Innocent treatment process for desulfurized gypsum

Abstract

The invention provides a harmless treatment process for desulfurized gypsum, and relates to the technical field of desulfurized gypsum. The harmless treatment process for the desulfurized gypsum comprises the following steps: adding a citric acid solution into desulfurized gypsum powder, uniformly stirring, then carrying out first-stage aging treatment, then adding an alkali neutralizer, uniformly stirring, and carrying out second-stage aging treatment, so as to obtain the harmless desulfurized gypsum. According to the harmless treatment process for the desulfurized gypsum, the fixing effect of phosphorus and fluorine is synchronously enhanced, the risk of secondary pollution is remarkably reduced, and the harmless treatment process has the green advantages of low energy consumption and low carbon emission. Meanwhile, by means of the citric acid solution and the alkali neutralizer which are low in cost and easy to obtain and in combination with the simple and controllable technological process, the operation cost is greatly reduced, and the method is suitable for industrial popularization and has good application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of desulfurized gypsum, and particularly relates to a harmless treatment process for desulfurized gypsum. Background Art

[0002] Desulfurized gypsum (FGD gypsum) is a by-product generated by flue gas desulfurization technology during the flue gas desulfurization process in industries such as thermal power generation and steel smelting. Its main component is calcium sulfate dihydrate (CaSO4·2H2O), with a content usually above 90%. In addition, it generally contains impurities such as Fe2O3, SiO2, soluble salts (such as chlorides), and trace heavy metals. The accumulation of a large amount of desulfurized gypsum occupies a large amount of valuable land resources. Long-term open stacking is vulnerable to the influence of precipitation scouring and wind action. Soluble harmful substances in it, such as heavy metal ions and fluorides, may seep into the soil and groundwater with rainwater, leading to soil pollution and deterioration of groundwater quality, and further affecting the balance and stability of the surrounding ecosystem. At the same time, some fine particles enter the atmosphere under the action of wind, which will also have a certain negative impact on air quality. Moreover, the free water content of desulfurized gypsum is relatively high (10%-17%), and its physical properties such as strong viscosity and poor water resistance limit its direct utilization. Therefore, if the desulfurized gypsum is not properly disposed of, a series of serious environmental problems will be caused.

[0003] The harmless treatment of desulfurized gypsum aims to eliminate its environmental risks and promote resource utilization, mainly including methods such as resource utilization, solidification or stabilization treatment, and high-temperature melting treatment. Among them, solidification or stabilization treatment is to mix desulfurized gypsum with solidifying agents (such as cement, lime, etc.) to make bricks or other solid materials. However, the durability of the solidified products is poor, and problems such as cracking are likely to occur during long-term use. High-temperature melting treatment is to melt desulfurized gypsum at high temperature to decompose or solidify it, so as to achieve harmless treatment. However, its operating cost and equipment requirements are relatively high, requiring high-temperature-resistant materials and complex process control. It can be seen that methods such as solidification or stabilization treatment and high-temperature melting treatment all have certain limitations. Therefore, the method of resource utilization that uses desulfurized gypsum to produce building materials (such as gypsum boards, gypsum blocks), improve soil, produce fertilizers, etc. is an ideal harmless treatment approach for desulfurized gypsum. However, the quality of the products obtained by harmless treatment is greatly affected by the quality of desulfurized gypsum, and strict control of the raw material quality is required to achieve significant economic and environmental benefits while realizing the harmlessness of desulfurized gypsum.

[0004] Therefore, the research and development of an efficient, economical and environmentally friendly harmless disposal technology for desulfurized gypsum is of crucial significance for realizing the reduction, harmlessness and resource utilization of industrial waste and promoting sustainable development. Summary of the Invention

[0005] To solve the above problems, the present invention provides a harmless treatment process for desulfurized gypsum. The treatment process of the present invention can remove harmful elements such as phosphorus and fluorine in desulfurized gypsum, and the treatment process is simple, low-cost, and has less secondary pollution, realizing the harmless and high-value treatment of desulfurized gypsum, and has good industrial promotion prospects.

