FR3063656A1 - METHOD FOR HYDROTHERMAL DESTRUCTION OF COMPOSITE MINERAL PRODUCT CONTAINING ASBESTOS, CORRESPONDING INSTALLATION - Google Patents

Abstract

The invention relates to a method for the hydrothermal destruction of an asbestos-containing mineral product in which the asbestos-containing mineral product is placed in a pressure reactor comprising an acid solution at elevated temperature and in which the mineral product is bathed. containing at least 0.2 MPa and the temperature of at least 125 ° C, the acidic solution comprising at least water and hydrochloric acid. According to the invention, there is also a solid compound comprising at least one fluorine atom in the reactor and in contact with the acid solution, the acidic solution not comprising hydrofluoric acid and the solid compound comprising at least one atom of fluorine allowing the release of fluorine ions at a concentration of less than 2.10-3 mol / L. A suitable installation is also described.

Description

Technical field to which the invention relates

The present invention relates generally to the field of destruction of asbestos products, without generating toxic and / or non-recoverable ultimate waste. It relates more particularly to a hydrothermal destruction process of a composite product containing asbestos in chrysotile form and commonly called asbestos-cement and all of its trade names: eternit®, fibrociment®, etc. It also relates to an installation for destruction allowing the implementation of the process. It relates in particular to a process for transforming the asbestos contained in asbestos-cement products into non-harmful products and which can even be recovered in certain applications.

TECHNOLOGICAL BACKGROUND

Asbestos poses very serious public health problems due to the dangerous nature of its fibers, which can be inhaled and can produce serious diseases in the more or less long term.

Asbestos removal and asbestos-containing products have therefore been implemented. However, "elimination", in the current sense of the term, essentially results in the burial and storage of asbestos in secure sites, at least at the moment and for the years to come. However, this policy leaves a particularly sensitive legacy for future generations, since asbestos is a particularly resistant and stable mineral under storage conditions such as those used. Thus, the mineral will be able to cross centuries, even millennia without being altered or destroyed. The risk of memory loss from landfills adds a hint of the unexpected to those who will accidentally rediscover them in a few centuries. Consequently, economically viable solutions for the destruction, in the first sense of the term, of asbestos remain to be defined and implemented.

It has hitherto been proposed to implement asbestos destruction processes by chemical means allowing its transformation into less dangerous products.

Thus we know from documents US 5,258,131, US 5,753,031, US 2010/0113859, US2011 / 0101267A1, FR09 / 57832 and WO2010 / 110477 various methods of treating asbestos, asbestos being treated in an acid bath.

The effectiveness of these first generation treatments still needs to be greatly improved since it may happen that asbestos remains present at the end of the treatment.

Object of the invention

The applicant has determined that the presence of spectator ions and in particular fluorine ions in the acid treatment medium within the reactor in which the products containing asbestos are treated made it possible to significantly improve the destruction and the transformation of the asbestos in non-toxic compounds. The fluorine ions used within the framework of the invention behave in practice like catalysts spectators of the reaction in acid solution, without modifying the chemical equilibrium of the reaction. The fluorine source is a solid compound comprising at least one fluorine atom and in particular a fluoropolymer.

To explain the beneficial effect of the solid compound containing fluorine, it can be thought that in the case of metal reactors, made up of anticorrosion walls, metal ions or compounds coming from the wall of the reactor contribute to saturating the acid solution too quickly, d where a negative effect on the asbestos destruction reaction. Conversely, the fact of covering / lining the wall of the reactor with a protective layer based on fluoropolymer has a beneficial effect at least by avoiding an additional concentration of metal ions in the bath.

One can also consider the proper action of fluorine of solid compounds by the production of fluorinated derivatives in the acid solution or the passage of fluorine ions in the acid solution and which can explain the positive effect on the reaction of destruction / transformation of l 'asbestos.

We can think that this specific action of fluorine in the solid compound is in fact predominant because the use of a metal-walled reactor and with the addition of solid granules containing fluorine in the acid bath also makes it possible to obtain satisfactory results, under the guise of respecting a concentration of fluorine ions of the same order, that is to say less than 2.10 ' ³ mole / L of acid bath.

