Methods for extracting scandium from FeSO4•H2O, a byproduct of the sulfuric acid process for titanium dioxide production.

Abstract

This invention discloses a method for extracting scandium from FeSO4H2O, a byproduct of the sulfuric acid process for concentrating waste acid in titanium dioxide production, belonging to the field of valuable resource recovery. The method first involves dissolving FeSO4H2O in water and filtering to obtain a ferrous sulfate solution. This solution is then subjected to freeze crystallization and filtration to obtain a scandium-containing solution, with repeated cycles to increase the scandium concentration. Next, the ferric iron in the solution is reduced, and the pH is adjusted with barium hydroxide to precipitate scandium, separating a mixed solid of barium sulfate and scandium hydroxide. Scandium hydroxide is then dissolved in acid, filtered, washed, and precipitated with oxalic acid or sodium oxalate. Finally, scandium oxalate is calcined at high temperature to obtain scandium oxide with Sc2O3 ≥ 99.99% and Sc2O3 / REO ≥ 99.9999%. This method offers advantages such as convenient operation, simple process flow, low production cost, and good environmental benefits. It is easily industrialized and can efficiently recover scandium from the byproduct of sulfuric acid process for concentrating waste acid in titanium dioxide production, achieving efficient resource utilization.

Description

Technical Field

[0001] This invention belongs to the field of valuable resource recycling, specifically relating to a method for recovering FeSO4, a byproduct of the sulfuric acid process for titanium dioxide waste. Methods for extracting scandium from H2O. Background Technology

[0002] Scandium, a rare earth element, is relatively abundant globally. However, over 75% of scandium occurs in association with other minerals, posing significant challenges to its extraction. The extraction process is complex, with low overall recovery rates and high costs, all of which contribute to the persistently high price of scandium, making it one of the most expensive metals in the world.

[0003] Scandium resources are mainly distributed in minerals such as bauxite, phosphate rock (including weathered leaching phosphate deposits), vanadium-titanium magnetite, tungsten, and rare earth minerals. Currently, most scandium extraction feedstocks come from secondary resources such as waste liquids or solid wastes generated during the comprehensive utilization of associated minerals. Common secondary resources that can be used as scandium extraction feedstocks include by-products of uranium ore mining, tungsten smelting slag, hydrolyzed acidic waste liquids from the sulfuric acid process for titanium dioxide production, chlorinated dust from fluidized bed titanium extraction, titanium-containing blast furnace slag, red mud, ion-adsorption type rare earth minerals, and Bayan Obo tailings.

[0004] Because different scandium-containing raw materials have different physicochemical properties, especially in terms of chemical composition and solubility in different leaching agents, the scandium extraction process for different raw materials is also different.

[0005] The waste acid from the sulfuric acid process used to extract titanium dioxide will generate FeSO4 during evaporation and concentration. Currently, there is insufficient attention paid to the recovery and utilization of scandium from H2O crystallization, and an efficient and mature recovery process has not yet been developed. Existing scandium extraction methods generally suffer from problems such as cumbersome processes, high costs, low recovery rates, and difficulty in guaranteeing product purity, which cannot meet the needs of large-scale industrial production. Summary of the Invention

[0006] Based on this, and to address the shortcomings of the existing technology, the present invention provides a method for extracting FeSO4, a byproduct of the sulfuric acid process for titanium dioxide waste concentration. A method for extracting scandium from H2O: This method can efficiently recover FeSO4, a byproduct of the acid evaporation and concentration process in the sulfuric acid process for titanium dioxide production. Scandium, a valuable element in H2O, is extracted to obtain high-purity scandium oxide. This process offers advantages such as ease of operation, simple process flow, high efficiency, low production cost, good environmental benefits, and ease of industrialization.

[0007] To achieve the above objectives, the following technical solution is adopted: This invention provides a method for extracting FeSO4, a byproduct of the sulfuric acid process for concentrating waste acid from titanium dioxide production. The method for extracting scandium from H2O includes the following steps: S1: FeSO4, a byproduct of the sulfuric acid process for concentrating waste acid from titanium dioxide production. H2O and water are thoroughly stirred and mixed until FeSO4 is formed. After complete dissolution by H2O, the first ferrous sulfate solution is obtained by filtering out the insoluble matter. S2: Freeze-crystallize the first ferrous sulfate solution obtained in step S1, and then filter to obtain FeSO4. 7H2O crystals and scandium-containing solutions; S3: Convert FeSO4 H2O was added to the scandium-containing solution obtained in step S2 and stirred thoroughly until FeSO4 was obtained. H2O completely dissolves the ferrous sulfate solution to obtain a second ferrous sulfate solution; the second ferrous sulfate solution is then subjected to freeze crystallization following the same procedure as in step S2, and then filtered to obtain FeSO4. 7H2O crystals and scandium-containing solution; repeat the above process several times until the scandium concentration in the obtained scandium-containing solution reaches the predetermined concentration; S4: Use a reducing agent to fully reduce the ferric iron formed by oxidation in the scandium-containing solution obtained in step S3 to a predetermined concentration, and then filter to obtain the filtrate; S5: Adjust the pH of the filtrate to the set value using barium hydroxide solution, and filter to obtain a mixed precipitate of barium sulfate precipitate and scandium hydroxide precipitate; S6: Dissolve scandium hydroxide in the mixed precipitate of barium sulfate precipitate and scandium hydroxide precipitate with acid solution. Stir vigorously during the dissolution process. After the scandium hydroxide is completely dissolved, filter and wash the system to obtain scandium-containing filtrate. S7: Precipitate scandium in the scandium-containing filtrate obtained in step S6 with oxalic acid or sodium oxalate. After complete precipitation, filter to obtain scandium oxalate as the precipitate. Scandium oxalate is then calcined at high temperature to obtain scandium oxide with Sc2O3≥99.99% and Sc2O3 / REO≥99.9999%.

