A combined smelting and separation process for rare earth concentrate

Abstract

The smelting and separation process for rare earth concentrates described in this invention employs an atmosphere roasting-hydrochloric acid leaching-sulfuric acid roasting method to treat rare earth concentrates containing bastnaesite. During the hydrochloric acid leaching process, a low-concentration hydrochloric acid step-by-step acid leaching method is used to obtain a high-concentration rare earth solution (150-250 g / L REO), resulting in a Ce leaching rate of over 60%. Furthermore, aging reduces the fluorine content of the leaching solution. ‑ The rare earth content is further recovered by roasting the leaching residue with sulfuric acid and then leaching it with water, achieving a total rare earth recovery rate of over 95%. The entire process has a wider range of industrial applicability and can comprehensively process a variety of complex rare earth minerals, realizing the green, environmentally friendly, efficient and clean production of mineral-type rare earth concentrates.

Description

[0001] This application is based on and claims priority to Chinese Patent Application No. CN201810912079.3, filed on August 10, 2018, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention belongs to the field of rare earth smelting and separation technology, specifically relating to a combined process for processing rare earth concentrates, applicable to one or more mixed rare earth minerals such as bastnaesite, bastnaesite and monazite, xenotime, and apatite. Background Technology

[0003] my country's rare earth resources are mainly mineral-type light rare earth minerals, accounting for more than 90% of the total reserves. The main industrial rare earth minerals are bastnaesite and monazite, with light rare earth content as high as 96%-98%. According to statistics, the light rare earth deposits with industrial application value are mainly the Bayan Obo rare earth mine in Baotou, the Mianning rare earth mine in Panzhihua, Sichuan, and the Weishan rare earth mine in Shandong.

[0004] Currently, approximately 90% of the mixed rare earth ore in Baotou is smelted using the third-generation sulfuric acid process patented technology developed by the China Academy of Petroleum & Chemical Research (CAMP). This process involves intensified roasting and decomposition with concentrated sulfuric acid, followed by water leaching, neutralization and impurity removal, ammonium bicarbonate precipitation followed by hydrochloric acid dissolution, or extraction and separation using P507 and P204. This process offers advantages such as simplicity, controllability, ease of continuous large-scale production, and high rare earth recovery rates. Furthermore, it has low requirements for concentrate grade and relatively low operating costs. However, the sulfuric acid-intensified roasting process generates complex tail gases containing sulfur and fluorine, which are difficult to recover and treat, require significant equipment investment, and thus increase overall operating costs.

[0005] Fluorocarbon cerium ore is generally treated using an oxidative roasting-hydrochloric acid leaching chemical process. The concentrate is decomposed by oxidative roasting to produce rare earth oxides, rare earth fluorides, or rare earth fluorides that are soluble in hydrochloric acid. Cerium is oxidized to tetravalent ions. During the hydrochloric acid leaching process, trivalent rare earths are leached to obtain cerium chloride rare earths. Cerium, along with some trivalent rare earths, fluorine, and thorium, remain in the slag. After alkaline defluorination, the resulting cerium-rich slag can be used to produce ferrosilicon alloys or to produce cerium oxide with a purity of about 98% through reduction leaching. The cerium chloride rare earths are then separated into single rare earths using P507 extractant. The advantages of this process are low investment and low production cost, but its disadvantages are that the process is discontinuous. During the hydrochloric acid leaching process, cerium, thorium, and fluorine do not dissolve and remain in the slag. After the slag is converted by alkali, fluorine will enter the wastewater in the form of sodium fluoride, while thorium and fluorine will be dispersed in the slag and wastewater and are difficult to recover and reuse. As a result, the entire process not only pollutes the environment, but also the purity of the recovered cerium product is only about 98%, which has low utilization value.

