Rivers and ponds near the Erdenet mine, one of the world's largest copper-molybdenum mines, exhibit high concentrations of molybdenum (Mo). This study evaluates the distribution and chemical speciation of Mo in surface sediments from ponds and rivers in Erdenet city to elucidate the mobility and solubility of Mo in the surface aquatic environments in the area. The waters and sediments were collected in two shallow ponds connected to the tailing pond and from three rivers flowing through Erdenet city. The distribution and chemical speciation of Mo in the sediments were examined using five-step sequential extraction and X-ray absorption fine structure (XAFS) analyses. The XAFS spectra of the sediments showed that large amounts of Mo in the sediments are molybdate or polymeric molybdate, weakly adsorbed onto ferrihydrite. Sequential extraction consistently showed a large amount of Mo distributed in the labile fractions. Results suggest that the surface sediments from ponds and rivers play a role as secondary contamination sources of Mo rather than as sinks of Mo in the area.

Knowledge of the chemical forms and binding types of metals enables evaluation of their behavior and bioavailability in soil. This study employed a combination of sequential extraction and X-ray absorption spectroscopic analyses to examine the speciation of As, Pb, and Cd in soils from the mine tailing area of the abandoned Kamegai mine in Japan. The results revealed that most As was As­(V) and was adsorbed primarily on goethite and secondarily on ferrihydrite formed by the oxidation of sulfide ores in the tailings. Most Pb was also adsorbed onto goethite, although the desorption behaviors of Pb and As differed. Cadmium, however, was adsorbed onto clay minerals in the soils around the mine tailings. The different mobility of Cd versus As and Pb was possibly related to its lower adsorption affinity to iron oxides but higher affinity to roots of the fern Athyrium yokoscense. River water in this area, which is characterized by slightly basic pH and very low electric conductivity, exhibited concentrations of As exceeding 10 μg/L but low concentrations of Pb and Cd. The difference of the solubilities of the heavy metals could be explained by river water chemistry and metal speciation.

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