Method for recovering rare earth elements from waste phosphate fluorescent powder and application of mixed acid

Abstract

The invention discloses a method for recovering rare earth elements from waste phosphate fluorescent powder and application of mixed acid. The method provided by the invention comprises the following steps: 1) carrying out acid pickling on the waste phosphate fluorescent powder to be treated at 10-60 DEG C by using a mixed acid solution to obtain acid pickling residues; wherein the mixed acid solution is a mixed solution of hydrochloric acid and organic acid; 2) mixing the pickling residues with a decomposing agent, roasting at 300-1000 DEG C, washing, and filtering to obtain a filter cake; 3) carrying out acid leaching on the filter cake at 30-90 DEG C, and filtering to obtain an acid leaching solution; and (4) ammonium sulfate is added into the pickle liquor to obtain a complex, then the pH value of the pickle liquor is adjusted to be 1.0-3.0, an oxalic acid solution is added, and precipitates containing rare earth elements are obtained. According to the method, the calcium and phosphorus content in the waste phosphate fluorescent powder can be remarkably reduced, and rare earth elements are extracted from the waste fluorescent powder with low cost and high efficiency.

Description

Technical Field

[0001] The invention relates to a method for recovering rare earth elements from waste phosphate-based fluorescent powder and application of mixed acid. Background Art

[0002] The rare earth elements contained in rare earth phosphors include yttrium, europium, cerium, terbium, lanthanum, gadolinium, etc. Among them, yttrium, europium and terbium are key metal elements in the field of clean energy. With the further elimination of incandescent lamps and the promotion and popularization of fluorescent lamps, a large number of waste fluorescent lamps will be generated and become solid waste. The phosphors of waste fluorescent lamps contain a considerable amount of high-value and high-grade rare earth resources. Many countries and regions are facing the risk of rare earth supply and have to recycle rare earth elements from secondary resources such as scrapped products and industrial waste slag containing rare earth elements, especially from waste phosphors to recycle scarce yttrium, europium and terbium. Recycling rare earth resources from waste phosphors, as an effective supplement to the mining of rare earth natural mineral resources, helps to ensure the balance of supply and demand of rare earth elements and promote the sustainable use of rare earth resources; at the same time, it can also avoid the over-exploitation of rare earth mines to a certain extent and alleviate the environmental pollution caused by the mining and smelting of rare earth minerals.

[0003] The key to successfully recovering rare earth elements is to dissolve rare earth elements in waste phosphors into the leaching solution. The commonly used tri-color phosphors on the market can be mainly divided into two categories: aluminate phosphors and phosphate phosphors. Specifically, red phosphors include: Y2O3:Eu 3+ , Green phosphor: CeMgAl 11 O 19 :Tb (magneto-plumbite structure); LaPO4:Ce,Tb (monazite structure), blue phosphor: Ba Mg Al 10 O 17 :Eu(β-alumina structure);(Sr,Ca,Ba) 10 (PO4)6Cl2:Eu (apatite structure). Red phosphor exists in the form of rare earth oxides, which are easily decomposed by hydrometallurgical processes. The Y and Eu elements present in them are relatively easy to recover. However, the chemical structure of green and blue phosphors is very stable and difficult to be destroyed by inorganic acids. The Tb, Ce, La and Eu in them are difficult to be leached and recovered under mild conditions, especially the more valuable Tb and Eu.

[0004] At present, there are many studies on the recovery of rare earth elements from waste rare earth phosphors. The main technologies include wet leaching separation, mechanical activation and alkaline roasting. Most of these studies focus on the recovery of rare earth elements from aluminate phosphors, but there are few reports on the recovery of rare earth elements from phosphate phosphors.

[0005] CN107630143A discloses a method for extracting rare earth from rare earth fluorescent powder waste and fluorine-containing rare earth electrolytic waste residue, firstly, the rare earth fluorescent powder waste, fluorine-containing rare earth electrolytic waste residue and alkali are mixed and roasted; the roasted material is washed with water, and after solid-liquid separation, the filter residue is acid-dissolved, and the pH value of the obtained acid-dissolved liquid is adjusted with alkali liquid, and the solid-liquid separation is performed to obtain a feed liquid of rare earth ions. The method is to simultaneously process two wastes, rare earth fluorescent powder waste and fluorine-containing rare earth electrolytic waste residue, and the rare earth fluorescent powder waste in the method is an aluminate-based fluorescent powder, and does not contain a phosphate-based fluorescent powder.

