Method for treating chlorinated rare earths with alkali metal precipitants and recycling

Abstract

The application discloses a method for treating chlorinated rare earth and recycling by using alkali metal precipitator, which comprises the following steps: (1) reacting alkali metal precipitator solution with chlorinated rare earth solution to obtain a precipitate, filtering and washing the precipitate to obtain rare earth oxide precursor, filtrate and washing liquid; (2) calcining the rare earth oxide precursor to obtain rare earth oxide and release CO2 gas; (3) removing impurities and concentrating the filtrate to obtain saturated chlorinated alkali metal solution; electrolyzing the chlorinated alkali metal solution to obtain alkali metal hydroxide solution, chlorine and hydrogen; (4) reacting the chlorine and hydrogen to obtain HCl, thereby preparing hydrochloric acid, using the hydrochloric acid for reverse extraction to obtain chlorinated rare earth solution; (5) using the alkali metal hydroxide solution of step (4) to absorb the released CO2 gas to obtain alkali metal precipitator solution. The method obtains rare earth oxide and realizes the recycling of precipitator, waste water and regenerated acid.

Description

Technical Field

[0001] This invention belongs to the field of rare earth metallurgy technology, and relates to a method for treating rare earth chlorides and recycling them using alkali metal precipitants, and more particularly to a method for treating rare earth chlorides and recycling them using alkali metal precipitant solutions. Background Technology

[0002] Industrially, the precursors for preparing rare earth oxides are mainly rare earth carbonates and rare earth hydroxides. Using hydroxides as precursors and calcining to prepare rare earth oxides consumes less energy and does not produce carbon dioxide gas; however, the resulting rare earth oxides have poor crystal structure and higher levels of impurities such as chlorine, resulting in lower product quality. Therefore, rare earth carbonate remains a better choice for preparing rare earth oxides. The traditional ammonium bicarbonate precipitation method for preparing rare earth carbonates generates large amounts of ammonia nitrogen wastewater, causing environmental pollution. While sodium carbonate and potassium carbonate precipitation methods can avoid ammonia nitrogen pollution, they do not solve the resource utilization problem of sodium chloride wastewater. Moreover, sodium carbonate and potassium carbonate are more expensive than ammonium bicarbonate, increasing production costs.

[0003] CN10282651A discloses a method for preparing high-purity rare earth oxides using a composite precipitant. The method involves a rare earth chloride solution and a composite precipitant solution undergoing a precipitation reaction. The composite precipitant used includes sodium bicarbonate and sodium carbonate, with a mass ratio of sodium bicarbonate to sodium carbonate of 0.2–10:1. This method prevents the formation of a paste-like rare earth hydroxide product due to excessive alkalinity of sodium carbonate, and yields rare earth carbonates with good crystallinity, stable crystal form, narrow particle size distribution, and low impurity content. However, this method generates a large amount of sodium chloride wastewater, which could pollute the environment if used industrially.

[0004] CN111041249A discloses a method for treating magnesium and / or calcium waste liquid. The method involves pyrolyzing the magnesium and / or calcium-containing waste liquid to obtain magnesium oxide and / or calcium oxide solids and hydrogen chloride-containing gas. The hydrogen chloride gas is used to produce acid, which is then returned for acid dissolution of rare earth minerals or rare earth extraction and separation. The obtained magnesium oxide and / or calcium oxide can be directly returned for rare earth extraction and separation, or purified by slurry preparation and carbonization, and used as an organic pretreatment agent for rare earth extraction and separation. However, this method has high energy consumption during the pyrolysis process, and the use of magnesium compounds as a precipitant results in even more wastewater during the precipitation process. Although recycling is implemented, the cost and energy consumption remain high.

[0005] CN105861828B discloses a rare earth composite compound containing rare earth hydroxide and rare earth carbonates, and its preparation method. This method uses a first precipitant containing a calcium and / or magnesium basic compound and a second precipitant containing a carbonate and / or bicarbonate containing at least one element selected from ammonium, sodium, and potassium. Although this method reduces the amount of ammonium precipitant used, the wastewater generated during the precipitation process is more complex, the subsequent waste treatment process is more complicated, and the production cost is higher. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a method for treating and recycling rare earth chlorides using an alkali metal precipitant. This method enables the recycling of the precipitant, wastewater, and regenerated acid during the production of rare earth oxides. The method of this invention can further reduce energy consumption and save costs in the rare earth oxide production process. It also achieves the recycling of regenerated acid and alkali metal ions through wastewater electrolysis, eliminating environmental pollution from alkali metal chloride wastewater.

