Physicochemical study of the sustainable preparation of nano-Fe2O3 from ferrous sulfate with coke

Abstract

A route to produce nano-Fe2O3 by reduction of ferrous sulfate with coke to was proposed to improve the utilization of waste residues from TiO2 production. The effects of thermodynamic factors on the reaction were analyzed via Factsage 6.0 software, which showed that SO2 and O2 atmospheres have a significant inhibition effect on the decomposition of ferrous sulfate. Then, the optimal reaction condition (heating at 600 °C for 40 min with ferrous sulfate to coke ratio of 4:8) was obtained by single-factor and orthogonal experiments. Under the optimal reaction condition, the average desulfurization rate was found to reach 99.92%. Moreover, scanning electron microscopy images showed that the products were nanopowders with a porous structure and particle sizes between 40 and 70 nm. Finally, the non-isothermal decomposition kinetic parameters and mechanism of the reaction were determined. Two reaction stages, which were named “random nucleation and then growth” and “symmetric cylindrical diffusion (3D),” were determined. Using the Coats–Redfern, Flynn–Wall Ozawa (FWO), and Kissinger–Akahira–Sunose (KAS) methods, the apparent activation energy and pre-factor of the first reaction stage were determined to be 291.10 kJ mol−1 and 1.41 × 1016 s−1, while those of the second reaction stage were determined to be 285.94 kJ mol−1 and 3.27 × 1014 s−1. The most probable mechanism functions of the two stages were also determined. This process can make use of ferrous sulfate not only highly valuable, but also to improve the recycling of sulfur and iron resources after the production of white titanium.