CN113354319B - A method for preparing α-type hemihydrate gypsum from high-salt wastewater of a desulfurization gypsum synergistic power plant - Google Patents

Abstract

The invention belongs to the field of building material preparation, and discloses a method for preparing alpha-hemihydrate gypsum by using desulfurization gypsum in cooperation with high-salt wastewater of a power plant, which comprises the following steps: adjusting Na in pretreated high-salt wastewater of power plant ⁺ 、K ⁺ 、Ca ²⁺ Adding a crystal form regulator into the mixture to adjust the pH value to 5-7 to obtain a reaction solution; drying and grinding the desulfurized gypsum, adding the desulfurized gypsum into the reaction liquid, and heating the reaction liquid to carry out dehydration reaction; and collecting the slurry after the reaction is finished, carrying out suction filtration, washing a filter cake with boiling water, carrying out secondary suction filtration, and drying to obtain the alpha-type semi-hydrated desulfurized gypsum. Aiming at the defect of large salt amount for preparing alpha-hemihydrate gypsum by using an ordinary-pressure salt solution method, the invention takes the desulfurized gypsum as a raw material, uses pretreated high-salt wastewater of the power plant as a reaction solution, adds a small amount of electrolyte salt according to the fluctuation of the water quality of the strong brine to adjust the salt concentration in the solution so as to enable the reaction to be carried out, and adds organic acid to adjust the crystal form, thereby obtaining the alpha-hemihydrate desulfurized gypsum with excellent strength, and realizing the high-value utilization of the high-salt wastewater of the power plant.

Description

A method for preparing α-type hemihydrate gypsum from high-salt wastewater of a desulfurization gypsum synergistic power plant

technical field

The invention belongs to the building material preparation technology, and designs a method for preparing alpha-type hemihydrate desulfurization gypsum by using pretreated high-salt wastewater.

Background technique

The information disclosed in this background section is only intended to increase the understanding of the general background of the present invention, and is not necessarily taken as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

Desulfurization gypsum is an industrial by-product gypsum obtained by wet desulfurization and purification of flue gas generated after combustion of sulfur-containing fuels (coal, oil, etc.). It mainly comes from industries such as electric power, thermal energy, iron and steel metallurgy, and chemical industry. The main component is calcium sulfate dihydrate, accompanied by a small amount of impurities, and has a high moisture content. Desulfurization gypsum has the advantages of wide sources and low price, but its quality is unstable and its whiteness is low, which restricts its resource utilization to a certain extent. In terms of construction material utilization, desulfurized gypsum is mainly used as a raw material for construction gypsum (β-type hemihydrate gypsum), and its product strength is low. In contrast, the α-type hemihydrate gypsum dehydrated under the condition of high water vapor partial pressure has the advantages of low water-cement ratio and high strength, and has a wider range of applications such as precision mold casting, new building materials and decorative materials, etc. .

The preparation methods of α-type hemihydrate gypsum mainly include autoclave method, pressurized hydrothermal method and normal pressure saline solution method, etc., among which the autoclaved method and pressurized hydrothermal method have relatively large initial investment, high energy consumption, and are harmful to gypsum. High grade requirements, generally natural gypsum. The atmospheric pressure salt solution method reduces the activity of water by adding electrolyte salts to the aqueous solution of the reaction, so that the reaction temperature required for the transformation of calcium sulfate dihydrate to α-type calcium sulfate hemihydrate is lowered to below the boiling point of the aqueous solution, thus making the reaction It can be carried out under normal pressure. The method has mild conditions, is easy to operate and control the process, and has simple equipment, but the amount of electrolyte salt that needs to be added is relatively large. In some inventions of this method, the quality of the salt added is about 0.5 to 1 times that of the reaction raw materials. The electrolyte salt will greatly increase the cost. In addition, α hemihydrate gypsum crystals tend to grow into needles or long columns in this environment, and it is necessary to add crystal form regulators to intervene in the crystal growth direction to make the crystals grow into short columns to obtain better strength properties.

Power plant high-salt wastewater is waste water with high salt content obtained through reverse osmosis technology in the chemical water treatment stage of power plant feed water, cooling water, etc., mainly containing Na ⁺ , K ⁺ , Mg ²⁺ , Ca ²⁺ , Cl ^- , For impurities such as salt ions such as SO ₄ ^2- , NO ^3- , and organic matter, the common domestic treatment method for power plant wastewater is to use cascade utilization first, and then treat the remaining wastewater by softening, degradation, evaporation and crystallization. In CN110255663B, the inventor disclosed a non-contact microwave catalytic water treatment device and water treatment method. The water treatment method can effectively save energy consumption while ensuring a degradation efficiency of more than 90% of organic waste water. However, the utilization of high-salt waste water in power plants Value could still be improved.

