REPOSITORY > RESULTS

Abstract

Current and especially past industrial and mining activities, including underground and open pit mining, have often resulted in soil pollution that has become a global and alarming environmental problem. Among contaminants, heavy metals and metalloids are under environmental scrutiny due to their potential toxicity, persistence, and because they can be released from anthropogenic emissions into terrestrial environment as easily soluble, highly mobile, and highly bioavailable chemical species.
Significant efforts are being made to remediate contaminated soil areas and rehabilitate abandoned pits. The best available technique for the remediation of contaminated soils is the use of immobilizing agents that reduce the mobility of potentially toxic elements (PTEs), while for the reclamation of surface pits or quarries, appropriate solution is their filling using geotechnical composites made from recycled waste.
Among the various immobilizing agents, paper ash is a promising additive for the remediation of contaminated soils with PTEs. However, the long-term remediation efficiency has not yet been investigated. There is also no evidence of PTEs immobilization mechanisms after remediation.
To investigate the environmental acceptability of geotechnical composites made from recycled wastes for their use in the rehabilitation of surface pits and quarries, laboratory tests were mainly carried out. Only few studies report the results of field trials. There is also no data on the influence of preparation of geotechnical composites on the leaching of potentially hazardous substances (PHSs) and what are the long-term environmental impacts of geotechnical composites.
To gain insights into the mechanisms of cadmium (Cd), lead (Pb) and zinc (Zn) immobilization using paper ash for remediation, a laboratory study was conducted in uncontaminated, artificially contaminated and remediated soils. Long-term remediation efficiency and partitioning of Cd, Pb, and Zn was investigated over year applying the sequential extraction procedure and a complementary X-ray diffraction analysis. This methodological approach enabled tracking the temporal redistribution of Cd, Pb and Zn from easily to sparingly soluble soil fractions, evaluation of the efficiency of remediation and the stability of the newly formed mineral phases. After remediation, Cd, Pb and Zn were effectively immobilized by the precipitation of insoluble hydroxides and through the carbonization process in insoluble carbonate minerals.
The environmental acceptability of three geotechnical composites made from recycled wastes was investigated in the laboratory and field scale, using lysimeters. The results of laboratory leaching tests showed that two composites were in compliance with national legislation, while field investigation proved that optimally installed geotechnical composites are environmentally acceptable for the rehabilitation of mining sites. The laboratory leaching tests also showed that concentrations of several PHSs leached from one composite exceeded the legislative limit values. Nevertheless, this composite can be used for closing landfills for non-hazardous wastes. The procedures utilized in the PhD are promising ways to reduce waste disposal, to sustainably rehabilitate degraded areas, and to preserve natural resources.