CN111945001B

CN111945001B - Treatment method of monazite optimal slag

Info

Publication number: CN111945001B
Application number: CN201910414540.7A
Authority: CN
Inventors: 张宝藏; 秦毓根; 殷留庆; 张香标
Original assignee: Yongzhou Xiangjiang River Rare Earth Co ltd
Current assignee: Yongzhou Xiangjiang River Rare Earth Co ltd
Priority date: 2019-05-17
Filing date: 2019-05-17
Publication date: 2021-12-03
Anticipated expiration: 2039-05-17
Also published as: CN111945001A

Abstract

The invention relates to a method for treating monazite high-quality slag. Specifically, the method is a method for extracting and separating iron, uranium, thorium and mixed rare earth from monazite optimum solution slag in a mixed acid solution of hydrochloric acid and nitric acid, and comprises the following steps: hot-dissolving and optimizing slag by hydrochloric acid; separating iron, uranium-thorium and rare earth; separating iron and uranium; preparing hydrochloric acid-nitric acid mixed acid feed liquid of thorium and rare earth; separating thorium and rare earth; and extracting the misch metal. The method has good uranium, thorium and rare earth separation effect and high recovery rate, can produce uranium and thorium products meeting the requirements of nuclear fuel, can realize the recycling of acid, and is environment-friendly.

Description

Treatment method of monazite optimal slag

Technical Field

The invention belongs to the field of hydrometallurgy, and particularly relates to a method for extracting and separating iron, uranium, thorium and mixed rare earth in monazite optimum-solubility slag in a mixed acid solution of hydrochloric acid and nitric acid.

Background

The monazite is treated in industrial scale in China, uranium, thorium and rare earth elements are extracted from the end of the fifties of the last century, a Yuan chemical plant in Shanghai dissolves monazite alkali soluble cakes completely with concentrated nitric acid, and then uses tributyl phosphate (TBP) to separate uranium, thorium and rare earth in nitric acid full solution. This method is used until the plant is shut down due to environmental problems at the beginning of this century. In addition to dissolving slag with nitric acid, CN104278165A discloses dissolving slag with sulfuric acid, which is less expensive than nitric acid, and extracting uranium, thorium and rare earth with amines (primary or tertiary amines) in a sulfuric acid medium. There are also processes for extracting uranium, thorium and rare earth (such as CN103014359A, CN 103014333A) by using ion exchange resin in a sulfuric acid medium, extracting thorium by using acidic phosphate (such as P-204) and extracting rare earth by using primary amine (such as CN 103014333A), but the processes are difficult to manage due to the fact that the ion exchange resin and liquid-liquid extraction technologies and two extracting agents are adopted, the separation effect is not ideal enough, and a large-scale production application report is not seen so far. CN104775026 discloses a method for dissolving monazite optimum dissolving slag with hydrochloric acid, extracting methyl phosphorus dimethylheptyl ester from hydrochloric acid solution, and separating uranium, thorium and rare earth by nitric acid liquid impurity washing, wherein the uranium-thorium product prepared by separation does not reach the quality requirement of the current practical application.

Therefore, an environment-friendly monazite dissolved slag treatment method with better separation effect, higher product purity, low raw material consumption, less waste acid discharge is urgently needed.

Disclosure of Invention

The invention provides the monazite dissolved slag treatment method which has the advantages of good separation effect, high product purity, low raw material consumption, less waste acid discharge and environmental friendliness.

The invention provides a method for treating monazite high-quality slag, which comprises the following steps:

(1) hot-melting and excellent-slag-dissolving of hydrochloric acid: mixing the monazite dissolved slag, heating the slurry, adding hydrochloric acid to dissolve, cooling and filtering to obtain filtrate, namely iron, uranium, thorium and rare earth full solution (A);

(2) separating iron, uranium-thorium and rare earth: extracting the full solution (A) by using a kerosene solution added with neutral phosphate as an extracting agent to obtain extracted water-phase thorium, rare earth liquid (B) and an iron-and-uranium-containing organic phase, and washing impurities of the iron-and-uranium-containing organic phase by using dilute hydrochloric acid as a washing liquid to obtain an iron-and-uranium-containing organic phase (C);

