Method for recovering scandium from byproduct ferrous sulfate monohydrate in sulfuric acid process titanium white waste acid concentration process

Abstract

The invention discloses a method for recovering scandium from a byproduct ferrous sulfate monohydrate in a sulfuric acid process titanium white waste acid concentration process, which comprises the following steps: adding water to dissolve the byproduct ferrous sulfate monohydrate, filtering to obtain a first ferrous sulfate solution, and enabling the pH value of the first ferrous sulfate solution to be less than or equal to 2.5; the first ferrous sulfate solution reacts with metallic iron, iron ions in the solution exist in the form of ferrous ions, then filtering is conducted, and a second ferrous sulfate solution is obtained; adjusting the pH value of the second ferrous sulfate solution to 3.5-5 by adopting an alkaline substance, and filtering to obtain a third ferrous sulfate solution and scandium-containing filter residues; and adding acid into the scandium-containing filter residue, stirring, and then filtering to obtain a scandium-containing solution and a mixed solid of an insoluble titanium compound and calcium sulfate. According to the method, scandium in the scandium can be efficiently recycled, high-purity scandium oxide can be obtained, and the method is convenient to operate, simple in technological process, high in efficiency, low in production cost, good in environmental protection benefit and easy to industrialize.

Description

Technical Field

[0001] The invention relates to the technical field of valuable resource recovery, in particular to a method for producing ferrous sulfate monohydrate as a by-product in the process of concentrating waste acid of titanium dioxide produced by a sulfuric acid process. Background Art

[0002] Scandium is a rare earth element and a strategic resource. The world is rich in scandium resources, with reserves of about 2 million tons. my country's scandium reserves are about 650,000 tons, but more than 75% of scandium is associated with other minerals. The complex scandium extraction process, low recovery rate throughout the process, and high costs are the main reasons for the high price of scandium products. Scandium is known as one of the most expensive metals in the world. Domestic scandium ore resources are primarily distributed in bauxite, phosphate rock (including weathered and leached phosphate deposits), vanadium-titanium magnetite, tungsten, and rare earth ores. Current raw materials for scandium extraction primarily come from secondary resources, such as wastewater or solid waste generated during the comprehensive utilization of associated minerals. These secondary resources include uranium byproducts, tungsten smelting slag, hydrolysis acidic wastewater from sulfuric acid titanium dioxide production, chlorinated fumes from boiling titanium extraction, titanium-containing blast furnace slag, red mud, ion-adsorbed rare earth ores, and Bayan Obo tailings. Different scandium-containing raw materials vary in their physical and chemical properties, particularly their chemical composition and solubility in different leaching agents, requiring different scandium extraction processes. Currently, research on the recovery of scandium from ferrous sulfate monohydrate, a byproduct of the waste acid concentration process for titanium dioxide production, is lacking in the industry.

[0003] Based on this, the existing technology still needs to be improved. Summary of the Invention

[0004] In order to solve the above technical problems, the embodiments of the present invention propose a method for recovering ferrous sulfate monohydrate, a by-product of the waste acid concentration process of titanium dioxide produced by the sulfuric acid method, so as to solve the problem of recovering the scandium element in the ferrous sulfate monohydrate, a by-product of the waste acid concentration process of titanium dioxide produced by the sulfuric acid method in the prior art.

[0005] To solve the above technical problems, some embodiments of the present invention disclose a method for recovering scandium from ferrous sulfate monohydrate, a by-product of the sulfuric acid process titanium dioxide waste acid concentration process, comprising: Step 1: dissolving the by-product ferrous sulfate monohydrate in water and filtering to obtain a first ferrous sulfate solution, and adjusting the pH value of the first ferrous sulfate solution to ≤2.5; Step 2: reacting the first ferrous sulfate solution with metallic iron to make the iron ions in the solution exist in the form of divalent iron ions, and then filtering to obtain a second ferrous sulfate solution; Step 3: Using an alkaline substance to adjust the pH value of the second ferrous sulfate solution to 3.5-5 and then filtering to obtain a third ferrous sulfate solution and a scandium-containing filter residue; Step 4: Add acid to the scandium-containing filter residue and stir, then filter to obtain a scandium-containing solution and a mixed solid of the insoluble titanium compound and calcium sulfate.

