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Research On The Preparation Process And Mechanism Of Calcium Carbonate Whisker By The Desulfurization Gypsum

Posted on:2018-12-08Degree:MasterType:Thesis
Country:ChinaCandidate:J J WangFull Text:PDF
GTID:2321330518479570Subject:Engineering
Abstract/Summary:PDF Full Text Request
Desulfurization gypsum is the waste residue by industrial desulfurization,It has become the second thermal power plant solid waste due to the huge production.Most of the desulfurization gypsum to heap storage in our country at present.as it can not be used effectively,not only occupy land resources,costs money,and will cause secondary pollution.If it can be used effectively,instead of natural gypsum,not only can save natural resources,but also "turning waste into treasure",so that the use of waste resources,environmental and social benefits to achieve a win-win situation.As the main component of FGD gypsum are gypsum dihydrate and calcium carbonate,it is a good choice to prepare calcium carbonate whiskers with high added value.In this study,calcium carbonate whiskers were prepared by ammonia conversion-carbonization method using gypsum as raw material.Firstly,the CaCO3-(NH4)2SO4-H2O system involved in the production process of calcium carbonate whisker were investigated,the basic data of solubility of calcium carbonate in ammonium sulfate solution were obtained and the variation of the solubility of calcium carbonate in ammonium sulfate solution and the physical parameters such as viscosity,density and refractive index were determined.Research shows that the solubility of calcium carbonate in ammonium sulfate solution is higher than the solubility in water,and increased with the increase of the concentration of ammonium sulfate and temperature,for example,the solubility rises from 3.3654 mmol·kg-1 to 16.5709 mmol·kg-1 at 298.15 K,rises from 3.9245 mmol·kg-1 to 25.6335 mmol·kg-1 at 323.15 K,and rises from 6.2443 mmol·kg-1 to 33.0588 mmol·kg-1 1 at 348.15 K,respectively.The viscosity and density of the solution increased with the increase of ammonium sulfate concentration,but decreased with the increase of temperature.Similarly,the refractive index of solution increases with the increase of ammonium sulfate concentration,and decreases with the increase of temperature.In addition,Solubility of calcium carbonate in ammonium sulfate aqueous solutions and viscosity of aqueous solution were correlated with the twice-order polynomial equation and semiempirical exponential model equation,respectively,Which the accuracy of the experimental data is verified,which provides guidance for optimizing the process conditions.Secondly,the reaction conditions and reaction mechanism of desulfurization gypsum-ammonium bicarbonate were studied,the effects of material ratio,temperature,stirring intensity and reaction time on the reaction were discussed,the optimum process conditions were determined:the molar ratio of raw material(NH4+/SO42-)was 2,the reaction temperature was 60 ?,the stirring speed was 350 rpm,the reaction time was 20 min,and the conversion rate was above 97%.The reaction of FGD gypsum and ammonium bicarbonate is a complex multiphase chemical reaction process,which includes chemical reaction,liquid film diffusion and solid film diffusion and the reaction can be described by the shrinking core model.In addition,the effects of impurities(Fe3+,Mg2+)on the conversion of the raw materials were also investigated,the results showed that Fe3+ and Mg2+ exist in the reaction process of gypsum and ammonium hydrogen carbonate will have a negative impact,the conversion rate of SO42-were reduced significantly with the increase of the content of them,for example,when the content of Fe3+ was 0.05%,the conversion rate of SO42-was decreased by an average of 1.79%compared with that without impurity ions,the conversion rate of SO42-decreased by an average of 3.13%and 5.00%,respectively with an increase of Fe3+ content to 0.2%and 0.4%.When the two interactions,the effect is the same,and is to inhibit SO42-transformation.Finally,the calcium carbonate whisker was prepared by the leaching solution of calcium carbonate residue from the reaction of desulfurized gypsum and ammonium bicarbonate as a raw material,which ammonia carbonization using the method of parallel feeding.The preparation conditions of calcium carbonate whiskers were studied systematically the the optimum preparation conditions of calcium carbonate whiskers were obtained.Optimum conditions for synthesis process as follows:the Ca2+ concentration:0.1108?0.3325 mol/L,the molar ratio of Ca2+/HCO3-:1:2?1:3,the reaction temperature:60?80?,the stirring speed:200 rpm?300rpm,dropping speed:1?2 mL/min.Finally,the calcium carbonate whiskers with a length of 10?30 microns,a diameter of 0.5?2 microns and a length diameter ratio of 10?20 were obtained,product pH 9.06,relative density 2.83 g/cm3 which reaches Q/HXK002-2003 standard.At the same time,the growth mechanism of calcium carbonate whisker was discussed.This article provides an effective method for the comprehensive utilization of FGD gypsum,and can obtain calcium carbonate whiskers with high added value,which has good social and economic benefits.
Keywords/Search Tags:FGD gypsum, calcium carbonate whisker, Ammonia conversion carbonization method, solubility, mechanism
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