A method for phase conversion-clean leaching of mixed rare earth concentrate

Abstract

A method for phase transformation and clean leaching of mixed rare earth concentrate belongs to the field of metallurgy. The method is: fluidizing the mixed rare earth concentrate for phase transformation, ball milling the phase transformation product, leaching the finely ground mixed rare earth concentrate with hydrochloric acid to obtain acid leaching residue and acid leaching liquid, alkali decomposing the acid leaching residue and washing it with water to obtain washing liquid and water washing residue respectively; mixing the washed residue with the acid leaching liquid obtained by S3 and stirring them together for acid leaching, and obtaining a chloride rare earth product after neutralization and impurity removal of the leaching liquid, and the slag phase is thorium-containing slag. The method can realize phase transformation of rare earth minerals, avoid the formation of tetravalent cerium in the product, improve the rare earth leaching rate, and can also avoid the generation of fluorine and chlorine waste gas to cause pollution.

Description

Technical Field

[0001] The invention relates to the field of beneficiation and smelting, and in particular to a method for phase conversion-clean leaching of mixed rare earth concentrate. Background Art

[0002] The Bayan Obo area in Inner Mongolia produces a lot of complex polymetallic symbiotic ores, which have great development value. However, due to the complex origin of its minerals, close symbiotic relationships and similar beneficiation properties of the main minerals, the enrichment effect of valuable elements in the beneficiation process is poor, making it difficult to obtain high-quality mixed rare earth concentrate products, and placing a burden on the subsequent smelting process.

[0003] At present, the mixed rare earth concentrate obtained by mineral processing in this area is mainly a mixture of fluorocarbon cerium ore and monazite. The further processing methods of this type of mixed rare earth concentrate mainly include concentrated sulfuric acid roasting method, caustic soda decomposition method and oxidation roasting-hydrochloric acid leaching method. Among them, the concentrated sulfuric acid roasting method for treating mixed rare earth concentrate is the earliest and most mature in industrial application, but it will inevitably produce a large amount of F and S-containing waste gas during the roasting process, which is not only highly polluting, but also difficult to reuse the mixed acid solution recovered by spraying. In addition, the radioactive thorium pyrophosphate waste residue produced by this method is also difficult to use, and it not only occupies a large amount of land but also brings great environmental pressure; the caustic soda decomposition method has the defects of high requirements for the grade of mixed rare earth concentrate, large alkali consumption and high production cost; the oxidation roasting-hydrochloric acid leaching method has Ce in the concentrated hydrochloric acid leaching process 4+ Will be Cl - Reduction to Ce 3+ Chlorine gas is generated, which requires the addition of a reducing agent to eliminate it; and part of the F will react with Ce during the leaching process. 4+ It is dispersed in the leachate in the form of a complex, which increases the difficulty of the extraction and separation process and reduces the economic benefits. Summary of the invention

[0004] In view of the problems existing in the above-mentioned prior art, the present invention provides a method for phase transformation-clean leaching of mixed rare earth concentrate, which can realize phase transformation of rare earth minerals, avoid the formation of tetravalent cerium in the product, improve the rare earth leaching rate, and simultaneously avoid the generation of fluorine and chlorine waste gas pollution.

[0005] In order to achieve the purpose of the present invention, the technical solution adopted by the present invention is as follows:

[0006] A method for phase conversion-clean leaching of a mixed rare earth concentrate of the present invention comprises the following steps:

[0007] S1. Fluidized mineral phase transformation:

[0008] The mixed rare earth concentrate is subjected to fluidized ore phase transformation, and a protective gas is introduced during the fluidized ore phase transformation to fluidize the mixed rare earth concentrate to obtain an ore phase transformation product;

[0009] S2. Grinding:

[0010] Ball milling the ore phase transformation product to obtain a finely ground mixed rare earth concentrate; wherein the finely ground mixed rare earth concentrate has a particle size of -45 μm accounting for 85 to 95 wt%;

[0011] S3, hydrochloric acid leaching:

[0012] The finely ground mixed rare earth concentrate is subjected to hydrochloric acid leaching to obtain acid leaching residue and acid leaching liquid;

[0013] S4, leaching residue alkali decomposition-water washing:

[0014] The acid leaching residue is alkali-decomposed and then washed with water to obtain a washing liquid and a washing residue respectively;

[0015] In the above-mentioned S4, the water washing liquid is collected and can be further processed to recover the fluorine, phosphorus components and alkali solution. The recovered alkali solution can be returned after treatment to continue to participate in the alkali decomposition of the acid leaching residue, forming a closed-loop cycle.

