Research On The Technology Of Extracting Phosphorus From Low-grade Phosphate Ores And Synthesizing Hydrate FePO₄

Abstract:Now facing the global resources and energy crisis,the development of mineral resources and the synthesis of new energy materials become a hot research field. In this paper, the relatively in-depth research was done about the extraction and purification of phosphorus from low-grade phosphate ores as a source of phosphorus, and the preparation of LiFePO4using the obtained phosphorus was also investigated.The technology of synthesizing LiFePO4from low-grade phosphate ores was proposed. The work is described as follows:Several methods including hydrochloric acid method, sulfuric acid method, NaCl improving sulfuric acid method, hydrochloric acid improving sulfuric acid method, the additive A improving sulfuric acid method, the additive A with hydrochloric acid improving sulfuric acid method were used to extract P from low-grade phosphate ores. And the additive A improving sulfuric acid method was chose to extract P and Fe from low-grde phosphate ores. The better conditionis as follows: L:S(ratio of liquid to solid)=5:1,T=70℃, t=90min, r=650r/min, c(the additive A)=100mgL-1and Cl:Ca(Molar ratio)=0.15:1.00in a closed system, and the leaching efficiency of target elements P and Fe is86.21%and25.43%,respectively; the leaching ratio of the impurity elements Ca, Mg and Al is6.09%,85.61%and7.01%, respectively.FI-TR,XRD,SEM,EDS were employed to study the leaching residues obtained from the wet-process decomposition of low-grade phosphate ores in diverse technology and the results indicates that the key factor for the increased leaching ratio of phosphorus in the improving sulfuric acid methods was the relative contents and crystallization characteristics of calcium salts in the solidified layer which were changed by the additives involved and improved the permeability of the solidified layer of calcium salts.The research on the leaching residues of poor phosphate ores partly explained the wet-process decomposition mechanism of low-grade phosphate ores.The complexing and masking-precipitation technology (CM-P)was proposed to synthesize hydrate FePO4from the crude phosphoric acid. Under the optimized conditions of CP=402.5mgL-1,CFe2(SO4)3=777.00mgL-1,CEdetate disodium=10.00mgL-l,CH2C2O4·2H2O=2.00mgL-1,pH=2.00,t=30min,T=50℃,r=867r/min, the Fe:P of the obtained hydrate FePO4is1.019:1.000and the impurity content of Ca、Mg、Al can both achieve the demands for battery grade, and the phosphorus utilization ratio was75.94%.LiOH·H2O was used as a lithium source, C6H12O6·H2O as a carbon source, the synthetic hydrate FePO4as a precursor, the cathode material LiFePO4for lithium-ion batteries was synthesized by the carbon thermal reduction. SEM and XRD results show the LiFePO4was a well crystallized, single olivine-type phase with no significant hetero-phase peaks, the mini-impurity elements of LiFePO4are all fully incorporated into the LiFePO4lattice; the LiFePO4particle diameter of primary particles was nanoscale.The electrochemical test results show that the synthetic LiFePO4exhibits the first discharge capacity of145.1mAh·g-1,138.3mAh·g-1,133.4mAh·g-1and120.2mAh·g-1at0.1C,0.2C,0.5C and1.0C, respectively, and the cycle performance is also excellent.Comparing to the industrial LiFePO4synthesis technology, the technology has the advantages of low cost, short technics flow, a good applicability of phosphate ores and the utilization rate of low-grade phosphate ores resources was61.83%in the whole process.