EP1598114B1 - Method of separating silica and olivine from a mixture containing these substances and device for carrying out said method - Google Patents

Abstract

Process for separating silica (I) and olivine (II) from a mixture comprises at least one magnetic separation step and at least one heat-treatment step to produce a mixture (9) regenerated in (I) and a mixture (11) regenerated in (II). An independent claim is also included for a device for the process comprising magnetic separators and a heat-treatment enclosure.

Description

The present invention relates to a process for separating silica and olivine in a mixture containing it.

The present invention also relates to a device for implementing this method.

More particularly, the invention relates to a process for recycling a mixture containing silica and olivine from the manufacture of metal parts by molding.

In such manufacture of metal parts, particles or a mixture of particles, often mixed with hardeners such as resins, are used to form the temporary rigid structure serving as a mold and intended to receive the molten metal.

When the metal is cooled and hardened, the resulting part is extracted from the mold by a shake operation of separating the particles from the metal part obtained.

Among the particles usually used, silica has many advantages. Indeed, this type of sand has an abundance of large deposits, its extraction is easy, its refractoriness is sufficient since its melting temperature is close to 1700 ° C and its cost is low.

Nevertheless, silica can react chemically and / or thermally with certain metals at the interface with the metal used which limits its use.

For example, during the manufacture of manganese steel parts, the contact between the silica and this type of steel is prohibited because of the formation of a eutectic with a low melting point resulting in watering and / or vitrification.

The use of other types of particles in contact with the steel is then necessary.

For this purpose, it is well known that chromite and olivine can be used as sand in contact with steel, said contact sand, the sand to fill the rest of the mold, said sand fill, which can be constituted of silica.

For the manufacture of this type of metal parts, the use of olivine as contact sand has certain advantages since its cost is lower than that of chromite, olivine does not have any constraints on the rejects contrary to chromite which can lead to the formation of Cr ^VI , and the fineness of the grain of olivine makes it possible to manufacture parts with properties of improved surfaces.

When using a mixture of olivine, as contact sand, and of silica, as filling sand, the shaking operation leads to obtaining a mixture of silica and olivine which can not be used as such for be reused in contact sand.

The document WO 02/48036 discloses a chemical and thermal process for the separation of silica / magnesium and olivine.

Unlike chromite, for which a separation process with silica is known by a simple magnetic sorting operation, no magnetic separation process of silica and olivine to obtain at least recyclable olivine has been , to date, brought to the attention of the applicant.

The main subject of the invention is therefore a process for separating olivine and silica in a mixture containing them for the purpose of recycling them.

1. (a) une étape de tri magnétique 2,8; et
2. (b) une étape de traitement thermique 6,

desquelles il résulte notamment un mélange régénéré en olivine 9 et un mélange régénéré en silice 11.For this purpose, the method of the invention mainly comprises the following steps:

1. (a) a magnetic sorting step 2,8; and
2. (b) a heat treatment step 6,

from which results in particular a regenerated mixture of olivine 9 and a regenerated mixture silica 11.

1. (a) une première étape de tri magnétique 2 dudit mélange 1 de laquelle il résulte notamment un premier mélange rééquilibré en olivine et en silice 4 et un mélange enrichi en silice 3;
2. (b) une étape de traitement thermique 6 du premier mélange régénéré en olivine 4 issu de l'étape (a) ; et
3. (c) une deuxième étape de tri magnétique 8 du mélange 7 issu de l'étape (b) de laquelle il résulte notamment un mélange régénéré en olivine 9 et un mélange régénéré en silice 11.

Advantageously, the method of the invention comprises the following steps:

1. (a) a first step of magnetic sorting 2 of said mixture 1 which results in particular a first equilibrium mixture of olivine and silica 4 and a mixture enriched in silica 3;
2. (b) a heat treatment step 6 of the first regenerated olivine mixture 4 from step (a); and
3. (c) a second step of magnetic sorting 8 of the mixture 7 resulting from step (b), which results in particular from a regenerated mixture of olivine 9 and a regenerated mixture of silica 11.