[0016] S5, acid leaching-neutralization:

[0017] The washed slag is mixed with the acid leaching solution obtained from S3 and stirred together for acid leaching. After the leaching solution is neutralized and impurities are removed, a chloride rare earth product is obtained, and the slag phase is a thorium-containing slag.

[0018] In the S5, the slag phase can be used as a raw material for thorium extraction or can be sealed uniformly.

[0019] In the S5, the trivalent cerium content in the rare earth chloride product is determined according to the properties of the feed ore.

[0020] Furthermore, in step S1, the fluidized mineral phase conversion temperature is 450-650°C, the conversion time is 1-2.5h; the protective gas introduced is nitrogen or argon;

[0021] Furthermore, in step S1, the purpose of introducing protective gas is to ensure that the mineral phase conversion process is carried out in an oxygen-free or low-oxygen environment to achieve CeCO 3 F is transformed into CeOF in a directional manner to prevent the formation of Ce(Ⅳ). The main reactions occurring during the mineral phase transformation are:

[0022] CeCO 3 F→CeOF+CO 2

[0023] 2CeCO 3 F→2Ce 2 O 3 F 2 +2CO 2

[0024] Furthermore, in step S1, the mineral phase conversion product is cooled by water to prevent oxidation of the product;

[0025] Furthermore, in step S3, the concentration of hydrochloric acid used is 8-13 mol / L, and in the finely ground mixed rare earth concentrate, REO: hydrochloric acid = 1: (1-3) by mass ratio, the leaching temperature is 65-100° C., and the leaching time is 1-3 h.

[0026] Furthermore, in step S4, NaOH is selected as a raw material for alkaline decomposition of acid leaching residue, the mass concentration of NaOH is 50% to 80%, and the mass ratio of REO in the acid leaching residue is 1: (0.5 to 2.5), the alkaline decomposition temperature of the acid leaching residue is 130 to 220° C., the alkaline decomposition time of the acid leaching residue is 1 to 2 hours, the water washing temperature of the alkaline decomposition residue is 60 to 100° C., and the pH value at the water washing end point is 7 to 9;

[0027] Furthermore, in step S5, the acid leaching temperature is 40-80°C, the mass ratio of water-washed slag to acid leaching liquid is 1:(5-10), and the time is 1-3h; the alkaline substance used for neutralization is ammonia water or NaOH, and the end point is pH=4-5.

[0028] The invention discloses a mixed rare earth concentrate ore phase conversion-clean leaching method, and the rare earth recovery rate is greater than 94%.

[0029] The present invention provides a method for phase conversion-clean leaching of mixed rare earth concentrate, which has the following beneficial effects:

[0030] (1) The present invention uses fluidized ore phase conversion technology to treat mixed rare earth concentrates. Compared with the traditional oxidative roasting technology for treating rare earth concentrates, the present invention can treat rare earths with lower grade requirements and has higher heat and mass transfer efficiency, and can achieve directional conversion of rare earth components at low temperature and in a short time;

[0031] (2) The present invention can convert CeCO into 3 The directional conversion of F into CeOF avoids the oxidation of Ce(III) in rare earths to Ce(VI) and the generation of HF gas, which improves the leaching rate of rare earths while also avoiding the interference of F in the leaching solution. In addition, it can also reduce the addition of reducing agents in the hydrochloric acid leaching process, saving reagent costs. There is no emission of fluorine, chlorine, sulfur and other gases in the entire process of mineral phase conversion and leaching, eliminating waste gas pollution and reducing environmental pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The figure is a specific process flow chart of the present invention. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below in conjunction with embodiments.

[0034] The rare earth grade REO in the mixed rare earth concentrate selected in the example of the present invention is 52% to 67%, and the iron grade TFe is 5% to 13%;

[0035] The present invention is further described below with reference to the accompanying drawings and examples. The methods, reagents and materials described in the following examples, unless otherwise specified, can all be obtained from commercial channels; the test methods described, unless otherwise specified, are all conventional methods.

