Chemical beneficiation method for upgrading and calcium reduction of mixed rare earth concentrate

Abstract

The present application relates to the technical field of mineral processing engineering, and particularly relates to a chemical beneficiation method for upgrading and reducing calcium content of mixed rare earth concentrate. The chemical beneficiation method of the present application mainly comprises multiple procedures such as chemical leaching, separation and optional drying, wherein the chemical leaching is carried out in two stages. The chemical beneficiation method of the present application reduces the content of calcium oxide in the rare earth concentrate, improves the grade of the mixed rare earth concentrate, provides conditions for separating bastnaesite from monazite and clean development of rare earth smelting, is beneficial to the optimization and improvement of the rare earth smelting process, and reduces the pollution to the environment; provides raw materials for niobium and scandium extraction; the generated intermediate products can be converted into products, basically realizing zero emission, achieving the purpose of comprehensive utilization, and the whole method is green, environmentally friendly and waste-free.

Description

Technical Field

[0001] This invention relates to the field of mineral processing engineering technology, specifically to a chemical beneficiation method for upgrading and reducing calcium content in mixed rare earth concentrates. Background Technology

[0002] The Bayan Obo mining area in Baotou, Inner Mongolia, is the world's largest rare earth mineral deposit. The mixed rare earth concentrate produced from this area is a unique composite rare earth ore in China, with a rare earth grade typically reaching approximately 50-58% by weight and a calcium oxide (CaO) content generally around 6-12% by weight. This mixed rare earth concentrate mainly contains cerium fluorocarbonate, monazite, calcium fluorophosphate, fluorite, apatite, dolomite, calcite, pyrite, pyrrhotite, and trace amounts of niobium and scandium oxides, among other multi-element mineral phases.

[0003] The mixed rare earth concentrate is currently typically smelted using either the "acid process" or the "alkali process".

[0004] The "acid process" in rare earth smelting typically refers to the high-temperature roasting method using concentrated sulfuric acid. This process is highly adaptable and tolerant of different raw materials; the type and content of impurities in the raw materials have little impact on the selected process, and it can operate normally within a wide range of raw material compositions. However, this "acid process" often becomes inefficient due to the high calcium content in rare earth concentrates. Calcium reacts with sulfuric acid to form calcium sulfate precipitate, carrying away some rare earth elements and reducing the rare earth yield, sometimes even below 90%. Furthermore, the presence of calcium in the "acid process" generates a large amount of waste residue, leading to severe pollution and serious environmental problems.

[0005] The "alkali process" for rare earth smelting has higher requirements for raw materials. Calcium in rare earth raw materials has a significant impact on the recovery rate of rare earths. Therefore, the "alkali process" also has strict requirements for the calcium content in the raw materials.

[0006] Therefore, it is evident that, regardless of whether it is the "acid method" or the "alkali method" process as described above, the presence of calcium in the raw materials is detrimental to subsequent smelting and production.

[0007] Currently, the most common technology is to use hydrochloric acid leaching to remove calcium from rare earth raw materials. This method has a large liquid-to-solid ratio, generally about 10:1, resulting in a large volume of waste acid that is difficult to handle. Furthermore, the loss of rare earth can sometimes be significant, reaching more than 5%. For example, in the article "Research on Hydrochloric Acid Calcium Washing Process of Baotou Mixed Rare Earth Ore" by Ma Shengfeng et al. (Rare Earth, Vol. 38, No. 5, pp. 75-82, October 2017), it was disclosed that when the hydrochloric acid calcium washing process was used to remove calcium impurities from high-grade mixed rare earth concentrate with a direct alkaline decomposition of more than 71% by weight, under the optimal acid washing process conditions of 16.67% slurry concentration, 3.5 mol / L initial acidity, 1.33 mol / kg acid consumption for water washing, and 40℃ leaching temperature, the CaO removal rate only reached about 70%. Finally, the CaO content in the calcium-free ore only decreased from the original 7.73% by weight to 2.25% by weight, and the rare earth quality only increased from 71.04% by weight to 77.88% by weight.

[0008] In addition, high-grade rare earth concentrate is a prerequisite for the effective separation of bastnaesite and monazite. The efficient separation of bastnaesite and monazite requires that the rare earth element oxide (REO) content in the rare earth concentrate be at least about 65% by weight. The higher the REO content, the better the separation effect. The efficient separation of the two is a necessary condition for realizing the separate smelting of rare earth concentrate.