[0006] CN102634667A discloses a method for recycling rare earth elements from discarded fluorescent lamps, including: crushing discarded energy-saving lamps; separating fluorescent powder and recycling rare earth elements in fluorescent powder. First, the discarded energy-saving lamps are mechanically crushed in a closed container, and the fluorescent powder in the discarded fluorescent lamps is separated by a simple mechanical separation method. Then, the rare earth elements and other useful elements can be separated and recovered by a two-step acid dissolution method and subsequent addition of oxalic acid precipitation. For solid powders that are insoluble in acid, alkali metal carbonates are melted and refined, and then simply processed. The object of this method is a mixture of multiple types of fluorescent powders in fluorescent lamps rather than a single type of fluorescent powder. After separating the glass, the method treats the fluorescent powder with hydrochloric acid twice, which cannot effectively remove the phosphorus in the fluorescent powder.

[0007] CN110512099A discloses a method for recovering rare earths from discarded CRT phosphors. First, the phosphors after devitrification are mixed with a strong base and an oxidant and heated to desulfurize the discarded phosphors. Then, a hydrometallurgical method is used to extract the europium oxide rare earths in the phosphors. This method is aimed at discarded CRT phosphors. CRT phosphors are made by mixing red, green, and blue monochrome powders in a certain proportion. The usual red powder composition is Y2O3S:Eu, the green powder is ZnS:Cu or Y2O3S:Tb, and the blue powder is ZnS:Ag. It can be seen that CRT phosphors are not mainly phosphate-based phosphors, and this method is not suitable for the recovery of rare earth elements in phosphate-based phosphors. Summary of the invention

[0008] In view of this, one object of the present invention is to provide a method for recovering rare earth elements from waste phosphate phosphors. The method sequentially treats waste phosphate phosphors through acid washing, decomposition roasting, acid leaching, and oxalic acid precipitation to enrich and extract rare earth elements in waste phosphate phosphors, thereby achieving low-cost and high-efficiency recovery of rare earth elements in waste phosphate phosphors. Another object of the present invention is to provide a use of the mixed acid of the present invention in reducing the calcium and phosphorus content in waste phosphate phosphors and improving the grade of waste phosphate phosphors.

[0009] The present invention adopts the following technical solutions to achieve the above-mentioned purpose.

[0010] In one aspect, the present invention provides a method for recovering rare earth elements from waste phosphate-based phosphors, comprising the following steps:

[0011] 1) pickling the waste phosphate phosphor to be treated with a mixed acid solution at 10-60° C. to obtain pickling residue; wherein the mixed acid solution is a mixed solution of hydrochloric acid and an organic acid;

[0012] 2) mixing the pickled slag with a decomposing agent, roasting at 300-1000° C., washing, filtering, and obtaining a filter cake; the decomposing agent is selected from at least one of alkali metal carbonates, alkali metal bicarbonates, and alkali metal hydroxides;

[0013] 3) acid leaching the filter cake at 30-90° C., filtering, and obtaining an acid leaching solution;

[0014] 4) adding ammonium sulfate to the acid leaching solution to obtain a complex, then adjusting the pH value of the acid leaching solution to 1.0-3.0, adding oxalic acid solution, and obtaining a precipitate containing rare earth elements.

[0015] According to the method of the present invention, preferably, the method further comprises the following steps:

[0016] The waste phosphate-based phosphor is sieved with a sieve to remove the glass, thereby obtaining the waste phosphate-based phosphor to be treated.

[0017] According to the method described in the present invention, preferably, in the mixed acid solution of step 1), the concentration of hydrochloric acid is 0.1-1.0 mol / L, and the concentration of organic acid is 0.01-0.5 mol / L; the liquid-solid ratio of the mixed acid solution to the waste phosphor to be treated is 5-20 mL:1 g; and the pickling time is 0.1-3 h.

[0018] According to the method of the present invention, preferably, the organic acid is selected from at least one of citric acid, malic acid, tartaric acid and ethylenediaminetetraacetic acid.

[0019] According to the method of the present invention, preferably, in step 2), the mass ratio of the pickling slag to the decomposing agent is 1:0.1 to 1:1.0; and the roasting time is 0.1 to 3 hours.

[0020] According to the method of the present invention, preferably, the decomposing agent is selected from at least one of alkali metal carbonates and alkali metal bicarbonates.

[0021] According to the method of the present invention, preferably, in step 3), hydrochloric acid with a concentration of 0.5 to 5 mol / L is used to acid-leach the filter cake; the solid-liquid ratio of the filter cake to the hydrochloric acid is 1 g:3 to 15 mL; and the acid-leach time is 0.1 to 3 h.