[0036] In the following examples, a process flow chart of a mixed rare earth concentrate ore phase conversion-clean leaching method is shown in Figure 1 .

[0037] Example 1

[0038] S1. Fluidized ore phase conversion: First, the mixed rare earth concentrate with a REO grade of 55.32% and a TFe grade of 8.10% was fed into the fluidized ore phase conversion device. The conversion temperature was 470°C and the conversion time was 1.5 h. During the ore phase conversion, N 2 As a protective gas, the conversion product is water-cooled.

[0039] S2, grinding: the ore phase transformation product is sent to a ball mill and ground to -45 μm accounting for 90 wt%, to obtain a finely ground mixed rare earth concentrate;

[0040] S3, hydrochloric acid leaching: the finely ground mixed rare earth concentrate is subjected to hydrochloric acid leaching, the hydrochloric acid concentration used is 11 mol / L, the amount of hydrochloric acid used is REO in the concentrate: hydrochloric acid = 1:2, the leaching temperature is 80°C, the leaching time is 3h, and the acid leaching residue and leachate are obtained;

[0041] S4, leaching residue alkaline decomposition - water washing: NaOH is used as the raw material for acid leaching residue alkaline decomposition, the NaOH concentration is 65%, the NaOH dosage is REO in the leaching residue: NaOH = 1: 1.5, the temperature is 185°C, and the time is 1.5h; after decomposition, water washing is performed, the alkaline decomposition residue water washing temperature is 80°C, and the water washing end point pH = 8; water washing liquid and water washing residue are obtained respectively, and the water washing liquid can be further treated to recover fluorine, phosphorus components and alkali solution, and the alkali solution can be returned after treatment to continue to participate in the acid leaching residue decomposition, forming a closed loop;

[0042] S5, acid leaching-neutralization: the washed slag and the acid leaching solution obtained in S3 were mixed and stirred together for acid leaching. The acid leaching temperature was 73°C, the mass ratio of washed slag to acid leaching solution was 1:8, and the time was 2h. The leaching solution was neutralized with NaOH, and the end point was pH = 4.5. After neutralization and impurity removal, a rare earth chloride solution was obtained, with a REO content of 236g / L and a rare earth recovery rate of 95.42%.

[0043] Example 2

[0044] S1. Fluidized ore phase conversion: First, the mixed rare earth concentrate with REO grade of 65.32% and TFe grade of 6.23% was sent to the fluidized ore phase conversion device. The conversion temperature was 550℃ and the conversion time was 2h. N was introduced during the ore phase conversion. 2 As a protective gas, the conversion product is water-cooled.

[0045] S2, grinding: the ore phase transformation product is sent to a ball mill and ground to -45 μm accounting for 90 wt%, to obtain a finely ground mixed rare earth concentrate;

[0046] S3, hydrochloric acid leaching: the finely ground mixed rare earth concentrate is subjected to hydrochloric acid leaching, the hydrochloric acid concentration used is 10.5 mol / L, the amount of hydrochloric acid used is REO in the concentrate: hydrochloric acid = 1:2.5, the leaching temperature is 75°C, the leaching time is 2.5h, and the acid leaching residue and leachate are obtained;

[0047] S4, leaching residue alkaline decomposition - water washing: NaOH is used as the raw material for acid leaching residue alkaline decomposition, the NaOH concentration is 70%, the NaOH dosage is REO in the leaching residue: NaOH = 1:2, the temperature is 170°C, and the time is 2h; after decomposition, water washing, the alkaline decomposition residue water washing temperature is 75°C, and the water washing end point pH = 7.5; water washing liquid and water washing residue are obtained respectively, and the water washing liquid can be further treated to recover fluorine, phosphorus components and alkali solution, and the alkali solution can be returned after treatment to continue to participate in the acid leaching residue decomposition, forming a closed loop;

[0048] S5, acid leaching-neutralization: the washed slag and the acid leaching solution obtained in S3 are mixed and stirred together for acid leaching. The acid leaching temperature is 68°C, the mass ratio of washed slag to acid leaching solution is 1:7.5, and the time is 2.5h. The leaching solution is neutralized with ammonia water, and the end point is pH=4.5. After neutralization and impurity removal, a rare earth chloride solution is obtained, with a REO content of 245g / L and a rare earth recovery rate of 95.89%.

