Method for roasting bastnaesite to remove fluorine and extracting rare earth through acid leaching

Abstract

The invention belongs to the technical field of rare earth metallurgy, and particularly relates to a method for extracting rare earth through bastnaesite roasting fluorine removal and acid leaching. According to the method provided by the invention, the bastnaesite concentrate, the fluorine removal additive and the pure water are mixed and subjected to wet grinding, and then drying and roasting are performed, so that more than 98% of fluorine in the bastnaesite is removed, and the bastnaesite is converted into hydrofluoric acid to be recycled. The bastnaesite subjected to fluorine removal treatment is subjected to acid leaching treatment, rare earth feed liquid can be obtained, and the rare earth leaching rate exceeds 99%. According to the method provided by the invention, separation and recovery of rare earth and fluorine in bastnaesite can be realized through ball milling and roasting by utilizing the fluorine removal aid, and the process is simple, efficient and easy to industrialize.

Description

Technical Field

[0001] The invention belongs to the technical field of rare earth smelting, and particularly relates to a method for extracting rare earths by roasting and removing fluorine from bastnaesite and then acid leaching. Background Art

[0002] Currently, China's rare earth mineral resources primarily consist of ionic rare earth ores in the south, mixed ores in the north, and bastnaesite in Sichuan and Shandong. Bastnaesite has a relatively simple mineral composition, often accompanied by quartz, fluorite, barite, and calcite. Sichuan bastnaesite is beneficiated to produce bastnaesite concentrate, which has a rare earth content (as RE₂O₃) of 50% to 70%.

[0003] Current bastnaesite smelting processes include oxidative roasting followed by hydrochloric acid leaching. After roasting, RE(CO3)F is oxidized to RE2O3 and REOF, while Ce(III) is oxidized to Ce(IV). Hydrochloric acid leaching produces cerium-rich slag and cerium-poor rare earth chloride. This process consumes large amounts of acid and alkali, produces large amounts of high-salt wastewater, and has a low overall rare earth yield. Another alternative is oxidative roasting followed by sulfuric acid leaching followed by extraction and separation. This process uses sulfuric acid to dissolve rare earth oxides, rare earth oxyfluorides, fluorides, and tetravalent cerium, and then extracts the cerium from non-cerium components. However, the extraction process in this process is susceptible to emulsification due to the influence of fluorine. Patent CN117305630A discloses a method using secondary sulfuric acid leaching, adding calcium chloride to convert rare earth chloride and calcium sulfate, followed by hydrogen peroxide to reduce Ce(IV) to Ce(III) and fluoride ions to form cerium fluoride. This method achieves a rare earth yield of 93.15%. Invention patent CN112074617B discloses a method for adding carbon powder during the roasting process of bastnaesite to prevent the oxidation of trivalent cerium, achieving a rare earth leaching rate of 98.3% and a Ce oxidation rate of 0.1%. Invention patent CN109517974A discloses a method for introducing water vapor during high-temperature roasting to remove fluorine from bastnaesite in the form of hydrofluoric acid, resulting in a rare earth leaching rate of 92.89% through acid leaching of the roasted slag. Invention patent CN113667841A discloses a method for separating rare earths and fluorine by dissolving REOF through roasting, acid leaching, aluminum ion complexation, and tempering of bastnaesite, achieving a total rare earth yield of 98.5%.

[0004] Another alkaline smelting process involves roasting bastnaesite with sodium hydroxide, washing with water to remove soluble fluorides, and then leaching with hydrochloric acid to produce a rare earth chloride solution. However, the high acidity of the leachate makes the large-scale use of acid and alkali expensive and introduces sodium ions as impurities. Patent CN113621809B discloses a method that involves acid leaching bastnaesite with NdFeB waste, converting the insoluble leached residue (REOF) with sodium hydroxide, and then performing a secondary acid leaching. This method achieves a rare earth yield of 96.8%. Summary of the Invention