[0006] In some embodiments, the present invention further comprises: Step 5: After using a precipitant to precipitate scandium in the scandium-containing solution, filtering to obtain a scandium salt; and performing a high-temperature roasting treatment on the scandium salt to obtain scandium oxide.

[0007] In some embodiments, in step 1, the scandium content in the by-product ferrous sulfate monohydrate is ≥1 g / t; during dissolution, the mass ratio of the by-product ferrous sulfate monohydrate to water is (5-7):10, and the dissolution temperature is 45-75°C.

[0008] In some embodiments, in step 1, making the pH value of the first ferrous sulfate solution ≤ 2.5 comprises: The pH of the obtained first ferrous sulfate solution is detected. If the pH is greater than 2.5, sulfuric acid is added to the first ferrous sulfate solution to adjust the pH.

[0009] In some embodiments, in step 2, the metallic iron is iron powder or iron filings.

[0010] In some embodiments, in step 3, the alkaline substance is one or a mixture of two or more of calcium oxide, calcium hydroxide, and calcium carbonate; Alternatively, adjusting the pH value of the second ferrous sulfate solution to 3.5-5 using an alkaline substance comprises: First, the alkaline substance is added at a rate of 0.5-5 g / (min·100 ml of the second ferrous sulfate solution) to adjust the pH of the second ferrous sulfate solution to 3, and then the pH of the second ferrous sulfate solution is adjusted to 3.5-5 at a rate of 0.1-1 g / (min·100 ml of the second ferrous sulfate solution).

[0011] In some embodiments, in step 4, the acid is a hydrochloric acid solution, the concentration of the hydrochloric acid solution is ≥0.1 mol / L; the reaction temperature is 0-90°C, and the liquid-to-solid ratio of the hydrochloric acid solution to the scandium-containing filter residue is ≥1 mL / g.

[0012] In some embodiments, in step 4, the acid is a hydrochloric acid solution having a concentration of 0.1-1.5 mol / L; the reaction temperature is 20-40° C., and the liquid-to-solid ratio of the hydrochloric acid solution to the scandium-containing filter residue is ≥3-10 mL / g.

[0013] In some embodiments, in step 5, the precipitant is oxalic acid or sodium oxalate, and the concentration of the precipitant is ≥0.1 mol / L, the amount of the precipitant added is 1 to 1.2 times the theoretical mass required for complete precipitation of scandium, the pH of the scandium precipitation endpoint is controlled at 2.5 to 3.5, and the precipitation temperature is ≥10°C; The high temperature calcination treatment is calcination at 500-900° C. for 4-9 hours.

[0014] In some embodiments, in step five, the concentration of the precipitant is 0.1-1.5 mol / L, and the precipitation temperature is 30-60°C.

[0015] By adopting the above technical solution, the present invention has at least the following beneficial effects: The present invention provides a method for producing ferrous sulfate monohydrate as a by-product in the sulfuric acid process titanium dioxide waste acid concentration process, which can efficiently recover scandium and obtain high-purity scandium oxide. The method is easy to operate, has a simple process flow, high efficiency, low production cost, good environmental benefits, and is easy to industrialize. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 The present invention discloses a process flow chart of a method for producing ferrous sulfate monohydrate as a by-product during the concentration of waste acid from titanium dioxide produced by a sulfuric acid process, according to some embodiments of the present invention. DETAILED DESCRIPTION

[0018] The following embodiments of the present disclosure are further described in detail with reference to the accompanying drawings and examples. The detailed description of the following examples and the accompanying drawings are intended to illustrate the principles of the present disclosure, but are not intended to limit the scope of the present disclosure. The present disclosure can be implemented in many different forms and is not limited to the specific embodiments disclosed herein, but rather includes all technical solutions within the scope of the claims.

