Method for treating fluorgypsum

Abstract

The application discloses a fluorogypsum treatment method, comprising the following steps: 1) mixing fluorogypsum, leaching aid and neutralizing agent to obtain a mixture; mixing the mixture with water to obtain mixed slurry I; leaching the mixed slurry I to obtain a leaching product; performing solid-liquid separation on the leaching product to obtain a leaching liquid and a water leaching residue; 2) adding a precipitant to the leaching liquid, stirring to perform a precipitation reaction, and obtaining mixed slurry II; performing solid-liquid separation on the mixed slurry II to obtain a precipitate containing rare earth elements and a filtrate I; 3) adding a water treatment agent to the filtrate I, stirring to perform a reaction, and obtaining mixed slurry III; performing solid-liquid separation on the mixed slurry III to obtain a mixed residue and a filtrate II. The application can effectively separate and recover rare earth elements in fluorogypsum.

Description

Technical Field

[0001] This invention relates to a method for processing fluorogypsum. Background Technology

[0002] Fluoropyrogypsum is a byproduct of the reaction of fluorite concentrate with concentrated sulfuric acid to produce hydrofluoric acid. Its main component is calcium sulfate (type II), and it is anhydrous. Approximately 3.4 tons of anhydrous fluoropyrogypsum are produced for every ton of hydrofluoric acid produced. Currently, fluoropyrogypsum is managed as Class II general industrial solid waste and is entirely transferred to solid waste disposal sites for storage. Large-scale stockpiling of fluoropyrogypsum can damage the surrounding environment. Long-term weathering from stockpiling can generate secondary dust, causing soil pollution and affecting the health of nearby residents. Furthermore, the large amount of calcium sulfate in fluoropyrogypsum that remains undeveloped and unutilized represents a waste of resources.

[0003] The Bayan Obo mine contains abundant fluorite resources, with fluorite concentrate containing 85-92 wt% CaF2 and 1-4 wt% rare earth oxides (REO). During the production of anhydrous hydrogen fluoride from fluorite concentrate, the rare earth oxides in the concentrate enter fluorogypsum, becoming secondary rare earth resources. The fluorogypsum can only be reused after prioritizing the recovery of rare earth resources. Furthermore, direct stockpiling of fluorogypsum wastes rare earth resources, reduces the company's economic efficiency, and long-term stockpiling and weathering of fluorogypsum will cause phase changes in rare earth elements, increasing extraction difficulty and cost. Therefore, developing extraction and utilization technologies for rare earth and calcium sulfate resources in fluorogypsum is of great significance and will bring significant economic and social benefits. Those skilled in the art have been researching how to reuse fluorogypsum.

[0004] CN118324481A discloses a highly water-resistant gypsum-based cementitious material. This highly water-resistant gypsum-based cementitious material, by mass ratio, comprises the following raw materials: 60-70 wt% fluorogypsum, 15-25 wt% fly ash, 9-15 wt% cement, 3-6% slag powder, 0.04-0.1% modified silica, and 0.1-0.5% CSH seed crystals. It also includes a pH adjuster and an activator; wherein the pH adjuster accounts for 1-5 wt% of the total mass of fluorogypsum and fly ash, and the activator accounts for 0.5-3 wt% of the total mass of fluorogypsum and fly ash. In this highly water-resistant gypsum-based cementitious material, the fluorogypsum is only used as a component of the cementitious material, and the resource-based elements contained in the fluorogypsum are not recycled.

[0005] CN116460952A discloses a method for producing non-fired hollow bricks using a compound of fluorogypsum and fly ash. The method includes the following steps: fluorogypsum, carbon fiber, lignosulfonate, fly ash, cement, and graded gravel are mixed in a mixer for 20-25 minutes for the first mixing. Then, the mixture is fed evenly into a spiral mixer for a second mixing, during which water and a high-efficiency water-reducing agent are added and mixed for 15-20 minutes. A foaming agent is then added and mixing continues for 10 minutes, while cold air is introduced during mixing until a uniform mixture is obtained. A release agent is applied to the inside of hollow brick molds, and the resulting mixture is evenly poured into multiple sets of hollow brick molds. Compaction is achieved through vibration, and the molds are placed in a curing chamber for 7-14 days. Finally, the hollow bricks are demolded. This method only uses fluorogypsum as a component of hollow bricks and does not recycle the resource-based elements contained in the fluorogypsum.

