Method for separating calcium and sulfur from industrial byproduct gypsum

Abstract

The invention provides a method for separating calcium and sulfur in industrial byproduct gypsum. The method comprises the following steps: mixing and stirring industrial byproduct gypsum and a cosolvent solution to react, and filtering after reacting for a period of time to obtain a first filtrate and a first filter residue; adding alkali metal hydroxide into the first filtrate to form calcium hydroxide slurry, and introducing carbon dioxide to precipitate calcium ions in the first filtrate to obtain a product calcium carbonate and second filtrate; adding calcium chloride into the second filtrate, reacting sulfate ions in the second filtrate with the added calcium chloride at a certain temperature, and filtering to obtain calcium sulfate and a third filtrate mainly containing potassium chloride; alkali metal chlorine salt is used as a cosolvent, the solubility of calcium sulfate in a liquid phase is improved, and then separation of calcium sulfate and impurities in the byproduct gypsum is achieved through solid-liquid separation; compared with an organic solvent as a phase transfer solution, solid-liquid separation with alkali metal chlorine salt as a cosolvent is more convenient and quicker, and the cost is low.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization technology, and in particular to a method for separating calcium and sulfur from industrial by-product gypsum. Background Technology

[0002] Industrial by-product gypsum refers to by-products or waste residues produced in industrial production, with calcium sulfate dihydrate as the main component. Calcium and sulfur in industrial by-product gypsum cannot be separated by heating in an alkaline environment.

[0003] Currently, the main methods for separating and utilizing calcium and sulfur in industrial by-product gypsum are the "ammonia-carbonation method" and the "phase transfer-precipitation method." The "ammonia-carbonation method" involves directly reacting industrial by-product gypsum with ammonium carbonate, ammonia, or carbon dioxide in a primary or secondary carbonation reaction to obtain calcium carbonate and ammonium sulfate. The primary carbonation method yields calcium carbonate and ammonium sulfate with low purity. The secondary carbonation method yields calcium carbonate with higher purity, but suffers from a long process and high cost. The "phase transfer-precipitation method" utilizes organic co-solvents such as sodium salicylate and sodium D-gluconate to conduct a phase transfer reaction with phosphogypsum. During the carbonation reaction, a complex crystal structure is added to control the preparation of active nano-calcium carbonate materials. The filtrate is separated using a membrane separation method to prepare by-product sodium sulfate, and the phase transfer agent is recycled. This process uses an organic salt phase transfer agent, which has high viscosity and is difficult to separate from calcium carbonate. Furthermore, separating by-product sodium sulfate and sodium D-gluconate using membrane separation is complex and costly. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for separating calcium and sulfur from industrial by-product gypsum. This invention uses industrial by-product gypsum, carbon dioxide, a fluxing agent, alkali metal hydroxide, and calcium chloride as raw materials to separate calcium and sulfur from industrial by-product gypsum and prepare calcium carbonate and calcium sulfate. The fluxing agent can be recycled during the process. The process is simple, low-cost, and achieves the goal of resource utilization of industrial by-product gypsum.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides a method for separating calcium and sulfur from industrial by-product gypsum, comprising the following steps:

[0007] S1. Industrial by-product gypsum is mixed and stirred with a co-solvent solution to react, and the first filtrate and the first filter residue are separated.

[0008] S2. Add the alkali metal hydroxide to the first filtrate, then pass carbon dioxide through, react, and filter to obtain calcium carbonate and the second filtrate.

[0009] S3. Add calcium chloride to the second filtrate, react, and filter to obtain calcium sulfate and a third filtrate containing potassium chloride.

[0010] The co-solvent solution includes at least one of potassium chloride, sodium chloride, and ammonium chloride.

[0011] Preferably, the co-solvent solution comprises a co-solvent and water, wherein the mass ratio of the co-solvent, water, and industrial by-product gypsum is (5-15):(40-80):1.