[0049] Example 3

[0050] S1. Fluidized ore phase conversion: First, the mixed rare earth concentrate with REO grade of 62.41% and TFe grade of 5.13% was sent to the fluidized ore phase conversion device. The conversion temperature was 620℃ and the conversion time was 1.5h. During the ore phase conversion, N 2 As a protective gas, the conversion product is water-cooled.

[0051] S2, grinding: the ore phase transformation product is sent to a ball mill and ground to -45 μm accounting for 92 wt%, to obtain a finely ground mixed rare earth concentrate;

[0052] S3, hydrochloric acid leaching: the finely ground mixed rare earth concentrate is subjected to hydrochloric acid leaching, the hydrochloric acid concentration used is 9 mol / L, the amount of hydrochloric acid used is REO in the concentrate: hydrochloric acid = 1:3, the leaching temperature is 70°C, the leaching time is 2h, and the acid leaching residue and leachate are obtained;

[0053] S4, leaching residue alkaline decomposition - water washing: NaOH is used as the raw material for acid leaching residue alkaline decomposition, the NaOH concentration is 65%, the NaOH dosage is REO in the leaching residue: NaOH = 1: 2.5, the temperature is 185°C, and the time is 2h; after decomposition, water washing, the alkaline decomposition residue water washing temperature is 70°C, and the water washing end point pH = 8; water washing liquid and water washing residue are obtained respectively, and the water washing liquid can be further treated to recover fluorine, phosphorus components and alkali solution, and the alkali solution can be returned after treatment to continue to participate in the acid leaching residue decomposition, forming a closed loop;

[0054] S5, acid leaching-neutralization: the washed slag and the acid leaching solution obtained in S3 were mixed and stirred together for acid leaching. The acid leaching temperature was 66°C, the mass ratio of washed slag to acid leaching solution was 1:7, and the time was 3h. The leaching solution was neutralized with NaOH, and the end point was pH=5. After neutralization and impurity removal, a rare earth chloride solution was obtained, with a REO content of 229g / L and a rare earth recovery rate of 96.64%.

[0055] Example 4

[0056] S1. Fluidized ore phase conversion: First, the mixed rare earth concentrate with REO grade of 57.05% and TFe grade of 7.30% was sent to the fluidized ore phase conversion device. The conversion temperature was 600℃ and the conversion time was 1h. During the ore phase conversion, N 2 As a protective gas, the conversion product is water-cooled.

[0057] S2, grinding: the ore phase conversion product is sent to a ball mill and ground to -45 μm accounting for 95 wt%, to obtain a finely ground mixed rare earth concentrate;

[0058] S3, hydrochloric acid leaching: the finely ground mixed rare earth concentrate is subjected to hydrochloric acid leaching, the hydrochloric acid concentration used is 10 mol / L, the amount of hydrochloric acid used is REO in the concentrate: hydrochloric acid = 1:2, the leaching temperature is 80°C, the leaching time is 1.5h, and the acid leaching residue and leachate are obtained;

[0059] S4, leaching residue alkaline decomposition - water washing: NaOH is used as the raw material for acid leaching residue alkaline decomposition, the NaOH concentration is 60%, the NaOH dosage is REO in the leaching residue: NaOH = 1:1, the temperature is 180°C, and the time is 1h; after decomposition, water washing, the alkaline decomposition residue water washing temperature is 90°C, and the water washing end point pH = 7.5; water washing liquid and water washing residue are obtained respectively, and the water washing liquid can be further treated to recover fluorine, phosphorus components and alkali solution, and the alkali solution can be returned after treatment to continue to participate in the acid leaching residue decomposition, forming a closed loop;

[0060] S5, acid leaching-neutralization: the washed slag and the acid leaching solution obtained in S3 are mixed and stirred together for acid leaching. The acid leaching temperature is 65°C, the mass ratio of washed slag to acid leaching solution is 1:6, and the time is 2h; the leaching solution is neutralized with ammonia water, and the end point is pH = 4.5. After neutralization and impurity removal, a rare earth chloride solution is obtained, with a REO content of 263g / L and a rare earth recovery rate of 95.04%.