[0006] In recent years, with the gradual improvement of domestic environmental protection regulations, the emission standards for pollutants from the rare earth industry have become increasingly stringent across the country. On January 24, 2011, the Ministry of Environmental Protection issued the world's first "Emission Standard for Pollutants from Rare Earth Industry" (GB26451-2011), which clearly stipulated the emission limits, monitoring, and control of water and air pollutants from existing and newly built rare earth industrial enterprises' production facilities. On May 10, 2011, the State Council issued the "Opinions on Promoting the Sustainable and Healthy Development of the Rare Earth Industry (Guofa

[2011] No. 12)". The new Environmental Protection Law, implemented on January 1, 2015, clearly stipulates the implementation of a total emission control system for key pollutants in key industries. In October 2016, the Ministry of Industry and Information Technology issued the "Rare Earth Industry Development Plan (2016-2020)," which clearly stipulated the production and green development indicators for the rare earth industry during the "13th Five-Year Plan" period. These national policies are of great strategic significance for pollution prevention and control in rare earth production, and the rare earth industry urgently needs new green and environmentally friendly smelting and separation technologies. Summary of the Invention

[0007] To address the problems of low Ce content in hydrochloric acid leaching solutions, low purity of cerium oxide products recovered from cerium-rich slag in existing fluorocarbon cerium ore processing technologies, and high fluorine content, high sulfuric acid emissions, high processing and recovery costs, and low rare earth leaching solution concentrations in mixed concentrate processing technologies, this invention provides a combined smelting and separation process for rare earth concentrates, comprising the following steps:

[0008] (1) Roasting and decomposing rare earth concentrate under a certain roasting atmosphere to obtain roasted ore;

[0009] (2) Add hydrochloric acid to the obtained roasted ore to leach rare earth, and collect the rare earth leachate and leaching residue separately after solid-liquid separation;

[0010] (3) After dehydrating the obtained leaching residue, concentrated sulfuric acid is added for roasting. The roasted product is collected, and after water leaching, neutralization and impurity removal, a rare earth sulfuric acid solution is obtained.

[0011] Preferably, the rare earth concentrate of the present invention includes, but is not limited to, bastnaesite or a mixture of bastnaesite and one or two of monazite or xenotime.

[0012] In step (1), the roasting atmosphere of the roasting step includes water vapor or a weak oxidizing atmosphere; the weak oxidizing atmosphere includes, but is not limited to, one or more of N2, CO, CO2, air, and inert gases, wherein the oxygen content can be reduced by controlling the gas flow rate; the purpose of the water vapor atmosphere is to remove fluorine and obtain pure HF as a recovery product; the purpose of the weak oxidizing atmosphere is to reduce the oxidation rate of cerium and increase the rare earth leaching yield.

[0013] In step (1), the HF gas obtained after defluorination is adsorbed and recovered using rare earth oxides or rare earth hydrated oxides to obtain rare earth fluoride products. The principle is that rare earth oxides form polynuclear hydroxyl compounds in water, causing the OH groups on them to... - It achieves a dual defluorination effect through ion exchange with fluoride ions. Through adsorption and recovery, the HF generated during the defluorination roasting and decomposition process of rare earth concentrate is effectively recovered, yielding fluorinated rare earth products, and the exhaust gas meets emission standards, resulting in significant environmental benefits.

[0014] In step (1), the roasting temperature is 350-650℃, preferably 400-600℃. Within a certain range, increasing the roasting temperature can improve the rare earth leaching rate. The roasting time is 0.5-6h. Within a certain range, extending the roasting time can improve the rare earth leaching rate.

[0015] In the process of this invention, the roasting process of the rare earth concentrate is mainly the decomposition of RECO3F in the concentrate, with the reaction formula: REFCO3=REOF(CeOF)+CO2↑. Under the presence of water vapor, a defluorination process occurs, with the reaction formula: REOF+H2O=RE2O3+HF↑. The released HF gas is used to recover fluorine through adsorbents such as rare earth oxides, with the reaction formula: 6HF↑+RE2O3=2REF3+3H2O.

[0016] In step (2), the concentration of hydrochloric acid is 3-10 mol / L, preferably 4-7 mol / L, and the ratio of hydrochloric acid to roasted concentrate is 0.4-2.0 mol hydrochloric acid / 100g rare earth concentrate, preferably 0.7-1.5 mol hydrochloric acid / 100g rare earth concentrate.

[0017] In step (2), the hydrochloric acid leaching step is preferably a two-step or multi-step countercurrent hydrochloric acid leaching. After the first step of hydrochloric acid leaching, solid-liquid separation is performed to obtain a first-step rare earth leaching solution and a first-step leaching residue. The first-step leaching residue is then subjected to the next step of hydrochloric acid leaching. After solid-liquid separation, the current step rare earth leaching solution and the current step leaching residue are obtained. The current step rare earth leaching solution is returned to be used as the bottom water for the previous step of hydrochloric acid leaching, and the current step leaching residue can be subjected to the next step of hydrochloric acid leaching.