(3) and (3) separating iron and uranium: taking an iron-and-uranium-containing organic phase (C) as a feed liquid, taking a dilute nitric acid solution as an iron washing liquid, taking a kerosene solution of neutral phosphate as an extracting agent, discharging iron from a water phase in a form of ferric nitrate, leaving uranium in an organic phase (F), performing back extraction on the organic phase (F) by taking a dilute alkali aqueous solution as a uranium stripping liquid, and acidifying and precipitating the back extraction liquid to obtain the diuranate;

(4) preparing hydrochloric acid-nitric acid mixed acid feed liquid of thorium and rare earth: adding nitric acid into the thorium and rare earth liquid (B) obtained in the step (2) to obtain thorium and rare earth mixed acid liquid (D);

(5) thorium and rare earth separation: extracting thorium and rare earth mixed acid feed liquid (D) by taking a kerosene solution of neutral phosphate as an extracting agent and dilute nitric acid as impurity washing liquid, discharging rare earth from a mixed acid water phase (E), remaining thorium in an organic phase (G), back-extracting thorium in the organic phase (G) by taking water as thorium-removing liquid to obtain a thorium nitric acid solution, and concentrating and crystallizing to obtain a thorium nitrate product; and

(6) extracting mixed rare earth: extracting nitric acid in a rare earth mixed acid water phase (E) by taking a kerosene solution of neutral phosphate as an extracting agent, wherein the water phase is a rare earth solution, heating, aging and filtering the rare earth solution to remove metatitanic acid precipitate, and precipitating a rare earth filtrate to obtain a mixed rare earth product.

In another preferred embodiment, each neutral phosphate ester is independently selected from: (RO)₃P＝O、(RO)₂RP＝O、ROR₂P＝O、R₃P ═ O, or a combination thereof, wherein each R is independently selected from: C1-C30 alkyl; preferably, C1-C20 alkyl, more preferably, C1-C12 alkyl.

In another preferred embodiment, each neutral phosphate ester is independently selected from: tributyl phosphate, dimethylheptyl methylphosphonate, trioctyloxyphosphine, or a combination thereof.

In another preferred embodiment, the neutral phosphate used in the step (2) and the step (3) is the same.

In another preferred embodiment, the neutral phosphate used in the step (5) and the step (6) is the same.

In another preferred example, the neutral phosphate used in the step (2), the step (3), the step (5) and the step (6) is the same.

In another preferred embodiment, the extractant components in the step (2) and the step (3) are the same.

In another preferred example, in the step (1), the filtered filter residue is washed by water to obtain the full-dissolved slag and washing water, and the washing water is returned for the pulp mixing of the optimal-dissolved slag.

In another preferred example, in the step (2), the aqueous phase after the hydrochloric acid impurity washing liquid is used for dissolving in the step (1) in a return mode.

In another preferred example, the nitric acid organic phase extracted in step (6) is back-extracted with water to obtain a dilute nitric acid solution, and the dilute nitric acid solution is concentrated and then returned to step (4) for preparing mixed acid feed liquid.

In another preferred embodiment, the nitric acid organic phase stripping section has one or more of the following characteristics:

(1) water: the organic phase containing nitric acid is preferably (1-3):1, more preferably (1-2): 1;

(2) the stage number of the stripping stage is 4-10, preferably 5-8, more preferably 5-7.

In another preferred example, in the step (3), the method further comprises the steps of:

and (3-1) sintering the diuranate at high temperature to obtain a high-purity triuranium octoxide product.

In another preferred embodiment, the method of claim 1, wherein step (1) has one or more of the following features:

(1) the pulp mixing concentration of the optimum-dissolving slag is controlled to Be 30-50Be ', preferably 35-45 Be';

(2) the dissolution temperature is 80-100 deg.C, preferably 85-100 deg.C, more preferably 85-95 deg.C;

(3) the concentration of the hydrochloric acid is 0.2-11.7mol/L, preferably 2-11mol/L, more preferably 5-10 mol/L;

(4) slag (Kg): hydrochloric acid (L) ═ 1 (1-10); preferably, 1 (1-5), more preferably, 1 (1.5-3);

(5) the aging time after cooling is 10-24h, preferably 12-20h, preferably 12-16 h.

