Method for preparing high-purity calcium sulfate dihydrate whiskers from electrolytic manganese residues

Abstract

The invention provides a method for preparing high-purity calcium sulfate dihydrate whiskers from electrolytic manganese residues. The preparation method comprises the following steps: drying the electrolytic manganese residues and preparing the electrolytic manganese residues into electrolytic manganese residue powder; mixing the electrolytic manganese residue powder with an ammonium chloride solution, and reacting to obtain a mixed solution; carrying out solid-liquid separation on the mixed solution to obtain a first filtrate; under the condition that the molar ratio of calcium to magnesium in the first filtrate is 13-20, aging to obtain a filter cake; under the condition that the molar ratio of calcium to magnesium in the first filtrate is not 13-20, adjusting the molar ratio of calcium to magnesium, and then aging to obtain a filter cake; washing and drying the filter cake to obtain high-purity calcium sulfate dihydrate whiskers; wherein the phase of the high-purity calcium sulfate dihydrate whisker is a gypsum phase, the content of calcium sulfate dihydrate is greater than 99%, the whiteness is greater than 90, the diameter of the whisker is 5-15 [mu] m, and the length-diameter ratio is 10-25. According to the method, the high-purity and high-whiteness calcium sulfate dihydrate crystal whiskers can be prepared by taking the electrolytic manganese residues as the raw material without adding a crystal form control agent.

Description

Technical Field

[0001] The present invention relates to the field of resource utilization of electrolytic manganese slag. Specifically, it relates to a method for preparing high-purity calcium sulfate dihydrate whiskers from electrolytic manganese slag. Background Art

[0002] A whisker is a fibrous material with a diameter of only a few micrometers and a length of dozens of micrometers generated in the form of a single crystal under artificially controlled conditions. It has characteristics such as a large aspect ratio and no grain boundaries. Due to this inherent integrity of the whisker, its strength is not strictly limited by the surface integrity, and it is tougher than polycrystalline fibers and glass fibers. Whisker materials can be widely used in industries such as plastics, rubber, papermaking, friction materials, coatings, paints, thermal insulation materials, environmental engineering, and lightweight building materials due to their excellent reinforcing properties.

[0003] In the production process of electrolytic metallic manganese, after a series of processes such as sulfuric acid leaching and solid-liquid separation of manganese ore, electrolytic manganese products are obtained, and electrolytic manganese slag is a by-product generated in this process. The production volume of electrolytic manganese slag is relatively large. Generally, for every 1 ton of electrolytic metallic manganese produced, 7 - 12 tons of electrolytic manganese slag are generated. China is a major producer of electrolytic manganese, with an annual new increase in electrolytic manganese slag of about 10 million tons, and the cumulative amount over the years has exceeded 100 million tons. Electrolytic manganese slag faces great pressure for resource utilization. Producing high-purity calcium sulfate dihydrate whiskers from electrolytic manganese slag can not only realize the resource utilization of electrolytic manganese slag but also save the natural gypsum resources used in the production of traditional high-purity calcium sulfate dihydrate whiskers.

[0004] So far, no research on preparing calcium sulfate dihydrate whiskers from electrolytic manganese slag has been found, and no relevant reports on preparing high-purity calcium sulfate dihydrate whiskers from electrolytic manganese slag under low-temperature and normal-pressure conditions using a salt solution as an auxiliary agent have been found. Summary of the Invention

[0005] The purpose of the present invention is to solve at least one of the above-mentioned deficiencies existing in the prior art. For example, the purpose of the present invention is to provide a method for preparing high-purity calcium sulfate dihydrate whiskers from electrolytic manganese slag.

[0006] To achieve the above object, the present invention provides a method for preparing high-purity calcium sulfate dihydrate whiskers from electrolytic manganese slag. The preparation method includes: (1) drying the electrolytic manganese slag and making it into electrolytic manganese slag powder; (2) mixing the electrolytic manganese slag powder and ammonium chloride solution, and obtaining a mixed solution after reaction; (3) performing solid-liquid separation on the mixed solution to obtain a first filtrate; (4) aging to obtain a filter cake when the molar ratio of calcium to magnesium in the first filtrate is 13-20; when the molar ratio of calcium to magnesium in the first filtrate is not 13-20, adjusting the molar ratio of calcium to magnesium, and then aging to obtain a filter cake; (5) washing and drying the filter cake to obtain high-purity calcium sulfate dihydrate whiskers; wherein, the phase of the high-purity calcium sulfate dihydrate whiskers is gypsum phase, the content of calcium sulfate dihydrate is greater than 99%, the whiteness is greater than 90, the diameter of the whiskers is 5-15 μm, and the aspect ratio is 10-25.

