A new process for preparing whiskers and recovering magnesium salts using white mud

Abstract

The present invention discloses a new process for preparing whiskers and recovering magnesium salts by using white mud, which includes: after separating white mud by sulfuric acid leaching, obtaining high-whiteness gypsum and magnesium sulfate solution containing calcium ions, then subjecting the magnesium sulfate solution containing calcium ions to decalcification treatment with carbonate to obtain high-purity magnesium sulfate solution; preparing high-purity magnesium sulfate monohydrate from the magnesium sulfate solution by a thermal crystallization method, preparing magnesium carbonate or magnesium bicarbonate by a carbonization process, and preparing high-purity magnesium oxide after calcination; preparing high-whiteness nanoscale calcium sulfate fibers and high-strength gypsum products from the high-whiteness gypsum by a hydrothermal method. The present invention not only turns waste into treasure, but also realizes the resource utilization, clean utilization and high-value utilization of white mud in the rare earth production industry.

Description

Technical Field

[0001] The present invention relates to the fields of solid waste recycling, environmental protection, and material preparation, and particularly to a new process for preparing whiskers from white mud to recover magnesium salts. Background Art

[0002] As a typical solid waste in the rare earth industry in China, white mud not only has relatively high contents of magnesium and calcium elements, but also has a finer particle size and a higher alkalinity. Although it belongs to the type of solid waste resources that are difficult to utilize in China, like the magnesium- and calcium-containing waste salts generated by industries such as petrochemical, coal chemical, and salt chemical industries, the key problems lie in the following aspects.

[0003] (1) The existing technology has poor economic benefits, resulting in too high costs when only extracting magnesium elements in the existing technology, making it difficult for enterprises to accept.

[0004] (2) There is no new technology for effectively and deeply separating magnesium, calcium, iron, and manganese elements, resulting in relatively high costs in the separation and utilization processes of magnesium and calcium elements, which are difficult for enterprises to accept.

[0005] (3) The existing technology overly focuses on the extraction and utilization of magnesium elements, while ignoring the utilization values of calcium elements, iron, manganese, and extractants, thus leading to too high costs when utilizing white mud resources.

[0006] (4) There are certain environmental problems in the process of utilizing white mud in the existing technology. If only magnesium elements are extracted, a large amount of by-product gypsum still needs to be discharged, which has limited significance for completely solving the problem of white mud discharge.

[0007] Therefore, if the resource-based, clean, and large-scale utilization of white mud can be achieved, it can not only solve the problem of clean production in the rare earth industry, but also have important reference significance for the comprehensive utilization of magnesium-containing waste salts and magnesium-containing resources.

[0008] Currently, the white mud generated in the rare earth industry is mostly disposed of by landfill, which not only wastes a large amount of resources, but also occupies a large amount of land and pollutes the environment. Although there are reports on white mud in the literature and patents, they are all about the utilization technologies of white mud in the paper-making industry, and there is no literature report on the resource-based utilization of white mud generated in the rare earth industry.

[0009] Publication No. CN202110542274.3 discloses a process for preparing modified straw pulp papermaking white mud and a process for desulfurization and gypsum production by desulfurization, which specifically includes: pretreatment of green liquor: the flue gas obtained by black liquor incineration is passed through a dust collector and then introduced into the green liquor formed by dissolving the black liquor after incineration in water to obtain a first reaction mixture; adding 3% - 5% by weight of bentonite or limestone to the first reaction mixture and reacting to obtain a second reaction mixture; filtering the second reaction mixture by pressure filtration to achieve double impurity removal, and the filtrate is the pretreated green liquor; obtaining modified straw pulp papermaking white mud: using the pretreated green liquor for causticization to obtain a causticization reactant, and after pressure filtration and washing, the modified straw pulp papermaking white mud is obtained; obtaining a mixed slurry: mixing the modified straw pulp papermaking white mud and limestone to make a slurry to obtain a mixed slurry; treating the mixed slurry by the limestone-gypsum wet desulfurization process to prepare gypsum. This invention only utilizes straw pulp papermaking white mud to prepare high-quality gypsum, and the added value of the product is relatively low. More importantly, it cannot solve the problem of comprehensive resource utilization of white mud in the rare earth industry (a solid waste with complex coexistence of components such as magnesium, calcium, iron, manganese, and extractant).

