Understanding the Role of the Composition of Alkaline Solutions in the Hardening Behaviour of Fe-Rich Binder Based on Jarosite Residue Slag

Abstract

The extraction of Pb and Zn from ores generates a large amount of solid waste, such as jarosite residues, that is often used to recover valuable metals and produce a cleaner slag for further dumping. In this work, jarosite residue slag was used to produce alkali-activated materials (AAMs) which can bring high-volume applications for these Fe-rich residues. The current work presents a concise investigation on the possible impact of the composition of the activating solution on the compressive strength, microstructure and microchemistry of Fe-rich binder based on jarosite residue slag. The obtained compressive strengths of the mortars activated with potassium and sodium hydroxide solutions were close, reaching 22.4 and 18.1 MPa at 28 days, respectively. The addition of sodium sulphate to sodium hydroxide solution lowered the resulting strength to about 5 MPa. Even the minimal content of liquid silica (10 wt.% of SiO 2 from the mass of the solution or 1 wt.% from the mass of the mortar) improved the resulting compressive strength up to 60 MPa. Besides, the hardening reaction took place fast for silicate solutions, and the maximum compressive strength of 70 MPa was measured only after 1 day after the synthesis. The reaction products characterised with FT-IR, XRD, TGA, and SEM-WDS techniques were represented by Fe-rich C-S-H gel (with an average composition of C 0.5 A 0.5 F 1.5 S 1 H 0.1 in cement chemist notation) of tobermorite-like structure and minor strätlingite for hydroxide solutions. The local aggregation of Na and Mg suggests the minor role of these elements in the reaction product. The positioning of the FT-IR peaks at high wavelength indicates an increased cross-linkage of the silicate network due to the high content of network-forming Fe 3+ ions. Due to many ecological and technological benefits, Fe-rich AAM based on jarosite residue slag is a viable option in the nearest future for the utilisation of these residues as an alternative to their dumping.

Keywords: geopolymer, inorganic polymer, Slag, jarosite residue, construction material, recycling.