A Novel Dry Treatment for Municipal Solid Waste Incineration Bottom Ash for the Reduction of Salts and Potential Toxic Elements

Abstract

The main obstacle to bottom ash (BA) being used as a recycling aggregate is the content of salts and potential toxic elements (PTEs), concentrated in a layer that coats BA particles. This work presents a dry treatment for the removal of salts and PTEs from BA particles. Two pilot-scale abrasion units (with/without the removal of the fine particles) were fed with different BA samples. The performance of the abrasion tests was assessed through the analyses of particle size and moisture, and that of the column leaching tests at solid-to-liquid ratios between 0.3 and 4. The results were: the particle-size distribution of the treated materials was homogeneous (25 wt % had dimensions <6.3 mm) and their moisture halved, as well as the electrical conductivity of the leachates. A significant decrease was observed in the leachates of the treated BA for sulphates (44%), chlorides (26%), and PTEs (53% Cr, 60% Cu and 8% Mo). The statistical analysis revealed good correlations between chloride and sulphate concentrations in the leachates with Ba, Cu, Mo, and Sr, illustrating the consistent behavior of the major and minor components of the layer surrounding BA particles. In conclusion, the tested process could be considered as promising for the improvement of BA valorization.

An Evaluation of the Physical and Chemical Stability of Dry Bottom Ash as a Concrete Light Weight Aggregate

“…Bottom ash has a high chloride concentration, a high unburned carbon content, and a high moisture content due to the use of seawater in the cooling process, and the chloride contained in the bottom ash causes corrosion of the embedded reinforcing bars. Moreover, the non-constant condition causes technical difficulties when using bottom ash and acts as an impediment to adding value as it cannot be used in a dry state [3,4].…”

Heavy metal recovery from the fine fraction of solid waste incineration bottom ash by wet density separation

“…However, chloride and sulfates are enriched in the washing water, so that recirculation is limited. Innovative treatments for the recovery of metals from BA have been proposed as wet processing directly after incineration [14] or as dry abrasion treatment to remove the superficial contamination of leaching salts [18]. The elemental composition and especially heavy metal concentrations of BA are variable; in the literature, the average content of copper is quoted with 3275 mg/kg, but with a range from 738 to 17,620 mg/ kg [19].…”