Slags with a high Al and Fe content as precursors for inorganic polymers

Slags from non-ferrous metallurgy are Fe rich, with Si as a minor constituent, and with low levels of Al. Due to variations in the slag cooling practice, they can exist as semi-amorphous or as crystalline solids. Considering that both higher Al in the slag and a higher cooling rate during solidification would have an impact on the availability of Al and ultimately on the formation of linkages in the inorganic polymer, we study the microstructure and reactivity of a Fe and Al rich slag cooled in different ways. Results show that high cooling rates lead to a predominantly amorphous material. For lower cooling rates the content of amorphous phase varies from 52 wt.% to 12 wt.%. Spinel is the primary phase precipitating, whereas, for the lowest cooling rate investigated, pyroxenes form as well. Dissolution tests in a 10 M NaOH solution for 96 h reveal that approx. 54 wt.% of Al and 33 wt.% of Si of the total content become available for the highly amorphous slag. On the contrary, the dissolved Al and Si are below 5 wt.% when slag pot cooling is applied. The above strongly influence the resulting inorganic polymers with the ones originating from the amorphous slag being superior in mechanical properties.

► Cooling of Fe, Al rich slags leads to an amorphous phase, spinel and pyroxenes.
► Depending on the cooling rate, the dissolution of these slags in alkalis varies.
► Inorganic polymers are produced from the slags cooled relatively fast.