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Publication numberUS3860513 A
Publication typeGrant
Publication dateJan 14, 1975
Filing dateJan 20, 1972
Priority dateJan 20, 1972
Publication numberUS 3860513 A, US 3860513A, US-A-3860513, US3860513 A, US3860513A
InventorsHart Porter, Hatch Asa Elliott
Original AssigneeHart Porter, Hatch Asa Elliott
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Method of recovering mineral values from ore
US 3860513 A
Abstract
An improvement in the recovery of mineral values from a finely ground ore slurried in water wherein the ionic charge density of the water and/or resulting slurry of ore is ascertained, and adjusted in accordance therewith, by admixing a controlled amount of a selected polyelectrolyte therewith to enhance the quantity and quality of the mineral values recovered.
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Description  (OCR text may contain errors)

United States Patent 1191 Hart et al. 1 Jan. 14, 1975 [54] METHOD OF RECOVERING MINERAL 3,255,881 6/1966 Holderreed 209/164 X VALUES FROM O 3,256,902 6/1966 Porter 235/l5l.l2 X 3,321,649 5/1967 De Benedictis 209/5 X [76] Inventors: Porter Hart, 52 Lake Rd.; Asa 3,3 3 145 2 19 g Elliott Hatch, 118 Post Oak, both Of 3,399,133 8/1968 Gerdes ,,210/42 Lake Jackson, Tex. 77566 3,425,549 2/1969 Dickson 209/166 3,462,364 8/1969 Carlson 210/42 1 Flledl 20, 1972 3,551,897 12/1970 Cooper...

. 3,669,915 6/1972 Jones 209/5 X [21] Appl' 219326 3,741,891 6/1973 Panzer 210/5 x R16,279 3/1926 Ellis 209/166 [52] US. Cl 209/1, 209/166, 210/42 [51] Int. Cl B03b 1/04, B03d -1/O2 Primary ExaminerRobert vl-lalper [58] Field of Search 209/1, 164, 166, 167; Attorney, Agent, or Firm-William M, Yates 324/32; 210/42 [57] ABSTRACT [56] References C'ted An improvement in the recovery of mineral values UNITED STATES PATENTS from a finely ground ore slurried in water wherein the 1,425,187 8/1922 Ellis 209/166 ionic charge density of the water and/or resulting 2,125,631 8/1938 Gutzeit 1 209/166 slurry of ore is ascertained, and adjusted in accor- 2,l68,762 8/1939 Clemmer 209/l66 dance therewith, by admixing a controlled amount of a selected polyelectrolyte therewith to enhance the a CW 3,094,484 (3/1963 Rizmpatmn quantity and quallty of the mlneral values recovered. 3,138,550 6/1964 Woolery 209/166 X 6 Claims, 4 Drawing Figures L l Po/ e/ec/ 0/ Il? 64 L61 l l l\ 4L:0 6.7 g

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METHOD OF RECOVERING MINERAL VALUES FROM ORE BACKGROUND OF THE INVENTION The invention pertains to an improvement in the recovery, by application of flotation principles, of mineral values from ores which have been crushed and ground to fine particles, slurried in water usually having admixed therewith a flotation-aid compound (sometimes called a collector) which increases the surface tension, usually a suppressant to reduce the amount of undesirable mineral that otherwise tends also to rise to the surface in a flotation operation, and pH-control additive, and the slurry so made subsequently subjected to a current of air moving upwardly therethrough while being agitated, whereby a foam is formed in a system which is floated off and thus provides for recovery thereof, comprising desirable minerals adhering to the bubbles in the foam, which continue to rise to the surface and overflow into collection troughs from which the desired mineral is usually conducted to separation means comprising subsequent filtration and drying.

Flotation systems are well known. Gold, copper, zinc, and other metals and compounds such as fluorite (CaF have long been recovered by applying flotation techniques. Because flotation is a highly sensitive operation and fraught with many processing problems, difficult to diagnose and remedy, sophisticated or highly effective techniques and devices for alleviating the difficulties associated therewith have not been forthcoming in the art. As a consequence, control and regulation of the processes have been guided much by personal experience and such rather crude techniques as handfeel and general appearance whereby the human factor has often introduced unexplained variations, oftentimes leading to reduced product quantity and quality or occasionally to some improvement in operation, the cause therefor in either case usually remaining illusive.

A need for more scientific control of flotation operations and improvements based thereon has long been experienced.

SUMMARY OF THE INVENTION The invention is a method of measuring and controlling the charge density associated with liquids and particles in suspension, as, for example, the water to be employed or the slurry being processed in a flotation system which, when not within required limits, results in failure to recover the sought mineral in economic quantity and sometimes failure to achieve acceptable quality.

