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 FeSO 4 obtained as an intermediate product was converted to Fe 2 (SO 4 ) 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 H 2 SO 4 solution, followed by the addition of ethanol to the leachate to crystallize FeSO 4 , from which ferric coagulants were obtained by oxidation reaction with H 2 O 2 . The performance of the coagulants was evaluated using the jar test method. The optimum condition for the production of FeSO 4 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 FeSO 4 ‧7H 2 O from 7.00 g of waste, with a high yield of 91 ± 1%, using 13% (v/v) H 2 SO 4 solution, a leaching time of 140 min, and 120 mL of ethanol. The phase composition of the FeSO 4 was investigated by X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The Fe 2 (SO 4 ) 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.