Abstract
Slags produced in the steelmaking industry could be a source of chromium. Slags contain, depending on different types of slags, between 2 to 5 wt.% of Cr. Roasting of slag with NaOH, followed by subsequent leaching can produce leachates which can be efficiently processed using electrocoagulation (EC). This paper provides results from the EC process optimization for Cr(VI) solutions with initial concentration 1000 mg/L of Cr(VI). Influence of pH, current intensity and NaCl concentration on the efficiency of chromium recovery, energy consumption as well as solid product composition is discussed in detail. Optimum of pH = 6 was chosen for EC processing of Cr leachates as well as current intensities of 0.1–0.5 A because of the higher Cr/Fe ratio in solid product compared to higher current intensities. Results of EC processing of four real leachates of electric arc furnace carbon steel slag (EAFC), electric arc furnace stainless steel slag (EAFS), low carbon ferrochrome slag (LC FeCr) and high carbon ferrochrome slag (HC FeCr) were evaluated. Comparison of the results of four real leachate samples is presented. Obtained final solid product was identified as (Fe0.6 Cr0.4)2O3 and with up to 20% of Cr could be used as source of chromium in the ferrochrome production.
Highlights
Chromium is an important element in the steelmaking industry, whether it is a production of steel, stainless steel or ferrochrome
Electrocoagulation experiments with model solutions prepared from potassium dichromate were realized for concentration of 1000 mg/L of Cr as well as the real leachates of 4 different slag types: electric arc furnace carbon steel slag (EAFC) (2.33% of Cr), electric arc furnace stainless steel slag (EAFS) (0.82% of Cr), low carbon ferrochrome slag (LC FeCr) (1.10% of Cr) and high carbon ferrochrome slag (HC FeCr) (11.21% of Cr)
LC FeCr slag had grain size of 2–4 mm (In further texts, these marks will be used for leachates of particular slags and solid products prepared by EC process)
Summary
Chromium is an important element in the steelmaking industry, whether it is a production of steel, stainless steel or ferrochrome. During these processes, several by-products, such as slags, dusts, mill-scales and sludges are produced. Several by-products, such as slags, dusts, mill-scales and sludges are produced It is 200 kg (in the scrap-based steelmaking) and 400 kg (in the iron ore-based steelmaking) per one ton of produced steel. According to the type of steel or ferrochrome, there are different levels of content of chromium present. The industry is working proactively to produce slag that can be used in different applications [1] by making sure the chromium found in the slag is in stable spinel compounds which have very low solubility [2]. Chromium can exist in unstable phases, such as dicalcium silicate (Ca2 SiO4 ,), merwinite (Ca3 MgSi2 O8 ), melilite (Ca2 Mg2 SiO7 ), gehlenite (Ca2 Al2 SiO7 ) and periclase
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