US2151175A - Ore dressing - Google Patents

Description

March 21,1939. c. E. w uE-NscH ORE DRESSING s Sheets-Sheet 1 Filed NOV. 23, 1935 INVENTOR C 169 1 [5 E26 WUfA/JC ATTORNEY I March '21, 1939. c. E. WUENSCH ORE DRESSING 3 Sheets-Sheet Filed Nov. 23 1935 INVENTOR (#4255 50/5 waf/vsc/e BY g M YW ATTO RN EY March "21 1939.

C. E. WUENSCH ORE DRESSING Filed Nov. 23, 1935 I 3 Sheets-Sheet 3 V 75 Juc'Z/an Pam a 7 7 INVENTOR 6,4424 5 m6 nz/f/vsc/l BY ay mwawfl,

ATTORNEYS Patented Mar. 21, 1939 PATENT OFFICE ORE DRESSING Charles Erb Wuensch,

Joplin, Mo., assignor to Wuensch Hetero Concentration Process Company, Wilmington, DeL, a corporation of Delaware Application November 23,1935, Serial No. 51,328

1 Claim.

' by employing gravitational forces in the presence of a heavy medium.

In the heretofore customary practice of ore dressing and alliedarts, mixtures of mineral particles having different densities have been separated by adding the mixture to a fluid of rela tively heavy density. Under such conditions the particles having a density greater than-that of the fluid tend to sink, whereas particles which are lighter than the fluid tend to float. The products thus become separated and may be withdrawn separately from different zones.

Theoretically at least, the ideal medium is a heavy fluid, such asan aqueous salt solution of high specific gravity or a heavy organic liquid such as tetrabromethane (CzHzBn). However, suchfluids are relatively expensive. Attempts have been made heretofore to replace such heavy fluids with multiphased mixtures of finely divided solids with liquids (usually called suspensions). Throughout the present specification the terms "medium and heavy medium are'used to include these multiphased mixtures of finely divided solids (such as galena) with liquids (such as water).

Due to the fact that heavy media tend to become contaminated with ore fines, etc., and due to the fact that there is a tendency for particles to settle out of the medium, they do not act as ,true fluids. These facts have been responsible for the failure of many prior proposals for separating heterogeneous mixtures of solid'fragments by immersing them in heavy media. When such media are fresh, the processes of some prior proposals arerelatively efiicient. However, attempts at continuous operations of this character have proved disappointing, chiefly, I believe, because of the failure to remove contaminating substances from the medium and to maintain the density and the consistency of the medium relatively constant at all times within the separating chamber.

colloidal gangue materials that form practically permanent suspensions in water (even in a relatively high state of dilution) has prevented the commercial application of continuous processes of this character except when there was a relatively great difference in specific gravity between the materials to be separated or when the gangue material itself may be used to make the medium.

As a result of my investigations, 1 have discovered that the separation of mixtures of solid fragments having different specific gravities is greatly facilitated, especially in a continuous process, if one or more of the following procedures are observed:

(1) The feed to be treated should be first thoroughly washed with water to remove possible contaminants, either small solid fragments or soluble or colloidal impurities. This washing step is preferably performed in a countercurrent washing or screening operation, that is to say, the feed is passed progressively over a screen or series of screens (or classifiers) to the last of which clear water is supplied. The drainage from theclear water screen is then freed of sands and used over again for washing. In other words, the clear water first comes in contact with the material which is already fairly clean while the dirtiest water is used to treat the feed as it is first introduced into the washing operation.

