Han Yuexin patent

Article number:1008-7524 (2005)12-0034-03 Research progress in preparation of gypsum whiskers ξ Mao Changming, Chen Xuexi (Qingdao University of Science and Technology, Qingdao, Shandong 266042) Abstract: The current preparation methods of gypsum whiskers are introduced, with emphasis on the green chemical process for manufacturing gypsum whiskers in wet-process phosphoric acid production. Keywords: whisker; Gypsum; Calcium sulfate; Phosphogypsum whisker; Classification number of wet-process phosphoric acid: TQ 126.3 Document ID: A 0 Introduction Whiskers refer to fibrous single crystals with fixed cross-sectional shape, complete shape, perfect internal structure and length-diameter ratio of 5 ~ 1000. Gypsum whisker (gypsum fiber) refers to the fibrous single crystal of semi-hydrated or anhydrous calcium sulfate, which is a new functional material with excellent performance and low price (one thousandth to one tenth of that of metal whiskers such as silicon carbide and titanium dioxide). It has high tensile strength and elastic modulus, and can be used as a high-value industrial material with low price. It can be used as reinforcing agent or functional filler in resin, rubber, coating and papermaking, and can also be used as friction material, building material, sealing material, thermal insulation and flame retardant material. , has a very broad development prospect. However, the current production methods at home and abroad are not only high in production cost, but also heavy in pollution, and their development prospects are worrying. Therefore, it is not only the need of environmental protection, but also the need of economic and social development to study the cheap preparation method of gypsum whiskers. The preparation methods of gypsum whiskers at present are summarized and compared, and the preparation methods of gypsum whiskers in wet-process phosphoric acid are emphatically introduced. This method has no precedent at home and abroad, and has great technical advantages and remarkable social benefits. 1 Preparation method of gypsum whisker 1. 1 There are two main methods to prepare gypsum whisker from natural gypsum [1] Preparation of calcium sulfate whisker from natural gypsum. Hydrothermal method is to add gypsum dihydrate suspension with mass fraction less than 2% into water heater for treatment. Under saturated vapor pressure, gypsum dihydrate becomes fine needle-like gypsum hemihydrate, and then the crystal form is stabilized to obtain calcium sulfate hemihydrate whiskers. This method has high production cost and limited application. Atmospheric acidification means that at a certain temperature, high concentration gypsum dihydrate suspension can be transformed into needle-like or fibrous calcium sulfate hemihydrate whiskers in acidic solution. Compared with hydrothermal method, this method does not need autoclave, the mass fraction of raw materials is greatly improved, the cost is greatly reduced, and it is easy to realize industrial production. Recently, Duan Qingkui and others [2] invented a method for preparing gypsum whiskers from natural gypsum dihydrate (or citric acid residue gypsum). Specifically, 30g of raw materials were mixed with 240g of water to make slurry, the pH value was adjusted to 4, and hydrothermal reaction was carried out at 1 15 ~ 150℃ for about 2 hours. When the reaction temperature rises to 90 ~ 92℃, 40mg of crystal seed gypsum whisker and 30mg of crystal transfer agent potassium dodecyl sulfate are added for full reaction and filtration. Surface treatment is carried out, and the spraying amount of polyvinyl alcohol is 0.0 1% ~ 0.05% of the mass of the material, and then it is dried in an oven at 120℃. The average diameter of gypsum whiskers obtained by this method is 2 ~ 4 microns, and the average length-diameter ratio is about 80. Excellent water resistance and wide application, but high production cost and difficult popularization. In addition, Han Yuexin et al. [3] prepared calcium sulfate whiskers from gypsum, the essence of which is the transformation of granular gypsum into fibrous anhydrous calcium sulfate. The prepared calcium sulfate whisker has a length of 50 ~ 100 micron and a diameter of 1 ~ 4 μ m, and the whisker size is uniform, which has obvious advantages in cost and price. However, the impurities in the above reaction system are difficult to remove, which easily affects the whisker product. Preparation of calcium sulfate whiskers from 1.2 brine residue? 43 summary? IM& Chemical Minerals and Processing, 12, 2005 ξ Date of receipt: August 26th, 2005: Fund Project: Supported by National Natural Science Foundation of China (20376036). The method takes bittern residue in sea salt bittern treated with lime milk as raw material, and the technological process is divided into two steps. Step 1: Lime milk is used to treat brine. Neutralize the brine after bromine extraction with calcium oxide emulsion, control the pH value of the brine to 7.6 ~ 8.0, and filter. The filtrate is used to prepare acicular magnesium hydroxide, and the residue is filtered for later use. Step 2: prepare whisker-like calcium sulfate. Dilute the brine residue with a certain amount of water, add industrial waste acid to dissolve, stir, adjust the pH value to 2-3, and heat the solution to boiling. At this time, most of Ca2+ in the residue has entered the solution, filtered while it is hot, and after cooling, white crystals are precipitated, which are slender and fibrous under the microscope. When the mother liquor is reused, the impurity iron needs to be removed when the color of the solution changes during the cycle. Generally, the pH value can be adjusted by Ca(OH)2 to filter out the precipitated iron [4]. The purity of calcium sulfate whiskers prepared by this method reaches (Ca2SO4? 