Hereinafter the term charge density or ionic charge density will be used to refer to charges associated with ions of a liquid including substantially pure or untreated liquids, e.g. water, and solutions and suspensions, even though, by strict interpretation, the value is determined by measuring qualitatively a weak current created by the charges associated with molecules of a liquid and, when present, dissolved and/or suspended particles.

We have discovered that, by the addition, to water to be used to make a slurry and/or to the slurryso made, a selected polyelectrolyte, in accordance with ascertained conditions and needs, the ionic charge density can thereby be adjusted to provide more efficient separation of minerals in suspension, e.g. more consistently efficient recovery by flotation of a desired mineral of greater purity.

DESCRIPTION OF THE INVENTION Although charges are associated with liquids in general, including pure liquids, the invention is concerned with the net effect of charges of suspensions as affected by the particles in a suspension. It has been known that such charges are of paramount importance if particles are to continue in suspension to any extent. We have discovered that the nature and intensity of charge determines the extent to which particles of specific minerals in a slurry comprising more than one mineral will adhere to bubbles of a foam, and thus be carried upwardly therewith, and thereby be separable from other minerals therein.

The charge density associated with ions comprising a liquid, including those associated with particles in solution or suspension, may now be measured by means of an instrument commonly called a streaming current detector. Such is described in recent literature and patents, e.g. US. Pat. Nos. 3,368,144; 3,368,145; 3,369,484; 3,399,133; and 3,502,965 and in publications, e.g. 7970 HYDROSCAN Streaming Current Detector Bull. 177507 Exhibit A, Leeds and Northrup or A New Instrument The Streaming Current Detector by Walter F. Gerdes, The Dow Chemical Company, Midland, Michigan. A particularly convenient and reliable type of streaming current detector is that described in US. Pat. No. 3,368,145, a model of which is available from the Leeds and Northrup Corporation, Philadelphia, Pennsylvania. Although the 7970 HY- DROSCAN is not made to operate under pressure (as is suggested in the drawing), periodic tapping of a water line or drawing a sample of the water line or slurry being used, the sample placed in the reservoir, and the charge density ascertained is quite acceptable for the practice of the invention. However, if a continuous reading is desired, a streaming current detector may be modified to be placed directly in the line of flow, under moderate pressure as suggested in the drawing.

The basic principles of such instrument apply to measurement of pure liquids as well as to solutions and slurries, e.g. ore,in suspension. Although the suspend-' ing liquid and particles suspended together impart a common charge to the suspension, the particles possess a different predominant charge than does the liquid. Therefore, immediately about a particle, particularly when substantially static, is a layer of opposite charges to those of the particle. This immediate layer is surrounded by a layer of charges corresponding to those of the particle. This latter layer draws a predominance of opposite charges to it. The effect of the particle charge diminishes markedly with distance from the particle.

For purposes of illustration, a negative particle in suspension will produce an effect shown diagramatically in FIG. 2 of the drawing.

The streaming current detector, broadly, comprises a plastic block or boot containing a dead-end bore, electrodes at each end and a loosely-fitting piston which reciprocates in the bore, the immediate effect of which is to cause a liquid therein to be moved back and forth through the annular space between bore and piston by its rushing into the space just vacated by the piston. A synchronous motor drives the piston and a synchronous rectifier switch provides means by which the alternating current generated by the motion of the alternating fluid containing ions is registered on a d.c. meter. An amplifier with adjustable negative feedback is used to provide an output proportional to the current collected by the electrodes. Read-out is usually by microameter, calibrated in convenient arbitrary units of sensitivity. The current measured through the microameter is directly proportional to the streaming current produced in the cell and, therefore, the read-out is a measure of the streaming current and any adjustments of particle charge density in the liquid will reflect in the read-out.

More specifically, e.g. in US. Pat. No. 3,368,145, in all accordance with the general principles, there is provided for use in this invention a loosely fitting, driven, reciprocating, electrically insulated piston in an insulated cylinder, closed at one end and connected by a pipe arrangement to a source of liquid (containing the charges to be measured) and provided with electrodes at the extremes of movement of the piston, which electrodes are wired to rectifying, amplifying, and the recording means. The insulating material is usually a polymerized resin, TEFLON being especially good. The wall of the cylinder is negative to water and aqueous liquids. Suspended mineral particles are likewise negative to the liquid. The charges on the particles in the suspension and on the cylinder wall may be considered identical. Positive charges in the liquid are attracted to and tend to adhere to the surface of both the suspended particles and the wall as the piston reciprocates in the liquid, liquid moves between the cylinder wall and the loosely-fitted piston to occupyspace just vacated by the piston. This causes a sweeping motion and shears layers of positive charges absorbed on the cylinder wall surface and carries them into alternating contact with and renders positive first one and then the other of the electrodes, thereby setting up alternating current. The current is rectified, amplified and recorded.