In another preferred embodiment, the step (2) has one or more of the following features:

(1) in the extracting agent, the neutral phosphate ester accounts for 10-40% of the volume of the extracting agent, preferably 15-30%, more preferably 15-25%;

(2) extracting agent: (1-5) to 1, preferably (1-4) to 1, more preferably (1-3) to 1;

(3) the number of stages of the extraction section is 5-20, preferably 8-15, more preferably 10-15;

(4) the HCl concentration in the hydrochloric acid mixed solution is 0.50-5.0mol/L, preferably 1-3mol/L, more preferably 2-3 mol/L;

(5) total solution (a): the ratio of the impurity washing liquid to (1-10) is 1, preferably, (2-8) is 1, more preferably, (2-5) is 1;

(6) the number of the impurity washing stages is 4 to 10, preferably 5 to 8, more preferably 5 to 7.

In another preferred embodiment, the step (3) has one or more of the following features:

(1) the iron washing liquid is 0.1-1.0mol/LHNO₃An aqueous solution, preferably, 0.15 to 0.8mol/L, more preferably, 0.2 to 0.5 mol/L;

(2) iron washing liquid in the iron washing section: the phase ratio of the iron-containing organic phase to the uranium-containing organic phase is 1 (1-10), preferably 1 (2-8), more preferably 1 (3-6);

(3) the number of stages of the iron washing stage is 3-10, preferably 4-10, more preferably 4-6;

(4) in the extracting agent, the neutral phosphate ester accounts for 10-40% of the volume of the extracting agent, preferably 15-30%, more preferably 15-25%;

(5) extracting agent in the extraction section: the phase ratio of the iron-containing organic phase to the uranium-containing organic phase (0.05-0.5) is 1, preferably (0.05-0.2) 1, more preferably (0.06-0.1) 1;

(6) the number of stages of the extraction section is 4-10, preferably 5-8, more preferably 5-7;

(7) the dilute alkali in the dilute alkali water solution is selected from the following group: ammonium bicarbonate, ammonium carbonate, sodium bicarbonate, sodium carbonate, aqueous ammonia, or a combination thereof;

(8) the concentration of the dilute alkali in the dilute alkali aqueous solution is 2-10 wt%, preferably 3-8 wt%, more preferably 4-6 wt%;

(9) uranium-depleted organic phase (F): the phase ratio of the transuranic liquid is (4-15):1, preferably, (4-10):1, more preferably, (5-8): 1;

(10) the number of anti-uranium segments is 4-10, preferably 4-8, more preferably 4-6.

In another preferred example, in the step (4), the thorium and the rare earth liquid (B) have one or more of the following characteristics when the mixed acid feed liquid is prepared:

(1) the concentration of the nitric acid is 1-14.5mol/L, preferably, 5-14mol/L, and more preferably, 8-12 mol/L;

(2) thorium and rare earth liquid: the ratio of nitric acid is 1 (0.1-5), preferably 1 (0.1-3), more preferably 1 (0.1-2).

In another preferred embodiment, the step (5) has one or more of the following features:

(2) the impurity washing liquid is 0.1-2.0mol/L HNO₃An aqueous solution, preferably, 0.15 to 1.5mol/L, more preferably, 0.2 to 0.8 mol/L;

(3) thorium and rare earth mixed acid material: liquid extraction section extractant: the ratio of the impurity washing liquid is 1 (2-10): (0.1-1), preferably 1 (2-8): 0.1-0.5, more preferably 1 (2-5): 0.2-0.3;

(4) the number of stages of the extraction section and the impurity washing section is 10-25, preferably 15-25, more preferably 18-22;

(5) thorium-containing organic phase (G) of the trans-thorium segment: (2-10) 1, preferably, (2-8) 1, more preferably, (2-5) 1;

(6) the number of stages of anti-thorium is 5-20, preferably 8-15, more preferably 8-12.

In another preferred example, the step (6) has one or more of the following features:

(1) in the extracting agent, the neutral phosphate ester accounts for 30-50% of the volume of the extracting agent, preferably 35-50%, more preferably 35-45%;

(2) extracting agent: the ratio of the rare earth mixed acid aqueous phase (E) is (5-1):1, preferably, (4-1):1, more preferably (3-1.5): 1;

(3) the number of stages of the extraction section is 4-10, preferably 5-8, more preferably 5-7;

(4) the rare earth precipitating agent is selected from: ammonium bicarbonate, ammonium carbonate, sodium bicarbonate, sodium carbonate, or a combination thereof;

(5) the aging time after precipitation is 1-12h, preferably 2-8h, more preferably 2-6 h.

It is to be understood that within the scope of the present invention, the above-described features of the present invention and those specifically described below (e.g., in the examples) may be combined with each other to form new or preferred embodiments. Not to be reiterated herein, but to the extent of space.

