Method for recovering an element from a porous substrate via an in-situ generated aqueous transport foam

Abstract

The present invention relates to a method for transferring and recovering, in situ and by means of an in-situ generated aqueous transport foam, at least one element present in a predetermined volume of a porous substrate, wherein the method comprises the following successive steps: delimiting a volume of the porous substrate by installing impermeable barriers surrounding the volume and extending to the surface of the porous substrate, and placing, over the entire surface of the delimited volume and in contact with the porous substrate, a porous retaining means capable of maintaining the porous substrate in position; bringing a foaming aqueous solution into contact with the delimited volume; generating a suction, either simultaneously with or subsequent to the preceding contact step, within the delimited volume and maintaining the suction, whereby a particle-transport foam is formed from the foaming aqueous solution and ambient air within the delimited volume of the porous substrate, wherein the foam rises toward the surface of the delimited volume while entraining the at least one element, and recovering the foam at the surface above the delimited volume and recovering the element from the foam thus recovered.

Description

[0001] METHOD FOR RECOVERING AN ELEMENT FROM A POROUS SUBSTRATE VIA AN IN-SITU GENERATED AQUEOUS TRANSPORT FOAM

[0002] TECHNICAL FIELD

[0003] The present invention relates to the general field of treatment of divided porous or solid substrates and, more particularly, to the field of recovery of elements, such as contaminants or substances of interest, contained in divided porous or solid substrates.

[0004] Indeed, the present invention proposes an in-situ method applicable on site making it possible to recover at least one element contained in a divided porous or solid substrate, in particular in the sub-surface zone and, more particularly, in the arable horizon of this porous substrate in the case of a soil (0 to 100 cm), this element typically being in the form of liquid or solid particles. This method involves or uses suction which allows the in-situ formation of an aqueous foam for transporting particles within the porosity of this porous substrate, the rise of the latter towards the surface of the porous substrate, then finally the recovery of this foam loaded with at least one element at the surface of the divided porous or solid substrate.

[0005] Such a process is of particular interest for on-site decontamination of soils that have been subject to radiological or industrial contamination, agricultural horizons treated with pesticides or for recovering recyclable materials.

[0006] The novelty is brought, more particularly, by the in-situ generation of the aqueous transport foam, made possible thanks to the porosity of the porous substrate which is most often finely divided in itself (particulate) and a suction system creating a depression in depth (up to 1 m) in the porosity of the porous substrate, the foam rising to the surface where it is recovered, by this same suction. The porous substrate, in particular in the form of earth, does not need to be excavated because it is treated directly, in the compact natural structural state i.e. in-situ, from the surface of this substrate (on site) STATE OF THE PRIOR ART

[0007] Soil contamination by radioactive substances can most often result from industrial or research activities involving these substances. However, contamination can unfortunately result from known incidents or accidents such as, for example, accidental spills or fires, which have led to the uncontrolled release of large quantities of pollutants into the environment.

[0008] After a nuclear accident, the subsurface horizon of the soil around a nuclear power plant becomes contaminated by the presence of radionuclides fixed mainly on more or less aggregated phyllosilicates (particles generally called isolated clays < 2 pm or aggregated from 2 to 50 pm). In the case of caesium, this fixation mechanism on phyllosilicates is almost irreversible and concentrates the contamination in the first 10 cm of the soil, making it possible, however, to avoid a deep migration of radionuclides.

[0009] Among the treatments used to remedy this type of contamination of the sub-surface horizon (0 to -100 cm), we mainly find ex-situ treatments, with excavation, on-site or off-site and in-situ treatments without or with rehabilitation.

[0010] Ex-situ processes with excavation are the most used following nuclear accidents. The main techniques implemented on excavated soils are (i) chemical washing such as washing with oxalic acid at a temperature of 95°C, (ii) thermal desorption, in particular by heating the soils to a temperature of 1300°C and (iii) liquid / solid separation techniques such as, for example, particle size sorting by sieving and / or hydrocycloning and / or flotation of contaminated fine particles.

[0011] However, most chemical and thermal washing processes are aggressive and destroy the agronomic properties of the soil. Some advantageously reduce the volume of waste by concentrating the contamination in a smaller clay volume (as in hydrocycloning or flotation), but they require costly land excavation that can degrade ecosystems and often heavy off-site treatments. In summary, the main limitations of ex-situ processes are related to their environmental impacts, implementation costs (excavation + transport + treatment) with problems of soil recycling and waste management / storage in the long term. The need to use in-situ processes for the treatment of subsurface radio-contaminated soils is therefore obvious.

[0012] In-situ methods without land reclamation include cement confinement, freezing confinement, and vitrification confinement. These methods have one or more of the following disadvantages: can only be used on porous and permeable soils, increase in volume, need for chemical compatibility, maintenance cost, energy cost, and generation of volatile compounds.

[0013] The literature shows that no in-situ process is truly satisfactory and used to treat sub-surface horizons (0 to -100 cm). For in-situ processes with land rehabilitation, there is phytoremediation, which is a process of transferring the contaminant from the soil to the plant in the form of a nutrient. It is very slow, suitable for moderate pollution levels, and not suitable for particulate pollutants. As for the second emerging method of electro-migration extraction, it is also suitable for ionized pollutants such as heavy metals and certain organic molecules. The nature of the soil must not be too permeable and heterogeneous; this process is therefore suitable for low-permeability clay soils with minimal electrical conductivity. Electrodes are implanted in such a way as to generate an electric current in the soil that causes the ions to migrate towards the oppositely charged electrodes.A solution called an "electrolyte" can be used to bring about ideal conditions in terms of pH and reactivity with the target pollutants to enable their extraction. Pollutant recovery can, for example, be done by pumping.

[0014] Laboratory tests on soils contaminated by non-radioactive cesium have shown that cesium extraction is possible by electromigration. However, as with phytoremediation, effectiveness depends on the sorption / desorption capacity of cesium present in clays, an element that competes with potassium K (a plant nutrient) regarding its ion exchange. In addition, the duration of these treatments is long, with the application of these methods over several days, months, or even years in the case of phytoremediation. In-situ treatment for the extraction of pollutants or non-nuclear recoverable materials particularly concerns the recovery of oil, metals and for the rehabilitation of in-situ soils.In these applications, many documents, such as US patent 6,210,955 [1], relate to the use of surfactants which can be used in foam form to improve the decontamination / extraction yields of a pollutant at depth.

[0015] These processes utilize the confinement / sealing properties of aquifers and rock reservoirs to allow foam flow into the deep subsurface. A pressure difference is used to vector the foam flow injected from an intrusive injection pipeline (well) into the ground to an intrusive recovery pipeline. The foam flowing in the porous medium is formed in situ by injection of foaming solution alternating with gas injection or ex-situ by an on-site generator. The use of a foaming solution for decontamination / recovery in the form of foam partially overcomes gravity and improves reservoir flushing (shrew-thinning property of foams). The surfactants that form the foam also increase oil mobilization by reducing surface energies.The use of foam for in-situ treatment of deep soils is a mature and industrialized process.

