US2106888A - Separatory flotation method - Google Patents

Description

mama Feb. i, was

No. Drawing. Application June 30, 1936, Serial No. 88,148

13 iDla,

This invention is a continuation in part and a development of my invention as disclosed in my application for Letters Patent of the United States, Serial Number 718,684, and relates to 5 separatory methods for the removal of impurities from material such as sands, sandstones, ores, minerals, and the like, which occur in granular form, and has as an object to provide an improved process or method operable to that 10 end.

A further object of the invention is to provide an improved separatory method particularly adapted for efficient removal of impurities from relatively hard granular material which occurs 13 naturally admixed with a binder having a more or less loose cementing effect on the separate material particles.

A further object of the invention is to provide an improved separatory method particularly efiicient in the removal of impurities, discolored particles and particles carrying iron oxide film or coating from natural sands and sandstones.

Av further object of the invention is to provide an improved separatory method efiiciently oper- 2,. able to float impure, stained, and discolored particles from natural silica sands and sandstones.

A further object of the invention is to provide an improved method whereby, through suitable modification thereof, the relative adsorptive w powers of various materials may be employed for eflicient froth fiotative separation of impure,

stained and discolored particles from natural silica sands and sandstones.

A further object of the invention is to provide an improved separatory process in the field and for the purpose set forth that is rapid and inexpensive of installation and operation, positive and efficient to the end desired and adaptable to various specific applications.

My invention consists in the various specific steps, and the sequence and combination thereof, set forth hereinafter and pointed out in my claims.

In certain arts, notably that of glass-making, materials occurring in natural granular form, such as silica sands, sandstones, ores, minerals, and the like, are employed, which materials are rarely found free from impurities and are quite commonly admixed with fine particles, clay, soil, and like foreign matter acting as a binder to more or less loosely cement the material particles together, hence it is necessary to submit the natural material to a process efiective to separate the particles of the desired material with- 55 out unduly pulverizing them with consequent production of an undesirably high ratio of fines and to remove the foreign and impure matter from the desired material. In the glass-making art, particularly, it is important that deleterious solid, stained and otherwise discolored particles of the sands employed be removed to prevent discoloration of the ultimate product. Various methods are employed to efiect the ends above set forth, but none of the conventional methods at present in use so perfectly attain the desired result in as rapid and economical manner as is possible through use of the improved method herebelow described.

A first'and essential step in the improved method is to subject the material under treatment to such action by suitable apparatus as will separate the natural particles of the material from any admixed binder or similar foreign matter and from each other, with a minimum of pulverizing, crushing or splintering of the individual particles, the apparatus to be employed for such purpose being adapted to the character of the ,p ecific material to be treated thereby. For example, certain loosely consolidated sands and sandstones may be disintegrated readily by tumbling, or by similar processes of moderate violence; more firmly cemented materials may require violent tumbling or passage through suitable mills arranged to prevent grinding, splintering or crushing of the individual particles, such as chaser mills or mills equipped with rubber covered elements arranged for direct contact with the material. The tightly cemented sandstones and similar materials may require a preliminary crushing to convenient mill size before final disintegration as above set forth. Whatever be the specific method employed, it is essential that the material be thoroughly disintegrated with the least possible destruction of the granular character thereof. Grinding, as the word is generally understood in the art, does not take place in the apparatus above specified and, being destructive of the individual material particles, is not within the contemplation of the herein described process.

After thorough disintegration of the material, the next step of the improved process involves washing thereof, which may be accomplished through any suitable apparatus in any desired manner to the end of separating the granular material from binder material, soil, clay, trash, soluble material, and other foreign matter admixed therewith. After washing, the cleansed granular material is dewatered, by draining and other suitable methods, to eliminate excess moisture to a degree more specifically set forth herebelow, the amount of moisture retained or finally contained by the material having a definite function in the further development of the improved terminology is not available, certain terms and phrases to be employed in the elaboration of the improved method herebelow'are herein specifically defined for limitation to the particular meaning readable therein throughout this exposition and the included claims.

Gram-a crystallographic unit as it is seen under the microscope--Gaudin, pages 131-132.

