Method for selectively separating calcium sulfate in complex reaction system

Abstract

The invention relates to the technical field of hydrometallurgy, in particular to a method for selectively separating calcium sulfate in a complex reaction system. The method comprises the following steps: adding a soluble sulfate solution and a precipitant solution into a base solution in a parallel flow manner, and reacting to obtain mixed slurry containing fibrous calcium sulfate; and separating the mixed slurry containing fibrous calcium sulfate to obtain fibrous calcium sulfate crystals, metal hydroxides and purified liquid. According to the method, on the basis of wastewater treatment through a traditional precipitation method, fibrous calcium sulfate is separated from other substances in a complex system by controlling growth of calcium sulfate crystals, the environmental influence caused by solid waste is reduced while the industrial wastewater containing sulfate radicals is treated at low cost, and finally resourceful treatment of the industrial wastewater is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of hydrometallurgy, and in particular to a method for selectively separating calcium sulfate from a complex reaction system. Background Art

[0002] The development and utilization of natural gypsum is low, and it mostly enters the domestic and foreign markets in the form of raw or primary products. The main use is cement retarder, and other uses include ceramic molds, gypsum products, wall materials, chemicals and other special industries, with low economic added value. In addition, the mining of gypsum mines will cause damage to the local ecological environment. Therefore, the application of industrial gypsum continues to develop. Industrial gypsum is often a by-product of the industrial wastewater treatment process. For example, in some industrial fields, a large amount of sulfate-containing wastewater will be generated, such as magnesium flue gas desulfurization, rare earth saponification transformation and other processes that produce a large amount of magnesium sulfate wastewater, and the electroplating industry production process produces a large amount of copper sulfate, cobalt sulfate, and nickel sulfate wastewater. Restricted by environmental protection policies, wastewater must be treated, and the traditional low-cost treatment method is lime direct precipitation. Due to the complexity of the reaction system, the precipitation process often generates mixed precipitates of gypsum and other metal hydroxides, forming mixed precipitation waste residues, resulting in resource waste and the formation of secondary solid waste pollutants. If gypsum is separated from the waste residue to realize its application value, it will not only reduce the cost of wastewater treatment, but also reduce the adverse effects of solid waste on the environment. Therefore, it is particularly important to develop a method for selectively separating calcium sulfate from a complex reaction system.

[0003] CN110714128B introduces a method for treating a cobalt precipitation solution, wherein the cobalt precipitation solution is mixed with lime milk for precipitation to obtain a liquid-solid mixture, the liquid-solid mixture is subjected to a concentration treatment to obtain an overflow containing cobalt hydroxide precipitation and an underflow containing calcium sulfate, the overflow containing cobalt hydroxide precipitation is filtered to obtain cobalt hydroxide and a filtrate having a calcium content of less than 6%, and at the same time, the underflow containing calcium sulfate is acid-washed to obtain relatively pure calcium sulfate. In the separation and purification process of calcium sulfate in the method, calcium sulfate and cobalt hydroxide are initially separated in a concentration device, but the final separation of calcium sulfate is still carried out through an acid dissolution process. Summary of the invention

[0004] The purpose of the present invention is to provide a method for selectively separating calcium sulfate from a complex reaction system. The method of the present invention uses calcium oxide or calcium hydroxide as a precipitant, controls the reaction conditions, generates calcium sulfate and other metal hydroxides with sulfate-containing wastewater in a complex reaction system, and realizes the selective separation of calcium sulfate, which greatly reduces the cost compared with the existing evaporation crystallization technology, and realizes the separation and reuse of solid waste compared with the existing direct precipitation technology.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention is a method for selectively separating calcium sulfate from a complex reaction system, comprising the following steps:

[0007] Adding the soluble sulfate solution and the precipitant solution into the bottom liquid in parallel to react, thereby obtaining a mixed slurry containing fibrous calcium sulfate;

[0008] The mixed slurry containing fibrous calcium sulfate is separated to obtain fibrous calcium sulfate crystals, metal hydroxide and purified liquid.

[0009] In some embodiments of the present invention, the soluble sulfate solution is at least one of a magnesium sulfate solution, a cobalt sulfate solution, a nickel sulfate solution, and a copper sulfate solution.

[0010] The second technical solution of the present invention is a method for preparing fibrous calcium sulfate crystals based on a sulfate solution, which adopts the method for selectively separating calcium sulfate using the above-mentioned complex reaction system; the fiber length of the fibrous calcium sulfate crystals is not less than 100 μm.

