Laboratory appraisal of organic carbon changes in mixtures made with different inorganic wastes.

Mixtures of organic and inorganic wastes were incubated to examine the changes in organic C (OC) contents. An anaerobic sludge and a CaO-treated aerobic sludge, with OC concentrations of 235 and 129 gkg(-1), were used. The inorganic wastes used - referred to as "conditioners" - were shot blasting scrap, fettling, Linz-Donawitz slag, foundry sand (FS), and fly ash from wood bark combustion (FA). The total OC (TOC) and KMnO(4)(-) oxidized OC were determined. DTA-TGA profiles and FTIR spectra were also obtained. Mixtures made with the FS contained significantly lower (P<0.05) amounts of TOC (45 gkg(-1)) than the rest of mixtures, which was attributed to the non-existence of reactive surfaces in the conditioner and the increased aeration induced by this material. Those made with FA contained significantly higher (P<0.05) amounts of TOC (170 gkg(-1)), which was attributed to: (i) the addition of an extra source of C - black carbon (BC) - in the FA, and (ii) the inhibition of mineralization from the compounds present in this conditioner (e.g., amorphous aluminosilicates, BC). The results highlight the importance of the characteristics of the conditioners on the fate of the OM originating from the sludges.

Extractability and leachability of heavy metals in Technosols prepared from mixtures of unconsolidated wastes.

Mixtures of wastes were prepared to improve on the characteristics of the individual ingredients as Technosols, with special attention given to heavy metal extractability. An anaerobic digested sewage sludge and a CaO-treated aerobic sludge were used. A mixture of the two sludges (50:50 DW basis) was also prepared to provide a third type of sludge. The residues were mixed with other types of waste, such as fly ash, Linz-Donowitz slag, foundry sand, shot blasting machine scrap, fettling and barley straw. Extractability of Cu, Cr, Ni, and Zn by 0.01 M CaCl(2) extraction (Me(CACI(2)) was carried out, and leachability of these elements was estimated by acidification of an aqueous suspension of the mixtures with 0.5 N acetic acid (Me(acetic)). The total concentrations of the metals were also determined (Me(T)). The Me(CACI(2)/Me(T) ratios for Cu and Ni (means: 4.0% and 3.1%) were higher than those for Cr and Zn (means: 0.07% each). The mean Me(acetic)/Me(T) ratios followed the order Ni, Zn, Cu, and Cr (19.5%, 4.1%, 3.7%, and 0.09%, respectively). The results highlight the existence of complex interactions among organic matter solubility, pH and heavy metal extractability.