Leachability of metals from sludge-based artificial lightweight aggregate.
Metal sludge from industrial wastewater treatment plants was mixed with mining residues to be recycled into lightweight aggregate (LWA) through sintering at different temperatures. The physical properties of the LWA thus obtained were examined by scanning electron microscopy analyzer (SEM) coupled with an energy dispersive X-ray analyzer (EDX). The sequential extraction method combined with inductively coupled plasma atomic emission spectrometry (ICP-AES) was employed to determine the concentration and distribution of hazardous toxic elements in the metal sludge-based artificial LWA. The results show that the leaching concentrations of Cd, Cr, Cu, and Pb present in the non-sintered raw aggregate pellets reached 7.4, 68.0, 96.0, and 61.4 mg/l, respectively, far exceeding the regulatory threshold. Sintering at 1150 degrees C for 15 min results in stronger chemical bonds being formed between the elements. Hence, after the first three steps of sequential extraction, the concentrations of Cr, Cu, and Pb reached 2.69, 1.50, and 1.88 mg/l at 1150 degrees C, while the final residues had total concentrations of 96.1, 88.4, and 60.6 mg/kg, respectively, with Cd undetected in both phases. The concentration levels fell within the regulatory threshold, indicating that the LWA fabricated from recycled metal sludge contains elements that are toxic and hazardous but not leached. Having no harmful effect on the environment, the metal sludge-based artificial LWA is not only safe but also practical with good physical properties.
Chang
Fang-Chih
FC
Research Center for Environmental Pollution Prevention and Control Technology, Graduate Institute of Environmental Engineering, National Taiwan University, 71 Chou-Shan Road, Taipei 106, Taiwan, ROC.
Lo
Shang-Lien
SL
Lee
Ming-Yu
MY
Ko
Chun-Han
CH
Lin
Jyh-Dong
JD
Huang
Su-Chen
SC
Wang
Chu-Fang
CF
D003247:Conservation of Natural Resources; D003252:Construction Materials / Q000032:analysis*; D004785:Environmental Pollutants / Q000032:analysis; D006358:Hot Temperature; D007220:Industrial Waste / Q000032:analysis; D019216:Metals, Heavy / Q000032:analysis*; D016062:Porosity; D012722:Sewage
D004785:Environmental Pollutants; D007220:Industrial Waste; D019216:Metals, Heavy; D012722:Sewage