Method for recovering rare earths from industrial solid waste fluorogypsum
By treating fluorogypsum with ammonium sulfate solution and oxalic acid, low-cost and high-efficiency recovery of rare earth elements has been achieved, solving the problems of high energy consumption, equipment corrosion and environmental pollution in traditional methods. The waste residue can be used for clinker-free cement production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZIBO YUNDA BUILDING MATERIALS CO LTD
- Filing Date
- 2026-03-18
- Publication Date
- 2026-06-30
AI Technical Summary
Existing technologies lack effective rare earth element recovery solutions when processing fluorogypsum. Furthermore, traditional methods are energy-intensive, cause severe equipment corrosion, generate toxic waste gases, and make it difficult to utilize the waste residue as a resource.
Low-temperature leaching of fluorogypsum with ammonium sulfate solution, combined with treatment with oxalic acid and ammonium bicarbonate, achieves low-cost and environmentally friendly recycling of rare earth elements, including pretreatment, leaching, precipitation, and filtrate recycling.
It achieves efficient recovery of rare earth elements, reduces production costs and energy consumption, reduces emissions of toxic gases, has low residual rare earth content in waste residue, and the waste residue can be used for clinkerless cement production, thus solving the problems of resource waste and environmental pollution.
Smart Images
Figure CN122303642A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of industrial solid waste treatment technology, specifically relating to a method for recovering rare earth elements from industrial solid waste fluorogypsum. Background Technology
[0002] Fluoropyrite is an industrial byproduct produced during the reaction of fluorite concentrate with sulfuric acid to produce hydrogen fluoride. Its main component is anhydrous calcium sulfate (CaSO4). This substance is also strongly acidic and contains trace amounts of calcium fluoride and unreacted sulfuric acid. Approximately 3.6-4 tons of fluoropyrite are produced for every ton of hydrofluoric acid produced. The presence of large amounts of fluoropyrite in solid waste dumps not only poses a land occupation problem but also pollutes the surrounding environment.
[0003] The Bayan Obo mine contains abundant mineral resources such as iron, niobium, scandium, thorium, and fluorite. The fluorite concentrate produced contains 85–92 wt% CaF2 and 1.2–2 wt% rare earth oxides (REO). During the production of anhydrous hydrogen fluoride from fluorite concentrate, the rare earth oxides in the concentrate enter fluorogypsum, making it a secondary rare earth resource. Therefore, the fluorogypsum can only be reused after prioritizing the recovery of rare earth resources.
[0004] However, existing fluorogypsum treatment technologies mostly employ neutralization, which involves adding 1.5% quicklime to bring the solution pH to 5.5-9.0, eliminating corrosiveness and converting water-soluble fluoride into sparingly soluble CaF2. Another approach involves adding 0.2%-1.5% sodium sulfate or sulfoaluminate activators to shorten the setting time to within 30 minutes and improve compressive strength. However, these technologies lack reasonable recovery schemes for rare earth elements, failing to ensure their proper recycling and utilization.
[0005] Chinese invention patent CN120700304A discloses a method for recovering rare earth elements from fluorogypsum, comprising the following steps: 1) pulverizing fluorogypsum and mixing it with sulfuric acid aqueous solution to obtain mixed slurry I; roasting mixed slurry I to obtain roasted ore; 2) mixing roasted ore with water to obtain mixed slurry II; leaching mixed slurry II to obtain leaching product; separating the leaching product into solid and liquid to obtain leachate and water leaching residue; 3) adding a precipitant to the leachate and stirring to carry out a precipitation reaction to obtain mixed slurry III; separating mixed slurry III into solid and liquid to obtain a precipitate containing rare earth elements and filtrate I; 4) adding a water treatment agent to filtrate I and stirring to carry out a reaction to obtain mixed slurry IV; separating mixed slurry IV into solid and liquid to obtain mixed residue and filtrate II. However, this method still has the following shortcomings: ① It requires the use of high-concentration sulfuric acid (80-98wt%) for high-temperature roasting (150-400℃), resulting in high energy consumption, severe equipment corrosion, and the generation of toxic waste gases such as SO2; ② The large amount of sulfuric acid used leads to high costs for subsequent wastewater treatment; ③ The roasting process causes gypsum lattice reconstruction, making it difficult to directly utilize the waste residue as a resource. Therefore, a milder, lower-consumption, and more environmentally friendly method for rare earth recovery from fluorogypsum still needs to be developed. Summary of the Invention
[0006] This invention provides a method for recovering rare earth elements from industrial solid waste fluorogypsum. It employs a milder ammonium sulfate solution to treat the fine fluorogypsum powder, significantly reducing production costs while avoiding toxic gas emissions and air pollution. This achieves low-cost and environmentally friendly absorption of rare earth elements from fluorogypsum.
