Multistage alkaline hydrolysis process for rare earth ore

Abstract

The invention belongs to the technical field of rare earth ore alkaline process smelting, and particularly relates to a rare earth ore multi-stage alkaline hydrolysis process. Comprising the following steps: (1) mixing alkaline hydrolyzable rare earth ore with tertiary alkaline water, carrying out primary alkaline hydrolysis, and carrying out plate-frame pressure filtration on slurry subjected to the primary alkaline hydrolysis to obtain a primary filter cake and primary filtrate; (2) mixing the primary filter cake with secondary alkaline water, carrying out secondary alkaline hydrolysis, carrying out plate-frame pressure filtration on the slurry subjected to the secondary alkaline hydrolysis to obtain a secondary filter cake and a secondary filtrate, and recycling the secondary filtrate as tertiary alkaline water; (3) mixing the secondary filter cake with primary alkaline water, adding sodium hydroxide, carrying out tertiary alkaline hydrolysis, and carrying out plate-frame pressure filtration on the slurry subjected to tertiary alkaline hydrolysis to obtain a tertiary filter cake and tertiary filtrate; and recycling the third-stage filtrate as primary alkaline water for recycling. Through a three-stage alkaline hydrolysis process, alkaline water grading cyclic utilization is combined, so that the alkali unit consumption is reduced, the alkali utilization rate is improved, the amount of discharged alkaline water is reduced, and the production cost is saved.

Description

Technical Field

[0001] The invention belongs to the technical field of rare earth ore alkali smelting, and in particular relates to a multi-stage alkali hydrolysis process of rare earth ore. Background Art

[0002] In the alkaline smelting process of rare earth ores, sodium hydroxide is usually used as an alkaline hydrolysis agent to carry out alkaline hydrolysis reaction on rare earth ores under high temperature, high pressure or normal pressure conditions, and then rare earth products are extracted through multi-stage plate and frame filtration and water washing processes. In the traditional process, the high-concentration primary alkaline water (alkali content 30-45wt.%) obtained by the first filtration can be completely recovered and used for bottom water replenishment in the subsequent alkaline hydrolysis process; while the secondary alkaline water (alkali content 18-22wt.%) is only partially recovered to adjust the system volume balance due to its low concentration, and the remaining part is directly discharged into the sewage treatment system; the tertiary alkaline water (alkali content 5-15wt.%) is considered to have no recovery value due to its low concentration and is completely discharged. In this mode, the recovery rate of low-concentration alkaline water is seriously insufficient, resulting in significant waste of alkali resources, while increasing the sewage treatment load and the consumption of neutralizers, and increasing production costs.

[0003] In the existing technology, some processes use two alkaline hydrolysis (one alkaline hydrolysis of raw ore, and the second alkaline hydrolysis of acid residue) to improve the rare earth recovery rate, but there are still the following defects: First, the alkali consumption is high (1.5-1.7t / tREO), which mainly relies on the one-time input of high-concentration alkaline water; second, the recovery rate of secondary and tertiary alkaline water is low, and a large amount of low-concentration alkaline liquid is discharged, causing resource waste and environmental hazards. Therefore, it is urgent to develop an optimized process that can not only efficiently recover low-concentration alkaline water, reduce alkali consumption, maintain high rare earth recovery, and be suitable for a variety of minerals, so as to solve the problems in the existing technology. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a multi-stage alkaline hydrolysis process for rare earth ores. Through a three-stage alkaline hydrolysis process combined with graded recycling of alkaline water, the unit consumption of alkali is reduced, the utilization rate of alkali is improved, the amount of alkaline water discharged is reduced, and the production cost is saved.