[0016] Among the processes applied to a sub-surface horizon of a soil, Budianta et al, 2006 [2] propose a concept of soil washing process by in-situ sedimentation. The principle is to separate the smallest particles which do not sediment or do so less quickly than the larger particles by adding water to a volume of soil confined by walls. This volume of soil is destructured dry then the earth is suspended in a solution and agitated by bubbling air. The soil suspension isolated from the surface undergoes an injection of air to maintain the mixture of particles within the suspension and allow washing and sedimentation of the particles. This suspension causes an increase in the polluted volume to be managed by the process (dispersion / washing solution). Fine particles carrying fixed heavy metals such as cesium, cadmium and copper and not washed are found more at the surface and concentrate the pollution.They could be collected by raking for further processing or stored.

[0017] This idea of ​​sorting by in-situ sedimentation and washing does not mention the recovery of fine particles sensitive to the fixation of pollutants (heavy metals) and accumulated on the surface of the soil. The proposed field application includes several stages to carry out the treatment of the soil, namely destructuring, isolation, suspension, bubbling, evaporation / drying and possibly recovery of particles on the surface.

[0018] Sedimentation sorting is a function of particle size, which requires efficient dispersion of all soil particles: despite their small size, clays are rarely free within the soil and its pore network. They are present in different forms, which limit the use of this process: in particulate form adhered to the surface of larger particles that are difficult to recover by in-situ sedimentation (large grains of sand) or agglomerated together.

[0019] For the treatment of porous media in the form of heaps, there is heap leaching (or in English "Heap Leaching") which is used in particular to leach so-called "low-grade" uranium ore. Drip irrigation or foam drainage is applied to the surface of the heap to gravity-feed the leaching liquid into the porous network of the heap, as described in international application WO 2023 / 203298 A1 [3]. The uranium, present in the heap in the form of agglomerated ore, is leached by a dilute acid solution which infiltrates and percolates gently by gravity (downward) into the porosity of the heap. The leaching solution is finally collected by percolation in a basin present below the heap, before undergoing a series of other treatments.

[0020] The use of foam layer irrigation described in [3] serves as a reservoir through which liquid is brought by surface drainage of the pile. It allows the surface of the pile to be completely covered and solves the problem of dry areas on the surface encountered with drip irrigation. But no foam is actually present in the porosity of the pile. The flow of liquid is directed downwards with the presence of preferential paths from gravity irrigation and the clogging of the pile by clays is still unresolved. US patent 4,080,419 [4] has the main objective of improving this type of heap leaching process of coarsely crushed or fragmented ores (centimeter-sized particles) by using foam introduced into the pile.The means of foam injection are not precisely described: most often the reactive and foaming solution percolates through the coarse porous network and then undergoes an injection of light gas from the bottom of the pile to form a foam which rises into the porosity. The use of gas heavier than air could allow gas injection from the top of the pile. The foam after drainage into the porosity can be regenerated several times in order to reduce the quantity of leaching solution.

[0021] The inventors therefore set themselves the main goal of proposing a safe, rapid and easy-to-implement method for treating in situ, from its surface, a soil presenting, at a depth of 0 to -100 cm, contamination such as particulate contamination with a radionuclide such as caesium trapped by fine phyllosilicates or more commonly called fine and agglomerated clays, without presenting the drawbacks of the methods of the prior art.

[0022] STATEMENT OF THE INVENTION

[0023] The present invention makes it possible to achieve the goal set by the inventors. Indeed, the latter propose an in-situ process, rapid, easy to implement and with low environmental impact because it does not require expensive technical devices, nor large volumes of chemical components or reagents, thanks to which, for example, it is possible to efficiently recover polluting elements (particular case of fine clay particles charged with caesium) or of interest in particular trapped in the horizon of a soil between 0 (i.e. at the level of the surface in contact with the external environment) and -100 cm (sub-surface / arable zone).

[0024] The arable horizon to be treated and targeted by the present invention is rather in competition with ex-situ surface processes because the earth can be directly excavated and no in-situ process is currently competitive. Treating in-situ the arable sub-surface horizons (0 to -100 cm) of soils with mosses presents a new and innovative aspect. Indeed, the process according to the invention makes it possible to treat in-situ a polluted area without excavation while minimizing disturbances to the surrounding ecosystems, without installing heavy instrumentation around the polluted site.

[0025] The present invention proposes a method with a device and mechanism for generating in-situ transport foam) which allows the direct in-situ extraction of radio-contaminated clays, by fixing cesium, from the soil. The device used allows for rapid intervention and application of the extraction process on the ground which is carried out by aqueous transport foam and is intended to be rapid and efficient, with extraction being carried out in a maximum of a few days. The method according to the invention is particularly well suited to the case of localized radiological contamination of the "hot spot" type.

[0026] The foam generated in-situ by suction has the role of detaching the contaminated clays from the environment and then this same suction allows the foam loaded with contaminated clays to be transported from the depth to the surface, in an upward manner, then recovered. The particles contaminated with cesium are contained in the foam network (in the liquid films and / or at the water-air pocket interfaces) which confines the radioactivity throughout the implementation of the process and secures it. Once the foam generated in-situ rises to the surface, thanks to the maintained suction, it rises above ground, advantageously in a recovery column placed on the ground, then is dried to recover only a residue of contaminated clays. In other words, the foam generated in-situ rises in an upward flow in the porous substrate of the soil type (finely divided) in the form of lamellae.

[0027] Foam lamellae in porous media are defined as thin, interconnected liquid films separating gas pockets. They constantly evolve and rearrange themselves as they move through the porous media.

[0028] The main objective of the foam used in the process according to the invention is, in addition to improving the sweeping / wetting of the porous medium, to exert a detachment force on micrometric particulate pollutants, typically phyllosilicate particles, adhered in the porous medium. Once detached, the particles are transported by these same lamellae to the surface for recovery and containment. In summary, the process according to the invention makes it possible to release, make mobile and then transport, out of the porous medium, the adhered, agglomerated and possibly contaminated fine particles thanks to the foam lamellae formed and in-situ upward flow under suction.

[0029] In addition, the method according to the invention uses a single suction which serves, at the same time, for the in-situ generation of the transport foam, the upward vectorization towards the surface of the latter and then its recovery. The method according to the invention is clearly distinguished from the methods of the prior art using transport foams for the in-situ remediation of soils [1]. In these methods, the remediation is carried out by pressurized injection of a flow of foam (pump / compressor) and an extraction pump. This pressurized supply is functional in the context of the treatment of confined or sealed reservoirs at depth but becomes troublesome for the in-situ treatment of arable surface horizons (0 to -100 cm). The present invention does not require any air supply since it is continuous air and ambient air which are used during the suction.

