WO1994022582A1

WO1994022582A1 - Slurry recovery process for ores

Info

Publication number: WO1994022582A1
Application number: PCT/CA1994/000168
Authority: WO
Inventors: Robert Ross Barefoot
Original assignee: Dcrs (Barbados) Ltd.
Priority date: 1993-03-26
Filing date: 1994-03-28
Publication date: 1994-10-13
Also published as: PE4895A1; AU6350394A

Abstract

The invention consists of forming an aqueous slurry (21) of water and particles of ore carrying both metals and/or minerals which are directed at relatively high speed to hit the top of the far edges of tiny cubic cells (25) in a series of overlapping (26) trays sloped at the appropriate angle. This causes the slurry to become entrapped, swirling down towards the bottom of the cell (25) and continue back up the opposite side and then back out into the main slurry flow. The centrifugal force generated by this turbulent eddy (22) can be in the hundreds of G's. Should the metals and minerals in the slurry be electrically charged opposite to the cell (25) and cell bottom, th high G-force generated by the centrifugal force of the mini swirl causes the two oppositely charged substances to come into close contact, thereby creating a substantial electrical attraction. When in close contact, the electrical force can be thousands of G's. When charged minerals, which have metals adhering electrostatically to them, come into contact with oppositely charged material, electrons are exchanged and the metals detach and remain in the cell (25) while the less dense minerals are carried out of the cell (25) by the slurry.

Description

SLURRY RECOVERY PROCESS FOR ORES

This invention relates to new and useful methods and structure for concentrating and recovering metals and minerals from a moving aqueous slurry.

A primary object of this invention is the provision of a simple method of generating high G-forces to enable the efficient recovery of precious metals from their ores in a high speed water slurry.

A second object of the invention is to provide a method of separating electrostatically bound metal particles from the ore to which the metal is bound.

According to a first aspect of the invention there is provided a method of separating a selected first ore component of higher density from a paniculate ore to leave a second ore component of lower density, the method comprising generating a slurry of the paniculate ore carried in water, causing a flow in the slurry longitudinally of a surface from a raised feed end of the surface to a lower discharge end thereof, providing on the surface an array of cells arranged side by side across a width of the surface and along a length of the surface, each cell having generally upstanding walls defining a hollow interior which is non-circular in side elevation, an open top and a substantially closed bottom, the walls including a first wall on an upstream side of the hollow interior and a second wall spaced from the first on a downstream side of the hollow interior, directing the flow of slurry at an angle relative to an imaginary plane perpendicular to the second wall downwardly into the hollow interior to cause the slurry to enter the open top of the cell, to swirl around the non-circular interior and to discharge from the open top, collecting the first ore component in the hollow interior and discharging the second ore component from the lower discharge end of the sur ace.

SUBSTITUTE SHEET According to a second aspect of the invention there is provided a method of separating metal from a mineral in paniculate form in which the metal is bonded to the panicles of the mineral by electrostatic forces comprising mixing the mineral in paniculate form and metal carried thereby with water to form a slurry, inducing an electrostatic charge onto the panicles of the mineral, providing an electrode having thereon a charge opposite to said electrostatic charge on the mineral, generating centrifugal forces on the panicles in a direction to cause the panicles to move toward the electrode and causing the panicles to contact the electrode to cause discharge of electrostatic charges from the panicles to break the bond between the metal and the panicles to release the metal for collection.

Embodiments of the invention are herein described by reference to the accompanying drawings tables and charts forming a part hereof, which includes a description of the best mode known to the applicant and the preferred typical embodiment of the principles to the present invention, in which:

Figure 1 is a schematic diagram showing four different circuits that can be used to create the appropriate slurry from different ores: circuit a) where the ore is first crushed and then pulverized, circuit b) where the ore is crushed only, circuit c) where the ore is trommeled, and circuit d) where the ore is screened. After mixing the appropriate ratios of water, the slurries are then piped into the system of the present invention (hereinafter referred to as HFMS) .

Figure 2 is a blow up cross section of a side view of an HFMS cubic cell showing the slurry swirling through the slanted cell and depositing the metals and minerals in the cell corners and rubber cups at the base of the cell.