[0019] The present disclosure provides these embodiments in order to make this disclosure thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that: unless otherwise specifically stated, the relative arrangement of parts and steps, the composition of materials, numerical expressions and numerical values ​​set forth in these embodiments should be interpreted as merely exemplary, and not as limiting.

[0020] It should be noted that, in the description of this disclosure, unless otherwise specified, "plurality" means greater than or equal to two; terms such as "upper," "lower," "left," "right," "inner," and "outer" indicating directions or positional relationships are intended solely to facilitate and simplify the description of this disclosure, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on this disclosure. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0021] In addition, the terms "first," "second," and similar terms used in this disclosure do not denote any order, quantity, or importance, but are merely used to distinguish different parts. "Perpendicular" does not mean perpendicular in the strict sense, but rather means within the tolerance range. "Parallel" does not mean parallel in the strict sense, but rather means within the tolerance range. "Include" or "comprising" and similar terms mean that the elements preceding the term include the elements listed after the term, and do not exclude the possibility of also including other elements.

[0022] It should also be noted that, in the description of this disclosure, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to direct connections or indirect connections through an intermediary. Those skilled in the art will understand the specific meanings of the above terms in this disclosure depending on the specific circumstances. When a specific device is described as being located between a first device and a second device, there may or may not be an intervening device between the specific device and the first or second device.

[0023] All terms used in this disclosure have the same meaning as understood by one of ordinary skill in the art to which this disclosure belongs, unless otherwise specifically defined. It should also be understood that terms defined in, for example, common dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant art, and should not be interpreted in an idealized or highly formal sense, unless explicitly defined as such herein.

[0024] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered part of the specification.

[0025] like Figure 1 As shown, some embodiments of the present invention disclose a method for producing ferrous sulfate monohydrate as a by-product from a sulfuric acid process titanium dioxide waste acid concentration process, comprising: Step 1: dissolving the by-product ferrous sulfate monohydrate in water and filtering to obtain a first ferrous sulfate solution, and adjusting the pH value of the first ferrous sulfate solution to ≤2.5; Step 2: reacting the first ferrous sulfate solution with metallic iron to make the iron ions in the solution exist in the form of divalent iron ions, and then filtering to obtain a second ferrous sulfate solution; Step 3: Using an alkaline substance to adjust the pH value of the second ferrous sulfate solution to 3.5-5 and then filtering to obtain a third ferrous sulfate solution and a scandium-containing filter residue; Step 4: Add acid to the scandium-containing filter residue and stir, then filter to obtain a scandium-containing solution and a mixed solid of the insoluble titanium compound and calcium sulfate.

[0026] Step 5: After using a precipitant to precipitate scandium in the scandium-containing solution, filtering to obtain a scandium salt; and performing a high-temperature roasting treatment on the scandium salt to obtain scandium oxide.

[0027] This embodiment uses water to dissolve ferrous sulfate monohydrate, and the ferric iron formed by oxidation during the reduction and dissolution of metallic iron as divalent iron. This not only avoids the introduction of other impurity elements but also reduces iron precipitation during subsequent pH adjustment for scandium precipitation. This method is easy to operate, has a simple process flow, low production costs, and is easily industrializable. It can efficiently recover the valuable element scandium from ferrous sulfate monohydrate, a byproduct of the sulfuric acid process for titanium dioxide waste acid concentration.

[0028] In some embodiments of the present invention, based on the above-described embodiment, in step 3, the alkaline substance can be selected from one or more mixtures of calcium oxide, calcium hydroxide, and calcium carbonate; When adjusting the pH value, the alkaline substance can be first added at a rate of 0.5 to 5 g / (min·100 ml of the second ferrous sulfate solution), and after adjusting the pH of the second ferrous sulfate solution to 3, the pH of the second ferrous sulfate solution is adjusted to 3.5 to 5 at a rate of 0.1 to 1 g / (min·100 ml of the second ferrous sulfate solution). The present embodiment adjusts the pH with calcium salts such as calcium oxide, calcium hydroxide, or calcium carbonate, which can precipitate scandium without introducing foreign ions, because the dissolved calcium can form insoluble calcium sulfate with a high concentration of sulfate radicals. At the same time, by strictly controlling the addition rate of the alkaline substance, the scandium in the solution can be better precipitated, thereby improving the extraction rate.

