Extraction of uranium from phosphate mineral matrices

Abstract

The invention firstly relates to a method for respectively extracting and producing uranium and, where appropriate, heavy metals and rare earths from phosphato-calcium mineral matrices comprising the steps of a) treatment of said phosphato-calcium mineral matrices with a source of fluoride anions; b) heat treatment of said mixture of fluorides in the presence of calcium metal; and c) separation followed by the individual collection of uranium metal and, where appropriate, of heavy metals and rare earths initially present in the starting material. The invention also relates to a series of methods derived from the implementation of the aforementioned and leading, depending on the pathways followed, to the production, respectively, of phosphoric acid, sulfuric acid, ammonium sulfate or NPK fertilizers and more particularly, respectively, of phosphoric acid, sulfuric acid, ammonium sulfate or NPK fertilizers free of metal contaminants. The invention is defined in the claims. Other objectives of the invention will become apparent over the course of the following description, in particular with reference to the reaction schemes illustrated by the figures below.

Description

[0001] URANIUM EXTRACTION FROM PHOSPHATE MINERAL MATRICES

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a process for the extraction, respectively the production of uranium on the one hand and rare earths on the other hand, from phosphate rocks, phosphate residues and phosphogypsum. This process also makes it possible to provide very high quality phosphoric acid or ammonium phosphate and NPK fertilizer free from impurities.

[0004] PREVIOUS ART

[0005] Due to A number of patents mention attacks with sulfuric, hydrochloric or nitric acid (1-3). The major problem associated with this type of attack is the dissolution of the metals of interest such as uranium and rare earths in phosphoric acid, in the form of cations. This dissolution makes their extraction extremely difficult.

[0006] Canadian patent CA2411977A1 ​​describes a known process for attacking phosphate rock using hydrofluoric acid to produce high-quality phosphoric acid and a mixture of CaF2 and heavy metals. However, this process does not propose purification of CaF2 by extracting the heavy metals.

[0007] The present invention therefore aims to overcome these drawbacks. More specifically, it proposes a process for extracting rare earths and uranium from CaF2. In addition, the CaF2 obtained has a very high quality, which makes it possible to regenerate the hydrofluoric acid used and produce usable gypsum. The present invention generalizes the recovery of metals present in phosphate matrices (raw, residues or waste) by proposing extraction by acid or basic fluoride treatment.

[0008] DESCRIPTION OF THE INVENTION

[0009] According to an implementation as illustrated in Figure 1, the process of the invention makes it possible to obtain pure phosphoric acid in liquid form, free of heavy metals. After this reaction, a solid mixture is obtained, which is then treated with calcium at a temperature generally between 800°C and 1500°C, for example 1450°C. This operation aims to obtain pure CaF2 as well as a metallic mixture comprising heavy metals, rare earths (RE) and uranium. The separation between CaF2 and the metals is carried out by gravimetry, according to the techniques applied in this field.

[0010] It should be noted that hydrofluoric acid is regenerated by attacking pure CaF2 with sulfuric acid, which also makes it possible to obtain pure calcium sulfate.

[0011] This particular aspect of the process (Figure 1) constitutes yet another implementation of the invention, i.e. the use of calcium fluoride CaF2 for the regeneration of hydrofluoric acid.

[0012] According to an implementation as illustrated in Figure 2, HF acidulation can be applied to the phosphogypsum (PG) matrix PG resulting from the attack of phosphate rocks by sulfuric acid to extract uranium and rare earths (RE) and sulfuric acid and high-quality gypsum (for construction) as secondary products.

[0013] An alternative implementation of the process of the invention is described in Figure 3. The main difference concerns the attack of phosphate rocks and phosphate residues. It is carried out by ammonium fluoride. It allows in the same way to extract valuable metals (U, RE, Cd, etc.). The other advantage of this 3rd variant of the process is that this approach makes it possible to obtain an ammonium phosphate directly without passing through the production of phosphoric acid and that the regeneration of the NH4F used is done in this case via a treatment of the CaF2 obtained by ammonia.