Figure 3 is a cross section of a side view of an array of HMFS cubic cells showing the generation of a dozen mini swirls as the slurry passes through.

SUBSTITUTE SHEET Figure 4 is a top view of trays with side removed to show overlapping cells with the trays hinged to belting below.

Figure 5 is a side view of slurry flowing into cells on trays hinged to lower belting.

Figure 6 is Hjoulstrom's diagram showing the relationship of erosion, transportation and deposition of various sedimentary particles moving at various slurry velocities.

Figure 7 is Hjoulstrom's diagram showing the effects on 18 micron quartz and gold crystals moving at 14 feet/second as various G-forces are applied on them.

Figure 8 is a table showing the velocity of slurry versus centrifugal force generated at various radii.

Figure 9 is a table showing the G-Forces generated at specific voltages versus various distances between the charges.

High speed mini swirl slurry (HDMS) recovery of metals for a particular ore involve the utilization of an array of relatively tiny cells to generate high G-forces that bring about the separation of heavy metal or mineral particles which may or may not be charged. To achieve this objective the system is designed to maximize turbulence or the generation of eddies in very small cells that are just large enough to allow all of the slurry 21 of ore to swirl through the cells producing eddies 22, and yet small enough to generate a substantial G-force. The slurry must be constantly realigned to direct it towards the cells at the appropriate entrapment angle. This is accomplished by cascading the slurry over each array of cells 25 on over- lapping trays mounted with hinges 28 from the lower smooth base of the tray 26 on to a lower belt 27, with hinges 28 from the lower smooth base of the tray 26, and by the angle of the tray itself being such that the slurry hits the far edge of

SUBSTITUTE SHEET the cell wall 29 and is forced to swirl down and around (Fig 2). This causes the denser metals and minerals to become entrapped in the cell corners 23 and rubber cups or pockets 24 at the base of the cell. The incoming slurry is also directed into the cell by slowing down as it drags over the top of inner cell wall 30. The resulting criss-crossing action of the out going slurry with the incoming slurry, along with the vortex created by the swirl, entraps substantial air which assists in the electrical charging of the slurry. The swirls also take place within the pear shaped pockets and as these are of smaller diameter, the G forces are significantly increased up to greater than 1000G.

In one embodiment, the cells and/or base are formed from a conductive material so as to inhibit or prevent the generation of electrostatic forces between the slurry and the surfaces. In this way collection of the heavier component is effected solely by the centrifugal forces.

When electrically insulative materials are used to construct the cells and the cell base, thereby insulating the slurry and cells from the ground, the charges created can be measured at the top of the cell in the 500 to 1000 millivolt and 350 to 700 milliamp range. Since the plastics and rubber used to accomplish this tend to charge negatively and since the water and contained metals and minerals are charged positively, the electrical force of attraction between them is a function of how close the charges are to each other. This force of attraction is directly proportional to the square of the distance between them. The high centrifugal force generated by the slurry following a swirl path into the cell, forces these opposite charges close enough so that the additional force of electrical attraction can assist in the deposition o f the metals and minerals.

Should the gold particles be large enough for the centrifugal force to entrap them in the collectors at the base of the cell, the additional force

SUBSTITUTE SHEET generated electrically may not be necessary. This can be determined by Hjoulstrom's Diagram (Fig. 6) which shows the erosion, transportation and deposition relationship of various size sedimentary particles (average specific gravity of 2.5) moving in a slurries at different velocities. For example, Hjoulstrom's diagram shows that a piece of sand (quartz) moving at 1 foot per second (12.5 cm/sec) will be in the transportation mode and will not settle until either the slurry velocity slows down to 0.02 feet/second (0.8 cm/sec), or, a force equal to 12.5/0.8 = 15.6 times its weight (15.6 G's) is exerted on it.

Since a substantial amount of the invisible gold found in lode ore exists as 18 micron octahedral gold crystals specific gravity of 19.20, the force that must be exerted on this gold in a slurry moving 14 feet/second (427 cm/sec) to cause it to deposit is 420 G's (Fig. 7,), or, only the force of gravity (1 G) would be required if the slurry were slowed down to 0.004 feet/second (0.12 cm/sec). Thus, the additional force of static electricity would be required to force the 18 micron gold to deposit from a slurry moving 14 feet/second (447 cm/second), 314 G's (Figure 8, Table 1 , see example calculations below), would be inadequate for deposition, thereby requiring the additional electrostatic force.