[0029] Some embodiments of the present invention also disclose a method for recovering scandium from ferrous sulfate monohydrate, a by-product of the sulfuric acid titanium dioxide waste acid concentration process. The method is easy to operate, has a simple process flow, high efficiency, low production cost, good environmental benefits, and is easy to industrialize. It can efficiently recover the valuable element scandium from ferrous sulfate monohydrate, a by-product of the sulfuric acid titanium dioxide waste acid evaporation concentration process, and obtain high-purity scandium oxide. Figure 1 As shown, specifically including: S1: ferrous sulfate monohydrate, a by-product of the sulfuric acid process titanium dioxide waste acid concentration process, and water are thoroughly stirred and mixed in an appropriate mass ratio under appropriate temperature conditions until the ferrous sulfate monohydrate is completely dissolved, and insoluble matter is filtered out to obtain a high-concentration ferrous sulfate solution 1. If the pH of the ferrous sulfate solution 1 is greater than 2.5, an appropriate amount of sulfuric acid is added to control the pH of the ferrous sulfate solution 1 to be ≤2.5; Generally, ferrous sulfate monohydrate, a by-product of the evaporation and concentration process of waste acid from sulfuric acid-based titanium dioxide, is usually yellow. The scandium content of ferrous sulfate monohydrate, which can be used to recover the scandium element, must be ≥1g / t, and its scandium content is usually in the range of 30~60g / t. Sometimes, changes in the raw materials of waste acid from sulfuric acid-based titanium dioxide and the evaporation and concentration process may cause the scandium content of ferrous sulfate monohydrate to reach 200~500g / t. During dissolution, the mass of ferrous sulfate monohydrate: the mass of water = (5~7):10, the dissolution temperature is 45~75℃, and there is no specific requirement for stirring intensity. As long as the ferrous sulfate monohydrate and water are fully mixed to achieve no solid deposition in the reactor, the water used to dissolve ferrous sulfate monohydrate can be tap water, distilled water, or reclaimed water with a total ion concentration of <0.1% obtained through comprehensive treatment in the factory. The dissolution time depends on the time it takes to completely dissolve. The higher the ferrous sulfate concentration in the solution obtained in this process, the better.

[0030] S2 uses metallic iron to reduce the ferric iron formed by oxidation of the divalent iron in the ferrous sulfate solution 1, so that all the iron in the solution exists in the form of divalent iron, and filters to obtain a second ferrous sulfate solution and residual iron powder, which is returned to the reduction step for further use; The metallic iron used in this process can be iron powder or iron filings. The amount added depends on the concentration of ferric iron in the ferrous sulfate solution 1. It is sufficient as long as all the ferric iron in the ferrous sulfate solution 1 is reduced to ferrous iron.

[0031] S3: adjusting the pH of the second ferrous sulfate solution to 3.5-5 with an alkaline substance such as calcium oxide, calcium hydroxide, or calcium carbonate that can form a chemical precipitate with sulfate ions. After the reaction is complete, filtering is performed to obtain a third ferrous sulfate solution and a scandium-containing filter residue. The ferrous sulfate solution 3 can be used for freeze crystallization to prepare FeSO4·7H2O or evaporation crystallization to prepare FeSO4·H2O. The pH of the second ferrous sulfate solution can be adjusted to 3 by first adding a precipitant such as calcium oxide, calcium hydroxide or calcium carbonate at a rate of 0.5-5 g / (min·100 ml of the second ferrous sulfate solution), and then further adjusting the pH of the second ferrous sulfate solution to 3.5-5 at a rate of 0.1-1 g / (min·100 ml of the second ferrous sulfate solution). During the entire process, stirring is strengthened to ensure that no solid is deposited at the bottom of the reactor. The reaction temperature is ≥0°C, preferably 30-60°C. The reaction time and the amount of the precipitant added depend on the initial pH and the end point pH.