[0006] The present invention provides a harmless treatment process for desulfurized gypsum, which specifically includes the following steps:

[0007] Add a citric acid solution to the desulfurized gypsum powder and stir evenly, then carry out the first-stage aging treatment, then add an alkali neutralizer and stir evenly, and carry out the second-stage aging treatment to obtain harmless desulfurized gypsum.

[0008] Further, the desulfurized gypsum powder is obtained by homogenizing the original desulfurized gypsum slag after crushing; the water content of the desulfurized gypsum powder is 15wt.% - 20wt.%; the concentration of the citric acid solution is 1wt% - 1.5wt%, preferably 1wt%; the material-liquid ratio of the desulfurized gypsum powder to the citric acid solution is 1g:(0.8 - 1)mL, preferably 1g:1mL; the stirring speed is 300 - 500rpm, preferably 300rpm, and the stirring time is 1.5 - 2h, preferably 2h; the temperature of the first-stage aging treatment is 15°C - 25°C, and the treatment time is 20 - 30h, preferably 27h; the alkali neutralizer is at least one of lime, calcium oxide, and carbide slag, and the addition amount of the alkali neutralizer is 0.1wt.% - 0.4wt.% of the desulfurized gypsum powder, preferably 0.1wt%; the temperature of the second-stage aging is 15°C - 25°C, and the treatment time is 1 - 3d, preferably 3d.

[0009] Compared with the prior art, the beneficial technical effects of the present invention are:

[0010] The harmless treatment process for desulfurized gypsum of the present invention realizes the goal of high efficiency and environmental protection through the synergistic effect of two stages: in the first stage, the citric acid solution is used for treatment, and its carboxyl group is used to complex with metal ions in the desulfurized gypsum to fix most of the soluble phosphorus and part of the soluble fluorine; in the second stage, by adding an alkali neutralizer, it not only neutralizes the acidity of the system to adjust the pH, but also promotes the formation of insoluble calcium fluoride by fluoride ions, and finally synchronously strengthens the fixation effect of phosphorus and fluorine in the form of precipitation, significantly reducing the risk of secondary pollution.

[0011] Compared with the traditional high-temperature calcination process, the desulfurized gypsum harmless treatment process technology of the present invention has the green advantages of low energy consumption and less carbon emissions. At the same time, relying on the cheap and easily available citric acid solution and alkali neutralizer, combined with a simple and controllable process flow, the operation cost is greatly reduced, which is suitable for industrial promotion. The harmless desulfurized gypsum after treatment can be widely used in ecological restoration, building materials (wall panels, fillers) and agricultural improvers and other fields, realizing the harmless and high-value treatment of desulfurized gypsum, providing double support for the efficient utilization of desulfurized gypsum and environmental protection, and having good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The present invention will be further described below in conjunction with the drawings.

[0013] Figure 1 It is a process flow chart of the desulfurized gypsum harmless treatment process of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0014] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0015] The present invention provides a desulfurized gypsum harmless treatment process, which specifically includes the following steps:

[0016] S1. Crush and homogenize the original desulfurized gypsum slag to obtain desulfurized gypsum powder;

[0017] S2. Add citric acid solution to the desulfurized gypsum powder and stir evenly to obtain pretreated desulfurized gypsum;

[0018] S3. Carry out the first-stage aging treatment on the pretreated desulfurized gypsum to obtain aged desulfurized gypsum;

[0019] S4. Add alkali neutralizer to the aged desulfurized gypsum and stir evenly, and carry out the second-stage aging treatment to obtain harmless desulfurized gypsum.

[0020] The homogenization process of the present invention is as follows: Ball mill the crushed original desulfurized gypsum slag and then screen it to complete homogenization to ensure that the particle size of the crushed desulfurized gypsum is uniform. Preferably, the ball mill rotation speed is 100 rpm, the ball mill time is 30 min, and the mesh size of the sieve is 32 mesh.

