TECHNOLOGIES FOR EXTRACTING IRON FROM PYRITE CINDER: CURRENT STATE AND PROSPECTS

Abstract

Pyrite cinders are large – tonnage waste from sulfuric acid production, the annual volume of which in the world reaches millions of tons. These wastes have an iron content of up to 50–63% and are therefore valuable secondary raw materials. However, their complex composition, including impurities of Cu, Zn, Pb, Co, and precious metals, as well as fine mineral inclusions, makes them difficult to use directly in metallurgy. The bulk of the iron in the freshly obtained cinder is represented by hematite Fe₂O₃. However, in landfilled (stale) cinder, which has been exposed to atmospheric influences for a long time, some of the iron passes into hydroxide forms, and the content of water-soluble compounds can reach up to 10–18%. This article presents a systematic overview of modern approaches to extraction of iron from pyrite cinders, including hydrometallurgical (acid, ammonia, bacterial leaching), pyrometallurgical (reducing melting to obtain matte) and combined methods (reducing firing – magnetic separation – leaching). Special attention is paid to the method of mineral phase reconstruction with controlled reduction firing, which makes it possible to achieve the extraction of iron into a concentrate of up to 98.9% with a Fe content of 63%. It is shown that the most promising are combined schemes that involve the complex extraction of non-ferrous and precious metals, as well as the production of an iron concentrate suitable for metallurgical processing. The gold-silver component has been potential to ensure profitability, even with a low Fe content, so schemes combining the extraction of precious metals (for example, cyanidation or thiosulfate leaching after firing) and the production of iron concentrate look the most attractive.