EP1584751B1 - Soil treatment process using at least one monopolar coaxial electrode system and apparatus for performance of the process - Google Patents

Description

The invention relates to a soil treatment method comprising the use of at least one system of coaxial monopolar electrodes driven at least partly into the ground. The invention also relates to a device intended more particularly for the implementation of such a method. The invention finally relates to the use of such a method or device for the dehydration and / or decontamination of quarry sludge and / or mining products and / or extraction by-products. mining.

Lagooning quarry sludge is a common practice. This practice can also be found in the mining sector, whether for coal mining residues or for mining sludges of various metals. In fact, sands, gravel, minerals or other matter extracted from the soil must generally be washed with water during or after extraction. So we end up with the presence of lagoons. These lagoons are spaces comprising a liquid-solid mixture that is to say mud, with usually a majority proportion of liquid which is most often at least partly supernatant. These lagoons pose problems in terms of environment and safety (ground more or less moving). The natural consolidation of these lagoons is all the longer as the regional climate is humid. For example, in Normandy, in France, it takes more than ten years for earthmovers to maneuver on the surface of quarry lagoons.

The principle of dehydration of such lagoons by electro-osmosis is known. Thus, in the publication "Stabilization Consolidation Treatments for Soft Clayey Soil", Fernando Veniale, Bul. Stiint. The Institute of Constructii Bucurestii, T.30, Nr.1, 1984, p.59-67 describes the application of electro-osmosis to the treatment of clay consolidation of quarries using electrodes. based on aluminum. Monopolar electrodes are thus alternated and driven regularly into the treated ground in order to dehydrate the quarry. Each electrode is of one polarity. The two polarities are represented and alternated within the system thus constituted.

From WO-A-0102626 there is furthermore known a soil treatment method comprising the deposition into the soil of coaxial monopolar electrodes, comprising a rod of first polarity and a hollow tube coaxial with the rod and of second polarity.

Such processes described in the prior art pose many technical problems such as the loss of contact between the electrodes disposed on the surface and the sludge during the treatment, resulting in excessive energy consumption, or the cracking of the sludge. before it is sufficiently dehydrated. In particular, the cracks thus created pose problems of parts of water that descend to the ground whereas they have been more or less raised by the treatment, as well as insulation problems (the electric field no longer working) because these cracks extend parallel to the rows of electrodes and intercalate between rows of electrodes of sign or opposite polarity (e) or opposite.

Another problem that is encountered is crusting on the lagoons (i.e. dehydration or even drying of the surface while the bottom is only slightly affected by the treatment).

The method and the device according to the invention make it possible to solve the problems of the prior art, in that they make it possible, by using at least one system of coaxial monopolar electrodes, preferably a plurality of coaxial monopolar electrode systems, treating, mainly dehydrating and / or depolluting, the interior of a soil (for example a quarry lagoon) by the use of said electrode system or systems planted vertically in said soil , usually from the surface. The depollution according to the invention comprises the possible treatment of pollutants, mainly of ionic and / or ionizable, organic and / or mineral species. Dehydration according to the invention is generally associated with a pumping system generally at the surface of the quarry, which makes it possible to extract the water therefrom.

1. a) Au moins un enfoncement sensiblement vertical au moins partiel dans le sol d'au moins un système d'électrodes monopolaires coaxiales sensiblement rectiligne, ledit système d'électrodes comprenant au moins une tige comportant au moins une zone de première polarité et au moins une zone isolante, et au moins un tube creux entourant au moins partiellement ladite tige et constituant au moins partiellement une zone de seconde polarité apte à coulisser au moins partiellement autour de ladite tige, ladite zone de seconde polarité étant placée de façon à découvrir au moins une zone de première polarité dudit système d'électrodes, de préférence la zone de première polarité située le plus près de l'extrémité inférieure de ladite tige,
2. b) Une mise sous champ électrique du système d'électrodes.

Thus, the method according to the invention is a soil treatment method comprising the following successive steps:

1. a) At least one substantially vertical at least partial depression in the ground of at least one substantially straight coaxial monopolar electrode system, said electrode system comprising at least one rod comprising at least one zone of first polarity and at least one insulating zone, and at least one hollow tube surrounding at least partially said rod and at least partially constituting a zone of second polarity able to slide at least partially around said rod, said second polarity zone being placed so as to discover at least one zone of first polarity of said electrode system, preferably the zone of first polarity located closest to the lower end of said rod,
2. b) An electric field of the electrode system.

Typically, step a) is generally such that the placement of said second polarity zone is such that said second polarity zone also at least partially discovers an insulating zone, generally located at least partly between said first polarity zone and said first polarity zone. second polarity zone.