[0011] The present invention discloses the following technical effects:

[0012] (1) The method of the present invention is based on the traditional precipitation method for treating wastewater. By controlling the growth of calcium sulfate crystals, the fibrous calcium sulfate is separated from other substances in a complex system. While treating industrial sulfate-containing wastewater at a low cost, the environmental impact caused by solid waste is reduced, and ultimately the resource-based treatment of industrial wastewater is achieved.

[0013] (2) Compared with the traditional evaporation crystallization treatment method, the present invention uses a low-cost calcium precipitant for reaction, which greatly reduces the water treatment cost.

[0014] (3) Compared with the traditional direct precipitation treatment method, the present invention realizes the selective separation of calcium sulfate in a complex reaction system by controlling the conditions, and can recover the second by-product metal hydroxide while recycling the calcium sulfate, thereby realizing the recycling of resources.

[0015] (4) Under the condition of the presence of a certain proportion of initial base liquid, the present invention controls the conditions for crystal nucleation and growth, such as temperature and growth time, and utilizes the principle that a low degree of supersaturation in the initial reaction system is conducive to crystal growth, thereby providing sufficient growth space for calcium sulfate and metal hydroxide. According to the different growth mechanisms of different products, the size difference between calcium sulfate and metal hydroxide is further increased to avoid the hybridization growth of two or more precipitates, thereby achieving selective separation of calcium sulfate and metal hydroxide in a complex system and ultimately achieving resource recycling. 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 drawings required for use in the embodiments will be briefly introduced below. 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 creative work.

[0017] Figure 1 This is the SEM image of the fibrous calcium sulfate crystals prepared in Example 2. DETAILED DESCRIPTION

[0018] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0019] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0020] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0021] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to the skilled artisan. The present invention description and examples are exemplary only.

[0022] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0023] The first aspect of the present invention provides a method for selectively separating calcium sulfate from a complex reaction system, comprising the following steps:

[0024] Adding the soluble sulfate solution and the precipitant solution into the bottom liquid in parallel to react, thereby obtaining a mixed slurry containing fibrous calcium sulfate;

[0025] The mixed slurry containing fibrous calcium sulfate is separated to obtain fibrous calcium sulfate crystals, metal hydroxide and purified liquid.

[0026] In some embodiments of the present invention, the soluble sulfate solution is at least one of a magnesium sulfate solution, a cobalt sulfate solution, a nickel sulfate solution, and a copper sulfate solution.

[0027] The metal hydroxide is at least one of magnesium hydroxide, cobalt hydroxide, nickel hydroxide and copper hydroxide.

[0028] In some embodiments of the present invention, the sulfate concentration in the soluble sulfate solution is 10 g / L-100 g / L.

[0029] In some embodiments of the present invention, the precipitant in the precipitant solution is calcium oxide and / or calcium hydroxide; the solvent of the precipitant solution is water and / or purified liquid; and the concentration of the precipitant solution is 0.5 mol / L-5 mol / L.

[0030] In some embodiments of the present invention, the SO4 in the soluble sulfate solution and the precipitant solution 2- :Ca molar ratio is 1:0.6-1.0.

[0031] In some embodiments of the present invention, the base liquid is at least one of water, purified liquid, soluble sulfate solution or precipitant solution.

[0032] The amount of the base solution added is 3-20 times the total volume of the soluble sulfate solution and the precipitant solution added in 1 hour; for example, in the actual production process, the rate of adding the soluble sulfate solution to the base solution can be 0.1-1m 3 / h.

[0033] In actual production and application, the amount of the base liquid added may vary with the volume of the reaction container.

[0034] In the present invention, the role of the base liquid is to provide a lower supersaturation when the crystal nucleus is formed, because the low supersaturation will not spontaneously form the crystal nucleus, and can only grow on the original crystal nucleus (or crystal) until it grows to the required crystal size.

[0035] If the amount of base liquid added is too high, the system operation equilibrium time will be prolonged. If the amount of base liquid added is too small, it will not reduce the supersaturation of the system and will be detrimental to crystal growth.

[0036] In some embodiments of the present invention, the base liquid further includes seed crystals; the seed crystals are fibrous calcium sulfate crystals and / or a mixed slurry containing fibrous calcium sulfate; the added amount of the seed crystals is 0-10% of the mass of the fibrous calcium sulfate crystals.