[0022] According to the method of the present invention, preferably, the amount of ammonium sulfate added in step 4) is 20-100 g / L per liter of acid leaching solution.

[0023] According to the method of the present invention, preferably, in step 4), the oxalic acid solution is added in a mass ratio of REO to H2C2O4 of 1:1 to 1:2.

[0024] On the other hand, the present invention also provides a use of a mixed acid in reducing the calcium and phosphorus content in waste phosphate-based phosphors and improving the quality of the waste phosphate-based phosphors, comprising the following steps:

[0025] The waste phosphate phosphor to be treated is pickled with a mixed acid solution at 10 to 60° C. to obtain pickled residue;

[0026] Wherein, the mixed acid solution is a mixed solution of hydrochloric acid and an organic acid; the organic acid is selected from at least one of citric acid, malic acid, tartaric acid, and ethylenediaminetetraacetic acid;

[0027] The waste phosphate-based phosphor to be treated has a REO content of 5 to 17 wt%, a Ca content of 16 to 34 wt% and a P content of 6 to 17 wt%.

[0028] The obtained pickling residue is the treated waste phosphate-based phosphor, wherein the content of REO in the pickling residue is 15-24wt%, the content of Ca is 10-18wt% and the content of P is 5-10wt%.

[0029] The method of recovering rare earth elements from waste phosphate phosphors of the present invention can significantly reduce the calcium and phosphorus contents in the waste phosphate phosphors, improve the rare earth grade of the waste phosphate phosphors, and achieve low-cost and high-efficiency extraction of rare earth elements from the waste phosphors. DETAILED DESCRIPTION

[0030] The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0031] The "REO leaching rate" mentioned in the present invention refers to the degree to which the rare earth oxides are leached, that is, the percentage of rare earth oxides leached, expressed as a percentage;

[0032] REO leaching rate = dissolved REO / total amount of REO in the raw material × 100%.

[0033] The "REO precipitation rate" mentioned in the present invention refers to the ratio of the precipitation amount of rare earth oxide in the entire reaction system to the total amount of the reaction system, expressed as a percentage;

[0034] REO precipitation rate = (mass of precipitated REO / total mass of REO in the reaction system) x 100%.

[0035] The "total recovery rate of REO" mentioned in the present invention refers to the percentage of the sum of the REO content in the products of each step to the REO content in the raw materials;

[0036] Total recovery rate of REO = (total content of REO in the products of each step / content of REO in the raw material) × 100%.

[0037] <Method for recovering rare earth elements from waste phosphate-based phosphors>

[0038] The present invention enriches rare earth elements in waste phosphate fluorescent powder by reducing calcium and phosphorus through acid washing, and then reduces the calcium and phosphorus content in the waste phosphate fluorescent powder through decomposition roasting, hydrochloric acid leaching, and oxalic acid precipitation in sequence, thereby realizing efficient recovery of rare earth elements. The REO content in the product after the waste phosphate fluorescent powder is treated by the present invention is increased by more than 5%, and can reach more than 10% at the highest; the Ca content is reduced by more than 12%; and the P content is reduced by more than 6%.

[0039] The method for recovering rare earth elements from waste phosphate phosphors of the present invention comprises an acid washing step, a decomposition and roasting step, an acid leaching step and an oxalic acid precipitation step, which are described in detail below.

[0040] Pickling steps

[0041] The waste phosphate-based phosphor to be treated is pickled with a mixed acid solution to obtain pickling residue.

[0042] According to one embodiment of the present invention, the mixed acid solution is a mixed solution of hydrochloric acid and an organic acid. The organic acid can be selected from at least one of citric acid, malic acid, tartaric acid, and ethylenediaminetetraacetic acid; preferably, the organic acid is selected from at least one of citric acid, malic acid, and tartaric acid; more preferably, the organic acid is selected from one of citric acid, malic acid, and tartaric acid.

[0043] According to one embodiment of the present invention, the pickling temperature can be 10-60°C, preferably 15-40°C, more preferably 20-35°C; the pickling time can be 0.1-3h, preferably 0.2-3h, more preferably 0.5-2h. Reasonable pickling temperature and time are more conducive to removing the high content of calcium halophosphate in the waste phosphate-based phosphor and achieving calcium and phosphorus reduction.