(2) After this preliminary washing the film of water on the fragments of feed should be substantially reducedin amount. I have found that the most advantageous way of doing this is to pass the feed over a screen onto which the heavy medium is fed. In this way the film of water on the fragments is replaced by a film of medium. Subsequent dilution of the medium in the separating chamber is prevented eifectively in this way. The amount of moisture retained on the fragments after the preliminary washing is likely to vary within wide limits, depending upon the proportion of fines present in the feed. Consequently, if this moisture were permitted to enter the separating chamber, there would be a variable dilution of the medium therein, and consequently a variation in medium density. Such dilution in a separating chamber increases the amount of circulating load of make-up medium to be handled in the circuit, and is therefore objectionable. On the other hand, it is not desirable to introduce the fragments into the chamber in an absolutely dry state because separation in the chamber is thereby impeded, and the subsequent removal of the medium from the fragments is made more difficult. In the case of coal or other minerals of trol is, however, not as desirable as the aforementioned replacement of the water film on the fragments with a film of medium.

(3) The separating medium and the fragments to be separated should be continuously introduced into the separating chamber, preferably near the top and the center of the chamber. I have also found that it is practically essential to withdraw the heavy fragments which settle to the bottom of the chamber substantially continuously together with a portion of the medium in order to secure a properly refined separation. The coarser solid particles in the medium, together with any sandy constituents of the feed, tend to ,settle out in the bottom of the chamber, thus increasing the density of the column at' this point and causing so-called crowding of the ore par- .ticles to be separated. This crowding must be prevented, 'or at least substantially offset, by

' more thoroughly discussed in succeeding parawithdrawing the material substantially continuously from the bottom of the chamber, and varying the rate of such withdrawal in response to variations in the density of the medium or vol ume of heavy material at the bottom or. the chamher. In this way undesirable crowding in the separating chamber is avoided and at the same time the density of the separating medium from top to bottom of the chamberis maintained with but slight increase from top to bottom. 7

(4) I have found it essential to so condition the medium before it is introduced into the separating chamber that substantially all ofthe sands and undesirable intermediate'sizes of particles are removed therefrom. I have also found it necessary to maintain the density of the medium at some predetermined andsubstantially constant value. In order that the medium may meet with this requirement, I introduce it into liquids to solids so as to obtain the desired predetermined density, as well as the volume being introducedinto the separating vessel.

(5) For economical operation and toprevent the handling of excessive quantities of liquid in the circuit, I have found it desirablefto drain of! the medium accompanying the concentrates and the tails or middlings remo'ved from the separating chamber before washing these products.

The medium thus drained is returned to the separating chamber after-the aforementioned conditioning.

(6) Followingthe drainage of the separated products, in order to reduce the volume wash water which must be thickened, I find that countercurrent washing of the products is necessary. This feature of countercurrent washing will be graphs. I l

(7) It is also desirable to remove sandy material from the wash water between each stage in the countercurrent washing operation of the products.

(8) To prevent an undue accumulation of objectionable colloidal constituents in the circuit I find that it is necessary to bleed of! a proportion of the overflow from the thickener or other means employed to increase the density of the medium (removed in the washing operation from the product and returned to the circuit after thickening). It is also essential to remove any oil or froth from the circuit and I find it expedient to remove this oil in a froth trap following the thickener overflow.

(9) To prevent an undue loss of valuable medium and at the same time to utilize water as completely as possible, it is necessary to maintain a. proper water balance in the circuit. That is to say, the amount of fresh water supplied to the washing operations should approximately equal the amount of ,Water removed from the circuit as entrained'moisture, plus the water which is bled out of the; circuit at the overflow of the froth trap.

These and other important elements of my discovery will become more clear if reference is made to the accompanying drawings,in which Fig, 1 is a flow-sheet of an ore dressing plant incorporating the elements of my invention, and

I .Fig. 2 is a schematic representation in section of a secondary separator of mydesign.

Referring now to Fig. '1, crushed ore of an appropriate size, say inch to 1 inch in diameter, is fed from a crushed ore storage bin 1 onto apreliminary washing screen 2, where it is washed in countercurrent by spraysfl, 4, and

5 in series. Fresh water is supplied'to the spray 5. The drain from the spray 5 is caught in a sand trap 6 and the overflow water from this sand trap is passed through a pump I into the spray 4. Similarly, the drain from spray 4 is' The preliminary screen is preferably of the vibrating type and of about 20 meshes to the inch.

