferably between 300 and 380 m2 / g;

[0022] iv) a hydrothermal treatment of the heat-treated solid obtained in step iii) is carried out by two impregnations with water or a preferably acidic aqueous solution, followed by a stay in an autoclave at a temperature above 80°C;

[0023] v) calcining the treated solid obtained in step iv), preferably at a temperature between 400 and 1300°C. DETAILED DESCRIPTION OF THE INVENTION

[0024] According to the present invention, the expression "between ... and ..." and "between .... and ..." are equivalent and mean that the limit values ​​of the interval are included in the range of values ​​described. If this is not the case and the limit values ​​are not included in the range described, such precision will be provided by the present invention.

[0025] In the sense of the present invention, the different parameter ranges for a given step such as pressure ranges and temperature ranges can be used alone or in combination. For example, in the sense of the present invention, a preferred pressure value range can be combined with a more preferred temperature value range.

[0026] In the following, particular embodiments of the invention may be described. They may be implemented separately or combined with each other, without limitation of combinations when this is technically feasible.

[0027] In the present application, the term "comprise" is synonymous with (means the same as) "include" and "contain", and is inclusive or open and does not exclude other elements not recited. It is understood that the term "comprise" includes the exclusive and closed term "consist". Effluent

[0028] The present invention relates to a method for treating an aqueous effluent, said effluent comprising:

[0029] - a metal chosen from the list consisting of copper, zinc, nickel, chromium, tin, aluminium, iron, cobalt, silver, gold, palladium and rhodium, alone or in combination, the metal concentration in the effluent being between 2 and 50 mg / L, preferably between 8 and 20 mg / l,

[0030] - a salt comprising an anion chosen from the list consisting of sulfate, chloride, nitrate, fluoride, sulfamate, acetate, carbonate, citrate, cyanide, hydroxide, nitrite, oxide and phosphate alone or in combination, and a cation chosen from the list consisting of calcium, sodium, potassium, ammonium, quaternary ammonium, iron, magnesium, pyridinium and lithium alone or in combination, the salt concentration in the effluent being between 1 and 50 g / L, preferably between 2 and 20 g / L.

[0031] Advantageously, the metal is chosen from the list consisting of copper, zinc, nickel, chromium and tin, alone or in combination.

[0032] In one embodiment, the aqueous effluent further comprises organic materials, for example oils, greases, solvents, wetting agents, brighteners.

[0033] In one embodiment, the aqueous effluent further comprises organohalogenated compounds, for example chlorinated oils, degreasing solvents, paint solvents.

[0034] In one embodiment, the aqueous effluent further comprises suspended particles, for example metal hydroxides, carbonates, dust.

[0035] In one embodiment, the aqueous effluent further comprises cyanides.

[0036] In one embodiment, the aqueous effluent further comprises compounds phosphorous.

[0037] In one embodiment, the aqueous effluent further comprises nitrogen compounds.

[0038] In one embodiment, the aqueous effluent further comprises fluorides.

[0039] In one embodiment, the aqueous effluent further comprises organic compounds ganohalogens, for example chloromethane and perchloroethylene.

[0040] In one embodiment, the aqueous effluent further comprises BTEX (benzene, toluene, ethylbenzene, xylenes). Step a) of contact

[0041] The method according to the invention comprises a step a) of bringing said effluent into contact with at least one alumina-based solid.

[0042] This step can be carried out by any means known to those skilled in the art.

[0043] Advantageously, step a) is carried out at a temperature between 0.5 and 45°C.

[0044] Advantageously, step a) is carried out at an hourly volumetric flow rate (HV) of between 0.5 and 30 h1, preferably between 10 and 15 h1. The HV is defined as the effluent flow rate per unit volume of solid used.

[0045] In one embodiment, the method according to the invention further comprises, upstream of step a), a step a0) of physicochemical treatment of the aqueous effluent comprising a step chosen from precipitation, neutralization, coagulation / flocculation and solid / liquid separation, optionally followed by a finishing treatment comprising a step chosen from neutralization, sand filtration, adsorption on activated carbon, adsorption on ion exchange resin.

