Study On The Leaching Law Of Phosphorus And Metal Elements In The Process Of Phosphoric Acid Decomposition Of Phosphate Rock

As an important strategic resource,phosphate rock is mainly used to produce phosphoric acid and phosphate fertilizer.my country's phosphate rock resources are rich,few and poor,with high impurity content,often accompanied by a large amount of metal elements such as Fe,Al,Mg,and toxic trace heavy metal elements such as Pb and As.When the wet-process phosphoric acid process produces phosphoric acid and phosphate fertilizer,these metal elements will gradually decompose into the phosphoric acid solution and phosphate fertilizer products with the gradual decomposition of the phosphate rock,which will seriously affect the process production and product quality.Phosphoric acid decomposition of phosphate rock is an important reaction process in the production of wet-process phosphoric acid.This article explores the leaching law of P and metal elements Fe,Al,Mg,Pb,As in the process of phosphoric acid decomposition of phosphate rock,which is in the process of wet-process phosphoric acid.The efficient utilization of P and the effective prevention of metallic elements Fe,Al,Mg,Pb and As from entering the solution provide theoretical guidance.(1)The influence of the main acidolysis process parameters in the process of phosphoric acid decomposing phosphate rock on the leaching law of P and metal elements Fe,Al,Mg,Pb,As in the phosphate rock was explored.The results show that the leaching rate of P and metal elements Fe,Al,Mg in phosphate rock increases with the increase of phosphoric acid concentration,reaction temperature,reaction time and liquid-solid ratio,and the stirring speed is not obvious;the leaching rate of metal element Pb increases with the increase of phosphoric acid the concentration,reaction temperature and liquid-to-solid ratio increase with the increase of stirring speed and reaction time.The leaching rate of metal element As increases first and then decreases with the increase of reaction temperature,and slightly decreases with the increase of reaction time.The concentration of phosphoric acid,stirring speed and liquid-solid ratio have no obvious influence on the leaching of As.Under the conditions of controlling phosphoric acid concentration of 30%P₂O₅,reaction temperature 80?,stirring speed 300r/min,reaction time 150min,liquid-solid ratio10:1,the leaching rate of P is 98.65%,the leaching rates of metal elements Fe,Al,Mg,Pb and As were 68.56%,48.54%,95.84%,32.85%and 84.62%,respectively.The optimization analysis of response surface experiments shows that the significance of the influence of various acid hydrolysis process parameters on the P leaching rate is:phosphoric acid concentration>liquid-solid ratio>reaction temperature.The best experimental conditions are phosphoric acid concentration 30%P₂O₅,reaction time150min,liquid The solid ratio is 10:1,and the average P leaching rate under this condition is 98.62%,which is very close to the predicted value,indicating that the model is credible and can be used for experimental prediction and optimization.(2)Through the thermodynamic and Eh-p H diagram analysis of the possible chemical reactions of the metal elements Fe,Al,Mg,Pb,As in the process of decomposing the phosphate rock with phosphoric acid,the results show that the Fe ions in the solution are mainly derived from the phosphoric acid in the phosphate rock.For limonite decomposed by the first hydrogen ion,the Al ion in the solution is mainly derived from the kaolin that is decomposed by the first hydrogen phosphate ion in the phosphate rock or the free hydrogen ion in the solution.At the same time,there may be a small amount of Fe and Al ions in the solution.Fe PO₄,Al As O₄,etc.precipitate out;while the metal element Mg in the phosphate rock is almost completely decomposed into the solution by the first hydrogen ion of phosphoric acid or the free hydrogen ion in the solution,and exists stably in the form of Mg²⁺;The metal element Pb in the phosphate rock mainly exists in the form of residue,and the Pb²⁺in the solution may react with PO₄^3-to form Pb₃(PO₄)₂ and solidify,so the leaching rate of lead is low;the metal element As in the phosphate rock It is easily released by the oxidation of Fe³⁺and O₂ in the solution,and exists in the solution in the form of H₃As O₄,H₃As O₃ and HAs O₃^-,and part of H₃As O₄ may react with metal ions such as Al to form arsenate precipitation,which affects the leaching rate of As Calculation.(3)The effect of the main acidolysis process parameters on the P leaching rate in the phosphate rock during the process of the phosphorus-sulfur mixed acid decomposing phosphate rock was explored,and orthogonal experiment was used to optimize the results.The results show that within the scope of investigation,the order of the influence of each factor on the P leaching rate It is:phosphoric acid concentration>liquid-solid ratio>liquid SO₃ concentration>reaction time.Orthogonal experimental design obtained better acid hydrolysis conditions with a liquid-solid ratio of 3:1,a reaction time of 5h,a liquid SO₃ concentration of 30?35g/L,a phosphoric acid concentration of 24%P₂O₅,and a reaction temperature of 80?.Under these conditions,the phosphate rock The leaching rate of medium P is above98%.And through the thermodynamics and Eh-p H diagram analysis of the possible chemical reaction of SO₄^2-in the process of decomposing phosphate rock with phosphate-sulfur mixed acid,the results show that the metal elements Fe,Al,Mg are The migration distribution of Pb,As may be mainly affected by the concentration of activated hydrogen ions and phosphoric acid in the solution,but may not have a direct influence on the concentration of sulfate ions in the solution.