Ferric coagulants produced from basic oxygen furnace sludge-Part II: optimization of ferrous sulfate production and application of ferric coagulants in water treatment.

A novel process was employed to produce ferric coagulants using iron recovered from the coarse and fine fractions of basic oxygen furnace (BOF) sludge. The FeSO4 obtained as an intermediate product was converted to Fe2(SO4)3 (final product), which was used as a coagulant in water treatment. The iron contents of the coarse and fine BOF sludge fractions were 82.51 ± 0.02% and 45.6 ± 0.5% (dry basis), respectively. Iron was recovered from the sludge fractions by acid leaching with H2SO4 solution, followed by the addition of ethanol to the leachate to crystallize FeSO4, from which ferric coagulants were obtained by oxidation reaction with H2O2. The performance of the coagulants was evaluated using the jar test method. The optimum condition for the production of FeSO4 from the fine fraction of the BOF sludge was established using a desirability function. This resulted in the formation of 13.1 ± 0.2 g of FeSO4‧7H2O from 7.00 g of waste, with a high yield of 91 ± 1%, using 13% (v/v) H2SO4 solution, a leaching time of 140 min, and 120 mL of ethanol. The phase composition of the FeSO4 was investigated by X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The Fe2(SO4)3 produced from the coarse and fine fractions of BOF sludge achieved high turbidity removals (95 ± 1% and 94.1 ± 0.9%, respectively), demonstrating its potential as a coagulant. Performance was compared with a commercial coagulant (polyaluminum chloride), confirming competitive efficiency (97 ± 1%). In addition, bench-scale production costs of ferric coagulants were estimated, and a sensitivity analysis was conducted to assess economic feasibility.