It should be noted that Hjoulstrom intended his chart to reflect sedimentation as the slurry passed over some reasonable distance, and not the relatively tiny distances through which the slurry passes in either a conventional gravity system of the HFMS system. This consideration more than offsets the effects of particle shape where a sphere deposits slightly more rapidly than a cube. Thus the additional thousands of G's generated electrically by the HFMS system (Fig 9, Table 2, see example calculations below) are more than adequate to collect the gold and other metals in less than five feet of slurry path.

SUBSTITUTE SHEET In addition, should the gold be less than 18 microns in size and /or attached electrostatically to other minerals, then the electrical system is necessary to provide both the necessary force for both electrical detachment and for deposition in the base of the cells with the lighter discharged minerals remaining in the slurry and passing out of the cell. The slurry must be constantly realigned to direct it towards the cells at the appropriate entrapment angle which is accomplished by cascading the slurry over each tray of cells from a lower smooth plate, and by the angle of the tray itself being such that the slurry catches on the far edge of the cell and is forced into the swirl. EXAMPLE OF G-FORCE CALCULATIONS FOR TABLE 1 (FIG. 8): From Force = mass x acceleration (where acceleration = velocity squared / radius) Thus Force = mass x velocity squared / radius

With 1 /2 inch diameter cells (1.25 cm diameter or 0.62 cm radius), a slurry moving 10 miles per hour or 447 centimeters per second that becomes entrapped and swirls in and out of the cell generates a G force on each gram of mass calculated as follows:

Force = 1.0 x 447 x 447 / 981 / 0.62

= 328.5 G's Note: The conditions calculated in the example are in an ideal range for a high force mini swirl (HFMS) velocity economical recovery system.

SUBSTITUTE SHEET EXAMPLE CALCULATIONS FOR TABLE 2 (FIG. 9)

@ 1 . * Weight of 18 micron octahedral gold crystal (Pictorial 2): density of gold = 19.2 grams / cubic centimeter thus, 1 cubic centimeter of gold = 19,2 grams

= 19,200 milligrams 1 cubic millimeter of gold = 19.2 milligrams

= 19,200 micrograms 1 cubic micrometer of gold = 0.0000192 micrograms since, 18 microns cubed = 5832 cubic microns

= 0.1 12 micrograms and since, octahedral crystal = 50 % of the volume of its cube then, weight of 18 miron crystal = 0.056 micrograms

Since this size of gold makes up a significant portion of the invisible gold in the world, the effect of the force exerted by an electrostatic charge is significant as the force is inversely proportional to the weight, which is extremely small resulting in a relatively extremely large force. CALCULATION OF G FORCE FROM STATIC VOLTAGE TEST It takes 4000 volts to pick up one inch of cigarette ash from a distance of one inch: or in other words, 4000 volts of electrostatic charge is required to overcome the force of gravity (1 G), for 75 milligrams of cigarette ash.

1 . The volume of a one inch 75mg cigarette ash is 0.8 cubic centimeters (800 cubic micrometers): thus its bulk weight in air is the weight of the contained air (air density of 0.0012 mg/ cubic mm) plus the weight of the ash (ash density of 2.5 mg/ cubic mm), or since: mass = density x volume

SUBSTITUTE SHEET then; bulk weight = (volume air x density air) + weight ash

= (800-75/2.5)mgxO.0012 mg/cm + 75mg = 75.924 mg Thus: the bulk density of ash in air

= bulk mass ash/volume ash = 75.924mg/ 800 cubic ul = 0.0949 mg/ cubic ul = 94.9 ug/cubic ul

2. 4,000,000 millivolts (mv) lift 75.924 milligrams ash (with a density of 94.4 ug/cubic ul) from a distance of 25,400 microns (1 ") in air.