[0021] The moisture content of the desulfurized gypsum powder described in the present invention is 15wt.% - 20wt.%. If the moisture content of the homogenized raw material is too high or too low, the moisture content of the raw material can be adjusted by conventional technical means in the art, such as accurately replenishing water through a high-pressure atomizing nozzle, introducing controllable hot air, or adding a desiccant.

[0022] In the technical solution of the present invention, the moisture content of the desulfurized gypsum powder is a very crucial technical index. The present invention uses this to ensure that the reaction system is in a slightly wet environment for effective reaction. If the moisture content of the desulfurized gypsum powder is too high, the particles will agglomerate, resulting in the agent not being able to effectively migrate between the tiny particles of the desulfurized gypsum. If the moisture content is too low, effective reaction cannot occur. Therefore, the present invention limits the moisture content of the desulfurized gypsum powder to be between 15wt.% - 20wt.%.

[0023] The concentration of the citric acid solution described in the present invention is 1wt% - 1.5wt%, preferably 1wt%. The material-liquid ratio of the desulfurized gypsum powder to the citric acid solution is 1g:(0.8 - 1)mL, preferably 1g:1mL. In the present invention, the citric acid solution is a strong organic chelating agent that can form stable water-soluble complexes with heavy metal ions present in the desulfurized gypsum. This chelation can reduce the mobility and bioavailability of heavy metals, thereby reducing environmental risks. In addition, if the addition amount of the citric acid solution is too low, chelation will be insufficient and not all heavy metals can be covered. If the addition amount of the citric acid solution is too high, it will introduce excess acidic substances, increase the subsequent neutralization cost, and also damage the gypsum crystal structure (such as the conversion of calcium sulfate dihydrate to hemihydrate or anhydrous form), affecting the product stability. Finally, the moisture content of the desulfurized gypsum and the addition amount of the citric acid solution have a synergistic effect. An appropriate amount of citric acid solution is evenly dispersed in a wet environment, promoting its contact with the harmful components on the surface and inside of the gypsum particles. The combined action of water and acid can avoid the problem of volume instability during the hardening process of the gypsum. Therefore, the present invention limits the addition amount of the citric acid solution to be 1wt% - 1.5wt% of the desulfurized gypsum powder.

[0024] The stirring speed described in the present invention is 300 - 500rpm, preferably 300rpm, and the stirring time is 1.5 - 2h, preferably 2h.

[0025] The aging treatment temperature in the first stage described in the present invention is 15°C - 25°C, the treatment time is 20 - 30h, preferably 27h; the alkali neutralizing agent is at least one of lime, calcium oxide, and carbide slag, and the addition amount of the alkali neutralizing agent is 0.1wt.% - 0.4wt.% of the desulfurized gypsum powder, preferably 0.1wt.%; the aging temperature in the second stage is 15°C - 25°C, and the treatment time is 1 - 3d, preferably 3d.

[0026] The core of the present invention, which adopts a two-stage aging process and strictly limits the parameters, is to achieve a balance between efficient stabilization of harmful substances and process economy by optimizing the reaction conditions in steps. The first stage of aging is carried out after treatment with citric acid solution. This process can promote the full chelation of citric acid solution and heavy metal ions and the fixation of soluble phosphorus and fluorine in a slightly moist environment formed by a moisture content of 15%-20%, while avoiding particle agglomeration or local overacidity to destroy the gypsum structure; the second stage of aging ensures that the acidic system is gradually neutralized to neutrality by adding an alkaline neutralizer, prompting fluoride ions and calcium to form insoluble calcium fluoride precipitation, and regulating the stability of the gypsum mineral phase to prevent later volume expansion. The two-stage parameter design takes into account both reaction kinetics and processing costs, and ultimately ensures the physical and chemical properties of the product while efficiently fixing phosphorus, fixing fluorine and stabilizing heavy metals, providing a reliable basis for the resource utilization of desulfurized gypsum (such as building materials, ecological restoration), and significantly superior to traditional high-energy consumption processes.

