SYSTEM FOR SINK-FLOAT SEPARATION OF SOLID PARTICLES

Abstract: The present invention relates to a system for separating solid particles in two fractions by means of a medium, the specific gravity of said medium situating in between the specific gravity of the particles of the first fraction and the specific gravity of the particles of the second fraction. The preferred system comprises: (a) a scrolled barrel (1) consisting of a central midsection in which the separation takes place; (b) a means (9) associated with said barrel (1) for driving it rotatively along its longitudinal center line; (c) means (5) for feeding or injecting into the barrel both the solid particles to be separated as well as the medium effecting this separation; (d) a means (6) for removing the sink fraction from said central mid-section; (e) a means (8) for removing the float fraction from the central mid-section, and (f) a means (28, 30) to prevent the float particles from crossing over into the sinks and thus reporting with the sink particles. The invention relates to a process for media separation.

Description: System for sink-float separation of solid particles. Abstract of Disclosure The present invention relates to a system for separating solid particles in two fractions by means of a medium, the specific gravity of said medium situating in between the specific gravity of the particles of the first fraction and the specific gravity of the particles of the second fraction. The preferred system comprises : (a) a scrolled barrel consisting of a central mid- section in which the separation takes place; (b) a means associated with said barrel for driving it rotatively along its longitudinal center line; (c) means for feeding or injecting into the barrel both the solid particles to be separated as well as the medium effecting this separation; (d) a means for removing the sink fraction from said central mid-section; (e) a means for removing the float fraction from the central mid-section, and (f) a means to prevent the float particles from crossing over into the sinks and thus reporting with the sink particles. The invention relates to a process for media separation. The Prior Art Heavy media separation generally involves the immersion of a raw product in a fairly quiescent fluid having a density intermediate between the densities of the two fractions to be separated. Even though heavy media vessels come in many sizes shapes and capacities, the basic principle of separation remains the same upon immersions into the separatory fluid, the less dense fraction floats whereas the more dense fractions sinks. Barrels, cones, cylinders and rectangular bath have all served as heavy media separatory vessels. However, the most common vessel shape within heavy media separation is that of a horizontal scrolled barrel. US 4,234,415 discloses an apparatus for separating mixed solids of different specific gravities by means of a liquid medium. The apparatus comprises a barrel in the form of a cone and which is not scrolled where the separation takes place. Solid particles are removed from said barrel by means of a cone provided with scrolls linked together, said cone acting in no way as system for separating solids. In said apparatus, medium flows substantially only through the opening having the minimum cross- section of the cone wherein the separation takes place, whereby the velocity of medium increases from the inlet of medium and solids to be separated towards said opening. Such an increase of velocity means that heavy solid particles are able to flow together with the float through said opening. Moreover, due to the lack of scrolls in the separating cone, float particles remains embedded with sink particles so that some float particles are removed together with the sink fraction or particles. There are also no disclosure of a curtain in the separation barrel, curtain preventing float particles from crossing into the sink evacuation cone or barrel. Scrolled barrels may be generally classified as mono- or bi-directional. Mono-directional barrels are constructed in such a manner that both the floats and the sinks move in the same direction and exit on the same end of the barrel. Bi-directional barrels have floats and sinks moving in opposite directions relative to one another and consequently the floats and sinks each exit at opposite ends of the barrel. In a bi¬ directional barrel the floats at the surface of the bath stream across the length of the barrel mid-section until they reach their point of overflow at the, discharge end of the floats overflow cone, whereas the sinks at the bottom of the bath are screwed in the opposite direction by means of scrolls until they reach the discharge end of the sinks evacuation cone. The large majority of heavy media barrels on the market today are mono-directional. On certain materials, bi-directionality has its distinct advantages and embodiments of the present invention relates to bi¬ directional barrels. In a bi-directional barrel the raw feed is introduced near the place where the sinks are evacuated. In this case, the only practical way of evacuating the sinks is by means of a scrolled cone. But all such bi¬ directional barrels sink evacuation cones are faced with a very annoying problem which up to now has never been solved in a satisfactory way namely, how to prevent a small percentage of floats from working their way toward the sinks side of the barrel and eventually reporting with the sinks being screwed up the sinks evacuation cone. One solution to this problem involves injecting medium at various points in the sinks evacuation cone so as to flush back down into the barrel any floats that tend to work their way toward the sink side of the barrel. -Another solution involves two curtains or barriers running the full length of the central barrel mid-section. These curtains are designed to prevent floats from getting caught up in the barrel scrolls and thus working their way toward the sink side of the barrel. 3oth of these solutions fail to assure a relatively perfect segregation of floats from sinks. A Brief Description of the Invention Heavy media separation generally involves the immersion of a raw product in a fairly quiescent fluid having a density intermediate between the densities of the two fractions to be separated. Upon immersion into the separation fluid the less dense floats whereas the more dense fraction sinks. This invention relates to heavy media scrolled barrels, and more specifically to heavy media bi-directional scrolled barrels. It assures that particles which float on the surface of a heavy media bi-directional barrel do indeed report to the float side of this barrel and in no way have the possibility of reporting incorrectly to the opposite sink side of said barrel. The system according to the present invention is a system for separating solid particles in two fractions by means of a medium, the specific gravity of said medium situating inbetween the specific gravity of a first fraction, namely the float fraction, and the specific gravity of the second fraction, namely the sink fraction, Said system comprises : , ' a) a first longitudinal scrolled barrel containing a liquid bath in which the separation takes place, 'b) means associated with said first barrel for driving it rotatively along its longitudinal axis, c) means for feeding or injecting into said first barrel both the solid particles to be separated as well as the medium effecting this separation, (d) means for removing the sink fraction, (e) means for removing the float fraction, (f) means for insuring a substantially uniform liquid level in the bath, and (g) means to prevent float particles from crossing into the means for removing the sink fraction, and thus from reporting with the sink fraction, the said means consisting of at least a curtain having an upper edge, a lower edge and lateral edges, the upper edge being at a level higher than the liquid level in the bath and the lower edge being at a level permitting the passage of sink particles into the means for removing sink particles, while the lateral edges are agenced so as to close the passage between the first barrel and the means for removing the sink fraction in the vicinity of the liquid level in the bath. Advantageously, the means for removing the sink fraction is a second scrolled barrel attached to and communicating with the first barrel. According