[0030] Furthermore, for the majority of these industrialized processes, the foam undergoes, at depth, a lateral flow with possible losses / migrations of liquid and pollutant. The invention generates a controlled, upward and secure flow of the contaminant to be transported from the sub-surface to the surface and then to its final suction above ground. This upward and confined flow in the polluted volume of the soil prevents the dispersion / migration of the pollutant into healthy areas of the soil.

[0031] Finally, the method according to the invention differs from US patent 4,080,419 [4] because the foam in this patent is a leaching (dissolving) foam and does not carry solid or liquid particles like the foam of the present invention. The foam lamellae are too wide and fragile in the macroporosity of the ore pile and only serve to wet the interior of the pile to wash it (leaching). In addition, the generation of the foam in US patent 4,080,419 [4] is carried out by injecting pressurized gas into the large porosity because it is fractured and heterogeneous, inducing a high permeability of the pile. The foam forms in the macroporosity by bubbling (bubbled) through the solution.The present invention relates to the treatment of finely divided porous media (particles ranging from micrometers to a few millimeters) with lower permeability and uses suction to bring both the foaming solution, most often, through the periphery of the volume to be treated and ambient air directly into the micro-porosity of the volume to be treated to form a foam with stable micro-lamellae capable of transporting particles. The present invention does not require any air servitude / injection. A homogeneous porosity of the porous substrate targeted in the present invention makes it possible to force the air / liquid mixture and generate the foam in-situ.

[0032] Remarkably, the properties of the method according to the present invention can be used not only in methods for remediating soils contaminated by radionuclides but also in methods for extracting particulate micropollutants in the context of decontaminating agricultural and industrial horizons but also in methods for extracting recoverable materials. The method according to the invention applies to non-soluble, solid or liquid particulate or interest pollutants of nanometric to micrometric size, transportable through the porous network of the substrate, of inorganic / mineral type, poorly soluble organic types (hydrocarbons), but also soluble.

[0033] In general, the present invention relates to a method for transferring and recovering on site and by aqueous transport foam generated in situ at least one element present in a predetermined volume of a porous substrate comprising the following successive steps:

[0034] - delimiting a volume of said porous substrate by installing impermeable barriers surrounding said volume and opening onto the surface of the porous substrate and placing, over the entire surface of the delimited volume and in contact with the porous substrate, a porous holding means making it possible to hold the porous substrate,

[0035] - bring a foaming aqueous solution into contact with the delimited volume,

[0036] - generating suction, simultaneously or deferred, with the previous contact in the delimited volume and maintaining this suction, whereby a particle transport foam is formed from said foaming aqueous solution and the ambient air in the delimited volume of the porous substrate and rises towards the surface of the delimited volume carrying said at least one element, and - recovering the foam on the surface above the delimited volume and recovering said element from the foam thus recovered.

[0037] By "porous substrate" or "porous substrate or divided solid" is meant a substrate in particulate, fragmentary and / or lumpy form. The constituents of this substrate are particles or aggregates of organic and / or inorganic elements, resulting from natural processes or grinding, crushing and / or agglomeration processes. The pores of such a porous substrate or divided solid correspond to the empty spaces present between the stack of solid elements constituting it. The size (i.e. the largest dimension) of the particles and aggregates composing the porous substrates targeted by the invention can range from micrometers to a few millimeters (for example, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm or even 8 mm) allowing generation, in situ by suction, of the foam containing stable liquid lamellae generated in the micropority of the porous substrate.The two expressions "porous substrate" or "porous or divided solid substrate" are equivalent in the present invention and can be used interchangeably.

[0038] Typically, the porous substrate from which one or more elements are to be extracted by the method according to the invention is in the form of soils or finely divided piles. This porous substrate is in particular chosen from the group consisting of land such as fallow land, bare land for agricultural activity, cultivated agricultural land, a green space, a stadium or field for sports activity or a horticultural garden; sand; broken or fractured geological rock formations; ore; ore concentrates; coal; mining residues; mining waste; slag; industrial, metallurgical and electronic waste; products containing strategic metals, such as, for example, nickel, cobalt and manganese, from the recycling of lithium batteries also known by the English expression "black-mass" and a mixture thereof.

[0039] The method according to the present invention is particularly suitable for finely divided porous substrates such as permeable and semi-permeable soils, i.e. porous substrates having a permeability coefficient of between 10 -22 m / s (gravel-sand mixture) at 10 -6 m / s (very fine sands and clayey-silty sand). The porous substrate used in the invention is typically dry, not saturated with water. The initial degree of water saturation (% by volume in the porosity) in this porous substrate prior to the implementation of the method according to the invention can be variable, preferably as little saturated as possible (0 to 40%), promoting the generation of foam.

[0040] Typically, the volume of the porous substrate from which at least one element is to be extracted is located in the area extending from the surface of the porous substrate (in contact with the external environment, i.e. level 0) to a depth of 100 cm. This area can be defined as the sub-surface of the porous substrate or as the arable zone of a soil.

[0041] In a particular form of implementation, the volume of the porous substrate from which at least one element is to be extracted is located in the zone extending from the surface of the porous substrate (in contact with the external environment, i.e. level 0 cm) to a depth of -100 cm. Indeed, the presence of pollution is significant in the subsurface of soils because it is essentially of anthropological origin, such as, for example, transport, industries, mines, pesticides or nuclear accidents. In this general context, we can cite phyllosilicate particles (clays) which trap radioactive caesium most often in the first ten cm of a soil containing clays.

[0042] The element(s) that are primarily desired to be extracted from the porous substrate are in the form of solid particles or small, non-soluble liquid droplets considered to be polluting or of interest. These particles or droplets have a size of between 1 nm and 10 pm in the steric limit of the lowest porosity zones (or in English "pore throat") of the porous substrate and in particular a colloidal size of less than 1 pm. Such a size is particularly suitable for allowing transport of the target fine particles by the foam lamellae within the network of interconnected pores of the porous substrate without clogging it.

[0043] Typically, the element(s) and in particular the colloidal-sized element(s) to be extracted from the porous substrate comprises / comprise or is / are made up of radionuclides, metals, ores, metal oxides, silicates, phyllosilicates, nanoparticles, organic matter, oils, organic solvents, and microorganisms. Water-soluble elements can also be extracted by the foam used in the invention created under suction.

[0044] In a particular embodiment, when the element(s) to be extracted from the porous substrate is / are one or more contaminating elements, it is or they are chosen from the group consisting of phyllosilicates or clay particles radio-contaminated for example with caesium, phyllosilicates or clay particles fixing metals such as toxic metals such as copper, asbestos fibers, mercury microdroplets, nanoparticles such as titanium dioxide nanoparticles (TiC>2) in particular from sun creams, cerium oxide in particular from diesel gasolines, particles of heavy metal oxides such as copper, zinc, nickel and lead, pesticides such as organochlorine pesticides and organophosphorus pesticides, oil microdroplets, organic solvent microdroplets (PCB), hydrophobic microsubstances such as per- and polyfluoroalkyl substances like, for example,surfactants such as PFAS used in fire extinguishers, plastic microparticles, colloidal organic matter and bacteria.