[0009] Chinese patent application CN102357421A discloses a method for removing calcium from high-calcium rare earth concentrate. The method employs flotation, using a roughing, scavenging, and cleaning process to obtain a high-grade rare earth concentrate with REO ≥ 65% and CaO content ≤ 2%, as well as a calcium-rich concentrate with CaO content ≥ 40% and REO ≤ 5%. For example, in its embodiments, a rare earth concentrate with a minimum CaO content of 1.1 wt% and a maximum REO content of 67.1 wt% was achieved.

[0010] There is still a need in this field to develop a chemical beneficiation method that uses industrially produced mixed rare earth concentrate as raw material without affecting the existing production of the beneficiation plant. This method can further reduce the calcium content in the mixed rare earth concentrate to below about 1% by weight with less waste, while further increasing the grade of the rare earth concentrate to above about 70% by weight, and maintaining a high rare earth recovery rate. Summary of the Invention

[0011] Purpose of the invention

[0012] Based on the problems described in the background section above, in order to solve the problem that the calcium content of the currently produced mixed rare earth concentrate is high and the rare earth grade is insufficient, which has an adverse effect on smelting, this invention provides a chemical beneficiation method for improving the quality and reducing the calcium content of mixed rare earth concentrate.

[0013] Technical solution

[0014] To achieve the above objectives, the present invention adopts the following technical solution:

[0015] Option 1. A chemical beneficiation method for upgrading and reducing the calcium content of mixed rare earth concentrates, wherein the mixed rare earth concentrates are preferably mixed rare earth concentrates with an REO content of about 50 to about 58% by weight and a CaO content of about 6 to about 12% by weight, the method comprising the following steps:

[0016] Step 1: React the mixed rare earth concentrate with concentrated hydrochloric acid to obtain a solid-liquid mixture, wherein the resulting liquid phase is an acidic solution, the pH of the liquid phase is preferably ≤3, more preferably between about 2 and about 3, the concentration of the concentrated hydrochloric acid is preferably about 8 to about 12 mol / L, and the reaction is preferably carried out at atmospheric pressure or under pressure at a temperature below 80°C, preferably at a temperature of about 60 to about 80°C.

[0017] Step 2: Separate the solid-liquid mixture obtained from Step 1 into a solid phase and a liquid phase;

[0018] Step 3: The solid phase obtained from Step 2 is mixed with concentrated hydrochloric acid at atmospheric pressure or under pressure at a temperature of about 90 to about 110°C, preferably about 100 to about 110°C, for about 4.5 to about 5.5 hours, wherein the concentration of the concentrated hydrochloric acid is preferably about 8 to about 12 mol / L.

[0019] Step 4: Add cationic polyacrylamide as a precipitant to the solution obtained from Step 3 at a temperature below about 85°C, preferably below about 80°C, to form a solid-liquid mixture. The amount of cationic polyacrylamide precipitant added is about 0.1 to about 0.3 g per liter of the solution, preferably about 0.2 g.

[0020] Step 5: Separate the solid-liquid mixture obtained from Step 4 into a liquid phase containing hydrochloric acid and a solid phase containing low-calcium, high-grade rare earth concentrate.

[0021] The total amount of concentrated hydrochloric acid used in steps 1 and 3 corresponds to about 0.40 to about 0.55 kg of HCl molecules per kilogram of the mixed rare earth concentrate, preferably about 0.43 to about 0.46 kg of HCl molecules.

[0022] Option 2. According to the chemical beneficiation method described in Option 1 above, nitric acid is added as a co-solvent during the mixing process in step 3, wherein the amount of nitric acid added is about 5 to about 10 g of HNO3 molecules per kilogram of the mixed rare earth concentrate.

[0023] Option 3. According to the chemical beneficiation method described in Option 1 or 2 above, boric acid is added as a co-solvent during the mixing process in step 3, wherein the amount of boric acid co-solvent added is about 0.8 to about 1.3 g of boric acid per kilogram of the mixed rare earth concentrate.

[0024] Scheme 4. The chemical beneficiation method according to any one of Schemes 1 to 3 above, wherein at least a portion of the concentrated hydrochloric acid used in step 1 comprises a hydrochloric acid-containing liquid phase obtained from step 5.