[0018] In step (2), the hydrochloric acid is added in a continuous co-current leaching process of 2-5 stages, with the concentration of hydrochloric acid added in a gradient at each stage. A lower concentration of hydrochloric acid is added in the first stage, and a higher concentration is added in the subsequent stages to maintain the acidity of the mixed solution at 0.01-0.6 mol / L, preferably 0.05-0.3 mol / L. Lower acidity is more conducive to rare earth leaching. The purpose is to ensure that tetravalent Ce is not reduced after entering the solution, thereby increasing the leaching rate of rare earths and fluorine. Through step-by-step leaching, a higher rare earth concentration can be obtained, reaching 150-250 g / L in the leachate. Simultaneously, because the residual acid content in the leachate is effectively reduced, the consumption of neutralizing agents in subsequent processes is also reduced.

[0019] In the process of leaching roasted ore with hydrochloric acid, a relatively low temperature is used because F is mainly in the form of [CeF]. x ] 4-x The coordination compound exists in solution, and low temperature conditions favor [CeF] x ] 4-x The stable state of coordination compounds allows for greater dissolution of rare earth elements and fluorine, with rare earth leaching rates reaching 70%-95%.

[0020] The leaching temperature of the hydrochloric acid leaching step is controlled at 10-75℃, preferably 20-65℃, and the total reaction time is controlled at 0.5-10h, preferably 1-6h, mainly to improve the leaching rate of rare earth elements and fluorine.

[0021] In step (3), the dehydration step is to dehydrate by natural air drying and / or baking. Preferably, the moisture content of the dehydrated leaching residue after treatment is <10%, and the REO content of the dehydrated leaching residue is 20%-60%, mainly REPO4. It can be mixed with other rare earth concentrates for sulfuric acid roasting.

[0022] In step (3), the mass ratio (w / w) of the concentrated sulfuric acid to the dehydrated leaching residue is 0.3-1.2:1, and preferably 0.5:1. Compared with the prior art, the present invention has a large amount of rare earth leaching in steps 1-2, and the amount of sulfuric acid used in the sulfuric acid roasting step is greatly reduced.

[0023] In step (3), the temperature of the sulfuric acid roasting step is 200-450℃, preferably 200-220℃ or 250-350℃, and the roasting time of the roasting step is 1-4h.

[0024] The temperature of the water immersion step is 20-50℃, preferably 25-40℃, the immersion time is preferably 2-5 hours, and preferably the immersion solution can be neutralized with an alkaline substance to a pH of 4-4.5, and the concentration of the obtained rare earth sulfate solution is 25-45 g / L (REO).

[0025] In step (3), the hydrochloric acid leaching residue is first washed with water, controlling the wash water to leaching residue ratio (w / w) to be 0.5-10:1, preferably 0.5-5:1. After drying, the moisture content of the leaching residue is 0-50%, preferably 0-30%. The treated wash water contains a rare earth concentration of 5-50 g / L (REO) and H. + Concentration <0.1mol / L. The purpose of washing water is to wash the rare earth chlorides entrained in the leaching residue into the solution, further improving the rare earth leaching rate, and at the same time removing chloride ions that may cause corrosion to the subsequent sulfation roasting equipment. A certain degree of dehydration treatment can reduce the dilution of concentrated sulfuric acid in the sulfuric acid enhanced roasting process. The washing liquid can be reused in step (2) for rare earth concentrate slurry preparation or hydrochloric acid preparation to achieve closed-loop circulation of the washing liquid.

[0026] Step (3) further includes the step of adding the obtained rare earth sulfate solution to iron powder for preparation, wherein the amount of iron powder added is 2%-10% of the mass of the hydrochloric acid leaching residue.

[0027] Step (3) further includes the step of extracting and transforming the obtained rare earth sulfate solution to obtain a rare earth chloride solution, which is then separated by extraction to obtain a single rare earth compound.

[0028] The extraction transformation step involves transformation treatment through precipitation or extraction.

[0029] Step (2) further includes aging the obtained rare earth leachate, separating the solid and liquid to obtain rare earth chloride solution and rare earth fluoride product; and merging the obtained rare earth chloride solution with the rare earth sulfate solution obtained in step (3) through transformation to obtain a rare earth chloride solution, and then extracting and separating to obtain a single rare earth compound.