[0012] Preferably, an alkali metal hydroxide is added to the first filtrate, carbon dioxide is then introduced, the reaction is carried out, and the mixture is filtered to obtain calcium carbonate and a second filtrate.

[0013] The carbon dioxide introduction rate is 100–300 mL / min;

[0014] The reaction temperature is 20–25℃ and the time is 40–60 min.

[0015] Preferably, calcium chloride is added to the second filtrate, and the reaction temperature is 25–100°C and the reaction time is 40–60 min.

[0016] Preferably, in the step of mixing and stirring industrial by-product gypsum with a co-solvent solution, the reaction temperature is 20-25°C and the time is 30-40 min.

[0017] Preferably, the third filtrate containing potassium chloride replaces the co-solvent solution in step S1 and is used as the co-solvent solution for steps S2 to S3.

[0018] Preferably, the first filter residue obtained in step S1 replaces the industrial by-product gypsum and is mixed and stirred with the co-solvent solution to proceed to steps S2 to S3.

[0019] Preferably, the alkali metal hydroxide includes at least one of KOH and NaOH.

[0020] Preferably, the mass ratio of the industrial by-product gypsum, alkali metal hydroxide, and calcium chloride is 5:(6-7):(6-7).

[0021] The method for separating calcium and sulfur in industrial by-product gypsum of the present invention has the following advantages compared with the prior art:

[0022] 1. The method for separating calcium and sulfur in industrial by-product gypsum of the present invention comprises the following steps: mixing and stirring industrial by-product gypsum with a co-solvent solution to increase the solubility of calcium sulfate in the liquid phase of the industrial by-product gypsum; filtering after a period of reaction to obtain a first filtrate and a first filter residue; adding an alkali metal hydroxide to the first filtrate to form a calcium hydroxide slurry; passing carbon dioxide through the slurry; filtering and drying after the reaction is complete to precipitate calcium ions in the first filtrate to obtain calcium carbonate and a second filtrate; adding calcium chloride to the second filtrate; reacting the sulfate ions in the second filtrate with the added calcium chloride under certain temperature conditions; filtering to obtain calcium sulfate and a third filtrate mainly containing potassium chloride; the present invention uses an alkali metal chloride salt as a co-solvent to increase the solubility of calcium sulfate in the liquid phase, and then achieves the separation of calcium sulfate and impurities in by-product gypsum through solid-liquid separation; compared with organic solvents as phase transfer solutions, solid-liquid separation using alkali metal chloride salts as co-solvents is more convenient, faster, and less expensive.

[0023] 2. This invention achieves the purification and whitening of calcium sulfate by adding an external calcium source. The filtrate after solid-liquid separation is mainly composed of alkali metal chloride salts, which can be recycled multiple times, further reducing production costs. The process is simple and the production efficiency is high. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a scanning electron microscope image of the calcium carbonate product obtained in step S2 of Example 1;

[0026] Figure 2 This is a scanning electron microscope image of the calcium sulfate product obtained in step S3 of Example 1. Detailed Implementation

[0027] To facilitate understanding of the present invention, a more comprehensive description of the invention will be provided below in conjunction with specific embodiments. Preferred embodiments of the invention are given in the specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0028] The order in which the embodiments are described below is not intended to limit the preferred order of the embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". Various embodiments of the invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0029] This invention provides a method for separating calcium and sulfur from industrial by-product gypsum, comprising the following steps:

[0030] S1. Industrial by-product gypsum is mixed and stirred with a co-solvent solution to react, and the first filtrate and the first filter residue are separated.

[0031] S2. Add the alkali metal hydroxide to the first filtrate, then pass carbon dioxide through, react, and filter to obtain calcium carbonate and the second filtrate.

[0032] S3. Add calcium chloride to the second filtrate, react, and filter to obtain calcium sulfate and a third filtrate containing potassium chloride.