[0027] In order to further illustrate the present invention, the following examples are provided for detailed description. The raw materials used in the following examples of the present invention are all commercially available.

[0028] Unless otherwise specified, all experiments were repeated three times. SPSS 21.0 was used for analysis of variance (ANOVA) and Duncan's multiple comparison analysis, and the results were expressed as mean values.

[0029] Example 1 A process for harmless treatment of desulfurized gypsum, the steps are as follows:

[0030] S1. Take the desulfurized gypsum slag, crush it, ball-mill it at 100 rpm for 30 min, and pass it through a 32-mesh sieve to obtain desulfurized gypsum powder with a moisture content of 18.04%;

[0031] S2. Add 1 wt.% citric acid solution to the desulfurized gypsum powder at a solid-liquid ratio of 1 g:1 mL, stir at 300 rpm for 1.5 h, and separate to obtain pretreated desulfurized gypsum;

[0032] S3, subjecting the pretreated desulfurized gypsum to a first-stage aging treatment for 30 hours to obtain aged desulfurized gypsum;

[0033] S4. Add 0.1 wt.% of calcium oxide to the aged desulfurized gypsum, stir thoroughly at 300 rpm for 2 hours, and then carry out the second stage aging treatment for 1 day to obtain harmless desulfurized gypsum.

[0034] Toxicity leaching experiments were carried out on the desulfurized gypsum raw material and the desulfurized gypsum after being decontaminated. The total phosphorus, soluble fluorine and pH in the leachate and the toxic leachate were measured. The results are shown in Table 1.

[0035] The toxic leached liquid refers to the liquid separated in step S2;

[0036] The toxicity leaching test is carried out in accordance with HJ 557-2009 "Solid Waste Leaching Toxicity Leaching Method Horizontal Oscillation Method".

[0037] Table 1 Detection Results of Toxicity Leaching Liquid and Harmless Filtrate

[0038]

[0039] As can be seen from Table 1, for the harmless desulfurized gypsum obtained in this example, whether it is the toxicity leaching liquid or the leaching liquid of the desulfurized gypsum after harmless treatment, all its indicators meet the standard requirements, that is, the pH value range is 6-9, the total phosphorus content ≤ 0.5 mg / L, meeting the requirements of the "Integrated Wastewater Discharge Standard" (GB8978—1996), the water-soluble fluorine content ≤ 10 mg / L, meeting the requirements of the "Groundwater Quality Standard" (GB / T 14848—2017).

[0040] Example 2 A harmless treatment process for desulfurized gypsum, the steps are as follows:

[0041] S1. Take the original desulfurized gypsum slag, after crushing and homogenization, obtain desulfurized gypsum powder with a moisture content of 16.57%.

[0042] S2. Add 1.5 wt.% citric acid solution to the desulfurized gypsum powder, and stir thoroughly at a speed of 300 rpm for 2 h to obtain pretreated desulfurized gypsum.

[0043] S3. Carry out the first-stage aging treatment on the pretreated desulfurized gypsum for 20 h to obtain aged desulfurized gypsum.

[0044] S4. Add 0.4 wt.% calcium oxide to the aged desulfurized gypsum, stir thoroughly at a speed of 300 rpm for 2 h, and then carry out the second-stage aging treatment for 3 d to obtain harmless desulfurized gypsum.

[0045] Carry out a toxicity leaching experiment on the harmless desulfurized gypsum, and at the same time measure the total phosphorus, soluble fluorine and pH in the harmless filtrate. The results are shown in Table 2.

[0046] Table 2 Detection Results of Toxicity Leaching Liquid and Harmless Filtrate

[0047]

[0048]

[0049] It can be seen from Table 2 that the harmless desulfurized gypsum obtained in this embodiment, whether it is the toxic leaching liquid or the harmless desulfurized gypsum leaching liquid, all its indicators meet the standard requirements. That is, the pH value range is 6-9, the total phosphorus content is ≤0.5 mg / L, which meets the requirements of the "Comprehensive Sewage Discharge Standard" (GB8978-1996) standard, and the water-soluble fluorine content is ≤10 mg / L, which meets the requirements of the "Groundwater Quality Standard" (GB / T 14848-2017) standard.