to an embodiment, the means for evacuating the sink fraction is comprised of a second scrolled barrel attached to and communicating with said first barrel, said second barrel having at its end adjacent to said first barrel an inner diameter greater than the inner diameter of that end of the first barrel adjacent to said second barrel. The lateral edges, for example, enclose a section of the outer edge of the first barrel, such enclosure preventing float particles in the first barrel from crossing into the second barrel, or have an end which is adjacent to a part of a surface adjacent to the junction of the first barrel with the second barrel or have an end adjacent to a part of the surface of the flange linking the first barrel to the second barrel. According to an embodiment of the system, the means for preventing float particles from crossing into the part of said second barrel located between said means and the opening for evacuating the sink fraction consists of a curtain having an upper edge, a lower edge and two lateral edges, the upper edge being at a level higher than the point of discharge of the first barrel, the lower edge extending down into the medium but never so far as to block the passage of the sink fraction from the first barrel into the second barrel, and the two lateral edges each being inserted relative to a flanged surface which i-es outside the working area of the scrolls of the first barrel yet inside the working area of the scrolls of the second barrel and which surface lies between the upper and lower edges of said curtain. In said embodiment, each end of the lateral edges of the curtain is advantageously adjacent to a part of the surface of the flange linking the first barrel to the second barrel . According to a particularity of said embodiment, the lateral edge of said curtain bears an elastomeric material which is directed towards the flanged surface linking the first barrel to the second barrel. The curtain is advantageously held in place by the means for feeding solid particles and/or medium into the first barrel and is provided with means for supplying medium into the first barrel, such as pipes for injecting medium into the first barrel and for directing said medium towards the end of the first barrel opposite to the end adjacent to the second barrel. According to another embodiment of the system according to the invention, the first barrel is cylindrical, while the second comprises a part with an inner space, the shape of which is a truncated cone extending between two ends, the diameter of the end adjacent to the first barrel being greater than the diameter at the other end. The central axis of said first and second barrels, which is preferably the rotational axis, forms an angle less than ten degrees with the horizontal. According to a characteristic of an embodiment, the first barrel at its end opposite to the end adjacent to the second barrel, is provided with a further third barrel having an inner space which bears the shape of a truncated cone extending between two ends, the diameter of the end adjacent to the first barrel being greater than the diameter at the other end. Said other end acts as a discharge for evacuating the float fraction and a part of the medium. According to another embodiment of the system according to the invention, the second barrel is provided with an element linking at least a part of its scrolls in such a way that it prevents the liquid from flowing freely through the linked part of its scrolls. For example, the element covers at least a part of its scrolls. In this way, the liquid in the bath is not disturbed. In said embodiment, both the first and second barrels have elements which maintain the level of the liquid in the bath, these elements being either in the form of a cone or a doughnut, with or without an opening for removing medium or floating particles from the bath. The second scrolled barrel has two basic forms. The first form allows for the eventual evacuation of the sinking solid particles by continuing their movement in the same direction as in the first scrolled barrel. The second form allows for the eventual evacuation of said solid particles by reversing their movement relative to the direction of their movement in the first scrolled barrel. In both forms of this second scrolled barrel, the inner diameter of this second barrel is advantageously greater than the inner diameter of the first barrel. This gives the second barrel an even greater capacity for removing sinking solid particles. As the sinking solid particles exit the first barrel, they fall downward into the second barrel where they are eventually evacuated from the bath. This downward movement implies far less wear, abrasion and energy relative to other evacuation devices which all lift the sinking solid particles out of the bath. Since the inner diameter of this second barrel is advantageously greater than the inner diameter of the first barrel, it is possible to insert curtains which serve, for example, in the event of separation, to prevent any floating solid particles from crossing over and reporting with the sinking solid particles. Advantageously, two curtains extend down into the medium and prevent floating solid particles from mixing with the sinking solid particles. In the first form of the second scrolled barrel, the two curtains close off the surface gap between the first scrolled barrel and that element which links or covers the scroll of the second barrel . In the second form of the second scrolled barrel, the two curtains close off the surface gap between the first scrolled barrel and the level- maintaining doughnut of the second barrel . In both cases, by closing off this gap, floating solid particles are effectively prevented from mixing with the sinking solid particles. In a preferred embodiment, that portion of the curtain actually making contact consists of an elastomeric material. Another system according to the invention for treating either solid particles in a liquid bath or a liquid by means of solid particles, is comprised of a single scrolled barrel which is comprised further of two parts : a first part wherein the treatment takes place, and a second part provided with a means for preventing the freeflow of liquid from out the bottom of the bath, while at the same time allowing for the free passage of solid particles through the bottom of the bath, and a means for rotating the barrel. The barrel is also provided with means for assuring a substantially uniform liquid level in the bath. According to an embodiment of this system, an element covers or links at least part or parts of the scrolls or scroll of the barrel in such a way that it prevents the liquid from flowing freely through the linked or covered scrolls or scroll. According to an embodiment of this other system, the barrel is rotated along its longitudinal axis, the barrel being provided with an inner annular protrusion (having advantageously such a height that the free end of said protrusion directed towards said longitudinal axis is located at a distance from said longitudinal axis which is at most equal to the distance separating the free ends of the parts of the scrolls adjacent to the said inner annular protrusion) , the said inner annular protrusion separating the barrel into the two said parts. When said embodiment is used for separating sinking solid particles from floating particles, the gap formed between the element and the protrusion is partly closed by two curtains, said curtains extending down in the bath for preventing floating particles from crossing and reporting with the solid particles passing through the gap. Still another system according to the invention which is particularly suitable for treatment such as scrubbing is comprised of a single barrel which is comprised of three parts : namely, a central part wherein the treatment takes place, and two end parts provided with means for preventing the freeflow of liquid from out of the bottom of the bath and at the same time allowing for the free passage of solid particles through the bottom of the bath, and means for rotating the barrel. This barrel is further provided with means for assuring a substantially uniform liquid level in the bath. Indeed, a first end part acts as means for feeding solid particles, possibly together with medium or liquid, into the central part, while the other end part acts as