[0045] In another particular embodiment, when the element(s) to be extracted from the porous substrate is / are one or more elements of interest, it is or they are chosen from the group consisting of gold, silver, uranium, platinum, palladium, lithium, nickel, cobalt, manganese, aluminum, zinc, copper, rare earths, niobium, tantalum, scandium, chromium and one of their alloys.

[0046] The first step of the method according to the invention consists of confining the volume of porous substrate from which one or more elements are to be extracted, from the surface of this porous substrate. This step comprises, on the one hand, the peripheral encircling of the volume and, on the other hand, the mechanical surface resistance of the volume of the porous substrate to be treated.

[0047] To achieve this strapping, waterproof barriers are installed, arranged, and embedded in the porous substrate. These waterproof barriers can be formed from a single module or several modules joined together, which allows the foam to be contained and produced in the environment and prevents its lateral migration but also from the surface for foam recovery.

[0048] The impermeable barriers used in the present invention are typically in the form of an enclosure, column or tube made of metal such as stainless steel or plastic. The ends of this enclosure, column or tube positioned opposite each other are open.

[0049] The impermeable barriers used, and in particular the enclosure, the column or the tube, have a cross-section having any shape and in particular a circular, oval, parallelepiped, rectangular, square or hexagonal section. The perimeter of this cross-section is between 10 cm and 2 m or 3 m and in particular between 10 cm and 100 cm. In a particular embodiment, the impermeable barriers used in the context of the present invention are typically in the form of an enclosure, a column or a tube with a circular or parallelepiped section.

[0050] The impermeable barriers used in the context of the present invention and in particular the enclosure, the column or the tube open onto the surface of the porous substrate and can extend vertically from this surface, thus forming a column called a "suction column" also referred to as a "recovery column" facilitating the rise and suction of the foam emerging on the surface of the delimited volume of the porous substrate. The height of the impermeable barriers corresponding to the sum of the height in the porous substrate and the possible height above the surface of the porous substrate is between 10 cm and 2 m and in particular between 40 cm and 100 cm, in particular for the case of contamination of 0 to - 10 cm with a suction column. A person skilled in the art will be able to determine, without inventive effort, the dimensions of the impermeable barriers best suited as a function of the surface and depth of the volume to be treated / confined.

[0051] The mechanical surface retention of the volume of the porous substrate to be treated consists of applying, on this surface, a porous means for holding the porous substrate. The latter must have a porosity allowing the passage of the foam containing the element(s) to be recovered, produced in the volume of the porous substrate during its treatment but limiting the suction and destructuring of the porous substrate when a suction (depression) is generated and maintained in the volume of the porous substrate to be treated. A person skilled in the art will be able to determine the size of the porosity of this holding means most suitable according to the granulometric properties of the porous substrate to be treated and the element(s) to be recovered.

[0052] In a particular embodiment, this holding means corresponds to a grid, in particular a metal grid, the shape of which is identical or substantially identical to the cross-section of the impermeable barriers used, and in particular of the enclosure, the column or the tube. Typically, the size of the pores of this holding means, and in particular of this grid, is between 10 μm and 1 mm (rubble, ores, etc.) and in particular between 20 μm and 100 μm, in particular to avoid clogging of the grid by the targeted particles, the diameter of which is advantageously less than 10 μm.

[0053] In the context of the method according to the invention, any means making it possible to create suction on the surface of the delimited volume and, in fact, in the delimited volume of porous substrate can be used.

[0054] Typically, the suction is generated in the limited volume of the porous substrate by means of a pump, such as a vacuum pump, connected, in a sealed manner, to the impermeable barriers, in particular via a suction cone. This suction cone has a first open end and a second end having an orifice, positioned opposite one another. The suction cone connects, via its first open end, to the impermeable barriers and in particular to the enclosure, the column or the tube at the open end of the latter at the ground surface and, when they have a suction column, at the open end of this column. Thus, the first open end of the suction cone has a shape identical or substantially identical to the cross-section of the impermeable barriers, in particular of the enclosure, the column or the tube and, more particularly, of the suction column.

[0055] Advantageously, the depression generated by the means making it possible to create suction on the surface of the delimited volume and in particular the vacuum pump is, at most, between -200 mBar and -400 mBar (case of a dry porous substrate without foam lamella) and maintained in this range for the time of contact of the limited volume of porous substrate with the foaming aqueous solution.

[0056] The foaming solution used in the process according to the invention comprises, as solvent, water, thus justifying the name of aqueous foaming solution. By "water" is meant tap water, deionized water or distilled water. Advantageously, the aqueous foam used in the process according to the invention may be a neutral, acidic or basic foam, in particular depending on the possible additional active ingredient(s) that it may contain, in particular to facilitate the extraction of more or less soluble elements.

[0057] The aqueous foaming solution used in the process according to the invention comprises at least one foaming agent. Any foaming agent known to those skilled in the art can be used in the context of the invention. In particular, the aqueous foaming solution used in the process according to the invention comprises at least one foaming organic surfactant.

[0058] By "organic surfactant" is meant an organic molecule comprising a lipophilic (apolar) part and a hydrophilic (polar) part. By "foaming organic surfactant" is meant an organic surfactant as previously defined, also having a hydrophilic / lipophilic balance (or HLB for "Hydrophilic-Lipophilic Balance") of between 3 and 8. As a reminder, the HLB value of a surfactant can easily be obtained using the Davies formula [5] and the HLB tables for different chemical groups, available to those skilled in the art.

[0059] In particular, the aqueous foaming solution constituting the aqueous foam used in the invention may comprise a single organic foaming surfactant or a mixture of at least two organic foaming surfactants chosen from non-ionic foaming surfactants, anionic foaming surfactants, cationic foaming surfactants, amphoteric surfactants, surfactants with a Bolaforme type structure, surfactants with a Gemini type structure and polymeric surfactants.

[0060] More particularly, the aqueous foaming solution used in the context of the present invention comprises a single foaming organic surfactant or a mixture of at least two foaming organic surfactants chosen from non-ionic foaming surfactants, anionic foaming surfactants and cationic foaming surfactants. In the mixtures of foaming organic surfactants, at least two surfactants are chosen from the same family or from two different families chosen from non-ionic foaming surfactants, anionic foaming surfactants and cationic foaming surfactants.