The sands washed through the screen are, therefore, minus 20'meshes in size. The sands from the three traps 6, 8, and I0 are sent to a classifier l2 in enclosed circuit with a ball mill l3. -The finely ground product of this ball mill is then sent to an ore thickener II. The purpose of the initial screening operation and the aforementioned subsequent trapping and grinding operations is to remove from the feed fine material which cannot advantageously be separated in a heavy medium. The sands and slimes thus removed are thickened so thatthey may be treated by flotation or other appropriate process in the event that their value warrants recovery.

The sand traps may be' of any appropriate de- Sign.

' From the preliminary washing operation the oversize is sent to a box I! into which is also continuously introduced a portion of the heavy medium. The mixture of medium and washed oversize then passes over a screen 15 of the vibrating or conveying-type. In this way, the water film present on the washed oversize is in large part replaced by a film of medium. The aforementioned medium draining screen I5 is of approximately the same mesh as the initial or preliminary washing screen. After leaving the screen l5, the oversize now coated witha film of medium is introduced into a separating vat 18. The undersize of the screen I5 is chiefly excess medium accompanied, however, by some attrition products formed on the screen plus fine material which was not removed in the preliminary washing operation. The undersize of the screen ,-I 5 is sent to a subsequent operation hereinafter described for the removal of the foreign material and the recovery of the medium.

The separating vat I5 is preferably of conical construction, or at least the bottom of. the vat should be conical with the apex of the cone downward. Within the cone is provided a downwardly extending hollow-shaft II. This shaft is provided with blades |8, l9 and 20. The pitch of these blades may be adjusted; Means, not shown, are provided for revolving the shaft and the associated arms ata relatively low, rate of speed. The peripheral speed of the end of the blades should not exceed I50 feet per minute. The purpose of the blades is not so much that of agitation as it is to impart acentrifugal impulse to the material introduced into the cone, thus causing the tailings to pursue a spiral path from the center to the upper periphery of the cone. Within the hollow shaft I1 is a rod 2| at thelower end of which is a' float 22 which is freely movable in a vertical direction. The upper end of the rod is provided with an insulated contact 23 which engages a companion contact 24 when the float is raised a struction. A pump 42 is connected to the bottom of the secondaryseparating cone and is arranged to operate at a variable speed by means (not shown) similar to the means shown in conjunction with the primary separating cone. Material withdrawn from the bottom of the secondary tudinal compartment of a screen 43.

cone'is pumped by. the pump 42 to one longi- Medium which is drained o'itthe products on the screen classifier 28 is introduced into the cone.

43 passes into ahopper 44 and thence into a sump 45 froinwhich it is returned to classifier "28 by means of a pump 46.

As hereinbefore indicated, the medium-coated oversize is continuously introduced into the cone. At the same time conditioned medium from the This classifier is of novel construction and is more Y fully described in my copending application Serial No. 51,329, filed November 23, 1935. Briefly, this classifier comprises a cylindrical upper section and a conical lower section. At the bottom of the conical section a conveyor housing 29- is connected; This housing containsa screw conveyor 3|! which rises outside and obliquely from the bottom of the conical section to approximately the top' of the cylindrical section. The classifier is equipped with ,a centrally disposed vertical hollow shaft 3| provided with .ablfidQS 32 in the cylindrical section and with an agitator 33 ofegg-beater type construction in rod has a float 36 at its lower end which is freely movable in a vertical direction. When the float is raised a suflicient distance it closes contacts 36, 31 and permits a power source 38 to energize a solenoid operated valve 39, which opens an out let in the conveyor housing 29 positioned about mid-way up the housing.

