method for recovering rare-earth in cerium-based rare-earth polishing powder waste by two-step acid leaching gradient separation

Abstract

The invention relates to a method of recovering rare-earth in cerium-based rare-earth polishing powder waste by two-step acid leaching gradient separation, characterized by: firstly, using a one-step acid leaching treatment on cerium-based rare-earth polishing powder waste to obtain a rare-earth leaching liquor which is rich in La; secondly, the leaching residue is then processed through alkali activation and transformation process, water washing and impurity removal process, secondary acid leaching process, filtration, and recovery to obtain high purity CeO.sub.2 products; thirdly, the acid leaching liquor obtained through first acid leaching and second acid leaching process is finally precipitated by oxalic acid, filtered and calcined at high temperature to obtain rare-earth oxide mixed products, which achieves the gradient separation and recovery of rare-earths from cerium-based rare-earth polishing powder waste. The total recovery efficiency of rare-earth of this invention reaches 97% or higher, with high efficiency of rare-earth recovery, wide process applicability, and low environmental pollution.

Claims

1. A method of separating and recycling rare-earth in cerium-based rare-earth polishing powder waste by two-step acid leaching, comprising the following specific steps: (1) Ball milling pretreatment: the cerium-based rare-earth polishing powder waste is ball-milled to a particle size below 160 mesh to obtain ball-milled waste; (2) First acid leaching: put the ball milled waste obtained in step (1) into a container and add an acid solution for a first acid leaching reaction, keep heating and stirring during the first acid leaching reaction, separate solid and liquid after the first acid leaching reaction to obtain leaching residue and leaching liquor 1, a molar concentration of the acid solution is 5-8 mol/L, a solid-liquid ratio of the ball milled waste to the acid solution is 1:4-1:8 kg/L, leaching temperature is 70-80° C., and leaching time is 1-2 hours; (3) Alkali roasting: mix the leaching residue obtained in step (2) with alkali to obtain a mixture and roast the mixture to obtain a roasted mixture, a mass ratio of the leaching residue to alkali is 1:1-1:3, roasting temperature is 450-650′C, and roasting time is 0.5-1.5 hours; (4) Water leaching: put the roasted mixture obtained in step (3) in water to conduct water leaching, a solid-liquid ratio of the roasted mixture to water is 1:4-1:9 kg/L, water leaching temperature is 80-90′C, water leaching time is 2-3 hours, and stirring speed is 300-500 rpm, after the water leaching is completed, separate solid from liquid, and water leaching residue is obtained by filtration; (5) Second acid leaching: mix the water leaching residue obtained in step (4) with an acid solution to carry out secondary acid leaching reaction, separate solid from liquid after the second acid leaching reaction is completed, and conduct filtration to obtain CeO.sub.2 product and leaching liquor 2, a molar concentration of the acid solution is 5-8 mol/L, a solid-liquid ratio of the water leaching residue to the acid solution is 1:2.5-1:6 kg/L, leaching temperature is 70-80° C., and leaching time is 2-3 hours; (6) Precipitation of rare-earths with oxalic acid: mix the leaching liquor 1 obtained in step (2) and the leaching liquor 2 obtained in step (5) to obtain a mixed solution, and add an oxalic acid solution with a mass concentration of 100 g/L to the mixed solution to precipitate rare-earths, a volume ratio of the mixed solution to the oxalic acid solution is 5:1-3:1, stir and add ammonia with a mass percentage concentration of 25%, until the pH value of the solution reaches 1.8-2.0, and precipitate at 80-90° C. for 2-3 hours, conduct filtration to obtain rare-earth oxalate; (7) Calcination: the rare-earth oxalate obtained in step (6) is calcined in a muffle furnace at 950° C. for 0.5-1 hour to obtain rare-earth oxide product; wherein: in step (2), the acid solution is hydrochloric acid solution or nitric acid solution; in step (2), the stirring speed is 300-500 rpm; in step (3), the alkali in the alkali roasting process is Na.sub.2O.sub.2 or K.sub.2O.sub.2; in step (5), the acid solution is hydrochloric acid solution or nitric acid solution.