1. (a)la première étape de tri magnétique 2;
2. (b)l'étape de traitement thermique 6 du mélange rééquilibré en olivine et en silice 4 obtenu à l'étape (a) ; et
3. (c)la deuxième étape de tri magnétique 8 du mélange 7 obtenu à l'étape (b).

Preferably, the method comprises, in the order, the following steps:

1. (a) the first magnetic sorting step 2;
2. (b) the heat treatment step 6 of the equilibrium mixture of olivine and silica 4 obtained in step (a); and
3. (c) the second magnetic sorting step 8 of the mixture 7 obtained in step (b).

According to the invention, the mixture containing silica and olivine 1 can be obtained from the shake-out operation carried out during the manufacture of metal parts by molding and contains between 5 and 40% of olivine, silica and highly magnetic particles such as iron oxide particles.

• (a1) une première étape de séparation magnétique 14 pour isoler des particules fortement magnétiques 5 du mélange contenant de l'olivine et de la silice 1; et
• (a2) une seconde étape de séparation magnétique 15 du mélange appauvri en particules fortement magnétiques 19 obtenu à l'étape (a1) pour éliminer les particules fortement magnétiques résiduelles 5 et obtenir :
  • le mélange enrichi en silice 3, et
  • le mélange rééquilibré en silice et en olivine 4.

Preferably, the first magnetic sorting step 2 of the process of the invention comprises at least the following steps:

• (a1) a first magnetic separation step 14 for isolating highly magnetic particles from the mixture containing olivine and silica 1; and
• (a2) a second step of magnetic separation 15 of the highly magnetic particulate depleted mixture 19 obtained at step (a1) for removing residual strong magnetic particles and obtaining:
  • the mixture enriched with silica 3, and
  • the rebalanced mixture of silica and olivine 4.

According to the invention, the mixture enriched with silica 3 can be used as filling sand.

Also according to the invention, the equilibrium mixture of olivine and silica 4 contains approximately 50% silica and 50% olivine.

Preferably, the heat treatment step 6 of the process of the invention consists in subjecting the rebalanced mixture to olivine and silica 4 at a temperature above 400 ° C.

Advantageously, the heat treatment step 6 comprises treating the rebalanced mixture of olivine and silica 4 in a fluidized bed furnace at a temperature of approximately 650 ° C.

It is also advantageous if the equilibrium mixture of olivine and silica 4 is cooled to a temperature of less than 50 ° C.

1. (c1) une première étape de séparation magnétique 34 pour séparer les particules fortement magnétiques 12 du mélange 7 issu de l'étape de traitement thermique 6; et
2. (c2) une deuxième étape de séparation magnétique 35 du mélange appauvri en particules fortement magnétiques 39 obtenu à l'étape (c1) pour éliminer les particules fortement magnétiques résiduelles 12 et obtenir :
   • le mélange régénéré en silice 11,
   • le mélange régénéré en olivine 9, et
   • le mélange d'olivine et de silice 10.

According to the invention, the second magnetic sorting step 8 advantageously comprises at least the following steps:

1. (c1) a first magnetic separation step 34 for separating the strongly magnetic particles 12 from the mixture 7 resulting from the heat treatment step 6; and
2. (c2) a second step of magnetic separation of the strongly magnetic particulate depleted mixture obtained in step (c1) to remove the residual strongly magnetic particles 12 and obtain:
   • the regenerated mixture of silica 11,
   • the regenerated mixture of olivine 9, and
   • the mixture of olivine and silica 10.

Advantageously, the regenerated mixture of silica 11 may be used as anchoring sand and the regenerated mixture of olivine 9 contains more than 90% olivine and may be used as contact sand.

According to the invention, the mixture of silica and olivine obtained in step (c2) can again undergo the second magnetic sorting step 8.

• une machine de tri magnétique 13, 33, et
• une enceinte de traitement thermique 25.

The invention also relates to a device for separating silica from olivine in a mixture 1 containing thereof which comprises at least:

• a magnetic sorting machine 13, 33, and
• a heat treatment chamber 25.

