CA2593900A1 - Method and installation for extracting mineral oil - Google Patents

Abstract

The present invention relates to an installation for implementing the extraction process of mineral oils. According to the invention, the installation comprises: - a crushing-grinding unit transforming the mineral material to obtain a sand or a granulate, - a mixer-mixer (3) for mixing and obtaining an intimate contact between the sand and a reversible sorbent (4). ) which is introduced into the mixer-mixer (3) by means of a metering system (5), - a decanting primary separation tank (8) containing water and intended to receive the mixture of sand and reversible sorbent agent (4) from the mixer-mixer (3), - extraction means (13) of the reversible sorbent (4) loaded with mineral oils (19), extending in the upper part of the separation vessel by settling (8), on the surface of water of said tank, - a separating device (17) of the mineral oils (19) of the reversible sorbent agent (4), - a means of evacuation (21) of the purified sand of the mineral oils (19) and resting at the bottom of the tank primary separation by dec antation (8), and - means for rerouting (5a) the reversible sorbent (4) from the separation device (17) to the metering system (5).

Description

METHOD AND SYSTEM FOR EXTRACTING OILS
MINI'RALES.
The present invention relates to the technical field of extraction oils, and more generally mineral oils contained in the sands or oil shale. In the following, we will talk more generally about mineral matter, defining a family including in particular sands and oil shale.
Mining of bituminous sand with extraction processes currently has a significant impact on ecosystems. We can see that the end of the open pit mining period, the vegetative original is not reconstituted. There is a degradation of the natural environment important particularly related to the discharge and the volume of wastewater that should be stored in decantation ponds, as well as a significant emission of gas andFet of greenhouse.
The high consumption of anergy to implement the procade of extraction, significantly increases the operating cost of such deposits sand or oil shale. Moreover, it should be noted that the Current extraction processes can only partially extract mineral oils contained in mineral matter. It results from this current exploitation a significant accumulation of sands and water discharges polluted by mineral oils. The accumulation of such handicaps environmental impacts add to the impact on extraction costs.
The purpose of the present invention is therefore to exploit the deposits of sand or oil shale by increasing the yield of such deposits and significantly decreasing the degradation of the natural environment generated by such exploitation.
The purpose of the present invention is achieved by means of a method mineral oil extraction contained in a mineral material, consisting of (a) take the mineral matter, (b) homogenize where appropriate, particularly in the presence of compacts of the shiste or rock type Ia granulometry of said material mineral to transform it into sand or granulate, (c) mixing the mineral material with a specified amount of an agent reversible sorbent fixing by surface effect the mineral oils contained in the mineral matter, (d) kneading the mixture thus obtained for a determined duration, for obtain a homogeneous diffusion of the reversible sorbent agent in the mineral matter,

2 (e) introducing the mixture obtained according to the preceding step into a tank of primary separation by decantation containing water and shake the contents of the primary separation tank by settling at the beginning of the cycle of decanting, (f) decant the mixture in the primary separation tank by decanting, (g) evacuate from the tank the reversible sorbent agent fixing the mineral oils to the water surface, (h) separating the mineral oils from the reversible sorbent by desorption mechanical, and (i) conditioning said mineral oils for transportation and / or treatment.
The terms "reversible sorbent agent" should be understood as a product for fixing mineral oils by surface effect and the release by mechanical desorption, the reversible sorbent agent then to be reused during a specified number of extraction cycles, By way of example, the reversible sorbent agent is produced from a matters polypropylene plastic of the polypropylene, polyethylene or polystyrene type expanded and crushed in the form of granulate adapted to the needs of the process extraction.
When mineral oils are particularly dense, it is possible also in the context of the extraction process according to the invention, dilutions of dense mineral oils with the aid of a solvent suitable for use, for example acetone or hot mixing water when of the kneading step.
The extraction method according to the invention makes it possible to achieve a yield substantially greater than the yield of known methods.
During the decantation phase, the process according to the invention allows to obtain a tri-phasic equilibrium between a solid phase constituted of sand locates at the bottom of the settling tank, a liquid phase relating to of unpolluted water above the sand, and at the surface of the water, a phase floating materials consisting of reversible sorbent oil lower densities.
Sabie can then be evacuated and reintroduced into a natural environment. The residues of mineral oils which may remain in sand are insignificant and in any case their negligible quantities can not be be assimilated to any nuisance. If the requirements environmental requirements require it, it is quite possible to proceed to a second extraction of residual mineral oils in an installation complementary.