A hydrometer 48, positioned within the classifier near the overflow level of the cylindrical section, is held horizontally by guides or pivoted (not shown) but is freely movable in a vertical direction. This hydrometer, when raised, serves to close contacts 48 and 49 and these contacts connected with an electrical circuit andapowersource (not shown) serve to open a solenoid operated valve 50 which introduces water into the sump 45, at the same time throttling down another solenoid operated valve which introduces fresh medium into the same sump. The two valves may, if desired, be operated by means of the same solenoid. A simple lever arm see-saw construction, well understood by those skilled in the art, will serve for thispurpose.

Near the upper periphery of the classifier 28 is afloat 52 which when lowered will open another solenoid operated valve 53 and introduce additional medium into the sump 45.

A peripheral launder 90 having a partition 9| in it (provided with a vertically adjustable bafile 16) surrounds the upper edge of the medium classifier. This baffle may be adjusted to regulate the amount of medium flowing to the primary separating cone.

Tailings withdrawn from the upper periphery of the primary separating cone l6, concentrates withdrawn from the bottom of the secondary separating cone 4|, and middlings taken at the upper periphery of the secondary separating cone are sent respectively to three parallel compartments in the long screen 43, which is of approxi mately 20 mesh. I

The upper portion of the screen 43, that is the portion above the hopper 44, is a drainage section. Succeeding sections of the screen are underlain respectively by hoppers 54, 55 and 56 and in these sections of the screen a countercurrent washingoperation of the tailings, middlings, and concentrates takes place. Fresh water is introduced on the outermost section of the screen, through a spray bank 13, and the drainage therefrom passes into the hopper 56 and thenceinto a sand trap 51 which is similar in construction to the sand traps 6, 8, and Hi, used in the preliminary washing operation. The overflow from this sand trap is forced by pump 58 ,into a second bank of sprays 59 in one of the mid-sections of the screen. The drainage from this mid-section passes into the hopper 55, and thence into a sand trap 60 from which the overflow is forced by pump 6| into a second bank of sprays 62. A third bank of sprays 63 is supplied with overflow water from a medium thickener 64. This overflow from the medium thickener is usually quite turbid. Drainage from the sprays 63 and 62 passes into the hopper 54 and thence into a sand trap 65. The overflow from this sand trap is sent to the medium thickener 64. The sands withdrawn from the bottom of the three sand traps 65, 62, and 51,. are sent to a classifier 66- in which the coarse sands and the medium are separated. The medium recovered in this classifier (which may be of any convenient design) is sent to the medium thickener 64. The sands from the classifier 66 are sent to the ball mill circuit |2, l3 and join the sands from the sand traps 6, 8, and I0.

Washed concentrates are recovered from the end of the screen 43, Washed tailings at this pointare sent to waste, and washed middlings are crushed to a size ranging from %.inch to inch in rolls 92 and sent back to the crushed ore bin I (for.return to the circuit).

The underflow from the medium thickener 54 is moved by diaphragm pump 61 to a surge tank 68 which feeds through the solenoid valve 5| into the sump 45.

The overflow from the medium thickener passes into a froth trap 68. This froth trap is bailled so that froth, oil, etc., are caught and removed from the circuit. At a point slightly below the overflow of the froth trap is a bleeder" 10 through which colloidal material and other contaminants in suspension may be bled oif substantially continuously, and sent to the ore thickener I I. In this way such impurities may be removed from'the medium circuit and prevented from fouling it. Underflow from the froth trap is forced by a pump H into the spray bank 63 and is there utilized for washing the concentrates, middlings and tailings.

In the froth trap is a float 12 which by wellknown means, such as a solenoid-operated valve (not shown) may be caused to regulate the volume of fresh water introduced into the spray bank 13 on the screen 43, thereby permitting water balance in the circuit.

Coarse medium withdrawn by the'spiral conveyor 30 from the medium classifier 28 may be sent to a medium grinding circuit comprising a ball mill 14 operated in closed circuit with the classifier 15.

contains heavy sulphide or ore sands which might be worth recovering (or else undesirable medium constituents) the material withdrawn by the spiral conveyor 30 may be passed over a very fine screen (say 100 mesh) before it is sent to the ball mill circuit '15. Material from which the solid constituent of the medium is manufactured (such as galena) is contained in a bin 16 and from there fed into the medium ball :mill circuit 15.