[0005] From the above, it can be seen that the fluorine in bastnaesite affects the design of various processes and consistently impacts the quality of rare earth products during production. The variable valence of cerium results in a low overall rare earth leaching rate. The present invention provides a method for bastnaesite roasting, defluorination, and acid leaching to extract rare earths. The bastnaesite concentrate is wet-milled with a defluorination agent and then roasted at 700°C to 1200°C. During roasting, 98% of the fluorine in the bastnaesite is removed in the form of hydrogen fluoride, which is then absorbed into an aqueous solution to form hydrofluoric acid, achieving separation of rare earths and fluorine. During roasting, RECO₃F is converted into RE₂O₃, REFeO₃, and other substances. The defluorinated bastnaesite is then acid-leached to produce a rare earth solution with a rare earth leaching rate exceeding 99%. This method achieves efficient bastnaesite defluorination and rare earth extraction in a short process, reducing production costs.

[0006] The present invention proposes a method for extracting rare earths by roasting bastnaesite to remove fluorine and then acid leaching, comprising the following steps: Step 1: mixing fluorocarbon cerium concentrate, a defluorination agent, and pure water in a certain proportion, placing the mixture in a ball mill, filtering the milled slurry to obtain a filtrate and a ball-milled ore, drying the ball-milled ore to obtain a dry ball-milled ore, and returning the filtrate to the ball milling process for recycling, wherein the defluorination agent includes a single substance or an oxide of iron, and a single substance or an oxide of one or more of silicon, aluminum, calcium, magnesium, and manganese; Step 2: The dry ball-milled ore obtained in step 1 is spread flat on a boat, placed in a tube furnace, and calcined at high temperature. Air is introduced into one end of the tube furnace, and an aqueous solution for absorbing fluorine-containing gas is connected to the other end. After the reaction, defluorinated bastnaesite and hydrofluoric acid solution are obtained; Step 3: After the fluorine is removed from the bastnaesite in step 2, the fluorine is leached with acid to obtain a rare earth-containing liquid.

[0007] Preferably, the fluorocarbon cerium concentrate comprises one or a mixture of gravity concentrate and flotation concentrate in any proportion, with a fluorine content of 0.1% to 15% and a rare earth content REO ≥ 50%.

[0008] Preferably, the weight ratio of fluorocarbon cerium concentrate to the defluorination auxiliary agent is (1-9):1.

[0009] Preferably, the ball milling is wet milling using a planetary ball mill, with a liquid-to-solid ratio of (1-5):1, a ball milling speed of 100 r / min-500 r / min, and a ball milling time of 60 min-180 min.

[0010] Preferably, the temperature for drying the ball-milled ore is 100° C. to 120° C., and the drying time is 180 min to 480 min.

[0011] Preferably, the calcination reaction temperature of bastnaesite is 700° C. to 1200° C., and the calcination reaction time is 60 min to 360 min.

[0012] Preferably, the flow rate of the incoming air is 0.1 L / min to 5 L / min.

[0013] Preferably, in the acid leaching process, the solid-liquid ratio of the defluorinated bastnaesite to the acid leaching solution is 1:(1-20), and the acid leaching solution is one or more of hydrochloric acid, sulfuric acid, and nitric acid, with an acid concentration of 2 mol / L-12 mol / L.

[0014] Preferably, the acid leaching temperature is 50° C. to 180° C., the acid leaching time is 60 min to 360 min, and the stirring speed is 100 r / min to 400 r / min.

[0015] Preferably, the rare earth concentration in the rare earth-containing solution is 20 g / L to 200 g / L.

