Iron recovery from the coarse fraction of basic oxygen furnace sludge. Part I : optimization of acid leaching conditions.

Abstract

In this study, a new reuse process of the coarse fraction of basic oxygen furnace (BOF) sludge based on iron recovery by the ferrous sulfate production was proposed. This study was based on three main steps: (i) characterization of the steel waste, (ii) evaluation and optimization of the recycling process, and (iii) characterization of ferrous sulfate produced. Acid leaching was used to solubilize the iron for obtaining ferrous sulfate heptahydrate. The ferrous sulfate crystallization was performed by adding anhydrous ethanol (EtOH). A multivariate optimization for iron leaching and ferrous sulfate precipitation in the same solution was employed. This optimization consisted of screening steps using a full factorial design followed by optimization. The coarse fraction of BOF sludge was predominantly composed of iron in metallic form (82.5%, dry weight). The sulfuric acid concentration and leaching time had significant effects on Fe(II) solubilization. The desirability function predicted the following optimized conditions: 20% (v/v) sulfuric acid solution, 200 min of leaching time, 7.00 g of waste, and 110 mL of anhydrous EtOH, producing 19.60 g of ferrous sulfate heptahydrate (yield of 70.8%). The characterization of ferrous sulfate was performed by X-ray diffraction, scanning electron microscopy coupled to energy-dispersive X-ray spectroscopy, thermogravimetric anal ysis, and differential scanning calorimetry. The characterization of the ferrous sulfate produced evidenced the effectiveness of the optimized process condition.