Separation method for monazite and bastnaesite in mixed rare earth concentrate

Abstract

The invention belongs to the technical field of rare earth mineral separation, and discloses a separation method for monazite and bastnaesite in mixed rare earth concentrate. According to the method, the mixed rare earth concentrate is firstly subjected to low-temperature treatment for 0.5-2 hours at 200-400 DEG C, and then is directly heated to 450-650 DEG C to be subjected to high-temperature treatment for 0.5-2.5 hours, so that selective recovery of the tail gas is realized, convenience is provided for recovery and treatment of the tail gas, bastnaesite can be decomposed, the separation difference between the bastnaesite and monazite is fundamentally expanded, and the mineral separation efficiency is improved. Further, two products, namely, bastnaesite concentrate and monazite concentrate with high purity and high recovery rate, can be obtained simultaneously through a method of'one-time acidic roughing and one-time alkaline scavenging '. Compared with a traditional separation process, the process is greatly simplified, and the rare earth recovery rate is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of rare earth mineral separation, and more specifically, to a combined beneficiation and smelting process based on the combination of thermal decomposition and flotation, which is used to separate bastnasite and monazite from mixed rare earth concentrates. Background Art

[0002] As the world's largest enrichment area of light rare earth resources, the unique mixed rare earth concentrate in the Bayan Obo mining area in Baotou, Inner Mongolia constitutes the core carrier of China's strategic resources. The rare earth minerals in this mixed ore body mainly coexist in the form of bastnasite and monazite, and the mass ratio of the two shows a significant fluctuation from 9:1 to 6:4 with the distribution of the ore deposit. Although there are significant differences in their smelting properties, due to the highly similar key physical properties (such as the density difference is only 0.2 - 0.3 g / cm 3 , and the difference in specific magnetic susceptibility is less than 2×10 -6 cm 3 / g), it is difficult for traditional beneficiation and smelting technologies (such as magnetic separation, flotation, etc.) to achieve efficient separation of the two. Therefore, the industrial production mainly uses concentrated sulfuric acid roasting and liquid alkali decomposition processes for decomposition, but these two processes have different technical defects such as high three-waste pollution indexes and low recycling utilization rate of thorium resources. At the same time, there are problems such as harsh reaction conditions, long process flow (alkali decomposition requires 12 - 14 hours), and prominent safety risks. Therefore, developing source separation technology to achieve the separation of bastnasite and monazite, and then adopting environmentally friendly differential smelting processes has become the key path to solve the pollution dilemma in the rare earth industry.

[0003] For the exploration of existing separation technologies, such as the one-rough-three-concentrate-four-scavenge flotation system constructed in Patent CN201210388991.6, although mineral separation is achieved through the combination of an alum / aluminum sulfate regulator and a specific collector, it exposes environmental load problems such as high reagent consumption and complex processes; while in CN201210388995.4, although a pre-roasting process at 480 - 650°C is introduced, the flotation process is still relatively long, and the N and F-containing tail gas and acidic wastewater generated during the roasting process are not properly treated. The fluoride ion complexation separation method proposed in CN201010600833.3 achieves the separation of bastnasite and monazite, but the introduction of Al 3+ will increase the burden of the extraction process. CN 202310948991.5 uses a non-oxidative selective mineral phase transformation - non-oxidative cooling - leaching - washing process route to achieve the separation of the two, but still introduces Al 3+ , which affects the product quality. CN202310054975.1 proposes to separate bastnasite and monazite through gravity separation - grinding - screening - rough separation of separation, but for fine particle sizes, it is difficult to use fine screen classification, and the middlings produced will affect the rare earth recovery rate.

[0004] Therefore, to address the technical shortcoming of low separation efficiency between bastnasite and monazite in traditional processes and to construct a new mineral separation system is an urgent problem that needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a method for separating monazite and bastnasite in a mixed rare earth concentrate, achieving efficient separation of the two major minerals: on the one hand, the rare earth recovery rate of the bastnasite concentrate exceeds 94% and the purity reaches over 97%, which can directly enter the acid leaching process, eliminating the subsequent secondary roasting link; on the other hand, the recovery rate of the monazite concentrate breaks through 87% and the purity exceeds 70%, which can be adapted to the existing smelting process. Through the optimization of the separation process, not only the production process is streamlined, but also the comprehensive energy consumption is reduced by more than 30%. While ensuring the product quality, the processing cost is significantly reduced, providing an industrial solution for the high-value utilization of rare earth resources.

