Air pressure assisted alkaline leaching method for monazite ore alkaline decomposition slag

Abstract

The invention belongs to the field of mineral resource application, and particularly relates to an air pressure auxiliary alkaline leaching method for monazite ore alkaline decomposition slag, which comprises the following steps: obtaining the monazite ore alkaline decomposition slag containing U, Th and rare earth; the method comprises the following steps: dispersing monazite ore alkaline decomposition slag in a leaching agent solution containing a component A and a component B, and carrying out air pressure assisted leaching at 70-90 DEG C under the pressure of 0.6-1.5 Mpa; then carrying out solid-liquid separation to obtain a leaching solution enriched with U and Th and leaching residues enriched with rare earth; the component A is at least one of sodium carbonate, potassium carbonate and ammonium carbonate; the component B is at least one of sodium bicarbonate, potassium bicarbonate and ammonium bicarbonate. According to the method, a combined leaching agent of the component A and the component B is adopted for carrying out combined alkaline leaching treatment on the monazite alkaline decomposition slag, control over the temperature and the air pressure in the leaching stage is further matched, in this way, synergistic and adaptive physical and chemical characteristics of the monazite alkaline decomposition slag can be achieved, U and Th in the monazite alkaline decomposition slag can be effectively and synchronously leached out, and in addition, selective leaching of U / Th and rare earth can be achieved.

Description

Technical Field

[0001] The present invention belongs to the field of mineral recovery, and in particular to the field of monazite ore recovery. Background Art

[0002] Monazite is one of the rare earth-rich minerals. Its main components are phosphate minerals of Ce, La, Nd, and Th. The mineral contains 50-60% REO, 0.3-0.5% U, 15-20% Th, and a small amount of impurities such as Si, Ti, Fe, and Al. The most commonly used processing technology for monazite concentrate is alkaline treatment, followed by dissolution with hydrochloric acid to obtain rare earth chloride. The discarded tailings contain about 20% uranium and thorium. Due to the high content of uranium and thorium and high radioactivity, many rare earth companies at home and abroad have to abandon monazite as the requirements for environmental protection are increasing. Effectively utilizing the valuable metals in monazite, solving the pollution problem of radioactive tailings, and effectively recovering uranium and thorium without changing the original rare earth extraction process are the guarantees for promoting the long-term development of the monazite concentrate industry.

[0003] The hydroxides of uranium, thorium and rare earth (alkali decomposition slag) obtained after monazite is decomposed by alkali. For the alkali decomposition slag, the existing means mainly include acid leaching. For example, the Chinese patent document with publication number CN116987893A discloses a method for recovering monazite slag, which records the scheme of using sulfuric acid with a mass concentration of 60% to 75% and monazite slag to carry out decomposition reaction at a temperature of 110°C to 130°C. For another example, the Chinese patent document with publication number CN115369246A discloses a method for recovering monazite slag, which specifically records that after mixing monazite slag and inorganic acid for the first decomposition, sulfite is added for the second decomposition to obtain a first filtrate; after adjusting the pH value of the first filtrate to 0.5 to 3, at least one of cerium hydroxide and lanthanum hydroxide is used to adjust the pH value to 3.8 to 4.2, solid-liquid separation is performed to obtain a second filtrate, and the second filtrate is mixed with a metal ion precipitant for precipitation treatment. For another example, Chinese patent document with publication number CN104775026A discloses a method for extracting high-purity uranium, thorium and mixed rare earths from eutectic slag, and also records a process of adding monazite eutectic slag to an acid solution for leaching.

[0004] In summary, the main existing method for monazite and its alkali decomposition slag is to treat it with acid leaching. In this process, uranium, thorium and rare earths are dissolved out by high acid, and then the pH value is adjusted to 4.2-4.5 with alkaline cake. At this time, impurities such as uranium, thorium and iron form precipitation, and rare earths enter the solution, achieving the purpose of separating uranium, thorium and rare earths. The optimal dissolution process has high acid consumption and cumbersome operation. Uranium and thorium repeatedly enter the process operation and uranium and thorium are not effectively separated and recovered. If it is recovered again, the optimal dissolution slag needs to be subjected to acid leaching and other operations, which will cause more acid consumption and process operation. Summary of the invention

[0005] In view of the difficulty in selectively recovering U, Th and rare earths from existing monazite mines and alkali decomposition slag thereof, the present invention aims to provide a gas pressure assisted alkali leaching method for monazite mine alkali decomposition slag, aiming to achieve one-pot efficient and highly selective separation and recovery of rare earths and U and Th.