[0005] The technical solution adopted by the present invention is as follows: The rare earth ore multi-stage alkaline hydrolysis process comprises the following steps: (1) Primary alkaline hydrolysis: put the alkaline hydrolyzable rare earth ore into an alkaline hydrolysis pulping tank, add tertiary alkaline water with a concentration of 5-15wt.%, stir and mix, then inject into a pressure reactor, heat and raise the temperature to perform primary alkaline hydrolysis. After the primary alkaline hydrolysis is completed, release the pressure in the pressure reactor, and filter the slurry through a plate and frame filter press to separate the primary filter cake and the primary filtrate with a residual alkali concentration of 0.9-4.5wt.%; (2) Secondary alkaline hydrolysis: The primary filter cake of step (1) is slurried with secondary alkaline water having a concentration of 18-22 wt.% at a mass volume ratio of 0.5:1, and the secondary alkaline water is added to a total volume of 20-22 ml. 3 Then the mixture is transferred to a pressure reactor, heated and heated to perform secondary alkaline hydrolysis. After the secondary alkaline hydrolysis is completed, the pressure reactor is depressurized. After the depressurization, the slurry is filtered through a plate and frame filter press to separate a secondary filter cake and a secondary filtrate with a residual alkali concentration of 5-15wt.%, and the secondary filtrate is recycled as tertiary alkaline water for reuse; (3) Tertiary alkaline hydrolysis: The secondary filter cake of step (2) is mixed with primary alkaline water of concentration 30-45wt.% and then pulped. After pulping, sodium hydroxide is added and primary alkaline water is replenished to a total volume of 20-22m 3 Then the mixture is transferred to a pressure reactor, heated and heated to perform tertiary alkaline hydrolysis. After the tertiary alkaline hydrolysis is completed, the pressure reactor is depressurized. After depressurization, the slurry is filtered through a plate and frame filter press to separate a tertiary filter cake and a tertiary filtrate with a residual alkali concentration of 30-45wt.%; The tertiary filtrate is recovered and used as primary alkaline water for recycling; The three-stage filter cake is firstly pulped and washed with water and then filter-pressed with a plate and frame to obtain a first-stage washing liquid with a concentration of 18-22wt.% and a first-stage washed filter cake, and the first-stage washing liquid is recovered and recycled as secondary alkaline water; The filter cake after the primary washing is subjected to a second pulping and water washing and plate-frame filter pressing to obtain a secondary washing liquid with a concentration of 8-15wt.%, and the secondary washing liquid is recycled as tertiary alkaline water for reuse; Among them, the primary alkaline water is the alkaline mother liquor separated by the first plate and frame filter press after the alkaline hydrolysis reaction of the rare earth ore, the secondary alkaline water is the washing liquid obtained by the first water washing and the second plate and frame filter press of the alkaline hydrolysis product after the primary alkaline water separation, and the tertiary alkaline water is the washing liquid obtained by the second water washing and the third plate and frame filter press of the washed filter cake after the secondary alkaline water separation.

[0006] The alkaline hydrolyzable rare earth ore is one of rare earth concentrate, low-grade ore, defluorinated slag or adjusted ore, wherein the defluorinated slag completes alkaline hydrolysis after primary alkaline hydrolysis and secondary alkaline hydrolysis.

[0007] The TREO of the rare earth concentrate is 58-70wt.%, the TREO of the low-grade ore is 40-70wt.%, the TREO of the defluorinated slag is 55-78wt.%, and the TREO of the adjusted ore is 48-60wt.%.

[0008] In the step (1), the mass volume ratio of the alkaline hydrolyzable rare earth ore to the tertiary alkaline water is 6: (20-22) t / m 3 .

[0009] In the step (1), the conditions for primary alkaline hydrolysis are: heating to 120°C and keeping warm for 30-60 minutes. During the keeping warm period, the temperature of the reaction system is maintained at 145-165°C and the pressure is maintained at 0.15-0.4 MPa.

[0010] In the step (2), the mass volume ratio of the primary filter cake to the secondary alkaline water is 6: (20-22) t / m 3 .

[0011] In the step (2), the conditions for the secondary alkaline hydrolysis are: heating to 120°C and keeping warm for 3-4.5 hours. During the keeping warm period, the temperature of the reaction system is maintained at 145-165°C and the pressure is maintained at 0.27-0.4 MPa.

[0012] In the step (3), the mass volume ratio of the secondary filter cake to the primary alkaline water is 15.5: (16-22) t / m 3 .

[0013] In the step (3), the temperature of the tertiary alkaline hydrolysis is 160-180°C, the pressure is 0.3-0.45 MPa, and the time is 8-15 hours.

[0014] In the step (3), the mass ratio of the amount of sodium hydroxide added to the amount of the filter cake obtained in the step (2) is (10-13):15.5, and the purity of the sodium hydroxide is above 97wt.%.

