Method for comprehensively recovering rare earth from low-grade zirconium concentrate

Abstract

The invention belongs to the technical field of hydrometallurgy metal ore recovery, and particularly relates to a method for comprehensively recovering rare earth from low-grade zirconium concentrate. According to the method, conversion of zirconium and rare earth minerals in the zirconium concentrate is promoted through the working procedures of alkali fusion decomposition, water washing and transformation, valuable metal minerals are converted into minerals easy to dissolve, and the content of silicon and sodium in materials is reduced; in addition, the content of impurity elements in the material before acidolysis is further reduced through the rare earth optimal dissolution procedure, rare earth elements are comprehensively recycled, and meanwhile a foundation is laid for subsequent preparation of qualified zirconium oxychloride products. In addition, the zirconium oxychloride crystallization mother liquor is returned to the transformation and optimal dissolution process, the recovery rate of ZrO2 is 88% or above, the comprehensive recovery rate of rare earth is improved, the recovery rate is 83% or above, and the economic additional value of zirconium concentrate treatment is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of hydrometallurgical metal ore recovery, and in particular relates to a method for comprehensively recovering rare earths from low-grade zirconium concentrate. Background Art

[0002] Rare earth elements have special physical and chemical properties and are widely used in metallurgy, chemical industry and materials. At present, my country mainly recovers rare earths from bastnaesite, monazite, ion adsorption type ores and mixed ores of bastnaesite and monazite. The decomposition methods of rare earth concentrates mainly include acid decomposition, alkali decomposition, oxidative roasting and chlorination.

[0003] Low-grade zirconium concentrate contains certain rare earth elements, and the rare earth distribution is good, the content of medium and heavy rare earth elements is high, and the value is relatively large. For low-grade zirconium concentrate, people often use the "one acid and one alkali" process to treat it, or further concentrate it. However, the above-mentioned low-grade zirconium concentrate treatment method does not recover rare earths, resulting in a waste of strategic rare earth resources and reducing the utilization value of low-grade zirconium concentrate. Summary of the invention

[0004] The object of the present invention is to provide a method for comprehensively recovering rare earths from low-grade zirconium concentrate. The method provided by the present invention effectively and comprehensively recovers rare earths from low-grade zirconium concentrate.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a method for comprehensively recovering rare earth from low-grade zirconium concentrate, comprising the following steps:

[0007] (1) mixing zirconium concentrate and alkali to perform alkali melting decomposition to obtain a sintering material;

[0008] (2) washing the sintered material with water until the pH value of the system is 10 to 12 to obtain a washed material;

[0009] (3) mixing the water-washed material and a transformation reagent to transform the mixture until the pH value of the system is 6 to 8, thereby obtaining a transformation material; the transformation reagent comprises one or more of zirconium oxychloride crystallization mother liquor and hydrochloric acid;

[0010] (4) mixing the transformation material with a pre-solubility agent to pre-solubility until the pH value of the system is 3.5 to 4, thereby obtaining a rare earth stock solution and a pre-solubility slag; the pre-solubility agent comprises one or both of a zirconium oxychloride crystallization mother solution and hydrochloric acid;

[0011] (5) Mixing the molten slag and an acid hydrolysis reagent for acid hydrolysis until the concentration of the acid hydrolysis reagent is 1.3 to 3 mol·L -1, obtaining acid hydrolysis residue and acid hydrolysis solution; the acid hydrolysis reagent includes zirconium oxychloride crystal mother liquor and a concentration of 4 to 10 mol·L -1 One or both of hydrochloric acid;

[0012] (6) subjecting the acid hydrolysis solution to a first crystallization to obtain zirconium oxychloride and zirconium oxychloride crystallization mother liquor; the zirconium oxychloride crystallization mother liquor is returned to step (3) for transformation, returned to step (4) for optimal dissolution, or returned to step (5) for acid hydrolysis;

[0013] (7) mixing the rare earth stock solution and the extractant for extraction to obtain a first rare earth-loaded organic phase;

[0014] (8) mixing the first rare earth-loaded organic phase and acidified water for washing to obtain a second rare earth-loaded organic phase;

[0015] (9) mixing the second rare earth loaded organic phase and hydrochloric acid for stripping to obtain a lean organic phase and a rare earth chloride solution; and subjecting the rare earth chloride solution to a second crystallization to obtain rare earth chloride.

