Reseach On Kinetics Of Vacuum Carbothermal Reduction Of Low-grade Phosphate Rock

Phosphorite is an irreplaceable strategic resource.China has rich phosphorite resources,but there are few rich ore and many poor ores.With the continuous exploitation of rich mineral resources has gradually become scarce,phosphorus industry production has to rely on the poor mineral resources with more impurities.Therefore,the rational development and use of middle and low-grade phosphate rock is undoubtedly the primary problem in the field of phosphorus industry.At present,methods for directly preparing phosphoric acid by using phosphate rock include wet-process phosphoric acid,thermal-process phosphoric acid and kiln-process phosphoric acid.However,these methods generally have technical problems such as high grade of phosphate rock used,high energy consumption of equipment,and great harm to the environment.Due to the high content of gangue in the low-grade phosphate rock,the gangue mineral and the phosphate mineral are closely co-existing,and the particle size of the mineral inlay is fine.It is difficult to deal with general physical methods,so the fire method will become the main research direction.Introducing vacuum metallurgy,the gaseous phosphorous produced after the phosphate rock was reduced and separated from the slag phase by volatilization,and then collected by condensation to obtain yellow phosphorous products.The subject carried out kinetic analysis during the research on the preparation of yellow phosphorus by vacuum carbothermal reduction of low-grade phosphate rock.The results show that:The reduction reaction process of low-grade phosphate was mainly carried out along the following processes:Ca₅?PO₄?₃F?Ca₃?PO₄?₂?CaO and Ca₅?PO₄?₃F?CaO+Ca F₂ reduction process.The residual SiO₂ in the sample first reacted with Ca₅?PO₄?₃F to form intermediate product Ca₃?PO₄?₂ in the early stage of reduction?1080??,and the second stage Ca₃?PO₄?₂ was formed by coke reduction CaO,and the last stage?1300??a large number of existing Ca₅?PO₄?₃F was directly reduced by coke to form CaO and Ca F₂.When the reduction temperature reached about1300?,the diffraction peaks of SiO₂ and Ca₃?PO₄?₂ phases disappeared and CaO and Ca F₂ phase characteristic peaks appeared..In the isothermal kinetics,the"model coordination method"was used for research:the phosphorus in the low-grade phosphate rock was kept at 1200?-1300?for the period of 0-30 min.The reduction reaction was regulated by the surface chemical reaction,and the dynamical equation was1-?1-a?^1/3=ktand the surface activation energy of the reaction was 339.49 k J/mol;at the later time of holding at 1200?-1250?,ie 30-90 min,the reduction reaction was controlled by external diffusion,and the dynamical equation.It was[1-?1-a?^1/3]²=ktand the apparent activation energy of the reaction was 604.77 k J/mol.The low-grade phosphate rock as a whole was kept at1200?-1350?during the early period of 0-30min,the reduction reaction was regulated by internal diffusion,the dynamical equation was1-2a/3-1?-a?^2/3=kt and the surface activation energy of the reaction was 265.9 k J/mol;at the later period of holding at 1200?-1350?,that was 30-90min,the reduction reaction was affected by the interface chemical reaction equation regulated,the dynamical equation was1-?1-a?^1/3=ktthe appearance activation energy of the reaction was 124.67 k J/mol.In the non-isokinetics,the two ways of?atava-?esták method and Coats-Redfern method were used to verify each other,and the integral expression of the reduction mechanism function of phosphorus in the reduction reaction of low-grade phosphate rock wasG?a?=[?1-a?^-1/3-1]²,the differential expression was f?a?=3/2?1-a?^4/3[?1-a?^-1/3-1]^-1,which was three-dimensional Controlled by the Zhuralev-Lesokin-Trounshtein model of diffusion,the appearance activation energy of the reduction was 430.09 k J/mol.The integral expression of the overall reduction mechanism function in the reduction reaction of low-grade phosphate rock was G?a?=1-?1-a?⁴,the differential of the mechanism function wasf?a?=1/4?1-a?^-3,which was controlled by the shrinking core model,and the appearance activation power of the reduction process was 77.58k J/mol.