[0061] More particularly, said at least one foaming organic surfactant contained in the aqueous foaming solution used in the context of the present invention is at least one anionic foaming organic surfactant. Alternatively, said at least one foaming organic surfactant contained in the aqueous foaming solution used in the context of the present invention is at least one cationic surfactant. As a further variant, said at least one foaming organic surfactant contained in the aqueous foaming solution used in the context of the present invention is at least one non-ionic surfactant.

[0062] Anionic surfactants are surfactants whose hydrophilic portion is negatively charged. A foaming anionic surfactant suitable for use in the present invention is typically selected from the group consisting of sulfuric acid esters, phosphoric acid esters, alkyl or aryl sulfonates, alkyl or aryl sulfates, alkyl or aryl phosphates, alkyl or aryl sulfosuccinates, or alkyl or aryl sarcosinates combined with a counterion such as an ammonium ion (NH4 + ), a quaternary ammonium such as tetrabutylammonium, and cations and in particular alkali metal cations, said cations being such as Na + , Li + , That 2+ , Mg 2+ , Zn 2+ and K +. As foaming anionic surfactants, it is possible, for example, to use tetraethylammonium paratoluenesulfonate, sodium dodecyl sulfate (or SDS), sodium lauryl sarcosinate (or sarcosyl), sodium palmitate, sodium stearate, sodium myristate, sodium di(2-ethylhexyl) sulfosuccinate, methylbenzene sulfonate and ethylbenzene sulfonate.

[0063] The cationic surfactants have at least one hydrocarbon chain and a polar head, the hydrophilic part of said agent being positively charged. A foaming cationic surfactant that can be used in the context of the present invention is advantageously chosen from quaternary ammoniums comprising at least one C4-C22 aliphatic chain associated with an anionic counterion chosen in particular from boron derivatives such as tetrafluoroborate or halide ions such as F-, Br, I' or Cl'. As foaming cationic surfactants that can be used, mention may be made of tetrabutylammonium chloride, tetradecylammonium chloride, tetradecyltrimethylammonium bromide (TTAB), alkylpyridinium halides bearing an aliphatic chain and alkylammonium halides.

[0064] Non-ionic (or neutral) surfactants are compounds whose surfactant properties, in particular hydrophilicity, are provided by uncharged functional groups such as an alcohol, an ether, an ester or an amide, and may contain heteroatoms such as nitrogen or oxygen. Due to the low hydrophilic contribution of these functions, non-ionic surfactant compounds are most often polyfunctional. Those skilled in the art will find information on non-ionic foaming surfactants that can be used in the invention in international application WO 2016 / 202879 [6].

[0065] In the aqueous foaming solution constituting the aqueous foam used in the process according to the invention, said at least one organic foaming surfactant, i.e. the organic foaming surfactant or the mixture of at least two organic foaming surfactants, is present, per liter of solution, in an amount of between 0.1 and 30 g and, in particular, between 1 and 20 g.

[0066] In a particular embodiment, the aqueous foaming solution used in the method according to the invention comprises or consists of:

[0067] - one or more foaming organic surfactants as previously defined and

[0068] - water.

[0069] In another particular embodiment, the aqueous foaming solution used in the method according to the invention comprises or consists of:

[0070] - one or more foaming organic surfactants as previously defined,

[0071] - water and - at least one other ingredient chosen from the group consisting of organic, gelling, viscosifying agents (foam stabilizers); acids / bases (to modify the reactivity of the solution with the porous medium) and oxidizing or reducing salts (to promote a modification of the initial state of the target elements (solubilization / detachment)).

[0072] The aqueous solution used in the process according to the invention is previously prepared by mixing together the water, the foaming organic surfactant(s) and any other ingredient(s) as previously defined.

[0073] In a first embodiment, the contact between the limited volume of the porous substrate to be treated and the aqueous foaming solution involves the supply of the aqueous foaming solution to the periphery of the delimited volume and mechanically held on the surface of the porous substrate to be treated. Indeed, this supply is done by partial irrigation of the surface of the porous substrate located at the periphery of the delimited volume. Irrigation, in particular in the form of a drip at different points of the free surface peripheral to the delimited volume of porous substrate to be treated, must be adapted so as not to saturate this free surface and consequently the porous network of the soil. The permeability of the latter must be taken into account. The water saturation value will determine the liquid fraction of the flowing foam.Typically, for a dry porous substrate, the water saturation value for the most stable foam flow is optimally between 5% and 25% of the total volume of the pore network. Such a saturation value makes it possible to form lamellae stabilized by the two-phase liquid / gas mixture when these two flows pass through the solid pore network of the porous substrate. The liquid / gas mixing is achieved by a first peripheral downward flow then an upward flow within the pores of the limited volume of the porous substrate to be treated.

[0074] In a second embodiment, the contact between the limited volume of the porous substrate to be treated and the aqueous foaming solution is achieved by supplying the aqueous foaming solution, typically at low pressure / flow rate, directly into the delimited volume and mechanically held on the surface of the porous substrate to be treated. Typically, the aqueous foaming solution is thus directly brought deep to the bottom of the impermeable barriers and in particular to the bottom of the enclosure, column or tube either at a single injection point or by different injection points at variable depth within the delimitation module. This second embodiment would make it possible to limit the quantities of aqueous foaming solution used and the dispersion of the aqueous foaming solution by percolation around the area to be treated and to accelerate the process according to the invention.

[0075] Once the limited volume of porous substrate to be treated has been brought into contact with the foaming aqueous solution, the suction to which the delimited volume of the porous substrate is subjected generates a depression greater than the depression obtained before this contact. This depression increases in particular up to a value greater than or equal to -800 mBar and in particular of the order of -900 mBar (i.e. -900 mBar ± 100 mBar). This increase is due to a resistance to the flow (or suction) of air resulting from the formation of a foam and in particular of lamellae of a foam stabilized and generated by mixing the flows of air and foaming aqueous solution through the restrictions of the pore network as well as their upward and homogeneous flow from the bottom of the limited volume towards the surface and the recovery of the foam.

[0076] In other words, the in-situ formation of lamellae of a foam in upward flow (pressure difference) within the delimited volume of the porous substrate to be treated is achieved by mixing, by the simultaneous flow at the periphery and within the delimited volume of the porous substrate, the flows of the foaming liquid solution (at low intermediate saturation) and the air supplied at the peripheral free surface. This formation of lamellae within the volume under suction causes an increase in the depression value, synonymous with the increase in the flow resistance (case of the formation and a stabilized flow of foam lamellae in the porous medium).