[0044] In the present invention, the concentrations of hydrochloric acid and organic acid in the mixed acid solution may be any concentration that can achieve the purpose of pickling. The concentration of hydrochloric acid may be 0.1 to 1.0 mol / L, preferably 0.2 to 0.8 mol / L, more preferably 0.3 to 0.5 mol / L. The concentration of organic acid may be 0.01 to 0.5 mol / L, preferably 0.02 to 0.2 mol / L, more preferably 0.04 to 0.1 mol / L.

[0045] According to one embodiment of the present invention, the liquid-to-solid ratio of the mixed acid solution to the waste phosphor to be treated may be 5-20 mL:1 g, preferably 6-18 mL:1 g, and more preferably 8-15 mL:1 g.

[0046] Reasonable concentration and dosage of the mixed acid solution are more conducive to the stable pickling process and saving the use of raw materials. At the same time, it can effectively ensure the removal of calcium halophosphate with a high content in the waste phosphate-based phosphor.

[0047] In the present invention, the waste phosphate phosphor is recycled from waste fluorescent lamps and is waste phosphate phosphor containing broken glass. The waste phosphate phosphor is composed of calcium halophosphate phosphor, broken glass, alumina binder, rare earth tri-color phosphor and residual part. Its element composition includes: REO content of 6-18wt%, Ca content of 17-35wt%; P content of 7-18wt% ， The Si content is 5-15wt%; preferably, its element composition includes: REO content is 8-16wt%, Ca content is 20-33wt%; P content is 8-16wt%, Si content is 6-12wt%; more preferably, its element composition includes: REO content is 9-15wt%, Ca content is 22-32wt%; P content is 10-15wt%, Si content is 8-10wt%. The method of the present invention is preferably applicable to the treatment of the waste phosphate phosphor.

[0048] According to one embodiment of the present invention, in view of the fact that the waste phosphate phosphor of the present invention contains broken glass, the waste phosphate phosphor can be screened with a sieve to remove the broken glass and obtain the waste phosphate phosphor to be treated. The mesh number of the sieve can be 200 to 1000 meshes, preferably 400 to 900 meshes, and more preferably 500 to 800 meshes.

[0049] Decomposition and calcination steps

[0050] The pickling residue is mixed with a decomposing agent, roasted, washed, and filtered to obtain a filter cake.

[0051] According to one embodiment of the present invention, the mass ratio of the pickling slag to the decomposing agent may be 1:0.1 to 1:1.0, preferably 1:0.3 to 1:0.8, and more preferably 1:0.4 to 1:0.6.

[0052] According to one embodiment of the present invention, the decomposition agent may be selected from at least one of alkali metal carbonates, alkali metal bicarbonates, and alkali metal hydroxides; preferably, the decomposition agent is selected from at least one of alkali metal carbonates and alkali metal bicarbonates; more preferably, the decomposition agent is selected from at least one of anhydrous sodium carbonate, anhydrous sodium bicarbonate, anhydrous potassium carbonate, and anhydrous potassium bicarbonate.

[0053] According to one embodiment of the present invention, the calcination temperature may be 300-1000° C., preferably 400-900° C., more preferably 500-800° C. The calcination time may be 0.1-3 h, preferably 0.2-1.5 h, more preferably 0.5-1 h.

[0054] Reasonable roasting temperature and roasting time are more conducive to the decomposition reaction, ensuring that the pickling slag is effectively decomposed, which is beneficial to the decomposition of waste phosphate-based phosphors into rare earth oxides and promoting the conversion of phosphorus into water-soluble phosphates.

[0055] According to one embodiment of the present invention, the washing temperature may be 20 to 90° C., preferably 30 to 85° C., more preferably 50 to 80° C. The washing time may be 20 to 120 min, preferably 20 to 60 min, more preferably 25 to 45 min.

[0056] In the present invention, deionized water or ultrapure water may be used for washing, and the number of washing times is at least 2 times, preferably 2 to 5 times, and more preferably 2 to 3 times.

[0057] Reasonable washing conditions are more conducive to washing away excess decomposers and soluble salts produced by the decomposition reaction.

[0058] In order to achieve the purpose of waste recycling, the washing liquid after washing can be used for the first washing of the roasting product next time.

[0059] In the present invention, filtration can be performed by any filtration method known in the art, without particular limitation, such as gravity filtration, pressure filtration, centrifugal filtration, vacuum filtration, etc. Various filtration methods can be performed using equipment known in the art.

[0060] Acid leaching steps

[0061] The filter cake is acid-leached and filtered to obtain an acid-leaching solution.

