Extraction and purification of uranium ore

The process of extracting uranium from uranium ore into a nuclear-purified (see radionuclide purity) uranium compound is an important step in the production of natural uranium. The main products are ammonium diuranate (commonly known as yellow cake) and uranyl tricarbonate. Purified (also known as refined) uranium compound products must meet nuclear purity requirements. The refined product is further dried, calcined and processed into uranium dioxide or uranium octaoxide for use in the manufacture of reactor components or uranium hexafluoride (for isotopic separation of U-235). The whole process must be carried out by the following units: crushing and grinding of uranium ore, leaching of uranium ore, solid-liquid separation of slurry, extraction of uranium concentrate by ion exchange and solvent extraction, and purification of uranium concentrate by solvent extraction. According to different ore types, product requirements, etc., the appropriate process consisting of the above unit operations can be selected.

1, broken and ground

The crushing is carried out by crushing, crushing and finely crushing the ore through a jaw crusher , a round crusher or a hammer crusher to achieve the required strength. Fine grinding is then carried out to achieve the desired particle size for the leaching process.

2, leaching

The uranium in the ore is selectively dissolved with a solvent. After leaching of uranium ore, uranium is separated from most of the gangue. The ratio of uranium to impurities in the leachate is about 10 to 30 times higher than that in the original ore. Therefore, the leaching process is also the process of preliminary separation of uranium and impurities.

Uranium ore leaching methods generally have two methods: acid method and alkali method. Most uranium hydrometallurgical plants use acid leaching, and a few plants use alkali leaching. Only some plants use both acid and alkali leaching processes. The acid leaching method generally uses sulfuric acid as a leaching agent, and uranium and sulfuric acid in the ore react to form soluble uranyl ion UO ₂ and uranyl sulphate ion [UO ₂ (SO ₄ )]; oxidizing agent is often added during leaching (usually two Manganese oxide , sodium chlorate) to maintain a suitable redox potential (about 450 millivolts) to oxidize tetravalent uranium to hexavalent to increase uranium leaching rate. The carbonate-bearing uranium ore is mainly leached by alkali method. The commonly used leaching agent is an aqueous solution of sodium carbonate and sodium hydrogencarbonate. Under the condition of bubbling air, uranium and sodium carbonate in the ore form uranyl carbonate sodium Na. ₄ [UO ₂ (CO ₃ ) ₃ ], soluble in leachate.

3. Solid-liquid separation of pulp

The solution and slag in the acidic or alkaline slurry (including uranium-containing solution, partial impurities and solid slag) obtained after ore leaching shall be separated. The coarse ore grading may also be carried out as needed to remove the coarse sand of +200 to 40 mesh to obtain a fine mud slurry. Commonly used solid-liquid separation equipment includes a filter and a settling tank (thickener); the classification equipment has a spiral classifier and a hydrocyclone. China also uses a fluidization tower for grading and washing.

The separated solution can be separated into uranium by ion exchange. The uranium can also be separated and purified by solvent extraction, or the uranium can be precipitated from the uranium-containing solution.

4. Ion exchange extraction of uranium

The content of uranium octaoxide in the leachate after solid-liquid separation is approximately 500 to 1000 mg/liter. It is more suitable to extract uranium by ion exchange method for leachate with low uranium concentration. The ion exchange method generally uses a strong basic anion exchange resin to adsorb uranium. According to the solid content of the adsorption liquid, the adsorption can be divided into clear liquid adsorption, turbid liquid adsorption and slurry adsorption. When the resin is saturated with water, it is washed with water, and then the uranium is dripped from the resin with an eluent (sodium sulfate, sodium chloride, ammonium chloride, sodium nitrate, sodium nitrate, nitric acid, ammonium nitrate, dilute sulfuric acid or dilute nitric acid). Wash it down.

COMCESS®UA380S(sulfate form) Ion Exchange Resin is a strongly basic, macro-reticular anion exchange resin. It is a true, macroporous network which differs completely from conventional gel-type resins,providing outstanding osmotic and physical stability as well as excellent kinetics. The crosslinked polystyrenic matrix makes this resin particularly stable mechanically.

UA380S uranium extraction resin has been specially developed for the extraction of uranium from ore, both for In Situ Leaching and RIP (Resin-In-Pulp) processes.

5. Extraction and purification of uranium by extraction

The solution treated by the uranium hydrometallurgical plant is a dilute solution with a large volume, low uranium concentration and high impurity content. The uranium and impurities should be separated and the uranium should be initially concentrated. In the refining process, a high concentration of uranium-containing solution is treated. Product quality requirements are nuclear purity. In the uranium extraction process commonly used organophosphine alkyl amine extractant with an acid Tributyl (TBP), di (2-ethylhexyl) phosphate, trioctyl amine.

In the uranium hydrometallurgical plant, the extraction of the sulfuric acid system uses two extraction processes of phosphorus and amine (the quaternary ammonium salt extraction process of the alkaline system), such as the alkylphosphine extraction process and the amine extraction process, the latter More applications in the world. More applications in China are the process of leaching. The saturated resin adsorbing uranium was rinsed with 1 mol/L of sulfuric acid, and then the eluent was extracted. For example, the extractant used in the leaching process is a 0.2 mol/L bis(2-ethylhexyl)phosphoric acid-0.1 mol/L trialkylphosphine oxide system. The saturation of the organic phase is controlled to be 85% or more. After washing with water, it is back-extracted with ammonium carbonate crystals to obtain nucleated pure uranyl tricarbonate. This rinsing process was extracted with binding, that the amount of treated liquid extraction reduction, high metal recovery, saving reagents, the purity of the product is also high.

The products produced by the uranium hydrometallurgical plant are generally industrial uranium concentrates, which still contain impurities such as sulfate, silicon, calcium and magnesium , which must be further refined to obtain nuclear pure products. The most commonly used in the refining process is the TBP extraction process. TBP has a large saturation capacity for uranium and can handle solutions with high uranium content. Under the condition that the organic phase is close to saturation, it has high purification ability for impurity elements.

6. Precipitation of uranium from uranium-containing solution

In the solution obtained by leaching, uranium may also be separated as an insoluble compound; and purification may be carried out by multiple dissolution and reprecipitation of the precipitate. There are mainly alkali neutralization methods and hydrogen peroxide precipitation methods:

(1) alkali neutralization method

An alkaline precipitant such as ammonia water, magnesium oxide, gaseous ammonia or the like is added to the acidic uranium-containing solution, and the final pH is controlled to be 6.5 to 8.0, and the uranium is completely precipitated as a diuranic acid salt. For the alkaline leach solution, sodium hydroxide precipitant is mainly used to precipitate sodium uranium or sodium diuranate. If uranium is precipitated from the purified acidic solution, the purity of the precipitated ammonium diuranate is higher.

(2) Hydrogen peroxide precipitation method

Adjust the pH of the uranium-containing solution to 2.5-4.0, slowly add 30% hydrogen peroxide in excess of the stoichiometric amount, and then add an appropriate amount of ammonia water to neutralize the acid formed during the reaction to a final pH of 2.8 to form uranium. The peroxide (UO ₄ × H ₂ O) precipitated. The hydrogen peroxide precipitation method has high selectivity to uranium and can be obtained as a crystalline, easy-to-handle product, which is also of industrial significance.