[0025] Scheme 5. A chemical beneficiation method according to any one of Schemes 1 to 4 above, wherein the method further includes drying the solid phase obtained from step 5 to obtain a low-calcium, high-grade rare earth concentrate that can be directly used for rare earth smelting.

[0026] Scheme 6. A chemical beneficiation method according to any one of Schemes 1 to 5 above, wherein the method further comprises recovering compounds containing rare earth elements, as well as niobium and calcium elements, from the liquid phase obtained in step 2 that may have dissolved in the liquid phase in step 1, wherein the recovered rare earth elements particularly include cerium, scandium, etc.

[0027] Scheme 7. A low-calcium, high-grade rare earth concentrate prepared by the chemical beneficiation method according to any one of Schemes 1 to 6 above, wherein the calcium oxide content is preferably about 1% by weight or less, and the REO content is preferably about 70% by weight or more.

[0028] Technical effect

[0029] First, the chemical beneficiation method of the present invention for upgrading and reducing calcium content in mixed rare earth concentrates can significantly reduce the calcium content in the mixed rare earth concentrates produced by the beneficiation plant, with the calcium oxide content reduced by more than 90%. The calcium oxide content in the obtained low-calcium, high-grade rare earth concentrate can be reduced to less than 1% by weight, thereby weakening the adverse effects of calcium on rare earth smelting and solving the problems of serious environmental pollution, complex processing technology, and high processing costs caused by high calcium content in industrial production of mixed rare earth concentrates.

[0030] Secondly, the chemical beneficiation method of this invention for upgrading and reducing the calcium content of mixed rare earth concentrates yields low-calcium, high-grade mixed rare earth concentrates through calcium reduction and upgrading. The REO recovery rate is over 90%, and the REO content in the obtained low-calcium, high-grade rare earth concentrate can reach approximately 70% by weight, or even over 73% by weight. Therefore, the method of this invention solves the problem caused by low-quality raw materials in current rare earth smelting, thus creating conditions for clean rare earth smelting.

[0031] In addition, the chemical beneficiation method of the present invention for upgrading and reducing the calcium content of mixed rare earth concentrates uses recyclable raw materials and generates significantly less waste than existing technologies, thereby reducing environmental pollution.

[0032] Finally, the chemical beneficiation method for upgrading and reducing calcium content of mixed rare earth concentrate of the present invention also yields a feed solution containing niobium, scandium, and calcium compounds. This niobium- and scandium-containing feed solution is not only a high-quality raw material for extracting niobium and scandium, but the inorganic matter, mainly CaCl2, abundant in the feed solution can also serve as a useful raw material for the subsequent production of dust suppressants.

[0033] In summary, the chemical beneficiation method for upgrading and reducing calcium content of mixed rare earth concentrates of the present invention improves the grade of rare earths, provides conditions for the separation of bastnaesite from monazite and the clean development of rare earth smelting, is conducive to the optimization and improvement of rare earth smelting processes, reduces environmental pollution, provides raw materials for niobium and scandium extraction, and all intermediate products generated can be converted into products, basically achieving zero emissions and realizing the purpose of comprehensive utilization. The entire method is green, environmentally friendly and has no waste emissions. Attached Figure Description

[0034] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the specific embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0035] Figure 1 A process flow diagram for implementing the chemical beneficiation method of the present invention for upgrading and reducing calcium content of mixed rare earth concentrate. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0037] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. The term "about" as used in this invention indicates that the number it modifies may fluctuate within ±20%, ±15%, ±10%, ±5%, or ±2% of that number. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0038] In a first aspect, the present invention provides a chemical beneficiation method for improving the quality and reducing the calcium content of mixed rare earth concentrates.

[0039] In the chemical beneficiation method provided in the first aspect of the present invention, the mixed rare earth concentrate refers to the mixed rare earth concentrate produced by Baogang Group's beneficiation plant. Specifically, the mixed rare earth concentrate is preferably a mixed rare earth concentrate with an REO content of about 50 to about 58% by weight and a CaO content of about 6 to about 12% by weight.

