CN107254710B - A kind of preparation method of the calcium sulfate crystal whiskers of low bulk density - Google Patents

Abstract

The invention discloses a preparation method of calcium sulfate whiskers with low bulk density. The method of the present invention mainly includes: preparing a precursor suspension with a solid content of no more than 30%; adjusting the pH value of the precursor suspension to 3-6.5, adding an activator, and stirring and activating at 60-80°C for 20-60 minutes ; Inject the pre-activated suspension into the reaction kettle, add a structural template, and react at 130-250 °C for 0.5-8 hours until the conversion is complete; perform solid-liquid separation on the suspension after the hydrothermal reaction is completed, and The solid-phase product is washed with hot water not lower than 70°C; the separated and washed solid-phase product is dried at 60-200°C for 0.5-5 hours to obtain the product. The calcium sulfate whisker produced by the present invention has a novel structure, large internal and external areas and low bulk density, and has good application prospects in the fields of carriers, fillers or adsorption purification; the proposed preparation method is simple and efficient, with a wide range of raw materials and low cost. lower.

Description

A kind of preparation method of the calcium sulfate whisker of low bulk density

technical field

The invention belongs to the technical field of material preparation, and in particular relates to a method for preparing calcium sulfate whiskers with low bulk density.

Background technique

Calcium sulfate whisker is a kind of fibrous environment-friendly inorganic material grown in the form of single crystal. It has certain strength and low price. It is increasingly used in the fields of reinforced composite materials and papermaking, and has potential in the fields of construction, medicine and environmental protection. application value.

A large number of patents and academic papers have discussed the preparation, modification and application of calcium sulfate whiskers. The whisker preparation methods that have been proposed mainly include hydrothermal method, atmospheric pressure acidification method and salt solution method. In order to improve the application effect of calcium sulfate whiskers, various surface modification methods have also been proposed. For example, Document 1 (Qian Liying, Liu Wenbo, He Beihai. A new method for coating and modifying chemical fibers with natural polymers [J]. Chinese Journal of Papermaking, 2006, 21(4): 107-110) adopts the coating method Inhibit whisker dissolution, improve paper retention and strength. Patent CN101994153A adopts direct modification of desulfurized gypsum hydrothermal reaction to prepare whiskers that can reduce hydration fracture and enhance its compatibility with polymer materials. Patent CN102219930A uses liquid paraffin and aluminate coupling agent LS-821 to mix by ultrasonic vibration, air-dry at room temperature and dry at 85-95°C to improve the interfacial compatibility between calcium sulfate whiskers and rubber and plastics. Calcium sulfate whiskers are also modified and used to adsorb heavy metals and other pollutants in waste water and waste gas. Modification helps to reduce the solubility of calcium sulfate whiskers and improve the affinity between its surface and pollutants.

However, the whisker products obtained by the disclosed synthesis and modification methods are all internal solid whiskers. Although the size and length-to-diameter ratio can be adjusted, the structure is single, the specific surface area is small, and the bulk density is large. Therefore, the application performance of traditional whiskers and their modified products as fillers and purification is limited to a certain extent, and the large bulk density also affects their economical efficiency. In order to break through the lack of application performance, the bulk phase structure of whisker products must be improved.

Polysaccharides are macromolecular compounds formed by dehydration condensation of more than 10 monosaccharide molecules, and their three-dimensional molecular chains contain abundant functional groups such as hydroxyl, amino, and carboxyl. Studies have shown that mineral crystals often have excellent orientations at polysaccharide-specific sites, and the use of polysaccharides as templates can achieve crystal structure and orientation growth regulation.

Contents of the invention

The object of the present invention is to provide a method for preparing calcium sulfate whiskers with low bulk density, aiming at the problem of large bulk density of traditional calcium sulfate whiskers. Specifically, calcium sulfate whiskers with special structure are prepared by preactivation and hydrothermal method, so that the bulk phase has a cavity, which reduces the bulk density and increases the specific surface area, providing a better structural basis for its functional application.

The preparation method of the calcium sulfate whisker of low bulk density of the present invention, comprises the step of following order:

(1) Precursor preparation: prepare a precursor suspension with a solid content of no more than 30%;

(2) Pre-activation: adjust the pH value of the precursor suspension obtained in step (1) to 3-6.5, add an activator with a mass concentration of 0.01-2%, and stir and activate at 60-80°C for 20-60 minutes;

(3) Hydrothermal reaction: inject the pre-activated suspension in step (2) into the reactor, add 0.1-20g/L structural template agent, and react at 130-250°C for 0.5-8h until the conversion is complete ;

(4) Product separation and washing: The suspension after the hydrothermal reaction is completed is subjected to solid-liquid separation, and the solid phase product is washed with hot water not lower than 70°C, and the reaction liquid and washing water are returned to the system for recycling;

(5) Drying: drying the solid-phase product separated and washed in step (4) at 60-200° C. for 0.5-5 hours to obtain the product; continuous calcination can also obtain anhydrous product.

