Batch experiments were conducted with granular iron (Fe(0)) in pH 10 solutions of 4-chloronitrobenzene (4ClNB) and mixed anions (ClO4-, SO(2-), and HCO3-). In pure solutions, SO4(2-) is known to enhance Fe(0) reactivity, whereas HCO3- has been variously reported to depress Fe(0) reactivity or enhance it ClO4- has been found to be minimally reactive with Fe(0). It was hypothesized that the effects of the anions on reactivity were mutually independent, and the combined effects could be predicted from simple mixing lines. In concentrated carbonate solutions (> 25% of the bicarbonate salt content in 8 mM ionic strength solutions), the hypothesis was supported. In mixtures where the aqueous carbonate species concentrations were low (< 25% of the salt content in 8 mM ionic strength solutions) an anomalous reactivity enhancement was noted. Geochemical modeling using PHREEQC suggested that precipitation of Fe(OH)2(a) in preference to FeCO3(s) in weak carbonate solutions freed CO3(2-) to corrode the iron, causing the deviation from the mixing line prediction. SEM analysis confirmed higher carbon presence on iron that had contacted carbonate rich solutions compared to iron that had not.
A benchtop sandbox constructed from nested storage tanks (NeSTs), was assembled for studying flow and transport in porous media. Molded plastic storage containers, purchased at a department store, were modified to fashion the tanks. The remaining construction materials were also inexpensive and the NeST design made it virtually leak‐proof. The uniformity of flow in the NeST was evaluated with three independent tracer tests. Estimated velocities were within about ±20% including all test results, indicating a high degree of predictability and uniformity in the flow. The NeST is a simple and robust tool suitable for research and teaching purposes, particularly for the testing of flow measurement sensors like the point velocity probes.
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