US2330875A - Method for mixing and conditioning pulp - Google Patents

Description

Oct. 5, 1943. E. .1. ELLIS ETAL METHOD FOR MIXING AND CONDITIONING PULP Original Filed Aug. 10

REAGENT grwe/wboos EDWARDsl-ELL/S JOHN W PAMPL/ V Patented Oct. 5, 1943 I UNITED STATES PATENT OFFICE Mimion FOR commoNlNd Edward J. Ellis and John Pamplin, Bartow,

Fla, assignors to Southern Phosphate Corporation, Baltimore, Md., a corporation of Delaware Original application August 10, 1938, Serial No.

224,209, now be! 23, 1941.

November 19, 1941, Serial No. 419,786

8 Claims.

The present application is in part a division and in part a continuation of our copending'application for Method for pneumatic flotation, Serial No. 224,209, filed August 10, 1938.

with the action of the flotation reagent and involves loss of both reagent and concentratesdestroy the effect of flotation the reagent forms coatings Agitation may also reagents, as where This application relates to apparatus and that are weakly bonded to certain of the particles, method fol-treating fluid pulps, the term pulp which weakly bonded coatings may be destroyed being used herein to define a mixture of solid parand dispelled when the pulp is agitated. ticles with a liquid medium. In most fields of mixing pulps it is highly de- The method and apparatus of the present insirable that the process be carried onv continuvention are intended primarily for forming pulps 10 ously rather than in batches. In certain procand subjecting the formed pulp to such physical treatment as causes a thorough circulation of the fluid medium of the pulp through and among the particles.

The apparatus and method of the invention are particularly adapted for treating certain types of mineral pulps made from ores, prior to subjecting them to a flotation process that permits separation of certain particle constituents of the pulp from others. In such processes it is'necessary to treat the pulp with selective flotation agents which have preferential afiinity for certain of the particles of the pulp and so aflect such particles that separation subsequently can be effected. It

is highly importantthat such flotation reagents be thoroughly dispersed throughout the pulp, so that it,is brought into intimate contact with substantially all of the particles thereof. I Such mixing of the pulp with the flotation reagents generally is designated conditioning, and is an example of the intimate and thorough type of mixing that the method and apparatus of this invention are capable ofperforming.

Heretofore such mixing orconditioning of the pulp commonly has been performed by means of more or less violent agitation in machines of the impeller or tumbler type, which operate by agitating the entire body of pulp, including the solid particles. In such machines, the thoroughness of the circulation of the fluid medium through and among the solid particles of the pulp depends upon the violence of the agitation and the length of the period during which agitation is continued. In certain processes violent agitation is detri-- mental. Thus, in the conditioning ofthe fines rejected by phosphate washery plants employed to separate the larger phosphate particles from the raw phosphate rock, which fines are known as phosphate debris, or recovery plant feed, with soaps of fatty acids for flotation of the phas 'phate particles, 3, process well known in the phosphate 'industry,.violent agitation tends to break down soft material that normally is present in the debris, and to form a certain amount'oi slimes. The presence of such slimes interferes oof these reagents exhibit esses speed is essential, for example, the effect of for a period sufliciently long to survive lengthy mixing even when accomplished with a minimum of agitation. V

One of the applicants herein has discovered that certain flotation reagents of the so-called cationic type have preferential afiinity for quartz sand over phosphate particles.

this preferential ailinity for quartz only when the proportion of reagent is rigidly restricted to such limits that the quartz particles 'are weakly and temporarily affected. Therefore, when using such reagents it is important that the entire conditioning procedure be carried out quickly and also with a minimum of agitation. Other cationic reagents which may have a more powerfullyselective afiinity for quartz, and which may therefore be used in larger quantities to provide a more lasting and less easily disrupted effect, are, for reasons of economy, preferably restricted to such proportions as give the more temporary and fragile ef fect.