Specifically, the preparation of the precursor described in step (1) is to crush the mineral raw material whose main component is CaSO ₄ and grind it to pass through a 40-mesh standard sieve, and dry it at 120-200°C for 0.5-2 hours, and then mix it with water be made of.

Alternatively, it can be prepared by directly or indirectly mixing salts or inorganic minerals containing Ca with sulfuric acid solution. The concentration ratio of the mixed reactants is not limited, and can be determined according to the routine debugging tests of those skilled in the art, and it is advisable to fully react completely and reduce the discharge of three wastes.

Alternatively, it is prepared by mixing two solutions containing Ca ²⁺ and SO ₄ ^2- ions. The concentration of the two solutions is not limited, and can be determined according to the routine debugging tests of those skilled in the art. It is advisable to fully react completely and reduce the discharge of three wastes.

Alternatively, it can be produced by mixing mineral salts containing Ca with gases containing SO ₂ or SO ₃ , and passing through air or oxygen for oxidation. The concentration of each material participating in the reaction is not limited, and can be determined according to the routine debugging tests of those skilled in the art. It is advisable to fully react completely and reduce the discharge of three wastes.

The above-mentioned precursor suspension needs to control the solid content to not exceed 30%. When using the three industrial wastes (acid waste water, acid waste gas and calcium-based mineral waste) as raw materials to prepare the precursor by one of the above methods, necessary impurity removal steps (such as water washing, pickling or flotation, etc.) can be taken to obtain higher Purity of the product.

Specifically, the activator in step (2) is water-soluble lithium salt, magnesium salt and mixtures thereof; the activator is preferably one or a mixture of lithium chloride, magnesium chloride, magnesium nitrate and magnesium sulfate.

Specifically, the structure regulating template agent added in step (3) is a mixture of cetyltrimethylammonium bromide (CTAB) and polysaccharide, and its mass ratio is CTAB:polysaccharide=1:(5～30); The polysaccharide is preferably a mixture of one or more of glucose, soluble starch, chitosan and soluble derivatives thereof.

The present invention prepares the calcium sulfate whisker with a hollow structure through the hydrothermal template control technology suitable for mass production, and creates favorable conditions for improving its performance as a carrier, filler or purification material and improving economic efficiency. The present invention combines activation and hydrothermal recrystallization techniques, and by virtue of the stereochemical complementary effect of the polysaccharide template and the molecular recognition effect at a specific interface, induces the preparation of calcium sulfate whiskers with a novel hollow cavity structure, thereby greatly reducing its bulk density , to improve its application performance and economy.

The product prepared according to the method of the invention is a semi-aqueous or anhydrous calcium sulfate whisker with a cavity structure, the length is 10-800 μm, and the diameter is in the range of 0.5-50 μm. Compared with the dense calcium sulfate whiskers prepared by conventional methods, this whisker with a cavity reduces the bulk density by 15% to 40%, and provides a richer inner surface, which is expected to be used in carriers, fillers or adsorption materials. Better results are obtained when applied in the field. The method has the advantages of being simple and efficient, having a wide range of raw materials and being suitable for large-scale production. The method of the invention can also be integrated with processes such as industrial acid wastewater or high-salt wastewater, flue gas desulfurization and chemical gypsum waste treatment to realize comprehensive utilization of resources.

Description of drawings

Figure 1 is an electron microscope image (SEM) of calcium sulfate whiskers prepared by a conventional hydrothermal method.

Fig. 2 is the SEM image of the calcium sulfate whisker with cavity structure prepared by the present invention.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. The accompanying drawings constitute a part of the specification and are used together with the following specific embodiments to explain the present invention, but not to limit the present invention. The equipment used in the examples is common equipment in the chemical and mining fields.

Embodiment one:

Use natural ore as raw material. Gypsum ore was crushed and ground through a 40-mesh sieve, 100 g was dried in a drying oven at 140 °C for 1 h, and then mixed with 600 mL of water for precursor preparation. The pH value of the precursor slurry was adjusted to about 4, and lithium chloride with a mass concentration of 0.2% was added, then placed in a beaker and stirred, and the temperature was raised to 60° C. for pre-activation. After 0.5 h, the slurry was transferred into a pressure-resistant reactor, and a total of 1.2 g of structure-regulating template was added. Wherein, cetyltrimethylammonium bromide (CTAB) is 0.2g, glucose is 0.8g, and chitosan is 0.2g. Then the temperature was raised to 140°C for hydrothermal reaction, and after 4 hours, it was taken out for suction filtration and washed three times with boiling water, and then the solid phase product after suction filtration and washing was placed in an oven at 60°C until it was completely dried to obtain the crystal of the present invention. beard products. This whisker product has a cavity structure and low bulk density, and can be used as a carrier, filler or adsorption material after proper modification.