[0040] The chemical beneficiation method of the present invention mainly includes multiple processes such as chemical leaching, separation and optional drying. The chemical leaching is carried out in two stages. The first stage of chemical leaching mainly decomposes minerals such as dolomite and calcite, and the second stage of chemical leaching mainly decomposes the remaining undecomposed carbonates and calcium-containing minerals such as fluorite and apatite.

[0041] Specifically, the chemical mineral processing method of the present invention includes the following steps 1 to 5.

[0042] The first chemical leaching process includes step 1, which involves reacting the mixed rare earth concentrate with concentrated hydrochloric acid to obtain a solid-liquid mixture.

[0043] In step 1, the reaction is preferably carried out under stirring to ensure uniform and complete reaction of the materials. During the reaction, the concentrated hydrochloric acid is preferably added slowly dropwise to the mixed rare earth concentrate under stirring to avoid an overly vigorous reaction. Additionally, it is preferable to absorb the escaping gases (mainly carbon dioxide produced by the reaction of minerals such as dolomite and calcite with hydrochloric acid) in an alkaline solution (preferably sodium hydroxide or calcium hydroxide solution).

[0044] The concentration of the concentrated hydrochloric acid used can vary over a wide range, but is preferably in the range of about 8 to about 12 mol / L. For example, concentrated hydrochloric acid of about 9 mol / L, about 9.85 mol / L, about 10 mol / L, or about 11 mol / L can be used. In step 1, if the concentration of the concentrated hydrochloric acid used is less than 8 mol / L, the volume of hydrochloric acid used will be too large, resulting in the need for larger and more expensive equipment; in addition, the decomposition of minerals such as dolomite and calcite in the mixed rare earth concentrate may be insufficient, or an excessively long reaction time may be required.

[0045] The reaction temperature is not particularly limited, but is preferably at a temperature not exceeding about 80°C, more preferably between about 60°C and about 80°C, and especially between about 65°C and about 78°C, for example, between about 75°C and about 78°C. Within this temperature range, the reaction rate of minerals such as dolomite and calcite with hydrochloric acid is suitable, and some substances in the ore to be leached during the second-stage leaching process will undergo certain changes, making the effect of the second-stage leaching process easier to achieve. If the reaction temperature is higher than about 80°C, the reaction may be too vigorous, difficult to control, and energy consumption may be too high, resulting in unnecessary waste; if the reaction temperature is lower than about 60°C, the decomposition of minerals such as dolomite and calcite may be insufficient, and the reaction rate may be too slow, requiring an excessively long reaction duration.

[0046] The reaction can be carried out at normal pressure, but may also be carried out under pressure depending on the circumstances.

[0047] When no more gaseous products escape from the obtained solid-liquid mixture, and the liquid phase stably maintains an acidic pH of ≤3, for example, when the pH value is stably maintained in the range of about 2 to about 3 (for example, for more than 10 minutes), the reaction in step 1 can be considered to be completed, and step 2 can be carried out.

[0048] The pH value of the liquid phase is preferably from about 2 to about 3. A pH value higher than about 3 makes it difficult to ensure the completion of the acid leaching reaction process in step 1 and is not conducive to the subsequent extraction of useful substances such as niobium and scandium from the separated liquid phase.

[0049] Step 2 includes separating the solid-liquid mixture obtained from step 1 into a solid phase and a liquid phase.

[0050] In step 2, the separation can be carried out by any method known in the art, including but not limited to sedimentation followed by decanting, decantation, filtration, vacuum filtration, and siphoning, or any combination thereof. For example, in a preferred embodiment of the invention, for ease of operation, the solid-liquid mixture from step 1 can first be cooled and allowed to settle naturally. Then, after the supernatant is poured out, the remaining material is vacuum filtered, and finally the filtrate is combined with the supernatant to obtain the separated liquid and solid phases.

[0051] The second chemical leaching process includes step 3, which involves mixing the solid phase obtained from step 2 with concentrated hydrochloric acid for about 4.5 to about 5.5 hours.

[0052] In step 3, the mixing is preferably carried out under stirring, which is usually carried out at normal pressure, but may also be carried out under appropriate pressure depending on the circumstances.