Contents of the invention

Aiming at the disadvantage of the large amount of salt used in the preparation of α-type hemihydrate gypsum by the normal-pressure salt solution method, the present invention uses desulfurized gypsum as raw material, uses pretreated high-salt wastewater from power plants as the reaction solution, and adds a small amount of electrolyte salt according to the fluctuation of concentrated brine water quality. Adjust the salt concentration in the solution to enable the reaction to proceed, and add organic acid to adjust the crystal form to obtain α-type hemihydrate desulfurization gypsum with excellent strength, and realize the high-value utilization of high-salt wastewater from power plants.

In order to realize the above-mentioned technical purpose, the present invention adopts following technical scheme:

The first aspect of the present invention provides a method for preparing α-type hemihydrate gypsum from high-salt wastewater of a desulfurization gypsum cooperative power plant, including:

adjusting the concentration of Na ⁺ , K ⁺ , and Ca ²⁺ in the pretreated high-salt wastewater of the power plant, and then adding a crystal form regulator to adjust the pH value to 5-7 to obtain a reaction solution;

Drying and finely grinding the desulfurized gypsum, adding it to the reaction liquid, and heating for dehydration reaction;

Collect the slurry after the reaction is completed, filter with suction, wash the filter cake with boiling water, filter with suction twice, and dry to obtain α-type hemihydrate desulfurization gypsum.

The study found that using the high-salt wastewater pretreated by the method of patent CN110255663B as the reaction solution for preparing α-type hemihydrate gypsum can minimize the adverse effects of organic pollutants on the reaction process. The process of preparing α-type hemihydrate gypsum from the pretreated high-salt wastewater of power plants adds a high-value intermediate utilization link to the cascade utilization stage of power plant wastewater, without the need to introduce a large amount of electrolyte salt, and the prepared products meet the standards.

The second aspect of the present invention provides α-type hemihydrate gypsum prepared by any one of the above-mentioned methods.

The third aspect of the present invention provides the application of the above-mentioned α-type hemihydrate gypsum in casting precision molds, producing building materials and decorative materials.

The beneficial effects of the present invention are:

(1) The present invention is an improved normal-pressure salt solution method for preparing α-type hemihydrate desulfurization gypsum, which uses high-salt wastewater after microwave catalytic water treatment to degrade organic matter into a salt solution that can carry out the reaction to prepare dynamic reaction at normal pressure The α-type hemihydrate gypsum solves the problem of large industrial salt consumption in this method, and adds an effective high-value utilization link for the cascade utilization of high-salt wastewater in power plants.

(2) The operation method of the present application is simple, low in cost, universal, and easy for large-scale production.

Description of drawings

The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention, and the schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations to the present invention.

Fig. 1 is a graph showing the change of crystal water content in Example 1 of the present invention.

Fig. 2 is a diagram showing the change of crystal water content in Example 2 of the present invention.

Fig. 3 is a diagram showing the change of crystal water content in Comparative Example 1 of the present invention.

Fig. 4 is a graph showing the change of crystal water content in Comparative Example 2 of the present invention.

Fig. 5 is a diagram showing the change of crystal water content in Comparative Example 3 of the present invention.

Fig. 6 is the XRD of the reaction products of Examples 1 and 2 of the present invention and Comparative Example 1.

Fig. 7 is the TG-DSC curve of the product in the 3.44mol/L NaCl solution in Comparative Example 2 of the present invention.

Fig. 8 is the XRD of the reaction product of Comparative Example 3 of the present invention.

Fig. 9 is the SEM of the reaction product of Example 1 of the present invention.

Fig. 10 is the SEM of the reaction product of Example 2 of the present invention.

Figure 11 is the SEM of the reaction product of Comparative Example 1 of the present invention.

Figure 12 is the SEM of the product in the 2.59mol/L NaCl solution of Comparative Example 2 of the present invention.

Figure 13 is the SEM of the product in the 2.02mol/L KCl solution of Comparative Example 3 of the present invention.

Fig. 14 is a schematic diagram of the process for preparing α-type hemihydrate gypsum from the high-salt wastewater of the desulfurization gypsum synergistic power plant of the present invention.

