Acta Montanistica Slovaca Volume 24 (2019), number 3, 188-197 188 Hydrocyclone separation as a tool for reduction of the amount of heavy metals in municipal solid waste incinerator (MSWI) residues Silvie Koval 1 , Helena Raclavska 2 , Hana Skrobankova 1 , Dalibor Matysek 2 , Lukas Koval 3 and Franz Winter 4 Municipal solid waste incineration residues such as fly ash and air pollution control residues are classified as hazardous waste and disposed of, although they contain potential resources. The most problematic elements in municipal solid waste incineration residues are leachable heavy metals and salts. Therefore, these residues usually do not meet the criteria for recycling as construction material or for landscaping, as they possess an environmental risk (and are classified as an H15 hazard material - waste capable by any means, after disposal, of yielding another substance, for example, leachate). Thus, an efficient treatment method should comprise a washing step to remove soluble chlorides, combined with an elimination step aiming to remove the heavy metals. As a consequence, it was proposed to use a cyclosizer device (hydrocyclone principle) for the separation of the incineration residues in order to prove the statement that the highest concentration of heavy metals can be found within the finest particles. Chemical and physical properties of two air pollution control residue samples and one fly ash sample were examined prior to sorting the samples into five size fractions by the cyclosizer. The results show that chloride salts can be removed from the residues during the cyclosizer separation process, and heavy metals were concentrated in the fine particle size fraction after the process. On the basis of these findings it can be assumed that removing the finest size fraction from the municipal solid waste incineration residues (fractions <12 μm and <14 μm respectively), will decrease the heavy metal content by Hg 51 – 60%; Ag 32 – 36%; Cd 37 – 46%; Co 23 – 27%; Cr 30 – 40%; Cu 27 – 37%; Ni 21 – 26%; Pb 34 – 42%; Sb 44 – 50%; Zn 33 – 40%. Concentrations of the heavy metals in the coarse fraction of these residues are below the regulatory limit, and therefore this study suggests that they can be used for recycling and reuse. Keywords: cyclosizer, waste incineration, MSWI residues, heavy metal, fly ash, APC Introduction The last two decades have seen a growing trend towards municipal solid waste incineration (MSWI) due to its unique benefits of mass and volume reduction of waste (Liu et al., 2016; Mikulčić, 2016). There are several types of MSWI residues, though the finer fraction, referred to as fly ash (FA) and air pollution control (APC) residue, pose serious environmental problems (Yao et al., 2015; Raclavská et al., 2017). Fly ash and APC residue consist of fine particles that contain significant amounts of leachable toxic elements, including heavy metals, chloride salts and sulphates (Saqib and Bäckström, 2016; Nowak et al., 2013). The concentrations of metals in APC from combustion of municipal waste decrease in the following series: Zn > Cu > Pb > Sb > Cr > As > Cd (Saqib and Bäckström, 2016) or Zn > Pb > Cu > Cr > Ni > Cd, and the concentrations of Zn and Pb are higher by one order or more than those of other metals (Pan et al., 2013). Metals which are present in ion-exchangeable form are leached in the following order: Cd > Cu > Sb > Zn> As > Pb > Cr (Saqib and Bäckström, 2016). In addition, highly toxic organic substances and organic pollutants such as dioxins (PCDD), furans (PCDF) and PAHs are also present making the utilization of MSWI residues even more problematic (Saikia et al. 2007). Therefore, they usually do not meet the criteria for recycling as construction material or for possessing an environmental risk (and are classified as an H15 hazard material - waste capable by any means, after disposal, of yielding another substance, for example, leachate) (Aguiar et al., 2009). Several researchers have developed different treatment methods to decrease the leachability of the MSWI residues. These methods are generally classified as separation, stabilization/solidification and thermal techniques (Quina and Bordado, 2009). A limited number of studies mentioned fly ash and APC residue treatment using a hydrocyclone for their separation (Ko et al., 2013). Several studies recommended water washing the residues to remove soluble chlorides before applying another treatment (Mangialardi, 2003; Wang et al., 2010; Chen et al., 2017). A single washing, followed by washing of the filtration cake removes up to 99% of soluble chlorides according to a previous study (Hartmann, 2015). Recently authors have published the link between particle size and chemical composition of fly ash and they conclude that with decreasing particle size, the concentration of heavy metals increases (Wang et al., 2002; De Boom and Degrez, 2012). The distribution of major elements in different particle size fractions is less predictable (Fedje et al., 2010). The release of heavy metals into flue gas is related to chloride content in MSWI fly ash. Evaporation 1 Silvie Koval, Hana Skrobankova, Centre ENET - Energy Units for Utilization of Non-Traditional, VSB - Technical University of Ostrava, 17. listopadu 15/2172, 708 33 Ostrava-Poruba, Czech Republic, silvie.koval@vsb.cz, hana.skrobankova@vsb.cz 2 Helena Raclavska, Dalibor Matysek, Department of Geological Engineering, Faculty of Mining and Geology, VSB – Technical University of Ostrava, 17. listopadu 15/2172, 708 33 Ostrava-Poruba, Czech Republic, helena.raclavska@vsb.cz, dalibor.matysek@vsb.cz 3 Lukas Koval, CSIRO Mineral Resources, Technology Court 1, 4069 Pullenvale, QLD, Australia, lukas.koval@csiro.au, 4 Franz Winter, Institute of Chemical Engineering, Vienna University of Technology, Getreidemarkt 9, 1060 Vienna, Austria, franz.winter@tuwien.ac.at