Abstract
Bottom ash is the major by-product of waste incineration and can contain trace elements (As, Cd, Co, Cu, Cr, Mo, Ni, Pb, and Zn) with concentrations up to thousands of mg·k−1. In this study, a combination of different extractions and leaching tests (i.e., CH3COOH and ammonium-EDTA (Ethylenediaminetetraacetic acid) extractions and pHstat leaching tests) was used to investigate the potential release of trace elements from bottom ash samples derived from hazardous waste incineration plants. Although large variations have been found in the release of trace elements by different extractions, in general, the highest concentrations of most trace elements (except As and Mo) were released with the CH3COOH extraction, whereas the release of As and Mo was highest with the ammonium-EDTA extraction. Kinetics of element release upon acidification based on a pHstat leaching test at pH 4 could be related to the solid-phase speciation of some selected trace elements. The relatively high-potential mobility and elevated total concentrations of some trace elements imply a threat to the environment if these bottom ashes are not treated properly. Results of the present study may be useful to develop potential treatment strategies to remove contaminants and eventually recover metals from bottom ash.
Highlights
When society moves towards more sustainable material cycles, recovery of metals from industrial waste can be an opportunity to turn waste into a valuable resource
Results and discussion mainly focus on trace elements (As, Cd, Co, Cr, Cu, Ni, Mo, Pb, and Zn), major elements (Al, Ca, Fe, K, Mg, P, S, and Si) are sometimes mentioned because of their relevance for interpretation of release mechanisms of elements of interest
Ammonium-EDTA extraction was used to determine the potential mobility of trace elements as a consequence of complexation and used as an estimation of the “pool” of a specific element that can deliver elements from the solid phase to the solution [13]
Summary
When society moves towards more sustainable material cycles, recovery of metals from industrial waste can be an opportunity to turn waste into a valuable resource. Sustainable reserves of these metals will remain for the future if they are recovered and the remaining reserves are used more efficiently [2]. Waste containing significant amounts of trace elements offers a potential for the recovery of these elements, since trace elements in anthropogenic matrices are often more labile compared to natural matrices (e.g., ores, rocks) [3]. The term “major elements” is used for elements which have concentrations greater than 1% and term “trace elements” has been used in geochemistry for chemical elements that occur in the Earth’s crust in amounts less than 0.1% (1000 mg·k−1 ) [4].
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