In practice, a hydrothermal dissolution process of asbestos cement is implemented in a mixture of hydrochloric acid and nitric acid and without the use of hydrofluoric acid. Fluorine ions are released by a solid coating comprising fluorine atoms, the solid coating covering the internal walls of the reactor, or by a solid material added in the acid bath, the fluorine ions in the acid solution being in very small quantity n ' not exceeding 2.10 ' ³ mole / L.

The present invention therefore provides a process for hydrothermal destruction of a composite mineral product containing asbestos in chrysotile form in which the composite mineral product containing asbestos is placed in a reactor under vapor pressure and comprising an acidic solution. high temperature and in which the composite mineral product containing asbestos is immersed, the pressure in the reactor being at least 0.2 MPa and the temperature at least 125 ° C, the acid solution comprising at least water, hydrochloric acid and nitric acid.

According to the invention, there is also a solid compound having at least one fluorine atom in the reactor and in contact with the acid solution, the acid solution not comprising hydrofluoric acid, and a solid compound is used comprising at least one fluorine atom, the release of fluorine ions of which in contact with the acid solution produces a very low concentration of fluorine ions in the acid solution, said very low concentration being less than 2.10 ' ³ mole / L.

Fluorine ions must remain spectators of the reaction, without participating in it.

It is therefore preferably used a solid fluoropolymer type compound because the fluoropolymers remain solid under the treatment conditions indicated because they have a very low rate of "dissolution", if not negligible, they are therefore essentially insoluble in the acid solution. In the case of a solid compound comprising at least one fluorine atom which would be soluble in the acid treatment bath, for example fluorine which is a solid compound whose solubility is high in the acid bath, the amount of said soluble solid compound added to the acid treatment solution is calculated and adjusted so as to generate only an extremely low concentration of fluorine ions, not exceeding 2.10 ' ³ mole / L in the acid treatment solution. For example for fluorite, this corresponds to an addition of fluorine not exceeding 0.1% by mass of the mass of asbestos cement composite introduced into the reactor, and in practice, much less than 0.1% by mass, for example less at 0.01% by mass relative to the initial mass of asbestos cement.

Other non-limiting and advantageous characteristics of the process according to the invention, taken individually or in any technically possible combination, are the following:

the pressurization of the reactor is obtained by the pressure rise, in a substantially constant closed volume, of the vapors produced by the heating of the acid treatment solution,

- the steam produced is also superheated,

the solid compound comprising at least one fluorine atom essentially insoluble in the acid solution has a solubility rate which is at most 0.01% according to standard ASTM-D-543,

the reactor has an internal wall and the solid compound comprising at least one fluorine atom is a protective layer for the internal wall of the reactor and lining the internal wall of the reactor,

the composite mineral product containing asbestos is introduced and maintained in the reactor on a sample holder support and the sample holder support is covered with the solid compound comprising at least one fluorine atom which forms a protective layer of said sample holder support ,

the reactor has an internal wall and the solid compound comprising at least one fluorine atom is a protective layer for the internal wall of the reactor and lining the internal wall of the reactor as well as the annexed organs in contact with the acid solution, in particular pipes, pumps and a sample holder with which the asbestos-containing composite mineral product is introduced and maintained in the reactor,

- in the case where the asbestos-containing composite mineral product is a plate of determined dimensions, in particular a typically corrugated cover plate, the sample holder support forms a template that is both dimensional and in quantity of composite mineral product, a number maximum determined number of plates that can be installed on the sample holder support template by staggering plate supports, each support stage can only receive one plate,

the protective layer lining the internal wall of the reactor is a fluoropolymer,

- pipes are connected to the reactor and the protective layer is extended to the internal walls of said pipes,