2. The method according to claim 1, wherein, in step (5), the stirring speed is 300-500 rpm.

3. The method according to claim 1, wherein, in step (5), when the solid is separated from the liquid after the second acid leaching reaction, the CeO.sub.2 product obtained is washed 4-8 times with a hydrochloric acid solution to remove impurities, a mass concentration of the hydrochloric acid solution is 2-5%.

4. The method according to claim 1, wherein the leaching liquor 1 obtained in step (2) is evaporated and concentrated until the molar concentration of HCl or HNO reaches 5-8 mol/L, a concentrated leaching liquor 1 is then incorporated into the secondary acid leaching reaction of step (5) to partially or completely replace the hydrochloric acid solution or nitric acid solution.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 is a flow chart of the method for separating and recovering rare-earth from cerium-based rare-earth polishing powder waste by two-step acid leaching gradient separation.

EXAMPLES

Example 1

[0026] The cerium-based rare-earth polishing powder waste is proceeded as follows:

[0027] (1) Ball milling pretreatment: the cerium-based rare-earth polishing powder waste, whose total mass fraction of rare-earth oxides is 15%, is ball-milled to a particle size of 160 mesh to obtain ball-milled waste. The phase structure of the cerium-based rare-earth polishing powder waste is analyzed with X-ray diffractometer (XRD), and the result shows that the rare-earth components in the cerium-based rare-earth polishing powder waste are mainly LaOF, La.sub.2O.sub.3, and CeO.sub.2;

[0028] (2) First acid leaching: put the ball milled waste obtained in step (1) into a container and add hydrochloric acid solution for the first acid leaching. Keep heating and stirring during the first acid leaching process. The molar concentration of the acid solution is 5 mol/L, the solid-liquid ratio of ball milling waste and acid solution is 1 kg:8 L, the leaching temperature is 80° C., the leaching time is 2 hours, and the stirring speed is 500 rpm. Separate the solid and the liquid after the first acid leaching reaction to obtain leaching residue and leaching liquor 1.

[0029] (3) Alkali roasting: mix the leaching residue obtained in step (2) with Na.sub.2O.sub.2 and roast the mixture to obtain roasted mixture. The mass ratio of leaching residue and alkali is 1:1, the roasting temperature is 650° C., and the roasting time is 1.5 hours;

[0030] (4) Water leaching: put the roasted mixture obtained in step (3) in water. The solid-liquid ratio of the roasted mixture to water is 1 kg:9 L, the water leaching temperature is 80° C., the water leaching time is 2 hours, and the stirring speed is 400 rpm. After the water leaching, separate the solid from the liquid, and the water leaching residue is obtained by filtration;

[0031] (5) Second acid leaching: mix the water leaching residue obtained in step (4) with nitric acid solution to carry out secondary acid leaching reaction. The molar concentration of the acid solution for the second acid leaching is 8 mol/L, the solid-liquid ratio of the water leaching residue and the acid solution is 1 kg:6 L, the leaching temperature is 70° C., the stirring speed is 300 rpm, and the leaching time is 3 hours. Separate the solid from the liquid after the second acid leaching, filter, and wash the product with hydrochloric acid resolution with a mass concentration of 2% for 8 times to obtain CeO.sub.2 product and leaching liquor 2.

[0032] (6) Precipitation of rare-earth with oxalic acid: mix the leaching liquor 1 obtained in step (2) and the leaching liquor 2 obtained in step (5) to obtain mixed solution, and add oxalic acid solution with a mass concentration of 100 g/L to the mixed solution to precipitate rare-earths. The volume ratio of the mixed solution and the oxalic acid solution is 5:1. Stir and add ammonia whose mass percentage concentration ratio is 25%, until the pH value of the solution reaches 1.8, and precipitate at 90° C. for 3 hours. Filtrate to obtain rare-earth oxalate;

[0033] (7) Calcination: the rare-earth oxalate obtained in step (6) is calcined in a muffle furnace at 950° C. for 0.5 hour to obtain mixed rare-earth oxide product.

[0034] The total recovery rate of rare-earth La and Ce in cerium-based rare-earth polishing powder waste is 97.5%.

