An Innovative Approach to Separate Iron Oxide Concentrate from High-sulfur and Low-grade Pyrite Cinders

High-sulfur and low-grade pyritc cinders are the waste products of sulfuric acid manufacturing plants. Many valuable components, such as iron oxide, are contained in pyrite cinders and difficult to be separated and purified just via the high temperature roasting process. Considering this, an innovative method including water-washing, aqua regia leaching, hydrothermal alkali activation and acid-washing was developed. And the effects of different parameters on recovery efficiency of iron oxide were systematically investigated. The optimum parameters were proposed as follows: water rinse-leaching at room temperature for 5 — 20 min, and melting at 160 °C for 2. Oh with NaOH (concentration of 30 mass%), followed by leaching with aqua regia solution (3. 0 vol. %) for 1. 0 h. After the treatment, the content of iron oxides increased from 54. 3 to 96. 0 mass% with the recovery rate exceeding 85%. Meanwhile, calcium sulphate was recovered as the high value-added products by alkali extraction liquid. Furthermore, the phase transformation and microstructure of the samples in the process were studied by physicochemical methods to reveal the separation mechanisms of different components in the pyrite cinders.