A method for preparing calcium sulfate dendrites from waste liquid disposal of gasification ash

Abstract

The application provides a method for preparing branch-shaped calcium sulfate whiskers from waste liquid treated by gasification ash, which mainly comprises two steps: the first step is to prepare calcium sulfate dihydrate, the waste liquid treated by gasification ash is mixed with calcium chloride, and the wet filter cake of calcium sulfate dihydrate is obtained after aging and filtration; the second step is to add anhydrous calcium sulfate whisker seeds in water, and add zinc acetate and ethylene glycol bis(2-aminoethylether) tetra sodium tetraacetate as a targeted control agent, and branch-shaped calcium sulfate hemihydrate is prepared under certain temperature and pressure conditions, and the finished product of branch-shaped calcium sulfate hemihydrate is obtained after filtration, washing and drying. The method is simple in operation and low in cost, branch-shaped calcium sulfate hemihydrate whiskers are prepared for the first time, the crystal is complete, the supporting force is strong, and the method is widely applied in rubber, paint, papermaking, friction material and other industries.

Description

Technical Field

[0001] This invention provides a method for preparing dendritic calcium sulfate from waste liquid from gasification ash treatment, relating to the fields of comprehensive utilization of high-salinity wastewater and functional materials. Background Technology

[0002] With increasing environmental protection efforts and increasingly stringent domestic environmental policies, the State Council issued the "Action Plan for Air Pollution Prevention and Control" in September 2013, which proposed restricting the import of high-sulfur petroleum coke. The current "Air Pollution Prevention and Control Law," which came into effect in January 2016, prohibits the import, sale, and burning of petroleum coke that does not meet quality standards. This has created new demands for the use of petroleum coke, and using it as a raw material for gasification plants is a better option. Currently, the main gasification technology used in domestic gasification plants is coal gasification. Although some companies' gasification plants incorporate petroleum coke, the amount is less than 30% and does not exceed 50%, resulting in low heavy metal content in the ash residue. However, the heavy metal content in the petroleum coke gasification residue exceeds the standard due to the heavy metals in the petroleum coke, thus requiring harmless treatment. Wet leaching is a commonly used method, but the use of large amounts of acids and alkalis during wet treatment leads to the generation of large amounts of high-salt sodium sulfate wastewater. In recent years, the national requirements for the discharge of high-salt wastewater have become increasingly stringent, and how to comprehensively utilize high-salt wastewater for high-value purposes has become a focus of attention and research.

[0003] Calcium sulfate whiskers, abbreviated as CSW, are also known as gypsum whiskers or gypsum fibers, and have the molecular formula CaSO4. They are fibrous single crystals of calcium sulfate, white, loose, needle-shaped, with a relatively complete structure, well-defined shape, and specific cross-section. They possess many excellent physical and chemical properties, including high strength, high modulus, high insulation, high temperature resistance, corrosion resistance, good infrared reflectivity, easy surface treatment, easy polymer compounding, and non-toxicity. Calcium sulfate whiskers exist in three forms: dihydrate, anhydrous, and hemihydrate. Based on the ionic arrangement of calcium sulfate, hemihydrate is more commonly used in practical applications due to its superior properties. However, hemihydrate is also easily hydrated to form dihydrate, but this hydration process destroys the original fibrous structure, causing it to lose its reinforcing and wear-resistant properties. However, because it can absorb water during hydration, it can be used to adsorb impurity ions in wastewater, thus purifying it.

