GB2064505A

GB2064505A - Method of increasing the separation rate of an emulsion

Info

Publication number: GB2064505A
Application number: GB8037217A
Authority: GB
Original assignee: Wyoming Mineral Corp
Current assignee: Wyoming Mineral Corp
Priority date: 1979-12-05
Filing date: 1980-11-20
Publication date: 1981-06-17
Also published as: PT72163B; PT72163A; YU299180A; CA1141254A; BE886503A; MA19008A1; FR2473339A1; MX158759A

Abstract

The separation rate of an oil-in- water or a water-in-oil emulsion is increased by first determining the HLB number of the emulsion and then adding to the emulsion a surfactant which has the - opposite HLB number.

Description

SPECIFICATION Method of increasing the separation rate of an emulsion This invention relates to a method of increasing the separation rate of an emulsion. In the treatment of Florida phosphate rock for making fertilizer, wet-process phosphoric acid is produced which typically contains about 0.2 gms of uranium per liter, about 2000 tons of dissolved U308 per year.

In the early 1 950's several processes were developed to recover this uranium, but the discovery of large amounts of relatively low-cost uranium in the western United States caused the abandonment of these processes. Recently, the rapid increase in uranium costs and rapid growth in the phosphate fertilizer industry has renewed interest in recovering uranium from wet-process phosphoric acid. The first major process for accomplishing this was based on pyrophosphoric acid as the extractant. The extractant was dissolved in kerosene which was mixed with the aqueous phosphoric acid solution, thereby extracting the uranium into the kerosene. A major disadvantage of this process was that the aqueous fluid and the kerosene tended to form an emulsion which separated only very slowly.For this reason that process was abandoned in favor of a process which used a combination of di(2-ethylhexyl) phosphoric acid (D2EHPA) plus trioctylphosphine oxide (TOPO) as the extractant. The D2EHPA--TOPO extractant had a lower extractant coefficient than the pyrophosphoric acid but emulsions did not form and the aqueous fluid and the kerosene separated rapidly, which more than made up for its lower extraction coefficient.

In U.S. Patent 3,154,376 gelatin is added to the emulsion formed during the extraction of uranium to reduce the phase separation time.

In U.S. Patents 3,306,714 and 3,278,277 polyoxyethylene compounds are used to increase the percipitation of solubilized humates and silica to make emulsions less stable.

According to the present invention a method of increasing the separation rate of an oil-in-water or water-in-oil emulsion comprises a method of increasing the separation rate of an oil-in-water or waterin-oil emulsion which comprises determining the HLB number of said emulsion and adding to said emulsion a surfactant having an opposite HLB number.

Pyrophosphoric acid can thus be used as the extractant and, because of its higher extraction coefficient, much more of the uranium can be economically recovered. As very little surfactant is used in our method, it is inexpensive and does not require much additional processing or apparatus.

This invention is applicable to eilher oil-in-water or water-in-oil emulsions in any proportion of water to oil or oil to water. Typically, however, the emulsion will be about 25 to about 55 pbw (parts by weight), water and about 45 to about 75 pbw oil. In addition, because the invention is used as part of the uranium extraction process, the emulsion may contain from 25 to 75 pbw phosphoric acid or sulfuric acid, from 25 to 50 pbw pyrophosphoric acid, and up to about 1 pbw U3O8. While the oil phase may be almost any organic solvent, in most uranium extraction processes it is kerosene as it is comparatively inexpensive. The amount of surfactant used should be at least about 0.01% (by weight based on total composition) as less has very little effect.More than about 1% /0 surfactant should not be used as it may result in forming the emulsion of the opposite type. The preferred amount of surfactant is from 0.01 to 0.5%. The surfactant may be added before the emulsion is formed, during its formation, or after it is formed, but preferably it is added during the mixture of the two phases as this facilitates subsequent seParation.

