Partitioning arsenic

Smith, K. S., W. H. Ficklin, G. S. Plumlee and A. L. Meier, 1992, Metal and arsenic partitioning between water and suspended sediment at mine-drainage sites in diverse geologic settings. In Y. K. Kharaka and A. S. Maest (eds.), Water-Rock Interaction. Balkema, Rotterdam, pp. 443M-47. 

Many of the important chemical reactions controlling arsenic partitioning between solid and liquid phases in aquifers occur at particle-water interfaces. Several spectroscopic methods exist to monitor the electronic, vibrational, and other properties of atoms or molecules localized in the interfacial region. These methods provide information on valence, local coordination, protonation, and other properties that is difficult to obtain by other means. This chapter synthesizes recent infrared, x-ray photoelectron, and x-ray absorption spectroscopic studies of arsenic speciation in natural and synthetic solid phases. The local coordination of arsenic in sulfide minerals, in arsenate and arsenite precipitates, in secondary sulfates and carbonates, adsorbed on iron, manganese, and aluminium hydrous oxides, and adsorbed on aluminosilicate clay minerals is summarized. The chapter concludes with a discussion of the implications of these studies (conducted primarily in model systems) for arsenic speciation in aquifer sediments. 

Figure 8.6. Postulated pathways and changes in arsenic partitioning (and transport) under As(V) (left side), Fe(ni) (top right), or Fe(in) and As(V) reducing conditions. (Width of arrows denotes magnitude of reaction.)...

Solvent extraction—purification of wet-process phosphoric acid is based on preferential extraction of H PO by an organic solvent vs the cationic impurities present in the acid. Because selectivity of acid over anionic impurities is usually not sufficient, precipitation or evaporation steps are included in the purification process for removal. Cmde wet-process acid is typically concentrated and clarified prior to extraction to remove post-precipitated sludge and improve partition of the acid into the solvent. Concentration also partially eliminates fluoride by evaporation of HF and/or SiF. Chemical precipitation of sulfate (as Ba or Ca salts), fluorosiUcates (as Na salt), and arsenic (as sulfides) may also be used as a prepurification step preceding solvent extraction. 

Coprecipitation is a partitioning process whereby toxic heavy metals precipitate from the aqueous phase even if the equilibrium solubility has not been exceeded. This process occurs when heavy metals are incorporated into the structure of silicon, aluminum, and iron oxides when these latter compounds precipitate out of solution. Iron hydroxide collects more toxic heavy metals (chromium, nickel, arsenic, selenium, cadmium, and thorium) during precipitation than aluminum hydroxide.38 Coprecipitation is considered to effectively remove trace amounts of lead and chromium from solution in injected wastes at New Johnsonville, Tennessee.39 Coprecipitation with carbonate minerals may be an important mechanism for dealing with cobalt, lead, zinc, and cadmium. 

Arsenic boron and mercury. As discussed in the following section, As, B, and Hg are typically enriched in geothermal fluids, as compared to surface- and groundwaters (Sakamoto et al. 1988 Ballantyne Moore 1988). Being quite fugitive, Hg partitions significantly into the steam phase at... 

A central problem in physics and chemistry has always been the solution of the Schrodinger equation (SE) for stationary states. Such stationary states may relate to electronic structure problems, in which case one is primarily interested in bound states, or to scattering problems, in which case the stationary solutions are continuum states. In both cases, one of the most powerful tools in the theoretical arsenal for solving such problems is the partitioning technique (PT), which has been developed in a series of papers prominently by Per-Olov Lowdin [1-6] and Herman Feshbach [7-9]. 

Moore, J. N. (1994). Contaminant mobilization resulting from redox pumping in a metal-contaminated river-reservoir system. In Environmental Chemistry of Lakes and Reservoirs, ed. L. A. Baker, pp. 451-71. Washington, D.C. American Chemical Society. Moore, J. N., Ficklin, W. H. Johns, C. (1988). Partitioning of arsenic and metals in reducing sulfidic sediments. Environmental Science and Technology, 22, 432-7. Morrison, G. M., Batley, G. E. Florence, T. M. (1989). Metal speciation and toxicity. Chemistry in Britain, 8, 791-5. 