[0032] S4: fully mixing the hydrochloric acid solution and the scandium-containing filter residue, strengthening the stirring so that all the scandium in the scandium-containing filter residue enters the solution, filtering and washing to obtain the scandium-containing solution and a mixed solid of the insoluble titanium compound and calcium sulfate, which can be recycled; The concentration of hydrochloric acid needs to be ≥0.1 mol / L, preferably 1-3.5 mol / L. Stirring should be strengthened during the mixing process to ensure that no solids are deposited at the bottom of the reactor. The reaction temperature should be controlled at 0-90°C, preferably 20-40°C. The liquid-solid ratio (ml:g) of hydrochloric acid and scandium-containing filter residue should be ≥1, preferably 3-10. Distilled water or deionized water should be used for washing, and the washing liquid-solid ratio (ml:g) should be ≥1, preferably 5-8. Countercurrent washing should be used, and the number of washing stages should be 3-6.

[0033] S5: precipitating the scandium in the scandium-containing filtrate with oxalic acid or sodium oxalate, filtering after complete precipitation, and reusing the obtained filtrate in the above-mentioned scandium precipitation process; washing and filtering the solid to obtain scandium oxalate and washing water; the washing water can be reused in the washing process; calcining the scandium oxalate at high temperature to obtain scandium oxide with Sc2O3≥99.99% and Sc2O3 / REO≥99.9999%; The concentration of oxalic acid or sodium oxalate used for scandium precipitation needs to be ≥0.1 mol / L, preferably 0.1~1.5 mol / L, the amount of precipitant added is 1~1.2 times the theoretical amount required for complete precipitation of scandium, the pH of the scandium precipitation endpoint needs to be controlled at 2.5~3.5, the precipitation temperature needs to be ≥10°C, preferably 30~60°C, the washing liquid-solid ratio (ml:g) needs to be ≥1, preferably 3~5 times, the scandium oxalate obtained by washing and filtration is calcined at 500~900°C for 4~9h, and finally scandium oxide with Sc2O3≥99.99% and Sc2O3 / REO≥99.9999% is obtained.

[0034] Example 1 This embodiment discloses a method for recovering scandium from ferrous sulfate monohydrate, a by-product of the sulfuric acid process titanium dioxide waste acid concentration process. The ferrous sulfate monohydrate by-product of the sulfuric acid process titanium dioxide waste acid concentration process is yellow and has a scandium content of 50 g / t, comprising: S1: The by-product ferrous sulfate monohydrate and water are thoroughly stirred and mixed at a mass ratio of 7:10 at 60° C. until the ferrous sulfate monohydrate is completely dissolved. After filtering out the insoluble matter, a high-concentration first ferrous sulfate solution is obtained, and the pH value of the solution is detected to be 0.3.

[0035] S2 uses metallic iron to reduce the ferric iron formed by oxidation of the divalent iron in the first ferrous sulfate solution, so that all the iron in the solution exists in the form of divalent iron. The solution is filtered to obtain a second ferrous sulfate solution and residual iron powder, and the residual iron powder is returned to the reduction step for continued use.

[0036] S3: The pH of the second ferrous sulfate solution is adjusted to 4.0 with calcium oxide. Specifically, the pH is first adjusted to 3 at a rate of 3 g / (min·100 ml) of the second ferrous sulfate solution, and then the pH is further adjusted to 4.0 at a rate of 0.5 g / (min·100 ml) of the second ferrous sulfate solution. The reaction temperature is 45°C, and stirring is increased during the reaction. The third ferrous sulfate solution is used for freeze crystallization to prepare FeSO4·7H2O or evaporation crystallization to prepare FeSO4·H2O.

