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Preparation of zinc sulfide

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Background and Overview of zinc sulfide
The chemical formula of zinc sulfide is ZnS. The chemical bond between Zn and S tends to be covalent. Crystals have three different configurations: low temperature type, namely sphalerite structure, abundant in nature, colorless cubic crystal, Zn, S coordination number are 4, the relative density is 4.10, at 1 020℃ to high temperature type; High temperature type, namely, fibronite structure, colorless hexagonal crystal, Zn, S coordination number are 4, the relative density is 3.98, melting point is about 1700℃, is high temperature stable structure of zinc sulfide ; The high pressure type, namely sodium chloride structure, Zn, S coordination number is 6, the relative density is 5.21.
The hydrohydrate ZnS·H2O is a white powder with a relative density of 3.98 and a melting point of 1049℃. Zinc sulfide is insoluble in water and dilute alkali, also insoluble in acetic acid, but soluble in hydrochloric acid and other low concentration of strong acid, hydrogen sulfide. In the highly acidic zinc salt solution, hydrogen sulfide gas is passed into the zinc sulfide can not get zinc sulfide precipitation. Zinc sulfide precipitate can be obtained by adding hydrogen sulfide gas into zinc salt solution, but the precipitate is not complete. With ammonium sulfide solution as precipitator, the zinc ions in the zinc salt solution can be completely precipitated into zinc sulfide. Because the ammonium sulfide solution is alkalescent, the acidity of the system can be reduced.
The above methods are used in industry and should be operated in isolation from air. White zinc sulfide darkens when it is exposed to light and is easily oxidized to zinc sulfate in the air. Zinc sulfide by itself or in combination with zinc oxide can be used as a white paint pigment. Pure zinc sulfide does not emit light, if the zinc sulfide crystal added trace of manganese, copper, silver as activator, after light irradiation, can emit different colors of fluorescence, is called fluorescent powder, used to make fluorescent screen, luminous paint. Zinc sulfide is also used in tanning, enamel, rubber, dye and other industries.
Application of zinc sulfide
As an important semiconductor material, zinc sulfide is widely used in luminescence, sensing, infrared window materials, photocatalysis and many other fields due to its fluorescence, phosphorescence and infrared transparency properties. Doped zinc sulfide should be used in a wide range of luminescent materials, such as phosphors (ZnS: Cu, Al), electroluminescent materials (ZnS: Mn), photoemitting photoluminescent materials (ZnS: Cu, Er), etc. Zinc sulfide used as white inorganic pigment, fluorescent pigment, can produce beautiful brilliance, high near-ultraviolet reflectivity, low wear and oil absorption, excellent rheological properties, photothermal stability, easy to react to the organic pigments and polymers, will not produce harmful catalytic effect.
Can be used in coating, printing ink, plastic, thermoplastic and thermosetting resin, resin elastomer, synthetic fiber, paper, lubricating oil, paint, glass, rubber and other aspects; If zinc sulfide contains trace copper and silver ions, it can produce fluorescent color, which can be used in TV sets, oscilloscopes and X-ray device components, various signs. Most of the zinc sulfide used in phosphor is made by solution method, which is characterized by large output and low cost. High purity zinc sulphide (HPZS) was prepared by direct gas phase synthesis of elements and crystallized needle-like, which was used to prepare high performance coating materials and single crystal raw materials.
Zinc sulfide single crystal can be grown by high pressure single crystal furnace and chemical vapor transport (CVD). Zinc sulfide sheets for optical materials can be prepared by hot pressing and CVD methods, which are widely used in laser window materials. In recent years, metal organic chemical vapor deposition is used to prepare zinc sulfide thin film materials. Due to low growth temperature, the thin film generated has good integrity and few defects, and it is easy to prepare heterojunction photoelectronic devices.
The preparation method of zinc sulfide
Method 1: Adding ammonium sulfide to zinc salt solution, white zinc sulfide precipitate can be prepared, and then recrystallization refining.
Method 2: Ammonium acetate was added to zinc sulfate solution, and hydrogen sulfide was added at pH= 2-3 to produce precipitation. The precipitation was filtered and dried under isolated air, and a good white crystalline zinc sulfide was obtained.
Method 3: A method for the preparation of fine zinc sulfide by a closed-circuit cycle, which includes the following steps:
Step 1. Mix ZnO solid powder with H2SO4 solution and add it into the first reaction kettle, where the mass ratio of ZnO solid powder to H2SO4 solution is 1: 1.5 ~ 2.5, the mass percentage concentration of H2SO4 is 20 ~ 25%, the reaction temperature is 65 ~ 75℃ for 25 ~ 35min, adjust the pH value of the solution after the reaction is 5.0 ~ 5.5, to get doped ZnSO4 solution; Then, the doped ZnSO4 solution was impurity treated to remove the impurities of nickel, molybdenum, chromium, copper, lead and iron in the ZnSO4 solution, and the pure ZnSO4 solution with impurity content less than 0.02% was obtained.
Step 2. Add the pure ZnSO4 solution and Na2S solution obtained in Step 1 into the second reaction kettle, where the mass ratio of ZnSO4 solution and Na2S solution is 2-2.5: 1, the mass percentage concentration of Na2S is 20 ~ 25%, and the reaction product is separated by a filter press for the first time, and the solid crude zinc sulfide with filter cake moisture less than 30% and Na2SO4 content less than 5% is obtained;
Step 3. Clean crude zinc sulfide with clean water in the wash tank. The specific gravity of the solution after cleaning is controlled between 0 ~ 0.2, and the content of Na2SO4 is less than 0.15%.
Step 4. The mixed liquid in the washing tank is separated by a filter press for the second time. The extracted solid zinc sulfide is dried at the temperature of 100 ~ 110℃, and burned for 30 ~ 50min at the high temperature of 745 ~ 755℃.
Step 5. After the mixed liquid in the washing tank is separated by a filter press for the second time, the exhalated liquid, namely the waste water containing 0.7%-1.7% sodium sulfate and 0.75-0.85% zinc sulfide by mass, is sent into the first reaction kettle and mixed with ZnO solid powder and H2SO4 solution to achieve a closed-circuit loop.
 

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