A reductive stripping flow sheet for recovery of uranium from wet-process phosphoric acid is described. Uranium is stripped from a uranium-loaded organic phase by a redox reaction converting the uranyl to uranous ion. The uranous ion is reoxidized to the uranyl oxidation state to form an aqueous feed solution highly concentrated in uranium. Processing of this feed through a second solvent extraction cycle requires far less stripping reagent as compared to a flow sheet which does not include the reductive stripping reaction.

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Patent
   RE31686
Priority
Jan 09 1974
Filed
Jan 09 1974
Issued
Sep 25 1984
Expiry
Sep 25 2001
Inventors
Hurst, Fre…
Assg.orig
The United…
Assg.curr
The United…
Entity
unknown
Referenced by
2
References
6
Maint.:
EXPIRED
BACKGROUND OF THE IN…
7. A process for the recovery of uranium from a wet-process phosphoric acid solution derived from the acidulation of uraniferous phosphate ores which comprises contacting said solution with an organic extractant consisting essentially of di(2-ethylhexyl)phosphoric acid and trioctylphosphine oxide dissolved in an organic diluent, reductively stripping the extractant of uranium with a strip solution in which ferrous ion is used to reduce uranyl ions in the extractant to uranous ions in the strip solution, and disengaging the strip solution from the organic phase. 8. process for obtaining uranium values from an extractant comprising di-(2-ethylhexyl)phosphoric acid and a trioctylphosphine oxide dissolved in a water-immiscible organic solvent which comprises stripping the extractant with an aqueous phosphoric acid solution containing from about 40 to 85 percent by weight H3 PO4 having dissolved therein a divalent iron salt.
1. A process for the recovery of uranium from a wet-process phosphoric acid solution derived from the acidulation of uraniferous phosphate ores which comprises contacting said solution with an organic extractant consisting essentially of di(2-ethylhexyl)phosphoric acid and trioctylphosphine oxide dissolved in an organic diluent, reductively stripping the extractant of uranium with a strip solution in which ferrous ion is used to reduce uranyl ions in the extractant to uranous ions in the strip solution, disengaging the strip solution from the organic phase, contacting said strip solution with an oxidizing reagent which converts quadrivalent uranium to hexavalent form, and then passing the resultant solution through a second liquid-liquid solvent extraction cycle where the uranium is stripped from the organic phase with an aqueous solution of ammonium carbonate to produce a product consisting essentially of ammonium uranyl carbonate.
2. The process according to claim 1 in which the reductive strip solution contains from 5 to 20 grams per liter of ferrous ion dissolved in a 5 to 7-molar solution of phosphoric acid.
3. The process according to claim 1 in which the ammonium uranyl tricarbonate product is converted to an oxide of uranium. 4. process for obtaining uranium values from a synergistic extractant comprising a dialkylphosphoric acid and a trialkylphosphine oxide dissolved in a water-immiscible organic solvent which comprises stripping the extractant with a 5- to 7-molar aqueous phosphoric acid solution having dissolved therein a divalent iron salt.
5. The process according to claim 4 wherein the aqueous phase is oxidized after uranium stripping.
6. process according to claim 4 wherein said phosphoric acid solution contains dissolved therein from 5 to 20 grams of divalent iron per liter of solution.
BACKGROUND OF THE INVENTION

The present invention relates to an improved process for the recovery of uranium as a by-product of phosphate fertilizer production. More particularly, it relates to a process for the recovery of uranium from the wet-process phosphoric acid that is produced in the treatment of phosphate rock found in Florida and other states of the United States and in several foreign countries. The invention described herein was made in the course of, or under, a contract with the United States Atomic Energy Commission.

The main purpose in mining phosphate rock is to recover a high-phosphate-containing fertilizer. The first step in winning the phosphate from the rock consists of digesting the rock with sulfuric acid under controlled temperature and concentration conditions to produce a phosphoric acid solution and an insoluble calcium sulfate (gypsum). Prior to further treatment to produce a commercially acceptable fertilizer product, this phosphate solution can be processed to remove valuable uranium values provided such processing is economically justified.

It is accordingly an object of this invention to provide a process for the recovery of uranium values from uraniferous phosphate mined deposits that satisfies this criterion.