[0006] Different mineral types, mineral types and inter-mineral intercalation relationships have different leaching behaviors, and the leaching effect is difficult to predict. For example, monazite is a phosphate ore, which is completely different from the properties and behaviors of conventional carbonate and oxidized minerals. In view of the characteristics of monazite minerals, the existing main means is to perform alkaline decomposition to obtain hydroxides containing U, Th and rare earths. For this hydroxide, the existing main means is acid leaching. However, acid leaching will have problems such as high consumption and unsatisfactory separation selectivity.

[0007] In order to solve this problem, the present invention has previously tried to use an alkali leaching process to treat alkali decomposition slag. However, it was found in the early stage of research and development that the difficulty of recovering elements in the alkali leaching of the alkali decomposition slag after alkali leaching has increased exponentially. Inappropriate alkali leaching processes make it difficult to achieve the joint efficient leaching of U and Th in monazite alkali decomposition slag. In addition, it is also difficult to achieve the selective leaching and separation of U, Th and rare earth. In order to solve this problem, the present invention has conducted in-depth research and provided the following improvement scheme:

[0008] A gas pressure assisted alkali leaching method for monazite alkali decomposition slag, which obtains monazite alkali decomposition slag containing U, Th and rare earth; the monazite alkali decomposition slag is dispersed in a leaching agent solution containing component A and component B and subjected to gas pressure assisted leaching at 70°C to 90°C and a pressure of 0.6 to 1.5 MPa; then solid-liquid separation is performed to obtain a leachate enriched with U and Th, and a leaching slag enriched with rare earth;

[0009] The component A is at least one of sodium carbonate, potassium carbonate and ammonium carbonate;

[0010] The component B is at least one of sodium bicarbonate, potassium bicarbonate and ammonium bicarbonate.

[0011] In view of the difficulty in alkaline leaching due to the special mineral type and special physical and chemical characteristics of monazite, the present invention innovatively adopts a combined leaching agent of component A and component B to carry out a combined alkaline leaching treatment, and further cooperates with the control of temperature and air pressure in the leaching stage, so as to achieve synergy, adapt to the physical and chemical characteristics of monazite alkali decomposition slag, and effectively and synchronously leach U and Th therein. In addition, selective leaching of U / Th and rare earth can also be achieved.

[0012] In the present invention, the steps for obtaining the monazite alkali decomposition slag are: mixing the monazite concentrate and alkali solution and performing pressurized alkali leaching, then performing solid-liquid separation, collecting the tailings, and then washing the tailings with hot water to obtain the monazite alkali decomposition slag.

[0013] In the present invention, the alkali solution is a 45-55% aqueous solution of an alkali metal hydroxide.

[0014] The mass ratio of monazite concentrate and alkali solution is 1:1.2~1.4.

[0015] The temperature of the pressure alkali leaching is 110-150°C, preferably 130-145°C.

[0016] The holding time at the pressurized alkali immersion temperature is 4 to 6 hours.

[0017] In the present invention, the temperature of the hot water is 90 to 95°C.

[0018] The liquid-to-solid ratio in the hot water washing stage is 3-6 ml / g.

[0019] In the present invention, the weight ratio of component A to component B is 1:1-5, preferably 1:1-4.

[0020] In the present invention, the total solute concentration of component A and component B in the leaching agent solution is 30% to 50%.

[0021] In the present invention, the dosage of leaching agent solutions A and B is 1.5 to 2.5 times the theoretical weight of the alkali decomposition slag reaction. The theoretical amount refers to the theoretical amount for converting U and Th in the alkali decomposition slag into dissolved states.

[0022] In the present invention, during the gas pressure-assisted leaching stage, a protective atmosphere is used for pressurization;

[0023] Preferably, the protective atmosphere includes at least one of nitrogen and an inert gas.

[0024] In the present invention, the pressure in the gas pressure-assisted leaching stage may be, for example, 0.8 to 1.2 MPa.

[0025] In the present invention, the duration of the gas pressure-assisted leaching stage may be, for example, more than 1 hour, and in consideration of efficiency, may further be 1 to 5 hours, and further may be 2 to 4 hours.

[0026] In the present invention, after the air pressure-assisted leaching and heat preservation is completed, the leaching solution is filtered while hot to obtain the leaching solution.

[0027] In the present invention, the filter cake filtered while hot is washed with a 5% to 10% sodium carbonate solution to obtain leaching residue, and the washing solution is used to prepare a leaching agent solution.

[0028] Technical Effects

[0029] 1. The present invention provides a new method for gas pressure-assisted alkali leaching of monazite alkali decomposition slag.

