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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., CH 3 COOH and ammonium-EDTA (Ethylenediaminetetraacetic acid) extractions and pH stat 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 CH 3 COOH extraction, whereas the release of As and Mo was highest with the ammonium-EDTA extraction. Kinetics of element release upon acidification based on a pH stat 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.

In recent years, shipping activities developed in Ninh Hoa district (south-central Vietnam), have raised an urgent environmental concern related to the use of copper slag as abrasive material for removing rust from the surface of the ships. This study was conducted to investigate the characteristics of the blasted copper slag (BCS). Enrichment Factors (EF) were used to assess the contamination status of sediments and soils in the surroundings of the BCS dump site. The potential release of As and heavy metals (HMs) from BCS was examined through pH stat and cascade leaching tests in combination with XRD analysis. From the results, As, Cr, Ni, Pb and Zn were characterized as moderate severely enriched to severely enriched while Cu showed extremely severe enrichment in the sediments. Regarding the soil collected at the dump site, it was strongly contaminated with As, Cu and Zn (extremely severe enrichment) whereas Cr, Ni and Pb were ranked as severely enriched. This study also demonstrates that it is important to use local background values of As and HMs in soils and sediments for a correct estimation of the degree of As or HM contamination. The cascade leaching test results from the BCS showed that the concentrations of the regulated HMs leached were lower than the EU limit for non-hazardous waste; except for Cu. Results from pH stat leaching tests at pH 4 with BCS indicated that upon acidification, HM release from the <1 mm fraction is higher compared to the bulk sample. A significant release of Cu from BCS was also observed for both fractions (<1 mm fraction and bulk sample) in pH stat leaching tests. In view of the elevated Cu concentrations found in the slag, the potential recovery of Cu from BCS should be investigated.

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In recent years, rapid industrial development has led to an increase in various types of industrial waste generation in Vietnam. Potentially toxic elements (PTEs) can contaminate water resources when waste is not properly treated and/or stored in confined disposal facilities. This study characterizes the occurrence and leaching behavior of PTEs from industrial sludge under the influence of oxidation and pH with implications for open dump disposal. Environmental issues related to possible management options are also addressed. Sludge samples from industrial parks at Binh Duong and Dong Nai, Southern Vietnam, were oxidized under atmospheric conditions. The results indicate that Fe and Mn (both samples) and Cu, Ni, and Zn (Binh Duong sample) may pose a potential threat to the water quality for sludge dumped near water bodies. Therefore, we recommend avoiding uncontrolled upland disposal of such sludge. Some preliminary treatment to immobilize PTEs should be applied to the sludge originating from Binh Duong prior to upland disposal. A recovery of Ni and Zn from this sludge could be considered. For the less contaminated sludge from Dong Nai, beneficial use, such as land application for agricultural purposes, is a possible option.

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