Performance and Mechanism Study on Co-reduction of Two Industrial Solid Wastes for Iron Recovering

An innovative technique that provides a new method to use red mud (RM) and phosphogypsum (PG) together has been developed. In the proposed route, phosphogypsum was added as an additive in the red mud reductive roasting process, which influenced the iron-recovering behavior from the roasted briquette through magnetic separation. The iron-recovering results in the absence and presence of phosphogypsum were comparably investigated. The advantage of phosphogypsum for iron recovery from red mud was verified. An iron concentrate containing 75.27% total iron content (TFe) with recovery of 89.88% was obtained with the addition of 6% phosphogypsum, which was upgraded by 6.20% with only 1.19% loss of iron when compared with that in the absence of phosphogypsum. Thermodynamic analysis indicated the theoretical possibility for the decomposition of iron-hosting Al- and Si-complexes with the help of phosphogypsum, which would otherwise be unfavorable to the magnetic separation of iron from the roasted briquette. Phase transformation analyses together with microstructure examination practically proved that phosphogypsum enhanced the iron separation by releasing iron from iron-bearing Al- and Si-complex minerals and promoting the reduction process, and also facilitating the growth and merging of iron grains due to the formation of low-melting point Fe–FeS eutectic substance. This research primarily attempts to achieve high value-added utilization of industrial wastes, control them mutually, and find out how it works.