[0053] The concentration of hydrochloric acid used is preferably in the range of about 8 to about 12 mol / L, for example, concentrated hydrochloric acid of about 9 mol / L, about 9.85 mol / L, about 10 mol / L, or about 11 mol / L can be used. Here, when the hydrochloric acid concentration is below about 8 mol / L, the dissolution of fluorite and non-carbonate minerals contained in the mixed rare earth concentrate may be insufficient during this stage of the process, resulting in a high CaO content in the concentrate and / or the inability to obtain a high-grade rare earth concentrate with an REO content of 70% by weight or more.

[0054] The mixing temperature should be maintained in the range of approximately 90 to approximately 110°C, preferably in the range of approximately 100 to approximately 110°C, for example, it can be maintained at a temperature of approximately 100 to approximately 105°C. When the temperature is above 110°C, the improvement in decomposition effect is not significant and results in significantly excessive energy consumption. When the temperature is below 90°C, the dissolution process is insufficient, the obtained high-grade rare earth concentrate does not achieve the desired effect, and / or the required time is too long.

[0055] The mixing time is not particularly limited, but in a preferred embodiment of the invention, the mixing time is preferably controlled within the range of about 4.5 to about 5.5 hours, for example, about 5 hours, in conjunction with the above-mentioned reaction temperature. Excessive mixing time leads to excessively high production costs, while insufficient mixing time may result in inadequate decomposition.

[0056] In step 3, to eliminate the formation of a thin film on the ore surface by any potential sulfides (e.g., from pyrite or pyrrhotite) that may hinder the reaction, a co-solvent is preferably added during the mixing process. The co-solvent preferably contains nitric acid, for example, commercially available analytical grade concentrated nitric acid. The amount of nitric acid added preferably corresponds to about 5 to about 10 g of HNO3 molecules per kilogram of the mixed rare earth concentrate; for example, about 6 g, about 6.7 g, about 6.8 g, about 7 g, about 8 g, or about 9 g of HNO3 molecules can be added. The amount of nitric acid added should not be less than 5 g, otherwise the decomposition of sulfides may be incomplete, nor should it exceed 10 g, otherwise the nitric acid may react with other mineral components, affecting the process efficiency.

[0057] In step 3, to accelerate the dissolution rate of non-carbonate calcium-containing minerals such as fluorite, a co-solvent is preferably added during the mixing process. The co-solvent preferably comprises boric acid. The boric acid co-solvent has a catalytic effect, its main function being to activate fluorides. In a preferred embodiment of the invention, the amount of boric acid added corresponds to about 0.8 to about 1.3 g per kilogram of the mixed rare earth concentrate; for example, about 0.9 g, about 1.0 g, about 1.1 g, or about 1.2 g of boric acid can be added.

[0058] In the chemical beneficiation method of the first aspect of the present invention described above, the total amount of concentrated hydrochloric acid used in steps 1 and 3 corresponds to about 0.40 to about 0.55 kg of HCl molecules per kilogram of the mixed rare earth concentrate, for example, about 0.42 kg, about 0.44 kg, about 0.46 kg, about 0.48 kg or about 0.50 kg of HCl molecules.

[0059] Step 4 includes adding a precipitant to the solution obtained from step 3 to form a solid-liquid mixture.

[0060] The precipitant used in step 4 preferably comprises cationic polyacrylamide (CPAM), which can be used in the form of an aqueous solution with a concentration of about 2% by weight. CPAM has a flocculation and precipitation effect; its addition can agglomerate difficult-to-settle fine particles into clusters, thereby accelerating the precipitation rate. There is no particular limitation on the amount of CPAM added, as long as it is sufficient to precipitate the fine particles containing rare earth elements dissolved in the solution. For example, in a preferred embodiment, about 0.1 to about 0.3 g of CPAM is added per liter of the solution, such as about 0.15 g, about 0.20 g, or about 0.25 g of CPAM. Adding excessive amounts of CPAM, such as more than 0.3 g, would result in unnecessary waste.

[0061] In step 4, the precipitant is preferably added to the solution obtained in step 3 at a temperature below about 85°C, more preferably below about 80°C. Here, if the temperature is too high, for example above about 85°C, insufficient precipitation may occur. It is also preferable that the temperature at which the precipitant is added is not lower than about 75°C, as excessively low temperatures result in excessively long cooling times, affecting the process progress.

[0062] Step 5 includes separating the solid-liquid mixture obtained from step 4 into a liquid phase containing hydrochloric acid and a solid phase containing low-calcium, high-grade rare earth concentrate.