The present method and apparatus are capable, among other uses, of conditioning fluid pulps of phosphate debris without harmful 'effect; resulting either from the breaking down oi constituents of the pulp, as when soaps of fatty acids are used to render the phosphate particles floatable; or-by such agitation or lapse of time,

' or by both agitation'and lapse of time, as will destroy the effect of the reagent, as when cationic reagents are used'to condition the quartz sand for flotation.

The above fields of usefulness are given solely by way of example, and the herein described method and apparatus may be used in any process where thorough mixing of a fluid pulp is to be accomplished continuously, and more especially where such mixing is to be accomplishe'dwith a minimum of agitation of the solid particles, or where such agitation should be carried out at high speed.

More specifically, the present invention involves Certain an apparatus and'method for thoroughly, rapidly and continuously mixing a flowing stream of fluid pulp without subjecting it to violent agitation such as would be detrimental thereto. In obtaining such mixing the pulp is substantially continuously introduced into a quietly flowing body of the pulp, preferably at one end thereof,

and continuously withdrawn therefrom, while simultaneously disseminating fine streams ofgas bubbles throughout the body of pulp in a volume suflicient to cause a thorough circulation of the fluid medium without violent agitation of the solid constituents.

The method of mixing and conditioning pulp will be further described in connection with the accompanying drawing which shows a preferred form of apparatus in which the mixing and conditioning may be carried out. .However, it is to be understood that such-further description of the apparatus and method is merely by way of arranged in a novel manner for effecting certain specialized processes; and

Fig. 4 is a perspective view of a flotation device that is peculiarly useful in combination with the mixer.

Referring now to the drawing, the mixer comprises an outer, vertically-disposed, substantially cylindrical container or shell 5 having an open top surrounded by an'overflow trough 6 formed with an inclined bottom 1. arranged to deliver liquid in the trough to an outlet spout 8 arranged at the lowermost point of the bottom 'I.' The lower end of the shell 5 is closed by a porous bottom 9, which may be of canvas or of any other material that will permit gas to pass therethrough in finely disseminated streams. A gas chamber V I II is arranged beneath the shell 5 so that gas introduced into it under suitable pressure, as by a valved connection H, will be delivered to the interior of the shell through the porous bottom 8 in fine streams distributed throughout the cross sectional area of the shell.

An induction pipe I! isarranged to receive pulp delivered to a hopper l3 ata level higher than the top edge of the'shell -5 and to conduct it to the lower portion of the shell. Advanta geously the induction pipe I2 is cylindrical and located centrally of the shell 5, so that an annular space II is formed between the inner surface of the shell and the outer surface of the induction pipe l2. However, the essential arrangement of the induction pipe relative to the shell is that its bottom edge be adjacent but spaced from the bottom 9 of the shell, and that sufiicient space be present ,within the shell and outside of the pipe for upward flow of the stream of pulp in a smooth, non-turbulent manner.

.In operation the fluid pulp .is continuously fed to the hopper I: from which it flows downwardly through the pipe l2 and is delivered to the'space I 4 through which it flows upwardly in a gently and quietly 'fiowing stream until it overflows at the top of'the shell 5 into the delivery trough 6.

I Gas is continuously supplied to the chamber I0 under suflicient pressure to cause it to pass through the porous bottom 9 and into the stream of pulp, where it forms fine bubbles 'that rise in the flowing pulp stream and causes the liquid medium of the pulp to circulate among the solid particles and causes a thorough dispersion and mixture of the fluid medium among such particles.

The phosphate debris which remains after crude phosphate pebble ore has been subjected to washing and classifying operations has a free slime content of about 0.5% to 5.0% by weight and a particle size ranging substantially from plus 100 mesh to minus 20 mesh. Phosphate rock is present in such debris to the extent of about 5-35%, and quartz sand to the extent of about 80-50%. There is also usually some clay present both as particles, and adhering to the other particles in the nature of coatings.

