Suctionable gel and method for eliminating a contamination contained in a surface organic layer of a solid substrate

Abstract

A suctionable gel for eliminating a contaminating species contained in an organic layer on the surface of a material, consisting of a colloidal solution comprising, preferably consisting of: 1 wt % to 25 wt %, preferably 5 wt % to 20 wt % based on the total weight of the gel, of at least one inorganic viscosifying agent; 13 wt % to 99 wt %, preferably 80 wt % to 95 wt % based on the total weight of the gel, of an organic solvent selected among the terpenes and the mixtures thereof; optionally, 0.01 wt % to 10 wt %, based on the total weight of the gel, of at least one dye and/or pigment; optionally 0.1 wt % to 2 wt %, based on the total weight of the gel, of at least one surfactant. The disclosure further relates to a decontamination method using the gel.

Claims

1. A suctionable gel for eliminating a contaminant species contained in a layer consisting of an organic material, on the surface of a solid substrate, consisting of a colloidal solution comprising: 1% to 25% by weight based on the total weight of the gel, of at least one inorganic viscosifying agent consisting of one or more alumina(s); 13% to 99% by weight, based on the total weight of the gel, of one or more organic solvent(s) selected from among the terpenes; 10% to 20% by weight, based on the total weight of the gel, of ethanol; optionally from 0.01% to 10% by weight, based on the total weight of the gel, of at least one dye and/or pigment; optionally from 0.1% to 2% by weight, in relation to the total weight of the gel, of at least one surfactant; optionally, from 0.1% to 10% by weight, based on the total weight of the gel, of at least one extracting agent for extracting the contaminant species.

2. A gel according to claim 1, wherein the terpenes are selected from among terpene hydrocarbons, oxygenated terpene compounds, and isomers thereof.

3. A gel according to claim 2, wherein the isomers are optical isomers.

4. A gel according to claim 2, wherein the terpenes are selected from among ocimene, α-pinene, β-pinene, limonene, menthol, menthone, terpineol, isoborneol, camphor, nerol, citronellal, citronellol, myrcene, myrcenol, linalool, geraniol, and isomers thereof.

5. A gel according to claim 4, wherein the isomers are optical isomers.

6. A gel according to claim 4, wherein the terpene is d-limonene.

7. A gel according to claim 6, wherein d-limonene is the only organic solvent.

8. A gel according to claim 6, comprising from 35% to 94% by weight, based on the total weight of the gel, of d-limonene.

9. A gel according to claim 1, wherein the alumina(s) is (are) selected from among pyrogenic aluminas.

10. A gel according to claim 9, wherein the pyrogenic alumina has a fine particle size distribution.

11. A gel according to claim 1, wherein the alumina(s) represent(s) from 5% to 25% by weight, based on the total weight of the gel.

12. A gel according to claim 1, wherein the surfactant is selected from among non-ionic surfactants.

13. A gel according to claim 12, wherein the non-ionic surfactant is selected from the group consisting of block copolymers, ethoxylated fatty acids, and mixtures thereof.

14. A gel according to claim 13, wherein the block copolymer is selected from the group consisting of ethylene oxide and propylene oxide copolymers.

15. A gel according to claim 1, consisting of a colloidal solution comprising: 1% to 25% by weight, based on the total weight of the gel, of at least one alumina; 35% to 94% by weight, based on the total weight of the gel, of d-limonene.

16. A gel according to claim 15, wherein the at least one alumina is pyrogenic alumina.

17. A gel according to claim 16, wherein the pyrogenic alumina has a fine particle size distribution.

18. A gel according to claim 1, wherein the colloidal solution consists of: 1% to 25% by weight, based on the total weight of the gel, of at least one inorganic viscosifying agent consisting of one or more alumina(s); 13% to 99% by weight, based on the total weight of the gel, of one or more organic solvent(s) selected from among the terpenes; 10% to 20% by weight, based on the total weight of the gel, of ethanol; optionally from 0.01% to 10% by weight, based on the total weight of the gel, of at least one dye and/or pigment; optionally from 0.1% to 2% by weight, in relation to the total weight of the gel, of at least one surfactant; optionally, from 0.1% to 10% by weight, based on the total weight of the gel, of at least one extracting agent for extracting the contaminant species.

19. A gel according to claim 18, wherein the terpene comprises 35% to 94% by weight, based on the total weight of the gel, d-limonene.