[0016] Preferably, in step (1), the temperature of the alkali fusion decomposition is 650-800° C., and the insulation decomposition time is 0.5-4 h.

[0017] Preferably, in step (2), the washing time is 0.5 to 3 hours.

[0018] Preferably, in step (3), the transformation time is 0.5 to 3 hours.

[0019] Preferably, in step (4), the optimal dissolution heat preservation reaction time is 0.5 to 3 hours.

[0020] Preferably, in step (5), the acid hydrolysis temperature is 60 to 90° C., and the insulation time is 2 to 5 hours.

[0021] Preferably, in step (7), the extractant is 2-ethylhexyl mono-2-ethylhexyl phosphate; the extractant is an extractant solution; and the volume concentration of the extractant solution is 10 to 50%.

[0022] Preferably, in step (7), the number of extraction stages is 4 to 10.

[0023] Preferably, in step (8), the number of washing stages is 2 to 3.

[0024] Preferably, in step (9), the number of back extraction stages is 3 to 7.

[0025] The present invention provides a method for comprehensive recovery of rare earths from low-grade zirconium concentrate. The present invention promotes the conversion of zirconium and rare earth minerals in zirconium concentrate through alkali melting decomposition, water washing and transformation processes, converts valuable metal minerals into easily soluble minerals, and reduces the content of silicon and sodium in the material; in addition, the present invention further reduces the content of impurity elements in the material before acid hydrolysis through the rare earth preferential dissolution process, comprehensively recovers rare earth elements, and lays a foundation for the subsequent preparation of qualified zirconium oxychloride products. In addition, the mother liquor of zirconium oxychloride crystallization returns to the transformation and preferential dissolution process, and the ZrO2 recovery rate is above 88%, which improves the comprehensive recovery rate of rare earths, and the recovery rate is above 83%, which improves the economic added value of zirconium concentrate processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 The present invention is a process flow chart for comprehensively recovering rare earths from low-grade zirconium concentrate. DETAILED DESCRIPTION

[0028] The present invention provides a method for comprehensively recovering rare earth from low-grade zirconium concentrate, comprising the following steps:

[0029] (1) mixing zirconium concentrate and alkali to perform alkali melting decomposition to obtain a sintering material;

[0030] (2) washing the sintered material with water until the pH value of the system is 10 to 12 to obtain a washed material;

[0031] (3) mixing the water-washed material and a transformation reagent to transform the mixture until the pH value of the system is 6 to 8, thereby obtaining a transformation material; the transformation reagent comprises one or more of zirconium oxychloride crystallization mother liquor and hydrochloric acid;

[0032] (4) mixing the transformation material with a pre-solubility agent to pre-solubility until the pH value of the system is 3.5 to 4, thereby obtaining a rare earth stock solution and a pre-solubility slag; the pre-solubility agent comprises one or both of a zirconium oxychloride crystallization mother solution and hydrochloric acid;

[0033] (5) Mixing the molten slag and an acid hydrolysis reagent for acid hydrolysis until the concentration of the acid hydrolysis reagent is 1.3 to 3 mol·L -1 , obtaining acid hydrolysis residue and acid hydrolysis solution; the acid hydrolysis reagent includes zirconium oxychloride crystal mother liquor and a concentration of 4 to 10 mol·L -1 One or both of hydrochloric acid;

[0034] (6) subjecting the acid hydrolysis solution to a first crystallization to obtain zirconium oxychloride and zirconium oxychloride crystallization mother liquor; the zirconium oxychloride crystallization mother liquor is returned to step (3) for transformation, returned to step (4) for optimal dissolution, or returned to step (5) for acid hydrolysis;

[0035] (7) mixing the rare earth stock solution and the extractant for extraction to obtain a first rare earth-loaded organic phase;

[0036] (8) mixing the first rare earth-loaded organic phase and acidified water for washing to obtain a second rare earth-loaded organic phase;

[0037] (9) mixing the second rare earth loaded organic phase and hydrochloric acid for stripping to obtain a lean organic phase and a rare earth chloride solution; and subjecting the rare earth chloride solution to a second crystallization to obtain rare earth chloride.

[0038] The present invention mixes zirconium concentrate and alkali for alkali melting decomposition to obtain sintering material. In the present invention, the zirconium concentrate is preferably low-grade zirconium concentrate; the chemical composition of the low-grade zirconium concentrate preferably includes: ZrO2 30-50wt%; REO 5-10wt%.