- The process is implemented within an installation and all the walls of the metallic elements of the installation are covered, coming into contact with a treatment liquid, at least one of the acids and the acid solution with a protective layer. formed by the solid compound comprising at least one fluorine atom,

the solid compound comprising at least one fluorine atom is in the form of powder or granules introduced into the reactor,

the solid compound comprising at least one fluorine atom is in the form of plates or bars introduced into the reactor,

the solid compound comprising at least one fluorine atom is a product of organic synthetic chemistry, in particular a fluoropolymer,

the powder or the granules are free within the acid solution, in the reactor the powder or the granules which can come into contact with the composite mineral product containing asbestos,

the granules have shapes chosen from spherical, ovoid, fusiform, elongated, irregular, or other shapes,

the granules are placed within at least one container placed in the reactor, said container having perforated walls allowing the passage of the acid solution but retaining the granules within the container in order to prevent the granules from coming into contact composite mineral product containing asbestos,

- the container is set in motion in the acid solution within the reactor,

- the container is in a fixed position in the acid solution within the reactor,

- the composite mineral product containing asbestos is asbestos-cement,

- the composite mineral product containing asbestos is set in motion in the acid solution within the reactor,

- the composite mineral product containing asbestos is in a fixed position in the acid solution within the reactor,

- the acid solution is set in motion in the reactor,

- the acid solution is circulated through the reactor,

the acid solution circulated in the reactor passes through said at least one container,

- the container is metallic,

the metal container has its walls covered with the solid compound comprising at least one fluorine atom,

at least some of the walls of the container are part of the internal wall of the reactor, the granules being in a closed pocket within the reactor, the acid solution coming into contact with the granules,

the solid compound comprising at least one fluorine atom is a fluoropolymer or a combination of fluoropolymers,

the solid compound comprising at least one fluorine atom is a spectator of the reaction, that is to say that it does not participate chemically in the chemical equilibrium of the reaction taking place in the reactor and said solid compound comprising at least one fluorine atom is chosen from compounds which are essentially insoluble in the acid solution or the compounds which are soluble in the acid solution,

the solid compound comprising at least one fluorine atom is chosen from polytetrafluoroethylene (PTFE), a polymer comprising perfluoroalkoxy groups, a fluorinated ethylene propylene copolymer (FEP), a copolymer of ethylene and chlorotrifluoroethylene (ECTFE), poly (ethylene-cotetrafluoroethylene) (ETFE), poly (vinyl fluoride) (PVF), poly (vinylidene fluoride) (PVDF), polychlorotrifluoroethylene (PCTFE), a copolymer of vinylidene fluoride and chlorotrifluoroethylene, perfluoropolyether groups (PFPE), perfluorosulfonic acid (PFSA), perflooroalkoxy (PFA) and their combinations,

- the pressure is between 0.2 MPa and 2 MPa,

- the temperature is between 125 ° C and 300 ° C,

- the temperature is between 125 ° C and 220 ° C,

- the temperature is between 200 ° C and 260 ° C,

- the temperature is around 220 ° C +/- 5%,

- in the case where the fluoropolymer introduced into the reactor is not a protective layer for the wall of the reactor, the temperature in the reactor is higher than 200 ° C. in order to physically solicit the fluoropolymer at the limits of its chemical stability conditions and physical,

- in the case where the fluoropolymer is a protective layer of the wall of the reactor, the temperature in the reactor is higher than 200 ° C. in order to physicochemically stress the fluoropolymer at the limits of its conditions of chemical and physical stability, said temperature being however lower than the degradation temperature of said fluoropolymer,

the pressure is between 0.2 MPa and 2 MPa, the temperature is between 125 ° C and 220 ° C for a duration of treatment of the composite mineral product containing asbestos within the reactor between 2 hours and 72 hours,

- the duration of treatment of the composite mineral product containing asbestos within the reactor is at least 2 hours,

- the acid solution contains between 10% and 90% by volume of 1N hydrochloric acid relative to the volume of water,

- the acid solution contains between 10% and 20% by volume of 1N hydrochloric acid relative to the volume of water,

- the acid solution contains between 80% and 90% by volume of 1N hydrochloric acid relative to the volume of water,

- the acid solution has a pH between 0 and 2 at 25 ° C at atmospheric pressure,

- the acid solution also contains nitric acid,

- the acid solution comprises between 1% and 20% by volume of nitric acid 3.6 N relative to the volume of water,

- the acid solution comprises between 1% and 2% by volume of nitric acid 3.6 N relative to the volume of water,

- the acid solution contains between 10% and 20% by volume of nitric acid 3.6 N relative to the volume of water,

