Preparation method of low-chloride high-purity rare earth carbonate under high-chlorine source system

Abstract

This invention discloses a method for preparing low-chloride high-purity rare earth carbonate under a high-chloride source system, comprising the following steps: (1) adding ammonium bicarbonate to ammonium chloride reuse wastewater to prepare a precipitant. After preparation, the mass concentration of ammonium bicarbonate is controlled at 110-130 g / L, and the mass concentration of ammonium chloride is controlled at no more than 210 g / L; (2) adding bottom water to the precipitation reactor, and gradually adding the precipitant generated in step (1) and the high-concentration rare earth chloride solution produced in the extraction section to the precipitation reactor according to a certain stoichiometric ratio, and then filtering and washing to remove ions. Rare earth carbonate precipitate is obtained by washing with water, low-concentration acid, and deionized water. The precipitate is then ignited to obtain qualified rare earth oxide (chlorine content ≤100ug / g). Control requirements: V(bottom water) / V(high-concentration rare earth chloride solution) = 1.6–10; stoichiometric ratio of ammonium bicarbonate to rare earth chloride 3.6–4.5 (molar ratio); reaction temperature: 20–55℃; reaction time: 1–2 h; the low-concentration acid is 1 mol / L hydrochloric acid or nitric acid, and the acid volume required per kilogram of rare earth carbonate precipitate is 125–600 mL.

Description

Technical Field

[0001] This invention belongs to the field of rare earth materials technology, and relates to a method for preparing low-chloride high-purity rare earth carbonate under a high-chloride source system, which is a method for preparing rare earth oxides. Background Technology

[0002] Rare earth elements, often referred to as "industrial vitamins," play a crucial role in various industries. Yttrium oxide, for example, is widely used in optoelectronics, high-performance ceramics, thermal spraying, catalysts, and as a high-efficiency additive in functional composite materials due to its excellent physicochemical properties. Because chloride ion impurities significantly affect the performance of electronic ceramics and the density of engineering ceramics, the purity of yttrium oxide, especially its chlorine content, is highly critical in the field of high-performance materials.

[0003] In rare earth industrial production, the rare earth feed solution produced in the extraction section has a concentration of over 140 g / L. In the precipitation section, sedimentation occurs through the action of precipitants to produce oxalates or carbonates. These precipitants mainly include oxalic acid, sodium carbonate, ammonium carbonate, and ammonium bicarbonate, with ammonium bicarbonate and sodium bicarbonate being inexpensive precipitants. Due to the low solubility product of rare earth carbonates, their tendency to form amorphous precipitates, and their poor ion selectivity, current technologies require diluting the feed solution concentration 5–8 times (20–80 g / L) or dissolving oxides with nitric acid before precipitation to control chloride impurities. These processes consume large amounts of water, have long production cycles, limited capacity, and are prone to causing work-in-process stockpiling, which is detrimental to industrial production.

[0004] Furthermore, the wastewater, after neutralization treatment, becomes high-salinity wastewater, and direct discharge of this wastewater exacerbates soil salinization, failing to meet green manufacturing requirements. Currently, high-salinity wastewater is mainly treated and discharged through evaporation and crystallization, but evaporation of saline wastewater is energy-intensive and costly. Many companies attempt to recycle this wastewater, reusing it in the preparation of feed solutions or precipitants. However, this increases the source of chloride ions in the raw materials, further hindering the control of chloride ion impurities in the products. Consequently, the impurity content in the products does not meet customer requirements, restricting the recycling of wastewater.

[0005] Therefore, given the problems of low yield, large amount of wastewater, and difficulty in reuse in the current process, it is necessary to develop a preparation technology for the direct preparation of low chloride (less than 100 μg / g) rare earth carbonates under a high chloride source system. Summary of the Invention

[0006] To address the shortcomings of existing technologies and based on existing experiments, the present invention aims to provide a method for preparing low-chloride, high-purity rare earth carbonates under a high-salt, high-chloride source system. This method can directly generate qualified rare earth oxides under high-chloride source conditions in a high-ammonium chloride system. The equipment is simple to operate, requiring no additional devices, greatly improving the process's tolerance to saline wastewater, and reducing the difficulty of wastewater recycling, resulting in significant social and economic benefits.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing low-chloride high-purity rare earth carbonate under a high-chloride source system includes the following steps: (1) adding ammonium bicarbonate to ammonium chloride recycling wastewater to prepare a precipitant. After preparation, the mass concentration of ammonium bicarbonate is controlled at 110-130 g / L, and the mass concentration of ammonium chloride is controlled at no more than 210 g / L; (2) adding bottom water to the precipitation reactor, and gradually adding the precipitant generated in step (1) and the high-concentration rare earth chloride solution produced in the extraction section to the precipitation reactor according to a certain stoichiometric ratio. After filtration and washing with deionized water + low-concentration acid + deionized water, rare earth carbonate precipitate is obtained. After calcination, qualified rare earth oxide (chloride content ≤100 ug / g) is obtained.

