US3033363A - Reagentizing solids for flotation separation - Google Patents

Description

y 1962 D. WESTON 3,033,363

REAGENTIZING SOLIDS FOR FLOTATION SEPARATION Filed Aug. 25, 1958 6 Sheets-Sheet l //v VENTOR DAV/o WESTON B Y WV ATTORNEYS.

May 8, 1962 D. WESTON 3,

REAGENTIZING SOLIDS FOR FLOTATION SEPARATION Filed Aug. 25, 1958 6 Sheets-Sheet 2 N VEN TOR DA v/a WES TON ATToR/vE YS.

D. WESTON 3,033,363

REAGENTIZING SOLIDS FOR FLOTATION SEPARATION 6 Sheets-Sheet 3 May a, 1962 Filed Aug. 25, 1958 m J 3 m Q 3 a m-G0 5 IEQHM N i m 1. M Q

/NVE'NTOR DAV/D WESTON BY w A TTORNEYS.

May 8, 1962 D. WESTON 3,033,363

REAGENTIZING SOLIDS FOR FLOTATION SEPARATION Filed Aug. 25, 1958 6 Sheets-Sheet 4 I /NVENTOR DAV/D WESTON ATTORNEYS y 8, 1962 D. WESTON 3,033,363

REAGENTIZING SOLIDS FOR FLOTATION SEPARATION Filed Aug. 25, 1958 6 Sheets$heet 5 ll 'lL ll .//v V'NTOR DA v/o WEsTo/v REAGENTIZING SOLIDS FOR FLOTATION SEPARATION Filed Aug. 25, 1958 D. WESTON May 8, 1962 6 Sheets-Sheet 6 //v VENTOR DA V/D WEsTo/v AT'roR/vE rs- United States Patent 9 ,9

REAGENTiZING SOLIDS FOR FLOTATION SEPARATION David Weston, 129 Adelaide St. W., Toronto, Ontario, Canada Filed Aug. 25, 1958, Ser. No. 756,949 Claims priority, application Canada Feb. 17, 1958 25 Claims. (Cl. 209-9) This invention relates to the treatment of particulate material, and in particular it relates to the treatment of such material with liquids for the purpose of beneficially affecting the subsequent metallurgical treatment thereof.

Certain materials, and in particular oxide ores and ores which in the comminuted state are associated with substantial quantities of slimes, are known to be refractory to treatment with liquid reagents. Where such materials are treated by conventional methods, it has heretofore proved necessary to subject the material to special, and

in most cases expensive, treatments of one sort or another, e.g. in the case of oxides, sulfidization to change the chemical nature of the, surfaces of the material, or egg. in the case of materials containing substantial quantities of slimes, to desliming. Such treatments are usually not entirely eflective, and in many cases place the treatment of such materials beyond economic limits.

The present invention provides a novel method whereby a substantial variety of such materials, whether refractory or not to conventional treatment processes, may be treated with liquid reagents in a simple, eiiective and economic manner. V

The present invention is based upon the surprising discovery that liquid reagents may be applied eifectively to particulate material if an airborne suspension of droplets of the reagent is comingled with particulate material While the latter is suspended in an airstream ina manner hereinafter to be described in some detail. A further surprising discovery is that the reagent may in this manner be applied selectively to certain components of the material, or may be applied substantially to all of the material at the will of an operator.

Broadly stated, the method of the present invention comprises forming an air suspension of droplets of a liquid reagent, suspending the particulate material to be treated in an airstream and comingling the suspension of reagent with the air-suspended 'comminuted material whereby to apply said reagent at least to a selected component of said material. According to one embodiment of the invention, the rate of supply of reagent is controlled so that the same is applied only to a selected component of the material undergoing treatment, and the thus treated material is then collected from the airstream in a condition in which it may proceed directly to a treatment stage in which a separation maybe effected as between the particles to which the reagent has been applied and those to which it has not.

According to a second embodiment of the invention, the rate of supply of reagent is controlled so that the same is applied to substantially all of the particles of the said material, and the material is then collected from the airstream in a condition in which .it is amenable to various treatments which will hereinafter be described and which are effective in developing a cliiferential upon the basis of which selected components of said material may be separated.

According to a third embodiment of the invention, both the rate of reagent supply and the time of contact of said reagent with said material are controlled whereby the application of the reagent to the material proceeds only to a predetermined extent, at which time separation of components of said material is effected.

3,033,363 Patented May 1 According to a still furtherembodiment of the'invention, completion of the application of the reagent is'permitted to take place subsequent to dry collection and storage thereof, and the material is then subjected to further treatments designed to develop a diilt'erential on the basis of which a separation of components may be effected. v

Various means are available for the production of an air suspension of droplets of reagent. A particularly convenient arrangement for the production of such a suspension embodies the use of a fog nozzle or other type of nozzle in which the liquid is introduced to the nozzle along with a compressed gas which atomizes it into a suspension of tiny droplets to produce a cloud eflect. Some such'nozzles which are available commercially embody simple impingement of a stream of compressed gas and a stream of liquid, while others employ spiral nozzles or rotating parts in the nozzle to assist in the breaking up of the liquid stream into atomized droplets. Another means of producing such asuspension in' thie form of a fog or cloud is to introduce the reagent as a stream of vapour which condenses into cloud-like form. Where pressure nozzles are used, the rate of supply of reagent may readily be controlled by means of valves or metering valves in the liquid line leading to the nozzle, whereas in the case of the introduction of the reagent as a vapour, control of the supply rate maybe had by con: trolling by regulation of a pressure regulator in the vapour line and by controlling the heat supply to the liquid reagent being vaporized.

The particulate material may be suspended in an airream in any conventional manner Where the material is produced in particulate form by dry comininution, the process of the invention may utilize the milling'circuit air system. In either event, the material will, at 'the time of comingling with the air dispersion of droplets, be

suspended in a rapidly moving airstrearn confined byei. suitable system of ducting leading to a collection system:-

The time of contactbetween the reagent and the ticulate material within such system may readily be con; trolled by suitable selection of the point at which the air dispersion of reagent is introduced. In some instances,

it may be desired tomaintain such contact for a longer period, and in such cases, the material collected by the collection system may either be stored. in the dry state, or subjected to re-suspension for a controlled period of time. l

As reagents for carrying out the processof the invem tion, there maybe used any materials which maybe suspended in line droplet or fog 'formin an airstream, and which produce a beneficial effect upon the metallurgical process which it is intended to carry out. As it is an outstanding feature of this invention thatit enables the application of reagent directly to particles of particulate material in the dry state, it is possible for the first time to apply to such particulate materials reagents which it has not heretofore been possible to apply except in dilute concentrations where the eiiect of such reagents may be presumed to differ greatly fromtheir effect when applied in substantially pure formdirectly to thematerial to he treated. Consequently, the present inventionopens up an entirely new field for treatment of particulate ma.- terial with liquid reagents and the reagents which may be used in carrying out the process of the invention, in addition to embracing reagents known to be effective inparticular metallurgical treatments, also embraces a vast field ofreagents which'have not previously been known to be eifective for such purposes because of the previous impossibility of applyin them to particulate material .9 in sufficiently concentrated or pure form. By the same token, it has now become possible to test and assess the metallurgical applicability of reagents on a basis involving a higher degree of predictability than has been the case heretofore by reason of the facts that the association of the reagent with the particulate material can be accomplished regardless of the affinity of a particular reagent for a particular material, and in addition the elimination of the large number of variables that occur in the normal wet methods. Consequently, a field has opened up for the development of entirely new families of reagents.

By way of example, it has proven entirely feasible to render amenable to flotation, using as the single reagent tall oil, both particles of silica and particles of hematite; despite the fact that it is well known that in conventional flotation practice tall oil has a differential affinity for hematite. In treating a material consisting of a mixture of particles of hematite and silica, such for instance as comminuted hematitic iron ore, the present invention makes it possible at the will of an operator, merely by control of the reagent rate and/or control of the contact time between reagent and material, to render substantially the entire mass of material amenable to flotation or selectively to render substantially only hematite particles amenable to flotation.

From the foregoing, it will be apparent that although the process of the invention has particular and perhaps outstanding application in the conditioning of materials for flotation, it has in addition considerable application outside the flotation field, for instance where conditioning to impart desired characteristics uniformly to a mass consisting of a mixture of dilferent types and/ or sizes of particles is desired.

In connection with the conditioning of materials for flotation, it is one of the outstanding advantages of the present invention that the presence of extremely fine particles in the material to be treated, such as are normally referred to in the flotation art as slimes, has no adverse effect. The reagent may be applied to such slime particles at least as eflectively as it is applied to particles normally considered of a more advantageous size for flotation, and when subsequently the material is subjected to flotation, the slime size particles behave in the same manner as the somewhat larger particles of material, and introduce no problem in the flotation circuit. This factor in itself is an extremely important advance in the art.