[0062] According to one embodiment of the present invention, hydrochloric acid can be used to leaching the filter cake. The concentration of hydrochloric acid can be 0.5 to 5 mol / L, preferably 1 to 4 mol / L, and more preferably 2 to 4 mol / L. The solid-liquid ratio of the filter cake to the hydrochloric acid can be 1 g:3 to 15 mL, preferably 1 g:5 to 12 mL, and more preferably 1 g:6 to 10 mL.

[0063] According to another embodiment of the present invention, the acid leaching temperature may be 30-90°C, preferably 35-85°C, more preferably 40-80°C; the acid leaching time may be 0.1-3h, preferably 0.5-2.5h, more preferably 1-2h.

[0064] Reasonable acid concentration, leaching temperature and leaching time are more conducive to the leaching of rare earth elements.

[0065] Oxalic acid precipitation steps

[0066] Ammonium sulfate is added to the acid leaching solution to obtain a complex, the pH value of the acid leaching solution is adjusted, and an oxalic acid solution is added to obtain a precipitate containing rare earth elements.

[0067] In the present invention, ammonium sulfate is used as Ca 2+ Complexing agent, forms complex with calcium ions in the acid leaching solution.

[0068] According to one embodiment of the present invention, the amount of ammonium sulfate added may be 20 to 100 g per liter of the pickling solution, preferably 30 to 90 g, and more preferably 40 to 80 g. A reasonable amount of ammonium sulfate can effectively remove calcium ions in the pickling solution.

[0069] According to one embodiment of the present invention, the pH value of the acid leaching solution can be adjusted to 1.0 to 3.0, preferably 1.2 to 2.5, and more preferably 1.5 to 2.0. A reasonable pH value of the acid leaching solution is conducive to the formation of precipitation between oxalic acid and rare earth elements to obtain a precipitate containing rare earth elements. The obtained precipitate containing rare earth elements can be rare earth oxalate.

[0070] The present invention can use oxalic acid solution of any concentration to precipitate rare earth elements, which can be 0.01 to 1.5 mol / L, preferably 0.1 to 1.0 mol / L, and more preferably 0.2 to 0.8 mol / L.

[0071] According to one embodiment of the present invention, the oxalic acid solution can be added according to a mass ratio of REO to H2C2O4 of 1:1 to 1:2, preferably 1:1.1 to 1:1.8, and more preferably 1:1.2 to 1:1.5. A reasonable amount of oxalic acid solution added is more conducive to obtaining a precipitate containing rare earth elements, ensuring that the rare earth elements are effectively recovered.

[0072] <Purpose>

[0073] The use of the mixed acid of the present invention in reducing the calcium and phosphorus content in waste phosphate-based phosphors and improving the quality of the waste phosphate-based phosphors comprises the following steps:

[0074] The waste phosphate phosphor to be treated is pickled with a mixed acid solution at 10 to 60° C. to obtain pickled residue;

[0075] Wherein, the mixed acid solution is a mixed solution of hydrochloric acid and an organic acid; the organic acid is selected from at least one of citric acid, malic acid, tartaric acid, and ethylenediaminetetraacetic acid;

[0076] The waste phosphate-based phosphor to be treated has a REO content of 5 to 17 wt%, a Ca content of 16 to 34 wt% and a P content of 6 to 17 wt%.

[0077] The obtained pickling residue is the treated waste phosphate-based fluorescent powder, in which the content of REO is 15-24wt%, the content of Ca is 10-18wt% and the content of P is 5-10wt%.

[0078] The quality of the treated waste phosphate phosphor is improved, and the calcium and phosphorus content is reduced. The detailed description is as described above, and will not be repeated here.

[0079] <Ingredients>

[0080] The waste phosphate-based phosphors used in the following examples are phosphate-based phosphors recovered from discarded fluorescent lamps, and are composed of: calcium halophosphate phosphors, broken glass, alumina binder, rare earth tri-primary color phosphors and residual parts.

[0081] The elemental composition of the waste phosphate phosphor used in Examples 1, 2, and 5 includes: REO content of 11.56wt%, Ca content of 26.18wt%, P content of 10.74wt%, and Si content of 8.76wt%. The elemental composition of the waste phosphate phosphor used in Examples 3 and 4 includes: REO content of 9.38wt%, Ca content of 29.93wt%, P content of 12.56wt%, and Si content of 9.98wt%.

[0082] The other raw materials in the following examples are all commercially available products unless otherwise specified.