As indicated above, and as is commonly known, the phosphate particles may be floated from the quartz by use of anionic reagents; such as soaps of fatty acids, which ordinarily are used with inert oily materials to promote agglomeration. In such cases the debris may be used as it comes from the washery. Asis also indicated above, cationic reagents may be used to render the quartz 'sand particles floatable from the phosphate. In such case, it is advisable to break down the easily slimable material, such as clay or other soft substance present in the debris, and remove it .from the debris prior to adding the flotation reagent, as'sucli materials interfere very seriously with the action of the flotation reagent.

Fig. 3 illustrates a plant including the abovedescribed mixer which is peculiarly suited for recovery of the phosphate content of phosphate debris. The debris is fed to the mixer, designated IS, in the form of a fluid pulp, a water content of about 40% producing a suitable degree of fluidity. The flotation reagent, of either cationic or anionic type, together with the inert oily material, if the latter is used; and any other desirable reagent is added to the pulp from a feeder, advantageously arranged to deliver to the hopper i3 into which the pulp is fed. As the pulp, after passing downwardly through the induction pipe i2, flows upwardly through the space I 4, gas bubbles rising from the porous bottom 9 gently agitate the. fluid medium of the pulp, causing such medium, and with it the reagent, to circulate through the pulp and flow between the solid particles thereof, dispersing the reagent thoroughly throughout the flowing pulp stream and bringing the reagent into-contact with substantially every solid'. particle. As the rising gas bubbles move quite gently and are of small weight compared with the solid particles, they tend to pass around the particles without moving them viole'ntly or to any great degree. The particles therefore are not agitated with sufllcient violence to set up attrition between them, and consequently harmful effects that may be caused by attrition, such When the top of the shell is reached the pulp,

as. breaking or abrasion of the particles, or dis.-

pelling of reagent coatings from them, are subbeing then thoroughly conditioned, overflows into the trough 6 and is delivered by the spout 8 to a separation device H, which may be of any a head wall 20 and an open delivery end 2|. The

trough is inclined from the head to the delivery end at a degree that provides a rapid flow of the pulp and that prevents sedimentation thereof upon the porous bottom. A gas chamber enclosed by walls 22 underlies the porous bottom so that gas supplied thereto under suitable pressure will pass upwardly into the stream of pulp flowing through the trough in finely divided streams that rise in the stream of pulp by reason of their own buoyancy. The water-repellent particles that have been afiected by the selective reagent used to condition the pulp are raised to the upper portions of the stream by the air bubbles, while the unaifected, water-wett-able particles sink and are carried along in the lower portion of the stream. The upper portion of the.

stream, containing the bulk of the reagentafiected particles, together with any froth that may be floatingon the surface of the stream, are intercepted and diverted from the stream through openings 24 to a delivery launder 22 by 'skimmers 23 spaced along the trough.

It will be seen that in the plant arrangement just described, the fast and gentle action of the mixer is continued by the particular separation trough disclosed in Fig. 4, so that the entire process is continuous, free from agitation and of such nature as to produce no violent agitation or attrition between the solid particles of the pulp, and isfalso very fast.

In utilizing cationic reagents, we regard it as preferable to so control the speed of the pulp stream with relation to the depth of the shell of the mixer, and to so arrange the inclination of the separation trough that the entireprocess ofmixing and conditioning the pulp and separating the constituents thereof is completed within oneminute from the introduction of the pulp to the hopper of the mixer. By inclining the separating trough to such a degree that the speed of the flow through it is of the order of 100 feet per minute the separation may be accomplished inabout. five seconds from the delivery of the pulp to the trough. Thorough conditioning may be accomplished by use of the bubble type mixing herein disclosed within a period of about 45 seconds, which period is of such length that at its expiration the cationic reagent will be fully effective.