3. The electrical force is inversely proportional to the density of the medium separating the charge, therefore: mass of ash lifted = (density of air/ density water) x force (25400 u in water) = 0.0012 mg/cc/1 .00 mg/cc x 75.924 mg = 0.091 1 mg (in water from 25.4 mm) = 91 .1 microgram (ug) in water Thus, 4,000,000 mv lift 91.1 ug of ash from 25,400 microns (um) in water.

4. As the force of attraction is directly proportional to the charged surface area, which is inversely proportional to the bulk density, the weight of gold (density 19.2 mg/ cubic ml) that can be lifted by the 4,000, 000 milli- volts is as follows: mass of gold lifted = bulk mass ash x (density ash / density gold) (25400 u in water) = 91 .1 x 0.0949 / 19.2

= 7.2045 ug Thus, 4000,000 mv lifts 7.2045 ug gold from 25400 microns (um) in water

SUBSTITUTE SHEET 5. But only 500 millivolts are generated by the HMFS system: thus the mass of gold that would be lifted in water from a distance of 25400 microns is 500mv/4,000,000mv x 7.2045 ug = 0. 0009005 ug

Thus, 500 millivolts lifts 0.0009005 ug of gold from 25400 u in water.

6. Since the electrical force exerted is inversely proportional to the square of the distance from the charge, at a distance of 0.1 centimeter or 100 microns, the 500 mv would lift: mass of gold lifted = square of 25400 microns/square of 100 microns (100 u in water) x the mass of gold lifted water at 25400 microns

= (25,400 x 25,400 / 100 x 100) x 0.0009005 = 58.09 ug (in water from 10 microns) Thus, 500 mv lifts 58.09 ug from 100 microns (0.1 ml) in water.

7. Since the weight of the average gold crystal (which has an 18 micron diameter) is 0.056 ug, the ratio of the force exerted by the 500 mill-- volts generated by the HFMS to the weight of the crystal is 58.09 / 0.056 or 1037 G's.

Thus, 500 mv exerts a force of "1037 G's" on a 18 micron octahedral gold crystal, from a distance of 100 microns or 0.1 millimeters in water.

The enclosed system as described in the following text is designed to utilize this generation of centrifugal force by thousands of mini swirls which may or may not be used in combination with electrostatic differential charging of the slurry to dramatically enhance the centrifugal force being exerted on precious metals and minerals in a high speed slurry. The key individual components may be described as follows:

Since the inner diameter of the cells are only one-half inch cubed, the system can only process ores with the water slurry containing paniculate matter no larger than one-eighth of an inch. This means that the ore

SUBSTITUTE SHEET should be either screened or crushed and/or pulverized below one-eighth of an inch so that when mixed with water in the appropriate ratios, usually less than 15 % and preferably 10 % by weight of the slurry being ore, the resultant slurry has the capability of swirling through the cells.

Should the slurry contain extremely fine to micron gold, the slurry can be positively charged electrostatically by constructing the slurry system with insulative materials, such as plastics and rubber, that tend to take on a negative charge. The slurry is then turbulently mixed with air, by generating vortexes in plastic pipes, which readily strips electrons from the water, the same process as the electrification of thunder clouds, making both the water and its contained minerals positively charged and producing voltages in the 500 millivolt range. The water alone is responsible for two-thirds of the voltage, which increases by 50% on the addition of ore (be: 365 millivolts with water going to 500 millivolts when ore is added). This suggests that triboelectricity may be generated by the ore rubbing something else, such as the air and plastics.

The high force mini swirl system is basically several arrays of cubic cells that are laid on overlapping trays at specific angles, as illustrated in Figs 2,3 and 4. The economics of processing ore requires that many tons per hour, in the 10 tons per hour range, be run which means that large volumes of slurry, 100 tons per hour, must be processed. This means that 333 pounds of ore per minute in 360 gallons of water per minute must be processed through the cells generating a high G-force. At this volume, the smallest cells that can be used to generate the highest G-force (see Table 1 ) are those with 1 /2 inch inner diameter cubes. Also at this volume, five trays each containing an array of cells 9 inches long by 30 inches wide appears to be the minimum required to ensure maximum swirl throughput by the slurry.