[0015] The reaction mechanism of the rare earth ore multi-stage alkaline hydrolysis process of the present invention is as follows: 1. Primary alkaline hydrolysis (1) Removal of aluminum impurities: Aluminum reacts with tertiary alkaline water (alkaline concentration 5-15wt.%) to generate soluble aluminate (Al(OH)4 - ), 45-56wt.% of aluminum ions were removed by filtration; (2) Acid-base neutralization: Sodium hydroxide reacts with residual hydrochloric acid in the mine (NaOH+HCl→NaCl+H2O) to avoid subsequent alkalinity loss; (3) Rare earth precipitation: free rare earth ions (RE 3+ ) and OH - Combined to form rare earth hydroxide precipitate (RE 3+ +3OH - →RE(OH)3↓); (4) Alkaline hydrolysis of the more active components: REF3 and REPO4 react with NaOH to generate RE(OH)3 precipitate (REF3+3OH - →RE(OH)3↓+3F - ; REPO4+3NaOH→RE(OH)3↓+Na3PO4).

[0016] 2. Secondary alkaline hydrolysis (1) Partial rare earth activation alkaline hydrolysis: The activated rare earth minerals are further dissolved at this alkalinity (alkali concentration 18-22wt.%), while removing 8-12% of residual aluminum impurities; (2) The reaction mechanism is the same as that of primary alkaline hydrolysis, but the focus is on improving the alkaline hydrolysis activity of minerals, laying the foundation for tertiary alkaline hydrolysis.

[0017] After primary and secondary alkaline hydrolysis, the activity of the less active components was improved.

[0018] 3. Tertiary alkaline hydrolysis (1) High concentration alkaline hydrolysis: At this alkalinity (alkaline concentration ≥ 30wt.%), insoluble rare earth minerals are completely decomposed under high temperature and pressure; (2) Add caustic soda flakes to ensure complete reaction, and the final rare earth yield reaches 89-94%, and the caustic soda consumption is reduced to less than 1.2t / tREO.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) The multi-stage alkaline hydrolysis process of rare earth ore described in the present invention reduces the alkali consumption to less than 1.2t / tREO through a three-stage alkaline hydrolysis process combined with graded recycling of alkaline water, while achieving effective recovery of secondary alkaline water and tertiary alkaline water, and increasing the alkali utilization rate to 92-97%. In addition, due to the reduction in the amount of discharged alkaline water, the consumption of hydrochloric acid in sewage treatment is reduced, saving production costs while reducing the environmental burden; (2) The rare earth ore multi-stage alkaline hydrolysis process of the present invention reduces the alkali consumption while maintaining the rare earth yield above 89%, and the overall cost is significantly optimized; (3) The multi-stage alkaline hydrolysis process of rare earth ores described in the present invention is applicable to a variety of rare earth ores (such as rare earth concentrates, low-grade ores, defluorination slag, and callback ores). The process has strong universality and is easy to promote industrialization. DETAILED DESCRIPTION

[0020] The present invention is further described below with reference to the embodiments, but they do not limit the implementation of the present invention.

[0021] The raw materials used in the examples and comparative examples are conventional commercially available raw materials unless otherwise specified, and the process methods used in the examples and comparative examples are conventional methods in the art unless otherwise specified.

[0022] Some of the raw materials used in the examples and comparative examples are described as follows: The primary alkaline water is the alkaline mother liquor separated by the first plate and frame filter press after the alkaline hydrolysis reaction of the rare earth ore, and the concentration is 30-45wt.%.

[0023] The secondary alkaline water is the washing liquid for the first water washing of the alkaline hydrolysis product and the secondary plate and frame filter pressing after the primary alkaline water separation, and the concentration is 18-22wt.%.

[0024] The tertiary alkaline water is the washing liquid for the secondary washing of the washed filter cake and the tertiary plate and frame filter pressing after the secondary alkaline water separation, and the concentration is 5-15wt.%.