[0008] In some embodiments, in step S1, FeSO4, a byproduct of the sulfuric acid waste acid concentration process for titanium dioxide, is... H2O and water are mixed at a mass ratio of (5-7):10 at 50℃-70℃ until FeSO4 is formed. H2O dissolves completely.

[0009] In some embodiments, in step S2, the freezing crystallization temperature is controlled at -5~10℃; the first ferrous sulfate solution obtained in step S1 is subjected to freezing crystallization according to a three-stage temperature control system. The first stage is from 50℃~70℃ to natural cooling or cooling at a rate of 1~20℃ / min to 30℃~40℃; the second stage is from 30℃~40℃ to 20℃~25℃ at a rate of 1~5℃ / min; and the third stage is from 20℃~25℃ to -5℃~10℃ at a rate of 0.02~1℃ / min. The cooling process is carried out by simultaneous stirring at a frequency of 100~500 rpm.

[0010] In some embodiments, in step S3, FeSO4 is... H2O and the scandium-containing solution obtained in step S2 are mixed thoroughly at 50-70°C in a mass ratio of (0.5~3):7 until FeSO4 is formed. The solution is completely dissolved by H2O to obtain a second ferrous sulfate solution; the predetermined concentration of scandium in the scandium-containing solution must be ≥0.01 g / L, and is usually selected as 0.04 g / L-0.1 g / L. In some embodiments, in step S5, the concentration of barium hydroxide is ≥0.01 mol / L, and the pH value of the filtrate is 3.5-5.5; after filtration, the filtrate also yields a ferrous sulfate solution, which is then recycled for use in steps S1-S3.

[0011] In some embodiments, in step S6, the acid solution is selected from sulfuric acid, hydrochloric acid or nitric acid with a concentration ≥0.1mol / L; after the scandium hydroxide is completely dissolved, the system is filtered and washed to obtain barium sulfate, which is then recovered after washing and filtration, and the obtained wash water is used to prepare an acid solution for dissolving scandium hydroxide. In some embodiments, in step S7, the concentration of oxalic acid or sodium oxalate is ≥0.1mol / L, the amount of oxalic acid or sodium oxalate used is 1-1.5 times the theoretical amount required to completely precipitate scandium, and the pH value of the final scandium precipitation mixture is controlled at 0-5.5.

[0012] In some embodiments, in step S5, the concentration of the barium hydroxide solution is 0.2-2 mol / L, the reaction temperature during the precipitation process is ≥0℃, and the rate of addition of the barium hydroxide solution is 4-10 ml / (min). 100ml scandium-containing solution).

[0013] In some embodiments, in step S6, the concentration of the acid solution is 1-3.5 mol / L, the reaction temperature during the dissolution process is controlled at 0-90℃, the liquid-to-solid ratio (ml:g) of the acid solution and the mixed precipitate is ≥1, and the liquid-to-solid ratio (ml:g) of the washing process is ≥1; countercurrent washing is performed, and the number of washing stages is 3-5.

[0014] In some embodiments, in step S7, the concentration of oxalic acid or sodium oxalate is 0.5-1.5 mol / L, the amount of oxalic acid or sodium oxalate used is 1-1.1 times the theoretical amount required to completely precipitate scandium, the precipitation temperature is ≥10℃, the washing liquid-to-solid ratio (ml:g) is ≥1, countercurrent washing is performed, and the number of washing stages is 3-5.

[0015] In some embodiments, in step S4, the reducing agent is selected from reduced iron powder, sulfur dioxide, or sodium metabisulfite.

[0016] In some embodiments, in step S7, scandium in the scandium-containing filtrate obtained in step S6 is precipitated with oxalic acid or sodium oxalate. After complete precipitation, the filtrate is filtered, and the obtained filtrate can be recycled for the above-mentioned oxalic acid or sodium oxalate precipitation process. The precipitate is washed countercurrently and filtered to obtain scandium oxalate and wash water. The wash water can be recycled for the process of washing the precipitate to obtain scandium oxalate. The scandium oxalate is calcined at 600-900℃ for 3-8 hours to finally obtain scandium oxide with Sc2O3≥99.99% and Sc2O3 / REO≥99.9999%.

[0017] The present invention has the following beneficial technical effects: 1. Simple and efficient process: This invention achieves the extraction of FeSO4, a byproduct of the sulfuric acid process for titanium dioxide waste acid concentration, from FeSO4 through a series of orderly steps, including dissolution, freeze crystallization, reduction, precipitation, dissolution again, reprecipitation, and calcination. Scandium is efficiently extracted from H2O. The entire process is rationally designed, and through multiple cycles of dissolution and crystallization, the concentration of the scandium-containing solution is effectively increased, laying a good foundation for subsequent precipitation and purification. The operation steps are simple, clear, and easy to control.

