Method for extracting a solid energetic material from contaminated soil
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-05-28
- Publication Date
- 2026-04-08
AI Technical Summary
Existing methods for extracting solid energetic materials from contaminated soil are inefficient and pose pyrotechnic safety risks due to the inability to effectively separate these materials from mineral aggregates and metal parts, which can lead to unsafe handling during treatment.
A process involving sieving, initial densimetric separation in a water bath, drying, and a second densimetric separation in a brine bath of alkali metal formate to separate energetic materials from metal parts and mineral aggregates, ensuring safe and efficient extraction.
The process achieves high-efficiency separation with low environmental impact and moderate viscosity, reducing pyrotechnic risks and allowing for the safe handling of energetic materials, while also enabling the reuse of alkali metal formate, thus lowering costs.
Smart Images
Figure FR2024050681_05122024_PF_FP_ABST
Abstract
Description
Description Title of the invention: Method for extracting a solid energetic material from contaminated soil Technical Field
[0001] This presentation concerns a process for extracting a solid energetic material for the decontamination of contaminated soil. Prior art
[0002] The soil of former production or storage sites may be contaminated by solid energetic materials of an explosive nature. A densimetric screening technique may be considered to extract the energetic material and carry out soil decontamination. This technique is, however, sensitive to the geometric shape of the materials, and the energetic material may be found in a mixture of elements of various shapes ranging from millimeter grains to platelets several tens of centimeters long in the case of powder B, for example. Furthermore, the contaminated soil will very frequently include centimeter-scale mineral aggregates and potentially metal parts (such as small hardware parts), which will not be separated from the energetic material during screening.The presence of these parts can pose a pyrotechnic safety problem during the preparation stage for the destruction of the energetic material, which typically involves prior crushing.
[0003] DE 195 26 371, KR 2017 0113841 and US 2020 / 0094301 are known, which disclose methods for treating contaminated soil. US 6,121,506 is also known, which discloses a method for destroying energetic materials.
[0004] It is therefore desirable to have a method for treating soil contaminated by an energetic material with improved efficiency and which provides all the guarantees of pyrotechnic safety for the subsequent treatment stages. Statement of the invention
[0005] This disclosure relates to a method for extracting a solid energetic material from contaminated soil comprising a mixture of the energetic material with plant substances, mineral aggregates and metal parts, the method comprising: - sieving and washing the contaminated soil to recover the said mixture and remove any earth and sand that may be present, - a first densimetric separation, between a light fraction comprising the plant substances and a heavy fraction comprising the energy material, the mineral aggregates and the metal parts, by immersion of the mixture thus recovered in a water bath, - an extraction of the heavy fraction obtained during the first densimetric separation, - drying or draining of the heavy fraction thus extracted, - a second densimetric separation, between the energetic material on the one hand, and the metal parts and mineral aggregates on the other hand, by immersion of the heavy fraction thus dried or drained in a brine bath of an alkali metal formate, said brine having a density greater than that of the energetic material and less than each of the densities of the metal parts and the mineral aggregates, and - an extraction of the energetic material obtained following the second densimetric separation.
[0006] The invention is remarkable in that it is based on the principle of densimetric separation, or flotation separation, to separate the energetic material from the metal parts and mineral aggregates.
[0007] During this step, the mineral aggregates and metal parts sink to the bottom of the brine bath, while the energetic material floats on the surface and can thus be easily extracted. Brine allows the extraction of energetic material regardless of its form with high efficiency, does not pose a pyrotechnic risk and allows for simple separation. It also has a very low environmental impact and moderate viscosity, even at a high formate concentration. In addition, the heavy fraction is dried or drained before the second densimetric separation in order to limit the water carried over, which would otherwise denature the brine bath.
[0008] In one exemplary embodiment, the alkali metal formate is potassium formate.
[0009] Such a formate salt advantageously has a lower cost compared to cesium formate.
[0010] In an exemplary embodiment, a difference between the density of the brine and the density of the energetic material does not exceed 0.05.
[0011] Such a feature allows to further improve the efficiency of energy material extraction.
[0012] In an exemplary embodiment, the method further comprises: - extraction of metal parts and mineral aggregates following the second densimetric separation, - extraction of the residual alkali metal formate, present on the energy material, on the metal parts and on the mineral aggregates thus extracted following the second densimetric separation, by rinsing with water, - recovery of the rinsing water comprising the residual alkali metal formate thus extracted, and - concentration of the residual alkali metal formate by vacuum evaporation of the rinsing water.
[0013] This embodiment aims to recover the residual alkali metal formate present on the metal parts, mineral aggregates and on the energetic material following the second densimetric separation, to make it available for subsequent reuse. This advantageously makes it possible to limit the consumption of material and therefore the cost of implementation.