• une première machine de tri magnétique 13,
• une enceinte de traitement thermique 26, et
• une deuxième machine de tri magnétique 33.

Preferably, the device of the invention comprises at least:

• a first magnetic sorting machine 13,
• a heat treatment chamber 26, and
• a second magnetic sorting machine 33.

Advantageously, the first magnetic sorting machine 13, the heat treatment chamber 25 and the second sorting machine 33 are arranged in this order and in series.

In addition, the first magnetic sorting machine 13 may comprise a first magnetic separator 16 set to separate the highly magnetic particles 12 from the mixture containing olivine and silica 1 and a second magnetic separator 21 to separate, from the mixture depleted in strongly magnetic particles 12, the residual strongly magnetic particles 12 and obtain a mixture enriched in silica 3 and a rebalanced mixture of olivine and silica 4.

Preferably, the first 16 and second 21 magnetic separators are constituted by first 16 and second 21 rotating magnetized metal drums on which the mixture to be separated 1, 19 circulates at an appropriate speed and by one or more shutters. adjustable inclination 20, 23, 24 disposed downstream of the drums 16,21 so as to separate the different jets of sand projected by the drums 16,21 and respectively corresponding to the strongly magnetic particles 5, to the mixture enriched in silica 3 and to the rebalanced mixture of olivine and silica 4.

More specifically, a flap 20 may be disposed downstream of the first magnetic drum 16 so as to separate the mixture containing olivine and silica 1 from the strongly magnetic particles 5.

As regards the second drum 21, two flaps may be arranged downstream of the second drum 21 so as to selectively separate from the mixture that is depleted in strongly magnetic particles 19, the residual high magnetic particles 5, the mixture enriched with silica 3, and the rebalanced mixture of olivine and silica 4.

Advantageously, the heat treatment chamber 25 is constituted by a fluidized bed furnace in which the equilibrium mixture of olivine and silica 4 progresses in the furnace by fluidization at a temperature of about 650 ° C.

Preferably, a cooler 32 is disposed downstream of the furnace and makes it possible to bring the equilibrium mixture back to olivine and silica 4 at a temperature below 50 ° C.

According to the invention, the second magnetic sorting machine 33 may comprise a first magnetic separator 36 set to separate the highly magnetic particles 12 from the mixture resulting from the heat treatment 7 and a second magnetic separator 41 set to separate, from this particulate-depleted mixture. strongly magnetic 39, the residual strongly magnetic particles 12, the regenerated mixture of silica 11, the regenerated mixture of olivine 9 and a mixture of olivine and silica 10.

Preferably, the first and second magnetic separators 36, 41 are constituted by first 36 and second 41 rotating magnetized metal drums on which the mixture to be separated 7,39 circulates at an appropriate speed and by one or more adjustable tilt flaps. 40, 43, 44, 45 arranged downstream of the drums 36, 41 so as to separate the different jets of sand thrown by the drums 36, 41 and respectively corresponding to the highly magnetic particles 12, to the regenerated mixture of silica 11, to the regenerated mixture olivine 9 and the mixture of olivine and silica 10.

With regard to the first drum 36, a flap 40 may be disposed downstream of this first magnetic drum 36 by being adjusted so as to separate, from the mixture resulting from the heat treatment 7 circulating on the first drum, the strongly magnetic particles 12.

With regard to the second drum 41, three flaps 43, 44, 45 may be arranged downstream of this second drum 41 by being adjusted so as to selectively separate the depleted mixture of highly magnetic particles 39 flowing on the second drum 41, the strongly magnetic residual particles 12, the regenerated mixture of silica 11, the regenerated mixture of olivine 9 and the mixture of olivine and silica 10.

In addition, the device of the invention may comprise means for the mixture of olivine and silica to be introduced again into the second magnetic sorting machine 33.

• la figure 1 est un organigramme illustrant les principales étapes du procédé de l'invention,
• la figure 2 représente schématiquement les principaux constituants de la première machine de tri,
• la figure 3 représente schématiquement le four à lit fluidisé utilisé pour le traitement thermique, et
• la figure 4 représente schématiquement les principaux constituants de la deuxième machine de tri.