3 In addition, the extraction method according to the invention has the advantage that the reversible sorbent agent is easy to prepare, inexpensive and not pollutant Another advantage resulting from the extraction process according to the invention reside in the implementation of a series of stages and particularly simple on a technical level.
It can thus be noted the absence of toxic products in the implementation of the method according to the invention.
A risk related to a possible leak or mishandling of a toxic product is thus available.
According to the method according to the invention, the land on which will be mineral material operations for the purposes of of mineral oil extraction, are found in an unspecified state a the issue of fa period of land use. No rehabilitation operation will be then necessary. The costs for such rehabilitation, often falling The operator of the land are therefore non-existent and the costs Oil extraction minerals are thus litges.
According to an example of covering, the method according to the invention consists in evacuating water and sand from the primary saparation tank by decantation to a secondary settling tank. During this evacuation, the method according to the invention also consists in collecting and storing The water flowing and drip off during this sand evacuation step in the secondary settling tank.
In the same way, the water drips during the evacuation of the sorbent reversible fixing the mineral oils is recovered and stored in the tank of additional decantation. The water used in the process of extraction then a secondary decantation in order to eliminate the sand residues or of mineral sediments.
The water thus obtained can then be prepared according to an example of implementation of another step of the method according to the invention, reinjectede after the phase decantation in the secondary dewatering tank, in a tank general feeding the primary separation tank by decantation.
The extraction method according to the invention thus makes it possible to use water of extraction process in quasi-steady cycle. Only a periodic upgrade is needed in the general feed tank. The quantity of water consumed for the implementation of the extraction process according to the invention is therefore particularly weak, which constitutes an advantage considerable environmental impact.

4 It is remarkable that such a method makes it possible to reduce or eliminate The use of additional settling ponds to receive and at storing the water of the extraction process not reused.
According to the method according to the invention, the latter consists in recovering The reversible sorbent agent after the separation step of the mineral oils and at store it for further use, reintroducing it into The enclosure mixing. The reversible sorbent agent can thus undergo a determined number of cycles corresponding to sorption / desorption before proceeding to renewal of said reversible sorbent agent.
By way of example, the reversible sorbent agent can be used during an A
several dozens of cycles depending on the characteristics of the oils extracted.
During each of the aforementioned cycles, the method according to the invention does not produces no pollutant or toxic waste. In addition, after the number determines the cycles of use, the reversible sorbent agent may be conditions in the form of fuel. The latter has a calorific value equivalent to that of fuel oil and can therefore be valued directly thermally. We can also predict a gasification whose energy produced can be used in a co-generation system for the purpose of to produce electrical energy, in particular for the extraction process, again, there is no production of polluting or toxic waste that should be treated or stored.
According to an example of implementation of the method according to the invention, the sand from decantation stages is reintroduced into the natural environment without pre-treatment. Such treatment is unnecessary in the measure or sands are clean.
According to an example of implementation in accordance with the invention, the oils minerals are separated from the reversible sorbent by compression or by centrifugation in order to obtain mechanical desorption or by washing with the use of suitable solvents.
The goal assigned to the present invention is also achieved through a extraction plant for mineral oils comprising:
- a crushing-grinding unit transforming the mineral matter to obtain a sand or granulate, a mixer-mixer to obtain an intimate contact between the sand and The reversible sorbent agent, which is introduced into the mixer-mixer thanks to a metering system, - a primary separation tank by decantation containing water and intended to receive the mixture of sand and reversible sorbent from the mixer-mixer, a means for extracting the reversible sorbent agent with oil filler minerals extending in the upper part of the primary decantation, on the surface of the water, distributed on the surface of the water of the tank primary settling,

