Impact of Soil Particle Size Distribution on Zinc Immobilization Using Nano Zero Valent Iron

Abstract

The unsafe disposal of sewage, industrial effluents, and solid waste has contaminated urban soil with heavy metals. Zinc (Zn), although it is a micronutrient, could be considered toxic when in excess quantities. In recent studies, the use of nanoscale materials for the remediation of toxic heavy metals has been established. In this study, nano zero valent iron (nZVI) is used to study the effect of the grain size distribution (GSD) on the immobilization of excess Zn in the soil. Three different soils, with 10% finer (10F), 50% finer (50F), and 90% finer (90F) particles less than 75 μm were considered in this study. The immobilization efficiency was obtained by comparing the leachability that was obtained by performing a toxicity characteristic leaching procedure (TCLP) on all the samples, which were spiked with Zn and treated with nZVI. The spiked samples with three levels of contamination were treated with three different nZVI doses, and variations in the speciation of Zn were analyzed using a sequential extraction procedure (SEP). The analysis was conducted using response surface methodology (RSM). The immobilization efficiency was influenced by the GSD of the soil, Zn concentration, and nZVI dosage. A 12%–15% increase in the immobilization efficiency for coarser soil compared with that of the finer soil was obtained. The models were validated using ANOVA and agreed with the experimental results. The preliminary estimates of the immobilization efficiency could be obtained based on a site-specific study, which is illustrated in this study using regression models.