[0039] In the present invention, the alkali is preferably sodium hydroxide.

[0040] In the present invention, the mass ratio of the alkali to the zirconium concentrate is preferably 0.8 to 1.5:1, specifically 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1 or 1.5:1.

[0041] In the present invention, the temperature of the alkali-melt decomposition is preferably 650-800°C, specifically 650°C, 675°C, 700°C, 725°C, 750°C, 775°C or 800°C, and the insulation decomposition time is preferably 0.5-4h, specifically 0.5h, 1h, 1.5h, 2h, 3h or 4h; the equipment for the alkali-melt decomposition is preferably an alkali melting pot.

[0042] After obtaining the sintering material, the present invention washes the sintering material with water until the pH value of the system is 10-12 to obtain a washed material. In the present invention, the volume mass ratio of the washing water to the sintering material is preferably (2-6) mL:1 g, specifically 4 mL:1 g.

[0043] In the present invention, the water washing time is preferably 0.5 to 3 hours, specifically 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours or 3 hours.

[0044] In the present invention, after the water washing, the step preferably further includes: filtering the water washed product to obtain a solid product, and then washing the solid product; the volume mass ratio of the washing water to the solid product is preferably 6 mL:1 g.

[0045] After obtaining the washed material, the present invention mixes the washed material and the transformation agent to transform until the pH value of the system is 6 to 8 to obtain the transformation material. In the present invention, the volume mass ratio of the transformation agent to the washed material is preferably (2 to 6) mL: 1 g, specifically 4 mL: 1 g.

[0046] In the present invention, the transformation time is preferably 0.5 to 3 hours, specifically 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours or 3 hours.

[0047] In the present invention, after the transformation, the process preferably further comprises: filtering the slurry obtained from the transformation and then washing it; the volume mass ratio of the washing water to the filtered product is preferably 3 mL:1 g.

[0048] After obtaining the transformation material, the present invention mixes the transformation material with a good dissolving agent to dissolve until the pH value of the system is 3.5 to 4, thereby obtaining a rare earth stock solution and a good dissolving slag. In the present invention, the mass ratio of the good dissolving agent to the transformation material is preferably 1 to 3:1, specifically 1:1, 1.5:1, 2:1, 2.5:1 or 3:1.

[0049] In the present invention, the optimal dissolution heat preservation reaction time is preferably 0.5 to 3 hours, specifically 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours or 3 hours.

[0050] In the present invention, after the optimal dissolution, the method preferably further comprises: filtering the slurry obtained by the optimal dissolution.

[0051] After obtaining the excellent slag, the present invention mixes the excellent slag with an acid hydrolysis agent for acid hydrolysis until the concentration of the acid hydrolysis agent is 1.3 to 3 mol·L -1 In the present invention, the acid hydrolysis reagent is preferably at a concentration of 4 to 10 mol·L -1 of hydrochloric acid, specifically 6 mol·L -1 or 8mol·L -1 .

[0052] In the present invention, the mass ratio of the acid hydrolysis agent to the molten slag is preferably 3 to 6:1, specifically 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1 or 6:1.

[0053] In the present invention, the acid hydrolysis temperature is preferably 60-90°C, specifically 60°C, 65°C, 70°C, 75°C, 80°C, 85°C or 90°C, and the insulation time is preferably 2-5h, specifically 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h.

[0054] In the present invention, the acid hydrolysis preferably further comprises: filtering the slurry obtained by the acid hydrolysis and then washing; the volume mass ratio of the washing reagent to the filtered product is preferably 4mL:1g; the washing reagent is preferably an acid solution; the acid solution is preferably a hydrochloric acid solution; the concentration of the hydrochloric acid solution is preferably 5g·L -1 .

[0055] After obtaining the acid hydrolysis solution, the present invention first crystallizes the acid hydrolysis solution to obtain zirconium oxychloride and zirconium oxychloride crystallization mother liquor; the zirconium oxychloride crystallization mother liquor is returned to step (3) for transformation, returned to step (4) for optimal dissolution, or returned to step (5) for acid hydrolysis. In the present invention, the first crystallization is preferably concentrated crystallization; the concentrated crystallization is preferably evaporative concentrated crystallization; the temperature of the concentrated crystallization is preferably 130-160°C, specifically 145°C.