The invention will be better understood and other objects, advantages and characteristics thereof will appear more clearly on reading the description which follows and which is made with reference to the accompanying drawings which show non-limiting examples of embodiment of the method and of the device of the invention and in which:

• the figure 1 is a flowchart illustrating the main steps of the process of the invention,
• the figure 2 schematically represents the main constituents of the first sorting machine,
• the figure 3 schematically represents the fluidized bed furnace used for heat treatment, and
• the figure 4 schematically represents the main constituents of the second sorting machine.

After the shakeout operation performed at a temperature below 200 ° C, the sand, consisting of a mixture of about 85% silica, 15% olivine and iron oxide particles and metal particles from casting in small quantities, is screened and screened to remove scrap or pieces of sintered sand.

After dedusting and cooling, the sand is sent by pneumatic transport to a buffer silo.

With reference to the figure 1 the sand from the shake-off operation 1 undergoes a first magnetic sorting step 2 at the end of which is separated a regenerated enriched silica mixture 3 containing about 85% of silica which is used as filling sand for the production of a metal part, a rebalanced mixture of olivine and silica 4 containing about 50% olivine and 50% of silica to undergo the subsequent heat treatment step and strongly magnetic particles which are removed from the circuit.

In quantitative terms, the silica-enriched mixture represents about 60% rebalanced of the mass of sand 1, the regenerated mixture of olivine and silica represents about 30% of the mass of sand 1 and the strongly magnetic particles about 10%.

The rebalanced olivine and silica mixture 4 then undergoes a heat treatment step 6 at a temperature of about 650 ° C followed by cooling to a temperature below 50 ° C.

This heat treatment step 6 notably makes it possible to obtain a physical dissociation of the grains silica and olivine which may be agglomerated by the presence of the chemical components used in the molding operation such as resins for example.

The rebalanced olivine and silica mixture 7 obtained at the end of the heat treatment step 6 then undergoes a second magnetic sorting step 8 at the end of which a regenerated silica 11 mixture containing more than 70% is separated. of silica which is directed to a storage silo for reuse as anchor sand, a regenerated mixture of olivine 9 containing more than 90% olivine and which can be reused as contact sand in the manufacture of a new metal part, strongly magnetic particles 12 which are removed from the circuit and a mixture of olivine and silica 10 which again undergoes the second magnetic sorting step 8.

In quantitative terms, the regenerated mixture of silica represents about 10% by weight of the mass of sand 1, the regenerated mixture of olivine represents about 15% by weight of the mass of sand 1, the strongly magnetic particles about 0.5% and the mixture of olivine and silica about 8.5%.

With reference to the figure 2 the shaking sand 1 undergoes, during the first magnetic sorting step 2 carried out by the first magnetic sorting machine 13, a first magnetic separation step 14 followed by a second magnetic separation step 15.

The first magnetic separation step 14 consists of recovering part of the highly magnetic particles such as iron oxide particles and cast metal particles in the shake sand 1 in order to facilitate the second magnetic separation step. 15.

For this, a first magnetic separation machine 16 is constituted by a first rotating drum 16 comprising a metal casing to inside which are permanent magnets in rare earths.

The shaking sand 1 is brought to the first rotating drum 16 by a vibrating mat 17 surmounted by a height-adjustable squeegee 18 for homogeneously distributing the sand on the carpet 17.

The sand 1 is then driven by the drum 16 and the various components of the sand 1 are, under the combined influence of their respective magnetic properties, centrifugal force from the drum 16 in rotation and the effect of gravity, projected downstream of the drum in the form of sand jets at different inclinations.

In the present case, the strongly magnetic particles which remain in contact with the magnetized drum 16 and a mixture of poorly magnetic particles 19 are recovered with an adjustable tilting flap 20 separating the two sand jets.

The inclination of the flap 20 is adjusted so as to recover a maximum of highly magnetic particles.

According to the same principle, the mixture depleted of strongly magnetic particles 19 is brought to a second rotating drum 21 by a vibrating belt 22.