[0010] The patent with publication number CN201510620787.6 discloses a method for preparing a composite adsorbent from white mud and oil shale ash: it relates to the technical field of preparation methods for preparing adsorbent materials from oil shale ash and white mud. The specific research plan: oil shale ash is microwave dissociated into an aluminum-silicate solution in an NaOH solution; then it is prepared into a metal ion solution and a sodium silicate solution, and white mud is processed into a CaCl2 solution; by adjusting the raw material ratio and optimizing the reaction conditions, a composite material with hydrated calcium silicate growing in-situ on the surface of hydrotalcite is obtained. Although this method can realize the utilization of white mud in the paper-making industry, the consumption space for large-scale products is limited.

[0011] The patent with publication number CN106883471B discloses a comprehensive utilization method for white mud recovery: directly mixing a strong acid-weak base salt with papermaking recycled white mud, drying and ball milling to obtain white mud powder with residual alkali removed. This powder is used as a filler to prepare rubber or plastic composites, which can not only reduce the production cost of the composites, but also improve the product performance. Although this invention directly uses a strong acid-weak base salt to remove the residual alkali in white mud, replacing strong inorganic acids and high-cost organic acids with stronger acidity, it can improve the whiteness of white mud, simplify the treatment process, and save the treatment cost. However, this method is only applicable to the recovery of calcium carbonate from white mud in the paper-making industry and is applied in the rubber and plastic fields. It has little reference significance for the resource utilization of white mud generated in the rare earth industry. Summary of the Invention

[0012] The object of the present invention is to provide a new process for preparing whiskers and recovering magnesium salts from white mud, which not only turns waste into treasure, realizes the resource utilization, clean utilization and high-value utilization of white mud in the rare earth production industry, but also can produce high-quality magnesium carbonate, magnesium bicarbonate, magnesium hydroxide, magnesium oxide, metallic magnesium, high-whiteness nano-calcium sulfate fibers and high-strength gypsum and other products. In the process flow, the aqueous solution is completely recycled, no solid waste is generated, and the exhaust gas emissions fully meet the national discharge standards. The process of the present invention is green and environmentally friendly.

[0013] To solve the above technical problems, the present invention adopts the following technical solutions:

[0014] A new process for preparing whiskers and recovering magnesium salts from white mud according to the present invention includes:

[0015] After the white mud is leached and separated by sulfuric acid, high-whiteness gypsum and magnesium sulfate solution containing calcium ions are obtained. Then, the magnesium sulfate solution containing calcium ions is subjected to decalcification treatment with carbonate to obtain a high-purity magnesium sulfate solution; the magnesium sulfate solution is prepared into high-purity magnesium sulfate monohydrate by a thermal crystallization method, and magnesium carbonate or magnesium bicarbonate is prepared by a carbonization process, and high-purity magnesium oxide is prepared after calcination; the high-whiteness gypsum is prepared into high-whiteness nano-calcium sulfate fibers and high-strength gypsum products by a hydrothermal method.

[0016] Further, it specifically includes the following steps:

[0017] (1) Add white mud to a 5%-35% sulfuric acid solution, under the condition of 10-90 revolutions per minute, control the reaction temperature at 30-90 °C, the reaction time is 10-90 minutes, and the ratio of sulfuric acid solution to white mud is 5:1-15:1;

[0018] (2) Control the growth mode of gypsum dihydrate crystals during the reaction. Since the crystal particles of the gypsum dihydrate raw material are small, the growth of each crystal plane of the crystal is not perfect, and even there are crystal plane defect phenomena. This structure is easy to adsorb moisture, resulting in poor water tightness; however, through the free sulfuric acid concentration and temperature of gypsum dihydrate, under certain stirring rate and time conditions, the concentration gradient of the solution changes, resulting in an increase in the ion migration rate on the crystal plane during the growth process of the crystal, so that the crystal plane can develop completely and the defects are reduced, and then a fast water-separating columnar octahedron crystal structure with better water tightness is formed. The ratio of the long axis to the longitudinal axis of the columnar crystal is 4:1-0.5:1;

[0019] (3) After the white mud is leached with sulfuric acid and treated in step (2), magnesium sulfate solution and columnar gypsum dihydrate are obtained through separation;

[0020] (4) The columnar gypsum dihydrate obtained in step (3) is directly prepared into nano-calcium sulfate fibers by a hydrothermal method;

[0021] (5) The magnesium sulfate solution obtained after the leaching of white mud contains not only magnesium sulfate, but also slightly soluble calcium sulfate, iron sulfate, manganese sulfate, and soluble salts such as sodium sulfate, as well as trace amounts of oily extractants.