Embodiment two:

Industrial gypsum (such as solid waste such as desulfurization gypsum, phosphogypsum and fluorine gypsum) is used as raw material. Fully grind the industrial gypsum and pass through a 60-mesh sieve, and perform necessary impurity removal treatment, such as washing and sorting. Take 20g and dry it in a drying oven at 150°C for 0.5h, and then mix it with 500mL of water to complete the preparation of the precursor. The pH value of the precursor slurry is adjusted to about 5, and magnesium chloride with a mass concentration of 0.8% is added to the slurry, and then placed in a beaker, and the temperature is raised to 70° C. while stirring for preactivation. After 20 minutes, the slurry was transferred into a pressure-resistant reactor, and a total amount of 2 g of structure-regulating template was added. Among them, 0.3 g of cetyltrimethylammonium bromide (CTAB), 1.2 g of soluble starch, and 0.5 g of chitosan. Then heat up to 150°C for hydrothermal reaction, take out suction filtration after 3.5h, and wash with boiling water 3 times at the same time, then place the solid phase product after suction filtration and washing in an oven at 60°C until it is completely dry to obtain the product of the present invention. Whisker products. This whisker product has a cavity structure and low bulk density, and can be used as a carrier, filler or adsorption material after proper modification. Embodiment three:

Natural ores rich in calcium such as dolomite, limestone or calcite are used as raw materials. The ore is crushed and ground through a 40-mesh sieve. Put 100g of mineral powder into a beaker, first add 200-300ml of hydrochloric acid with a concentration of 5%-15% to dissolve the mineral, filter out the sediment, and then add 100ml-300ml of sulfuric acid solution with a concentration of 5%-40% to the filtrate , stirring and mixing the reaction to complete the preparation of the precursor. Then the pH value of the precursor slurry was adjusted to about 3.5, and magnesium sulfate with a mass content of 1.2% was added, and it was placed in a beaker and heated to 60° C. while stirring for preactivation. After 1 hour, the slurry was transferred into a pressure-resistant reactor, and a total of 10.2 g of structure-regulating templates were added, including 0.4 g of CTAB, 4.8 g of glucose, and 5.0 g of soluble starch. Then heat up to 160°C for hydrothermal reaction, take out suction filtration after 4 hours, wash with boiling water 3 times at the same time, then place the solid phase product after suction filtration and washing in an oven at 80°C until completely dry to obtain the crystal of the present invention. beard products. This whisker product has a cavity structure and low bulk density, and can be used as a carrier, filler or adsorption material after proper modification.

Embodiment four:

A solution containing calcium chloride and sodium sulfate (or sulfuric acid) is used as raw material. Take 250ml of solutions containing Ca ²⁺ ions and SO ₄ ^2- ions respectively and mix them in beakers. Depending on the difference in the initial concentration of the two solutions and whether the reaction is complete or not, add complementary ones containing Ca ²⁺ ions and SO ₄ ^2- ions. solution (which can also be replaced by sulfuric acid, calcium salt or lime), stirring and mixing the reaction to ensure less calcium ion residue, and complete the preparation of the precursor. Adjust the pH value of the precursor slurry to about 6, add 0.2% lithium chloride and 0.6% magnesium chloride by mass, place it in a beaker and raise the temperature to 80°C while stirring for preactivation. After 0.5 h, the slurry was transferred into a pressure-resistant reactor, and a total of 6 g of structure-regulating templates were added, including 0.4 g of CTAB, 5.2 g of glucose, and 0.4 g of carboxymethyl chitosan. Then the temperature was raised to 180°C for hydrothermal reaction, and after 3 hours, it was taken out for suction filtration, and at the same time washed three times with boiling water, and then the solid phase product after suction filtration and washing was placed in an oven at 70°C until it was completely dried to obtain the crystal of the present invention. beard products. This whisker product has a cavity structure and low bulk density, and can be used as a carrier, filler or adsorption material after proper modification.

