Title: Microstructure, short-term and long-term leaching behaviour of zinc encapsulated by calcium carbide residue-fly ash

Authors: Kiatsuda Somna; Chai Jaturapitakkul; Puangrat Kajitvichyanukul

Addresses: Department of Environmental Engineering, Faculty of Engineering, King Mongkut's University of Technology, Thonburi, Bangkok, 10140, Thailand ' Department of Civil Engineering, Faculty of Engineering, King Mongkut's University of Technology, Thonburi, Bangkok, 10140, Thailand ' Center of Excellence for Environmental and Hazardous Waste Management, Department of Environmental Engineering, Faculty of Engineering, King Mongkut's University of Technology, Thonburi, Bangkok, 10140, Thailand; Department of Civil Engineering, Faculty of Engineering, Naresuan University, Phitsanulok, 65000, Thailand

Abstract: This study evaluates the use of a calcium carbide residue-fly ash mixture as a new material to encapsulate zinc. Zinc was added into both calcium carbide residue-fly ash pastes (ZnCF) and ordinary Portland cement (ZnOPC) for comparison purposes. The fracture surfaces, crystalline phases, and zinc leaching behaviours of pastes were determined. A new crystalline phase of calcium zincate (Ca(Zn₂(OH)₆).2H₂O) was detected. The compressive strengths of ZnCF pastes were dramatically decreased, whereas the strengths of the ZnOPC pastes were slightly decreased. However, the compressive strengths of the ZnCF pastes after curing for 28 days were comparable to those of solidification cements used for hazardous waste disposal in secured landfills. Evaluation of the short-term leaching behaviour showed that the zinc concentrations that leached out were much lower than the allowable limit (500 mg/L). The diffusion coefficient (De) and leachability index (LX) for long-term leaching of samples were not significantly different.

Keywords: immobilisation; Portland cement; microstructure; leaching behaviour; zinc leaching; calcium carbide residue; fly ash; fracture surfaces; crystalline phase; calcium zincate; compressive strength; solidification; hazardous waste disposal.

DOI: 10.1504/IJEWM.2016.076424

International Journal of Environment and Waste Management, 2016 Vol.17 No.1, pp.26 - 43

Received: 09 Jan 2015
Accepted: 24 Sep 2015
Published online: 06 May 2016 *

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