The conditions which exist in the airstream in which the material is suspended may be varied to enhance or suppress the progress of the application of reagent to the particulate material and to some extent the specific conditioning effect of the reagent. For each particular operation, conditions of airstream temperature and dew point will be found which produce the best results. Generally speaking, efiective results are obtained over fairly broad ranges of temperature and dew point, but it will be appreciated by those skilled in the art that operation close to the dew point or close to the volatilization temperature of the reagent will give diiferent results than operation in the area between these two extremes.

Another factor which may be varied is the concentration of the particulate material in the airstream. This may be varied within wide limits as may the concentration of the suspension of reagent, and for any particular operation, there will be an optimum concentration of particulate material and an optimum concentration of reagent which will lead to the most eflicient operation of the process. As is well known, there is a limit to the amount of material which can be carried by a particular volume of air, and it should be noted that operation in the region of the maximum limit can lead to operational difliculties within the system, for instance deposition of solids and the development of circulating loads. On the other hand, if the concentration is too dilute, the requisite time of contact between reagent and particulate material may be unduly lengthened.

Another factor which may be varied is the turbulence of the airstream. In general, the greater the turbulence the shorter the time that is required to bring the droplets of reagent into contact with the particles of material. On the other hand, increased turbulence requires an increase of power in the equipment which is motivating the airstream.

A further factor which may be varied is the nature of the material from which the ducting confining the airstream is composed and the nature of the collection equipment at the downstream side of the equipment. The preferred type of collection equipment is one or more dry cyclones as may be appropriate having regard to the particle sizes of material undergoing treatment. The application of the reagent is enhanced by the action of a cyclone collector, and where such enhancement is desired, collection of the particulate material by means of cyclone collectors is the preferred embodiment of the present invention.

Generally speaking, all-round efliciency of the process of the invention is achieved by operating at normal or slightly elevated temperatures of the order of 65 to F., well above the dew point with a concentration of solids of less than one pound solids per pound of air in an air system which includes one or more cyclone collectors.

Although the nature of the association of the reagent with the particulate material is at present unknown, it is believed that such association is a phenomenon which occurs over a period of time which is different for different materials, and which takes place preferentially in dependence upon some characteristic of the particulate material which has not as yet been recognized. Thus, when 1.3 pounds per ton of tall oil is applied in accordance with the present invention to comminuted hematite iron ore, it is observed that the collected product consists of substantially reagent free silica particles, and hematite particles with which is associated substantially the entire amount of tall oil which has been applied. If several times the above amount of tall oil is applied to the same material, the collected product is observed to contain as much tall oil associated with the silica on a percentage basis as is associated with the hematite. However, in this case, the tall oil becomes dissociated from the silica without affecting the association of the tall oil and hematite after a short period of wet conditioning. If instead of subjecting this latter product to wet conditioning immediately the same is stored for a period of several days, it is observed than an hour of wet conditioning is insufficient to dissociate the tall oil from the silica particles, and substantially the whole mass of material will float in a subsequent flotation operation. It appears that a comparatively short time of less than about 10 seconds, for example of the order of less than about three seconds, is suflicient for the completion of the association of the reagent with the hematite but that the association of the reagent with the silica requires a substantially longer period of time.

Where the process of the present invention is applied for the purpose of preparing for flotation materials which contain only a single mineral value, the primary object is to differentially associate the reagent used with the particles of mineral value and then to conduct the flotation or the wet conditioning and then flotation before the association of the reagent with the gangue particles has become complete. Where, however, the particulate material being treated contains a mixture of different mineral values, which must be separated both from the gangue and from each other, such for instance as is the case in many base metal sulfide ores, the process of the present invention may be applied to associate a collecting agent such as an appropriate xanthate with all of the particles by storing the collected product for a sufficient period, and then by generally conventional flotation pracone.

tice to activate the diiferent mineral constituents selectively in a series of flotation operations, the advantage of the invention in this instance being primarily that-it enables the xanthate to be applied to the slirnes which, as is well known, is something which can only be done in the wet condition by the use of concentrations of xan-thate well beyond the realm of economic feasibility.

Alternatively, it may be desired to utilize the present invention for the purpose of bringing about a chemical change in one of the components of the particulate material or on the surface of the particles thereof. For instance, in the case of copper oxide, sodium hydrosulfide (NaSH) may be used as the reagent. In such case, the sodium hydro-sulfide may be used at a rate calculated preferentially to associate substantially only with the copper oxide particles, or it may be used at a rate in which it will associate with substantially all the particles, and the particles may then be dry stored. At the same time, xanthate may be incorporated with the sodium hydrcsulfide or may be added as a separate fog or dispersion at a point downstream from. the point of introduction of the sodium hydrosulfide or alternatively the xanthate may be added in subsequent wet conditioning. The principal advantage of the method of the invention in relation to the addition of reagents which are intended to react chemically with particles of the particulate material is that such reagents may be applied to the particles at a concentration which is controlled and which is independent of the total volume of material to be treated. If the dew point of the airstream is controlled (e.g. in the manner described in application Serial No. 608,728, now Patent No. 2,916,215), the reagent may be a solution of an appropriate chemical or chemicals at. an optimum concentration for the performance of a chemical reaction upon selected par-ticles of the particulate material so that the droplets of dispersion or fog will have such optimum concentration at their point of contact with particles of the particulate material during the comingling of the reagent dispersion and the air suspension of particulate material. The chemical action may in some cases take place during the passage of the materials through the air system employed or the chemical effect may be a latent For instance, if concentrated sulfuric acid is the reagent, it may be deposited on the particles as concentrated sulfuric acid which is relatively unreac-tive, and the desired chemical reaction may then be brought about by adding a predetermined quantity of water to the collected material to bring the concentration of the acid to the optimum for attack on the selectively coated particles.

In this manner, extremely effective use of reagents is possible, and controlled concentration at the point of chemical action is achieved to an extent which is not possible where is is necessary as in prior leaching processes to use large volumes of water in order to suspend the Whole of the material in a leaching tank.

A further alternative in the case of such materials as copper oxide which are to be subjected to flotation is to use as the reagent a combination of pine oil or other frother with xanthate or another suitable collector at an appropriate rate and/ or with an appropriate contact time to selectively associate the reagent with the copper oxide particles.

In its preferred form, the process of the present invention is carried out in the air system associated with a combined dry crushing and grinding mill of the type described in my prior United States Patents Nos. 2,555,- 171 and 2,704,636. In carrying out the process of the invention in association with the air system of such a mill, the additional advantage is achieved that the reagent is applied to the particulate material while the surfaces of the particles of the latter are in freshly produced condition. This is beneficial from threeprinpical points of view. Firstly, it ensures that the surfaces of mineral particles are clean and unmodified by contaminants which may be present, and secondly it appears that a particle which has been freshly produced associates more readily with a reagent that particles which have been in existence as a particle for some period of time, and in which the interior stresses produced by the act of comminution have been dissipated. Thirdly', the particles in the air circuit of this type of mill are individually suspended in the air, and have had no opportunity to become associated with each other in agglomerations brought about by static electrical etfects, such as is usually the case with material produced in dry ball mills. a

To assist in a better. understanding of the present invention, a number of operating examples Will be given,

and the operation of various embodiments of the process of the invention will be described in association with the accompanying drawings which illustratesuitable apparatus. It will be appreciated that both the operating examples and the apparatus illustrated are purely exemplary and are not intended to be construed as a limitation of the invention, the scope whereof isdefined in the appended claims. I In the drawings,

FIGURE'l is a schematic illustrationcf-an apparatus suitable for carrying out the process of the invention where the method is not carried out in the air current of a dry comminution mill;

FIGURE 2 is a side elevation of a dry. combined crushing and grinding installation with which the present invention in some of its preferred embodiments may suitably be associated;

FIGURE 3 is a top elevation of the installation illustrated in FIGURE 2;

FIGURE 4 is an end elevation of the installation illustrated in FIGURE 2; FIGURE 5 is a schematic of the reagent supply sys tem for the installation illustrated in FIGURES 2, 3 and 4; FIGURE 6 illustrates an alternative form of reagent supply;

FIGURE 7 illustrates a suitable form of reagent supply where the reagent is to be introduced to the airstream .as a vapour;

FIGURE 8 is a functional schematic of a preferred form' of combined milling and conditioning circuit for shown in the installation illustrated in FIGURES 2, 3 and 4, or may be used in association with apparatus of I a type illustrated in FIGURE 1 where the air systemis not associated directly with a comminution unit.

