RU2843350C1 - Method of processing eudialyte concentrate - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to processing of eudialyte concentrates. Method involves leaching the concentrate with nitric acid to obtain a productive solution and silica gel. Then, valuable components and cake are extracted from silica gel. In order to extract valuable components from silica gel in form of a residue of silicates of Zr and rare-earth elements, sodium hydroxide is added to the silica gel, wherein simultaneously a sodium metasilicate solution is obtained and the obtained residue is returned for leaching. Hydroxide of Zr and rare-earth elements is separated from the productive solution through successive chemical deposition. At the first deposition step, Zr hydroxide is extracted by neutralizing the solution with calcium carbonate to pH 4, and at the second deposition step, rare-earth elements are extracted by neutralizing the solution with sodium carbonate to pH 6. Zr hydroxide is dissolved with acidic water obtained when washing the silica gel, and precipitation is carried out with calcium phosphate to obtain zirconium phosphate and calcium nitrate solution. Calcium carbonate is recovered from the spent calcium nitrate solution by adding ammonia and carbon dioxide obtained at the first precipitation step, or ammonium carbonate, while simultaneously obtaining ammonium nitrate.

EFFECT: providing recovery and processing of reagents, reducing losses of Zr and rare-earth elements and obtaining additional commercial products.

1 cl, 1 dwg, 1 ex

Description

Field of technology to which the invention relates

The invention relates to methods for processing eudialyte concentrate and can be used to obtain zirconium phosphate, rare earth carbonates, sodium metasilicate and ammonium nitrate.

State of the art

A method for processing eudialyte concentrate is known (RU No. 2626121, C 22 B 34/14, 59/00, 3/08, 2017), which consists of treating the eudialyte concentrate with sulfuric acid with the addition of sodium fluoride, which helps to destroy the amorphous structure of silica gel at a ratio of F:Zr = 3, filtering the insoluble precipitate, washing it and feeding the solution after washing and acid opening to the extraction stage of separation of REE and zirconium cations.

The disadvantage of the method is the need to separate zirconium and REE by extracting from corrosive sulfate-fluoride media with low distribution coefficients of the target components.

A method for processing eudialyte concentrate is known (RU No. 2649606, C 22 B 34/14, 59/00, 3/08, C01B 33/12 2018), which consists of decomposing the concentrate with 30-40% sulfuric acid at a temperature of 80-120 °C, separating the residue from the Zr-containing solution, washing it with water in two stages, separating zirconium from the solution by extraction with a mixture of trioctylamine, octanol and kerosene and extracting REE from the silica-containing residue.

The disadvantages of this method are the low degree of extraction of REE from eudialyte concentrate - no more than 60%.

Also known, adopted as a prototype, is a method for processing eudialyte concentrate (RU No. 2742330 C 22 B 59/00, 34/14, 3/06, 3/26 2021), including its decomposition with nitric acid to obtain a gel, drying the gel at a temperature of 180 ° C to 200 ° C, aqueous leaching of the gel, followed by nitric acid leaching in the presence of fluorine-containing compounds in an amount of 4.0 to 4.5 mol of fluorine per 1 mol of zirconium. The combined solution after nitric acid leaching and washing the precipitate is neutralized in two stages, first to pH = 5-6 to separate the precipitate of zirconium compounds, and then to pH = 9-11 to separate manganese hydroxide. The precipitate of zirconium compounds is dissolved in nitric acid and sent to a cycle of extraction separation of zirconium and hafnium using a solution of tributyl phosphate in a hydrocarbon diluent to obtain highly pure zirconium and hafnium compounds.

The disadvantages of the method are: the use of high temperatures during gel drying, the formation of significant volumes of liquid salt waste, and the use of multi-stage leaching in nitric acid.

Disclosure of the essence of the invention

The present invention is aimed at achieving a technical result, which consists in developing a technology for the complex processing of eudialyte concentrate, including energy-efficient and resource-saving technological solutions that ensure the regeneration and processing of reagents, a reduction in the loss of Zr and REE with the resulting silica gel and in the processes of processing productive solutions, as well as obtaining additional marketable products.