A device for separating the mineral oils from the sorbent agent reversible, a means of evacuation of the sand 6pure mineral oils and resting at the bottom of the primary separation by decantation, and a means for re-routing the reversible sorbent agent from from the separation device to the metering system.
The installation according to the invention is therefore particularly simple to achieve and can be dimensioned according to the amount of mineral oils that Ion wants to extract and the amount of sands and oil shales that one wish to treat. Each of the components of the installation complies with A
the invention therefore presents a configuration and a simple operation facilitating by the same time the maintenance operations. In addition, the installation complies the invention makes it possible to implement the above-mentioned extraction process in obtaining remarkable results, both economically and economically.
the environmental plan.
According to an exemplary embodiment, the installation according to the invention comprises a drainage system associated with the extraction means, for dehydrate the reversible sorbent agent loaded with mineral oils before its introduction into the separation device. The drainage system allows to convey the harvested water to a secondary settling tank.
Unstallation according to the invention may also comprise a device allowing recover residues of reversible sorbent agent loaded with mineral oils a from the secondary settling tank.
With the installation in accordance with. Invention, after separation, one obtains a reversible sorbent agent, mineral oils not mixed with water of decantation and clean decantation water.
The installation may also include a drainage system associated with the means of evacuation of pure sand, conveying the collected water to the tank of secondary decantation. This gives a sand with a degree of advanced dehydration and intended for reintroduction into the natural environment or at another valuation. Dehydrated sand has a diminishing weight thus reducing the costs of its transport.
The installation according to the invention comprises for example a means of pumping to collect clean water from the secondary settling tank and to transport it to a general rack feeding the separation tank

6 primary by decantation. The water used in the extraction process circulates therefore in an almost firm circuit and the installation according to the invention does not consumes a very small amount of water compared to the facilities extraction known.
The extraction means comprises, for example, an endless auger or an overflow or ratcheting system. Other systems allowing to collect the reversible sorbent filler in mineral oil on the surface of Water from the primary settling tank may also be provided.
The separation device comprises, for example, a compression screw or a centrifuge, a tank for the recovery of mineral oils and a reservoir receiving the reversible sorbent agent gets rid of its oils Mineral.
The means of evacuation of the sand remove mineral oils, of the type conveying screw-drainer, conveys said sand or granulate to a carpet filtering or to a 6-band filter to obtain dehydration additional said sand. The filter mat or band filter is arranged above the secondary settling tank and allows recovery of the water used during Extraction and still contained in the sand. The latter is for example provided in the vicinity of its bottom of a complementary evacuation screw, archimbde screw type, to periodically evacuate sand and sediments deposited in its lower part.
Other features and benefits will also emerge from the detailed description given below, given as an example with reference to the non-restrictive annexed drawings in the esqueis:
FIG. 1 is a schematic representation of an exemplary embodiment an installation according to the invention;
FIG. 2 represents a functional diagram of the extraction process according to the invention, said logigram having steps of said method.
An installation according to the invention is for example represented schematically in Figure 1. The installation comprises a unit of preparation and crushing-grinding (1) receiving the mineral matter and transforming this last, if necessary, in sand or granulate.
A conveying means (2) then makes it possible to transport the sand towards a mixing-blender (3). The unit of preparation and crushing-grinding (1) where the mixer-blender (3) also allows the addition of a solvent fits or warm water when the mineral material is impregnated with oils Minerals are very dense or heavy.The crushing-grinding unit (1) allows to reduce pieces of rock or oil shale for

7 bring back a. The state of sand and the case of diluting the mineral oils heavy with the mixer-mixer (3).
The conveying means (2) advantageously comprises a hopper bituminous sand feed metering device of the mixer-mixer (3). This last is for example the central type ~ concrete and any suitable system continuous mixing, allows to obtain an intimate contact between the sand bituminous and a reversible sorbent (4). The latter is brought into the blender mixer (3) via a metering system (5) of the type additional dosing hopper. Metering disasters are known as that such. The dosing hopper is fed with reversible sorbent agent (4) by a storage tank (4a) and this by any known means, in particular by mechanical or pneumatic conveying, The installation according to the invention also comprises a general reservoir (6) containing water (7) This general reservoir (6) is used to supply water (7) a primary separation tank (8) by decantation. Near the bottom of the primary separation tank (8) is arranged a stirrer (9) driven by a 6lecirical, hydraulic or thermal motor M. We can also improve Ia phase separation via an air injection system A
low pressure in the primary separation tank by decantation (8) for cause a bubbling or bubbling phenomenon. The agitator (9) allows at the beginning of a decantation cycle to accelerate the separation in three phases distinct from the contents of the primary separation tank by decantation (8).
After introducing the mixture from the blender (3) into the the primary separation tank by decantation (8), i1 is established gradually after a certain duration of agitation, a first solid phase (10) and dense at the bottom of the primary separation tank by decantation (8), a second liquid phase (11) in the middle part of the tank and a second solid phase (12) of lower density in the upper part of said vessel.
In the lower part, the solid phase (10) is composed of sand, partly the liquid phase (11) is composed of water (7) and the second phase solid (12) is composed of a reversible sorbent agent (4) fixing the oils Mineral.
The installation also includes means for extracting (13) the agent reversible sorbent (4) loaded with mineral oils and distributed on the surface of the water (11) of the primary separation tank by decantation (8). The way extraction device (13) is for example an endless extraction screw (14).
In order to dehydrate the constituent material of the secone solid phase (12) during its evacuation, the installation includes a drainage system (13a) associates with the extraction means (13). The water collected by this system

