TY - BOOK

T1 - Characterization of Electric Arc Furnace Slags to Identify Possible Leaching Control Mechanisms and Conditioning Methods

AU - Neuhold, Simone Franziska

N1 - no embargoed

PY - 2020

Y1 - 2020

N2 - The present doctoral thesis describes the characterization of electric arc furnace (EAF) slags by a multi-methodological approach in combination with hydrogeochemical and metallurgical models. The aim of this thesis was to identify leaching control mechanisms for Cr, V, Mo, and F in EAF slags and to derive possible conditioning methods to minimize the environmental impact of EAF slags when used as a recycling building material. Obtained results are summarized in three publications and supplementary chapters. The mineralogical binding of Cr, V, and (partially) Mo was determined by a combination of x‑ray diffraction, electron microprobe analyses, and nano-scale secondary ion mass spectroscopy (only for Mo). Chromium and V are bound in spinel, wuestite, and olivine, V was additionally found in larnite. The results for Mo have to be validated further. In addition, the oxidation state of Cr in leached and non-leached EAF slags was determined using x-ray absorption near-edge structure spectroscopy, which revealed that Cr was incorporated in its trivalent and not in its hexavalent state in all investigated samples. The mineralogical occurrence of F in EAF slags could not be clarified. By combining leaching tests, especially pH dependence leaching tests, with geochemical calculations, possible leaching control mechanisms were identified for Cr and V. It was shown that the chemical composition, i.e., the FeO/SiO2 ratio and the mineralogical phase composition and distribution correlate and that these factors subsequently influence the leached concentrations of Cr and V. Hence, the FeO/SiO2 ratio in EAF slags characterized by a high Cr and V leaching was lowered in melting experiments, thus optimizing the mineral phase composition and distribution and minimizing the released concentrations. Metallurgical equilibrium calculations served as a basis for the performed melting experiments. In addition to EAF slags, natural aggregates used in road construction were investigated with regard to a possible link between mineralogy and leachability. As with EAF slags, it was shown that the binding form of heavy metals is decisive for the leached concentrations. Besides, leaching control mechanisms identified in natural aggregates are partially transferable to EAF slags. The present doctoral thesis increased the knowledge of possible correlations between metallurgical parameters, mineralogy, and leachability in EAF slags. Furthermore, on this basis, the leached concentrations of V and Cr were minimized in laboratory and pilot scale melting experiments. These results can be adduced for the evaluation of existing and planned legal regulations for assessing the environmental impact of EAF slags toward a more targeted and resource-efficient use of EAF slags in the future.

AB - The present doctoral thesis describes the characterization of electric arc furnace (EAF) slags by a multi-methodological approach in combination with hydrogeochemical and metallurgical models. The aim of this thesis was to identify leaching control mechanisms for Cr, V, Mo, and F in EAF slags and to derive possible conditioning methods to minimize the environmental impact of EAF slags when used as a recycling building material. Obtained results are summarized in three publications and supplementary chapters. The mineralogical binding of Cr, V, and (partially) Mo was determined by a combination of x‑ray diffraction, electron microprobe analyses, and nano-scale secondary ion mass spectroscopy (only for Mo). Chromium and V are bound in spinel, wuestite, and olivine, V was additionally found in larnite. The results for Mo have to be validated further. In addition, the oxidation state of Cr in leached and non-leached EAF slags was determined using x-ray absorption near-edge structure spectroscopy, which revealed that Cr was incorporated in its trivalent and not in its hexavalent state in all investigated samples. The mineralogical occurrence of F in EAF slags could not be clarified. By combining leaching tests, especially pH dependence leaching tests, with geochemical calculations, possible leaching control mechanisms were identified for Cr and V. It was shown that the chemical composition, i.e., the FeO/SiO2 ratio and the mineralogical phase composition and distribution correlate and that these factors subsequently influence the leached concentrations of Cr and V. Hence, the FeO/SiO2 ratio in EAF slags characterized by a high Cr and V leaching was lowered in melting experiments, thus optimizing the mineral phase composition and distribution and minimizing the released concentrations. Metallurgical equilibrium calculations served as a basis for the performed melting experiments. In addition to EAF slags, natural aggregates used in road construction were investigated with regard to a possible link between mineralogy and leachability. As with EAF slags, it was shown that the binding form of heavy metals is decisive for the leached concentrations. Besides, leaching control mechanisms identified in natural aggregates are partially transferable to EAF slags. The present doctoral thesis increased the knowledge of possible correlations between metallurgical parameters, mineralogy, and leachability in EAF slags. Furthermore, on this basis, the leached concentrations of V and Cr were minimized in laboratory and pilot scale melting experiments. These results can be adduced for the evaluation of existing and planned legal regulations for assessing the environmental impact of EAF slags toward a more targeted and resource-efficient use of EAF slags in the future.

KW - Elektroofenschlacke

KW - Auslaugung

KW - Mineralogie

KW - Modellierung

KW - Konditionierung

KW - Electric Arc Furnace Slag

KW - Leachability

KW - Mineralogy

KW - Modeling

KW - Conditioning Method

M3 - Doctoral Thesis

ER -