US3308946A

US3308946A - Sink float method of classifying wet flocculated solid particles

Info

Publication number: US3308946A
Application number: US321399A
Authority: US
Inventors: Mitzmager Abraham; Mizrahi Joseph
Original assignee: ISRAEL MINING IND INST FOR RES
Current assignee: ISRAEL MINING IND INST FOR RES; ISRAEL MINING INDUSTRIES-INSTITUTE FOR RESEARCH AND DEVELOPMENT
Priority date: 1962-12-24
Filing date: 1963-11-05
Publication date: 1967-03-14
Anticipated expiration: 1984-03-14

Description

United States Patent ()fiice 3,13%,946 Patented Mar. 14,1967

SINK FLQAT METHOD F CLASSIFYING WET FLOCULATED SQLID EARTIQLES Abraham Mite ranger, Kiriat Bialilr, and Joseph Mizrahi, Kiriat Hahn, Ksraei, assignors, by mesne assignments, to Israel Mining Industriee-lnstitute for Research and Development, a company of lsraei No Drawing. Filed Nov. 5, 1963, Ser. No. 321,399 Claims priority, application Israel, Dec. 24, 1962, 13,443/62 8 (Iiaims. (Ci. 269-) The present'invention concerns the sink-float classification of granular solid materials.

It is known that when a ground dry ore composed, for example, of two minerals of different specific gravities is dispersed in a water-immiscible organic liquid of a specific gravity intermediate between those of the two minerals and the dispersion is allowed to settle, the minerals separate into a heavier'fraction which sinks to the bottom, and a lighter fraction which floats. If, however, the solid material is wetted with water or an aqueous liquor, some of the light and heavy particles flocculate in common and their separation in the aforesaid manner is not possible. It is, therefore, the usual practice first to dry the wet granular material and then to classify it, but an extra unit operation is required for the drying operation.

' It has now surprisingly been found that notwithstanding the flocculation of the wet granular material in organic liquids otherwise suitable for sink-float separation operations, the lighter and heavier fractions of the material can be separated from each other if the sink-float classification is carried out under conditions of an artificially increased gravitational field in a cyclone or a like device.

It has been known that the sink-float classification of granular materials in heavy liquids can be accelerated by the use of centrifuges, cyclones or similar devices, but this knowledge has been limited to the sink-fioat classification of dry materials, which would proceed even without the application of an increased gravitational field though more slowly. However, it has not been known, nor could it be anticipated, that the increase of the gravitational field makes possible the sink-float classification of wet granular material which cannot normally be so classified. This new observation on which the invention is based, is surprising and constitutes a departure from accepted beliefs and practices.

The respective specific gravities of the particles of a wet granular solid mixture dispersed in an organic liquid have not necessarily the same relation to each other and to that of the organic liquid as have those of the same particles it dry, since they may have been modified by the water or aqueous liquid with which the particles are wetted. The observable specific gravity of the wet particles will be called herein their apparent specific gravity, irrespective whether it is the same as that of the particles in the dry state or a different one. It is the rule rather than the exception that the several components of an ore mixture have different surface affinities for water. Therefore, the sink-float separation of wet mixtures in accordance with this invention can in many cases efficaciously classify fractions of markedly difierent apparent specific gravities, which are chemically or mineralogically different components of an ore mixture, while in the dry state the same components have so nearly equal specific gravities that they cannot be classified by the sink-float method by means of a water-immiscible organic solvent in the absence of water.

The present invention, therefore, consists in a method for the sink-float classification of wet granular mineral materials, wherein a dispersion containing the wet material in a flocculated state dispersed in a water-immiscible organic liquid having a specific gravity intermediate between the average apparent specific gravities of the lighter and heavier particles to be separated is subjected to sinkfioat separation under conditions of a gravitational field increased in relation to the natural gravitational field of the place of operation.

As a rule the artificial gravitational field applied in accordance with the invention will be of the order of 5g or higher (where g=9.81 m./sec.

