Study on the factors affecting the deep reduction of coal gangue containing high contents of iron and sulfur

Although coal gangue (CG) contains various valuable metal elements, it has not been utilized efficiently. It is of great significance for the sustainable development of the coal industry to improve the added value of comprehensive CG utilization by adopting a deep reduction method. In this study, the effects of a reducing agent and desulfurizer on the properties of the CG reduction products were studied via deep reduction experiments. The results show that CG exhibits a self-reduction effect, which can reduce the amount of external reductant. In addition to the lignite coal (LC) reducing agent, the iron grade reaches its maximum when the other reducing agents are added at a ratio of 10%. Due to the high content of iron minerals in CG, the H-2 produced by the individual pyrolysis of CG undergoes a reduction reaction with iron minerals. The addition of CaCO3 improves the reduction condition of iron minerals and promoted their direct reduction. However, an excessive amount of CaCO3 leads to the failure of iron particles to aggregate into large particles or iron-linked crystals, which reduces the recovery of iron. Prolonging the reduction time promotes the migration and diffusion of the iron phase, which is conducive to the aggregation and growth of iron particles. The finer the particle size of the raw material, the worse the permeability of the material layer which results in the incomplete reaction of the sulfur-containing minerals contained in the particles and lead to a higher the S content in the direct-reduction iron obtained after magnetic separation.

Automated summary

Efficient utilization of coal gangue (CG) is essential for the sustainable development of the coal industry. Through deep reduction experiments, it was found that CG has a self-reduction effect and the addition of other reducing agents can improve the iron grade. Moreover, the addition of CaCO3 can promote the reduction condition of iron minerals.