means for evacuating solid particles, together with some medium or liquid, from the central part . According to an embodiment of said last embodiment, the barrel is provided with two elements, a first element linking parts of scrolls or scroll of its first end part in such a way that it prevents liquid from flowing freely through the linked parts of scrolls or scroll of said first end part, while the second element links parts of scrolls or scroll of its second end part in such a way that it prevents liquid from flowing freely through the linked parts of scrolls or scroll of said second end part. In a preferred embodiment of said last embodiment, the barrel is rotated along its longitudinal axis and is provided with an annular protrusion having such a height that the free end of said protrusion directed towards said longitudinal axis is located at a distance from said longitudinal axis which is at most equal to the distance separating the free ends of the parts of the scrolls adjacent to the said inner annular protrusion, the said inner annular protrusion separating the central part from the second end part. The barrel is provided with an element linking parts ' of its scrolls in its second end part in such a way that it prevents liquid from flowing freely through the linked parts of scrolls of said second end part, and in such a way that a gap is formed between the said element and the protrusion, said system being provided with two curtains closing partly said gap, said curtains extending down in the bath for preventing floating particles from crossing and reporting with the solid particles passing through the gap. The invention relates as well to a process for separating solid particles in two fractions by means of a medium, the specific gravity of said medium situating inbetween the specific gravity of a first fraction, namely the float fraction and the specific gravity of the second fraction, namely the sink fraction. In said process the solid particles to be separated as well as medium are fed into a scrolled barrel or a first part of a barrel wherein said particles are separated into a float fraction and a sink fraction. The float fraction as well as medium stream towards one end of the scrolled barrel, while at the same time the scrolled barrel is rotated so as to move the sink fraction towards the opposite end of the scrolled barrel and furthermore so as to bring said sink fraction into a second scrolled barrel attached to and communicating with the first barrel or into a second part of said barrel. A curtain is preferably positioned at or near the junction of the two barrels or parts that is, between that end of the first barrel or nearest to the second barrel or part and that end of the second barrel nearest to the first barrel or part. Said curtain serves to prevent the passage of the float fraction into that part of the second barrel or second part located between said curtain and the end opposite to the end to which the float fraction stream. The float fraction as well medium are evacuated at the end of the first barrel opposite to the end adjacent to the second barrel or part, while, as a result of the rotation of the second barrel, the sink fraction is evacuated at the end of the second barrel or part opposite to the end to which the float fraction stream. A higher pressure cf the medium is created on that side of the curtain nearest the means for removing the sink fraction. In said process, preferably at least one parameter selected from among the group consisting of the speed of rotation of the barrels, the density of the medium, the viscosity of the medium, the feed rate of medium into the first or second barrels or parts, the feed rate of solids into the first barrel or part, etc is controlled so as to obtain a sink fraction containing less than 0.01 % by weight of particles having a specific gravity lower than the specific gravity of the medium and at the same time to obtain a float fraction containing less than 0.01 % by weight of particles having a specific gravity higher than the specific gravity of the medium. Brief Description of the Drawings Figure 1 is a side view with cross-sections of a system according to the invention; Figure 2 is a view along line II-II of the system shown in Figure 1; Figure 3 is a top view with cross-sections of the system shown in Figure 1; Figure 4 is a view along the line IV-IV of the system shown in Figure 1; - Figure 5 is a view along the line V-V of the system shown in Figure 1; Figures 6A and 5B are schematic views of a plant using an embodiment of the system shown in Fiσure 1; Figure 7 is a side view with cross-sections of another embodiment of a system according to the inven ion; Figure 8 is a cross-section view along the line VIII-VIII of the system shown in Figure 7; Figure 9 is a side view of still another embodiment of a system according to the invention; Figure 10 is a cross-section view along line X-X of the system shown in Figure 9; - Figure 11 is a cross-section view along line XI-XI of the system shown in Figure 10; Figure 12 is a side view with cross-sections of a system according to the invention preferred for scrubbing solid particles; - Figure 13 is a side view of the system of Figure 12 but for the separation of sinking solid particles from floating solid particles; Figure 14 is a cross-section view along line XIV- XIV of the system of Figure 14 ; - Figure 15 is a side view of a further embodiment of a system according to the invention; Figures 16 and 17 are cross-section views along the lines XVI-XVI and XVII-XVII of the system of figure 15, and - Figure 18 is a cross-section side view of a further embodiment . Description of Embodiments Figure 1 shows a system for separating solid particles in two fractions by means of a medium, the specific gravity of which being comprised between the specific gravity of a first fraction - the floating fraction and the specific gravity of the second fraction - the sinking fraction. The system of figure 1 comprises : (a) a first longitudinal scrolled barrel I in which the separation takes places, said barrel stretching between a first open end 2 and a second open end 3 Ξ and being provided with five scrolls 41,42,43,44,45 having a right-handed pitch; (b) means 5 for feeding a mixture medium and solid particles to be separated; (c) means 6 for evacuating through an opening 7 the 0 sink fraction out of the system; (d) a discharge 8 associated with said barrel 1 for removing through an opening 10 the float fraction as well as the medium; (e) means 9 associated with said barrel 1 for driving it rotatively along a longitudinal axis A-A. The opening 10 of the discharge 8 has a lower edge 101 located at a level 1 lower than the level L of the lower edge 71 of the opening 7 for the removal of the sink fraction. The means 9 rotates clockwise Rl the barrel 1 so as to ensure the movement of the sink fraction towards the means 6 for removing the sink fraction (arrow S) . The barrel 1 is supported by 10 pneumatic wheels 13,14 , five wheels 13 being located on the left side of the barrel 1, while the five other wheels 14 being located on the right of barrel 1. Said wheels 13,14 are mounted on shafts 15,16, the axis B-B, C-C of which are parallel to the central axis A-A of the barrel 1. Said shafts are held in place by ball bearings 17 located at the free end of the uprights 18. Shaft 16 is driven by a motor 19, such as an electrical motor or a diesel motor via pulley 20 connecting sheave 21 secured on shaft 16 with sheave 22 secured on shaft 23 of the motor 19. Due to the rotation of the shaft 23 of the motor 19, wheels 13 are driven so that due to the friction of said wheels 13 on barrel I, the latter is turned along its longitudinal axis A-A. The means 5 for feeding the mixture of medium and solid particles to be separated consists of an injector 24 held in position by structure 25. This injector 24 is inclined so that particles present in said injector 24 move in the direction of barrel 1. The free end 26 of said injector 24 is within the inner separatory space of the barrel 1. Near to this free end 26, the injector 24 supports a curtain 27 consisting of a central plate 28 provided at each of its lateral edges 29 with a section 30 directed towards that end of barrel 31 connecting to barrel 1. Like barrel 1, barrel 31 is scrolled. Said barrel 31 attaches to and communicates with barrel 1, thereby acting