[0007] The technical solution of this invention is as follows: A method for recovering rare earth elements from industrial solid waste fluorogypsum includes the following steps: 1) Pretreatment of solid waste fluorogypsum: Fluorogypsum is screened and crushed to a fineness of 100-200 mesh, and then put into the raw material pool; First, solid waste fluorogypsum is screened with a 100-200 mesh screen. The waste fluorogypsum that passes the screen is directly put into the raw material pool, and the waste that does not pass the screen is transported to the grinding equipment for grinding until the fineness reaches 100-200 mesh.
[0008] 2) Leaching of rare earth elements: Ammonium sulfate solution is added to a raw material pool containing fluorogypsum with a fineness of 100-200 mesh and then the solid and liquid are separated to obtain leachate and water leaching residue. The water leaching residue is subjected to a second solid-liquid separation to obtain waste residue with a moisture content of no more than 10-20% and filtrate. 3) Separation of precipitates containing rare earth elements: The precipitant is added to the leachate to carry out the precipitation reaction, and mixed slurry one is obtained. Mixed slurry one is then subjected to solid-liquid separation to obtain precipitates containing rare earth elements and filtrate two. 4) Filtrate recycling: Mix filtrate one and filtrate two to obtain a mixed solution, add water treatment agent to the mixed filtrate, stir to react, and recycle after the pH value reaches 5-7.
[0009] Preferably, the mass concentration of the ammonium sulfate solution in step 2) is 4%-7%.
[0010] Preferably, in step 2), the weight ratio of fluorogypsum to ammonium sulfate solution is 1:1-1.5, the soaking temperature is 10-40℃, and the soaking time is 30-50min.
[0011] Preferably, the ammonium sulfate is industrial grade ammonium sulfate, with a nitrogen content of not less than 21%, a moisture content of not more than 0.3%, and a free acid content of not more than 0.05%.
[0012] Preferably, the precipitant in step 3) is oxalic acid, and the mass concentration of the precipitant is 1%-5%.
[0013] Preferably, the precipitation reaction time in step 3) is 30-50 min.
[0014] Preferably, in step 3), the mass ratio of leachate to precipitant is 1:0.1-0.15.
[0015] Preferably, the water treatment agent in step 4) is ammonium bicarbonate, and the nitrogen content in ammonium bicarbonate is not less than 17%.
[0016] Compared with the prior art, the present invention has the following advantages: 1. This invention adopts an environmentally friendly and resource-free method, which grinds fluorogypsum into powder, abandoning the traditional high-energy-consuming roasting and concentrated sulfuric acid dissolution method. It uses a milder ammonium sulfate solution to treat the waste fluorogypsum fine powder, resulting in a shorter and more energy-efficient process. This greatly saves production costs, reduces the safety hazards caused by concentrated sulfuric acid, and eliminates the use of natural gas resources and the emission of sulfur dioxide and nitrogen oxides caused by roasting.
[0017] 2. The residual rare earth element content in the waste residue of this invention is as low as 0.051%, and the recovery rate of rare earth elements in fluorogypsum reaches more than 95wt%, realizing a low-cost and environmentally friendly method for efficient recovery of rare earth elements in fluorogypsum.
[0018] 3. This invention uses low-temperature reaction processing throughout the entire process, which greatly reduces energy consumption, significantly shortens the production cycle, and improves equipment utilization efficiency. Attached Figure Description
[0019] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation
[0020] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions will be clearly and completely described below in conjunction with the embodiments of this invention.
