Effect of fine coal tailing porosity on the mobility and speciation of heavy metals in the leachates

Abstract

The effect of porosity of coal tailings on the mobilization and speciation of heavy metals is important for the implementation of management strategies. In this study, column leaching experiments were carried out to assess the mobilization of metal from coal tailings collected from a Witbank Stream 4 in the province of Mpumalanga, South Africa. Various parameters, including the pH, RedOx potential (RP), electrical conductivity (EC), acidity and sulphate and chloride ion concentrations were analyzed to conduct the speciation of the heavy metals in the leachates. The mineralogical composition of the tailings were determined using X-ray diffraction (XRD) and the metal analyses were conducted using inductively coupled plasma-optical emission spectrometry (ICP-OES). Speciation of the heavy metals within the leachates were determined with PHREEQC modelling software. The XRD results indicated that, excluding quartz, pyrite was the dominant mineral, representing 6 % of the sample. The ICP analysis indicated that the six major heavy metals leached were Cd, Co, Mn, Ni, Pb and Zn, with Mn and Zn having the highest concentrations. The paste samples indicated higher concentrations of the pollutants in the leachate than that of the filter cake samples. The PHREEQC results indicated that free hydrated ion species were dominant in the leachates of the paste samples than the filter cakes, which indicates higher mobility and toxicit