[0033] The co-solvent in the co-solvent solution includes at least one of potassium chloride, sodium chloride, and ammonium chloride.

[0034] The present invention discloses a method for separating calcium and sulfur in industrial by-product gypsum, comprising the following steps: mixing and stirring industrial by-product gypsum with a co-solvent solution to increase the solubility of calcium sulfate in the liquid phase of the industrial by-product gypsum; filtering after a period of reaction to obtain a first filtrate and a first filter residue; adding an alkali metal hydroxide to the first filtrate to form a calcium hydroxide slurry; introducing carbon dioxide; filtering and drying after the reaction is complete to precipitate calcium ions in the first filtrate, obtaining calcium carbonate and a second filtrate; adding calcium chloride to the second filtrate; reacting the sulfate ions in the second filtrate with the added calcium chloride under certain temperature conditions; and filtering to obtain calcium sulfate and a third filtrate mainly containing potassium chloride.

[0035] This invention uses alkali metal chloride salts as a co-solvent to increase the solubility of calcium sulfate in the liquid phase, and then achieves the separation of calcium sulfate from impurities in by-product gypsum through solid-liquid separation. Compared with organic solvents as phase transfer solutions, solid-liquid separation using alkali metal chloride salts as co-solvents is more convenient, faster, and cheaper.

[0036] This invention purifies and whitens calcium sulfate by adding an external calcium source (i.e., calcium chloride). The filtrate after solid-liquid separation is mainly composed of alkali metal chloride salts, which can be recycled multiple times, further reducing production costs. The process is simple and has high production efficiency.

[0037] In some embodiments, the cosolvent solution comprises a cosolvent and water, wherein the mass ratio of the cosolvent, water, and industrial by-product gypsum is (5-15):(40-80):1.

[0038] In some embodiments, an alkali metal hydroxide is added to the first filtrate, carbon dioxide is then introduced, the reaction is carried out, and the filtrate is filtered to obtain calcium carbonate and a second filtrate.

[0039] The carbon dioxide introduction rate is 100–300 mL / min;

[0040] The reaction temperature is 20–25℃ and the time is 40–60 min.

[0041] In some embodiments, calcium chloride is added to the second filtrate, and in the reaction step, the reaction temperature is 25–100°C and the time is 40–60 min.

[0042] In some embodiments, in the step of mixing and stirring industrial by-product gypsum with a co-solvent solution, the reaction temperature is 20–25°C and the reaction time is 30–40 min.

[0043] In some embodiments, the third filtrate containing potassium chloride replaces the co-solvent solution in step S1 and is used as the co-solvent solution for steps S2 to S3, that is, the third filtrate containing potassium chloride can be recycled as the co-solvent solution.

[0044] In some embodiments, the industrial by-product gypsum is phosphogypsum.

[0045] In some embodiments, the first filter residue obtained in step S1 replaces the industrial by-product gypsum and is mixed and stirred with the co-solvent solution to proceed to steps S2 to S3. When the industrial by-product gypsum is phosphogypsum, the first filter residue is a silicon-containing filter residue, which can be further leached in step S1 to improve the silicon content in the filter residue and facilitate subsequent recycling.

[0046] In some embodiments, the alkali metal hydroxide includes at least one of KOH and NaOH.

[0047] In some embodiments, the mass ratio of industrial by-product gypsum, alkali metal hydroxide, and calcium chloride is 5:(6-7):(6-7).

[0048] The following specific embodiments further illustrate the method for separating calcium and sulfur in industrial by-product gypsum according to the present invention. This section further explains the content of the present invention in conjunction with specific embodiments, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0049] In the following examples and comparative examples, the industrial by-product gypsum was phosphogypsum. XRF analysis revealed that the main chemical components of phosphogypsum were CaO and SO3; XRD analysis showed that the main mineral component was CaSO4·2H2O; the mass fraction of CaSO4·2H2O was 85.2%, and it also contained F. - (Mass fraction approximately 0.6%), P such as phosphate and phosphate ions (mass fraction approximately 1.5%), the remainder being organic matter, metal elements, etc.