Example 2

[0035] The cerium-based rare-earth polishing powder waste is proceeded as follows:

[0036] (1) Ball milling pretreatment: the cerium-based rare-earth polishing powder waste, whose total mass fraction of rare-earth oxides is 30%, is ball-milled to a particle size of 200 mesh to obtain ball-milled waste. The phase structure of the cerium-based rare-earth polishing powder waste is analyzed with X-ray diffractometer (XRD), and the result shows that the rare-earth components in the cerium-based rare-earth polishing powder waste are mainly LaOF, La.sub.2O.sub.3, and CeO.sub.2;

[0037] (2) First acid leaching: put the ball milled waste obtained in step (1) into a container and add hydrochloric acid solution for the first acid leaching. Keep heating and stirring during the first acid leaching process. The molar concentration of the acid solution is 8 mol/L, the solid-liquid ratio of ball milling waste and acid solution is 1 kg:4 L, the leaching temperature is 75° C., the leaching time is 2 hours, and the stirring speed is 300 rpm. Separate the solid and the liquid after the first acid leaching reaction to obtain leaching residue and leaching liquor 1.

[0038] (3) Alkali roasting: mix the leaching residue obtained in step (2) with K.sub.2O.sub.2 and roast the mixture to obtain roasted mixture. The mass ratio of leaching residue and alkali is 1:1.8, the roasting temperature is 650° C., and the roasting time is 1 hours;

[0039] (4) Water leaching: put the roasted mixture obtained in step (3) in water. The solid-liquid ratio of the roasted mixture to water is 1 kg:4 L, the water leaching temperature is 90° C., the water leaching time is 3 hours, and the stirring speed is 500 rpm. After the water leaching, separate the solid from the liquid, and the water leaching residue is obtained by filtration;

[0040] (5) Second acid leaching: mix the water leaching residue obtained in step (4) with nitric acid solution to carry out secondary acid leaching reaction. The molar concentration of the acid solution for the second acid leaching is 7 mol/L, the solid-liquid ratio of the water leaching residue and the acid solution is 1 kg:4.5 L, the leaching temperature is 75° C., the stirring speed is 400 rpm, and the leaching time is 2.5 hours. Separate the solid from the liquid after the second acid leaching, filter, and wash the product with hydrochloric acid resolution with a mass concentration of 5% for 4 times to obtain CeO.sub.2 product and leaching liquor 2.

[0041] (6) Precipitation of rare-earth with oxalic acid: mix the leaching liquor 1 obtained in step (2) and the leaching liquor 2 obtained in step (5) to obtain mixed solution, and add oxalic acid solution with a mass concentration of 100 g/L to the mixed solution to precipitate rare-earths. The volume ratio of the mixed solution and the oxalic acid solution is 3:1. Stir and add ammonia whose mass percentage concentration ratio is 25%, until the pH value of the solution reaches 2.0, and precipitate at 90° C. for 2.5 hours. Filtrate to obtain rare-earth oxalate;

[0042] (7) Calcination: the rare-earth oxalate obtained in step (6) is calcined in a muffle furnace at 950° C. for 1 hour to obtain mixed rare-earth oxide product.

[0043] The total recovery rate of rare-earth La and Ce in cerium-based rare-earth polishing powder waste is 98.6%.

Example 3

[0044] The cerium-based rare-earth polishing powder waste is proceeded as follows:

[0045] (1) Ball milling pretreatment: the cerium-based rare-earth polishing powder waste, whose total mass fraction of rare-earth oxides is 30%, is ball-milled to a particle size of 400 mesh to obtain ball-milled waste. The phase structure of the cerium-based rare-earth polishing powder waste is analyzed with X-ray diffractometer (XRD), and the result shows that the rare-earth components in the cerium-based rare-earth polishing powder waste are mainly LaOF, La.sub.2O.sub.3, and CeO.sub.2;

[0046] (2) First acid leaching: put the ball milled waste obtained in step (1) into a container and add hydrochloric acid solution for the first acid leaching. Keep heating and stirring during the first acid leaching process. The molar concentration of the acid solution is 6 mol/L, the solid-liquid ratio of ball milling waste and acid solution is 1 kg:6.5 L, the leaching temperature is 80° C., the leaching time is 1.5 hours, and the stirring speed is 400 rpm. Separate the solid and the liquid after the first acid leaching reaction to obtain leaching residue and leaching liquor 1.