8 dewatering (13a) is then conveyed to a decanting tank secondary (16).
The extraction means (13) for example entra7M by an electric motor M, conveys the reversible sorbent agent (4) impregnated with minkal oils into a separation device (17). The separation device (17) is example consisting of a compression system (18). Atitre of variation, the device of separation (17) could also be constituted by a centrifuge or still to be replaced by a washing system by the use of a solvent adapted. The separation device (17) is for example electric motor M which separates the mineral oils (19) running in an oil tank (20), reversible sorbent (4).
The reversible sorbent agent (4) then returns to its initial state and is transports or conveys to the storage tank (4a) by the separation (17) or by any other suitable means. The reversible sorbent agent (4) can again be routed to the dosing hopper.
The installation according to the invention also comprises a means for discharging (21) purified sand into mineral oils (19) and resting in the bottom or bottom of the primary separation tank by decantation (8).
The evacuation means (21) is for example a screw of Archimede (22) driven by an electric motor M and associated with a complementary drainage system (21 a) contributing to the dehydration of the clean sand 6vacue from the primary separation tank by decantation (8).
The water harvested by the complementary drainage system (21 a) is then fed to the secondary settling tank (16).
The sand evacuated by the evacuation means (21) is conveyed on a carpet filter (23) for increasing the degree of dehydration of said sand before the latter arrives in a storage bin (24). The sorbent agent reversible (4) is reachemine or redirects to the dosing hopper (5) by Through a means of re-routing (5a) From the reservoir of storage (4a).
Water from the drip systems (21 a) and (13a) harvested in ha secondary settling tank (16) is then decanted complementary before being evacuated for example by overflow into a adjacent vessel (16a) From which it may be taken from Pump P and routed through a line (25) in the supply tank (6), The secondary settling tank (16) is advantageously provided with in its lower part of an auger (26) of the auger type

9 driven by an electric motor M. The sand brought by the tank of secondary decantation (16) is also conveyed through this way to the tank of storage (24).
The supply reservoir (6) also comprises a controlled valve (27) for making the water supply and a controlled valve (28) sequentially allowing the filling of the separation tank with water by decantation (8) before each extraction cycle. The bottom of reservoir genaral (6) is equipped with a sand evacuation system and residual sediments.
The installation makes it possible to evacuate simultaneously the water and the sand decantation of the primary settling tank (8) as the sorbent reversible (4) was taken from said tank.
With the installation according to the invention, it is therefore possible to recycle a 100% of the reversible sorbent (4) and to reuse in a closed loop the water of the extraction process. Only a booster in water limits from time to time proves necessary. The installation therefore consumes only a very small amount of water during its operation, It is also possible in the context of the present invention to increase the degree of cleanliness of the sand recovered in the storage tank (24), or by reintroducing the latter into the mixer-mixer (3) for a new extraction cycle, either by routing the latter to a installation complementary extraction identical to that previously described, and downstream of the latter. The installation according to the invention allows to obtain a sand whose degree of cleanliness can be adapted to any use in any environment and any environmental standard.
It is also possible to provide a use of the apparatus according to the invention to treat sands from current extraction systems and less performing, delivering sand containing still non mineral oils extracted. The installation according to the invention and the method implemented in said installation thus make it possible to camplate extraction systems known to substantially improve the efficiency of the extraction of a go and to meet environmental constraints on the other hand.
The installation, according to an example, comprises a second mixer-mixer or a system comprising a mixing screw to feed the first mixing-blender (3), so as to operate continuously said installation.
The installation according to the invention therefore makes it possible to implement a process for extracting mineral oils contained in a mineral matter.