Referring now more particularly to the drawings, in the apparatus illustrated in FIGURE 1 the numeral 11 indicates a hopper for the supply of particulate material which is arranged to discharge into the vertical section 12 of ducting under the control of the rotary delivery valve 13. Within the duct 12, there may suitably be disposed'conical baffle 14 which is. suitably disposed above an air inlet duct 15 so as to prevent particulate material from falling directly into the duct 15. I

The vertical section of duct 12 communicates in closed circuit with the bucket elevator 16 which recycles any of the material not picked up by the airstream. The upper end of the vertical section 12 isconnected with the duct 17 which leads to a cyclonecollector 18, which has a discharge trap 19 for collecting material and whichalso has an air discharge 20 which leads to a multicyclone fine products collector 21. The latter has a discharge trap n 22 for the discharge of fine particulate products, and

the air discharged from the multicyclone through conduit 23 connects to the fan 24 which motivates the airstream.

fresh air in order to provide for control of any build up of dust or moisture in the recirculating air.

The duct 17 may be of substantial length to provide for a desired time of contact between the particulate material suspended in the airstream and the air suspension of reagent. One or more nozzles are provided in duct 17 for the introduction of an air suspension of reagent. Alternatively, the nozzles may be provided at position 25a or 25b. The nozzles 25 or 25a and 25b are connected to a reagent supply which may suitably be of the type illustrated in FIGURES 5, 6 or 7, the nozzles themselves being of any well known type capable of producing an air suspension or fog of the reagent material.

In operation, the particular material to be treated is fed from the feed hopper 11 at a rate which is controlled by the rotary delivery valve 13 and as the material is discharged into the section of duct 12, it becomes suspended in the airstream and is carried out towards the cyclone collection system consisting of the cyclone 18 and the multicyclone 21. Any material which casually fails to become airborne is picked up by the bucket elevator 16 and recirculated. The Velocity of the airstrearn is ad justed so that the largest particles will be picked up and carried along by the airstream. Reagent suitable for the intended operation is supplied through nozzle 25, which is positioned appropriately for the carrying out of the intended operation, and the rate of reagent addition is co-related to the rate of supply of particulate material from hopper 11. The treated material is collected from the discharge traps 19 and 22.

In the apparatus illustrated in FIGURES 2, 3 and 4, wherein like references indicate like components, a combined dry crushing and grinding unit 39 is supported on the base 31 and is driven by the electric motor 32 through reducer 33 and the chain drive 34. The feed chute 35 feeds material through hollow trunnion 36 and mill product is withdrawn through hollow trunnion 37 whence it is carried through the air system associated with mill 30 by an airstream motivated by fan 38 which is driven by motor 39. Coarse mill product is collected in the coarse air classifier 40 and discharged through the trap 41 from whence it may be recirculated mechanically to the feed chute 35 for further reduction. The airstrearn and entrained product pass from the coarse classifier 44 through duct 42 to a cyclone collector 43 where a main product is collected and discharged through rotary air lock 44. The airstream and entrained fines which are of a particle size too small to be efficiently collected in the cyclone 43 pass through duct 45 into the fine products collector 46 which is of the multicyclone type, and the fine product is discharged through rotary air lock 47. The airstream, which is now substantially free of solids, passes through duct 48 to the fan 38 from where it is discharged into the air return duct 49, which is close circuited with the feed chute 35. Connected with the return air duct 49 is the bleed off duct 56 with the adjustable damper 51 which may be used to control the proportion of bleed off substantially from ()100%. The bleed off duct 50 will generally discharge to atmosphere through a dust filter or bag (not shown).

In the system illustrated and thus far described, fog nozzles 51, 51a and 5117 may be suitably mounted in the positions indicated. The said nozzles may suitably be associated with reagent supply systems of the type illustrated in FIGURES 5, 6 or 7. In FIGURE 5, there is shown a reagent reservoir 52 which is provided with a sight glass 53 and an electric heater 54. The reservoir 52 has the drain cock 55, and the delivery line 56 containing filter 57 and a circulating pump 58, which recirculates the reagent through line 59. Situated in the delivery line 56 is the thermometer 60 and connections for delivery lines 61 and 62 which supply nozzles 63 and 64. Also connected to the top of the reservoir 52 is a low pressure nitrogen line 65, which is connected to a suitable supply of nitrogen gas (not shown). The air line 66 supplies air or other gas to the nozzles 63 and 64, which air is supplied from a high pressure source of air through line 67 and pressure regulator 68.

The nozzles 63 and 64 are fog nozzles of conventional design embodying a nozzle design providing for the impingement of a high velocity stream of air or gas upon a stream of liquid, such for instance, as the type of nozzle commonly found in paint spraying apparatus. The nozzles may rely entirely upon the impingement of the gas and liquid streams to produce an air dispersion of droplets of the reagent, or the nozzles may be of the type employing rotating parts which utilize mechanical impingement and centrifugal force to enhance the dispersing action of the nozzle. Accurate control of reagent supply may be obtained by adjustment of valves 69 and 70.

An alternative form of reagent supply is illustrated in IGURE 6 where the reservoir 71 is provided with the electrical heater 72, the thermometer 73, the drain cock 74, the breather cock 75, and the sight glass 76. Reagent is circulated through the circulating line 77 by pump 78, and a controlled amount of reagent is fed to the nozzle supply line 79 through the bypass valve 80. Details of the nozzles and air supply are similar to those illustrated in connection with the reagent supply arrangement illustrated in FIGURE 5.

Most reagents of an organic nature cannot satisfactorily be volatilized because of chemical breakdown caused by the high temperatures necessary for volatilization. However, for reagents which can be volatilized, the reagent supply system illustrated in FIGURE 7 may be used wherein a reagent reservoir 81 is equipped with the heater 82, the sight glass 83 and the thermometer 84. The dclivery line 85 is equipped with the pressure indicator 86, the pressure regulating valve 87 and the expanding delivery tube 88. The vapour line 89 leads to the condenser tank 90 through the blow off safety valve 91 and the condenser tank 96 and the sight glass 92, cooling coils 93 and the safety blow tube 94. Reagent is recycled as desired from the condenser tank 90 to the reservoir 81 through line 95 by the pump 96. The heater S2 is provided with a rheostat 97 by means of which the rate of heat supply can be varied.

In operation, the reagent from reservoir 81 is delivered through delivery tube 88 as a vapour at a rate controlled by adjustment of the valve 87 and the rheostat 97. On expanding through delivery tube 88 and contacting the airstream, the reagent will condense as a cloud of finely divided droplets.

The apparatus illustrated in FIGURE 8 in functional schematic form is a preferred apparatus for carrying out the process of the invention in association with the air circuit of a combined dry crushing and grinding system. The milling circuit illustrated is essentially the same as the milling circuit described in the copending application Serial No. 608,728. In the circuit illustrated, the mill 1% discharges into the discharge duct 101 which leads to the coarse products collector or air classifier 102 which discharges a coarse product through the discharge trap 183. The coarse product discharged at 103 will in general be close circuited by conventional means (not shown) with the mill 1% for further comminution. The material which is carried past the classifier 102 is passed along the duct 104- to a cyclone collection system consisting in'the circuit illustrated of the three cyclones 105a 18511 and 1650. Each of these cyclones discharges product through the air lock discharge traps 106a, 1061) and 1660. The air which passes through the cyclones enters the duct 107 leading to the intake of fan 108, which motivates the whole airstream. The fan 108 discharges into the air return duct 109 and into the bleed otf duct 110, the proportion of bleed off being controlled by a damper 111, either manually or automatically in accordance with the teachings of the above-mentioned copending applica tion Serial No. 608,728. The return air duct passes the return air to the feed chute 112 of the mill 100.

The bleed otf duct 110 passes the bleed olf air to a venturi scrubber 113 which connects with the wet collection chamber 114, the latter discharging a slurry of collected dust down the liquid line 115. Saturated air from the Wet collection chamber 114 is drawn oil and discharged to atmosphere through the duct 116 and the bleed oil fan 117.

Material in controlled amounts is fed to the feed chute 112 for comminution in the mill 100 by the feed belt 118 While the main products of comminution which are discharged through the traps 106a, 1061) and 106a are collected in the dry storage bin 119 from whence they may be discharged at will by magnetic pulse feeders 120 and 221 into the slurry tank 122 into which the liquid line 115 also discharges. Make-up water for the slurry tank 122 may be added from the liquid supply line 123-. The slurry in the slurry tank 122 is kept agitated by conventional agitator 124 and is drawn off for further processing to slurry pump 12S and slurry line 126.