[0004] Commonly used methods for preparing calcium sulfate whiskers include the salt solution method, alcohol solution method, hydrothermal method, and autoclaving method. For example, patent CN105948547B discloses a method for preparing α-type calcium sulfate hemihydrate using calcium sulfate dihydrate. The method involves uniformly mixing calcium sulfate dihydrate with an additive solution to form a mixture; heating the mixture to 130-150℃ and maintaining it for 20-120 minutes, during which the calcium sulfate dihydrate in the mixture crystallizes into α-type calcium sulfate hemihydrate; and then drying to obtain the finished α-type calcium sulfate hemihydrate. Patent CN110818304B proposes a method using citric acid as a crystallization agent to prepare calcium sulfate dihydrate with gypsum, and then using calcium sulfate hemihydrate whiskers as seed crystals. In this process, the added citric acid reduces the nucleation rate, resulting in calcium sulfate hemihydrate with large particle size and high strength. However, in this process, the gypsum hemihydrate, acting as a seed crystal, partially hydrates during the reaction and therefore cannot serve as a support point for the calcium sulfate hemihydrate crystals to adhere. Patent CN113089076B discloses a method for preparing calcium sulfate whiskers based on chlor-alkali salt mud. This method involves adding calcium sulfate seeds to a pretreated salt mud solution, followed by the addition of sulfuric acid to prepare rod-shaped unidirectional fiber calcium sulfate whiskers. This method simultaneously reduces the volume of salt mud and utilizes calcium and magnesium resources. CN111809228B provides a method for preparing calcium sulfate mineral crystal fibers using micro-irradiation vapor phase conversion. The calcium sulfate crystal fibers prepared by this method are both novel and hollow tubular, giving them additional functionalities.

[0005] Different researchers have used these methods to prepare ordinary fibrous calcium sulfate whiskers. During the research process, they have also modified the morphology of calcium sulfate whiskers by changing the preparation conditions or adding some surfactants. Some have made needle-like, some plate-like, some rod-like, and some flower-like whiskers. However, no dendritic or forked calcium sulfate has been found. This is because calcium sulfate grows along the axial one-dimensional growth plane and does not branch without external interference. On the other hand, the crystallization growth rate of calcium sulfate whiskers is fast. They may have already grown into fibrous shapes before they have a chance to be disturbed by external factors. Therefore, it is necessary to provide external interference while controlling its growth rate so that it grows in a predetermined direction in order to form dendritic or forked calcium sulfate. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing dendritic calcium sulfate from waste liquid from gasification ash disposal, providing a reference and basis for the subsequent preparation of dendritic calcium sulfate.

[0007] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0008] 1. A method for preparing dendritic calcium sulfate from waste liquid from gasification ash disposal, comprising the following steps:

[0009] Step 1: Mix the waste liquid from the gasification ash treatment with a urea solution of calcium chloride, stir and age it for a period of time, and then filter to obtain calcium sulfate dihydrate.

[0010] Step 2: Add anhydrous calcium sulfate seed crystals to water, add tetrasodium ethylene glycol bis(2-aminoethyl ether)tetraacetic acid, stir for a certain time, add calcium sulfate dihydrate obtained in step 1, and add zinc acetate. After the reaction is complete, filter and dry to obtain dendritic calcium sulfate whiskers.

[0011] The main components of the gasification slag treatment waste liquid in step 1 are 10% to 20% sodium sulfate, and small amounts of calcium sulfate, magnesium sulfate, aluminum sulfate, ferrous sulfate, vanadium oxysulfate, etc., with a pH of 5 to 8.

[0012] In step 1, the waste liquid from the gasification ash treatment is added simultaneously and in parallel with calcium chloride, and the supersaturation is controlled to be 0.05-0.1. The molar ratio of urea to calcium chloride is 1-5:1 to avoid local agglomeration of large particles that cause disorder of the calcium sulfate dihydrate crystal form.

[0013] In step 1, the reaction and aging temperature is <5℃ and the aging time is >12h. Preferably, the aging temperature is controlled at 0℃ and the aging time is 16-20h. Under this temperature and time, the dihydrate obtained has a high degree of regularity and fewer fine particles.

[0014] In step 1, the gasification ash refers to petroleum coke gasification ash. The properties of petroleum coke gasification ash are closely related to the amount of petroleum coke in the gasification feedstock. Gasification ash with a higher amount of petroleum coke contains more heavy metals, and the concentration of sodium sulfate in the waste liquid obtained during the treatment process also varies. However, in the process of preparing dihydrate, the high concentration of raw material mixing leads to excessive nucleation and poor crystal regularity. Therefore, it is preferable to control the concentration at 10-15% during use. This can meet the industrial solid content requirements and obtain a calcium sulfate dihydrate precursor that meets the requirements.