Drawings

FIG. 1 is a flow chart of the method for producing uranium, thorium and rare earth products by extracting and separating iron, uranium, thorium and mixed rare earth from monazite rare earth excellent slag.

Detailed Description

The inventor comprehensively improves the treatment method of monazite high-quality slag through extensive and intensive research and a large number of screening and tests. The method not only basically maintains the original flow framework and can continue to use the original production equipment to a great extent, but also makes full use of the difference of extraction performance of the neutral phosphate extractant in hydrochloric acid, nitric acid and mixed acid thereof, reasonably converts the extraction medium, obviously improves the separation effect of iron, uranium, thorium and rare earth, has high recovery rate, can produce uranium and thorium products meeting the nuclear fuel requirement, can realize the recycling of acid, and is environment-friendly. The present invention has been completed based on this finding.

Term(s) for

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

As used herein, the term "compared" refers to the volume ratio of two phases, unless otherwise specified.

As used herein, the term "extraction section" refers to the extraction operation stage, and the terms "stripping section", "impurity washing section", "iron washing section" and the like refer to the corresponding operation stage.

As used herein, the term "stage number" refers to the definition of "stage" for each mixing-clarification unit in a liquid-liquid extraction process. If the number of iron washing stages is 4-10 stages, the iron is extracted and separated by iron washing liquid and passes through 4-10 mixing-clarifying units; typically, the extraction apparatus may be a mixer-settler.

Monazite slag

As used herein, the term "monazite slag" is a monazite slag recognized in the art, also referred to as "monazite rare earth slag" or "optimum rare earth slag", and the raw material to be treated used in the method of the present invention may be entirely or partially monazite slag, preferably, the monazite slag accounts for 50 to 100%, more preferably, 80 to 100%, and most preferably, 90 to 100% of the total weight of the raw material to be treated.

Neutral phosphoric acid ester

Neutral phosphate is a compound in which three hydroxyl groups in the phosphate are esterified or substituted with an alkyl group, and is represented by (RO)₃P＝O、(RO)₂RP＝O、ROR₂P＝O、R₃P ═ O four types, where each R is independently selected from C1-C30 alkyl; preferably, C1-C20 alkyl, more preferably, C1-C12 alkyl. The alkyl group includes straight chain and branched chain alkyl groups. For example, the neutral phosphate esters include (but are not limited to): tributyl phosphate, dimethylheptyl methylphosphonate, trioctyloxyphosphine, and the like.

Monazite optimum soluble slag treatment method

A method for treating monazite slag comprises the following steps:

In the step (2), hydrochloric acid is used as impurity washing liquid for the iron-and-uranium-containing organic phase obtained after extraction, so that the iron-and-uranium-containing organic phase (C) meeting the process requirement purity can be obtained, the impurity content in the iron-and-uranium-containing organic phase (C) is reduced, and the improvement of the purity of the uranium product after iron-uranium separation is facilitated.

In the step (3), dilute nitric acid solution is added into the organic phase (C) containing iron and uranium to serve as iron washing liquid, so that iron is formed into ferric nitrate, the ferric nitrate is not easily extracted by kerosene solution of neutral phosphate, and iron and uranium can be efficiently separated.

Before thorium and rare earth are separated, thorium and rare earth liquid (B) are added with nitric acid to prepare thorium and rare earth mixed acid liquid (D), after the nitric acid is added, thorium exists in the form of thorium nitrate and is easy to be extracted by an extracting agent, and rare earth chloride and nitrate are not easy to be extracted by a kerosene solution of neutral phosphate, so that the method for separating thorium and rare earth is further optimized, and the separation effect is improved.

In the step (5), dilute nitric acid is added as impurity washing liquid, so that trace impurities such as rare earth, titanium, zirconium and the like in the organic phase can be effectively removed, and the purity of thorium is improved.

The method for treating monazite high-quality slag reserves the flow framework of the traditional high-quality slag treatment method in the field, makes full use of the difference of extraction performances of neutral phosphate extractants in hydrochloric acid, nitric acid and mixed acid thereof, skillfully converts extraction media, and obviously improves the separation effect of iron, uranium, thorium and rare earth.

The main advantages of the invention include:

1. the method has reasonable comprehensive flow design, optimizes reagents and operation steps, basically keeps the original flow frame, can continue to use original production equipment to a great extent, has better uranium, thorium and rare earth separation effect, high product purity and high recovery rate, and can produce uranium and thorium products meeting the requirements of nuclear fuel.