Associated with the air system described above is a relative humidity control which may suitably be of the type described in copending application Serial No. 608,728. This control which is illustrated schematically at 127 receives a sensed signal of the temperature existing in the separator chamber 114 which is a rough indication of the dew point of the air system, and a sensed signal corresponding to the temperature in the duct 107. The control 127 is arranged to maintain a predetermined difference between the dew point in the air system and the actual temperature of the air system, and when the difference between the temperature in duct It)? and the temperature 1 in the chamber 114 exceeds a predetermined maximum,

the control opens a valve controlling operation of a fog nozzle 123, which delivers a fine spray of water to the return air duct 109 until the relative humidity within the system has been raised to the desired extent.

Also associated with the air circuit is a heater 129 which also may suitably be of the type described in copending application Serial No. 608,728. Said heater is designed to heat the air in the air system, and is provided with a conventional temperature control 130 which is provided with a conventional thermostat arrangement designed to maintain the temperature in the return air duct 109 at a predetermined value.

Indicated diagrammatically at 131, 132 and 133 are nozzles arranged to deliver a fog of liquid droplets to the interior of the air system, the position indicated being convenient but illustrative only as for any particular operation. It may be found convenient or desirable to position such nozzles in positions other than those illustrated in FlGURE 8. It is to be understood also that although nozzles have been indicated in three positions a particular operation may call for the use of only one nozzle in one of the three indicated positions, or two nozzles in two of the indicated positions. In any event, the nozzles which are operative in any particular operation will be connected to a reagent supply of the type illustrated in FIGURES 5, 6 and 7.

The apparatus illustrated in FIGURE 8 and described above may be used in a number of different applications of the process of the invention. Its operation will, however, be described in connection with three principal embodiments of the invention, namely the diiferential coating of a component of a particulate product of mill 1100, the application of reagent to the entire mass of product of mill 109, and the subsequent dry and/or wet conditioning of the said product, and the application of reagents to particulate material for the purpose of producing chemical changes either of the substance of the particulate material or the surfaces of certain particles of said material, together with the subsequent dry or wet treatment of the thus treated material. It will be understood, however, that any of the other embodiments of the invention wherein the process is carried out in association with a milling unit may be carried out in apparatus of the type illustrated in FIGURE 8, and further that if the mill 100 is substituted by means for suspending an already particulate material in the air circuit illustrated, the circuit itself is adapted for the carrying out of embodiments of the process of the invention wherein the material to be treated is already in the particulate condition.

In utilizing the apparatus illustrated in FIGURE 8 for thedilferential application of reagent to a selected component of the particulate material, a typical example is in the treatment of uranium ore. In this instance, the relative humidity control 127 will be set to maintain a relative humidity in the neighbourhood of 50%, and the temperature control will be set to maintain an airstream temperature of about 100-130" F. As a substantial differential grind is usually obtained with uranium ores in a mill like the mill 100 (the uranium oxide values being of much finer grain size and also of appreciably higher specific gravity than the gangue materials) the velocity of the airstream through mill 100 is maintained at a value where a substantial percentage of combined particles will be carried out of the mill to be separated in classifier 162, which in this case is close circuited with the mill liili. Under these conditions up to of the uranium oxide content of the material may report in the minus 200 mesh fraction of the product at a comparatively coarse grind, e.g. less than 40 200 mesh.

A suitable reagent such as tall oil or fatty acid such as mono dioctyl acid is atomized through a suitable fog nozzle placed, preferably at 131. During passage through the air system downstream of the mill, the fog of tall oil, and the finely divided mill product, which is suspended in the airstream commingle, and the tall oil rapidly becomes preferentially applied to the uranium oxide particles. The exact mechanics of the application are not yet known, but the efiect is believed to derive from the fact that the droplets of reagent possess a substantial amount of free surface energy, as do the particles of material to a perhaps lesser extent by virtue of the recent formation of their surfaces in mill 100. Additionally turbulence in the airstream imparts additional energy to the particles both of reagent and of material which may appear either as kinetic energy or static electrical energy with an energy level, or potential which is higher the smaller the particle.

It is believed that the presence of this free energy associated with the particles initiates the association of particles of reagent with particles of particulate material, and that the rate at which a particle of reagent can become firmly applied to a particle of material de ends upon the nature of the material itself. With mineral particles the application appears to be substantially instantaneous in most cases, while the application of the reagent to gangue materials such as silica appears to require a much longer time to run to completion, enabling the reagent usually to be effectively removed from the gangue by wet conditioning carried out before its application thereto has been C0111? pleted.

In selecting a suitable reagent, due regard must be had to the chemical properties of the components of the partisulate material. While tall oil is an efiective reagent in many cases because of the ease with which it lends itself to flotation, and its comparative cheapness and availability, it contains abietic acid which renders it subject to sequestration by'calc-ium and magnesium containing minerals. Thus where the gangue is principally silica, tall oil is very efiective. Where, however, substantial amounts of calcite or magnesite are present in the gangue a nonionic or cationic type of reagent is to be preferred.

In the operation under consideration as it is desired to enhance the free energy level of the reagent droplets and particles of material as much as possible, it is desired to maintain the relative humidity of the air circuit as low as is practical having regard to the general ambient atmospheric conditions and the moisture condition of the ore. At the same time, it is desired to operate at a somewhat elevated temperature since a combination of low relative humidity and elevated temperature may be considered to decrease the conductivity of the airstream and hence to favour the development of higher electrical potentials on the airborne droplets and particles. For practical purposes, a temperature of about 130 F. and a relative humidity in the neighbourhood of 50% is satisfactory.

As the application of reagent to the uranium oxide particles may be presumed to be substantially instantaneous, it will be normal to eliminate the dry conditioning bin 119 and to discharge the cyclones 165a, 1651; and R50 directly into the wet slurry tank 122. The treated material discharged into the tank 122 is suitably wet conditioned for a short period in order to dissociate reagent from the gangue materials, the appropriate period in most cases being from 1944) minutes. Various dispersing agents, such as sodium silicate, may be added to increase the effectiveness of the conditioning, and if desired an orthophosphate may be added in suitable amount as a promoter to increase the etticiency of the subsequent flotation. The outstanding feature is that the uranium values, a substantial proportion of which are of a size range falling within what is normally termed slimcs, may efficiently be floated to produce a final concentrate of high grade at a high recovery.

A typical example of the use of the type of apparatus illustrated in FIGURE 8 in carrying out an embodiment of the present invention designed to apply a reagent to all of the material followed by dry conditioning thereof is the application of a xanthate reagent to sulfide or oxidized sulfied ores of mixed mineral content, such for instance as lead zinc ores, which may contain in addition appreciable quantities of pyrite and other minor mineral components. In this case, the mill 100 will be operated at a comparatively fine grind, sufiiciently line to liberate the finest of the mineral components. Once again the discharge from the classifier 1'32 will be close circuited with the mill while the main product will be delivered for dry conditioning to the dry conditioning bin 11?, which in this instance will be of a suitable size to provide a holdup time of appropriate duration to enable complete application of the reagent to all or substantially all of the material. A substantial proportion of the very finest particles will report at the wet separation chamber 114, but as such fine particles require a shorter period of contact with the reagent than the somewhat larger particles which in general report to the dry conditioning bin 119, it is not in general necessary to provide for dry conditioning of such particles. Where dry conditioning of the extreme fines is required, the bleed-off system embodying the venturi scrubber 113 and separation chamber 114 will be replaced by a multicyclone dust collector which discharges into ry conditioning bin 119 or to a separate dry conditioning bin depending upon the particular circumstances of the operation.

Once again, the xanthate reagent in this instance may conveniently be introduced as a fog at point 131. Once again, as it is desired to enhance the energy level of the particles in the airstream as much as possible, the relative humidity of the airstream will be maintained as low as practically possible, e.g. in the neighbourhood of 50%, and the airstream temperature will be maintained somewhat elevated, i.e. in the neighbourhood of 136-140" F. The material discharged from bin 119 which has been held up an appropriate time to complete application of the xanthate to substantially the whole mass of material is discharged together with the slurry from wet separation chamber 114 into the wet slurry tank 112 to which is added suflicient make-up water and reagent to prepare and condition the slurry at a suitable pH for the initial flotation operation of what may be regarded as essentially a conventional diit'erential flotation circuit designed to float selectively each of the mineral constituents in turn. During the conditioning period in slurry tank 122, the

xanthate, due to its water solubility, becomes dissociated from the gangue materials. The outstanding feature of an operation of the type described is the application of the xanthate to the slime size particles enabling their efiicient flotation and recovery along with the somewhat larger particles of mineral which are usually considered to be of a more advantageous size for flotation.