[0018] 2. Low cost: In terms of raw materials, FeSO4, a byproduct originally considered waste during the sulfuric acid process for titanium dioxide production, is utilized. Using H2O as a raw material for scandium extraction transforms waste into a valuable resource, reducing raw material costs. Regarding reagents, the selected reducing iron powder, sulfur dioxide, sodium metabisulfite, barium hydroxide, oxalic acid, or sodium oxalate are all common chemical raw materials, relatively inexpensive, and used in reasonable quantities. Furthermore, the recycling design in the process, such as the recycling of ferrous sulfate solution and the reuse of wash water, further reduces production costs and improves resource utilization.

[0019] 3. High Product Purity: After processing using the method of this invention, the final scandium oxide obtained has extremely high purity, with Sc2O3 ≥ 99.99% and Sc2O3 / REO ≥ 99.9999%. This is due to the precise control of reaction conditions in each step, such as temperature, pH value, and reagent dosage, which effectively removes impurities, ensures high product purity, and meets the stringent purity requirements of high-end fields for scandium oxide.

[0020] 4. Easy to industrialize: The method involved in this invention is easy to operate, has undemanding equipment requirements, and the process parameters and operating conditions used are easy to implement and control in industrial production. Whether it is the reaction temperature, stirring speed, or reagent addition amount, these can all be precisely adjusted using conventional industrial equipment and control systems, making it suitable for large-scale industrial production and providing a feasible technical solution for the industrial recycling of scandium resources. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 The present invention relates to FeSO4, a byproduct of the sulfuric acid process for concentrating waste acid in titanium dioxide production. A flowchart of the method for extracting scandium from H2O. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0024] It should be understood that the embodiments of the invention shown in the exemplary embodiments are merely illustrative. Although only a few embodiments have been described in detail in this invention, those skilled in the art will readily recognize that various modifications are possible without substantially departing from the teachings of the invention. Accordingly, all such modifications should be included within the scope of the invention. Other substitutions, modifications, variations, and deletions can be made to the design, operating conditions, and parameters of the following exemplary embodiments without departing from the spirit of the invention.

[0025] Based on the above objectives, a first aspect of the embodiments of the present invention provides a method for extracting FeSO4, a byproduct of the sulfuric acid process for concentrating waste acid from titanium dioxide production. Methods for extracting scandium from H2O. Figure 1 The diagram shown is a schematic flowchart of the method.

[0026] like Figure 1 As shown, the method may include the following steps: S1: FeSO4, a byproduct of the sulfuric acid process for concentrating waste acid from titanium dioxide production. H2O and water are thoroughly stirred and mixed until FeSO4 is formed. After complete dissolution by H2O, the first ferrous sulfate solution is obtained by filtering out the insoluble matter. S2: Freeze-crystallize the first ferrous sulfate solution obtained in step S1, and then filter to obtain FeSO4. 7H2O crystals and scandium-containing solutions; S3: Convert FeSO4 H2O was added to the scandium-containing solution obtained in step S2 and stirred thoroughly until FeSO4 was obtained. H2O completely dissolves the ferrous sulfate solution to obtain a second ferrous sulfate solution; the second ferrous sulfate solution is then subjected to freeze crystallization following the same procedure as in step S2, and then filtered to obtain FeSO4. 7H2O crystals and scandium-containing solution; continue the above process several times until the scandium concentration in the obtained scandium-containing solution reaches the predetermined concentration, which must be ≥0.01g / L, usually 0.04 g / L-0.1g / L; several times is defined as n times, n≥0.

[0027] S4: Use a reducing agent to fully reduce the ferric iron formed by oxidation in the scandium-containing solution obtained in step S3 to a predetermined concentration, and then filter to obtain the filtrate; the reducing agent is selected from reduced iron powder, sulfur dioxide or sodium metabisulfite.

[0028] S5: Adjust the pH of the filtrate to 3.5-5.5 with barium hydroxide solution, and filter to obtain a mixed precipitate of barium sulfate and scandium hydroxide; the mixed precipitate of barium sulfate and scandium hydroxide is used for the next step of scandium extraction and barium sulfate recovery. S6: Dissolve scandium hydroxide in the mixed precipitate of barium sulfate precipitate and scandium hydroxide precipitate with acid solution. Stir vigorously during the dissolution process. After the scandium hydroxide is completely dissolved, filter and wash the system to obtain scandium-containing filtrate. S7: Precipitate scandium in the scandium-containing filtrate obtained in step S6 with oxalic acid or sodium oxalate. After complete precipitation, filter to obtain scandium oxalate as the precipitate. Scandium oxalate is then calcined at high temperature to obtain scandium oxide with Sc2O3≥99.99% and Sc2O3 / REO≥99.9999%.

[0029] Scandium in the scandium-containing filtrate obtained in step S6 is precipitated with oxalic acid or sodium oxalate. After complete precipitation, the filtrate is filtered and can be recycled for the above-mentioned oxalic acid or sodium oxalate precipitation process. The precipitate is washed and filtered to obtain scandium oxalate and wash water. The wash water can be recycled for the process of washing the precipitate to obtain scandium oxalate. The scandium oxalate is calcined at 600-900℃ for 3-8 hours to finally obtain scandium oxide with Sc2O3≥99.99% and Sc2O3 / REO≥99.9999%.

[0030] In some embodiments, in step S1, FeSO4, a byproduct of the sulfuric acid waste acid concentration process for titanium dioxide, is... H2O and water are mixed at a mass ratio of (5-7):10 at 50℃-70℃ until FeSO4 is formed. H2O dissolves completely.

