Study On Phosphate Decomposition By Mixed Acid And Purification Of Phosphogypsum

Phosphoric acid is the basic raw material of phosphate compound fertilizerindustry and phosphate industry, which is in great demand and widely used. Currentlydomestic and foreign phosphoric acid is obtained from traditional mixture of sulfuricphosphoric acid wet-process phosphoric acid, with the continuous development andutilization of phosphate resources, high-grade phosphate rock resources becomeexhausted, Therefore, the development and utilization of low grade phosphate rock isimminent. The decomposition rate of middle-low grade phosphate rock usingparathion mixed acid is low, the existence of some harmful impurities and low contentof CaSO4limits the application of phosphogypsum, making the large accumulation ofwaste phosphogypsum. Therefore, how to improve the decomposition rate oflow-grade phosphate rock and purification of phosphogypsum has become animportant research topic.in chemical industryThis paper aims to study the process of the preparation of phosphoric acid byphosphate rock decomposition using nitric-phosphoric mixed acid or hydrochloric-phosphoric mixed acid and separation and purification of phosphogypsum. First, Bystudying the effects of the experimental factors on the decomposition of phosphaterock, determine the optimum process conditions of the decomposition of phosphaterock using nitric-phosphoric mixed acid and hydrochloric-phosphoric mixed acidrespectively. Then, conduct the study of separation and purification ofphosphogypsum using gas-solid-liquid three-phase fluidized bed to determine theoptimum process conditions. Finally, establish the reaction kinetic model ofdecomposition of phosphate rock through observing the relationship between theconversion rate of P2O5and the four factors of reaction time, reaction temperature,concentration of mixed acid, phosphate rock particle.The optimum process conditions for decomposition of middle-low gradephosphate rock using nitric-phosphoric mixed acid: the ratio of mixed acid is4:1, thereaction temperature is55℃, the reaction time is50min, liquid-solid ratio is3.5:1, the amount of additive ammonium sulfate is0.1times of the content of CaO of phosphate rock, The actual dosage of mixed acid is1.1times of the theoretical dosage. The rate of decomposition of phosphate rock is99.24%, the concentration of phosphoric acid obtained is16.54%under the optimum process conditions. The optimum process conditions for decomposition of middle-low grade phosphate rock using hydrochloric-phosphoric mixed acid:the ratio of mixed acid is5:1, the reaction temperature is45℃, the reaction time is40min, liquid-solid ratio is4:1, the amount of additive ammonium sulfate is0.1times of the content of CaO of phosphate rock, The actual dosage of mixed acid is1.3times of the theoretical dosage. The rate of decomposition of phosphate rock is99.03%, the concentration of phosphoric acid obtained is14.20%under the optimum process conditions.Decompose phosphate rock using mixed acid of nitric acid and phosphoric acid under the experimental temperature is293-358K, the mass fraction of mixed acid nitric acid and phosphoric acid is24%-50%, phosphate rock particle is0.075～0.150mm, observe the relationship between the conversion rate of P2O5and the four factors of reaction time t, reaction temperature T,the concentration of mixed acid Co, phosphate rock particle rs. Establish the reaction kinetic model of decomposition of phosphate rock: The maximum relative error between calculated value of the reaction kinetic model and experimentally measured value less than10%, the reaction activation energy of decomposition of phosphate rock Ea=7402.0J/mol.Conduct the study of separation and purification of phosphogypsum using gas-solid-liquid three-phase fluidized bed, obtain optimum process conditions:the solid holdup of slurry is8%, superficial gas velocity is0.2m/s, opening rate of gas sparger is1.82%. The content of CaSO4·2H2O of phosphogypsum is increased from81.76%to88.50%, the removal rate of impurities of phosphogypsum is36.95%, The content of total P2O5reduced from1.50%to0.63%, wherein the content of soluble P2O5reduced from0.99%to0.13%, the removal rate is86.87%under the optimum process conditions. the content of CaSO4·2H2O of phosphogypsum is higher than85%, meet the national first grade standard level of phosphogypsum.