The ionic charge density is related to zeta potential. The latter is a measure of work required to bring two similar particles closer together until their shear planes are tangent. A method of measuring it is setforth in the Gerdes publication supra and in modern physics text books. The zero value on a zeta potential instrument or meter and the zero ionic charge density on a streaming current detector represent the same value when the identical colloid or slurry is measured. The positive and negative values will correspond as to type of charge but will require specific calibration for actual values to correspond. Accordingly, a zeta potential meter could be used for periodic charge determinations of a slurry. However such use has definite drawbacks. A zeta potential instrument requires a specifically trained technician to take readings thereon; (2) obtaining such values is tedious; (3) it does not lend itself at all to continuous automatic readings; (4) it can be used only on colloids, suspensions, and slurries and is not useable to obtain readings of simple liquids such as water; (5) it is a potential (rather than a high impedence current measurement as is the streaming current detector) and is also required to be read logarithmically.

We have discovered that ascertainment, and preferably continuous recordation, of the charge density in a slurry, 'e.g. mineral particles in aqueous suspension including foamed suspension, is a unique highly reliable way of determining the efficiency of flotation operations and a basis for changes to increase efficiency.

This invention encompasses the use of a streaming current detector at one or at several stages of a flotation operation. In accordance with the invention, the ionic charge density of the water is ascertained prior to its introduction into the system and/or of the aqueous ore slurry at any stage in the process that such information can be used to make an adjustment in the opcration to effectuate an improvement in the end produce.

The preferred code of practicing the invention also employs a density-probe system in automatic cooperation with an optimizer, sometimes called a peakseeking optimizer.

The optimizer recommended is of the type also known as an experimenting controller" which provides a changing output signal to drive a process measurement to a maximum value, herein the largest density differential between unfrothed and frothed slurry, called sometimes the AD value. It is referred to as experimenting because at preselected intervals it continues to call for a change in conditions, e.g. in the alkalinity agent, in a given direction until the density differential no longer increases as a result of the change. It thereupon, reverses and calls for a change of the opposite type until such periodic incremental or decremental change does not result in increased AD, whereupon it reverses to resume the change in the preceding direction. For example, the optimizer may be preset to change every 5 minutes. To illustrate, say the last previous or penultimate reading had shown AD to have been 0.19 gm/ml of slurry. The reading just prior to that reading had been 0.17 gm/ml and as a result the system had been calling for increments in the alkalinity agent because 0.17 AD had resulted from decreases in the agent. However a present reading shows the AD value to have dropped from 0.19 to 0.18 gm/ml. It is clear that further increments in the alkalinity agent would be inadvisable (since AD has fallen below the 0.19 previously proved optimum); accordingly the optimizer now changes to call for decreased alkalinity agent.

Model 571 Syncro Optimizer, available from Moore Products Co. Spring House, Pennsylvania, U.S.A. (as described in Booklet MS-27 6071 illustrates an optimizer which is fully acceptable for use in the practice of the invention.

The optimizer and density probe or sensor density control system are described in co-pending application Ser. No. 219,221 entitled Device and Method of Density Measurement and Control of Liquid Systems" of Porter Hart, filed concurrently herewith. Although the instant invention can be practiced without the aid of the optimizer and density probe system, the use thereof is highly recommended.

After the ionic charge density has been so determined, a selected polyelectrolyte is admixed with the water and/or slurry and the efficiency of the process, as thus altered, ascertained as by calculating the per cent recovery of the desired minerals based on that available in the feed and assaying the end product to determine the quality. The new ionic charge density should be ascertained. Correlation of efficiency and ionic charge density of the slurry forms a reliable basis for thereafter adding an amount of polyelectrolyte to attain the desired ionic charge density.

The type and amount of polyelectrolyte to select in the practice of the invention are dependent upon (1) the charge of the water, (e.g. whether deionized well water, or river water and type and extent of dissolved or suspended materials is employed in the system); (2) the nature of ore being treated and of the mineral being recovered; (3) the nature and extent of treating ingredients admixed with the systems and (4) the design and lay-out of the equipment. For example, in the recovery of fluorite (CaF from fluorspar ore, if the water has a negative charge the water is adjusted from its negative charge toward zero or to a positive charge. Further adjustment may advantageously be made by admixture of the polyelectrolyte in the ore slurry prior to flotation and/or in one or more of the rougher and/or cleaner cells.

A comprehensive discourse on polyelectrolytes is presented in Encyclopedia of Polymer Science and Technology Vol. 10, pp 781 to 854, Interscience Publishers, New York (1969).

