Extractabilities of heavy metals in chemically-fixed sewage sludges
Journal
Journal of Hazardous Materials
Journal Volume
58
Journal Issue
1-3
Pages
73-82
Date Issued
1998
Author(s)
Abstract
Chemically-fixed sewage sludges, including lime-treated sludge (LS), lime-sodium silicate-treated sludge (LSS), cement-treated sludge (CS), and cement-sodium silicate-treated sludge (CSS), were produced from sewage sludge by bench processes using lime, cement, and sodium silicate as additives. The extractabilities of heavy metals (Cu, Pb, Cr, and Zn) in these chemically-fixed sludges were studied using sequential extraction and single extraction. For comparative objectives, untreated sewage sludge (S) was also studied. Sequential extraction revealed that the percentages of the heavy metals of organically-bound form in S were in the order of Cu > Pb > Cr > Zn (73.7 > 46.6 > 35.2 > 21.4%) and those of exchangeable form, the most labile form, in four chemically-treated sludges investigated were also in this order (Cu > Pb > Cr > Zn), implicating that the heavy metals (e.g. Cu) having higher affinity for organics become more labile in the sewage sludge after chemically-fixed, but those (e.g. Zn) having less affinity for organics become more stable. The results of single extraction conducted at various pH suggested that this effect was attributed to the irreversible dissolution of the metals (e.g. Cu) having higher affinity to organics at very high pH (10.64-12.05) during processing and air drying (20-25°C) of these chemically-fixed sludges. Chemically-fixed sewage sludges, including lime-treated sludge (LS), lime-sodium silicate-treated sludge (LSS), cement-treated sludge (CS), and cement-sodium silicate-treated sludge (CSS), were produced from sewage sludge by bench processes using lime, cement, and sodium silicate as additives. The extractabilities of heavy metals (Cu, Pb, Cr, and Zn) in these chemically-fixed sludges were studied using sequential extraction and single extraction. For comparative objectives, untreated sewage sludge (S) was also studied. Sequential extraction revealed that the percentages of the heavy metals of organically-bound form in S were in the order of Cu>Pb>Cr>Zn (73.7>46.6>35.2>21.4%) and those of exchangeable form, the most labile form, in four chemically-treated sludges investigated were also in this order (Cu>Pb>Cr>Zn), implicating that the heavy metals (e.g. Cu) having higher affinity for organics become more labile in the sewage sludge after chemically-fixed, but those (e.g. Zn) having less affinity for organics become more stable. The results of single extraction conducted at various pH suggested that this effect was attributed to the irreversible dissolution of the metals (e.g. Cu) having higher affinity to organics at very high pH (10.64-12.05) during processing and air drying (20-25 °C) of these chemically-fixed sludges.
SDGs
Type
conference paper