Oxidation of Aqueous Pollutants Using Ultrasound:  Salt-Induced Enhancement

Abstract

Ultrasound can be used to oxidize aqueous pollutants; however, due to economic reasons, higher oxidation/destruction rates are needed. This study reports enhancements of reaction rates by the addition of sodium chloride salt. Using 20 kHz ultrasound, large salt-induced enhancements are observed6-fold for chlorobenzene, 7-fold for p-ethylphenol, and 3-fold for phenol oxidation. The reaction rate enhancements are proportional to the diethyl ether−water partitioning coefficient of the pollutants. It appears that the majority of oxidation reactions occur in the bubble−bulk interface region. The addition of salt increases the ionic strength of the aqueous phase which drives the organic pollutants toward the bubble−bulk interface. A first order reaction rate equation is proposed which can represent the observed enhancement with a good accuracy. A new sonochemical-waste-oxidation process is proposed utilizing the salt-induced enhancement.

A parametric review of sonochemistry: Control and augmentation of sonochemical activity in aqueous solutions

“…Seymour et al found an increase in oxidisation reactions occurring at the bubble surface with the use of sodium chloride [210]. The group suggested that there was an increase in the ionic strength of the liquid which drove organic pollutants to the region.…”

Electro ultrasonic remediation of polycyclic aromatic hydrocarbons from contaminated soil

“…It shows that the efficiency of It was found that the oxidation of organic compounds by sonocation highly depends on the concentration [29,30]. That means the expose with ultrasound covers more in low concentration.…”

Sonochemical degradation of Basic Red 29 in aqueous media

“…57 Under the rise of ionic strength induced by the presence of salts, the solute is expected to migrate from bulk solution to the interface of the bubble/solution where the concentration of hydroxyl radicals is high and degradation is likely to occur fast. 58 Simultaneously, the presence of salts reduces the amount of dissolved gas, and hence the bubble coalescence will also be reduced, resulting in a greater number of small bubbles of higher sonochemical activity. 37 However, the lower positive effect of seawater compared to those of mineral and river waters was attributed to the ultrasound attenuation due to the high solution viscosity and surface tension induced by the high quantity of salts presents in seawater.…”