What we claim is:

l. The method of dispersing a flotation. reagent throughout a pulp of solid particles and a liquid medium preparatory to selective separation of constituents forming the solid particles of the pulp, which comprises introducing the pulp and the reagent to be dispersed therein into a mixing zone'in which pulp is flowing upwardly, introducing finely disseminated gas bubbles to pass upwardly through the body of pulp in the mixing zone at a speed greater than the upward speed of the pulp and in suillcient volume to keep the solid particles of the pulp in suspension and to cause an upward movement of the liquid medium between and about the solid particles of the I portion of the body of the pulp.

2. The method of dispersing a flotation reagent throughout a pulp of solid particles and a liquid medium, preparatory to selective separation of constituents forming the solid particles of the pulp, which comprises substantially continuously introducing the pulp and-the reagent to" be dispersed therein into thelower portion of a quietly flowing body of the pulp, introducing finely disseminated gas bubbles to pass upwardly through the flowing body of pulp in sufiicient volume to keep the solid particles of the pulp in suspension and to cause an upward movement of the liquid medium between and about the solid particles of the pulp so that the reagent is substantially uniformly dispersed throughout the flowing body of pulp and is brought into contact with the solid particles thereof, the volume of air being insuflicient to agitate'the solid particles of the pulp with sufiicientwiolence to cause attrition between them, such as would cause appreciable. breaking or abrasion of the particles, or an appreciable dispelling of reagent coatings from them, and substantially continuously removing the pulp and dispersed reagent as an unseparated, intimate mixture from the upper portion of .the body of pulp at a rate substantially equal to that at which the pulp was introduced.

3. The method of dispersing a flotation reagent throughout a pulp of solid particles and a liquid medium, preparatory to selective separation of constituents forming the solid particles of the pulp, which comprises introducing the pulp and the reagent to be dispersed therein into a quietly flowing body of the pulp, introducing.

finely disseminated gas bubbles to pass upwardly through the quietly flowing body of the pulp in suflicient volume to keep the solid particles of the pulp in suspension and to cause an upward movement of the liquid medium between and about the solid particles of the pulp so that the is substantially uniformly dispersedreagent throughout the flowing body of pulp and is brought into contact with the solid particles thereof, the volume of air being insuficient to agitate the solid particles of the pulp with sufficient violence to cause attrition between them,

such as would cause appreciable breaking or abrasion of the particles or an appreciable dispelling of reagent coatings from them, and substantially continuously removing the pulp and dispersed reagent as an unseparated, intimate mixture.

4. The method of dispersing a flotation re-I agent throughout a pulp of phosphate debris and a liquid medium, preparatory to selective separation of constituents forming the phosphate debris, which comprises introducing the pulp and the reagent to be dispersed therein into a quietly flowing body of pulp, introducing finely disseminated gas bubbles to pass upwardly through the body of pulp in suflicient volume to keep the parpension and to cause upward movement. of the liquid medium about the particles of the phosphate debris so that the reagent is substantially uniformly dispersed throughout the flowing body 01' the pulp and is brought into contact with the particles of the phosphate debris, the volume of, air being insuflicient to .agitate the particles of the phosphate debris of the pulp with suflicient violence to cause attrition between them, such as would cause appreciable breaking or abrasion of such particles, o1 an appreciable dispelling of reagent coatings from them, and substantially continuously removing the pulp and dispersed reagent as an unseparated, intimate mixture.

5. The method of dispersing a selective flotation reagent throughout a pulp of phosphate debris and a liquid medium, preparatory to selective sepa ration of constituents of the phosphate debris which comprises introducing .the pulp and the reagent to be dispersed therein into a quietly flowing body of the pulp, i'ntroducingflnely disseminated gas bubbles to pass upwardly through the body of the pulp in sumcient volume to keep the particles of the phosphate debris in suspension and to cause an upward movement ofthe liquid medium between and about them so that, the reagent is substantially uniformly dispersed throughout the flowing bodyof the pulp andis brought into contact with the particles of the phosphate debris, the volume of air being insui'-.

ficient to agitate the particles of the phosphate debris with 'sufficient violence to cause attrition between them, such as would cause appreciable breaking or abrasion of the particles, or an appreciable dispelling of reagent coatings from them, and substantially continuously removing the pulp and dispersed reagent as an unseparated, intimate mixture at a rate substantially equal to that at which the pulp and reagent were introduced into the body of pulp.

