Arsenic aqueous chemistry

The oxo acids and anions in both lower and higher states are a very important part of the chemistry of phosphorus and arsenic and comprise the only real aqueous chemistry of these elements. For the more metallic antimony and bismuth, oxo anion formation is less pronounced, and for bismuth only ill-defined bismuthates exist. 

Chatteijee A, Das D, Mandal BK, Chowdhury TR, Samanta G, Chakraborti D (1995) Arsenic in groundwater in six districts of West Bengal, India The biggest arsenic calamity in the world. Part I. Arsenic species in drinking water and urine of affected people. Analyst 120 643-650 Cheah S-F, Brown GE Jr, Parks GA (1997) The effect of substrate type and 2,2 -bipyridine on the sorption of copper(II) on silica and alumina. In Voigt JA, Bunker BC, Casey W, Wood , Crossey LJ (eds) Aqueous Chemistry and Geochemistry of Oxides, Oxyhydroxides, and Related Materials, Mat Res Soc SympProc 432 231-236... 

Here then, we offer much of the descriptive aqueous chemistry in the older sources, with corrections, interpreted with the added insights and improved symbolism of recent decades, plus new information, including reactions of the recently discovered elements, but without many of the older strictly analytical techniques. Still, we mention the Marsh test for arsenic, for example, because not all laboratories around the world have the instmments that give quicker results. 

The aqueous chemistry of iron is also important in a number of other settings. Iron can be the dominant cation released in acid rock drainage, due to the oxidation of pyrite (FeS2(s)) when it becomes exposed to air and water. This process is catalysed by bacteria which cycle ferrous iron back to ferric iron which, in turn, can oxidise further pyrite. Thus, the rate of oxidation will depend on the aqueous concentration of ferric iron. If insufficient iron (and acid) is produced or the iron is removed by the inherent neutralisation capacity of the material, the rate of oxidation will be substantially reduced. The precipitation of iron oxyhydroxide phases and their ability to adsorb other aqueous elements have also been studied in detail (Dzombak and Morel, 1990). The removal of arsenic from drinking water by hydrous iron oxides is one example of these adsorption reactions. 

Immobilizing DENs within a sol-gel matrix is another potential method for preparing new supported catalysts. PAMAM and PPI dendrimers can be added to sol-gel preparations of silicas " and zinc arsenates to template mesopores. In one early report, the dendrimer bound Cu + ions were added to sol-gel silica and calcined to yield supported copper oxide nanoparticles. Sol-gel chemistry can also be used to prepare titania supported Pd, Au, and Pd-Au nanoparticle catalysts. Aqueous solutions of Pd and Au DENs were added to titanium isopropoxide to coprecipitate the DENs with Ti02. Activation at 500°C resulted in particles approximately 4 nm in diameter. In this preparation, the PAMAM dendrimers served two roles, templating both nanoparticles and the pores of the titania support. 

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). 

Raposo, J.C., Sanz, J., Zuloaga, O. et al. (2003) Thermodynamic model of inorganic arsenic species in aqueous solutions, potentiometric study of the hydrolytic equilibrium of arsenious acid. Journal of Solution Chemistry, 32(3), 253-64. 

Many factors affect the oxidation rates of sulfide minerals and the chemistry of their oxidation products. A few of the important factors are briefly introduced in this section and discussed in further detail in this and later chapters. As a result of the complex interactions between these different factors, high-arsenic rocks and mining wastes will not automatically produce high-arsenic weathering products and aqueous solutions (Piske, 1990). 

Geochemical modeling is often used to identify the compounds that primarily control the chemistry of arsenic in aqueous solutions. Modeling studies indicate that the arsenic concentrations of Kelly Lake, Ontario, Canada, are controlled by the precipitation and dissolution of Fe(II) arsenates rather than calcium or Fe(III) arsenates (Sadiq et al., 2002). The arsenic in the lake originated from runoff from the nearby Sudbury mining district and airborne particles from local ore smelters (Sadiq et al., 2002). 

Amin, M.N., Kaneco, S., Kitagawa, T. et al. (2006) Removal of arsenic in aqueous solutions by adsorption onto waste rice husk. Industrial and Engineering Chemistry Research, 45(24), 8105-10. 

Rau, I., Gonzalo, A. and Valiente, M. (2000) Arsenic(V) removal from aqueous solutions by iron(III) loaded chelating resin. Journal of Radioanalytical and Nuclear Chemistry, 246(3), 597-600. 

Yang, L., Shahrivari, Z., Liu, P.K.T. et al. (2005) Removal of trace levels of arsenic and selenium from aqueous solutions by calcined and uncalcined layered double hydroxides (LDH). Industrial and Engineering Chemistry Research, 44(17), 6804-15. 

Yang, L., Wu, S. and Chen, J.P. (2007) Modification of activated carbon by polyaniline for enhanced adsorption of aqueous arsenate. Industrial and Engineering Chemistry Research, 46(7), 2133-40. 

Ivakin, A. A., Vorobeva, S. V., Gorelov, A. M., and Gertmann, E. M., 1979b, Solubility of arsenic(HI) sulphide in aqueous NaCl solutions Russian Journal of Inorganic Chemistry,... 

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