[0031] In some embodiments, FeSO4 is a byproduct of the sulfuric acid waste acid evaporation and concentration process in the sulfuric acid process for titanium dioxide production. H2O is typically yellow, and its scandium content is ≥5 g / t, with common scandium content ranges from 30 to 60 g / t. FeSO4 There are no specific requirements for the stirring intensity when mixing H2O and water, as long as FeSO4 is stirred. The H2O and water should be thoroughly mixed to ensure no solid sediment remains in the reactor, thus dissolving FeSO4. The water used for H2O can be tap water, distilled water, or treated water with a total ion concentration of <0.1% obtained from the factory. The dissolution time depends on the time required for complete dissolution. The higher the concentration of scandium and ferrous sulfate in the solution obtained from this process, the better.

[0032] In some embodiments, in step S2, the freezing crystallization temperature is controlled at -5 to 10°C. The first ferrous sulfate solution obtained in step S1 is subjected to freezing crystallization according to a three-stage temperature control regime. The first stage involves natural cooling from 50°C to 70°C or cooling to 30°C to 40°C at a cooling rate of 1 to 20°C / min. The second stage involves cooling from 30°C to 40°C to 20°C to 25°C at a cooling rate of 1 to 5°C / min. The third stage involves cooling from 20°C to 25°C to -5°C to 10°C at a cooling rate of 0.02 to 1°C / min. Stirring is performed simultaneously during the cooling process at a stirring frequency of 100 to 500 rpm. The purpose of this process is to convert ferrous sulfate in the solution into FeSO4. Crystallization with 7H2O was used to control the cooling gradient and cooling rate to improve the FeSO4 concentration. The crystallization efficiency of 7H2O and the reduction of FeSO4 The loss of scandium in the solution caused by the precipitation of 7H2O crystals.

[0033] In some embodiments, in step S3, FeSO4 is... H2O and the scandium-containing solution obtained in step S2 are mixed thoroughly at 50-70°C in a mass ratio of (0.5~3):7 until FeSO4 is formed. The FeSO4 solution is completely dissolved in H2O to obtain a second ferrous sulfate solution. There are no specific requirements for the stirring intensity, as long as FeSO4 is stirred thoroughly. The H2O and scandium-containing solution should be thoroughly mixed until no solid deposits are observed in the reactor. The freezing crystallization temperature can be controlled between -5 and 10°C, with the following three-stage temperature control: the first stage involves natural cooling from 50-70°C or a cooling rate of 1-20°C / min to 30-40°C; the second stage involves cooling from 30-40°C to 20-25°C at a cooling rate of 1-5°C / min; and the third stage involves cooling from 20-25°C to -5-10°C at a cooling rate of 0.02-1°C / min. Stirring must be performed simultaneously during the cooling process at a frequency of 100-500 rpm. The purpose of this process is to convert ferrous sulfate in the solution into FeSO4. Crystallize in 7H2O and filter to obtain FeSO4. 7H2O crystals and scandium-containing solution; continue repeating the above process for "FeSO4". The process of "mixing and dissolving scandium in H2O and scandium-containing solution", "freezing and crystallizing ferrous sulfate solution and filtering" is repeated n times, n≥0, until the scandium concentration in the scandium-containing solution n reaches a predetermined concentration, i.e., ≥0.01g / L, usually 0.04~0.1g / L. The purpose of this process is to increase the scandium concentration in the scandium-containing solution n, which will be used as the raw material for subsequent scandium precipitation. However, the scandium concentration should not be too high, as an excessively high concentration can easily lead to the freezing and crystallization of scandium sulfate and FeSO4. Co-crystallization occurs in 7H2O or FeSO4 Scandium sulfate is trapped in the 7H2O crystals, leading to the loss of scandium in the scandium-containing solution.

[0034] In some embodiments, in step S5, the concentration of barium hydroxide is ≥0.01mol / L, and the precipitation process is stirred to ensure that no solids are deposited at the bottom of the reactor; the reaction time depends on the endpoint pH, preferably the endpoint pH is controlled at 3.5~5.5; after filtration, the filtrate also yields a ferrous sulfate solution, which is then recycled for use in steps S1-S3.

[0035] In some embodiments, in step S6, the acid solution is selected from sulfuric acid, hydrochloric acid or nitric acid with a concentration ≥0.1mol / L; after the scandium hydroxide is completely dissolved, the system is filtered and washed to obtain barium sulfate, which is then washed and filtered to recover the barium sulfate, and the obtained wash water is used to prepare an acid solution for dissolving scandium hydroxide.

[0036] In some embodiments, in step S7, the concentration of oxalic acid or sodium oxalate is ≥0.1 mol / L, and the amount of oxalic acid or sodium oxalate used is 1-1.5 times the theoretical amount required to completely precipitate scandium; the pH value of the scandium precipitation endpoint mixture is controlled at 0-5.5, preferably at 2.5-3.5.

[0037] In some embodiments, in step S5, the concentration of the barium hydroxide solution is 0.2-2 mol / L, the reaction temperature during precipitation is ≥0℃, preferably 30-60℃; and the rate of addition of the barium hydroxide solution is 4-10 ml / (min). The "100ml scandium-containing solution" refers to the filtrate adjusted with barium hydroxide solution in step S5. This filtrate is obtained by filtering the scandium-containing solution in step S4, and therefore is also a scandium-containing solution.