[0006] To achieve the above object, the present invention provides a method for separating monazite and bastnasite in a mixed rare earth concentrate, comprising the following steps:

[0007] (1) Low-temperature pyrolysis: Place the mixed rare earth concentrate in a thermal decomposition device for low-temperature pyrolysis. The temperature should be lower than the decomposition temperature of bastnasite and be treated at 200 - 400 °C for 0.5 - 2 h. Collect the tail gas 1 generated during the reaction and discharge it after treatment.

[0008] The main purpose of this step is to remove the flotation reagents on the surfaces of both bastnasite and monazite minerals through low-temperature pyrolysis, involving the volatilization of flotation reagents, mainly including collectors, foaming agents, etc. In addition, low-temperature pyrolysis facilitates the selective recovery of tail gas.

[0009] (2) High-temperature pyrolysis: After low-temperature pyrolysis, directly carry out high-temperature pyrolysis. Heat up to 450 - 650 °C and treat for 0.5 - 2.5 h. After pyrolysis, cool to room temperature to obtain the high-temperature pyrolysis material, which is used as the raw material for acidic rough selection in flotation. Collect the tail gas 2 generated during the reaction and directly discharge it after recovery by water washing.

[0010] The main purpose of this step is to directionally convert the bastnasite (REFCO3) in the mixed rare earth concentrate into rare earth minerals such as rare earth oxyfluoride (REOF) and rare earth oxide through high-temperature pyrolysis, while monazite and other minerals remain unchanged. The main chemical reactions that occur are:

[0011] REFCO3 → REOF + CO2↑ (1)

[0012] CeFCO3 + O2 = 2CeO2 + 2CO2↑ + F2↑ (2)

[0013] After low-temperature pyrolysis, the flotation reagents remaining on the surfaces of bastnaesite and monazite minerals have been basically removed. As the pyrolysis temperature increases, bastnaesite decomposes (Equations 1 and 2), releasing a large amount of CO2. However, a large amount of precious F resources will also overflow at this time. According to the data (book: Rare Earth Mining and Dressing and Environmental Protection), in the process of treating bastnaesite, when producing one ton of REO, 16,000 m 3 waste gas will be generated, and the relative content of F in it reaches 19 mg·m -3 . Therefore, recycling HF in the high-temperature pyrolysis tail gas is of great significance for both improving the comprehensive utilization of resources and environmental protection. Since the organic matter has been removed by low-temperature pyrolysis, the recycling of HF is easier, and the impurity content of the obtained product index is less. Therefore, adopting two-stage pyrolysis of low temperature and high temperature not only realizes the selective recovery of the tail gas but also provides convenience for the recovery and treatment of the tail gas.

[0014] (3) Acidic roughing: Transfer the high-temperature pyrolysis material to the flotation cell, quantitatively inject water and stir to form pulp, and sequentially add inhibitors, collectors and frothers for roughing operation; after flotation, the foam product on the upper layer of the cell is the acidic concentrate pulp, and the pulp at the bottom is the acidic tailing pulp.

[0015] The main purpose of this step is to realize the preliminary enrichment and separation of bastnaesite and monazite by regulating the interface between the flotation reagents and bastnaesite and monazite minerals, laying a material foundation for the subsequent cleaning process. It should be noted that in this process, bastnaesite is used as the positive flotation target mineral.

[0016] (4) Filtration: Filter the acidic concentrate pulp and acidic tailing pulp respectively to separate solid and liquid, and obtain acidic concentrate, acidic filtrate 1, acidic tailings and acidic filtrate 2.

[0017] The main purposes of this step are three: ① Solid-liquid separation is required to obtain acidic concentrate (containing a large amount of rare earth oxyfluoride) and acidic tailings (containing a large amount of monazite). ② The acidic tailings need to be flotated under alkaline conditions in the next step, so the acidic filtrate needs to be separated to avoid acid-base neutralization reaction. ③ Acidic filtrate 1 and 2 need to be collected for subsequent acid leaching and neutralization preparation.