The extraction process consists of step a) AL take the matter and add it to the blender (3). This last includes for example rotary arms (3a) driven by an electric motor M.
Step b) then consists of homogenizing the particle size of the material 5 mineral. According to step (c), the mineral material thus prepared is with the sorbent agent r $ versible (4). According to step (d), the mixture is kneaded obtained for a given period in order to obtain a diffusion homogeneity of the reversible sorbent (4) in said mineral matter and a fixing by surface effect of the oils on said reversible sorbent agent (4).

In step e), the mixture thus obtained is introduced into the vessel of separation primer (8) containing water (7). We then leave decant the me [angel in the primary settling separation tank (8).
According to an example of implementation, the beginning of the cycle of decantation at agitation of the contents of the primary separation tank by decantation (8), Then, the method according to the invention consists of evacuating under step g) of the separation tank (8) the reversible sorbent (4) fixing by surface effect the oils minera [es and supernatant on the surface of the water under low density solid phase form (12). We then separate under the step h) the mineral oils (19) and the reversible sorbent (4) by a surgery mechanical desorption. Mineral oils (19) are then collected in a tank (20) and can be conditioned under step i) for transport and / or treatment, The method according to the invention also comprises under step I) evacuate a portion of the water from the primary settling tank (8) to the secondary settling tank (16). The process consists also [step (1)) to evacuate the sands constituting the solid phase (10) in the lower part of the separation tank (8). The water drips during of The previous step is retrieved and stored in the settling tank secondary (16) under step k,). The water drips during the stage of separation (g) is also recovered and stored in the secondary settling tank (16) under step k2). Steps 11) and 12) are advantageously work simultaneously. The water is thus evacuated with the decanted sand.
The extraction process according to the invention under step k) consists Then, according to a determined frequency, to reinject the water of the tank of secondary decantation (16) or a part of this water after a phase of decantation in the general tank (6) feeding the separation tank primary decantation (8). The water used in the process according to the invention thus constitutes a media circulating in closed circuit.

11 According to the extraction procedure, the sorbent is recovered under stage (j) reversible (4) after step h) of separation so as to store it in the storage tank (4a) for a new use. Step j,) precedence is repeated in the method according to the invention for a number of of cycles determined before proceeding with the renewal of the sorbent reversible (4). The extraction plant therefore operates continuously from a continuous supply of mineral matter.
The number of cycles can vary between one and several tens. The process according to the invention can be implemented sequentially or continuously. A
sequence, for example, corresponds to one or more cycles of use of The reversible sorbent agent (4).
The extraction process therefore delivers as final products on the one hand mineral oils (19) and on the other hand a sand whose degree of cleanliness can be adapted for reintroduction in a natural environment without treatment prior. The sand from the extraction is therefore reintroduced to the middle natural according to the process.
According to the method, an alveolar plastic material is used as an agent.
reversible sorbent (4). According to step h) of separation of the process extraction, the mineral oils (19) are separated from the reversible sorbent (4) by example by compression or centrifugation.
After a determined number of cycles, the reversible sorbent agent (4) reused is conditioned as a solid or gasified fuel. The The extraction process according to the invention thus produces a final material.
complementary, which can be thermally enhanced from faron interessanfie, such as cogeneration.

Claims (21)

