Synthesis Of Battery-grade Iron Phosphate By Homogeneous Precipitation From Titanium White Waste By-Product Ferrous Sulfate

Due to the advantages of excellent electrical performance,good cycling performance,safety,environmental friendliness,cheap and easy access to raw materials,lithium iron phosphate in 5G backup power supply,energy storage,electric light vehicle market demand surge.On the other hand,titanium white waste by-product ferrous sulfate increases at the rate of 10 million tons per year,which will seriously pollute the environment if not properly solved.The existing technology of preparing battery-grade iron phosphate from by-product ferrous sulfate has many defects,such as complex impurity removal process,large iron loss and low tap density of iron phosphate product.In view of the above problems,this paper proposes a new synthesis process of battery grade iron phosphate,which prioritizes precipitation removal of high-value metals and selectively precipitates Fe PO₄·2H₂O under the coexistence of bivalent metals.That is,in the purification stage of titanium white waste by-product ferrous sulfate,only the high-value metal ions Al³⁺and Ti⁴⁺which are easy to be removed by preferential precipitation are removed.In the synthesis stage of Fe PO₄·2H₂O,Fe SO₄ solution containing Divalent metal ions such as Mg²⁺/Mn²⁺/Ca²⁺was used as iron source,and the purity of battery-grade Fe PO₄ was prepared by selective deposition by optimizing the synthesis conditions.The main research contents and results are as follows:（1）To explore the factors influencing the tap density of Fe PO₄ in high acid environment and master the regulation technology of homogeneous precipitation for the preparation of Fe PO₄.Using pure Fe SO₄·7H₂O and NH₄H₂PO₄ as raw materials,the effects of p H value,reaction temperature,reaction time,P/Fe ratio of solid to liquid,dosage of oxidizer and seed addition amount on the properties of Fe PO₄ products were studied,and the control methods of particle size,tap density,P/Fe ratio and other physical and chemical properties were also studied.The results show that initial Concentration of Fe^2﹢is 1.5 mol/L,dosage of NH₄H₂PO₄ is 1.8 mol/L,adjust p H to 0.6,then slowly add 27.9 m L H₂O₂,stir for 30 min,then transfer into oil bath.Maximum tap density of Fe PO₄·2H₂O was 1.414 g/cm³,and particle D50 was 37μm,Morphology of Fe PO₄·2H₂O was a spheroid structure with a porous surface formed by stacking of flake monomers,and crystal structure wasα-monoclinic,corresponding to the standard card PDF#33-0666.（2）The purification method of titanium white waste by-product ferrous sulfate and the effect of impurity coexistence on the purity of Fe PO₄·2H₂O were studied by using ferrous sulfate solution from titanium dioxide byproduct containing various impurities as iron source.Based on the thermodynamic analysis of metal ion hydrolytic precipitation and phosphate precipitation,The feasibility of selective precipitation of Fe PO₄·2H₂O in the presence of bivalent metals is verified theoretically and verified by experiment.The experimental results of Al³⁺and Ti⁴⁺removal by precipitation method showed that Ti⁴⁺/Al³⁺can be removed and iron can be recovered efficiently under the conditions of Fe²⁺concentration 90 g/L,p H 4.5-5.0 and stirring temperature 45℃for 1.5 h.The experimental results of the preparation of Fe PO₄·2H₂O with Fe SO₄solution containing divalent metal ions such as Mg²⁺/Mn²⁺/Ca²⁺as iron source（purified solution of titanium white waste by-product ferrous sulfate）,concentration of Fe²⁺is 83.88 g/L,initial concentration of NH₄H₂PO₄ is 1.8 mol/L,dosage of H₂O₂ is 27.9 m L,and p H is adjusted to 1.0,stirred reaction at 95℃was 8.0 h.The impurities in the product met the standard of Battery-grade Fe PO₄ HG/T T4701-2014[S],the spherical particles of the product were better,and tap density was about1.01 g/cm³.（3）In order to have a clearer understanding of the preparation process of Fe PO₄·2H₂O in high temperature and high acid environment,interval sampling method was adopted.Combined with XRD,SEM,elemental analysis,crystal water content and functional group changes and other characterization,the growth mechanism and growth mechanism of Fe PO₄·2H₂O were clarified.The whole process of the reaction is mainly spiral growth-surface nucleation mixed growth mechanism.High-valence metal ions Al³⁺and Ti⁴⁺were removed by precipitation method,and tap density spherical Fe PO₄·2H₂O was prepared by using Fe SO₄ solution containing Mg²⁺/Mn²⁺/Ca²⁺and other divalent metal ions as iron source.It not only realizes the high-value resource utilization of solid waste,but also effectively improves the economic benefits,and meets the development needs of lithium battery industry.It is a feasible technical scheme for effective utilization of titanium white waste by-product ferrous sulfate.There are 68 figures,18 tables and 157 references in this dissertation.