2. The method of the invention makes full use of the difference of extraction performance of neutral phosphate extractants in hydrochloric acid, nitric acid and mixed acid thereof, skillfully converts the extraction medium, and obviously improves the separation effect of iron, uranium, thorium and rare earth.

3. The method disclosed by the invention has the advantages that the industrial hydrochloric acid is used for dissolving monazite optimum-dissolving slag, the price is low, the steps of washing water and size mixing by using the hydrochloric acid, extracting and recovering nitric acid and the like are adopted, the cyclic utilization of the hydrochloric acid and the nitric acid is realized, the production cost can be reduced, the waste acid discharge is reduced, and the method is environment-friendly.

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. The experimental procedures, in which specific conditions are not noted in the following examples, are generally carried out under conventional conditions or conditions recommended by the manufacturers. Unless otherwise indicated, percentages and parts are percentages and parts by weight. The materials and equipment used in the examples of the present invention are commercially available unless otherwise specified.

Example 1

Dissolving slag (Kg) of monazite of a certain batch: industrial hcl (L) (about 9.5mol/L) ═ 1.0:2.0 was dissolved by the method of the above step (1) and the slurry concentration was adjusted to 40Be' to obtain a whole solution having the composition shown in table 1;

TABLE 1 composition of the total solution obtained from the preferential dissolution of monazite

Components	U₃O₈	ThO₂	REO	Fe₂O₃	HCl
						Concentration (g/L)	2.6	50	35	6	2.5N

According to the step (2), 20% tributyl phosphate (TBP) -kerosene solution is used as an extracting agent, and the obtained iron and uranium-containing organic phase is washed with impurity washing liquid of 2.5 mol/LHCl; wherein, the extraction agent for the iron extraction uranium is as follows: the total solution: the impurity washing liquid phase ratio is 2.0:1.0:0.33, the extraction section is 12 grades, and the impurity washing section is 6 grades;

according to the step (3), 20 percent of tributyl phosphate (TBP) -kerosene solution is used as an extracting agent, and 0.25mol/LHNO is added₃Is iron washing liquid, 5% Na₂CO₃Is transuranium liquid. Extracting a uranium extracting agent: iron and uranium containing organic phase: washing iron liquid: the uranium-removing liquid is 0.72:9.0:1.8:2.0, the extraction section is of 6 grades, the iron washing section is of 4 grades, and the uranium-removing section is of 5 grades; the transuranium solution is acidified by nitric acid, and ammonia water is precipitated to obtain ammonium diuranate, and the obtained product triuranium octoxide is calcined at high temperature, and the analysis result is shown in table 2.

TABLE 2 results of triuranium octaoxide analysis

Analytical elements

U₃O₈

ThO

REO

Fe₂O₃

TiO₂

P₂O₅

CaO

Content (%)

>99

<0.001

<0.002

Adding HNO into each liter of thorium and rare earth solution according to the step (4)₃(about 12mol/L)0.15L to prepare thorium and rare earth mixed acid material liquid; according to the step (5), 20 percent of dimethylheptyl methylphosphonate (P-350) -kerosene solution is used as an extracting agent, and 0.25mol/LHNO is added₃The impurity washing liquid is used (the impurity washing liquid is mixed into the feed liquid), the water is thorium-resisting liquid, and the separation parameters are as follows: thorium extraction extractant: thorium and rare earth mixed acid feed liquid: washing the impurities: the extraction section has 20 grades with water being 3.0:1.0:0.25:1.0, the impurity washing section has 20 grades, and the thorium stripping section has 10 grades. The analysis results of the thorium nitrate product obtained after collecting the obtained thorium nitrate solution by CCl4, concentrating and crystallizing are listed in Table 3.

TABLE 3 analysis of thorium nitrate as hexahydrate

Analytical elements

ThO

U₃O₈

REO

Fe₂O₃

TiO₂

P₂O₅

CaO

Content (%)

45-46

<0.001

<0.002

Extracting a rare earth mixed acid aqueous phase by using 40 percent methyl phosphoester dimethylheptyl ester (P-350) -kerosene solution as an extracting agent, and back extracting nitric acid in an organic phase by using water, wherein the flow ratio (phase ratio) is as follows: extracting agent: rare earth mixed acid water phase: 2.0:1.0:1.0, 6 grades of extraction and 6 grades of back extraction. The dilute nitric acid solution obtained by back extraction is concentrated and returned to prepare mixed acid feed liquid. Heating raffinate, aging, filtering out metatitanic acid precipitate to obtain rare earth solution with 10-20% NH₄HCO₃Precipitating rare earth in the solution, aging for 3-4 hours after precipitation, centrifuging and drying to obtain rare earth carbonate, wherein the REO content of the rare earth carbonate can reach more than 40%, and about 60% of nitric acid in the rare earth raffinate is recovered.

