Characterization of Mine Tailings and Fly Ash from Bulgaria as Raw Materials for Geopolymerisation

Geopolymers present a modern low CO2 footprint alternative of traditional building materials. The reuse of industrial waste or by-products as raw materials could address important ecological problems. The aim of this study is to evaluate the characteristics of mine tailings and coal combustion by-products from Bulgaria as raw materials for the preparation of geopolymers. Three mine tailings and two coal combustion by-products from thermal power stations were characterized. Appropriate validated analytical methods were combined to retrieve detailed information. The studied samples contented relatively high percentage of Al2O3 ­(17-21%) and SiO2 (68-53%), and low concentration of sulfur (0.02-3.5% as SO3). The alumosilicates, proved by XRD, are expected to show high reactivity in alkaline media, however some less reactive mineral phases were also observed. The aqueous slurry was alkaline pH 8-11, the fly ash contained the highest concentration of components ionized in water solution. Heavy metals content was found to be at micro or trace levels. The copper content was 56-818 mg/kg, Pb 127-2 mg/kg, Cr 1-71 mg/kg. The results showed that the studied mine tailings and fly ash could be used as precursors for geopolymer obtaining after fine adjustment of the technology to account for the specific characteristics of raw materials.