[0083] Example 1

[0084] The recovered waste phosphate phosphor was sieved with a 500-mesh sieve, the part above the sieve was discarded, and the part below the sieve was used as the waste phosphate phosphor to be treated. Take 100g of the waste phosphate phosphor to be treated, and use a mixed acid solution of hydrochloric acid and citric acid at a solid-liquid ratio (g / mL) of 1:15 at room temperature (25°C) to stir and wash the waste phosphate phosphor to be treated for 1 hour. After the acid washing is completed, filter to obtain the acid washing residue and the acid washing liquid; wherein the concentration of hydrochloric acid in the mixed acid solution is 0.4mol / L, and the concentration of citric acid is 0.04mol / L.

[0085] The pickling residue and anhydrous sodium carbonate are fully mixed in a crucible at a mass ratio of 1:0.5, and the crucible is placed in a muffle furnace and roasted at 700°C for 1.0h to decompose the pickling residue under the action of anhydrous sodium carbonate. Deionized water is added to the roasted product at a solid-liquid ratio (g / mL) of 1:10, stirred and washed at 50°C for 30min, and allowed to stand for solid-liquid separation, and the supernatant is decanted, and deionized water is added again at a solid-liquid ratio (g / mL) of 1:10, stirred and washed at 50°C for 30min, and filtered to obtain a filter cake. The second washing filtrate can be used for the first washing of the next roasting product.

[0086] The filter cake was leached with 3 mol / L hydrochloric acid at a solid-liquid ratio (g / mL) of 1:6 in a 50°C water bath with stirring for 1.5 h, and filtered to obtain an acid extract.

[0087] At room temperature (25°C), ammonium sulfate was added to the acid leaching solution to make the concentration of ammonium sulfate in the solution 60 g / L, the pH value of the solution was adjusted to 1.8, and 0.5 mol / L oxalic acid solution was added according to the mass ratio of REO to H2C2O4 of 1:1.4, and a precipitate was precipitated and filtered to obtain rare earth oxalate.

[0088] Example 2

[0089] The recovered waste phosphate phosphor was sieved with a 500-mesh sieve, the part above the sieve was discarded, and the part below the sieve was used as the waste phosphate phosphor to be treated. Take 100g of the waste phosphate phosphor to be treated, and use a mixed acid solution of hydrochloric acid and tartaric acid at a solid-liquid ratio (g / mL) of 1:10 at room temperature (25°C) to stir and wash the waste phosphate phosphor to be treated for 1 hour. After the acid washing is completed, filter to obtain the acid washing residue and the acid washing liquid; wherein the concentration of hydrochloric acid in the mixed acid is 0.4mol / L, and the concentration of tartaric acid is 0.04mol / L.

[0090] The pickling residue and anhydrous sodium carbonate are fully mixed in a crucible at a mass ratio of 1:0.5, and the crucible is placed in a muffle furnace and roasted at 800°C for 0.5h to decompose the pickling residue under the action of anhydrous sodium carbonate. Deionized water is added to the roasted product at a solid-liquid ratio (g / mL) of 1:10, stirred and washed at 50°C for 30min, and allowed to stand for solid-liquid separation, and the supernatant is decanted, and deionized water is added again at a solid-liquid ratio (g / mL) of 1:10, stirred and washed at 50°C for 30min, and filtered to obtain a filter cake. The second washing filtrate can be used for the first washing of the next roasted product.

[0091] The filter cake was heated in a water bath at 50°C with 3 mol / L hydrochloric acid at a solid-liquid ratio (g / mL) of 1:6, stirred and leached for 1.5 h, and filtered to obtain an acid leaching solution.

[0092] At room temperature (25°C), ammonium sulfate was added to the acid leaching solution to make the concentration of ammonium sulfate in the solution 60 g / L, the pH value of the solution was adjusted to 1.8, and 0.3 mol / L oxalic acid solution was added according to the mass ratio of REO to H2C2O4 of 1:1.3, and a precipitate was precipitated and filtered to obtain rare earth oxalate.

[0093] Example 3

[0094] The recovered waste phosphate phosphor was sieved with a 500-mesh sieve, the part above the sieve was discarded, and the part below the sieve was used as the waste phosphate phosphor to be treated. Take 100g of the waste phosphate phosphor to be treated, and use a mixed acid solution of hydrochloric acid and citric acid at a solid-liquid ratio (g / mL) of 1:15 at room temperature (25°C) to stir and wash the waste phosphate phosphor to be treated for 1 hour. After the acid washing is completed, filter to obtain the acid washing residue and the acid washing liquid; wherein the concentration of hydrochloric acid in the mixed acid solution is 0.3mol / L, and the concentration of citric acid is 0.05mol / L.