[0030] The aging step is carried out under static or stirring conditions, and the lanthanum cerium fluoride product is obtained by filtration; the temperature of the aging step is controlled at 60-90℃, more preferably 65-80℃, and preferably the temperature of the aging step should be equal to or higher than the hydrochloric acid leaching temperature; the aging step time is 0.5-10h, preferably 1-4h.

[0031] Since the F in the leachate is mainly in the form of [CeF] x ] 4-x Coordination compounds exist in solution, Cl2 / Cl – The electrode potential decreases with increasing temperature, and is significantly lower than that of Ce. 4+ / Ce 3+ The electrode potential causes the formation of [CeF] x ] 4–x The complex was Cl – Restore and release F– ; generated F – Immediately with RE 3+ The rare earth fluorides combine (mainly with Ce surrounding F ions) to form rare earth fluoride precipitates. Furthermore, the solubility product of rare earth fluorides is inversely related to temperature; the higher the temperature, the lower the solubility product. For example, CeF3 at 25℃ has a Ksp = 8.0 × 10⁻⁶. -16 At 100℃, Ksp = 9.3 × 10⁻⁶ -18 This further promotes the precipitation of rare earth fluorides. Therefore, the high-temperature aging step in the process of this invention can effectively separate F from the leachate into the residue. The F content in the leachate is <8 mg / L. Increasing the aging temperature and extending the aging time can further reduce the F content, avoiding the influence of F on subsequent extraction and separation.

[0032] In this step, the aging treatment can obtain rare earth fluoride precipitate, and preferably the F in the leaching solution is controlled to be <8 mg / L, more preferably <2 mg / L; the residual F in the leaching residue obtained by solid-liquid separation in step (2) is less than 5% relative to the F content in the rare earth concentrate, preferably less than 1%; the rare earth concentration of the rare earth chloride solution obtained after aging and filtration is 150-250 g / L (REO), the rare earth leaching rate is 70%-95%, of which the Ce leaching rate is 60%-95%. Table 1 below shows the comparison between the hydrochloric acid leaching solution obtained by this method and the traditional bastnaesite treatment method. It can be seen that the concentration of the leaching solution obtained by this method, the total rare earth leaching rate, and the Ce leaching rate are all higher than those of the traditional bastnaesite method. + With a low concentration and virtually no sulfur in the leachate, it has significant technological advantages.

[0033] Table 1 Comparison of hydrochloric acid leachate obtained by this method and traditional fluorocarbon cerium ore treatment methods.

[0034]

[0035] The combined process for processing rare earth concentrates includes a step of treating the fluorine-containing tail gas generated in step (1) by spraying it with water or alkaline liquid, or by using one or two adsorbents of rare earth oxides and rare earth hydrated oxides to defluorinate and recover rare earth fluoride products; and / or, a step of treating the sulfur-containing tail gas generated in step (3) by desulfurization and recovery to obtain sulfuric acid products.

[0036] After desulfurization and recovery treatment, the sulfur-containing tail gas generated in the sulfuric acid roasting process not only meets the emission standards, but also can be recovered to obtain high-purity sulfuric acid products with a concentration of over 80%. This effectively solves the problems of tail gas containing F, severe equipment corrosion and wear, difficulty in separating F from S-containing substances, difficulty in meeting treatment standards, and high operating costs in traditional processes.

[0037] The smelting and separation process for rare earth concentrates described in this invention employs an atmosphere roasting-hydrochloric acid leaching-sulfuric acid roasting method to process rare earth concentrates containing bastnaesite. During the hydrochloric acid leaching process, a low-concentration hydrochloric acid step-by-step acid leaching method is used to obtain a high concentration of rare earth chloride solution (150-250 g / L REO). Simultaneously, [CeF] x ] 4-x The presence of coordination compounds allows more Ce to enter the solution, resulting in a Ce leaching rate of 60%-95% and a total rare earth leaching rate of 70%-95%. Furthermore, the process of this invention utilizes Cl... - The relationship between reducing properties and the solubility product of rare earth fluorides with temperature; high-temperature aging further reduced the F content of the leachate. - Content. Compared with the traditional oxidation roasting-hydrochloric acid leaching process for treating bastnaesite, the concentration of the leaching solution and the rare earth leaching rate are significantly improved. It eliminates the step of further evaporation and concentration required by the traditional process to obtain a high concentration of rare earth chloride solution. Moreover, the F content in the solution is very low, avoiding the formation of three phases by F entering the extraction system. It can be directly introduced into the P507-HCl system for the separation and purification of single rare earth elements.

