Sorption processes ionic charge

We begin with a discussion of the most common minerals present in Earth s crust, soils, and troposphere, as well as some less common minerals that contain common environmental contaminants. Following this is (1) a discussion of the nature of environmentally important solid surfaces before and after reaction with aqueous solutions, including their charging behavior as a function of solution pH (2) the nature of the electrical double layer and how it is altered by changes in the type of solid present and the ionic strength and pH of the solution in contact with the solid and (3) dissolution, precipitation, and sorption processes relevant to environmental interfacial chemistry. We finish with a discussion of some of the factors affecting chemical reactivity at mineral/aqueous solution interfaces. 

The variety of mechanisms that may be involved in the sorption process of metal ions onto activated carbon induces a great number of factors that control the adsorption the surface oxygen complex content, the pH of point of zero charge, the pore texture of carbon, the solution pH and its ionic strength, the adsorption temperature, the nature of the metal ion given by its speciation diagram, its solubility, and its size in adsorption conditions. The influence of these various conditions is detailed in Section 24.2.1.4. 

Ionizable compounds such as basic compounds (triazines and pyridinones) and acidic compounds (carboxylic acids and phenols) can sorb by ionic mechanisms when they are ionized. Weakly basic compounds may sorb by cation exchange weakly acidic compounds may sorb by anion exchange. For these chemicals ion exchange is not the sole sorption mechanism. For instance, sorption of bipyridylium cations, ie, diquat and paraquat, is primarily the result of cation exchange. Other physicochemical forces, such as charge-transfer interactions, hydrogen bonding, and van der Waals forces, can also be involved in the sorption process. 

The mechanism of complex formation of metals with chitosan is manifold and is probably dominated by different processes such as adsorption, ion exchange, and chelation under different conditions. In Fig. 15.6, it can be seen that the sorption capacity of chromium and cadmium is similar, while zinc has approximately double the affinity of these two metal ions for chitosan. Chitosan has almost three times the removal capacity for copper sorption than that for cadmium or chromium. These effects have proved complex to interpret but are a function of a number of parameters ionic radii ionic charge electron structure and possibly some hydration capacity of the metal ions solution pH and nature and availability of sites for chitosan. 

It is particularly interesting and instructive to note that application of Henry + Langmuir dual-mode sorption and diffusion models is not confined to glassy polymer-gas systems. Sorption and transport of high affinity ionic species, exemplified by anionic dyes, in charged polymers, exemplified by polyamides at low pH, has been treated in the same way. These systems are of considerable importance both from the bio-mimetic and from the textile processing point of view, but have received limited atten-... 

As sorption of organic phosphates occurs on surfaces with variable charges, the process is affected by the characteristics of the bulk solution, including pH, ionic strength, the nature and concentration of electrolytes, and... 

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