[0095] The pickling residue and anhydrous sodium carbonate are fully mixed in a crucible at a mass ratio of 1:0.5, and the crucible is placed in a muffle furnace and roasted at 700°C for 1.0h to decompose the pickling residue under the action of anhydrous sodium carbonate. Deionized water is added to the roasted product at a solid-liquid ratio (g / mL) of 1:10, stirred and washed at 50°C for 30min, and allowed to stand for solid-liquid separation, and the supernatant is decanted, and deionized water is added again at a solid-liquid ratio (g / mL) of 1:10, stirred and washed at 50°C for 30min, and filtered to obtain a filter cake. The second washing filtrate can be used for the first washing of the next roasting product.

[0096] The filter cake was heated in a water bath at 50°C with 3 mol / L hydrochloric acid at a solid-liquid ratio (g / mL) of 1:6, stirred and leached for 1.5 h, and filtered to obtain an acid leaching solution.

[0097] At room temperature (25°C), ammonium sulfate was added to the acid leaching solution to make the concentration of ammonium sulfate in the solution 60 g / L, the pH value of the solution was adjusted to 1.8, and 0.2 mol / L oxalic acid solution was added according to the mass ratio of REO to H2C2O4 of 1:1.4, and a precipitate was precipitated and filtered to obtain rare earth oxalate.

[0098] Example 4

[0099] The recovered waste phosphate phosphor was sieved with a 500-mesh sieve, the part above the sieve was discarded, and the part below the sieve was used as the waste phosphate phosphor to be treated. Take 100g of the waste phosphate phosphor to be treated, and use a mixed acid solution of hydrochloric acid and tartaric acid at a solid-liquid ratio (g / mL) of 1:10 to stir and wash the waste phosphate phosphor to be treated at room temperature (25°C) for 1 hour. After the acid washing is completed, filter to obtain the acid washing residue and the acid washing liquid; wherein the concentration of hydrochloric acid in the mixed acid solution is 0.4mol / L, and the concentration of tartaric acid is 0.04mol / L.

[0100] The pickling residue and anhydrous sodium carbonate are fully mixed in a crucible at a mass ratio of 1:0.5, and the crucible is placed in a muffle furnace and roasted at 800°C for 0.5h to decompose the pickling residue under the action of anhydrous sodium carbonate. Deionized water is added to the roasted product at a solid-liquid ratio (g / mL) of 1:10, stirred and washed at 50°C for 30min, and allowed to stand for solid-liquid separation, and the supernatant is decanted, and deionized water is added again at a solid-liquid ratio (g / mL) of 1:10, stirred and washed at 50°C for 30min, and filtered to obtain a filter cake. The second washing filtrate can be used for the first washing of the next roasting product.

[0101] The filter cake was heated in a water bath at 50°C with 4 mol / L hydrochloric acid at a solid-liquid ratio (g / mL) of 1:6, stirred and leached for 1.5 h, and filtered to obtain an acid extract.

[0102] At room temperature (25°C), ammonium sulfate was added to the acid leaching solution to make the concentration of ammonium sulfate in the solution 60 g / L, the pH value of the solution was adjusted to 1.8, and 0.5 mol / L oxalic acid solution was added according to the mass ratio of REO to H2C2O4 of 1:1.3, and a precipitate was precipitated and filtered to obtain rare earth oxalate.

[0103] Example 5

[0104] The only difference from Example 1 is that malic acid is used instead of citric acid. The concentration of malic acid in the mixed acid solution is 0.44 mol / L.

[0105] Comparative Example 1

[0106] The only difference from Example 1 is that hydrochloric acid solution is used instead of the mixed acid solution of hydrochloric acid and citric acid. The concentration of hydrochloric acid is 0.5 mol / L. The results are shown in Table 1.

[0107] Experimental example

[0108] Referring to Table 1, the contents of designated elements before and after designated steps in Examples 1 to 5 and Comparative Example 1 were tested, and the leaching rate, precipitation rate and total recovery rate of REO were calculated. The relevant test and calculation results are detailed in Table 1.

[0109] Table 1

[0110]

[0111]

[0112] Note: The percentages in the table refer to the mass percentages; M is the mass percentage of the pickling residue and the waste phosphate-based phosphor to be treated.

[0113] It can be seen from Table 1 that in the pickling step of the present invention, only using hydrochloric acid solution to pickle the waste phosphate-based phosphor to be treated cannot effectively remove calcium halophosphate, and further hinders the effective decomposition of the pickling slag during the decomposition and roasting process.

