Adsorption of trace elements

The redox cycling of these elements have pronounced effects on the adsorption of trace elements onto oxide surfaces and trace element fluxes under different redox conditions. The hydrous Mn(III,IV) oxides are important mediators in the oxidation of oxidizable trace elements e.g., the oxidation of Cr(lll), As(III) and Se(III) is too slow with 02 however, these elements subsequent to their relatively rapid adsorption on the Mn(III,IV) oxide are rapidly oxidized by MnfUI.IV). 

Factor-1 samples contain high concentrations of many trace elements, particularly boron and the transition elements Co, Cu, Mo, Ni, Pb, Zn, and V (Table III). These samples also contain illite (CR-2 core) and relatively high concentrations of analcime and oil (both cores) which suggests that adsorption of trace elements onto clay, altered tuffaceous material, and (or) organic matter may be important 1n controlling the distribution of these trace elements. The sulfide phase also may control the occurrence of these metals (10-11). Factor 1 samples also... 

The analysis of environmentally-relevant samples is a major field of application. Based on the work of Garbarino and Taylor [421], a method has been proposed by the US EPA (Environmental Protection Agency) [422] and later by DIN [423] for waste water analysis. The latter, standardized procedure describes the sample decomposition, the analytical range for 22 elements and frequent interferences of ICP-AES in waste water analysis. For the analysis of natural waters, hydride generation [424], preconcentration based on liquid-liquid extraction of the dithiocarbamate complexes [425], adsorption of trace elements onto activated carbon [426] and also co-precipitation [e.g. with In(OH)2] [427], etc. have been reported and special emphasis has been given to speciation (as given in the Refs, in [428]) and on-line preconcentration [134]. 

Although the adsorption of trace elements on container surfaces from biological specimens has not been thoroughly studied, it seems that this process is not equally important as it is in the storage of water specimens. 

Robertson, D.E. (1968b). The adsorption of trace elements in sea water on various container surfaces. Anal. Chim. Acta, 42, 533. 

Effects of organic ligands on the adsorption of trace elements onto metal oxides and organo-mineral complexes... 

Adsorption of trace elements in cationic form is pH-dependent and is characterized by a pH range, where the amount of a heavy metal that is bound to a sorbent increases abruptly to nearly 100%, known as adsorption edge. Fig. 1 shows the adsorption of Pb, Cu, Zn, and Co at different pH values onto selected short-range-ordered oxides (a noncrystalline A1 precipitation product [RO], ferrihydrite [Roo], and mixed Fe-Al oxides formed at different initial Fe/Al molar ratios [Rl-RlO]) (Table 1), whereas Fig. 2 shows the adsorption of Cu onto well-crystallized metal oxides, goethite, and bayerite. In the region in which adsorption increases rapidly, the species MeOH and Me(OH)2 of each metal were negligible. 

In contrast to the trace elements in cationic form, the adsorption of trace elements in anionic form (e.g. As, selenite, molybdate, chromate) usually decreases with increase in pH owing to a decrease in the positive charge of the sorbent at higher pH values (Fig. 3). However, some ligands (e.g. arsenite and selenite) may be adsorbed more easily at high pH values because they form weak acids at low pH values and may consequently only be dissociated in alkaline environments (Sparks, 1995 Goldberg etal, 1996). 

The presence of organic and inorganic ligands that strongly interact with variable-charge minerals and soils also affects the adsorption of trace elements in anionic form through competition for available binding sites. The competition... 

Adsorption of trace elements in the presence of organic ligands as affected by the sequence of their addition on the sorbents... 

The adsorption of trace elements on variable-charge minerals is influenced not only by the presence and concentration of organic ligands but also by the sequence of addition of heavy metals or metalloids and organic ligands to the sorbents. 

The effectiveness of non-humic organic ligands such as amino acids and organic acids, in influencing adsorption of trace elements upon soil... 

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