Particle-a small unattached piece of solidcomposed of one or more'grains. If all the particles in a ground ore are composed of one grain each they are said to be free and the liberation of the minerals by grinding is perfect. If some particles are multigranular, liberation is imperfect. Liberation of the particles of an ore is accomplished by comminution, consisting of crushing and grinding. Ideal comminution consists in breaking the bonds between contiguous dissimilar grains without rupturing the grains." Gaudin, pages 131-132.

The improved process'herein described is particularly concerned with and applicable to loose sand, loosely consolidated sands and sandstones, which are cemented" sands, and hence contemplates comminution of the material to liberation of its constituent particles, one from the other, and avoids, so far as is practicable, such comminution methods as would destroy the identity of the particles or rupture the grains of material.

- Adsorptive power-is used to designate the force with which chemical reagents other than water are attracted to and held on the surfaces of mineral particles; this force varies with the nature of the mineral particle and will vary for a given particle in respect to diiferent reagents.

Adsorptive capacity-refers to the amount of reagent or thickness of reagent film held to a mineral particle against removal therefrom by a particle of relatively lower adsorptive power.

Aflim'tyas herein usedmeans surface attraction and adhesion between a mineral particle and water, only; in other words, the adsorptive power of the mineral as evidenced in respect to water, and not in respect to any other chemical reagent.

Dru-for purposes of this exposition defines a condition of ore, sand or mineral wherein all water held to the surface of the particles has been removed. This condition can be obtained only through evaporation of the water at temperatures considerably above atmospheric and can be maintained only through maintenance of such temperatures in the ore or mineral, since the material, when at lower temperatures, will adsorb moisture from the air. A dry ore, as here considered, may have free water still within the interior of the particles.

Free water-refers to the moisture or water content of an ore, sand or mineral other than the water of chemical combination of such material and includes both adsorbed and absorbed water as well as interstitial water. Free water includes all water that can be drained, filtered or evaporated from the ore at temperatures below 212 degrees 1'.

Variable-film water-is herein limited to a designation to the amount of water that can be adsorbed on the exterior surfaces of the various mineral particles and held to these surfaces by the afiinity of the particle.

M oistdefines an ore or sand condition wherein the variable-film water varies from just above the dry condition as a lower limit to an upper limit determined by that total amount of water which can be held to the surfaces of all the particles by afiinity. This maximum amount is substantially that which would be adsorbed from the atmosphere of difierent humidity.

determined by the average size of the mineral particles being treated; the finer the size of par-' ticles the greater the total surface area and the more water is needed to cover this area to satisfy the afilnitive needs of the mass. A sand having a grain size from minus 16 mesh to plus mesh and from which the slimes have been removed The total amount of water used or needed is, of course,

will have an upper limit of three percent of water,

by weight, to satisfy its afilnitive needs while a percent of water to equally satisfy its afiinitive needs. The specific gravity of the material particles may also be a factor. To get the desired fiotative effect of variable-film water there must be no interstitial water present, and unless the sand is in the proper condition to start with, evaporation must be employed to eliminate any excess water, since under no conditions can the small amount required by the improved process be obtained by natural drainage alone, or water must be added to bring the material to the desired moist condition. If natural drainage is used as a step in the dewatering of the material, it must be supplemented by evaporation or other similar means. A sand in the moist condition may have some free water absorbed within the interior of the particles, but this water has no harmful effect on the actual flotation of the desired particles; The improved method, as described, deals entirely with the materials in the moist condition. Moisture, as herein used, has the same limitations of meaning as are above employed in respect to moist.

Wet-refers to that condition of a material where there is sufficient free water to give an excess over that needed to satisfy the afilnitive needs of the particles of sand or ore. A sand which has been allowed to drain naturally for a long time but which has not undergone any other treatment for the removal of excess water, is in the wet condition.