The classified product from the medium ball mill circuit is sent to the medium thickener 84.

Having in mind the flow-sheet of the process just described, the method of operation may be outlined as follows:

The feed from the crushed ore storage bin, together with returned crushed middlings, is first countercurrently washed on the preliminary washing screen 2, mixed with medium in the box I4 and passed over the screen l5 from which excess medium, together with any contaminating sands, is drained. The oversizeof the-screen l5 (now coated with medium) is introduced into the primary separator, together withconditioned medium from the classifier 28. In the primary separator the tailings, together with some of the medium, are caused to pass outwardly in a spiral path to the upper edge of the separator and are then removed and taken to the screen 43. The rough concentrates from the primary separator are continuously withdrawn from the bottom thereof, together with a portion of the medium, and pumped into the top of the secondary cone 4|. The rate of withdrawal of the medium and concentrate from the primarysecondary cone is governed by the density of the medium in the bottom of the primary secondary cone or by the accumulation of concentrate at this point. If

crowding occurs from either of these sources, the speed control mechanism 23, 24, 28, 21 increases .the speed of. the pump 25 and withdraws more material, thereby overcoming the crowding.

If,-as is'sometimes the case, the material withdrawn from the spiral conveyor 30 In the secondary separating cone the process is repeated, except that a middling product is withdrawn from the upper periphery of the cone and sent to the screen 43. A cleaned concentrate is withdrawn from the bottom of the secondary separator and is also sent to one of the parallel partitions in thc screen 43.

In the drainage zone on the screen 43 the greater portion of the medium is removed and (after automatic conditioning by addition of water from the valve 58 or of medium from the valves 5| and 53) the medium is, pumped into the classifier 28. In this classifier three automatic controls, are maintained. By means of the float 35, the segregated coarse material is withdrawn by the solenoid operated valve 39 and returned to the ball mill circuit 14, I5 where the medium is ground. Should the float 52 fall so that the level in the classifier 28 is too low to maintain a sumcient volume of flow to the medium wetting screen l5, the float 52 will cause more medium to be introduced into the circuit through the solenoid operated valve 53. Other means of control comprises the hydrometer 48 which serves to regulate the proportions of solids and liquids introduced into rounding the classifier 28 may be raised or lowered manually to control the volume of medium sent directly to the primary secondary cone I6.

The countercurrent washing system on the screen 43, which has already ben described, permits maximum washing efliciency with a minimum quantity. of water, thus reducing the volume of material which has to be handled in the medium thickener 64, at the same time permitting thebalancing of thewater used in the circuit.

Segregations of sandy material which might otherwise interfere in the, separation are rapidly removed from the separating circuit at all points of segregation, so that interference from this source is completely eliminated.

The continual bleeding of colloidal material from the circuit through the drain 10 on the froth trap prevents an accumulation of such impurities in the circuit which would otherwise foul the medium.

When, as in the case of coal, the natural slimes in the material can be utilized for making the medium, the preliminary washing step may be eliminated, but not otherwise.

