Method for preparing calcium sulfate whisker with high length-diameter ratio based on calcium-based solid waste

Abstract

The invention belongs to the technical field of calcium sulfate preparation, and particularly relates to a method for preparing calcium sulfate whiskers with a high length-diameter ratio based on calcium-based solid waste. The method comprises the following steps: mixing cleaned red gypsum and water granulated slag in proportion, and adding a proper amount of water into the mixture to prepare mixed slurry; heating the mixed slurry, reacting, and slowly adding a control agent in the reaction process; and after the reaction is finished, carrying out ultrasonic treatment on the obtained calcium sulfate slurry, and then filtering, washing and drying to obtain the nano calcium sulfate whisker. The nano calcium sulfate whisker prepared by the method provided by the invention has wide application in the fields of papermaking, plastics, rubber, asphalt, cement, ceramics, adhesives, friction materials and the like. In the applications, the nano calcium sulfate whisker can be used as a filler or a reinforcing and toughening material.

Description

Technical Field

[0001] The invention belongs to the technical field of calcium sulfate preparation, and particularly relates to a method for preparing calcium sulfate whiskers with a high aspect ratio based on calcium-based solid waste. Background Art

[0002] Calcium sulfate whiskers, a safe and environmentally friendly new fibrous material, are widely used in a variety of industries, including textiles, coatings, papermaking, rubber, and adhesives, due to their high strength, good toughness, high temperature resistance, dimensional stability, high chemical stability, and low production cost. Calcium-based solid waste primarily comes from byproducts generated during the production of building materials, chemical raw materials, and ceramics, such as limestone, slag, carbide slag, and red gypsum. These solid wastes contain abundant calcium resources, but traditional disposal methods such as landfills and stockpiling not only consume significant land resources but also pose significant environmental risks.

[0003] Currently, calcium sulfate whiskers are mostly produced using a hydrothermal method, but this method requires high temperature and pressure, which places high demands on the reaction equipment and limits industrial-scale production. Other methods for producing calcium sulfate whiskers, such as ion exchange and atmospheric pressure acidification, are relatively complex, and the resulting calcium sulfate whiskers are only micrometer-sized, limiting their further application. Summary of the Invention

[0004] In response to the problems existing in the prior art, the present invention provides a method for preparing high aspect ratio calcium sulfate whiskers based on calcium-based solid waste. This method uses calcium-based solid waste to produce nano-calcium sulfate, which can not only effectively reduce the environmental pollution problem of solid waste, but also expand the application field of calcium-based solid waste and realize high-value utilization of solid waste.

[0005] The technical solutions adopted by the present invention to achieve the above-mentioned purpose are as follows:

[0006] The present invention provides a method for preparing calcium sulfate whiskers with a high aspect ratio based on calcium-based solid waste, comprising the following steps:

[0007] (1) Mix the cleaned red gypsum and water slag in proportion, add an appropriate amount of water to the mixture to prepare a mixed slurry;

[0008] (2) heating the mixed slurry and reacting the mixture, and slowly adding a control agent during the reaction;

[0009] (3) After the reaction is completed, the obtained calcium sulfate slurry is subjected to ultrasonic treatment, and then filtered, washed, and dried to obtain nano calcium sulfate whiskers.

[0010] Preferably, in step (1), the mass ratio of the red gypsum to the water slag is 3:2.

[0011] Preferably, in step (1), the solid-to-liquid ratio of the mixture to water in the mixed slurry is 1:3-5.

[0012] Preferably, in step (2), the reaction temperature is controlled at 80-100°C, stirring is continuously performed during the reaction, the stirring speed is 300-500 r / min, and the reaction time is 2-3 h.

[0013] Preferably, in step (2), the amount of the control agent added is 0.5-1% of the total mass of the reactants; the control agent is composed of citric acid and diglycolamine in a mass ratio of 1:0.2.

[0014] Preferably, in step (3), the ultrasonic treatment is first performed at a power of 200-350 W for 30 min, and then at a power of 400-500 W for 30 min.

[0015] Preferably, in step (3), the drying temperature is 60-80°C.

[0016] The method provided by the present invention has the following reaction equation:

[0017] The calcium sulfate in red gypsum (CaSO4·2H2O) reacts with certain components in the slag (such as calcium oxide that may be contained), CaSO4·2H2O+CaO→2CaSO4+H2O.

[0018] The slag used in this invention (also known as water coal slag, wet coal slag, or water-quenched slag) is the solid waste residue formed after coal is quenched and rapidly cooled by water during industrial combustion or gasification. Its composition is complex and depends primarily on the type of coal, the combustion process, and the water quenching conditions. It generally consists of the following components:

[0019] 1. Main chemical components

[0020] SiO2 (silicon dioxide): accounts for about 30% to 50%, is the main skeleton component of coal slag, and comes from the high-temperature melting of minerals in coal (such as clay).

[0021] Al2O3 (aluminum oxide): accounts for about 15% to 30%, and comes from aluminum silicate minerals in coal (such as kaolin).

