Study On The Effect Of Microwave Crystallization Kinetics Of Nesquehonite

Despite that microwave has been proven to be an effective method to control crystallization process,to our knowledge,the quantitative study of microwave effect on crystallization kinetics is limited.The aim of this study is to investigate the effect of microwave on the crystallization mechanisms in water-based system by analyzing the variation of crystallization kinetic parameters in microwave field.The crystallization experiments were carried out under fixed temperature and various microwave power inputs.Magnesium carbonate is used as the working substance precipitated in a laboratory MSMPR crystallizer settled in the cavity of microwave reactor.A population balance model considering nucleation,growth,agglomeration and breakage is constructed and solved with HMMC.The crystallization kinetic parameters were fitted against experimental data.The mechanisms of the microwave effecting on kinetic parameters are discussed as well.It is found that in 25?,the exponent of nucleation(n)and the breakage rate constant(kbr)remains constant or changes only slightly with higher microwave energy inputs.However,the nucleation rate constant(kn),the growth rate constant(kg)and the collision efficiency(?ag)are increased significantly with microwave energy input.Furthermore,the growth rate exponent(g)is decreased.The reason for above phenomenon is the increase of mass transfer rate in microwave field.Because of the electromagnetic shielding effect caused by raising suspension density of MgCO3 crystals in solution,the microwave effects on crystallization kinetic parameters attenuate with the increase of energy input.It is further found that when the crystallization temperature is changed to30? and 35?,compared to 25 ?,the exponent of nucleation(n)changes slightly.Meanwhile,the nucleation rate constant(kn),the growth rate constant(kg)and the collision efficiency(?ag)are increased significantly.The growth rate exponent(g)is further decreased.Because of the increase of the temperature,the crystals are tending to be broken in the crystallization system.