[0006] CN116835626A discloses a method for the comprehensive utilization of fluorogypsum and aluminum electrolyte. The method includes the following steps: (1) roasting a mixture mainly composed of aluminum electrolyte waste residue powder, fluorogypsum, and a roasting agent, wherein the roasting agent is ammonium carbonate; (2) leaching the solid roasted product obtained in step (1) with an alkaline solution to separate the solid and liquid, then using an adsorbent to adsorb lithium ions from the liquid obtained after solid-liquid separation, and then eluting the adsorbent after adsorption treatment to obtain a lithium ion solution. Simultaneously, the liquid after adsorption treatment is mixed with hydrogen peroxide to prepare an aluminate solution. This method mainly utilizes fluorogypsum to extract lithium from aluminum electrolyte waste residue powder, but does not extract or treat the resource-type elements in the fluorogypsum. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a method for processing fluorogypsum. This method achieves a REO recovery rate of over 40 wt% in fluorogypsum, effectively separating and recovering rare earth elements from the fluorogypsum.

[0008] The present invention achieves the above objectives using the following technical solutions.

[0009] The method for treating fluorogypsum provided by this invention includes the following steps:

[0010] 1) Fluorogypsum, leaching aid, and neutralizing agent are mixed at a weight ratio of 1:0.02-0.1:0.01-0.05 to obtain a mixture; the mixture is mixed with water at a mass ratio of 1:1-5 to obtain mixed slurry I; mixed slurry I is leached at 15-40°C to obtain a leaching product; the leaching product is separated into solid and liquid components to obtain a leachate and a water-leached residue; wherein the leaching aid is selected from at least one of alumina and aluminum sulfate; and the neutralizing agent is selected from at least one of magnesium oxide and magnesium hydroxide.

[0011] 2) Add the precipitant to the leachate and stir to carry out the precipitation reaction to obtain mixed slurry II; separate the solid and liquid of mixed slurry II to obtain a precipitate containing rare earth elements and filtrate I; wherein, the precipitant is selected from at least one of oxalic acid and hydroxycarboxylic acid; the amount of the precipitant added is 1 to 8 wt% of the weight of fluorogypsum;

[0012] 3) Add the water treatment agent to filtrate I and stir to react, obtaining mixed slurry III; separate the solid and liquid of mixed slurry III to obtain mixed residue and filtrate II; wherein, the water treatment agent is a calcium oxide slurry with a mass fraction of 5-20 wt%; the amount of water treatment agent added is 5-15 wt% of the weight of fluorogypsum.

[0013] In this invention, the fluorogypsum can be any fluorogypsum product containing rare earth elements. Preferably, the fluorogypsum is produced during the production of anhydrous hydrogen fluoride using fluorite concentrate from Bayan Obo. In this fluorogypsum, the fluorine content can be 1–5 wt%, preferably 1.1–3 wt%. The REO content can be 1–4 wt%, preferably 1.5–3.5 wt%.

[0014] In step 1) of the present invention, the weight ratio of the fluorogypsum, the impregnation aid and the neutralizing agent can be 1:0.02-0.1:0.01-0.05, preferably 1:0.03-0.06:0.015-0.03.

[0015] In this invention, the weight ratio of the mixture to water can be 1:1 to 5, preferably 1:2 to 4.

[0016] According to the processing method of the present invention, preferably, in step 1), the leaching temperature can be 15-40°C, more preferably 18-30°C. The leaching time can be 10-60 min, more preferably 12-40 min.

[0017] According to the processing method of the present invention, preferably, in step 1), the leaching aid can be selected from at least one of alumina and aluminum sulfate, preferably alumina or aluminum sulfate. The neutralizing agent can be selected from at least one of magnesium oxide and magnesium hydroxide, preferably magnesium oxide or magnesium hydroxide.

[0018] In step 1) of the present invention, leaching under stirring conditions may also be included, and the stirring speed may be 2000-4000 rpm, preferably 2500-3500 rpm.

[0019] Reasonable leaching conditions can ensure that rare earth elements are effectively leached and enriched in the leachate, which is beneficial to improving the recovery rate of rare earth elements; at the same time, it is beneficial to enrich calcium sulfate in the water leaching residue.

[0020] According to the processing method of the present invention, preferably, in step 1), the water-leached residue can also be washed with water to obtain washing water. The weight ratio of water-leached residue to water can be 1:1 to 5, preferably 1:1 to 3. The washing water can replace fresh water in mixing with the mixture for leaching, thereby realizing the recycling of wastewater. In the present invention, fresh water is used for the first leaching, and for the second and subsequent leaching cycles, the washing water obtained in the previous cycle can be used for leaching. If the amount of washing water is insufficient, fresh water is added.

[0021] The water involved in this invention can be any type of water known in the art that can be used for the leaching and separation of rare earth elements, and is not particularly limited herein. For example, it can be tap water, reclaimed water after wastewater treatment, etc.

[0022] The leaching process of this invention can be implemented in any type of leaching equipment known in the art, and is not particularly limited herein. For example, it can be a colloid mill, a stirred mill, etc.