as means 6 for evacuating the sink fraction. Said second barrel 31 comprises a first cylindrical part 32 attached by means of a flange 33 to the cylindrical barrel 1 and a second part 34 with an inner space having the shape of a truncated cone. Said cone stretches between two ends 7,341. The diameter D of the cross- section of the cone 34 at its end 341 adjacent to the first barrel 1 is gre ' ater than the diameter d of the cross-section of said cone 34 at its other end 7. Said diameter D corresponds to the diameter of the inner cross-section of the cylindrical part 32 which is greater than the diameter E of the inner cross-section of barrel 1. Said diameter D is advantageously greater than 1.1 x E, and is preferably comprised between 1.15 x E and 1.25 x E. In the embodiment as shown, the central axis of the second barrel 31 corresponds to the central axis of the first barrel 1 and is the rotation axis of said barrels. The sections 30 of the curtain 27 are provided at their lateral free ends with a layer 35 of an elastomeric material. Said layers 35 are in very close proximity to a part of the flange 33 which creates the junction between the first barrel I and the second barrel 31. The upper edge 36 of curtain 27 is at a level X higher than the level I of the point of discharge 10 of the float fraction and the medium, while the lower edge 37 of curtain 29 is at a level Y permitting the passage of said sink fraction from barrel 1 to the opening 7 for the evacuation of the sink fraction. Said curtain 27 acts therefore as a means to prevent float particles from crossing into the part of said second barrel located between said means and the opening for removing the sink fraction. In order to ensure that float particles near the curtain 27 will move towards the opening 10 through barrel 1, the curtain 27 features pipes 38 for supplying medium in the neighbourhood of the curtain 27 and on the side adjacent to the first barrel 1. In order to ensure a good separation that only sink particles pass underneath the curtain 27, medium is advantageously fed through pipe 129 into that part of barrel 6 located between the opening 7 and the curtain 27. In this way a flow of medium underneath the curtain from its sink side to its float side can be created. The first scrolled barrel 1 is provided at its end 3 opposite to the end 2 adjacent to the second scrolled barrel 31 with a third barrel 39 which does not have any scrolls. Said third barrel 39 has an inner space having the shape of a truncated cone. Said third cone 39 is attached to and communicates with the first barrel 1. Said barrel 39 extends between two ends, the diameter F of the cross-section of the cone -it its end adjacent to the first barrel 1 being greater than the diameter G of the cross-section of the cone at its other end. Said barrel 39 has a central axis which corresponds to the central axis A-A of the barrel 1. Openings 7 and 10 constitute respectively the discharge for the sink fraction and the discharge for the float fraction. The central axis A-A cf the barrels forms advantageously an angle from 1 to 10°, for example 5° with the horizontal . In order to obtain said inclination, blocks 50 are placed under the support 55 of the system. the inclination is such that the level P of the axis at the end of the barrel 1 adjacent to the barrel 39 is lower than the level Q of the axis at the end of the barrel 1 adjacent to the barrel 31. Two pneumatic wheels 51 roll against the outer surface of the flange 33. Said wheels are mounted on shafts 52 supported by ball bearings secured at the end of uprights 54. The axis T of said shaft 52 extends in a radial direction with respect to the central axis A-A of the barrels. Due to the rotation of barrels 1,31 the sink particles move towards opening 7 (arrow S) . The system according to the invention is ideally suited for separating particles with a size from 3 mm up to 300 mm or even more. These particles cover a broad range of materials such as non-ferrous metals, plastic, diamonds, vegetables, etc. The specific gravity of the medium may be as low as 1.0 and as high as 3.5. The actual medium is usually water-based with very fine colloidal particles in suspension. Suspension-creating materials such as clay, sand, magnetite and ferrosilicon are typically used. After filing the barrels with medium up to the level 1, a mixture of medium and solid particles are conveyed into the barrel 1 by means of an injector 24. The particles are separated in said barrel 1 into a float fraction and a sink fraction. The barrels are rotated so that due to the rotative screwing effect of the scrolls, the sink fraction is moved towards the opening 7 of barrel 31. More specifically, the sink fraction falls from barrel 1 into barrel 31 and from there it exits through opening 7. The evacuation of the sink fraction does not influence the medium in barrel 1. The curtain 27 blocks float particles from crossing over into barrel 31 and eventually from joining the sinks exiting through opening 7. Advantageously medium is injected in the neighbourhood cf the curtain 27 in the direction of opening 10 so as to prevent float particles from congregating near the curtain 27. Many parameters may be controlled so as to obtain a satisfactory separation, such as the speed of rotation of the barrels, the density and viscosity of the medium, the feed rate of medium into the first or second barrels, the feed rate of solids into the first barrel, etc. The curtain 27 assures that no float particles will report with the sink particles being evacuated through opening 7. More specifically the curtain 27 assures that the percentage of floats in sinks will not be greater than the percentage cf sinks in floats, and that, under normal operating conditions, it becomes feasible to obtain a sink fraction containing less than 0.01 % by weight of particles having a specific gravity lower than the specific gravity of the medium and at the same time to obtain a float fraction containing less than 0.01 % by weight of particles having a specific gravity higher than the specific gravity of the medium. A prototype of the system according to the invention was built. With respect to this prototype as represented in Figure 1, the characteristics of barrel 1 were as follows diameter E approximately 2.4 meters, diameter D approximately 3.0 meters, diameter d approximately 1.25 meters, diameter G approximately 1.1 meters . The length of barrel 1 was approximately 4.0 meters, while the length of barrel 6 was approximately 2.0 meters and the length of barrel 8 was approximately 1.0 meters . The angle a was approximately 3 degrees. The pitch of the scrolls was 1.5 meters and the number of the scrolls was five. The speed of rotation of the barrels was varied from 6 to 12 rpm. Fifty tons per hour of non-ferrous metal particles were fed to the barrels of which approximately 50 % were floats and 50 % were sinks. The medium consisted of water and atomized ferrosilicon. The specific gravity of separation was approximately 2.20. Samples of both floats and sinks were collected over a two-week period and after analysis they were found to be without any trace of misplaced material . Figures 6A and 6B are shematic views of plant using an embodiment of a system according to the invention. Said plant comprises : (a) a conveyor belt 100 for feeding the mixture of solid particles to be treated, ' said mixture coming from a fragmentizer, for example, as in the case of a non-ferrous metal application; (b) an air separator 101 for treating the particles coming from conveyor belt 100. The function of this air separator, for example, as in the case of a non-ferrous metal application, is to remove very light porous material fabric, textile, foam, simulated leather, dust and other such materials which should not enter into the dense medium circuit; (c) the system according to the invention (indicated by 99) in which the particles free from this undesirable light fraction are fed together with the medium through means (injector) 5 and in which said particles are separated into a sink fraction and a float fraction; (d) a chute 102 for collecting medium as well as float particles and for distributing them on a vibratory screen 103; (e) a vibratory screen 103 supported by air cushions 105 which in turn are supported by a steel structure 106, said vibratory screen 103 consisting of a first section known as