[0061] Example 5

[0062] S1. Fluidized ore phase conversion: First, the mixed rare earth concentrate with a REO grade of 52.68% and a TFe grade of 8.31% was fed into the fluidized ore phase conversion device. The conversion temperature was 650°C and the conversion time was 1.5 h. During the ore phase conversion, N 2 As a protective gas, the conversion product is water-cooled.

[0063] S2, grinding: the ore phase transformation product is sent to a ball mill and ground to -45 μm accounting for 90 wt%, to obtain a finely ground mixed rare earth concentrate;

[0064] S3, hydrochloric acid leaching: the finely ground mixed rare earth concentrate is subjected to hydrochloric acid leaching, the hydrochloric acid concentration used is 13 mol / L, the amount of hydrochloric acid used is REO in the concentrate: hydrochloric acid = 1:2, the leaching temperature is 70°C, the leaching time is 2.5h, and the acid leaching residue and leachate are obtained;

[0065] S4, leaching residue alkaline decomposition - water washing: NaOH is used as raw material for acid leaching residue alkaline decomposition, the NaOH concentration is 65%, the NaOH dosage is REO in the leaching residue: NaOH = 1:1, the temperature is 200°C, and the time is 1h; after decomposition, water washing, the alkaline decomposition residue water washing temperature is 75°C, and the water washing end point pH = 7; water washing liquid and water washing residue are obtained respectively, and the water washing liquid can be further treated to recover fluorine, phosphorus components and alkali solution, and the alkali solution can be returned after treatment to continue to participate in the acid leaching residue decomposition, forming a closed loop;

[0066] S5, acid leaching-neutralization: the washed slag and the acid leaching solution obtained in S3 were mixed and stirred together for acid leaching. The acid leaching temperature was 55°C, the mass ratio of washed slag to acid leaching solution was 1:7, and the time was 2h. The leaching solution was neutralized with NaOH, and the end point was pH = 4.5. After neutralization and impurity removal, a rare earth chloride solution was obtained, with a REO content of 243g / L and a rare earth recovery rate of 95.69%.

[0067] Example 6

[0068] S1. Fluidized ore phase conversion: First, the mixed rare earth concentrate with REO grade of 61.65% and TFe grade of 6.12% was sent to the fluidized ore phase conversion device. The conversion temperature was 550℃ and the conversion time was 2h. N was introduced during the ore phase conversion. 2As a protective gas, the conversion product is water-cooled.

[0069] S2, grinding: the ore phase conversion product is sent to a ball mill and ground to -45 μm accounting for 95 wt%, to obtain a finely ground mixed rare earth concentrate;

[0070] S3, hydrochloric acid leaching: the finely ground mixed rare earth concentrate is subjected to hydrochloric acid leaching, the hydrochloric acid concentration used is 10 mol / L, the amount of hydrochloric acid used is REO in the concentrate: hydrochloric acid = 1:3, the leaching temperature is 80°C, the leaching time is 2h, and the acid leaching residue and leachate are obtained;

[0071] S4, leaching residue alkaline decomposition - water washing: NaOH is used as the raw material for acid leaching residue alkaline decomposition, the NaOH concentration is 60%, the NaOH dosage is REO in the leaching residue: NaOH = 1: 1.5, the temperature is 160°C, and the time is 1.5h; after decomposition, water washing, the alkaline decomposition residue water washing temperature is 75°C, and the water washing end point pH = 7.5; water washing liquid and water washing residue are obtained respectively, and the water washing liquid can be further treated to recover fluorine, phosphorus components and alkali solution, and the alkali solution can be returned after treatment to continue to participate in the acid leaching residue decomposition, forming a closed loop;

[0072] S5, acid leaching-neutralization: the washed slag and the acid leaching solution obtained in S3 were mixed and stirred together for acid leaching. The acid leaching temperature was 60°C, the mass ratio of washed slag to acid leaching solution was 1:7, and the time was 2h. The leaching solution was neutralized with NaOH, and the end point was pH = 4. After neutralization and impurity removal, a rare earth chloride solution was obtained, with a REO content of 253g / L and a rare earth recovery rate of 95.12%.

[0073] Example 7

[0074] S1. Fluidized ore phase conversion: First, the mixed rare earth concentrate with REO grade of 64.80% and TFe grade of 6.33% was sent to the fluidized ore phase conversion device. The conversion temperature was 500℃ and the conversion time was 2h. N 2 As a protective gas, the conversion product is water-cooled.

