Regulation of Electrochemically Generated Ferrous Ions from an Iron Cathode for Pd-Catalytic Transformation of MTBE in Groundwater

Abstract

An effective approach is developed to regulate the generation of Fe 2+ from an iron cathode in a three-electrode system. The Fe 2+ is then used for the Pd-catalytic transformation of methyl tert-butyl ether (MTBE) in simulated groundwater. Under conditions of pH 3, a total current of 50 mA, and 1 g/L Pd/Al 2 O 3 , 20 mg/L MTBE was completely transformed within 60 min in an undivided electrolytic cell using the iron cathode, with 14 mg/L of accumulated Fe 2+. Fe 2+ accumulation follows pseudo-first-order kinetics and the rate is regulated by electric current and groundwater pH, giving the relation of k = 5.3 × 10 4 • 10-2pH-7.25 • I 2-8.8 × 10 11 • 10 2pH-28 , where k is the rate constant of Fe 2+ accumulation (min-1) and I is the current (mA). In a modified three-electrode column using iron as the first cathode, the localized acidic and oxidizing conditions developed automatically in the iron cathode zone by partitioning the current between the two cathodes, leading to controllable generation of Fe 2+ for MTBE transformation. The stable transformation of MTBE in a long-term study suggests that this method is a sustainable approach to supplying Fe 2+ for Pd-catalytic transformation of organic contaminants in groundwater.

Insights into the Role of Humic Acid on Pd-catalytic Electro-Fenton Transformation of Toluene in Groundwater

“…The pseudo-first-order kinetics rate constant for toluene transformation increased from 0.010 min −1 in the absence of HA to 0.015 min −1 in the presence of 10 mg/L HA ( Table 1 ). The rate constants normalized by Pd concentration (0.05 gPd/L) is 0.2 and 0.3 L/gPd/min in the absence and presence of 10 mg/L HA, respectively, which is in the same level as that reported by our recent work 14 and one order of magnitude smaller than that reported by Lowry and Reinhard using Pd and H 2 for TCE hydrodechlorination 24 . The solution pH increased from 3.0 to 3.4 during the course of experiments in the absence and presence of 10 mg/L HA, which is attributed to the consumption of H + by chemical corrosion of the iron cathode ( eq.…”

“…Moreover, regarding the supply of Fe(II), sacrificial iron anode can be effective but it may produces excess amount of iron sludge 11 13 . To overcome the limitation of applying E-Fenton process in subsurface remediation, we have recently developed a novel Pd-based E-Fenton process 14 . As illustrated in Figure S1 , the process was performed in a modified three-electrode system, which contains a mixed metal oxides (MMO) anode, an iron cathode, and another MMO cathode (the composition was the same as MMO anode).…”

“…Under acidic condition ( eqs. 1 – 3 ), Pd catalyzes the in situ production of H 2 O 2 from the combination of electrochemically generated H 2 and O 2 5 6 14 15 . Using an iron cathode, Fe(II) is generated in situ from the corrosion of iron electrode under acidic condition ( eq.…”

“…5 , 6 ) Due the balance of electrons in the electric loop, neutral effluent is attained when groundwater passes through the second cathode 6 14 15 . Our recent results show that this improved Pd-based E-Fenton process can efficiently transform methyl tert -butyl ether (MTBE) in artificial groundwater with representative concentrations of inorganic compositions 14 . However, the role of ubiquitous natural organic matter (NOM) on the efficiency of the Pd-based E-Fenton process has not been characterized yet and remains a knowledge gap for field application of this process in groundwater remediation.…”

Pd-catalytic hydrodechlorination of chlorinated hydrocarbons in groundwater using H2 produced by a dual-anode system

“…Without current applied to the iron anode (20/0), TCE was only reduced by 25.3% within 4 h; when 5 mA current was applied to the iron anode (15/5), the removal increased to 66.0%; and when the applied current further increased, the removal efficiency stabilized at about 79.5%. Previous studies showed that TCE degradation shifted from reductive dechlorination in the absence of Fe(II) to OH oxidation in the presence of Fe(II) under acidic conditions, but OH oxidation was negligible at the pH above 6 because the generation of H 2 O 2 was limited and most Fe(II) was precipitated (Liao et al, 2013;Yuan et al, 2013aYuan et al, , 2012. Therefore, hydrodechlorination mechanism predominated for TCE degradation under the neutral circumstance in this work.…”