| In recent years,a great deal of industrial solid waste which named phosphogypsum(PG)is produced continually in the process of a wet-process phosphoric acid technology with the rapid development of productivity in phosphorus chemical industry enterprises.It is PG which includes a variety of impurities in an open pit that directly causes serious environmental problems in our country.Calcium sulfate whiskers(CSW)are prepared with PG which replaces natural gypsum not only supplying a unregenerated gap of natural gypsum,but also exploring a new domain as the high added-value and grade-inter mediate type material.Calcium sulfate whiskers,a kind of novel and excellent crystalline material,have a series of features such as high modul us,high strength,high temperature resistance and acid resistance and so on.High performance to price ratio is beneficial to have a strong market competitiveness as well as a wide application prospect.The paper mainly study on calcium sulfate whiskers are prepared from PG,and totally research on optimum reaction parameters,effect of impurities on calcium sulfate whiskers,type option and optimum dosage of crystal promoters,the surface modification of calcium sulfate whiskers.Taking processed PG as raw material,magnesium chloride as crystal promoter and natural gypsum as seed crystal,calcium sulfate whiskers were prepared by the liquid phase growth method.The effect of whisker properties on reaction temperature,reaction time,slurry mass fraction,crystal seed dosage and systemic stirring rate was investigated respectively.The results show that optimal reaction parameters as follows: the reaction temperature is 130 ℃,the reaction time is 4.0 h,the slurry mass fraction is 2.5%,the dosage of crys tal seed is 9.0%,and systemic stirring rate is 100 r/min.The mean aspect ratio of obtain calcium sulfate whiskers is 112.65 on the basis of optimal conditions.Since PG impurities have various types and complex components,the influences of its impurities on calcium sulfate whiskers were investigated specifically through the external mixed simulation method on the basis of optimal reaction parameters.Experimental results show that phosphoric acid dramatically inhibits the growth of calcium sulfate whisk ers.The length and aspect ratio of calcium sulfate whiskers is 6.92 when the dosage of phosphoric acid is 4.4%.Hydrogen fluoride has little influence on the length of the calcium sulfate whiskers,but it dramatically coarsens diameter,causing the aspect ratio of whiskers decrease.The average aspect ratio of whiskers is 7.71 when the dosage of hydrogen fluoride is 1.5%.Organics can adsorb the surface of whiskers combining primary physical adsorption and subordinate activated absorption,inhibiting the growth of whiskers.The average aspect ratio of calcium sulfate whiskers is 17.64 when the dosage of organics is 1.6%.Crystal promoter has a inducement and promotion effect for the growth of calcium sulfate whiskers.Effects of dodecyl ferric and magnesium salt crystal promoter on calcium sulfate whisker performances were researched respectively on the basis of optimum reaction parameter.The results show that the promoting effect sequence of dodecyl ferric salt crystal promoter for calcium sulfate whiskers is FX-3 > FX-2 > FX-5 > FX-6 > FX-4 > FX-1.In addition,FX-3 crystal promoter has a best promoting effect for the growth of calcium sulfate whiskers.The mean aspect ratio of whiskers is 139.50.The promoting effect order of dodecyl magnesium salt crystal promoter for whiskers is MX-3 > MX-2 > MX-1 > MX-6 > MX-4 > MX-5.MX-3 crystal promoter has optimal effect for the growth of calcium sulfate whiskers.The average aspect ratio of whiskers is 140.12.The length and aspect ratio of whiskers increase firstl y and decrease lastly with the dosage of FX-3 and MX-3 crystal promoter increase.The optimum dosages of these crystal promoters are 1.0% respectively in the reaction system.The surface of calcium sulfate whiskers was modified by sodium silicate as a kind of stable modifier.The influence of modification effect of whiskers ’ surface on modifier dosage,modified temperature,modified time and drying temperature was researched respectively.The results show that optimal reaction parameters as follows: the dosage of modifier is 1.5%,modified temperature is 60 ℃,modified time is 20 min and drying temperature is 105 ℃(2 h).The activation index of modified calcium sulfate whiskers is 91% under these conditions. |
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