Detailed ways

It should be noted that the following detailed description is exemplary and intended to provide further explanation of the present invention. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

A method for preparing α-type hemihydrate gypsum from high-salt wastewater of a desulfurization gypsum cooperative power plant, specifically comprising the following steps:

1. Dilute the pretreated high-salt wastewater with water so that the concentration of Na ⁺ is 0.07-0.34mol/L, and the concentration of K ⁺ is less than 0.12mol/L. According to the diluted Ca ²⁺ concentration, add CaCl ₂ to adjust the Ca ²⁺ content Until the Ca ²⁺ concentration in the solution reaches 0.8-0.97 mol/L, a crystal form regulator is added, and the pH value of the solution is adjusted to 5-7 with HCl and NaOH to prepare a reaction solution.

2. Dry the desulfurized gypsum raw material, grind it finely, add it to the reaction solution described in 1. at a solid-to-liquid ratio of 1:4~6, heat it in the reaction kettle to 95°C~100°C, and keep the stirring rate at 200~400r/ min, dynamic reaction 2 to 6 hours.

3. Rapid suction filtration of the slurry after the reaction is completed, washing the filter cake with boiling water, suction filtration again, and drying the product in an oven at 80-120°C to obtain α-type hemihydrate desulfurization gypsum.

In some embodiments, the crystal form regulator is succinic acid, and the amount added is 0.12% to 0.24% of the mass of the desulfurized gypsum raw material participating in the reaction. The adsorption of calcium ions with similar spacing on the surface inhibits the growth of the crystal along the c-axis, making the crystal short columnar, thereby making the hydration product more dense and improving the strength performance.

In some embodiments, the step of washing with boiling water is to wash with boiling water 10 times the mass of the reaction product and then suction filter, and repeat twice. Although the salt in the high-salt solution will not directly participate in the phase transition reaction of calcium sulfate dihydrate, part of it will remain in the product, affecting product quality. The product obtained after boiling water washing and drying in the method is measured by an X-ray fluorescence spectrometer so that the sodium is less than 0.01% of the product mass, and the chlorine is less than 0.006%, which basically does not affect product performance.

In some embodiments, the concentration of the salt in the salt solution determines whether or not the reaction can proceed and the rate of the reaction. In high-salt wastewater, the cations are mostly Na ⁺ and Ca ²⁺ , and contain a small amount of K ⁺ and traces of Mg ²⁺ and Al ³⁺ and other cations, and the anions are mostly Cl ^- and SO ₄ ^2- , containing a small amount NO ₃ ^- and other anions. According to the experimental results, all the above salt ions can reduce the conditions required for the reaction to occur and accelerate the reaction rate, but too much Na ⁺ and K ⁺ will affect the phase transition process, change the structure of the target product, and have adverse effects. For example, when Na ⁺ is too much, the crystal form of the product will change, from α-type hemihydrate gypsum to β-type hemihydrate gypsum, which will reduce the performance of the product, so its content should be limited. The reaction process and product properties of high content will be in the comparative example 1 shown. However, the effect of Na ⁺ on accelerating the reaction rate is very significant, so it is appropriate to adjust the concentration of Na ⁺ in the high-salt solution to 0.07-0.34mol/L. However, when the K ⁺ content is too high, heterogeneous phase potassium gypsum will be generated in the product, which will greatly reduce the strength performance, so its content should also be limited, and its concentration should be less than 0.12mol/L.

The present invention will be described in further detail below in conjunction with specific examples. It should be pointed out that the specific examples are to explain rather than limit the present invention.

The chemical composition of the desulfurized gypsum raw material used in all the following examples is as follows:

Example 1

(1) Dry the desulfurized gypsum raw material, use a crusher, crush and grind it finely.

(2) Use industrial salt to prepare a high-salt solution to simulate the high-salt wastewater environment of a power plant. The concentration of each ion in the solution is Na ⁺ 0.07mol/L, Ca ²⁺ 0.97mol/L, K ⁺ 0.09mol/L, Mg ²⁺ 0.02mol /L, Cl ^- 1.76mol/L, SO ₄ ^2- 0.10mol/L, adjust the pH value of the solution to 4.9 with dilute hydrochloric acid, and finally add 0.3g of succinic acid.

(3) Put the prepared 500mL solution in a 1000mL three-necked flask, and dynamically heat it to 95°C with an electric heating mantle at a stirrer speed of 300r/min. .