[0018] (5) Alkaline tailing separation: Transfer the acidic tailings to the flotation cell, quantitatively inject water and stir to form pulp, add collectors for separation, and obtain alkaline tailing pulp and monazite concentrate pulp.

[0019] The main purpose of this step is to separate bastnaesite and monazite in the alkaline tailings again after strengthening the reagent diffusion to improve the overall recovery rate index of the two. In addition, separation under alkaline conditions can provide convenience for treating the acidic filtrate. It should be noted that in this process, monazite is used as the positive flotation target mineral.

[0020] (6) Filtration: Filter the alkaline tailings slurry and the monazite concentrate slurry separately for solid-liquid separation to obtain alkaline tailings, alkaline filtrate 1, monazite concentrate, and alkaline filtrate 2. Mix the alkaline tailings with the acidic concentrate to obtain bastnaesite concentrate.

[0021] The main purpose of this step is that after solid-liquid separation, alkaline tailings (mainly bastnaesite), monazite concentrate, and alkaline filtrates 1 and 2 will be obtained. Mixing the alkaline tailings with the acidic concentrate to obtain bastnaesite concentrate can improve the rare earth leaching rate.

[0022] (7) Acid leaching and neutralization: Mix acidic filtrate 1, acidic filtrate 2, alkaline filtrate 1, and alkaline filtrate 2, and discharge them after the acid-base neutralization meets the standard.

[0023] The main purpose of this step is to use the acidic filtrate and alkaline filtrate, two kinds of wastewater generated by the process, for treating waste with waste, thereby improving the feasibility of the process.

[0024] Preferably, in step (3), the mass concentration of the slurry is 30% - 50%; based on the mass of the pyrolyzed material at high temperature, the dosage of the inhibitor is 3 - 5 kg / t, the dosage of the collector is 4 - 6 kg / t, and the dosage of the frother is 100 - 150 g / t.

[0025] Preferably, the inhibitor is an N-inhibitor containing amino phosphate, which is used to selectively inhibit the flotation activity of non-target minerals; the collector is a phthalic acid-based collector, and preferably phthalic acid is a high-efficiency collector; the frother is a pine oil-based frother, preferably M oil, and its foaming performance remains stable in acidic to alkaline slurries.

[0026] Preferably, in step (3), the roughing operation is carried out at 25°C and a pH value of 3 - 5.

[0027] Preferably, in step (5), the mass concentration of the slurry is 30% - 50%; based on the mass of the acidic tailings, the dosage of the collector is 0.3 - 0.6 kg / t.

[0028] Preferably, the collector is a hydroxamic acid-based C-collector to enhance the recovery of monazite.

[0029] Preferably, in step (5), the separation is carried out at 25°C and a pH value of 7.1 - 12.

[0030] Preferably, in step (7), the pH value of the acid-base neutralization mixture is 6.5 - 7.5 to eliminate the corrosiveness and pollutant risk of the wastewater and achieve discharge up to the standard.

[0031] The technical concept of the present invention is: the present invention adopts low temperature and high temperature two-stage pyrolysis to not only realize the selective recovery of tail gas, but also provide convenience for the recovery and treatment of tail gas, and can decompose fluorocarbon cerium ore, fundamentally expand the sorting difference between fluorocarbon cerium ore and monazite, and improve the ore dressing efficiency. Specifically, since the mixed rare earth concentrate is obtained by flotation, the same flotation agent must remain on the surface of fluorocarbon cerium ore and monazite, which will reduce the sorting difference between fluorocarbon cerium ore and monazite. Low temperature pyrolysis (200-400°C) is to volatilize or decompose the residual flotation agent on the surface of fluorocarbon cerium ore and monazite, so as to expand the flotation difference between the two. At this time, the main component of the tail gas is the flotation agent or its thermal decomposition product, which is not friendly to the environment despite the low content, so it needs to be recycled.