Preferably, said rod comprises alternating zones of first polarity and insulating zones. According to the invention, "an alternation of zones of first polarity and insulating zones" means at least two successions of a zone of first polarity and of an insulating zone, a succession consisting of a zone of first polarity followed by an insulating zone, the zones of first polarity generally adjoining each one or two insulating zones, the insulating zones generally adjoining each one or two zones of first polarity.

In step a), said electrode system once sunk into the ground preferably has an upper end off the ground, i.e. above the ground surface as will be explained by the following, at least one zone of second polarity in the ground, and a lower end having at least one zone of first polarity in the ground. Thus, in step b), the current flows and there is a potential difference between the first polarity zone discovered by the second polarity zone and said second polarity zone, generally separated from the second polarity zone at least partially. by at least one insulating zone.

By "soil" is meant according to the invention any surface on which one could walk, essentially comprising a more or less hydrated material whose constituents are essentially of geological and / or pedological origin, that they are in place naturally and / or or as a result of at least one human intervention. Sludge mainly of mineral origin, including quarry sludge, is included in this definition, even if it can not be walked without danger (more or less moving soil).

By "sludge" is meant according to the invention a solid-liquid mixture, with generally more liquid than solid. Typically, in the case of quarry sludge, the liquid is water and the solid is a clay or other finely divided material. In order of magnitude, it can be indicated that a sludge contains an amount of solid of at least 50 g / l in the liquid. For example, a quarry slurry may comprise about 800g / l of clay in water, or 50 to 60% by weight of dry matter, for a density of about 1.8.

According to the invention, the term "system of coaxial monopolar electrodes" means an electrode system, comprising at least one zone of first polarity, for example anodic, and at least one zone of second polarity, which is opposite, for example cathodic, that is to say generally comprising at least one anode and at least one cathode. Unlike the prior art, this system comprises within it the two polarities, and not a single polarity. This electrode system is biased under the action of an electric field, for example by closing a circuit comprising at least one generator at the terminals of zones of opposite polarity. It therefore works most often at constant tension. By "electrode" is meant according to the invention cathode or anode. According to the invention, a zone of first polarity is generally either cathodic or anodic, and a zone of second polarity, of opposite polarity to that of the zone of first polarity, is either anodic or cathodic.

Activation step b) allows the treatment, mainly by electro-osmosis and / or electromigration, of the water and ionized species present in the soil in the vicinity of said electrode system, that is to say in an area of influence around the system. Consequently, according to the invention, by the judicious and adapted choice of the zones of opposite polarity, the water and the ionized species (that is to say coming from ionic and / or ionizable species) are able to migrate towards the zone of second polarity.

Such a zone of influence is necessarily limited in size, and depends on many parameters such as the soil type, water content and / or pollution, geometry, nature and number of electrode systems etc. Such a zone of influence is easily known to the person skilled in the art in each of the particular cases that he approaches, at least after a few tests on the soil undergoing the treatment according to the invention. It is not possible to define it precisely in advance, even if the person skilled in the art practicing such treatment can know its order of magnitude.

Advantageously, the coaxial shape of the electrode systems allows any cracks, which may be generated during the treatment process according to the invention, to appear radially so as not to hinder the passage of the electric field.

1. c) Une désactivation du système d'électrodes par arrêt au moins partiel du champ électrique,
2. d) Une remontée partielle de la zone de seconde polarité permettant de découvrir au moins une nouvelle zone de première polarité et/ou au moins une zone isolante, et
3. e) Eventuellement une remise sous champ électrique du système d'électrodes.

In a preferred embodiment, the method according to the invention further comprises at least one succession of the following successive steps:

1. c) A deactivation of the electrode system by at least partial stopping of the electric field,
2. d) a partial rise of the second polarity zone making it possible to discover at least one new zone of first polarity and / or at least one insulating zone, and
3. e) Possibly a refitting in electric field of the electrode system.

Typically, step d) is such that the partial rise of the second polarity zone makes it possible to at least partially discover a new zone of first polarity and at least partially a new insulating zone, that is to say a succession of zone of first polarity and insulating zone. The new zone insulation is generally located at least partly between said new first polarity zone and said second polarity zone.

In one embodiment of the method according to the invention, said method comprises dismantling any superfluous second polarity zone. For example, when performing step d), it has brought to the surface an area of second polarity that has no more use, and is therefore superfluous. It is possible to provide that this zone of second polarity can be dismantled in whole or in part. Thus the method according to the invention may comprise the dismantling of said zone of superfluous second polarity.

Advantageously, during use in dehydration, the method according to the invention comprises at least partially, preferably almost completely, a liquid pumping, generally comprising water, on the surface of the soil.

The hollow tube constituting at least partially the second polarity zone generally comprises at least one inner insulating zone, generally over substantially its entire length.

