TY - THES

T1 - Phosphorus behaviour during carbo-thermal reduction of iron-, chromium-, and manganese-rich slags

AU - Gatschlhofer, Christoph

N1 - no embargo

PY - 2022

Y1 - 2022

N2 - Despite the Covid-19 pandemic steelmaking in 2020 climbs up again to an anew production maximum with a volume of 1878 Mt crude steel. Therefrom 73.2% can be attributed to the production via the blast furnace/basic oxygen furnace route. During the refining step in the converter unwanted steel-constituents such as sulphur, phosphorus, and silicon are transferred in their oxidic state into a calcium-silicate-slag, better known as basic oxygen furnace slag. Inevitably metal oxides of iron, chromium, and manganese are also incorporated to a large extent into the converter slag during refining. The considerable annual quantities of crude steel, for which 100 – 150 kg of basic oxygen furnace slag accumulates for each tonne produced, demonstrate the enormous potential of recyclable valuable slag-components. In the light of a zero-waste steel production towards an efficient circular economy further processing steps for the converter slag valorisation are recommendable. The slag should be separated into different usable fractions by returning each stream to a suitable reuse possibility with defined product qualities to competitive market prices. One approach for the treatment of basic oxygen furnace slag can be pyrometallurgical high temperature reduction. The main challenge of this method poses the affinity between highly reactive gaseous phosphorus, and metals, resulting in the formation of unwanted phosphide species, which restricted the reuse possibilities of converter slag. In addition to the iron content in the basic oxygen furnace slag, metals such as chromium and manganese are also involved in the formation mechanism of phosphides during carbo thermal treatment. As a result, this thesis deals with the outcome of an executed carbo-thermal reduction experiment. Since slag mixtures with such compositions are not available, slag samples with a basicity B2 = 1.4 of lower (4 m.-%) and higher (17 m-%) metal concentrations of either iron, chromium, or manganese need to be produced synthetically. Subsequently, all slag samples are processed in MgO-crucibles with the help of fine carbon powder by carbo-thermal reduction at 1873 K under inert gas. The results emphasize the complexity behind carbo-thermal treatment of a multi-component system such as slag. All samples with lower metal-content of iron, chromium, or manganese couldn’t be reduced at all. For high concentrated slag samples, a characteristic behaviour for iron, chromium, and manganese can be determined. However, the results serve as a firm basis for the optimization of follow-up experiments. The final objective results in the identification of suitable slag-mixtures for carbo-thermal treatment in order to maximize the phosphorus gasification by simultaneously minimize the phosphide content in the obtained metal product.

AB - Despite the Covid-19 pandemic steelmaking in 2020 climbs up again to an anew production maximum with a volume of 1878 Mt crude steel. Therefrom 73.2% can be attributed to the production via the blast furnace/basic oxygen furnace route. During the refining step in the converter unwanted steel-constituents such as sulphur, phosphorus, and silicon are transferred in their oxidic state into a calcium-silicate-slag, better known as basic oxygen furnace slag. Inevitably metal oxides of iron, chromium, and manganese are also incorporated to a large extent into the converter slag during refining. The considerable annual quantities of crude steel, for which 100 – 150 kg of basic oxygen furnace slag accumulates for each tonne produced, demonstrate the enormous potential of recyclable valuable slag-components. In the light of a zero-waste steel production towards an efficient circular economy further processing steps for the converter slag valorisation are recommendable. The slag should be separated into different usable fractions by returning each stream to a suitable reuse possibility with defined product qualities to competitive market prices. One approach for the treatment of basic oxygen furnace slag can be pyrometallurgical high temperature reduction. The main challenge of this method poses the affinity between highly reactive gaseous phosphorus, and metals, resulting in the formation of unwanted phosphide species, which restricted the reuse possibilities of converter slag. In addition to the iron content in the basic oxygen furnace slag, metals such as chromium and manganese are also involved in the formation mechanism of phosphides during carbo thermal treatment. As a result, this thesis deals with the outcome of an executed carbo-thermal reduction experiment. Since slag mixtures with such compositions are not available, slag samples with a basicity B2 = 1.4 of lower (4 m.-%) and higher (17 m-%) metal concentrations of either iron, chromium, or manganese need to be produced synthetically. Subsequently, all slag samples are processed in MgO-crucibles with the help of fine carbon powder by carbo-thermal reduction at 1873 K under inert gas. The results emphasize the complexity behind carbo-thermal treatment of a multi-component system such as slag. All samples with lower metal-content of iron, chromium, or manganese couldn’t be reduced at all. For high concentrated slag samples, a characteristic behaviour for iron, chromium, and manganese can be determined. However, the results serve as a firm basis for the optimization of follow-up experiments. The final objective results in the identification of suitable slag-mixtures for carbo-thermal treatment in order to maximize the phosphorus gasification by simultaneously minimize the phosphide content in the obtained metal product.

KW - Phosphor

KW - Phosphidbildung

KW - carbo-thermische Reduktion

KW - Konverter-Schlacke

KW - Metallrückgewinnung

KW - Schlackenbehandlung

KW - Kreislaufwirtschaft

KW - Pyrometallurgie

KW - phosphorus

KW - phosphide formation

KW - carbo-thermal reduction

KW - basic oxygen furnace slag

KW - metal recovery

KW - slag-treatment

KW - circular economy

KW - pyrometallurgy

M3 - Master's Thesis

ER -