[0025] Example 1 The rare earth ore multi-stage alkaline hydrolysis process comprises the following steps: (1) Primary alkaline hydrolysis: 6 tons of rare earth concentrate with a TREO content of 67.2 wt.% was placed in an alkaline hydrolysis pulping tank, and tertiary alkaline water with a concentration of 14.7 wt.% (mass to volume ratio of 6:20 t / m 3 ), after stirring and mixing, inject into a pressure reactor, heat to 120°C, keep warm for 30 minutes for primary alkaline hydrolysis, during which the temperature of the reaction system is maintained at 155±10°C and the pressure is maintained at 0.275±0.125 MPa. After the primary alkaline hydrolysis is completed, the pressure reactor is depressurized, and the slurry is filtered through a plate and frame filter press to separate the primary filter cake and the primary filtrate with a residual alkali concentration of 4.38wt.%; (2) Secondary alkaline hydrolysis: 6 tons of primary filter cake from step (1) and 8 tons of 3 After mixing with secondary alkaline water with a concentration of 18.65wt.%, the pulping is carried out. After the pulping is completed, the secondary alkaline water is added to a total volume of 20m 3 Then transfer to a pressure reactor, heat to 120°C, and keep warm for 3 hours for secondary alkaline hydrolysis. During the heat preservation period, the temperature of the reaction system is maintained at 155±10°C and the pressure is maintained at 0.335±0.065 MPa. After the secondary alkaline hydrolysis is completed, the pressure reactor is depressurized. After the depressurization, the slurry is filtered through a plate and frame filter to separate the secondary filter cake and the secondary filtrate with a residual alkali concentration of 10.4wt.%, and the secondary filtrate is recovered and used as tertiary alkaline water for recycling; (3) Third-stage alkaline hydrolysis: 15.5t of the secondary filter cake from step (2) and 8m 3 After mixing with primary alkaline water with a concentration of 30.8wt.%, the mixture was pulped. After pulping, sodium hydroxide was added (the mass ratio of sodium hydroxide to filter cake was 10:15.5), and primary alkaline water was added to a total volume of 20m 3 Then transfer to a pressure reactor, heat to 170±10°C, maintain the pressure at 0.375±0.075MPa, react for 8h, and perform tertiary alkaline hydrolysis. After the tertiary alkaline hydrolysis is completed, release the pressure of the pressure reactor, and filter the slurry through a plate and frame filter press to separate the tertiary filter cake and the tertiary filtrate with a residual alkali concentration of 32.4wt.%; The tertiary filtrate is recovered and used as primary alkaline water for recycling; The three-stage filter cake is firstly pulped and washed with water and then plate-frame filter press is performed to obtain a first-stage washing liquid with a concentration of 20.1wt.% and a first-stage washed filter cake, and the first-stage washing liquid is recovered and used as a secondary alkaline water for recycling; The filter cake after the primary washing is subjected to a second pulping and water washing and plate and frame filter pressing to obtain a secondary washing liquid with a concentration of 12.4wt.%, and the secondary washing liquid is recovered and used as tertiary alkaline water for recycling.

[0026] Example 2 The rare earth ore multi-stage alkaline hydrolysis process comprises the following steps: (1) Primary alkaline hydrolysis: 6 tons of low-grade ore with a TREO of 68 wt.% was placed in an alkaline hydrolysis pulping tank, and tertiary alkaline water with a concentration of 14.7 wt.% (mass-to-volume ratio of 6:20 t / m 3 ), after stirring and mixing, inject into a pressure reactor, heat to 120°C, keep warm for 30 minutes for primary alkaline hydrolysis, during which the temperature of the reaction system is maintained at 155±10°C and the pressure is maintained at 0.275±0.125 MPa. After the primary alkaline hydrolysis is completed, the pressure reactor is depressurized, and the slurry is filtered through a plate and frame filter press to separate the primary filter cake and the primary filtrate with a residual alkali concentration of 0.9wt.%; (2) Secondary alkaline hydrolysis: 6 tons of primary filter cake from step (1) and 8 tons of 3 After mixing with secondary alkaline water with a concentration of 21.7wt.%, the pulping is carried out. After the pulping is completed, the secondary alkaline water is added to a total volume of 22m 3 Then transfer to a pressure reactor, heat to 120°C, and keep warm for 3 hours for secondary alkaline hydrolysis. During the heat preservation period, the temperature of the reaction system is maintained at 155±10°C and the pressure is maintained at 0.335±0.065 MPa. After the secondary alkaline hydrolysis is completed, the pressure reactor is depressurized. After the depressurization, the slurry is filtered through a plate and frame filter to separate the secondary filter cake and the secondary filtrate with a residual alkali concentration of 12.7wt.%, and the secondary filtrate is recovered and used as tertiary alkaline water for recycling; (3) Third-stage alkaline hydrolysis: 15.5t of the secondary filter cake from step (2) and 8m 3 After mixing with primary alkaline water with a concentration of 33.7wt.%, the mixture was pulped. After pulping, sodium hydroxide was added (the mass ratio of sodium hydroxide to filter cake was 11.5:15.5), and primary alkaline water was added to a total volume of 22m 3 Then transfer to a pressure reactor, heat to 170±10°C, maintain the pressure at 0.375±0.075MPa, react for 8h, and perform tertiary alkaline hydrolysis. After the tertiary alkaline hydrolysis is completed, release the pressure of the pressure reactor, and filter the slurry through a plate and frame filter press to separate a tertiary filter cake and a tertiary filtrate with a residual alkali concentration of 35.7wt.%; The tertiary filtrate is recovered and used as primary alkaline water for recycling; The three-stage filter cake is firstly pulped and washed with water and then plate-frame filter press is performed to obtain a first-stage washing liquid with a concentration of 18.9wt.% and a first-stage washed filter cake, and the first-stage washing liquid is recovered and used as a secondary alkaline water for recycling; The filter cake after the primary washing is subjected to a second pulping and water washing and plate and frame filter pressing to obtain a secondary washing liquid with a concentration of 13.7 wt.%, and the secondary washing liquid is recovered and used as tertiary alkaline water in a cycle.