[0038] In some embodiments, in step S6, the concentration of the acid solution is preferably 1-3.5 mol / L, and the dissolution process is intensified by stirring to ensure that no solids are deposited at the bottom of the reactor; the reaction temperature during the dissolution process is controlled at 0-90℃, preferably 20-40℃; the liquid-to-solid ratio (ml:g) of the acid solution and the mixed precipitate is ≥1, preferably 5-10; the washing process has a washing liquid-to-solid ratio (ml:g) ≥1, preferably 3-5; countercurrent washing is performed, and the number of washing stages is 3-5.

[0039] In some embodiments, in step S7, the concentration of oxalic acid or sodium oxalate is 0.5-1.5 mol / L, the amount of oxalic acid or sodium oxalate used is 1-1.1 times the theoretical amount required to completely precipitate scandium, the precipitation temperature is ≥10℃, the washing liquid-to-solid ratio (ml:g) is ≥1, countercurrent washing is performed, and the number of washing stages is 3-5.

[0040] In some embodiments, in step S4, the amount of reduced iron powder, sulfur dioxide, and sodium metabisulfite added depends on the concentration of ferric iron in the scandium-containing solution n, as long as all the ferric iron in the scandium-containing solution n is reduced to ferrous iron.

[0041] This invention utilizes FeSO4, a byproduct of the sulfuric acid process for concentrating waste acid in titanium dioxide production. The solution is fully dissolved in H2O, and the leachate is subjected to freeze crystallization to remove FeSO4. 7H2O, then use the filtrate obtained by freeze crystallization and filtration to fully dissolve FeSO4. H2O, then freeze-crystallize the filtrate to remove FeSO4. 7H2O, thus cycling FeSO4 The dissolution of H2O and FeSO4 The method of this invention involves crystallizing 7H2O to obtain a high-scandium concentration solution as a raw material for scandium precipitation. Then, a reducing agent is used to reduce the ferric iron in the solution. Next, barium hydroxide is used to precipitate scandium, resulting in a mixture of barium sulfate and scandium hydroxide. The scandium hydroxide in this mixture is dissolved in acid to obtain a scandium-containing solution. Scandium ions in this solution are then precipitated with oxalic acid or sodium oxalate. After filtration and washing, scandium oxalate is obtained. Scandium oxalate is then calcined to obtain scandium oxide with Sc2O3 ≥ 99.99% and Sc2O3 / REO ≥ 99.9999%. This method is convenient to operate, has a simple process flow, low production cost, good environmental benefits, and is easy to industrialize. It can efficiently recover FeSO4, a byproduct of the sulfuric acid process for concentrating waste acid in titanium dioxide production. Scandium is a valuable element in H2O.

[0042] This method prioritizes environmental protection throughout the scandium extraction process. Wastewater and waste generated at each step are rationally treated and recycled, reducing waste emissions. For example, the recovery and reuse of barium sulfate precipitate and the recycling of washing water not only reduce environmental pollution but also maximize resource utilization, aligning with the concept of sustainable development.

[0043] The present invention will be further illustrated by the following examples.

[0044] Example 1 Step S1: Take FeSO4, a byproduct of the sulfuric acid waste acid concentration process for titanium dioxide production. H2O, with a scandium content of 40 g / t, weigh out 500 g of this FeSO4. Add H2O to 1000g of distilled water and stir at 60℃ and 200rpm until FeSO4 is obtained. The H2O completely dissolved the solution. The solution was then filtered to obtain a high-concentration ferrous sulfate solution 1.

[0045] Step S2: Transfer ferrous sulfate solution 1 to a freeze crystallization apparatus and perform freeze crystallization according to a temperature control regime. First, allow it to cool naturally from 60°C to 30°C, then reduce the temperature from 30°C to 20°C at a cooling rate of 3°C / min, and finally reduce the temperature from 20°C to 0°C at a cooling rate of 0.05°C / min. Throughout the cooling process, maintain the stirring frequency at 300 rpm. After freeze crystallization, filter the solution to obtain FeSO4. 7H2O crystals and scandium-containing solution 1.

[0046] Step S3: Weigh 150g of FeSO4 H2O was added to scandium-containing solution 1, and the mixture was stirred at 60°C and 200 rpm to mix FeSO4. H2O completely dissolved, yielding a high-concentration ferrous sulfate solution 2. Ferrous sulfate solution 2 was then subjected to freeze crystallization under the same conditions as in step S2. After filtration, FeSO4 was obtained. 3. 7H₂O crystals and scandium-containing solution. Repeat the "FeSO₄" process. The process of mixing and dissolving scandium in H2O and a scandium-containing solution, freezing and crystallizing in a high-concentration ferrous sulfate solution, and filtering was repeated three times to finally obtain scandium-containing solution 4. The scandium concentration in scandium-containing solution 4 was found to be 0.035 g / L.

[0047] Step S4: Add an appropriate amount of reduced iron powder to the scandium-containing solution 4. Calculate the amount of reduced iron powder to be added based on the concentration of ferric iron in the solution (excess iron powder can also be used for reduction). Stir the reaction thoroughly to reduce all ferric iron to ferrous iron. Then filter to obtain the filtrate.