Example 2

Dissolving the monazite rare earth optimum slag (Kg) with industrial HCl (L) (about 9.5mol/L) as 1.0:2.0(L) according to the method in the step (1), adjusting the slurry concentration to 45Be', and properly controlling the dilution volume to obtain a full solution with high concentration. The composition is shown in Table 4.

TABLE 4 composition of the total solution obtained from the preferential dissolution of monazite

Components	U₃O₈	ThO₂	REO	Fe₂O₃	HCl
						Concentration (g/L)	3.5	62	40	8	2.5N

According to the step (2), 20% of dimethylheptyl methylphosphonate (P-350) -kerosene solution is used as an extracting agent, and the obtained iron-and uranium-containing organic phase is used as a impurity washing liquid by using 2.5 mol/LHCl; extracting the iron and the uranium: the total solution: impurity washing liquid is 2.0:1.0:0.33, extraction section is 12 grades, and impurity washing section is 6 grades;

according to the above step (3), 20% of dimethylheptyl methylphosphonate (P-350)) Kerosene solution as extractant, 0.25mol/LHNO₃Is iron washing liquid, 5% Na₂CO₃Is transuranium liquid; extracting a uranium extracting agent: uranium-containing organic phase: washing iron liquid: the uranium-removing liquid is 0.72:9.0:1.8:2.0, the extraction section is of 6 grades, the iron washing section is of 4 grades, and the uranium-removing section is of 5 grades; after the transuranium solution is acidified by nitric acid and precipitated by ammonia water, the obtained ammonium diuranate is calcined at high temperature, and the analysis result of the obtained triuranium octoxide is shown in table 5.

TABLE 5 results of triuranium octaoxide analysis

Analytical elements

U₃O₈

ThO

REO

Fe₂O₃

TiO₂

P₂O₅

CaO

Content (%)

>99

<0.001

<0.002

Adding HNO into each liter of thorium and rare earth solution according to the method in the step (4)₃(about 12mol/L)0.20L to prepare thorium and rare earth mixed acid feed liquid.

According to the method of the step (5), 25 percent of dimethylheptyl methylphosphonate (P-350) -kerosene solution is used as an extracting agent, and 0.25mol/LHNO is adopted₃The impurity washing liquid is used (the impurity washing liquid is mixed into the feed liquid), the water is thorium-resisting liquid, and the separation parameters are as follows: thorium extraction extractant: thorium and rare earth mixed acid feed liquid: washing the impurities: 3.0:1.0:0.30:1.0, 20 grades in an extraction section, 20 grades in a impurity washing section and 10 grades in a thorium stripping section. The analysis results of the thorium nitrate product obtained after collecting the obtained thorium nitrate solution by CCl4, concentrating and crystallizing are listed in Table 6.

TABLE 6 analysis of thorium nitrate as hexahydrate

Analytical elements

ThO

U₃O₈

REO

Fe₂O₃

TiO₂

P₂O₅

CaO

Content (%)

45-46

<0.001

<0.002

According to statistics, the recovery rate of each element in the method is more than 95% (except the monazite which is not decomposed by alkali).

In conclusion, the method for integrally extracting uranium, thorium and rare earth from monazite excellent slag basically keeps the flow frame unchanged, can continue to use the original production equipment to a great extent, fully utilizes the difference of extraction performances of neutral phosphate extractants in hydrochloric acid, nitric acid and mixed acid thereof, skillfully converts extraction media, obviously improves the separation effect of iron, uranium, thorium and rare earth, has high recovery rate, can produce nuclear fuel grade uranium and thorium products, can recycle hydrochloric acid and nitric acid, can reduce the production cost and reduce the emission of waste acid.

All documents referred to herein are incorporated by reference into this application as if each were individually incorporated by reference. Furthermore, it should be understood that various changes and modifications of the present invention can be made by those skilled in the art after reading the above teachings of the present invention, and these equivalents also fall within the scope of the present invention as defined by the appended claims.