An example of application of the process of the invention in order to produce a chemical effect using apparatus of the type illustrated in FIGURE 8 is the application of a sulfidizing agent to badly oxidized sulfide ores. In this instance, a highly concentrated solution of sodium polysulfide may be sprayed as a fog at point 131 and the relative humidity in the system will be maintained by appropriate setting of control 127 at as high a value as is practical, for instance in the region of to At the same time, as it is desired that as little evaporation of water should take place as possible from the drop let suspension in order not to cause precipitation of solid sodium polysultide, the heater 129 will not be used and the temperature of the airstream will be maintained at as low a value as possible. The association of the sulfidizing agent with the mineral particles may be presumed to take place extremely rapidly and preferentially on the particles of oxidized minerals. Where such association is sufiiciently rapid, a fog of a suitable xanthate may also be introduced to the air system at point 133, and the collected treated material will be held in bin 119 for a period of dry conditioning suflicient to enable the complete association of the xanthate with substantially the whole mass of the material. The material is then discharged into slurry tank 122 where suitable conditioning agents and frothers are added at a controlled pI-I appropriate for the initiation of a diiferential flotation operation of generally conventional character designed selectively to activate the diiferent mineral constituents of the material successively in the usual way. The oustanding feature of this embodiment of the invention is that the sulfidizing agent may be applied to the oxidized particles at an extremely low rate, and at a concentration productive of an extremely rapid and complete chemical transformation which does not add to any substantial degree to the moisture content of the particulate material. The product treated in this manner is transformed from a product which under conventional methods would be extremely difficult, if not impossible, to concentrate by flotation into a material which behaves like the readily fiotable sulfide ores.

In order to compare the metallurgy obtained through use of the present invention with that obtained using standard methods tests were conducted on two types of hematitic iron ores from the State of Michigan. In order to have a direct comparison, on the first ore standard tests for optimum metallurgy were firstly obtained by wetting the material with water following dry grinding and adding the reagents to the pulp. The second standard was a wet ground ore with the reagents added to the material in pulp form. As is a well-known factor in the art, the first important step is to normally make What is termed a rougher concentrate, rejecting as much of the waste material as possible with the lowest possible loss in the valued constituent, or alternatively, where the material contains more than one valued constituent, to float as much as possible of the most readily flotable mineral and take it in the so-called rougher concentrate form to a separate circuit. For a direct comparison, these tests are compared as closely as possible on the rougher metallurgy. In order to compare the standard tests with the process of the invention in preparing material for use in the following examples which illustrates its application, the material was dry ground under the same set of conditions as the standard test with the only basic change made being in the addition of the reagents to the air stream at various places under varied conditions and in a finely divided liquid state.

13 EXAMPLE I Standard Tests Ratio of rougher tailing rejection per 1.0% iron loss Percent Weight rejected in Method of material preparation Method of adding collector Assay of rougher tailing iron Percent iron loss rougher tailing Wet ground.-- To pulp". 15. 9 .4 1.65 9.5: Dry grounddo 16.4 .76 1. 70 9. 6:

cod

In the case of the wet ground pulp the head assay was 41% as against 37% for the dry ground material. All of the comparative testing on the dry activated material in the following examples was from the same batch of ore that was used for the fdry ground sample in this test.

EXAMPLE II Comparative Testing Results With Dry Activated" Prodact Illustrating Basically'Difierential Activation of Constituents in Ore, and Near Complete Initial Activation of All Constituents In bearing out the inventors new concept in flotation, that is, selectively coating particles, or coating basically the majority of the particles and then deactivating the more weakly coated material, the following tests show the comparison of how the weight rejection with conditioning time diminishes with the present normal method of addition of reagents, and how it increases with the new concept of, let us say, de-activation after activation in the air system, and showing an increased rejection with time factor of conditioning after activation.

The standard test on the dry ground material in Example I was conducted with 25 minutes conditioning time after the addition of reagent. Other tests were at 2, 5, 10, 15 and 20 minutes conditioning time respectively, and gave the following results:

Percent weight rejected in rougher tailing Assay of rougher tailing iron Method of material preparation Method of adding collector Time of conditioning, mins.

Dry ground To pulp--.

cent:

[ONION :000

are

This series of tests show the continuous activation of both the iron and the waste rock as the period of conditioning time is increased. The amount of collector used was the same in all tests, and the rougher flotation was of approximately two minutes duration.

The following tests were carried out activating the dry ground material according to the inventors teachings by finely dividing the collector in high pressure air nozzles to form a visual cloud effect, and feeding it in a nozzle to the airstream at the feed hopper of the comminution unit and one nozzle to the airstream at the classifier for the 0 mins., 2.0 mins., mins. and mins. conditioning tests. The 2-minute test was run with one spray at the feed chute only and reduced reagent collector, which was a tall oil, in all tests. The collector was pre-heated in a tank to 200 degrees F.

Percent Time of weight condirejected tlonlng, in

rougher tailing Method of material preparation Method of adding collector mms.

To air stream of commi- 0 nution system in 2 o finely divided form, undiluted with any 15 other materials. Heated to 200 F.

Dry ground..

In all of these tests the rougher flotation time was approximately 2.0 minutes in a neutral circuit, and with the exception of the 20-minute conditioning time test, the amount of reagent used was 6.0 to 10.0 pounds per ton ore.

This series of tests confirms the differential coating of nearly the entire mass. It will be noted that up to 2 minutes conditioning time, over 90% of the total mass of material was floated. In spite of this factor the maximum amount of iron loss in the tougher tailings assayed but 5.83% from a head value of approximately 37.0%. If differential coating of the particles had not taken place, the rougher tailings should have analyzed the same in iron as the head values, that is, approximately 37% iron.

The second outstanding feature of these tests is the increase in rougher tailing rejection up to 15 minutes conditioning time, with 20 minutes being approximately the same as the 15-minute period. A new factor would seem to take over at 20 minutes where the greater percentage of the waste rock under certain conditions drops out on the first cleaner stage with but a low loss in iron values, allowing the rejection of this first cleaner stage as a final tailing along with the rougher tailing.

It will be further noted that at the comparative amoun of Weight rejection between the two series of tests, at 20 minutes the weight rejection is the same, that is, 19.0%, while the iron analysis of the dry activated product was only 2.76% iron as against 4.60% iron by current flotation methods. This decrease in iron loss is equivalent to 1.84 -X lilo-40% This illustrates one of the important metallurgical advantages in increased recovery of the valued constituent by the use of the inventors new concept. Again, there is a continued increase in tailings weight rejection up to 15 minutes conditioning time with a continuous decrease in iron loss per unit of tailings rejection up to 20 minutes conditioning time. This indicates either dissolution of the collector on the waste material particles or migration by other means from the surfaces of the waste particles to the surfaces of the valued constituent.

EXAMPLE III Testing Programme to Illustrate Selective Activation of Ore Constituents In this series of tests the collector reagent was reduced to amounts where selective coating of the valuable iron constituent of the ore was achieved according to the inventors new teachings. In the previous tests, part of the air was re-circulated to the mill. In this series of tests all re-circulated air was out 01f and the system was operated as an open circuit with the fresh air entering the feed hopper and finally discharging to atmosphere directly from the main fan, with none of this air re-circulated to the mill, and thus a complete loss ensued of any reagent that was not deposited within the system on its initial pass-through.

The nozzles on the discharge side of the mill were out OE and the total reagent supply was through a single nozzle at the feed hopper spraying the reagent into the air stream at this point in cloud form and pre-heated in the reservoir tank to approximately 200 degrees F.

In this series the reagent was varied from 1.3 pounds to 2.0 pounds per ton of ore treated, the 1.3 pounds being considered, under conditions of pilot plant operation, to be close to the minimum to coat all of the iron particles, and the 2.0 pounds being considered in excess of the requisite amount. All tests had a rougher float time of approximately 2 minutes.

1.: 1 Time of Combn. Percent Assay of Reagent Frother condirougher and weight rerougher Percent Ratio of rougher lbs/ton of ore to float tioniug, cleaner jected in tailiug loss tailing rejection lbs/ton mlns. tailing rougher iron or iron per 1.0% iron loss tailing 1. 3 None 30 No 25. 6 2.91 2.0 12. 8:1 1. 3 0.15 30 Yes 31. 3.18 2. 6 11. 9:1

Ore wet taken from outside 1.3 fl. 45 35.1 2. 93 2. 9 12.121 1.6 0.15 30 18.6 3.13 1. 5 12.411 1.65 0. 1O 45 32. 2 3. 40 2. 9 11. 1:1 2.0 None 45 29. 5 2.91 2.3 12. 8:1

1 Slightly acid circuit as against neutral for above tests.

In comparing the metallurgical results of this series of tests with the standard, we note that in the standard we were able to reject 16.4% by weight of the original ore assaying 3.76% iron. In the two 45-minute conditioning tests of this series using 1.3 and 1.65 pounds of collector per ton of ore respectively, we were able to reject approximately twice the weight in the rougher tailings combined with the first cleaner tailings, that is, 35.1 and 32.2% by wei ht respectively, and assaying lower in iron, that is, 3.18% and 3.40% iron as against 3.76% iron in the standard.

