Prevention of Fluorine Elution from Electric Arc Furnace Reducing Slag into Water

Abstract

Elution of fluorine from landfill slag by rainwater or groundwater causes serious problems; hence, fixation of fluorine in electric arc furnace reducing slag (EAFRS) is crucial. The phase including fluorine was identified for some EAFRS specimens and confirmed is as (3CaO·2SiO₂)·CaF₂ in the current work. Experiments to determine the dissolution of fluorine from the EAFRS into water were conducted at pH 4, 7, and 10. It was found that fluorine tended to elute under acidic conditions. Therefore, the elution of fluorine from fluorine-containing substances into water at pH 4 was investigated in detail. It was found that 2(2CaO·SiO₂)·CaF₂, (3CaO·2SiO₂)·CaF₂, and CaF₂ were unstable, while the 3(3CaO·P₂O₅)·CaF₂ phase was stable; further, fluorine elution from 3(3CaO·P₂O₅)·CaF₂ into water was found to be limited. On the basis of these results, it was concluded that the dissolution of fluorine into water can be suppressed by adding a sufficient amount of P₂O₅ to EAFRS, so that the formation of unstable fluorine-containing substances is prevented.