[0027] Example 3 The rare earth ore multi-stage alkaline hydrolysis process comprises the following steps: (1) Primary alkaline hydrolysis: 6 tons of 52wt% TREO callback ore were put into the alkaline hydrolysis pulping tank, and 5.4wt% tertiary alkaline water (mass volume ratio of 6:22t / m 3 ), after stirring and mixing, inject into a pressure reactor, heat to 120°C, keep warm for 60 minutes for primary alkaline hydrolysis, during which the temperature of the reaction system is maintained at 155±10°C and the pressure is maintained at 0.275±0.125MPa. After the primary alkaline hydrolysis is completed, the pressure reactor is depressurized, and the slurry is filtered through a plate and frame filter press to separate a primary filter cake and a primary filtrate with a residual alkali concentration of 1.1wt.%; (2) Secondary alkaline hydrolysis: 6 tons of primary filter cake from step (1) and 8 tons of 3 After mixing with secondary alkaline water with a concentration of 18.6wt.%, the pulping is carried out. After the pulping is completed, the secondary alkaline water is added to a total volume of 22m 3 Then transfer to a pressure reactor, heat to 120°C, and keep warm for 4.5 hours for secondary alkaline hydrolysis. During the heat preservation period, the temperature of the reaction system is maintained at 155±10°C and the pressure is maintained at 0.335±0.065 MPa. After the secondary alkaline hydrolysis is completed, the pressure reactor is depressurized. After the depressurization, the slurry is filtered through a plate and frame filter to separate the secondary filter cake and the secondary filtrate with a residual alkali concentration of 13.4wt.%, and the secondary filtrate is recovered and used as tertiary alkaline water for recycling; (3) Third-stage alkaline hydrolysis: 15.5t of the secondary filter cake from step (2) and 8m 3 After mixing with primary alkaline water with a concentration of 44.8wt.%, the mixture was slurried. After slurrying, sodium hydroxide was added (the mass ratio of sodium hydroxide to filter cake was 11.5:15.5), and primary alkaline water was added to a total volume of 22m 3 Then transfer to a pressure reactor, heat to 170±10°C, maintain the pressure at 0.375±0.075MPa, react for 15h, and perform tertiary alkaline hydrolysis. After the tertiary alkaline hydrolysis is completed, release the pressure of the pressure reactor, and filter the slurry through a plate and frame filter press to separate a tertiary filter cake and a tertiary filtrate with a residual alkali concentration of 37.8wt.%; The tertiary filtrate is recovered and used as primary alkaline water for recycling; The three-stage filter cake is firstly pulped and washed with water and then plate-frame filter press is performed to obtain a first-stage washing liquid with a concentration of 22wt.% and a first-stage washed filter cake, and the first-stage washing liquid is recovered and used as a secondary alkaline water for recycling; The filter cake after the primary washing is subjected to a second pulping and water washing and plate and frame filter pressing to obtain a secondary washing liquid with a concentration of 8.2wt.%, and the secondary washing liquid is recovered and used as tertiary alkaline water for recycling.