Embodiment five:

The flue gas desulfurization process and desulfurization slag are used as raw materials to prepare precursors, and then to prepare whiskers with low bulk density. The conventional and more economical wet flue gas desulfurization process is to use calcium carbonate or lime slurry as the absorbent, and achieve the purpose of purification by contacting and _reacting with the exhaust gas containing SO2 in the absorption tower. A sufficient amount of air is introduced into the calcium sulfite by-product (desulfurization slag) produced in the flue gas desulfurization process to completely oxidize it, and the solid content is controlled below 30% to complete the preparation of the precursor. Take 500ml of precursor slurry, control the pH value at 6.5, add magnesium sulfate with a mass content of 1%, raise the temperature to 65°C and stir for preactivation for 1h. Then the slurry was transferred into a pressure-resistant reactor, and a total amount of 8 g of structure-regulating template was added. Among them, CTAB0.5g, soluble starch 2.5g, chitosan 0.15g. Heat up to 200°C for hydrothermal reaction, take out suction filtration after 3.5 hours, and wash with boiling water 3 times at the same time, then place the solid phase product after suction filtration and washing in an oven at 70°C until it is completely dry to obtain the Whisker products. This whisker product has a cavity structure and low bulk density, and can be used as a carrier, filler or adsorption material after proper modification.

The product prepared by the above method is a hemiaqueous phase calcium sulfate whisker with a cavity structure, and the anhydrous phase whisker can also be taken out by high-temperature calcination. The length of the product is 10-800 μm, the diameter is in the range of 0.5-50 μm, and the bulk density is 15%-40% lower than that of traditional dense whiskers, as shown in Figure 1 and Figure 2.

The above are only a few examples of the flexible implementation of the present invention. For those of ordinary skill in the art, on the basis of the principle of the present invention, some modifications can also be made, and these modifications should also be regarded as the present invention. scope of protection. Obviously, the same product effect of the present invention can also be obtained by appropriately adjusting the individual steps of the present invention, changing the form of raw materials, or integrating key steps of the present invention into acidic or saline wastewater or acid waste gas treatment processes. After understanding the innovation of the present invention, it can be realized without paying creative labor. Therefore, these changes and adjustments obviously also fall within the protection scope of the present invention.

Claims (5)

1. a kind of preparation method of the calcium sulfate crystal whiskers of low bulk density, it is characterised in that including following steps in sequence:

(1) precursor preparation: forerunner's liquid suspension that solid holdup is no more than 30% is prepared；

(2) pre-activate: being adjusted to 3~6.5 for presoma suspension pH value obtained by step (1), and it is 0.01 that mass concentration, which is added, ~2% activator, 20~60min of stir-activating under the conditions of 60~80 DEG C；

(3) hydro-thermal reaction: the suspension after step (2) pre-activate is injected into reaction kettle, and the structure of 0.1~20g/L is added Template, and 0.5~8h is reacted at 130~250 DEG C, it is complete until converting；

(4) product separation and washing: the suspension after the completion of hydro-thermal reaction is separated by solid-liquid separation, and not low to solid product use It is washed in 70 DEG C of hot water, reaction solution and washing water return system are recycled；

(5) dry: the solid product after step (4) are separated and washed dries 0.5~5h under the conditions of 60-200 DEG C to get production Product；No aquatic products can also be obtained by continuing calcining；

Activator is the mixture of one or more of lithium chloride, magnesium chloride, magnesium nitrate and magnesium sulfate；

The structure regulating template that step (3) is added is the mixture of cetyl trimethylammonium bromide (CTAB) and polysaccharide, Its quality proportioning is CTAB: polysaccharide=1:(5~30)；

Polysaccharide is one of glucose, soluble starch, chitosan and its soluble derivative or a variety of mixtures.

2. the preparation method of the calcium sulfate crystal whiskers of low bulk density according to claim 1, it is characterised in that: before step (1) is described Driving body preparation to be is CaSO by main component₄Raw mineral materials it is broken after be ground to 40 mesh standard sieves, and in 120~200 DEG C Under the conditions of dry 0.5~2h, be then mixed to prepare with water.

3. the preparation method of the calcium sulfate crystal whiskers of low bulk density according to claim 1, it is characterised in that: before step (1) is described Driving body preparation is, is directly or indirectly made with sulfuric acid solution hybrid reaction with the salt or inorganic mineral of the element containing Ca.

4. the preparation method of the calcium sulfate crystal whiskers of low bulk density according to claim 1, it is characterised in that: before step (1) is described Driving body preparation is, with containing Ca²⁺And SO₄ ^2-Two kinds of solution mixing systems of ion obtain.

5. the preparation method of the calcium sulfate crystal whiskers of low bulk density according to claim 1, it is characterised in that: before step (1) is described Driving body preparation is with the mineral salt of the element containing Ca and to contain SO₂Or SO₃Gas mixing reaction, and be passed through air or oxygen oxidation After be made.