Revisiting the Role of Dissolved Silicate in Catalyzing the Hydrogen Peroxide Process with Iron-Bearing Minerals

• Published in: ACS ES&T water 2023-10, Vol.3 (10), p.3200-3205
• Main Authors: Qiu, Yicheng, Sun, Lingkai, Cui, Jiaxin, Li, Zijun, Zeng, Xiang, Liu, Yuxiao, Alshawabkeh, Akram N., Mao, Xuhui
• Format: Article
• Language: English
• ISSN: 2690-0637; 2690-0637
• DOI: 10.1021/acsestwater.2c00557

Injecting H2O2 into aquifers is a widely used in situ chemical oxidation (ISCO) technology for groundwater remediation. Dissolved silicate has been reported to decrease the reactivity of iron (III)-bearing minerals toward H2O2. In this study, the effect of naturally occurring levels of dissolved silicate (≤1 mM) on the catalyzing hydrogen peroxide (CHP) with Fe­(II) minerals is revaluated, and new observations that contradict previous studies are reported. Specifically, dissolved silicate enhances the CHP process with Fe­(II) minerals. In the presence of Fe­(II) minerals, siderite and ferrous oxide (FeO), which had a stronger dissolution tendency than Fe­(III) minerals, dissolved silicate could prevent the dissolved iron species from precipitation through a coordinating effect, therefore reinforcing the homogeneous CHP process and the degradation of 2,4-dichlorophenol. The solution pH decreased due to the generation of degradation intermediates, and the solution acidification in turn promoted further dissolution of Fe­(II) minerals. FeO particles exhibited the strongest silicate adsorption among the minerals; therefore, a higher initial silicate concentration of 1 mM was needed to observe the enhancing effect. This study redefines the role of dissolved silicate in the CHP process and provides clues to the design of an efficient H2O2-based ISCO system for the remediation of groundwater.