Heavy metal stabilization in contaminated road-derived sediments.
There is increasing interest in the stabilization of heavy metals in road-derived sediments (RDS), to enable environmentally responsible reuse applications and circumvent the need for costly landfill disposal. To reduce the mobility of heavy metals (i.e. Cu, Pb and Zn) the effectiveness of amendments using phosphate, compost and fly ash addition were investigated using batch leaching experiments. In general, phosphate amendments of RDS were found to be ineffective at stabilizing heavy metals, despite being used successfully in soils. Phosphate amendment resulted in enhanced concentrations of dissolved organic carbon (DOC), which increased the solubilisation of heavy metals via complexation. Amendment with humified organic matter (compost) successfully stabilized Cu and Pb in high DOC leaching RDS with an optimum loading of 15-20% (w/w). Compost, however, was ineffective at stabilizing Zn. Increasing the pH by amending RDS/compost blends with 2.5-15% (w/w) coal fly ash resulted in the stabilization of Zn, Cu and Pb. However, above a pH of approximately 7.5 and 8 enhanced leaching of organic matter resulted in an increase in leached Cu and Pb, respectively. Accordingly, the optimum level of fly ash amendment for the RDS/compost blends was estimated to be ca. 10%. Boosted regression trees analysis (BRT) of the data revealed that DOC accounted for 56% and 65% of the Cu and Pb leaching, respectively, whereas pH only accounted for ca. 18% of Cu and Pb leaching. RDS sample characteristics (i.e. metal concentrations, size fractionation and organic matter content) were more important at reconciling the leaching concentrations of copper Cu (27%) than Pb (16%). The most important parameter explaining Zn leaching was pH. Overall, the choice of a suitable stabilization agent/s depends on the composition of RDS with respect to the amount of organic matter present, and the sorption chemistry of the heavy metal of interest.
Rijkenberg
Micha J A
MJ
National Institute of Water and Atmospheric Research, PO Box 11-115, Hamilton, New Zealand. m.rijkenberg@niwa.co.nz
Depree
Craig V
CV
D000327:Adsorption; D002244:Carbon / Q000737:chemistry; D060729:Coal Ash; D019015:Geologic Sediments / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D019216:Metals, Heavy / Q000032:analysis* / Q000737:chemistry; D052638:Particulate Matter / Q000737:chemistry; D010710:Phosphates / Q000737:chemistry; D012987:Soil; D012989:Soil Pollutants / Q000032:analysis* / Q000737:chemistry; D012995:Solubility
D060729:Coal Ash; D019216:Metals, Heavy; D052638:Particulate Matter; D010710:Phosphates; D012987:Soil; D012989:Soil Pollutants; D002244:Carbon