[0022] CaO (calcium oxide): accounts for about 5% to 20%, which may come from carbonates in coal (such as calcite) or added desulfurizers (such as limestone).

[0023] Fe2O3 (iron oxide): accounts for about 5% to 15%, and is derived from the high-temperature oxidation product of pyrite (FeS2) or hematite in coal.

[0024] MgO (magnesium oxide): present in small amounts, usually from magnesia minerals in coal.

[0025] 2. Minor ingredients

[0026] Unburned carbon (residual carbon): The carbon remaining when combustion is incomplete (accounting for 1% to 10%), which affects the activity of slag and subsequent utilization.

[0027] SO3 (sulfur trioxide): If the coal contains sulfur, it may exist in the form of sulfate (such as CaSO4) after combustion.

[0028] K2O, Na2O (alkali metal oxides): small amounts, probably from salts or additives in coal.

[0029] 3. Trace elements and heavy metals

[0030] Heavy metals: such as arsenic (As), lead (Pb), mercury (Hg), cadmium (Cd), etc. The content is related to the coal source, and we need to be vigilant about environmental risks.

[0031] Radioactive elements: Some coal mines contain trace amounts of uranium (U), thorium (Th), etc., which may be enriched during combustion.

[0032] 4. Physical properties

[0033] Porous structure: Water quenching and rapid cooling form a glassy structure with high porosity and certain adsorption properties.

[0034] Particle shape: mostly irregular glassy particles with a wide particle size distribution (0.1 to 5 mm).

[0035] 5. Ingredient Difference Factors

[0036] Coal type: The ash composition of lignite, bituminous coal and anthracite varies significantly.

[0037] Process: Fluidized bed combustion slag (high CaO), coal gasification slag (high glass), etc. have different compositions.

[0038] Additives: desulfurizer (limestone), flux, etc. will change the chemical composition of the slag.

[0039] The industrial waste red gypsum (also known as phosphogypsum) used in the present invention is a by-product produced during the production of wet-process phosphoric acid. Its main components and characteristics are as follows:

[0040] 1. Main Ingredients

[0041] Calcium sulfate (CaSO4·2H2O): accounts for more than 90% of the total amount of red gypsum, usually in the form of calcium sulfate dihydrate (gypsum).

[0042] 2. Impurity components

[0043] Red gypsum may contain the following impurities due to the differences in raw phosphate rock and production process:

[0044] Metal oxides:

[0045] Iron oxide (Fe2O3): gives red gypsum its red or yellow-brown appearance.

[0046] Aluminum oxide (Al2O3), magnesium oxide (MgO): impurities from phosphate rock.

[0047] Acidic residue:

[0048] Incomplete reaction of sulfuric acid (H2SO4) and phosphoric acid (H3PO4).

[0049] Heavy metal elements:

[0050] Such as cadmium (Cd), lead (Pb), arsenic (As), etc., which may come from phosphate rock or processing.

[0051] Radioactive elements:

[0052] Naturally occurring radioactive substances in phosphate rock, such as uranium (U), thorium (Th), and radium (Ra), may remain in it.

[0053] Fluoride (F-):

[0054] Phosphate rock usually contains fluorine, and some of the fluorine remains in the form of fluoride after processing.

[0055] 3. Physical properties

[0056] Color: Red, grayish white or yellowish brown depending on the iron oxide content.

[0057] pH value: Usually acidic (pH 2-5) due to residual sulfuric acid and phosphoric acid.

[0058] Particle size: mostly fine particles or powder.

[0059] The beneficial effects of the present invention are:

[0060] (1) The nano calcium sulfate whiskers prepared by the method provided by the present invention have a wide range of applications in the fields of papermaking, plastics, rubber, asphalt, cement, ceramics, adhesives, friction materials, etc. In these applications, the nano calcium sulfate whiskers can be used as fillers or reinforcing and toughening materials.

[0061] (2) The method of the present invention is simple and applicable, and the process conditions can be varied in a wide range. It has the advantages of abundant and cheap raw materials, low production cost, good product performance, and is green and environmentally friendly, and is suitable for large-scale production. DETAILED DESCRIPTION

[0062] The technical solution of the present invention is further explained and illustrated by means of specific embodiments below.

[0063] Example 1

[0064] (1) The cleaned red gypsum and water slag were mixed in a mass ratio of 3:2, and then water accounting for 5 times the mass of the mixture was added to prepare a mixed slurry;

[0065] (2) The mixed slurry was heated and controlled at 100° C. The mixture was stirred continuously during the reaction at a stirring speed of 3 r / min and a reaction time of 2.5 h. During the reaction, a control agent (citric acid and diglycolamine in a mass ratio of 1:0.2) accounting for 0.8% of the total mass of the reactants was slowly added;

[0066] (3) After the reaction is completed, the obtained calcium sulfate slurry is subjected to ultrasonic treatment (first at a power of 200-350 W for 30 min, and then at a power of 400-500 W for 30 min), and then filtered, washed, and dried at 60° C. to obtain nano calcium sulfate whiskers.

