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

Bing Gong,Li-Ya Ge,Weizhong Yang,Yi Deng,Yong He,Yuanyi Yang,Xiaolong Sun,Kewei Zhang

doi:10.1371/journal.pone.0178816

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.

Highlights

With the flourishing development of global economy and urbanization, a large quantity of municipal solid waste (MSW) and its sharp increase have been two of the most critical issues worldwide
For heavy metals in raw incineration fly ash (IFA), Pb leaching concentration merely exceeded the limits according to environmental protection law of China, and we only focused on the leaching behavior of Pb before and after the thermal treatment
Calcium oxide (CaO) and chlorine accounted for 46.6% and 21.1% in IFA, respectively

Summary

Introduction

With the flourishing development of global economy and urbanization, a large quantity of municipal solid waste (MSW) and its sharp increase have been two of the most critical issues worldwide. It was reported that the amount of MSW was soaring at a rate of 2 billion tons annually [1]. The existing landfills tend to be fully filled and there is little land space for new sites. It is widely confirmed that the disposal of MSW in landfills has induced sever. Role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section

Methods

Results

Conclusion