In Ammonia, Potassium Sulfate Crystallization Process And Its Improvement

THE STUDY ON CRYSTALLIZATIONALPROCESS AND IMPROVEMENT OF PARTICLESIZE OF PATAS SlUM SULFATE IN AMMONIAAQUEOUS SOLUTIONMajor: chemical technicsPostgraduate: Jiang WeiAdvisor: Liu DaijunPotassium sulfate can be obtained directly by gypsum and potassium chloride in ammonia aqueous solution in order to solve difficult problem of discarding gypsum and develop the industiy production of no-chloric fertilizer. But the study of this process is still not perfect and the the crystal size of the product in the process is still too fine. It is urgent to find a ~vay to promote the quality of product by increasing the particle size.It is hard to enlarge the granulity because of lack of the kinetics data of the crystallization of potassium sulfate in ammonia aqueous solution. A lot of useful parameters on different conditions, including the nuclei rate, the growth rate, maximum supersaturation degree, density of crystallization and the interfacial energy, are measured and the equations are formed..The influence of interfacial energy in crystallization process is always neglected inIf Itesting the kinetics of crystallization in many papers. For learning this influence, increasing the particle size and promoting the growth rate, restraining the nuclei rate, the different contrastive experiments are done. The dynamic interfacial energy= xy~ is brought forward, and the multifarious influence is summed up to the changement of the dynamic coefficient, K. Combining with the other parameter, the interfacial energy can be look on as a parameter which can evalue the terminate granulity in some degree.By understanding the kinetics of the crystallization and simulating the possible spatial structure by quantum mechanics method on computer, the level of choosing the reasonable additive is gained. Combing with the result of blank experiment, and with the normal methods used in industry, it is indicated that adding additives can effectively promote increase of crystal size and modify the crystal habits and quality. By measuring the interfacial energy as well as investigating crystallization process, effectiveness of some additives is confirmed, although different additive has different working mechanism. Some of them, high electrovalent metal ion and retarded agent, are proved to play a important role on increasing interfacial energy and varing the crystallization process.