[0037] S4: fully mix the hydrochloric acid solution and the above-mentioned scandium-containing filter residue, strengthen stirring, so that all the scandium in the scandium-containing filter residue enters the solution, filter and wash to obtain the scandium-containing solution and a mixed solid of the insoluble titanium compound and calcium sulfate, and the mixed solid of the titanium compound and calcium sulfate can be recycled; the hydrochloric acid concentration is 2.2 mol / L, and the stirring is strengthened during the mixing process to ensure that no solid is deposited at the bottom of the reactor. The reaction temperature needs to be controlled at 30°C, the liquid-solid ratio (ml:g) of hydrochloric acid and the scandium-containing filter residue is 7, and distilled water or deionized water is used for washing in the washing process. The washing liquid-solid ratio (ml:g) is 6.5, and countercurrent washing is adopted, and washing is performed 5 times.

[0038] S5: precipitating the scandium in the scandium-containing filtrate with oxalic acid, filtering after complete precipitation, and reusing the obtained filtrate in the above-mentioned scandium precipitation process; washing and filtering the solid to obtain scandium oxalate and washing water; the washing water can be reused in the washing process; calcining the scandium oxalate at high temperature to obtain scandium oxide with Sc2O3≥99.99% and Sc2O3 / REO≥99.9999%; The concentration of oxalic acid used for scandium precipitation is 0.7 mol / L, the amount of precipitant added is 1.1 times the theoretical amount required for complete precipitation of scandium, the pH of the scandium precipitation endpoint is controlled at 3, the precipitation temperature is 45°C, the washing liquid-solid ratio (ml:g) is ≥1, and washing is performed 4 times. The scandium oxalate obtained by washing and filtration is calcined at 500~900°C for 4~9h, and finally scandium oxide with Sc2O3≥99.99% and Sc2O3 / REO≥99.9999% is obtained.

[0039] Example 2 Based on Example 1, the scandium content in the by-product ferrous sulfate monohydrate produced during the sulfuric acid process titanium dioxide waste acid concentration process is 300 g / t.

[0040] In S1, the by-product ferrous sulfate monohydrate and water are fully stirred and mixed at a mass ratio of 5:10 at 45° C. until the ferrous sulfate monohydrate is completely dissolved.

[0041] In S3, the pH of the second ferrous sulfate solution is adjusted to 4.5 with calcium hydroxide. Specifically, the pH is first adjusted to 3 at an addition rate of 0.5 g / (min·100 ml of the second ferrous sulfate solution), and then the pH is further adjusted to 4.5 at a rate of 1 g / (min·100 ml of the second ferrous sulfate solution). The reaction temperature is 30°C.

[0042] In S4, the concentration of hydrochloric acid is 3.5 mol / L, and stirring is strengthened during the mixing process to ensure that no solids are deposited at the bottom of the reactor. The reaction temperature needs to be controlled at 20°C. The liquid-to-solid ratio (ml:g) of hydrochloric acid and scandium-containing filter residue is 3. Distilled water or deionized water is used for washing, and the washing liquid-to-solid ratio (ml:g) is 8. Countercurrent washing is used and washed 3 times.

[0043] In S5, scandium in the above scandium-containing filtrate is precipitated with sodium oxalate. The concentration of sodium oxalate used for scandium precipitation is 0.1 mol / L. The amount of precipitant added is 1.2 times the theoretical amount required for complete precipitation of scandium. The pH of the scandium precipitation endpoint is controlled at 2.5, the precipitation temperature is 60°C, the washing liquid-to-solid ratio (ml:g) is ≥1, and washing is performed 5 times.

[0044] Example 3 Based on Example 1, the scandium content in the by-product ferrous sulfate monohydrate during the sulfuric acid process titanium dioxide waste acid concentration process is 42 g / t.

[0045] In S1, the by-product ferrous sulfate monohydrate and water are fully stirred and mixed at a mass ratio of 6:10 at 75° C. until the ferrous sulfate monohydrate is completely dissolved.

[0046] In S3, the pH of the second ferrous sulfate solution is adjusted to 3.5 with calcium hydroxide. Specifically, the pH is first adjusted to 3 at an addition rate of 5 g / (min·100 ml of the second ferrous sulfate solution), and then the pH is further adjusted to 3.5 at a rate of 0.1 g / (min·100 ml of the second ferrous sulfate solution). The reaction temperature is 60°C.