Thus, by a method implementing the use of coaxial electrode system (s) and physical phenomena of electro-osmosis, that is to say of setting in motion the water molecules contained in a matrix more or less solid by the action of a continuous electric field, and / or electromigration, that is to say the setting in motion of ionized species (that is to say ionic and / or ionizable which have ionized) by the same electric field, the method according to the invention makes it possible to dehydrate or even consolidate soils, especially quarry sludge lagoons. As will be explained below, the consolidation of these soils is advantageously from the bottom of the humidified or even drowned space, that is to say from the bottom of the lagoon to the surface. Particularly advantageously, such consolidation is possible under water, that is to say if the surface is embedded under a certain thickness of water, for example at least 1.5 meters (inclusive).

"Off the ground" therefore means according to the invention generally in atmospheric air and / or in water.

The invention thus advantageously makes it possible, with respect to the state of the art, thanks to the clever and combined use of at least one electrode system with a particular geometry and an implementation of a zone movement of second polarity towards the surface, discovering at least one zone of first polarity, a progressive dehydration from the bottom of the lagoon even a consolidation, even under water.

Another advantage of the method according to the invention is a low energy consumption, because the space between the first polarity zone and the second polarity zone is generally minimum, ie relatively low. Such a space is generally dimensioned according to various parameters such as for example the number of electrode systems; the geometry of each electrode system; the quantity a priori of water to be eliminated; the ionic or ionizable species pollution that can be treated according to the method of the invention.

Another advantage of the method according to the invention is the relative ease of implantation of the electrode system or systems.

In a particular embodiment of the invention, the electrode system consisting mainly of assemblable parts called sections, the depression of the electrode system in the soil is carried out by a progressive process of driving and assembly successive steps of the sections to each other, said process comprising at least one step of at least partial depression of at least one section, creating a set of at least partially depressed sections, followed by at least one assembly step at at least part of at least one other section to the assembly of at least partially embedded section (s) already constituted. Such an embodiment advantageously facilitates the insertion of the electrode system into the ground. Preferably, such an assembly comprises at least one screwing.

Advantageously, such a particular embodiment allows the relatively simple implementation of the method according to the invention, since it involves pressing vertically short sections of electrode system, to screw one or more new short sections on these, to sink again and start again until reaching the bottom of the "basin" (space where is most of the soil moistened or drowned).

The electrode systems used are or are not two by two similar, in terms of dimensions, geometry and / or polarity.

In an advantageous embodiment of the invention, the method according to the invention is such that a plurality of electrode systems are used, said electrode systems preferably being all, preferably all, of identical polarities. (That is, areas of the same polarity have the same sign), and the various steps, preferably substantially simultaneously, are performed for each of said electrode systems. Thus the treatment of a soil, for example a lagoon of several hectares is simply by implanting as many electrode systems as necessary. The number of electrode systems varies according to different parameters such as the surface of the soil to be treated. As explained above, the geometry of the electrode systems determines at least in part the area of influence of said electrode systems. Preferably all the electrode systems are of substantially identical geometry but it is also possible according to the invention that they are at least partially of substantially different geometry, ie at least two, or more two of them are of substantially different geometry.

In the case of the use for the dehydration of quarries, the dewatered or consolidated lagoons thus obtained are the first to be obtained efficiently and for a reasonable duration by a method of using coaxial monopolar electrode systems, which presents a considerable progress of the invention compared to the state of the art.

By "activation" of the electrode system according to the invention is meant an electromagnetic field. Such placing in an electric field allows the treatment of water or even ionic and ionizable species in the soil, as has been explained previously. The imposed voltage is generally substantially constant, and the intensity varies according to the parameters such as the nature of the ground ...

The invention also relates to a soil dehydration and / or soil depollution process comprising at least one soil treatment method, in particular a quarry, according to the invention.

The invention also relates to a soil treatment device comprising at least one system of substantially straight coaxial monopolar electrodes, said electrode system comprising at least one rod comprising at least one zone of first polarity and at least one insulating zone, and at least one hollow tube at least partially surrounding said rod and at least partially constituting a zone of second polarity capable of sliding at least partially around said rod, said electrode system being able to be placed in an electric field.

The electrode system is generally and preferably adapted to be depressed at least partially into the ground, most often so, once pushed into the ground, to have an upper end out of the ground and a lower end having a first polarity in the ground. A way of driving into the ground is for example a sharp form and beveled of the lower end to be driven into the ground.

Said rod preferably comprises alternating zones of first polarity and insulating zones.

In a preferred embodiment of the device according to the invention, said zone of second polarity is furthermore capable of being raised at least partially upwards so as to be able to discover at least one new zone of first polarity, preferably a new alternation. first polarity zone and insulating zone, and this if possible as often as necessary.

Preferably, the zone of second polarity is able to be disassembled at least partially, preferably almost completely.

According to the invention, the device comprises at least one activation means of the electrode system, that is to say at least one means for placing the electrode system in an electric field.