[0014] This particular aspect of the above process constitutes yet another implementation of the invention, i.e. the use of calcium fluoride CaF2 obtained according to step b) for the regeneration of ammonium fluoride, respectively potassium fluoride.

[0015] Another implementation of the process of the invention is described in Figure 4. It allows the extraction of metals (U, RE, Cd, etc.) and the direct production of NPK fertilizers from phosphate rocks and phosphate residues, by slightly modifying the process presented in Figure 3. In fact, the attack is carried out by a mixture of fluoride (NH4F + KF) and no longer NH4F only.

[0016] The terms "phosphate rocks, respectively phosphate residues" are common in the relevant technical field: they encompass all types of phosphate-calcium mineral matrices, such as natural phosphate-calcium rocks, natural phosphate rocks, residues from the processing of natural phosphate rocks, phosphate mining waste and phosphogypsum.

[0017] The various metals and / or rare earths (RE) referred to in the context of the present invention are typical of the exploitation of natural deposits of phosphate ores and are known to those skilled in the art; present in variable quantities depending on the deposits or the extraction techniques used, and often in trace amounts, they may constitute, depending on the case, impurities which should be eliminated both from the uranium to be extracted and from the regenerated reagents according to figures 1 to 4 above. Conversely, the recovery, separation or purification of such minerals or rare earths, by means of technologies available to those skilled in the art, represents a significant additional use of the invention.

[0018] BRIEF DESCRIPTION OF FIGURES AND TABLES

[0019] As shown in Figures 1 to 4 above, the first variant of the uranium and rare earth production process comprises a first step (1) of acidulation with HF which consequently allows the production of a solid phase composed of CaF2 and uranium fluorides such as UF4 and / or UF6, rare earth fluorides and other metals (Cd, Cr, etc.). Step (1) also allows the production of pure phosphoric acid. Then a second step (2) of heat treatment in the presence of calcium which allows the production of elemental metals easily separable by gravimetry. The secondary product CaF2 is then subjected to a (3) reaction with sulfuric acid to reproduce HF to be recycled in (1) and high-quality gypsum. This process makes it possible to orient the treatment of phosphate rock and phosphate rock residues independently of its P content, for the recovery of precious metals.

[0020] As shown in Figure 2, the same process can be applied for the extraction of metals in PG. This second process allows the recovery of metals as in step (1), however, the secondary product in this case is sulfuric acid (4). In the same way steps (2) and (3) allow the extraction of metals, the recycling of HF and the recovery of high quality gypsum.

[0021] As shown in Figure 3, the 3rd variant of the uranium and rare earth production process comprises a first step (5) of basic treatment by NH4F which consequently allows the production of a solid phase composed of CaF2 and uranium fluorides, rare earth fluorides and other metals (Cd, Cr, etc.). Step (5) also allows the production of ammonium phosphate free of metals. Then step (2) allows the production of elemental metals easily separable by gravimetry. The secondary product CaF2 is then subjected to a reaction with sulfuric acid and ammonia (6) to obtain NH4F to be recycled in (5) and high-quality gypsum. This process makes it possible to orient the treatment of phosphate rock and phosphate rock residues independently of its P content, for the recovery of precious metals by producing ammonium phosphate directly without going through the production of phosphoric acid.

[0022] As shown in Figure 4, the 4th variant of the uranium and rare earth production process includes a first step (7) of basic treatment by NH4F and KF which consequently allows the production of a solid phase composed of CaF2 and uranium fluorides, rare earth fluorides and other metals (Cd, Cr, etc.). (7) also allows the production of NPK free of metals. Then step (2) allows the production of elemental metals easily separable by gravimetry. The secondary product CaF2 is then subjected to step (6) to reproduce NH4F and KF to be recycled in (7) and high-quality gypsum. As is the case of variant no. 3 of the process, this route makes it possible to orient the treatment of phosphate rock and phosphate rock residues independently of their P content, for the recovery of precious metals by producing NPK directly without going through the production of phosphoric acid.