[0032] It can be seen from the above technical solution that, compared with the prior art, the beneficial effects achieved by the present invention are:

[0033] 1. The fluorocarbon cerium ore concentrate obtained by the present invention does not need to be roasted again and can be directly used in the back-end rare earth leaching process. Specifically, high-temperature pyrolysis-hydrochloric acid leaching is already a classic treatment method for fluorocarbon cerium ore, and the fluorocarbon cerium ore product obtained by the traditional sorting process still needs to be oxidatively roasted. The present invention first performs a pyrolysis process before sorting, and then the fluorocarbon cerium ore obtained after the sorting process does not need to be pyrolyzed at high temperature, and can be directly leached with hydrochloric acid. In essence, the present invention only transfers the high-temperature pyrolysis to before the sorting process, and does not increase the processing cost.

[0034] 2. The present invention adopts a sorting method of "one acid roughing and one alkaline scavenging" to simultaneously obtain two products of high purity and high recovery rate, namely, bastnaesite concentrate and monazite concentrate. Compared with the traditional sorting process, the process has been greatly simplified and the recovery rate of rare earths has been improved. Specifically: compared with the one roughing, three concentrating and four scavenging process of CN 102886309 A, the process flow of the present invention is greatly shortened. Compared with the one reselection, one roughing and two concentrating process of CN 116273433 A process, the present invention not only shortens the process flow, but also does not produce middlings, thereby reducing the loss of rare earths.

[0035] 3. The present invention solves the problem of wastewater recycling difficulties and provides a new direction for the reform of mixed rare earth oxidative roasting concentrate smelting process. Specifically, the traditional sorting process does not treat the ore dressing wastewater, but directly discharges it into the designated tailings pond (CN 102886312 A). The present invention utilizes the two wastewater characteristics of "one acid roughing and one alkaline scavenging" and the neutralization reaction to achieve the reasonable disposal of ore dressing wastewater, which is more environmentally friendly.

[0036] Therefore, from a long-term perspective, the present invention provides a feasible solution for the recovery of F and P in the Bayan Obo mixed rare earth resources. Brief Description of the Drawings

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the provided drawings.

[0038] Figure 1 TG-DSC analysis of mixed rare earth concentrate

[0039] Figure 2 Process flow chart of the present invention Detailed Embodiments

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0041] Embodiment 1:

[0042] Taking mixed rare earth concentrate with a rare earth grade of 67.28% as raw material, it is measured that the content of bastnaesite in this raw material is 58.78% and the purity is 68.67%, the content of monazite is 19.56%, and the purity is 26.87%. Using the process technology of the present invention, the beneficiation separation of bastnaesite and monazite is carried out. The specific steps are as shown in the figure:

[0043] Low-temperature pyrolysis: First, place the mixed rare earth concentrate in a pyrolysis device for low-temperature pyrolysis (300 °C), and the decomposition time is 1.0 h.

[0044] High-temperature pyrolysis: After the low-temperature pyrolysis is completed, directly raise the pyrolysis temperature to 500 °C, the pyrolysis time is 1 hour, and then cool to room temperature to obtain high-temperature pyrolysis materials, which are used as raw materials for flotation for rough selection.

[0045] Acidic rough selection: Add the high-temperature pyrolysis materials to the flotation cell for rough selection, add water and stir, adjust the pulp concentration to 30%, add N-inhibitor 3 kg / t, phthalic acid 4 kg / t and M oil 100 g / t in sequence for rough selection. The foam product on the upper layer of the cell is acidic concentrate pulp, and the pulp at the bottom is used as acidic tailing pulp. The pulp temperature is 25 °C, and the pH of the pulp is 3;

[0046] Filtration: The acidic concentrate slurry and the acidic tailing slurry are filtered separately. After solid-liquid separation, acidic concentrate, acidic filtrate 1, acidic tailings, and acidic filtrate 2 are obtained.

[0047] Alkaline scavenging: Transfer the acidic tailings to a scavenging flotation cell, quantitatively inject water and stir to adjust the pulp mass concentration to 30%. Subsequently, add C-collector (0.3 kg / t) according to the mass ratio of the rougher tailings. Conduct secondary flotation at a constant temperature of 25°C and in an alkaline environment (pH 8) to finally separate the monazite concentrate slurry and the alkaline tailing slurry.

[0048] Filtration: Filter the alkaline tailing slurry and the monazite concentrate slurry separately. After solid-liquid separation, alkaline tailings, alkaline filtrate 1, monazite concentrate, and alkaline filtrate 2 are obtained. Mix the alkaline tailings with the acidic concentrate to obtain bastnaesite concentrate.