[0028] Example 4 The rare earth ore multi-stage alkaline hydrolysis process comprises the following steps: (1) Primary alkaline hydrolysis: 6 tons of defluorinated slag with a TREO content of 74 wt.% was placed in an alkaline hydrolysis pulping tank, and tertiary alkaline water with a concentration of 14.8 wt.% (mass to volume ratio of 6:22 t / m 3 ), after stirring and mixing, inject into a pressure reactor, heat to 120°C, keep warm for 60 minutes for primary alkaline hydrolysis, during which the temperature of the reaction system is maintained at 155±10°C and the pressure is maintained at 0.275±0.125MPa. After the primary alkaline hydrolysis is completed, the pressure reactor is depressurized, and the slurry is filtered through a plate and frame filter press to separate a primary filter cake and a primary filtrate with a residual alkali concentration of 4.1wt.%; (2) Secondary alkaline hydrolysis: 6 tons of primary filter cake from step (1) and 8 tons of 3 After mixing with secondary alkaline water with a concentration of 21.9wt.%, the pulping is carried out. After the pulping is completed, the secondary alkaline water is added to a total volume of 22m 3 The product was then transferred to a pressure reactor, heated to 120°C, and kept warm for 4.5 hours for secondary alkaline hydrolysis. During the insulation period, the temperature of the reaction system was maintained at 155±10°C and the pressure was maintained at 0.335±0.065 MPa. After the secondary alkaline hydrolysis was completed, the pressure reactor was depressurized. After the depressurization, the slurry was filtered through a plate and frame filter to separate the secondary filter cake and the secondary filtrate with a residual alkali concentration of 10.2wt.%, and the secondary filtrate was recovered and used as tertiary alkaline water.

[0029] Comparative Example 1 Take 15.5t of TREO 67.2wt.% rare earth concentrate and 8m 3 After mixing with primary alkaline water with a concentration of 30.8wt.%, pulping is carried out. After pulping, sodium hydroxide is added (the mass ratio of sodium hydroxide to concentrate is 10:15.5), and primary alkaline water is added to a total volume of 20m 3 Then transfer to a pressure reactor, heat to 170±10°C, maintain the pressure at 0.375±0.075MPa, react for 8h, and perform alkaline hydrolysis. After the alkaline hydrolysis is completed, release the pressure of the pressure reactor. After the pressure is released, the slurry is filtered through a plate and frame filter to separate the filter cake and the filtrate with a residual alkali concentration of 33.5wt.%; The filtrate is recovered and used as primary alkaline water in circulation; The filter cake is firstly pulped and washed with water and then filtered by plate and frame to obtain a primary washing liquid with a concentration of 21.4wt.% and a filter cake after primary washing. 10wt.% of the primary washing liquid is recycled into the primary alkaline water to make up for the volume loss of the primary alkaline water caused by alkaline hydrolysis. The remaining primary washing liquid is all discharged for sewage treatment. The filter cake after the primary washing is subjected to a second pulping and water washing and plate and frame filter pressing to obtain a secondary washing liquid with a concentration of 8.7wt.%, and all the secondary washing liquid is discharged to sewage treatment.

[0030] Comparative Example 2 Take 15.5t of TREO 52wt.% callback ore and 8m 3 After mixing with primary alkaline water with a concentration of 44.8wt.%, pulping is carried out. After pulping, sodium hydroxide is added (the mass ratio of sodium hydroxide to concentrate is 11.5:15.5), and primary alkaline water is added to a total volume of 22m 3 Then transfer to a pressure reactor, heat to 170±10°C, maintain the pressure at 0.375±0.075MPa, react for 15h, and perform alkaline hydrolysis. After the alkaline hydrolysis is completed, release the pressure of the pressure reactor. After the pressure is released, the slurry is filtered through a plate and frame filter to separate the filter cake and the filtrate with a residual alkali concentration of 36.5wt.%; The filtrate is recovered and used as primary alkaline water in circulation; The filter cake is firstly pulped and washed with water and then filtered by plate and frame to obtain a first-level washing liquid with a concentration of 19.7wt.% and a first-level washed filter cake, 10wt.% of the first-level washing liquid is recycled into the first-level alkaline water to supplement the volume loss of the first-level alkaline water caused by alkaline hydrolysis, and the remaining first-level washing liquid is all discharged for sewage treatment; The filter cake after the primary washing is subjected to a second pulping and water washing and plate and frame filter pressing to obtain a secondary washing liquid with a concentration of 8.7wt.%, and all the secondary washing liquid is discharged to sewage treatment.

[0031] Comparative Example 3 The difference from Example 1 is that in step (3), the temperature of the tertiary alkaline hydrolysis is 120° C., and the rest is the same as Example 1.