[0050] Example 1

[0051] This embodiment provides a method for separating calcium and sulfur from industrial by-product gypsum, including the following steps:

[0052] S1. Under normal temperature conditions (25℃), weigh 50g of KCl solid and add it to 300mL of distilled water. Mix and stir until homogeneous to obtain KCl solution.

[0053] 5g of industrial by-product gypsum (specifically phosphogypsum) was weighed and added to KCl solution. After stirring and reacting for 40 minutes, the mixture was filtered to obtain calcium ion leachate A (i.e., the first filtrate) and the first filter residue. The calcium ion concentration in leachate A was detected by ICP-OES (inductively coupled plasma optical emission spectrometry). At this point, the calcium ion leaching rate in phosphogypsum was 60%, which is the percentage of the amount of calcium ions in leachate A relative to the amount of calcium ions in 5g of phosphogypsum.

[0054] S2. At room temperature (25℃), 6.5g of KOH solid was added to leachate A. Carbon dioxide gas was introduced into leachate A at a rate of 200mL / min. After stirring and reacting for 40min, calcium ions precipitated to form calcium carbonate. After filtration and drying, calcium carbonate product and sulfate ion-containing filtrate B (i.e., the second filtrate) were obtained. The purity of the calcium carbonate product was 97.8%, which is the percentage of the mass of calcium carbonate in the total mass of the calcium carbonate product.

[0055] S3. Under normal temperature conditions (25℃), 6.5g of calcium chloride is added to filtrate B containing sulfate ions. After reacting for 30 minutes, the mixture is filtered to obtain calcium sulfate product and filtrate C containing potassium chloride (i.e., the third filtrate), thus realizing the separation and utilization of calcium and sulfur elements in phosphogypsum.

[0056] Example 2

[0057] This embodiment provides a method for separating calcium and sulfur from industrial by-product gypsum, including the following steps:

[0058] S1. Following the method in Example 1, filtrate C (i.e., the third filtrate) is obtained;

[0059] At room temperature (25℃), 5g of industrial by-product gypsum (specifically phosphogypsum) was added to filtrate C. After stirring and reacting for 40 minutes, the mixture was filtered to obtain calcium ion leachate D and filter residue. The calcium ion concentration in leachate D was detected using ICP-OES (inductively coupled plasma optical emission spectrometry). At this point, the calcium ion leaching rate in the phosphogypsum was 57%. This indicates that alkali metal chloride solution can be recycled as a co-solvent in the process system.

[0060] S2. At room temperature (25℃), 6.5g of KOH solid was added to leachate D. Carbon dioxide gas was introduced into leachate D at a rate of 200mL / min. After stirring and reacting for 40min, calcium ions precipitated to form calcium carbonate. After filtration and drying, calcium carbonate product and sulfate ion-containing filtrate E were obtained. The purity of calcium carbonate product was 95.4%.

[0061] S3. At room temperature (25℃), add 6.3g of calcium chloride to filtrate E containing sulfate ions. After reacting for 40 minutes, filter to obtain calcium sulfate product and filtrate F containing potassium chloride.

[0062] Example 3

[0063] This embodiment provides a method for separating calcium and sulfur from industrial by-product gypsum, including the following steps:

[0064] S1. Obtain the first filter residue according to the method in Implementation 1;

[0065] At room temperature (25℃), 50g of KCl solid was weighed and added to 300mL of distilled water and mixed and stirred until homogeneous to obtain a KCl solution.

[0066] The first filter residue was added to KCl solution, stirred and reacted for 40 min, and then filtered to obtain calcium ion leachate G. The calcium ion concentration in leachate G was detected by ICP-OES. At this time, the overall leaching rate of calcium ions in phosphogypsum was 98%, which proved that after multiple leachings, most of the calcium sulfate dihydrate in phosphogypsum could be effectively decomposed into calcium ions and sulfate ions.