[0056] After obtaining the rare earth stock solution, the present invention mixes the rare earth stock solution and an extractant for extraction to obtain a first rare earth loaded organic phase. In the present invention, the extractant is preferably 2-ethylhexyl phosphate mono-2-ethylhexyl ester (P507); the extractant is preferably an extractant solution; the solvent of the extractant solution is preferably kerosene; the volume concentration of the extractant solution is preferably 10-50%, specifically 10%, 20%, 30%, 40% or 50%.

[0057] In the present invention, the volume ratio of the rare earth stock solution to the extractant (calculated as the extractant solution) is preferably 1:1-10, specifically 1:3, 1:5, 1:7 or 1:9.

[0058] In the present invention, the number of extraction stages is preferably 4 to 10, specifically 6 or 8; the extraction equipment is preferably a mixer-settler.

[0059] After obtaining the first rare earth-loaded organic phase, the present invention mixes the first rare earth-loaded organic phase with acidified water for washing to obtain a second rare earth-loaded organic phase. In the present invention, the pH value of the acidified water is preferably 3.5 to 4.0, and specifically can be 4.0.

[0060] In the present invention, the volume ratio of the first rare earth-loaded organic phase to the acidified water is preferably 5 to 10:1, specifically 6:1 or 8:1.

[0061] In the present invention, the number of washing stages is preferably 2 to 3; the washing equipment is preferably a mixer-settler.

[0062] After obtaining the second rare earth loaded organic phase, the present invention mixes the second rare earth loaded organic phase with hydrochloric acid for stripping to obtain a lean organic phase and a rare earth chloride solution; and the rare earth chloride solution is subjected to a second crystallization to obtain rare earth chloride. In the present invention, the concentration of the hydrochloric acid is preferably 5 to 10 mol·L -1 , specifically 5moL·L -1 、6moL·L -1 、7moL·L -1 、8moL·L -1 、9moL·L -1 or 10moL·L -1 .

[0063] In the present invention, the volume ratio of the second rare earth-loaded organic phase to hydrochloric acid is preferably 8 to 30:1, specifically 8:1, 10:1, 12:1, 15:1, 18:1, 20:1, 25:1 or 30:1.

[0064] In the present invention, the number of the stripping stages is preferably 3 to 7, specifically 3, 4, 5, 6 or 7; the stripping equipment is preferably a mixer-settler.

[0065] In the present invention, the second crystallization of the rare earth chloride solution is preferably concentrated crystallization; the concentrated crystallization is preferably evaporative concentrated crystallization; the temperature of the concentrated crystallization is preferably 108-115°C, specifically 110°C.

[0066] The present invention comprehensively recovers rare earth from low-grade zirconium concentrate. The main process flow is as follows: Figure 1 As shown: the present invention decomposes zirconium concentrate by alkali melting to obtain a sintering material, then washes, filters and washes the sintering material to obtain a washed material, then transforms, filters and washes the washed material to obtain a transformed material, then preferentially dissolves the transformed material and filters it to obtain a rare earth stock solution and preferentially dissolved slag, then acid-lyzes the preferentially dissolved slag to obtain acid-lyzed slag and acid-lyzed liquid, the acid-lyzed liquid is crystallized to obtain zirconium oxychloride and zirconium oxychloride crystallization mother liquor, and the zirconium oxychloride crystallization mother liquor is returned to the preferential dissolution or acid-lyzed process for recycling; in addition, the present invention extracts the rare earth stock solution to obtain a first rare earth-loaded organic phase, then washes the first rare earth-loaded organic phase to obtain a second rare earth-loaded organic phase, then reversely extracts the second rare earth-loaded organic phase to obtain a lean organic phase and a rare earth chloride solution, and then crystallizes the rare earth chloride solution to obtain rare earth chloride. The method provided by the present invention is simple to operate, low in cost and good in stability.

[0067] In order to further illustrate the present invention, the scheme of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments, but they should not be understood as limiting the protection scope of the present invention.

[0068] Example 1

[0069] The ZrO2 content of a low-grade zirconium concentrate is 42.3% and the REO content is 6.54%.

