Analysis Of Element Migration And Variation During Carbothermal Reduction Of Phosphate Ores And Residue Features After Reaction

China has the second largest phosphate ore reserves in the world,and as a big producer and consumer of yellow phosphorus,it occupies a huge market of phosphorus products in the world.Yellow phosphorus is the essential basic raw material in many industries,its production method is mainly electric heating method,each production of1 ton of yellow phosphorus,power consumption between 13000～15000k W·h,and will produce 8～10 tons of yellow phosphorus slag,slag utilization rate is only 10%,and slag furnace with a large amount of waste heat can not be recycled.The migration and variation of calcium and silicon and the melting temperature of different systems were studied in the conventional production process of yellow phosphorus and the unconventional production process with the addition of active component Mg O.The influence of different cooling methods on the formation and phase structure of yellow phosphorus slag is discussed,which provides reference value for the follow-up treatment of slag and the realization of full resource utilization.In this paper,Factage7.1 thermodynamic calculation software was used to calculate the possible reactions in the carbothermal reduction of conventional and unconventional phosphate ores,and the phase diagrams of different systems were calculated.It is found that in the unconventional system,the possible substances are Ca Mg Si O₄、Ca Mg Si₂O₆、Ca₂Mg Si₂O₇ and Ca₃Mg Si₂O₈.According to the calculation results of phase diagram,it is found that at atmospheric pressure,the composition region of pure liquid phase in the system appears at 1400°C,indicating that the addition of Mg O can promote the melting of the system and produce liquid phase.The melting temperatures of conventional and unconventional systems were measured with a microcomputer ash fusibility tester.Under the conventional system,when Si O₂/Ca O（mass ratio）is between 0.85 and 1.45,various temperature indexes of the system increase with the increase of the addition amount of Si O₂.When Si O₂/Ca O is 0.85,various temperature indexes of the system are the lowest,and the flow temperature is 1406°C.In the unconventional system,when the fixed Si O₂/Ca O is 0.85and the Mg O/Ca O is between 0.5 and 1.5,various temperature indexes of the system increase with the increase of Mg O addition amount.When the Mg O/Ca O is 0.5,various temperature indexes of the system are the lowest,and the flow temperature is 1250°C.The addition of Mg O can reduce the flow temperature of the system by 156°C.Tubular furnace experiments were carried out on conventional and unconventional systems.The main reaction processes,the existence forms and migration processes of Ca,Si,Al and Mg elements in different systems were discussed by thermodynamic calculation and slag XRD analysis.The results indicate that the defluorination of Ca₅（PO₄）₃F occurs first in different systems,With the increase of temperature,CS,C₂S and C₃S are produced in the conventional system,while Mg₂Si O₄,Ca Mg Si O₄ and Ca Mg Si₂O₆ are produced in the unconventional system.The form of Al in different systems is Ca₂Al₂Si O₇.In the unconventional system,the introduction of Mg O changed the migration path and phase existence form of Ca and Si,resulting in the emergence of magnesium olivine and calcium magnesium olivine and other minerals in the system.These minerals are easy to eutectic with other silicate at low temperature and produce liquid phase,which is the main reason for the reduction of the melting temperature of the unconventional system.It is found that Al₂O₃,Fe₂O₃,Mg O and KF have different effects on the reduction process of calcium phosphate through the experiment of impurity influence.The Fe produced by the reduction reaction between C and Fe₂O₃ combines with the spilled P₄to form Fe₂P and remains in the slag,thus reducing the reduction rate of phosphorus;The introduction of KF will make F enter the slag,which will have a certain influence on the subsequent treatment;Mg O may cause low temperature eutectic and increase material fluidity;Al₂O₃ will enhance the acidity of the charge and increase the viscosity of the system,which will hinder the full contact between materials,thus reducing the reaction rate and yield.The kinetics of carbothermal reduction reaction of phosphate ore with different systems were analyzed.The results show that the activation energies of conventional and unconventional systems are 157.39 k J/mol and 98.42 k J/mol,the activation energy of unconventional system is obviously smaller than that of conventional system.The possible mechanism function of carbothermal reduction of phosphate ore in conventional system has been solved.The results show that the conventional carbothermal reduction of phosphate ore conforms to the shrinking spherical phase boundary reaction model.The most probable mechanism function is （?）=3（1-α）^2/3.The slag of different systems was treated by natural cooling,water quenching cooling and wind quenching cooling at different slag discharge temperatures.Combined with XRD and SEM analysis methods,it was found that under the experimental conditions,different cooling methods in the same system had no significant effect on the phase structure of slag.Wind quenching can make the slag with higher vitreous content form in the conventional system at lower slag discharge temperature,while water quenching can make the slag with higher vitreous content form in the unconventional system at lower slag discharge temperature.The microstructure of slag with different cooling methods is different.The surface of natural cooling slag will have different shape of grain crystallization,and it decreases with the increase of slag discharge temperature.The surface of water quenching slag is relatively smooth and bright,and the surface of particles may crack because of stress change.The pore structures of different sizes appear on the surface of wind quenching slag,and the particle size is small.