[0021] Example 1 In this embodiment, a 5kg sample of fluorogypsum was used for the experiment. The rare earth oxide content in the fluorogypsum sample was 1.73wt.
[0022] A method for recovering rare earth elements from industrial solid waste fluorogypsum includes the following steps: 1) Pretreatment of solid waste fluorogypsum: The fluorogypsum is placed in a 200-mesh screen. The waste fluorogypsum that passes the screen is directly put into the raw material pool. The fluorogypsum that does not pass through the screen is transported to the grinding equipment for grinding until the fineness reaches 200 mesh, and then enters the raw material pool.
[0023] 2) Leaching of rare earth elements: A 5% ammonium sulfate solution was added to a raw material tank containing fluorogypsum with a fineness of 200 mesh for immersion and solid-liquid separation. The ammonium sulfate was commercially available industrial-grade ammonium sulfate with a nitrogen content of not less than 21%, a moisture content of not more than 0.3%, and a free acid content of not more than 0.05%. The weight ratio of fluorogypsum to ammonium sulfate solution was 1:1.5. The immersion temperature was 40℃ and the immersion time was 40 minutes. This immersion time was sufficient to fully decompose rare earth elements from the solid waste fluorogypsum. Leachate and water-leached residue were obtained. The water-leached residue was subjected to a second solid-liquid separation to obtain waste residue with a moisture content of 13% and filtrate one. 3) Separation of precipitates containing rare earth elements: Oxalic acid, the precipitant, is added to the leachate to carry out a precipitation reaction. The precipitation reaction time is 30 min, the mass concentration of oxalic acid is 3%, and the mass ratio of leachate to oxalic acid is 1:0.1 to obtain mixed slurry one. Mixed slurry one is then subjected to solid-liquid separation to obtain precipitates containing rare earth elements, which are crystalline rare earth oxalate and filtrate two. 4) Filtrate recycling: Mix filtrate one and filtrate two to obtain a mixed solution. Add a 4% ammonium bicarbonate solution (by mass concentration) of water treatment agent to the mixed filtrate. The nitrogen content of the ammonium bicarbonate used should not be less than 17%. Stir to react. After the pH value reaches 6, the solution is recycled to the rare earth leaching step.
[0024] After treatment using the above method, the residual rare earth oxide content in the waste residue was 0.077%, and the rare earth oxide recovery rate of fluorogypsum was 95.55%.
[0025] Example 2 In this embodiment, a 5kg sample of fluorogypsum was used for the experiment. The rare earth oxide content in the fluorogypsum sample was 1.53wt.
[0026] A method for recovering rare earth elements from industrial solid waste fluorogypsum includes the following steps: 1) Pretreatment of solid waste fluorogypsum: The fluorogypsum is placed in a 150-mesh screen. The waste fluorogypsum that passes the screen is directly put into the raw material pool. The fluorogypsum that does not pass through the screen is transported to the grinding equipment for grinding until the fineness reaches 150 mesh, and then enters the raw material pool.
[0027] 2) Leaching of rare earth elements: A 5% ammonium sulfate solution was added to a raw material tank containing fluorogypsum with a fineness of 150 mesh for immersion and solid-liquid separation. The ammonium sulfate was industrial grade, with a nitrogen content of not less than 21%, a moisture content of not more than 0.3%, and a free acid content of not more than 0.05%. The weight ratio of fluorogypsum to ammonium sulfate solution was 1:1.5. The immersion temperature was 40℃ and the immersion time was 50 minutes. This immersion time was sufficient to fully decompose rare earth elements from the solid waste fluorogypsum. Leachate and water-leached residue were obtained. The water-leached residue was subjected to secondary solid-liquid separation to obtain waste residue with a moisture content of 16% and filtrate one. 3) Separation of precipitates containing rare earth elements: Oxalic acid, the precipitant, is added to the leachate to carry out a precipitation reaction. The precipitation reaction time is 50 min, the mass concentration of oxalic acid is 5%, and the mass ratio of leachate to oxalic acid is 1:0.1 to obtain mixed slurry one. Mixed slurry one is then subjected to solid-liquid separation to obtain precipitates containing rare earth elements, namely crystalline rare earth oxalate and filtrate two. 4) Filtrate recycling: Mix filtrate one and filtrate two to obtain a mixed solution. Add a 4% ammonium bicarbonate solution (by mass concentration) of water treatment agent to the mixed filtrate. The nitrogen content of the ammonium bicarbonate used should not be less than 17%. Stir to react. After the pH value reaches 6, the solution is recycled to the rare earth leaching step.
