Method for decomposing bastnaesite in short process

Abstract

The invention belongs to the field of rare earth metallurgy, and discloses a method for decomposing bastnaesite in a short process, which comprises the following steps: grinding the bastnaesite through a Raymond mill to obtain ground ore powder; oxidizing and roasting the ground ore powder to obtain oxidized and roasted ore; adding water into the oxidized roasted ore for size mixing, and carrying out first-time acid dissolution under low-temperature and low-acid conditions; carrying out heating and constant-temperature stirring reaction on the feed liquid after the first-time acid dissolution is completed, and carrying out second-time acid dissolution by utilizing residual acid of the feed liquid; after the reaction is completed, filtering feed liquid to obtain acid leaching liquid and acid leaching residues, washing the acid leaching residues with water to remove entrained rare earth, circulating part of washing water as size mixing water, and adding an alkaline precipitator into residual washing water to precipitate to obtain rare earth carbonate for neutralizing residual acid of the acid leaching liquid; and freezing and concentrating the acid leaching solution after neutralizing the residual acid, separating crystal from liquid to obtain high-concentration rare earth feed liquid, and separating ice crystals as an additive for maintaining low-temperature acid dissolution. According to the method, the decomposition process of bastnaesite is greatly shortened, washing water, rare earth and ice crystals are recycled in the whole process, and dual circulation of materials and energy is achieved.

Description

Technical Field

[0001] The invention belongs to the field of rare earth metallurgy and relates to a method for decomposing bastnaesite in a short process. Background Art

[0002] Fluorocarbon cerium ore is the main source of rare earth products in the world. Its raw ore grade is about 3%. After a series of mineral processing processes such as flotation, gravity separation and magnetic separation, a concentrate with a rare earth grade of 50%-70% can be obtained. According to different mineral processing methods, it can be divided into flotation concentrate and gravity separation concentrate. In addition to the differences in physical properties such as particle size and density, the main difference between the two is the main non-rare earth impurities they contain. However, both have the same rare earth mineral composition and distribution. Both concentrates can be used as raw materials for this method.

[0003] The smelting process for bastnaesite originated in the 1960s. Leaching techniques include oxidation roasting-hydrochloric acid leaching and combined acid-base leaching. Currently, the oxidation roasting-hydrochloric acid leaching process is the most mature in industrial application. This process first roasts bastnaesite concentrate at 500-600°C to produce a smelted ore. After the roasted ore is partially leached with hydrochloric acid, a large amount of high-value praseodymium and neodymium (Nd) remains in the acid leached residue due to the deposition of rare earth fluorides. Therefore, the smelting residue requires an alkaline conversion, water washing for fluoride removal, and hydrochloric acid leaching. These two acid leaching processes produce a cerium-low, lanthanum-rich rare earth solution with a Pr and Nd leaching rate exceeding 95% and a cerium-rich slag. However, this process is lengthy, requiring two acid leaching steps. Furthermore, the water washing and fluoride removal process after the alkaline conversion produces a large amount of fluoride-containing wastewater, which is detrimental to ecological protection.

[0004] CN100532595C provides a method for decomposing bastnaesite. Bastnaesite is mixed with rare earth carbonate and then roasted. The cerium in the rare earth carbonate solidifies the fluorine in the bastnaesite. Hydrochloric acid is then added for acid dissolution at room temperature to 80°C to produce a lanthanum-rich rare earth chloride with a very low fluorine content and a cerium-rich slag with a high cerium distribution. However, this technical solution requires the addition of cerium-containing rare earth carbonate to solidify the fluorine during the roasting process before meeting the conditions for direct acid dissolution with hydrochloric acid. Furthermore, the technical solution does not address the leaching effect of praseodymium and neodymium during the bastnaesite decomposition process, thus presenting certain limitations.