[0022] (6) First, add a demulsifier to (5) in a proportion of 0.1% - 1%, and then treat it by distillation to obtain the demulsifier fatty alcohol or ethylene oxide, as well as the extractant. The demulsifier can be recycled.

[0023] (7) The magnesium sulfate solution after removing the extractant is adjusted to a pH value of 3 - 7 by adding sodium hydroxide, so that iron and manganese ions in the magnesium sulfate solution form iron hydroxide and manganese hydroxide precipitates, which can be removed by separation. The obtained iron hydroxide and manganese hydroxide can be used as raw materials for the production of ferromanganese alloy.

[0024] (8) Add an appropriate amount of benzoic acid, lactic acid, or oxalic acid to the magnesium sulfate solution containing trace amounts of calcium sulfate in a proportion of 1:1 - 1:1.2 of the reaction amount of calcium benzoate, calcium lactate, or calcium oxalate. After separating the precipitate, a relatively pure magnesium sulfate solution containing sodium sulfate or sodium chloride can be obtained.

[0025] (9) Add sodium carbonate to the relatively pure magnesium sulfate solution containing sodium sulfate or sodium chloride to prepare magnesium bicarbonate or magnesium carbonate products, as well as raw materials that can be used for the production of magnesium oxide and magnesium metal products.

[0026] (10) Add calcium chloride to the solution containing sodium sulfate and sodium chloride after separating magnesium to obtain calcium sulfate and a sodium chloride solution. The sodium chloride solution is subjected to crystallization and drying treatment to obtain an industrial-grade sodium chloride product.

[0027] Further, in the step (4), the diameter of the nano calcium sulfate fiber is 100nm - 500nm, the aspect ratio is 50 - 200, and the whiteness can reach more than 95%.

[0028] Further, in the step (6), the demulsifier used to separate the oily extractant from the white mud is fatty alcohol or ethylene oxide.

[0029] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0030] The present invention can achieve the complete recycling and reuse of magnesium, calcium, iron, manganese, sodium salts, and extractants. It not only has low production costs and high resource utilization rates, but also has no problems of three-waste pollution. The process is green and environmentally friendly, and fundamentally solves the problems of land occupation and environmental pollution caused by the discharge of white mud in the rare earth industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The following further describes the present invention with reference to the accompanying drawings.

[0032] Figure 1It is a process flow for the resource-based, clean and large-scale utilization of white mud in the rare earth industry;

[0033] Figure 2 It is the microscopic structure of octahedral columnar gypsum in the embodiment;

[0034] Figure 3 It is the microscopic morphology of the raw materials;

[0035] Figure 4 It is the high-whiteness nano-calcium sulfate fiber prepared in the embodiment. Specific embodiments

[0036] The present invention will be further elaborated in combination with specific implementation cases.

[0037] Example 1

[0038] (1) Add white mud to a 5% sulfuric acid solution. Under the condition of 90 revolutions per minute, control the reaction temperature at 90 °C, the reaction time is 10 minutes, and the ratio of sulfuric acid solution to white mud is 5:1.

[0039] (2) Control the growth mode of dihydrate gypsum crystals during the reaction. Since the crystal particle size of the dihydrate calcium sulfate raw material is small, the growth of each crystal plane of the crystal is not perfect, and even there are crystal plane defect phenomena. This structure is very easy to agglomerate water, resulting in poor water closure; however, through the free sulfuric acid concentration and temperature of dihydrate gypsum, under certain stirring rate and time conditions, the concentration gradient of the solution changes, resulting in an increase in the ion migration speed on the crystal plane during the growth process of the crystal, enabling the crystal plane to develop completely and the defects to be reduced. Furthermore, it forms a fast water-separating columnar octahedral crystal structure with better water closure, and the microscopic morphology changes from Figure 3 to Figure 2 , and the ratio of the long axis to the longitudinal axis of the columnar crystal is 4:1.