In simple language, a polyelectrolyte comprises a chain of atoms, sort of flagellum-like elongated macromolecules. The cationic-type are positive. We have discovered that they cling to and even coat less positive surfaces, e.g. the wall of the streaming current detector chamber and of particles of ores in the aqueous slurry. It matters not whether the polyelectrolyte or the ore is admixed with the water first. This addition, we have learned, has far-reaching effects on the behavior of the particles of suspended material during flotation. Whether a cationic or anionic polyelectrolyte is used depends on the composite result of the above enumerated conditions. If the flotation system is initially or by nature negative (as is the more common situation) then a cationic polyelectrolyte is employed.

Specific polyelectrolytes to employ in negative systems includes polyethylenimine, any of the polyalkylenepolyamine polyvinyl amines, Mannich reacted polyacrylamide and cationic starches. The molecular weight is not highly critical. Between about 50,000 and about 1,000,000 is usual. Polyelectrolytes, made according to U.S. Pat. Nos. 3,203,910 and 3,210,308 are illustrative as being satisfactory.

The presence of the polyelectrolyte has no detectable adverse effect on any aspect of the flotation process, e.g. the varying electrode potential, referred to herein for convenience as pH, is unaffected by the polyelectrolyte.

In flotation operations the ionic charge density may be expected to change as each treating ingredientis added and also may further change during the processing steps, i.e. as the slurry moves through the rougher and cleaner cells. lnprocess measurement and further adjustment in addition to the initial adjustment are recommended in the practice of the invention.

The invention is illustrated and described herein to include the use of a pair of electrodes of especially selected material whereby the EMF or electrode potential of the slurry (considered for practical purposes to be a pH value although it is not due to only the hydrogen ion concentration) is continuously measured. Actually the continuous EMF recordation is an independent set of values largely obtained for reference purposes. It is described fully in application Ser. No. 219,230, now U.S. Pat. No. 3,779,265, entitled Method of Continuous Measurement and Control of Flotation Conditions of Porter Hart, filed concurrently herewith.

THE DRAWING The practice of the invention is better understood by reference to the annexed drawing wherein:

FIG. 1 represents a flow sheet of a fluorspar flotation system;

FIG. 2 is a schematic sketch of a suspended particle surrounded by ionic charges;

FIG. 3 is a block diagram of a streaming current detector.

FIG. 4 is a graph showing two curves (1.) the change in ionic charge density plotted against the amount of polyelectrolyte added and (2) the performance as shown by per cent CaF concentrate recovered based on the CaF content of the ore when the process of the invention is followed as measured by the ionic charge density changes effectuated by addition of polyelectrolyte.

In the drawing, flow pipes are referred to as lines, air pipes or tubes as conduits, and electric connections as wiring or wires.

ln'more detail, the various significant members of the assembled flotation system of FIG. 1 are represented by the following designations:

Item 2 is a moving endless apron for conveying crushed ore from a crusher (not shown) which is supplied directly from a mine or storage pile. A water supply system for water from a convenient source (not shown, e.g. a river or reservoir) includes water tank 3 with controlled outlet therefrom, polelectrolyte bin or reservoir 9 with controlled outlet therefrom into the outlet from tank 3, and streaming current detector (SCD) through which a controlled flow of water fron tank 3 passes for ascertaining the ionic charge density of the water containing the polyelectrolyte. Item 4 is a supply system for a suppressant (e.g. sodium silicate or quebracho in solution) and 8 for an EMF or varying electrode potential control agent which is herein usually referred to as an alkalinity agent or sometimes herein referred to as simply a pH control agent, although other factors than the concentration of the hydrogen ion contribute to the effect. (Soda ash in solution is commonly used.) Items 10 and 5 are supply flow lines: line 10 provides soda ash solution from system 8; line 5 provides quebracho solution received from system 4, with the desired amount of additional water and bifurcatesv into lines 6 and 7, the amount entering each being controlled by air-operated valves a and b to provide a controlled amount of water desired through line 6 to be present during ball milling and a controlled amount through line 7 to result in suitable solids for good flotation after ball milling. Valves a and b are usually adjusted to permit about equal volumes of water through lines 6 and 7, as actuated by automatic control (later discussed). Item 12 is a ball mill (i.e. a drum rotating about a substantially horizontal axis or slightly inclined therefrom toward the outlet end, which contains loose steel balls). Item 13 is the outlet flow line from 12 which by force of pump p powered by motor m leads the slurry to cyclone type separator 14 which separates coarser and finer grind slurried ore. Item 16 is an outlet flow line for finer grind ore from 14 leading directly to further processing and I8 is an outlet flow line for coarser grind ore from 14 leading back to the entrance end of 12 for regrinding. Item 19, positioned in line 16, is a total ore volume measuring instrument which is connected by electric wire 20 to a first pen which records volume (V) on mass-volume meter 21. Line 16 continues into a conditioning tank 22 for finely ground ore, provided with a high speed agitator A. Positioned in 22 are a pair of electrodes 24 of erosionresistant material which are provided with electric wiring 25 connected to a first recording pen for continuous slurry EMF or varying electrode potential (which for simplicity shall be called pH) recordation on meter 26. Also feeding into tank 22 is surface tensionimprover flotation aid or collector, e.g. oleic acid, system 27.