Two adjustable inclination flaps 23 and 24 are arranged downstream of the second rotating drum so as to recover the residual strongly magnetic particles 5, a mixture enriched in silica containing about 85% of silica and a first equilibrium mixture of olivine and silica 4 containing about 50% silica and 50% olivine.

The presence of the first drum 16 is preferable to prevent fouling of the second drum 21 and thus obtain optimum separation at the second drum 21.

With reference to the figure 3 the equilibrium mixture of olivine and silica 4 is directed to the enclosure of heat treatment consisting of a fluidized bed furnace well known to those skilled in the art.

The fluidized bed furnace mainly comprises a metal enclosure thermally insulated by a refractory lining 26, fluidization boxes 27, burner manifolds consisting of perforated tubes equipped with injectors 28 and pilot burners 29 intended to ignite the air-gas mixture. used in the ramps and the standby of the installation.

The flue gases from the combustion are directed into an afterburner chamber 30 in which a gas burner will bring them to a temperature of about 800 ° C to destroy the toxic compounds.

These fumes are then directed to a bag dust collector, not shown, via an energy recuperator for recovering the heat energy which is then used to heat the fluidizing air.

The equilibrium mixture olivine and silica 4 is introduced into the furnace via a vibrating tube 30a for dosing the flow of the injected mixture.

This mixture 4 is then suspended and stirred by the fluidization chambers 27. The burner ramps then ensure the combustion of resins coating the sand grains contained in the mixture 4 suspended in the oven at a temperature of about 650 ° vs.

The sand progresses in the oven during a treatment time that the skilled person can determine and which is preferably between 10 minutes and two hours and then the sand is discharged to a cooler 32 by overflow.

The cooler 32 consists of two boxes, not shown, comprising a tubular heat exchanger shown fed with water itself cooled in a cooling tower.

The cooler 32 also comprises a not shown fluidized bed which ensures the mixing of the sand in the cooling boxes.

At the outlet of the cooler, the maximum temperature of the rebalanced mixture of olivine and silica 7 is about 40 ° C and this mixture 7 is discharged by overflow.

With reference to the figure 4 the equilibrium mixture of olivine and silica 7 resulting from the heat treatment operation 6 undergoes the second magnetic sorting step 8 carried out by a second magnetic sorting machine 33.

Similar to the first magnetic sorting step 2 and the first magnetic sorting machine 13, the mixture 4 undergoes a first magnetic separation step 34 followed by a second magnetic separation step 35.

The first magnetic separation step 34 consists in recovering the strongly magnetic particles 12 in order to facilitate the second magnetic separation step 35.

For this, a first magnetic separation machine 36 is constituted by a first rotating drum having a metal envelope inside which are arranged permanent magnets in rare earths.

The equilibrium mixture of olivine and silica 7 is brought to the first rotating drum 36 by a vibrating mat 37 surmounted by a height-adjustable squeegee 38 for homogeneously distributing the sand on the carpet 37.

The mixture 7 is driven by the drum 36 and an adjustable tilting flap 40 disposed downstream of the drum 36 makes it possible to recover the particles strongly. magnetic 12 and a mixture depleted of highly metallic particles 39.

This mixture 39 is fed to a second rotating power drum 41 by a vibrating belt 42.

Three adjustable tilt flaps 43, 44 and 45 are arranged downstream of the second rotating drum 41 so as to recover the residual strongly magnetic particles 12, the regenerated silica mixture 11 containing more than 70% of silica and which can be used as bonding sand, the mixture of silica and olivine 10 to undergo again the second magnetic sorting step 33 and the regenerated mixture of olivine 9 containing more than 90% olivine.

This regenerated mixture olivine 9 can then be used as contact sand to make a metal part requiring sand as contact sand other than silica.

In the second sorting machine 33, the power of the magnets of the two drums 36, 41 is preferably greater than that of the magnets arranged in these two drums 16, 21 of the first sorting machine 13.

The separation process of the invention can particularly be applied to the manufacture of large parts of cast steel such as the hearts of channels made most often in a steel with 13% manganese.