The granular material to which this invention is applicable may especially be a mixture of minerals comminuted by any conventional operation such as crushing or grinding, or an ore found naturally in a fine-grained state.

The average apparent specific gravities of the lighter and heavier float fractions of wet granular material dispersed in the water-immiscible organic solvent in accordance with the invention depend on the intensity of the induced increased gravitational field. It is thus possible to control the composition of the two fractions obtained by the classification in accordance with the invention by a suitable adjustment of the intensity of the induced gravitational field.

The invention is applicable, on the one hand, to the classification of minerals of different specific gravities that are obtained in a wet state at some stage of the ore dressing process, and on the other hand to the classification of dry-ground minerals having equal or nearly equal specific gravities, if they differ from each other by their surface afiinities for water. For the sink-float classification of ore mixtures of this kind, the mixture is slurried in an organic liquid immiscible with water and sufiicient water is added to the dry mixture or to the organic liquid, or to the mixture of the ore and liquid.

For the production of increased gravitational fields in accordance with the invention, conventional devices such as cyclones can be employed.

The water-immiscible organic liquid will have to be selected or composed in accordance with the apparent specific gravities of the sink and fioat fractions of each particular mixture. It may be a single substance or a mixture of substances. An example of an organic liquid suitable for use by itself or as a component of a mixture is tetrabromoethane. Since the presence of a water film on the particles to be separated lowers their absolute specific gravities, it becomes possible to fractionate wet mixtures all of whose components have a higher specific gravity in the dry state than the water-immiscible organic liquid employed for the separation.

The invention is illustrated by the following examples to which it is not limited:

Example 1.Separati0n of chromite (sp. gr. 4.5) from serpentine (sp. gr. 2.6)

A chromite ore containing about 35% by weight of chromite, is ground in water to 20 mesh in order to liberate the minerals. The wet pulp is drained to a resid ual moisture content of 23-10%. If the resulting wet sand is introduced in tetrabromoethane, it is flocculated and the mass of fiocs floats to the surface of the liquid and no separation takes place. Now the slurry is vigorously mixed by a mechanical stirrer so that the fiocs are uniformly distributed through the whole body of liquid and this suspension is fed by gravity or by a pump to a hydraulic cyclone. In the cyclone, separation takes place, and chromite and serpentine report respectively to the underfiow and overflow of the cyclone. In this case, 'both solids have similar surface properties with respect to water wetting, but widely different specific gravities.

Example 2.-Separati0n of galena (sp. gr. 7.5) from calamine (sp. gr. 3.5)

The ore is ground dry to -35 mesh to liberate both minerals. Enough water is added to bring the average specific gravity of the wet ore to below the specific gravity of 'tetrabromoethane (2.96). For an ore containing 10% of galena in calamine, this amount of water is of the order of 11% of the weight of dry ore. The wet ore is slurried in tetrabromoethane, the slurry is mixed vigorously and passed through a cyclone under a moderate pressure. The galena goes into the underflow, andthe calamine 7 into the overflow.

In this case separation takes place owing to both the wide difierence in specific gravities and the surface properties of the minerals, as calamine has a much higher affinity for water than galena. Owing to th centrifugal force acting. onthe mixture during its passage through the, underflow, while calamine retains the water and since the specific gravity of the wet calamine is lower than thatof tetrabromoethane, the calamine goes to the overflow.

Example 3.Separati0n of cassiterite from hematite and quartz An alluvial sand (-35 mesh) containing cassiteri-te (sp. gr. 7.4), hematite (sp. gr. 4.8), quartz (sp. gr. 2.65) and other gangue minerals of sp. gr; 3 to 3.5 is washed to separate fine slimes and the clean sands dewatered'to about 10% .moisture. The wet sand is slurried in tetrabromoethane and fed to a cyclone by means of a centritugal pump, with a feed pressure of about 1 atmosphere above atmospheric pressure. Cassiterite is obtained in the underflow, while quartz, hematite and the other gangue minerals are discharged in the overflow.