[0075] S2, grinding: the ore phase transformation product is sent to a ball mill and ground to -45 μm accounting for 92 wt%, to obtain a finely ground mixed rare earth concentrate;

[0076] S3, hydrochloric acid leaching: the finely ground mixed rare earth concentrate is subjected to hydrochloric acid leaching, the hydrochloric acid concentration used is 8 mol / L, the amount of hydrochloric acid used is REO in the concentrate: hydrochloric acid = 1:2, the leaching temperature is 80°C, the leaching time is 2h, and the acid leaching residue and leachate are obtained;

[0077] S4, leaching residue alkaline decomposition - water washing: NaOH is used as the raw material for acid leaching residue alkaline decomposition, the NaOH concentration is 65%, the NaOH dosage is REO in the leaching residue: NaOH = 1:2, the temperature is 170°C, and the time is 1.5h; after decomposition, water washing, the alkaline decomposition residue water washing temperature is 70°C, and the water washing end point pH = 8; water washing liquid and water washing residue are obtained respectively, and the water washing liquid can be further treated to recover fluorine, phosphorus components and alkali solution, and the alkali solution can be returned after treatment to continue to participate in the acid leaching residue decomposition, forming a closed loop;

[0078] S5, acid leaching-neutralization: the washed slag and the acid leaching solution obtained in S3 were mixed and stirred together for acid leaching. The acid leaching temperature was 55°C, the mass ratio of washed slag to acid leaching solution was 1:6, and the time was 2.5h. The leaching solution was neutralized with ammonia water, and the end point was pH = 4.5. After neutralization and impurity removal, a rare earth chloride solution was obtained, with a REO content of 266g / L and a rare earth recovery rate of 96.21%.

[0079] Example 8

[0080] S1. Fluidized ore phase conversion: First, the mixed rare earth concentrate with REO grade of 54.51% and TFe grade of 7.67% was sent to the fluidized ore phase conversion device. The conversion temperature was 550℃ and the conversion time was 2h. N was introduced during the ore phase conversion. 2 As a protective gas, the conversion product is water-cooled.

[0081] S2, grinding: the ore phase conversion product is sent to a ball mill and ground to -45 μm accounting for 95 wt%, to obtain a finely ground mixed rare earth concentrate;

[0082] S3, hydrochloric acid leaching: the finely ground mixed rare earth concentrate is subjected to hydrochloric acid leaching, the hydrochloric acid concentration used is 9 mol / L, the amount of hydrochloric acid used is REO in the concentrate: hydrochloric acid = 1:2, the leaching temperature is 75°C, the leaching time is 3h, and the acid leaching residue and leachate are obtained;

[0083] S4, leaching residue alkaline decomposition - water washing: NaOH is used as the raw material for acid leaching residue alkaline decomposition, the NaOH concentration is 65%, the NaOH dosage is REO in the leaching residue: NaOH = 1: 1.5, the temperature is 180°C, and the time is 1.5h; after decomposition, water washing, the alkaline decomposition residue water washing temperature is 75°C, and the water washing end point pH = 7.5; water washing liquid and water washing residue are obtained respectively, and the water washing liquid can be further treated to recover fluorine, phosphorus components and alkali solution, and the alkali solution can be returned after treatment to continue to participate in the acid leaching residue decomposition, forming a closed loop;

[0084] S5, acid leaching-neutralization: the washed slag and the acid leaching solution obtained in S3 are mixed and stirred together for acid leaching. The acid leaching temperature is 75°C, the mass ratio of washed slag to acid leaching solution is 1:7, and the time is 2.5h. The leaching solution is neutralized with NaOH, and the end point is pH = 4.5. After neutralization and impurity removal, a rare earth chloride solution is obtained, with a REO content of 210g / L and a rare earth recovery rate of 94.32%.