[0038] The smelting and separation process for rare earth concentrates described in this invention involves atmosphere roasting, hydrochloric acid leaching, and high-temperature aging of the rare earth concentrate. Only 5%-30% of the rare earth remains in the hydrochloric acid leaching residue. Compared with traditional processes for processing mixed rare earth concentrates, this significantly reduces the consumption of concentrated sulfuric acid and also greatly reduces the water consumption in the water leaching process. Since 70%-95% of the rare earth directly enters the chlorination system for extraction and separation, the acid and alkali consumption in the conversion of sulfuric acid leaching solution into rare earth chloride solution is also greatly reduced.

[0039] In the combined smelting and separation process for rare earth concentrate described in this invention, the flow of fluorine is effectively controlled. Firstly, during atmospheric roasting, most of the fluorine is converted into hydrogen fluoride gas, which enters the tail gas and is then recovered through adsorption to prepare fluorine-containing products. Secondly, during hydrochloric acid leaching, a small amount of fluorine is leached into a rare earth chloride solution, and after aging, rare earth fluoride products are obtained, thus reducing the fluorine concentration in the rare earth chloride solution. -With a concentration <8mg / L, fluorine is prevented from entering the leaching residue, solving the problem of difficult treatment of mixed fluorine and sulfur-containing tail gas in the sulfuric acid roasting process. Because the amount of residual rare earth elements in the hydrochloric acid leaching residue is significantly reduced, the amount of concentrated sulfuric acid used in the sulfuric acid roasting process is also reduced accordingly, and SO2 emissions generated during sulfuric acid roasting are reduced by more than 60%, significantly lowering waste gas and wastewater treatment costs, bringing it closer to the goal of clean production, and demonstrating significant economic and environmental advantages. The effective recovery and treatment of fluorine also solves the problem of large volumes of fluorine-containing wastewater and difficulty in meeting treatment standards in traditional processes. The entire process has wider industrial adaptability and can comprehensively treat various complex minerals, achieving green, environmentally friendly, efficient, and clean production of mineral-type rare earth concentrates such as Baotou mixed rare earth concentrate and fluorocarbon cerium concentrate, resulting in significant economic and social benefits. Attached Figure Description

[0040] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein...

[0041] Figure 1 This is a flowchart of the smelting and separation process for processing rare earth concentrate using the combined method described in this invention. Detailed Implementation

[0042] Example 1

[0043] The rare earth concentrate processed in this embodiment is a mixed rare earth ore of bastnaesite and monazite, processed according to the following... Figure 1 The process flow diagram shown in this embodiment illustrates the combined method for processing rare earth concentrate through smelting and separation, which includes the following steps:

[0044] (1) A mixed rare earth concentrate of bastnaesite and monazite was roasted at 500°C for 4 hours in an air atmosphere (oxygen content 21%) to obtain roasted ore.

[0045] In this step, the HF that escapes during the roasting process is treated by water spraying.

[0046] (2) The obtained roasted ore was leached with hydrochloric acid at 25°C using a four-stage continuous co-current process. The initial concentration of hydrochloric acid was 6 mol / L, and the ratio of hydrochloric acid to the roasted concentrate was 1.0 mol / 100g rare earth concentrate. After solid-liquid separation, the rare earth leachate and leaching residue were collected separately. The rare earth leachate had a rare earth content of 238 g / L, a rare earth leaching rate of 77%, and a Ce leaching rate of 70%.

[0047] In this step, the hydrochloric acid leaching step is preferably a two-step or multi-step countercurrent hydrochloric acid leaching. After the first step of hydrochloric acid leaching, solid-liquid separation is performed to obtain a first-step rare earth leaching solution and a first-step leaching residue. The first-step leaching residue is then subjected to the next step of hydrochloric acid leaching, and solid-liquid separation is performed to obtain the current step rare earth leaching solution and the current step leaching residue. The current step rare earth leaching solution is returned to be used as the bottom water for the previous step of hydrochloric acid leaching, and the current step leaching residue can be subjected to the next step of hydrochloric acid leaching.

