Recovery of valuable elements from pyrite pyrolysis slag using magnetic separation-flotation technique

Abstract

Pyrite concentrate is a common by-product obtained after Pb and Zn sulfide minerals flotation. Pyrolysis at 600 ∼ 700 °C in an inert atmosphere is an effective way to comprehensively utilize pyrite concentrate. However, the content of Pb and Zn in pyrolysis slag is relatively high, which is not conducive to subsequent utilization. The pyrrhotite in the pyrolysis slag is magnetic, and lead and zinc mainly exist in the form of sulfide, which has good floatability. This inspired us to purify pyrolysis slag by magnetic separation and flotation method. The results show that when the grinding particle size of −0.040 mm accounts for 80.1 %, the content of Pb and Zn in pyrolysis slag decreased to 0.32 % and 0.17 %, respectively, by only using the magnetic separation method. Then the combined method of magnetic separation and flotation is used. Lead and zinc can be reduced to 0.14 % and 0.10 %, while the iron grade increased to 57.32 %. Then pyrrhotite concentrate is oxidized and roasted at 900 °C to obtain a product that meets the first grade of pyrite cinder. At the same time, the phase, coexistence relationship, and dissociation degree of iron, lead, and zinc minerals in the samples were characterized by MLA and chemical methods to analyze the transformation mechanism of pyrolysis slag in the process of magnetic separation and flotation. The results of this study provide an economical and green process for the comprehensive utilization of pyrite concentrate.