Example 4.Sepamti0n of a fraction enriched in diamonds from diamond bearing sand A wet sand from South Africa in the size range 10-48 mesh containing 4.8% of minerals heavier than tetrabromoethane, including laterite, staurolite, rutile, leucoxene,

il'menite and diamonds, while the fraction lighter than.

We claim:

1. A method for the sink-float classification of granular solid materials composed of at least two fractions which, in a water-wet condition, have different apparent specific gravities, comprising the steps of: producing a dispersion of said granular material in a water-wet condition and fiocculated state in an organic liquid having a specific gravity intermediate between the apparent specific gravities of said fractions, said fractions being incapable of being separated from each other in said organic liquid in the natural gravitational field of the place of-operation,.subjecting said dispersion to sink-float, separation in a cyclone, under conditions of a gravitational field increased in relation to thenatural gravitational field of the place of operation and separately collecting said fractions of different apparent specific gravity.

2. A method according to claim 1, wherein the sinkfloat separation is carried out under the action of a gravitational field having an intensity of at least 5g (g=9.81 m./sec.

3. A method according to claim 1, wherein said waterwet condition of said mineral mixture is. initiated in a preceding processing operation.

4. A method according to claim 1, wherein said at least two fractions of said granulanmaterial have, in the dry state, nearly equal specific gravities but, in the wetstate, have sufiiciently difierent apparent specific gravities to allow their being separated from each other by said sinkfloat classification, and wherein said water-wet condition is initiated during said methodto obtain said different apparent specific gravities.

5. A method according to claim 4, wherein the mineralmixture is introduced in the wet state into theorganic liquid.

6. A method according to claim 4, wherein first water andthen the mineral mixture in the dry state are introduced into the organic liquid.

7. A method according to claim 4, wherein the A dry mineral mixture and water are introduced concurrently into the organic liquid.

8. A method according to claim 1, wherein the organic liquid consists at least in part of tetrabromoethane.

References Cited by the Examiner UNITED STATES PATENTS 1,839,117 12/1931 Nagelvoort 209l72 2,150,917 3/1939 Foulke 209-172 2,165,607 7/1939 Blow 209-472 2,686,592 8/1954 Miller 209+172 X 2,859,917 11/1958 Reerink 209-9 X 2,893,557 7/1959 Teuteberg 209-1725 FRANK W. LUTTER, Primary Examiner.

Claims

1. A METHOD FOR THE SINK-FLOAT CLASSIFICATION OF GRANULAR SOLID MATERIALS COMPOSED OF AT LEAST TWO FRACTIONS WHICH, IN A WATER-WET CONDITION, HAVE DIFFERENT APPARENT SPECIFIC GRAVITIES, COMPRISING THE STEPS OF: PRODUCING A DISPERSION OF SAID GRANULAR MATERIAL IN A WATER-WET CONDITION AND FLOCCULATED STATE IN AN ORGANIC LIQUID HAVING A SPECIFIC GRAVITY INTERMEDIATE BETWEEN THE APPARENT SPECIFIC GRAVITIES OF SAID FRACTIONS, SAID FRACTIONS BEING INCAPABLE OF BEING SEPARATED FROM EACH OTHER IN SAID ORGANIC LIQUID IN THE NATURAL GRAVITATIONAL FIELD OF THE PLACE OF OPERATION, SUBJECTING SAID DISPERSION TO SINK-FLOAT SEPARATION IN A CYCLONE, UNDER CONDITIONS OF A GRAVITATIONAL FIELD INCREASED IN RELATION TO THE NATURAL GRAVITATIONAL FIELD OF THE PLACE OF OPERATION AND SEPARATELY COLLECTING SAID FRACTIONS OF DIFFERENT APPARENT SPECIFIC GRAVITY.