Utilisation of industrial waste for ferrite pigments production

Abstract

AbstractPreliminary results of research focused on the utilisation of specific waste from metallurgical and mining activities to obtain ferrite pigments are presented. As a source of iron in the spinel-type ferrites with the general structure MFe2O4 (where M is a bivalent metal such as Ca and Zn), three types of industrial wastes were used: metallurgical slag from the production of non-ferrous metals and two types of AMD (acid mine drainage) sludge: one of natural origin (Fe-sediment) and the second one synthetically prepared from AMD (Fe-precipitate). This waste was homogenised by ZnO and CaCO3 in various stoichiometric ratios n(Ca): n(Zn): n(Fe) and calcined at the temperature of 1000–1095°C. Mineralogical (XRD) analysis of the metallurgical slag pigments confirmed the formation of zinc ferrite and hematite only (Ca from reaction components entered into other phases). The ferric component of the AMD sludge (Fe-precipitate and Fe-sediment) formed a mixture of zinc ferrite, calcium ferrite, and hematite while increased calcination temperature supported the ferritic structure formation. Prepared pigments have no considerable colour differences; they were in brown colour tones. Pigments from the AMD sludge were more dark brown coloured than those from slag. Pigments were applied in an alkyd-resin paint and consequently basic anticorrosive tests were performed. Pigments obtained from metallurgical slag showed better anticorrosive properties than those from AMD. However, because of high Pb content in pigments from the slag (0.67–1.10 mass % Pb in pigments), utilisation of these pigments in coatings is problematic. Ferrite pigments from the AMD sludge, mainly that with zinc ferrite, have promising application in anticorrosive paints but optimisation of the preparation process is required.