Adsorption of heavy metals

Clay ion-exchange model May be useful for predicting adsorption of heavy metals. Aqueous-phase-... 

As the figure shows the exchange of Sr2+ on Na+-montmorillonite fits the ion exchange theory very well. But the adsorption of heavy metals cannot be accounted for by this theory. Co(II) behaves as if it were monovalent Kd for americium is independent of [Na+] (americium occurs at pH = 6.5 as a hydroxo complex). 

Adsorption of heavy metal ions to the surface of goethite and of natural particles... 

Table 5.4 Adsorption of heavy metals on goethite as a function of pH. Data expressed as percent of initial amount of metalhc cation solution. Reprinted from Quirk JP, Posner AM (1975) Trace element adsorption by soil minerals. In Nicholas DJ, Egan AR (eds) Trace elements in soil plant animal system. Academic Press, New York pp 95-107. Copyright 1975 with permission of Elsevier...

The existing methods for the removal of heavy metals from the environment can be grouped as biotic and abiotic. Biotic methods are based on the accumulation of heavy metals by plants or microorganisms abiotic methods include physicochemical processes such as precipitation, coprecipitation, and adsorption of heavy metals by a suitable adsorbent. 

As in pure systems, the adsorption of anions and cations on iron oxides is strongly pH dependent. This has to be kept in mind when an optimum pH is to be obtained with liming. The adsorption of phosphate, arsenate etc. increases as the pH falls below 7, whereas the adsorption of heavy metal cations rises as pH goes up (see eq. 11.18 11.19). Therefore, as soils become more acidic, heavy metals will be released into the soil solution. Conversely, liming soils has the opposite effect. 

Hoins, U. Charlet, L. Sticher, H. (1993) Ligand effect on the adsorption of heavy metals. The sulphate-cadmium goethite case. Water, Air, Soil Pollution 68 241-255 Holm, G. (1985) Substitution selectivity of some transition elements (Cr, Mn, Co, Ni, Cu, Zn) during formation of P-FeOOH. Geologiska Foreningsi Stockholm Forhandlingar 107 297-300... 

The fate of heavy metals in aquatic systems depends on partitioning between soluble and partieulate solid phases. Adsorption, precipitation, coprecipitation, and complexation are processes that affect partitioning. These same processes, which are influenced by pH, redox potential, the ionic strength of the water, the concentration of complexing ions, and the metal concentration and type, affect the adsorption of heavy metals to soil (Richter and Theis 1980). 

Say, R., Emir, S Garipcan, B. et al. (2003a) Novel methacryloylamidophenylalanine functionalized porous chelating beads for adsorption of heavy metal ions. Advances in Polymer Technology, 22(4), 355-64. 

A. M. Liu, K. Hidajat, S. Kawi, and D. Y. Zhao, A new class of hybrid mesoporous materials with functionalized organic monolayers for selective adsorption of heavy metal ions, Chem. Commun. 1145-1146 (2000). 

INFLUENCE OF THE NATURE OF ACTIVE SURFACE SITES OF HIGHLY DISPERSE OXIDES ON ADSORPTION OF HEAVY METAL IONS... 

A common theme throughout this volume involves the adsorption and interfacial, especially biointerfacial, behaviour of all of the above mentioned nanomaterials. For environmental and human protection, the adsorption of heavy metal ions, toxins, pollutants, drugs, chemical warfare agents, narcotics, etc. is often desirable. A healthy mix of experimental and theoretical approaches to address these problems is described in various contributions. In other cases the application of materials, particularly for biomedical applications, requires a surface rendered inactive to adsorption for long term biocompatibility. Adsorption, surface chemistry, and particle size also plays an important role in the toxicological behaviour of nanoparticles, a cause for concern in the application of nanomaterials. Each one of these issues is addressed in one or more contributions in this volume. 

Abollino, O., M. Aceto, M. Malandrino, C. Sarzanini, and E. Mentasti. 2003. Adsorption of heavy metals on Na-montmorillonite Effect of pH and organic substances. Water Res. 37 1619-1627. 

A further report of the oxidation ability of manganese nodules is that of Nitta.53 Several reactions were carried out with natural manganese oxide nodules including oxidative dehydrogenations of alkanes and cycloalkanes, reduction of NO, total oxidation of CO, and use in the gettering of metal and mixed metal ions. For example, nodules were found to have a tremendous capacity for adsorption of heavy metals and toxic metals like Pb2+, and Hg2+. in addition, nodules have been used to sequester metals that are present in petroleum fractions that can contain metals like V and Ni. These metals can cause degradation of the fluid cracking catalysts even at levels as low as 1 ppm. 

They acknowledge that the exact mechanism of the adsorption of heavy metal chelates is quite complex but do not hesitate to propo.se the formation of an electron donor-acceptor complex of the chelate and the active sites (e.g., carbonyl groups) and possible beneficial effect of hydrogen bonding between the... 

Figure 10.15. Adsorption of heavy metal ions to the surface of goethite and of natural particles (data from Muller and Sigg, 1990). Surface complex formation of on goethite and the surface of natural particles (Glatt River). The data can be fitted by Langmuir adsorption isotherms (or surface complex formation constants). The comparison between goethite and natural particles at pH = 8 shows a slightly larger tendency of the natural particles to bind Pb than of goethite.

Balkose, D. and Baltacioglu, H. (1992). Adsorption of heavy metal cations from aqueous solutions by wool fibers.. Chem. Technol. Biotechnol. 54, 393-397. 

The adsorption of heavy metals onto amorphous or crystalline forms of iron oxide and clays occurs in nature and is phenomenologically related to the binding of contaminant to the superhcial ferric and/or aluminium ions. Although, this behavior explains the concentration of metal contaminants in soils, it does not constitute a viable method for trapping low concentrations of contaminants from aqueous streams because of its limited adsorption capacity. 

M. O. Corapcioglu and C. P. Huang, The Adsorption of Heavy Metals onto Hydrous Activated Carbon, Water Research, 21, pp. 1031-1044 (1987). 

S. K. Srivasta, R. Tyagi and N. Pant, Adsorption of Heavy Metal Ions on Carbonaceous Material Developed from the Waste Slurry Generated in Local Fertilizer Plants, Water Research, 23, 1161-1165 (1989). 

Many publications report adsorption of heavy metal cations on activated carbon. Apparently, binding of metal cations is due to formation of surface complexes that are similar to chelate complexes in solution and some of them are very stable. The stability of these complexes is certainly dependent on the surface treatment. However, in some publications the sorption on activated carbons is treated as ion exchange. 

Violante, A., Ricciardella, M., and Pigna, M. (2003). Adsorption of heavy metals on mixed Fe-Al oxides in the absence or presence of organic ligands. Water Air Soil Pollut. 145, 289-306. 

Hoins, U., Chailet. L., and Sticher, H., Ligand effect on the adsorption of heavy metals The sulfate-cadmium-goethite case. Water Air Soil Poll., 68, 241, 1993. 

Okazaki, M., Takamidoh, K,. and Yamane. 1., Adsorption of heavy metal cations on hydrated oxides and oxides of iron and aluminum with different crystallinities. Soil Sci. Plant Nutr.. 32. 523. 1986. 

Lantenois, S. et al.. Flow microcalorimetry Experimental development and apphcation to adsorption of heavy metal cations on silica, Appl. Surf. Sci., 253, 5807, 2007. 

---