[0009] Control requirements: V(bottom water) / V(high-concentration rare earth chloride solution) = 1.6-10; stoichiometric ratio of ammonium bicarbonate to rare earth chloride precipitate: 3.6-4.5 (molar ratio); reaction temperature: 20-55℃; reaction time: 1-2h; the low-concentration acid is 1mol / L hydrochloric acid or nitric acid, and the acid volume required per kilogram of rare earth carbonate precipitate is 125-600mL.

[0010] Ammonium bicarbonate solution and rare earth chloride solution are added to the precipitation reactor via co-current precipitation.

[0011] The burning temperature is 950–1000℃.

[0012] By adopting the above technical solution, this invention can reduce the entrainment and binding of impurity ions in the solid precipitate by controlling parameters such as reactant ratio, feeding rate, reaction temperature, and time. The chloride ion impurities adsorbed on the surface are then removed by dissolving and washing with low-concentration acid and washing with deionized water. This reduces the chloride content in the rare earth oxides obtained by high-temperature calcination. Under high chloride source conditions in a high-ammonium chloride system, it is possible to directly precipitate low-chloride, high-purity rare earth carbonates without the need for batching. The equipment is simple to operate and does not require additional devices, greatly improving the application scenarios of high-concentration ammonium chloride wastewater.

[0013] Implementation Cases

[0014] The present invention will be further described in detail below with reference to the embodiments.

[0015] In the rare earth carbonate production process, chloride ions in rare earth carbonate precipitates can generally be considered to exist in three ways: bound, adsorbed, and entrained. Adsorbed chloride ions can be removed by washing with deionized water, while bound and entrained chloride ions are more difficult to remove. RE: represents the collective term for rare earth elements.

[0016] This invention discloses a method for preparing low-chloride high-purity rare earth carbonates in a high-chloride source system, comprising the following steps:

[0017] (1) Add ammonium bicarbonate to the ammonium chloride reuse wastewater to prepare a precipitant. After preparation, the mass concentration of ammonium bicarbonate is controlled at 110-130 g / L and the mass concentration of ammonium chloride is controlled at no more than 210 g / L.

[0018] (2) Add bottom water to the precipitation reactor, and directly use the high-concentration rare earth chloride solution and ammonium bicarbonate solution containing ammonium chloride produced by the extraction section to gradually add to the precipitation reactor according to the stoichiometric ratio. After filtration and washing with deionized water + low-concentration acid + deionized water, rare earth carbonate precipitate is obtained. After calcination, rare earth oxide is obtained.

[0019] Control requirements: V(bottom water) / V(high-concentration rare earth chloride solution) = 1.6–10; stoichiometric ratio of ammonium bicarbonate to rare earth chloride ψ = 3.6–4.5 (molar ratio); reaction temperature: 20–55℃; reaction time: 1–2 h; the low-concentration acid is hydrochloric acid or nitric acid with a concentration of 1 mol / L, and the acid volume required per kilogram of rare earth carbonate precipitate is 125–600 mL; the stoichiometric ratio of ammonium bicarbonate solution to rare earth chloride solution added to the precipitation reactor is ψ = 3.6–4.5 (molar ratio).

[0020] The ammonium bicarbonate solution and rare earth chloride solution are added to the precipitation reactor in a co-current precipitation manner.

[0021] Its characteristic is that the calcination temperature is 950-1000℃.

[0022] In summary, this invention controls the material reaction ratio (i.e., stoichiometry), feeding rate, reaction time, and reaction temperature to ensure that the aggregation rate of positive and negative ions forming crystal nuclei is less than the rate at which crystal-forming ions arrange themselves in a certain order within the crystal lattice. This allows ions to slowly aggregate and precipitate, providing sufficient time for lattice arrangement and reducing the entrainment and binding of impurity ions. Furthermore, the adsorbed impurity ions are further removed through a process of deionized water washing + low-concentration acid washing + deionized water washing. Specifically, the initial washing of rare earth oxides with deionized water removes weakly adsorbed chloride ions, while the low-concentration acid washing dissolves and leaches out strongly adsorbed chloride ions, which are then removed by further washing with deionized water. This reduces the chloride content of the rare earth oxides obtained from high-temperature calcination. The addition of low-concentration acid washing reduces the amount of washing water used, and the addition of dilute acid (hydrochloric acid and nitric acid) effectively reduces bound and entrained chloride ions. In the following examples, ammonium bicarbonate is added to ammonium chloride recycling wastewater to prepare an ammonium bicarbonate solution containing ammonium chloride. The rare earth chloride solution is illustrated by yttrium chloride solution. The reaction equation is: 2YCl3+6NH4HCO3=Y2(CO3)3↓+6NH4Cl+3CO2↑+3H2O.