[0030] 2. In view of the technical problems faced by the new idea, the present invention innovatively adopts a combined leaching agent of component A and component B to carry out a combined alkaline leaching treatment, and further cooperates with the control of temperature and air pressure in the leaching stage, so as to achieve synergy, adapt to the physical and chemical characteristics of monazite alkali decomposition slag, and effectively and synchronously leach U and Th therein. In addition, selective leaching of U / Th and rare earth can be achieved.

[0031] The leaching rates of uranium and thorium in the method of the present invention can reach 94% and 99% or more respectively. The method has the advantages of good uranium and thorium separation effect, simple process, low acid consumption, etc., and has high application value for the recovery of uranium and thorium resources in monazite concentrate.

[0032] This process is aimed at the selective leaching of uranium and thorium, does not affect the original rare earth extraction process, avoids the leaching of rare earths that account for the main part of the mineral during the uranium and thorium recovery process, reduces the amount of leaching agent used, and achieves effective separation of the radioactive elements uranium and thorium from rare earths, providing an effective way to achieve radioactivity standards for rare earth products in the rare earth industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a process flow chart of the method of the present invention. Specific implementation plan

[0034] The method for selective leaching of uranium and thorium from monazite concentrate according to the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0035] The present invention provides an optional method for processing monazite concentrate, which comprises the following steps:

[0036] (1) Take a certain amount of monazite concentrate to be treated, and mix it with a NaOH solution with a concentration of 45-55%, according to the mass ratio of concentrate to alkali solution of 1:1.2-1.4, and react for 4-6 hours at a temperature of 110-150°C, preferably 130-145°C. The reaction state is in a slightly boiling state, and a small amount of water is added according to the evaporation situation;

[0037] (2) The solution obtained in step (1) is allowed to stand, hot water at 90 to 95° C. is added, and countercurrent decantation is performed at a liquid-to-solid mass ratio of 1:3 to 6, and solid-liquid separation is performed to obtain an alkaline decomposition slag filter cake of uranium, thorium and rare earth hydroxides, wherein U and Th are both in the hydroxide phase.

[0038] (3) In step (2), the alkali decomposition slag filter cake is mixed with component A-component B having a mass concentration of 30% to 50%, and the mixed slurry is placed in an autoclave at a reaction pressure of 0.6 to 1.5 MPa, a reaction temperature of 70° C. to 90° C., and a reaction time of 2 to 4 hours. The reaction temperature should be ensured not to be lower than 70° C., as the reaction temperature has a greater influence on the selective leaching of thorium. When ammonium carbonate-ammonium bicarbonate leaching is used, the reaction temperature is not greater than 85° C.

[0039] (4) After the carbonate-bicarbonate leaching in step (3), the leaching rate of uranium can reach more than 94%, and the leaching rate of thorium can reach more than 99%. After leaching, the filter cake is filtered while hot, and the filter cake is washed with 5% to 10% sodium carbonate solution and then disposed. The washing water is returned to the carbonate-bicarbonate solution preparation, and the washed filter cake is removed from the rare earth recovery process.

[0040] In the present invention, the leaching reaction is, for example:

[0041] (1)UO2(OH)2+3(NH4)2COз→(NH4)4[UO2(CO3)3]+2(NH4)OH:

[0042] (2)Th(OH)4+5(NH4)2COз→(NH4)6[Th(CO3)5]+4(NH4)OH:

[0043] (3)Re(OH)3+4(NH4)2COз→Re2(CO3)3(NH4)2COз+6(NH4)OH:

[0044] (4)(NH4)OH+(NH4)2COз→(NH4)2COз+H2O;

[0045] The theoretical amount of the leaching agent refers to the theoretical amount of component A in the leaching agent to complete reactions 1 and 2.

[0046] Example 1

[0047] (1) A certain amount of monazite concentrate to be treated is mixed with a 45% NaOH solution at a mass ratio of 1:1.2 and reacted at a temperature of 135°C for 4 hours.

[0048] (2) The solution obtained in step (1) was allowed to stand, and hot water at 95° C. was added, and countercurrent decantation was performed at a liquid-to-solid mass ratio of 1:4 (4 ml / g). A filter cake (alkali decomposition residue) was obtained by filtration. The filter cake was sampled and analyzed, and the contents of U, Th and total rare earth were approximately 0.37%, 5.74% and 49.6% respectively.