[0047] In S4, the concentration of hydrochloric acid is 1 mol / L, and stirring is strengthened during the mixing process to ensure that no solids are deposited at the bottom of the reactor. The reaction temperature needs to be controlled at 40°C. The liquid-to-solid ratio (ml:g) of hydrochloric acid and scandium-containing filter residue is 10. Distilled water or deionized water is used for washing, and the washing liquid-to-solid ratio (ml:g) is 8. Countercurrent washing is used and washed 6 times.

[0048] In S5, scandium in the scandium-containing filtrate is precipitated with sodium oxalate. The concentration of sodium oxalate used for scandium precipitation is 1.5 mol / L. The amount of precipitant added is 1 times the theoretical amount required for complete precipitation of scandium. The pH at the scandium precipitation endpoint is controlled at 3.5, the precipitation temperature is 30°C, the washing liquid-to-solid ratio (ml:g) is ≥1, and washing is performed 4 times.

[0049] The method for recovering scandium from ferrous sulfate monohydrate, a by-product of the waste acid concentration process of titanium dioxide produced by the sulfuric acid process, disclosed in the above embodiment of the present invention, comprises the following steps: fully dissolving the ferrous sulfate monohydrate, a by-product of the waste acid concentration process of titanium dioxide produced by the sulfuric acid process, reducing the trivalent iron in the solution with metallic iron, adjusting the pH with calcium oxide, calcium hydroxide or calcium carbonate, filtering to obtain a scandium-containing filter residue, dissolving the scandium hydroxide in the scandium-containing filter residue with hydrochloric acid, filtering to obtain a scandium-containing solution, precipitating the scandium ions in the solution with oxalic acid or sodium oxalate, filtering and washing to obtain scandium oxalate, and roasting the scandium oxalate to obtain scandium oxide with Sc2O3≥99.99% and Sc2O3 / REO≥99.9999%. The method is easy to operate, has a simple process flow, low production cost, good environmental benefits, is easy to industrialize, and can efficiently recover the valuable element scandium in ferrous sulfate monohydrate, a by-product of the waste acid concentration process of titanium dioxide produced by the sulfuric acid process.

[0050] Thus far, various embodiments of the present disclosure have been described in detail. To avoid obscuring the concept of the present disclosure, some details known in the art have not been described. Based on the above description, those skilled in the art can fully understand how to implement the technical solutions disclosed herein.

[0051] Although some specific embodiments of the present disclosure have been described in detail through examples, those skilled in the art will understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the present disclosure. Those skilled in the art will understand that the above embodiments may be modified or some technical features may be replaced with equivalents without departing from the scope and spirit of the present disclosure. In particular, as long as there are no structural conflicts, the various technical features mentioned in the various embodiments may be combined in any manner.

Claims

1. A method for recovering scandium from ferrous sulfate monohydrate, a by-product of the concentration process of waste acid from titanium dioxide produced by the sulfuric acid process, characterized in that: include: Step 1: dissolving the by-product ferrous sulfate monohydrate in water and filtering to obtain a first ferrous sulfate solution, and adjusting the pH value of the first ferrous sulfate solution to ≤2.5; Step 2: reacting the first ferrous sulfate solution with metallic iron to make the iron ions in the solution exist in the form of divalent iron ions, and then filtering to obtain a second ferrous sulfate solution; Step 3: adjusting the pH value of the second ferrous sulfate solution to 3.5-5 with an alkaline substance and filtering to obtain a third ferrous sulfate solution and a scandium-containing filter residue; Step 4: Add acid to the scandium-containing filter residue and stir, then filter to obtain a scandium-containing solution and a mixed solid of the insoluble titanium compound and calcium sulfate.

