Distribution and Chemical Speciation of Molybdenum in River and Pond Sediments Affected by Mining Activity in Erdenet City, Mongolia

Abstract

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.

Ecological and Human Health Risk Assessment of Heavy Metal Pollution in the Soil of the Ger District in Ulaanbaatar, Mongolia

“…In the first step, solid samples of 0.05 g each was digested completely in 3 mL 60% HNO 3 with 3 mL 48% hydrofluoric acid (HF) and heated at 120 °C for 48 h. In the second step, 3 mL of 30 % hydrochloric acid (HCl) was added and heated at 120 °C for 24 h until dry. In the third step, 10 mL of 0.6% HNO 3 was extracted and mixed for 24 h in the mix-rotor [ 17 ]. The obtained extraction solutions were filtered to the I-boy through a 0.20-µm cellulose membrane filter in the fourth step.…”

Comparison of Chemical Speciation of Lead, Arsenic, and Cadmium in Contaminated Soils from a Historical Mining Site: Implications for Different Mobilities of Heavy Metals

“…The target of the second step (F2) was the elements in the carbonate fraction. The residue from F1 was treated with 1 M sodium acetate adjusted to pH 5 with acetic acid on a mix rotator for 16 h at room temperature. , Although Mg is an important major element in soils, the approach just described cannot be used to measure the Mg content of the soil because of the high concentration of MgCl 2 used in the first step. To estimate the Mg content after the first step, we treated duplicates of the original soil samples with 1 M sodium acetate at pH 5 instead of the MgCl 2 treatment.…”

“…The target of the third step (F3) was the elements in amorphous iron and manganese oxides. The residue after the second 1 M sodium acetate extraction was treated with a 20 mL solution of 0.2 M ammonium oxalate adjusted to pH 3 with oxalic acid on a mix rotator for 4 h at room temperature. ,, The target of the fourth step (F4) was the elements in crystalline iron and manganese oxides. The residue from F3 was treated with a mixture of 0.3 M Na 3 C 6 H 5 O 7 , 0.2 M NaHCO 3 , and 1.125 g of sodium dithionite (CDB solution) at pH 7.6 on a mix rotator for 8 h at room temperature .…”

“…A combination of SEP and XAFS methodologies can facilitate identification of chemical speciation and quantification of heavy metals in natural samples. However, relatively few studies have as yet been undertaken using both methods. ,,− …”

Assessing the Self-Purification Capacity of Surface Waters in Lake Baikal Watershed

“…The decrease in metal concentration is in turn due to a decrease in the occurrence of carbonaceous rocks (limestone, marble, etc.) containing Sr and Ba [57] and ore-bearing porphyry containing Mo [58] in the downstream direction. The removal rates of Sr and Ba exceed the rates calculated for all considered elements.…”