TRANSPORT OF CHLORIDE SALTS AND TIRE-DERIVED CHEMICALS THROUGH ROADSIDE SOILS: EXPERIMENT AND MODELING STUDY

Taiwo Olawale Akinleye

This dissertation addresses two main problems and is divided into two sections. In the first section, we examined the fate and transport of chloride (Cl⁻) salts with and without the use of organic additives in roadside soils that are commonly encountered in the United States. Chloride (Cl⁻) salts with agro-based additives have been increasingly used as anti-icers or deicing chemicals on roadways in North America for improved safety and mobility during the winter season. They facilitate improved road pavement surface conditions during the harsh winter season and reduce traffic accidents and hindrance to socio-economic activities. In many cases, however, roadside soils are often the recipients of these chloride salts through runoff actions and deposition from snow ploughing activities. While their use provides immense benefits to commuters, their fate and transport through roadside soil haven’t been examined. There is no holistic study that has investigated the fate and transport of this composite material (i.e., chloride salts and agro-based additives) in roadside soils. In this study, we examined the fate and transport of two chloride salt (sodium and magnesium) ions and the effect of beetroot juice additive on them. To achieve this, we conducted extensive laboratory soil column and batch experiments and evaluated the effect of the direction of flow on the fate and transport of these chloride salt ions by utilizing vertical and horizontal soil columns. Results obtained from this study suggest that beetroot juice altered the surface properties of the soil. This influenced the adsorption capacity and affinity of the ions on the soil particle, thus increasing the probability of chloride salt ion migration to groundwater at a faster rate. The mechanism of alteration was explained to have resulted from (1) surface coating of the soil particle and increasing the functional group for ion interaction. (2) binding of the chloride salt ion within the functional group of the beetroot juice, thereby limiting the interaction of these ions with the soil particle surfaces.In the second section, we explored the use of biochar as a sink for 6PPD-Q by leveraging its favorable characteristics of a stable carbon structure with long-term stability, surface functionality, high porosity, and high surface area. We further explored the effect of surface modification of the biochar using chemical oxidation techniques on the adsorption potential of 6PPD-Q. Specifically, we examined the correlation of 6PPD-Q adsorption to two surface functional groups (phenolic and quinone). To achieve this, we conducted extensive laboratory experiments, including chemical oxidation with hydrogen peroxide and nitric acid, batch experiments for sorption studies, BET analysis for surface and pore structure evaluation, and others. Results obtained from this study suggest that (1) oxidation of biochar using hydrogen peroxide and/or nitric acid increased the concentration of phenolic and quinone surface functional groups on biochar. There is, however, no clear evidence of a linear increase in the quantity of these functional groups with respect to the concentration of the oxidant used (2); the adsorption of 6PPD-Q on the biochar surface was independent of the phenolic and quinone surface functional group concentration. Perhaps correlation with the total oxygen-containing surface functional group may be a good metric for this (3). Oxidizing biochar with strong acid altered the carbon structure of the biochar. However, the influence of this modification was not reflected in the adsorption characteristics of 6PPD-Q on it. These findings reinforce that biochar provides excellent physicochemical properties for the adsorption of 6PPD-Q with an adsorption efficiency of about 99%. However, the adsorption mechanism is a combined effect of its physical characteristics and more beyond what was examined in this study.

TRANSPORT OF CHLORIDE SALTS AND TIRE-DERIVED CHEMICALS THROUGH ROADSIDE SOILS: EXPERIMENT AND MODELING STUDY

Files and links (1)

Abstract

Metrics

Details