[0016] The beneficial effects achieved by the present invention are as follows: (1) The fluorocarbon cerium concentrate of the present invention is mixed with a fluorine removal auxiliary agent and subjected to high-temperature roasting. More than 98% of the fluorine in the fluorocarbon cerium concentrate is removed and can be recovered through an aqueous solution, thereby achieving the separation of rare earth and fluorine in the fluorocarbon cerium concentrate. The process is simple and easy to operate. Compared with the conventional method of adding acid, alkali, and salt combined with high-temperature roasting to recover rare earth molten salt slag rare earth, the present invention significantly reduces the material input cost. (2) The present invention achieves efficient extraction of rare earth from the fluorocarbon cerium concentrate, with a total rare earth leaching rate of more than 99%, and fluorine can be recycled as a resource. The process of the present invention is green, efficient, and has a short process flow, and does not produce fluorine-containing wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The present invention is a process flow chart of a method for extracting rare earths by roasting bastnaesite to remove fluorine and then acid leaching. DETAILED DESCRIPTION

[0018] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0019] Example 1 S1. Take 100g of fluorocarbon cerium concentrate with a REO content of 57.06% and a fluorine content of 9.78%, add 15g of defluorination agent A with a Fe content of 69.8%, take 115ml of pure water and place them together in a planetary ball mill. Set the ball mill speed to 200r / min and the ball milling time to 3h. Filter to obtain the filtrate and ball-milled ore. Dry the ball-milled ore in an oven at 105℃ for 360min. After drying, 114g of ball-milled ore is obtained, and the filtrate is returned to the next ball milling for continued use.

[0020] S2. Take 50 g of the dried ball-milled ore described in S1 and spread it flat on a boat and place it in a tube furnace and roast it at 1000°C for 3 h with an air flow rate of 0.1 L / min. After roasting, the mass of the ball-milled ore is 42.2 g, the rare earth content is 58.82%, the fluorine content is 2.74%, and the fluorine removal rate is 72.82%.

[0021] Example 2 S1. Take 50g of fluorocarbon cerium concentrate with an REO content of 57.8% and a fluorine content of 5.71%. Take 50g of defluorination agent B, which has an Fe content of 45%, a Si content of 5%, an Al content of 5%, a Mg content of 2%, and a Mn content of 0.5%. Add 100ml of pure water and place them together in a planetary ball mill. Set the ball mill speed to 200r / min and mill for 3h. Filter to obtain the filtrate and ball-milled ore. Place the ball-milled ore in an oven at 105°C for 360min to dry. After drying, the ball-milled ore reaches 99.4g. The filtrate is returned to the next ball mill for further use.

[0022] S2. Take 50 g of the dried ball-milled ore described in S1, spread it flat on a boat and place it in a tube furnace and roast it at 1000°C for 3 h with an air flow rate of 0.1 L / min. After roasting, the mass of the ball-milled ore is 46.6 g, the rare earth content is 45.06%, the fluorine content is 0.038%, and the fluorine removal rate is 98.75%.

[0023] S3. Weigh 10 g of the calcined, ball-milled ore obtained in S2 and add 5.85 mol / L hydrochloric acid solution for acid leaching. The solid-to-liquid ratio of the calcined ore to the hydrochloric acid solution is 1:5. The reaction temperature is 120°C, the reaction time is 3 h, and the stirring speed is 200 r / min. After the reaction, filter to obtain the leachate and acid leaching residue. The acid leaching residue is 1.2 g, with a rare earth content of 2.38% and a rare earth leaching rate of 99.36%. The rare earth concentration of the acid leaching liquid is 22.3 g / L.

[0024] Example 3 S1. Take 80g of fluorocarbon cerium concentrate with an REO content of 55.74% and a fluorine content of 5.5%. Take 20g of defluorination agent C with an Fe content of 59%, a Si content of 2%, an Al content of 3.5%, a Ca content of 0.5%, and a Mn content of 0.5%. Add 100ml of pure water and place them together in a planetary ball mill. Set the ball mill speed to 200r / min and the ball milling time to 3h. Filter to obtain the filtrate and ball milled ore. Place the ball milled ore in an oven at 105°C for 360min to dry. After drying, the ball milled ore reaches 99.3g. The filtrate is returned to the next ball milling for further use.

[0025] S2. Take 50 g of the dried ball-milled ore described in S1 and spread it flat on a boat and place it in a tube furnace and calcine it at 1000° C. for 3 h with an air flow rate of 0.1 L / min. After calcination, the mass of the mixed fluorocarbon cerium ore is 42.0 g, the rare earth content is 53.54%, the fluorine content is 0.084%, and the fluorine removal rate is 98.40%.