[0015] In step 1, the aspect ratio of calcium sulfate dihydrate is 20-30. The aspect ratio of calcium sulfate dihydrate is calculated by analysis using a high-power microscope and a scanning electron microscope.

[0016] In step 2, the anhydrous calcium sulfate seed crystals are anhydrous calcium sulfate that has been calcined at 600°C and has an aspect ratio >20. Only anhydrous calcium sulfate that has been calcined at high temperature will be stable and retain its own morphology. It will not hydrate back into dihydrate calcium sulfate in the solution, thus becoming the grafting matrix in the process of converting dihydrate calcium sulfate into hemihydrate calcium sulfate.

[0017] In step 2, the molar ratio of ethylene glycol bis(2-aminoethyl ether)tetraacetic acid tetrasodium to calcium sulfate dihydrate is 3-5:1, and the molar ratio of zinc acetate to calcium sulfate dihydrate is 10-15:1. After adding ethylene glycol bis(2-aminoethyl ether)tetraacetic acid tetrasodium, the temperature is raised to 80-90°C, and after adding zinc acetate, the temperature is raised to 100-105°C. The reaction is carried out in a closed system. During this process, the added ethylene glycol bis(2-aminoethyl ether)tetraacetic acid tetrasodium can complex with the calcium ions in anhydrous calcium sulfate and arrange them along one side of the anhydrous calcium sulfate seed crystal, thereby forming an arrangement with a certain degree of regularity. Then, it forms a synergistic effect with zinc acetate, inducing the calcium ions and sulfate ions in the calcium sulfate dihydrate to be oriented and arranged to form dendritic whiskers.

[0018] In step 2, the stirring speed is 50-150 r / min and the stirring time is 2-5 h;

[0019] The calcium sulfate dihydrate added in step 2 is the wet filter cake after filtration without drying. The moisture content of the filter cake after drying at 110°C for 2 hours is 30% to 40%.

[0020] All separation methods in the above steps are vacuum filtration or centrifugation, and the filtration time is controlled to be less than 5 minutes. During the filtration of calcium sulfate hemihydrate, the temperature should be kept as low as possible. During the drying process of the sample, the drying temperature of the dendritic calcium sulfate hemihydrate whiskers is 140-160℃.

[0021] Compared with the prior art, the advantages of the present invention are:

[0022] 1. This invention uses a method of controlling the crystal growth rate to change the morphology of the hemihydrate calcium sulfate precursor, and synthesizes dendritic calcium sulfate under low-pressure hydrothermal conditions. The synthesis process is simple, easy to implement, and highly operable.

[0023] 2. The seed crystals used in this invention are high-temperature calcined. Only anhydrous calcium sulfate that has been calcined at high temperature will be stable and retain its original morphology. It will not hydrate back into calcium sulfate dihydrate in the solution, thus becoming a grafting matrix in the process of calcium sulfate dihydrate being converted into calcium sulfate hemihydrate. Otherwise, after hydrating into calcium sulfate dihydrate, it will lose its original morphology and cannot be used as a grafting matrix.

[0024] 3. This invention employs the synergistic effect of seed crystals and targeting agents to jointly control the directional growth of calcium sulfate hemihydrate. The organic anions in the added tetrasodium ethylene glycol bis(2-aminoethyl ether)tetraacetate can complex with the calcium ions in the anhydrous calcium sulfate seed crystals, arranging them along one side of the anhydrous calcium sulfate seed crystals to form an arrangement with a certain degree of regularity. Then, it synergistically interacts with the acetate ions in zinc acetate to induce the calcium ions and sulfate ions in the dihydrate calcium sulfate to directionally arrange and form dendritic whiskers.

[0025] 4. The dihydrate preparation method in this invention is to generate dihydrate calcium sulfate crystal nuclei under the premise of urea as a crystal growth inhibitor and a uniform calcium sulfate supersaturation concentration. This can limit the large-area aggregation of dihydrate calcium sulfate and allow it to grow into a precursor with a certain aspect ratio morphology.

