CMA

44 Table 7. Concentration ranges of different constituents in MSWI fly ash and threshold values for certain constituents in hazardous waste in Norway Constituent Unit Concentration rangea Hazardous waste limitsb As mg/kg 18 to 960 > 1000 Ba mg/kg 34 to 14000 - Cd mg/kg 10 to 2100 > 1000 Cl g/kg 18 to 380 - Cr (total) mg/kg 10 to 860 - Cr (III) mg/kg - > 25000 Cr (VI) mg/kg - > 1000 Cu mg/kg 16 to 4100 > 25000 Mn mg/kg 200 to 1700 - Ni mg/kg 19 to 710 > 2500 Pb g/kg 0.25 to 27 > 2.5 Sb mg/kg 58 to 3300 - S g/kg 1.4 to 120 - Zn g/kg 0.4 to 100 > 25 aData from Šyc et al. (2010); bIssued by the Norwegian Climate and Pollution Agency 3.3 Pre treatment (Secondary Treatment) The measures conducted at the incineration plant, for controlling residue outputs (burn out of carbon and volatilization of heavy metals out of fuel bed), are defined as the primary treatment whereas additional external measures (e.g., metal scrap recycling from bottom ash) is considered as secondary treatment or pre-treatment of the ash residues for final disposal or further processing (e.g., landfill, raw material in new products, etc.). The secondary treatment involves pre treatment technologies that do not necessarily need to be applied at the incineration plant. To make the ash fraction less harmful to the environment, several studies have been carried out regarding possible treatment processes, to MSWI fly ash (including ESP ash) and APC (air pollution control) residues as reviewed by Quina et al (2008). They compile the methods in the following treatment categories: separation (magnetic separation, washing, acid leaching, etc.), solidification/stabilisation (S/S) (e.g., use of cementitious binder) and thermal treatment methods (sintering and vitrification/melting). Costs will be a crucial factor regarding pre-treatment efforts and this aspect is not necessarily sufficiently dealt with in the studies. Pre treatment by washing is gaining significant interest and may be applied on the problematic APC residues (e.g., fly ash) for removing chlorine, sulphur, alkalis, heavy metals etc, and make the ash amenable to use in cement industry (destroy POPs and use ash as pozzolana) or brick production. The concentrations of constituents like As, Cd, Cl, K, Na, Pb, Sb and Zn increase in the sequence of bottom ash, boiler pass ash and ESP ash Table 8. Overview of available washing procedures for MSWI ash fractions. Ash type Extraction Agent Liq to Solid Ratio (L/kg) Extraction Time (hrs) Process/mixing device Reference Boiler, ESP and catalytic filter ash Acidified water - 0.75 Commercial process Syc et al., 2010 Bottom ash Water 5 6 Concrete mixer in laboratory Cossu et al., 2012 APC residues Distilled water 3 1 to 2 Containers in laboratory Chimenos et al., 2005 Fly ash (cyclone ash) Distilled water > 2 1 Containers in laboratory Wang et al., 2001 Fly ash (fabric filter) Distilled water 20 3 Containers in laboratory Saikia et al., 2007a Fly ash Distilled water + acid 10 + 20 0.25 + 0.5 Containers in laboratory Pan et al., 2008a Fly ash (cyclone and fabric filter) Water 10 1/6 Tested in real scale Wang et al., 2010b aWashed material tested in preparation of cement clinker in laboratory; bWashed material tested in full scale in the cement clinker production