[0085] Comparative Example 1

[0086] Same as Example 1, except that:

[0087] 1. Directly roast the mixed rare earth concentrate with a REO grade of 57.85% and a TFe grade of 7.67% at a temperature of 650°C for 2 hours in an air atmosphere without any other gas introduced;

[0088] 2. The roasted product was leached with hydrochloric acid, the concentration of hydrochloric acid used was 12 mol / L, the amount of hydrochloric acid used was REO in the concentrate: hydrochloric acid = 1:2, the leaching temperature was 85°C, and the leaching time was 3h;

[0089] 3. The concentration of NaOH is 70%, the amount of NaOH is REO:NaOH=1:1.5 in the leaching residue, the temperature is 210℃, and the time is 2h; the alkali decomposition slag water washing temperature is 75℃, and the water washing end point pH=7.5;

[0090] 4. The acid leaching temperature was 80°C, the solid-liquid ratio was 1:8, and the time was 3h; the leaching solution was neutralized with NaOH, the end point was pH = 5, the REO content of the obtained rare earth chloride solution was 156g / L, and the rare earth recovery rate was 86.83%.

Claims

1. A method for phase conversion-clean leaching of mixed rare earth concentrate, characterized in that: The following steps are involved: S1. Fluidized mineral phase transformation: The mixed rare earth concentrate is subjected to fluidized ore phase transformation, and protective gas is introduced during the fluidized ore phase transformation to fluidize the mixed rare earth concentrate to obtain an ore phase transformation product; during the ore phase transformation process, CeCO3F can be directionally transformed into CeOF; S2. Grinding: Ball milling the mineral phase transformation product to obtain a finely ground mixed rare earth concentrate; S3, hydrochloric acid leaching: The finely ground mixed rare earth concentrate is subjected to hydrochloric acid leaching to obtain acid leaching residue and acid leaching liquid; S4, leaching residue alkali decomposition-water washing: The acid leaching residue is alkali-decomposed and then washed with water to obtain a washing liquid and a washing residue respectively; S5, acid leaching-neutralization: The washed slag is mixed with the acid leaching solution obtained from S3 and stirred together for acid leaching. After the leaching solution is neutralized and impurities are removed, a chloride rare earth product is obtained, and the slag phase is a thorium-containing slag; Wherein, the S4 also includes collecting the water washing liquid and treating it to recover the fluorine, phosphorus components and alkali solution, and the recovered alkali solution is returned after treatment to continue to participate in the alkali decomposition of the acid leaching residue, forming a closed loop.

2. The method for phase conversion-clean leaching of mixed rare earth concentrate according to claim 1, characterized in that: In step S1, the fluidized mineral phase conversion temperature is 450-650° C., and the conversion time is 1-2.5 h.

3. The method for phase conversion-clean leaching of mixed rare earth concentrate according to claim 1, characterized in that: In the step S1, the protective gas introduced is nitrogen or argon.

4. The method for phase conversion-clean leaching of mixed rare earth concentrate according to claim 1, characterized in that: In the step S2, the particle size of the finely ground mixed rare earth concentrate is -45 μm, accounting for 85-95 wt %.

5. The method for phase conversion-clean leaching of mixed rare earth concentrate according to claim 1, characterized in that: In step S3, the concentration of hydrochloric acid used is 8-13 mol / L, and in the finely ground mixed rare earth concentrate, the mass ratio of REO: hydrochloric acid is 1:(1-3), the leaching temperature is 65-100°C, and the leaching time is 1-3h.

6. The method for phase conversion-clean leaching of mixed rare earth concentrate according to claim 1, characterized in that: In the step S4, NaOH is selected as a raw material for alkaline decomposition of the acid leaching residue, the mass concentration of NaOH is 50%~80%, and the mass ratio of REO:NaOH in the acid leaching residue is 1:(0.5~2.5), the alkaline decomposition temperature of the acid leaching residue is 130~220°C, the alkaline decomposition time of the acid leaching residue is 1~2h, the water washing temperature of the alkaline decomposition residue is 60~100°C, and the pH at the water washing end point is 7~9.

7. The method for phase conversion-clean leaching of mixed rare earth concentrate according to claim 1, characterized in that: In step S5, the acid leaching temperature is 40-80° C., the mass ratio of water-washed slag to acid leaching solution is 1:(5-10), and the time is 1-3 hours; the alkaline substance used for neutralization is ammonia water or NaOH, and the end point is pH=4-5.

8. The method for phase conversion-clean leaching of mixed rare earth concentrate according to any one of claims 1 to 6, characterized in that: Rare earth recovery rate is >94%.

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