The slope of this line is the distribution coefficient (Kd), which is the ratio of the arsenic concentration on the adsorbent (Cads) to the concentration of the associated remaining arsenic in the aqueous solution (Csdn). With each linear adsorption isotherm, Kd has only one value. That is, a linear distribution indicates that the partitioning of arsenic between the adsorbent and the solution is constant over the given range of arsenic concentrations (Eby, 2004), 221. If both concentrations (Cads and Csoin) are in the same units (such as molal), Kd is unitless. However, if the adsorbed concentration is given in molal and the dissolved concentration is molar, then Kd has the units of liter/kilogram. 

Once hydrothermal fluids approach the surface, lower pressures cause the liquids to boil. As steam separates from hydrothermal water, arsenic preferentially remains in the liquid phase. Above 200 °C, only about 0.1-0.5% of the arsenic in surface and near-surface hot springs partitions into steam (Ballantyne and Moore, 1988, 477). Table 3.6 lists the arsenic concentrations in condensates of gases from various volcanoes and hot springs. 

Coker, V.S., Gault, A.G., Pearce, C.I. et al. (2006) XAS and XMCD evidence for species-dependent partitioning of arsenic during microbial reduction of ferrihydrite to magnetite. Environmental Science and Technology, 40(24), 7745-750. 

Seames, W.S. and Wendt, J.O.L. (2000) The partitioning of arsenic during pulverized coal combustion. Symposium International on Combustion, 28(2), 2305-312. 

Wilkin, R.T. and Ford, R.G. (2006) Arsenic solid-phase partitioning in reducing sediments of a contaminated wetland. Chemical Geology, 228(1-3 Special Issue), 156-74. 

Moore, J.N., Ficklin, W.H. and Johns, C. (1988) Partitioning of arsenic and metals in reducing sulfidic sediments. Environmental Science and Technology, 22(4), 432-37. 

Environmental Arsenic Different species Reverse-phase partition 300 pg Beauchemin et al. (1989)... 

The average crustal abundance of selenium is 0.05mgkg (Jacobs, 1989). Like arsenic, selenium is strongly chalcophile and is partitioned into sulfides and rare selenides, such as... 

Arsenic and selenium demonstrate many similarities in their behavior in the environment. Both are redox sensitive and occur in several oxidation states under different environmental conditions. Both partition preferentially into sulfide minerals and metal oxides and are concentrated naturally in areas of mineralization and geothermal activity. Both elements occur as oxyanions in solution and, depending on redox status, are potentially mobile in the near-neutral to alkaline pH conditions that typify many natural waters. However, there are also some major differences. Selenium is immobile under reducing conditions while the mobility of arsenic is less predictable and depends on a range of other factors. Selenium also appears to partition more strongly with organic matter than arsenic. 

Kuhlmeier P. D. (1997) Partitioning of arsenic species in finegrained soils. J. Air Waste Manage. Assoc. 47, 481-490. 

Dushenko W. T., Bright D. A., and Reimer K. J. (1995) Arsenic bioaccumulation and toxicity in aquatic macrophytes exposed to gold-mine effluent relationships with environmental partitioning, metal uptake and nutrients. Aquat. Bot. 50, 141-158. 

Krupka K. M. and Seme R. J. (2000) Understanding Variation in Partition Coefficient, Kd, Values, Volume III Review of Geochemistry and available Kd values for Americium, Arsenic, Curium, Iodine, Neptunium, Radium, and Technetium. Pacific Northwest National Laboratory, Richland, WA. 

It is better to use Jurecev s method for this estimation it consists in passing a known volume of the aerosol [e.g., 50 litres) through a wash-bottle with a porous partition containing ether. The solvent is then evaporated off on the water-bath, the residue decomposed by one of the methods described on p. 329 et seq., and the arsenic determined colorimetrically by means of mercuric chloride paper (see p. 326). 

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