[0063] In step 5, the separation can be carried out by any method known in the art, including but not limited to settling followed by decantation, filtration, vacuum filtration, and siphoning, or any combination thereof. For example, in a preferred embodiment of the invention, for ease of operation, the solid-liquid mixture from step 4 can first be cooled and allowed to settle naturally. Then, after pouring out the supernatant, the remaining material is vacuum filtered, and finally the filtrate is combined with the supernatant, thereby obtaining a separated liquid phase containing hydrochloric acid and a solid phase containing low-calcium, high-grade rare earth concentrate.

[0064] Preferably, the chemical beneficiation method of the first aspect of the present invention further includes drying the solid phase obtained from step 5 to obtain a low-calcium, high-grade rare earth concentrate that can be directly used for rare earth smelting.

[0065] More preferably, the chemical beneficiation method of the first aspect of the present invention further includes recovering compounds containing rare earth elements, niobium, and calcium elements that may have dissolved into the liquid phase in step 1 from the liquid phase obtained in step 2, wherein the rare earth elements particularly include cerium and scandium.

[0066] Furthermore, preferably, in the chemical beneficiation method of the first aspect of the present invention described above, at least a portion of the concentrated hydrochloric acid used in step 1 comprises the hydrochloric acid-containing liquid phase obtained in step 5. Here, the hydrochloric acid-containing liquid phase obtained in step 5 can be used directly as the concentrated hydrochloric acid in step 1, or it can be further concentrated and / or purified before use, or the hydrochloric acid-containing liquid phase obtained in step 5 can be mixed with fresh concentrated hydrochloric acid and then used as the concentrated hydrochloric acid in step 1.

[0067] In a second aspect, the present invention also provides a low-calcium, high-grade rare earth concentrate prepared by the chemical beneficiation method according to the first aspect of the present invention.

[0068] In the low-calcium, high-grade rare earth concentrate provided in the second aspect of the present invention, the CaO content is preferably about 1% by weight or less, and the REO content is preferably about 70% by weight or more.

[0069] Example

[0070] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0071] The mixed rare earth concentrate raw materials used in the following examples and comparative examples were sourced from the mixed rare earth concentrate produced by the Baogang Baoshan Mining (Shanshang Beneficiation Area) beneficiation plant. The mixed rare earth concentrate mainly comprises cerium fluorocarbonate, monazite, calcium fluorophosphate, fluorite, apatite, dolomite, calcite, pyrite, pyrrhotite, and trace amounts of niobium and scandium oxides, among other multi-element mineral phases. Before chemical beneficiation, the raw materials were dried, mixed, bagged, and stored for later use.

[0072] The chemical elemental analysis results of the mixed rare earth concentrate raw material are shown below:

[0073]

[0074]

[0075] The general implementation process of chemical mineral processing in Examples 1-2:

[0076] According to the appendix Figure 1 The process flow diagram shown illustrates the chemical beneficiation process of the mixed rare earth concentrate raw materials from Examples 1-2 of this invention. The specific process is as follows:

[0077] A chemical leaching process:

[0078] The weighed mixed rare earth concentrate raw material was added to a three-necked flask equipped with a stirrer, thermometer, dropping funnel, gas delivery tube, and reflux condenser. While stirring, concentrated hydrochloric acid with a concentration of approximately 9.85 mol / L was slowly added dropwise, with the temperature controlled at approximately 60 to approximately 78°C during the addition. The concentrated hydrochloric acid may include freshly purchased concentrated hydrochloric acid or filtrate obtained from the following two-stage chemical leaching process. Gas generated in the flask was absorbed by passing it through the gas delivery tube into limewater. After the addition was complete, the temperature was maintained below approximately 78°C until no more bubbles were observed in the flask. Heating and stirring were stopped after the pH of the liquid phase in the flask reached approximately 2 to approximately 3 and remained stable within this range for approximately 10 minutes. The solid-liquid mixture in the flask was allowed to cool to room temperature and settle naturally. The supernatant was poured off, and the remaining material in the flask was filtered. The filtrate and supernatant were combined and labeled as liquid phase X.