In the standard test the first cleaner tailing assayed 10.28% iron and it would therefore have been impossible to combine it with the first cleaner tailing as a reject to waste.

The results of these tests show that not only will a higher recovery of the valued constituents of the ore be achieved by the inventors new concept, but also greatly improved selectivity is achieved with a resultant higher grade of concentrated mtaerial.

In comparing the results of the Dry Activated products from the use of varying amounts of primarily, reagent collector, it will be noted that the most outstanding metallurgy was obtained in the test using 1.3 pounds of collector per ton of material treated, with 0.15 pound of frother to the fioation cell and using 45 minutes conditioning. In this test 35.1% by weight was rejected in the rougher tailing assaying but 2.93% in iron.

Considering that this was run under open air circuit conditions, that is, with no air returned to the mill once it passed through the system, and thus total loss of any reagent that remained in the air stream, and also that under the conditions of pilot plant operation approximately three times the volume of air per unit of solid treated was used as compared to the larger operational units, thus the figure of 1.3 pounds of reagent per ton of material treated is probably low in comparison to the amount now required in current methods of usage.

EXAMPLE IV Dry Condition of Dry Activated Material In the comparative work carried out in the foregoing tests the original sample was prepared by spraying the reagent collector in a cloud condition through the nozzle at the feed hopper of the comminution unit and one nozzle to the classifier with the reagent pro-heated in the reservoir tank to 200 degrees F. A test was run on the product the same day and shortly after its production from the comminution-activation system. A large sample of the remaining product was stored in a dry open drum for a period of five days and then again tested.

As previous work had shown that with prolonged conditioning time an increased rejection in the rougher tailings could be expected, particularly if the first cleaner tailing was low enough in iron content to be combined with the rougher tailing for rejection. For this reason the first test on this stored product was with a conditioning time of one hour. Surprisingly, practically the complete mass of material floated, and again very little was dropped in the first cleaner tailing, showing that the whole mass had become activated by the collector during its dry storage.

To check on the conditioning, the time of conditioning was reduced to 20 minutes in an acid circuit which in previous work produced much more severe in its de activation properties than the neutral circuit, and thus an appreciably high weight of rougher tailing rejection would be expected. Again, very little weight was rejected in the rougher or cleaner tailings, with the nearly whole mass floating and thus again confirming the near total heavy activation of all minerals present in the ore. The results of these tests were as follows:

This test is included to indicate firstly that the application of reagent takes place over a period of time depending upon the nature of the material being treated. Whereas the previous tests indicate that application of the reagent to mineral particles is substantially instantaneous, being complete by the time the material has reached the collection system of the air circuit (a time which is of the order of three seconds), particles of silica or other gangue materials do not associate with the reagent as quickly, and the application of reagent to them requires a substantial period of dry storage of the treated material. Once application of the reagent has been completed, however, it appears that the association of the reagent and silica or gangue particles is a strong one. Although it is not necessarily desirable to activate both the values and the gangue in the manner illustrated in this test, there are many instances where it is desired to associate a reagent with the whole mass of material. An example of this is in the flotation of a copper oxide mineral using xanthate'. As is well-known in the art, it is difiicult to activate the surface of a copper oxide mineral with xanthate; normally the host rock is siliceous. In such a case the material could be ground in a dry comminution unit and activated by the addition of the Xanthate to the air stream, coating, say initially, nearly all of the particles, or alternatively, selectively, according to the inventors new teachings. The material could then be stored in bins Where the chemical action could take place between the surfaces of the copper oxide mineral and the Xanthate, while coating on the silica particles would remain a physical one and once introduced into the wet flotation stage would quickly dissolve,

17 and thus only the chemically activated coating on the copper particles would act to enhance flotation of the copper oxide minerals. Further, steam may be passed through the material in storage or in a semi-fluid bed to produce further effects upon the flotability together with the de-activation of the silica even before the flotation process.

EXAMPLE V Efiect of Spraying Reagent Collector at Room Temperature and on Discharge Side of Comminution Unit and Classifier Only In Example II all of the tests (with the exception of one) were with one spray to the feed hopper air stream of the comminution unit, and one spray to the classifier.

In all cases the reagent collector was heated to 200 degrees F.

In Example III one spray only was used to the air stream in the feed hopper of the comminution unit, and with the reagent collector heated to 200 degrees F.

Example IV was the same as the main system used in Example II. In this example two sprays were used above the classifier outlet feeding into the duct leading to the cyclone and multicyclones. As no air was returned to the comminution unit, no reagent collector passed through either the comminution unit or the classifier. Further, the reagent collector was unheated, being fed at room temperature. As in all tests, unless specifically mentioned, the conditioning and rougher flotation was carried out at tap water pH which was nearly neutral varying from between 7.0 to 7.2, and the rougher flotation time 1 Including first and second cleaner tailings.

As can be readily seen, there is practically no difference in metallurgy in comparing this series of tests with Example III. To further check the selectivity of the reagent collector under the conditions of this example, 2.2 pounds of reagent collector per ton of ore was sprayed through the two nozzles above the classifier in an unheated condition. The product as produced by the circuit was conditioned for two minutes only and floated for 2 /2 minutes. The rougher tailing was 19.0% by weight and assayed 5.44% in iron. As the head value was 37.6% iron, this test showed excellent selectivity with a comparatively large weight reject for but 2 minutes conditioning time.

The following comparative test was carried out close to what was considered the minimum reagent collector requirement.

Rougher tailing Lbs. Condireagcnt per tioning 7 ton ore time, Percent Assay,

mins. weight Fe Example In for comparison This comparative test would indicate that when'using reagent collector close to the minimum requirements either the longer time factor of adding it ahead of the comminution unit drum or a factor or factors between the feed hopper and classifier are of benefit in the activation of the particle surfaces.

It will be noted in Unis series of tests that the equipment involved in the activation of the air-borne material consisted essentially of the two sprays mounted in the intake duct of the cycle, the reagent collector supplied in the form of a visual cloud by means of pressure through an atomizer-type nozzle, a cyclone solids collector, and a fan. The product from the multitubular cyclone collector was not used as part of these tests.

In all of the series of testing so far covered, the minimum amount of material in this product was 0.5% and the maximum 2.2%. As this product assayed in iron but approximately two-thirds of the head value of the material, it represented an iron loss of 0.33% to 1.47%, or an average of 0.9% which can be considered negligible on the value of this material.

EXAMPLE VI Effect of a Dispersant on Particles Activated for Flotation by the Inventor's New Teachings The dry activated products in this programme were prepared by using one nozzle only directed into the feed hopper airstream of the comminution unit. The reagent collector was fed to the airstream at room temperature. In the first test the dry activated material was conditioned for 25 minutes, then 0.10 pound per ton of ore of sodium silicate was added to the conditioner and conditioning continued for 5 minutes. The object of .this test was to study the effect of the dispersant after a period of deactivation of the waste material.

In the second test 0.25 pound of sodium silicate was added to the conditioner at the beginning of the conditioning cycle, and the pulp conditioned for 30 minutes. The object of the test was to study the efiect of the dispersant on the selectively coated dry activated product.

The product used in the third comparative test was activated by the use of two nozzles in the discharge duct airstream of the comminution unitjust above the classifier.

In the fourth comparative test one nozzle was used in the feed hopper airstream of the comminution unit, and the first and second cleaner tailings were combined with the rougher tailings to give approximately the same weight rejection. 7

The maximum difference in weight rejection of the four tests is 1.3%, and for this reason the figures are within a reasonable range for direct comparison.

These results would indicate that once the waste material or the desired material for rejection has been deactivated according to the inventors teachings, a dispersing reagent is more effective. vIt will be noted that in comparing Test 1 to Test 3 the reduction in iron content of the rejected material is 1.08% or This is an appreciably high increase in recovery of the valued constituent and particularly as compared to the activated product without de-activation first where two and one-half times the amount of dispersant was required to give approximately the same weight rejection, and with a higher iron loss although still lower than in the comparative tests without dispersant.

EXAMPLE VII Use of Mixed, Diluted and Emulsified Collectors for the Dry Activation Process According to the Inventor's Teachings In the testing work so far recorded, pure reagent collector, that is, undiluted with any other substance or mixed with any other liquid, has been used. It was fed into the air system of the comminution unit in a finely divided liquid condition, visually resembling a cloud effect and both at room temperature and preheated to approximately 200 degrees F. Further, it was introduced into the airstream of the circuit at the intake and discharge side of the comminution unit concurrently, and also at the intake side alone of the comminution unit and the discharge side alone of the comminution unit. It was also introduced in the air classifier and on the upstream air side of the classifier.