a dewatering section 107a and a second section known as a rinse section 107b; (f) a medium tank 110 for collecting the medium flowing through the first section 107a of the vibratory screen 103 ; (g) a rinse tank 111 for collecting the rinse water flowing through the second section 107b of the vibratory screen 103; (h) a chute 112 for collecting medium as well as particles and for distributing them on a vibratory screen 113; (i) a vibratory screen 113 supported by air cushions 105 which in turn are supported by a steel structure 106, said vibratory screen 113 consisting of a first section known as a dewatering section 114a and a second section known as rinse section 114b; (j) a medium tank 115 for collecting the medium flowing through the first section 114a of the vibratory screen 113; (k) a rinse tank 116 for collecting the rinse water flowing through the second section 114b of the vibratory screen 113. The float particles on screen 103 travel first over the dewatering section 107a and then over the rinse section 107b, and finally they exit screen 103 at that end opposite chute 102 (cf arrow fp) , whereas the sink particles on screen 113 travel first over the dewatering section 114a and then over the rinse section 114b, and finally they exist screen 113 at that end opposite chute 112 (cf arrow fs) . Part of the medium collected in tank 110 is injected through pipe 131 into barrel 1 by means of the injector 5. A second part of said medium is injected through pipes 38 on the float side of the curtain 27 to prevent the accumulation of floats near the curtain. Finally a third part of said medium is injected through pipe 129 on the sink side of the curtain 27 so as to create a flow of medium underneath the curtain from its sink side to its float side. These three parts of the medium in tank 110 are all pumped out of said tank by means of the primary medium pump 130. In this way the primary medium pump 130 also restores to the system the medium overflowing barrel 8. A regulation system such as a valve 132 is mounted on pipe 129 so as to regulate the flow of medium underneath the curtain 27 from its sink side to its float side. This assures that only sink particles pass underneath the curtain to its sink side. The medium collected in tank 115 is pumped by means of the secondary medium pump 133 through pipe 134 into the second barrel 6 so as to restore to said barrel the medium being screwed out together with the sink particles . The apparatus 101 comprises a series of trays such as descending, cascading, vibratory trays 117,118,119. As the particles drop from one tray to the next, they are subjected to a current of air so as to deflect the lighter particles of dust, textile and foam, as in the case cf a nor -ferrous metal application, for example, from the heavier particles which are then to report for further separation to the system according to the invention 99. The current of air is produced by means of an injection system comprised for example of special air nozzles 120 which in turn are fed by a ventilator. According to a preferred embodiment, each tray has its own air nozzle and each air nozzle has an opening whose length corresponds to the width of the tray. As soon as the particles to be separated fall from a particular tray, they are immediately subjected to a current of air deflecting the lighter particles in a direction generally opposite to the movement of the heavier particles on the trays. The light particles are deflected in such a manner that they are no longer able to fall back onto a tray and they fall instead into a collection bin 125 situated generally underneath the trays. The collection bin 125 is situated in a sealed housing 150 which communicated through an opening 151 to the tray system 101 and which communicates as well as through an opening 152 to the ventilator which feeds the air nozzles. Preferably an air filtration unit is incorporated into the circuit . The embodiments of Figures 7 to 10 described hereafter are particularly suitable for heavy media separation, but are also suitable for other uses, such scrubbing, treatment cf liquids as waste water with solid such as lime, dolomite, calcium carbonate. Figure 7 shows a system for separating solid particles in two fractions by means of a medium, the specific gravity of which being comprised between the specific gravity of the first fraction -the floating fraction, and the specific gravity of the second fraction - the sinking fraction. The system comprises : (a) a first longitudinal scrolled barrel 201 in vhich the separation takes place, said barrel being provided with five scrolls 241,242,243,244,245 having a right-handed pitch; (b) means 2C5 for feeding a mixture medium and solid particles to be separated; (c) means 206 for evacuating through an opening 207 the sink fraction out of the system; (d) a discharge 208 in the form of a cone associated with said barrel 201 for removing through an opening 210 the float fraction as well as medium, and (e) means 209 associated with said barrel 201 for dri¬ ving it rotatively along a longitudinal axis A-A. The opening 210 of the discharge 208 has a lower edge 301 located at a level LL lower than the level -----L-L of the lower edge 271 of the opening 272 through which the mixture is fed into the barrel 201. The means 209 rotates clockwise Rl the barrel 201 so as to ensure the movement of the sink fraction towards the means for remowing the sink fraction (arrow S) . The barrel 201 is supported by pneumatic tyres 213. Seven tyres 213 are located on the left side of the barrel 201 while seven other tyres 214 being located on the right side of barrel 201. Said tyres 213 are mounted on shaft 215, the axis B-B of which are parallel to the central axis A-A of the barrel 201. Said shafts are held in place by ball bearings 217 located at the free end of uprights 218. One shaft is driven by a motor (not shown) such as an electrical motor or a diesel motor, via pulley connecting a sheave secured on shaft with a sheave secured on the shaft of the motor. Due to the rotation of the shaft of the motor, tyres 213 are driven so that due to the friction of said tvres 213 on barrel 201, the latter is turned along its longitudinal axis -A-A. The means 205 for feeding the mixture of medium and solid particles to be separated consists of an injector 224 held in position by a structure 225. This injector 224 is inclined so that particles present in said injector 224 move in the direction of barrel 201, said injector 224 is within the inner separatory space cf the barrel 201. Like barrel 201, barrel 231 is scrolled. Said barrel 231 attaches to and communicates with barrel 201, thereby acting as means 206 for evacuating the sink fraction. In the embodiment as shown, the central axis of the second barrel 231 corresponds to the central axis cf the first barrel 201 and is the rotation axis of said barrels . The barrel 231 is attached to barrel 201 by means of scrolls 232,233 of barrel 231. Barrel 201, i.e. its outer surface, acts as element for linking scrolls of barrel 231 so as to define a passage 234 wherein scrolls stretch so as to prevent the freeflow of medium through said passage and the opening 207. The second barrel 231 is provided with an end wail or doughtnut 236 showing the opening 272 through which the solid particles to be treated are fed through the injector 224, said end wall or doughnut 236 acting as means for preventing any flow of medium out of the barrel 231 in a direction opposite to barrel 201. Thus, the freeflow of medium M out of the system is only possible through opening 210, while the removal of medium through opening 207 with sinking particles is not free as it depends on the rotation speed of the barrels 201,231. In the embodiment of Figure 7, barrel 1 is provided with scrolls having a right-handed pitch, while barrel 231 is provided with scrolls having left-handed pitch (i.e. barrels 201 and 231 have scrolls with opposite handed pitch) . The evacuation of sinking particles is thus obtained by reversing their movement relative to their movement in the first barrel. In the embodiment shown, the central axis A-A is horizontal so that for evacuating the sink fraction out of the system, it is not necessary to raise upwardly the said sink fraction. Barrel 231 has an inner diameter which is greater than the outer diameter of the barrel 201 so that the sinking particles escaping barrel 201 