[0005] CN109266838A provides a method for treating fluorocarbon cerium ore and a mixed ore containing fluorocarbon cerium ore, the method comprising roasting fluorocarbon cerium ore to obtain a roasted product, leaching the roasted product with hydrochloric acid to obtain a leached product, performing solid-liquid separation on the leached product to obtain an leaching solution and a leaching residue; and performing selective precipitation treatment on the leaching solution to obtain a precipitate product, performing solid-liquid separation on the precipitate product to obtain a cerium fluoride precipitate and a low-cerium rare earth chloride solution; the reaction temperature of the selective precipitation treatment is higher than the reaction temperature of the hydrochloric acid leaching. The technical solution of this invention is to decompose fluorocarbon cerium ore by full leaching with hydrochloric acid and selective precipitation of the acid leaching solution, so as to obtain a low-fluorine content, low-cerium, lanthanum-rich rare earth feed solution and a high-purity cerium fluoride product. This makes it necessary not only to control the leaching environment at a relatively low temperature during the hydrochloric acid leaching process, but also to add an auxiliary agent and tetravalent cerium to form a coordination ion so that it is not reduced by chloride ions, so as to improve the leaching rate of cerium and the leaching rate of lanthanum-rich rare earth. However, the addition of additives will cause sulfate or nitrate residues to remain in the cerium-rich lanthanum rare earth feed solution, which cannot meet the impurity requirements of extraction and separation production and requires further impurity removal treatment. At the same time, the large-scale leaching of cerium in the hydrochloric acid leaching process requires more acid and higher acidity, and the leachate obtained by acid leaching separates cerium fluoride by selective precipitation, which will also lead to a decrease in the concentration of cerium-rich lanthanum rare earth. In summary, the cerium-rich lanthanum rare earth feed solution obtained by this process has problems such as the introduction of non-rare earth impurities by additives, excessive residual acid and low rare earth concentration, and cannot meet production requirements well.

[0006] Light rare earth elements are highly enriched in fluorocarbon cerium ore. The four rare earth elements of lanthanum, cerium, praseodymium and neodymium account for more than 98% of the rare earth distribution in fluorocarbon cerium ore. However, judging from the current rare earth market, the smelting and separation of lanthanum and cerium is still in a stage of cost inversion. Summary of the Invention

[0007] The purpose of the present invention is to develop a fluorocarbon cerium ore decomposition process with a shorter process, lower chemical reagent usage, and greater environmental protection. This process not only meets the requirements of a praseodymium-neodymium leaching rate greater than 95%, selective separation of cerium and lanthanum-rich materials during the decomposition process, and a cerium distribution greater than 90% in the cerium-rich slag, but also achieves a fluorine leaching rate of less than 10% during the decomposition and leaching of fluorocarbon cerium ore, significantly reducing the generation of fluorine-containing wastewater and the diffusion and migration of fluorine during the decomposition process. After freeze concentration, the rare earth liquid concentration can reach 200-300g / L and can be directly used for extraction and separation production. Wash water, rare earths, and ice crystals are all recycled throughout the entire process, achieving a dual recycling of materials and energy.

[0008] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions: A method for decomposing bastnaesite in a short process comprises the following steps: (1) The fluorocarbon cerium ore is ground by Raymond mill to obtain ground ore powder; (2) Oxidative roasting of ground ore powder to obtain oxidized roasted ore; (3) Add water to the oxidized roasted ore to prepare the slurry, and carry out the first acid dissolution under low temperature and low acid conditions; (4) After the first acid dissolution is completed, the feed liquid is heated and stirred at a constant temperature for reaction, and the residual acid in the feed liquid is used for the second acid dissolution; (5) After the reaction is completed, the feed liquid is filtered to obtain acid leaching liquid and acid leaching residue. The acid leaching residue is washed with water to remove the rare earths carried by it. Part of the washing water is recycled as slurry water. The remaining washing water is added with an alkaline precipitant to recover the rare earths. The recovered rare earths can be used to neutralize the residual acid in the acid leaching liquid. (6) After neutralizing the residual acid, the acid leaching liquid is freeze-concentrated and crystal-liquid separated to obtain a high-concentration rare earth liquid. The separated ice crystals are used as an additive to maintain low-temperature acid dissolution, thereby realizing energy recycling.