[0079] Two-stage chemical leaching process:

[0080] The solid filter cake obtained from the above process was added to a flask. While stirring, commercially available concentrated hydrochloric acid with a concentration of approximately 9.85 mol / L was slowly added dropwise, with the temperature controlled at approximately 90 to approximately 110°C during the addition. Appropriate amounts of 65% by weight analytical grade concentrated nitric acid and analytical grade boric acid solid were added during the addition. After the addition was complete, stirring was continued at a temperature not exceeding approximately 110°C or approximately 105°C for approximately 4.5 to approximately 5.5 hours. Heating and stirring were then stopped. When the temperature of the material in the flask dropped to below approximately 80°C, the precipitant CPAM was added, and a large amount of precipitate immediately appeared in the solution in the flask. After cooling and settling, the supernatant was poured off, and the remaining material in the flask was filtered. The filtrate and supernatant were combined and used for a stage of chemical leaching in another experiment. The filter cake contained low-calcium, high-grade rare earth concentrate. The obtained high-grade rare earth concentrate filter cake was dried at a constant temperature and weighed, labeled as concentrate K.

[0081] The obtained concentrate K was analyzed by chemical analysis.

[0082] Liquid phase X can further recover compounds containing rare earth elements, as well as niobium and calcium, that may be dissolved therein. These rare earth elements particularly include cerium and scandium. For example, compounds containing useful elements such as scandium and niobium can be extracted through processes such as extraction, and CaCl2 can be extracted therein as a useful raw material for subsequent production of substances such as dust suppressants.

[0083] The general implementation process of chemical mineral processing in Comparative Examples 1-4:

[0084] The chemical beneficiation processes in Comparative Examples 1-4 are similar to the chemical beneficiation processes in Examples 1-2 of the present invention as described above, except for the following process parameters:

[0085] In Comparative Example 1, the temperature during the first stage of chemical leaching was set to not exceed approximately 56°C.

[0086] In Comparative Example 2, the pH value was set to approximately 3.2 during the first stage of chemical leaching.

[0087] In Comparative Example 3, the temperature during the second stage of chemical leaching was set to not exceed approximately 85°C.

[0088] In Comparative Example 4, the total amount of concentrated hydrochloric acid used in the two-stage chemical leaching process was approximately 0.38 times the weight of the rare earth ore.

[0089] Table 1 below summarizes the process parameters of chemical mineral processing in Examples 1-2 and Comparative Examples 1-4 of the present invention.

[0090] Table 1:

[0091]

[0092] Table 2 below summarizes the total weight of hydrochloric acid / weight ratio of rare earth ore raw materials in Examples 1-2 and Comparative Examples 1-4 of the present invention, the weight of the obtained low-calcium high-quality concentrate K, and the results of the chemical analysis of concentrate K.

[0093] Table 2:

[0094]

[0095] Table 3 summarizes the quality improvement rate ((REO% of concentrate - REO% of raw material) / REO% of raw material), REO recovery rate (concentrate weight × REO% / raw material weight × REO%) and calcium oxide reduction rate in concentrate ((raw material weight × CaO% - concentrate weight × CaO%) / raw material weight × CaO%) of low-calcium high-grade rare earth concentrate in Examples 1-2 and Comparative Examples 1-4 of the present invention.

[0096] Table 3:

[0097]

[0098] As can be seen from the experimental procedure and the data and results in Tables 1 to 3,

[0099] When the temperature is controlled below 60℃ during the first stage of acid leaching (Comparative Example 1), not only is the first stage of acid leaching too time-consuming, but the CaO content in the obtained concentrate is as high as 2.80% by weight, and the CaO reduction rate is far below 90%, only 69.42%.

[0100] When the pH value is controlled above 3.0 during the first stage of acid leaching (Comparative Example 2), the CaO content in the obtained concentrate reaches 1.34% by weight, and the CaO reduction rate is less than 90%.

[0101] When the temperature is controlled below 90°C during the second stage of acid leaching (Comparative Example 3), the CaO content in the obtained concentrate reaches 1.41% by weight, and the CaO reduction rate is less than 90%.

[0102] When the total weight of concentrated hydrochloric acid used in the two-stage acid leaching process / the weight of rare earth raw materials is less than 0.40 (Comparative Example 4), not only is the time required for the first-stage leaching step significantly extended, but also the CaO content in the obtained concentrate is relatively high, reaching 1.33% by weight, due to insufficient dissolution during the leaching process, and the CaO reduction rate is less than 90%.

