Zitronensäurelaugung von thermisch konditionierten LD-Schlackenproben

This thesis, written as part of K1-MET Project 1.7 (Valorisation of steelmaking slags), investigates selective leaching of dicalcium ferrite in BOF slag using citric acid. Following previous research works in this field, the focus lies on the removal of phosphorus from the C2S phase of the BOF slag with a minimum loss of iron. Phosphorus causes embrittlement in steel and should therefore only be used in small and controlled doses as an alloying element [1]. BOF slag is a by-product of the basic oxygen furnace process in steel production. In Austria, around 800.000 tonnes annually are produced, of which 650.000 tonnes are produced at voestalpine [2]. The slag typically contains 45 % CaO, 32 % FeO, 16 % SiO2 and 7 % MnO with trace amounts of phosphorus, chromium, and carbon [3]. The literature part covers the different ionic forms of phosphorus as well as possibilities to remove them from aqueous solutions. It also discusses the process of leaching and potential adaptions of the current process idea, particularly in the slag pre-treatment. The experimental part focuses on the preparation of the slag before leaching. Especially the oxidation of the slag and its impact on the transition from divalent to the trivalent state of iron are highlighted. A detailed property class analysis of an oxidized slag sample serves to characterise the slag used for leaching. Furthermore, several washing liquids are investigated to remobilize the phosphorous from the precipitate of the lixiviant (calcium citrate). Due to the increased kinetics of leaching in fine particle sizes, an enhanced leaching process by recycling the coarse product from a hydrocyclone separation is simulated in the final experimental part of the thesis.