In the case of coal, considerablefine coal may be caught in the sand traps 51, 62 and 85. In this case it is desirable to recoverthe fine coal at this point so that in place of the classifier 86 the apparatus shown in Fig. 2 may be substituted. This apparatus briefly comprises a cone ll which'in general is similar in construction to the medium classifier 28. A peripheral launder 18 surrounds the upper edge of the cone and is provided with a drain [9 from which the overflow watermay be sent to the medium thickener 54. A splash ring 88 is positioned concentrically inthe upper portion of the cone 11. A hollow shafted agitator and float structure I00 of the separator in Fig. 2 is similarto that of the classifier 28 and is sufliciently shown in Fig. 2. However, when the float in this apparatus rises, it closes a circuit 8| equipped with contact points 82 and 83 and through a variable speed regulator 84 increases the speed of a pump 88 which withdraws material from the bottom of the cone. Means (not shown) are provided for revolving the hollow shafted If it should prove necessary to supply medium to the separating cone of Fig. 2 to increase the density therein, this is automatically accomplished through a valve 85 which is actuated by a hydrometer 86. The additional medium is added only to increase the density in the midsection of the cone. The overflow lip serves to discharge the very dilute medium just as clear water is decanted from a thickener. In other words, the separating vat performs the function of a thickener as well as a'separating cone.

About two-thirds of the way up on the cone an outlet 81 is provided. .By means of a suction pump (not shown) fine coal which collects in the zone (near said outlet) together with medium may be continuously withdrawn from the cone, washed and recovered.

The coal withdrawn may be recovered by fine screening or by appropriate water classification in a highly diluted circuit.

The outflow from the pump 88 is refuse or "bone which may be treated in a manner similar to that for the fine coal withdrawn from the cone of Fig. 2. That is to say, it may be screened or classified so that the medium is recovered and the refuse is eliminated and sent to waste. Any very fine coal which leaves the separator of Fig. 2 through the pump 85 will automatically be eliminated from the circuit by bleeding through the medium trap 69 and the outlet 10.

Fine coal may be recovered from the medium thickener as a froth which collects in the froth trap 69. If the amount of fine coal in the circult is considerable, the amount removed as a froth may be increased by adding a small amount of oil into the wash water spray circuit which feeds into the medium thickener.

While the apparatus which I have described is primarily adapted to separation wherein the density of the medium is intermediate the density of the two products to be separated, essentially the same process may be employed with a medium which is slightly lighter than the lightest constituent in the ore. However, in such case it is necessary to substitute jigs or like devices for the separating cones which I have illustrated and the auxiliary medium control and washing stepswill be equally vital in controlling the separation.

In place of the pumps 25, I2, and 85, which I have shown for recovering material from the bottom of the separating cones, air lifts may be substituted, in which case the volume of air rather than the pump speed would be regulated in order to produce an equivalent effect.

- In place of the plurality of feed traps 51, 62,

65 which I have shown for removing the sandy material from the wash water a slightly inclined screen having a sand trap at its lower end may be substituted to provide the necessary countercurrent wash for elimination of the. sandy material, or a plurality of cones with a common spiral conveyor and valve control.

The overflow launders on the classifier 28 and on the sand traps 6, 8, I0, 51, 62 and 65 should be of sufiicient capacity to serve as surge tanks, thereby preventing the associated pumps from sucking air when sand withdrawal valves, such as valve 39, are open.

Instead of the single screen 43 provided with the longitudinal baffles, a set of three individual screens could be employed. However, for simplicity of construction, I find that the apparatus illustrated is particularly effective.

In place of the secondary separating cone 4!, it is possible to employ a jig of the conventional type which will permit the production of a concentrate and a middling. This jig, which replaces the secondary cone, may operate in the position shown for the secondary cone and using the medium; or the product may be separated in the presence of water alone after it has been screened and the medium removed by washing.

' I claim:

A process for separating heterogeneous mixtures of ore fragments which comprises first washing the ore fragments with water, then wash-- ing the ore fragments with heavy medium comprising a suspension of finely divided solid particles in liquid, introducing the resulting mediumcoated fragments together with the heavy medium into a separating chamber, withdrawing heavy fragments together with medium from the bottom of the separating chamber and introducing them into a second chamber, withdrawing heavy fragments together with medium from the bottom of the second separating chamber, withdrawing relatively lighter fragments from the top of the second separating chamber, removing medium from said relatively lighter fragments, crushing said relatively lighter fragments and returning them to the circuit with the fresh ore fragments.

CHARLES ERB WUENSCH.

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