Continuing the description of the improved method, the moist, cleansed particles of the material under treatment are next mixed with the proper reagent before going to the froth fiotation cell. Experiment has definitely established that, by employing a suitable organic reagent, and more especially one of the fatty acid group,

both coarse and fine silicaparticles and similar iii?) amass ticles. Further, it has been definitely established that certain impure, discolored, and stained particles remaining after washing of the material have adsorptive powers for the fatty acids and their derivatives which are higher than those characteristic of the clean-surfaced, pure silica particles. This higher adsorptive characteristic doubtless results from the metallic nature of the substance or compound contained in or as a film covering on these certain grains. The difierence in adsorptive power will vary according to the degree of impurity, stain ordiscoloration presented in a given instance. This difierence in adsorptive powers for certain reagents oi the pure and impure particles having been established, eliminative selection of the impure particles can readily be had through a conventional froth flotation cell in the presence of an organic reagent, such as oleic acid and the like, by adjusting the free water content of the washed material and admixture thereof with the reagent so that there will be a sumcient amount of water present to prevent efiectively fiotative combination between the reagent and the particles char= acterized by lower adsorptive powers for the reagent used; only those particles having higher adsorptive powers being thus floatabie.

The amount of free water necessary to efiect the selective separation just above described will vary with the specific material under treatment and with the degree of separation to be obtained. In the case of certain silica sands it may be desirable, after disintegration and washing of the material, to dry the washed material, then add the proper amount of water and thoroughly mix it with the material, or allow the sand to take up water from the air, the reagent then being added to and thoroughly mixed with the waterregulated material prior to agitation thereof in the flotation cell. A further step is frequently of advantage with sands and consists in leaving the mixed water-regulated material and reagent in intimate contact for a predetermined length or" time prior to introduction thereof into the flotation cell, thus permitting the reagent to thoroughly establish its combination with the particles of higher adsorptive powers prior to dilution of the reagent in the flotation medium.

With a relatively higher moisture content in the material, all of the particles have their affinities for water satisfied so that only certain of the more impure particles will float readily in the cell, a relatively lower moisture content acting to progressively float more of the stained and discolored particles as said moisture content is reduced to the minimum, beyond which the particles having the lower adsorptive powers will be filmed with the reagent and. float. Where the moisture content of the mixture is below eight percent by weight of the material, the reagent is mixed with the material prior to introduction of either to the flotation cell, and the resulting mixture is thoroughly agitated to uniformly spread the reagent therethrough..

Where sand carries impure grains which are easily floated, the material may be deslimed, partially dewatered, as is standard flotation practice, and put directly into the flotation cell where the reagents are added, less than one percent of reagent by weight of the material being required for satisfactory results with this form of the method. This treatment will not remove the minerals of lower adsorptive powers nor iron stained grains. The tailings are then removed from the cell, the moisture content thereof regulated and, after mixing with the proper reagents, the mixture is again put through the flotation cell for further purification.

Once themixture of material and reagent has been put in the flotation cell, the concentrate should be removed as soon as possible. If the material is allowed to condition in the cell for any considerable length of time the film of reagent surrounding the particles in the froth may be washed off with a consequent loss of concentrate. This is especially true where the pure silica particles are being floated, since the silica grains, having a higher aidnity for water than adsorptive power for oleic acid or similar reagents, will have the film of reagent removed and replaced by water film, and they will then sink out of the froth. @ne advantage of the improved method is derived from the unstable froth carrying the concentrate, since the very rapid formation of the concentrate bearing froth and the necessity for its rapid removal increases the capacity of the cell unit materially.

Where the sand particles are coarse, from minus sixteen to plus eighty mesh, it has been determined that "as little as one tenth of one percent (0.1%) oi variable-film water, by weight of material, may prevent the flotation or the cleaned silica particles. The finer the sand partieles, the more water may be needed to prevent their flotation, as the surface area to be waterfilmed is proportionately increased. The free water content of the material before being mixed with the reagent may vary within narrow limits according to the fineness of the separation desired and the practical considerations involved. For most emcient results the sand should carry less than eight percent of free water by weight before being mixed with the reagent.

