Leaching characteristics of chlorine from municipal solid waste incineration fly ash by up-flow percolation column tests

Abstract

To determine the potential release of chlorine from municipal solid waste incineration (MSWI) fly ash, the leaching behaviors of MSWI fly ash from Likeng waste incineration power plant in China were characterized according to the US EPA method 1314. Chlorine leaching characteristics were investigated over a wide range of liquid-to-solid ratios (L/S 0.2–10 mL/g-dry) and different pH conditions (2, 4 and 6). The test results revealed that the pH of eluate increased with increasing L/S ratio due to the increased release of CaO in fly ash. An initial fast early chlorine release followed by a slower, final release period was obtained. Chlorine release widely exceeds the limit of 2500 mg/L at initial stage. A maximum extractable amount (43–48 %) was obtained when the cumulative L/S ratio is about 2. The leachability of chlorine was almost pH independent due to the strong solubility. The leaching of chlorine is controlled by solution followed by diffusion of capillary. Exponential decay equation could well fit the cumulative chlorine release curves. X-ray diffraction results showed that the water-soluble chlorides, such as sodium chloride (NaCl), potassium chloride (KCl) and calcium chloride (CaCl2·2H2O), were easy to leach out, while calcium chloride hydroxide [Ca(OH)Cl] was hard to release.