6. The method of dispersing a flotation reagent throughout a pulp of phosphate debris and a liquid medium, preparatory to selective separation of constituents of the phosphate debris, which comprises substantially continuously introducing the pulp and the reagent to be dispersed therein into the lower portion of a'mixing zone in which the pulp is flowing upwardly, introducing flnely disseminated gas bubbles to pass upwardly through the body of pulp in the mixing zone at a speed greater thanv the upward speed of the pulp and in suiflcientvolume to keep the phosphate debris particles thereof in suspension and'to cause an upward movement of the liquid I medium between and about the particles of the phosphate debris so that the reagent is substantially uniformly dispersed throughout the body of pulp and is brought into contact with the particles of the phosphate debris, the volume of air being insufllcient to agitate the particles of the phosphate debris with 'suflicient violence to cause attrition between them, such as would cause appreciable breaking or abrasion of the'particles, or an appreciable dispelling oi. reagent coatings from them, andfsubstantially continuously-rem'ovingthe pulp and dispersed reagent as an un separated,-intimate mixture from the upper por-. tion of said mixing zone at a rate substantially equal to that at which the pulp and reagent are introduced into the lower portion of the mixing zone, the rate of introduction and withdrawal of the pulp from said body being such that intro- 5 duced pulp remains in said body for. a period of time not substantially exceeding one minute.

, 7. The method of dispersing a flotation reagent throughout a pulp of phosphate debris and a liquid medium, preparatory to selective separation of constituents forming the solid particles of the pulp, which comprises substantially contintion reagent which has a preferential aflinity for quartzsand over phosphate'particles and forms 5 weakly bonded coatings thereon into the lower portion of a quietly flowing-body of such pulp, introducing flnely disseminated gas bubbles to pass upwardly through the quietly flowing body of pulp in sufllcient volume to keep the particles 0 of phosphate-debris of the pulp in suspension and to cause an upward movement of theliquid medium between and about the particles of the phosphate debris so that the reagent is substantially uniformly dispersed throughout the body of pulp and is brought into contact with the par ticles'of the phosphate debris,the volume of air being insuilicient to agitate the particles of phosphate debris with suflicient violence to cause attrition between them, such as would cause appreciable breaking or abrasion of the particles, or an appreciable dispelling of liquid coatings from them, and substantially continuously removing the pulp and dispersed reagent as an unseparated, intimate mixture fromthe upper portion of the body of pulp at a rate substantially equal to that at which the pulp and reagent are introduced into the lower portion thereof, the rate of introduction and withdrawal of pulp from the mixing zone being sueh that introduced pulp re- 40 mains in said body for a period of time not substantially exceeding one minute. 7 8. The method 01. dispersing a flotation reagent throughout a pulp of solid particles and a liquid medium preparatory to selective separation of constituents forming the solid particles of the pulp, which comprises introducing the pulp and the reagent to be dispersed therein into the quietly flowing body of the pulp, introducing finely disseminated gas bubbles throughout substantially the entire cross-sectional area of the body of pulp in the mixing zone in sufllcient volume to keep the solid particles oi! the pulp in suspension and to cause a circulation of the liquid medium between and about the solid particles of the pulp so that the reagent is substantially uniformly dispersed throughout thebody of pulp and is brought into contact with the solid particles thereof, the volume of air being insuflicient to agitate'the solid particles of the pulp tween them, such as would cause appreciable EDWARD J. JOHN w. PAMPLIN.

uously introducing the pulp and a selective flotawith sufllcient violence to cause attrition be-

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