Analytical Study on Non-isothermal Kinetics of Phosphorus Extraction by Silica Thermal Process

Objective To develop a new process for extracting yellow phosphorus from phosphate rock powder by silicon thermal reduction and study its non-isothermal kinetic behavior, Method the reduction rate, residual phosphorus content, mineral phase structure and morphology were analyzed by ICP-OES, XRD and SEM-EDS. The activation energy (Eα) and mechanism function G(α) were calculated by Coats-Redfern method and statava-stestak method. Result Silicothermic reaction of phosphate ore started at about 1 000 ℃. The reduction process can be divided into two stages: the initial stage involved a small portion of Ca₅(PO₄)₃F in the ore powder reacting with SiO₂ to form the intermediate product Ca₃(PO₄)₂, which subsequently reacted with silicon, whereas the latter stage comprised the remaining Ca₅(PO₄)₃F reacting directly with silicon. A large number of pores were formed due to the escape of the produced phosphorous gas, and the phase was identified as calcium silicate. Conclusion The phosphorus extraction reaction by the silicon thermal method is controlled by the Avrami-Erofeev nucleation and growth model. Increasing the heating rate can reduce the apparent activation energy. The reduction process occurs significantly above 1 000 ℃ and undergoes two reaction stages.