[0048] Step S5: Prepare a 0.5 mol / L barium hydroxide solution. Slowly add the barium hydroxide solution to the filtrate while stirring, controlling the addition rate to be 6 ml / min. 100 ml of scandium-containing solution was used, and the reaction temperature was controlled at 40℃. The pH of the solution was adjusted to 4.0, and after the pH stabilized, it was filtered to obtain a mixed precipitate solid of ferrous sulfate solution, barium sulfate precipitate, and scandium hydroxide precipitate. The ferrous sulfate solution was collected for subsequent dissolution of FeSO4. H2O.

[0049] Step S6: Dissolve the mixed precipitate of barium sulfate and scandium hydroxide using 2 mol / L sulfuric acid. Stir at 30°C, maintaining a liquid-to-solid ratio of 8:1. After complete dissolution of the scandium hydroxide, filter and wash with distilled water at a liquid-to-solid ratio of 4:1, using a three-stage countercurrent process. This yields a scandium-containing filtrate and barium sulfate. The barium sulfate is recovered after washing and filtration, and the wash water is used to prepare sulfuric acid for dissolving scandium hydroxide.

[0050] Step S7: Prepare a 1 mol / L oxalic acid solution. Add the oxalic acid solution to the scandium-containing filtrate, using 1.1 times the theoretical amount required for complete scandium precipitation. Perform the precipitation reaction at 40°C, controlling the final pH of the precipitation to 3.0. After complete precipitation, filter the solution, reusing the filtrate for the scandium precipitation process. Wash and filter the solid to obtain scandium oxalate, with a washing liquid-to-solid ratio of 4:1, washing three times. Place the scandium oxalate in a muffle furnace and calcine at 700°C for 5 hours to finally obtain scandium oxide with a Sc2O3 content of 99.99% and a Sc2O3 / REO ratio of 99.9999%.

[0051] Example 2 Step S1: Select FeSO4, a byproduct of the sulfuric acid waste acid concentration process for titanium dioxide production. H2O, with a scandium content of 85 g / t, 600 g of this FeSO4 was weighed out. Add H2O to 1200g of dilute water with a total ion concentration <0.1%, and stir at 55℃ and 250rpm until FeSO4 is obtained. H2O completely dissolved. After filtration, a high-concentration ferrous sulfate solution 1 was obtained.

[0052] Step S2: Place ferrous sulfate solution 1 into a freeze crystallization apparatus and perform freeze crystallization according to the temperature control regime. The temperature is lowered from 55°C to 30°C at a rate of 10°C / min, then from 30°C to 20°C at a rate of 2°C / min, and finally from 20°C to -2°C at a rate of 0.03°C / min, while maintaining a stirring frequency of 350 rpm. After freeze crystallization, filter to obtain FeSO4. 7H2O crystals and scandium-containing solution 1.

[0053] Step S3: Weigh 200g of FeSO4 H2O was added to scandium-containing solution 1, and the mixture was stirred at 55°C and 250 rpm to mix FeSO4. H2O completely dissolved, yielding a high-concentration ferrous sulfate solution 2. Ferrous sulfate solution 2 was then subjected to freeze crystallization under the same conditions as in step S2. After filtration, FeSO4 was obtained. 3. 7H₂O crystals and scandium-containing solution. Repeat "FeSO₄". The process of mixing and dissolving scandium in H2O and a scandium-containing solution, freezing and crystallizing in a high-concentration ferrous sulfate solution, and filtering was repeated three times to obtain scandium-containing solution 4, in which the scandium concentration was 0.081 g / L.

[0054] Step S4: Pass an appropriate amount of sulfur dioxide gas into the scandium-containing solution 4. Determine the amount of sulfur dioxide to be passed in based on the concentration of ferric iron in the solution. Allow the ferric iron to react completely and be reduced to ferrous iron. Then filter to obtain the filtrate.

[0055] Step S5: Prepare a 0.3 mol / L barium hydroxide solution. Slowly add the barium hydroxide solution dropwise to the filtrate while stirring, controlling the dropping rate to 5 ml / min. 100 ml of scandium-containing solution was used, and the reaction temperature was maintained at 35°C. The pH of the solution was adjusted to 4.2, and after the pH stabilized, it was filtered to obtain a mixed solid of ferrous sulfate solution, barium sulfate precipitate, and scandium hydroxide precipitate. The ferrous sulfate solution was collected for subsequent dissolution of FeSO4. H2O.

[0056] Step S6: Dissolve the mixed solid of barium sulfate and scandium hydroxide in 1.5 mol / L hydrochloric acid at 25°C with stirring. The liquid-to-solid ratio of acid to mixed solid is 7:1. After the scandium hydroxide is completely dissolved, filter and wash with deionized water at a liquid-to-solid ratio of 3:1, using a 4-stage countercurrent washing process. This yields a scandium-containing filtrate and barium sulfate. The barium sulfate is recovered after washing and filtration, and the wash water is used to prepare hydrochloric acid for dissolving scandium hydroxide.

[0057] Step S7: Prepare a 0.8 mol / L sodium oxalate solution. Add the sodium oxalate solution to the scandium-containing filtrate, using 1.05 times the theoretical amount required for complete scandium precipitation. Conduct the precipitation reaction at 35°C, controlling the final pH of the precipitation to 2.8. After complete precipitation, filter the solution, reusing the filtrate for the scandium precipitation process. Wash and filter the solid to obtain scandium oxalate, with a washing liquid-to-solid ratio of 3:1, washing four times. Place the scandium oxalate in a muffle furnace and calcine at 650°C for 6 hours to finally obtain scandium oxide with a Sc2O3 content of 99.99% and a Sc2O3 / REO ratio of 99.9999%.