[0023] The solid-liquid separation involved in this invention can be achieved using any filtration method or filtration equipment known in the art, without any particular limitation herein. For example, a plate and frame filter, a vacuum filter, etc., can be used.

[0024] According to the processing method of the present invention, preferably, in step 2), the amount of precipitant added can be 1-8 wt% of the weight of fluorogypsum, more preferably 2-6 wt%. The stirring speed can be 200-400 rpm, more preferably 250-350 rpm. The stirring time can be 10-60 min, more preferably 20-45 min.

[0025] According to the processing method of the present invention, preferably, in step 2), the precipitant can be selected from at least one of oxalic acid and hydroxycarboxylic acid, and more preferably from at least one of oxalic acid, tartaric acid, citric acid and lactic acid.

[0026] According to the treatment method of the present invention, preferably, in step 3), the water treatment agent can be a calcium oxide slurry with a mass fraction of 5-20 wt%, more preferably a calcium oxide slurry with a mass fraction of 8-15 wt%. The amount of the water treatment agent added can be 5-15 wt% of the weight of fluorogypsum, preferably 7-12 wt%.

[0027] Reasonable precipitation reaction conditions can ensure that rare earth elements are effectively precipitated, which is beneficial to improving the recovery rate of rare earth elements.

[0028] In step 3) of the present invention, the stirring speed can be 200-400 rpm, preferably 250-350 rpm. The stirring time can be 10-60 min, preferably 20-45 min.

[0029] According to the processing method of the present invention, preferably, in step 3), the filtrate II can be used to wash the washing water residue obtained in step 1), thereby realizing the recycling of wastewater. Fresh water is used for the first washing of the water residue. For the second and subsequent leaching cycles, the previously obtained filtrate II can be used for washing. If the amount of filtrate II is insufficient, fresh water is added.

[0030] Reasonable reaction conditions can ensure that impurity elements are effectively enriched and precipitated in the mixed residue, which is conducive to the filtrate meeting the conditions for reuse.

[0031] In this invention, the REO content in the rare earth element-containing precipitate can be 45.3 wt% or more, preferably 45.5 wt% or more. The REO content in the water leaching residue can be less than 1 wt%, preferably less than 0.98 wt%. The REO recovery rate in fluorogypsum can be 44 wt% or more, preferably 44.5 wt% or more.

[0032] The rare earth element precipitate obtained by this invention has an REO content of over 45.3 wt%, while the REO content in the water-leached residue is less than 1 wt%. The REO recovery rate in fluorogypsum is over 44 wt%, achieving effective separation and recovery of rare earth elements from fluorogypsum. Simultaneously, this invention enables the recycling of wastewater. Attached Figure Description

[0033] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0034] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0035] In this invention, "REO" refers to rare earth oxides.

[0036] <Testing Method>

[0037] REO content determination: Refer to GB / T 18114.1-2010.

[0038] REO recovery rate calculation: Recovery rate = Product yield × Product REO content ÷ Raw material REO content.

[0039] <Ingredient Description>

[0040] Unless otherwise specified, all raw materials used in the following examples are commercially available products.

[0041] Fluorogypsum was purchased from Inner Mongolia Jin'ebo Fluorochemical Co., Ltd.

[0042] Example 1

[0043] The fluorine content of the fluorine plaster used in this embodiment is 1.20 wt%, and the REO content is 1.62 wt%.

[0044] This embodiment recovers rare earth elements from 3 kg of fluorogypsum, and includes the following steps:

[0045] (1) Fluorogypsum, aluminum sulfate, and magnesium oxide were mixed at a weight ratio of 1:0.04:0.022 to obtain a mixture. The mixture was then mixed with water at a weight ratio of 1:3 to obtain slurry I. Slurry I was placed on a colloid mill and leached for 15 minutes at 20°C and a stirring speed of 3000 rpm to obtain a leaching product. The leaching product was then filtered using a plate and frame filter press to obtain a leachate and a water-leached residue. The water-leached residue was washed with water at a weight of 3 times that of the water-leached residue to obtain wash water. The wash water was used to replace fresh water in the next leaching process and was added to the mixture for leaching. If the amount of wash water was insufficient, fresh water was added.

[0046] (2) Add 3.5 wt% 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, obtaining mixed slurry II. Filter mixed slurry II using a plate and frame filter press to obtain rare earth element oxalate precipitate and filtrate I.

[0047] (3) Add 8.5 wt% (10 wt%) of calcium oxide slurry (calcium oxide mass fraction) to filtrate I and stir for 30 min at 300 rpm to obtain mixed slurry III. Filter mixed slurry III 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.

