Enhanced redox degradation of chlorinated hydrocarbons by the Fe(II)-catalyzed calcium peroxide system in the presence of formic acid and citric acid

Abstract

Two carboxylic acids (formic acid (FA) and citric acid (CIT)) enhanced the Fenton process using Fe(II)-activated calcium peroxide (CP) to develop a hydroxyl radical (HO•) and carbon dioxide radical (CO 2 •-) coexistence process for the simultaneous redox-based degradation of three chlorinated hydrocarbons (CHs), namely carbon tetrachloride (CT), tetrachloroethene (PCE), and trichloroethene (TCE), was investigated. The experimental results showed that CT removal was increased while PCE and TCE degradation were decreased with the addition of FA to the Fe(II)/CP system. However, addition of CIT to the Fe(II)/CP/FA system enhanced the removal efficiency of all three contaminants. For example, 81.7%, 79.4%, and 96.1% of CT, PCE, and TCE, respectively, were removed simultaneously under the optimal molar ratio of 12/12/12/12/1 of CIT/CP/Fe(II)/FA/CHs. Investigations of the degradation mechanism confirmed the specific roles of HO• and the secondarily generated CO 2 •radical, i.e., PCE and TCE were degraded oxidatively by HO• while CT was degraded via reductive dechlorination by CO 2 • −. Carbonate reduced PCE and TCE degradation in actual groundwater as it consumed reactive oxygen species, whereas humic acid and neutral pH had minimal impact on contaminant removal. These results can help us better understand the synergistic effects of different carboxylic acids in the modified Fenton process for the redox-based degradation of refractory chlorinated hydrocarbons.

Trace-Dissolved S(-II) Triggers the Fe(III)-Activated H2O2 Process for Organic Pollutant Degradation by Promoting the Fe(III)/Fe(II) Cycle: Kinetics, Toxicity, and Mechanisms

“…As the two most common oxidants in AOPs, PDS and PMS have been studied for many years. , Figure c shows that the additive DS­(-II) also significantly enhanced the removal of the target contaminant BPA in PDS/Fe­(III) and PMS/Fe­(III) systems. This result indicates that DS­(-II) is a perspective co-activator for accelerating the Fe­(III)/Fe­(II) cycle in AOPs and provides some inspirations for Fe­(II)-activation of some emerging peroxides, such as calcium peroxide, peracetic acid − and percarbonate …”

Identification of Superoxide Contribution through the Quenching Method and Model System

“…Since no inhibition was observed, O 2 •– is often regarded as ineffective; although the conclusion may be a fact due to the low reactivity of O 2 •– , using chloroform as an O 2 •– quencher is unreasonable and may potentially spread misleading information. The high second-order reaction rate constant ( k = 3 × 10 10 M –1 s –1 ) between chloroform and O 2 •– has been referenced in various literatures; ,,− however, there is no relevant information in the original source literature . The mentioned reaction rate constant ( italick normale aq − , CHCl 3 = 3 × 10 10 M –1 s –1 ) is indeed attributed to the reaction between chloroform and e aq – .…”

Effect of carboxylic acids in promoting the radical decomposition of H 2 O 2 in Fenton processes for the treatment of agrochemicals

“…According to the authors, carboxylic acids form complexes with Fe 2+ that change the reaction rates of the iron redox cycle (Baba et al, 2015). Jiang et al (2019) applied the Fenton process promoted by formic acid and citric acid to the degradation of chlorinated hydrocarbons, and both enhanced the removal of the contaminant.…”