Cheap Mineral Raw Materials Hydrothermal Synthesis Of Zeolite Molecular Sieve Formation Mechanism Of Crystal Growth Model

On basis of integrated analysis of a great deal of literatures and data about the synthesis and application and formation mechanism of zeolite molecular sieves as well as the theories of crystal growth model, This paper entirely and systematically studies the formation mechanism and crystal growth model of zeolite molecular sieves that are prepared in hydrothermal system of taking such cheap mineral materials as the stellerite and vitric tuff as the feedstock by using of modem material testing and analysing techniques. The main contents of the paper is as follows.The resource characteristics of the stellerite in Ziyuan county of Guangxi and the vitric tuff in Linli county of Hunan are evaluated after their mineral constitutes and chemical compositions and some technics performances are analyzed. According to their resource characteristics these two cheap mineral materials are pretreated adequately, then turned into eligible stocks that is used to prepare zeolite molecular sieves in hydrothermal method.Taking the stellerite or vitric tuff (pretreated) as the feedstock, a series of zeolite products are prepared by using the hydrothermal method. It is discussed in depth how the constitutes of the reaction mixture and hydrothermal conditions influence the hydrothermal preparation of zeolites, the best technical parameters of hydrothermal preparation of zeolite A and X and P are confirmed.Combining with the transformative characteristics of the chemical compositions and IR spectrum of the solid phases in the process of hydrothermal reaction, the author integratedly analyses the forming conditions of zeolite molecular sieves, formation of crystal nucleus and its influencing factors, crystal growth and its influencing factors. It is pointed out that the formation mechanism of zeolite molecular sieves hi hydrothermal system is the solution-mediated transformation crystallization mechanism.By using FKM method, the reaction mixture hi the earliest of hydrothermal reaction are made to the samples that can be used in TEM analysis. The TEM observation and electron diffraction analysis of these samples indicate that along with the dissolution of the feedstocks, zeolite nucleus are formed, simultaneously the small particles of several nanometer are formed, these small particles aggregate and form the crystal particles of about 50nm. These analytical results are the mighty evidences that are provided to prove that the nano-particles is formed by the aggregation of nano-small-particles.On basis of the hydrothermal preparation experiments of zeolite and its testing and analysing token as well as kinetics curve of crystal growth, the process of zeolite crystal growth hi hydrothermal conditon is investigated. It is put forward that there are such two kinds of growth mode as aggregation and coalescence. The crystal aggregation growth model is established. The aggregation growth is the process that the aggregation of small particles form big particles because the mutual action of the small particles. Thecoalescence growth is the recrystallizing process of particles because the small particles transport to big particles. The thennaldynamics drive force of the two growth is that the total surface free energy is reduced because the accretion of the average granularity of the particles. In hydrothermal condition, the formation of the zeolite crystal come through such four phases as from the dissolution of the feedstocks to the growth of nucleus and the formation of nano-small-particles to the aggregation growth of nano-crystal and micro-crystal to the coalescence growth of micro-crystal. The crystal that is prepared finally is the integrated results of aggregation and coalescence growth that aggregation growth give priority to coalescence.The study about the preparation and formation mechanism and crystal growth model of zeolite molecular sieves in hydrothermal system by taking the cheap mineral materials as the feedstock opens out the basic law of zeolite crystal growth in hydrothermal condition, improves and dev...