[0049] (3) In step (2), the filter cakes of uranium, thorium and rare earth hydroxides are mixed with a leaching agent, wherein the leaching agent is a solution of ammonium carbonate-ammonium bicarbonate (the mass ratio of ammonium carbonate to ammonium bicarbonate is 1:1) with a mass concentration of 30%, and the amount of ammonium carbonate-ammonium bicarbonate is 230wt% of the theoretical amount. The mixed slurry is placed in an autoclave with a reaction pressure of 1Mpa (pressurized by nitrogen), a reaction temperature of 80°C and a reaction time of 2h.

[0050] After the ammonium carbonate-ammonium bicarbonate leaching in step (3), the leaching rate of uranium can reach more than 94.3%, the leaching rate of thorium can reach 99.6%, and the leaching rate of rare earth can reach less than 0.2%.

[0051] (4) After the air pressure-assisted leaching in step (3), the slurry is filtered while hot, and the filter cake is washed with a 10% ammonium carbonate solution, with the washing liquid and the filter cake washing volume ratio of 1:1, and washed three times. The washing water is returned to the carbonate-bicarbonate solution preparation, and the washed filter cake is subjected to rare earth recovery process.

[0052] Comparative Example 1

[0053] Compared with Example 1, the only difference is that in step 3, the leaching process is also carried out in a closed container, but during the leaching process, no additional nitrogen is used for pressurization, and the pressure of the closed system in the leaching stage is between 0.3 and 0.45 MPa. Other operations and parameters are the same as in Example 1.

[0054] In step 4, the leaching rate of U was 79.4%, and the leaching rate of Th was 68.4%.

[0055] It can be seen from Example 1 and Comparative Example 1 that the use of nitrogen or other protective gas for additional pressurization can promote the effective transformation of the hydroxide phases of U and Th in the alkali decomposition slag and improve the combined leaching effect.

[0056] Comparative Example 2

[0057] Compared with Example 1, the only difference is that in step 3, the leaching agent is single ammonium carbonate (the amount of the leaching agent is the same as the weight of the total leaching agent in Example 1), and the other operations and parameters are the same as Example 1.

[0058] In step 4, the leaching rate of U was 54.1%, and the leaching rate of Th was 24.3%.

[0059] Comparative Example 3

[0060] Compared with Example 1, the only difference is that in step 3, the leaching agent is single ammonium bicarbonate (the amount of the leaching agent is the same as the weight of the total leaching agent in Example 1), and the other operations and parameters are the same as in Example 1.

[0061] In step 4, the leaching rate of U is 33.6%, and the leaching rate of Th is 18.6%.

[0062] Example 2

[0063] (1) A certain amount of monazite concentrate to be treated (same as in Example 1) was mixed with a 45% NaOH solution at a mass ratio of 1:1.4 and reacted at 145°C for 5 hours.

[0064] (2) the solution obtained in step (1) was allowed to stand, hot water at 93° C. was added, and countercurrent decantation was performed at a liquid-to-solid mass ratio of 1:5 (5 mL / g) to obtain alkaline decomposition slag;

[0065] (3) The alkaline decomposition slag of step (2) is mixed with ammonium carbonate-ammonium bicarbonate (ammonium carbonate-ammonium bicarbonate mass ratio is 1:3) with a mass concentration of 40%, and the amount of ammonium carbonate-ammonium bicarbonate is 180wt% of the theoretical amount. The mixed slurry is placed in an autoclave with a reaction pressure of 0.8Mpa (pressurized by nitrogen), a reaction temperature of 90°C, and a reaction time of 4h.

[0066] After the ammonium carbonate-ammonium bicarbonate leaching in step (3), the leaching rate of uranium can reach more than 93.6%, the leaching rate of thorium can reach 97.8%, and the leaching rate of rare earth can reach less than 0.2%.

[0067] (4) After the carbonate leaching in step (3), the slurry is filtered while hot, and the filter cake is washed with a 10% sodium carbonate solution, with the washing liquid and the filter cake washing volume ratio of 1:1, and washed three times. The washing water is returned to the carbonate-bicarbonate solution preparation, and the washed filter cake is subjected to rare earth recovery process.

[0068] Example 3

[0069] (1) A certain amount of monazite concentrate to be treated (same as in Example 1) was mixed with a 55% NaOH solution at a mass ratio of 1:1.4 and reacted at 135° C. for 4 h.

[0070] (2) The solution obtained in step (1) was allowed to stand, hot water at 90° C. was added, and the liquid-to-solid mass ratio was 1:3 (3 mL / g), and countercurrent decantation was performed to obtain alkaline decomposition slag;

[0071] (3) The alkali decomposition slag of step (2) was mixed with 20 g / L sodium carbonate-80 g / L sodium bicarbonate, and the amount of ammonium carbonate-ammonium bicarbonate was 180 wt % of the theoretical amount. The mixed slurry was placed in an autoclave with a reaction pressure of 1.0 MPa (pressurized by nitrogen), a reaction temperature of 90° C., and a reaction time of 3 h.