[0058] Example 3 Step S1: Take FeSO4, a byproduct of the sulfuric acid waste acid concentration process for titanium dioxide production. H2O, with a scandium content of 50 g / t, is weighed out as follows: 700 g of this substance FeSO4 Add H2O to 1400g of tap water and stir at 70℃ and 300rpm until FeSO4 is obtained. The H2O completely dissolved the solution. After filtration, a high-concentration ferrous sulfate solution was obtained.

[0059] Step S2: Transfer ferrous sulfate solution 1 to a freeze crystallizer and perform freeze crystallization according to a controlled temperature regime. The temperature is lowered from 70°C to 30°C at a rate of 15°C / min, then from 30°C to 20°C at a rate of 4°C / min, and finally from 20°C to 5°C at a rate of 0.08°C / min, while maintaining a stirring frequency of 400 rpm. After freeze crystallization, filter to obtain FeSO4. 7H2O crystals and scandium-containing solution 1.

[0060] Step S3: Weigh 250g of FeSO4 H2O was added to scandium-containing solution 1, and the mixture was stirred at 70°C and 300 rpm to mix FeSO4. H2O completely dissolved, yielding a high-concentration ferrous sulfate solution 2. Ferrous sulfate solution 2 was then subjected to freeze crystallization under the same conditions as in step S2. After filtration, FeSO4 was obtained. 3. 7H₂O crystals and scandium-containing solution. Repeat "FeSO₄". The process of mixing and dissolving H2O with a scandium-containing solution, freezing and crystallizing with a high-concentration ferrous sulfate solution, and filtering was repeated five times to obtain scandium-containing solution 6. The scandium concentration in scandium-containing solution 6 was measured to be 0.066 g / L.

[0061] Step S4: Add an appropriate amount of sodium metabisulfite to the scandium-containing solution 6. Calculate the amount of sodium metabisulfite to be added based on the concentration of ferric iron in the solution. Stir the reaction thoroughly to reduce all ferric iron to ferrous iron. After the reaction is complete, filter to obtain the filtrate.

[0062] Step S5: Prepare a 1 mol / L barium hydroxide solution. Slowly add the barium hydroxide solution to the filtrate while stirring, controlling the addition rate to be 8 ml / min. 100 ml of scandium-containing solution was used, and the reaction temperature was controlled at 50℃. The pH of the solution was adjusted to 4.5, and after the pH stabilized, it was filtered to obtain a mixed solid of ferrous sulfate solution, barium sulfate precipitate, and scandium hydroxide precipitate. The ferrous sulfate solution was used for subsequent dissolution of FeSO4. H2O.

[0063] Step S6: Dissolve the mixed solid of barium sulfate and scandium hydroxide in 3 mol / L nitric acid at 35°C with stirring. The liquid-to-solid ratio of acid to mixed solid is 9:1. After the scandium hydroxide is completely dissolved, filter and wash with distilled water at a liquid-to-solid ratio of 5:1, repeating the washing process three times. This yields a scandium-containing filtrate and barium sulfate. The barium sulfate is recovered after washing and filtration, and the wash water is used to prepare nitric acid to dissolve the scandium hydroxide.

[0064] Step S7: Prepare a 1.2 mol / L oxalic acid solution. Add the oxalic acid solution to the scandium-containing filtrate, using 1.1 times the theoretical amount required for complete scandium precipitation. Perform the precipitation reaction at 50°C, controlling the final pH of the precipitation to 3.2. After complete precipitation, filter the solution, reusing the filtrate for the scandium precipitation process. Wash and filter the solid to obtain scandium oxalate, using a 5:1 solid-liquid ratio, and perform a three-stage countercurrent washing process. Place the scandium oxalate in a muffle furnace and calcine at 800°C for 4 hours to obtain scandium oxide with a Sc2O3 content of 99.99% and a Sc2O3 / REO ratio of 99.9999%.

[0065] The above are exemplary embodiments disclosed in this invention. However, it should be noted that various changes and modifications can be made without departing from the scope of the embodiments of this invention as defined by the claims. Although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular number.

[0066] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of different aspects of the invention exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method for extracting FeSO4, a byproduct of the sulfuric acid process for concentrating waste acid from titanium dioxide production. The method for extracting scandium from H2O is characterized by... Includes the following steps: S1: FeSO4, a byproduct of the sulfuric acid process for concentrating waste acid from titanium dioxide production. H2O and water are thoroughly mixed until FeSO4 is formed. After complete dissolution by H2O and filtration to remove insoluble matter, the first ferrous sulfate solution is obtained. S2: Freeze-crystallize the first ferrous sulfate solution obtained in step S1, and then filter to obtain FeSO4. 7H₂O crystals and scandium-containing solutions; S3: Convert FeSO4 H2O was added to the scandium-containing solution obtained in step S2 and stirred thoroughly until FeSO4 was obtained. H2O completely dissolves the ferrous sulfate solution to obtain a second ferrous sulfate solution; the second ferrous sulfate solution is then subjected to freeze crystallization following the same procedure as in step S2, and then filtered to obtain FeSO4. 7H2O crystals and scandium-containing solution; repeat the above process several times until the scandium element concentration in the obtained scandium-containing solution reaches the predetermined concentration; S4: Use a reducing agent to fully reduce the ferric iron formed by oxidation in the scandium-containing solution obtained in step S3 to a predetermined concentration, and then filter to obtain the filtrate; S5: Adjust the pH of the filtrate to 3.5-5.5 with barium hydroxide solution, and filter to obtain a mixed precipitate of barium sulfate precipitate and scandium hydroxide precipitate; S6: Dissolve scandium hydroxide in the mixed precipitate of barium sulfate precipitate and scandium hydroxide precipitate with acid solution. Stir vigorously during the dissolution process. After the scandium hydroxide is completely dissolved, filter and wash the system to obtain scandium-containing filtrate. S7: Precipitate scandium in the scandium-containing filtrate obtained in step S6 with oxalic acid or sodium oxalate. After complete precipitation, filter and wash to obtain scandium oxalate as precipitate. Scandium oxalate is then calcined at high temperature to obtain scandium oxide with Sc2O3≥99.99% and Sc2O3 / REO≥99.9999%.