20. A gel according to claim 1, wherein the at least one extracting agent is selected from the group consisting of zeolites and clays.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 (A, B, C, D, E) presents photographs that show the elimination of a bitumen spot/patch on a dense, smooth surface, as has been carried out in Example 2, by using the gel according to the invention, referred to as gel “Limo-1” prepared in Example 1.

(2) FIG. 2 (A, B, C, D, E, F, G) presents photographs that show the elimination of a bitumen spot, patch on a porous surface, as has been carried out in Example 2, by using the gel according to the invention, referred to as gel “Limo-1”, prepared in Example 1.

(3) FIG. 3 (A, B, C) presents photographs that show the elimination of a spot, patch of bitumen contaminated with .sup.137Cs bonded, stuck, to a dense, smooth surface, as has been carried out in Example 4, by using the gel according to the invention, referred to as gel “Limo-1”, prepared in Example 1.

(4) FIG. 4A illustrates Example 6, and presents a photograph of the surface of an epoxy resin prior to the deposition of a layer of gel according to the invention, referred to as gel “Limo-1”, prepared in Example 1, on the surface of an epoxy resin (on the left) and after the deposition of a layer of gel, the drying of this layer and the elimination of the dry gel flakes (on the right).

(5) FIG. 4B, illustrates Example 6, and shows the surface profiles corresponding to the surface areas photographed in FIG. 4A, prior to the deposition of a layer on the surface of the epoxy resin (on the left) and after the deposition of a gel layer, the drying of this layer and the elimination of the dry gel flakes (on the right).

(6) FIG. 5 is a graph which shows the evolution of the viscosity (in Pa.Math.s) as a function of the shear rate (1/s), for the gel according to the invention, referred to as gel “Limo-1” prepared in Example 1 (see Example 7).

(7) FIG. 6 is a graph which shows the evolution of the shear stress (in Pa) as a function of the deformation, strain (in Pa) for the gel according to the invention, referred to as gel “Limo-1” prepared in Example 1 (see example 7).

(8) FIG. 7 is a graph which shows the evolution of the loss of mass (in %) as a function of the time (in min) of the gel according to the invention, referred to as gel “Limo-1” prepared in Example 1, deposited with a thickness of 2 mm (see Example 8).

(9) FIG. 8 is a photograph of flakes obtained after drying of the gel according to the invention, referred to as the gel “Limo-1” prepared in Example 1 (see Example 8).

(10) FIG. 9 (A, B, C) presents photographs that show the elimination of a bitumen spot/patch on a dense, smooth surface, as has been carried out in Example 9, by using the gel according to the invention, referred to as gel “Limo-2” prepared in Example 9.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

(11) The gel according to the invention can be easily prepared at ambient temperature.

(12) For example, the gel according to the invention may be prepared by adding, preferably progressively the inorganic viscosifying agent(s), for example the alumina(s) and/or the silica(s), to the terpene solvent(s) optionally mixed with ethanol, or to the mixture of the organic solvent(s) (optionally with ethanol) and the optional adjuvant(s).

(13) The optional adjuvants are generally the surfactant(s), the dye(s) and/or pigment(s), and the extracting agent(s) for extracting the contaminant species, for example, the extracting agent for extracting radionuclides.

(14) This admixture of the solvent(s) and the optional adjuvant(s) may be prepared by mechanical agitation, for example by means of a mechanical agitator equipped with a three blade impeller. The rotational speed is, for example, 200 revolutions per minute (rpm), and the duration of the agitation is for example 3 to 5 minutes.

(15) The addition of the inorganic viscosifying agent(s) to the solvent(s), or to the mixture of the solvent(s) and of the optional adjuvant (s) may be effected by simply pouring the viscosifying agent(s) into said solvent(s) or into said mixture.

(16) During the adding of the inorganic viscosifying agent(s), to the solvent(s), or to the mixture of the solvent(s) and of the optional adjuvant(s), this or these solvent(s) or this mixture are generally maintained under mechanical agitation.

(17) This agitation may be, for example, carried out by means of a mechanical agitator equipped with a three blade impeller.

(18) The speed of agitation is generally increased gradually as the viscosity of the solution increases, so as to finally reach a speed of agitation, for example, comprised between 400 and 600 revolutions/minute, without there being any projections.

(19) After the end of the addition of the mineral viscosifying agent(s), the agitation is continued, for example for a period of 2 to 5 minutes, in a manner so as to obtain a perfectly homogeneous gel.

(20) It is indeed obvious that other preparation protocols for preparing the gels used according to the invention may be operationally implemented with the addition of the gel components in an order that is different from the one mentioned here above.