[0070] The method for comprehensively recovering rare earth from low-grade zirconium concentrate in this embodiment comprises the following steps:

[0071] (1) Sodium hydroxide and zirconium concentrate are mixed in a mass ratio of 1:1 and then sent to an alkali melting pot, heated to 700° C. for alkali melting decomposition, and the reaction time is 2.0 h for decomposition and conversion to obtain a sintering material;

[0072] (2) washing the sintered material in step (1) with water at a liquid-to-solid volume mass ratio of 6:1 for 0.5 h. The pH value at the end of the washing was 10.35. The obtained washed material slurry was filtered and washed to obtain a washed material;

[0073] (3) The washed material of step (2) is transformed according to a liquid-to-solid volume mass ratio of 4:1, and zirconium oxychloride crystallization mother liquor is added to adjust the pH value. The pH value at the transformation end point is 7.2, and the transformation time is 2.0 h. The obtained transformation slurry is filtered and washed to obtain a transformation material;

[0074] (4) adding the transformation material described in step (3) to the zirconium oxychloride crystallization mother liquor for optimal dissolution, the liquid-to-solid ratio of the optimal dissolution is 1:1, the reaction time is 2 hours, the pH value at the reaction end point is 4.2, and the slurry is filtered to obtain a rare earth stock solution and optimal dissolution slag;

[0075] (5) Add hydrochloric acid to the slag prepared in step (4) for acid hydrolysis. The liquid-to-solid ratio of the acid hydrolysis is 4:1. The reaction time is 2 h. The reaction temperature is 90° C. The hydrochloric acid concentration at the end of the reaction is 2.3 mol·L -1 , the acid-lyzed slurry is filtered and washed to obtain acid-lyzed slag and acid-lyzed liquid; the acid-lyzed liquid is evaporated, concentrated and crystallized to obtain a zirconium oxychloride product and a zirconium oxychloride crystallization mother liquor, and the zirconium oxychloride crystallization mother liquor is returned to the optimal dissolution or acid-lyzation process;

[0076] (6) sending the rare earth stock solution and P507 kerosene solution of step (4) to a mixer-settler for extraction, wherein the volume concentration of the kerosene solution P507 is 25%, and the extraction stage is 5, to obtain a first rare earth-loaded organic phase;

[0077] (7) sending the first rare earth-loaded organic phase and acidified water with a pH value of 4.0 in step (6) to a mixer-settler and washing the phases in two stages to obtain a second rare earth-loaded organic phase;

[0078] (8) The second rare earth-loaded organic phase in step (7) and 6 mol·L -1 The hydrochloric acid is sent to a 4-stage mixer-settler for stripping to obtain a lean organic phase and a rare earth chloride solution; the rare earth chloride solution is evaporated, concentrated and crystallized to obtain a rare earth chloride product.

[0079] In this embodiment, the yield of the acid-hydrolyzed slag is 18.6%, the ZrO2 mass content is 23.2%, and the ZrO2 leaching rate is 88.9%; the REO mass content is 4.32%, and the REO leaching rate is 90.7%.

[0080] Example 2

[0081] The ZrO2 content of a low-grade zirconium concentrate is 45.7% and the REO content is 5.49%.

[0082] The method for comprehensively recovering rare earth from low-grade zirconium concentrate in this embodiment comprises the following steps:

[0083] (1) Sodium hydroxide and zirconium concentrate are mixed in a mass ratio of 0.9:1 and then sent to an alkali melting pot, heated to 720° C. for alkali melting decomposition, and the reaction time is 2.0 h for decomposition and conversion to obtain a sintering material;

[0084] (2) washing the sintered material in step (1) with water at a liquid-to-solid volume mass ratio of 4:1 for 1.0 h, with a pH value of 10.20 at the end of the washing, filtering the obtained washed material slurry and washing it to obtain a washed material;

[0085] (3) The washed material in step (2) is transformed according to a liquid-to-solid volume mass ratio of 5:1, and zirconium oxychloride crystallization mother liquor is added to adjust the pH value. The pH value at the transformation end point is 7.5, and the transformation time is 1.0 h. The obtained transformation slurry is filtered and washed to obtain a transformation material;

[0086] (4) adding the transformation material described in step (3) to the zirconium oxychloride crystallization mother liquor for optimal dissolution, the liquid-to-solid ratio of the optimal dissolution is 1:1, the reaction time is 3 hours, the pH value at the reaction end point is 3.8, and the slurry is filtered to obtain a rare earth stock solution and optimal dissolution slag;