1. Process for extracting mineral oils (19) contained in a material mineral, characterized in that it consists of:
(a) take the mineral matter, (b) homogenize if appropriate, especially in the presence of compact of the shale or rock type, the particle size of said material mineral to transform it into sand or granulate, (c) mixing the mineral material with a predetermined amount of an agent reversible sorbent (4) fixing by surface effect the mineral oils (19) contained in the mineral matter, (d) kneading the mixture thus obtained for a determined period of time, for obtain a homogeneous diffusion of the reversible sorbent agent (4) in the mineral matter, (e) introducing the mixture obtained according to the preceding step into a tank of primary separation by settling (8) containing water and shaking the content of the primary separation tank by decantafion (8) at the beginning of the decantation cycle, (f) decant the mixture in the primary separation tank by settling (8), (g) evacuate the primary separation tank by decantation (8) reversible sorbent (4) fixing the mineral oils (19) and floating at the surface of the water, (h) separating the mineral oils (19) from the reversible sorbent (4) by mechanical desorption, and (i) conditioning the extracted mineral oils (19) for transport and / or a treatment. 2. Extraction process according to claim 1, characterized in that consists of:
(11) evacuate part of the water from the primary separation tank by settling (8) to a secondary settling tank (16). 3. Extraction process according to claim 2, characterized in that consists of:
(12) evacuate the sands from the primary separation tank by settling (8) simultaneously at step (11). 4. Extraction process according to claim 2 or 3, characterized in that consists of;
(k1) recovering and storing the water dripping and flowing during step (I1) or (I2) in the secondary settling tank (16). 5. Extraction process according to any one of claims 2 to 4, characterized in that it consists of:
(k2) recovering and storing the water dripping during step (g) in the tank secondary settling (16). 6. Extraction process according to any one of claims 2 to 5, characterized in that it consists of:
(k) reinjecting the water from the secondary settling tank (16) after a decantation phase, in a general tank (6), feeding the tank of primary separation by settling (8). 7. Extraction process according to any one of claims 1 to 5, characterized in that it consists of:
(j1) recovering the reversible sorbent agent (4) after step (h) and at store for further use under (c) during another extraction cycle. 8. Extraction process according to claim 7, characterized in that consists of repeat step (j1) during a specified number of extraction cycles, before of proceed with the renewal of the reversible sorbent (4). 9. Extraction process according to claim 8, characterized in that consists of:
(j2) conditioning the reversible sorbent (4) after the last cycle extraction, in the form of fuel. 10. Extraction process according to claim 3, characterized in that consists of reintroduce the sand from extraction to the natural environment. 11. Extraction method according to any one of claims 1 to 10, characterized in that it consists of (h) separating the mineral oils (19) of The reversible sorbent (4) by compression, washing or centrifugation. 12. Extraction process according to any one of claims 1 to 11, characterized in that it operates continuously, from a power supply continuous mineral matter. 13. Extraction process according to any one of claims 1 to 11, characterized in that it consists in using a reversible sorbent agent (4) to based of cellular plastics. 14.Installation to implement the oil extraction process mineral (19) according to any one of claims 1 to 12, characterized in that that it comprises:
- a crushing-grinding unit transforming the mineral matter to obtain a sand or a granulate, - a mixer-mixer (3) for mixing and obtaining an intimate contact between the sand and a reversible sorbent (4) which is introduced in the mixer-mixer (3) by means of a metering system (5), - a primary separation tank by decantation (8) containing water and intended to receive the mixture of sand and sorbent reversible (4) from the mixer-mixer (3), extraction means (13) for the reversible sorbent agent (4) loaded of mineral oils (19), extending in the upper part of the tank of primary separation by settling (8) at the water surface of said tank, a device (17) for separating the mineral oils (19) from the agent reversible sorbent (4), - means for evacuation (21) of the purified sand of the mineral oils (19) and resting at the bottom of the primary separation tank by settling (8), and means for re-routing (5a) the reversible sorbent agent (4) from the separating device (17) to the dosing system (5). 15.Installation according to claim 14, characterized in that it comprises a dewatering system (13a) associated with the extraction means (13) for dehydrate the reversible sorbent agent (4) loaded before its introduction into the separation device (17), said dewatering system (13a) conveying the water collected to a secondary settling tank (16). 16. Installation according to claim 14 or 15, characterized in that includes a dewatering system (21a) associated with the means for discharging (21) the sand unloaded and conveying the water thus harvested to one or the tank of secondary settling (16). 17. Installation according to any one of claims 14 to 16, characterized in what it comprises a pumping means (P) for taking water from the secondary settling tank (16) and route it to a general tank (6) feeding the primary separation tank by decantation (8). 18. The installation according to any one of claims 14 to 17, characterized in the extraction means (13) comprises a skimming auger (14) or an overflow or scraping system. 19. Installation according to any one of claims 14 to 18, characterized in the separation device (17) comprises a compression screw (18) or a centrifuge, a collection tank (20) of mineral oils (19) and a storage tank (4a) receiving the reversible sorbent (4) desorbed. 20. Installation according to any one of claims 14 to 19, characterized in what the means for discharging (21) sand freed of mineral oils (19), of the dripping conveyor screw type, conveys said sand or granulate to a filter mat (23) or to a band filter, to increase the degree of dehydration of said sand and recovering the water used during extraction and still contained in the sand, said filter mat (23) or said filter band being disposed above the secondary settling tank (16). 21. Installation according to any one of claims 14 to 20, characterized in what it comprises a second mixer-mixer (3) or a system having a mixing screw for feeding the first mixer mixer (3), so as to operate continuously said installation.