(21) Generally, the gel used according to the invention should have a viscosity of less than 200 mPa.Math.s under a shear of 1000 s.sup.−1 in a manner so as to enable the spraying on the surface to be decontaminated, from a distance (for example at a distance of 1 to 5 m) or in proximity (for example at a distance of less than 1 m, preferably from 50 to 80 cm). The time for recovering the viscosity of the gel should generally be less than one second and the viscosity under low shear greater than 10 Pa.Math.s in order for it to not run-off over a wall.

(22) It should be noted that the optional surfactant of the gel according to the invention favourably and significantly influences the rheological properties of the gel used according to the invention. This surfactant in particular makes it possible for the gel used according to the invention to be implemented by means of spraying and avoids the risk of spreading or running-off during the treatment of vertical surfaces and ceilings. This surfactant also makes it possible to limit the phenomenon of bleeding observed during the storing of the gel.

(23) The gel thus prepared is then applied on to the surface layer containing a contaminant species, for example a radioactive contaminant species, to be treated.

(24) According to the second variant of the method according to the invention, this surface layer containing a contaminant species, for example a radioactive contaminant species, is a layer that is found on a surface of a solid substrate, this layer being present in the form of a spot/patch or discrete spots/patches of the organic material containing a contaminant species, for example a radioactive contaminant species.

(25) In this second variant, there is virtually no limitation with respect to the material which constitutes the substrate, in fact the gel according to the invention provides the ability to treat without any damage, all kinds of materials even fragile materials.

(26) The gel according to the invention does not generate any chemical, mechanical or physical etching, erosion, alteration, of the material of the substrate treated. The gel according to the invention is therefore in no way detrimental to the integrity of the treated materials and indeed even enables the reuse thereof. This material of the substrate may therefore be selected from among the materials already enumerated here above, for example from among metals or alloys such as stainless steel, polymers such as plastic materials or rubbers, among which mention may be made of PVCs, Ps, PEs in particular HDPEs, PMMAs, PVDFs, PCs, glasses, cements, mortars and concretes, plasters, bricks, natural or artificial stones, coatings, ceramics.

(27) In any case, whatever the material that constitutes the substrate, for example stainless steel, painted lacquered steel, glass, ceramic, concrete, PVC, in this second variant, the spot/patch or the discrete spots/patches of the organic material containing a contaminant species, for example a radioactive contaminant species is (are) completely dissolved by the gel.

(28) There is also no limitation with respect to the shape/form, the geometry and the size of the layer to be treated and of the solid substrates of the first and the second variants, the gel according to the invention makes it possible to treat surfaces of large size, having complex geometries, for example having hollows, angles, recesses.

(29) The gel according to the invention provides for the effective treatment not only of horizontal surfaces, but also of vertical surfaces such as walls, facades, bridge piers, doors, or inclined or overhanging surfaces such as ceilings.

(30) The gel according to the invention also ensures a complete and effective elimination of the contamination regardless of the organic material of the contaminated layer and the nature of the contamination.

(31) Compared to existing techniques which implement liquids such as solutions, the invention implements a gel, which is particularly advantageous for the treatment of materials having large surface area non-transportable, and implanted outdoors. Indeed, the method according to the invention on account of the implementation of a gel, makes possible cleaning in situ by preventing the spread of chemical solutions in the environment and the dispersion of contaminant species.

(32) The gel according to the invention may be applied on to the surface to be treated by all the application methods known to the man skilled in the art.

(33) The conventional methods are spraying, for example by using a spray gun, or application by means of a brush, or a trowel.

(34) For the spray application of the gel on the surface to be treated, the colloidal solution may for example be conveyed by means of a low pressure pump, for example a pump which implements a pressure of less than or equal to 7 bars, which is about 7.Math.10.sup.5 Pascals.

(35) The bursting of the jet of gel on the surface may be obtained for example by means of a fan/slit jet nozzle or round jet nozzle.

(36) The distance between the pump and the nozzle may be anything, for example the distance may be from 1 to 50 m, in particular from 1 to 25 m.

(37) The sufficiently short time for recovering the viscosity of the gels used according to the invention allows for the sprayed gels to adhere to all surfaces, for example to walls.

(38) The quantity of gel deposited on the surface to be treated is as indicated above.

(39) The quantity of gel deposited per unit surface area and, as a consequence, the thickness of the deposited gel influences the rate of drying.

