Desulfurization (iron melt)

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Desulfurization is the process of removing sulfur from molten iron.

Procedure

During the melting process, the iron melt, especially when melting in a cupola furnace , is enriched with sulfur from the coke (sulphurisation). For the production of spheroidal graphite cast iron using magnesium treatment with master alloys (FeSiMg), the sulfur content in the base melt must not exceed max. Be 0.020%. In order to achieve this, a desulfurization stage very often has to be switched on between the melting furnace and the treatment vessel.

Theoretically, desulfurization could be carried out with all substances that have a higher affinity for sulfur than iron itself (e.g. magnesium , cerium , calcium , sodium, etc.). For economic and technical reasons, calcium compounds such as calcium carbide (CaC 2 ) and calcium oxide (CaO) are used in practice. The calcium reacts with the iron sulphide (FeS) and the sulfur is transferred to the slag as calcium sulphide (CaS). The slag is then removed. The problem is that CaS is water soluble and therefore poses a threat to groundwater. For this reason, the desulphurisation slag has to be disposed of in sealed special landfills.

In order to enable the reaction between the calcium carriers (CaO, CaC 2 ), these substances must be fine-grained. In order to reduce the formation of a passive layer over the grains, flux (e.g. fluorspar CaF 2 ) is added to liquefy the slag. The contact between the desulfurizing agent and the iron melt is supported by intensive bath mixing - either mechanically or by inert gas (mostly nitrogen). Continuous or discontinuous processes are used in foundries. The most frequently used method is continuous desulphurisation in an intermediate pan (so-called GASAL method), in which mixing with nitrogen, which is fed through a porous stone in the bottom of the pan, is ensured. The residence time of the melt in the pan is around 6 to 10 minutes. The temperature losses of the melt are between 80 and 110 ° C. After desulfurization, the melt must be reheated to the required treatment temperature.

Web links

Individual evidence

  1. ^ Simone Franke: Giesserei-Lexikon 2019 . Schiele & Schoen, 2019, ISBN 978-3-7949-0916-2 , pp. 181 ( limited preview in Google Book search).