[Comparison of Different Leaching Methods for Heavy Metals in Sludge Fly Ash and Comprehensive Toxicity Evaluation].

ABSTRACT

Fly ash from sludge incineration was separated into five different sizes (<1 µm, 1-2.5 µm, 2.5-10 µm, 10-50 µm, and > 50 µm) by high-precision air classification equipment. The leaching of heavy metals was contrastively studied using the HJT 299-2007-sulfuric acid/nitric acid method, HJ 557-2009-Horizontal Oscillation Method, toxicity characteristic leaching procedure (TCLP), and European standard protocol (EN 12457-3) for the different size fractions of the fly ash. Based on the leaching results, an evaluation method for the comprehensive toxicity of heavy metal leaching was established. The results show that the content of heavy metals and the amount of leaching from the fly ash decrease with the increase in fly ash particle size. The leaching of the heavy metals Zn and Cu in the < 1 µm particle size range of TCLP leaching method was the highest, at 107.34 mg·kg-1 and 318 mg·kg-1, respectively. The TCLP and sulfuric acid/nitric acid methods of heavy metal leaching were more effective than the EU (EN 12457-3) and horizontal oscillation methods. According to the value of OPTI, the OPTI value of < 10 µm fly ash was much larger than that of fly ash that was > 10 µm. This indicated that the fly ash of particle size < 10 µm was more toxic and more harmful.