Insights into the speciation of heavy metals during pyrolysis of industrial sludge

Chanaka Udayanga W D; Andrei Veksha; Apostolos Giannis; Yen Nan Liang; Grzegorz Lisak; Xiao Hu; Teik-Thye Lim

doi:10.1016/j.scitotenv.2019.07.095

Insights into the speciation of heavy metals during pyrolysis of industrial sludge

Sci Total Environ. 2019 Nov 15:691:232-242. doi: 10.1016/j.scitotenv.2019.07.095. Epub 2019 Jul 7.

Authors

Chanaka Udayanga W D¹, Andrei Veksha², Apostolos Giannis³, Yen Nan Liang², Grzegorz Lisak⁴, Xiao Hu⁵, Teik-Thye Lim⁶

Affiliations

¹ Residues and Resource Reclamation Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, CleanTech One, Singapore 637141, Singapore; School of Civil and Environmental Engineering, Nanyang Technological University, Singapore 639798, Singapore; Interdisciplinary Graduate School, Nanyang Technological University, Singapore 639798, Singapore.
² Residues and Resource Reclamation Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, CleanTech One, Singapore 637141, Singapore.
³ Residues and Resource Reclamation Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, CleanTech One, Singapore 637141, Singapore; School of Environmental Engineering, Technical University of Crete, University Campus, 73100 Chania, Greece.
⁴ Residues and Resource Reclamation Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, CleanTech One, Singapore 637141, Singapore; School of Civil and Environmental Engineering, Nanyang Technological University, Singapore 639798, Singapore.
⁵ School of Materials Science and Engineering, Nanyang Technological University, 639798, Singapore.
⁶ Residues and Resource Reclamation Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, CleanTech One, Singapore 637141, Singapore; School of Civil and Environmental Engineering, Nanyang Technological University, Singapore 639798, Singapore. Electronic address: cttlim@ntu.edu.sg.

PMID: 31323569
DOI: 10.1016/j.scitotenv.2019.07.095

Abstract

The purpose of this study was to determine the mechanisms in heavy metals immobilisation during pyrolysis of industrial sludge (IS). Pyrolysis was conducted in a fixed-bed unit at the temperature range between 400 and 800°C. Conventional and advanced analytical techniques were employed to assess the influencing parameters on the transformation of heavy metals during pyrolysis process. The examined heavy metals (i.e. Mn, Ni, Cu, Zn, Cd, and Pb) were effectively immobilised in the char derived at ≤600°C. In contrast, for the char derived at ≥700°C, Mn, Cu, and Zn leaching efficiencies were significantly increased. According to BCR sequential extraction procedure (SEP) results, pyrolysis of IS conducted at ≤600°C transformed heavy metals into stable fractions (i.e. associated with Fe-Mn nodules, and organics and sulphides), while Mn, Cu, and Zn bound in these fractions decomposed into easily soluble forms at higher temperatures. Advanced analytical characterisation (XRD, EDX, XPS, and FTIR) of the derived char and anion concentrations in the leachate have demonstrated that the increase in metal leaching was probably due to the formation of metal halides.

Keywords: Char; Heavy metals; Immobilisation; Industrial sludge; Pyrolysis; Speciation.