HEAVY METALS IMMOBILIZATION IN COAL COMBUSTION FLY ASH-
PORTLAND CEMENT COMPOSITES
Authors: Zaleska Martina , Pavlikova Milena , Pivak Adam , Nabelkova Jana , Pavlik Zbysek 
Published: April 2024

With the rapid growth of the population and urbanization, the demand for industrial production has continued to increase, and industrial solid waste has become more and more abundant. Industrial solid waste mainly includes fly ashes, slags, tailings, red mud, bottom ashes and other wastes, which account for approximately 80% of the total waste produced on Earth. Industrial wastes generally contain various heavy metal components such as Pb, Zn, Cu, Cd, Cr, As, Ba and Mn. The low recycling rate of solid waste results in significant land use for disposal, and the heavy metals and alkaline substances contained in solid waste spread pollution through weathering in the form of dust and leaching into soil and groundwater resources, leading to water contamination and land salinization. Heavy metal pollution not only has a negative impact on soil and water quality, but also gradually accumulates in the human body, causing serious health problems and diseases, such as Parkinson's disease, muscular dystrophy, and Alzheimer's disease, while some metals can even cause cancer. Contamination by heavy metals and other solid wastes poses serious consequences for the environment and sustainable development and, in the longer term, essentially threatens the very existence of an industrial and prosperous human society. Coal is the world's most abundant fossil fuel accounting for approximately 70% of the world's total proven fossil fuel resources. Coal combustion produces not only common pollutants such as SOx, NOx and dust, but also highly toxic heavy metal pollutants. As heavy metals in coal have the characteristics of low content, large total emission, easy to migrate and difficult to degrade, which cause a great harm to human body and environment, there is necessary to control the emission of heavy metals from coal combustion and treat them in a safe way. On that ground the use of fly ash (FA) from coal combustion in a cement-based composite intended for the construction industry, combined with the immobilization of heavy metals in the final product, may be a suitable solution to this problem. In this study, the immobilization of As, Ba and Cu contained in fly ash from coal combustion was experimentally investigated. Fly ash was used to replace 10 wt.% and 20 wt.% of Portland cement (PC) and 0-2 mm silica sand was used as an aggregate. The evaluation of the basic physical and mechanical properties was carried out. Special attention was paid to the evaluation of the immobilization of the studied heavy metals in the prepared composites; the leaching test was performed with a liquid/solid ratio of 10 L/kg. The concentration of As, Ba and Cu in the leachates was analysed by atomic absorption spectroscopy (AAS). The results showed that the concentrations of the studied heavy metals in the leachates of the prepared composites were very low, which suggests that they were completely immobilized in the matrices. The mechanical resistance of the prepared mortars was slightly reduced by PC substitution by FA, but from the quantitative point of view it remained high enough for practical use of prepared composites in development of "green" building materials.