[0007] The present invention achieves the above objectives using the following technical solutions.

[0008] This invention provides a method for treating and recycling rare earth chlorides using an alkali metal precipitant, comprising the following steps:

[0009] (1) React the alkali metal precipitant solution with the rare earth chloride solution, control the pH value at the reaction endpoint, and obtain the precipitate. Filter and wash the precipitate to obtain rare earth oxide precursor, filtrate and washing liquid.

[0010] (2) The rare earth oxide precursor is calcined to obtain rare earth oxides and release CO2 gas.

[0011] (3) Remove impurities and concentrate the filtrate from step (1) to obtain a saturated alkali metal chloride solution; electrolyze the saturated alkali metal chloride solution to obtain an alkali metal hydroxide solution, chlorine gas and hydrogen gas;

[0012] (4) Chlorine and hydrogen are reacted to obtain HCl, thereby preparing hydrochloric acid. The hydrochloric acid is used to back-extract rare earth ions to obtain rare earth chloride solution, which is then returned to step (1) and used as a reaction raw material.

[0013] (5) The CO2 gas released in step (2) is absorbed by the alkali metal hydroxide solution from step (4) to obtain an alkali metal precipitant solution, which is then returned to step (1) as a reaction raw material. This allows for the recycling of the precipitant, wastewater, and regenerated acid during the preparation of rare earth oxides, with virtually no wastewater discharge, thus avoiding environmental pollution and saving costs. Although electrolysis and calcination are common production processes individually, the inventors of this application have combined the precipitation of rare earth chlorides, the calcination of rare earth oxide precursors, the electrolysis of saturated alkali metal chloride solutions, back-extraction, and the absorption of carbon dioxide to achieve circular production with virtually no wastewater discharge, conforming to the concept of green environmental protection, and also obtaining rare earth oxide products. This is not a conventional approach.

[0014] In step (1), an alkali metal precipitant solution can be added to a rare earth chloride solution to carry out the reaction. The pH value at the end of the reaction is controlled to be 6-8 to obtain a precipitate. Specifically, the precipitate is filtered to obtain a filter cake and a filtrate; the filter cake is washed with water to obtain a rare earth oxide precursor and a washing solution. The rare earth chloride solution can be a chloride solution of a single rare earth element or a chloride solution of mixed rare earth elements.

[0015] The rare earth elements in the rare earth chloride solution refer to lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium, and yttrium, with lanthanum, cerium, praseodymium, and neodymium being preferred.

[0016] In step (2), laboratory calcination can be carried out in a muffle furnace. The calcination temperature in the muffle furnace can be 920–980°C, preferably 950–970°C; the calcination time is 3–5 h, preferably 4–5 h. Industrially, calcination can be continuous dynamic calcination, which can be carried out in an externally heated pyrolysis device, such as an externally heated rotary kiln. Any known externally heated rotary kiln can be used, and no particular limitation is made here. Industrially, the calcination temperature in an externally heated rotary kiln can be 920–980°C, preferably 950–970°C, and the calcination time can be 15–22 h, preferably 15–20 h.

[0017] In step (3), the filtrate is purified to remove impurities, which means removing organic matter, for example, by using resin adsorption. The saturated alkali metal chloride solution is a saturated potassium chloride solution or a saturated sodium chloride solution, preferably a saturated sodium chloride solution.

[0018] In step (3), during electrolysis, the voltage is 1.8–3.6V, preferably 1.9–3.3V; the current density is 190–250A / m. 2 Preferably 200-230 A / m 2 The temperature is 50-60℃, preferably 50-55℃.

[0019] In step (4), chlorine and hydrogen are reacted by ignition or light to obtain HCl gas, which is then dissolved to obtain hydrochloric acid. However, if the gas purity is insufficient during ignition, it is prone to explosion, and the light reaction also poses a safety hazard. When reacting chlorine and hydrogen, a catalyst can be added, such as activated carbon-supported copper chloride or activated carbon-supported ferric chloride, to lower the activation energy of the reaction, allowing the reaction to proceed under milder conditions (such as room temperature or lower temperatures, such as below 10°C), thereby increasing the reaction rate and reducing side reactions and safety risks.