[0026] S3. Weigh 10 g of the roasted mixed bastnaesite obtained in S2 and add 6 mol / L hydrochloric acid solution for acid leaching. The solid-to-liquid ratio of the roasted ore to the hydrochloric acid solution is 1:5. The reaction temperature is 120°C, the reaction time is 3 h, and the stirring speed is 200 r / min. After the reaction, filter to obtain a leachate and acid leaching residue. The acid leaching residue is 1.3 g, with a rare earth content of 2.4% and a rare earth leaching rate of 99.42%. The rare earth concentration of the acid leaching liquid is 100.71 g / L.

[0027] Comparative Example 1 S1. Take 100g of fluorocarbon cerium concentrate with an REO content of 57.06% and a fluorine content of 9.78%. Add 100ml of pure water and place them together in a planetary ball mill. Set the ball mill speed to 200r / min and the ball milling time to 3h. Filter to obtain the filtrate and ball milled ore. Place the ball milled ore in an oven at 105℃ for 360min to dry. After drying, the ball milled ore is 99.2g. The filtrate is returned to the next ball milling for further use.

[0028] S2. Take 50 g of the dried ball-milled ore described in S1 and spread it flat on a boat and place it in a tube furnace and roast it at 1000°C for 3 h with an air flow rate of 0.1 L / min. After roasting, the mass of the ball-milled ore is 40.33 g, the rare earth content is 70.55%, the fluorine content is 7.2%, and the fluorine removal rate is 40.62%.

[0029] Comparative Example 2 S1. Take 50g of fluorocarbon cerium concentrate with an REO content of 57.8% and a fluorine content of 5.71%. Take 50g of defluorination agent D with a Si content of 15%, an Al content of 25%, a Mg content of 12%, and a Mn content of 5.5%. Add 100ml of pure water and place them together in a planetary ball mill. Set the ball mill speed to 200r / min and mill for 3h. Filter to obtain the filtrate and ball-milled ore. Dry the ball-milled ore in an oven at 105°C for 360min. After drying, the ball-milled ore reaches 99.3g. The filtrate is returned to the next ball mill for further use.

[0030] S2. Take 50 g of the dried ball-milled ore described in S1, spread it flat on a boat and place it in a tube furnace and roast it at 1000°C for 3 h with an air flow rate of 0.1 L / min. After roasting, the mass of the ball-milled ore is 46.9 g, the rare earth content is 30.81%, the fluorine content is 0.84%, and the fluorine removal rate is 72.4%.

[0031] Comparative Example 3 S1. Take 80g of fluorocarbon cerium concentrate with an REO content of 55.74% and a fluorine content of 5.5%. Take 20g of defluorination agent E with a Si content of 22%, an Al content of 25%, a Ca content of 15%, and a Mn content of 7.5%. Add 100ml of pure water and place them together in a planetary ball mill. Set the ball mill speed to 200r / min and the ball milling time to 3h. Filter to obtain the filtrate and ball milled ore. Place the ball milled ore in an oven at 105°C for 360min to dry. After drying, the ball milled ore reaches 99.1g. The filtrate is returned to the next ball milling for further use.

[0032] S2. Take 50 g of the dried ball-milled ore described in S1 and spread it flat on a boat and place it in a tube furnace and roast it at 1000°C for 3 h with an air flow rate of 0.1 L / min. After roasting, the mass of the mixed fluorocarbon cerium ore is 42.6 g, the rare earth content is 52.33%, the fluorine content is 1.26%, and the fluorine removal rate is 79.21%.