Probe or sensor 28 (described more fully hereinbelow) consists essentially of two cooperating vertically positioned tubes immersed in the slurry in 22. These tubes are open-ended at the lower ends but are immersed to different depths so that together they provide two slurry contact levels which create a constant specified stratum of slurry volume between the two levels, regardless of fluctuations in the surface level in the conditioner. Both tubes of the sensor are maintained full of substantially dead air so that any change in pressure therein (since the height of slurry measured is constant) is due to a change in the density of the horizontal slurry stratum defined between the open-bottom ends. The upper ends of the tubes open into conduits 29, which are narrow continuations thereof, which deadend (and thereby trap air in the tubes) against a diaphragm (which provides an entrancechamber and an exit chamber) in density-pressure instrument 30 whereby variations in slurry density cause responsive variations in pressure, designated D Conduit 31 via conduit 34 connects instrument 30 with a first recording pen on meter 39, whereby D is recorded thereon. This value is used as a basis for ascertaining the amount of water to admix with the ore entering ball mill 12, the means for the attainment of which will be discussed later. Branching off conduit 31 is conduit 32 which leads to mass flow computer 35 to feed thereinto the D value. By means of conduit 36 from mass-volume meter 21, the value of V (obtained from total volumeinstrument 19) is relayed to computer 35 which calculates the mass flow by multiplying V times D Conduit 37 leading from 35 back to 21 then provides the means for recording the calculated mass flow by a second pen on meter 21. This value gives the density of the slurry prior to any flotation and thus a basis for calculating the per cent total solids of the slurry as it leaves the ball mill. This is important for a number of reasons among which is the prevention of cavitation of the gear pump for slurry leaving the ball mill. V X D,, calculated to give mass flow, is an excellent technique for knowing and controlling the ore input on apron 2. Also branching off conduit 31 is conduit 33 leading to computer 38 to provide the D, value used for calculating the per cent mineral recovered, as explained hereinafter.

Flow line 41 conveys conditioned slurry from 22 to cell C-l, the first ofa series of rougher cells designated collectively as item 42. The density of the slurry is conditioner 22 (i.e. D will differ from that in cell C-l (D',) due to the air released into Cl.

As the slurry progresses from the bottom of a preceding cell to the next succeeding cell of roughers 42, it is subjected to flotation separation by means of upwardly rising air aided by agitation whereby concentrate comprising the desired mineral (e.g. CaF is frothed and floated off into collecting trough system 82. As the slurry progresses, the density becomes less since CaF is more dense than the other ore components. The principle flotation occurs in cells Cl to C6. In C1 cell is vertically immersed density probe 44 which is of similar construction to tubes in probe 28 in conditioner 22 except that it functions singly since Cl operates full and has therefore a fixed level measured from the surface. The depth of immersion of probe 44 is not critical but is usually immersed to a depth of C1 so that the lower and open end thereof is about 20 to 30 inches from the surface.

Conduit 46 connected to the top of probe 44 leads to a flexible membrane forming the inner wall of one chamber of bichambered instrument 48 where density D' value is received. For control of the process to achieve greatest efficiency of rougher cells 42, a second density probe is necessary. This is provided here in cell C6 by probe 50 (substantially identical to probe 44) which, through conduit 52 exerts pressure, in accordance with the density of C-6 (i.e. D g), against the flexible membrane which forms the dividing wall of instrument 48. There is thus created a pressure differential which correlates with the density differential (D,D or AD) between slurry in cell C1 and that in cell C-6. This density differential is relayed through conduit 54 and then through branching conduit 58 to a second pen on meter 26. The density differential shows the efficiency of roughers 42 and is a reliable record of the flotation process.

