Adsorption of heavy metals and metalloid

Adsorption of heavy metals and metalloids onto Fe and/or A1 oxides... 

We have demonstrated that the adsorption of heavy metals and metalloids is affected not only hy the presence, nature, and concentration of organic ligands but also by the sequence of reaction of pollutants and organics with the sorhents. 

Adsorption to mineral surfaces such as Fe and Al (hydr)oxides has long been known to be an important process that limits the mobility of heavy metals and metalloid species in aqueous systems (e.g., Stumm 1992). The sorption of ionic species in MSWI bottom ash has been recently studied in detail by Meima Comans (1998, 1999). These authors used a sequence of selective chemical extractions to determine sorbent concentration, namely Fe and Al (hydr)oxides. Their model calculations suggested that Zn(II) and M0O4 sorbed to Fe (hydr)oxides, while Pb(II) and Cu(II) appeared to have a greater affinity for Fe (hydr)oxides. The sorption of Cd(Il) was found to be very weak. The interpretation of... 

Goldberg, S., and L. J. Criscenti. 2008. Modeling adsorption of metals and metalloids by soil components. In Biophysico-chemical processes of heavy metals and metalloids in soil environments. Ed. A. Violante, P. M. Huang, and G. M. Gadd. 215-264. Hoboken, NJ Wiley-Interscience. 

For many of the more abundant elements, such as Al, Fe, and Mn, precipitation of mineral forms is common and may greatly influence or even control their solubility. For most trace elements, direct precipitation from solution through homogeneous nucleation appears to be less likely than adsorption-desorption, by virtue of the low concentration of these metals and metalloids in soil solutions in well-aerated dryland soils. When soils become heavily polluted, metal solubility may reach a level to satisfy the solubility product to cause precipitation. Precipitation may also occur in the immediate vicinity of the phosphate fertilizer zone, where the concentration of heavy metals and metalloids present as impurities may be sufficiently high. Precipitation of trace metals as sulfides may have a significant role in metal transformation in reduced environments where the solution sulfide concentration is sufficiently high to satisfy the solubility product constants of metal sulfides (Robert and Berthelin, 1986). 

Recently, we have carried out studies on the effect of LMMOAs on the adsorption of selected heavy metals and metalloids onto/from metal oxides, variable-charge soils, and organomineral complexes. The aim of this work is to present some of our significant findings on the effect of biomolecules, usually present in the rhizosphere, on the mobility of trace elements in soil environments. We also compare our results with those reported in the literature. 

The large specific surface areas of the Fe solid phases (Fe(II,III)(hydr)oxides, FeS2, FeS, Fe-silicates) and their surface chemical reactivities facilitate specific adsorption of various solutes. This is one of the causes for the interdependence of the iron cycle with that of many other elements, above all with heavy metals, some metalloids, and oxyanions such as phosphate. 

Biosorption is a process where metal ions (or metalloid species), compoimds and particulate substances are removed from solution by biological material through adsorption of the contaminant on a surface site of the biomass. It can be by physical forces (e.g. van der Waals, electrostatic interaction) and/or involving a chemical reaction. It is believed that biosorption using dead biomass is based on the physical sorption phenomenon, whereas sorption using live biomass occurs through both physical and chemical processes as well as transmembrane transport and accumulation of heavy metals in the algal cell. ... 

In the case of heavy metals, non-electrolytic accumulation is not widely used. Perhaps, adsorptive pre-concentration is more frequent for the determination of copper (see references (55, 57-60) plus references therein), whereas the other heavy metals and both metalloids are preferably determined by ESA with electrolytic deposition (see Table 5.1) and the choice of other methodologies is rather a research topic than practical routine. 

Figure 19. Transformations of Fe(II, III) at an oxic anoxic boundary in the water or sediment column (modified from Davidson, 1985). Peaks in the concentration of solid Fe(III) (hydr)oxides and of dissolved Fe II) are observed at locations of maximum Fe(III) and Fe(II) production, respectively. The combination of ligands and Fe(ll) produced in underlying anoxic regions are most efficient in dissolving Fe(III) (hydr)oxides. Redox reactions of iron—oxidation accompanied by precipitation, reduction accompanied by dissolution—constitute an important cycle at the oxic-anoxic boundary which is often coupled with transformations (adsorption and desorption) or reactive elements such as heavy metals, metalloids, and phosphates.

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