[0048] In this step, the hydrochloric acid is added in a continuous co-current leaching process with four stages, and the concentration of hydrochloric acid is controlled. Hydrochloric acid of 1.5 mol / L, 2 mol / L, 6 mol / L and 8 mol / L is added in the first to fourth stages, respectively, and the acidity of the mixture decreases in a gradient between 0.1 and 0.05 mol / L.

[0049] In this step, the rare earth leachate is aged at 65℃ for 4 hours, and solid-liquid separation is performed to obtain rare earth chloride solution and rare earth fluoride precipitate. The F content in the rare earth chloride solution is 1.9 mg / L. After drying the rare earth fluoride precipitate, rare earth fluoride product is obtained.

[0050] (3) After washing, drying and dehydrating the obtained leaching residue to a moisture content of 9%, concentrated sulfuric acid is added and calcined at 300°C for 3 hours, and the mass ratio (w / w) of the concentrated sulfuric acid to the leaching residue is controlled to be 0.3:1;

[0051] The calcined product was collected and soaked in water at 25°C for 4 hours. After neutralization and impurity removal, a rare earth sulfate solution of 32 g / L was obtained; the total rare earth yield was 97%. The obtained rare earth sulfate solution was extracted and transformed to obtain a rare earth chloride solution, which was then combined with the rare earth chloride solution in step (2) and extracted and separated to obtain a single rare earth compound product.

[0052] In this step, the sulfur-containing waste gas generated during the sulfuric acid roasting process is recovered by washing water spray absorption to obtain sulfuric acid products.

[0053] Example 2

[0054] The rare earth concentrate processed by the process described in this embodiment is a mixed rare earth ore of bastnaesite and monazite. The smelting and separation process for processing the rare earth concentrate using the combined method described in this embodiment includes the following steps:

[0055] (1) A mixture of bastnaesite and monazite was roasted at 500°C for 4 hours in a weak oxidizing atmosphere (the oxygen content was controlled to be 12% by adjusting the opening of the air inlet valve, etc.) with the air inlet valve opening at 50% to obtain roasted ore.

[0056] In this step, the HF that escapes during the roasting process is recovered by water spraying.

[0057] (2) The obtained roasted ore was leached with hydrochloric acid at 25°C using a four-stage continuous co-current process. The initial concentration of hydrochloric acid was 6 mol / L, and the ratio of hydrochloric acid to the roasted concentrate was 1.0 mol / 100g rare earth concentrate. After solid-liquid separation, the rare earth leachate and leaching residue were collected separately. The rare earth leachate had a rare earth content of 250g / L, a rare earth leaching rate of 80%, and a Ce leaching rate of 75%.

[0058] In this step, the hydrochloric acid leaching step is preferably a two-step or multi-step countercurrent hydrochloric acid leaching. After the first step of hydrochloric acid leaching, solid-liquid separation is performed to obtain a first-step rare earth leaching solution and a first-step leaching residue. The first-step leaching residue is then subjected to the next step of hydrochloric acid leaching, and solid-liquid separation is performed to obtain the current step rare earth leaching solution and the current step leaching residue. The current step rare earth leaching solution is returned to be used as the bottom water for the previous step of hydrochloric acid leaching, and the current step leaching residue can be subjected to the next step of hydrochloric acid leaching.

[0059] In this step, the hydrochloric acid is added in a continuous co-current leaching process with four stages, and the concentration of hydrochloric acid is controlled. Hydrochloric acid of 1.5 mol / L, 2 mol / L, 6 mol / L and 8 mol / L is added in the first to fourth stages, respectively, and the acidity of the mixture decreases in a gradient between 0.1 and 0.05 mol / L.

[0060] In this step, the rare earth leachate is aged at 80℃ for 4 hours, and solid-liquid separation is performed to obtain rare earth chloride solution and rare earth fluoride precipitate. The F content in the rare earth chloride solution is 1.2 mg / L. After drying the rare earth fluoride precipitate, rare earth fluoride product is obtained.