2. The FeSO4 byproduct from the sulfuric acid waste acid concentration process of titanium dioxide production according to claim 1. The method for extracting scandium from H2O is characterized by... In step S1, FeSO4, a byproduct of the sulfuric acid waste acid concentration process for titanium dioxide production, is... H2O and water are mixed thoroughly at a mass ratio of (5-7):10 at 50℃-70℃ until FeSO4 is formed. H2O dissolves completely.

3. The FeSO4 byproduct from the sulfuric acid waste acid concentration process of titanium dioxide production according to claim 1. The method for extracting scandium from H2O is characterized by... In step S2, the freezing crystallization temperature is controlled at -5~10℃. The first ferrous sulfate solution obtained in step S1 is subjected to freezing crystallization according to a three-stage temperature control system. The first stage is from 50℃~70℃ to natural cooling or cooling at a rate of 1~20℃ / min to 30℃~40℃. The second stage is from 30℃~40℃ to 20℃~25℃ at a rate of 1~5℃ / min. The third stage is from 20℃~25℃ to -5℃~10℃ at a rate of 0.02~1℃ / min. The cooling process is carried out simultaneously with stirring at a frequency of 100~500 rpm.

4. The FeSO4 byproduct from the sulfuric acid waste acid concentration process of titanium dioxide production according to claim 1. The method for extracting scandium from H2O is characterized by... In step S3, FeSO4 is... H2O and the scandium-containing solution obtained in step S2 are mixed thoroughly at 50-70°C in a mass ratio of (0.5~3):7 until FeSO4 is formed. After complete dissolution by H2O, a second ferrous sulfate solution is obtained; the predetermined concentration of scandium in the scandium-containing solution must be ≥0.01 g / L.

5. The FeSO4 byproduct from the sulfuric acid waste acid concentration process of titanium dioxide production according to claim 1. The method for extracting scandium from H2O is characterized by... In step S5, the concentration of barium hydroxide is ≥0.01 mol / L; after filtration, the filtrate also yields a ferrous sulfate solution, which is then recycled for use in steps S1-S3.

6. The FeSO4 byproduct from the sulfuric acid waste acid concentration process of titanium dioxide production according to claim 1 The method for extracting scandium from H2O is characterized by... In step S6, the acid solution is selected from sulfuric acid, hydrochloric acid or nitric acid with a concentration ≥0.1mol / L; after the scandium hydroxide is completely dissolved, the system is filtered and washed to obtain barium sulfate, which is then washed and filtered to recover the barium sulfate. The obtained wash water is used to prepare an acid solution for dissolving scandium hydroxide.

7. The FeSO4 byproduct from the sulfuric acid waste acid concentration process of titanium dioxide production according to claim 1. The method for extracting scandium from H2O is characterized by... In step S7, the concentration of oxalic acid or sodium oxalate is ≥0.1mol / L, the amount of oxalic acid or sodium oxalate used is 1-1.5 times the theoretical amount required to completely precipitate scandium, and the pH value of the final scandium precipitation mixture is controlled at 0-5.

5.

8. The FeSO4 byproduct from the sulfuric acid waste acid concentration process of titanium dioxide production according to claim 4. The method for extracting scandium from H2O is characterized by... In step S5, the concentration of barium hydroxide solution is 0.2-2 mol / L, the reaction temperature during precipitation is ≥0℃, and the rate of addition of barium hydroxide solution is 4-10 ml / min.

9. The FeSO4 byproduct from the sulfuric acid waste acid concentration process of titanium dioxide production according to claim 5. The method for extracting scandium from H2O is characterized by... In step S6, the concentration of the acid solution is 1-3.5 mol / L, the reaction temperature during the dissolution process is controlled at 0-90℃, the liquid-to-solid ratio of the acid solution and the mixed precipitate is ml:g≥1, the liquid-to-solid ratio during the washing process is ml:g≥1; countercurrent washing is performed, and the number of washing stages is 3-5.

10. The FeSO4 byproduct from the sulfuric acid waste acid concentration process of titanium dioxide production according to claim 6. The method for extracting scandium from H2O is characterized by... In step S7, the concentration of oxalic acid or sodium oxalate is 0.5-1.5 mol / L, the amount of oxalic acid or sodium oxalate used is 1-1.1 times the theoretical amount required to completely precipitate scandium, the precipitation temperature is ≥10℃, the washing solution-to-solid ratio is ml:g≥1, countercurrent washing is performed, and the number of washing stages is 3-5.

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