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. 2017 Jun 6;12(6):e0178816.
doi: 10.1371/journal.pone.0178816. eCollection 2017.

Stabilization of lead in incineration fly ash by moderate thermal treatment with sodium hydroxide addition

Bing Gong  1 , Yi Deng  1 , Yuanyi Yang  2 , Yong He  3 , Xiaolong Sun  4 , Li-Ya Ge  4 , Kewei Zhang  1 , Weizhong Yang  1
Affiliations

Stabilization of lead in incineration fly ash by moderate thermal treatment with sodium hydroxide addition

Bing Gong et al. PLoS One. .

Abstract

Municipal solid waste (MSW) incineration fly ash (IFA) can be potentially reused as a substitute for some raw materials, but treatment for detoxification is indispensable owing to high contents of heavy metals in fly ash. In the present work, due to excessive leaching concentration of lead (Pb), a moderate thermal treatment with sodium hydroxide (NaOH) addition was employed to stabilize Pb in IFA. The moderate thermal treatment was performed under relatively low temperature ranging from 300 to 500°C and at retention time from 1 to 3 h with NaOH addition in a range of 1 to 9%. Leaching results showed that leaching concentrations of Pb in IFA leachates decreased below the standard for hazardous waste identification (5 mg/L) in China under all treatment scenarios. With the increase of temperature, retention time and the amount of NaOH, the concentration of Pb were further suppressed in IFA leachates. Especially, at 500°C for 3 h with 9% NaOH addition, the concentration of Pb dropped to 0.18 mg/L, which was below the standard for sanitary landfill (0.25 mg/L) in China. In thermal process, needle-like crystallites melted to form granules and clumps with compacter structure and less pores. After the thermal treatment, water-soluble and exchangeable fractions of Pb significantly decreased. Therefore, the thermal treatment coupled with NaOH could be applied to realize the environmentally sound management of MSW IFA.

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Conflict of interest statement

Competing Interests: Yong He, Xiaolong Sun and Li-Ya Ge are employed by CECEP Chengdu Renewable Energy Co., Ltd. and Zerowaste Asia Co., Ltd. There are no patents, products in development or marketed products to declare. This does not alter our adherence to all the PLOS ONE policies on sharing data and materials, as detailed online in the guide for authors.

Figures

Fig 1
Fig 1. The experimental scheme of thermal treatment process.
Fig 2
Fig 2. Particle size distribution of raw IFA.
Fig 3
Fig 3. TCLP leaching concentrations of Pb in different treated residues.
Fig 4
Fig 4. TCLP leaching concentrations of Pb as a function of the amount of NaOH addition.
Fig 5
Fig 5. XRD pattern of (a) raw IFA; (b) R319; (c) R439; (d) R519, F; (e) R539.
Fig 6
Fig 6. SEM images of (a) raw IFA; (b) R319,; (c) R339; (d) R439; (e) R519; (f) R539.
Fig 7
Fig 7. Microstructure images of (a) raw IFA; (b) R319; (c) R339; (d) R439; (e) R519; (f) R539.
Fig 8
Fig 8. SEM and corresponding EDS images of (a) raw IFA: a1, composition of needle-like crystallites; a2, composition of flake-like crystallite; (b) R539: b1, composition of granules; b2, composition of clump.
Fig 9
Fig 9. Distribution pattern of Pb in (a) raw IFA; (b) R539.
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