[0047] (3) Alkali roasting: mix the leaching residue obtained in step (2) with Na.sub.2O.sub.2 and roast the mixture to obtain roasted mixture. The mass ratio of leaching residue and alkali is 1:2.5, the roasting temperature is 550° C., and the roasting time is 1 hours;

[0048] (4) Water leaching: put the roasted mixture obtained in step (3) in water. The solid-liquid ratio of the roasted mixture to water is 1 kg:8 L, the water leaching temperature is 90° C., the water leaching time is 2.5 hours, and the stirring speed is 400 rpm. After the water leaching, separate the solid from the liquid, and the water leaching residue is obtained by filtration;

[0049] (5) Second acid leaching: mix the water leaching residue obtained in step (4) with nitric acid solution to carry out secondary acid leaching reaction. The molar concentration of the acid solution for the second acid leaching is 7 mol/L, the solid-liquid ratio of the water leaching residue and the acid solution is 1 kg:5 L, the leaching temperature is 75° C., the stirring speed is 500 rpm, and the leaching time is 2.5 hours. Separate the solid from the liquid after the second acid leaching, filter, and wash the product with hydrochloric acid resolution with a mass concentration of 4% for 6 times to obtain CeO.sub.2 product and leaching liquor 2.

[0050] (6) Precipitation of rare-earth with oxalic acid: mix the leaching liquor 1 obtained in step (2) and the leaching liquor 2 obtained in step (5) to obtain mixed solution, and add oxalic acid solution with a mass concentration of 100 g/L to the mixed solution to precipitate rare-earths. The volume ratio of the mixed solution and the oxalic acid solution is 4:1. Stir and add ammonia whose mass percentage concentration ratio is 25%, until the pH value of the solution reaches 1.9, and precipitate at 90° C. for 3 hours. Filtrate to obtain rare-earth oxalate;

[0051] (7) Calcination: the rare-earth oxalate obtained in step (6) is calcined in a muffle furnace at 950° C. for 0.75 hour to obtain mixed rare-earth oxide product.

[0052] The total recovery rate of rare-earth La and Ce in cerium-based rare-earth polishing powder waste is 98.2%.

Example 4

[0053] The cerium-based rare-earth polishing powder waste is proceeded as follows:

[0054] (1) Ball milling pretreatment: the cerium-based rare-earth polishing powder waste, whose total mass fraction of rare-earth oxides is 40%, is ball-milled to a particle size of 400 mesh to obtain ball-milled waste. The phase structure of the cerium-based rare-earth polishing powder waste is analyzed with X-ray diffractometer (XRD), and the result shows that the rare-earth components in the cerium-based rare-earth polishing powder waste are mainly LaOF, La.sub.2O.sub.3, and CeO.sub.2;

[0055] (2) First acid leaching: put the ball milled waste obtained in step (1) into a container and add hydrochloric acid solution for the first acid leaching. Keep heating and stirring during the first acid leaching process. The molar concentration of the acid solution is 8 mol/L, the solid-liquid ratio of ball milling waste and acid solution is 1 kg:8 L, the leaching temperature is 80° C., the leaching time is 2 hours, and the stirring speed is 300 rpm. Separate the solid and the liquid after the first acid leaching reaction to obtain leaching residue and leaching liquor 1.

