Green industry work: production of FeCl3 from iron and steel industry waste (mill scale) and its use in wastewater treatment

Abstract

Mill scale (MS) is considered to be a significant metallurgical waste, but there is no economical method yet to utilize its metal content. In this study, which covers various processes in several stages, the solution of iron in MS, which is the Iron and Steel Industry (I&SI) waste, as FeCl₃ (MS-FeCl₃) in the thermoreactor in the presence of HCl, was investigated. In the next step, the conditions for using this solution as a coagulant in the treatment of I&SI wastewater were investigated using the jar test. The results of the treated water sample were compared by chemical oxygen demand (COD), total suspended solids (TSS), color, and turbidity analyses using commercial aluminum sulfate (Al₂(SO₄)₃) and FeCl₃ (C-FeCl₃). Additionally, heavy metal analyses were conducted, and the treatment performance of three coagulants was presented. Accordingly, while 2.0 mg/L anionic polyelectrolyte was consumed at a dosage of 4.05 mg/L Al₂(SO₄)₃ at pH 7.0, 0.25 mg/L anionic polyelectrolyte was consumed at a dosage of 1.29 mg/L at pH 5.0 in the C-FeCl₃ and MS-FeCl₃ studies. Also, Fe, Cr, Mn, Ni, Zn, Cd, Hg, and Pb removal efficiencies were over 93.56% for all three coagulant usage cases. The results showed that the wastewater treatment performance of MS-FeCl₃ by the recycling of MS, which is an I&SI waste, was at the same level as C-FeCl₃. Thus, thanks to recycling, waste scale can be used as an alternative to commercial products for green production.

Keywords: Coagulation-flocculation; FeCl3 production; Heavy metal; Iron and steel wastewater; Mill scale.

Fig. 1

XRD (a) and SEM (2000X)-EDX (b) images of MS

Fig. 2

Effect of HCI concentration on the concentration and conversion efficiency of Fe³⁺ from MS (leaching time, 120 min; leaching temperature, 378 K; solid/liquid ratio, 10 (g/mL))

Fig. 3

Effect of reaction temperature and time on the concentration and conversion efficiency of Fe³⁺ from MS (HCI concentration, 7M; solid/liquid ratio, 10 (g/mL)); A Fe³⁺ concentration, B Fe³⁺ conversion

Fig. 4

Eh–pH diagram for the Fe-HCI-H₂O system at (a) 318 K and (b) 378 K

Fig. 5

Raman spectra of MS leaching solution (HCI concentration, 7 M; leaching time, 120 min; leaching temperature, 378 K; solid/liquid ratio, 10 g/mL)

Fig. 6

COD, TSS, color, and turbidity removal rates at different pHs, varying coagulant dosages, and a fixed 1.0 mg/L anionic polyelectrolyte dosage. A Al₂(SO₄)₃. B C-FeCl₃. C MS-FeCl₃

Fig. 7

Study results to determine the optimum anionic poly dosage

Fig. 8

Visual of coagulation/flocculation mechanism

Fig. 9

SEM (× 5000) micrographs and EDX spectrums of sludge formed during coagulation (a) Al₂(SO₄)₃, (b) C-FeCl₃, and (c) MS-FeCl₃ (optimum condition for Al₂(SO₄)₃ of 4.05 mg/L and anionic polyelectrolyte of 2.0 mg/L, for C-FeCl₃ and MS-FeCl₃ of 1.29 mg/L and anionic polyelectrolyte of 0.25 mg/L)

Fig. 10

Proposed flow sheet mechanism for the treatment of I&SI using the coagulation method with FeCl₃ produced from MS