[0103] Compared with the existing method of removing calcium from rare earth raw materials by hydrochloric acid leaching (see the article "Research on Hydrochloric Acid Calcium Washing Process of Baotou Mixed Rare Earth Mine", Rare Earth, Vol. 38, No. 5, October 2017) by Ma Shengfeng et al., the method of the present invention yields rare earth concentrates with significantly lower CaO content (<1 wt% vs. ≥2.25 wt%), a much higher CaO reduction rate (>90% vs. about 70%), and a greater improvement in concentrate quality (>23% vs. 9.63%).

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions claimed by the present invention.

Claims

1. A chemical beneficiation method for upgrading and reducing the calcium content of mixed rare earth concentrates, the method comprising the following steps: Step 1: React the mixed rare earth concentrate with concentrated hydrochloric acid at a temperature not exceeding 80°C to obtain a solid-liquid mixture, wherein the resulting liquid phase is an acidic solution with pH ≤ 3; Step 2: Separate the solid-liquid mixture obtained from Step 1 into a solid phase and a liquid phase; Step 3: Mix the solid phase obtained from Step 2 with concentrated hydrochloric acid at atmospheric pressure or under pressure at a temperature of 90 to 110°C for 4.5 to 5.5 hours; Step 4: Add cationic polyacrylamide as a precipitant to the solution obtained in Step 3 at a temperature below 85°C to form a solid-liquid mixture, wherein the amount of cationic polyacrylamide precipitant added is 0.1 to 0.3 g per liter of the solution; Step 5: Separate the solid-liquid mixture obtained from Step 4 into a liquid phase containing hydrochloric acid and a solid phase containing low-calcium, high-grade rare earth concentrate. The total amount of concentrated hydrochloric acid used in steps 1 and 3 corresponds to 0.40 to 0.55 kg of HCl molecules per kilogram of the mixed rare earth concentrate; Step 1 is carried out at a temperature of 60 to 80°C; The concentration of concentrated hydrochloric acid used in steps 1 and 3 is 8 to 12 mol / L.

2. The chemical mineral processing method according to claim 1, characterized in that, The mixed rare earth concentrate is a mixed rare earth concentrate with an REO content of 50 to 58% by weight and a CaO content of 6 to 12% by weight.

3. The chemical mineral processing method according to claim 1, characterized in that, The pH of the liquid phase obtained in step 1 is 2 to 3, and / or, Step 1 is performed under normal or pressurized conditions at a temperature of 60 to 80°C, and / or, Step 3 is performed at a temperature of 100 to 110°C.

4. The chemical mineral processing method according to claim 1, characterized in that, Nitric acid is added as a co-solvent during the mixing process in step 3, wherein the amount of nitric acid added corresponds to 5 to 10 g of HNO3 molecules per kilogram of the mixed rare earth concentrate.

5. The chemical mineral processing method according to claim 1, characterized in that, Boric acid is added as a co-solvent during the mixing process in step 3, and the amount of boric acid added corresponds to 0.8 to 1.3 g of boric acid per kilogram of the mixed rare earth concentrate.

6. The chemical mineral processing method according to claim 1, characterized in that, At least a portion of the concentrated hydrochloric acid used in step 1 comprises a liquid phase containing hydrochloric acid obtained from step 5.

7. The chemical mineral processing method according to claim 1, characterized in that, The method further includes drying the solid phase obtained from step 5 to obtain a low-calcium, high-grade rare earth concentrate that can be directly used for rare earth smelting.

8. The chemical mineral processing method according to any one of claims 1 to 7, characterized in that, The method also includes recovering compounds containing rare earth elements, as well as niobium and calcium elements, from the liquid phase obtained in step 2 that were dissolved into the liquid phase in step 1.

9. The chemical mineral processing method according to claim 8, characterized in that, The rare earth elements include cerium and scandium.

10. Low-calcium, high-grade rare earth concentrate prepared by the chemical beneficiation method according to any one of claims 1 to 9.

11. The low-calcium, high-grade rare earth concentrate according to claim 10, characterized in that, This low-calcium, high-grade rare earth concentrate contains less than 1% by weight of calcium oxide and more than 70% by weight of REO.

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