[0046] In a particular embodiment, step a) of contacting is implemented within step a0) of physicochemical treatment of the aqueous effluent, by adding the alumina-based solid in a dispersed manner within the physicochemical treatment. In this particular embodiment, the alumina-based solid added in a dispersed manner within the physicochemical treatment is advantageously in powder form. Alumina-based solid

[0047] The alumina-based solid is obtained by a process comprising the following steps:

[0048] i) an aluminum hydroxide or an oxy is abruptly dehydrated by flashing aluminum hydroxide, to obtain an active alumina powder;

[0049] ii) the active alumina powder obtained in step i) is shaped so as to obtain a solid in the form of a ball or extrudate, preferably in the form of a ball, with a raw filling density of between 500 and 1100 kg / cm3, preferably between 600 and 950 kg / cm3;

[0050] iii) a heat treatment is carried out on the solid obtained in step ii) so as to provide it with a specific surface area of ​​between 50 and 450 m2 / g, preferably between 150 and 400 m2 / g, more preferably between 300 and 380 m2 / g;

[0051] iv) a hydrothermal treatment of the heat-treated solid obtained in step iii) is carried out by two impregnations with water or an aqueous solution, preferably acidic, followed by a stay in an autoclave at a temperature above 80°C;

[0052] v) calcining the treated solid obtained in step iv), preferably at a temperature between 400 and 1300°C.

[0053] In one embodiment, in step i), the aluminum hydroxide is chosen from the group consisting of hydrargillite, gibbsite and bayerite alone or in a mixture, preferably the aluminum hydroxide is hydrargillite.

[0054] In one embodiment, in step i), the aluminum oxyhydroxide is chosen from the group consisting of bohemite, pseudo-bohemite and diaspore alone or as a mixture.

[0055] The term "flashing" means a sudden dehydration of an aluminum hydroxide or an aluminum oxyhydroxide, using a stream of hot gas to eliminate and carry away the evaporated water very quickly. The temperature is between 400 and 1200°C, and the contact time of the material to be dehydrated with the hot gas is between a fraction of a second and 4 or 5 seconds. Such a flashing method is described in particular in document FR2823193.

[0056] Advantageously, in step ii) when the solid is in the form of beads, the beads have an average diameter of between 0.01 and 6 mm, preferably between 0.1 and 4 mm, more preferably between 0.15 and 2 mm.

[0057] Advantageously, the hydrothermal treatment in step iv) is carried out at a temperature of between 150 and 270°C, preferably between 170 and 250°C, for a duration of more than 45 minutes, preferably between 1 and 24 hours, more preferably between 1.5 and 12 hours.

[0058] Advantageously, in step iv), the hydrothermal treatment is carried out using an acidic aqueous solution comprising one or more mineral and / or organic acids, for example nitric acid, hydrochloric acid, perchloric acid, sulfuric acid, weak acids whose solution has a pH lower than 4 such as acetic acid or formic acid. Said acidic aqueous solution advantageously comprises one or more compounds capable of releasing anions capable of combining with aluminum ions, for example compounds comprising a nitrate ion (such as aluminum nitrate), chloride, sulfate, perchlorate, chloroacetate, trichloroacetate, bromoacetate, dibromoacetate, and anions of general formula: R-COO- such as formates and acetates.

[0059] The solid is based on alumina, that is to say that the solid contains at least 80%, preferably at least 85%, and more preferably at least 90% by weight of alumina relative to the weight of the solid.

[0060] The BET specific surface area is measured by nitrogen physisorption according to ASTM D3663-03 as described in Rouquerol F.; Rouquerol J.; Singh K. “Ad-sorption by Powders & Porous Solids: Principle, methodology and applications”, Academie Press, 1999.

[0061] In the following, the groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, publisher CRC press, editor-in-chief DR Lide, 81st edition, 2000-2001). For example, group VIII according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IUP AC classification.

[0062] The alumina advantageously has a crystallographic structure of the delta, gamma or theta alumina type, alone or as a mixture. Preferably, the alumina is present mainly in gamma form, that is to say that the solid contains at least 80%, preferably at least 85%, and particularly preferably at least 90% by weight of gamma alumina relative to the total weight of alumina present in the solid.