SUBSTITUTE SHEET The 1 /2 inch cube cells, constructed with 0.042 inch thick plastic walls, are pressed into cupped rubber belting (seven 1 /4 inch deep pair shaped cups per inch in rubber belting that is 1 /2 inch thick) and is attached to plastic trays overlaid on more of the same rubber belting. Although conventional use of gravity by sluicing usually generates a slurry running at about 7 feet per second, the addition of large amounts of air (about 50% by volume) introduced by the vortex action of the HFMS system causes the HFMS system to run in the 14 feet per second range, generating forces greater than 200G and preferably in the 300G range (see Figure 8). The trays with side plates to direct the slurry flow and containing thousands of cells are sloped at 1.5 inches to the foot to allow the cascading water from each successive waterfall to hit the far edge of the cells at just the right angle to ensure the maximum swirl to generate the maximum G-force to force precious metals and minerals to become entrapped in the cell corners and rubber cups in the cell base. This critical angle of slurry entry has been found by experimentation to lie in the range 20° to 35° to the plane of the array of cells and preferably of the order of 30°. This is attained by flowing the slurry over four inches of the smooth, flat plastic base to which the cell rubber base is attached, thereby reducing the slurry angle. The capacity for concentrate storage can be increased slightly by having a slight outward taper towards the bottom of each cell wall. This is achieved as shown in Figure 2 by reducing the thickness of the wall 29,30 toward the bottom.

The critical angle indicated at A is achieved by adjusting the flow rate relative to the angle of the plane of the array to the horizontal. Thus in the example above, the angle of the tray is of the order of 12° to the horizontal. In an example using significantly less flow, the angle of the arrays may be increased to 45° to the horizontal.

SUBSTITUTE SHEET Smaller units can be built by reducing the width of the cell tray and proportionally reducing the slurry volume to maintain the same critical parameters. For example, an HFMS system with 6 inch wide trays uses 72 gallons per minute of water and can process 55.5 pounds per minute of ore (approximately 1 .7 tons/hour). Minimizing the overall parameters of the system increases the G- force but results in smaller size ore requirements and also less ore being processed. Maximizing the overall requirements would result in ineffective G-forces being generated for the majority of the world's micron gold: however, the width of the trays should be expandable allowing, with increased slurry, for higher volume throughput.

Since the majority of the world's micron gold is less than 18 microns in size, the laws of physics that demonstrate the erosion, transportation and deposition relationship of various size particles versus the velocity of the slurry (Hjoulstrom's Diagram Fig 6) show that at one G, sedimentary particles (with average specific gravity of 2.5) will never deposit from a slurry moving 14 feet per second (or 427 cm/sec). Gold, with a specific gravity of 19.2 would need a diameter greater than 7 millimeters or have other forces, such as those generated by backwashes that produce centrifugal eddies, to cause gold smaller than 7 ml (1 /4 in) to deposit from a slurry moving 14 feet per second. The same laws of physics show (Hjoulstrom Diagram Fig 7) that 18 micron gold requires hundreds of G's to force it to deposit in the same slurry, and the gold which is even smaller requires thousands of G's. This explains why, although the HFMS recovers large quantities of micron gold (and therefore must be generating hundreds to thousands of G's), conventional gravity systems processing the same type of ore recover very little micron gold. Even cyclones producing up to 60 G's can only catch gold greater than 30 microns at this velocity. The very high G-force generated by the

SUBSTITUTE SHEET HFMS system allows for the concentration of only the densest metals and minerals, or in other words, allows for the production of very rich concentrate in the thousands of ounces per ton range that do not have to be upgraded, as is the case with most conventional gravity concentrates, in order to be refinery acceptable.