[0040] (3) After the white mud is leached with sulfuric acid and treated in step (2), magnesium sulfate solution and columnar dihydrate gypsum can be obtained through separation.

[0041] (4) The columnar dihydrate gypsum obtained in (3) can be directly prepared into nano-calcium sulfate fibers by the hydrothermal method. The diameter of the nano-calcium sulfate fibers is 500 nm, the aspect ratio is 100, and the whiteness can reach more than 95%.

[0042] (5) The magnesium sulfate solution obtained after leaching white mud contains not only magnesium sulfate, but also slightly soluble calcium sulfate, iron sulfate, manganese sulfate and sodium sulfate soluble salts, as well as trace amounts of oily extractants;

[0043] (6) First, add a demulsifier to (5). The demulsifier used to separate the oily extractant from the white mud is fatty alcohol, and the addition ratio is 1%. Then, it is processed by distillation to obtain the demulsifier fatty alcohol and the extractant, and the demulsifier can be recycled.

[0044] (7) The magnesium sulfate solution after removing the extractant is adjusted to a pH value of 3 by adding sodium hydroxide, so that iron and manganese ions in the magnesium sulfate solution form iron hydroxide and manganese hydroxide precipitates, which can be removed by separation. The obtained iron hydroxide and manganese hydroxide can be used as raw materials for the production of ferromanganese alloy.

[0045] (8) Add an appropriate amount of benzoic acid to the magnesium sulfate solution containing trace calcium sulfate, and the addition ratio is 1:1 of the reaction amount of calcium benzoate. After separating the precipitate, a relatively pure magnesium sulfate solution containing sodium sulfate or sodium chloride can be obtained.

[0046] (9) Add sodium carbonate to the relatively pure magnesium sulfate solution containing sodium sulfate or sodium chloride to prepare a magnesium bicarbonate product.

[0047] (10) Add calcium chloride to the solution containing sodium sulfate and sodium chloride after separating magnesium to obtain calcium sulfate and a sodium chloride solution. The sodium chloride solution can be processed by crystallization and drying to obtain an industrial-grade sodium chloride product.

[0048] Example 2

[0049] (1) Add white mud to a 35% sulfuric acid solution. Under the condition of 10 revolutions / min, the reaction temperature is controlled at 30 °C, the reaction time is 10 min, and the ratio of sulfuric acid solution to white mud is 15:1.

[0050] (2) Control the growth mode of the gypsum dihydrate crystals during the reaction to form a columnar octahedron crystal structure with better water-blocking and fast water-separating properties. The ratio of the major axis to the minor axis of the columnar crystals is 0.5:1.

[0051] (3) After the white mud is leached with sulfuric acid and processed by step (2), magnesium sulfate solution and columnar gypsum dihydrate can be obtained by separation.

[0052] (4) The columnar gypsum dihydrate obtained from (3) can be directly prepared into nano calcium sulfate fibers by hydrothermal method. The diameter of the nano calcium sulfate fibers is 100 nm, the aspect ratio is 50, and the whiteness can reach more than 95%.

[0053] (5) The magnesium sulfate solution obtained after leaching the white mud contains not only magnesium sulfate, but also slightly soluble calcium sulfate, ferric sulfate, manganese sulfate and sodium sulfate soluble salts, as well as trace amounts of oily extractant;

[0054] (6) First, add a demulsifier to (5). The demulsifier used to separate the oily extractant from the white mud is ethylene oxide, and the addition ratio is 0.1%. Then, it is processed by distillation to obtain the demulsifier ethylene oxide and the extractant, and the demulsifier can be recycled.

[0055] (7) The magnesium sulfate solution after removing the extractant is adjusted to a pH value of 7 by adding sodium hydroxide, so that iron and manganese ions in the magnesium sulfate solution form iron hydroxide and manganese hydroxide precipitates, which can be removed by separation. The obtained iron hydroxide and manganese hydroxide can be used as raw materials for the production of ferromanganese alloy.