In practicing the invention it is first necessary to determine the HLB (hydrophobic-lipophobic balance) number of the emulsion. This number may be determined by identifying whether the emulsion is an oil-in-water emulsion or a water-in-oil emulsion because oil-in-water emulsions have an HLB number of 3 to 7 and water-in-oil emulsions have an HLB number of 7 to 18. Whether the emulsion is oil-in-water or water-in-oil can be determined by measuring its electrical resistance. A resistance of less than 1000 ohms indicates that the emulsion is oil-in-water and a resistance of more than 1000 ohms indicates that the emulsion is a water-in-oil emulsion. Alternatively, the type of emulsion can be identified by applying 200 volts DC at 40 milliamps across one inch of the emulsion. If current flows it is an oil-in-water emulsion and if no current flows it is a water-in-oil emulsion.Once the HLB number of the emulsion is determined, a surfactant is selected which has the opposite HLB number. For example, if the HLB number of the emulsion is 3 to 7, a surfactant is selected which has an HLB number of 7 to 18.

And if the HLB number of the emulsion is 7 to 18 a surfactant is selected which has an HLB number of 3 to 7. The surfactant selected may be non-ionic, anionic, or cationic. At the present time it is not yet possible to determine which of the three types of surfactants will maximize the separation of the emulsion except by trying all three. The following example further illustrates this invention.

The invention will now be illustrated with reference to the following Example:~ EXAMPLE A mixture of 7.5 grams P205, 13.7 grams of 1-octanol and 83.2 grams of kerosene was prepared.

This mixture produced octyl pyrophosphoric acid (C8H21P2O7) in kerosene. One part of the mixture was mixed with one part of a 54% aqueous solution of phosphoric acid (Texigulf) containing minor amounts of uranium, and either no surfactant, 0.4% surfactant, or 0.8% surfactant to produce a water-in-oil emulsion. The surfactant used was a polyoxyethylene glyceride ester sold as "Tween 20" by Imperial Chemical Industries. The time required for different percentages of separation to be achieved were measured. The following table gives the result.

% Separation Time After Mixing Amount Of Surfactant (Minutes) 0 0.4% 1 0.8 0.0 0 0.7 40 0.9 20 1.0 80 1.5 90 40 2.0 100 60 2.5 80 3.5 100 7.5 20 9.0 30 The above table shows that 100% separation was achieved in 20 minutes using 0.4% surfactant and in 35 minutes using 0.8% surfactant. However, after 90 minutes only 30% separation occurred when no surfactant was used. The fact that 0.4% surfactant resulted in a more rapid separation than 0.8% surfactant indicates that 0.4% surfactant is closer to the optimal amount of surfactant and that at 0.8% surfactant the opposite type of emulsion may be forming to a small extent.

Claims

1. A method of increasing the separation rate of an oil-in-water or water-in-oil emulsion which comprises determining the HLB number of said emulsion and adding to said emulsion a surfactant having an opposite HLB number.

2. A method according to Claim 1, wherein the HLB number is determined by identifying whether said emulsion is an oil-in-water emulsion or a water-in-oil emulsion, and using an HLB number of 3 to 7 if said emulsion is an oil-in-water emulsion, and using an HLB number of 7 to 18 if said emulsion is a water-in-oil emulsion.

3. A method according to claim 2 wherein the emulsion is identified by measuring its electrical resistance, a resistance of less than 1000 ohms indicating an oil-in-water emulsion, and a resistance of more than 1000 ohms indicating a water-in-oil emulsion.

4. A method according to claim 1,2 or 3 wherein the amount of the surfactant is from 0.01 to 1%.

5. A method according to claim 4, wherein the emulsion comprises from 25 to 55 pbw water and 45 to about 75 pbw kerosene.

6. A method according to claim 5, wherein the emulsion includes from 25 to 75 pbw phosphoric acid or sulfuric acid, from 25 to 50 pbw pyrophosphoric acid, and up to 1 pbw U308.

7. A method according to claim 6, wherein the emulsion is a water-in-oil emulsion and the surfactant is non-ionic polyoxyethylene glyceride ester in an amount from 0.01 to 0.5%.

8. A method according to any of claims 1 to 7, wherein the surfactant is added before or during the formation of the emulsion.

9. A method of increasing the separation of an oil-in-water or water-in oil emulsion, said method being substantially as described herein with particular reference to the foregoing Example.