[0007] Optionally, the concentration of the ammonium chloride solution is 1-5 mol / L; the ratio of the ammonium chloride solution to the electrolytic manganese slag powder is 15-25 mL / g.

[0008] Optionally, the reaction in step (2) includes reacting in a constant temperature water bath shaking table, the rotation speed of the shaking table is 150-240 r / min, the reaction temperature is room temperature-100 °C, and the reaction time is 2-60 min.

[0009] Optionally, the aging temperature is 0-5 °C, and the aging time is 12-48 h.

[0010] Optionally, the electrolytic manganese slag powder in step (1) can pass through an 80-mesh sieve, and the drying includes drying by baking, and the baking temperature does not exceed 40 °C.

[0011] Optionally, the drying in step (5) includes drying by baking, the baking temperature does not exceed 40 °C, and drying until the adsorbed water of the calcium sulfate dihydrate whiskers is removed.

[0012] Optionally, the preparation method further includes repeating steps (1)-(5) with the second filtrate instead of the ammonium chloride solution to continue preparing high-purity calcium sulfate dihydrate whiskers.

[0013] Further optionally, when repeating steps (1)-(5) until the soluble salts in the filtrate are supersaturated, ammonium chloride and ammonium sulfate in the filtrate are recovered; then, by adding ammonia water to adjust the pH value, the manganese ions enriched in the filtrate are precipitated in the form of manganese hydroxide and separated and recovered to obtain a third filtrate, and the third filtrate is used to prepare the ammonium chloride solution in step (2).

[0014] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0015] (1) Innovatively, ammonium chloride is used as an auxiliary agent in the present invention. First, calcium sulfate dihydrate in the electrolytic manganese residue is separated and dissolved to separate it from pyrite, mica, etc. that affect whiteness. Moreover, this method directly and completely utilizes the calcium sulfate dihydrate in the electrolytic manganese residue, which is essentially different from some existing studies that only use calcium components to prepare calcium carbonate.

[0016] (2) Since the electrolytic manganese residue itself contains magnesium ions, the present invention can use it to replace magnesium chloride as a crystal form control agent for preparing whisker materials, laying a foundation for obtaining calcium sulfate dihydrate whiskers without adding a crystal form control agent under specific conditions. Furthermore, it is possible to prepare high-purity and high-whiteness calcium sulfate dihydrate whiskers using the electrolytic manganese residue as the raw material without adding a crystal form control agent.

[0017] (3) Ammonium chloride is used as an auxiliary agent to extract calcium sulfate dihydrate from the electrolytic manganese residue in the present invention. The original calcium sulfate dihydrate, ammonium magnesium sulfate, and manganese ions in the raw material are transferred into the solution, and the remaining pyrite, mica, quartz, etc. that are insoluble in the ammonium chloride solution are enriched. The direct reason restricting the application of electrolytic manganese residue in building materials is the large amount of soluble salts and heavy metal ions it contains. Through the dissolution of ammonium chloride, these soluble components have been separated from components such as quartz, so that the ammonium chloride leaching residue of the electrolytic manganese residue can be directly used in the building materials field, thereby realizing the full-component resource utilization of the electrolytic manganese residue.

[0018] (4) The present invention fully utilizes the calcium sulfate dihydrate in the electrolytic manganese residue. The added ammonium chloride auxiliary agent always exists in the solution in the form of ions and can be recycled for dissolving calcium sulfate dihydrate in the raw material until the amount of ammonium magnesium sulfate dissolved in the filtrate continuously increases and the ammonium sulfate contained in the solution reaches supersaturation and precipitates. Therefore, the entire preparation process is carried out at low temperature and normal pressure, and the auxiliary agent can be recycled multiple times. There is no wastewater discharge in the whole process, which is green and efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Through the following description in conjunction with the drawings, the above and other objects and / or features of the present invention will become clearer, where:

[0020] Figure 1 Shows the XRD pattern of the product obtained in Example 1 of the present invention.

[0021] Figure 2 Shows the SEM image of the product obtained in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, a method for preparing high-purity calcium sulfate dihydrate whiskers from electrolytic manganese residue according to the present invention will be described in detail in conjunction with exemplary embodiments.

