Reactive synthesis of ferrous sulfide using elemental iron/pyrite ore: Kinetics study and application

The transformation of pyrite into ferrous sulfide (FeS) has a substantial significance in gold extraction from gold-bearing pyrite. This work proposed to treat pyrite by reactive diffusion with added elemental Fe for generating FeS. The diffusion kinetics and transformation mechanism during reactive synthesis were investigated via constructing Fe-FeS2 powder diffusion couples. The results indicated that the formation of the pyrrhotite phase (Fe1-xS, x = 0-0.5) firstly occurred at the interface of the diffusion couple. The interdiffusion coefficient ranged from 10(-16) m(2) s(-1) similar to 10(-12) m(2) s(-1) at 723-873 K and the apparent activation energy of the product layer was about 147.59 kJ mol(-1). XRD and HRTEM results demonstrated that with the increase of sintering temperature, the diffusion of Fe played the pivotal role in the phase transformation of Fe1-xS to FeS. Furthermore, the conversion rate of FeS can reach 95.82 % by optimizing sintering process. The synthesized FeS can be readily dissolved by sulfuric acid and the mass ratio of leaching residue is only 2.3 %, indicating that the precious metals in pyrite such as gold can be concentrated by nearly 43.5 times. This proposed method with the green economy characteristic would be a promising candidate for the pretreatment of gold-bearing pyrite.