Work Packages 1 and 2 of the SOCRATES project are working on the extraction and recovery of critical and economically important metals that are present in the investigated tailings, sludges, slags and ashes. This leaves behind residual mineral matrices that can be used in our Work Package 3: “Residual matrix valorization”, possibly requiring prior treatment processes. By activating these (treated) residues with alkaline solutions (i.e. solutions with high pH) a 3D network consisting of inorganic (e.g. Si, Al, Fe) elements is formed, which is called an inorganic polymer (IP).
In my thesis we focus on the production of IPs from amorphous synthetic slags, resembling these residual mineral matrices. More specifically, the focus lies on iron-rich residues mainly originating from the non-ferrous industry. The structure and the chemistry of the slags, that are used as precursors for the synthesis of the IPs, are of great importance, which is why I am studying the compositional dependence of reactivity and strength development. Previous studies have shown that by increasing the amorphous fraction of the slags, the reactivity can be boosted drastically, leading to a more suitable precursor for inorganic polymers.
The most common method of producing an amorphous solid is to rapidly cool the molten form of the material, i.e. quenching, which is also employed here. More precisely, quenching is a multi-step process, beginning with heating of the sample up to a temperature which is some hundreds degrees above the liquidus (lowest temperature at which a material is completely liquid), in order to assure that the material is completely molten. Careful attention must be paid on keeping the temperature throughout the material uniform. When the material (slag) is completely molten, is then quenched into water, for which I will let the video speak for itself! (the most interesting bit starts at 32″!) After quenching, a beautiful shiny amorphous slag is obtained, which can then be used as precursor for the synthesis of inorganic polymers.