[0009] Preferably, the particle size of the ore powder after grinding by the Raymond mill is 13-125 μm, preferably 44-74 μm.

[0010] Preferably, the ground ore powder is roasted in normal air with oxygen, at a temperature of 480°C-600°C, preferably 500°C-550°C, for 1-4 hours, preferably 2-3 hours. After roasting, the rare earth distribution contains 90%-100% of the total cerium in the tetravalent cerium, preferably 94-98%.

[0011] Preferably, the oxidized roasted ore is slurried with water or recycled washing water, and the slurrying solid-liquid ratio is 1:1-1:5, preferably 1:1-1:3.

[0012] Preferably, after the oxidized roasted ore is slurried, hydrochloric acid is added for acid dissolution, the hydrochloric acid concentration is 1-6 mol / L, preferably 2-4 mol / L, the amount of hydrochloric acid added is 4.2-5.0 times, preferably 4.5-4.7 times, the molar amount of trivalent (lanthanum-rich rare earth) rare earth contained in the oxidized roasted ore, the acid dissolution temperature is -10-10°C, preferably -5-5°C, and the low-temperature acid dissolution process also includes recycling the acid leaching liquid to freeze the ice crystals separated from the concentrated crystal liquid to maintain the low temperature.

[0013] Preferably, the temperature after the first acid dissolution is raised to 30-60° C., preferably 40-50° C., and the constant temperature stirring time is 0.5-4 h, preferably 1-2.5 h.

[0014] Preferably, the slurry is filtered by conventional suction filtration, plate and frame filter press, or centrifugal separation. The acid leaching residue is washed with conventional stirring or leaching to discharge and recover the rare earth slurry entrained in the slag. To avoid hydrolysis and precipitation of rare earth slurry during the washing process, the washing frequency is 1-6 times, preferably 2-4 times. The first washing is performed with acid water prepared with hydrochloric acid having a pH of 1-3, preferably a pH of 1.5-2.5. Subsequent washing is performed with pure water. The solid-to-liquid ratio of each washing is 1:1-10, preferably 1:2-5. The washing is performed until the rare earth concentration in the washing water is less than 1g / L.

[0015] Preferably, the remaining wash water after recycling is added with an alkaline precipitant to recover rare earths, and the rare earth compounds obtained by precipitation are then added to the acid leaching solution to neutralize the residual acid. The alkaline precipitant includes one of ammonium bicarbonate, sodium bicarbonate, magnesium bicarbonate, liquid alkali or ammonia water.

[0016] Preferably, the freeze concentration temperature of the acid leaching liquid after neutralization of the residual acid is -20°C to -40°C, preferably -25°C to -30°C. The concentration of the rare earth liquid after freeze concentration can reach 200-300g / L, preferably 230-260g / L. The ice crystals obtained after crystal-liquid separation are returned to the acid-soluble liquid to control the acid leaching temperature.

[0017] The present invention uses fluorocarbon cerium ore powder ground to a certain particle size by a Raymond mill as raw material. After simple roasting and hydrochloric acid leaching, a low-cerium lanthanum-rich rare earth liquid with a praseodymium and neodymium leaching rate greater than 95% and a cerium-rich slag with a cerium distribution greater than 90% can be obtained. The residual acid in the low-cerium lanthanum-rich rare earth liquid can be controlled below 0.5 mol / L. The rare earth carbonate obtained by precipitation in the wash water can be adjusted to a pH value of 3.8-4.2 after neutralization. After freeze concentration, the rare earth liquid concentration can reach 200-300 g / L, which can meet the inlet tank requirements of extraction and separation. The wash water, rare earth and freeze-concentrated ice crystals are all comprehensively recovered throughout the entire process, realizing a dual cycle of materials and energy in the fluorocarbon cerium decomposition process. Compared with the existing industrially commonly used oxidative roasting-hydrochloric acid leaching process, the process is shorter, the amount of chemical reagents used is less, no secondary alkaline defluorination is required, and therefore no fluorine-containing wastewater is produced. It is an efficient and low-carbon fluorocarbon cerium decomposition process with good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0019] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific implementation methods.