Preferably, the electrode system consists mainly of assemblable parts called sections, and even more preferably such an assembly comprises at least one screwing.

The region of first polarity or second polarity, when cathodic, generally comprises, preferably consists mainly of (el) stainless steel (or stainless steel) or non-stainless steel, preferably el) 'stainless steel. In the case where it mainly comprises non-stainless steel, it is a consumable electrode.

The zone of second polarity or first polarity, when it is anodic, generally comprises Preferably, predominantly titanium, preferably all titanium, is coated with at least one metal compound, precious or not, said metal compound, valuable or not, being preferably selected from the group. formed by ruthenium, iridium, tantalum, tin, and antimony, in at least partially oxidized forms or not, and mixtures thereof.

Preferably, the insulating zone of said rod mainly comprises plastic such as at least one polymeric compound selected from the group consisting of polyvinyl chloride, polyethylenes (all densities), polypropylenes (all densities), and mixtures thereof.

In the case where the rod has anodic zones and insulating zones, the rod may for example in a first version be entirely a bar made of titanium coated with precious metal and having at regular intervals, over said titanium, a sheath by example heat shrinkable typically HDPE (Poly Ethylene High Density) forming insulating areas. A second, less expensive, version of this example is a rod consisting of alternating parts, one of the parts comprising titanium uncoated with precious metal and covered with such a sheath HDPE, and the other parts being made of titanium covered with precious metal.

In a preferred embodiment of the device according to the invention, the hollow tube constituting at least partially the second polarity zone comprises at least one inner insulating zone generally over substantially its entire length. In such a case, that internal insulation zone generally comprises plastic such as at least one polymeric compound selected from the group consisting of polyvinyl chloride, polyethylenes (all densities), polypropylenes (all densities), and mixtures thereof.

Preferably, the device according to the invention further comprises at least one placing means (that is to say placing it by at least partial depression in the ground), mechanical or manual, of at least one control system. electrodes. Such placement means is generally manual for low thicknesses and low soil resistance, for example at least one hammer or hammer. Otherwise, such a means is mechanical; it includes for example at least one drill.

The electrode systems used are or are not two by two similar, in terms of dimensions, geometry and / or polarity.

According to a preferred embodiment, the device of the invention comprises a plurality of electrode systems, said electrode systems preferably being all, preferably all, of identical polarities, that is to say that the areas of first polarity are of the same polarity and the zones of second polarity are of the same polarity. The number of electrode systems varies according to different parameters such as the lagoon surface to be treated as explained above.

The device according to the invention is particularly suitable for implementing the method according to the invention as described above.

Similarly, the invention relates to the use of a device as described above, for the dehydration of soil and / or soil remediation, in particular quarry sludge (quarry lagoon) and / or products of mining and / or mining by-products.

In the case of dewatering or even consolidation of quarry sludge lagoons, a zone of second polarity is cathodic and zones of first polarity are anodic. The phenomenon of electro-osmosis gradually leads at least partially, preferably almost completely, water to the cathode zone. Thus, as the lagoon is treated, the second polarity zone is slid upwards along the insulating and first polarity zones which are kept fixed. Thus, the water is forced back up the electrode system towards the cathode and thus progressively towards the surface. The water thus gradually returned to the surface is particularly easy to pump, and possibly to recycle. This treatment is accompanied by a depollution when there is in the soil cations for example metals. These cations go back to the surface with the water in which they are dissolved. This is particularly effective in the case of recent pollution, that is typically a few months.

The invention also allows an inorganic depollution, mainly in the case where a zone of second polarity is anodic and zones of first polarity are cathodic. As and when treatment, the second polarity zone is slid upwards along the insulating and first polarity zones which are kept fixed. The phenomenon of electromigration gradually leads at least partially, preferably almost completely, polluting anions that are for example nitrate ions NO ₃ ^- and / or cyanide CN ^- , to the anode and therefore to the surface. On the other hand, the water and the cations possibly present in the water, such as calcium Ca ²⁺ , are driven by electro-osmosis and gravity phenomenon towards the cathodic zone, and thus toward the bottom; it is therefore generally necessary to provide at least one water supply system to the electrode system from the inside and / or the outside of the tube, to avoid excessive dehydration that would significantly disturb the phenomenon of electromigration. Such use is very significant in the case of accidental pollution, for example nitrates from a soil above a water table. It makes it possible to sustainably protect said layer of pollution by treating said soil.

The invention also allows an injection of water to the bottom of a soil such as a sump. In this case, the treatment according to the invention makes it possible to circulate the water towards the bottom of the soil, without the risk of abrupt rise of the water table and without the need to manufacture a well. In this case, a zone of second polarity is anodic and a zone of first polarity is cathodic, and located at the end of the rod which otherwise consists of an insulating zone. The electrode system thus formed can advantageously pass through more or less impermeable clay layers without altering their impermeability. important way. The cathode is located below said layers in a permeable zone. Advantageously, the clay also makes it possible to filter the water passing through it. Out of the ground, said system emerges in the water that we want to transfer in depth. The water (and the cations possibly present in the water, such as calcium Ca ²⁺ ), is gradually driven at least partially, preferably almost completely, towards the cathode zone, and thus towards the bottom. The water can thus pass through said clay layer.