[0063] In one embodiment, the alumina-based solid comprises impurities such as oxides of metals from groups IIA, IIIB, IVB, IIB, IIIA, IVA, preferably silica, titanium dioxide, zirconium dioxide, zinc oxide, magnesium oxide and calcium oxide, or alkali metals, preferably lithium, sodium or potassium, and / or alkaline earths, preferably magnesium, calcium, strontium or barium or even sulfur.

[0064] Advantageously, the alumina-based solid has a mesoporous volume of between 0.05 and 1 ml / g, preferably between 0.1 and 0.9 ml / g, more preferably between 0.2 and 0.7 ml / g.

[0065] Advantageously, the alumina-based solid has a macroporous volume of between 0.02 and 0.5 ml / g, preferably between 0.03 and 0.4 ml / g, more preferably between 0.04 and 0.3 ml / g.

[0066] Advantageously, the alumina-based solid has a total pore volume advantageously between 0.1 and 1.5 cmVg, preferably between 0.2 and 1.4 cm3 / g, and even more preferably between 0.25 and 1.3 cmVg.

[0067] The total pore volume is measured by mercury porosimetry according to ASTM D4284-92 with a wetting angle of 140°, for example using an Autopore® III model device from Microméritics®.

[0068] In one embodiment, the alumina-based solid is in the form of beads, powder, or extruded form, for example trilobed or quadrilobed. Advantageously, the alumina-based solid is in the form of beads or powder.

[0069] When the alumina-based solid is in the form of beads, the average diameter of the beads is between 0.01 and 6 mm, preferably between 0.1 and 4 mm, more preferably between 0.15 and 2 mm.

[0070] When the alumina-based solid is in the form of a cylindrical, trilobed or quadrilobed extrudate, the average length of the extrudate is generally between 2 and 10 mm, preferably between 2 and 8 mm, and more preferably between 3 and 6 mm. When the solid is in the form of a quadrilobed extrudate, the extrudates have an average diameter generally between 0.5 and 10 mm, preferably between 0.8 and 3.2 mm and very preferably between 1.0 and 2.5 mm and an average length between 0.5 and 2.0 mm. EXAMPLES

[0071] Solid 1 is a cation exchange resin referenced Lewatit® MonoPlus TP 207 supplied by the company LanXess.

[0072] Solid 2 is a NaX zeolite referenced AxTrap™813 supplied by the company Axens.

[0073] Solid 3 is an alumina obtained according to the preparation method described in Environmental Technology & Innovation 22 (2021) 101439, which follows a route called precipitation of aluminum nitrate by a base which is urea. After autoclaving, a bohemite is obtained. The bohemite to alumina transition is then carried out by cal- cination at 1000°C for 4 hours.

[0074] Solid 4 is an alumina-based solid obtained according to the process of the invention by the so-called “flash” route.

[0075] Example 1: Process for treating a saline solution comprising Ni and Cu:

[0076] A solution is prepared containing 10 g / L of NaCl, 1 g / L of KC1 and CaCl2. Cu(NO3)2.3H2O and Ni(NO3)2.6H2O are added to the solution to obtain a concentration of 25 mg / L Ni and 25 mg / L Cu. This solution is analyzed for Ni and Cu concentrations using ICP-OES (Induced Couple Plasma -Optical Emission Spectroscopy: EN ISO 11 885) after mineralization (EN ISO 15587-2).

[0077] Volumes of 1.5 cm3, 4.5 cm3 and 7.5 cm3 of different solids were placed in containers.

[0078] 150 ml of the previously prepared Ni / Cu solution was added to each container.

[0079] Using an oscillating stirrer, the containers were moved for 5 hours at room temperature.

[0080] Approximately 50 ml of sludge was taken by syringe from each container and filtered.

[0081] The nickel and copper concentrations of each filtered solution were analyzed by ICP-OES after mineralization.

[0082] The characteristics of the different solids tested are described in the table below:

[0083] [Tables 1] Properties Solid 1 (comparative) Solid 2 (comparative) Solid 3 (comparative) Solid 4 (according to the invention) BET surface area (m2 / g) 21 677 335 343 Total pore volume (cm3 / g) 0.181 0.334 0.357 0.456 Mesoporous volume (cm3 / g) 0.03 0.07 0.19 0.32 Macroporous volume (cm3 / g) 0 0.18 0.06 0.06

[0084] The initial concentration of nickel and copper is 25 mg / L. The results shown in the table below are the final concentrations of Ni and Cu in mg / L.

