Trace element oxyanions

Fe(III)(hydr)oxides introduced into the lake and formed within the lake - Strong affinity (surface complex formation) for heavy metals, phosphates, silicates and oxyanions of As, Se Fe(III) oxides even if present in small proportions can exert significant removal of trace elements. - At the oxic-anoxic boundary of a lake (see Chapter 9.6) Fe(III) oxides may represent a large part of settling particles. Internal cycling of Fe by reductive dissolution and by oxidation-precipitation is coupled to the cycling of metal ions as discussed in Chapter 9. 

As discussed in the previous section, trace elements are essentially retained in the solid combustion products and, because many are present on the surfaces of the particles, they are potentially leachable. Our data show the elements Mo, As, Cu, Zn, Pb, U, Tl, and Se will be readily accessible for leaching. A significant fraction of the V, Cr, and Ni, and a minor proportion of the Ba and Sr will also be potentially leachable because of the surface association, but most of these elements appear to be located in particles and will be released more slowly as the dissolution of the glass and other phases takes place. Rubidium, Y, Zr, Mn, and Nb are contained almost entirely within the particles and dissolution is potentially slower. The extent to which elements are leached also depends on their speciation and solubility in the porewaters, and the pH exerts a major control. In oxidizing solutions, elements such as, Cd, Cu, Mn, Ni, Pb, and Zn form hydrated cations that adsorb onto mineral surfaces at higher pH values and desorb at lower pH values. In contrast, the elements As, U, Mo, Se, and V, under similar Eh conditions, form oxyanions that adsorb onto mineral surfaces at low pH values and desorb at higher values (Jones 1995). 

Strong affinity (surface complex formation) for heavy metals, phosphates, silicates, and oxyanions of As and Se Fe(III) oxides, even if present in small proportions, can exert significant removal of trace elements. 

The leaching of saline-sodic soil with good water (low salinity, low SAR) causes the pH to rise. This can result in the mobilization of trace elements such as selenium in some soils (selenium exists in the soil as an oxyanion, selenite or selenate), elements that adsorb better at low pH than high pH. How would you prevent this potential environmental risk to groundwater during the reclamation of the saline-sodic soil ... 

Anthropogenic Trace Elements in the Ocean. Atmospheric Input of Pollutants. Land-Sea Global Transfers. Metalloids and Oxyanions. Pore Water Chemistry. Refractory Metals. River Inputs. Transition Metals and Heavy Metal Speciation. 

As both elements are important environmental contaminants whose mobility and environmental impact depend on redox reactions, we expect that Cr and Se isotope analyses will be used widely as indicators of oxyanion reduction. It may also be possible to trace the origin of the Se or Cr via isotopic signatures, but only if the possible confounding effects of reduction can be constrained. 

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