[0056] (8) Add an appropriate amount of benzoic acid, lactic acid or oxalic acid to the magnesium sulfate solution containing trace calcium sulfate, and the addition ratio is 1:1.2 of the reaction amount of calcium oxalate. After the precipitate is removed by separation, a relatively pure magnesium sulfate solution containing sodium sulfate or sodium chloride can be obtained.

[0057] (9) Add sodium carbonate to the relatively pure magnesium sulfate solution containing sodium sulfate or sodium chloride to prepare magnesium bicarbonate or magnesium carbonate products.

[0058] (10) Add calcium chloride to the solution containing sodium sulfate and sodium chloride after separating magnesium to obtain calcium sulfate and a sodium chloride solution. The sodium chloride solution can be obtained as an industrial-grade sodium chloride product after crystallization and drying.

[0059] Example 3

[0060] (1) Add white mud to a 20% sulfuric acid solution. Under the condition of 60 revolutions / min, the reaction temperature is controlled at 60 °C, the reaction time is 45 min, and the ratio of sulfuric acid solution to white mud is 10:1.

[0061] (2) Control the growth mode of the gypsum dihydrate crystals during the reaction to form a columnar octahedral crystal structure with better water closure and faster water separation. The ratio of the major axis to the minor axis of the columnar crystals is 1:1.

[0062] (3) After the white mud is leached with sulfuric acid and treated by step (2), magnesium sulfate solution and columnar gypsum dihydrate can be obtained by separation.

[0063] (4) The columnar gypsum dihydrate obtained from (3) can be directly prepared into nano calcium sulfate fibers by hydrothermal method. The diameter of the nano calcium sulfate fibers is 200 nm, the aspect ratio is 100, and the whiteness can reach more than 95%.

[0064] (5) The magnesium sulfate solution obtained after leaching the white mud contains not only magnesium sulfate, but also slightly soluble calcium sulfate, ferric sulfate, manganese sulfate and sodium sulfate soluble salts, as well as trace amounts of oily extractants;

[0065] (6) First, add a demulsifier to (5). The demulsifier used to separate the oily extractant from the white mud is fatty alcohol, and the addition ratio is 0.5%. Then, it is processed by distillation to obtain the demulsifier fatty alcohol and the extractant, and the demulsifier can be recycled.

[0066] (7) The magnesium sulfate solution after removing the extractant is adjusted to a pH value of 5 by adding sodium hydroxide, so that iron and manganese ions in the magnesium sulfate solution form iron hydroxide and manganese hydroxide precipitates, which can be removed by separation. The obtained iron hydroxide and manganese hydroxide can be used as raw materials for the production of ferromanganese alloy.

[0067] (8) Add an appropriate amount of lactic acid to the magnesium sulfate solution containing trace calcium sulfate, and the addition ratio is 1:1 of the reaction amount of calcium lactate. After separating the precipitate, a relatively pure magnesium sulfate solution containing sodium sulfate or sodium chloride can be obtained.

[0068] (9) Add sodium carbonate to the relatively pure magnesium sulfate solution containing sodium sulfate or sodium chloride to prepare magnesium bicarbonate or magnesium carbonate products.

[0069] (10) Add calcium chloride to the solution containing sodium sulfate and sodium chloride after separating magnesium to obtain calcium sulfate and a sodium chloride solution. The sodium chloride solution can be processed by crystallization and drying to obtain industrial-grade sodium chloride products.

[0070] Example 4

[0071] (1) Add white mud to a 10% sulfuric acid solution. Under the condition of 30 revolutions / min, the reaction temperature is controlled at 45 °C, the reaction time is 45 min, and the ratio of sulfuric acid solution to white mud is 8:1.

[0072] (2) Control the growth mode of calcium sulfate dihydrate crystals during the reaction to form a columnar octahedral crystal structure with better water closure and faster water separation. The ratio of the long axis to the longitudinal axis of the columnar crystals is 2:1.

[0073] (3) After the white mud is leached with sulfuric acid and processed through step (2), magnesium sulfate solution and columnar calcium sulfate dihydrate can be obtained by separation.

[0074] (4) The columnar calcium sulfate dihydrate obtained from (3) can be directly prepared into nano calcium sulfate fibers by hydrothermal method. The diameter of the nano calcium sulfate fibers is 300 nm, the aspect ratio is 80, and the whiteness can reach more than 95%.

