Method for recovering rare earth from neodymium iron boron waste through low-temperature chlorination and water immersion

Abstract

The invention discloses a method for recovering rare earth from neodymium iron boron waste through low-temperature chlorination and water leaching, which adopts the principle that rare earth elements and compounds thereof are easy to react with ammonium chloride at low temperature to form rare earth chloride ions, and iron and oxides thereof are not easy to chloridize, so that the rare earth is selectively chlorinated; the rare earth ions enter the water solution to complete separation of the rare earth and the iron. The main process comprises the following steps: firstly, carrying out chloridizing roasting reaction on ammonium chloride and rare earth in the neodymium iron boron waste material at a certain temperature; the method comprises the following steps: firstly, carrying out water leaching on rare earth chloride to obtain rare earth ions, finally, carrying out iron removal and oxalic acid precipitation on the leached rare earth ions, and then firing the precipitate to obtain mixed rare earth oxides such as neodymium oxide and praseodymium oxide.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for recovering praseodymium (Pr), neodymium (Nd), dysprosium (Dy) and terbium (Tb) and other rare earth metals from neodymium iron boron waste, belonging to the field of valuable metal recovery and utilization in waste materials. BACKGROUND

[0002] Neodymium iron boron magnetic material is an important rare earth functional material, widely used in new energy vehicles, wind power and electronic information industries, with the rapid development of high-tech, the demand for neodymium iron boron magnetic material is increasing year by year. However, a large amount of waste such as grinding mud, slag, smelting slag, hydrogen broken furnace ash, metal powder, oil sludge, grinding mud, chamfering mud, head, skin, and corner material is produced in the process of neodymium iron boron magnetic material processing. These waste materials contain a large amount of Nd, Pr, Dy and Tb and other rare earth elements. Recovering rare earth elements from these waste materials not only can save valuable rare earth resources, but also can achieve significant economic benefits.

[0003] Currently, there are two main methods for recovering rare earth metals from neodymium iron boron waste, namely, fire method and wet method. The fire method uses high temperature to melt iron and its transition metals into liquid in the form of alloy, and separates rare earth oxides in the form of refractory slag. This method has high energy consumption, many intermediate products, low product purity, and serious environmental pollution. Application No. (201910009571.4) discloses a method for one-step comprehensive recovery of neodymium iron boron waste by flash roasting. This method uses a high-temperature vertical reaction tower to rapidly oxidize rare earth metals in neodymium iron boron waste into rare earth oxides and iron into magnetite, and then separates rare earth metals and iron by magnetic separation. This method has long oxidation time, high energy consumption, and low rare earth recovery rate, making it difficult to be industrialized. The wet method mainly uses acid dissolution. This method has good rare earth leaching effect, but has problems such as long leaching time, large amount of acid wastewater, large amount of iron hydroxide slag, and low rare earth recovery rate. Application No. (202311220140.5) discloses a method for leaching mixed rare earth compounds from neodymium iron boron waste. This method roasts neodymium iron boron waste at about 900℃ for 3h to oxidize iron and rare earth metals in the waste into magnetite and rare earth oxides, and then leaches rare earth metals with hydrochloric acid or sulfuric acid. Since this process uses high-temperature roasting, the energy consumption is very high. In the acid leaching process, a large amount of iron ions enter the leaching solution, and a large amount of iron hydroxide slag is generated during the subsequent iron removal. On the one hand, the iron hydroxide slag adsorbs rare earth ions, reducing the recovery rate of rare earth metals. On the other hand, the treatment process of iron hydroxide slag is complex and costly, which reduces the benefits of rare earth metal recovery from neodymium iron boron waste.

