Cation exchange and adsorption

H saturated humic, fulvic and hydrophilic macromolecular natural organic matter was isolated from the river Dodder, Ireland, by adsorption and cation exchange chromatography (Hayes, personal communication). 

Ever since the first landfills became operative in the UK in 1912 (Hasan 1995), leachate has been an environmental problem. These landfills exploited soils and rock formations rich in clay, relying upon their natural characteristics for the containment of contaminants present in the leachates. Due to the low permeability of the clay minerals they contain (1 x 10 and 1 x 10 cm/s), formations such as the Oxford Clay in the UK and Fort Benton in the USA were the primary target of landfill engineers. It was hoped that clay minerals present in situ in rock formations underlying the chosen landfill sites would reduce the flow of leachate. In addition, the clay formations were relied on to attenuate the potentially harmful substances contained in the leachates by a variety of sorption processes absorption, adsorption and cation exchange. 

The clay-water system. II. Water adsorption and cation exchange in montmorillonite. 

Methyl parathion is only slightly soluble in pH 7 water (55-60 ppm). This affects its mobility in water and its ability to be leached or solubilized into the water phase of a soil-water system. Factors most likely to affect the adsorption of methyl parathion in soil are organic matter content and cation exchange capacity. In soils of low organic matter (e.g., subsurface soils), calcium concentration, which affects the hardness of the water, may also be important (Reddy and Gambrell 1987). Several studies have shown... 

Soils and vadose zone information, including soil characteristics (type, holding capacity, temperature, biological activity, and engineering properties), soil chemical characteristics (solubility, ion specification, adsorption, leachability, cation exchange capacity, mineral partition coefficient, and chemical and sorptive properties), and vadose zone characteristics (permeability, variability, porosity, moisture content, chemical characteristics, and extent of contamination)... 

Zinc Complexation withp-tosyl-8-aminoquinoline and adsorption on cation exchange resin Spectrofluorimetry 0.1 nM absolute [609]... 

Kitakouji, M., T. Miyoshi, S. Tanada, and T. Nakamura. 1989. In vitro adsorption removal of paraquat by activated carbon and cation exchange resin. Bull. Environ. Contam. Toxicol. 42 926-930. 

A wide variety of solvents have been utilized for the extractions. Other procedures have been used, particularly with urine in drug screening programs. Included are drug adsorption on cation-exchange resin paper, XAD-2 nonionic resin, and charcoal. 

Because so much of the behavior of suspensions is determined or modified by charge associated with the solid phases, ZPC may be inferred from a wide variety of experiments involving pH as a master variable. For example, coagulation and sedimentation rates are maximum at the ZPC, and anion and cation exchange capacities (measured with nonspecific, symmetrical electrolytes) are equal and minimum at the ZPC. More direct and less ambiguous are electrophoresis and streaming potential, in any of their modifications. One can estimate the IEP(s) by measuring adsorption of H+ and OH" if one is certain that no specific adsorption of other species occurs. 

Terbutylazine and its degradation products Hot acetone then adsorption on cation exchange solid-phase cartridge High-performance liquid chromatography with photodiode array detection [393,394]... 

This was shown, for example, by electrokinetic measurements of Kavanagh and Quirk177) in the system Fe203-illite at pH 2.5. Electrophoretic and cation-exchange data indicated that the net charge of clay surface became strongly positive at low pH values as a result of adsorption of polycations Fe3+. Further examples of metal ion hydrolysis in oxide and silicate flotation systems were published by Fuerstenau178) and Stumm et al.62). 

Figure 10.16 Conceptual model by Gardner et al. (1991) which suggests that while adsorption or cation-exchange sites will reduce the mobility of NH4+ in both sediment types, sea salts in estuaries should in effect neutralize the cation-exchange sites, thereby enhancing NH4+ diffusion and ultimately flux rates. (Modified from Gardner et al., 1991.)...

As discussed in Chapter 1, Section 1.3.3, cations can usually be sorbed onto geological formations (rocks and soils) by adsorption (Chapter 1, Section 1.3.3.1) and cation exchange (Chapter 1, Section 1.3.3.2). 

Both adsorption and ion exchange can be treated by isothermal equations Equations 1.73, 1.74, 1.94, and 1.95 in Chapter 1 can be used for the competitive adsorption or cation exchange. Radioactive ions are usually present in extremely low concentrations in the geological environment. In Chapter 1, Equations 1.73 and 1.94, c, = 0. So, Equations 1.73 and 1.94 can be simplified as follows ... 

Because of their large surface-to-volume ratio and high metabolic activity, microorganisms are important vectors in the introduction of heavy metal and radionuclide pollutants into food webs. As discussed in Chapter 5, heavy metals in soils and sediments tend to be immobilized by precipitation at neutral to alkaline pH and/or adsorption to cation exchange sites of clay minerals. Microbial production of acid and chelating agents can reverse this adsorption and mobilize toxic metals. Microbial metabolism products that can chelate metals include... 

R. A. Hux and F. F. Cantwell, Surface adsorption and ion exchange in chromatographic retention of ions on low-capacity cation exchangers, Anal. Chem. 56 (1984), 1258-1263. 

Another standardized database for the diffuse layer model was developed for montmorillonite by Bradbury and Baeyens (2005). Surface complexation constants for strong and weak sites and cation exchange were fit to adsorption data for various metals using constant site densities and protonation-dissociation constants in a nonelectrostatic modeling approach. Linear free energy relationships were developed to predict surface complexation constants for additional metals from their aqueous hydrolysis constants. 

Hang, P.T., and G.W. Brindley. 1970. Methylene blue adsorption by clay minerals. Determination of surface areas and cation exchange capacities. Clay Clay Miner. 18 203-212... 

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