Sorption and ion-exchange technologies

With water treatment technologies, adsorption refers to the removal of contaminants by causing them to attach onto the surfaces of solid materials (adsorbents or sorbents) (Chapters 2 and 3). Sometimes the adsorbed solute is called the adsorbate (Krauskopf and Bird, 1995, 145). Adsorption usually involves ion exchange (Eby, 2004, 345). For example, adsorbing arsenic oxyanions will replace other ions on the surface of the sorbent (Chapter 2). 

Absorption is the assimilation of a chemical species into the interior of a solid material. Absorption may include the migration of solutes into internal pores (Fetter, 1993, 117) or the migration or exchange of atoms within the crystalline structure of a mineral (Krauskopf and Bird, 1995, 150). Some researchers use the generic term sorption to refer to a treatment method where adsorption and/or absorption are involved or if adsorption and absorption cannot be distinguished. 

4 Regeneration and disposal of spent sorbents and ion-exchange materials 

Fe2+ can then react with OH- to form Fe(OH)2. Over hours to days, Fe(OH)2 further oxidizes to form magnetite or maghemite (Manning et al., 2002b, 5455 Farrell et al., 2001, 2030). 

Fe2+ can also form under more aerobic conditions (Su and Puls, 2001a, 1490)  

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Plicka, J., J. Cabicar, K. Stamberg, and M. Fabian. 1984. The kinetics of ion exchange sorption in ternary systems, p. 331-236. In D. Naden and M. Streat (ed.) Ion exchange technology. Ellis Horwood, Chichester, United Kingdom. 

Verma, V.K., Tewari, S., and Rai, J.P.N., Ion exchange during heavy metal bio-sorption from aqueous solution by dried biomass of macrophytes, Bioresource Technology, 99 (6), 1932-1938, 2008. 

In natural waters, arsenic may exist as one or more dissolved species, whose chemistry would depend on the chemistry of the waters. Over time, arsenic species dissolved in water may (1) interact with biological organisms and possibly methylate or demethylate (Chapter 4), (2) undergo abiotic or biotic oxidation, reduction, or other reactions, (3) sorb onto solids, often through ion exchange, (4) precipitate, or (5) coprecipitate. This section discusses the dissolution of solid arsenic compounds in water, the chemistry of dissolved arsenic species in aqueous solutions, and how the chemistry of the dissolved species varies with water chemistry and, in particular, pH, redox conditions, and the presence of dissolved sulfides. Discussions also include introductions to sorption, ion exchange, precipitation, and coprecipitation, which have important applications with arsenic in natural environments (Chapters 3 and 6) and water treatment technologies (Chapter 7). 

Current economic and ecological analyses of the various processes available for recovery of minerals from seawater (evaporation, solvent extraction, sorption, ion exchange, flotation, fractional precipitation, distillation, electrolysis, electrodialysis, and electrocoagulation) favor ion exchange and sorption technology. 

Equilibration with water vapor Substantially less work was done in this area in the early phase of research on PFSAs because of previous emphasis on membranes which would be in contact with liquid water or aqueous solutions (e.g., for chlor-alkali technology). However, water supplied from the vapor phase could be a principal mode of external hydration of the membrane in a PEFC, particularly hydration of the anode side, and thus it is an important focus of study in fuel cell R D. The shape of the sorption isotherms shown in Fig. 29 (a) and (b) is generic for ion-exchange polymers. With increasing PhsO. water is sorbed in two steps as evidenced by the sorption isotherm ... 

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