[0114] The method for recovering rare earth elements from waste phosphate phosphors of the present invention reduces the content of harmful impurity elements such as calcium, phosphorus and silicon in the waste phosphate phosphors, and at the same time improves the grade of the waste phosphate phosphors; the waste phosphate phosphors are pre-enriched after screening and acid washing, and the mass is reduced by 42% after pre-enrichment, which effectively reduces the processing volume, raw material consumption and energy consumption of the subsequent decomposition and roasting process, and reduces the emission of harmful substances. The subsequent decomposition and roasting, acid leaching and oxalic acid precipitation can all efficiently and maximally recover rare earth elements from the waste phosphate phosphors after acid washing. In the entire processing process of the present invention, the loss of rare earth elements is small.

[0115] The present invention is not limited to the above-mentioned embodiments. Without departing from the essential content of the present invention, any deformation, improvement and substitution that can be conceived by those skilled in the art shall fall within the scope of the present invention.

Claims

1. A method for recovering rare earth elements from waste phosphate-based phosphors, comprising the following steps: 1) pickling the waste phosphate phosphor to be treated with a mixed acid solution at 10-60° C. to obtain pickling residue; wherein the mixed acid solution is a mixed solution of hydrochloric acid and an organic acid; 2) mixing the pickled slag with a decomposing agent, roasting at 300-1000° C., washing, filtering, and obtaining a filter cake; the decomposing agent is selected from at least one of alkali metal carbonates, alkali metal bicarbonates, and alkali metal hydroxides; 3) acid leaching the filter cake at 30-90° C., filtering, and obtaining an acid leaching solution; 4) adding ammonium sulfate to the acid leaching solution to obtain a complex, then adjusting the pH value of the acid leaching solution to 1.0-3.0, adding oxalic acid solution, and obtaining a precipitate containing rare earth elements.

2. The method according to claim 1, characterized in that The method further comprises the following steps: The waste phosphate-based phosphor is sieved with a sieve to remove glass, thereby obtaining the waste phosphate-based phosphor to be treated.

3. The method according to claim 1, characterized in that In step 1), the concentration of hydrochloric acid in the mixed acid solution is 0.1-1.0 mol / L, and the concentration of organic acid is 0.01-0.5 mol / L; the liquid-solid ratio of the mixed acid solution to the waste fluorescent powder to be treated is 5-20 mL:1 g; and the pickling time is 0.1-3 h.

4. The method according to claim 1 or 3, characterized in that: The organic acid is selected from at least one of citric acid, malic acid, tartaric acid and ethylenediaminetetraacetic acid.

5. The method according to claim 1, characterized in that Step 2) The mass ratio of the pickling slag to the decomposing agent is 1:0.1 to 1:1.0; and the roasting time is 0.1 to 3 hours.

6. The method according to claim 1 or 5, characterized in that: The decomposing agent is selected from at least one of alkali metal carbonates and alkali metal bicarbonates.

7. The method according to claim 1, characterized in that In step 3), the filter cake is leached with hydrochloric acid having a concentration of 0.5 to 5 mol / L; the solid-liquid ratio of the filter cake to the hydrochloric acid is 1 g:3 to 15 mL; and the leaching time is 0.1 to 3 h.

8. The method according to claim 1, characterized in that In step 4), 20 to 100 g of ammonium sulfate is added to each liter of the acid leaching solution.

9. The method according to claim 1, characterized in that: In step 4), oxalic acid solution is added according to the mass ratio of REO to H2C2O4 of 1:1 to 1:

2.

10. A use of a mixed acid in reducing the calcium and phosphorus content in waste phosphate-based phosphors and improving the quality of waste phosphate-based phosphors, comprising the following steps: The waste phosphate phosphor to be treated is pickled with a mixed acid solution at 10 to 60° C. to obtain pickled residue; Wherein, the mixed acid solution is a mixed solution of hydrochloric acid and an organic acid; the organic acid is selected from at least one of citric acid, malic acid, tartaric acid, and ethylenediaminetetraacetic acid; The waste phosphate-based phosphor to be treated has a REO content of 5 to 17 wt%, a Ca content of 16 to 34 wt% and a P content of 6 to 17 wt%. The obtained pickling residue is the treated waste phosphate-based fluorescent powder, in which the content of REO is 15-24wt%, the content of Ca is 10-18wt% and the content of P is 5-10wt%.

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