(4) After the reaction was completed, the slurry was suction-filtered, then washed twice with 1000 mL of boiling water, and the product was obtained by suction filtration, dried in an oven at 100°C, and then used. During the reaction period, 10 mL of the solution in the reaction was extracted every 30 minutes and processed according to the above steps to obtain a sample, which was used to determine the crystal water content and XRD pattern at the current stage.

As shown in Figure 1 crystallization water content, desulfurization gypsum has been completely converted into α-type hemihydrate gypsum in about 60 minutes in this solution environment, and the reaction product is a short columnar crystal as shown in Figure 9, which shows that the crystal form regulator butadiene The acid effectively restricts crystal growth along the c-axis, reducing the aspect ratio. The strength performance of the product is good, which meets the strength standard of α30 in "JC/T2038-2010".

Example 2

(1) Dry the desulfurized gypsum raw material, use a crusher, crush and grind it finely.

(2) Use industrial salt to prepare a high-salt solution to simulate the high-salt wastewater environment of a power plant. The concentration of each ion in the solution is Na ⁺ 0.34mol/L, Ca ²⁺ 0.87mol/L, Mg ²⁺ 0.13mol/L, Cl ^- 1.69mol /L, SO ₄ ^2- 0.21mol/L, the pH of the solution was 7.2, and 0.6g of succinic acid was added.

(3) Put the prepared 500mL solution in a 1000mL three-necked flask, and dynamically heat it to 95°C with an electric heating mantle at a stirrer speed of 300r/min. .

(4) After the reaction was completed, the slurry was suction-filtered, then washed twice with 1000 mL of boiling water, and the product was obtained by suction filtration, dried in an oven at 100°C, and then used. During the reaction period, 10 mL of the solution in the reaction was extracted every 30 minutes and processed according to the above steps to obtain a sample, which was used to determine the crystal water content and XRD pattern at the current stage.

As shown in the crystal water content in Figure 2, the crystal water content of desulfurized gypsum was 8.85% at 4 hours in the solution environment, indicating that there is still a small part of the raw materials that have not been converted, and the reaction completion time under this condition is more than 4 hours. As shown in Figure 10, there are hexagonal flaky α-type hemihydrate gypsum crystals and a small amount of unreacted massive dihydrate gypsum crystals in the reaction product, which proves that when the amount of succinic acid added is more, the inhibitory effect on crystal growth is greater. Strong, so that the crystal hardly grows along the c-axis. However, the strength performance of the product under this condition still meets the strength standard of α25 in "JC/T 2038-2010".

Comparative example 1

(1) Dry the desulfurized gypsum raw material, use a crusher, crush and grind it finely.

(2) Use industrial salt to prepare a high-salt solution to simulate the high-salt wastewater environment of a power plant. The concentration of each ion in the solution is Na ⁺ 0.07mol/L, Ca ²⁺ 0.97mol/L, K ⁺ 0.09mol/L, Mg ²⁺ 0.02mol /L, Cl ^- 1.76mol/L, SO ₄ ^2- 0.10mol/L, and the pH value of the solution is 7.2.

(3) Put the prepared 500mL solution in a 1000mL three-necked flask, and dynamically heat it to 95°C with an electric heating mantle at a stirrer speed of 300r/min. .

(4) After the reaction was completed, the slurry was suction-filtered, then washed twice with 1000 mL of boiling water, and the product was obtained by suction filtration, dried in an oven at 100°C, and then used. During the reaction period, 10 mL of the solution in the reaction was extracted every 30 minutes and processed according to the above steps to obtain a sample, which was used to determine the crystal water content and XRD pattern at the current stage.

As shown in Figure 3 crystal water content, desulfurization gypsum is completely converted into α-type hemihydrate gypsum in 60 to 90 minutes under the solution environment. Compared with Example 1, the reaction in Example 1 is under the inhibition of succinic acid The speed is still slightly faster than the reaction speed of Comparative Example 1, indicating that reducing the pH value of the reaction system can accelerate the reaction speed. The reaction product is a long columnar crystal as shown in Figure 11, with an aspect ratio of 9-15:1, and the peak of the (204) crystal plane in Figure 6 is relatively weak, which proves that the crystallinity of the product is poor. 1d compressive strength is only 10.3Mpa.

Comparative example 2

(1) Dry the desulfurized gypsum raw material, use a crusher, crush and grind it finely.

(2) NaCl solutions with concentrations of 2.59 mol/L and 3.44 mol/L were prepared, and 0.3 g of succinic acid was added.

(3) Put the prepared 500mL solution in a 1000mL three-necked flask, and dynamically heat it to 95°C with an electric heating mantle at a stirrer speed of 300r/min. .