[0023] It should be noted that "first", "second", "third", etc. are only for convenience of description and easy distinction, and should not be construed as indicating or implying relative importance.

[0024] Exemplary Embodiment 1

[0025] This exemplary embodiment provides a method for preparing high-purity calcium sulfate dihydrate whiskers from electrolytic manganese slag. The preparation method may include:

[0026] S1. Dry the electrolytic manganese slag and make it into electrolytic manganese slag powder.

[0027] In this embodiment, the electrolytic manganese slag powder can pass through a 80-mesh sieve. The drying may include drying by baking, and the baking temperature does not exceed 40°C, such as 15°C, 25°C, 36°C, and 40°C, etc.

[0028] Among them, the electrolytic manganese slag powder can pass through a 80-mesh sieve to improve the dissolution rate of calcium sulfate dihydrate in the electrolytic manganese slag. The purpose of drying is to remove the adsorbed water of the electrolytic manganese slag.

[0029] S2. Mix the electrolytic manganese slag powder and ammonium chloride solution, and obtain a mixed solution after reaction.

[0030] In this embodiment, the concentration of the ammonium chloride solution is 1-5 mol / L, such as 1.1 mol / L, 1.6 mol / L, 2.7 mol / L, 3.8 mol / L, and 4.9 mol / L, etc.

[0031] Among them, too low a concentration of ammonium chloride is not conducive to the dissolution of calcium sulfate dihydrate in the electrolytic manganese slag, and too high a concentration of ammonium chloride is close to the supersaturation of ammonium chloride, which is not conducive to the preparation of the solution.

[0032] In this embodiment, the ratio of the ammonium chloride solution to the electrolytic manganese slag powder is 15-25 mL / g, such as 15 mL / g, 18 mL / g, 19.5 mL / g, 21 mL / g, and 24.5 mL / g, etc.

[0033] Among them, the electrolytic manganese slag contains a large amount of soluble salts. The addition of ammonium chloride solution makes the concentration of total soluble ions in the solution relatively high. Therefore, too low a liquid-solid ratio makes the concentration of soluble ions in the system relatively high, which is not conducive to the dissolution of calcium sulfate dihydrate in the electrolytic manganese slag; while too high a liquid-solid ratio will reduce the concentration of calcium ions in the system, affect the molar ratio of calcium to magnesium in the system, and thus is not conducive to the precipitation of calcium sulfate dihydrate whiskers in the subsequent process.

[0034] In this embodiment, the reaction includes reacting in a thermostatic water bath shaker, the rotation speed of the shaker being 150 - 240 r / min, such as 160 r / min, 170 r / min, 210 r / min, 230 r / min, etc.; the temperature of the reaction being room temperature - 100 °C, such as 25 °C, 38 °C, 55 °C, 75 °C, 99 °C, etc.; and the time of the reaction being 2 - 60 min, such as 3 min, 15 min, 28 min, 40 min, 59 min, etc.

[0035] Among them, too low reaction temperature and too short reaction time are not conducive to the dissolution of calcium sulfate dihydrate, while too high reaction temperature and too long reaction time will increase the reaction cost. Therefore, the above reaction time and reaction temperature.

[0036] S3. Perform solid-liquid separation on the mixed solution to obtain a first filtrate.

[0037] The solid-liquid separation in step S3 also yields a filter cake, which is washed, dried, and used for subsequent resource utilization research. For example, through chemical composition analysis, it can be used as a raw material in the building materials field.

[0038] S4. Add magnesium chloride or water to the first filtrate as needed to adjust the molar ratio of calcium to magnesium to 13 - 20, and age to obtain a filter cake; of course, if the molar ratio of calcium to magnesium is between 13 and 20, no adjustment is required.

[0039] In this embodiment, the main purpose of adjusting the molar ratio of calcium to magnesium to 13 - 20 is to facilitate the attachment of magnesium ions to the surface of the crystal nuclei of calcium sulfate dihydrate during the recrystallization of calcium ions and sulfate ions in the solution into calcium sulfate dihydrate, enabling it to grow along the one-dimensional direction and thus grow into calcium sulfate dihydrate whiskers.

[0040] In this embodiment, the temperature of the aging is 0 - 5 °C, such as 0 °C, 1 °C, 3 °C, 4 °C, etc.; the time of the aging is 12 - 48 h, such as 12.5 h, 18 h, 25 h, 38 h, 47 h, etc.

