Hydrocyclone separation as a tool for reduction of the amount of heavy metals in municipal solid waste incinerator (MSWI) residues

Abstract

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 mu m and <14 mu m 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.