(4) After the reaction was completed, the slurry was suction-filtered, then washed twice with 1000 mL of boiling water, and the product was obtained by suction filtration, dried in an oven at 100°C, and then used. During the reaction period, 10 mL of the solution in the reaction was extracted every 30 minutes and processed according to the above steps to obtain a sample, which was used to determine the crystal water content and XRD pattern at the current stage.

As shown in Figure 4 crystal water content, desulfurization gypsum reacts quickly in NaCl solution, and is completely converted into hemihydrate gypsum within 30 minutes at a concentration of 3.44mol/L, but the crystal particle size is relatively large and the length and diameter are relatively large , is 8～16:1. As shown in Figure 7 of the TG-DSC curve, the exothermic peak of β-type soluble anhydrite transforming into β-type insoluble anhydrite appears in the differential thermal curve at around 355°C, which proves that the product is β-type hemihydrate gypsum. The product strength performance is poor and decreases with the increase of NaCl.

Comparative example 3

(1) Dry the desulfurized gypsum raw material, use a crusher, crush and grind it finely.

(2) KCl solutions with concentrations of 2.02 mol/L and 2.70 mol/L were prepared, and 0.3 g of succinic acid was added.

(3) Put the prepared 500mL solution in a 1000mL three-necked flask, and dynamically heat it to 95°C with an electric heating mantle at a stirrer speed of 300r/min. .

(4) After the reaction was completed, the slurry was suction-filtered, then washed twice with 1000 mL of boiling water, and the product was obtained by suction filtration, dried in an oven at 100°C, and then used. During the reaction period, 10 mL of the solution in the reaction was extracted every 30 minutes and processed according to the above steps to obtain a sample, which was used to determine the crystal water content and XRD pattern at the current stage.

As shown in Figure 8 XRD, desulfurized gypsum will generate heterogeneous potassium gypsum K ₂ Ca ₅ (SO ₄ ) ₆ ·H ₂ O in addition to hemihydrate gypsum in KCl solution. As shown by the SEM of the reaction product in Figure 13, a small amount of α-type hemihydrate gypsum crystals grew intact, but the crystal structure of hemihydrate gypsum mixed with potassium gypsum became broken, and the product had almost no strength.

The intensity performance of the product in all embodiments is shown in the table below:

Finally, it should be noted that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, it is still The technical solutions described in the foregoing embodiments may be modified, or part of them may be equivalently replaced. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (3)

1. The method for preparing alpha-hemihydrate gypsum by using desulfurization gypsum in cooperation with high-salt wastewater of a power plant is characterized by comprising the following steps of:

adjusting Na in pretreated high-salt wastewater of power plant ⁺ 、K ⁺ 、Ca ²⁺ The concentration is then added with a crystal form regulator to regulate the pH value to 57, obtaining a reaction solution;

drying and grinding the desulfurized gypsum, adding the desulfurized gypsum into the reaction liquid, and heating the reaction liquid to carry out dehydration reaction; the solid-liquid ratio of the desulfurization gypsum to the reaction liquid is 1:4 to 6;

the specific conditions of the reaction are as follows: dynamically reacting for 2-6 hours at the temperature of 95-100 ℃ under the condition of mechanical stirring; the stirring speed of mechanical stirring is 200-400 r/min;

collecting slurry after the reaction is completed, carrying out suction filtration, washing a filter cake with boiling water, carrying out secondary suction filtration, and drying to obtain alpha-type semi-hydrated desulfurized gypsum; the boiling water washing step is to wash with boiling water with the mass 10-12 times of the reaction product, and then suction-filter, and repeat for two to three times; the drying temperature is 80-120 ℃;

in the reaction solution, na ⁺ The concentration is 0.07 to 0.34mol/L, K ⁺ The concentration is less than 0.12mol/L, ca ²⁺ The concentration is 0.8-0.97 mol/L;

the crystal form regulator is succinic acid, and the addition amount is 0.12-0.24% of the mass of the desulfurized gypsum raw material;

the pretreatment method of the high-salt wastewater of the power plant adopts a non-contact microwave catalytic water treatment device for treatment.

2. An alpha-type semi-hydrated gypsum, which is characterized by being prepared by the method for preparing the alpha-type semi-hydrated gypsum by using the desulfurization gypsum and the high-salt wastewater of a power plant according to claim 1.

3. Use of the alpha hemihydrate gypsum of claim 2 in casting precision molds to produce building materials and decorative materials.