Adsorption of metal ions from aqueous solution by recycled aggregate: estimation of pretreatment effect

Abstract

Heavy metal ions (Pb²⁺, Cd²⁺, Cu²⁺, Ni²⁺, and Zn²⁺) were adsorbed by recycled aggregate (RA), which was pretreated with acidic or basic solution. Brunauer–Emmett–Teller analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy/energy dispersive spectroscopy were used to investigate the differences in the physicochemical and adsorption characteristics between RA and pretreated RA. The results suggest that RA treated with NaOH (NRA) had improved physical and chemical characteristics. The adsorption kinetics of NRA for heavy metals was pseudo-second-order, and most of the heavy metal ions were bound to the NRA within 360 min. The maximum adsorption capacities assumed by Langmuir isotherms were in the order Pb²⁺ > Cu²⁺ > Cd²⁺ > Ni²⁺ > Zn²⁺. Equilibrium adsorption data for the heavy metal ions fit well with the Langmuir model with regression coefficients R² > 0.95. At solution pH lower than 5, the adsorption specificity of the NRA for heavy metals was Pb²⁺ ≥ Cu²⁺ > Cd²⁺ > Zn²⁺ ≥ Ni²⁺. Moreover, in harmful substance tests, all the heavy metals were detected in small amounts, but were found to be below the corresponding acceptance standards (as defined by the waste official test and toxicity characteristic leaching procedure).

Keywords:

• Adsorption
• Construction waste
• Heavy metals
• Pretreatment
• Recycled aggregate

Acknowledgments

We thank Dr D.Y. Kang, Center for Research Facilities (YCRF), Yonsei University for providing analytical facility for heavy metal analysis. This research was a part of the project titled “Development of Sustainable Remediation Technology for Marine Contaminated Sediments” funded by Ministry of Oceans and Fisheries, Korea.