[0014] In one embodiment, the energetic material is based on nitrocellulose.
[0015] This disclosure also relates to a method of destroying a solid energetic material extracted from contaminated soil, comprising: - extraction of solid energetic material from the contaminated soil by implementing a process as described above, - grinding of the energy material thus extracted, and - destruction of the energy material thus crushed.
[0016] The invention is of particular interest in this context insofar as the grinding step no longer presents a pyrotechnic risk due to the separation of the energetic material from the metal parts and mineral aggregates. Brief description of the drawings [Fig. 1] Figure 1 represents a succession of steps of an example of a method according to the invention. Description of the embodiments
[0017] The invention is now described by means of Figure 1, which is provided for descriptive purposes to illustrate one embodiment of the invention and which should not be interpreted as limiting the latter.
[0018] The method described relates to the treatment of a volume of soil 10 contaminated by an energetic material. The soil 10 comprises earth, possibly sand, mineral aggregates such as stones, plant substances (leaves, branches, etc.) and metal parts (screws, nuts, metal waste or others), as well as the energetic material.
[0019] The soil sample 10 to be treated is first sieved and washed (step SI) so as to recover a mixture 14 comprising, in the example illustrated, the energetic material, the plant substances, the mineral aggregates and the metal parts, and to separate it from the other constituents of the soil such as the earth and the sand. Step SI makes it possible to eliminate particles 12 of earth and sand having a dimension smaller than a predefined dimension, for example less than or equal to 2 mm. Step SI can be carried out using a trommel, possibly under flowing water to facilitate the elimination of the particles 12.
[0020] The mixture 14 thus recovered is immersed in a water bath BE so as to carry out a first densimetric separation between the elements present (step S2). During step S2, the plant substances 15 float on the surface of the bath BE because they have a density lower than that of water. The rest of the mixture 14 comprising the energetic material 171, the metal parts 173 and the mineral aggregates 175 sinks to the bottom of the bath BE, because its constituents each have a density greater than that of water.
[0021] It will be noted that the energetic material 171 does not have a homogeneous particle size, and may, as illustrated, be in the form of a mixture of grains, having a substantially spherical shape, and platelets, distinct from the grains, having a slender shape. The person skilled in the art will recognize that the invention can be applied to many types of energetic materials. For example, the energetic material may be an explosive material. The energetic material may be based on nitrocellulose, possibly with a plasticizer such as nitroglycerin and / or an energetic filler, such as nitroguanidine. The energetic material may be powder B. Still by way of example, the energetic material may have a mass content of nitrocellulose greater than or equal to 95%, for example greater than or equal to 98%.
[0022] The first densimetric separation separates the light fraction, formed by the plant substances 15, which floats on the surface of the water bath BE, from the heavy fraction 17, comprising the energetic material 171, the metal parts 173 and the mineral aggregates 175, which is at the bottom of the water bath BE. The floating plant substances 15 are removed from the water bath BE using techniques known per se, for example manually with a scoop or automatically using floating recovery technologies used in the field of water treatment. The light fraction has a density lower than that of water and lower than that of the heavy fraction 17. The heavy fraction 17 has a density higher than that of water. The water bath BE is then evacuated to extract the fraction heavy 17, or the heavy fraction falls into a container, for example in the form of a basket, which is removed without draining the bath.
[0023] The heavy fraction 17 thus extracted is then dried or drained to remove any residual water present. For example, high-speed air blowing can be used, which is a technique suitable for automation, for example on either side of a perforated conveyor belt.
[0024] The extracted heavy fraction 17, dried or drained, is then immersed in a BS bath of brine, i.e. an aqueous solution, of an alkali metal formate salt, so as to carry out a second densimetric separation (step S3). The formate salt can be potassium formate or cesium formate. As indicated above, potassium formate has a lower cost than cesium formate and a sufficient density for the application case. Cesium formate is significantly more expensive but allows access to higher densities, which is useful for the extraction of energetic materials with a density greater than 1.7.
[0025] The density of the brine is a function of the formate concentration; a higher concentration results in an increase in density. The density of the brine is intermediate between that of the energetic material 171 and that of the metal parts 173. The density of the brine is also intermediate between that of the energetic material 171 and that of the mineral aggregates 175. In other words, the density of the brine is greater than the density of the energetic material 171 but less than that(s) of the metal parts 173 (and less than that(s) of the mineral aggregates 175). Thus, during step S3, the energetic material 171 floats on the surface of the bath BS because it has a density lower than that of the brine. The metal parts 173 and the mineral aggregates 175, on the other hand, sink to the bottom of the bath BS because they each have a density higher than that of the brine, and form a heavy residue 19.