[0072] After the ammonium carbonate-ammonium bicarbonate leaching in step (3), the leaching rate of uranium can reach more than 93.8%, the leaching rate of thorium can reach 98.6%, and the leaching rate of rare earth can reach less than 0.2%.

[0073] (4) The slurry after leaching in step (3) is filtered while hot, and the filter cake is washed with a 10% sodium carbonate solution, with the washing liquid and filter cake washing volume ratio of 1:1, and washed three times. The washing water is returned to the carbonate-bicarbonate solution preparation, and the washed filter cake is used for rare earth recovery process.

[0074] Comparative Example 4

[0075] Compared with Example 3, the only difference is that in step 3, nitrogen is not used for additional pressurization, and other operations and parameters are the same as those in Example 1.

[0076] In step 4, the leaching rate of U is 63.4%, and the leaching rate of Th is 22.6%.

[0077] Through Example 3 and Comparative Example 4, for the sodium carbonate-sodium bicarbonate system, the nitrogen pressure leaching process can be used to obtain a better conversion effect of U and Th hydroxide phases, and in the monazite ore alkali decomposition slag described in the present invention, a better U and Th combined leaching effect can be obtained.

Claims

1. A gas pressure assisted alkali leaching method for monazite alkali decomposition slag, characterized in that: Obtaining monazite alkali decomposition slag containing U, Th and rare earth; dispersing the monazite alkali decomposition slag in a leaching agent solution containing component A and component B and performing gas pressure-assisted leaching at 70°C to 90°C and a pressure of 0.6 to 1.5 MPa; then performing solid-liquid separation to obtain a leachate enriched with U and Th, and a leaching slag enriched with rare earth; The component A is at least one of sodium carbonate, potassium carbonate and ammonium carbonate; The component B is at least one of sodium bicarbonate, potassium bicarbonate and ammonium bicarbonate.

2. The gas pressure assisted alkali leaching method of monazite ore alkali decomposition slag according to claim 1, characterized in that: The steps for obtaining the monazite ore alkali decomposition slag are: mixing the monazite concentrate and alkali solution and performing pressurized alkali leaching, then separating the solid and liquid, collecting the tailings, and then washing the tailings with hot water to obtain the monazite ore alkali decomposition slag.

3. The gas pressure assisted alkali leaching method of monazite ore alkali decomposition slag according to claim 2, characterized in that: The alkali solution is a 45-55% aqueous solution of alkali metal hydroxide; The mass ratio of monazite concentrate to alkali solution is 1:1.2-1.4; The temperature of the pressurized alkali leaching is 110-150°C, preferably 130-145°C; The holding time at the pressurized alkali immersion temperature is 4 to 6 hours.

4. The gas pressure assisted alkali leaching method of monazite alkali decomposition slag according to claim 2 or 3, characterized in that: The temperature of hot water is 90-95℃; The liquid-to-solid ratio in the hot water washing stage is 3-6 ml / g.

5. The gas pressure assisted alkali leaching method of monazite alkali decomposition slag according to claim 1, characterized in that: The weight ratio of component A to component B is 1:1-5, preferably 1:1-4.

6. The gas pressure assisted alkali leaching method of monazite alkali decomposition slag according to claim 1, characterized in that: In the leaching agent solution, the total solute concentration of component A and component B is 30% to 50%.

7. The gas pressure assisted alkali leaching method of monazite ore alkali decomposition slag according to claim 1, characterized in that: The dosage of leaching agent solutions A and B is 1.5 to 2.5 times the theoretical weight of the alkali decomposition slag reaction.

8. The gas pressure assisted alkali leaching method of monazite alkali decomposition slag according to claim 1, characterized in that: During the gas pressure-assisted leaching stage, a protective atmosphere is used for pressurization; Preferably, the protective atmosphere includes at least one of nitrogen and an inert gas.

9. The gas pressure assisted alkali leaching method of monazite alkali decomposition slag according to claim 1, characterized in that: After the air pressure-assisted leaching and heat preservation is completed, the leaching solution is filtered while hot to obtain the leaching solution.

10. The gas pressure assisted alkali leaching method of monazite alkali decomposition slag according to claim 9, characterized in that: The hot filtered cake is washed with 5% to 10% sodium carbonate solution to obtain leaching residue, and the washing solution is used to prepare the leaching agent solution.

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