[0023] Example 1:

[0024] Prepare an ammonium bicarbonate solution containing ammonium chloride, with an ammonium bicarbonate concentration of 110–130 g / L and an ammonium chloride concentration of 200–210 g / L. After preparation, seal and store for later use.

[0025] 1.0 L of deionized water was added to the precipitation reactor as bottom water and stirred evenly. A yttrium chloride solution (concentration 181 g / L) produced in the extraction section and an ammonium bicarbonate solution containing ammonium chloride (ammonium bicarbonate concentration: 113.3 g / L, NH4Cl concentration: 205 g / L) were simultaneously added to the precipitation reactor at a stoichiometric ratio of ammonium bicarbonate to yttrium chloride of 3.6. The flow rate of the yttrium chloride solution was 1.018 mL / min, the flow rate of the ammonium bicarbonate solution was 4.093 mL / min, the reaction temperature was 23.5℃, the volume of the yttrium chloride solution was 0.122 L, and the reaction time was 2 h. Afterwards, the sample was filtered and washed with 50℃ deionized water. 31.01 g of the filtered and washed sample was added to 4 mL of 1 mol / L HCl solution for low-concentration acid washing, followed by washing twice with 50℃ deionized water to obtain yttrium carbonate precipitate. After ignition at 950℃, a sample was taken to test the chloride content, which was <30 μg / g.

[0026] Example 2:

[0027] 0.4 L of deionized water was added to the precipitation reactor as bottom water and stirred thoroughly. The yttrium chloride solution (concentration 165.85 g / L) produced in the extraction section and an ammonium bicarbonate solution containing ammonium chloride (ammonium bicarbonate concentration: 119.29 g / L, NH4Cl concentration: 202 g / L) were simultaneously added to the precipitation reactor at a stoichiometric ratio of 3.8 to yttrium chloride. The flow rate of the yttrium chloride solution was 2.083 mL / min, the flow rate of the ammonium bicarbonate solution was 7.694 mL / min, the reaction temperature was 34.7℃, the volume of the yttrium chloride solution was 0.25 L, and the reaction time was 2 h. Afterwards, the sample was filtered and washed with 50℃ deionized water. 31.92 g of the filtered and washed sample was added to 4 mL of 1 mol / L... The product was washed with a low-concentration acid in a solution of HNO3, and then washed twice with deionized water at 50°C to obtain yttrium carbonate precipitate. After calcination at 950°C and 1000°C, samples were taken and the chloride content of the product was found to be 45 μg / g and 40 μg / g, respectively.

[0028] Example 3:

[0029] 0.6 L of deionized water was added to the precipitation reactor as bottom water and stirred evenly. The yttrium chloride solution (concentration 172.89 g / L) produced in the extraction section and the ammonium bicarbonate solution containing ammonium chloride (ammonium bicarbonate concentration: 116.76 g / L, NH4Cl concentration: 210 g / L) were simultaneously added to the precipitation reactor at a stoichiometric ratio of ammonium bicarbonate to yttrium chloride of 4.45. The flow rate of the yttrium chloride solution was 4.17 mL / min, the flow rate of the ammonium bicarbonate solution was 19.210 mL / min, the reaction temperature was 55℃, the volume of the yttrium chloride solution was 0.25 L, and the reaction time was 1 h. Afterwards, the sample was filtered and washed with 50℃ deionized water. 30.5 g of the filtered and washed sample was added to 16 mL of 1 mol / L HNO3 solution for low-concentration acid washing, followed by two washes with 50℃ deionized water. After ignition at 950℃, a sample was taken to determine the chloride content, which was 60 μg / g.

[0030] Example 4:

[0031] 1.0 L of deionized water was added to the precipitation reactor as bottom water and stirred evenly. The yttrium chloride solution (concentration 185.32 g / L) produced in the extraction section and an ammonium bicarbonate solution containing ammonium chloride (ammonium bicarbonate concentration: 126 g / L, NH4Cl concentration: 208 g / L) were simultaneously added to the precipitation reactor at a stoichiometric ratio of ammonium bicarbonate to yttrium chloride of 4.2. The flow rate of the yttrium chloride solution was 4.0 mL / min, the flow rate of the ammonium bicarbonate solution was 17.275 mL / min, the reaction temperature was 25.4℃, the volume of the yttrium chloride solution was 0.48 L, and the reaction time was 2 h. Afterwards, the sample was filtered and washed with 50℃ deionized water. 31.12 g of the filtered and washed sample was added to 6 mL of 1 mol / L HCl solution for low-concentration acid washing, followed by washing twice with 50℃ deionized water to obtain yttrium carbonate precipitate. After ignition at 950℃, a sample was taken to determine the chloride content, which was 54 μg / g.