Conduit 54 also leads directly to optimizer 56. Optimizer 56 continually seeks and maintains the highest density differential. The peak density differential adjusts the flow of alkalinity control agent, e.g. soda ash, automatically. This is accomplished by its passing an impulse at desired preset periodic intervals via conduit 59 from the optimizer to a pointer on instrument 26 which shows the optimum varying electrode potential, here called pH, for reference purposes, and thence via conduit 61 or by by-passing 26 and passing directly into conduit 61 which bifurcates into conduits 62 and 63 to attain such control. Gap action controller 64 proportions the impulse. These impulses through lines 62 and 63 control the amount of aqueous alkalinity agent being supplied from system 8. The alkalinity agent enters from system 8 through valve c controlling flow into line 10 to ball mill 12 and through valve d controlling flow into line 65 leading to conditioner 22. By means of controller 64, about twice as much alkalinity agent by volume is directed through valve 0 into line 10 as through valve d into line 65.

Item 66 represents a source of air being supplied to air line 67 which branches into lines 68, 69 and 70 which supply air pressure under moderate pressures to the conduits to operate the pneumatic system.

Cells C7 and C8 are referred to as scavenger cells. Some flotation is accomplished in them, but such constitutes but a small per cent (often insignificant per cent) of the overall recovery. Therefore, for control the AD is used.

However, for calculating the per cent of total CaF recovered, based on that available in the ore it is recommended that the densities D and D i.e. of the fresh slurry in the conditioner and of the tailings leaving the roughers, respectively, be used. Accordingly, a third density probe, 72, (similar to 28, 44 and 50) is immersed in cell C-8. Via conduit 73 the density (as a correlative pressure impulse) is passed to pressure density instrument 74 whereby the D value is obtained.

Conduit 76 then carries the impulse so created to a second pen on meter 39. By means of branch conduit 77 (off 76), the D value is provided to computer 38. There the calculation D,D /D is made which provides the per cent CaF recovered, i.e. per cent R). The so calculated per cent R is conveyed by pneumatic impulse via conduit 79 to a third pen on meter 39.

From meter 39 conduit 40 leads to water control valves a, which controls the amount of water admitted into line 6, and b, which controls the amount of water admitted into line 7, to attain the desired ore solids.

Referring now to the tailings leaving the C8 cell of 42, there is shown effluent line 81, which by aid of pump p and motor m, forces them to the tailings pond.

From rougher overflow troughs 82 is shown line 83 leading to additional flotation cells (called cleaners) designated collectively 84, which are very similar to rougher cells 42, but are designed to accept the once frothed high CaF -content slurry rather than fresh feed. The concentrate from 82 may be diluted with additional water if necessary for good flow characteristics. That portion of the slurried concentrates which is not frothed off at cleaners 84 (similarly, as from roughers 42) passes out from a point near the bottom of the last cleaner cell through line 85 into line 81 and thence to the tailings pile.

The recovered frothed reworked fluorite concentrate passes into trough 86 leaving through line 87 and goes into slowly agitated thickener vessel 88, where it loses most of the entrapped air and some water, the latter chiefly by a gradual overflow or decantation operation. From the bottom of thickener 88, as a high viscosity fluid, the fluorite slurry passes through line 89 into dewatering filter system 90 comprising envelopes mounted on a horizontal axis at the surface and subjected to interior vacuum and arranged to revolve on a rotating wheel. As the wheel rotates, the envelopes are alternately submerged in the thickened slurry body and exposed to vertically positioned parallel scraper blades. The contacted slurry, while that portion of the wheel was submerged, clings thereto to form a cake, and is thence brought out of the slurry body into contact with the scraper blades that remove the cake (not shown in detail). Water is lost through the internal vacuum system while the cake is clinging thereto. The revolving envelopes and the stationary scraper blades are identified schematically as items 91 and 92, respectively. The so-removed cake (now wet crumbles) falls and is collected on conveyor 94 which conveys it to dryer 96 which, in practice, customarily consists of a series of dryers. A product of 97.4 to 99.0 weight per cent anhydrous CaF powder leaves the dryer, ready for further processing or market.

It is to be understood that FIG. 1 is schematic and that pumps, air for flotation, stirrers, electricity sources, wiring, and other conventional but necessary operating facilities are not specifically shown in detail.

The flotation system described in detail herein requires an alkaline flotation system. It should be borne in mind that where an acidic system is required, e.g. in recovery of copper values, that the system can be as well operated to provide such condition as when alkalinity is desired.

A further modification from the system and apparatus illustrated herein and which falls well within the invention is to the use of electric signal rather than pneumatic conduits for all uses except the transfer of density values through the density probes and connecting tubes to the pressure-density instrument, e.g. items 30, 48, or 74. Signals from there on can be electrical.