[0020] A method for decomposing bastnaesite in a short process comprises the following steps: (1) The bastnaesite concentrate is ground by Raymond mill to obtain ground ore powder; (2) Oxidative roasting of ground ore powder to obtain oxidized roasted ore; (3) Add water to the oxidized roasted ore to prepare the slurry, and carry out the first acid dissolution under low temperature and low acid conditions; (4) After the first acid dissolution is completed, the feed liquid is heated and stirred at a constant temperature for reaction, and the residual acid in the feed liquid is used for the second acid dissolution; (5) After the reaction is completed, the feed liquid is filtered to obtain acid leaching liquid and acid leaching residue. The acid leaching residue is washed with water to remove the rare earths carried by it. Part of the washing water is recycled as slurry water. The remaining washing water is added with an alkaline precipitant to recover the rare earths. The recovered rare earths can be used to neutralize the residual acid in the acid leaching liquid. (6) After neutralizing the residual acid, the acid leaching liquid is freeze-concentrated and crystal-liquid separated to obtain a high-concentration rare earth liquid. The separated ice crystals are used as an additive to maintain low-temperature acid dissolution, thereby realizing energy recycling.

[0021] The following is a detailed description of a short-process method for decomposing bastnaesite provided by the present invention in conjunction with examples, but they should not be construed as limiting the scope of protection of the present invention.

[0022] Example 1: The composition analysis results of the fluorocarbon cerium ore gravity separation concentrate provided by a rare earth mine in Sichuan are shown in Tables 1 and 2.

[0023] Table 1 Main components of bastnaesite gravity concentrate (%) Table 2 Rare earth distribution of bastnaesite gravity concentrate (%) Fluorocarbon cerium ore gravity concentrate, the ore powder is ground and passed through a 200 mesh sieve (74μm). After screening, 100g of the ore powder is taken and roasted in an air atmosphere at 500℃ for 2h. The obtained oxidized roasted ore powder is slurried with water at a solid-liquid ratio of 1:1. At a water bath temperature of 10℃, 487ml of 2mol / L hydrochloric acid solution is added at 4.5 times the molar amount of trivalent rare earth in the ore powder using a peristaltic pump for the first acid dissolution. After the first acid dissolution is completed, the feed liquid is heated to 45℃ in a water bath and maintained at this temperature with stirring for 60min. The second acid dissolution is carried out using the residual acid in the feed liquid. After the reaction is completed, the acid leaching liquid and acid leaching residue are obtained by filtration. The acid leaching residue is first rinsed once with acid water prepared with hydrochloric acid at a pH of 1, and then rinsed twice with pure water. The solid-liquid ratio of each washing is 1:3. The washed cerium-rich slag is dried and sent for inspection. The acid leaching solution and the water-washed cerium-rich slag from the first and second acid dissolutions were sampled and tested. The test results of the acid leaching solution are shown in Table 3, and the test results of the water-washed cerium-rich slag are shown in Table 4.

