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Behavior of Sequential Extraction of Lead from Thermally Treated Lead(II)-Doped Alumina

Department of Environmental Science, Tunghai Univ., No. 181, Sec. 3, Taichung-Kang Road, Taichung City, Taiwan, R.O.C.

^* Corresponding author (yulin{at}s867.thu.edu.tw).

ABSTRACT

There are environmental concerns about emission of heavy metals in flue gases during incineration of hazardous wastes. Low temperature injection of sorbents has been suggested as a way to reduce the heavy metal content of the emitted gases. We investigated the extractive behavior of Pb in thermally treated Pb²⁺-doped alumina using the USEPA toxicity characteristics leachability procedure (TCLP) and a sequential extraction method to obtain information on the Pb-alumina reaction. Thermal treatment of Pb²⁺-doped alumina was in the 100 to 900°C range for 10 to 60 min. Results indicated that the Pb²⁺-doped alumina treated at higher temperature for longer duration was resistant to the TCLP and to the sequential extraction for the first four fractions, but not for the residual fraction (Fraction 5). The relationship between total extracted Pb of the first four fractions and the TCLP concentration was strong (r = 0.993 for the 100°C and r = 0.996 for the 500°C treatments). Almost all of the doped Pb was distributed between conceptual fractions that were either bound to carbonates or were residual that was extracted with 10% HF and H₂O₂. The shift in distribution of Pb that was carbonate-bound to that bound in the residual fraction as treatment temperature increased from 100 to 500°C was more than that which shifted from 500 to 900°C. After treatment at 900°C most of the Pb was associated with the residual fraction (indicating a strong sorption between Pb and alumina) and the TCLP concentration dropped to nondetectable levels.