[0077] In the method according to the invention, the transport of the element(s) to be recovered is done directly in the porous substrate by its / their detachment then its / their presence in the liquid lamellae in upward flow of the foam and recovery on the surface of the element(s) contained in a suctionable foam. In the case of one or more adhered element(s) (nanoparticles, clays, oxides, etc.), two transport mechanisms are identified and applicable within the porous substrate: (i) the hydrodynamic entrainment of the element(s) made mobile by the friction induced by the upward flow of the lamellae and / or (ii) the capture at the air / liquid interfaces of the lamellae or liquid films of the flowing foam, in particular for naturally hydrophobic particles (used oils, polychlorinated biphenyls (PCBs), organic solvents) or hydrophilic particles whose surface hydrophilicity is previously reduced.Adsorption of at least one cationic surfactant on the surface of clays with a negative overall charge and hydrophilic character allows for sufficient hydrophobicity to be achieved to promote attachment of particles to the interfaces of the lamellae. This capture promotes both the detachment of the adhered particles constituting the porous medium and their selective transport to the surface.

[0078] Thus, in the method according to the present invention, the transport and surface recovery of the element(s) are then carried out in a single step thanks to the in-situ formation of continuous lamellae within the porous substrate by suction. The transported element remains in a closed and sealed circuit from its initial state contained in the porous substrate until its final state when it is contained in the suctionable foam recovered at the surface. In other words, the foam flowing in-situ in the limited volume of the porous substrate is formed and recovered by the same suction.

[0079] The aspirated foam containing the element(s) to be recovered may be dried, in particular at a temperature between 40°C and 100°C to remove the water it contains, or filtered to recover the element(s) selectively extracted for storage or packaging. In other words, the element(s) to be recovered may be obtained after drying or filtration of the recovered, i.e. aspirated, foam. After drying or filtration, the residue or filtrate contains the element(s) to be recovered, in particular the polluting or interest particles.

[0080] In the context of the present invention, the steps of contacting, generating and maintaining suction and recovering the foam may be continuous or discontinuous in batches. In a first embodiment, the method according to the invention may be implemented continuously over several hours.

[0081] In a second embodiment, the steps of contacting, generating and maintaining suction and recovering the foam can be repeated at least once, with aqueous foaming solutions whose composition is identical or different. In a particular embodiment, the first aqueous foaming solution, by gravity irrigation or by suction in the form of in-situ foam, comprises at least one foaming surfactant which aims to selectively change the hydrophobicity of the element or elements of interest by adsorption on the surface (i.e. cationic surfactant to pre-treat negative and hydrophobic clays). The second aqueous foaming solution comprises at least one foaming surfactant and serves to form ascending in-situ transport lamellae by suction.

[0082] The present invention was developed for the main problem of radiological decontamination of soils by transporting contaminated clays. It therefore also concerns the use of a method as previously defined for

[0083] - radiological decontamination of soils by transporting contaminated clays,

[0084] - the decontamination of agricultural horizons after spreading or treatment with pesticides, the rehabilitation of soils contaminated by nanoparticles, the decontamination of industrial horizons after unauthorized leaks,

[0085] - asbestos removal from earth, piles, rubble, spoil containing volatile micrometric fibers (old buildings, deconstruction / construction sites, etc.) or

[0086] - the extraction of recyclable materials.

[0087] Other characteristics and advantages of the present invention will become apparent upon reading the examples below given for illustrative and non-limiting purposes and referring to the appended figures.

[0088] BRIEF DESCRIPTION OF THE DRAWINGS

[0089] Figure 1 shows the general principle diagram of the method implemented within the framework of a TRL 3-4 proof of concept of the present invention. Figure 2A shows the diagram of the “field” device A for in-situ suction transport foam from the laboratory tests implemented within the framework of the application proof of concept (example 1) of the method of the present invention.

[0090] Figure 2B details the dimensions of Device A.

[0091] Figure 3 shows the extraction curves of illite 15 centered on 5 pm untreated (-20 mV) and partially neutralized with TTAB (between -12 and +20 mV) contained in the layer (-1-2 cm) of washed and sieved 0-2 quarry sand >150 pm, m is the extracted mass and mO the initial mass contained in the treated volume.

[0092] Figure 4 shows the schematic of study device B for measuring the particle transport efficiencies of clay deposited on the surface of glass beads stacked in a column by upward flow of pre-formed foam injected by microfluidic chip.

[0093] Figure 5 shows the quantities of clay recovered on study device B as a function of the initial mass of clay deposited on the glass beads for the first foam flow composed of TTAB (30mL) then the second flow composed of SDS (30mL), m is the extracted mass and mO the initial mass.

[0094] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0095] Example 1: Laboratory tests for implementation in “field” conditions, device A (TRL 3-4)

[0096] To validate the proof of concept application of the present invention, a first laboratory device was designed and produced. Figure 1 shows a detailed general principle diagram of the process and Figure 2A a diagram of the device A used in this example 1. The sand simulating a soil is placed in a beaker of 10 cm diameter. The dimensions of the device are described in Figure 2B.

[0097] Blocks 1 to 5 shown in Figure 1 correspond to:

[0098] 1. Volume of the porous medium to be treated confined by hooping and maintained on the surface by a retaining grid, 2. Suction by vacuum pump (which serves both for the formation and recovery of the foam),

[0099] 3. A. Peripheral ambient air introduced into the subsurface of the soil by suction,

[0100] 3. B. Drip irrigation flow rate,

[0101] 4. A. Mixing of liquid and gas flows which percolate simultaneously through the porosity of the porous substrate: formation of the lamellae of foam A,

[0102] 4. B. Ascending transport lamellae in the confined volume (foam A), and

[0103] 5. Formation of surface-charged foam A' by accumulation of ascending lamellae of foam A.

[0104] In its preferred configuration, the process uses a sealed device composed of two modules:

[0105] - a first column (cylindrical impermeable barriers) called the "ringing column" which is driven into the earth to be treated. The foam, in the form of lamellae called "A foam", for transporting the particles to be extracted generated in situ is in upward flow in this ringing column,

[0106] - a second one which remains above ground is called "suction or recovery column" of the foam A' resulting from the accumulation on the surface of the foam A. This vertical column allows the recovery on the surface of the particles contained in the foam A'. It can influence the selectivity of the extracted particles by selecting the particles best attached to the interfaces and by eliminating the particles possibly entrained in the water of the foam by drainage.

[0107] These two parts of the column are separated by a metal grid which maintains the structure of the soil and prevents its suction and destructuring. The surface horizon is therefore mechanically held, once the column is in place, by a grid with a controlled mesh adapted to the granulometric distribution of the porous medium.

[0108] Once in place, suction is created by a vacuum pump connected to the top of the column's suction cone and then maintained throughout the tests. The foam solution is supplied by drip irrigation pipes, fed by a low-flow peristaltic pump. They are placed on the peripheral surface of the column. The generation of foam lamellae in situ is obtained by partial irrigation of the surface peripheral to the column and the simultaneous suction applied in the polluted volume circled up to the peripheral surface. The recovery of the charged foam A', formed on the surface and rising in the above-ground recovery column, is done within a vacuum flask installed between the column and the pump. This system allows foam generation and recovery by a single suction in a closed circuit, therefore a safe process and therefore usable in the context of radiological decontamination.