[0075] (5) The magnesium sulfate solution obtained after leaching the white mud contains not only magnesium sulfate, but also slightly soluble calcium sulfate, iron sulfate, manganese sulfate and sodium sulfate soluble salts, as well as trace amounts of oily extractants;

[0076] (6) First, add a demulsifier to (5). The demulsifier used to separate the oily extractant from the white mud is fatty alcohol or ethylene oxide, and the addition ratio is 0.3%. Then, it is processed by distillation to obtain ethylene oxide as the demulsifier and the extractant, and the demulsifier can be recycled.

[0077] (7) The magnesium sulfate solution after removing the extractant is adjusted to a pH value of 4 by adding sodium hydroxide, so that iron and manganese ions in the magnesium sulfate solution form iron hydroxide and manganese hydroxide precipitates, which can be removed by separation. The obtained iron hydroxide and manganese hydroxide can be used as raw materials for the production of ferromanganese alloy.

[0078] (8) Add an appropriate amount of benzoic acid to the magnesium sulfate solution containing trace calcium sulfate. The addition ratio is 1:1.2 of the reaction amount of calcium benzoate. After separating the precipitate, a relatively pure magnesium sulfate solution containing sodium sulfate or sodium chloride can be obtained.

[0079] (9) Add sodium carbonate to the relatively pure magnesium sulfate solution containing sodium sulfate or sodium chloride to prepare magnesium bicarbonate or magnesium carbonate products.

[0080] (10) Add calcium chloride to the solution containing sodium sulfate and sodium chloride after separating magnesium to obtain calcium sulfate and a sodium chloride solution. The sodium chloride solution can be processed by crystallization and drying to obtain industrial-grade sodium chloride products.

[0081] Example 5

[0082] (1) Add white mud to a 30% sulfuric acid solution. Under the condition of 70 revolutions / min, the reaction temperature is controlled at 80 °C, the reaction time is 20 min, and the ratio of sulfuric acid solution to white mud is 7:1.

[0083] (2) Control the growth mode of gypsum dihydrate crystals during the reaction to form a columnar octahedron crystal structure with better water-closure and fast water separation. The ratio of the major axis to the minor axis of the columnar crystals is 3:1.

[0084] (3) After the white mud is leached with sulfuric acid and treated by step (2), magnesium sulfate solution and columnar gypsum dihydrate can be obtained by separation.

[0085] (4) The columnar gypsum dihydrate obtained from (3) can be directly prepared into nano calcium sulfate fibers by hydrothermal method. The diameter of the nano calcium sulfate fibers is 400 nm, the aspect ratio is 150, and the whiteness can reach more than 95%.

[0086] (5) The magnesium sulfate solution obtained after leaching the white mud contains not only magnesium sulfate, but also slightly soluble calcium sulfate, iron sulfate, manganese sulfate and sodium sulfate soluble salts, as well as trace amounts of oily extractant;

[0087] (6) First, a demulsifier is added to (5). The demulsifier used to separate the oily extractant from the white mud is fatty alcohol, and the addition ratio is 0.8%. Then, it is processed by distillation to obtain the demulsifier fatty alcohol or ethylene oxide, and the extractant, and the demulsifier can be recycled.

[0088] (7) The magnesium sulfate solution after removing the extractant is adjusted to a pH value of 4 by adding sodium hydroxide, so that the iron and manganese ions in the magnesium sulfate solution form iron hydroxide and manganese hydroxide precipitates, which can be removed by separation. The obtained iron hydroxide and manganese hydroxide can be used as raw materials for the production of ferromanganese alloy.

[0089] (8) Appropriate amounts of benzoic acid, lactic acid or oxalic acid are added to the magnesium sulfate solution containing trace calcium sulfate, and the addition ratio is 1:1.1 of the reaction amount of calcium benzoate, calcium lactate or calcium oxalate. After the precipitate is removed by separation, a relatively pure magnesium sulfate solution containing sodium sulfate or sodium chloride can be obtained.

[0090] (9) Sodium carbonate is added to the relatively pure magnesium sulfate solution containing sodium sulfate or sodium chloride to prepare magnesium bicarbonate or magnesium carbonate products.