The technology for complex waste-free processing of eudialyte concentrate (Fig. 1) includes:

- leaching of eudialyte concentrate with nitric acid to obtain a productive solution and silica gel;

- extraction of cake (undissolved mineral particles) from silica gel by washing with water;

- obtaining a solution of sodium metasilicate from washed silica gel using sodium hydroxide;

- extraction of Zr and REE from the productive solution by the method of sequential chemical precipitation;

- obtaining zirconium phosphate and a saturated solution of calcium nitrate from a Zr-containing precipitate using calcium phosphate;

- regeneration of calcium carbonate from calcium nitrate solution using ammonia and carbon dioxide;

- washing of the resulting precipitates with subsequent filtration and drying, ensuring the production of zirconium phosphate (with a Zr content of at least 30%) and REE carbonates (with a REE oxide content of at least 25%).

The technical result is achieved due to the fact that the leaching of the eudialyte concentrate is carried out with a nitric acid solution of 450 g/l at a temperature of 80°C and a solid:liquid ratio of 1:20. The resulting suspension is centrifuged to separate the productive solution and silica gel containing the remains of undissolved mineral particles.

When silica gel is washed with water at a ratio of 1:10 s and a temperature of 75°C to 80°C, the remaining mineral components precipitate under the action of gravitational forces, after which the silica gel is separated from the liquid phase by centrifugation.

When sodium hydroxide is added, the washed silica gel changes from a gel-like state to a liquid state - a sodium metasilicate solution, the evaporation of which allows obtaining sodium metasilicate pentahydrate. Along the way, a low-soluble precipitate of silicates and hydroxides of Zr, REE, Al, Mn, Fe and other metals will fall out. The extraction of Zr and REE into the precipitate is more than 85%, which, when it is returned to the leaching operation, ensures an increase in the Zr and REE content in the productive solution by more than 12% and the total extraction of valuable components by more than 8%.

In the first stage of precipitation, neutralization of nitric acid with precipitation of Zr with Al and Fe impurities was ensured by increasing the pH of the solution to 4 using calcium carbonate. In the second stage, precipitation of REE was achieved by increasing the pH of the solution to 6 using sodium carbonate.

In view of the low concentration of zirconium in the product obtained in the first stage of precipitation (represented to a greater extent by calcium nitrate tetrahydrate and to a lesser extent by zirconium hydroxide), its subsequent processing is proposed, including the following operations: dissolution of the precipitate with acidic waters at a ratio of 1:2, used in the process of washing the silica gel; agitation of the Zr-containing solution with calcium phosphate; washing; filtration; drying. The spent solution saturated with calcium nitrate after separation of the zirconium phosphate precipitate enters the operation of regenerating calcium carbonate.

In the process of REE precipitation (second stage of precipitation) from the productive solution during its neutralization to pH 6, a more soluble compound - sodium carbonate - was used. The resulting REE carbonate precipitate is sent for filtration, followed by washing with water and drying.

Regeneration of calcium carbonate (with the concomitant production of ammonium nitrate) from solutions saturated with calcium cations (solutions after the separation of zirconium phosphate) is carried out by adding carbon dioxide released in the first stage of precipitation and ammonia (ammonium hydroxide) or ammonium carbonate. Regeneration up to 98% calcium carbonate used in significant quantities in the first stage of precipitation to neutralize the nitric acid solution ensures a reduction in Zr and REE losses by 3-7% due to the fact that previously unrecovered cations of valuable components pass into the regenerated (precipitated) calcium carbonate from the spent productive solutions and wash waters.

Closing the water circuits with full circulation of spent productive solutions and wash waters helps to increase the efficiency and environmental safety of the developed technological scheme for processing eudialyte concentrate. For example, only replacing the water entering the leaching process for acid dilution with a solution after washing silica gel ensures an increase in the concentration of valuable components in the productive solution by more than 5% and a decrease in nitric acid consumption by 12.2%.