[0020] Preparation of activated carbon-supported copper chloride or activated carbon-supported ferric chloride catalyst: Using activated carbon as a carrier, a copper chloride solution (or ferric chloride solution) is impregnated onto the carrier. The concentration of the copper chloride solution (or ferric chloride solution) in the impregnation solution (15-25 wt%), the impregnation time (40-90 minutes), and the impregnation ratio (the volume-to-mass ratio of the impregnation solution to the carrier is 4-6 mL:1 g) are controlled to achieve efficient loading of copper or iron ions. The impregnation temperature is room temperature. The source of activated carbon is not particularly limited. According to one embodiment of the present invention, columnar activated carbon from Fujian Xinsen Carbon Industry Co., Ltd. is selected. The concentration of the impregnation solution is preferably 20-23 wt%. The impregnation time is preferably 60-70 minutes. The impregnation ratio is preferably 5-5.5 mL:1 g.

[0021] In step (4), back-extraction is a key step in the rare earth solvent extraction and separation process. Its core is to add acid or alkali to the organic phase loaded with metal (i.e., the loaded organic phase) to allow the target metal ions to re-enter the aqueous phase, thereby achieving metal enrichment and extractant regeneration. In this invention, the hydrochloric acid formed is used for back-extraction of rare earth ions in the loaded organic phase.

[0022] According to the method of the present invention, preferably, in step (1), the alkali metal precipitant in the alkali metal precipitant solution is selected from one or more of alkali metal carbonates, alkali metal bicarbonates, alkali metal basic carbonates, and alkali metal hydroxides; wherein the alkali metal is potassium or sodium.

[0023] In some embodiments, the alkali metal precipitant solution is selected from one or more of sodium carbonate solution, potassium carbonate solution, sodium bicarbonate solution, and potassium bicarbonate solution. In other embodiments, the alkali metal precipitant solution may be a mixture of one or two of sodium hydroxide solution and potassium hydroxide solution with carbon dioxide gas.

[0024] According to one specific embodiment of the present invention, the alkali metal precipitant solution is a sodium carbonate solution. According to another specific embodiment of the present invention, the alkali metal precipitant solution is a mixture of sodium carbonate solution and sodium bicarbonate solution. According to yet another specific embodiment of the present invention, the alkali metal precipitant solution is formed by reacting sodium hydroxide solution with CO2 gas.

[0025] According to the method of the present invention, preferably, in step (1), the reaction temperature is 10-100°C. The reaction temperature is preferably 20-80°C, more preferably 30-60°C, for example, 30°C, 40°C, 45°C, 50°C, 55°C, or 60°C.

[0026] According to the method of the present invention, preferably, in step (1), the pH value at the reaction endpoint is 6-8. This is beneficial to ensuring the yield and purity of the obtained rare earth oxide precursor.

[0027] According to the method of the present invention, preferably, in step (1), the pH value at the reaction endpoint is 6.7 to 7.2.

[0028] According to the method of the present invention, preferably, in step (1), the rare earth oxide precursor is selected from one of the following substances:

[0029] (a) Rare earth carbonates

[0030] (b) Combinations of rare earth carbonates and rare earth basic carbonates.

[0031] (c) Rare earth basic carbonates

[0032] (d) Combinations of rare earth basic carbonates and rare earth hydroxides.

[0033] According to one specific embodiment of the present invention, the rare earth oxide precursor is a rare earth carbonate. According to another specific embodiment of the present invention, the rare earth oxide precursor is a combination of a rare earth carbonate and a rare earth basic carbonate.

[0034] According to the method of the present invention, preferably, the washing liquid from step (1) is used as the precipitation base liquid in step (1), for diluting alkali metal hydroxides in step (3), and / or for absorbing HCl to prepare hydrochloric acid in step (4). This facilitates the recycling of wastewater, saves costs, and is environmentally friendly.

[0035] According to the method of the present invention, preferably, in step (4), the concentration of hydrochloric acid is 3-12 mol / L. The concentration of the obtained hydrochloric acid is preferably 3-6 mol / L, more preferably 5-6 mol / L. This is beneficial for improving the back-extraction efficiency.

[0036] According to the method of the present invention, preferably, in step (5), the absorption rate of CO2 gas is greater than 90%. The absorption rate of CO2 gas is preferably greater than 93%, more preferably 94.5-96%.