[0091] (10) Calcium chloride is added to the solution containing sodium sulfate and sodium chloride after separating magnesium to obtain calcium sulfate and a sodium chloride solution. The sodium chloride solution can be processed by crystallization and drying to obtain industrial-grade sodium chloride products.

[0092] Example 6

[0093] (1) The white mud is added to a 10% sulfuric acid solution. Under the condition of 40 revolutions / min, the reaction temperature is controlled at 90 °C, the reaction time is 90 min, and the ratio of the sulfuric acid solution to the white mud is 10:1.

[0094] (2) During the reaction process, the growth mode of the gypsum dihydrate crystals is controlled to form a columnar octahedron crystal structure with better water-closure and fast water separation. The ratio of the major axis to the minor axis of the columnar crystals is 3:1.

[0095] (3) After the white mud is leached with sulfuric acid and treated by step (2), magnesium sulfate solution and columnar gypsum dihydrate can be obtained by separation.

[0096] (4) The columnar gypsum dihydrate obtained from (3) can be directly prepared into nano-calcium sulfate fibers by hydrothermal method. The diameter of the nano-calcium sulfate fibers is 200 nm, the aspect ratio is 90, and the whiteness can reach more than 95%.

[0097] (5) The magnesium sulfate solution obtained after leaching the white mud contains not only magnesium sulfate, but also slightly soluble calcium sulfate, iron sulfate, manganese sulfate and sodium sulfate soluble salts, as well as trace amounts of oily extractants;

[0098] (6) First, add a demulsifier to (5). The demulsifier used to separate the oily extractant from the white mud is ethylene oxide, and the addition ratio is 0.6%. Then, it is processed by distillation to obtain the demulsifier ethylene oxide and the extractant, and the demulsifier can be recycled.

[0099] (7) The magnesium sulfate solution after removing the extractant is adjusted to a pH value of 6 by adding sodium hydroxide, so that iron and manganese ions in the magnesium sulfate solution form iron hydroxide and manganese hydroxide precipitates, which can be removed by separation. The obtained iron hydroxide and manganese hydroxide can be used as raw materials for the production of ferromanganese alloy.

[0100] (8) Add an appropriate amount of benzoic acid, lactic acid or oxalic acid to the magnesium sulfate solution containing trace calcium sulfate. The addition ratio is 1:1.1 of the reaction amount of calcium benzoate, calcium lactate or calcium oxalate. After the precipitate is removed by separation, a relatively pure magnesium sulfate solution containing sodium sulfate or sodium chloride can be obtained.

[0101] (9) Add sodium carbonate to the relatively pure magnesium sulfate solution containing sodium sulfate or sodium chloride to prepare magnesium bicarbonate or magnesium carbonate products.

[0102] (10) Add calcium chloride to the solution containing sodium sulfate and sodium chloride after separating magnesium to obtain calcium sulfate and a sodium chloride solution. The sodium chloride solution can be obtained as an industrial-grade sodium chloride product after crystallization and drying.

[0103] The high-quality nano-calcium sulfate fibers prepared in the embodiments of the present invention are as Figure 4 shown. The whiteness can reach over 95%, and the purity can reach over 98%. The purity of magnesium sulfate, magnesium carbonate and magnesium bicarbonate can reach over 98%.

[0104] Compared with the similar patents of this project, "A Method and Process for Preparing Dry Desulfurizer, Gypsum, Magnesium Sulfate and Magnesium Hydroxide by Using Dolomite", "A Method and Device for Preparing Calcium Carbonate and Magnesium Hydroxide by Using Dolomite" and "A Method for Preparing Magnesium Hydroxide and Calcium Hydroxide Flame Retardant by Using Dolomite", the resource utilization rate is higher, the product purity is better, the added value is greater, and the degree of clean utilization is higher. More importantly, the technology proposed in this patent is not only different in industry and raw materials, but more importantly, it solves the key common problems of the comprehensive utilization of magnesium- and calcium-containing minerals and solid wastes in China, that is, the problems of clean utilization, resource utilization and high-value utilization.