[0085] [Tables2] Volume of solid 1.5 cm3 4.5 cm3 7.5 cm3 Metals and concentration Ni (mg / L) Cu (mg / L) Ni (mg / L) Cu (mg / L) Ni (mg / L) Cu (mg / L) Solid 1 (comparative) 1.6 5.8 - - 1.7 1.2 Solid 2 (comparative) 16.5 8.7 - - 9.2 15.9 Solid 3 (comparative) 12.4 0.7 16 0.3 0.4 3.4 Solid 4 (according to the invention) 6.0 0.4 0.7 0.4 0.1 0.1

[0086] It is observed that the solid according to the invention makes it possible to effectively treat the saline solution comprising Cu and Ni, from a certain volume of solid used, and to achieve concentration values ​​close to or lower than 0.5 mg / L for the two metals Cu and Ni which are the target values ​​recommended for industrial discharges.

Claims

Claims

1. A method for treating an aqueous effluent, said effluent comprising: - a metal selected from the list consisting of copper, zinc, nickel, chromium, tin, aluminum, iron, cobalt, silver, gold, palladium and rhodium, alone or in combination, the metal concentration in the effluent being between 2 and 50 mg / L, - a salt comprising an anion selected from the list consisting of sulfate, chloride, nitrate, fluoride, sulfamate, acetate, carbonate, citrate, cyanide, hydroxide, nitrite, oxide and phosphate alone or in combination, and a cation selected from the list consisting of calcium, sodium, potassium, ammonium, quaternary ammonium, iron, magnesium, pyridinium and lithium alone or in combination, the salt concentration in the effluent being between 1 and 50 g / L, the method comprising a step a) of bringing said effluent into contact with at least one solid based on of alumina,said solid being obtained by a process comprising the following steps: i) an aluminum hydroxide or an aluminum oxyhydroxide is abruptly dehydrated by flashing, to obtain an active alumina powder; ii) the active alumina powder obtained in step i) is shaped so as to obtain a solid in the form of a ball or extrudate, with a raw filling density of between 500 and 1100 kg / cm3; iii) a heat treatment is carried out on the solid obtained in step ii) so as to provide it with a specific surface area of ​​between 50 and 450 m2 / g; iv) a hydrothermal treatment is carried out on the heat-treated solid obtained in step iii) by two impregnations with water or an aqueous solution, followed by a stay in an autoclave at a temperature above 80°C; v) calcination of the treated solid obtained in step iv).

2. Method according to claim 1, further comprising, upstream of step a), a step aO) of physicochemical treatment of the aqueous effluent comprising a step chosen from precipitation, neutralization, coagulation / flocculation and solid / liquid separation.

3. Process according to claim 2, in which step aO) of physicochemical treatment of the aqueous effluent is followed by a treatment of finishing comprising a step chosen from neutralization, sand filtration, adsorption on activated carbon, adsorption on ion exchange resin.

4. Method according to claim 2, in which step a) of contacting is carried out within step a0) of physicochemical treatment of the aqueous effluent, by adding the alumina-based solid in a dispersed manner within the physicochemical treatment.

5. A method according to any one of the preceding claims, wherein in step i) the aluminum oxyhydroxide is selected from the group consisting of bohemite, pseudo-bohemite and diaspore alone or as a mixture.

6. A method according to any one of the preceding claims, wherein in step iv) the hydrothermal treatment is carried out using an acidic aqueous solution comprising one or more mineral and / or organic acids.

7. A method according to any one of the preceding claims, wherein the alumina-based solid contains at least 80% by weight of gamma alumina relative to the total weight of alumina present in the solid.

8. A method according to any preceding claim, wherein the alumina-based solid has a mesoporous volume of between 0.05 and 1 ml / g.

9. A method according to any one of the preceding claims, wherein the alumina-based solid has a macropore volume of between 0.02 and 0.5 ml / g, preferably between 0.03 and 0.4 ml / g, more preferably between 0.04 and 0.3 ml / g.

10. A method according to any one of the preceding claims, wherein the alumina-based solid has a total pore volume of between 0.1 and 1.5 cmVg, preferably between 0.2 and 1.4 cm 3 / g, and even more preferably between 0.25 and 1.3 cmVg.