A multi-physical field coupling modeling incorporated the non-thermal effect: carbothermic reduction of ZnFe2O4 by using microwave heating

Abstract

Abstract

Microwave heating has recently gained significant attention and is increasingly applied in the pyrometallurgical recovery of Zn (ZnFe2O4) from electric arc furnace dust (EAFD). Under microwave irradiation, a portion of the microwave energy is stored within molecules, enhancing the carbothermic reduction (non-thermal effect). However, quantifying the influence of the non-thermal effect in experiments remains challenging due to the invisibility of microwaves. For advancing the scalability of microwave-assisted EAFD processing, the present study focuses on ZnFe2O4 and develops a multiphysics model incorporating the non-thermal effect to elucidate the enhancement mechanism of microwaves on the reduction process. The main conclusions indicate that increasing microwave input power and graphite addition effectively enhances both the heating and reaction efficiency of the ZnFe2O4-graphite mixture. Higher power input improves efficiency while mitigating thermal runaway risks more effectively than increasing graphite addition. However, the uneven distribution of microwaves leads to localized thermal effects, impacting heating uniformity and overall reaction consistency within the mixture. Furthermore, non-isothermal kinetic analysis reveals that microwave irradiation enhances the carbothermic reduction of ZnFe2O4 through both thermal and non-thermal effects. With a stoichiometric coefficient of 1.2 for graphite addition, localized thermal and non-thermal effects reduce the apparent activation energy by 34.3 % and 25.8 %, respectively.