Studies On Phosphate Rock-Sulfuric Acid Reaction Kinetics Under The Action Of Active Porous Agent

Single superphosphate is an old phosphoric fertilizer . But its process also have some difficult problems which have not been solved for long time , such as the longer stacking and curing time ,badly caking produces. So far , there is a new technology named adding activator and porous agent(abbreviated as APA) process widely applyed in China . Started from settling the disadvantages in the process , the subject research the activator and porous agent 's influence on the acid-rock reactionAPA is a compound in which surface active agent is the main ingredient. According to some special properties of surface active agent , we observed and studied APA's influence on CaSO4's crystal form with the electronic microscope. The results indicate that APA is propitious to improve CaSCVs crystal form , and to get coarse and regular crystal. Through series acid-rock reaction experiments ,we can get the conclusion that APA can change the CaSCVs crystal form ,and lead to the coating layer around the unreacted phosphate ore grains loose and pervious ,and then make the resistance of the next reaction decreased and the percent conversion of the phosphate ore increased .Unreacted-core shrinking model can be used as physical model of the second stage of the reaction .We assumed that the radium of unreacted core was RO at to,and at this time the coating layor around the unreacted core was called as coating- I ,in which the expansion factor of liquor reactant was assumed as Kis.The reaction after to seemed as stationary state process. And the coating growing in this process was called as coating- II in which the effective expansion factor of liquor reactant was assumed as Deff2 According to the character of stationary state process, we can get the mathematic model of the second stage:On the basis of mathematic model and experimental data , the empirical equation can be derived:from the calculation results , we can get the conclusion that the expansion factor of liquor reactant in the reaction of adding APA is larger than that in the check, which means that adding APA can reduce the resistance force of coating layor so that the reaction speed is increased .During the derivation , some hypothesis and model simplifications were made . The equation still have some deficiencies to describe the process .So it need to be improved further .Combining the empirical equation with the Arrhenius equation , a rate equation for the digestion process was fitted to experimental results as follows:The results show that in the reaction of adding APA the reaction rate constant is larger than that in the check , which indicate that APA can increase the coating layer's perviousness and make the reaction speed up.The reaction temperature is varied from 341 to 353K,the initial mean particle size 0.128to 0.154mm,and the initial sulphuric acid concentration is 63%, the stirrer speed 300rpm.Under such conditions , the equation is fitting well with the experimental data .The results indicated that the error between calculation and actual value is no more than 5%.Acid-rock reaction is the major technology of phosphoric fertilizer , and the crystallization is usually involved .So the study of the APA's influence on the reaction not only supply assurance for the industrial implement of the no stacking and curing time technology (or called as adding APA process )in single superphosphate process, but also can infer some reference to adding APA in other acid-rock reaction.