(40) Thus, when spraying a film, layer of gel having a thickness of 0.5 mm to 1 cm on the layer to be treated, the drying time, which is then generally the effective contact time, is sufficient for a proper treatment of the layer, leading to dissolution of the layer and to absorption of the contaminant species.

(41) The effective time of contact is the period during which the active ingredient contained in the gel which is other than the solvent(s) will interact with the layer.

(42) The drying time is not only related to the thickness of the layer of applied gel, but also to the climatic conditions, that is to say the relative humidity and the temperature.

(43) The man skilled in the art can easily determine, depending on the climatic conditions, and within the thickness range mentioned here above, the thickness of the gel layer to be applied on to the surface layer so as to ensure that the gel is effective, that the layer is dissolved and that the contaminant species are absorbed by the gel.

(44) So if it is found that relative humidity RH is 20%, and temperature is 40° C., it is possible that the drying of a layer of gel of a thickness of 0.5 mm applied on a layer would be too rapid to allow for the dissolution of this layer and the absorption of the contaminant species in the gel. On the contrary, if conditions are at 15° C., and at 50% RH, the rate of drying of a layer of the same thickness of the same gel allows for dissolution of this layer and the absorption of the contaminant species in the gel.

(45) In addition, it has been shown in a surprising manner that the quantity of gel deposited when it is situated in the ranges mentioned here above and, in particular, when it is greater than 500 g/m.sup.2 and in particular in the range of 500 at 5000 g/m.sup.2, which corresponds to a minimum thickness of gel deposited, for example greater than 500 microns μm for a quantity of gel deposited greater than 500 g/m.sup.2, made it possible after drying of the gel to obtain a fracturing of the gel in the form of millimetre sized flakes, for example of a size of 1 to 10 mm, preferably from 2 to 5 mm, that are suctionable.

(46) The quantity of gel deposited and therefore the thickness of gel deposited, preferably greater than 500 g/m.sup.2′ that is to say 500 μm, is the fundamental parameter which influences the size of the dry residues formed after drying of the gel and which thus ensures that millimetre sized dry residues rather than pulverulent residues are formed, such residues being easily eliminated by a mechanical process and preferably by suction.

(47) However, it should also be noted that when the gel contains a surfactant at low concentration, the drying of the gel is improved and leads to a phenomenon of homogeneous fracturing with dry residues of a mono-dispersed size and an increased ability of the dry residues to detach from the support.

(48) The gel is then maintained on the surface to be treated for the entire duration necessary for drying thereof.

(49) During this step of drying, which can be considered as constituting the active phase of the method according to the invention, the solvent(s) contained in the gel evaporate(s) until a dry and solid residue is obtained.

(50) The drying time depends on the composition of the gel in the concentration ranges of its constituents given above, but also, as has already been stated, on the quantity of gel deposited per unit surface area, that is to say on the thickness of gel deposited.

(51) The drying time also depends on the climatic conditions, that is to say on the temperature, the ventilation and the relative humidity of the atmosphere in which the solid surface is located.

(52) The method according to the invention may be carried out under extremely broad climatic conditions, that is to say at a temperature T of 1° C. to 50° C. and at a relative humidity RH of 20% to 80%.

(53) The drying time of the gel according to the invention is therefore generally from 15 minutes to 24 hours, preferably from 1 hour to 24 hours at a temperature T of 1° C. to 50° C. and at a relative humidity RH of 20% to 80%.

(54) It should be noted that the formulation of the gel used according to the invention especially when it contains surfactants such as “Pluronics®” generally ensures (that is to say, in particular, generally under reasonable climatic conditions, as has been indicated here above) a drying time which is substantially equivalent to the time of contact between the gel and the surface layer that is necessary, required in order to dissolve the organic material.

(55) In other words, the formulation of the gel ensures a drying time which is none other than the time necessary for dissolving the organic material and absorbing the contaminant species. After the drying of the gel, the gel fractures in a homogeneous manner so as to give millimetre sized solid dry residues, for example of a size of 1 to 10 mm, preferably from 2 to 5 mm, that are non-pulverulent, generally in the form of solid flakes. The solid and dry residues contain the contaminant species, for example the radioactive contaminant species, and the organic material that has been dissolved from the surface layer.

(56) The dry residues, such as flakes, obtained at the end of the drying have a weak adhesion to the surface of the cleaned material. As a result thereof, the dry residues obtained after drying of the gel can be easily recovered by simple brushing and/or suction, aspiration. However, the dry residues can also be evacuated by a gas jet, for example by a compressed air jet.

