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Ferrous monosulfide mackinawite (FeS) forming under iron-rich sulfate-reducing conditions is an effective scavenger of heavy metals and metalloids. In this work, we studied the mechanisms of cadmium­(II) [Cd­(II)] (a toxic chalcophile metal generally considered redox-inactive) reactions with FeS under an anoxic condition over ranges of geochemical variables. The batch uptake experiments show that dissolved Cd­(II) is almost completely removed from the FeS suspensions without a distinct pH or ionic strength dependency under all the experimental conditions studied. The batch uptake results do not support (Cd,Fe)S solid-solution formation. Instead, identification of the solid-phase reaction products by a suite of surface chemical probes suggests that the major Cd reaction product is CdS, with minor amounts of metallic Cd (Cd0) and surface-complexed Cd­(II). Density functional theory calculations support the favorability of pure CdS formation compared to Fe-doped CdS or Cd-doped FeS. This study shows that sulfide precipitation largely controls the mobility of Cd, similar to previously reported Hg and As, implicating the presence of dissolved or solid-phase sulfides to be a key parameter in sulfate-reducing natural and engineered environments.

Partitioning interwell tracer test (PITT) is a method to quantify and qualify a site contaminated with NAPLs (Non-Aqueous Phase Liquids). Analytical description of PITT assumes that the injection-pumping well pair is on the line of the ambient groundwater flow direction, but the test-well pair could frequently be off the line in a real field site, which could be an erroneous factor in analyzing PITT data. The purpose of this work is to study the influence of the angle of the testwell pair on the ambient groundwater flow direction based on the result from PITT. From the experiments, it was found that the obliqueness of the test-well pair to the ambient groundwater flow direction could affect the tracer test resulting in a decreased NAPL estimation efficiency. In case of an oblique arrangement of the test-well pair to the ambient flow direction, it was found that the injection of a chase fluid could enhance the estimation efficiency. An increase of the pumping rate could enhance the recovery rate but it cannot be said that a high pumping rate can increase the test efficiency because a high pumping rate cannot give partitioning tracers enough time to partition into NAPLs. The results have a implication that because the arrangement of the test-well pair is a controlling factor in performing and interpreting PITT in the field in addition to the known factors such as heterogeneity and the source zone architecture, flow direction should be seriously considered in arranging test-ell pair.

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Various types of inorganic and organic colloids are present in natural water including groundwater. Previous studies showed that Fe, Mn and Al are colloid-forming elements and dissolved concentrations can be erroneous for these elements if water samples are not properly filtered. Dissolved concentrations of elements including Ca, Na, Mg, K, Fe, Mn, Si and Al in groundwater from alluvial and bedrock aquifers, and surface water near Nakdong River were determined to evaluate effects of colloids on dissolved concentrations in natural water samples using various pore sizes of filters. Groundwater is mostly anoxic and have elevated concentrations of Fe and Mn, which provides a unique opportunity to observe the effects of colloids on dissolved concentrations of colloid-forming elements. Membrane filters with four kinds of pore sizes of 1000 nm, 450 nm, 100 nm, and 15 nm were used for filtration of water samples. Concentrations of dissolved concentrations in each filtrate did not show significant differences from 1000 nm to 100 nm. However, concentrations of all elements considered were decreased in the filtrates obtained using 15 nm pore size filters by 10 to 15% compared to those using 450 nm except for bedrock groundwater. Al in surface water showed a distinct linear decrease with the decrease of filter pore sizes. These results showed that 100 nm pore size had little effect to remove colloidal particles in alluvial groundwater and surface water in our study. In contrast, significant concentration decreases in 15 nm pore size filtrates indicate that the presence of 15 to 100 nm colloidal particles may affect determination of dissolved concentrations of elements in natural water.