[0105] The above-described embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A new process for preparing whiskers and recovering magnesium salts using white mud, characterized in that, Including: After separating white mud by sulfuric acid leaching, high-whiteness gypsum and magnesium sulfate solution containing calcium ions are obtained. Then, the magnesium sulfate solution containing calcium ions is subjected to decalcification treatment with carbonate to obtain high-purity magnesium sulfate solution. The magnesium sulfate solution is used to prepare high-purity monohydrate magnesium sulfate by thermal crystallization method, and magnesium carbonate or magnesium bicarbonate is prepared by carbonization process, and high-purity magnesium oxide is prepared after calcination. High-whiteness gypsum is used to prepare high-whiteness nano-scale calcium sulfate fiber and high-strength gypsum products by hydrothermal method technology; Specifically, it includes the following steps: (1) Add white mud into 5%-35% sulfuric acid solution, under the condition of 10-90 r / min, control the reaction temperature at 30-90 °C, the reaction time is 10-90 min, and the ratio of sulfuric acid solution to white mud is 5:1-15:1; (2) Control the growth mode of gypsum dihydrate crystals during the reaction. Since the crystal particle size of the gypsum dihydrate raw material is small, the growth of each crystal plane of the crystal is not perfect, and even there are crystal plane defect phenomena. This structure is very easy to agglomerate water, resulting in poor water-blocking property. However, through the free sulfuric acid concentration and temperature of gypsum dihydrate, under certain stirring rate and time conditions, that is, under the conditions of step (1), the concentration gradient of the solution changes, resulting in an increase in the ion migration rate on the crystal plane during the growth process of the crystal, so that the crystal plane can develop completely and the defects are reduced, and then a fast water-separating columnar octahedron crystal structure with better water-blocking property is formed. The ratio of the long axis to the longitudinal axis of the columnar crystal is 4:1-0.5:1; (3) After the white mud is leached with sulfuric acid and treated by step (2), magnesium sulfate solution and columnar gypsum dihydrate are obtained through separation; (4) The columnar gypsum dihydrate obtained from step (3) is directly prepared into nano calcium sulfate fiber by hydrothermal method; (5) The magnesium sulfate solution obtained after leaching white mud contains not only magnesium sulfate, but also slightly soluble calcium sulfate, iron sulfate, manganese sulfate and sodium sulfate soluble salts, as well as trace amounts of oily extractants; (6) First, add a demulsifier to (5), the addition ratio is 0.1%-1%, and then treat it by distillation to obtain the demulsifier fatty alcohol or ethylene oxide, and the extractant. The demulsifier is recycled; (7) The magnesium sulfate solution after removing the extractant is adjusted to a pH value of 3-7 by adding sodium hydroxide, so that iron and manganese ions in the magnesium sulfate solution form iron hydroxide and manganese hydroxide precipitates, which can be removed by separation. The obtained iron hydroxide and manganese hydroxide are used as raw materials for the production of ferromanganese alloy; (8) Add appropriate amounts of benzoic acid, lactic acid or oxalic acid to the magnesium sulfate solution containing trace amounts of calcium sulfate, and the addition ratio is 1:1-1:1.2 of the reaction amount of calcium benzoate, calcium lactate or calcium oxalate. After the precipitate is removed by separation, a relatively pure magnesium sulfate solution containing sodium sulfate or sodium chloride can be obtained; (9) Add sodium carbonate to the relatively pure magnesium sulfate solution containing sodium sulfate or sodium chloride to prepare magnesium bicarbonate or magnesium carbonate products, and raw materials that can be used for the production of magnesium oxide and magnesium metal products; (10) Calcium chloride is added to the solution containing sodium sulfate and sodium chloride after magnesium separation to obtain calcium sulfate and a sodium chloride solution, and the sodium chloride solution is subjected to crystallization and drying treatments to obtain an industrial-grade sodium chloride product.

2. The new process for preparing whiskers and recovering magnesium salts by using white mud according to claim 1, characterized in that, In the step (4), the diameter of the nano calcium sulfate fiber is 100 nm - 500 nm, the aspect ratio is 50 - 200, and the whiteness can reach more than 95%.

3. The new process for preparing whiskers and recovering magnesium salts using white mud according to claim 1, characterized in that, In the step (6), the demulsifier for separating the oily extractant from the white mud is fatty alcohol or ethylene oxide.

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