[0049] Acid leaching and neutralization: Conduct acid-base neutralization on acidic filtrate 1, acidic filtrate 2, alkaline filtrate 1, and alkaline filtrate 2, and control the pH of the final mixed solution to be 6.5 - 7.5 to eliminate the corrosiveness and pollutant risks of the wastewater and achieve up-to-standard discharge.

[0050] After measurement, the relative purity of the bastnaesite concentrate is 94.18% and the recovery rate is 90.93%; the relative purity of the monazite concentrate is 71.3% and the recovery rate is 85.98%.

[0051] Example 2:

[0052] Using mixed rare earth concentrate with a rare earth grade of 63.28% as the raw material, after measurement, the bastnaesite content in this raw material is 57.28% and the purity is 65.66%, the monazite content is 21.55%, and the purity is 27.87%. Using the process technology of the present invention, conduct beneficiation separation of bastnaesite and monazite. The specific steps are as shown in the figure:

[0053] Low-temperature pyrolysis: First, place the mixed rare earth concentrate in a pyrolysis device for low-temperature pyrolysis (350°C), and the decomposition time is 0.5 h.

[0054] High-temperature pyrolysis: After the low-temperature pyrolysis ends, directly raise the pyrolysis temperature to 550°C, the pyrolysis time is 1 hour, and then cool to room temperature to obtain high-temperature pyrolysis materials, which are used as raw materials for flotation for rougher separation.

[0055] Acidic rougher separation: Add the high-temperature pyrolysis materials to a flotation cell for rougher separation, add water and stir to adjust the pulp concentration to 40%, sequentially add 4 kg / t of N-inhibitor, 5 kg / t of phthalic acid, and 130 g / t of M oil for rougher separation. The rougher separation obtains rougher separation foam products and rougher separation pulp in the cell. The pulp temperature is 25°C and the pH of the pulp is 4.

[0056] Filtration: The acidic concentrate pulp and acidic tailing pulp are filtered separately. After solid-liquid separation, acidic concentrate, acidic filtrate 1, acidic tailings, and acidic filtrate 2 are obtained.

[0057] Alkaline scavenging: Transfer the acidic tailings to a scavenging flotation cell, quantitatively inject water and stir to adjust the pulp mass concentration to 40%. Subsequently, add C-collector (0.4 kg / t) according to the mass ratio of rougher tailings. At a constant temperature of 25°C and an alkaline environment (pH 9), finally, monazite concentrate pulp and alkaline tailing pulp are separated.

[0058] Filtration: The alkaline tailing pulp and monazite concentrate pulp are filtered separately. After solid-liquid separation, alkaline tailings, alkaline filtrate 1, monazite concentrate, and alkaline filtrate 2 are obtained. Mix the alkaline tailings with the acidic concentrate to obtain bastnasite concentrate.

[0059] Acid leaching and neutralization: Acid-base neutralization is carried out on acidic filtrate 1, acidic filtrate 2, alkaline filtrate 1, and alkaline filtrate 2. Control the pH of the final mixed solution to be 6.5 - 7.5 to eliminate the corrosiveness and pollutant risks of the wastewater and achieve up-to-standard discharge.

[0060] It is measured that the relative purity of the rare earth fluoride concentrate is 97.15% and the recovery rate is 94.17%. The relative purity of the monazite concentrate is 73.7% and the recovery rate is 87.97%.

[0061] Example 3:

[0062] Using mixed rare earth concentrate with a rare earth grade of 66.88% as the raw material, it is measured that the bastnasite content in this raw material is 58.67% and the purity is 68.55%, the monazite content is 20.94%, and the purity is 28.88%. Using the process technology of the present invention, the ore dressing separation of bastnasite and monazite is carried out. The specific steps are as shown in the figure:

[0063] Low-temperature pyrolysis: First, place the mixed rare earth concentrate in a pyrolysis device for low-temperature pyrolysis (200°C), and the decomposition time is 2.0 h.

[0064] High-temperature pyrolysis: After the low-temperature pyrolysis ends, directly raise the pyrolysis temperature to 600°C, and the pyrolysis time is 0.5 hour. Then cool it to room temperature to obtain high-temperature pyrolysis materials, which are used as raw materials for flotation for rougher separation.

