Abstract
The aim of this study is to evaluate the potential of using solidification/stabilisation (S/S) for the treatment of electric arc furnace dust (EAFD) and examine the effects of using a variety of industrial by-products, i.e., pulverised fuel ash (PFA), hydrated lime (hlime), steel slag and low-grade magnesium oxide (LGMgO) as cement replacements. LGMgO, steel slag and PFA with 0%, 40% and 70% EAFD additions met the Waste Acceptance Criteria (WAC) requirements with respect to unconfined compressive strength (UCS), initial and final setting times and consistency results. The acid neutralisation capacity (ANC) results showed that PFA and steel slag do not have as high buffering capacity as LGMgO and hlime when exposed to acid attacks. The pH level was reduced to 5 when 10 meq/g acid was added into both LGMgO and hlime-blended mixtures. The monolithic leaching test results showed that the fixation of the heavy metals was hardly possible in almost all the mixtures studied. The granular leaching tests yielded very good results with no metals leaching except for Mo. Mo fixation was achieved only for CEMI-hlime and CEMI-LGMgO 1:2:40 mix ratios at 28 days', and for CEMI-LGMgO 1:4:40 and CEMI-slag 1:4:70 mix ratios at both 7 and 28 days' curing age. Depletion-controlled release was observed throughout most of the testing (intervals 1-7) and was the dominant leaching mechanism for LGMgO, PFA, slag, hlime and CEMI blended samples. X-ray Diffraction (XRD) analyses showed that EAFD is mainly composed of zincite (ZnO), franklinite (ZnFe2O4) and magnetite (Fe3O4). Scanning Electron Microscopy (SEM) analysis confirmed the presence of zincite, a compound known to hinder strength development. The XRD results of LGMgO and waste blended products at 28 days' curing age indicated the presence of zincite. Overall, this study demonstrated that the optimum combinations where S/S of EAFD was successful were for CEMI-LGMgO 1:4:40 and CEMI-slag 1:4:70 mix ratios.