[0067] The prepared nano calcium sulfate whiskers were characterized by X-ray diffractometer (XRD) and field emission scanning electron microscopy (SEM), and their crystalline structure was CaSO4·0.5H2O. The whiskers were 80-110 μm in length, 1-2 μm in diameter, with an aspect ratio of 50-100 and an absolute density of 2.98 g / cm 3 , loose density 0.24g / cm 3 More preferably, the length of the nano calcium sulfate whiskers is preferably 90-110 μm, the diameter is preferably 1-2 μm, and the aspect ratio is preferably 80-100.

[0068] Comparative Example 1

[0069] (1) The cleaned red gypsum and water slag were mixed in a mass ratio of 3:2, and then water accounting for 5 times the mass of the mixture was added to prepare a mixed slurry;

[0070] (2) The mixed slurry was heated and controlled at 100°C. The mixture was stirred continuously during the reaction at a stirring speed of 3 r / min and a reaction time of 2.5 h. During the reaction, a control agent (citric acid) accounting for 0.8% of the total mass of the reactants was slowly added;

[0071] (3) After the reaction is completed, the obtained calcium sulfate slurry is subjected to ultrasonic treatment (first at a power of 200-350 W for 30 min, and then at a power of 400-500 W for 30 min), and then filtered, washed, and dried at 60° C. to obtain nano calcium sulfate whiskers.

[0072] Effect Example 1

[0073] The calcium content in the nano-calcium sulfate whiskers prepared in Example 1 and Comparative Example 1 was detected by EDTA titration, and the yield of the nano-calcium sulfate whiskers was calculated. The specific results are shown in Table 1.

[0074] Table 1

[0075] Yield (%) Example 1 18.7 Comparative Example 1 15.3

[0076] Effect Example 2

[0077] The nano calcium sulfate whiskers prepared in Example 1 and Comparative Example 1 were added to asphalt:

[0078] (1) Experimental equipment: electric blast drying oven, digital display blast drying oven, BH20 asphalt mixture mixer, Marshall electric compactor, constant temperature overflow water bath, Marshall stability tester, balance scale;

[0079] (2) Specific raw material ratio:

[0080] Table 2

[0081]

[0082] The specific preparation method is as follows:

[0083] 1. Dry the large stones, small stones, stone powder and mineral powder to 170℃ respectively.

[0084] 2. Heat the asphalt to 180℃ and keep it warm for 2 hours.

[0085] 3. Add large stones (particle size 10-15), small stones (particle size 05-10), stone powder and asphalt in batches and mix for 3 minutes.

[0086] 4. Add wood fiber and mineral powder to the mixed materials above and continue mixing for 3 minutes.

[0087] 5. Place the mixed material into a round mold and heat to 180°C;

[0088] 6. Brush the test barrels with oil, and put the samples of each batch into 4 round test barrels and mark them.

[0089] 7. Use a Marshall electric compactor to hammer each round test barrel 75 times on both sides (place round white paper on both sides before hammering to prevent sticking to the equipment).

[0090] 8. Use the Marshall stability tester to test the module stability and peak flow value data in batches. The experiment ends after recording the data.

[0091] The stability and peak point flow value test data are shown in Table 3.

[0092] Table 3

[0093]

Claims

1. A method for preparing high aspect ratio calcium sulfate whiskers based on calcium-based solid waste, characterized in that: The following steps are involved: (1) Mix the cleaned red gypsum and water slag in proportion, add an appropriate amount of water to the mixture to prepare a mixed slurry; (2) heating the mixed slurry and reacting the mixture, and slowly adding a control agent during the reaction; (3) After the reaction is completed, the obtained calcium sulfate slurry is subjected to ultrasonic treatment, and then filtered, washed, and dried to obtain nano calcium sulfate whiskers.

2. The method according to claim 1, characterized in that In step (1), the mass ratio of the red gypsum to the water slag is 3:

2.

3. The method according to claim 1 or 2, characterized in that In step (1), the solid-to-liquid ratio of the mixture to water in the mixed slurry is 1:3-5.

4. The method according to claim 1, wherein In step (2), the reaction temperature is controlled at 80-100°C, stirring is continued during the reaction process, the stirring speed is 300-500 r / min, and the reaction time is 2-3 h.

5. The method according to claim 1 or 4, characterized in that In step (2), the amount of the control agent added accounts for 0.5-1% of the total mass of the reactants; the control agent is composed of citric acid and diglycolamine in a mass ratio of 1:0.

2.

6. The method according to any one of claims 1 to 5, characterized in that In step (3), the ultrasonic treatment is first performed at a power of 200-350 W for 30 min, and then at a power of 400-500 W for 30 min.

7. The method according to claim 1 or 6, characterized in that In step (3), the drying temperature is 60-80°C.

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