FIG. 3 of the drawing shows a known and readily available streaming current detector of a type that is required for preferred practice of the invention, when periodic sampling is practiced. In FIG. 3, the following numbers identify the more significant features thereof:

is a synchronous motor; 127 is a combined eccentric drive wheel and commutator composed of electrically conductive semicircles bonded at the diameter by an insulated adhesive; 129 is a piston rod; 130 is a connection for easy disassemblage; 132 is a cutaway or sectioned block having an electrically insulated lining and providing therein reservoir 134; 136 is a loosefitting piston of electrically insulated material; 138 is the cylinder in which 136 oscillates; 139 and 140 are electrodes e.g. of silver; 142 is an amplifier provided with feed-back control 143 to control the amplification; 144 is a synchronous rectifier having oscillating switch 145 therein; 148 schematically represents the connection (whether mechanical or electrical) by which the AC. is converted to DC. by means of 127 and 145; 150 is a registering or recording meter for reading the streaming current values, termed herein often as ionic current density.

EXAMPLES Example A illustrates a conventional practice for recovering CaF values from fluorspar ore employing modern up-to-date equipment and techniques known prior to the invention including those disclosed in copending application, Ser. ,No. 219,230, now U.S. Pat. No. 3,779,265, entitled Method of Continuous Measurement and Control of Flotation Conditions and Ser. No. 219,221 entitled Device and Method of Density Measurement and Control of Liquid Systems of Porter Hart. Example 1 illustrates the practice of the invention for recovering CaF, values from the same quality fluorspar ore obtained from the same mine as that used in Example A except that a streaming current detector was used to ascertain the ionic charge and a controlled amount of a selected polyelectrolyte was added according to the invention.

Ore used in Examples A and 1 showed the following average weight percentages for those minerals for which analyses were conducted:

The rate of ore fed into conveyor 2 for both examples averaged about 138 kilograms per minute. 7

The quebracho and soda ash were each provided as a l0 percent by weight aqueous solution. The amount of each, for both the conventional example and that of the invention, averaged about 400 milliliters per minute. Oleic acid was provided at between about 3 milliliters for the invention and about 6 milliliters for the conventional example per minute.

The procedure and apparatus for each of the contrasting conventional example and that of the invention were the same except (l) that softened water was used in the conventional example and untreated river water (except for allowance for settling of some suspended sediments) was used in the example of the invention and (2) that the ionic charge of the particles as determined by the streaming current detector (which read initially -80'for the water used for both examples) was adjusted up to +25 by the admixture therewith of polyethylenimine (PEI), prepared in general as described in U.S. Pat. No. 3,203,910. The PEI was procured as 37 percent by weight solution, i.e. 37 percent active PEI. This was diluted with water to produce about a 4 percent by weight PEI solution. Sufficient of the 4 percent solution was admixed with the ore slurry to provide 0.05 percent by weight PEI based on the dry weight of ore. The PEI solution was added to the water prior to its admixture with the ore at the ball mill. Enough water was employed to result in a total solids in the ore slurry, leaving the ball mill, of 32 percent by weight. In both examples ore slurry was stirred and heated to 120F. in the conditioner before passing into the rougher cells.

The following results were obtained:

Example A 1 Per cent product recovered 72% 75% Avg. per cent SiO in product 1.09% 1.01% Per cent Cal in product 974% 97.5%

This is based upon the CaF content of the ore.

EXAMPLE 2 It appeared from the observation of Examples A and 1 above that a greater through-put of ore was possible when practicing the invention. Example 2 was therefore conducted wherein the average rate of crushed ore put into the mill was increased to an average of 153 kilograms per. minute. The conditioning additaments and water were increased proportionately. No lessening of efficiency or quality of product resulted with the higher production. The per cent CaF recovered, based on the CaF content of the ore was 77.4 percent.

EXAMPLE 3 Example 1 was repeated in a series employing ores of varying CaF content. The ore rate through the mill was increased by a factor of about 25 percent, i.e. the weight of ore was 1% times the customary rate when polyelectrolyte was not used. The per cent CaF recovered continued to be from 3 to 5 percent above that recovered by conventional practice. It was also shown that there was no advantage in using softened or deionized water in the practice of the invention, as has been considered essential in conventional practice, representing a substantial savings.

The conditions established in the mill were then applied, to the extent possible, to a laboratory size flotation test cell in a batch process. The identical ore, wa-

ter, and conditioning agents were added but the type and amount of polyelectrolyte were varied.

The following listed cationic polyelectrolytes were admixed in aqueous solution in the test cell in an amount sufficient to provide from 0.05 to 1.0 kilogram of polyelectrolyte per metric ton (1000 kilograms) of ore:

PURIFLOC C-3l: a polyalkylene polyamine;

Dow CP-7: a Mannich-reacted polyacrylamide;

Tex-A-1729-0: a polyepihalohydrin-ethylenediamine-ethylene dichloride reaction product;

NATRO N 86: an ethylenimine-polymethacrylic acid;

Cationic starch: an ethylenimine treated corn starch;

Cationic cornflour: an ethylenimine treated corn flour;

STALOC 400: chlorethylamine starch.