The present invention is not limited to the embodiments described above and in particular, those skilled in the art can implement any magnetic separation machine for performing the first 2 and second 8 stages of magnetic sorting and any processing device thermal allowing to bring to a temperature above 400 ° C the equilibrium mixture of olivine and silica 4 from the first step of magnetic sorting 2.

Claims (28)

1. A method for separating silica and olivine in a mixture containing same (1), said method including at least the following steps:

   a. a magnetic sorting step (2, 8);

   b. a heat treatment step (6),

   from which notably results an olivine-regenerated mixture and a silica-regenerated mixture (11).
2. The method according to claim 1, including at least the following steps:

   a. a first step (2) for magnetically sorting said mixture (1) from which notably results a mixture rebalanced in olivine and in silica (4) and a mixture enriched in silica (3);

   b. a step for heat treatment (6) of the mixture rebalanced in olivine and in silica (4) stemming from step (a); and

   c. a second step (8) for magnetically sorting the mixture (7) stemming from step (b) from which notably results an olivine-regenerated mixture (9) and a silica-regenerated mixture (11).
3. The method according to any of the preceding claims, including at least the following steps in this order:

   a. the first magnetic sorting step (2);

   b. the heat treatment step (6) for the first mixture rebalanced in olivine and silica (4) obtained in step (a); and

   c. the second step (8) for magnetically sorting the mixture (7) obtained in step (b).
4. The method according to any of the preceding claims, wherein the mixture containing silica and olivine (1) stems from the knock-out operation carried out during the making of metal parts by casting and contains between 5 and 40% of olivine, silica and strongly magnetic particles such as iron oxide particles.
5. The method according to any of the preceding claims, wherein the first magnetic sorting step (2) includes at least the following steps:

   (a1) a first magnetic separation step (14) for isolating strongly magnetic particles (5) from the mixture containing olivine and silica (1); and

   (a2) a second step (15) for magnetically sorting the mixture depleted in strongly magnetic particles (19) obtained in step (a1) in order to remove the residual strongly magnetic particles (5) and to obtain:

   - the mixture enriched in silica (3), and

   - the mixture rebalanced in olivine and in silica (4).
6. The method according to any of the preceding claims, wherein the mixture enriched in silica (3) is recycled and used as filling sand.
7. The method according to any of claims 4 to 6, wherein the mixture rebalanced in olivine and silica (4) contains approximately 50% of silica and 50% of olivine.
8. The method according to any of the preceding claims, wherein the heat treatment step (6) consists of submitting the mixture rebalanced in olivine and in silica (4) to a temperature above 400°C.
9. The method according to any of the preceding claims, wherein the heat treatment step (6) consists of treating the mixture rebalanced in olivine and in silica (4) in a fluidized bed oven (25) at a temperature of approximately 650°C.
10. The method according to claim 9, wherein the mixture rebalanced in olivine and silica (4) is cooled to a temperature below 50°C.
11. The method according to any of the preceding claims, wherein the second magnetic sorting step (8) includes at least the following steps:

    (c1) a first magnetic separation step (34) for separating the strongly magnetic particles (12) from the mixture (7) stemming from the heat treatment step (6); and

    (c2) a second step (35) for magnetically sorting the mixture depleted in strongly magnetic particles (39) obtained in step (c1) in order to remove the residual strongly magnetic particles (12) and to obtain:

    - the silica-regenerated mixture (11),

    - the olivine-regenerated mixture (9), and

    - the mixture of olivine and silica (10).
12. The method according to claim 11, wherein the silica-regenerated mixture (11) may be used as a bonding sand.
13. The method according to any of the preceding claims, characterized in that the olivine-regenerated mixture (9) contains more than 90% of olivine and may be used as a contact sand.
14. The method according to any of claims 12 and 13, wherein the mixture of silica and olivine (10) obtained in step (c2) again undergoes the second magnetic sorting step (8).
15. A device for separating silica from olivine in a mixture (1) containing same, comprising at least:

    - one magnetic sorting machine (13, 33), and

    - one heat treatment enclosure (25).
16. The device according to claim 15, comprising at least:

    - a first magnetic sorting machine (13),

    - one heat treatment enclosure (26), and

    - a second magnetic sorting machine (33).
17. The device according to claim 16, wherein the first magnetic sorting machine (13), the heat treatment enclosure (25) and the second sorting machine (33) are positioned in this order and in series.
18. The device according to any of claims 16 and 17, wherein the first magnetic sorting machine (13) includes a first magnetic separator (16) adjusted for separating strongly magnetic particles (12) from the mixture containing olivine and silica (1) and a second magnetic separator (21) for separating the residual strongly magnetic particles (12) from the mixture depleted in strongly magnetic particles (12), and obtaining a mixture enriched in silica (3) and a mixture rebalanced in olivine and silica (4).
19. The device according to claim 18, wherein the first (16) and second (21) magnetic separators are formed by rotating first (16) and second (21) magnetized metal drums over which the mixture to be separated (1, 19) circulates at a suitable speed and by one or more flaps with adjustable tilt (20, 23, 24) positioned downstream from the drums (16, 21) so as to separate the different sand jets projected by the drums (16, 21) and corresponding to the strongly magnetic particles (5), to the mixture enriched in silica (3) and to the mixture rebalanced in olivine and silica (4), respectively.
20. The device according to claim 19, wherein a flap (20) is positioned downstream from the first magnetic drum (16) and is positioned so as to separate the strongly magnetic particles (5) from the mixture containing olivine and silica (1).
21. The device according to any of claims 19 and 20, wherein two flaps are positioned downstream from the second drum (21) and are positioned so as to selectively separate the residual strongly magnetic particles (5), the mixture enriched in silica (3), and the mixture rebalanced in olivine and silica (4), from the mixture depleted in strongly magnetic particles (19).
22. The device according to any of claims 15 to 21, wherein the heat treatment enclosure (25) is formed by a fluidized bed oven in which the mixture rebalanced in olivine and silica (4) advances in the oven by fluidization at a temperature of about 650°C.
23. The device according to claim 22, comprising a cooler (32) positioned downstream from the oven allowing the mixture rebalanced in olivine and silica (4) to be set to a temperature below 50°C.
24. The device according to any of claims 16 to 23, wherein the second magnetic sorting machine (33) includes a first magnetic separator (36) adjusted for separating the strongly magnetic particles (12) from the mixture stemming from the heat treatment (7) and a second magnetic separator (41) adjusted for separating the residual strongly magnetic particles (12), the silica-regenerated mixture (11), the olivine-ragenerated mixture (9) and a mixture of olivine and silica (10), from this mixture depleted in strongly magnetic particles (39).
25. The device according to any of claims 18 to 24, wherein the first and second magnetic separators (36, 41) are formed by rotating first (36) and second (41) magnetized metal drums over which the mixture to be separated (7, 39) circulates at a suitable speed and by one or more flaps with adjustable tilt (40, 43, 44, 45) positioned downstream from the drums (36, 41) so as to separate the different sand jets projected by the drums (36, 41) and corresponding to the strongly magnetic particles (12), to the silica-regenerated mixture (11), to the olivine-regenerated mixture (9) and to the mixture of olivine and silica (10), respectively.
26. The device according to claim 25, wherein a flap (40) is positioned downstream from the first magnetic drum (36) and is adjusted so as to separate the strongly magnetic particles (12) from the mixture stemming from the heat treatment (7) circulating over the first drum.
27. The device according to any of claims 25 and 26, wherein three flaps (43, 44, 45) are positioned downstream from the second drum (41) and are adjusted so as to selectively separate the residual strongly magnetic particles (12), the silica-regenerated mixture (11), the olivine-regenerated mixture (9) and the mixture of olivine and silica (10), from the mixture depleted in strongly magnetic particles (39) circulating over the second drum (41) .
28. The device according to any of claims 24 to 27, including means in order that the mixture of olivine and silica (10) is again introduced into the second magnetic sorting machine (33).

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