[0037] In the present invention, the fibrous calcium sulfate crystals are used as seed crystals to provide a template for crystal formation and improve the crystal structure; adding too much seed crystals may cause the product to crystallize too quickly during the reaction, thereby affecting the uniformity and stability of the reaction.

[0038] In some embodiments of the present invention, the reaction temperature is 50-99° C.; the reaction time is 1-8 h.

[0039] In the present invention, if the reaction temperature is too high, the reaction energy consumption will be increased, while if the reaction temperature is too low, the crystal growth will be affected, thereby affecting the separation of calcium sulfate. If the reaction time is too long, the reaction efficiency will be reduced and the processing capacity will be affected for actual production, while if the reaction time is too short, the crystal growth will be incomplete.

[0040] The invention realizes the dissolution and growth of calcium sulfate grains by controlling the temperature and the reaction (growth) time, and obtains a mixed slurry containing fibrous calcium sulfate.

[0041] In some embodiments of the present invention, the separation is specifically: first gravity separation or screening separation, and then solid-liquid separation.

[0042] The present invention provides a method for selectively separating calcium sulfate from a complex reaction system, which can be produced continuously in practical applications, for example, after connecting multiple stages of reactors in series, continuous feeding and continuous discharging are performed.

[0043] The second aspect of the present invention provides a method for preparing fibrous calcium sulfate crystals based on sulfate solution, which adopts the method for selectively separating calcium sulfate using the above-mentioned complex reaction system; the fiber length of the fibrous calcium sulfate crystals is not less than 100 μm. The aspect ratio of the fibrous calcium sulfate crystals is ≥20.

[0044] The shape of calcium sulfate crystals affects their use. Compared with ordinary calcium sulfate crystals, fibrous calcium sulfate not only plays a role in strengthening and toughening plastics and rubber products, but can also replace asbestos as thermal insulation materials, building materials, and friction materials, which can enhance the processability of products, reduce molding shrinkage, and improve surface smoothness. Therefore, the technical solution of the present invention based on the preparation and separation of fibrous calcium sulfate crystals by a complex sulfate reaction system has important practical application value.

[0045] The seed crystals used in the embodiments of the present invention are from the fibrous calcium sulfate crystals obtained by the reaction; the purpose of adding the seed crystals is to provide a template for crystal formation and improve the crystal structure. The technical solutions described in the present invention are conventional solutions in the art unless otherwise specified, and the reagents or raw materials used are purchased from commercial channels or have been disclosed unless otherwise specified.

[0046] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0047] Example 1

[0048] First, a calcium hydroxide solution (precipitant solution) is prepared, the solvent is water, and the molar concentration of the calcium hydroxide solution is 0.5 mol / L. Then, a cobalt sulfate solution with a sulfate concentration of 10 g / L and a precipitant solution are mixed, wherein the cobalt sulfate solution and the precipitant solution are mixed according to SO4 2- :Ca (molar ratio) is 1:1 and is continuously mixed and added to the bottom liquid. The bottom liquid is water, and its volume is 3 times the total volume of the cobalt sulfate solution and the calcium hydroxide precipitant solution added in 1 hour. The bottom liquid temperature is 90°C. The temperature is controlled at 90°C and the growth time is 1h to achieve the growth of calcium sulfate grains to obtain a mixed slurry containing fibrous calcium sulfate. After the above slurry is re-selected and separated, solid-liquid separation is performed to obtain fibrous calcium sulfate crystals, cobalt hydroxide and purified liquid. Among them, the fiber length of the fibrous calcium sulfate crystals (fibrous calcium sulfate dihydrate) is ≥100μm, the purity of cobalt hydroxide is 71%, the yield is 85%, and the purity of fibrous calcium sulfate dihydrate is 90%, and the yield is 92%.

[0049] Example 2

[0050] First, a calcium hydroxide solution (precipitant solution) is prepared, the solvent is water, and the molar concentration of the calcium hydroxide solution is 2 mol / L. Then, a magnesium sulfate solution with a sulfate concentration of 40 g / L and a precipitant solution are mixed, wherein the magnesium sulfate solution and the precipitant solution are mixed according to SO4 2- :Ca (molar ratio) is 1:0.8 and is continuously mixed and added to the bottom liquid containing seeds. The seeds are fibrous calcium sulfate crystals, and the amount added is 5% of the mass of fibrous calcium sulfate generated. The bottom liquid solvent is a purified liquid, and its volume is 10 times the total volume of the magnesium sulfate solution and the calcium hydroxide precipitant solution added in 1 hour, and the bottom liquid temperature is 80°C. The temperature is controlled at 80°C and the growth time is 4h to achieve the growth of calcium sulfate grains to obtain a mixed slurry containing fibrous calcium sulfate. After the above slurry is sieved and separated, solid-liquid separation is performed to obtain fibrous calcium sulfate crystals, magnesium hydroxide and purified liquid. Among them, the fiber length of the fibrous calcium sulfate crystal is ≥100μm, the purity of magnesium hydroxide is 85%, and the yield is 95%; the purity of fibrous calcium sulfate dihydrate is 96%, and the yield is 95%.