In this series of tests the reagent collector was diluted with water and partially emulsified. The following mixture was used:

Tall oil-One part (1) Water-Three parts (3) Emulsifying agent-One twenty-first part In the following tests the reagent mixture used was 7.6 pounds per ton of ore, or equivalent to approximately 1.95 pounds of pure tall oil.

It was placed in the airstream of the comminution system with one nozzle at the feed hopper location and two in the duct on the upstream side of the classifier.

In Test No. 1 the Activated Product was removed from the comminution unit conditioned but 2 minutes and floated for 2 minutes.

In Test No. 2 the Activated Product was conditioned for 30 minutes and floated for 2 minutes.

In comparing Tests No. l and 3, it is obvious that appreciably less equivalent diluted reagent is required to activate the mass of material than the pure reagent. In comparing Tests No. 2 and 4 however, it will be noted that the pure reagent gave very much improved recovery of the valued constituent.

The analysis of this data would indicate that the water diluted reagent shows much less selectivity than the reagent in pure form.

EXAMPLE VIH "Dry Activation with Reagent Mixtures and Emulsions This series of tests was carried out on the second type of hematitic iron ore. It was an extremely fine-grained type of material with the silica being in very fine dissemination. It was considered rnost diflicult to float by present known means and desliming was considered a necessity. For these reasons no attempt was made to arrive at a standard using currently known methods. Although the grind used in these tests was considered a fine grind and showed approximately of the product reporting in the cyclone discharge and 15% in the multi-cyclone dis charge, the fineness of the grind was still too coarse for optimum metallurgy.

From past experience the inventor would judge the multi cyclone product to average less than 5 microns in size with at least 40% of this product less than one micron in size. In the following tests, no desliming was carried out prior to flotation and the cyclone and multicyclone products were mixed in their direct proportions of production (with the exception of Tests 1 and 2) for the flotation tests.

EXAMPLE IX Tall Oil and Fuel Oil Mixtures In Test 1 a reagent mixture of one tall oil to two of fuel oil was used and was fed into the air system with one nozzle at the feed hopper and two nozzles in the duct on the upstream side of the classifier. The combined reagent was fed in excess and at room temperature. Conditioning time was 2 minutes in a neutral circuit and rougher float time was 2 minutes in a neutral circuit. Cyclone product only was used to observe the activation effect on the coarser fraction of the product.

Test 2 was a duplicate of Test 1 with the exception that multicyclone product only was used to observe the activation eitect on the finer fraction of the product. In addition, the reagent collector was reduced to 3.8 pounds per ton of ore and the conditioning time was increased to 8 minutes.

Test 3 used the same reagent mixture and amount as in Test 2 with the treated product being in proportion to its production from the comminution unit, that is, 85.4% cyclone and 14.6% multicyclone. The conditioning time was NOTE.-Calculated head-34.8% iron.

With the rougher concentrate representing less 11.9 or 88.1% by weight, nearly all of the material must have been activated though still differentially, as the rougher tailing analyzed but 12.72% iron with a head value of 34.8% iron.

TEST 2 Percent Analysis, Percent Product weight Fe distribution, Ie

Rougher tailing 6. 4 4. 21 0.8 Cleaner tailing 5. 2 4. 29 0. 6 Ito-cleaner concentrate S8. 4 39. 99 98. 6

Nora-Calculated head-35.8% iron.

This test showed near complete activation of the entire mass although still differentially, as the rougher tailing analyzed but 4.21% iron with a head value of 35.8% iron.

NOTE.Calculated head38.0% iron.

The analyses of the two screen fractions on the rougher tailings illustrate the fact that too coarse a grind was being used for optimum metallurgy.

EXAMPLE X Efiect of Emulsion In this series of tests the following emulsion was used at the rate of 26.20 pounds per ton of ore.

Lbs.

Tall oil 1.99 Fuel oil 3.98 Kreelon 0.28 Water 19.95

Total 26.20

In all tests the cyclone and muiticyclone products were mixed in their produced proportions from the comminution unit, that is, 84% cyclone product and 16% multicyclone product. In both tests the conditioning and rougher float was in an acid circuit and the cleaners at a pH of and 4.

Test 4 had 45 minutes conditioning at 70% solids, two minutes rougher float, and Test 5 and 45 minutes conditioning at 50% solids and a two-minute rougher float.

TEST 4 Percent Analysis, Percent Product Weight Fe distribution, Fe

Rougher tails..-. 26. 8 13.18 10.0 Cleaner tail N0. 1 13. 3 16. 78 6. 3 Cleaner tail No. 2 8.9 21. 98 5. 5 Cleaner tail No. 3.. 6. 3 28. 65 5.1 Cleaner tail No. 4....-- 4. 8 36.00 4. 9 Re-cleaner concentrate 39. 9 60. 36 68. 2

Norm-Calculated head-35.35% Fe. TEST 5 Percent Analysis, Percent Product weight Fe distribution, Fe

Rougher tails 39. 2 17. 77 19. 4 12. 7 18. 69 6. 6 7. O 28. 19 5. 5 4. 2 36. 23 4. 2 3. 3 48. 35 4. l 33. 6 64. 50 60. 2

Nora-Calculated head-36.0% Fe.

EXAMPLE XI Efiect of a Pure Tall Oil-Fuel Oil Mixture This series of tests was run with a pure mixture of tall oil and fuel oil. The ratio was one of tall oil to two of fuel oil. The total amount of mixture used was 6.0 pounds per ton of ore treated, or 2 pounds of tall oil and 4 pounds of fuel oil. This reagent mixture was fed at room temperature to one nozzle in the feed hopper airstrearn and through two nozzles in the comminution discharge duct on the upstream side of the classifier. Test 6 had 60 minutes conditioning time and Test 7 had 90 minutes conditioning time. Both had 2-minute rougher floats.

TEST 6 Percent Analysis, Percent Product weight Fe distribution, Fe

Rougher tail +65 mesh-... 3.0 15. 49 1. 3 Rougher tall 65 mesh.- 18. 7 7. 21 3. 7 Cleaner tail N0. 1 11.4 11.20 3. 5 Cleaner tail No. 7. 5 17. 26 3. 6 Cleaner tail No. 3--. 6. 3 22. 55 3. 3 Cleaner tail N0. 4--- 3. 4 28. 69 2. 7 Cleaner tail No. 5 2. 9 34. 21 2. 7 Re-cleaner concentrate 47. 7 60. 21 79. 2

Norn.0alculated head-36.3% Fe.

Using the rule-of-thumb method of 50% of the cleaner tailings in a closed circuit reporting at the re-cleaner concentrate grade, that is, 60.21%, the calculated recovery would be:

79.2 plus /2 X 15.8) =79.2+7.9=-- 87.1%

NOTE.Calculated head-36.1% Fe.

Calculated recovery at grade of 63.2% Fe-- It is pointed out that although the invention is primarily applicable to flotation, it is not limited to this process alone. It is accepted in the art that in some forms of dry concentration, such as dry magnetic or electrostatic, one of the greatest weaknesses is the flocculation of particles following either dry or wet comminution. In dry comminution particularly, this is attributable to a static charge that is carried on the finer particles. By coating the particles according to the authors invention, the formation of such a static charge following coating of the particles would be minimized. Again, in wet cornminution ultra-fine particles are produced which are in the colloidal size range and as colloids would tend to carry an electrical charge and thus tend to flocculate and again be detrimental to such a proccss as wet magnetic concentration, entraining fine particles of iron which, in effect, if attracted by the magnetic field will bring with them flocculated particlesof waste rock with which they are coated and form part of the mass and tend to lower the grade of concentrate, or alternatively, if sufliciently within the mass of waste material not attracted at all, and thus represent a loss of valuable constituents. Again, where activation of the solids material is accomplished in an airstream or in a dry cornmin-ution circuit accordingto the invention, it may be desirable to regrind, either wet or dry, part or the whole of the product where complete liberation of the minerals can only be obtained in a finer state of sub-division. It is accepted in the art that to successfully float a particle only a small percentage of its surface need be activated. Thus, when such particles go through a re-grind stage, on the law of averages part of the original activated surfaces of the particle will remain and would still result in appreciably improved metallurgy over what is presently known to the art. Y

Although certain specified reagents are illustratedin the 23 examples in the pure or undiluted form, in mixed pure form, in diluted and emulsified form, the invention is in no way limited to these reagents, as the invention is applicable to not only practically all reagents known at present that can be placed in liquid form, but will also bring about the development of whole new families of reagents which will be more economically applicable than the current used reagents in view of the ability of the invention to apply them successfully to substantially any material in airborne particulate condition.

Further, in such potential applications as either Wet or dry magnetic separation and such processes as electrostatic separation, not only can present known reagents be used to coat the particles to nullify electrical charges, but also it will probably result in the development of new, more efiicient and probably cheaper reagents for use in these fields and thus prove of benefit to the applicable industries.

