Leaching Toxicity and Bioaccessibility of Heavy Metals in MSWI Fly Ash with Various Particle Sizes

Abstract

Size fractionation and chemical composition of municipal solid waste incinerator (MSWI) fly ash were investigated. And the leaching efficiency of heavy metals was contrastively studied using toxicity characteristic leaching procedure (TCLP), European standard protocol (EN12457-2), sequential extraction procedure (SEP) and physiologically based extraction test (PBET) for different size-fractionated fly ash. The results indicated that the main compositing elements of fly ash were Ca, Si, Al, Mg, Fe, Na, K. 58.7% of fly ash particles were in the range of 38-106 μm and the amount in the<150 μm particle-size fraction accounted for more than 90% of in total, Cu, Pb and Cd mainly existed in the residual form with a minor amount of exchange fraction for any size-fractioned fly ash particles. TCLP result showed that leaching amounts of Zn, Cu and Pb, except for As and V, firstly increased and then decreased with the reduction of particle size. The leaching amount of Zn reached the highest value of 547 mg·kg-1 in the range of 38-106 μm, whereas the leaching amount of heavy metals exhibited a lower level for all size-fractioned fly ash particles. The extraction concentrations of Zn, Pb, Cu and As reached 3270, 339, 335 and 16.8 mg·kg-1 for the PBET tests, respectively, which were significantly higher than those of the TCLP. Therefore, heavy metals in MSWI fly ash had the potential bioavailability to human body.