2h2o) is 98.0%, the impurity removal effect is good, and needle-like magnesium hydroxide flame retardant is obtained, but the experimental steps are complicated and it is not easy to industrialize. 1.3 gypsum solution method The process flow of this method is: gypsum dihydrate → grinding → slurry → hydrothermal reaction → filtration → drying → hemihydrate gypsum crystal → calcination → anhydrite whisker. Among them, gypsum is optional, but the content of calcium sulfate is better than 95%, the fineness is better than 80%, and it is basically free of harmful impurities. The mass fraction of slurry is usually controlled between 5%- 10%, and mass fraction is an important control factor. The hydrothermal reaction temperature is generally 105 ~ 150℃ or higher, the pressure is 202.65~506.63kPa, and the time is 0.5 ~ 8 hours. At the optimum reaction temperature, the temperature should be kept for a period of time, so that all calcium sulfate can be converted into whiskers, and the loose whiskers can be separated from the excess water immediately after the fiber is formed. Generally, filter pressing is adopted, and the temperature during filter pressing is not lower than 100℃. The filter cake was dried immediately and stabilized when it was hot, and then it was made into hemihydrate gypsum whiskers with an average L/d of 60 ~ 100. Anhydrous gypsum whiskers are calcined at high temperature (400 ~ 600℃) to form dead-burned insoluble anhydrite whiskers. The product can remain stable for a long time, and it is not easy to restore the hydration state when there is water [5]. This method can make part of waste gypsum dihydrate into gypsum whiskers, but hydrothermal reaction requires higher temperature and pressure. 1.4 waste gas desulfurization method The process flow of this method is waste gas cooling → absorption → pH adjustment and oxidation → filtration → fiber drying. Lime milk absorbs SO2 to form calcium sulfite slurry, then sulfuric acid is added or waste flue gas is introduced, and the pH value of the slurry is controlled to be 3-4. Adding crystallization AIDS and oxidation catalysts such as ammonium chloride, manganese chloride, copper sulfate and manganese sulfate into the slurry, and the dosage range is 0.0 1%-0.2%. Then enter the oxidation stage, and carry out oxidation by introducing oxygen or air. After the oxidation reaction, φ 1 ~ 2 μ m L 100 mm whiskers can be obtained by hot filtration, washing and drying at 90℃. The advantage of this method is that the waste gas is made into cheap gypsum whiskers, which is suitable for industrial production and has certain market potential. It provides a new idea for the manufacture of gypsum whiskers, which is developing rapidly in Germany and Japan at present. 1.5 Other methods Among the many preparation methods of gypsum whiskers, steam blowing continuous production method and liquid phase direct preparation method are also common. The steam injection continuous production method is to blow 4kg/cm3 of steam into gypsum dihydrate slurry through a gas-liquid mixing device, keep the slurry at 1 15 ~ 140℃ while stirring, continuously pump the slurry into an autoclave, keep the kettle temperature, and control the mixing time of unreacted gypsum dihydrate and crystalline needle-like whiskers to the minimum, so as to obtain a diameter of/kloc-. This method can be used for continuous production with high thermal efficiency. The liquid-phase direct preparation method is to mix the methanol solution containing sulfuric acid and the methanol solution containing calcium chloride according to the ratio of 4∶ 1 (by volume), age for 5 minutes to 72 hours, filter and dry (45℃), and obtain the type II gypsum whisker with L/D >: 100. This method does not need gypsum hemihydrate, and directly prepares type II gypsum whiskers. The process is simple, and the hydrothermal reaction and high-temperature calcination procedures are omitted. Most of the methanol used can be recovered by distillation. 2. Experimental method for manufacturing phosphogypsum whiskers in wet-process phosphoric acid 2. 1. In the traditional manufacturing process of wet-process phosphoric acid, every time 1t wet-process phosphoric acid is produced (calculated by P2O5), the by-product phosphogypsum [7] is about 4 ~ 5t, and the global annual phosphogypsum emission is close to 200 million tons, but the actual utilization rate is less than110 of the total. A large number of phosphogypsum piled up in the open air, occupying land and seriously polluting the environment, has become a worldwide problem. The method of preparing gypsum whiskers by wet-process phosphoric acid invented by Chen Xuexi et al. [8] improves the traditional wet-process phosphoric acid production process, and uses calcium ions and sulfate ions in the wet-process phosphoric acid production process to prepare snow-white phosphogypsum whiskers, which avoids the production of phosphogypsum waste residue from the source of chemical reaction, and is a typical green and clean chemical process. ? 