Removal of Inorganic Anions

Velizarov, S., Crespo, J. Reis, M. (2004) Removal of inorganic anions from drinking water supplies by membrane bio/processes. Reviews in Environmental Science and Biotechnology, 3 (4), 361-380. 

The exchange resins 6nd application in (i) the purification of water (cation-exchange resin to remove salts, followed by anion-exchange resin to remove free mineral acids and carbonic acid), (ii) removal of inorganic impurities from organic substances, (iii) in the partial separation of amino acids, and (iv) as catalysts in organic reactions (e.g., esterification. Section 111,102, and cyanoethylation. Section VI,22). 

Ion-exchange chromatography has many clinical applications, including the separation of amino acids, peptides, proteins, nucleotides, oligonucleotides, and nucleic acids. Another important application of ion-exchange chromatography is the separation and removal of inorganic ions from aqueous mixtures. Thus most water purification units used to prepare deionized water for the laboratory contain "mixed-bed columns of cation and anion resins (see Chapter 1). 

Work by Ruiz et al. in the analysis of water soluble inorganic phosphates in vegetables, such as tomato, lettuce, marrow, mushroom, celery, cauliflower, chard, onion, carrot, used SPE with Sep-Pak C18 cartridges for removal of organic compounds prior to IC analysis. Spiro and co-workers studied the kinetics of extraction of inorganic anions, including phosphate, from different types of tea into water. 

Solid-phase extraction on anion exchange resins is very rarely used. Recoveries for the organic acids may show great variabihty which may be caused by incomplete removal from the resin, especially at low concentrations, or it may be attributed to breakthrough of the carboxylate ions during the extraction process if the matrix contains significant amounts of inorganic anions. 

In addition to the standard XAD resins, other materials such as diethylaminoethyl (DEAE)-cellulose, a weak anion exchanger, have also been developed for HS isolation. The DEAE-cellulose is particularly convenient for HS isolation from large volumes of samples. Studies have demonstrated that DEAE isolates and the main XAD fractions consist of similar organic compounds.DEAE-cellulose has several advantages over the macroporous XAD resins in that it allows a higher flow rate, it does not require preacidification of the water samples, and the absorption efficiency is relatively high. About 76% of the adsorbed HS can be recovered by elution with 0.1 M NaOH. However, if pure HS samples are required, further purified procedures such as reprecipitation and HCl/HF treatment for removal of inorganic impurities have to be carried out with both methods. ... 

Sequential approaches are developed where (a) anionic metals are removed first and then cationic metals when mixed metal contamination is present and (b) organic compounds are removed first followed by the removal of heavy metals when coexisting heavy metal and organic contaminants are found. For example, the simultaneous electrokinetic removal of inorganic and organic pollutants (SEKRIOP)... 

Elektorowicz and Hakimipour (2001,2003a) presented a technology that permitted the simultaneous removal of heavy metals and PAHs from natural soil called Simultaneous Electrokinetic Removal of Inorganic and Organic Pollutants (SEKRIOP). This technology used EDTA for metal mobility and zwitterionic surfactants for hydrocarbon mobility. Furthermore, the application of cationic reactive membranes permitted capturing free metallic ions generated by electrokinetic phenomena before their precipitation in the cathode area. The capture of metal-EDTA complexes was done on anionic reactive membranes. 

Figure 15.1. Configuration of the electrokinetic system Simultaneous Electrokinetic Removal of Inorganic and Organic Pollutants (SEKRIOP). CET, cation exchange textile AET, anion exchange textile.

Demineraliza tion of water is the removal of essentially all inorganic salts by ion exchange. In this process, strong acid cation resin in the hydrogen form converts dissolved salts into their corresponding acids, and strong base anion resin in the hydroxide form removes these acids. Demineralization produces water similar in quaHty to distillation at a lower cost for most fresh waters. 

Deasbing The removal from solution of inorganic salts by means of adsorption by ion-exchange resins of both the cations and the anions that comprise the salts. See deionization. 

In experiments where Mono Lake water was acidified to remove carbonate and bicarbonate ions and again adjusted to pH 10, more than 90 percent of the soluble plutonium moved to the sediment phase. When carbonate ion concentration was restored, the plutonium returned to solution—strong evidence of the importance of inorganic carbon to solubility in that system(13). Early studies with Lake Michigan water, which has low DOC, had also implicated bicarbonate and carbonate as stabilizing ligands for plutonium at pH 8(14). This latter research characterized the soluble species as mainly anionic in character. 

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