| As an important industry chain of phosphorus resource,the technology of producting Mono-Ammonium phosphate(which was also called MAP)has excited most of researcher's attention,during the industrial manufacture of MAP,The product purity is not the only test standard,the particle sizes distribution of crystal product and morphology are also have some regulations.This is regulated to the crystallizing process of MAP.There are plenty of zwitterions in the wet-process phosphoric acid,during the industry process to product MAP using wet-process phosphoric acid,the crystal product was collected by cooling crystallization.With double stage neutralization,even though,most of the impurities were removed from the solution,there still has about 0.5%Mg exist on the solution,and these Mg will go directly into the crystallization mother liquor to effect the whole crystal process.For the moment,the study for the crystallization of mono-ammonium phosphate is rarely,especially the industrial crystallization with the existence of impurities and with cooling down under different cooling modes.Figuring out the non isothermal crystallization mechanism and the mechanism during the crystallization with impurities are very meaningful for the industry process.In this paper,the solubility and metastable zone width of mono-ammonium phosphate have been tested by on-line laser system,and Mg2+ was added to the solution of mono-ammonium phosphate to study the influence on them.it turns to that solubility and metastable zone width of MAP will increase while Mg2+ was in.it also invests the effect of stirring speed and equilibrium temperature on the solubility and metastable zone width of MAP,it shows that the width of metastable zone will narrow with the enlargement of stirring rates,while the temperature ranged 30?to 55?,the width of metastable zone of MAP was decreased from 14?to 4.9??The physical property of saturated solution to MAP was also studied in this paper.Magnesium was added to the saturated solution to research the indensity and viscosity.the datas onto experiment show that the viscosity of saturated MAP solution will increase from 2.03mpa/s to 5.77mpa/s while the quantity of magnesium was from 0.5% to 10%,meanwhile,the density if solution will increase from 1.208g/cm~3 to 1.286g/cm~3.In addtion to this,this paper also studies the crystallization kinetics of ammonium phosphate based on different cooling rates.in order to achieve a variety of cooling methods,a temperature control system was designed,which realized the natural cooling,cooling linear,constant temperature cooling and ladder type cooling.The real-time concentration of ammonium phosphate in crystallization was determined by density method.In the process of crystallization,every once in a while to take out some solution to measure the density,then inverse computation the standard curve to get the concentration decay curves,and the crystallization kinetics of ammonium phosphate was obtained by using the nonlinear optimization method based on the established crystallization kinetics model.The results show that the growth order for all the cases is equal to 1,but the growth kinetic constant depends on the cooling mode,from which the nature cooling gives the larges value and the linear cooling give the smallest.At last,this paper has invested the difference particle size distribution and appearance of mono-ammonium phosphate crystal before and after the addition of magnesium.the particle sizes distribution of MAP crystal will increase to the addition of Mg2+,and the shape of MAP will become longer.Some small crystal will aggregate at the surface of MAP,and this phenomenon will be more general with the increaseof addition amount of Mg2+.Besides,the existence of Mg2+ in the crystalline solution will repair the crystal defect inside of the MAP crystal. |
PDF Full Text Request