[0109] The representative tests presented below were carried out with the device of Figure 2A, the specificities of which are shown in Figure 2B.

[0110] The sequence used on a laboratory scale to implement the method according to the invention is as follows:

[0111] 1. installation of the column: it is pushed into the sand up to the stop between the retaining grid and the surface of the porous medium,

[0112] 2. start and maintain suction by vacuum pump connected to the top of the column: a depression of -200 to -400 mBar is thus formed in the column and in the porous volume of the soil to be treated,

[0113] 3. partial saturation of the porous network by spraying with foaming solution on the periphery of the hoop. A homogeneous peripheral wetting front outside the hoop is observed in which the first lamellae of foam A are formed: progressive rise in the depression value induced by the generation of lamellae in the porous medium up to a value of approximately -900 mBar,

[0114] 4. start of peripheral irrigation in foaming solution by drip, at low flow rate, continuously to maintain an intermediate saturation value in the pore network favorable to the continuous formation of stabilized lamellae,

[0115] 5. visualization of the foam A' on the surface, then in the suction column and recovery of the foam loaded with particles transported into a vacuum flask by the suction.

[0116] In the illustrative example shown in Figure 2B, the column has an internal diameter of 8 cm and a height of 40 cm. The first 10 cm are embedded in a coarse 0-2 mm white sand model and sieved (> 150 pm to eliminate fine sand particles also transportable by these tests during the blank tests which can distort the material balance applied to clays mixed with sand) from the Bagnols-sur-Cèze quarry which constitutes the porous medium. The particles chosen to be extracted are illites 15 (clays) with an average size of 5 pm and less than 10 pm and partially neutralized on the surface by adsorption of cationic TTAB in solution to become partially hydrophobic (from -20 to +20 mV). These suspensions loaded with clays are mixed with a volume of dry sand by wet method, the mixture is dried at 40°C and constitutes the so-called contaminated sand (by clays).This mixture loaded with 0.5% clay (by mass) is introduced dry into the circled volume to form a 1 cm layer placed on the sand, itself covered with 1 cm of sand to level the surface. The so-called contaminated layer is therefore at a depth of 1 to 2 cm compared to the maintained surface of the porous medium.

[0117] The first step of irrigation in foam solution is done by watering the periphery with 20 mL of anionic SDS foam solution (20 g / L) which homogeneously wets the sand around the column to a depth of 10 cm. The depression then increases and goes from -350 mBar (± 100 mBar) dry to -900 mBar (± 100 mBar) as soon as the sand is homogeneously wetted at intermediate saturation: this informs on the presence of stabilized lamellae within the system. To maintain a constant generation of lamellae of foam A in the porous medium, a continuous drip irrigation (0.75 mL / min) is implemented and the maximum depression recorded can be, for example, -940 mBar. The maximum depression value varies according to the saturation rate of the medium, consequently, the stability of the lamella network (its resistance to flow).Foam A' emerges from the soil after a few minutes and rises in the column continuously and repeatably over several hours as long as suction and simultaneous irrigation are maintained.

[0118] The foam recovered by suction is filtered and then the solid is dried at 40°C to remove water and the particles are weighed to calculate the extraction yield. The graph in Figure 3 shows the extraction yields of the fine solid particles extracted over time (mass m extracted relative to the initial mass of transportable particles m0, namely the clays 15 and the fine sand particles persisting despite the sieving step).

[0119] In one hour, the best extraction yields of fine particles are between 90 and 99%, obtained for sands containing illites 15 whose surface charge is between -6 and +20 mV. These TTAB surface treatments have a faster extraction tendency than that for raw clays -20mV. This pretreatment promotes detachment then particle transport by capture at the interfaces of the lamellae (adapted hydrophilic / hydrophobic balance). These two tendencies for raw and modified clays validate the principle of in-situ foam transport of the process according to the invention.

[0120] For these 4 best tests at a concentration of 0.5% by mass of illite in the so-called contaminated layer, additional experiments have shown that all the clays 15 located at a depth of -1 cm to -2 cm are extracted. At the same time, fine particles, not treated on the surface, from the sand of the entire treated zone (0 to -10 cm) are also carried along and represent a third of the extracted particles (i.e. 0.25 g out of 0.75 g of totally extracted solid). In the contaminated zone, the proportion of illite transported is estimated at 95% compared to the proportion of fine sands from this same zone (5%).

[0121] Example 2: Transport test of clays, not surface treated (-20mV), deposited on a stack of 2 mm glass beads in a column by microfluidic foam

[0122] The diagram of device B used for this preformed foam and column transport test on beads "contaminated" with untreated clay particles 15 on the surface is shown in Figure 4.

[0123] The device is composed of a convergent flow microfluidic foam generator, connected at the outlet to a column filled with a structured stack of 2 mm diameter beads, the column measuring 2.2 cm in diameter and 13 cm high. This type of generator makes it possible to form a low flow rate foam flow with a controlled liquid fraction within the column. Tl

[0124] The foam / lamella flow is preformed by supplying 1800 mBar of gas and 1000 mBar of liquid within the generator and then rearranges during its stabilized and ascending flow within the base of the column composed of clean balls.

[0125] The mixture of beads and clays is made dry by stirring according to the coverage limit depending on the bead sizes and then sieving: the 2 mm diameter beads used have a dry coverage rate of 2.5 to 3% depending on the batch. The mixture is placed under a humid atmosphere (100% relative humidity) for 12 hours and then dried at 50°C for 12 hours. 29.12 g of this mixture (28.35 g of beads + 0.77 g of clays ~2.7%) were prepared and contained in the upper part of the column, to a height of 6 cm. The bottom of the column is composed of uncontaminated 2 mm beads which serve as a diffuser. During this test, the adhered clays are not treated on the surface, their charge is therefore -20 mV which does not promote capture at the interfaces of the lamellae in upward flow.

[0126] In this test, a first foam flow is composed of 4 g / L of cationic TTAB which should act on the surface charge of the clays adhered to the beads. Subsequently, a foam flow of 10 g / L of anionic SDS is introduced. Thus, a first TTAB foam flow of 30 mL (volume corresponding to the depletion of particles transported by the TTAB foam flow) was followed by 30 mL of SDS.

[0127] Visually, differences in particle transport are observed between the two foam flows.

[0128] The first mL of TTAB (0-10 mL) are loaded with thick lamellae recovered at the column outlet. Subsequently, the lamellae become thinner and become less and less loaded (10-20 mL). Finally, unloaded foam portions form at the outlet (20-30 mL). Particle transport is possible with the TTAB foam flow but it diminishes over time and becomes almost zero for the last 10 mL. Despite this particle transport, the front between the contaminated beads and the "new" one in the diffuser zone is still visible: There are still particles adhered to the surface of all the contaminated beads.