[0026] Regardless of the embodiment considered, the density of the energetic material 171 may be less than or equal to 1.6. It may be advantageous, to further improve the efficiency of the separation, to adjust the density of the brine to a value close to the density of the energetic material 171, while remaining greater than it. Regardless of the embodiment considered, the difference between the density of the brine and the density of the energetic material does not exceed 0.05, or even 0.02. For example, the density of the energetic material 171 may be substantially equal to 1.6 and the density of the brine may be substantially equal to 1.62. Still for example, when a potassium formate brine is used, the potassium formate concentration may be greater than or equal to 80% by mass, for example 81%. The brine may possibly be a saturated aqueous solution of potassium formate. Unless otherwise stated, the density and concentration of the brine are taken before immersion of the dried or drained heavy fraction 17.
[0027] The floating energetic material 171 is extracted from the BS bath using techniques known per se, for example manually with a scoop or automatically using floating recovery technologies used in the field of water treatment. The BS bath is then evacuated to extract the heavy residue 19. Alternatively, the heavy residue 19 falls into a container, for example in the form of a basket, which is removed without draining the bath. The BS bath can be stored for later use.
[0028] It should be noted that steps S2 and S3 have the advantage of being able to be carried out at a moderate temperature, for example less than or equal to 30°C, for example between 5°C and 30°C, or even at room temperature (20°C). This contributes to the highly safe nature of the proposed process.
[0029] The example illustrated in Figure 1 proposes recycling of the formate used for the second densimetric separation through steps S41, S42, S5 and S6 which will now be described. However, it does not go beyond the scope of the invention if this recycling is omitted.
[0030] Steps S41 and S42 make it possible to extract the residual alkali metal formate present on the energetic material 171 and on the heavy residue 19, after the second densimetric separation. This recovery is carried out by rinsing with water. At the end of the rinsing of step S41, an energetic material 171' cleaned of the formate is obtained. Depending on the state of the material 171', it can be destroyed, or recycled and reintegrated into an energetic composition. The destruction of the material 171' uses techniques known per se such as incineration, basic hydrolysis or more advantageously supercritical hydrothermal oxidation as for example described in application WO2020188221. It is preceded by grinding of the material 171'. Metal parts 173' and mineral aggregates 175' cleaned of the formate are also obtained after step S42.
[0031] The rinsing water 21 from steps S41 and S42 is recovered and then undergoes vacuum evaporation to concentrate the residual alkali metal formate that has been extracted (step S5). It is thus possible to obtain a brine of residual alkali metal formate 23 of density suitable for its direct reuse or crystallized alkali metal formate which can then be mixed with water E, or with a brine, to obtain a concentrated brine that can be used for a new second densimetric separation (step S6).
[0032] The expression "between ... and ..." must be understood as including the limits.
Claims
Claims
1. A method of extracting a solid energetic material from contaminated soil (10) comprising a mixture (14) of the energetic material (171) with plant substances (15), mineral aggregates (175) and metal parts (173), the method comprising: - screening and washing (SI) of the contaminated soil to recover the said mixture and eliminate any earth and sand that may be present, - a first densimetric separation (S2), between a light fraction comprising the plant substances and a heavy fraction comprising the energetic material, the mineral aggregates and the metal parts, by immersion of the mixture thus recovered in a water bath (BE), - an extraction of the heavy fraction obtained during the first densimetric separation, - drying or draining of the heavy fraction thus extracted, - a second densimetric separation (S3), between the energetic material on the one hand, and the metal parts and mineral aggregates on the other hand, by immersion of the heavy fraction thus dried or drained in a bath (BS) of brine of an alkali metal formate, said brine having a density greater than that of the energetic material and less than each of the densities of the metal parts and the mineral aggregates, and - an extraction of the energetic material obtained following the second densimetric separation.
2. The method of claim 1, wherein the alkali metal formate is potassium formate.
3. A method according to claim 1 or 2, wherein a difference between the density of the brine and the density of the energetic material (171) does not exceed 0.
05.
4. A method according to any one of claims 1 to 3, wherein the method further comprises: - extraction of metal parts (173) and mineral aggregates following the second densimetric separation, - an extraction (S41; S42) of the residual alkali metal formate, present on the energetic material (171), on the metal parts and on the mineral aggregates thus extracted following the second densimetric separation (S3), by rinsing with water, - a recovery of the rinsing water (21) comprising the residual alkali metal formate thus extracted, and - a concentration (S5) of the residual alkali metal formate by vacuum evaporation of the rinsing water.
5. A method according to any one of claims 1 to 4, wherein the energetic material (171) is nitrocellulose based.
6. A method of destroying a solid energetic material extracted from contaminated soil (10), comprising: - an extraction of the energetic material (171) from the contaminated soil by implementing a method according to any one of claims 1 to 5, - grinding of the energy material thus extracted, and - destruction of the energy material thus crushed.