It will be noted that in the comminution equipment used for part of this work, one series of tests used the so-called closed air circuit in which the air is drawn in through the intake side of the unit and drawn out through the discharge side of the unit, the solids particles removed in cyclonetype collectors, part of the air returned to the intake side of the unit and part discharged to atmosphere. This comminution unit was used for ease of testing and the inventor would like to make it clear that the invention is in no way limited to the type of dry comminution unit wherein air or some other gaseous media is used to place the material in a total or partial airborne condition. For instance, a type of system may be used where the finer fraction of the material is removed from the comminution unit by air and the coarser fraction by gravity. In addition, a type of comminution unit may be used where air is forced in at the discharge side of the unit and out through the discharge end.

In addition, material already in a comparatively fine state of sub-division, such as beach sands or fine, clayey types of deposits, may not require any comminution unit. In such a case the material may be placed in an airborne or partially airborne condition in apparatus of the type illustrated in FIGURE 1 and the reagent or reagents added to the airstream prior to or after the material is placed in such a state.

What I claim as my invention is:

1. A method of treating particulate material with a liquid reagent which comprises; forming an air suspension of droplets of a liquid flotation reagent; suspending the particulate material in an airstream, commingling the suspension of reagent with the air suspended particulate material, whereby to apply the same to at least a selected component thereof, and collecting the treated material and subjecting the treated material to flotation.

2. A method of treating particulate material with a liquid reagent which comprises; forming an air suspension of droplets of a liquid flotation reagent; suspending the particulate material in an airstream, commingling the suspension of reagent with the air suspended particulate material, whereby to apply the same to substantially all the particulate material; collecting the treated material; wet conditioning the collected material to remove the reagent from a selected component thereof; and subjecting the conditioned material to flotation.

3. A method as defined in claim 2 wherein a dispersing agent is added during the wet conditioning.

4. A method of treating particulate material with a liquid reagent which comprises; forming an air suspension of droplets of a liquid flotation reagent; suspending the particulate material in an airstream, commingling the suspension of reagent with the air suspended particulate material, whereby to apply the same to at least a selected component thereof; collecting the treated material; subjecting the collected material to wet conditioning; and then subjecting the conditioned material to flotation.

5. A method of treating particulate material with a liquid reagent which comprises; forming an air suspension of droplets of a liquid flotation reagent capable of chemically reacting with a component of said particulate material; suspending finely particulate material in an airstream, commingling the suspension of reagent with the air suspended particulate material, whereby to effect a chemical reaction between said reagent and a selected component thereof, collecting the treated material and then subjecting the treated material to flotation.

6. A method as defined in claim 5 wherein the reagent is an aqueous solution of desired concentration and the relative humidity of the air is controlled to minimize evaporation of said air suspension of droplets.

7. A method as defined in claim 5 wherein the reagent is a sulphidizing agent and the particulate material is produced from an oxide copper ore.

8. A method of treating particulate material with a liquid flotation reagent which comprises; forming an air suspension of droplets of a liquid reagent capable of having a chemical efiect upon a component of said particulate material; suspending particulate material in an airstream, commingling the suspension of reagent with the air suspended particulate material, whereby to effect a latent effect upon a selected component thereof, and collecting the treated material for the subsequent flotation thereof.

9. A method as defined in claim 8 wherein the reagent is concentrated sulphuric acid.

10. A method as defined in claim 8 wherein the material is a base metal ore and the reagent is a xanthate.

11. A method as defined in claim 10 wherein the collected material is dry stored to permit the development of said latent efliect.

12. A method of treating particulate hematite ore with an oily collection agent therefor which comprises; forming an air suspension of droplets of a hematite oily collection agent; suspending the particulate ore in an airstream, commingling the suspension of collection agent with the air suspended ore, whereby to apply the same to at least the hematite particles contained therein, collecting the treated material and then subjecting the collected material to flotation.

13. A method of treating particulate hematite ore with tall oil which comprises; forming an air suspension of droplets of tall oil; suspending the particulate ore in an airstream, commingling the suspension of tall oil with the air suspended ore, whereby to apply the same to at least the hematite particles contained therein, collecting the treated material, wet conditioning the material and then subjecting the collected material to flotation.

14. A method as defined in claim 13 wherein the rate of supply of tall oil is controlled to apply the tall oil to substantially all of the ore.

15. A method of treating particulate material with a liquid reagent which comprises; forming an air suspension of droplets of a liquid flotation reagent; suspending the particulate material in an airstream which is maintained at a temperature of from about 65 to F., well above the dew point, in an amount of less than one pound solids to one pound of air; commingling the suspension of reagent with the air suspended particulate material, whereby to apply the same to at least a selected component thereof, collecting the treated material, wet conditioning said material and then subjecting the collected material to flotation.

16. A method of concentrating material which comprises; dry comminuting the material to a fineness suitable for flotation; forming an air suspension of droplets of a liquid flotation agent; suspending the comminuated material in an airstream under conditions conducive to the development and maintenance of static electrical charges on the particles thereof; commingling the suspension of flotation agent with the air suspended comminuted material, whereby to coat at least a selected component thereof with said flotation agent; collecting the treated material; and subjecting the same to flotation.

17. A method of treating material for the subsequent metallurgical separation thereof which comprises; dry comminuting the material to a fineness suitable to effect said separation; suspending the comminuted material in an airstream under conditions of turbulence; commingling a suspension of droplets of a flotation agent with the thus suspended comminuted material, whereby to coat at least a selected component thereof with said flotation agent, collecting the treated material and subjecting said collected material to flotation.

18. A method of treating material for the subsequent metallurgical separation thereof which comprises; dry comminuting the material to a suitable fineness; suspending the comminuted material in an airstream under conditions of turbulence while the same is in freshly produced comminuted form; commingling a suspension of droplets of a flotation agent with the thus suspended comminuted material, whereby to coat at least a selected component thereof with said flotation agent, collecting the treated material and subjecting said collected material to flotation.

19. A method of treating material for the subsequent metallurgical separation thereof which comprises; dry comminuting the material to a suitable fineness; suspending the comminuted material in an airstream under conditions of turbulence; commingling a suspension of droplets of a flotation agent with the thus suspended comminuted material for a period less than about three seconds, whereby to coat at least a selected component thereof with said flotation agent, collecting the treated material and subjecting said collected material to flotation.

20. A method of treating material for the subsequent metallurgical separation thereof which comprises; dry comminuting the material to a suitable fineness; suspending the comminuted material in an airstream under conditions of turbulence; commingling a suspension of droplets of a flotation agent with the thus suspended comminuted'material, whereby to coat substantially all the comminuted material with said flotation agent; collecting the treated material; wet conditioning the collected material to remove the reagent from a selected component thereof; and subjecting the conditioned material to a separation treatment by flotation.

21. The method of claim 16 wherein each particle is independently airborne.

22. The method of claim 16 wherein the collected material is subjected to wet conditioning prior to separation by flotation.

23. A method of treating material for flotation which comprises; dry comminuting the material to a fineness suitable for flotation; suspending the comminuted material in an airstream under conditions conducive to the development and maintenance of static electrical charges on the particles thereof; commingling a suspension of droplets of a flotation agent with the thus suspended comminuted material, whereby to coat at least a selected component thereof with said agent, subjecting the treated material to the action of a cyclone collector system, and then subjecting said material to separation by flotation.

24. A method of treating material for flotation which comprises; dry comminutin-g the material to a fineness suitable for flotation; suspending the comminuted material in an airstream under conditions conducive to the development and maintenance of static electrical charges on the particles thereof; bringing the suspended com minuted material in contact with a suspension of droplets of a flotation agent under conditions effective to produce a film of said flotation agent on at least a selected component of said comminuted material; collecting the treated material, and then subjecting said material to separation by flotation.

25. A method of treating material for flotation which comprises; dry comminuting the material to a fineness suitable for flotation; suspending the comminuted material in an airs-tream under conditions conducive to the development and maintenance of static electrical charges on the particles thereof; commingling a suspension of droplets of a flotationagent with the thus suspended comminuted material for a period of less than three sec onds, whereby to coat at least a selected component thereof with said flotation agent; collecting the treated material, and then subjecting said material to separation by flotation.

References Cited in the file of this patent UNITED STATES PATENTS 2,106,887 Earle Feb. 1, 1938 2,197,865 Johnson Apr. 23, 1940 2,207,576 Brown July 9, 1940 2,330,875 Ellis et all. Oct. 5, 1943 2,358,497 Eglofi Sept. 19, 1944 2,586,818 Harms Feb. 26, 1952 2,593,431 Fraas .Apr. 22, 1952 2,762,505 Lawver Sept. 11, 1956 FOREIGN PATENTS 568,755 Germany Jan. 23, 1933

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