- the acid solution comprises between 80% to and 90% by volume of 1 N hydrochloric acid and between 10 and 20% of 3.6 N nitric acid,

- the acid solution, after 1 to 5 hours at more than 125 ° C, contains fluorine ions in solution, in a concentration of less than 2.10 ' ³ mole / L,

the process does not generate any final waste, the neo-products obtained being usable industrially in specific consumption sectors,

- in addition, at the end of the treatment of the composite mineral product containing asbestos within the reactor, the residual solution obtained is used as a raw material for mineral synthesis operations,

- in addition, at the end of the treatment of the composite mineral product containing asbestos within the reactor, the residual solution obtained is reused in the context of a mineral synthesis process in which the pH of the solution is neutralized acid residue, in order to extract the metal ions therefrom and recover clear, uncharged water, the latter being able to be used again in the context of the present invention.

The invention also provides an installation for hydrothermal destruction of a mineral composite product containing asbestos comprising at least one reactor, which installation is specially configured to carry out the process of the invention.

With the proposed process, the hydrothermal asbestos destruction process generates no ultimate waste. All neo-products, including silica and residual solution, are the subject of identified consumption channels.

Detailed description of an exemplary embodiment

The description which follows with reference to the accompanying drawings, given by way of nonlimiting examples, will make it clear what the invention consists of and how it can be carried out.

In the attached drawing:

- Figure 1 shows an example of an industrial installation specially configured for the implementation of the method of the invention.

Process

The asbestos-containing composite mineral product which can be treated is typically a used fiber cement cover plate as will be seen in relation to FIG. 1. This plate results from the mixture of a cement composition with asbestos fibers .

Preferably, first of all, the plates are cleaned to remove foreign elements, in particular organic, which may have become attached to them over time, such as lichen or mosses.

The plates are then placed in a reactor which is an enclosure which can be closed to allow it to be pressurized and which can be heated directly and / or indirectly. An acid solution is present or introduced into the reactor and the plates are immersed in this acid solution. Indirect heating can be obtained by heating the acid solution which is sent to the reactor. Preferably, this reactor is thermally insulated in order to reduce heat losses.

The acid solution includes water, hydrochloric acid, nitric acid. A solid compound comprising at least one fluorine atom is placed in the reactor in contact with the acid solution. This solid compound is essentially insoluble in the solution and in practice its solubility is at most 0.01% according to standard ASTM-D-543. In a variant, a solid compound is added comprising at least one fluorine atom soluble in the acid solution. In all cases, the generation of fluorine ions is very low and the concentration of fluorine ions during treatment does not exceed 2.10 ' ³ mole / L in the acid treatment solution.

It is important to note that unlike the process of document US5258131, there is in the present invention no addition of hydrofluoric acid to a high dosage (in this document US5258131, hydrofluoric acid is added to obtain a concentration between 1 and 10%, i.e. 2 to 8% by mass) and, above all, the siliceous skeleton of the treated composite mineral product is preserved, even microscopically up to a nanometric scale, unlike the process of this same document. The silica obtained at the end of the treatment according to the invention is amorphous, very pure (> 95%), has retained its fibriform appearance and has not been transformed into fluorosilicate.

An example of the composition of this acid solution is as follows: 850 to 900 liters of hydrochloric acid diluted to 1N to which is added 100 to 150 liters of nitric acid diluted to 3.6N for the treatment of 100 kg of plates.

Under these conditions, a duration of treatment of the plates is expected to be approximately 48 hours with this acid solution maintained at approximately 200 ° C. and under a pressure of approximately 16 bars. However, depending on the conditions and the type of plaques, the treatment may be shorter and treatment is envisaged for 2 to 4 hours.