[0032] Comparative Example 4 (1) Same as Example 4; (2) Same as Example 4; (3) Third-stage alkaline hydrolysis: 15.5t of the secondary filter cake from step (2) and 8m 3 After mixing with primary alkaline water with a concentration of 37.7wt.%, the mixture was pulped. After pulping, sodium hydroxide was added (the mass ratio of sodium hydroxide to filter cake was 11.5:15.5), and primary alkaline water was added to a total volume of 22m 3Then transfer to a pressure reactor, heat to 170±10°C, maintain the pressure at 0.375±0.075MPa, react for 8h, and perform tertiary alkaline hydrolysis. After the tertiary alkaline hydrolysis is completed, release the pressure of the pressure reactor, and filter the slurry through a plate and frame filter press to separate a tertiary filter cake and a tertiary filtrate with a residual alkali concentration of 58.8wt.%; The three-stage filter cake is firstly pulped and washed with water and then filter-pressed with a plate and frame to obtain a first-stage washing liquid with a concentration of 35.6wt.% and a first-stage washed filter cake; The filter cake after the primary washing was subjected to a second pulping and water washing and plate and frame filter pressing to obtain a secondary washing liquid with a concentration of 24.7 wt.%.

[0033] 500 g of the final filter cakes of Examples 1-4 and Comparative Examples 1-4 were taken respectively, washed with clean water until the pH value was 7.5±0.5, filtered, and then the obtained filter cakes were slurried with clean water, the water-to-solid ratio of the slurry was 0.5:1, then heated to 92.5±2.5° C., hydrochloric acid was added for acid dissolution until the pH value of the slurry was 1.25±0.25, and then adjusted to pH 3.25±0.25 with ammonium bicarbonate, filtered to obtain a filtrate and a filter cake, and the rare earth concentration (mol / L) in the filtrate, the filtrate volume (L), the filter cake mass (g), and the TREO of the rare earth in the filter cake were measured respectively, and the rare earth yield was calculated according to the formula (filtrate volume×rare earth concentration) / (filtrate volume×rare earth concentration+filter cake mass×TREO of rare earth)×100%; Calculation method of alkali utilization rate: alkali utilization rate = 1-volume of discharged alkali water × alkali water concentration of discharged alkali water × specific gravity / total alkali consumption weight × 100%; Calculation method of alkali unit consumption: alkali unit consumption = total alkali consumption weight / (REO of alkali-hydrolyzable rare earth ore × rare earth yield) × 100%.

[0034] The calculation results are shown in Table 1.

[0035] Table 1 Data results

[0036] It can be seen from the test data in Table 1 that after the multi-stage alkaline hydrolysis of rare earth ore in Examples 1-4 is completed by the multi-stage alkaline hydrolysis process of the present invention, the rare earth yield is more than 89%, the alkali utilization rate is higher than 92%, the alkali unit consumption is lower than 1.2t / tREO, and the alkaline hydrolysis effect is good.

[0037] Comparative Example 1-2 adopts the traditional rare earth alkaline hydrolysis process, and does not perform primary and secondary alkaline hydrolysis, which results in difficult alkaline hydrolysis during the alkaline hydrolysis process, increased alkali consumption, and a rare earth yield much lower than that of Examples 1 and 3. At the same time, due to the discharge of secondary and tertiary alkaline water, the alkali utilization rate decreases.

[0038] In Comparative Example 3, since the temperature of the tertiary alkaline hydrolysis was reduced to 120°C, the temperature of the tertiary alkaline hydrolysis stage was insufficient, the alkaline hydrolysis reaction was insufficient, and the alkali was not fully utilized, which led to a decrease in rare earth yield, an increase in alkali consumption, and a decrease in alkali utilization.

[0039] In Comparative Example 4, a third-stage alkaline hydrolysis process is additionally added when alkaline hydrolysis is performed on the defluorination residue, so that the defluorination residue is overly fully alkaline hydrolyzed, and thus the rare earth yield is higher. However, the alkali consumption is too high, and the alkali concentrations of the primary alkaline water, the secondary alkaline water, and the tertiary alkaline water generated during the alkaline hydrolysis are too high and cannot be effectively utilized, so the alkali utilization rate is lower than that of Example 4.