[0037] According to the method of the present invention, preferably, in step (5), the concentration of the obtained alkali metal precipitant solution is 1.5–3.3 mol / L. More preferably, the concentration of the obtained alkali metal precipitant solution is 2–3.3 mol / L, and more preferably 2–3 mol / L. Such a concentration of alkali metal precipitant solution can better generate rare earth oxide precursors, allowing for complete precipitation of rare earth ions.

[0038] The method of this invention can simultaneously obtain rare earth oxides and recycle precipitants, wastewater, and regenerated acid. This method can further reduce energy consumption and save costs in the production process of rare earth oxides, and achieve the recycling of regenerated acid and alkali metal ions through wastewater electrolysis, thus eliminating environmental pollution from alkali metal chloride wastewater. Detailed Implementation

[0039] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0040] The following examples illustrate the preparation of activated carbon-supported copper chloride catalysts: Activated carbon was used as a carrier, and a copper chloride solution was impregnated onto the carrier. Copper ion loading was achieved by controlling the concentration of the copper chloride solution (20 wt%), the impregnation time (60 minutes), and the impregnation ratio (i.e., the volume-to-mass ratio of the impregnation solution to the carrier was 5 mL:1 g). The activated carbon used was columnar activated carbon from Fujian Xinsen Carbon Industry Co., Ltd.

[0041] Example 1

[0042] (1) A 1 mol / L sodium carbonate solution was added in portions to a praseodymium-neodymium chloride solution, and the reaction was carried out at 55 °C. The pH value at the end of the reaction was controlled to be 6.8, and a precipitate was obtained. The precipitate was filtered and washed to obtain praseodymium-neodymium carbonate (i.e., rare earth oxide precursor), sodium chloride filtrate, and washing solution.

[0043] (2) Praseodymium-neodymium carbonate (i.e. rare earth oxide precursor) was calcined in a muffle furnace at 950°C for 3 hours to obtain praseodymium-neodymium oxide (i.e. rare earth oxide) and CO2 gas was released.

[0044] (3) The sodium chloride filtrate was purified (organic matter removed) and concentrated to obtain a saturated sodium chloride solution. The saturated sodium chloride solution was then subjected to a voltage of 1.9V and a current density of 200A / m². 2 Electrolysis at 50°C yields chlorine and hydrogen as anolyte products at the anode and sodium hydroxide solution as cathode product at the cathode.

[0045] (4) The chlorine and hydrogen obtained in step (3) are reacted in the presence of a catalyst (copper chloride supported on activated carbon) to obtain HCl, thereby preparing hydrochloric acid. The hydrochloric acid is used to back-extract rare earth ions to obtain praseodymium-neodymium chloride solution, which is then returned to step (1) and used as a reaction raw material.

[0046] (5) The CO2 gas released in step (2) is absorbed by the cathode product sodium hydroxide solution obtained by electrolysis to obtain sodium carbonate solution, which is then returned to step (1) and used as a reaction raw material.

[0047] Example 2

[0048] (1) A mixed solution of sodium carbonate and sodium bicarbonate (in which the molar ratio of sodium carbonate to sodium bicarbonate in the mixed solution is 2:1 and the total molar concentration is 2.6 mol / L) was added in batches to a lanthanum chloride solution, and the reaction was carried out at 50 °C. The pH value at the end of the reaction was controlled to be 7, and a precipitate was obtained. The precipitate was filtered and washed to obtain lanthanum carbonate (i.e., rare earth oxide precursor), sodium chloride filtrate, and washing solution.

[0049] (2) Lanthanum carbonate (i.e. rare earth oxide precursor) was calcined in a muffle furnace at 950°C for 4 hours to obtain lanthanum oxide (i.e. rare earth oxide) and release CO2 gas.

[0050] (3) The sodium chloride filtrate is purified (organic matter removed) and concentrated to obtain a saturated sodium chloride solution. The saturated sodium chloride solution is then subjected to a voltage of 3.3V and a current density of 230A / m². 2 Electrolysis at 50°C yields chlorine and hydrogen as anolyte products at the anode and sodium hydroxide solution as cathode product at the cathode.