[0051] The SEM image of the fibrous calcium sulfate crystals prepared in this embodiment is as follows: Figure 1 As shown. Figure 1 It can be seen that the obtained calcium sulfate crystals are in the form of fibers with a certain aspect ratio, and most of the lengths are ≥200 um.

[0052] Example 3

[0053] First, a calcium oxide solution (precipitant solution) is prepared, the solvent is the purified liquid, and the molar concentration of the calcium oxide solution is 5 mol / L. Then, a nickel sulfate solution with a sulfate concentration of 100 g / L and a precipitant solution are mixed, wherein the nickel sulfate solution and the precipitant solution are mixed according to SO4 2- :Ca (molar ratio) is 1:0.6 and is continuously mixed and added to the bottom liquid containing seeds. The seeds are mixed slurry containing fibrous calcium sulfate, and the amount added is 10% of the mass of fibrous calcium sulfate generated. The bottom liquid solvent is a mixed solution of water and purified liquid mixed in a ratio of 1:1, and its volume is 20 times the total volume of nickel sulfate solution and calcium oxide precipitant solution added in 1 hour, and the bottom liquid temperature is 60°C. The temperature is controlled at 60°C and the growth time is 3h to achieve the growth of calcium sulfate grains to obtain a mixed slurry containing fibrous calcium sulfate. After the above slurry is sieved and separated, solid-liquid separation is performed to obtain fibrous calcium sulfate crystals, nickel hydroxide and purified liquid. Among them, the fiber length of the fibrous calcium sulfate crystal is ≥100μm, the purity of nickel hydroxide is 88%, and the yield is 95%; the purity of fibrous calcium sulfate dihydrate is 96%, and the yield is 94%.

[0054] Example 4

[0055] First, a calcium hydroxide solution (precipitant solution) is prepared, the solvent is water, and the molar concentration of the calcium hydroxide solution is 2 mol / L. Then, a copper sulfate solution with a sulfate concentration of 20 g / L and a precipitant solution are mixed, wherein the copper sulfate solution and the precipitant solution are mixed according to SO4 2- :Ca (molar ratio) is 1:0.7 and is continuously mixed and added to the bottom liquid containing seeds. The seeds are fibrous calcium sulfate crystals, and the amount added is 5% of the mass of fibrous calcium sulfate generated. The bottom liquid solvent is a purified liquid, and its volume is 10 times the total volume of the copper sulfate solution and the calcium hydroxide precipitant solution added in 1 hour, and the bottom liquid temperature is 50°C. The temperature is controlled at 50°C and the growth time is 6h to achieve the growth of calcium sulfate grains to obtain a mixed slurry containing fibrous calcium sulfate. After the above slurry is sieved and separated, solid-liquid separation is performed to obtain fibrous calcium sulfate crystals, copper hydroxide and purified liquid. Among them, the fiber length of the fibrous calcium sulfate crystal is ≥100μm, the purity of copper hydroxide is 78%, and the yield is 90%; the purity of fibrous calcium sulfate dihydrate is 90%, and the yield is 93%.

[0056] Example 5

[0057] First, a calcium hydroxide solution (precipitant solution) is prepared, the solvent is the purified liquid, and the molar concentration of the calcium hydroxide solution is 3 mol / L. Then, a magnesium sulfate solution with a sulfate concentration of 30 g / L and a precipitant solution are mixed, wherein the magnesium sulfate solution and the precipitant solution are mixed according to SO4 2- :Ca (molar ratio) is 1:0.9 and is continuously mixed and added to the bottom liquid containing seeds. The seeds are fibrous calcium sulfate crystals, and the amount added is 3% of the mass of fibrous calcium sulfate generated. The bottom liquid solvent is water, and its volume is 15 times the total volume of magnesium sulfate solution and calcium hydroxide precipitant solution added in 1 hour, and the bottom liquid temperature is 70°C. The temperature is controlled at 70°C and the growth time is 8h to achieve the growth of calcium sulfate grains to obtain a mixed slurry containing fibrous calcium sulfate. After the above slurry is sieved and separated, solid-liquid separation is performed to obtain fibrous calcium sulfate crystals, magnesium hydroxide and purified liquid. Among them, the fiber length of the fibrous calcium sulfate crystal is ≥100μm, the purity of magnesium hydroxide is 87%, and the yield is 96%; the purity of fibrous calcium sulfate dihydrate is 96%, and the yield is 97%.