[0087] (5) Add hydrochloric acid to the slag prepared in step (4) for acid hydrolysis. The liquid-to-solid ratio of the acid hydrolysis is 3:1. The reaction time is 3 h. The reaction temperature is 70° C. The hydrochloric acid concentration at the end of the reaction is 1.8 mol·L -1 , the acid-lyzed slurry is filtered and washed to obtain acid-lyzed slag and acid-lyzed liquid; the acid-lyzed liquid is evaporated, concentrated and crystallized to obtain a zirconium oxychloride product and a zirconium oxychloride crystallization mother liquor, and the zirconium oxychloride crystallization mother liquor is returned to the optimal dissolution or acid-lyzation process;

[0088] (6) sending the rare earth stock solution and the P507 kerosene solution of step (4) to a mixer-settler for extraction, wherein the volume concentration of the kerosene solution P507 is 20%, and the extraction stage is 5, to obtain a first rare earth-loaded organic phase;

[0089] (7) sending the first rare earth-loaded organic phase and acidified water with a pH value of 4.0 in step (6) to a mixer-settler for washing, with two washing stages, to obtain a second rare earth-loaded organic phase;

[0090] (8) The second rare earth-loaded organic phase in step (7) and 8 mol·L -1 The hydrochloric acid is sent to a mixer-settler, and three back-extraction stages are performed to obtain a lean organic phase and a rare earth chloride solution; the rare earth chloride solution is evaporated, concentrated, and crystallized to obtain a rare earth chloride product.

[0091] In this embodiment, the yield of the acid hydrolysis slag is 20.4%, the ZrO2 mass content is 24.8%, and the ZrO2 leaching rate is 89.8%; the REO mass content is 3.28%, and the REO leaching rate is 83.9%.

[0092] Example 3

[0093] The ZrO2 content of a low-grade zirconium concentrate is 38.7% and the REO content is 4.85%.

[0094] The method for comprehensively recovering rare earth from low-grade zirconium concentrate in this embodiment comprises the following steps:

[0095] (1) Sodium hydroxide and zirconium concentrate are mixed in a mass ratio of 1.2:1 and then sent to an alkali melting pot, heated to 650° C. for alkali melting decomposition, and the reaction time is 4.0 h for decomposition and conversion to obtain a sintering material;

[0096] (2) washing the sintered material in step (1) with water at a liquid-to-solid volume mass ratio of 4:1 for 2.0 h, with a pH value of 11.30 at the end of the washing, filtering the obtained washed material slurry and washing it to obtain a washed material;

[0097] (3) The washed material of step (2) is transformed according to a liquid-to-solid volume mass ratio of 6:1, and zirconium oxychloride crystallization mother liquor is added to adjust the pH value. The pH value at the transformation end point is 6.8, and the transformation time is 3.0 h. The obtained transformation slurry is filtered and washed to obtain a transformation material;

[0098] (4) adding the transformation material described in step (3) to the zirconium oxychloride crystallization mother liquor for optimal dissolution, the liquid-to-solid ratio of the optimal dissolution is 1:1, the reaction time is 3.0 hours, the pH value of the reaction end point is 4.0, and the slurry is filtered to obtain a rare earth stock solution and optimal dissolution slag;

[0099] (5) Add hydrochloric acid to the slag prepared in step (4) for acid hydrolysis. The liquid-to-solid ratio of the acid hydrolysis is 5:1. The reaction time is 4 h. The reaction temperature is 60° C. The hydrochloric acid concentration at the end of the reaction is 2.8 mol·L -1 , the acid-lyzed slurry is filtered and washed to obtain acid-lyzed slag and acid-lyzed liquid; the acid-lyzed liquid is evaporated, concentrated and crystallized to obtain a zirconium oxychloride product and a zirconium oxychloride crystallization mother liquor, and the zirconium oxychloride crystallization mother liquor is returned to the optimal dissolution or acid-lyzation process;

[0100] (6) sending the rare earth stock solution and P507 kerosene solution of step (4) to a mixer-settler for extraction, wherein the volume concentration of the kerosene solution P507 is 15%, and the extraction stage is 6, to obtain a first rare earth-loaded organic phase;

[0101] (7) sending the first rare earth-loaded organic phase and acidified water with a pH value of 4.0 in step (6) to a mixer-settler and washing the phases for 3 stages to obtain a second rare earth-loaded organic phase;

[0102] (8) The second rare earth-loaded organic phase in step (7) and 5 mol·L -1 The hydrochloric acid is sent to a mixer-settler, and six stages of stripping are performed to obtain a lean organic phase and a rare earth chloride solution; the rare earth chloride solution is evaporated, concentrated, and crystallized to obtain a rare earth chloride product.