[0026] 5. The separation methods and drying conditions used in this invention are all conventional experimental methods, and the laboratory reproducibility is high. Detailed Implementation

[0027] To more intuitively and clearly illustrate the technical advantages of this invention, the following examples and comparative figures illustrate the innovation of this invention.

[0028] Example 1

[0029] Step 1: Take 500 ml of waste liquid from the gasification ash treatment, where the sodium sulfate concentration is 12.3% and the magnesium sulfate concentration is 0.8%. Prepare a calcium chloride solution with the same molar concentration as the sodium sulfate in the waste liquid. Add urea at a molar ratio of 3 to the calcium chloride solution to dissolve it. After uniform dissolution, measure the required amount of calcium chloride-urea solution according to a calcium-to-sulfur ratio of 1. Add the two solutions in parallel, controlling the reaction temperature at 3°C. Control the supersaturation of calcium sulfate dihydrate during nucleation in the system to 0.07 using a large circulation ratio. After the reaction is complete, age at 3°C ​​for 14 hours. After aging, filter to obtain calcium sulfate dihydrate with a water content of 32%.

[0030] Step 2: Take 100ml of tap water, add anhydrous calcium sulfate seed crystals to the water, stir and disperse, then add 50g of tetrasodium bis(2-aminoethyl ether)tetraacetate, heat to 85℃, stir for 30min, then add 4g of calcium sulfate dihydrate filter cake obtained in Step 1, and add 40g of zinc acetate, continue to heat to 100℃, seal the reaction, control the rotation speed at 100r / min, react for 3h, filter, and wash with 80℃ hot water. After washing, place in an oven at 150℃ to dry to obtain dendritic calcium sulfate whiskers, and analyze the morphology, chemical composition, and phase composition of the sample.

[0031] Example 2

[0032] Step 1: Take 500 ml of waste liquid from the gasification ash treatment, where the sodium sulfate concentration is 12.8% and the magnesium sulfate concentration is 0.7%. Prepare a calcium chloride solution with the same molar concentration as the sodium sulfate in the waste liquid. Add urea at a molar ratio of 3 to the calcium chloride solution to dissolve it. After uniform dissolution, measure the required amount of calcium chloride-urea solution according to a calcium-to-sulfur ratio of 1. Add the two solutions in parallel, controlling the reaction temperature at 3°C. Control the supersaturation of calcium sulfate dihydrate during nucleation in the system to 0.05 using a large circulation ratio. After the reaction is complete, age at 3°C ​​for 14 hours. After aging, filter to obtain calcium sulfate dihydrate with a water content of 32%.

[0033] Step 2: Take 100ml of tap water, add anhydrous calcium sulfate seed crystals to the water, stir and disperse, then add 40g of tetrasodium bis(2-aminoethyl ether)tetraacetate, heat to 85℃, stir for 30min, then add 4g of calcium sulfate dihydrate filter cake obtained in Step 1, and add 40g of zinc acetate, continue to heat to 100℃, seal the reaction, control the rotation speed at 100r / min, react for 3h, filter, and wash with 80℃ hot water. After washing, place in an oven at 150℃ to dry to obtain dendritic calcium sulfate whiskers, and analyze the morphology, chemical composition, and phase composition of the sample.

[0034] Example 3

[0035] Step 1: Take 500 ml of waste liquid from the gasification ash treatment, where the sodium sulfate concentration is 12.3% and the magnesium sulfate concentration is 0.8%. Prepare a calcium chloride solution with the same molar concentration as the sodium sulfate in the waste liquid. Add urea at a molar ratio of 3 to the calcium chloride solution to dissolve it. After uniform dissolution, measure the required amount of calcium chloride-urea solution according to a calcium-to-sulfur ratio of 1. Add the two solutions in parallel, control the reaction temperature at 5°C, and control the supersaturation of calcium sulfate dihydrate during nucleation to 0.07 using a large circulation ratio. After the reaction is complete, age at 5°C for 16 hours. After aging, filter to obtain calcium sulfate dihydrate with a water content of 32%.