The presence of any of the above polyelectrolytes in the ore slurry showed comparable results to the use of an equal amount of polyethylenimine. Anionic polyelectrolytes either failed to improve the recovery or lessened recovery.

Although the range of polyelectrolyte employed varied between 0.005 and 0.05 percent (based on the dry weight of ore), indications based on extrapolation were that as little as 0.001 percent and as much as 1.0 percent based on dry ore weight can be used. As a matter of observation, larger amounts than 1 per cent of the polyelectrolytes can be used would be of no economic advantage.

EXAMPLE 4 To show the effect of adding increased amounts of a polyelectrolyte to the water to be used in slurrying finely ground fluorspar ore from which Cal was to be recovered by flotation, the following tests were conducted. Water was used in an amount sufficient to yield 32 percent total solids.

The overflow of river water from a settling reservoir was tested by use of a Leeds and Northrup Streaming Current Detector No. 7970. It showed a reading of 80. This water was then used in a regular mill operation to recover the CaF values from 74 percent Cal fluorspar ore as described hereinbefore. The per cent recovery of CaF product of 97.4% CaF based on the CaF content of the ore, was calculated. Thereafter in succession, water for the milling process had admixed therewith increasing amounts of the polyethylenimine (PEI) polyelectrolyte described earlier. The results are set out below:

-Cont1nued Ave. CaF Parts by active product wt. of 40% PEI recovered sol, of based based Ionic PEl per on dry on Cal Charge million weight content Density water* of ore of ore (footnolc to table above) Since the on: slurry is about 32% ore solids, and thus about 6871 water, in 40 parts PEl per million parts water calculates to be about 20 parts of PEI per million parts of on: which is 0.002% by weight based on the dry weight ofore, 60, H0, and I00 ppm PEI would calculate out proportionately when based on the ore weight.

FIG. 4 shows the results of these tests graphically. It shows that the ionic charge density becomes definitely more positive as the water employed in making the ore slurry had admixed therewith increasing amounts of the polyelectrolyte until a clearly positive value was obtained.

It should be borne in mind that the values obtained on a streaming current detector are relative, rather than absolute, The actual readings are on an arbitrary scale and are affected by concentrations, volume flow, and the like. However, the relative values are significant and when the same instrument is used in a system of somewhat constant flow wherein known components are changed, the values obtained are reliable guides to the positive-negative trend of the liquid being tested.

Provision of a cationic, and to a lesser extent a nonionic, polyelectrolyte in an ore slurry, regardless of the means of process control, makes a cleaner more efficient operation in flotation systems.

Having described our invention, what we claim and desire to protect by Letters Patent is:

1. In a flotation process for the recovery of mineral values from a slurry of finely ground ore in water by employing in the .slurry an electrode potentialmodifying agent, a flotation aid and a suppressant, and passing upwardly therethrough a gaseous foaming agent to produce a collectable foam at or near the surface, containing desirable minerals to be recovered,the improvement characterized by determining the ionic charge density of the water prior to mixture with said ore, the slurry or both and adjusting said charge density by the addition of an organic polymeric cationic polyelectrolyte to the water, slurry or both in amount necessary to provide a predetermined optimum ionic charge density to effectuate a more efficient recovery of mineral values. 1

2. The method according to claim 1 wherein the polyelectrolyte is selected from polyethylenimine, a polyalkylene polyamine, a Mannich-reacted polyacrylamide, polyepichlorohydrinethylene diamine-ethylene dichloride reaction product, polyethyleniminepolyacrylic acid reaction product, ethylenimine treated corn starch, ethylenimine treated corn flour, chloroethylamine treated starch, and mixtures thereof.

3. The method according to claim 2 wherein the ore is fluorspar.

4. The method according to claim 2 wherein the polyelectrolyte is polyethylenimine of an average molecular weight of between about 50,000 and 1,000,000 and the adjusted ionic charge density of the water is no less positive than minus 20 as measured on the streaming current detector.

5. The method according to claim 1 wherein the ionic charge density of the water employed is ascertained by obtaining a reading on a streaming current detector and the polyelectrolyte thereafter is selected and the amount thereof added are those which produce a more positive ionic charge density as determined by the streaming current detector.

6. The method according to claim 1 wherein the existing ionic charge density of slurry is ascertained in at least one flotation cell, a said polyelectrolyte admixed in at least one flotation cell, and the resulting ionic charge density of slurry in the cell to which said polyelectrolyte had been added determined after such addi-

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Classifications
U.S. Classification209/1, 210/703, 209/166, 210/709
International ClassificationB03B1/04, B03B1/00
Cooperative ClassificationB03B1/04
European ClassificationB03B1/04