Electrodialytic remediation of municipal solid waste incineration fly ash as pre-treatment before geopolymerisation with coal fly ash.

Municipal solid waste incineration (MSWI) fly ash is classified as hazardous waste and needs to be disposed of according to strict regulations. By disposal, valuable resources in the MSWI fly ash is lost, and other solutions are sought for. The effect of electrodialytic remediation (ED) as a pre-treatment for removing heavy metals from MSWI fly ash before using the treated ash in geopolymerization with coal fly ash was explored. ED pre-treatment for MSWI fly ash increased the Si reactivity and the Si/Al ratio. The mixture of 80% coal fly ash and 20% ED treated fly ash with 8 M NaOH (L/S 0.37 mL/g) was found optimal, with a resulting compressive strength of 15.3 MPa, which was higher than the reference coal fly ash geopolymer. The leaching concentrations of Pb, Zn, Cr, Cu and Ni were below 0.02 mg/L with Mn and Cd at 0.023 and 0.027 mg/L, respectively. The enhanced mechanism for ED treated MSWI fly ash in geopolymer was confirmed by FTIR analysis and SEM images. The resistance against extreme leaching environments for treated fly ash geopolymer was stronger than raw fly ash geopolymer, and physical encapsulation of geopolymeric gels contributed to the heavy metal immobilization.

Screening of heavy metal containing waste types for use as raw material in Arctic clay-based bricks.

In the vulnerable Arctic environment, the impact of especially hazardous wastes can have severe consequences and the reduction and safe handling of these waste types are therefore an important issue. In this study, two groups of heavy metal containing particulate waste materials, municipal solid waste incineration (MSWI) fly and bottom ashes and mine tailings (i.e., residues from the mineral resource industry) from Greenland were screened in order to determine their suitability as secondary resources in clay-based brick production. Small clay discs, containing 20 or 40% of the different particulate waste materials, were fired and material properties and heavy metal leaching tests were conducted before and after firing. Remediation techniques (washing in distilled water and electrodialytical treatment) applied to the fly ash reduced leaching before firing. The mine tailings and bottom ash brick discs obtained satisfactory densities (1669-2007 kg/m3) and open porosities (27.9-39.9%). In contrast, the fly ash brick discs had low densities (1313-1578 kg/m3) and high open porosities (42.1-51. %). However, leaching tests on crushed brick discs revealed that heavy metals generally became more available after firing for all the investigated materials and that further optimisation is therefore necessary prior to incorporation in bricks.