[0051] (4) Chlorine and hydrogen are reacted in the presence of a catalyst (copper chloride supported on activated carbon) to obtain HCl, thereby preparing hydrochloric acid. The hydrochloric acid is used to back-extract rare earth ions to obtain a lanthanum chloride solution, which is then returned to step (1) and used as a reaction raw material.

[0052] (5) The CO2 gas released in step (2) is absorbed by the cathode product sodium hydroxide solution obtained by electrolysis to obtain sodium carbonate solution, which is then returned to step (1) and used as a reaction raw material.

[0053] Example 3

[0054] (1) A 2 mol / L sodium hydroxide solution was added to a lanthanum chloride solution while CO2 gas was introduced, and the reaction was carried out at 50 °C. The pH value at the end of the reaction was controlled to be 6.7, and a precipitate was obtained. The precipitate was filtered and washed to obtain a mixture of lanthanum carbonate and basic lanthanum carbonate (i.e., rare earth oxide precursor), sodium chloride filtrate, and washing solution.

[0055] (2) A mixture of lanthanum carbonate and basic lanthanum carbonate (i.e. rare earth oxide precursor) was calcined in a muffle furnace at 950°C for 4 hours to obtain lanthanum oxide (i.e. rare earth oxide) and release CO2 gas.

[0056] (3) The sodium chloride filtrate is purified (organic matter removed) and concentrated to obtain a saturated sodium chloride solution. The saturated sodium chloride solution is then subjected to a voltage of 2.5V and a current density of 220A / m². 2Electrolysis is performed at a temperature of 55℃, yielding chlorine and hydrogen as anolyte products at the anode and sodium hydroxide solution as cathode product at the cathode.

[0057] (4) Chlorine and hydrogen are reacted in the presence of a catalyst (copper chloride supported on activated carbon) to obtain HCl, thereby preparing hydrochloric acid. The hydrochloric acid is used to back-extract rare earth ions to obtain a lanthanum chloride solution, which is then returned to step (1) and used as a reaction raw material.

[0058] (5) The CO2 gas released in step (2) is absorbed by the cathode product sodium hydroxide solution obtained by electrolysis to obtain sodium carbonate solution, which is then returned to step (1) and used as a reaction raw material.

[0059] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A method for treating and recycling rare earth chlorides using an alkali metal precipitant, characterized in that, Includes the following steps: (1) The alkali metal precipitant solution is reacted with the rare earth chloride solution, and the pH value at the end of the reaction is controlled to obtain the precipitate. The precipitate is filtered and washed to obtain rare earth oxide precursor, filtrate and washing liquid; wherein, the alkali metal precipitant is an alkali metal carbonate; the alkali metal in the alkali metal precipitant is potassium or sodium; the pH value at the end of the reaction is 6.7 to 7.

2. (2) The rare earth oxide precursor is calcined to obtain rare earth oxides and release CO2 gas; (3) The filtrate from step (1) is purified and concentrated to obtain a saturated alkali metal chloride solution; the saturated alkali metal chloride solution is electrolyzed to obtain an alkali metal hydroxide solution, chlorine gas, and hydrogen gas; wherein, during electrolysis, the voltage is 1.8–3.6V and the current density is 190–250A / m 2 The temperature is 50–60℃. (4) Chlorine and hydrogen are reacted to obtain HCl, thereby preparing hydrochloric acid. The hydrochloric acid is used to back-extract rare earth ions to obtain rare earth chloride solution, which is returned to step (1) and used as a reaction raw material. The washing liquid in step (1) is used as the precipitation bottom liquid in step (1), for diluting alkali metal hydroxide in step (3), and / or for step (4) to absorb HCl and prepare hydrochloric acid. (5) The alkali metal hydroxide solution from step (3) is used to absorb the CO2 gas released in step (2) to obtain an alkali metal precipitant solution, which is then returned to step (1) and used as a reaction raw material. The absorption rate of CO2 gas is greater than 90%.

2. The method according to claim 1, characterized in that, In step (1), the reaction temperature is 10 to 100°C.

3. The method according to claim 1, characterized in that, In step (1), the rare earth oxide precursor is a rare earth carbonate.

4. The method according to claim 1, characterized in that, In step (4), the concentration of hydrochloric acid is 3 to 12 mol / L.

5. The method according to any one of claims 1 to 4, characterized in that, In step (5), the concentration of the obtained alkali metal precipitant solution is 1.5 to 3.3 mol / L.