[0028] After treatment using the above method, the residual rare earth oxide content in the waste residue was 0.051%, and the rare earth oxide recovery rate of fluorogypsum was 96.67%.
[0029] Comparative Example 1 The method for recovering rare earth elements from industrial solid waste fluorogypsum employs traditional roasting and sulfuric acid leaching, specifically the method described in Example 1 of patent CN120700304A. The rare earth oxide content in the fluorogypsum sample used is 1.62 wt.%. The specific steps include: (1) Fluorogypsum was crushed to a particle size of 1 mm using an impact crusher and then mixed with a concentrated sulfuric acid aqueous solution with a mass concentration of 95 wt% at a weight ratio of 1:0.1 to obtain mixed slurry I. Mixed slurry I was placed in a rotary kiln and roasted at 250℃ for 1.5 h to obtain roasted ore.
[0030] (2) Roasted ore and water were mixed at a mass ratio of 1:2 to obtain mixed slurry II. Mixed slurry II was placed on a colloid mill and leached for 0.3 h at 25 °C and a stirring speed of 3000 rpm. Magnesium oxide was added during the leaching process to adjust the pH of mixed slurry II to 1.6, thus obtaining the leaching product. The leaching product was then filtered using a plate and frame filter press to obtain leachate and water-leached residue. The water-leached residue was washed with water of twice its weight to obtain wash water. The wash water was used to replace fresh water in the next leaching process and was mixed with the roasted ore. If the amount of wash water was insufficient, fresh water was added.
[0031] (3) Add 3.5 wt% of oxalic acid (based on the weight of fluorogypsum) to the leachate and stir for 30 min at 300 rpm to carry out a precipitation reaction, thus obtaining mixed slurry III. Filter mixed slurry III using a plate and frame filter press to obtain rare earth element oxalate precipitate and filtrate I.
[0032] (4) Add 9 wt% (by weight of fluorogypsum) of calcium oxide slurry (calcium oxide mass fraction of 10 wt%) to filtrate I, and stir for 30 min at 300 rpm to obtain mixed slurry IV. Filter mixed slurry IV using a plate and frame filter press to obtain mixed residue and filtrate II. Filtrate II is used to replace fresh water for washing the water-leached residue in the next leaching. If the amount of filtrate II is insufficient, add fresh water.
[0033] After treatment using the above method, the residual rare earth content in the waste residue was 0.15%, and the rare earth element recovery rate of fluorogypsum was 95.2%. In this comparative example, calcination at 250°C for 1.5 hours is required, which consumes significantly more energy than the room temperature leaching in the example. The use of 95% concentrated sulfuric acid requires high corrosion resistance of the equipment, increasing equipment investment and maintenance costs. High-temperature calcination may produce toxic gases such as SO2, posing environmental hazards. At the same time, calcination may cause gypsum lattice reconstruction, making it difficult to directly utilize the subsequent waste residue.
[0034] Comparative Example 2 Unlike Example 1, this comparative example does not include the pretreatment of solid waste fluorogypsum in step 1). The remaining preparation methods and steps are the same as in Example 1. After treatment by the above method, the residual rare earth oxide content in the waste residue is 0.62%, and the rare earth oxide recovery rate of fluorogypsum is 64.16%. In this comparative example, no pretreatment was performed on the solid waste fluorogypsum because its particles were too large, resulting in insufficient rare earth leaching, excessively high rare earth oxide content after the waste residue was crushed, and low rare earth yield.