Different sands require difierent treatments depending on the type of impurities to be removed. If a silica sand contains impurities such as biotite mica, magnetite, specular hematite, et cetera, only, these can be floated away from the pure silica particles by keeping suflicient water film around all the sand particles to prevent the adsorption of the reagent by the silica particles but not enough to prevent such action by the impure particles. With most sands of this class not less than one half of one percent (0.50%) moisture must be present before mixing with the reagent, since, with less than this amount of water, there is danger of floating some of the pure silica particles. If the sand particles are fine it may be necessary to have three to eight percent of moisture present to prevent the flotation of the pure silica particles and give a clean concentrate of the impure particles. The best amount of moisture to be used for each sand can readily be determined by simple test. Other sands do not contain the above minerals but do contain certain dark colored and other particles that can be separated from the silica particles by keeping the moisture content below one half of one percent (0.50%) before mixing with the reagent. In this case, best results are usually obtained if the water film on the particles is kept at a minimum. Such sands, when mixed with a fatty acid, such as oleic acid, in amounts of between one tenth pound and five pounds per ton, will have the pure silica particles, only, covered by the reagent and can be separated in a flotation cell. The best amount of reagent to be used for the sand in question must be determined by test. Care must be used not to employ too much reagent, as excess reagent washes ing.

Where sands contain a mix of the two kinds ofimpurities mentioned above, the procedure would be; first, after desliming, the free water content is regulated to that amount which will of! in the cell and prevents frothpermit adsorption of the reagent by the mica,

dition, mixed with more reagent, time-conditioned, if necessary, while still in the moist condition, and again introduced into the flotation cell forseparation of the pure silicaparticles as a froth concentrate from the impure particle remaining as tails'in the cell.

Th'e speciflc reagent employed may be one of the fatty-acid or soap group or a derivative thereof, and since certain of such reagents are not liquid at normal temperatures, it may be desirable to mix the reagent and material at a temperature above normal, though said temperature should be held below that point where too rapid evaporation of the water in the mixture would result. Oleic acid functions well in the improved method at 'normal room temperatures.

It is usually desirable and on occasion necessary to add a frother, such as pine oil, terpineol, or the like, to the mixture under treatment, during or prior to agitation thereof in the flotation cell, the frother aiding in the froth flotation effect produced by such cell, as is well known practice.

Certain tests, have resulted as follows:

employing the new method,

A natural sand screened to minus thirty plus,

one hundred mesh was found to carry fourteen one-hundredths (0.14%) of FeaOa. was deslimed, dewatered' to a six percent free water content and treated accordingto the improved method with three-fourths of a pound of oleic acid to each ton of sand. Impure grains amounting to one-half of one percent (0.50%) of thetreated sand weightwere floated and thus selectively eliminated, the sand after treatment testing forty-two one-thousandths (0.042%) FezOa. By no other method were results obtained which could compare favorably with those above set forth inrespect to either lower iron content or cheapness of operation.

A-glass sand from Southern California containing solid particles of garnet, magnetite,

specular hematite, et cetera, pure silica particles, and particles of lower adsorptive power, such as feldspar, mica, et cetera, was thoroughly disintegrated and cleaned of its slimes by treating the material while wet in a rubber-lined rod mill wherein rubber-covered steel rods were emoughly mixed with three drops (.3 lb. per ton) of oleic acid. This mixture was then put through a 1000 gram flotation-cell with 2 drops (.2 -lb'. per ton) of pine oil added as a frother. The froth concentrateresulting from the above Thlssand' weighed 7 grams and consisted of the solid particles, such as garnet, et cetera.

B. The tails from the foregoing paragraph were dried and then water-regulated to that amount of free water adsorbable from theatmosphere and 200 grams thereof was mixed with 4 drops (1 lb. per ton) of oleicacid, which mixture was then put through the same flotation cell with 2'drops of pine oil. The concentrate resulting from this treatment weighed 170 grams and contained 5.8% A110: and .038% Fezoa,

while the tails weighed grams and contained 'cetera.

The foregoing tests show that:.

A. Proper treatment of the clean sand regulated, in this instance, to 5% of moisture permits the flotation of certain grains .but prevents the flotation of thesilica andlower adsorptive powered grains, and, f

B. With the material regulated to that amount of moisture adsorbable from the atmosphere, or less the mix of material and reagent, when immediately floated, permitted the separation of the silica from the feldspar and other impure grains. The feldspar, in this case, has a lower adsorptive power for the oleic acid than has the silica and, even though there is an excess of reagent present beyond the needs .of

silica, the. feldspar does not adsorb at once and hence a separation of the two kinds of grains can be made in the flotation cell.