[0004] Based on the above analysis, the existing neodymium iron boron waste rare earth metal recovery method, mostly using oxidation roasting-acid leaching method, has high rare earth element yield, but large acid consumption, resulting in large amount of acid wastewater discharge, large amount of iron hydroxide slag discharge, high wastewater and residue treatment cost, and poor comprehensive benefit. Therefore, further research and exploration of other recovery methods are needed to realize green, environmentally friendly and more efficient rare earth recovery method. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the existing neodymium iron boron waste rare earth metal recovery technology, and to provide a green, efficient and environmentally friendly rare earth metal recovery method. The method is simple, the raw materials are easy to obtain, the cost is low, and it is friendly to the environment. Through the retrieval, novelty search and comparison of the neodymium iron boron waste rare earth metal recovery technology at home and abroad, compared with the previous rare earth recovery technology, it is found that by adding an appropriate amount of ammonium chloride to the neodymium iron boron waste, roasting at low temperature, selectively chlorinating rare earth, and leaving metal iron or iron oxide in the slag, then through water leaching to separate and purify the rare earth, the present application is completed.

[0006] The purpose of the present application is achieved by a low-temperature chlorination water leaching rare earth recovery method of neodymium iron boron waste, which is mainly achieved by the following steps:

[0007] Pretreatment: the neodymium iron boron waste is dried at 105-120℃, ball milled and sieved to obtain a neodymium iron boron waste test sample with a particle size of less than 200 mesh;

[0008] Low-temperature chlorination: 0.7-5.0 times of ammonium chloride is added to the neodymium iron boron waste with particle size less than 200 mesh for chlorination roasting reaction, the roasting temperature is 200-450℃, the amount of ammonium chloride is calculated based on the theoretical requirement of chlorination of all rare earth elements, the chlorination roasting time is 2.0-6.0h, and the chlorination endpoint is that the chlorination rate of rare earth in the neodymium iron boron waste is greater than 99.5%;

[0009] Water leaching: 1-7 times of water leaching agent is added to the chlorinated neodymium iron boron waste, the leaching temperature is controlled at 40-95℃, the amount of water leaching agent is calculated based on the mass of all neodymium iron boron waste, the leaching time is 0.5-5h, and the endpoint is that the pH is less than 1, i.e. the total amount of rare earth in the filter residue is less than 0.1%;

[0010] Iron removal: potassium permanganate is added to the water leaching solution to oxidize and remove iron, the concentration of potassium permanganate solution is 0.5%-10%, the oxidation temperature is 40-55℃, the oxidation time is 20-35min, and the oxidation endpoint is that the Fe 2+ concentration in the leaching solution is less than 0.01%. After the reaction is completed, filtration is carried out, sodium hydroxide solution is added to the filtrate, and Fe 3+ is removed by filtration and precipitation.

[0011] Precipitation and calcination: An excess of oxalic acid solution is added to the filtrate after iron removal to induce precipitation. The mixture is filtered to obtain a mixed rare earth oxalate precipitate, which is then calcined in a muffle furnace to obtain a mixed rare earth oxide. The following is a further description of the present invention;

[0012] The present invention describes a method for recovering rare earth elements from neodymium iron boron waste by low-temperature chlorination in water, characterized in that: step (2) roasting is carried out at room temperature, at normal pressure, and under a nitrogen atmosphere.

[0013] The present invention describes a method for recovering rare earth elements from neodymium iron boron waste by low-temperature chlorination water leaching, characterized in that: the rare earth chlorination endpoint in step (2) is defined as a rare earth chlorination rate in the neodymium iron boron waste being greater than 99.5%.

[0014] The present invention discloses a method for recovering rare earth elements from neodymium iron boron waste by low-temperature chlorination in water, characterized in that: step (3) water leaching is carried out at room temperature, normal pressure, and in an air atmosphere. The water is pure water with a conductivity of less than 0.1.

[0015] The present invention describes a method for recovering rare earth elements from neodymium iron boron waste by low-temperature chlorination in water, characterized in that: the endpoint of rare earth leaching in step (3) is that the total amount of rare earth elements in the filter residue is less than 0.1% of the total residue amount.