[0067] S2. At room temperature (25℃), 6.5g of KOH solid was added to the leachate G. Carbon dioxide gas was introduced into the leachate G at a rate of 200mL / min. After stirring and reacting for 40min, calcium ions precipitated to form calcium carbonate. After filtration and drying, calcium carbonate product and sulfate ion-containing filtrate C were obtained.

[0068] S3. Under normal temperature conditions (25℃), 6.5g of calcium chloride is added to the sulfate ion-containing filtrate C. After reacting for 30 minutes, the mixture is filtered to obtain calcium sulfate product and potassium chloride-containing filtrate D, thereby achieving the separation and utilization of calcium and sulfur elements in phosphogypsum.

[0069] Furthermore, different masses (10-50g, specifically 10g and 50g) of co-solvents (potassium chloride, sodium chloride, and ammonium chloride, respectively) were added to 300mL (300g) of distilled water to obtain a co-solvent solution. 5g of industrial by-product gypsum (specifically phosphogypsum) was added to the co-solvent solution, and the mixture was stirred and reacted at room temperature (25℃) for 20-40min (specifically 20min and 40min). The solubility rate of calcium sulfate dihydrate in phosphogypsum (the percentage of calcium sulfate dissolved from the co-solvent solution relative to the total mass of calcium sulfate in the phosphogypsum) was tested, and the results are shown in Table 1 below.

[0070] Table 1 - Effect of co-solvents on the solubility of calcium sulfate dihydrate in phosphogypsum

[0071] Types of cosolvents Co-solvent concentration (mass concentration / %) Stirring time / min Solubility / % Potassium chloride 3.33 40 37.62 Potassium chloride 16.67 40 60.17 Potassium chloride 16.67 20 51.76 Sodium chloride 3.33 40 30.12 Sodium chloride 16.67 40 52.16 Sodium chloride 16.67 20 43.52 ammonium chloride 3.33 40 28.65 ammonium chloride 16.67 40 54.63 ammonium chloride 16.67 20 45.15

[0072] In Table 1, the cosolvent concentration refers to the mass concentration of the cosolvent in the cosolvent solution. For example, if the cosolvent is potassium chloride with a concentration of 16.67%, the calculation method is cosolvent mass / distilled water mass × 100%, 50g / 300g = 16.67%. The concentrations of other cosolvents are calculated using the same method.

[0073] As can be seen from Table 1, when 50g of potassium chloride, a co-solvent, is added to 300mL of distilled water, a co-solvent solution is obtained. 5g of industrial by-product gypsum (specifically phosphogypsum) is added to the co-solvent solution, and the mixture is stirred for 40min at room temperature (25℃). At this time, the solubility of calcium sulfate dihydrate in the phosphogypsum is the highest, reaching 60.17%. Therefore, this process parameter is used in Example 1.

[0074] The potassium chloride-containing filtrate C from step S3 of Example 1 was used as a carrier for recycling. 5g of phosphogypsum was added to the potassium chloride-containing filtrate C, and the mixture was stirred and reacted for 40 minutes at room temperature (25℃). The solubility of calcium sulfate dihydrate in the phosphogypsum was tested, and the calcium ion leachate was obtained by filtration. The potassium chloride-containing filtrate was obtained again according to steps S2-S3 of Example 1. The phosphogypsum was leached again using the potassium chloride-containing filtrate in the same way. This process was repeated 5 times, and the solubility of calcium sulfate dihydrate in the phosphogypsum was tested each time. The results are shown in Table 2 below.

[0075] Table 2 - Solubility of calcium sulfate dihydrate in phosphogypsum when potassium chloride solution is recycled as a carrier.

