Municipal waste incineration fly ashes: from a multi-element approach to market potential evaluation

Background: Fly ashes from municipal solid waste incineration contain significant amounts of (technology critical) elements. Processes to recover Cu or Zn are already in practice, but it still remains difficult to evaluate the full secondary resource potential of the ashes. One reason is the absence of a worldwide comparable analytical basis for detailed market analyses. To encounter this, (i) an advice on how to analyse 65 elements after microwave-assisted digestion by ICP-OES and ICP-MS is delivered, (ii) the heterogeneity (hours to annual cycle) is evaluated for a incineration plant, (iii) leaching efficiency with three different eluents and (iv) the market potential of the elements as commodities are evaluated.

Results and conclusions: Aqua regia digestion was found to be sufficient to evaluated the recovery potential; except for the mass constituents Al, Si, Sn, Ti and the trace components Cr, Hf, Nb, U and W, for which HF-containing digestions delivered better recoveries. On different time scales, ashes were very homogenous and HCl- as well as H₂SO₄-supported leaching delivered, satisfying results within an hour (exceptions are, e.g., Bi and Sb). By applying characterisation factors of the life cycle assessment impact category "Resource depletion-minerals and metals" supplemented by the list of critical raw materials of the EU: Ag, Bi, Cd, Ga, In and Sb are most interesting elements to be recovered in future activities.