[0129] Following the end of the particulate transport of the foam in the TTAB, an SDS foam is injected into the column. The first 2 mL of SDS (0-2 mL) form portions of foam at the outlet which appear very loaded (probably due to the transport of clays but especially to the precipitate formed by mixing the two surfactants used successively). Foam lamellae form and are increasingly humid / thick (2-10 mL) as during the first mL of the TTAB flow. At this point, the lamellae load and begin to visually remove all the clay from the beads (10-30 mL). The front of contaminated beads rises, the height of the "new / washed" beads increases.

[0130] At the end of the test, the beads appear to have been visually washed from the bottom to the top of the column. Clay plugs are still present in the interstices of the stack. These plugs could indicate that the bead network needs to be optimized.

[0131] The clay extraction curve from this test as a function of the volume and type of foam used is shown in Figure 5.

[0132] The latter clearly reflects the visual observations of the test with the impoverishment of the particle transport obtained by the first foam flow with cationic TTAB around 30% which is then restarted by the contribution of the foam flow with anionic SDS. The transport of clays by the SDS is almost complete (97%), which corresponds to the disappearance of the front between contaminated beads and new beads.

[0133] Bibliographic references

[0134] [1] US Patent 6,210,955 B1 in the name of Gas Research Institute, published on April 3, 2001.

[0135] [2] “In situ soil washing on metal-contaminated sandy soil by sedimention method: a new approach on soil remediation”, Philippine Engineering Journal (2006) vol.27, pages 65-76.

[0136] [3] International application WO 2023 / 203298 Al in the names of CEA and Orano Mining, published on October 26, 2023.

[0137] [4] US Patent 4,080,419 B1 in the name of The United States of America as represented by the Secretary of the Interior, published March 21, 1978. [5] “A quantitative kinetic theory of emulsion type, I. Physical chemistry of the emulsifying agent” Gas / Liquid and Liquid / Liquid Interface. Proceedings of the International Congress of Surface Activity (1957): 426-438.

[0138] [6] International application WO 2016 / 202879 Al in the name of the CEA, published on December 22, 2016.

Claims

CLAIMS 1. Method for transferring and recovering on site and by aqueous transport foam generated in situ at least one element present in a predetermined volume of a porous substrate comprising the following successive steps: - delimiting a volume of said porous substrate by installing impermeable barriers surrounding said volume and opening onto the surface of the porous substrate and placing, over the entire surface of the delimited volume and in contact with the porous substrate, a porous holding means making it possible to hold the porous substrate, - bring a foaming aqueous solution into contact with the delimited volume, - generate suction, simultaneously or deferred, with the previous contact in the delimited volume and maintain said suction, whereby a particle transport foam is formed from said foaming aqueous solution and the ambient air in the delimited volume of the porous substrate and rises towards the surface of the delimited volume carrying said at least one element, and - recover the surface foam above the delimited volume and recover said element from the foam thus recovered.

2. Transfer and recovery method according to claim 1, characterized in that said porous substrate is selected from the group consisting of earth such as fallow land, bare land for agricultural activity, cultivated agricultural land, a green space, a stadium or field for sports activity or a horticultural garden; sand; broken or fractured geological rock formations; ore; ore concentrates; coal; mining residues; mining waste; slag; industrial, metallurgical and electronic waste; products containing strategic metals, such as, for example, nickel, cobalt and manganese, from the recycling of lithium batteries also known by the English expression "black-mass" and a mixture thereof.

3. Transfer and recovery method according to claim 1 or 2, characterized in that said at least one element is considered to be a contaminating element and is chosen from the group consisting of radio-contaminated phyllosilicates or clay particles, metal-binding phyllosilicates or clay particles, titanium dioxide nanoparticles (TiC>2), cerium oxide, heavy metal oxide particles, pesticides, oil microdroplets, organic solvent microdroplets, hydrophobic microsubstances, plastic microparticles, colloidal organic matter and bacteria.

4. Transfer and recovery method according to claim 1 or 2, characterized in that said at least one element is considered as an element of interest and is chosen from the group consisting of gold, silver, uranium, platinum, palladium, lithium, nickel, cobalt, manganese, aluminum, zinc, copper, rare earths, niobium, tantalum, scandium, chromium and one of their alloys.

5. Transfer and recovery method according to any one of claims 1 to 4, characterized in that said impermeable barriers are in the form of an enclosure, a column or a tube with a circular or parallelepiped section.

6. Transfer and recovery method according to any one of claims 1 to 5, characterized in that said holding means corresponds to a grid, in particular a metal grid, the shape of which is identical or substantially identical to the cross-section of said impermeable barriers.

7. Transfer and recovery method according to any one of claims 1 to 6, characterized in that said suction is generated in said limited volume of the porous substrate by means of a pump, such as a vacuum pump, connected, in a sealed manner, to said impermeable barriers.

8. Transfer and recovery method according to any one of claims 1 to 7, characterized in that said foaming aqueous solution comprises a single foaming organic surfactant or a mixture of at least two foaming organic surfactants chosen from non-ionic foaming surfactants, anionic foaming surfactants and cationic foaming surfactants.

9. Transfer and recovery method according to any one of claims 1 to 8, characterized in that said foaming aqueous solution additionally comprises at least one other ingredient chosen from the group consisting of organic gelling agents, viscosifiers; acids / bases; and oxidizing or reducing salts.

10. Transfer and recovery method according to any one of claims 1 to 9, characterized in that said contacting between the limited volume of the porous substrate and the foaming aqueous solution involves the supply of the foaming aqueous solution to the periphery of the delimited volume and mechanically held on the surface of the porous substrate.

11. Transfer and recovery method according to any one of claims 1 to 9, characterized in that said contacting between the limited volume of the porous substrate and the foaming aqueous solution is done by adding the foaming aqueous solution directly into the delimited volume and mechanically held on the surface of the porous substrate.

12. Transfer and recovery method according to any one of claims 1 to 11, characterized in that said in-situ flowing foam in the limited volume of the porous substrate is formed and recovered by suction.

13. Recovery method according to any one of claims 1 to 12, characterized in that said at least one element is obtained after drying or filtration of said recovered foam.

14. Transfer and recovery method according to any one of claims 1 to 13, characterized in that said method is carried out continuously over several hours.

15. Transfer and recovery method according to any one of claims 1 to 13, characterized in that the steps of contacting, generating and maintaining suction and recovering the foam are repeated at least once, with aqueous foaming solutions whose composition is identical or different.

16. Use of a method according to any one of claims 1 to 15 for - radiological decontamination of soils by transporting contaminated clays, - the decontamination of agricultural horizons after spreading or treatment with pesticides, - the decontamination of industrial horizons after unauthorized leaks, - the rehabilitation of soils contaminated by nanoparticles, - asbestos removal from soils containing volatile micrometric fibers (old buildings, deconstruction / construction sites, etc.) or - the extraction of recyclable materials.

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