(57) No rinsing is generally necessary and the method according to the invention does not generate any secondary effluent.

(58) However, a light rinsing, for example with water, of the treated surfaces, without mechanical action such as brushing, may exceptionally be necessary in order to possibly eliminate residual traces of paint and small residues of gel.

(59) According to the invention, thus first of all a significant saving in chemical reagents is achieved as compared to a method of decontamination by washing with a solution. Then, on account of a waste in the form of a directly suctionable dry residue being obtained, an operation of rinsing with water or with a liquid is generally avoided. This very obviously results in a decrease in the quantity of effluents produced but also in a significant simplification in terms of treatment system and outlet. In particular, according to the invention, the wastes obtained at the end of the treatment are not released into the rainwater drainage networks in violation of the regulations.

(60) Because of the composition of the gel used according to the invention, the wastes produced, once dry, represent only a small volume and are essentially minerals. They can therefore be stored or sent to a disposal system without prior treatment.

(61) By way of example, in the common case that involves application of 1000 grams of gel per m.sup.2 of treated surface, the mass of dry wastes produced is less than 300 grams per m.sup.2.

(62) The invention will now be described with reference to the following examples, given by way of non-limiting illustrations.

EXAMPLES

Example 1

(63) In this example, a description is provided of the formulation of a gel according to the invention, referred to as gel “Limo-1”, used in Examples 2 to 7.

(64) The gel according to the invention, referred to as gel “Limo-1”, is a gel whose composition is as follows: 10% by weight of alumina; 90% by weight of an active agent which is d-limonene.

(65) The alumina is the alumina Aeroxide® Alu C marketed by EVONIK INDUSTRIES® which is a pyrogenic alumina with a specific surface area of 100 m.sup.2/(BET), and the d-limonene is d-limonene marketed by the company MERCK®.

(66) This gel is prepared according to the following protocol:

(67) The d-limonene is first weighed in a suitable container.

(68) The d-limonene is agitated with a mechanical agitator, equipped with a three-bladed agitator, at a speed of 200 rotations/min., for a period of 3 to 5 minutes.

(69) The alumina, in a proportion of 10% by weight, is then progressively added to the d-limonene, and agitated with the aid of the mechanical agitator. Progressively along with the addition of alumina, the viscosity of the agitated medium increases.

(70) The rotational speed is thus also gradually increased as the viscosity of the agitated medium increases, in order to reach about 400 to 600 revolutions per minute (rpm) when the alumina has been added in its entirety, while so ensuring that there are no projections.

(71) The gel thus prepared is finally maintained under agitation for a period of 5 minutes, and left to rest for a period of at least one hour prior to use thereof.

Example 2

(72) This example serves to demonstrate the capacity of the gel according to the invention, referred to as gel “Limo-1”, prepared in Example 1, to eliminate bitumen spots/patches, just as effectively when they are on a dense, smooth surface, as when they are on a porous surface. The bitumen spots/patches are produced by depositing on the dense, smooth surface, and on the porous surface, and under a heavy load, a small bitumen bead slightly heated in advance. The load is left for a period of 24 hrs in order to provide for a good adhesion of the bitumen spots/patches to the dense, smooth surface, and to the porous surface.

(73) The gel according to the invention, referred to as gel “Limo-1”, is then deposited, here with a spatula, in a sufficient quantity on each of the bitumen spots/patches and then allowed to dry over a period of 48 hours. Finally, the solid waste obtained upon completion of the drying is recovered by brushing.

(74) FIG. 1 shows the results obtained on a dense, smooth epoxy resin surface.

(75) It is observed that in one pass of the gel “Limo-1”, the totality of the bitumen spot/patch could be eliminated. One pass consists of the depositing of the gel on the bitumen spot/patch, the drying of the applied gel, then followed by the brushing of the solid waste obtained at the end of the drying.

(76) FIG. 2 shows the results obtained on a porous surface (a concrete).

(77) It is observed that two successive passes of the gel “Limo-1” were necessary in order to eliminate the bitumen spot/patch.

(78) It is indeed necessary to optimise the ratio of the quantity of gel/size of the bitumen spot/patch in order to be able to reduce to the maximum extent the number of gel passes to be performed.

(79) These results thus demonstrate the ability of a gel according to the invention to totally or almost totally eliminate an organic matrix from a dense or porous surface.

