Self-solidification/stabilisation of electrolytic manganese residue: Mechanistic insights

Abstract

Electrolytic manganese residue (EMR) is a type of industrial solid waste with high content of sulphur and heavy metals (HMs). In this study, a novel cementitious material composite is synthesised from ground granulated blast furnace slag, clinker, lime and EMR. It is used to solidify and stabilise EMR. The solidified products are characterised by mechanical properties and environmental effect. The solidification/stabilisation mechanism is revealed by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy with energy dispersive X-ray analyser. The experiment results show that the UCS of solidified bodies increases with the curing age and dosage of cementitious materials. HMs in solidified samples meet the standard threshold. HMs switch to a stable form during curing, that is, S/S has a significant inactivation effect on HMs and can protect HMs from leaching in long-term. The contents of gypsum, charmarite and calcium manganese silicate gradually appear with curing time. Charmarite and gypsum can contribute the increasing trend of compressive strength with curing time. The formation of calcium manganese silicate shows that the presence of HMs in EMR can be involved in the hydration reaction. The binding energy of Si 2p decreases over curing time due to the enlarged degree of polymerisation of Si. The Si–O energy of S/S samples verifies the formation of zeolite-like structure, which can provide sufficient adsorption capacity to HMs and mechanical strength. The microstructure of S/S samples becomes dense with curing time. Gypsum is conducive to the rapid stabilisation of HMs (except Mn). Meanwhile, CSH gel can effectively immobilise all HMs by HM–gel reaction. Incorporating EMR into cementitious materials to solidify/stabilise itself is one way of utilising solid wastes as construction materials for civil engineering applications.