The phosphate rock mined in Florida contains 0.01 to 0.02 weight percent uranium or from 0.2 to 0.4 pound of uranium per mined ton. While this appears to be a relatively small concentration, it represents a large supply of uranium because of the large amount of phosphate rock processed. For example, it has been estimated that in 1970 the wet-process phosphoric acid produced from Florida phosphate rock BRIEF DESCRIPTION OF THE DRAWING

The drawing is a flow diagram of a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION synergistic extract combinations of D2EHPA or other dialkylphosphoric acids with other phosphine oxides or phosphonates as disclosed in ORNL-TM-2522 are to be considered as falling within the scope of our invention. In comparative tests of a number of neutral organophosphorus compounds in combination with D2EHPA, none of the combinations tested had greater extraction power than the combination of D2EHPA and TOPO as shown in the Tables below. These compounds include several phosphine oxides, a diphosphine oxide, a diphosphonate, and two phosphonates. It is anticipated that results obtained with phosphine oxides having n-alkyl chains shorter than n-octyl (e.g., tri-n-hexyl phosphine oxide) will be equivalent to those observed with TOPO inasmuch as they are all trialkyl phosphine oxides. A number of extractants of different types and structure were screened to determine the capabilities for extracting as set forth in the following Tables A-1 and A-2.

TABLE A-1
______________________________________
Extraction of Uranium with Synergistic Reagent Combinations
Organic-phase:
0.2 M concentration of an acid reagent
plus TOPO in NDD diluent
Aqueous phase:
5.3 M H3 PO4, 0.2 g U(VI)/liter
Contact: 5 min at phase ratio of 1/1; 25°C
Uranium
TOPO Extraction
Conc. Coefficient
Acid Reagent (M) (Eao)
______________________________________
Monoheptadecylphosphoric acid
0.0 0.10
0.05 0.15
di(2-ethylhexyl)phosphoric acid
0.0 <0.01
(D2EHPA) 0.05 2.6
di(n-decyl)phosphoric acid
0.0 <0.1
0.1 2.1
di(n-octyl)phosphoric acid
0.05 4.3
1-hydroxy-2-ethylhexylphosphonic acid
0.0 0.15
0.1 0.4
2-ethylhexyl phenylphosphonatea
0.0 0.9
0.1 4.0
Dinonylnapthalenesulfonic acid
0.0 <0.01
(DNNSA) 0.05 0.16
0.10 0.70
0.15 1.3
0.20 2.1
0.25 2.6
0.30 3.0
______________________________________
a 0.4 M
NDD = nDodecane
All of the uranium in the tests in this series was present as U(VI).
Table A-2
______________________________________
Extraction of Uranium with Combinations of D2EHPA and
Various Neutral Reagents
Organic phase:
0.18 M D2EHPA, 0.05 M additive,
NDD diluent
Aqueous phase:
5.3 M H3 PO 4, 0.2 g U(VI)/liter
Contact: 5 min at phase ratio of 1/1;
25°C
Uranium Extraction
Additive Coefficient (Eao)
______________________________________
Trioctylphosphine oxide (TOPO)
2.6
Phenyldibutylphosphine oxide
1.8
Butyldiphenylphosphine oxide
0.78
Tri(2-ethylhexyl)phosphine oxide
0.41
Methylenebis(di-n-hexylphosphine oxide)
2.5
Diamylamylphosphonate 0.61
Di(sec-butyl)phenylphosphonate
0.11
Tetrakis(2-ethylhexyl)ethylene
0.26
Diphosphonate
______________________________________
INVENTORS:

Hurst, Fred J., Crouse, David J.

THIS PATENT IS REFERENCED BY THESE PATENTS:
Patent Priority Assignee Title
4778663, Aug 27 1987 American Cyanamid Company Uranium recovery from wet process phosphoric acid unsymmetrical phosphine oxides
4836956, Mar 10 1986 WHITE SPRINGS AGRICULTURAL CHEMICALS, INC Extraction of polyvalent metals with organodiphosphonic acids
THIS PATENT REFERENCES THESE PATENTS:
Patent Priority Assignee Title
2860031,
2866680,
2937925,
3052513,
3243257,
3737513,
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