[0041] Among them, when the aging temperature is below 0 °C, the solution freezes and cannot precipitate; the formation process of calcium sulfate dihydrate whiskers in the system is a process of recrystallization - dissolution - recrystallization. Too high an aging temperature increases the solubility of calcium sulfate dihydrate in the system, thus being unfavorable for the formation of calcium sulfate dihydrate whiskers. Too short an aging time is not conducive to the growth of calcium sulfate dihydrate whiskers, while too long an aging time leads to an increase in cost. Therefore, the above aging time and aging temperature are selected.

[0042] S5. Wash and dry the filter cake to obtain high-purity calcium sulfate dihydrate whiskers; wherein, the phase of the high-purity calcium sulfate dihydrate whiskers is the gypsum phase, the content of calcium sulfate dihydrate is greater than 99%, the whiteness is greater than 90, the diameter of the whiskers is 5-15 μm, and the aspect ratio is 10-25.

[0043] In this embodiment, the drying may include drying by baking, and the temperature of baking does not exceed 40°C, such as 20°C, 25°C, 36°C, and 40°C, etc., until the adsorbed water on the surface of the calcium sulfate dihydrate whiskers is removed.

[0044] In this embodiment, the preparation method further includes repeating steps S1-S5 with the second filtrate instead of the ammonium chloride solution to continue preparing high-purity calcium sulfate dihydrate whiskers.

[0045] In this embodiment, when repeating steps S1-S5 until the soluble salts in the filtrate are supersaturated, ammonium chloride and ammonium sulfate in the filtrate are recovered; then, the pH value is adjusted by adding ammonia water so that the enriched manganese ions in the filtrate precipitate in the form of manganese hydroxide and are separated and recovered to obtain a third filtrate, and the third filtrate is used to prepare the ammonium chloride solution described in step S2, such as replacing water to prepare the ammonium chloride solution.

[0046] To better understand the above exemplary embodiments of the present invention, the following further illustrates them with specific examples.

[0047] Example 1

[0048] Take a certain amount of electrolytic manganese slag sample, dry it at 40°C, grind it into powder, and pass it through an 80-mesh sieve to obtain electrolytic manganese slag powder; take 20 g of electrolytic manganese slag powder and place it in a 1000 mL conical flask, add 500 mL of 2.5 mol / L ammonium chloride solution to the conical flask, place the conical flask in a shaker, the shaker speed is 200 r / min, and after reacting at 50°C for 50 min, filter it to obtain the first filtrate.

[0049] Take 400 mL of the above Ca 2+ The leaching solution, i.e., the first filtrate, is poured into a 500 mL beaker, and the molar ratio of calcium to magnesium in the solution is controlled to be 13 by adding magnesium chloride or water; the beaker is placed in a reactor, and the temperature of the reactor is controlled by a high and low temperature integrated machine. After aging and reacting at 5°C for 30 hours, filter it to obtain a filter cake, wash the filter cake, and dry it at 40°C to obtain calcium sulfate dihydrate whiskers. The phase of the obtained whiskers is gypsum ( Figure 1 ), the microscopic morphology is fibrous, the diameter of the fiber is about 5-8 μm, the length is about 15-35 μm, the whiteness of the whiskers is 96.8, and the content of calcium sulfate dihydrate in the whiskers is 99.74%.

[0050] Perform XRD testing on the obtained product, and the results are as Figure 1 shown, as Figure 1As shown, the phase of the obtained product is the gypsum phase, and the diffraction peaks of gypsum are relatively sharp, indicating that the crystallization degree of gypsum crystals in the sample is good; no diffraction peaks of other crystals are found except for gypsum, indicating that the purity of the product is high and its phase is the only gypsum phase.

[0051] The obtained product was tested by scanning electron microscopy, and the SEM image shown in Figure 2 was obtained. It can be seen from Figure 2 that the microscopic morphology of the obtained product is fibrous, the diameter of the fiber is about 5 - 8 μm, and the length is about 15 - 35 μm.

[0052] Example 2

[0053] A certain amount of electrolytic manganese slag sample was taken, dried at 40 °C, ground into powder, and passed through an 80 - mesh sieve to obtain electrolytic manganese slag powder; 40 g of electrolytic manganese slag powder was placed in a 1000 mL conical flask, 900 mL of 0.5 mol / L ammonium chloride solution was added to the conical flask, the conical flask was placed in a shaker, the shaker speed was 200 r / min, and after reacting at 80 °C for 60 min, filtration was carried out to obtain the first filtrate.