The invention will be better described and other features and advantages will become apparent on reading the following description, given in a non-limiting manner, with reference to FIGS. 1 to 10.

FIG. 1 schematically represents a system 12 of coaxial monopolar electrodes with mobile sliding cathode 1 according to the invention.

Figures 2 to 9 show schematically a three-phase treatment for dewatering a lagoon 14 quarry sludge according to the invention, by a device comprising the system 12 of electrodes of Figure 1. Thus Figure 2 represents FIGS. 3 and 4 show a partial rise of the cathodes (a mobile cathode per electrode), FIG. 5 represents a disassembly of superfluous cathodic parts, FIG. 6 represents a reset under electric field, FIG. partial rise of the cathodes, Figure 8 shows a disassembly of superfluous cathodic parts, and Figure 9 shows an electric field of the end of the treatment.

Figure 10 shows, schematically, another system 13 of concentric monopolar electrodes with mobile sliding anode 9 according to the invention.

FIG. 1 schematically represents a system 12 of coaxial monopolar electrodes with mobile sliding cathode 1 according to the invention. It comprises a sliding mobile cathode 1 having an inner insulation (not shown), a set 2 of insulating zones fixed on a set 3 of fixed anode zones. The cathode 1 may consist of parts 1a, 1b, 1c, 1d, 1e, 1f, 1g and 1h (not shown in Figure 1). It can be seen that the set 2 of insulating zones consists of the parts 2a, 2b, 2c and 2d, and that the set 3 of anode zones consists of the anode zones 3a, 3b, 3c, 3d and 3e. Only the insulating zones 2a and anode 3a are exposed by the cathode 1.

Figures 2 to 9 show, schematically, a three-phase treatment for dewatering a lagoon 14 quarry mud according to the invention. They correspond, as will be explained below, to a first system 12 of electrodes according to the invention, as shown for example in Figure 1. This treatment will serve us, after detailed description of Figures 2 to 9, to illustrate the advantages of the invention.

FIG. 2 according to the invention represents the beginning of the treatment of lagoon 14, bottom 15 and surface 16 of quarry sludge, in which at least eleven electrode systems 12 have been put in place as shown in FIG. Figure 1. Water 4 rises above the surface 16, a portion 14a already dried out of the lagoon 14 is located above the bottom 15 thereof, and a portion 14b not yet dried or wet (or even flooded) of the lagoon 14 is located above said portion 14a. It can be seen that, for this first phase of treatment, zones 8 of initial dewatering are formed, which join through intermediate zones 7 which are also progressively dried. The set of zones 8 and zones 7 corresponds to the dried part 14a. The arrows 6 illustrate the upward movement of the water towards the cathode 1, which causes a capillary rise towards the surface 16. The water 4 which has appeared above the surface 16 of the lagoon 14 is pumped by least one line 5, the pumping being symbolically represented by an arrow. In the case where water 4 was present above the surface 16 before the start of the treatment, it is possible but not obligatory according to the invention to carry out a pumping operation before the beginning of said treatment.

FIG. 3 symbolizes the beginning of the rise of the cathodes 1. It can be seen that, in addition to the anode zone 3a and the insulating zone 2a, a new anode zone 3b has been discovered on each system 12a. electrodes.

FIG. 4 shows the end of the rise of the cathodes 1. In addition to the anode zone 3b previously discovered (see FIG. 3), a new insulating zone 2b appears. For the lagoon periphery electrode systems 12 which were sunk less deeply because of the shallower depth of the lagoon 14 at this location, the anode areas 3a and insulating areas 2a are now discovered.

FIG. 5 shows the disassembly of the superfluous cathode parts 1a, and possibly 1b, 1c, 1d and 1e of the cathodes 1, according to the length of each system 12 of starting electrodes and therefore of each cathode 1.

FIG. 6 shows the return of the lagoon 14 to the electric field. New arrows 6a for rising water towards the surface 16 appear, new zones 8a for dewatering around the electrode systems 12, and new zones. 7a intermediate between the zones 8a. Thus, in this second phase, there is a wet portion 14c of the lagoon 14, which is smaller than the wet portion 14b of the first phase, and a dried portion 14d, which corresponds to all the zones 8a and 7a , and which is larger than the dried zone 14a of the first phase. The pumping is still illustrated by the pumping line.

In Figure 7, we see the rise of the cathodes 1 following the second phase of treatment, discovering anode areas 3c and insulating areas 2c.

