Anionic pollutants

Churchman GJ (2002) Formation of complexes between bentonite and different cationic polyelectrolytes and their use as sorbents for non-ionic and anionic pollutants. Appl Clay Sci 21 177-189... 

Anions play key roles in chemical and biological processes. Many anions act as nucleophiles, bases, redox agents or phase transfer catalysts. Most enzymes bind anions as either substrates or cofactors. The chloride ion is of special interest because it is crucial in several phases of human biology and in disease regulation. Moreover, it is of great interest to detect anionic pollutants such as nitrates and phosphates in ground water. Design of selective anion molecular sensors with optical or electrochemical detection is thus of major interest, however it has received much less attention than molecular sensors for cations. 

Modeling and optimization of pertraction into emulsion in HF contactors is discussed in refs. [77, 138]. The design and optimization of a network of HF contactors with minimum cost that permits the selective separation and recovery of anionic pollutants, for example, Cr(VI), using BLME process for groundwater remediation is presented in ref. [139] and for waste-water treatment in ref. [140]. 

Ortiz, I., Bringas, E., Samaniego, H., San Roman, F. and Urtiaga, A. (2006) Membrane processes for the efficient recovery of anionic pollutants. Desalination, 193, 375. 

Bringas, E., Roman, M.F., and Grtiz, I., Separation and recovery of anionic pollutants by the emulsion pertraction technology. Remediation of polluted groundwaters with Cr(VI), Ind. Eng. Chem. Res., 45, 4295, 2006. 

Ratanatamskul, C. et al.. Effect of operating conditions on rejection of anionic pollutants in the water environment by nanofiltration especially in very low pressure range. Water Sci. Technol., 34(9, Water Quality International 96 art 5), 149, 1996. 

A. Rios, M. D. Luque de Castro, and M. Valcarcel, New Approach to the Simultaneous Determination of Pollutants in Waste Waters by Flow Injection Analysis. Part I. Anionic Pollutants. Analyst, 109 (1984) 1487. 

The major components of most soils are silicate and aluminosilicate minerals. Under natural conditions, these components have negative charges. Anionic pollutants are less attracted to negatively charged surfaces. The high solubility of anionic pollutants and low adsorptive capacity of soils can result in the persistence of high concentration of anionic pollutants, including d , Cr(VI), NOi, Se(VI), Se(IV), As(V), As(III),Tc(VII), Mo(VI), POi, F-, ClOj, and SOj (Blowes et aL, 2000). 

TABLE 6.1. Permissible Limits and Health Effects of Representative Anionic Pollutants... 

In electrokinetic processes, there are two major transport mechanisms electromigration and electro-osmosis. Generally, in an electrical field, electromigration causes cationic metals such as cadmium, zinc, lead, nickel, and copper to move from the anode toward the cathode in electro-osmosis, the direction of movement of the pore water is toward the cathode when the zeta potential of the soil surface is negative. This can result in an enhanced removal of metals because the direction of transport of the ions in both mechanisms is the same. However, the direction of electromigration for anionic pollutants is toward the anode and that for electroosmosis is from anode to cathode, as stated previously. The opposite direction of movement means that the removal rate of anionic pollutants could be reduced. 

Soil pH plays an important role in the adsorption and desorption of pollutants and, ultimately, influences transport. Generally, the desorption of cationic metals would be enhanced by acidic conditions because of ion exchange reactions between hydrogen ions and cationics. However, anionic pollutants would be desorbed more easily in an alkaline condition than in an acidic environment, indicating that the process fluid should be changed for the electrokinetic removal of anionic pollutants. 

As-prepared Co to -LDHs can incorporate additional Mg " or AP" into their lattices (128). LDHs can also show exchange of constituent cations, with MgAl-LDHs being extremely selective for such transition metal cations as Cu +, Ni +, Co, and Zn + (437). Reactions of this kind will no doubt receive more attention in the future, as a way of using LDH to remove cationic, as well as anionic, pollutants. 

The pH of the BGE is an important factor in optimizing chiral resolution, as it is thought to be responsible for the stability of the diastereomeric complexes formed between the enantiomers and the chiral selector. However, an increase in the buffer pH, from pH 4 to pH 9, may result in an increase in the EOF therefore, the analysis time may be reduced by increasing the pH. It is also important to note that the pH value of the buffer may be altered in a secondary manner that is, by other parameters such as temperature, ion depletion and so on. The suitable pH ranges for various buffers are summarized in Table 9.3 [50]. The literature reported herein indicates that a wide range of pHs have been used for the chiral resolution of environmental pollutants. Some reports indicate chiral resolution at acidic pH values, while others indicate basic pH values, which reveals that the pH requirements depend upon the type of the buffer used and other CE conditions. In general, a low pH is used to resolve cationic pollutants, while a high pH is required for the chiral resolution of anionic pollutants. 

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