[0050] Embodiment 3 A desulfurized gypsum harmless treatment process, the steps are as follows:

[0051] S1. Take the desulfurized gypsum slag, crush and homogenize it to obtain desulfurized gypsum powder with a moisture content of 15.41%;

[0052] S2. Add 1.3wt.% citric acid solution to the desulfurized gypsum powder and stir at 300rpm for 2h to obtain pretreated desulfurized gypsum;

[0053] S3, subjecting the pretreated desulfurized gypsum to a first-stage aging treatment for 30 hours to obtain aged desulfurized gypsum;

[0054] S4. Add 0.3 wt.% of calcium oxide to the aged desulfurized gypsum, stir thoroughly at 300 rpm for 2 hours, and then carry out the second stage aging treatment for 3 days to obtain harmless desulfurized gypsum.

[0055] The toxicity leaching experiment was carried out on the harmless desulfurized gypsum, and the total phosphorus, soluble fluorine and pH in the harmless filtrate were measured. The results are shown in Table 2.

[0056] Table 2 Test results of toxic leaching liquid and harmless filtrate

[0057]

[0058] It can be seen from Table 3 that the harmless desulfurized gypsum obtained in this embodiment, whether it is the toxic leachate or the harmless desulfurized gypsum leachate, all indicators meet the standard requirements, that is, the pH value range is 6-9, the total phosphorus content is ≤0.5 mg / L, which meets the requirements of the "Integrated Sewage Discharge Standard" (GB8978-1996) standard, and the water-soluble fluorine content is ≤10 mg / L, which meets the requirements of the "Groundwater Quality Standard" (GB / T 14848-2017) standard.

[0059] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A harmless treatment process for desulfurized gypsum, characterized in that, It includes the following steps: Add a citric acid solution to the desulfurized gypsum powder and stir evenly, then carry out the first-stage aging treatment, then add an alkali neutralizer and stir evenly, and carry out the second-stage aging treatment to obtain harmless desulfurized gypsum; The concentration of the citric acid solution is 1wt%-1.5wt%, and the material-liquid ratio of the desulfurized gypsum powder to the citric acid solution is 1g:(0.8-1)mL; the alkali neutralizer is at least one of lime, calcium oxide and carbide slag; the addition amount of the alkali neutralizer is 0.1wt.%-0.4wt.% of the desulfurized gypsum powder.

2. The harmless treatment process of desulfurized gypsum according to claim 1, characterized in that, The desulfurized gypsum powder is obtained by homogenizing the original desulfurized gypsum slag after crushing.

3. The harmless treatment process of desulfurized gypsum according to claim 1, characterized in that, The moisture content of the desulfurized gypsum powder is 15wt.%-20wt.%.

4. A desulfurized gypsum harmless treatment process according to claim 1, characterized in that, Preferably 1wt%.

5. A desulfurized gypsum harmless treatment process according to claim 1, characterized in that, The stirring speed is 300-500rpm, and the stirring time is 1.5-2h.

6. The harmless treatment process of desulfurized gypsum according to claim 5, characterized in that, The stirring speed is 300rpm, and the stirring time is 2h.

7. A desulfurized gypsum harmless treatment process according to claim 1, characterized in that, The temperature of the first-stage aging treatment is 15°C-25°C, and the treatment time is 20-30h.

8. A desulfurized gypsum harmless treatment process according to claim 1, characterized in that, The addition amount of the alkali neutralizer is 0.1wt.% of the desulfurized gypsum powder; 9. The harmless treatment process of desulfurized gypsum according to claim 1, characterized in that, The second-stage aging temperature is 15°C-25°C, and the treatment time is 1-3d.

10. A desulfurized gypsum harmless treatment process according to claim 9, characterized in that, The treatment time of the second-stage aging treatment is 3d.

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