Study On The Effect Of Phosphoric Acid On The Leaching Of Phosphate Ore And Its Kinetics

Phosphate ore is an important strategic resource in China,and is the main raw material for the production of phosphoric acid and phosphate compound fertilizer.At present,the production process of phosphoric acid is mainly wet process phosphoric acid,among which sulfuric acid process is dominant.However,due to the low decomposition rate of phosphate rock in the process of phosphoric acid decomposition of phosphate rock,low P2O5 recovery rate of phosphoric acid decomposition of phosphate rock is relatively large liquid and solid problems,this paper took the phosphate rock in Weng an County as raw material,to carry out the experimental research on the efficient decomposition of phosphate rock by phosphoric acid,by exploring the key process parameters:The effect of phosphoric acid concentration,liquid-solid ratio,reaction temperature and particle size of phosphate rock on P2O5 conversion rate of phosphate rock was studied.The reaction process of phosphoric acid decomposition of phosphate rock was studied and a kinetic model was established to provide theoretical guidance for phosphoric acid production process.The effect of process parameters on P2O5 conversion rate was explored by single factor experiment.The results showed that with the increase of phosphoric acid concentration,liquid-solid ratio,stirring speed,reaction time and reaction temperature,the P2O5 conversion rate of phosphate rock increased.With the decrease of phosphate rock particle size,the P2O5 conversion rate increased first and then decreased.The optimum process conditions were as follows:phosphoric acid concentration(P2O5):30%,liquid-solid ratio of 10:1,reaction temperature of 70℃,particle size of phosphate rock of 160 mesh,stirring speed of 300 r/min,the conversion rate of P2O5 is 98.85%.When the phosphoric acid concentration is more than 30%and the reaction temperature is more than 80℃,the P2O5 conversion rate is decreasing.The significant factors affecting the conversion rate of phosphate rock decomposed by phosphoric acid are particle size,phosphoric acid concentration and liquid-solid ratio.The response surface is used to optimize the process design of phosphate rock decomposed by phosphoric acid,and the three factors and one level experiment aimed at the significant factors is carried out.The results show that the optimal process of response surface is phosphoric acid concentration(P2O5):31%,liquid-solid ratio of 11:1,phosphate rock particle size of 160 mesh and P2O5 conversion rate of 99.58%,the conversion rate of P2O5 under the optimal conditions is 98.87%,which is close to the optimal value.Under the same process conditions,by comparing and analyzing the effects of phosphorus concentrate,raw ore and roasted ore on the conversion rate of P2O5 after reacting with phosphoric acid,the result shows that the change trend of the conversion rate of the three kinds of ore is similar.Under the same process conditions,the conversion rate of phosphorus concentrate is the highest,followed by roasted ore.Through the object image representation of the acid insoluble substance of the three kinds of ore,it can be found that after 120 min of reaction,silica and a small amount of fluorapatite are found in the acid insoluble matter of phosphor concentrate and raw ore.After 120 min reaction under the same conditions,the most acid insoluble substance is fluorapatite,which indicates that the roasted ore has not completely reacted with phosphoric acid.The mechanism of the reaction between phosphoric acid and phosphate rock is analyzed by thermodynamics.The results show that most of the components in phosphate rock can spontaneously react with phosphoric acid,and the Gibbs free energy is less than 0,most of the reactions are exothermic.The reaction of fluorapatite with phosphoric acid in phosphate rock mainly produces calcium dihydrogen phosphate,hydrogen fluoride and carbon dioxide.Some metal elements react with phosphoric acid in the system,such as dolomite react with phosphoric acid to get calcium salt and carbon dioxide.The existence of these elements can affect the reaction of phosphoric acid with fluorapatite and the conversion rate of P2O5.Through kinetic analysis of the process of phosphoric acid decomposition of phosphate rock,it is found that the process of phosphoric acid decomposition of phosphate rock can be described by the shrinkage core model,the control step of the process of phosphoric acid decomposition of phosphate rock is the diffusion of solid product layer(ash layer).Rate of phosphoric acid decomposing phosphate rock dynamics parameters and the liquid-solid ratio,concentration of phosphoric acid,phosphate rock particle size,reaction temperature,stirring speed,rate of liquid-solid ratio and concentration of phosphate dynamics parameters influence is positive,phosphate rock grain size parameters effect on the rate of negative,combined with the Arrhenius equation is the apparent activation energy of phosphoric acid decomposing phosphate rock is 11.36 KJ/mol,dynamic equation is:1-3(1-X)2/3+2(1-X)=1061×10-5C0.987(L/S)1.06G-0.161(SS)0.154exp(-11.36/RT)t...