[0056] (3) Alkali roasting: mix the leaching residue obtained in step (2) with K.sub.2O.sub.2 and roast the mixture to obtain roasted mixture. The mass ratio of leaching residue and alkali is 1:5, the roasting temperature is 650° C., and the roasting time is 0.5 hours;

[0057] (4) Water leaching: put the roasted mixture obtained in step (3) in water. The solid-liquid ratio of the roasted mixture to water is 1 kg:6 L, the water leaching temperature is 85° C., the water leaching time is 3 hours, and the stirring speed is 500 rpm. After the water leaching, separate the solid from the liquid, and the water leaching residue is obtained by filtration;

[0058] (5) Second acid leaching: mix the water leaching residue obtained in step (4) with nitric acid solution to carry out secondary acid leaching reaction. The molar concentration of the acid solution for the second acid leaching is 6 mol/L, the solid-liquid ratio of the water leaching residue and the acid solution is 1 kg:6 L, the leaching temperature is 80° C., the stirring speed is 400 rpm, and the leaching time is 2.5 hours. Separate the solid from the liquid after the second acid leaching, filter, and wash the product with hydrochloric acid resolution with a mass concentration of 2.5% for 6 times to obtain CeO.sub.2 product and leaching liquor 2.

[0059] (6) Precipitation of rare-earth with oxalic acid: mix the leaching liquor 1 obtained in step (2) and the leaching liquor 2 obtained in step (5) to obtain mixed solution, and add oxalic acid solution with a mass concentration of 100 g/L to the mixed solution to precipitate rare-earths. The volume ratio of the mixed solution and the oxalic acid solution is 5:1. Stir and add ammonia whose mass percentage concentration ratio is 25%, until the pH value of the solution reaches 1.8, and precipitate at 85° C. for 3 hours. Filtrate to obtain rare-earth oxalate;

[0060] (7) Calcination: the rare-earth oxalate obtained in step (6) is calcined in a muffle furnace at 950° C. for 1 hour to obtain mixed rare-earth oxide product.

[0061] The total recovery rate of rare-earth La and Ce in cerium-based rare-earth polishing powder waste is 98.3%.

Example 5

[0062] The cerium-based rare-earth polishing powder waste is proceeded as follows:

[0063] (1) Ball milling pretreatment: the cerium-based rare-earth polishing powder waste, whose total mass fraction of rare-earth oxides is 45%, is ball-milled to a particle size of 200 mesh to obtain ball-milled waste. The phase structure of the cerium-based rare-earth polishing powder waste is analyzed with X-ray diffractometer (XRD), and the result shows that the rare-earth components in the cerium-based rare-earth polishing powder waste are mainly LaOF, La.sub.2O.sub.3, and CeO.sub.2;

[0064] (2) First acid leaching: put the ball milled waste obtained in step (1) into a container and add hydrochloric acid solution for the first acid leaching. Keep heating and stirring during the first acid leaching process. The molar concentration of the acid solution is 7 mol/L, the solid-liquid ratio of ball milling waste and acid solution is 1 kg:6 L, the leaching temperature is 80° C., the leaching time is 1.5 hours, and the stirring speed is 400 rpm. Separate the solid and the liquid after the first acid leaching reaction to obtain leaching residue and leaching liquor 1.

[0065] (3) Alkali roasting: mix the leaching residue obtained in step (2) with Na.sub.2O.sub.2 and roast the mixture to obtain roasted mixture. The mass ratio of leaching residue and alkali is 1:2.1, the roasting temperature is 550° C., and the roasting time is 1.5 hours;

[0066] (4) Water leaching: put the roasted mixture obtained in step (3) in water. The solid-liquid ratio of the roasted mixture to water is 1 kg:8 L, the water leaching temperature is 85° C., the water leaching time is 2 hours, and the stirring speed is 300 rpm. After the water leaching, separate the solid from the liquid, and the water leaching residue is obtained by filtration;

[0067] (5) Second acid leaching: mix the water leaching residue obtained in step (4) with nitric acid solution to carry out secondary acid leaching reaction. The molar concentration of the acid solution for the second acid leaching is 5 mol/L, the solid-liquid ratio of the water leaching residue and the acid solution is 1 kg:5 L, the leaching temperature is 80° C., the stirring speed is 400 rpm, and the leaching time is 3 hours. Separate the solid from the liquid after the second acid leaching, filter, and wash the product with hydrochloric acid resolution with a mass concentration of 4% for 5 times to obtain CeO.sub.2 product and leaching liquor 2.