Example 3

(80) This example provides a description of the protocol for the artificial contamination of bitumen with .sup.137Cs, which has been developed, followed then by a description of the preparation of a dense, smooth, surface or support consisting of epoxy resin which is contaminated with an adherent spot/patch of this bitumen artificially contaminated with .sup.137Cs.

(81) The contamination of the bitumen was fixed at 40,000 Bq/g in order to best simulate the bitumen spots/patches present on the ground in nuclear facilities.

(82) This protocol includes the following successive steps: 2 mL of an aqueous solution of .sup.137Cs at about 40,000 Bq/mL are deposited at the bottom of a dish (Petri dish type) with a fairly high rim.

(83) This solution is then allowed to evaporate. The .sup.137Cs contamination is therefore deposited in a labile manner at the bottom of the dish. 2 grams of uncontaminated bitumen are then deposited in the dish, and this dish is then placed on a heating plate heated to 100° C. for about 1 minute. The bitumen becomes much less viscous, almost liquid, and spreads at the bottom of the dish. The bitumen may then be slowly stirred in the dish by using a spatula, in order to integrate in a homogeneous manner into the bitumen, the .sup.137Cs contamination deposited at the bottom of the dish, as has been described here above. The dish is held by means of insulated pliers that serve to prevent all contact between the user and the system consisting of the hotplate and the hot dish. Small beads of the contaminated bitumen thus prepared, and still warm are then deposited on the surfaces to be contaminated. A sheet of parchment paper (which does not stick to the bitumen) is placed on the bitumen beads thus deposited, then a light load is applied on these bitumen beads in order to flatten them as much as possible. Finally, the same is left to cool and left to rest for a period of 24 hours.

(84) Measurements of radiological activity, that is to say a y count are performed on each system consisting of a support, surface, and a contaminated bitumen spot/patch, before carrying out the decontamination operation.

Example 4

(85) This example, the elimination of a bitumen spot/patch contaminated with .sup.137Cs bonded, stuck, to a dense surface has been carried out, and thus it shows the decontamination power of the gel according to the invention, referred to as gel “Limo-1”, described in Example 1, on a support, which is a dense surface contaminated with an adherent spot/patch of bitumen artificially contaminated with .sup.137Cs.

(86) Bitumen artificially contaminated with .sup.137Cs is prepared, according to the protocol described in Example 3, followed then by the preparation, in accordance with Example 3, of a dense support or surface made of epoxy resin contaminated with an adherent bitumen spot/patch artificially contaminated with .sup.137Cs (FIG. 3A). After a first counting of the radiological activity, with the help of a spatula some gel “Limo-1” is deposited on the contaminated bitumen spot/patch and then left to dry for a period of 48 hrs.

(87) Flakes are then obtained which can be easily removed by brushing (FIG. 3B).

(88) A second count of the radiological activity is then carried out and a first Decontamination Factor (DF) may be calculated.

(89) It is recalled that DF=Value of the initial contamination/value of the final contamination.

(90) A DF of 23 is thus obtained for an initial contamination of 4600 Bq.

(91) The application of a second layer of gel makes it possible to increase this DF up to 156. Thus, only a very small contamination remains on the dense, smooth support (FIG. 3C).

(92) The values of the radiological activity measured over the course of the decontamination operation carried out in Example 4 are summarised in Table I here below.

(93) TABLE-US-00001 TABLE I Values of radiological activity measured over the course of the decontamination operation of a dense, smooth surface. Gel Limo-1 Initial contamination (support + bitumen) 4600 Bq (±15%) Contamination after 1 gel pass (±5%)  199 Bq DF_1  23 Contamination after 2 gel passes  29 Bq (±5%) DF_2 156

(94) These results clearly show the effectiveness of the gel according to the invention referred to as gel “Limo-1” for the decontamination of a support with a dense, smooth surface, such as an epoxy resin support contaminated with a contaminated bitumen spot/patch.

Example 5

(95) In this example, the elimination of a bitumen spot/patch contaminated with .sup.137Cs bonded, stucl, to a porous surface is carried out, which thus serves to show the decontamination power of the gel according to the invention, referred to as gel “Limo-1”, described in Example 1, on a porous support, surface contaminated with an adherent bitumen spot/patch artificially contaminated with .sup.137Cs.

(96) Bitumen artificially contaminated with .sup.137Cs is prepared according to the protocol described in Example 3, followed then by the preparation, in accordance with Example 3, of a concrete porous support or surface contaminated with an adherent spot/patch of this bitumen artificially contaminated with .sup.137Cs.