[0065] Acidic rougher separation: Add the high-temperature pyrolysis materials to a flotation cell for rougher separation, add water and stir to adjust the pulp concentration to 50%. Sequentially add 5 kg / t of N-inhibitor, 6 kg / t of phthalic acid, and 150 g / t of M oil for rougher separation. The rougher separation obtains rougher froth products and pulp in the rougher cell. The pulp temperature is 25°C, and the pH of the pulp is 5.

[0066] Filtration: The acidic concentrate slurry and the acidic tailing slurry are filtered separately. After solid-liquid separation, acidic concentrate, acidic filtrate 1, acidic tailings, and acidic filtrate 2 are obtained.

[0067] Alkaline scavenging: Transfer the acidic tailings to a scavenging flotation cell, quantitatively inject water and stir to adjust the pulp mass concentration to 50%. Subsequently, add C-collector (0.5 kg / t) according to the mass ratio of the roughing tailings. Conduct secondary flotation at a constant temperature of 25°C in an alkaline environment (pH 10), and finally separate the monazite concentrate slurry and the alkaline tailing slurry.

[0068] Filtration: The alkaline tailing slurry and the monazite concentrate slurry are filtered separately. After solid-liquid separation, alkaline tailings, alkaline filtrate 1, monazite concentrate, and alkaline filtrate 2 are obtained. Mix the alkaline tailings with the acidic concentrate to obtain bastnaesite concentrate.

[0069] Acid leaching and neutralization: Acid-base neutralization is carried out on acidic filtrate 1, acidic filtrate 2, alkaline filtrate 1, and alkaline filtrate 2. Control the pH of the final mixed solution to 6.5 - 7.5 to eliminate the corrosiveness and pollutant risks of the wastewater and achieve up-to-standard discharge.

[0070] It is determined that the relative purity of the rare earth fluoride concentrate is 96.34% and the recovery rate is 92.41%; the relative purity of the monazite concentrate is 73.34% and the recovery rate is 84.89%.

[0071] Experiment: Optimization of pyrolysis temperature

[0072] The present invention selects 450 - 650°C as the temperature range for high-temperature pyrolysis, mainly based on the test results of TG-DSC ( Figure 1 ). It can be seen that when the pyrolysis temperature is <450°C, there is no obvious weight loss phenomenon in the mixed rare earth concentrate, which is the reason for the preferred temperature range of 200 - 400°C for low-temperature pyrolysis. When the pyrolysis temperature >450°C, there is no obvious weight loss phenomenon in the mixed rare earth concentrate, the weight loss rate reaches 12.76%, and heat is released. This is considered to be the starting temperature for the directional conversion of bastnaesite (REFCO3) in the mixed rare earth concentrate into rare earth minerals such as rare earth fluoride (REOF) and rare earth oxide. However, when the pyrolysis temperature is greater than 650°C, the weight loss rate remains basically unchanged. Therefore, the preferred temperature range for high-temperature pyrolysis is 450 - 650°C.

[0073] Through experimental comparison, it is found that under the same conditions, there are obvious differences in the separation efficiency of bastnaesite and monazite before and after pyrolysis (Table 1). Compared with before pyrolysis, the recovery efficiency and purity of bastnaesite and monazite after high-temperature pyrolysis have been significantly improved. This shows that the pyrolysis process increases the separation difference between bastnaesite and monazite, providing high-quality raw materials for the subsequent acidic roughing process.

[0074] Table 1

[0075]

[0076] Further comparison:

[0077] If only high-temperature pyrolysis is carried out, the components in the tail gas will include the products after the decomposition of flotation reagents, HF, CO2, etc. This not only brings difficulties to the tail gas recovery, but also affects the purity of the recovered products.

[0078] Further comparison:

[0079] If the low-temperature pyrolysis and high-temperature pyrolysis processes are placed after the flotation process, then according to the results in Table 1, the recovery rates and purity indexes of bastnaesite and monazite obtained by directly separating the minerals without pyrolysis are 50.48%, 62.55% and 45.89%, 68.66% respectively. However, these indexes are significantly lower than the separation indexes of the pyrolyzed minerals. Moreover, since bastnaesite and monazite have been separated, these indexes have been fixed, and no matter what pyrolysis system is adopted subsequently, so its indexes will not change at all. Therefore, the pyrolysis process must be placed before the flotation process.