The solid compound comprising at least one fluorine atom is preferably TEFLON® but, in practice, it is possible to use other products and for example polymers comprising fluorine (fluoropolymers) including in the form of powder, granules, plates or bars or, again, of the internal coating of the reactor. Examples of fluoropolymers that may be mentioned: polytetrafluoroethylene (PTFE), a polymer comprising perfluoroalkoxy groups, a fluorinated ethylene propylene copolymer (FEP), a copolymer of ethylene and chlorotrifluoroethylene (ECTFE), poly (ethylene- cotetrafluoroethylene) (ETFE), poly (vinyl fluoride) (PVF), poly (vinylidene fluoride) (PVDF), polychlorotrifluoroethylene (PCTFE), a copolymer of vinylidene fluoride and chlorotrifluoroethylene, compounds containing perfluoropolyether groups (PFPE) or perflooroalkoxy (PFA).

The solid compound comprising at least one fluorine atom is a spectator of the chemical reaction which takes place in the reactor and is therefore found practically unchanged at the end of the reaction.

At the end of the treatment, a solid residue of approximately 30 Kg having retained the initial geometric shape is obtained as well as 1070 Kg of residual solution originating from the initial acid solution and from the dissolution of the leached ions of the composite mineral product which has been treated.

Concerning the residual solution, a concentration of a few tens of mg of fluorine ion in the residual acid eluate is typically measured, ie approximately 30 mg / l. This fluorine ion not being part of the basic acid cocktail (HCl + HNO3), nor common drinking water at this concentration, can therefore come, either partly from the asbestos-cement composite material, certain cements which may contain a little fluorite, or, for all or part, of the fluoropolymer coating since it alone is capable of supplying it in the case where only one fluoropolymer is present. In the variant where a solid compound is added comprising at least one fluorine atom and which is soluble in the acid solution, this addition will be made at a very low concentration so as not to exceed the 2.10 ³ mol / L provided.

The solid residue is the result of the extraction of metal ions from the treated composite mineral product, the solid compound comprising fluorine in particular in powder form not being considered as belonging to the solid residue. The solid residue is 95% minimum consisting of silica, SiO ₂ , amorphous which can find various uses because of its high reactivity and high purity. This pure and amorphous siliceous residue can be used, for example, in the fields of construction, the cement industry, photovoltaics, glass, and electronics.

It is also possible to use the eluate for the synthesis of salts, gypsum or other minerals. The acid eluate therefore represents a raw material for the synthesis of salt, gypsum and other minerals (hydrotalcite, hydroxyapatite, ...) after separation, concentration or precipitation. The ultimate aqueous phase can be directly reused in the context of this device.

Thus, the method of the invention does not generate any ultimate waste, the neoproducts obtained being usable industrially in specific consumption sectors.

Device

In Figure 1, there is shown an installation for the treatment of ίο fiber cement sheets 10 containing asbestos. This installation comprises two reactors 1, 2. The first reactor 1 is open and its cover 9 has been removed in order to allow the introduction of plates 10 which are arranged on a suitable support 11. To maneuver these various elements, a gantry crane 12 is used here. The second reactor 2 is closed, its cover being fixed in place, and it can therefore be pressurized. Reservoirs allow the storage of the various liquid products used and / or of the residual solution obtained after treatment. The acid solution used can be delivered ready for use and stored in one of the tanks or, as in the example shown, the products used to make the solution are stored separately in the tanks. In the example of FIG. 1, the tank 4 is used for the storage of water and the tank 3 for the storage of hydrochloric acid, these products being adequately mixed in the reactor. Pipes 5, 6, 7 allow the circulation of liquids within the installation and pumping and pressurizing means 8 are also used. Heating means, not shown, are also present in order to heat the acid solution in which the plates bathe.

Depending on the mode of implementation chosen, the reactor has an internal wall lined with a coating based on fluorine and for example TEFLON® and / or another fluoropolymer and / or the fluoropolymers are introduced into the reactor in the form powder, granules, bars, plates or any other form allowing the fluoropolymers to come into contact with the acid treatment solution.

Given the pressurization of the reactor and the heating of its contents, the reactor is metallic in order to be able to resist the stresses which result therefrom. For the choice of reactor metals, one can consult the document "Engineering Techniques - Metallic Materials", Pierre-Jean Cunat, 2000, vol. MB3, n ° M4541, pp. M4541.1-M4541.31 (ISSN 17628733). In this document, pages 7 and 8, it is advisable for a reaction in a hot environment and in the presence of HCl (corrosive product), alloys of the "austenitic" type with a high content of chromium and nickel, slight content of Molybdenum and low carbon, type: 304L, 316L, 904L. There is also a very strong alloy called "Inconel 625".

