Recycling sulfur and iron resources in the waste ferrous sulfate

Abstract

Many methods have been used to treat ferrous sulfate, but the large volume of waste ferrous sulfate produced has become a bottleneck for the sustainable development of the titanium dioxide industry in China. However, a newly developed process can utilize the massive volumes of waste, thereby facilitating the sulfur cycle and the recycling of iron resources, where the ferric sulfate obtained from ferrous sulfate by oxidation is decomposed reductively by pyrite, and the decomposition products are magnetite and sulfur dioxide. The reductive decomposition of ferric sulfate by pyrite is a key step in this process. In this study, thermodynamic analysis, tubular reactor experiments, thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy were used to analyze the mechanism and to determine the kinetic model of the decomposition reaction in a nitrogen atmosphere. The results of the reaction mechanism analysis showed that the process involved in the generation of Fe3O4 is a two-step reaction, i.e., pyrite reacts directly with ferric sulfate to produce Fe2O3, before Fe2O3 reacts with pyrite to generate Fe3O4. Accordingly, the results of the kinetic analysis indicated that the first process follows an n-th order model with autocatalysis (C n), n = 1.344; and the second process follows the Avrami–Erofe’ev nuclei growth model (A n), n = 0.520.