[0032] Example 5:

[0033] 30L of deionized water was added to a 200L precipitation reactor as bottom water and stirred evenly. A yttrium chloride solution (concentration 186.45 g / L) produced in the extraction section and an ammonium bicarbonate solution containing ammonium chloride (ammonium bicarbonate concentration: 119 g / L, NH4Cl concentration: 210 g / L) were simultaneously added to the precipitation reactor at a stoichiometric ratio of ammonium bicarbonate to yttrium chloride of 4.15. The flow rate of the yttrium chloride solution was 166.67 mL / min, the flow rate of the ammonium bicarbonate solution was 757.690 mL / min, the reaction temperature was 35℃, the volume of the yttrium chloride solution was 10L, and the reaction time was 1 h. Afterwards, the sample was filtered and washed with 50℃ deionized water. 30.2 g of the filtered and washed sample was added to 4 mL of 1 mol / L HCl solution for low-concentration acid washing, followed by washing twice with 50℃ deionized water to obtain yttrium carbonate precipitate. After ignition at 950℃, a sample was taken to determine the chloride content, which was 35 μg / g.

[0034] Example 6:

[0035] 0.6 L of deionized water was added to the precipitation reactor as bottom water and stirred evenly. The yttrium chloride solution (concentration 172.89 g / L) produced in the extraction section and the ammonium bicarbonate solution containing ammonium chloride (ammonium bicarbonate concentration: 119.29 g / L, NH4Cl concentration: 0 g / L) were simultaneously added to the precipitation reactor at a stoichiometric ratio of ammonium bicarbonate to yttrium chloride of 3.8. The flow rate of the yttrium chloride solution was 2.083 mL / min, the flow rate of the ammonium bicarbonate solution was 8.024 mL / min, the reaction temperature was 55℃, the volume of the yttrium chloride solution was 0.25 L, and the reaction time was 2 h. Afterwards, the sample was filtered and washed with 50℃ deionized water. 30.5 g of the filtered and washed sample was added to 4 mL of 1 mol / L HCl solution for low-concentration acid washing, followed by two washes with 50℃ deionized water. After ignition at 950℃, a sample was taken to determine the chloride content in the product, which was 50 μg / g.

[0036] This invention, through experimental verification during the rare earth carbonate production process, reveals that chloride ions generally exist in rare earth carbonate precipitates in three ways: bound, adsorbed, and entrained. Adsorbed chloride ions can be removed by washing with deionized water, while bound and entrained chloride ions are more difficult to remove. The experiments also found that under certain conditions, adding dilute acids (hydrochloric acid and nitric acid) as a washing agent can effectively reduce both bound and entrained chloride ions.

[0037] The technical content and features of this invention have been disclosed above. However, the application of this invention is not limited to the above description. For ease of explanation, those skilled in the art may make various substitutions and modifications based on the disclosure of this invention without departing from its inventive spirit. Therefore, the scope of protection of this invention should not be limited to the embodiments disclosed, but should include various substitutions and modifications that do not depart from this invention, and is covered by the claims.

Claims

1. A method for preparing low-chloride high-purity rare earth carbonate under a high-chlorine source system, characterized in that, Includes the following steps: (1) Add ammonium bicarbonate to the ammonium chloride recycling wastewater to prepare a precipitant. After preparation, the mass concentration of ammonium bicarbonate is controlled at 110~130g / L, and the mass concentration of ammonium chloride is controlled at no more than 210g / L. (2) Add bottom water to the precipitation reactor, and directly use the high concentration rare earth chloride solution and ammonium bicarbonate solution containing ammonium chloride produced by the extraction section to gradually add to the precipitation reactor according to the stoichiometric ratio. After filtration and washing with deionized water + low concentration acid + deionized water, rare earth carbonate precipitate is obtained. After calcination, rare earth oxide is obtained. Control requirements: V(bottom water) / V(high-concentration rare earth chloride solution) = 1.6~10; molar ratio of ammonium bicarbonate to rare earth chloride ψ = 3.6~4.45; reaction temperature: 20~55℃; reaction time: 1~2h; the low-concentration acid is hydrochloric acid or nitric acid with a concentration of 1mol / L, and the acid volume required per kilogram of rare earth carbonate precipitate is 125~600mL.

2. The method for preparing low chloride high purity rare earth carbonate under high chloride source system according to claim 1, characterized in that: The ammonium bicarbonate solution and rare earth chloride solution are added to the precipitation reactor in a co-current precipitation manner.

3. The method for preparing low-chloride high-purity rare earth carbonate in a high-chloride source system as described in claim 1 or 2, characterized in that: The burning temperature is 950~1000℃.