In addition to the devices described above, other devices are present in particular as a function of the pre-treatments of the plates and / or post-treatments (after the destruction of the asbestos in the reactor) of the residual solution and / or the solid products. obtained.

Sensors and detectors are implemented within the installation in order to monitor the treatment, to detect anomalies and to be able to regulate the treatment by means of control and command, in particular valves, pumps and the heating means.

Preferably, the installation and the storage means are arranged in one or more suitable retention tanks in order to be able to recover the products used in the event of a leak and / or neutralize them locally. Preferably, the installation is arranged in a room having means for aeration and also for filtering the gases or vapors which can be released by the products used. In practice, the installation is adapted to comply with the standards in force.

Claims (10)

1. Process for hydrothermal destruction of a composite mineral product containing asbestos in chrysotile form in which the composite mineral product containing asbestos is placed in a reactor under vapor pressure and comprising an acid solution at high temperature and in which bathes the composite mineral product containing asbestos, the pressure in the reactor being at least 0.2 MPa and the temperature at least 125 ° C, the acid solution comprising at least water, l hydrochloric acid and nitric acid, characterized in that there is also a solid compound containing at least one fluorine atom in the reactor and in contact with the acid solution, the acid solution not comprising hydrofluoric acid and in that a solid compound is used comprising at least one fluorine atom, the release of fluorine ions of which in contact with the acid solution produces a very low concentration of fluorine ions in the acid solution , said very low concentration being less than 2.10 ' ³ mole / L. 2. Method according to claim 1, characterized in that the reactor has an internal wall and in that the solid compound comprising at least one fluorine atom is a protective layer of the internal wall of the reactor and lining the internal wall of the reactor as well as the ancillary members in contact with the acid solution, in particular pipes, pumps and a sample holder with which the composite mineral product containing asbestos is introduced and maintained in the reactor. 3. Method according to claim 1 or claim 2, characterized in that the solid compound comprising at least one fluorine atom is in the form of powder or granules introduced into the reactor. 4. Method according to any one of the preceding claims, characterized in that the solid compound comprising at least one fluorine atom is a spectator of the reaction, that is to say that it does not participate chemically in the chemical equilibrium of the reaction taking place in the reactor and in that the said solid compound comprising at least one fluorine atom is chosen from the compounds essentially insoluble in the acid solution or the compounds soluble in the acid solution. 5. Method according to claim 4, characterized in that the solid compound comprising at least one fluorine atom is chosen from polytetrafluoroethylene (PTFE), a polymer comprising perfluoroalkoxy groups, a fluorinated ethylene propylene (FEP) copolymer, a copolymer d ethylene and chlorotrifluoroethylene (ECTFE), poly (ethylene-cotetrafluoroethylene) (ETFE), poly (vinyl fluoride) (PVF), poly (vinylidene fluoride) (PVDF), polychlorotrifluoroethylene (PCTFE) vinylidene fluoride and chlorotrifluoroethylene, compounds having perfluoropolyether groups (PFPE), perflooroalkoxy (PFA) and combinations thereof. 6. Method according to any one of the preceding claims, characterized in that the pressure is between 0.2 MPa and 2 MPa, and in that the temperature is between 125 ° C and 220Ό for a treatment time of the product mineral containing asbestos within the reactor between 2 hours and 72 hours. 7. Method according to any one of the preceding claims, characterized in that the acid solution comprises between 80% and 90% by volume of 1N hydrochloric acid and between 10 and 20% of 3.6N nitric acid. 8. Method according to any one of the preceding claims, characterized in that the composite mineral product containing asbestos is asbestos-cement. 9. Method according to any one of the preceding claims, characterized in that, in addition, at the end of the treatment of the composite mineral product containing asbestos within the reactor, the residual solution obtained is used as raw material for mineral synthesis operations. 10. Installation for hydrothermal destruction of a composite mineral product containing asbestos comprising at least one reactor (1,2), characterized in that it is specially configured to carry out the process of any one of the preceding claims.