pH-dependent release of elements from hardened and non-hardened wood ash

• Published in: Waste management (Elmsford) Vol. 138; pp. 140 - 147
• Main Authors: Rehl, Erwin, Reimer, Kerry B., Rutherford, Perry Michael
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 01.02.2022
• Subjects: Ash pretreatment; Batch extraction; Biomass; Biomass ash; Bottom ash; Canada; Coal Ash - analysis; Gasifier; Hydrogen-Ion Concentration; Canada; BCCSR; BC; QA/QC; Gasifier; HBA; MS; Ash pretreatment; USEPA; FAL; Bottom ash; L/S; Biomass ash; DW; ICP; MAL; Batch extraction; OES; UNBC; EC; BA
• DOI: 10.1016/j.wasman.2021.11.046
• ISSN: 0956-053X

•Wood ash may be self-hardened to alter physical and chemical properties.•Ash may be exposed to acidity during disposal, storage or use as a soil amendment.•Acidification increases leachability of many trace elements of concern.•Self-hardening reduces leachability of many trace elements over a wide pH range. Bioenergy systems that utilize clean wood feedstocks are becoming more common in western Canada to produce heat and electricity. But, wood combustion leads to ash residuals that need to be managed. Although there is growing interest in value-added uses for these wood ashes, large quantities of wood ashes are currently stockpiled or landfilled. Wood ash may be self-hardened as a pretreatment strategy to improve handling and reduce reactiveness prior to land application. This study determined aqueous concentrations of constituents released from wood bottom ash (BA) and hardened wood bottom ash (HBA) when subjected to increasing levels of acidity (pH 10 to 4). Such acidic conditions are not common but may exist during some storage, landfilling or land reclamation scenarios. Acidification of BA and HBA increased aqueous concentrations of B, Ca, Cd, Co, Cu, Mg, Mn, Ni, Sr, and Zn, whereas Cr, Hg and Mo showed decreased concentrations. Hardening reduced aqueous concentrations of As, Ca, Co, Fe, Ni, P, and Pb, in HBA compared to BA over a pH range. When properly managed, hardened and non-hardened bottom ashes generated from the combustion of clean wood should pose minimal risk to the environment.