Comprehensive use of products generated during acid leaching of basic oxygen furnace sludge

Abstract

A novelty process based on acid leaching basic oxygen furnace sludge by means of medium of 2,5M H2SO4 and 1M HCl was proposed. The new medium used in the study leaches franklinite ZnFe2O4 present in the tested sludge, which is hardly soluble in weak sulphuric acid solutions and well soluble in HCl solutions. This allows for 100% zinc extraction from the basic oxygen furnace sludge. The component of the leaching medium in the form of a sulphuric acid solution transforms the calcium compounds contained in the basic oxygen furnace sludge into insoluble calcium sulphate. The study examined the effect of solid to liquid ratio S/L (g/mL), temperature, time and rotational speed of stirrer on zinc and iron extraction from the sludge. Optimal leaching conditions were: t = 120 min, T = 60 °C, n = 500 min−1, S/L: 0.2. The leached solid filtration product obtained after leaching, dried and magnetically processed is separated into pure iron-bearing concentrate, which contains 77% Fe3O4 and 23% Fe2O3 and calcium sulphate waste. Their composition is confirmed by the X-ray diffraction analysis. The use of ethyl alcohol to precipitate sulphate iron compounds is a new alternative to recover and reuse the precipitant. The pure iron sulphate compounds with different hydration are obtained, which is confirmed by the X-ray diffraction analysis. The utilitarian aim of the study was to specify technological guidelines of the presented process and its material balance. Acid leaching of basic oxygen furnace sludge helps solve the problem of lack of selectivity in acid leaching of zinc and iron. This suggests the possibility of comprehensive use of the obtained products.