[0036] Step 2: Take 100ml of tap water, add anhydrous calcium sulfate seed crystals to the water, stir and disperse, then add 40g of tetrasodium bis(2-aminoethyl ether)tetraacetate, heat to 85℃, stir for 30min, then add 4g of calcium sulfate dihydrate filter cake obtained in Step 1, and add 50g of zinc acetate, continue to heat to 100℃, seal the reaction, control the rotation speed at 100r / min, react for 3h, filter, and wash with 80℃ hot water. After washing, place in an oven at 150℃ to dry to obtain dendritic calcium sulfate whiskers, and analyze the morphology, chemical composition, and phase composition of the sample.

[0037] Example 4

[0038] Step 1: Take 500 ml of waste liquid from the gasification ash treatment, where the sodium sulfate concentration is 12.3% and the magnesium sulfate concentration is 0.8%. Prepare a calcium chloride solution with the same molar concentration as the sodium sulfate in the waste liquid. Add urea at a molar ratio of 3 to the calcium chloride solution to dissolve it. After uniform dissolution, measure the required amount of calcium chloride-urea solution according to a calcium-to-sulfur ratio of 1. Add the two solutions in parallel, controlling the reaction temperature at 3°C. Control the supersaturation of calcium sulfate dihydrate during nucleation to 0.08 using a large circulation ratio. After the reaction, age at 3°C ​​for 14 hours. After aging, filter to obtain calcium sulfate dihydrate with a water content of 32%.

[0039] Step 2: Take 100ml of tap water, add anhydrous calcium sulfate seed crystals to the water, stir and disperse, then add 50g of tetrasodium bis(2-aminoethyl ether)tetraacetate, heat to 85℃, stir for 30min, then add 4g of calcium sulfate dihydrate filter cake obtained in Step 1, and add 60g of zinc acetate, continue to heat to 100℃, seal the reaction, control the rotation speed at 120r / min, react for 3h, filter, and wash with 80℃ hot water. After washing, place in an oven at 150℃ to dry to obtain dendritic calcium sulfate whiskers, and analyze the morphology, chemical composition, and phase composition of the sample.

[0040] Comparative Example 1

[0041] Step 1: Take 500 ml of waste liquid from the gasification ash treatment, wherein the concentration of sodium sulfate in the waste liquid is 12.3% and the concentration of magnesium sulfate is 0.8%. Prepare a calcium chloride solution with the same molar concentration as sodium sulfate in the waste liquid, and measure the required amount of calcium chloride solution according to a calcium-to-sulfur ratio of 1. Add the two solutions in parallel, control the reaction temperature at 25℃, and age at 25℃ for 3 hours. After aging, filter to obtain calcium sulfate dihydrate with a water content of 32%.

[0042] Step 2: Take 100ml of tap water, add anhydrous calcium sulfate seed crystals to the water, stir and disperse, then add 50g of tetrasodium bis(2-aminoethyl ether)tetraacetate, heat to 85℃, stir for 30min, then add 4g of calcium sulfate dihydrate filter cake obtained in Step 1, and add 40g of zinc acetate, continue to heat to 100℃, seal the reaction, control the rotation speed at 100r / min, react for 3h, filter, and wash with 80℃ hot water. After washing, place in an oven at 150℃ to dry to obtain calcium sulfate hemihydrate whiskers, and analyze the morphology, chemical composition, and phase composition of the sample.

[0043] Comparative Example 2

[0044] Step 1: Take 500 ml of waste liquid from the gasification ash treatment, where the sodium sulfate concentration is 12.3% and the magnesium sulfate concentration is 0.8%. Prepare a calcium chloride solution with the same molar concentration as the sodium sulfate in the waste liquid, measuring the required amount of calcium chloride solution according to a calcium-to-sulfur ratio of 1. Add the two solutions in parallel flow, controlling the reaction temperature at 3°C. Maintain the supersaturation of calcium sulfate dihydrate during nucleation at 0.07 using a large circulation ratio. After the reaction, age at 3°C ​​for 14 hours. After aging, filter to obtain calcium sulfate dihydrate with a water content of 32%.

