Assessment of the chemical and mineral stability of ash – slag mixtures and the leachability of heavy metals under simulated weathering conditions

Abstract

Solid waste from coal combustion deposited in landfills many years ago may constitute a potential secondary raw material resource for industrial applications. However, this requires the examination of a wide range of parameters of these wastes. This study aimed to determine the changes in chemical and mineralogical composition of ash-slag mixtures derived from coal-based power generation, as well as the leachability of heavy metals under the influence of accelerated weathering conditions. The study was based on samples collected from different depths of an ash-slag landfill. The samples were subjected to innovative testing in a chamber simulating variable humidity and temperature conditions, followed by aging in a separate chamber designed primarily to evaluate the effects of ultraviolet radiation. Chemical composition analysis revealed the dominance of silica, aluminum, and iron, with only minor changes after simulated processes. X-ray diffraction methods confirmed the presence of amorphous phases, quartz, mullite, and hematite, as well as calcite as a secondary phase formed during long-term storage. Heavy metals exhibited low leachability (total ≤ 1.56 mg/kg_d.m.)_, with concentrations below the permissible limits for non-hazardous waste landfills. The stability of pH and the absence of significant changes in mineral composition after testing indicate good resistance of the mixtures to weathering processes.