fall into barrel 231, whereby the sinking particles do not disturb the treatment of solid particles into barrel 201. When the system of Figure 7 is used for separating sinking solid particles from floating particles, the system is advantageously provided with curtains 239 extending down in the bath for preventing floating particles F from crossing and reporting with the solid particles passing through the bottom of the bath BA into the barrel 231, i.e. all the floating particles F are evacuated through the opening 210. The curtains are attached to arm 240 attached to the injector 224. The curtains are comprised of an arc section of a cylinder, one end edge 391 contacts the doughnut 226 while the other end of which contacts the element or first barrel 201. Figure 9 is a view of a system similar to that shown in Figure 7, except that barrel 231 is attached to barrel 201 by means of a flange 237 and forms an extension of barrel 201. An inner cylinder 238 covers the free end of scrolls of the second barrel 231 so as to define a passage 234 wherein scrolls stretch, said passage acting as means for evacuating sinking solid particles. The end of the cylinder 238 opposite to the end adjacent to barrel 201 is provided with a doughnut 236 having an opening 272 through which the solid particles are fed in barrel 201 together with medium by means of the injector. Said doughnut acts as means for preventing medium to flow freely cut cf the barrel 231 through the opening 272, as the level LLL of the lower edge 271 of the opening 272 is located upwardly with respect to the lower edge 301 of the opening 210. Said doughnut and the cone 208 act as means for assuring a substantially uniform level of the bath, i.e. for assuring a maximum level of the bath BA. In said embodiment, the sinking particles are evacuated through opening 207 by continuing their movement S2 in the passage 234 in the same direction S as in the first scrolled barrel. As solid particles deposit on the inner surface of the cylinder 238, said inner surface is advantageously provided with scrolls 381 having a pitch opposite to the pitch of the first barrel 201, so that, when the barrels 201, 231 rotate, the sinking particles deposited on barrel 201 move (S) towards the gap G formed between the cylinder 238 and the barrel 201, while the sinking particles deposited on the inner surface of the cylinder 238 also move (SI opposite to S) towards said gap G, i.e. so that the sinking particles fall into the barrel 231. The solid particles falling in the barrel 231 are then moved towards the opening 207 through the scrolls of said barrel 231. The parts of the scrolls 311 of the barrel 231 located in the gap G have advantageously such a height h that a curtain 239 is able to stretch from the outer surface of the cylinder 238 towards the first barrel, preferably to the flange 237. The embodiments cf Figures 7 and 9 overcome the difficulties surrounding the evacuation of solids from a liquid bath. It allows large quantities of solid particles to be evacuated simply and efficiently with a small initial capital cost, requiring little energy or power, and incurring little wear or abrasion. In fact, in its such embodiments, it even allows solid particles to be removed from a liquid bath without having to lift the particles out of the bath and at the same time without disturbing the dynamics of the bath in any significant way. The present invention, in these embodiments, in evacuating solid particles from a liquid bath, does not require any upward movement of the solid particles relative to the bath, and it does not require that the solid particles be lifted to some point above the bath. As in the system of Figure 7, two curtains 239 (arc section of a cylinder, the inner diameter of which is equal to or greater than the inner diameter of barrel 201 and than the inner diameter of cylinder 238) are secured to the injector 224 by means of arms 240. Said curtains contact the flange 237 and the cylinder 238 and extend down in the bath BA for preventing floating particles from crossing and reporting with the sinking solid particles. Advantageously, the edges of the curtains making contact consist of an elastomeric material . Figure 12 is a view of another embodiment of a system according to the invention, which is also suitable and preferred for the scrubbing cf the solid particles . The system comprises a scrolled barrel 201 comprising three parts, a central part 1000 wherein the treatment takes place, a first end part 1001 for feeding solid particles into the central part and a second end part 1002 for evacuating solid particles through the bottom cf the bath of the central part 1000. Scrolls of the first end part 1001 are linked by a cylinder 1003 so as to define a passage 341. The scrolls stretching in the said passage 341 preventing the freeflow from out of the bath BA through said passage. The cylinder 1003 is provided with a doughnut 1004 so as to prevent any flow of medium from out the inner space 351 of cylinder 1003 in a direction opposite to the central part 1000. Scrolls of the second end part 1002 are linked by a cylinder 1005 so as to define in said end part a passage 342. Scrolls stretching in the passage prevent the freeflow of medium through said passage 342. The cylinder 1005 is provided with a doughnut 1006 having an opening 210 through which medium and float fraction are possibly discharged. The cylinders 1003 and 1005 are provided with scrolls 1007 so as t,o ensure that any sinking particles deposited thereon will move towards the central part 1000 so as to be treated again or so as to be evacuated through passage 342. Barrel 1 is provided with a scrolled extension 1008 with a wail 1009 in which the solid particles to be treated and possibly medium for the treatment are fed by means of the injector 224. Cylinder 1005 is also provided with an extension 1010 in order to avoid that medium and floating particles F flowing through the opening 210 are mixed again with the medium and sinking particles S flowing through the opening 207. The means for driving into rotation barrel 201 are for example similar to that disclosed for the system of Fiσure 1. The system of Figure 13 is similar to that shown in Figure 12, except that it is provided with curtains for preventing floating particles from crossing over and reporting into the sinking solid particles removed through the passage 342. Such a system is thus particularly suitable for separating sinking solid particles from floating particles. The barrel is provided with an inner annular protrusion 1011 which forms a separation between the central part 1000 and the second end part (evacuation) 1002, a gap G being so created between said annular protrusion 1011 and the cylinder 1005. The height hi cf the protrusion 1011 is advantageously lower to the height h2 of the passage 342 and therefore to the height h.2 of the scrolls of the second end part 1002. The scrolls of the central part 1000 have a height equal to the height of the scroll in the second end part, except that said height decreases in the neighbourhood of the annular protrusion 1011. The inner surface of cylinder 1005 is, in the neighbourhood of the annular protrusion 1011, not provided with scroll so as to form a contact surface for curtains 239 fcr preventing floating particles from crossing and reporting with the sinking solid particles. The system is provided with two curtains attached to an arm 1012 of a structure, said arm 1012 stretching through the opening 210 through which floating particles are removed. The curtains 239 close partly the gap G formed between the annular protrusion 1011 and the cylinder 1005 and extend down into the bath BA. The curtains 239 (in the form cf an arc section of a cone) have two opposite .edges 391, 392, a first contacting the surface 1013 of the protrusion directed towards the longitudinal axis A-A of the barrel while the other contacts the inner surface 1014 of the cylinder 1005, contacts the inner surface 1014 of the cylinder 1005, which is not provided with scrolls. Figure 15 is a view of a further embodiment according to the invention. In this embodiment, the system comprises : a scrolled barrel 201 in which the separation takes place ; an injector 224 for feeding the barrel 201 with medium and particles to be treated ; - a cone 208 attached to and communicating with the barrel 201, said cone having an opening 