FIG. 8 shows the dismantling of the superfluous parts 1f, and possibly 1g and 1h of the cathodes 1.

FIG. 9 shows a third phase of dewatering by electric field delivery, again including dewatering zones 8b near the electrode systems 12, the upwelling 4 towards the surface 16 being indicated by the arrows 6b, and intermediate zones 7b of junction between the dewatering zones 8b. Thus in this second phase, there is a wet portion 14e of the lagoon 14, which is smaller than the wet portion 14c of the second phase, and a dry portion 14f, which corresponds to the set of zones 8b and 7b zones, and which is larger than the 14d dry zone of the second phase. The pumping is still illustrated by the pumping line.

For the end of the treatment, there remains on the surface 16 of lagoon 14 only a thin layer 14e of relatively soft mud. The latter, being no longer fed (by capillary rise) by the large body of water that was initially between the bottom 15 and the surface 16 of the lagoon 14, dries naturally with the wind and water. sun in a very short time. Possibly a PANDA® type light penetrometer measuring series makes it possible to determine the mechanical strength of the dehydrated materials, and thus the end of the construction site. At the end, the electrode systems 12 are extracted from the lagoon 14 to be possibly reconditioned for reuse on another site or on the same lagoon 14 when it will be full again. Such reconditioning generally comprises at least one cleaning and / or at least one repositioning deposit on at least one electrode. There is then only to empty the lagoon 14 to the tractor-shovel if necessary, the lagoon 14 dehydrated and consolidated is now accessible to construction equipment.

FIG. 10 schematically represents another coaxial monopolar electrodes system 13 with moving sliding anode 9 according to the invention. The electrode system 13 comprises a sliding anode 9 insulated therein (insulation not shown) and lubricated externally, for example with water or bentonite, and an assembly 10 of isolated insulating zones fixed on a set 11 fixed cathode zones. The anode 9 may consist of parts 9a, 9b, etc. (not shown) It can be seen that the set of insulating zones 10 consists of the insulating zones 10a, 10b, 10c and 10d, and that the set 11 of cathode zones consists of the zones 11a, 11b, 11c, 11d and 11e. Only the insulating zone 10a and cathode zone 11a are discovered by the anode 9.

Thus, FIG. 10 shows an electrode system 13 for the progressive destruction of organic pollutants and / or for raising anionic pollutants (such as nitrates and / or cyanides) to the surface of a soil. The electrode system 13 of FIG. 10 thus allows the depollution of a soil 14 and / or a water table polluted by at least one anionic species, for example chosen from the group formed by nitrates and cyanides. Said anionic species can be raised to the surface 16 to facilitate its treatment which can be biological and / electrochemical in the case of cyanide, and / or physicochemical and / or phytoremediation type (or treatment with at least one plant). In the case of the treatment of a soil, the device comprising this system 13 of electrodes can prevent contamination of a water table that is not yet affected by the pollution of said anionic species.

The rise of pollutants by means of a device comprising the electrode system 13 of FIG. 10 is exactly in the same operating mode as that of the electrode system 12 described in FIGS. 2 to 9.

According to the invention, it is possible to have additional means for modifying the influence of the electrode systems. For example it is possible to extend the (the) zone (s) insulating (s) to expand the areas of influence of the electric field and thus reduce the number of electrode systems necessary to cover an area of several hectares.

According to another embodiment, independent or not of the previous embodiment, it is possible to increase the length of an electrode system, for example and preferably by increasing the number of sections which is preferably constituted by the system. of electrodes, to go deeper into the lagoon.

According to a third embodiment, independent or not of each of the two previous embodiments, it is possible to increase the number of electrode systems to accelerate the work.

It is interesting to note that, according to the method of the invention, it is very advantageous to dehydrate the lagoon starting from the bottom. On the one hand, the cracks which appear possibly during treatment are radial and do not hinder the dehydration process. On the other hand, it is important to note that the system can work under water, that is, it can "pack" sedimentary sludge under the surface of a water reservoir and thus allow at least to space out the usual cleaning operations.

According to the invention, in the case of the electrode system 12 described in FIGS. 1 to 9, the zones of first polarity, here anodic zones, are activated in discovering them. The water around the cathode serving as a lubricant, the mechanical forces are thus advantageously limited. When the zone around the first zone of first polarity becomes too strong, the second polarity zone is the cathode, the distance between the cathode and the nearest anode being always the same, with a content of water always favorable to the passage of the current.