Implementation of the invention

Example 1

A 30 g sample of eudialyte concentrate (less than 630 μm in size) containing 6.88% zirconium and 1.55% REE was leached at 80°C and a solid:liquid ratio of 1:20 with a 450 g/l nitric acid solution. The resulting suspension was centrifuged to separate the productive solution and silica gel containing the remains of undissolved mineral particles. Silica gel was washed with water in a solid:liquid ratio of 1:10 while heating to 75-80°C for 1.5 hours. During the washing process, mineral particles precipitated under the force of gravity. The silica gel solution after separating the mineral particle sediment (leaching cake) was centrifuged to obtain washed silica gel and a nitric acid solution. The extraction of Zr and REE into the cake was 9.02% and 15.98%, respectively. The partial extraction of Zr and REE into the acidic solution during silica gel washing was 57%. Sodium hydroxide (5 g per 100 g of silica gel) was added to the washed silica gel, transferring the silica gel into the liquid phase - a sodium metasilicate solution, in which a precipitate of silicates of Zr, REE, Al, Mn, Fe and other metals precipitates within 10 minutes. This precipitate was separated in a centrifuge and returned for leaching in order to increase the concentration of Zr and REE in the productive solution. The partial extraction of Zr and REE into the sediment was 85.6% and 85.1%, respectively. In total, taking into account washing and processing of silica gel into sodium metasilicate solution, the extraction of Zr and REE from silica gel was 97.3 and 97.1%, respectively. After the extraction of valuable components, the sodium metasilicate solution was dried to meet the requirements (e.g., HG/T2568-08 standard). The losses of Zr and REE in the metasilicate were 1.51% and 1.40%, respectively, of their total content in the concentrate.

Productive nitric acid leaching solution was combined with nitric acid waters obtained during silica gel washing in a ratio of 1:5 (or more) and neutralized with calcium carbonate (at a consumption of 6.7 tons per ton of concentrate) to a pH of 4 to obtain a precipitate of Zr hydroxide with Al and Fe impurities. Subsequently, this precipitate was dissolved in nitric acid waters of silica gel washing at a ratio of 1:2 and the resulting solution was agitated with calcium phosphate (at a consumption of 0.13 tons per ton of concentrate) to precipitate zirconium phosphate. After that, the precipitate was washed with water at a ratio of at least 1:5, filtered and dried, which ensured the production of a zirconium concentrate with a valuable component content of at least 30%. The total extraction of Zr and REE into zirconium concentrate (zirconium phosphate) according to the proposed scheme was 89.44% and 0.62%, respectively.

At the second stage of precipitation, by increasing the pH of the productive solution to 6 with sodium carbonate (at a consumption of 0.14 tons per ton of concentrate), a precipitate of REE carbonates was obtained. The obtained carbonate precipitate of REE was sent for filtration, followed by washing with water at a ratio of more than 10:1, repeated filtration and drying. The total extraction of Zr and REE into the carbonate precipitate of REE was 0.02% and 82.00%, respectively, with a REE content of at least 25%.

Regeneration of calcium carbonate in calcium cation-saturated solutions (solutions after zirconium phosphate extraction) was carried out by adding ammonium carbonate to them (at a consumption rate of 287 g per 1 l). Regeneration of calcium carbonate ensures a reduction in Zr and REE losses by 3-7%.

Claims (1)

A method for processing eudialyte concentrate, including its leaching with nitric acid to obtain a pregnant solution and silica gel, extracting valuable components and cake from the silica gel by washing it with water followed by its processing, separating a precipitate of Zr hydroxide and REE from the pregnant solution by a method of sequential chemical precipitation, characterized in that in order to extract valuable components from silica gel in the form of a precipitate of Zr and REE silicates, sodium hydroxide is added to it, while simultaneously obtaining a solution of sodium metasilicate, and the resulting precipitate is returned for leaching, in the first stage of precipitation, Zr hydroxide is separated from the pregnant solution by neutralizing it with calcium carbonate to pH 4, in the second stage of precipitation, REE are separated from the pregnant solution by neutralizing it with sodium carbonate to pH 6, the resulting Zr hydroxide is dissolved in acidic waters obtained during the washing process silica gel, in a ratio of 1:2 or more, and precipitation is carried out with calcium phosphate to obtain zirconium phosphate and a calcium nitrate solution, while regeneration of calcium carbonate is carried out from the spent calcium nitrate solution by adding ammonia and carbon dioxide obtained in the first stage of precipitation, or ammonium carbonate with the concomitant production of ammonium nitrate.