Magnetizing roasted copper tailings to recover iron concentrate

Copper mine tailings, as a type of non-ferrous metal tailings in industrial solid waste, have attracted more and more attention for comprehensive disposal and resource utilization. It is estimated that for every ton of copper produced, approximately 400 tons of tailings are produced.

Copper tailings contain pyrrhotite (Fe (1– x ) S, where 0≤x<0.223), which has three homogeneous multicolor variants of iron sulfide minerals and is prone to produce acidic mine wastewater due to oxidation. In order to effectively prevent the environmental risks of copper mine tailings and recycle the sulfur resources in copper mine tailings, the sulfur released in the form of SO2 can be collected and oxidized and roasted to produce sulfuric acid. At the same time, iron units are enriched in the roasting slag and exist in the form of γ-Fe 2 O 3.

Maghemite is a defective spinel structure, Fe 3+ occupies the A tetrahedral position and the B tetrahedral position, and has a certain number of vacancies. In addition, γ-Fe 2 O 3 is widely used as a magnetic material with the advantages of stability, non-toxicity, low consumption, etc., and has broad application prospects. Therefore, recycling γ-Fe2O3 in roasted copper mine tailings is of great significance for saving iron resources, making copper mine tailings more sustainable and respecting the ecological environment.

It is known that both iron concentrate (Fe3O4) and sponge iron (Fe) have certain magnetism; therefore, magnetic separation is an effective method to recover iron, where Fe3O4 and Fe are used for ironmaking and steelmaking respectively. Not all certain phases of iron in tailings and solid waste are Fe3O4 or Fe. It requires magnetization roasting and direct reduction to transform non-magnetic iron into magnetic iron. Utilizing the magnetism of γ-Fe 2O3 will greatly promote the recovery of iron in roasting slag.

Through experiments, it was determined that the optimal roasting magnetization separation conditions are: roasting at 1200°C for 30 minutes, air flow 5L min -1, and the ratio of SDS to roasting slag (120 μm) is 1:25. Magnetic field strength 220 mT. Under these conditions, the yield is 67.21%, the γ-Fe 2 O 3 content in the roasting slag is 66.86%, the sulfur content is 0.08%, and the Ms of the magnetic concentrate is 12.94emu/g. The magnetization roasting wet magnetic separation technology to recover γ-Fe 2 O 3 can be extended to other iron-containing tailings or waste materials, including iron ore tailings, pyrite-containing iron ore tailings, pyrrhotite-containing tailings, etc.