Can halloysite nanotubes be used to remediate zinc and lead-contaminated marine clay? A solidification/stabilization approach

Abstract

This paper presents details of an experimental study employing the solidification/stabilization (S/S) technique to treat zinc (Zn) and lead (Pb) contaminated marine clay using two types of halloysite nanotubes [Matauri Bay (MB-Hal) and Dragonite (DG-Hal)]. To this end, an extensive laboratory-testing matrix was developed to investigate the effects of MB-Hal and DG-Hal contents (2, 4, 6, and 8% by mass of dry clay) and Zn and Pb concentrations (0.5, 1, and 2% by mass of dry clay) on the engineering properties of the clay, including, grading characteristics, Atterberg limits, compaction characteristics, unconfined compressive strength (UCS), and secant modulus. Furthermore, X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests were performed to gain an insight into the mechanisms responsible for the changes in engineering properties of the contaminated-stabilized clay. In addition, descriptive statistics were employed to better assess the effect of MB-Hal and DG-Hal treatments on the strength development. The findings reveal that 6% MB-Hal and DG-Hal content was optimal in improving the UCS for the uncontaminated clay. The level of Zn and Pb concentrations were found to have considerable influence on the engineering properties and microstructural characteristics of the stabilized clay. MB-Hal and DG-Hal improve the UCS of the contaminated clay up to 1% Zn and Pb concentrations; beyond that, the UCS decreased. A comparison of the two treatment materials reveals that DG-Hal treatment is more effective than MB-Hal treatment in improving the strength properties of the contaminated clay. SEM analysis further shows that the stabilization process modified the porous network of the clay as the pores of the clay were filled by the halloysite nanoparticles. The findings suggest that both MB-Hal and DG-Hal can be effectively used as sustainable S/S agents for contaminated soft soils.