Claims

1. A rare earth ore multi-stage alkaline hydrolysis process, characterized in that: The following steps are involved: (1) Primary alkaline hydrolysis: the alkaline hydrolyzable rare earth ore is mixed with tertiary alkaline water with a concentration of 5-15wt.% and then subjected to primary alkaline hydrolysis. The slurry after the primary alkaline hydrolysis is subjected to plate and frame filter pressing to obtain a primary filter cake and a primary filtrate; (2) Secondary alkaline hydrolysis: the primary filter cake of step (1) is mixed with secondary alkaline water having a concentration of 18-22 wt.% and then subjected to secondary alkaline hydrolysis. The slurry after the secondary alkaline hydrolysis is subjected to plate and frame filter pressing to obtain a secondary filter cake and a secondary filtrate. The secondary filtrate is recovered and used as tertiary alkaline water for recycling; (3) tertiary alkaline hydrolysis: the secondary filter cake of step (2) is mixed with primary alkaline water having a concentration of 30-45 wt.%, sodium hydroxide is added, and tertiary alkaline hydrolysis is performed at 160-180° C. The slurry after the tertiary alkaline hydrolysis is subjected to plate and frame filter pressing to obtain a tertiary filter cake and a tertiary filtrate; The tertiary filtrate is recovered and used as primary alkaline water for recycling; The three-stage filter cake is firstly pulped and washed with water and then filter-pressed with a plate and frame to obtain a first-stage washing liquid and a first-stage washed filter cake, and the first-stage washing liquid is recovered and used as a secondary alkaline water for recycling; The filter cake after the primary washing is subjected to a second pulping and water washing and plate-frame filter pressing to obtain a secondary washing liquid, which is recycled as tertiary alkaline water for recycling; The primary alkaline water is the alkaline mother liquor obtained by the first plate-frame filter press separation after the alkaline hydrolysis reaction of the rare earth ore, the secondary alkaline water is the washing liquid obtained by the first water washing of the alkaline hydrolysis product and the second plate-frame filter press after the primary alkaline water separation, and the tertiary alkaline water is the washing liquid obtained by the second water washing of the washed filter cake and the third plate-frame filter press after the secondary alkaline water separation; The alkaline hydrolyzable rare earth ore is one of rare earth concentrate, low-grade ore, defluorinated slag or adjusted ore, wherein the defluorinated slag completes alkaline hydrolysis after primary alkaline hydrolysis and secondary alkaline hydrolysis.

2. The multi-stage alkaline hydrolysis process of rare earth ore according to claim 1, characterized in that: The TREO of the rare earth concentrate is 58-70wt.%, the TREO of the low-grade ore is 40-70wt.%, the TREO of the defluorinated slag is 55-78wt.%, and the TREO of the adjusted ore is 48-60wt.%.

3. The multi-stage alkaline hydrolysis process of rare earth ore according to claim 1, characterized in that: In the step (1), the mass volume ratio of the alkaline hydrolyzable rare earth ore to the tertiary alkaline water is 6: (20-22) t / m 3 .

4. The multi-stage alkaline hydrolysis process of rare earth ore according to claim 1, characterized in that: In the step (1), the conditions for primary alkaline hydrolysis are: heating to 120°C and keeping warm for 30-60 minutes. During the keeping warm period, the temperature of the reaction system is maintained at 145-165°C and the pressure is maintained at 0.15-0.4 MPa.

5. The multi-stage alkaline hydrolysis process of rare earth ore according to claim 1, characterized in that: In the step (2), the mass volume ratio of the primary filter cake to the secondary alkaline water is 6: (20-22) t / m 3 .

6. The multi-stage alkaline hydrolysis process of rare earth ore according to claim 1, characterized in that: In the step (2), the conditions for the secondary alkaline hydrolysis are: heating to 120°C and keeping warm for 3-4.5 hours. During the keeping warm period, the temperature of the reaction system is maintained at 145-165°C and the pressure is maintained at 0.27-0.4 MPa.

7. The multi-stage alkaline hydrolysis process of rare earth ore according to claim 1, characterized in that: In the step (3), the mass volume ratio of the secondary filter cake to the primary alkaline water is 15.5: (16-22) t / m 3 .

8. The multi-stage alkaline hydrolysis process of rare earth ore according to claim 1, characterized in that: In the step (3), the pressure of the tertiary alkaline hydrolysis is 0.3-0.45 MPa and the time is 8-15 hours.

9. The multi-stage alkaline hydrolysis process of rare earth ore according to claim 1, characterized in that: In the step (3), the mass ratio of the amount of sodium hydroxide added to the amount of the filter cake obtained in the step (2) is (10-13):15.5.

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