The Optimization of Metals and Metalloids Extraction From Fly Ash

Abstract

Fly ash originating from coal combustion in thermal power plants is generated in landfills in large amounts, and due to the high content of heavy metals and metalloids whose mobility is hazardous to the environment and human health, it causes soil and groundwater pollution. Scientific research in the field of "alternative mining" is significant, where heavy metals and rare earth elements would be recovered from waste materials such as fly ash using various extraction methods. The aim of this paper is to determine the optimal extraction process of the examined elements: V, Cr, Mn, Co, Ni, Cu, Zn, As, Cd, and Pb from fly ash. Two extraction agents were used: sulfuric and acetic acid. In the first set of experiments, the fly ash was immersed immediately in acids, and in the second set, this process was preceded by the addition of sodium hydroxide, which effectively destroys the alumina-silicate matrix. Several different parameters were also monitored: ratio of fly ash and acid/acid mixture (1:5, 1:30), temperature (25 and 45°C), duration of the process (4 and 24 h), and stirring. For the extraction of Pb - H2SO4, temperature and time were shown as significant parameters, while for Cd, only H2SO4 was an effective extractant. Concerning the As metalloid, the acetic acid, solid/liquid ratio, and time were significant, while for Zn, Cu, Co, Mn, and V metals only the solid/liquid ratio was significant. Determination of the content of heavy metals and metalloids was done by the ICP-MS.