[0103] In this embodiment, the yield of the acid hydrolysis slag is 17.3%, the ZrO2 mass content is 22.8%, and the ZrO2 leaching rate is 89.8%; the REO mass content is 2.87%, and the REO leaching rate is 89.8%.

[0104] Cost accounting

[0105] The economic benefit of the method provided by the present invention is calculated. The REO grade of the low-grade zirconium concentrate is calculated as 5%, and the recovery rate is calculated as 85%. According to its distribution, the price of rare earth oxide is 230,000 yuan / ton. The economic added value generated by processing 1 ton of low-grade zirconium concentrate is 9,700 yuan, and the economic benefit is significant.

[0106] It can be seen from the above embodiments that the method provided by the present invention effectively recovers rare earths from low-grade zirconium concentrate, with a ZrO2 recovery rate of more than 88%, thereby increasing the comprehensive recovery rate of rare earths to more than 83%, thereby increasing the economic added value of low-grade zirconium concentrate processing.

[0107] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for comprehensive recovery of rare earths from low-grade zirconium concentrate, characterized in that: The following steps are involved: (1) mixing zirconium concentrate and alkali to perform alkali melting decomposition to obtain a sintering material; (2) washing the sintered material with water until the pH value of the system is 10 to 12 to obtain a washed material; (3) mixing the water-washed material and a transformation reagent to transform the mixture until the pH value of the system is 6 to 8, thereby obtaining a transformation material; the transformation reagent comprises one or more of zirconium oxychloride crystallization mother liquor and hydrochloric acid; (4) mixing the transformation material with a pre-solubility agent to pre-solubility until the pH value of the system is 3.5 to 4, thereby obtaining a rare earth stock solution and a pre-solubility slag; the pre-solubility agent comprises one or both of a zirconium oxychloride crystallization mother solution and hydrochloric acid; (5) Mixing the molten slag and an acid hydrolysis reagent for acid hydrolysis until the concentration of the acid hydrolysis reagent is 1.3 to 3 mol·L -1 , obtaining acid hydrolysis residue and acid hydrolysis solution; the acid hydrolysis reagent includes zirconium oxychloride crystal mother liquor and a concentration of 4 to 10 mol·L -1 One or both of hydrochloric acid; (6) subjecting the acid hydrolysis solution to a first crystallization to obtain zirconium oxychloride and zirconium oxychloride crystallization mother liquor; the zirconium oxychloride crystallization mother liquor is returned to step (3) for transformation, returned to step (4) for optimal dissolution, or returned to step (5) for acid hydrolysis; (7) mixing the rare earth stock solution and the extractant for extraction to obtain a first rare earth-loaded organic phase; (8) mixing the first rare earth-loaded organic phase and acidified water for washing to obtain a second rare earth-loaded organic phase; (9) mixing the second rare earth-loaded organic phase with hydrochloric acid for stripping to obtain a lean organic phase and a rare earth chloride solution; The rare earth chloride solution is subjected to a second crystallization to obtain rare earth chloride.

2. The method according to claim 1, characterized in that In step (1), the temperature of the alkali melting decomposition is 650-800° C., and the insulation decomposition time is 0.5-4 h.

3. The method according to claim 1 or 2, characterized in that: In step (2), the water washing time is 0.5 to 3 hours.

4. The method according to claim 1, characterized in that: In step (3), the transformation time is 0.5 to 3 hours.

5. The method according to claim 1 or 4, characterized in that: In step (4), the optimally soluble heat preservation reaction time is 0.5 to 3 hours.

6. The method according to claim 1 or 2, characterized in that: In step (5), the acid hydrolysis temperature is 60 to 90° C. and the insulation time is 2 to 5 hours.

7. The method according to claim 1 or 4, characterized in that: In step (7), the extractant is 2-ethylhexyl mono-2-ethylhexyl phosphate; the extractant is an extractant solution; and the volume concentration of the extractant solution is 10 to 50%.

8. The method according to claim 1, characterized in that In step (7), the extraction stages are 4 to 10.

9. The method according to claim 1 or 8, characterized in that: In step (8), the washing stages are 2 to 3.

10. The method according to claim 1 or 8, characterized in that: In step (9), the number of stages of back extraction is 3 to 7.

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