[0045] Step 2: Take 100ml of tap water, add 50g of tetrasodium bis(2-aminoethyl ether)tetraacetate, heat to 85℃, stir for 30min, add 4g of calcium sulfate dihydrate filter cake obtained in Step 1, and add 40g of zinc acetate, continue to heat to 100℃, seal the reaction, control the rotation speed at 100r / min, react for 3h, filter, and wash with 80℃ hot water. After washing, place in an oven at 150℃ to dry to obtain calcium sulfate hemihydrate whiskers, and analyze the morphology, chemical composition and phase composition of the sample.

[0046] Comparative Example 3

[0047] Step 1: Take 500 ml of waste liquid from the gasification ash treatment, where the sodium sulfate concentration is 12.3% and the magnesium sulfate concentration is 0.8%. Prepare a calcium chloride solution with the same molar concentration as the sodium sulfate in the waste liquid, measuring the required amount of calcium chloride solution according to a calcium-to-sulfur ratio of 1. Add the two solutions in parallel flow, controlling the reaction temperature at 3°C. Maintain the supersaturation of calcium sulfate dihydrate during nucleation at 0.07 using a large circulation ratio. After the reaction, age at 3°C ​​for 14 hours. After aging, filter to obtain calcium sulfate dihydrate with a water content of 32%.

[0048] Step 2: Take 100ml of tap water, add anhydrous calcium sulfate seed crystals to the water, stir and disperse, then add 4g of calcium sulfate dihydrate filter cake obtained in Step 1, and add 40g of zinc acetate. Continue to heat to 100℃, seal the reaction, control the rotation speed at 100r / min, and filter after 3h. Wash with hot water at 80℃. After washing, dry in an oven at 150℃ to obtain calcium sulfate hemihydrate whiskers. Analyze the morphology, chemical composition and phase composition of the sample.

[0049] Comparative Example 4

[0050] Step 1: Take 500 ml of waste liquid from the gasification ash treatment, where the sodium sulfate concentration is 12.3% and the magnesium sulfate concentration is 0.8%. Prepare a calcium chloride solution with the same molar concentration as the sodium sulfate in the waste liquid, measuring the required amount of calcium chloride solution according to a calcium-to-sulfur ratio of 1. Add the two solutions in parallel flow, controlling the reaction temperature at 3°C. Maintain the supersaturation of calcium sulfate dihydrate during nucleation at 0.07 using a large circulation ratio. After the reaction, age at 3°C ​​for 14 hours. After aging, filter to obtain calcium sulfate dihydrate with a water content of 32%.

[0051] Step 2: Take 100ml of tap water, add anhydrous calcium sulfate seed crystals to the water, stir and disperse, then add 50g of tetrasodium bis(2-aminoethyl ether)tetraacetate, heat to 85℃, stir for 30min, then add 4g of calcium sulfate dihydrate filter cake obtained in Step 1, continue to heat to 100℃, seal the reaction, control the rotation speed at 100r / min, react for 3h, filter, and wash with 80℃ hot water. After washing, place in an oven at 150℃ to dry to obtain calcium sulfate hemihydrate whiskers, and analyze the morphology, chemical composition and phase composition of the sample.

[0052] The data and images from the specific implementation methods are summarized below:

[0053] Table 1. Aspect Ratio Data of Calcium Sulfate Dihydrate

[0054] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Aspect Ratio 25 28 24 20 2 purity / % 99.3 99.5 99.1 99.2 98.7

[0055] Table 2

[0056] The chemical composition data of calcium sulfate hemihydrate were analyzed using X-ray diffraction fluorescence spectrometry, as follows:

[0057] SO3 CaO <![CDATA[Na2O]]> <![CDATA[Al2O3]]> Cl <![CDATA[Fe2O3]]> MgO <![CDATA[K2O]]> Example 1 54.38 44.88 0.05 0.03 0.08 0.01 0.04 0.02 Example 2 54.44 44.91 0.03 0.03 0.06 0.01 0.04 0.02 Example 3 54.28 44.81 0.06 0.03 0.08 0.01 0.06 0.02 Example 4 54.35 44.86 0.05 0.03 0.08 0.01 0.05 0.02 Comparative Example 1 54.41 44.93 0.06 0.03 0.08 0.01 0.06 0.02 Comparative Example 2 54.38 44.85 0.05 0.03 0.09 0.01 0.04 0.02 Comparative Example 3 54.33 44.68 0.07 0.03 0.10 0.01 0.04 0.02 Comparative Example 4 54.28 44.78 0.05 0.03 0.08 0.01 0.08 0.02

[0058] Attached image description: Figure 1 Microscopic images of dihydrate from Example 1 and Comparative Example 1 (left image is Example 1, right image is Comparative Example 1).

