Long-Term Effects of Dissolved Carbonate Species on the Degradation of Trichloroethylene by Zerovalent Iron

Abstract

The effect of different concentrations of total inorganic carbon (TIC) and flow rates on the reactivity of iron metal with trichloroethylene (TCE) was studied in column experiments to verify whether concentration or mass flux of TIC is the major key parameter for barrier performance. First-order rate coefficients (kobs) for TCE degradation vary initially between 0.15 and 0.32 h-' and are positively related to TIC influent concentration. Maximal kobs were reached after 164 and 591 PV, varied between 0.55 and 1.1 h(-1), and were positively correlated to the TIC mass flux, followed by a decrease resulting in values similar to the reference system at the end of the experiments. Enhancement of iron corrosion (0.7 to 3.5 mmol kgFe(-1) d(-1) and formation of gas bubbles during the initial experimental phase were observed and were also positively correlated to TIC mass flux. The higher gas bubble formation probably has a more significant effect on porosity than mineral precipitations in Fe0-systems. The results suggest that higher TIC mass fluxes cause a more pronounced acceleration in CHC degradation, but also a faster inhibition in the longer-term. This faster inhibition has serious implication for the design of funnel and gate systems.

Influence of dissolved inorganic carbon and calcium on gas formation and accumulation in iron permeable reactive barriers

“…Corrosion rates obtained from both static (Reardon, 1995(Reardon, , 2005 and continuous column experiments (Kamolpornwijit and Liang, 2006;Parbs et al, 2007) can therefore not be used for comparison between different experimental setups with different iron amounts. Filter dimensions have an effect on corrosion rate: The longer a column the lower are averaged corrosion rates.…”

“…Parbs et al (2007) reported on gas generation in continuous column experiments starting gas collection at day 60. They suggested that mass flux of total inorganic carbon (TIC) determines corrosion rates and reduction of chlorinated hydrocarbons.…”

Influences of nanoscale zero valent iron loadings and bicarbonate and calcium concentrations on hydrogen evolution in anaerobic column experiments

“…Corrosion experiments with granular iron have indicated that the formation of mineral precipitates affect the long-term reactivity of PRB (Kober et al, 2002;Klausen et al, 2003;Kohn et al, 2005;Parbs et al, 2007;Weber et al, 2013). In particular, mainly iron hydroxide carbonate (chukanovite, Fe 2 CO 3 (OH) 2 ) is formed in the presence of carbonate on the iron surface (Ruhl et al, 2011) and influences significantly the reactivity (Jeen et al, 2006;Lee and Wilkin, 2010;Ruhl et al, 2012).…”

“…In particular, mainly iron hydroxide carbonate (chukanovite, Fe 2 CO 3 (OH) 2 ) is formed in the presence of carbonate on the iron surface (Ruhl et al, 2011) and influences significantly the reactivity (Jeen et al, 2006;Lee and Wilkin, 2010;Ruhl et al, 2012). High concentrations of inorganic carbon increase not only the dehalogenation rates of chlorinated groundwater contaminants but also the inhibition of reactive sites in the long-term (Parbs et al, 2007). Based on results of field-scale PRBs, Lee and Wilkin (2010) calculated the phase stability of siderite (FeCO 3 ), chukanovite and ferrous hydroxide in a Fe(II)eCO 2 eH 2 O-system.…”

Formation of chukanovite in simulated groundwater containing

“…[1][2][3][4] Corrosion products formed on the surface of Fe 0 through chemical reactions have major effects on the reactivity, porosity, permeability, and consequent longevity of Fe 0 -PRB technology. [5][6][7][8] Several researchers [7][8][9][10][11] have attempted to characterize the surface precipitate that is generated in laboratory or field studies, and the corrosion products on the surface of Fe 0 was found to include aragonite, calcite, iron carbonate (siderite), sulfides and oxides (goethite, lepidocrocite, magnetite, and hematite), hydroxide, hydroxy oxides, and other intermediate products. Other efforts [12][13][14][15] have discovered the presence of the Fe 2 (OH) 2-CO 3 , which is a frequently detected secondary mineral precipitate in bicarbonate (carbonate) solutions and is overlooked for a long time.…”