Modeling of amphoteric heavy metals solubility in stabilized/solidified steel foundry dust

Abstract

The influence of pH on the leaching of metals from waste materials can be described by geochemical and empirical models. These equations may be integrated into dynamic leaching models in order to describe the longterm behavior of waste-derived forms or they can be used to predict the concentration of metals in equilibrium leaching tests at a given pH. The aim of this work is to describe the equilibrium concentration of the main metals (Zn, Pb, and Cr) contained in untreated and stabilized/solidified (S/S) electric arc furnace dust (EAFD) using experimental data obtained from a pH-dependence leaching test (acid neutralization capacity, ANC). EAFD is a hazardous waste generated in steel factories. Steel foundry dust coming from an electric arc furnace was characterized by acid digestion, x-ray fluorescence (XRF), and x-ray diffraction (XRD). The waste mainly contains Zn and Fe, which were identified in zincite and zinc ferrite phases. Pb and Cr were also detected at lower concentrations. Cement/EAFD formulations ranging from 7 to 20% dry wt of cement were prepared and the ANC leaching test was performed. The amphoteric behavior of Zn, Pb, and Cr was described by the geochemical model Visual MINTEQ and by an empirical model developed for these metals. Zinc and lead solubilities were well described by both models; however, Visual MINTEQ failed to describe the chromium behavior quantitatively.