[0061] (3) After washing, drying and dehydrating the obtained leaching residue to a moisture content of 9%, concentrated sulfuric acid is added and calcined at 300°C for 3 hours, and the mass ratio (w / w) of the concentrated sulfuric acid to the leaching residue is controlled to be 0.3:1;

[0062] The calcined product was collected and soaked in water at 25°C for 4 hours. After neutralization and impurity removal, a rare earth sulfate solution of 32 g / L was obtained; the total rare earth yield was 97%. The obtained rare earth sulfate solution was extracted and transformed to obtain a rare earth chloride solution, which was then combined with the rare earth chloride solution in step (2) and extracted and separated to obtain a single rare earth compound product.

[0063] In this step, the sulfur-containing waste gas generated during the sulfuric acid roasting process is recovered by washing water spray absorption to obtain sulfuric acid products.

[0064] Example 3

[0065] The rare earth concentrate processed by the process described in this embodiment is a mixed rare earth ore of bastnaesite and monazite. The smelting and separation process for processing the rare earth concentrate using the combined method described in this embodiment includes the following steps:

[0066] (1) A mixed rare earth ore of bastnaesite and monazite was roasted at 650°C for 4 hours in a steam atmosphere with the air inlet valve open at 100% to obtain roasted ore.

[0067] In this step, the HF released during the roasting process is recovered using a rare earth oxide adsorbent to obtain rare earth fluoride products.

[0068] (2) The obtained roasted ore was leached with hydrochloric acid at 25°C using a four-stage continuous co-current process. The initial concentration of hydrochloric acid was 6 mol / L, and the ratio of hydrochloric acid to the roasted concentrate was 1.0 mol / 100g rare earth concentrate. After solid-liquid separation, the rare earth leachate and leaching residue were collected separately. The rare earth leachate had a rare earth content of 235 g / L, a rare earth leaching rate of 75%, and a Ce leaching rate of 69%.

[0069] In this step, the hydrochloric acid leaching step is preferably a two-step or multi-step countercurrent hydrochloric acid leaching. After the first step of hydrochloric acid leaching, solid-liquid separation is performed to obtain a first-step rare earth leaching solution and a first-step leaching residue. The first-step leaching residue is then subjected to the next step of hydrochloric acid leaching, and solid-liquid separation is performed to obtain the current step rare earth leaching solution and the current step leaching residue. The current step rare earth leaching solution is returned to be used as the bottom water for the previous step of hydrochloric acid leaching, and the current step leaching residue can be subjected to the next step of hydrochloric acid leaching.

[0070] In this step, the hydrochloric acid is added in a continuous co-current leaching process with four stages, and the concentration of hydrochloric acid is controlled. Hydrochloric acid of 1.5 mol / L, 2 mol / L, 6 mol / L and 8 mol / L is added in the first to fourth stages, respectively, and the acidity of the mixture decreases in a gradient between 0.1 and 0.05 mol / L.

[0071] In this step, the rare earth leachate is aged at 80℃ for 4 hours, and solid-liquid separation is performed to obtain rare earth chloride solution and rare earth fluoride precipitate. The F content in the rare earth chloride solution is 1.5 mg / L. After drying the rare earth fluoride precipitate, rare earth fluoride product is obtained.

[0072] (3) After washing, drying and dehydrating the obtained leaching residue to a moisture content of 9%, concentrated sulfuric acid is added and calcined at 300°C for 3 hours, and the mass ratio (w / w) of the concentrated sulfuric acid to the leaching residue is controlled to be 0.3:1;

[0073] The calcined product was collected and soaked in water at 25°C for 4 hours. After neutralization and impurity removal, a rare earth sulfate solution of 32 g / L was obtained, with a total rare earth yield of 95%. The obtained rare earth sulfate solution was extracted and transformed to obtain a rare earth chloride solution, which was then combined with the rare earth chloride solution from step (2) and extracted and separated to obtain a single rare earth compound product.

[0074] In this step, the sulfur-containing waste gas generated during the sulfuric acid roasting process is recovered by washing water spray absorption to obtain sulfuric acid products.

[0075] The steps of Examples 4-23 are the same as those of Examples 1-3, and the conditions for each step are shown in Tables 2-4 below. The final total rare earth yield is shown in Table 4.

