Characterisation of slag leachability in support of slag recycling: Development of experimental methodology

While the amount of metallurgical slag grows rapidly, its recycling has great potential. Main concern associated with the use of slags in various applications is their susceptibility to natural leaching. Characterisation and prediction of the leaching phenomena are essential to minimize the environmental impact of the slag recycling. The current study focuses on fundamentals of leaching behaviour of synthetic amorphous slags with the CaO-“FeO”-MgO-SiO 2 matrix with heavy elements Pb and Cu, added to imitate the common impurities in the copper and lead smelting slags. The original experimental methodology has been developed with an aim to derive the mechanisms of the reactions between slag and aqueous solution. It consists of high-temperature slag synthesis and quenching, bulk leaching or macro leaching type of experiments, and micro-leaching experiments investigating controlled leachability of well characterised surface, followed by characterisation using advanced analytical methods including high-resolution Scanning Electron Microscopy (SEM), Electron Probe X-ray Microanalysis (EPMA), Inductively Coupled Plasma Mass Spectroscopy (ICP-MS), Focus Ion Beam (FIB) sample preparation, and Transmission Electron Microscopy (TEM) equipped with Energy Dispersive Spectrometry (EDS). Leachability of Fe, Mg, Si, Pb and Cu was investigated and analysed. The effect of pH on the slag leachability kinetics has been established. Initial results show the formation of altered layer of approximately 300 nm thickness on the surface of the amorphous slag subjected to leaching in acidic conditions, which is an important finding for further modelling of leaching process combining thermodynamics and kinetics. • Ecological feasibility of reusing and recycling metallurgical residues is studied using advanced analytical techniques. • Dissolution of copper from amorphous fayalite slag is higher than of other elements and does not exceed 3 %. • Potential mechanisms of interaction between amorphous glass and aqueous solutions are proposed.