[0080] Further comparison:

[0081] If the traditional acidic system is still used for acidic tail selection after acidic rough selection, then the pH of the wastewater generated in the whole flotation system will be less than 7, and chemical reagents (such as NaOH) need to be added additionally during the discharge process for treatment, resulting in a significant increase in production costs. Therefore, alkaline tail selection is adopted, and the generated alkaline wastewater (pH>7) can be used to neutralize the acidic wastewater (pH<7) generated by acidic rough selection, reducing the wastewater treatment cost.

[0082] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for separating monazite and bastnasite in a mixed rare earth concentrate, characterized in that, It includes the following steps: (1) Low-temperature pyrolysis: The mixed rare earth concentrate is treated at a low temperature of 200-400 °C for 0.5-2 h, and the generated tail gas 1 is collected and discharged after treatment; (2) High-temperature pyrolysis: After the low-temperature pyrolysis is completed, it is directly heated to a high temperature of 450-650 °C and treated for 0.5-2.5 h to obtain high-temperature pyrolysis materials. The generated tail gas 2 is collected, washed and recycled and then discharged; (3) Acidic rough selection: The high-temperature pyrolysis materials are transferred to a flotation cell, water is injected and stirred to form a pulp, an inhibitor, a collector and a foaming agent are added in sequence, and a rough selection operation is carried out; After the flotation is completed, an acidic concentrate pulp and an acidic tailing pulp are obtained; (4) Filtration: The acidic concentrate pulp and the acidic tailing pulp are filtered respectively to obtain acidic concentrate, acidic filtrate 1, acidic tailings and acidic filtrate 2; (5) Alkaline tail selection: The acidic tailings are transferred to a flotation cell, water is injected and stirred to form a pulp, a collector is added, and separation is carried out to obtain an alkaline tailing pulp and a monazite concentrate pulp; (6) Filtration: The alkaline tailing pulp and the monazite concentrate pulp are filtered respectively to obtain alkaline tailings, alkaline filtrate 1, monazite concentrate and alkaline filtrate 2. The alkaline tailings are mixed with the acidic concentrate to obtain bastnasite concentrate; (7) Acid leaching and neutralization: The acidic filtrate 1, acidic filtrate 2, alkaline filtrate 1 and alkaline filtrate 2 are mixed, and after the acid-base neutralization reaches the standard, they are discharged.

2. The separation method of monazite and bastnaesite in a mixed rare earth concentrate according to claim 1, characterized in that, In step (3), the mass concentration of the pulp is 30%-50%; based on the mass of the high-temperature pyrolysis materials, the dosage of the inhibitor is 3-5 kg / t, the dosage of the collector is 4-6 kg / t, and the dosage of the foaming agent is 100-150 g / t.

3. The separation method of monazite and bastnaesite in a mixed rare earth concentrate according to claim 2, characterized in that, The inhibitor is an N-inhibitor containing amino phosphate, the collector is a phthalic acid-based collector, and the foaming agent is a pine oil-based foaming agent.

4. A method for separating monazite and bastnaesite in a mixed rare earth concentrate according to claim 1, characterized in that, In step (3), the rough selection operation is carried out at 25 °C and a pH value of 3-5.

5. The separation method of monazite and bastnaesite in a mixed rare earth concentrate according to claim 1, characterized in that, In step (5), the mass concentration of the pulp is 30%-50%; based on the mass of the acidic tailings, the dosage of the collector is 0.3-0.6 kg / t.

6. The separation method of monazite and bastnaesite in a mixed rare earth concentrate according to claim 5, characterized in that, The collector is a hydroxamic acid-based C-collector.

7. A method for separating monazite and bastnaesite in a mixed rare earth concentrate according to claim 1, characterized in that, In step (5), the separation is carried out at 25 °C and a pH value of 7.1-12.

8. A method for separating monazite and bastnaesite in a mixed rare earth concentrate according to claim 1, characterized in that, In step (7), the pH value of the mixed solution for acid-base neutralization is 6.5-7.5.

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