210 for evacuating floating particles and medium; a barrel 206 attached to and communicating with the barrel 201 for the evacuation of sinking particles and medium, and means for driving rotatively the barrels so that floating particles (M) and sinking particles (S) flow in opposite direction. Scrolls of barrel 206 are linked together by means of a cylinder 1005 which is provided with a doughnut 1009 with a central opening 1020 through which injector 224 passes so as to feed barrel 201 with particles to be treated. Said cylinder 1005 and doughnut 1009 prevent the freeflow of medium and sinks out of the system. Barrel 201 is provided with an inner annular protrusion 1012 having a part 1021 reducing progressively the inner cross-section or/and diameter of barrel 201 and provided with the scrolls 1022 intended to raise sinks with respect to the bottom of barrel 201. Such an inner protrusion due to the raise of sinks and due to the reduction of cross-section of barrel 201 (reduction of the velocity of medium towards barrel 206) acts already as means for preventing as much as possible floats to report with sinks. So as to ensure an -excellent separation, the system is further provided with a curtain 27 having an upper edge at a level higher than the level cf the bath, a lower edge at a level allowing the passage of sinks and lateral edges contacting a surface of barrel 201 but preferably a part 1023 of the protrusion 1012, part 1023 which is free of scrolls. For example, part 1023 increases progressively the cross-section or diameter of the barrel 206 with respect to the minimum cross-section or diameter due to the protrusion 1012, so that sinks passing over the upper edge 1024 of the protrusion slip or glide on said part 1023 towards barrel 206. Part 1023 forms thus a slope which is contacted by the lateral edges of the curtain 27, the form of which is a section of a circle. The maximum height hi of the protrusion 1012 with respect to barrel 201 is advantageously equal to, preferably greater than, the height h.2 of the scrolls of the barrel 206. Figure 18 shows an embodiment similar to that shown in Figure 12. Said embodiment is advantageously provided with a curtain 27 such as shown in the embodiment of figure 13. In the embodiment of Figure 18, cylinder 1003 is closed by two doughnuts 1004a, 1004b, whereby there is no treatment bath BA in the inner space of said cylinder, whereby there is also no need to provide said cylinder with any scrolls. Cylinder 1005 is provided with a doughnut 1006 with an opening 210 located in the inner space of barrel 201. Said doughnut 1006 is advantageously attached to the end of the cylinder 1005 directed towards to injector 224 or cylinder 1003, whereby there is no need to provide cylinder 1005 with scrolls. However, in specific embodiment cylinder 1005 may be provided with scrolls so as to facilitate the evacuation of medium and floats (F) through opening 210 into cylinder 1005. An advantage to use doughnut 1006 and 1004b located in the barrel 201 is to limit the weight cf treatment bath in the barrel 201 and therefore to limit the power required for the rotation thereof. When using a curtain 27, said curtain 27 will, for example, extend between the doughnut 1006 and an annular protrusion such as disclosed in Figure 13 or in Figure 15.

Claims: WHAT I CLAIM IS : 1. A system for separating solid particles in two fractions by means of a medium, the specific gravity of said medium situating in between the specific gravity of the particles of the first fraction or float and the specific gravity of the particles of the second fraction or sink fraction, said system comprised of : --a) a first longitudinal scrolled barrel containing a liquid bath in which the separation takes place, (b) means associated with said first barrel for driving it rotatively along its longitudinal axis, (c) means for feeding or injecting into said first barrel the solid particles to be separated and medium effecting this separation, d) means for removing the sink fraction, (e) means for removing the float fraction, ,' f1 means for insuring a substantially uniform liquid level in the bath, and (g) means to prevent float particles from crossing into the means for removing the sink fraction, and thus from reporting with the sink fraction, the said means consisting of at least one curtain having an upper edge, a lower edge and lateral edges, the upper edge being at a level higher than the liquid level in the bath and the lower edge being at a Ti level permitting the passage of sink particles into the means for removing sink particles, while the lateral edges are agenced so as to close the passage between the first barrel and the means for removing the sink fraction in the vicinity of the liquid level in the bath. 2. The system according to claim 1, in which the means for removing the sink fraction is a second scrolled barrel attached to and communicating with the first barrel . 3. The system according to claim 2, in which the means for evacuating the sink fraction is comprised of a second scrolled barrel attached to and communicating with said first barrel, said second barrel having at its end adjacent to said first barrel an inner diameter greater than the inner diameter of that end of the first barrel adjacent to said second barrel. 4. The system according to claim 3 , in which the lateral edges of the curtain enclose a section of the outer edge of the first barrel, such enclosure preventing float particles in the first barrel from crossing into the second barrel. 5. The system according to claim 3 , in which the lateral edges of the curtain have an end which is adjacent to a part of a surface adjacent to the junction of the first barrel with the second barrel. 6. The system according to claim 5, in which each end of the lateral edges of the curtain is adjacent to a part of the surface cf the flange linking the first barrel to the second barrel. 7. A system according to claim 5, in which the curtain consists of a central plate provided at each of its lateral ends with a section directed towards the first barrel, the free end of the section adjacent to the first barrel bearing a layer of an elastomeric material. 3. A system according to claim 5, in which the curtain is supported by the means for feeding the solid particles into the first barrel. 3. A system according to claim 5, which comprises at least one pipe for feeding medium into a barrel selected from the group consisting cf the first barrel and the second barrel . 10. A system according to claim 5, which comprises a means for assuring a flow of medium underneath the curtain from its sink side to its float side. 11. A system according to claim 5, which comprises a means for creating a higher pressure of the medium on that side of the curtain nearest the point of discharge cf the sink fraction. 12. A system according to claim 2, in which the first barrel is cylindrical while the second comprises a part with an inner space , the shape of which is a truncated cone extending between two ends, the diameter of the end adjacent to the first barrel being greater than the diameter at the other 'end and in which the central axis of said first and second barrels forms an angle less than ten degrees with the horizontal. 13. A system according to claim 2, in which the first barrel is provided at its end opposite to the end adjacent to the second barrel with a third barrel with an inner space having the shape of an truncated cone extending between two ends, the diameter of the end adjacent to the first barrel being greater than the diameter at the other end, said other end acting as a discharge for evacuating the float fraction and a part of the medium. 14. The system according to claim 2 , in which the second barrel is provided with an element linking at least a part of its scrolls in such a way that it prevents the liquid from flowing freely through the linked part of its scrolls. 15. The system of claim 14, in which the second barrel is provided with an element covering at least a part of its scrolls in such a way that it prevents the liquid from flowing freely through the covered part of its scrolls. 