[0076] Table 2

[0077]

[0078] Table 3

[0079]

[0080]

[0081]

[0082] Table 4

[0083]

[0084] Therefore, this invention can comprehensively process various complex rare earth minerals, and the entire process has wide industrial applicability. Atmospheric roasting converts most of the fluorine into hydrogen fluoride gas, which enters the tail gas and is then treated by adsorption and recovery to prepare fluorine-containing products. Multi-stage continuous hydrochloric acid leaching with controlled acidity yields a high-concentration rare earth chloride solution (150-250 g / L REO) while ensuring a rare earth leaching rate of over 70%. Aging reduces the fluorine content of the leachate. - This method improves the rare earth content, obtaining fluorinated rare earth products to prevent fluorine from entering the leaching residue, thus solving the problem of difficult treatment of mixed fluorine and sulfur-containing tail gas in the sulfuric acid roasting process. The leaching residue is further processed by sulfuric acid roasting and water leaching to recover rare earth, achieving a total rare earth recovery rate of over 95%. This enables green, environmentally friendly, efficient, and clean production of mineral-based rare earth concentrates.

[0085] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A combined smelting and separation process for rare earth concentrate, characterized in that, Includes the following steps: (1) The rare earth concentrate is roasted and decomposed under a certain roasting atmosphere to obtain roasted ore; the rare earth concentrate includes bastnaesite, or a mixed rare earth ore of bastnaesite and at least one of monazite, xenotime and apatite; the roasting temperature is 450-650℃. (2) Add hydrochloric acid to the obtained roasted ore to leach rare earth, and collect the rare earth leachate and leaching residue after solid-liquid separation; (3) After dehydrating the obtained leaching residue, concentrated sulfuric acid is added for roasting. The roasted product is collected and then subjected to water leaching, neutralization and impurity removal to obtain rare earth sulfate solution. The obtained rare earth sulfate solution is subjected to extraction transformation or precipitation transformation to obtain rare earth chloride solution. In step (1), the roasting atmosphere of the roasting step includes one or more of water vapor, N2, air, CO, CO2, and inert gas, and is a weak oxidizing atmosphere; in step (2), the obtained rare earth leachate is aged at 60-90℃ for 1-5 hours, and solid-liquid separation is performed to obtain rare earth chloride solution and rare earth fluoride powder product; and the obtained rare earth chloride solution is combined with the rare earth chloride solution obtained in step (3), and a single rare earth compound is obtained by extraction separation.

2. The smelting and separation process for rare earth concentrate using the combined method according to claim 1, characterized in that, In step (2), the hydrochloric acid leaching step is a multi-step hydrochloric acid countercurrent leaching. After the first step of hydrochloric acid leaching, solid-liquid separation is performed to obtain a first-step rare earth leaching solution and a first-step leaching residue. The first-step leaching residue is then subjected to the next step of hydrochloric acid leaching. After solid-liquid separation, the current step rare earth leaching solution and the current step leaching residue are obtained. The current step rare earth leaching solution is returned to be used as the bottom water for the previous step of hydrochloric acid leaching, and the current step leaching residue can be subjected to the next step of hydrochloric acid leaching.

3. The smelting and separation process for rare earth concentrate using the combined method according to claim 1, characterized in that, In step (2), the hydrochloric acid is added by performing 2-5 stages of continuous co-current leaching during the leaching process, and the hydrochloric acid is added in a concentration gradient during each stage of leaching to maintain the acidity of the leaching mixture at 0.01-0.6 mol / L.

4. The smelting and separation process for rare earth concentrates using the combined method according to claim 1, characterized in that, In step (2), the leaching temperature of the hydrochloric acid leaching step is controlled to be 10-75℃.

5. The smelting and separation process for rare earth concentrates using the combined method according to claim 1, characterized in that, In step (3), the mass ratio (w / w) of the concentrated sulfuric acid to the dehydrated leaching residue is 0.3-1.2:

1.

6. The smelting and separation process for rare earth concentrate according to claim 1, characterized in that, In step (3), the temperature of the sulfuric acid roasting step is 200-450℃, and the temperature of the water immersion step is 20-50℃.

7. The smelting and separation process for processing rare earth concentrate using a combined method according to any one of claims 1-6, characterized in that, The fluorine-containing tail gas generated during the roasting process in step (1) is treated by spraying with water or alkaline liquid, or by defluorination and recovery of rare earth fluoride products by one or two adsorbents of rare earth oxides and rare earth hydrated oxides; the sulfur-containing tail gas generated during the sulfuric acid roasting process in step (3) is treated by desulfurization and recovery to obtain sulfuric acid products.

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