[0054] 800 mL of the above - mentioned Ca 2+ leaching solution, that is, the first filtrate, was poured into a 1000 mL beaker, and the molar ratio of calcium to magnesium in the solution was controlled to be 16.5 by adding magnesium chloride or water; the beaker was placed in a reactor, and the temperature of the reactor was controlled by a high - low temperature integrated machine. After aging at 1 °C for 40 hours, filtration was carried out to obtain a filter cake. The filter cake was washed and dried at 40 °C to obtain calcium sulfate dihydrate whiskers. The phase of the obtained whiskers is gypsum, the microscopic morphology is fibrous, the diameter of the fiber is about 2 - 6 μm, the length is about 12 - 28 μm, the whiteness of the whiskers is 95.7, and the content of calcium sulfate dihydrate in the whiskers is 99.65%.

[0055] Although the present invention has been described above in conjunction with exemplary embodiments and the accompanying drawings, those of ordinary skill in the art should clearly understand that various modifications can be made to the above - mentioned embodiments without departing from the spirit and scope of the claims.

Claims

1. A method for preparing high-purity calcium sulfate dihydrate whiskers from electrolytic manganese slag, characterized in that, The preparation method includes the following steps: (1) drying electrolytic manganese residue and making it into electrolytic manganese residue powder; (2) mixing the electrolytic manganese residue powder with ammonium chloride solution, and obtaining a mixed solution after reaction; (3) performing solid-liquid separation on the mixed solution to obtain a first filtrate; (4) aging to obtain a filter cake when the molar ratio of calcium to magnesium in the first filtrate is 13-20; when the molar ratio of calcium to magnesium in the first filtrate is not 13-20, adjusting the molar ratio of calcium to magnesium, and then aging to obtain a filter cake; (5) washing and drying the filter cake to obtain high-purity calcium sulfate dihydrate whiskers; wherein the phase of the high-purity calcium sulfate dihydrate whiskers is gypsum phase, the content of calcium sulfate dihydrate is greater than 99%, the whiteness is greater than 90, the diameter of the whiskers is 5-15 μm, and the aspect ratio is 10-25.

2. The method for preparing high-purity calcium sulfate dihydrate whiskers from electrolytic manganese residue according to claim 1, wherein, The concentration of the ammonium chloride solution is 1-5 mol / L; the ratio of the ammonium chloride solution to the electrolytic manganese residue powder is 15-25 mL / g.

3. The method for preparing high-purity calcium sulfate dihydrate whiskers from electrolytic manganese slag according to claim 1, characterized in that, The reaction in step (2) includes reacting in a constant temperature water bath shaking table, the rotation speed of the shaking table is 150-240 r / min, the reaction temperature is room temperature - 100 °C, and the reaction time is 2-60 min.

4. A method for preparing high-purity calcium sulfate dihydrate whiskers from electrolytic manganese slag according to claim 1, characterized in that, The temperature of the aging is 0-5 °C, and the time of the aging is 12-48 h.

5. The method for preparing high-purity calcium sulfate dihydrate whiskers from electrolytic manganese slag according to claim 1, wherein, In step (1), the electrolytic manganese residue powder can pass through an 80-mesh sieve, and the drying includes drying by baking, and the temperature of baking does not exceed 40 °C.

6. The method for preparing high-purity calcium sulfate dihydrate whiskers from electrolytic manganese residue according to claim 1, wherein, The drying in step (5) includes drying by baking, the temperature of baking does not exceed 40 °C, and drying until the adsorbed water on the surface of the calcium sulfate dihydrate whiskers is removed.

7. A method for preparing high-purity calcium sulfate dihydrate whiskers from electrolytic manganese slag according to claim 1, characterized in that, The preparation method further includes repeating steps (1)-(5) with the second filtrate instead of the ammonium chloride solution to continue preparing high-purity calcium sulfate dihydrate whiskers.

8. A method for preparing high-purity calcium sulfate dihydrate whiskers from electrolytic manganese slag according to claim 2, characterized in that, When repeating steps (1)-(5) until the soluble salts in the filtrate are supersaturated, ammonium chloride and ammonium sulfate in the filtrate are recovered; then the pH value is adjusted by adding ammonia water so that the enriched manganese ions in the filtrate precipitate in the form of manganese hydroxide and are separated and recovered, obtaining a third filtrate, and the third filtrate is used to prepare the ammonium chloride solution in step (2).

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