Claims

1. A method for treating monazite slag is characterized by comprising the following steps:

2. The method of claim 1, wherein each neutral phosphate ester is independently selected from the group consisting of: (RO)₃P＝O、(RO)₂RP＝O、ROR₂P＝O、R₃P ═ O, or a combination thereof, wherein each R is independently selected from: C1-C30 alkyl.

3. The method of claim 1, wherein each neutral phosphate ester is independently selected from the group consisting of: tributyl phosphate, dimethylheptyl methylphosphonate, trioctyloxyphosphine, or a combination thereof.

4. The method according to claim 1, wherein in the step (1), the filtered filter residue is washed by water to obtain the full soluble slag and washing water, and the washing water is returned for the pulp mixing of the optimal soluble slag.

5. The method of claim 1, wherein in step (2), the aqueous phase after the hydrochloric acid impurity washing liquid is returned to step (1) for dissolution.

6. The method of claim 1, wherein the organic phase of nitric acid extracted in step (6) is back-extracted with water to obtain a dilute nitric acid solution, which is then concentrated and returned to step (4) for preparing mixed acid feed liquid.

7. The method of claim 1, wherein step (1) has one or more of the following features:

(1) the pulp mixing concentration of the optimum-dissolving slag is controlled to Be 30-50 Be';

(2) the dissolving temperature is 80-100 ℃;

(3) the concentration of the hydrochloric acid is 0.2-11.7 mol/L;

(4) optimal slag dissolution: 1- (1-10) in kg/l;

(5) the aging time after cooling is 10-24 h.

8. The method of claim 1, wherein step (2) has one or more of the following characteristics:

(1) in the extractant, the neutral phosphate ester accounts for 10-40% of the volume of the extractant;

(2) extracting agent: the phase ratio (1-5) of the whole solution (A) is 1;

(3) the number of stages of the extraction section is 5-20 stages;

(4) the HCl concentration in the hydrochloric acid impurity solution is 0.50-5.0 mol/L;

(5) total solution (a): the phase ratio of the impurity washing liquid is (1-10) 1;

(6) the number of the impurity washing stages is 4 to 10.

9. The method of claim 1, wherein step (3) has one or more of the following characteristics:

(1) the iron washing liquid is 0.1-1.0mol/LHNO₃An aqueous solution;

(2) iron washing liquid in the iron washing section: the phase ratio of the iron-containing organic phase and the uranium-containing organic phase is 1 (1-10);

(3) the number of stages of the iron washing stage is 3-10 stages;

(4) in the extractant, the neutral phosphate ester accounts for 10-40% of the volume of the extractant;

(5) extracting agent in the extraction section: the phase ratio of the iron-containing organic phase and the uranium-containing organic phase (0.05-0.5) is 1;

(6) the number of stages of the extraction section is 4-10 stages;

(8) the concentration of the dilute alkali in the dilute alkali water solution is 2-10 wt%;

(9) uranium-depleted organic phase (F): the phase ratio of the transuranium liquid is (4-15) 1;

(10) the number of anti-uranium stage is 4-10.

10. The method of claim 1, wherein in step (4), the thorium-containing rare earth liquid (B) is prepared with one or more of the following characteristics:

(1) the concentration of the nitric acid is 1-14.5 mol/L;

(2) thorium and rare earth liquid: the nitric acid phase ratio is 1 (0.1-5).

11. The method of claim 1, wherein step (5) has one or more of the following features:

(2) the impurity washing liquid is 0.1-2.0mol/L HNO₃An aqueous solution;

(3) thorium and rare earth mixed acid material: liquid extraction section extractant: the phase ratio of the impurity washing liquid is 1 (2-10) to 0.1-1;

(4) the number of stages of the extraction section and the impurity washing section is 10-25 stages;

(5) thorium-containing organic phase (G) of the trans-thorium segment: the phase ratio of water is (2-10) 1;

(6) the grade number of the anti-thorium section is 5-20.

12. The method of claim 1, wherein step (6) has one or more of the following features:

(1) in the extracting agent, the neutral phosphate ester accounts for 30-50% of the volume of the extracting agent;

(2) extracting agent: the phase ratio of the rare earth mixed acid water phase (E) (5-1) is 1;

(3) the number of stages of the extraction section is 4-10 stages;

(5) the aging time after precipitation is 1-12 h.