(106b) Carbon Nanotubes to Immobilize Heavy Metals in Contaminated Soils (Invited)

António Alberto S. Correia¹, Martim P. S. R. Matos ² and Maria G. Rasteiro³

¹ Department of Civil Engineering and CIEPQPF – Research Centre for Chemical Processes and Forest Products, Univ. of Coimbra, Rua Sílvio Lima, 3030-788 Coimbra, Portugal

² MSc Student, Department of Civil Engineering, Univ. of Coimbra, Rua Sílvio Lima, 3030-788 Coimbra, Portugal

³ Department of Chemical Engineering and CIEPQPF – Research Centre for Chemical Processes and Forest Products, Univ. of Coimbra, Rua Sílvio Lima, 3030-790 Coimbra, Portugal

The contamination of soils with heavy metals is a growing concern in modern societies. When a soil is contaminated with heavy metals, which are inorganic, destruction of the contaminants is not an option since they are not biodegradable (Lone et al. 2008; Kroopnick 1994). To avoid the spread of contamination, soil stabilization techniques can be applied mixing materials with the soil in order to partially immobilize heavy metals. Carbon Nanotubes (CNTs) are nanomaterials known for its exceptional properties, like high surface area and adsorption capacity. Due to these unique properties, the potential use of CNTs in heavy metal contaminated water treatment has been studied, with very satisfactory results (Kabbashi et al. 2009; Abdel Salam 2013), however their application in contaminated soils is practically unexplored.

This experimental work is focused on studying the potential of using CNTs in soil remediation, especially to immobilize heavy metals. First, a large quantity of soil was collected and artificially contaminated with several heavy metals: lead (Pb2+), copper (Cu2+), nickel (Ni2+) and zinc (Zn2+), commonly present in contaminated soils. In order to avoid CNTs agglomeration, which originates the loss of their beneficial properties, an aqueous suspension of CNTs was prepared using a non-ionic or anionic surfactant combined with ultrasonic energy, to promote CNTs dispersion. Combination of two surfactants was also explored. Then, the soil, with and without the addition of CNTs, was subjected to adsorption tests to evaluate the CNTs capacity to improve heavy metals immobilization. To validate the adsorption test results, permeability tests were executed, simulating the conditions of a real case scenario.

The results obtained led to conclude that the addition of a small amount of dispersed CNTs can successfully increase the adsorption capacity of the soil and consequently improve the immobilization of heavy metals in the soil matrix (Matos 2016). The immobilization percentage varies with the type of heavy metals under study. For the soil studied, CNTs were most effective in the case of Ni2+ and Zn2+ immobilization, while in the case of Pb2+ and Cu2+ the addition of CNTs had almost no effect. Moreover, lixiviation tests conducted proved that CNTs were not released into water once they had been properly adsorbed in the soil.

Acknowledgement

The authors would like to acknowledge the financial support of Pest/C/EQB/UI0102/2013 from FCT/MCTES (PIDDAC), co-financed by the European Regional Development Fund (ERDF) through the program COMPETE (POFC).

References

Abdel Salam, M. 2013. 'Removal of heavy metal ions from aqueous solutions with multi-walled carbon nanotubes: Kinetic and thermodynamic studies', International Journal of Environmental Science and Technology, 10: 677-88.

Kabbashi, Nassereldeen A, Muataz A Atieh, Abdullah Al-Mamun, Mohamed ES Mirghami, MDZ Alam, and Noorahayu Yahya. 2009. 'Kinetic adsorption of application of carbon nanotubes for Pb(II) removal from aqueous solution', Journal of Environmental Sciences, 21: 539-44.

Kroopnick, P. M. 1994. "Vapor abatement cost analysis methodology for calculating life cycle costs for hydrocarbon vapor extracted during soil venting." In Remediation of hazardous waste contaminated soils, 779-90. RC Press.

Lone, Mohammad Iqbal, Zhen-li He, Peter J Stoffella, and Xiao-e Yang. 2008. "Phytoremediation of heavy metal polluted soils and water: Progresses and perspectives " In Journal of Zhejiang University. Science. B, 210-20. Hangzhou.

Matos, Martim. 2016. "Soil Decontamination using Nanomaterials." Msc Thesis, University of Coimbra, Coimbra, Portugal. (in Portuguese)