[0033] It can be seen from Examples 1-3 and Comparative Examples 1-3 that the fluorine removal rate of fluorocarbon cerium concentrate by roasting is only 40.62%. When the iron-containing defluorination agent A is added, the fluorine removal rate of fluorocarbon cerium concentrate by roasting is 72.82%. When the silicon, aluminum, magnesium, and manganese-containing defluorination agent D is added, the fluorine removal rate of fluorocarbon cerium concentrate by roasting is 72.4%. When the silicon, aluminum, calcium, and manganese-containing defluorination agent E is added, the fluorine removal rate of fluorocarbon cerium concentrate by roasting is 79.21%. It can be seen from Examples 2 and 3 that by optimizing the ratio of each element in the defluorination agent, the roasting of fluorocarbon cerium concentrate can achieve a fluorine removal rate of more than 98%. Moreover, after defluorination, the fluorocarbon cerium ore can achieve a rare earth leaching rate of more than 99% by acid leaching.

[0034] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for extracting rare earths by roasting and removing fluorine from bastnaesite and then acid leaching, characterized in that: include: Step 1: mixing fluorocarbon cerium concentrate, a defluorination agent, and pure water in a certain proportion, placing the mixture in a ball mill, filtering the milled slurry to obtain a filtrate and a ball-milled ore, drying the ball-milled ore to obtain a dry ball-milled ore, and returning the filtrate to the ball milling process for recycling, wherein the defluorination agent includes a single substance or an oxide of iron, and a single substance or an oxide of one or more of silicon, aluminum, calcium, magnesium, and manganese; Step 2: The dry ball-milled ore obtained in step 1 is spread flat on a boat, placed in a tube furnace, and calcined at high temperature. Air is introduced into one end of the tube furnace, and an aqueous solution for absorbing fluorine-containing gas is connected to the other end. After the reaction, defluorinated bastnaesite and hydrofluoric acid solution are obtained; Step 3: After the fluorine is removed from the bastnaesite in step 2, the fluorine is leached with acid to obtain a rare earth-containing liquid.

2. The method for extracting rare earths by roasting and removing fluorine from bastnaesite and acid leaching according to claim 1, characterized in that: The fluorocarbon cerium concentrate comprises one or a mixture of any proportion of gravity separation concentrate and flotation concentrate, with a fluorine content of 0.1% to 15% and a rare earth content REO ≥ 50%.

3. The method for extracting rare earths by roasting and removing fluorine from bastnaesite and acid leaching according to claim 1, characterized in that: The weight ratio of fluorocarbon cerium concentrate and defluorination auxiliary agent is (1-9):

1.

4. The method for extracting rare earths by roasting and removing fluorine from bastnaesite and acid leaching according to claim 1, characterized in that: Ball milling is wet milling using a planetary ball mill, with a liquid-solid ratio of (1-5):1, a ball milling speed of 100 r / min-500 r / min, and a ball milling time of 60 min-180 min.

5. The method for extracting rare earths by roasting and removing fluorine from bastnaesite and acid leaching according to claim 1, characterized in that: The drying temperature of ball milled ore is 100℃~120℃; the drying time is 180min~480min.

6. The method for extracting rare earths by roasting and removing fluorine from bastnaesite and acid leaching according to claim 1, characterized in that: The calcination reaction temperature of fluorocarbon cerium ore is 700° C. to 1200° C., and the calcination reaction time is 60 min to 360 min.

7. The method for extracting rare earths by roasting and removing fluorine from bastnaesite and acid leaching according to claim 1, characterized in that: The flow rate of air entering is 0.1L / min~5L / min.

8. The method for extracting rare earths by roasting and removing fluorine from bastnaesite and acid leaching according to claim 1, characterized in that: In the acid leaching process, the solid-liquid ratio of the defluorinated bastnaesite to the acid leaching solution is 1:(1-20), and the acid leaching solution is one or more of hydrochloric acid, sulfuric acid, and nitric acid, with an acid concentration of 2mol / L-12mol / L.

9. The method for extracting rare earths by roasting and removing fluorine from bastnaesite and acid leaching according to claim 1, characterized in that: The acid leaching temperature is 50° C. to 180° C., the acid leaching time is 60 min to 360 min, and the stirring speed is 100 r / min to 400 r / min.

10. The method for extracting rare earths by roasting and removing fluorine from bastnaesite and acid leaching according to claim 1, characterized in that: The rare earth concentration in the rare earth-containing liquid is 20g / L to 200g / L.

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