[0059] Figure 2 Microscopic images of calcium sulfate hemihydrate from Example 1 and Comparative Example 3 (left image shows dendritic sample from Example 1, right image shows ordinary fibrous whiskers).

[0060] Figure 3 XRD phase diagram of dendritic calcium sulfate hemihydrate

[0061] In summary, the method proposed in this application, which uses anhydrous calcium sulfate as a seed crystal and zinc acetate and ethylene glycol bis(2-aminoethyl ether)tetraacetic acid tetrasodium as synergistic targeting agents, can synthesize dendritic calcium sulfate with well-formed morphology under certain temperature and pressure conditions. Moreover, the preparation process is simple, the product has good purity, the process conditions are mild, and the cost is low.

[0062] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing dendritic calcium sulfate from waste liquid from gasification ash treatment, characterized in that, Includes the following steps: Step 1: Add a mixture of calcium chloride and urea to the waste liquid from the gasification ash treatment, stir and age for a period of time, then filter to obtain calcium sulfate dihydrate. Step 2: Add anhydrous calcium sulfate seed crystals to water, add tetrasodium ethylene glycol bis(2-aminoethyl ether)tetraacetic acid, stir for a certain time, add calcium sulfate dihydrate obtained in step 1, and add zinc acetate. After the reaction is complete, filter and dry to obtain dendritic calcium sulfate whiskers. The main component of the gasification slag treatment waste liquid in step 1 is sodium sulfate, with a molar concentration of 10% to 20%, and also calcium sulfate, magnesium sulfate, aluminum sulfate, ferrous sulfate, and vanadium oxysulfate, with a pH of 2 to 3. In step 1, the waste liquid from the gasification ash treatment is added simultaneously and in parallel with calcium chloride, and the supersaturation of the system is controlled to be 0.05~0.1, and the molar ratio of urea to calcium chloride is 1~5:

1. In step 1, the aging temperature is <5℃ and the aging time is >12h; In step 1, the gasification ash refers to petroleum coke gasification ash. In step 1, the aspect ratio of calcium sulfate dihydrate is 20-30; In step 2, the anhydrous calcium sulfate seed crystals are anhydrous calcium sulfate that has been calcined at 600°C and has an aspect ratio > 20. In step 2, the molar ratio of ethylene glycol bis(2-aminoethyl ether)tetraacetic acid tetrasodium: calcium sulfate dihydrate is 3~5:1, and the molar ratio of zinc acetate: calcium sulfate dihydrate is 10~15:

1. After adding ethylene glycol bis(2-aminoethyl ether)tetraacetic acid tetrasodium, the temperature is raised to 80~90℃, and after adding zinc acetate, the temperature is raised to 100~105℃. The reaction is carried out in a sealed environment. In step 2, the stirring speed is 50~150 r / min and the stirring time is 2~5 h; The calcium sulfate dihydrate added in step 2 is the wet filter cake after filtration without drying. The moisture content of the filter cake after drying at 110°C for 2 hours is 30%~40%.

2. The method for preparing dendritic calcium sulfate from waste liquid treated by gasification ash as described in claim 1, characterized in that, The filtration method used is centrifugation or vacuum filtration.

3. The method for preparing dendritic calcium sulfate from waste liquid treated by gasification ash as described in claim 1, characterized in that, The filtration time in step 2 is <5 min, and the filtrate is used as chlor-alkali salt dissolution water.

4. The method for preparing dendritic calcium sulfate from waste liquid treated by gasification ash as described in claim 1, characterized in that, The drying temperature of the dendritic calcium sulfate whiskers is 140~160℃.

Images