2. The method for recovering scandium from ferrous sulfate monohydrate, a by-product of the concentration process of waste acid from titanium dioxide produced by the sulfuric acid process, according to claim 1, characterized in that: Also includes: Step 5: Precipitating scandium in the scandium-containing solution with a precipitant, and filtering to obtain a scandium salt; The scandium salt is subjected to high-temperature calcination to obtain scandium oxide.

3. The method for recovering scandium from ferrous sulfate monohydrate, a by-product of the concentration process of waste acid from titanium dioxide produced by the sulfuric acid process, according to claim 1, characterized in that: In step 1, the scandium content in the by-product ferrous sulfate monohydrate is ≥1 g / t; during dissolution, the mass ratio of the by-product ferrous sulfate monohydrate to water is (5-7):10, and the dissolution temperature is 45-75°C.

4. The method for recovering scandium from ferrous sulfate monohydrate, a by-product of the concentration process of waste acid from titanium dioxide produced by the sulfuric acid process, according to claim 1, characterized in that: In step 1, making the pH value of the first ferrous sulfate solution ≤2.5 comprises: The pH of the obtained first ferrous sulfate solution is detected. If the pH is greater than 2.5, sulfuric acid is added to the first ferrous sulfate solution to adjust the pH.

5. The method for recovering scandium from ferrous sulfate monohydrate, a by-product of the concentration process of waste acid from titanium dioxide produced by the sulfuric acid process, according to claim 1, characterized in that: In step 2, the metallic iron is iron powder or iron filings.

6. The method for recovering scandium from ferrous sulfate monohydrate, a by-product of the concentration process of waste acid from titanium dioxide produced by the sulfuric acid process, according to claim 1, characterized in that: In step 3, the alkaline substance is one or a mixture of two or more of calcium oxide, calcium hydroxide, and calcium carbonate; Alternatively, adjusting the pH value of the second ferrous sulfate solution to 3.5-5 using an alkaline substance comprises: First, the alkaline substance is added at a rate of 0.5-5 g / (min·100 ml of the second ferrous sulfate solution) to adjust the pH of the second ferrous sulfate solution to 3, and then the pH of the second ferrous sulfate solution is adjusted to 3.5-5 at a rate of 0.1-1 g / (min·100 ml of the second ferrous sulfate solution).

7. The method for recovering scandium from ferrous sulfate monohydrate, a by-product of the concentration process of waste acid from titanium dioxide produced by the sulfuric acid process, according to claim 1, characterized in that: In step 4, the acid is a hydrochloric acid solution, the concentration of the hydrochloric acid solution is ≥0.1 mol / L; the reaction temperature is 0-90° C., and the liquid-to-solid ratio of the hydrochloric acid solution to the scandium-containing filter residue is ≥1 mL / g.

8. The method for recovering scandium from ferrous sulfate monohydrate, a by-product of the concentration process of waste acid from titanium dioxide produced by the sulfuric acid process, according to claim 1, characterized in that: In step 4, the acid is a hydrochloric acid solution having a concentration of 0.1-1.5 mol / L; the reaction temperature is 20-40° C., and the liquid-to-solid ratio of the hydrochloric acid solution to the scandium-containing filter residue is ≥3-10 mL / g.

9. The method for recovering scandium from ferrous sulfate monohydrate, a by-product of the concentration process of waste acid from titanium dioxide produced by the sulfuric acid process, according to claim 2, characterized in that: In step 5, the precipitant is oxalic acid or sodium oxalate, and the concentration of the precipitant is ≥0.1 mol / L. The amount of the precipitant added is 1 to 1.2 times the theoretical mass required for complete precipitation of scandium. The pH of the scandium precipitation endpoint is controlled at 2.5 to 3.5, and the precipitation temperature is ≥10°C. The high temperature calcination treatment is calcination at 500-900° C. for 4-9 hours.

10. The method for recovering scandium from ferrous sulfate monohydrate, a by-product of the concentration process of waste acid from titanium dioxide produced by the sulfuric acid process, according to claim 9, characterized in that: In step 5, the concentration of the precipitant is 0.1-1.5 mol / L, and the precipitation temperature is 30-60°C.

Images