[0024] Table 3 Acid leaching solution analysis results Table 4 Analysis results of water-washed cerium-rich slag Analysis of the acid leaching solution and the water-washed cerium-rich slag revealed that only a portion of the rare earth elements in the ore powder were dissolved under the first acid dissolution conditions, with a relatively high concentration of residual acid remaining. At this point, the rare earth distribution in the acid leaching solution was similar to that of the original ore, and rare earth dissolution did not exhibit significant selectivity. The second acid dissolution using the residual acid after heating significantly reduced the total rare earth content (REO) and cerium distribution in the acid leaching solution, while the cerium distribution in the water-washed cerium-rich slag reached 95.5%, significantly higher than the first acid dissolution sampling, demonstrating good dissolution selectivity. Ultimately, a cerium-poor, lanthanum-rich rare earth feed solution with a praseodymium-neodymium leaching rate exceeding 95% and a cerium-rich slag with a cerium distribution exceeding 90% were obtained, achieving efficient leaching of valuable praseodymium and neodymium from bastnaesite and pre-separation of lanthanum-rich rare earth elements from cerium.

[0025] Ammonium bicarbonate is added to the acid leaching residue washing water to precipitate rare earth carbonate, which is added to the cerium-poor lanthanum-rich rare earth solution to adjust the pH value to 4.0, and freeze-concentrated at -24°C. After separating the ice crystals, a high-concentration rare earth solution with a rare earth concentration of 200 g / L is obtained.

[0026] Comparative Example 1: 100g of the same fluorocarbon cerium ore gravity concentrate as in Example 1 was roasted in an air atmosphere at 500°C for 2h. The resulting oxidative roasted ore powder was slurried with water at a solid-liquid ratio of 1:2, and 10mol / L concentrated hydrochloric acid was slowly added in a water bath at 60°C for leaching. The leaching end point was the pH of the leaching solution = 0.5. After the leaching was completed, the liquid was filtered, the leaching residue was washed with water three times, and the leaching residue after water washing was added with liquid alkali and subjected to alkaline conversion reaction at 95°C in a water bath for about 4h, filtered, and the alkali conversion residue was washed with water several times until the pH of the washing water was below 9, filtered, and the filter residue was slurried with water at a solid-liquid ratio of 1:2. Concentrated hydrochloric acid with a mass concentration of 31% (about 10mol / L) was slowly added and dissolved in a water bath at 60°C. After dissolution, it was filtered, and the soluble residue was washed with water several times until no rare earth was detected in the washing water. The obtained washed cerium-rich slag was dried and sent for inspection. The test results are shown in Table 5.

[0027] Table 5 Analysis results of water-washed cerium-rich slag in Comparative Example 1 By comparing the analysis results of the water-washed cerium-rich slag in Comparative Example 1 and Example 1, it can be found that although the process flows are different, both can meet the requirements of a praseodymium-neodymium leaching rate greater than 95% and a cerium distribution greater than 90% in the cerium-rich slag. In comparison, the present method does not require alkali conversion and secondary hydrochloric acid dissolution, shortens the process flow, and significantly reduces the amount of chemical reagents and fluorine leaching, thereby avoiding the generation of fluorine-containing wastewater. The technical improvement advantages are significant.

[0028] Example 2: The composition analysis results of the fluorocarbon cerium ore flotation concentrate provided by a rare earth mine in Sichuan are shown in Tables 6 and 7.

[0029] Table 6 Main components of bastnaesite flotation concentrate (%) Table 7 Rare earth distribution of bastnaesite flotation concentrate (%) Bastnaesite flotation concentrate was ground and passed through a 325-mesh sieve (44 μm). 100 g of the sieved ore was calcined in air at 520°C for 2 h. The resulting oxidatively roasted ore was slurried with the wash water from Example 1 at a solid-to-liquid ratio of 1:1. The slurry was then acid-dissolved using 327 ml of a 3 mol / L hydrochloric acid solution (4.6 times the molar amount of the trivalent rare earth element in the ore) in a water bath at 5°C using a peristaltic pump. After the first acid dissolution, the solution was heated to 50°C in a water bath and maintained at that temperature with stirring for 60 min. A second acid dissolution was then performed using the residual acid in the solution. After the reaction, the solution was filtered to obtain an acid leaching solution and an acid leaching residue. The acid leaching residue was rinsed once with acid water prepared with hydrochloric acid at a pH of 1 and then twice with pure water, with a solid-to-liquid ratio of 1:3 for each wash. The washed cerium-rich slag was dried and submitted for testing. The test results of the acid leaching solution are shown in Table 8, and the test results of the washed cerium-rich slag are shown in Table 9.