0. Through time-conditioning of the mix, while in this moist cohdition, in this instance for twenty-four hours, the weaker feldspar particles are given opportunity to adsorb the oleic acid and are then floated of! with the pure silica particles. The particles still remaining as tails would re- -quire for their flotation a greater amount of retact between reagent and material while in the moist condition, it is possible to flotatively eflect separations of the various minerals as given. This can be done only through application of the above described method.

E. By elimination of the fines and the use of small amounts of material in the tests, the worst possible flotation conditions were provided.' The fact that the various separations were made under such conditions clearly evidences the novelty of the method. In no other way can such coarse silica grains be floated.

Since variations and modifications in the specific nature and sequence of the steps comprised in the improved method may be had, and may in fact be highly expedient in applying the method to specific materials, all without departing from the spirit of the invention, I wish to be understood as being limited solely by the scope of the appended claims rather than by any details of the foregoing exposition.

I claim as my invention- 1. The method of purifying naturally granular material which comprises disintegration of said material toits constituent elements without crushing or splintering of the particles, washing lll of said material and discard of slimes therefrom, dewaterin'g of said material to a water content less than will satisfy the afiinitive capacities of all of the separated particles and to that minimum essential for selective flotatively eifective limitation of the adsorptive powers of the particles relative to flotation reagents, agitation of said waterregulated material with a fatty acid and agitation of said mixture in a froth flotation cell for separation and removal of impure particles through said cell:

2. The method of purifying naturally granular material which comprises non-destructive disintegration of said material to its constituent particles, washing of the disintegrated material and discard of slimes therefrom, regulation of the water content of the material to an amount less than will satisfy the afdnitive capacities of all of the separated particles of the material, agitation of said water-regulated material with one of the soapy reagents, and separation in a froth flotation cell of those material particles having the higher adsorptive powers from the particles of lower adsorptive powers.

3. The method of purifying sands which comprises non-destructive disintegration of the sand to its constituent particles, washing of the disintegrated sand and discard of slimes therefrom, drying of the sand, addition to the dried sand of that minimum proportion of water below an upper limit less than will satisfy the affinitlve capacities of all of the separated particles and. which will sufficiently limit the effective adsorptive powers of the material to prevent fiotatively efiective adsorptlve affiliation between a fatty acid and the pure silica grains, admixture of said water-regulated sand with a fatty acid, and subsequent agitation of the resultant mixture in a froth flotation cell for separatory flotation of the impure partlcles.

4. The method of purifying sands which comprises non-destructive disintegration of the sand to its constituent particles, washing of the disintegrated sand and discard of slimes therefrom, addition to the dried sand or that minimum proportion of water below an upper limit less than will satisfy the amnitive capacities of all of the separated particles and which will sumciently limit the effective adsorptive powers of the material to prevent flotatively effective adsorptive aihliation between a fatty acid and the pure silica grains, admixture of said water-regulated sand with a fatty acid. prolongation of contact between said reagent and water-regulated sand a determined length of time to the end of selective concentration of said reagent on and about the impure particles characterized by higher adsorptive powers, and subsequent agitation oi the resultant mixture in a froth flotation cell for separatory flotation of said impure particles.

5. The method of purifying naturally granular material which comprises blunglng of the material for disintegration thereof without crushing or splinterlng of the natural material particles, washing of the blunged material for discard of slimes therefrom, drying of the granular material, thorough mixing of the dried material with a minimum. proportion of water below an upper limit less than will satisfy the affinitive capacities of all of the separated particles and which will sufficiently limit the effective adsorptive powers of the material to prevent fiotatively effective adsorptive affiliation between a fatty acid and the material particles of lower adsorptive powers, thorough admixture of the water-regulated material with a fatty acid to the end of selective concentration of said reagent on and. about the material particles characterized by higher adsorptive powers, and subsequent agitation of the resultant mixture in a froth flotation cell for separatory flotation of the impure particles.

