Basic Research On Preparation Of Lithium Iron Phosphate Precursor From Titanium Dioxide Waste Liquid

With the rapid development of China’s economy,China’s titanium dioxide industry has achieved great development,but China’s production technology is still relatively backward.Most of it uses the sulfuric acid method with high material consumption and low economic benefits.If it is discharged without treatment,it will have a serious impact on the ecological environment.How to solve the waste acid problem has always been one of the problems that plagued titanium dioxide production enterprises and environmental protection departments.To comprehensively treat the titanium dioxide waste acid,a sustainable development method should be adopted to treat the waste acid to improve the utilization rate of resources.At the same time that the waste acid reaches the nationally required emission standard,the valuable metals in the titanium white waste acid are comprehensively utilized,thereby promoting the development of the sulfuric acid method titanium white industry.Therefore,this article takes titanium white waste acid as the research object,and mainly studies the comprehensive recycling of iron element in titanium white waste acid.Firstly,the E-pH diagrams of Fe-S-P-H2O system,V-S-P-H2O system,Ca-S-P-H2O system,Mn-S-P-H2O system,Mg-S-P-H2O system and AI-S-P-H2O system were calculated and drawn.The results of thermodynamic research show that in this system,the iron in the solution has a stable area of FePO4 at pH<7;the aluminum in the solution also has a stable area of AlPO4;the magnesium in the solution exists as Mg2+at low pH and low potential.When the pH>4.5,magnesium in the solution begins to exist as Mg3(PO4)2;when the pH<1.5,the calcium in the solution will exist as Ca2+ions,and when the pH<1.5,the pH will be CaHPO4 exists as Ca3(PO4)2 when pH>3.8;Manganese in solution will exist as Mn2+ at low pH,and as Mn3(PO4)2 when pH>2.2 it exists stably;in the divalent iron system,the vanadium in the solution mainly exists stably in the form of VO2+,and in the trivalent iron system,there is a stable existence region of(VO2)3PO4.Next,a graph plotting the concentration dominant regions of each orthophosphate and hydroxide is plotted.The results show that in the ferric solution system,the order of precipitation of orthophosphate is from easy to difficult:FePO4,AlPO4,Mn3(PO4)2,Ca3(PO4)2,Mg3(PO4)2;The order of precipitation is from easy to difficult:Fe(OH)3,Al(OH)3,Mn(OH)2,Mg(OH)2,Ca(OH)2.In the ferrous solution system,we can get the order of precipitation of orthophosphate from easy to difficult:AlPO4,Mg3(PO4)2,Ca3(PO4)2,Mn3(PO4)2,Fe3(PO4)2;The order of precipitation of hydroxide is from easy to difficult:Al(OH)3,Fe(OH)2,Mn(OH)2,Mg(OH)2,Ca(OH)2.On the basis of thermodynamics,the optimal conditions for the preparation of iron phosphate by one oxidation selective precipitation were studied from the single factor of reaction temperature,solution pH,and molar ratio of P/Fe,and based on this,the microstructure of the product was investigated by polyethylene glycol and CTAB The effect of morphology and particle size distribution,and the effect of firing temperature on the structure of the product.The results show that the best conditions for preparing FePO4 by one-step precipitation are T reaction=60℃,pH=2.5,P/Fe=1.1;roasting at 700℃ for 8 h can obtain hexagonal FePO4;and polyethylene The addition of diol or CTAB can greatly improve the dispersibility of the sample,the particle size of the sample is smaller,and the surface activity is higher.In the process of one-step precipitation to prepare FePO4,it was found that the purity of the sample prepared under the best conditions can only reach 99.13%,so the research of twostep precipitation to prepare high-purity FePO4 was started.Firstly,the effect of phosphoric acid addition method on the purity of the product was studied.After several experiments,it was shown that the purity of FePO4 prepared by adding phosphoric acid once was higher than that of phosphoric acid added twice.Then during the pre-precipitation process,the effects of three single factors,reaction temperature,pH of the solution system,and molar ratio of P/Mn+,on the impurity removal of the pre-precipitation were studied.The experimental results show that when the experimental conditions are T1=75℃,pH1=4.5,and P/Mn+=1.1,the effect of preprecipitation removal is the best.Then,under the experimental conditions of reaction temperature T2=60℃,pH2=2.5,A high-purity FePO4·2H2O with a purity of 99.90%was prepared.In this sample,w(Fe)=28.24%,w(P)=17.52%,Fe/P=0.89,w(H2O)=19.38%,which is close to the technical index of battery grade iron phosphate.