Although the hundreds of G's generated by the HFMS system explains the recovery of some of the detached 10 micron gold crystals, it cannot by itself be responsible for the recovery of the 10 micron or smaller gold as the majority of this gold is attached to the minerals contained in the ore, such as magnetite and pyrite. The vast majority of these minerals pass through the HFMS system leaving their micron gold behind in the system. Since the gold is attached to the cracks and crevices of these minerals by electrical charge, the minerals must be electrically detached from the gold. To accomplish this, the HFMS system is built to generate electrical voltages in the hundreds of millivolts range. The high HFMS G-force swirls the charged metals and minerals into such close proximity to the oppositely charged cell base that the electrical force of attraction, which is inversely proportional to the square of the distance between the two electrical charges, can rise to several thousands of G's (see Table 2, G-forces generated electrically by the HFMS system). Upon contact with the cell base, electrons are transferred to the minerals resulting in the electrical discharging of the gold from the minerals. Thus the HFMS system enables the charged metals and minerals in electrostatically charged slurries to come into close enough proximity to both generate enormous G-forces as well as electrically detach the metals from their minerals.

The HFMS system as described requires periodic process shutdowns so that the concentrate collector trays can be removed and cleaned out with water into a suitable container to remove and recover the concentrates. By

UBSTITUTE SHEET attaching the overlapping trays with hinges to the lower belting which can be wrapped around rollers, the belting and trays can be rotated allowing new trays to replace the concentrate filled trays. Water that jets from spray bars can be use to wash out the concentrate filled cells while replacement trays continue to concentrate the slurry, thereby eliminating shutdowns. APPLICATIONS AND HFMS CONFIGURATIONS

In Fig. 1 , the process for recovering free milling gold from Lode ore is diagrammed in circuit a. After passing the ore through the grizzly screen 10 to remove the oversize, the ore which passes through is transferred via conveyer 1 1 to the crusher 12 from which the crushed ore is transferred via conveyor 1 1 (circuit a) to a ballmill 13. The pulverized ore is dropped into a mixing chamber 16 to make a slurry which is directed into pipe 19 leading to the HFMS system 20, where the precious metals are concentrated by both the high G-forces produced by the mini swirls and electrostatic attraction when necessary. The concentrates are washed into container 21 after they have attained a refinery desirable level of approximately 1000 oz per ton. Free Milling Gold Recovery from Placer. Waste Rock or Tailings in Fig. 1 (b, c, and d), schematic representation of the systems is shown for treating a variety of original material such as placer gravels, mine waste dump low grade material and mine hard rock ore tailings. All three ores enter at a grizzly screen 10 to remove large rocks and boulders.

In the cases of placer gravels and tailings, the ore passing through the grizzly can be made into a slurry by either washing it through a trommel 14 (circuit c) or transferring it via conveyor 1 1 , (circuit d) to a spray bar 15 and water jet entrance and through a wet screen 18. In each case, the slurries produced

SUBSTITUTE SHEET are directed into pipes 19 leading to the HFMS system 20. The screened oversize from both systems are passed over nugget traps 17 to catch the coarse gold.

With mine waste dump also entering at the grizzly screen 10, the ore passing through is transferred via conveyor 1 1 , (circuit b) to a crusher 12 and then on to a conveyor 1 1 to a mixing chamber 16 where water is added to make the slurry which is directed into pipe 19 leading to the HFMS system 20. Mixed Ore Extraction: Free Milling and Sulfide Bearing Gold

Ores containing both free milling and sulfide gold are processed through the "a circuit". Since the majority of the sulfide gold will not detach from the sulfide mineral, the sulfides containing most of the gold must be concentrated. This means that the limited capacity HFMS system must be cleaned out frequently producing substantial amounts of concentrates which must be sent for processing through a cyanide circuit, or if rich enough, may be sent to a smelter. Many ores sulfide rich ores, that can only be modestly concentrated by conventional froth flotation, have been highly concentrated by the HFMS system. Gold Extraction in Black Sand Concentrate

Alluvial ores containing black sands which are basically composed of magnetite to which gold sometimes adheres, can be processed through either the "c circuit" or the "d circuit". Since theses ores usually contain substantial blacks (a few per cent by weight) which are also usually not amenable to effective cyanide extraction, producing large amounts of concentrates which contain the gold does not serve the end point of extracting the gold. Thus, the gold must be detached from the magnetite to which it is electrically bound. Insulating the slurry system to produce differential electrical charging serves to accomplish the detachment. The HFMS system enhances the procedure resulting in very rich refinery acceptable concentrates-.

SUBSTITUTE SHEET Copper and Gold Extraction From Porphyries Copper Tailings

Porphyries copper ores usually contain copper from a variety of sources.