6. The method of purifying naturally granular material which comprises biunging of the material for disintegration thereof without crushing or splintering of the material particles, washing of the hlunged material for discard of slimes there from, drying of the granular material, thorough mixing of the dried material with a minimum proportion of water below an upper limit less than will satisfy the afinitive capacities of all of the separated particles and which will suficiently limit the effective adsorptlve powers of the material to prevent flotatively effective adsorptive afila iation between a fatty acid and the material particles of lower adsorptive powers, thorough admixture of the water-=regulated material with a fatty acid, prolongation of contact between said reagent and water-regulated material a determined length of time to the end of selective concentration of said reagent on and about the material particles characterized by higher adsorptive powers, and agitation of the resultant mixture in a froth flotation cell for separatory flotation of the impure particles.

' 7. The method of puriiyinl glass sands and naturally granular ores which comprises disin-= tegration oi the material without grinding and consequent crushing or splintering of the material particles, washing of the material and elimination: of the slimes therefrom, dewatering of the granular material to a water content less than will satisfy the amnitive capacities of all of the separated particles, agitation of the dewatered material with less than one percent, by weight, of a fatty acid, and subsequent separation of the pure-and impure material particles in a froth flotation cell.

8. The method of purifying naturally granular ores which comprises disintegration of the material without grinding and consequent crushing or splintering of the material particles, washing of the material and elimination of the slimes therefrom, dewatering of the granular material to a water content less than will satisfy the afiinitive capacities of all of the separated particles, agitation of the dewatered material with less than one percent, by weight, of a soap, and subsequent separation of the pure and impure material particles in a froth flotation cell.

9. The method of purifying naturally granular ores which comprises disintegration of the material without grinding and consequent crushing or splintering of the material particles, washing of the material and elimination of the slimes therefrom, drying of the granular material, addition to the dried material of water in an amount less than will satisfy the afdnitive capacities of all of the separated particles, admixture of the water-regulated material with less than one percent, hy weight, of a fatty acid, and subsequent agitation of the resultant moist mixture in a froth flotation cell for separation of the pure and impure material particles.

10. The method of purifying sands which comprises non-destructive disintegration of the sand to its constituent particles, washing of the disintegrated sand, regulation of the water content of the sand to substantially that minimum adsorbable by the sand from the atmosphere for selective fiotatively effective limitation of the adsorptive power of the sand particles relative to flotation reagents, agitation of said water-regulatedsand with a fatty acid and subsequent agitation of said mixture in a froth flotation cell for separation and removal of impure particles through said cell.

11. The method of purifying sands which comprises non-destructive disintegration of the sand to its constituentparticles, washing of the disin rated sand, regulation of the water content of he, sand to substantially that minimum adsorbable by the sand from the atmosphere for selective flotatively effective limitation of the adsorptive power of the sand particles relative to flotation reagents, agitation of said water-regulated sand with a soapy reagent and subsequent agitation of said mixture in a froth flotation cell for separation and removalof impure particles through said cell. 1

12. The method of purifying sands which comprises non-destructive disintegration of the sand to its constituent particles, washing of the disintegrated sand, regulation of the free water content of the sand to that minimum less than will satisfy the afllnitive capacities of the separated particles eflective for flotative inhibition of the silica particles in the presence of a'fatty acid, agitation of said water-regulated sand with a fatty acid, agitation of the resultant mixture in a froth flotation cell for separation of'impurities as a concentrate from said sand, water-regulation of the tailings from said flotation cell to that minimum free water content effective to permit flotation of the silica particles in the presence of a fatty'acid, agitation of said flnally water-regulated sand with a fatty, acid, and agitation of the resultant mixture in a froth flotation cell for recovery of pure silica particles as a froth concentrate.

13. The method of purifying sands which comprises non-destructive disintegration of the sand to its constituent particles, washing of thedisintegrated sand, regulation of the free water content of the sand to that minimum less than will satisfy the aflinitive capacities of the separated particles eflfective for flotative inhibition of the silica particles in the presence of a soapy reagent, agitation of said water-regulated sand with a soapy reagent, agitation of the resultant mixture in a froth flotation cell for separation of impurities as a concentrate from said sand, waterregulation of the tailings from said flotation cell to that minimum free water content effective to permit flotationof the silica particles in the presence of a soapy reagent, agitation of said finally water-regulated sand with a soapy reagent, and agitation of the resultant mixture in a froth flotation cell for recovery of pure silica particles. as a froth concentrate.

THEODORE EARL-E.