[0016] The present invention discloses a method for recovering rare earth elements from neodymium iron boron waste by low-temperature chlorination in water, characterized in that: the oxidant in step (4) is one of hydrogen peroxide and potassium permanganate, and the endpoint of the oxidation reaction is the amount of Fe in the leachate. 2+ Concentration less than 0.01%, except for Fe 3+ The required concentration of the precipitant sodium hydroxide is 0.5%-8%.

[0017] The present invention describes a method for recovering rare earth elements from neodymium iron boron waste by low-temperature chlorination in water, characterized in that: in step (5), the amount of oxalic acid precipitant is calculated based on the theoretical amount required to generate rare earth oxalic acid precipitate from all rare earth elements, the concentration of oxalic acid is 2%-10%, the precipitation temperature is 40-60℃, the time is 0.5-3h, and the precipitation endpoint is pH 1.5-2.8, that is, the concentration of mixed rare earth elements in the filter residue is less than 0.01%.

[0018] The present invention describes a method for recovering rare earths from neodymium iron boron waste by low-temperature chlorination with water, characterized in that: in step (5), the calcination temperature for obtaining mixed rare earth oxides by calcination with oxalic acid is 750-800℃ and the calcination time is 1-3h.

[0019] Invention Principle: Selective chlorination controlled leaching separation method. This method utilizes the principle that rare earth elements and their compounds readily react with ammonium chloride at low temperatures to form rare earth chloride ions, while iron and its oxides are not easily chlorinated. This allows for the selective chlorination of rare earth elements to form rare earth chloride salts. The rare earth chloride salts are then dissolved in water to form an aqueous solution of rare earth chloride ions. Iron remains in the leaching residue as iron slag, thus separating the rare earth elements from the iron. Compared with the prior art, the advantages of this invention are:

[0020] This invention employs a selective chlorination controlled leaching method to separate rare earth elements from metallic iron, recovering mixed rare earth elements such as Nd, Pr, and Dy from NdFeB waste. It utilizes ammonium chloride for selective chlorination of the rare earth elements, leaving metallic iron in the slag. Compared to acid dissolution and hydrochloric acid preferential dissolution methods, this method eliminates the high-temperature roasting process of NdFeB waste, using direct roasting with ammonium chloride at a lower temperature. The rare earth recovery rate can reach over 97.8%, and the production of ferric hydroxide is reduced by 80%, wastewater discharge by 90%. The process is simple, requires minimal investment, and the ammonium chloride can be recycled and reused, demonstrating excellent application prospects. Detailed Implementation

[0021] A method for recovering rare earth elements from neodymium iron boron waste by low-temperature chlorination with water is further illustrated below with specific embodiments:

[0022] Example 1:

[0023] Experimental conditions and results

[0024] Example 2:

[0025] Experimental conditions and results

[0026] Example 3:

[0027] Experimental conditions and results

[0028] Example 4:

[0029] Experimental conditions and results

[0030] Comparing Examples 1-5, Example 3 showed the highest rare earth yield, reaching 97.8%. Its process conditions were as follows: NH4Cl to NdFeB waste mass ratio 3.0:1.0; chlorination roasting temperature 310℃; chlorination roasting time 2.0h; water leaching temperature 80℃; leaching time 2.0h; solid-liquid ratio 1:6; potassium permanganate oxidant concentration 1%; iron removal oxidation temperature 50℃; oxidation time 30min; oxalic acid precipitant concentration 4%; precipitation temperature 50℃; precipitation time 30min; oxalic acid rare earth calcination temperature 780℃; calcination time: 1.5h. Attached Figure Description Figure 1 Flowchart of rare earth element recovery process from NdFeB waste Figure 2 The main rare earth element chemical composition of neodymium iron boron waste Figure 3 Phase analysis of NdFeB waste Figure 4 Transmission electron microscope images of rare earth oxides obtained by chlorination in water Figure 5 Transmission electron microscope images of rare earth oxides obtained by leaching in chlorinated water.