[0068] (6) Precipitation of rare-earth with oxalic acid: mix the leaching liquor 1 obtained in step (2) and the leaching liquor 2 obtained in step (5) to obtain mixed solution, and add oxalic acid solution with a mass concentration of 100 g/L to the mixed solution to precipitate rare-earths. The volume ratio of the mixed solution and the oxalic acid solution is 5:1. Stir and add ammonia whose mass percentage concentration ratio is 25%, until the pH value of the solution reaches 1.9, and precipitate at 90° C. for 2.5 hours. Filtrate to obtain rare-earth oxalate;

[0069] (7) Calcination: the rare-earth oxalate obtained in step (6) is calcined in a muffle furnace at 950° C. for 0.75 hour to obtain mixed rare-earth oxide product.

[0070] The total recovery rate of rare-earth La and Ce in cerium-based rare-earth polishing powder waste is 97.1%.

Example 6

[0071] The cerium-based rare-earth polishing powder waste is proceeded as follows:

[0072] (1) Ball milling pretreatment: the cerium-based rare-earth polishing powder waste, whose total mass fraction of rare-earth oxides is 60%, is ball-milled to a particle size of 200 mesh to obtain ball-milled waste. The phase structure of the cerium-based rare-earth polishing powder waste is analyzed with X-ray diffractometer (XRD), and the result shows that the rare-earth components in the cerium-based rare-earth polishing powder waste are mainly LaOF, La.sub.2O.sub.3, and CeO.sub.2;

[0073] (2) First acid leaching: put the ball milled waste obtained in step (1) into a container and add hydrochloric acid solution for the first acid leaching. Keep heating and stirring during the first acid leaching process. The molar concentration of the acid solution is 6 mol/L, the solid-liquid ratio of ball milling waste and acid solution is 1 kg:8 L, the leaching temperature is 75° C., the leaching time is 1.5 hours, and the stirring speed is 450 rpm. Separate the solid and the liquid after the first acid leaching reaction to obtain leaching residue and leaching liquor 1.

[0074] (3) Alkali roasting: mix the leaching residue obtained in step (2) with K.sub.2O.sub.2 and roast the mixture to obtain roasted mixture. The mass ratio of leaching residue and alkali is 1:1, the roasting temperature is 450° C., and the roasting time is 0.5 hours;

[0075] (4) Water leaching: put the roasted mixture obtained in step (3) in water. The solid-liquid ratio of the roasted mixture to water is 1 kg:9 L, the water leaching temperature is 80° C., the water leaching time is 2 hours, and the stirring speed is 500 rpm. After the water leaching, separate the solid from the liquid, and the water leaching residue is obtained by filtration;

[0076] (5) Second acid leaching: mix the water leaching residue obtained in step (4) with nitric acid solution to carry out secondary acid leaching reaction. The molar concentration of the acid solution for the second acid leaching is 6.5 mol/L, the solid-liquid ratio of the water leaching residue and the acid solution is 1 kg:4 L, the leaching temperature is 75° C., the stirring speed is 400 rpm, and the leaching time is 2.5 hours. Separate the solid from the liquid after the second acid leaching, filter, and wash the product with hydrochloric acid resolution with a mass concentration of 5% for 5 times to obtain CeO.sub.2 product and leaching liquor 2.

[0077] (6) Precipitation of rare-earth with oxalic acid: mix the leaching liquor 1 obtained in step (2) and the leaching liquor 2 obtained in step (5) to obtain mixed solution, and add oxalic acid solution with a mass concentration of 100 g/L to the mixed solution to precipitate rare-earths. The volume ratio of the mixed solution and the oxalic acid solution is 4:1. Stir and add ammonia whose mass percentage concentration ratio is 25%, until the pH value of the solution reaches 1.9, and precipitate at 85° C. for 2.5 hours. Filtrate to obtain rare-earth oxalate;

[0078] (7) Calcination: the rare-earth oxalate obtained in step (6) is calcined in a muffle furnace at 950° C. for 1 hour to obtain mixed rare-earth oxide product.

[0079] The total recovery rate of rare-earth La and Ce in cerium-based rare-earth polishing powder waste is 97.4%.