Most of the copper is usually complexed with numerous sulfides while a small - metallic portion remains undetached. Since the ore grades are usually quite low, porphyry copper ores must be processed on a massive basis. This, along with multi-source nature of the ore, results in recoveries that leave substantial amounts of copper in the tailings. The froth flotation concentration- process is quite effective for some sulfides, but is quite ineffective for both the metallic copper and gold that occurs sporadically in the ores. The high G-force generated by the HFMS system is quite effective at recover- both. Toxic metals from Tailings and Soils

The most common toxic metal in tailings is mercury. Contrary to con- conventional gravity systems which break up the mercury into microscopic balls too fine to recover efficiently, the HFMS system is extremely effective at removing mercury at high volume in both tailings and contaminated soils. Other metals, such as gallium, and metallic lead and zinc can also be quickly and efficiently recovered by the HFMS system.

SUBSTITUTE SHEET

Claims

(1 ) A method of separating a selected first ore component of higher density from a particulate ore to leave a second ore component of lower density, the method comprising generating a slurry of the particulate ore carried in water, causing a flow in the slurry longitudinally of a surface from a raised feed end of the surface to a lower discharge end thereof, providing on the surface an array of cells arranged side by side across a width of the surface and along a length of the surface, each cell having generally upstanding walls defining a hollow interior which is non-circular in side elevation, an open top and a substantially closed bottom, the walls including a first wall on an upstream side of the hollow interior and a second wall spaced from the first on a downstream side of the hollow interior, directing the flow of slurry at an angle relative to an imaginary plane perpendicular to the second wall downwardly into the hollow interior to cause the slurry to enter the open top of the cell, to swirl around the non-circular interior and to discharge from the open top, collecting the first ore component in the hollow interior and discharging the second ore component from the lower discharge end of the surface.

(2) The method according to Claim 1 including inhibiting the generation of electrostatic charges between the slurry and the cell such that separation of the first component in the cell occurs solely by centrifugal forces.

(3) The method according to Claim 1 wherein the flow of slurry is arranged at a selected angle to the second wall and the second wall is spaced from the first wall by a distance such that the slurry on swirling around the hollow interior generates a centrifugal force greater than 200G.

(4) The method according to Claim 1 wherein the collecting of the first ore component includes insulating the turbulent slurry and the cells from

SUBSTITUTE SHEET the ground to induce the slurry to become electrostatically charged such that the charge on the slurry is opposite to the charge on the cell, the swirl of the slurry around the interior of the cell generating a centrifugal force sufficient to drive the first ore component close enough to the cell so that the electrostatic forces between the first component and the cell are sufficient to extract the first component to collect in the cell.

(5) The method according to Claim 1 wherein the angle lies in the range 20° to 35°.

(6) The method according to Claim 3 wherein the centrifugal force lies in the range 200G to 400G.

(7) The method according to Claim 1 wherein the angle is of the order of 30°.

(8) The method according to Claim 4 wherein the electrostatic forces are used to detach and recover microscopic metal particles adhering electrostatically to minerals where the high centrifugal force drives the charged mineral into contact with oppositely charged material resulting in an electron exchange that liberates the metal which remains in the base of the cell because of the substantial forces generated by the eddies, while the discharged lighter mineral remains in the slurry passing out of the cell.

(9) The method according to Claim 1 including causing entrapment of air in the slurry as the slurry swirls in the cell.

(10) The method according to Claim 9 wherein the volume of air entrapped is of the order of 50% of the total volume of slurry and air.

(1 1 ) A method of separating metal from a mineral in particulate form in which the metal is bonded to the particles of the mineral by electrostatic forces comprising mixing the mineral in particulate form and metal carried thereby

SUBSTITUTE SHEET with water to form a slurry, inducing an electrostatic charge onto the particles of the mineral, providing an electrode having thereon a charge opposite to said electrostatic charge on the mineral, generating centrifugal forces on the particles in a direction to cause the particles to move toward the electrode and causing the particles to contact the electrode to cause discharge of electrostatic charges from the particles to break the bond between the metal and the particles to release the metal for collection.

SUBSTITUTE SHEET