Claims

1. A method for recovering rare earth elements from neodymium iron boron waste by low-temperature chlorination with water, characterized in that, This can be achieved through the following steps: (1) Pretreatment of test samples: The NdFeB waste was dried at 105-120℃, ground and sieved by ball mill to obtain NdFeB waste with a particle size of less than 200 mesh. (2) Low-temperature chlorination: Add 0.7-5.0 times the amount of ammonium chloride to NdFeB waste with a mesh size of less than 200 to carry out chlorination roasting reaction of rare earth elements. The roasting temperature is 200-450℃ and the chlorination roasting time is 2.0-6.0h. The amount of ammonium chloride added is calculated based on the theoretical amount required for chlorination of all rare earth elements in NdFeB waste. (3) Water leaching: Add 1-7 times the amount of water to the chlorinated NdFeB waste for leaching, control the leaching temperature at 40-95℃, the leaching time at 0.5-5h, control the pH to be less than 1 during the process, and the pH endpoint at 1.5-2. (4) Iron removal: An oxidant is added to the water leachate to remove iron. The concentration of the oxidant is 0.5%-10%, the oxidation temperature is 40-55℃, and the oxidation time is 20-35 min. After the reaction is complete, the solution is filtered, and sodium hydroxide solution is added to the filtrate. The precipitate is then removed by filtration. 3 + . (5) Precipitation and calcination: Add an excess of oxalic acid solution to the filtrate after iron removal to precipitate the mixture. Filter the mixture to obtain a mixed rare earth oxalate precipitate. Calcin the rare earth oxalate precipitate in a muffle furnace to obtain a mixed rare earth oxide.

2. The method for recovering rare earth elements from neodymium iron boron waste by low-temperature chlorination in water, as described in this invention, is characterized by: Step (2) is carried out in a normal temperature, normal pressure and nitrogen atmosphere.

3. The method for recovering rare earth elements from neodymium iron boron waste by low-temperature chlorination in water, as described in this invention, is characterized by: Step (2) The rare earth chlorination endpoint is defined as a rare earth chlorination rate of greater than 99.5% in the neodymium iron boron waste.

4. The method for recovering rare earth elements from neodymium iron boron waste by low-temperature chlorination in water, as described in this invention, is characterized by: Step (3) water leaching is carried out at normal temperature, normal pressure, and in an air atmosphere. The water is pure water with a conductivity of less than 0.

1.

5. The method for recovering rare earth elements from neodymium iron boron waste by low-temperature chlorination in water, as described in this invention, is characterized by: Step (3) The endpoint of rare earth leaching is when the total amount of rare earth in the filter residue is less than 0.1% of the total residue.

6. The method for recovering rare earth elements from neodymium iron boron waste by low-temperature chlorination in water, as described in this invention, is characterized by: In step (4), the oxidant is either hydrogen peroxide or potassium permanganate, and the endpoint of the oxidation reaction is the amount of Fe in the leachate. 2+ Concentration less than 0.01%, except for Fe 3 + The required concentration of the precipitant sodium hydroxide is 0.5%-8%.

7. The method for recovering rare earth elements from neodymium iron boron waste by low-temperature chlorination in water, as described in this invention, is characterized in that: Step (5) The amount of oxalic acid precipitant is calculated based on the theoretical amount required to generate rare earth oxalic acid precipitate from all rare earth elements. The concentration of oxalic acid is 2%-10%, the precipitation temperature is 40-60℃, the time is 0.5-3h, and the precipitation endpoint is pH 1.5-2.8, that is, the concentration of mixed rare earth elements in the filter residue is less than 0.01%.

8. The method for recovering rare earth elements from neodymium iron boron waste by low-temperature chlorination in water, as described in this invention, is characterized in that: Step (5) Oxalic acid mixed with rare earth to obtain mixed rare earth oxides. The calcination temperature is 750-800℃ and the calcination time is 1-3h.

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