(97) After a first counting of the radiological activity, with the help of a spatula some gel “Limo-1” is deposited on the contaminated bitumen spot/patch and then left to dry for a period of 48 hrs.

(98) Flakes are then obtained which can be easily removed by brushing.

(99) A second count of the radiological activity is then carried out and a first Decontamination Factor (DF) can be calculated.

(100) It is recalled that DF=Value of the initial contamination/value of the final contamination.

(101) A DF of 2 is obtained for an initial contamination of 5500 Bq.

(102) The application of a second layer of gel makes it possible to achieve a DF of 27.

(103) The application of a third layer of gel makes it possible to achieve a DF of 85.

(104) Thus, only a very small amount of contamination remains on the porous support.

(105) The values of the radiological activity measured over the course of the decontamination operation carried out in Example 5 are summarised in Table II here below.

(106) TABLE-US-00002 TABLE II Values of the radiological activity measured over the course of the decontamination operation of a porous surface. Gel Limo-1 Initial contamination (gel + bitumen) 5500 Bq (±15%) Contamination after 1 gel pass 2300 Bq (±15%) DF_1  2 Contamination after 2 gel passes  205 Bq (±5%) DF_2 27 Contamination after 3 gel passes  65 Bq (±15%) DF_3 85

(107) These results clearly show the effectiveness of the gel according to the invention referred to as gel “Limo-1” for the decontamination of a support with a porous surface such as a concrete support contaminated with a contaminated bitumen spot/patch.

Example 6

(108) This example serves to show the capacity of the gel according to the invention referred to as gel “Limo-1”, to chemically attack an organic matrix such as an epoxy resin matrix.

(109) For this purpose, an optical profilometer is used which will make it possible to characterise the surface state of an epoxy resin prior to and after application of the gel.

(110) FIG. 4A thus presents a photograph of the surface of an epoxy resin prior to the deposition of a layer on the surface of the epoxy resin (on the left) and after the deposition of a layer of gel, the drying of this layer, and the elimination of flakes of dry gel (on the right).

(111) FIG. 4B shows the surface profiles corresponding to the surfaces photographed in FIG. 4A, prior to the deposition of a layer on the surface of the epoxy resin (on the left) and after the deposition of a layer of gel, the drying of this layer and the elimination of flakes of dry gel (on the right).

(112) It is observed that the epoxy resin is clearly degraded on the right-hand portion of FIG. 4A which shows the surface obtained subsequent to the deposition, the drying and the elimination of flakes of the gel “Limo-1”.

(113) This degradation is obtained over a thickness of a few micrometres (FIG. 4B).

(114) These results thus demonstrate that the gel “Limo-1” according to the invention attacks the epoxy resin over a thickness of a few microns.

(115) This property will thus allow the gel according to the invention to release and then capture encrusted, embedded contaminants present under the surface (in the subsurface) of this type of organic matrices.

Example 7

(116) In this example, it is shown that the gel according to the invention, referred to as gel “Limo-1” prepared in Example 1 can be implemented by means of spraying.

(117) A rheological study of the gel “Limo-1” according to the invention, prepared in Example 1, has been carried out and makes it possible to show that this method is suitable and adapted to be implemented by means of spraying.

(118) In order for this type of gel to be able to be applied according to a spraying process, it is necessary for it to possess the properties of a thixotropic, rheofluidifying fluid, with a very short time for recovering the viscosity thereof (less than one second), as well as possessing a threshold stress (typically greater than 10-15 Pa).

(119) Various rheological measurements were carried out making use of a rheometer, the TA Instruments® AR-1000 rheometer with “Vane” geometry, and are presented in this example.

(120) In an initial step, the viscosity of the gel was measured as a function of the shear rate.

(121) After a pre-shearing of 5 minutes at a shear rate of 20 s.sup.−1, then of 1 minute at 0.015 s.sup.−1, several plateaux of shear rate ranging from 0.015 s.sup.−1 to 100 s.sup.−1 are carried out with a measurement of the viscosity performed every 30 seconds.

(122) FIG. 5 gives the evolution of the viscosity (Pa.Math.s) of the gel “Limo-1” according to the invention as a function of the shear rate (s.sup.−1) for shear rates comprised between 0.015 and 100 s.sup.−1. It is observed that there is a linear drop (in log scale) of the viscosity with the shear rate, characteristic of the behaviour of a rheofluidifying fluid with a threshold stress.

