Physicochemical speciation of trace elements in river waters by size fractionation

Abstract

in natural gas combustion because the moisture level is lower. Anything that reduces the moisture level, such as lowering the stoichiometric ratio or predrying the coal, will help to increase fuel rich sulfur capture, especially at lower sulfur levels. Increasing temperature will increase fuel rich sulfur capture only if the sulfur level is significantly above the thermodynamic limit (which increases with temperature).These results suggest that the rate-limiting step under fuel rich conditions is distinctly different than under fuel lean conditions. Theoretical calculations using a distributed pore model (19) have suggested that the relative insensitivity of calcium utilization to SOz concentration under fuel lean conditions is a result of pore closure effeds, as the SOz concentration is increased, the kinetic and diffusion rates increase but this further aggravates the problem of pore closure and results in essentially no overall increase in sulfur capture. The increased calcium utilization measured with increasing sulfur species concentrations under fuel rich conditions may be the direct result of enhanced product layer diffusion; pore closure would not be expected to limit calcium utilization under fuel rich conditions because the molar volume of calcium sulfide is less than either parent sorbent.Size fractionation method has been used for the speciation of trace elements in river waters. Both filtration and ultrafiltration techniques were applied to fractionate the trace elements into various sizes and/or molecular weight ranges. The size distribution was determined for 39 elements by means of neutron activation analysis to estimate their physicochemical forms. Alkali and alkaline earth elements, heavy rare earth elements (REEs), As, Co, Mn, Ni, Sb, Se, V, W, and Zn were mainly present in the dissolved phase, while Ag, Al, Fe, Sc, and light REEs were predominantly associated with the suspended particles. The dominant dissolved species for alkali and alkaline earth elements, Al, V, Mn, Sb, and Au were regarded as simple ions, while heavy REEs, Sc, Co, Ni, and Zn were apt to form soluble complexes with organic ligands. Light REEs, Fe, and Ag were mainly associated with colloidal materials.

Distribution Pattern of Rare Earth Ions between Water and Montmorillonite and Its Relation to the Sorbed Species of the Ions

“…Humic acid is another important constituent in a natural aquifer that can influence the REE behavior in the hydrosphere. [11][12][13][14] The relation between the REE patterns and the REE species at the solid-water interface was consistent with spectroscopic data obtained by laser-induced fluorescence for Eu(III) and Cm(III) species at the solid-water interface. These REE (rare earth element) distribution coefficients (Kd) between the aqueous phase and montmorillonite surface were obtained to investigate the relation between the REE distribution patterns and the species of REE sorbed on the solidwater interface.…”

Antimony in aquatic systems

“…However, significant binding by metal oxides has been reported [6]. [7]) : truly dissolved species predominate. b) Sb distribution in different size classes as a function of DOC percentage in the " dissolved fraction " [6] : no correlation observed.…”

Systematic change in relative stabilities of REE-humic complexes at various metal loading levels

“…Organic matter plays an important role as a carrier of REEs in natural terrestrial water as is similar to Fe-Mn hydroxides and clay minerals (Tanizaki et al, 1992;Ingri et al, 2000). Humic substances (HSs) such as fulvic and humic acids (FA and HA) are typical organic matter, which interacts with metal ions in natural terrestrial water (Tipping, 2002).…”