[0058] Example 6

[0059] First, a calcium hydroxide solution (precipitant solution) is prepared, the solvent is water, and the molar concentration of the calcium hydroxide solution is 1 mol / L. Then, a mixed solution of cobalt sulfate and nickel sulfate with a sulfate concentration of 60 g / L is mixed with the precipitant solution (n Co :n Ni =1:1), wherein the mixed solution of cobalt sulfate and nickel sulfate and the precipitant solution are in the ratio of SO4 2- :Ca (molar ratio) is 1:0.7 and mixed and added to the bottom liquid containing seeds, the seeds are fibrous calcium sulfate crystals, and the addition amount is 7% of the mass of fibrous calcium sulfate generated. The bottom liquid solvent is water, and its volume is 5 times the total volume of cobalt sulfate, nickel sulfate mixed solution and calcium hydroxide precipitant solution added in 1 hour, and the bottom liquid temperature is 80°C. The temperature is controlled at 80°C and the growth time is 2h to achieve the growth of calcium sulfate grains to obtain a mixed slurry containing fibrous calcium sulfate. After the above slurry is sieved and separated, solid-liquid separation is performed to obtain fibrous calcium sulfate crystals, cobalt hydroxide and nickel hydroxide and purified liquid. Among them, the fiber length of the fibrous calcium sulfate crystal is ≥100μm, the purity of the fibrous calcium sulfate dihydrate is 96%, and the yield is 90%.

[0060] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for selectively separating calcium sulfate from a complex reaction system, characterized in that: The following steps are involved: Adding the soluble sulfate solution and the precipitant solution into the bottom liquid in parallel to react, thereby obtaining a mixed slurry containing fibrous calcium sulfate; The mixed slurry containing fibrous calcium sulfate is separated to obtain fibrous calcium sulfate crystals, metal hydroxide and purified liquid.

2. The method for selectively separating calcium sulfate from a complex reaction system according to claim 1, characterized in that: The soluble sulfate solution is at least one of a magnesium sulfate solution, a cobalt sulfate solution, a nickel sulfate solution, and a copper sulfate solution.

3. The method for selectively separating calcium sulfate from a complex reaction system according to claim 1, characterized in that: The sulfate concentration in the soluble sulfate solution is 10 g / L-100 g / L.

4. The method for selectively separating calcium sulfate from a complex reaction system according to claim 1, characterized in that: The precipitant in the precipitant solution is calcium oxide and / or calcium hydroxide; the solvent of the precipitant solution is water and / or purified liquid; the concentration of the precipitant solution is 0.5 mol / L-5 mol / L.

5. The method for selectively separating calcium sulfate from a complex reaction system according to claim 1, characterized in that: The SO4 in the soluble sulfate solution and the precipitant solution 2- :Ca molar ratio is 1:0.6-1.

0.

6. The method for selectively separating calcium sulfate from a complex reaction system according to claim 1, characterized in that: The base liquid is at least one of water, purified liquid, soluble sulfate solution or precipitant solution.

7. The method for selectively separating calcium sulfate from a complex reaction system according to claim 1, characterized in that: The base liquid also includes crystal seeds; the crystal seeds are fibrous calcium sulfate crystals and / or mixed slurry containing fibrous calcium sulfate; the added amount of the crystal seeds is 0-10% of the mass of the fibrous calcium sulfate crystals.

8. The method for selectively separating calcium sulfate from a complex reaction system according to claim 1, characterized in that: The reaction temperature is 50-99° C.; the reaction time is 1-8 h.

9. The method for selectively separating calcium sulfate from a complex reaction system according to claim 1, characterized in that: The separation is specifically: first gravity separation or screening separation, and then solid-liquid separation.

10. A method for preparing fibrous calcium sulfate crystals based on sulfate solution, characterized in that: A method for selectively separating calcium sulfate using a complex reaction system as described in any one of claims 1 to 9; the fiber length of the fibrous calcium sulfate crystals is not less than 100 μm.

Images