(123) FIG. 6 represents the value of shear stress as a function of the deformation obtained at a shear rate imposed for the gel according to the invention, referred to as gel strain “Limo-1” described in Example 1. A low shear rate (0.015 s.sup.−1) is applied in a constant manner in order to deform the gel starting from rest state and thus to determine the flow threshold. An already quasi-stationary flow is observed with shear stress values greater than 60 Pa. Indeed the threshold stress of the very high deformation material will therefore be much greater than 20 Pa, which will allow for the gel to hold fast on a wall for thicknesses comprised between 0 and at least 2 mm.

(124) In conclusion, this example shows that the gel “Limo-1” according to the invention has the appropriate rheological properties that enable it to be very easily sprayable on surfaces, whether or not horizontal.

Example 8

(125) In this example, it is shown that the gel according to the invention, referred to as gel “Limo-1” prepared in Example 1 is suctionable after the application and drying thereof.

(126) In other words, it is intended in this example to show that the gel according to the invention, referred to as gel “Limo-1” prepared in Example 1 indeed fractures well producing non-pulverulent flakes that are millimetre sized and can be easily suctioned off.

(127) In order to carry out this study, the gel Limo-1 is put to dry in a Binder® climatic chamber whose temperature and percentage of relative humidity are set at 25° C. and 50% respectively.

(128) The gel is spread over a nacelle made of stainless steel machined so as to obtain a controlled thickness of 2 mm of gel in the nacelle.

(129) In the climatic chamber, a Sartorius® precision balance is installed, as well as a Moticam® camera surrounded by a circular LED lamp (VWR) which is placed on the top of the balance.

(130) The balance and the Moticam® camera are connected to a computer placed outside the climatic chamber, thus enabling the weight and images of the gel-filled nacelle to be acquired simultaneously during the drying in controlled atmosphere.

(131) It should be noted that the nacelle containing the gel is placed in the precision balance and that all the doors of the balance are closed, with the exception of the door located opposite the air supply blower of the climatic chamber, which is open 3 cm, in order to maintain the controlled atmosphere in the housing compartment of the balance, while also limiting the airflow related to the operation of the climatic chamber. The recording of the weight during the drying then makes it possible to draw a curve which gives the loss in weight as a function of time and which therefore represents the drying kinetics.

(132) The evolution of the loss in weight as a function of time is presented in FIG. 7, and a photograph showing the final size of the gel flakes is presented in FIG. 8.

(133) It is thus observed that a thickness of 2 mm of the gel “Limo-1” dries in a few hours, more exactly in about 1200 minutes, that is 20 hours. It also appears additionally that the number of flakes formed and especially their size is indeed in conformity with the fact that these flakes are of millimetric sizes and are not pulverulent.

Example 9

(134) In this example, the elimination of a bitumen spot/patch is carried out by making use of a gel referred to as “Limo-2” whose composition is as follows: 14% by weight of alumina 19% by weight of ethanol 67% by weight of d-limonene

(135) The alumina is the alumina Aeroxide® Alu C marketed by EVONIK INDUSTRIES® which is a pyrogenic alumina with a specific surface area of 100 m.sup.2/g (BET), and the d-limonene is d-limonene marketed by the company MERCK®. The Ethanol is marketed by MERCK®.

(136) This gel was prepared according to the protocol described in Example 1.

(137) A bitumen spot/patch is produced by depositing on a dense, smooth surface, and under a heavy load, a small bitumen bead slightly heated in advance. The load is left for a period of 24 hrs on the spot/patch in order to provide for the good adhesion thereof on the surface.

(138) The gel “Limo-2” is then deposited, here with a spatula, in a sufficient quantity on the bitumen spot/patch and then allowed to dry over a period of 48 hours. Finally, the solid waste obtained upon completion of the drying is recovered by brushing.

(139) FIG. 9 shows the result obtained on a dense, smooth surface.

(140) It is observed that in one pass of the gel “Limo-2”, the totality of the bitumen spot/patch could be eliminated.

(141) One pass consists of the depositing of the gel on the bitumen spot/patch, the drying of the applied gel, then followed by the brushing of the solid waste obtained at the end of the drying.

REFERENCES

(142) [1] FR-A1-2 827 530. [2] FR-A1-2 891 470. [3] WO-A1-99/09134. [4] FR-A1-3 027 310. [5] FR-A1-2 957 929. [6] FR-A1-2962046 and WO-A1-2012/00104. [7] FR-A1-3003763 and WO-A1-2014/154818.