[0030] Table 8 Acid leaching solution analysis results Table 9 Analysis results of water-washed cerium-rich slag Sodium bicarbonate is added to the acid leaching residue washing water to precipitate rare earth carbonate, which is added to the cerium-poor lanthanum-rich rare earth solution to adjust the pH value to 4.2, and freeze-concentrated at -28°C. After separating the ice crystals, a high-concentration rare earth solution with a rare earth concentration of 250 g / L is obtained.

Claims

1. A method for decomposing bastnaesite in a short process, characterized in that: The following steps are involved: (1) The fluorocarbon cerium ore is ground by Raymond mill to obtain ground ore powder; (2) Oxidative roasting of ground ore powder to obtain oxidized roasted ore; (3) Add water to the oxidized roasted ore to prepare the slurry, and then add hydrochloric acid to carry out the first acid dissolution under low temperature and low acid conditions, wherein the concentration of hydrochloric acid is 1-6 mol / L, the amount of hydrochloric acid added is 4.2-5.0 times the molar amount of trivalent rare earth contained in the oxidized roasted ore, and the acid dissolution temperature is -10-10°C; (4) After the first acid dissolution is completed, the feed solution is heated and stirred at a constant temperature for reaction, and the residual acid in the feed solution is used for the second acid dissolution; (5) After the reaction is completed, the feed liquid is filtered to obtain acid leaching liquid and acid leaching residue. The acid leaching residue is washed with water to remove the rare earths carried by it. Part of the washing water is recycled as slurry water. The remaining washing water is added with an alkaline precipitant to recover the rare earths. The recovered rare earths are used to neutralize the residual acid in the acid leaching liquid. (6) After neutralizing the residual acid, the acid leaching liquid is freeze-concentrated and crystal-liquid separated to obtain a high-concentration rare earth liquid of 200-300 g / L. The separated ice crystals are used as an additive to maintain low-temperature acid dissolution. The freeze-concentration temperature is -20°C to -40°C.

2. The method according to claim 1, characterized in that The bastnaesite includes one or both of gravity concentrate and flotation concentrate obtained in a beneficiation process.

3. The method according to claim 1, characterized in that The particle size of the ground mineral powder after being ground by the Raymond mill is 13-125 μm.

4. The method according to claim 1, wherein The oxidative roasting of the ground ore powder is oxygen roasting in a normal air atmosphere, with a roasting temperature of 480° C.-600° C. and a roasting time of 1-4 hours. After roasting, the proportion of tetravalent cerium in the total cerium in the rare earth distribution is 90%-100%.

5. The method according to claim 1, wherein Add water to the oxidized roasted ore or reuse the washing water to prepare the slurry, and the solid-liquid ratio of the slurry is 1:1-1:

5.

6. The method according to claim 1, characterized in that The temperature after the first acid dissolution is raised to 30-60° C., and the constant temperature stirring time of the second acid dissolution after the temperature is raised is 0.5-4 h.

7. The method according to claim 1, characterized in that The slurry is filtered by conventional suction filtration, plate and frame filter press or centrifugal separation, and the acid leaching residue is washed by conventional stirring washing or leaching. The number of washings is 1-6 times. The first washing is acid water prepared with hydrochloric acid with a pH value of 1-3, and then pure water is used for washing. The solid-liquid ratio of a single washing is 1:1-10, and the washing is carried out until the rare earth concentration in the washing water is less than 1g / L.

8. The method according to claim 1, characterized in that The alkaline precipitant includes one or more of ammonium bicarbonate, sodium bicarbonate, magnesium bicarbonate, liquid alkali or ammonia water.

Images