[0048] In this embodiment, the REO content in the rare earth element oxalate precipitate is 45.97 wt%, the REO content in the water leaching residue is 0.95 wt%, and the REO recovery rate in fluorogypsum is 45.2 wt%; meanwhile, no new wastewater is generated.

[0049] Example 2

[0050] The fluorine content of the fluorine plaster used in this embodiment is 1.81 wt%, and the REO content is 2.52 wt%.

[0051] This embodiment recovers rare earth elements from 3 kg of fluorogypsum, and includes the following steps:

[0052] (1) Fluorogypsum, aluminum sulfate, and magnesium oxide were mixed at a weight ratio of 1:0.06:0.022 to obtain a mixture. The mixture was then mixed with water at a mass ratio of 1:2.5 to obtain slurry I. Slurry I was placed on a colloid mill and leached for 15 minutes at 20°C and a stirring speed of 3000 rpm to obtain a leaching product. The leaching product was then filtered using a plate and frame filter press to obtain a leachate and a water-leached residue. The water-leached residue was washed with 2.5 times its weight of water to obtain wash water. The wash water was used to replace fresh water in the next leaching process and was added to the mixture for leaching. If the amount of wash water was insufficient, fresh water was added.

[0053] (2) Add 4 wt% 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, obtaining mixed slurry II. Filter mixed slurry II using a plate and frame filter press to obtain rare earth element oxalate precipitate and filtrate I.

[0054] (3) Add 10 wt% (by weight of fluorogypsum) of calcium oxide slurry to filtrate I, and stir for 30 min at 300 rpm to obtain mixed slurry III. Filter mixed slurry III 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 leached residue in the next leaching. If the amount of filtrate II is insufficient, add fresh water.

[0055] In this embodiment, the REO content in the rare earth element oxalate precipitate is 45.51 wt%, the REO content in the water leaching residue is 0.97 wt%, and the REO recovery rate in fluorogypsum is 44.5 wt%; meanwhile, no new wastewater is generated.

[0056] Comparative Example 1

[0057] The only difference from Example 1 is that aluminum sulfate, the leaching aid, is not added in step (1). The REO content in the obtained rare earth element oxalate precipitate is 45.03 wt%, the REO content in the water leaching residue is 1.92 wt%, and the REO recovery rate in fluorogypsum is 22.57 wt%.

[0058] Comparative Example 2

[0059] The only difference from Example 2 is that calcium oxide was used instead of magnesium oxide as a neutralizing agent in step (1). The REO content in the obtained rare earth element oxalate precipitate was 40.56 wt%, the REO content in the water leaching residue was 1.54 wt%, and the REO recovery rate in fluorogypsum was 37.02 wt%.

[0060] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A method for treating fluorogypsum, characterized in that, Includes the following steps: 1) Mix fluorogypsum, leaching aid, and neutralizing agent at a weight ratio of 1:0.03-0.06:0.015-0.03 to obtain a mixture; mix the mixture with water at a mass ratio of 1:2-4 to obtain mixed slurry I; leach mixed slurry I at 18-30℃ for 12-40 min to obtain the leaching product; The leaching product is subjected to solid-liquid separation to obtain a leachate and a water-leached residue; wherein the leaching aid is aluminum sulfate; the neutralizing agent is magnesium oxide or magnesium hydroxide; the fluorogypsum is fluorogypsum produced during the production of anhydrous hydrogen fluoride from fluorite concentrate in Bayan Obo, and the fluorogypsum contains 1.1–3 wt% fluorine and 1.5–3.5 wt% REO. 2) Add the precipitant to the leachate and stir for 20-45 minutes to carry out the precipitation reaction, obtaining mixed slurry II; separate the solid and liquid components of mixed slurry II to obtain a precipitate containing rare earth elements and filtrate I; wherein, the precipitant is selected from at least one of oxalic acid and hydroxycarboxylic acid; the amount of precipitant added is 2-6 wt% of the weight of fluorogypsum; 3) Add the water treatment agent to filtrate I and stir for 20-45 minutes to react and obtain mixed slurry III; separate the solid and liquid of mixed slurry III to obtain mixed residue and filtrate II; wherein the water treatment agent is a calcium oxide slurry with a mass fraction of 8-15 wt%; the amount of water treatment agent added is 7-12 wt% of the weight of fluorogypsum.

2. The processing method according to claim 1, characterized in that, In step 1), the water-soaked residue is washed with water to obtain washing water.

3. The processing method according to claim 2, characterized in that, The washing water is returned to step 1) and mixed with the mixture for leaching.

4. The processing method according to claim 1, characterized in that, In step 2), the hydroxycarboxylic acid is selected from at least one of tartaric acid, citric acid, and lactic acid.

5. The method according to claim 1, characterized in that, The filtrate II obtained in step 3) is used to wash the water-soaked residue obtained in step 1).

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