53 summary? IM & ampp Chemical Minerals and ProcessNo.12, 2005, Wang Lixin et al. used two-step process [9] and selected excellent crystal modifier to prepare snow-white phosphogypsum whiskers in wet-process phosphoric acid. The first step: leaching phosphate rock with phosphoric acid, controlling the technological conditions of leaching chemical reaction, reducing the pollution of chemical reaction itself to the target product and obtaining relatively pure phosphoric acid. Step 2: Provide suitable crystallization conditions to make gypsum crystallize perfectly and regularly, which is beneficial to its application in other industries. 2.2 Morphology of Phosphogypsum Whiskers The phosphogypsum whiskers prepared by the above method are white and fine needles with good filtration performance. Observed by B5-223I microscope, the typical shape is 2 ~ 4μ m in diameter, and the aspect ratio is 10 ~ 100. Observed by JSM-6700F electron microscope, the cross section is hexagonal. 2.3 Application of Phosphogypsum Whiskers in Wet-process Phosphoric Acid Gypsum Whiskers are made by converting industrial wastes into useful materials, and the production cost is very low. At present, there is no precedent at home and abroad, and it has strong technical advantages and broad application prospects. The preliminary study shows that the phosphogypsum whisker product obtained in this paper can replace calcium carbonate as the filling reinforcement material of rubber, plastic and other polymer materials, which can improve the elasticity of rubber products by 30%. The phosphogypsum whiskers obtained in this paper can replace 30% ~ 70% of wood pulp or straw pulp when used in papermaking. When phosphogypsum whiskers are mixed with wood pulp in the proportion of 36%, 52% and 65%, the paper made is white and smooth, and the whiteness, tensile strength and other performance indexes are not much different from those of pure wood pulp paper. There is no precedent for phosphogypsum to be used in papermaking in China. At present, the market price of wood pulp is about 5,000 yuan /t, but the manufacturing cost of phosphogypsum whisker is not more than 500 yuan/t. If 30% of wood pulp is replaced, the production cost per ton of paper can be reduced 1350 yuan, and the market potential is huge. Conclusion By comparing the above preparation methods of gypsum whisker, it can be seen that the method of manufacturing gypsum whisker in wet-process phosphoric acid production has the advantages of low production cost and excellent gypsum whisker products. This method is completely different from the traditional thinking of "pollution first, then treatment", which solves the utilization problem of phosphogypsum from the chemical source, fully meets the requirements of sustainable development strategy, and is a typical green chemical process. After it is put into production, it will certainly play a great role in promoting economic and social development and have a far-reaching impact on the harmonious development of society and environment. 4 references [1] Li Ailing. Research progress of natural gypsum and its development and utilization [J]. Minerals and Geology, 2004, (5):498-50 1. Duan Qingkui, Wang, et al. A gypsum whisker and its manufacturing method and application [P]. National patent, CN660. 2004.[3] Han Yuexin. Synthesis of calcium sulfate whisker from gypsum and its application [J]. Mineral processing of foreign metal ores, 1996, (4):50-53. Xiao Chumin, Zhang Yongqi, et al. Study on Preparation of Calcium Sulfate Whisker Fiber from Brine Residue [J]. Hubei Metallurgy, 6596, et al. Effect of pH value on the diameter of calcium sulfate whisker [J]. Metal Ore, 2004, (10):39-42. [6] Fei, Li. Summary of Preparation and Application of Calcium Sulfate Whiskers [J]. Chemical Minerals and Processing, 2002, (9): 365438+ 2003, (4):3-36. [8] Chen Xuexi. Method for preparing gypsum whisker in phosphoric acid [P]. China patent, CN 1584 130A. Xu Lixin, Chen Xuexi, et al. Study on production technology of high-quality phosphogypsum [J]. Chemical minerals. (5):28-3 1. Abstract: The preparation method of Polygonum cuspidatum was introduced. Emphasized on the introduction of AEENVIRONMENTAL PROTECTION PROCESS OF PREPARING gypsumwhiskerf PRODUCTION OF WET 2 PROCESP PHOPHORICIDWASEX 2. Keywords: whisker; Gypsum; Calcium sulfate; Phosphogypsum whisker; Wet2processphosphoricacid Cache (continued from page 32) Table 2 Cash flow calculation table of investment projects Unit: ten thousand yuan T 123445 Cash flow from investment and operation-106.4106.4/kloc-0. 70.4 Total cash flow-38+006.4 106.4 According to the mine drainage system and hydrogeological conditions, the reformed underground water storage tank can accommodate 1.6 hours of normal water inflow, concentrated in the low-power drainage period, saving 993,000 yuan annually.