[0023] INDUSTRIAL APPLICATION

[0024] The four processes according to the invention are particularly intended for the phosphate industry which will make it possible to recover phosphate rocks, phosphate rock residues and phosphogypsum, resulting from the attack of phosphate rocks by sulfuric acid, to produce uranium, rare earths and heavy metals as primary products. Phosphoric acid, ammonium phosphate, NPK and CAF2 or Gypsum as secondary products.

[0025] REFERENCES

[0026] 1- US2898207A. Acidulation of Phosphate.

[0027] 2-US3205062A. Nitric acid acidulation of phosphate rock

[0028] 3-US7824634B2. Method for etching phosphate ores

[0029] ABRIDGED

[0030] The invention relates to a process for producing uranium, various metals and rare earths from phosphate matrices (raw and residues). This process involves an attack by hydrofluoric acid, ammonium fluoride or a fluoride mixture (KF+NH4F).

[0031] The same HF acidulation procedure can be applied to other matrices such as phosphogypsum (PG) to extract uranium, various metals and rare earths after gravimetric separation. In the case of PG, sulfuric acid is generated as a by-product.

Claims

CLAIMS 1. Process for extracting uranium and, where appropriate, heavy metals and rare earths from phosphato-calcium mineral matrices, characterized in that it comprises the steps of a) treatment of said phosphato-calcium mineral matrices using a source of fluoride anions to obtain a mixture of metal fluorides comprising CaF2 and Uranium fluorides (UF4 and / or UF6), where appropriate heavy metal fluorides and rare earth fluorides; b) heat treatment of said mixture of fluorides in the presence of metallic calcium to obtain a mixture of CaF2 and metallic uranium and, where appropriate, heavy metals and rare earths in their metallic form; and c) separation of said metals by gravimetry followed by the individual collection of metallic uranium and, where appropriate, heavy metals and rare earths in their metallic form.

2. Method according to claim 1, characterized in that the phosphato-calcic mineral matrices are chosen from natural phosphato-calcic rocks, natural phosphate rocks, residues from the treatment of natural phosphate rocks, phosphate mining waste and phosphogypsum.

3. Method according to at least one of claims 1 and 2, characterized in that the source of fluoride anions (step a) is chosen from hydrofluoric acid, ammonium fluoride, potassium fluoride or a mixture of these.

4. Method according to at least one of claims 1 to 3, characterized in that the heat treatment of the mixture of metal fluorides obtained according to step a) is carried out in the presence of metallic calcium at a temperature between 800°C and 1500°C, preferably at approximately 1450°C.

5. Method according to at least one of claims 1 to 4, characterized in that the treatment of natural phosphato-calcic or phosphate rocks, residues from the treatment of natural phosphate rocks or phosphate mining waste using hydrofluoric acid according to step a) leads to the production of phosphoric acid, in particular phosphoric acid free from metallic contaminants.

6. Method according to at least one of claims 1 to 4, characterized in that the treatment of natural phosphato-calcic or phosphated rocks, or of the residues from the treatment of natural phosphated rocks using ammonium fluoride according to step a) leads to the production of ammonium phosphate, in particular ammonium sulfate free from metallic contaminants.

7. Method according to at least one of claims 1 to 4, characterized in that the treatment of natural phosphato-calcium or phosphate rocks, residues from the treatment of natural phosphate rocks using potassium fluoride and ammonium fluoride according to step a) leads to the production of NPK-type mineral fertilizer, in particular an NPK-type fertilizer free from metallic contaminants.

8. Method according to at least one of claims 1 to 4, characterized in that the treatment of phosphogypsum using hydrofluoric acid according to step a) leads to the production of sulfuric acid, in particular sulfuric acid free from metallic contaminants.

9. Use of calcium fluoride CaF2 obtained according to step b) of the process according to at least one of claims 1 to 8, for the regeneration of hydrofluoric acid by treatment using sulfuric acid.

10. Use of calcium fluoride CaF2 obtained according to step b) of the process according to at least one of claims 1 to 8, for the regeneration of ammonium fluoride, respectively potassium fluoride and ammonium fluoride by treatment with ammonia.

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