A combined kinetic and thermodynamic approach for interpreting the complex interactions during chloride volatilization of heavy metals in municipal solid waste fly ash

• Published in: Waste management (Elmsford) Vol. 87; pp. 204 - 217
• Main Authors: Kurashima, Kenta, Matsuda, Kaho, Kumagai, Shogo, Kameda, Tomohito, Saito, Yuko, Yoshioka, Toshiaki
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 15.03.2019
• Subjects: Carbon; Chloride volatilization; Coal Ash; Fly ash; Heavy metal; Incineration; Kinetics; Metals, Heavy; Particulate Matter; Refuse Disposal; Solid Waste; Thermodynamic calculation; Thermodynamics; Volatilization; Fly ash; Chloride volatilization; Kinetics; Thermodynamic calculation; Heavy metal
• ISSN: 0956-053X; 1879-2456
• DOI: 10.1016/j.wasman.2019.02.007

[Display omitted] •Target heavy metals were volatile as PbCl2, (CuCl)3, ZnCl2, KZnCl3, and NaMnCl3.•Cr was immobilized by MgO and formed (MgO)(Cr2O3).•Pb, Zn, and Mn chlorination were facilitated in the presence of unburned carbon.•Unburned carbon inhibited chlorination of CuO by reduction of it. This study elucidated complex interactions during the chloride volatilization of heavy metals (Pb, Cu, Zn, Mn, and Cr) from municipal solid waste fly ash by combining thermodynamic and kinetic approaches. Chloride volatilization tests under HCl flow at 900 °C and subsequent rinsing with water achieved almost complete removal of Pb, Zn, and Mn. In contrast, almost 100 % of Cr and ∼40 % of Cu were not removed by either volatilization or rinsing processes. Kinetics indicated that the chlorination of Pb, Zn, and Mn followed a pseudo second order reaction and their apparent activation energies were 96.3, 89.2, and 43.5 kJ/mol, respectively. Further thermodynamic calculation revealed that the components contained in fly ash greatly influenced the chlorination of each heavy metal. Unburned carbon facilitated the chlorination of Pb, Zn, and Mn, while it inhibited Cu chlorination. MgO immobilized Cr and inhibited chlorination. KCl and NaCl promoted Zn and Mn chlorination, respectively. The revealed chloride volatilization behavior and effects of co-existing elements could be useful in the design of high-efficiency recovery process of heavy metals from fly ash and the utilization of residues as raw materials for cement. Furthermore, these findings could guide the realization of a recycling-oriented society in terms of reducing waste disposal.