16. The system of claim 2, in which the second barrel has an inner diameter which is greater than the inner diameter of the first barrel and in which the second barrel is attached to the first barrel and is scrolled with respect to the first barrel, so that the direction of the movement of solid particles in said second barrel is reversed with respect to the direction of the movement of sinking solid particles in the first barrel, in which a gap is formed between the first and second barrels through which solid particles of the first barrel move into the second barrel, in which the first and second barrels are provided with a level maintaining means, said system being provided with two curtains closing partly, the gap between the first barrel and the level maintaining means of the second barrel, said curtains extending down in the bath for preventing floating particles on the bath from crossing and reporting with the solid particles passing into the second barrel . 17. The system of claim 2, in which the second barrel is attached to the first barrel and is scrolled with respect to the first barrel, in such a way that the evacuation of solid particles through said second barrel is effected by continuing their movement in the same direction as in the first barrel, in which the said barrel is provided with an element linking at least a part of its scrolls in such a way that it prevents the liquid from flowing freely through the linked scrolls, said system being provided with two curtains closing partly the gap between the first barrel and the said element, said curtains extending down in the bath for preventing floating particles on the bath from crossing and reporting with the solid particles passing into the second barrel . 18. The system according to claim 1, said system comprised of a scrolled barrel which is comprised of two parts, a first part for containing a liquid bath wherein the separation takes place and a second part provided with a means for preventing the freeflow of liquid from out of the bottom of the bath while at the same time allowing for the free passage of solid particles through the bath, said barrel being provided with an inner annular protrusion separating the barrel into the two said parts . 19. The system of claim 18, in which the barrel is provided with an element linking parts of its scrolls in its second part in such a way that it prevents the liσuid from flowing freely through the linked part of its scrolls and in such a way that a gap is formed between the said element and the scroll. 20. The system of claim 1, said system comprised of : (a) a scrolled barrel which is comprised of three parts, a central part for containing the bath and wherein the treatment takes place, a first end part for feeding solid particles into the central part and which is provided with a means for preventing the freeflow of liquid out of the bath while at the same time allowing for the free passage of solid particles into the central part, a second end part for evacuating solid particles from the central part and which is provided with a means for preventing the freeflow of liquid from out of the bottom of the bath while at the same time allowing for the free passage of solid particles from the central part through the bottom of the bath; (b) means for insuring a substantially uniform level in the bath, and (c) a means for rotating the barrel. 21. The system of claim 20, in which the barrel is provided with two elements, a first element linking parts of scrolls of its first end part in such a way that it prevents liquid from flowing freely through the linked parts of scrolls of said first end part, while the second element links parts of scrolls of its second end part in such a way that it prevents liquid from flowing freely through the linked parts of scrolls cf second end part . 22. The system of claim 20, the barrel is provided with two elements, a first element linking parts of scroll (s) of its first end part in such a way that it prevents liquid from flowing freely through the linked parts of scroll (s) of said first end part, while the second element links parts of scroll (s) of its second end part in such a way that it prevents liquid from flowing freely through the linked parts of scroll (s) of said second end part . 23. The system of claim 20, in which the barrel is provided with an inner annular protrusion having such a height that the free end of said protrusion directed towards said longitudinal axis is located at a distance from said longitudinal axis which is at most equal to the distance separating the free ends of the parts of the scrolls of the barrel which are adjacent to the said inner annular protrusion, the said inner annular protrusion separating, the central part from the second end part, and in which the barrel is provided with an element linking parts of its second end part in such a way that it prevents liquid from flowing freely through the linked parts of scrolls of said second end part, and in such a way that a gap is formed between the said element and the protrusion, said system being provided with two curtains closing partly said gap, said curtains extending down in the bath for preventing floating particles from crossing and reporting with the solid particles passing through the gap. 24. The system of claim 20, for separating sinking solid particles from floating particles, in which the barrel is rotated along its longitudinal axis, in which the barrel is provided with an inner annular protrusion having such a height that the free end of said protrusion directed towards said longitudinal axis is located at a distance from said longitudinal axis which is at most equal to the distance separating the free ends of the parts of the scroll adjacent to the said inner annular protrusion, the said inner annular protrusion separating the central part from the second end part, and in which the barrel is provided with an element linking parts of its scroll in its second end part in such a way that it prevents liquid from flowing freely through the linked parts of scroll of said second end part, and in such a way that a gap is formed between the said element and protrusion, said system being further provided with two curtains closing partly said gap, said curtains extending down in the bath for preventing floating particles from crossing and reporting with the solid particles passing through the gap. 25. A process for the separation of solid particles in two fractions by means of a medium, the specific gravity of which situating inbetween the specific gravity of a float fraction and the specific gravity of a sink fraction, in which the solid particles to be separated as well as medium are fed into a scrolled barrel wherein said particles are separated in a float fraction and a sink fraction; the float fraction as well as medium stream towards one end of the scrolled barrel, while at the same time the scrolled barrel is rotated so as to move the sink fraction towards the opposite end of the scrolled barrel and furthermore so as to bring said sink fraction into a second scrolled barrel attached to and communicating with the first barrel; a curtain is positioned between the end of the first barrel opposite to the end adjacent to the second barrel and the end of the second barrel opposite to the end of the first barrel, said curtain serving to prevent the passage of the float fraction into that part of the second barrel located between said curtain and the end opposite to the end adjacent to .the first barrel; the float fraction as well medium is evacuated at the end of the first barrel opposite to the end adjacent to the second barrel, while as a result of the rotation of the second barrel, the sink fraction is evacuated at the end of the second barrel opposite to the end adjacent to the first barrel, and in which a higher pressure of the medium on that side of the curtain nearest the means for removing the sink fraction is created. 26. A process according to claim 25, in which at least one parameter selected among the group consisting of the rotation speed cf the barrels, the flow rate of the medium, the feed rate of solid particles, is controlled so as to obtain a sink fraction containing less than 0,1 % by weight of particles having a specific gravity lower than the specific gravity of the medium. 27. A process according to claim 25, in which medium is injected in the first barrel so as to propell the float particles towards the point cf discharge of said float particles.

Inventors: OLIVIER PAUL, OLIVIER, PAUL
Applicants: OLIVIER PAUL, OLIVIER, PAUL
Application year: 1993
Main classification: B03B5
IPC codes: B03B5, B03B11