Depending on the intended application, any of the possible physical phenomena will be favored. Without wishing to be bound by a given explanation, one can try to give the following explanation. In particular, the phenomena of electro-osmosis relate at least in part to sludge lagoon dewatering applications or settlement of sediments in a water reservoir. The phenomenon of electromigration, which generally makes it possible to trace back at least partly to the surface of mineral pollution and / or which favors the in-situ destruction of organic pollution, mainly concerns depollution applications. On the other hand, all the electrokinetic phenomena taking place at almost the same time, in some cases the electro-osmosis will help to depollute at least in part whereas the electromigration will not dehydrate. In this case, it is arranged to prevent drying of the anode or even lubricate the outside of the sliding anode with, for example, bentonite sludge conventionally used during drilling.

To favor one or the other of the phenomena, it is possible to act on the electrode materials, in particular deposits on one or other of the electrodes, on the connection of the electrodes, that is to say to choose a device with sliding anode or sliding cathode, on the adaptation of the draining material possibly present on the cathode and on the injection of water, of products dissolved or suspensions, at different levels of each electrode system. For example, the injection of suspensions at different levels of the electrode system can be used to lubricate a sliding anode.

The invention has been successfully tested on the dewatering of quarry lagoons and unpolluted dredging sludges.

It is also possible to use the invention for the dehydration of phosphate sludge, coal sludge, mining sludge, and / or used drilling muds.

It is also possible to use the invention for the depollution by in-situ degradation of organic pollutants, for the depollution of water tables (nitrates, cyanides, metals, arsenic, etc.) by raising pollutants on the surface of the surface. soil for subsequent disposal, for the decontamination of soils even clay by raising surface pollutants for disposal, or for pumping deep water in arid areas.

Example

The following example serves to illustrate the invention without limiting its scope.

An assay was performed on site, with a given electrode system described below.

This is one of the trials of a ten-day campaign that took place in July 2003 at a clay loam lagoon site containing a majority of smectite. The purpose was simply to show the feasibility of the invention. The tests were relatively short (2 hours). The purpose was to compare the effects of three factors: the voltage, the length of the anode and the length of the isolated area. Efficiency was evaluated by measuring the amount of water that was surface-enhanced during the two hours with only one electrode system in operation.

The maximum working depth for the tip of the anode was consistently 2 meters deep.

The activated part of the anode was 30 cm long and 20 mm in diameter with a tip forming an angle of 15 ° to the axis of the anode. Sections of about 50 cm were assembled by screwing. The material of the anode was titanium covered with metal oxides, mainly iridium (DSA type).

The insulation length was 97 cm, made of High Density Polyethylene (HDPE) material in the form of heat-shrinkable material placed directly on the anode.

The cathode length was about 150 cm for an outer diameter of 48.5 mm, an internal diameter of 27 mm (insulation included), and outer material stainless food and PVC inner material (Poly Vinyl Chloride). The length of each cathode section was about 560 mm. This particular piece was embellished with additional parts allowing the internal sealing of the cathode and the subjection of the cathode to the anode. The sealed junction between the cathode sections was provided by a flat nitrile rubber gasket.

The total length of the electrode system was about 350 cm.

The system was set up by hand and supported by a support that distributed its weight (about 15 kg) over 1 m ² .

The upper layer of lagoon (20 cm in height) being relatively solid (after several months of drought), wide planks placed on its surface were enough to effectively support the operators. In order not to interact with the dry layer of the lagoon a 30 cm hole was made and cased to collect the water that the electrode system went up.

The initial concentration of the sludge is of the order of 40% after 6 years without the addition of granular washing water in it. No rise in water is observed after several hours in an identical hole without electrode system.

The volume of water raised is about 500 ml in two hours.

The amount of water recovered in two hours is characteristic of the zone of influence of the electrode system for a given configuration. On the other hand, it is not representative of the amount of water that would have risen over a longer period, per unit of time. In the space of two hours, the process has just enough time to initiate the rise of the water (which comes from about two meters deep), the nominal flow not yet reached. It would probably take several days for it to be reached.

The dimensions of the prototype will be about the same as the industrial version of the electrode system.

Claims (24)

1. A process for soil treatment comprising the following successive steps:

   a) At least partially essentially vertical sinking into the soil (14) of at least one system (12; 13) of essentially linear coaxial monopolar electrodes, said system (12; 13) of electrodes containing at least one rod (2, 3; 10, 11) containing at least one first polarity zone (3a, 3b, 3c, 3d, 3e; 11a, 11b, 11c, 11d, 11e), at least one insulating zone (2a, 2b, 2c, 2d; 10a, 10b, 10c, 10d), and at least one hollow tube (1, 9) coaxial to said rod (2, 3; 10, 11), at least partially enclosing said rod (2, 3; 10, 11) and forming at least partially a second polarity zone (1; 9) capable of sliding at least partially around said rod (2, 3; 10, 11), said second polarity zone (1; 9) being positioned so as to uncover at least one first polarity zone (3; 11) of said electrode system (12; 13),

   b) Placing of the electrode system (12; 13) under an electric field.
2. A process according to Claim 1, further comprising a sequence of at least the following successive steps:

   c) Deactivating the electrode system (12; 13) by at least partially stopping the electric field,

   d) Partially raising the second polarity zone (1; 9) to permit uncovery of at least one new first polarity zone (3a, 3b, 3c, 3d, 3e) and/or at least one insulating zone (2a, 2b, 2c, 2d),

   e) Returning the electrode system (12; 13) to an electric field.
3. A process according to one of the preceding claims, such that said rod (2, 3; 10, 11) includes an alternation of first polarity zones (3a, 3b, 3c, 3d, 3e; 1a, 11b, 11c, 11d, 11e) and insulating zones (2a, 2b, 2c, 2d; 10a, 10b, 10c, 10d).
4. A process according to one of the preceding claims, such that said electrode system (12; 13), once immersed in the soil (14), has an upper end above the surface (16) of the soil (14), at least one second polarity zone (1; 9) in the soil (14), and a lower end containing at least one first polarity zone (3; 11) in the soil (14).
5. A process according to one of the preceding claims, such that said second polarity zone (1; 9) is placed so as to uncover the first polarity zone (3a; 11a) situated closest to the lower end of said rod (2, 3; 10, 11).
6. A process according to one of the preceding claims, comprising disassembly of all or part of the superfluous second polarity zone (1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h).
7. A process according to one of the preceding claims, containing at least partial pumping (5) of surface liquid (16) of the soil (14).
8. A process according to one of the preceding claims, in which the electrode system (12; 13) essentially consists of assembled parts called sections, sinking the electrode system (12; 13) into the soil (14) is carried out by a progressive sinking process and successive assembly of the sections one after the other, said process comprising at least one stage of at least partial sinking of at least one section, creating an assembly of at least partly immersed sections, followed by at least one at least partial assembly step of at least one other section to the least partly immersed assembly of sections already formed.
9. A process according to the preceding claims, in which the assembly contains at least one threaded joint.
10. A process according to one of the preceding claims, in which a plurality of electrode systems (12; 13) is used, said electrode systems (12; 13) being practically all of identical polarity, and one proceeds with the various steps for each of said electrode systems (12; 13).
11. A process for dehydration of soil and/or depollution of soil, comprising at least one soil treatment process according to one of the preceding claims.
12. A device for soil treatment, comprising at least one system (12; 13) of essentially linear coaxial monopolar electrodes, said system of electrodes (12; 13) containing at least one rod (2, 3; 10, 11) containing at least one first polarity zone (3a, 3b, 3c, 3d, 3e; 1 1a, 11b, 11c, 11d, 11e), at least one insulating zone (2a, 2b, 2c, 2d; 10a, 10b, 10c, 10d), and at least one hollow tube (1; 9) coaxial to said rod (2, 3; 10, 11), enclosing at least partially said rod (2, 3; 10, 11) and forming at least partially a second polarity zone (1; 9) capable of sliding at least partially around said rod (2, 3; 10, 11), said electrode system (12; 13) also being capable of being activated.
13. A device according to the preceding claim, in which said electrode system (12) is also capable of being at least partially immersed into the soil (14).
14. A device according to one of Claims 12 or 13, in which the second polarity zone (1) is capable of being disassembled (1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h), at least partially.
15. A device according to one of Claims 12 through 14, containing at least one means for activating the electrode system (12; 13).
16. A device according to one of Claims 12 through 15, in which the electrode system (12; 13) is essentially formed from assembled parts.
17. A device according to one of Claims 12 through 16, in which, when it is cathodic, the zone of first polarity (3a, 3b, 3c, 3d, 3e; 11a, 11b, 11c, 11d, 11e) or second polarity (1; 9) contains stainless steel or non-stainless steel.
18. A device according to one of Claims 12 through 17, in which, when it is anodic, the zone of second polarity (1; 9) or first polarity (3a, 3b, 3c, 3d, 3e; 1 1 a, 11b, 11c, 11d, 11e) contains titanium coated with at least one metal compound, precious or not.
19. A device according to one of the preceding claims, in which said metal compound, precious or not, is chosen among the group formed by ruthenium, iridium, tantalum, tin, and antimony, in at least partially oxidized form or not oxidized and mixtures thereof
20. A device according to one of Claims 12 through 19, in which the hollow tube (1; 9) forming at least partially the second polarity zone (1; 9) contains at least one internal insulating zone covering almost its entire length.
21. A device according to one of Claims 12 through 20, also containing at least one means of mechanical or manual positioning of at least one electrode system (12; 13).
22. A device according to one of Claims 12 through 19, containing a plurality of electrode systems (12; 13), said electrode systems (12; 13) being practically all of identical polarity.
23. A device according to one of Claims 12 through 22, for use in a process according to one of Claims 1 through 9.
24. Use of a device according to one of the Claims 12 to 21 for dehydration of soil and/or depollution of soil.

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