[0035] Comparative Example 3 Unlike Example 1, this comparative example does not include the 3% concentration of ammonium sulfate solution in step 2). The remaining preparation methods and steps are the same as in Example 1. After treatment by the above method, the residual rare earth oxide content in the waste residue is 0.27%, and the rare earth oxide recovery rate of fluorogypsum is 84.4%. The ammonium sulfate concentration in this comparative example is too low (3%), which is insufficient to effectively replace or dissolve the rare earth elements in the fluorogypsum.
[0036] Comparative Example 4 Unlike Example 1, this comparative example does not include step 2) where the concentration of ammonium sulfate solution is 8%. The remaining preparation methods and steps are the same as in Example 1. After treatment by the above method, the residual rare earth oxide content in the waste residue is 0.081%, and the rare earth oxide recovery rate of fluorogypsum is 95.32%. Although the ammonium sulfate concentration in this comparative example is too high, its recovery rate is basically the same as that in Example 1. Excessively high reagent concentration will increase production costs.
[0037] In this embodiment of the invention, the residual waste residue after extracting rare earth elements can be produced into clinkerless cement through invention patent CN120117847A (a clinkerless slag cement and its preparation method) or CN116903280A (a clinkerless cement and a method for preparing clinkerless cement entirely using industrial solid waste). This cement is used for local wind power projects, mine restoration, and underground mine backfilling, maximizing the utilization of rare earth element resources in solid waste fluorogypsum while solving the environmental problems caused by waste residue dumping.
[0038] Although the present invention has been described in detail by way of preferred embodiments, the invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.
Claims
1. A method for recovering rare earth elements from industrial solid waste fluorogypsum, characterized in that, Includes the following steps: 1) Pretreatment of solid waste fluorogypsum: The fluorogypsum is screened and crushed to a fineness of 100-200 mesh, and then put into the raw material pool; 2) Leaching of rare earth elements: Ammonium sulfate solution is added to a raw material pool containing fluorogypsum with a fineness of 100-200 mesh and then the solid and liquid are separated to obtain leachate and water leaching residue. The water leaching residue is subjected to a second solid-liquid separation to obtain waste residue with a moisture content of no more than 10-20% and filtrate. 3) Separation of precipitates containing rare earth elements: The precipitant is added to the leachate to carry out the precipitation reaction, and mixed slurry one is obtained. Mixed slurry one is then subjected to solid-liquid separation to obtain precipitates containing rare earth elements and filtrate two. 4) Filtrate recycling: Mix filtrate one and filtrate two to obtain a mixed solution, add water treatment agent to the mixed filtrate, stir to react, and recycle after the pH value reaches 5-7.
2. The method for recovering rare earth elements from industrial solid waste fluorogypsum as described in claim 1, characterized in that, The mass concentration of the ammonium sulfate solution in step 2) is 4%-7%.
3. The method for recovering rare earth elements from industrial solid waste fluorogypsum as described in claim 1, characterized in that, In step 2), the weight ratio of fluorogypsum to ammonium sulfate solution is 1:1-1.5, the soaking temperature is 10-40℃, and the soaking time is 30-50min.
4. The method for recovering rare earth elements from industrial solid waste fluorogypsum as described in claim 1, characterized in that, The ammonium sulfate mentioned is industrial grade ammonium sulfate.
5. The method for recovering rare earth elements from industrial solid waste fluorogypsum as described in claim 1, characterized in that, In step 3), the precipitant is oxalic acid, and the mass concentration of the precipitant is 1%-5%.
6. The method for recovering rare earth elements from industrial solid waste fluorogypsum as described in claim 1, characterized in that, The precipitation reaction time in step 3) is 30-50 min.
7. The method for recovering rare earth elements from industrial solid waste fluorogypsum as described in claim 1, characterized in that, In step 3), the mass ratio of leachate to precipitant is 1:0.1-0.
15.
8. The method for recovering rare earth elements from industrial solid waste fluorogypsum as described in claim 1, characterized in that, In step 4), the water treatment agent is ammonium bicarbonate.