[0076] Loop count Solubility / % 1 56.92 2 46.12 3 52.46 4 33 5 34.44

[0077] As can be seen from Table 2, the solubility gradually decreases due to the common ion effect and the accumulation of impurities in phosphogypsum. However, due to the increase in the number of cycles and the continuous addition of KOH solid, the potassium ion content during leaching increases, and the leaching efficiency tends to reach equilibrium at around 33%-34%.

[0078] Figure 1 This is a scanning electron microscope image of the calcium carbonate product obtained in step S2 of Example 1;

[0079] from Figure 1 As can be seen from the reaction, the calcium carbonate product prepared by the reaction is rhomboid calcium carbonate crystals.

[0080] Figure 2 This is a scanning electron microscope image of the calcium sulfate product obtained in step S3 of Example 1.

[0081] from Figure 2 As can be seen from the reaction, the calcium sulfate products prepared are calcium sulfate whiskers with different aspect ratios.

[0082] It is understood that the technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0083] The above are merely preferred embodiments of this application, and only specifically describe the technical principles of this application. These descriptions are only for explaining the principles of this application and should not be construed as limiting the scope of protection of this application in any way. Based on this explanation, any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, as well as other specific embodiments of this application that can be conceived by those skilled in the art without creative effort, should be included within the scope of protection of this application.

Claims

1. A method for separating calcium and sulfur from industrial by-product gypsum, characterized in that, Includes the following steps: S1. Industrial by-product gypsum is mixed and stirred with a co-solvent solution to react, and the first filtrate and the first filter residue are separated. S2. Add the alkali metal hydroxide to the first filtrate, then pass carbon dioxide through, react, and filter to obtain calcium carbonate and the second filtrate. S3. Add calcium chloride to the second filtrate, react, and filter to obtain calcium sulfate and a third filtrate containing potassium chloride. The co-solvent solution includes at least one of potassium chloride, sodium chloride, and ammonium chloride.

2. The method for separating calcium and sulfur in industrial by-product gypsum as described in claim 1, characterized in that, The co-solvent solution comprises a co-solvent and water, wherein the mass ratio of the co-solvent, water, and industrial by-product gypsum is (5-15):(40-80):

1.

3. The method for separating calcium and sulfur in industrial by-product gypsum as described in claim 1, characterized in that, An alkali metal hydroxide was added to the first filtrate, and then carbon dioxide was introduced to react. After filtration, calcium carbonate and the second filtrate were obtained. The carbon dioxide introduction rate is 100–300 mL / min; The reaction temperature is 20–25℃ and the time is 40–60 min.

4. The method for separating calcium and sulfur in industrial by-product gypsum as described in claim 1, characterized in that, Calcium chloride is added to the second filtrate. In the reaction step, the reaction temperature is 25-100℃ and the time is 40-60 min.

5. The method for separating calcium and sulfur in industrial by-product gypsum as described in claim 1, characterized in that, In the step of mixing and stirring industrial by-product gypsum with a co-solvent solution, the reaction temperature is 20–25°C and the reaction time is 30–40 min.

6. The method for separating calcium and sulfur in industrial by-product gypsum as described in claim 1, characterized in that, The third filtrate containing potassium chloride replaces the co-solvent solution in step S1 and is used as the co-solvent solution for steps S2 to S3.

7. The method for separating calcium and sulfur in industrial by-product gypsum as described in claim 1, characterized in that, The first filter residue obtained in step S1 replaces the industrial by-product gypsum and is mixed and stirred with the co-solvent solution to proceed to steps S2 to S3.

8. The method for separating calcium and sulfur in industrial by-product gypsum as described in claim 1, characterized in that, The alkali metal hydroxide includes at least one of KOH and NaOH.

9. The method for separating calcium and sulfur in industrial by-product gypsum as described in claim 1, characterized in that, The mass ratio of the industrial by-product gypsum, alkali metal hydroxide, and calcium chloride is 5:(6-7):(6-7).

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