Arsenic solid phases

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. 

Primary copper processing results in air emissions, process wastes, and other solid-phase wastes. Particulate matter and sulfur dioxide are the principal air contaminants emitted by primary copper smelters. Copper and iron oxides are the primary constituents of the particulate matter, but other oxides, such as arsenic, antimony, cadmium, lead, mercury, and zinc, may also be present, with metallic sulfates and sulfuric acid mist. Single-stage electrostatic precipitators are widely used in the primary copper industry to control these particulate emissions. Sulfur oxides contained in the off-gases are collected, filtered, and made into sulfuric acid. 

Solid - phase arsenic concentrations are low in aquifer sands in both high and low arsenic zones - generally 2 parts per million (ppm) or less. In fine grain sediments, arsenic levels are typically 5 -10 ppm in both the low and high arsenic zones, peaking at 20 ppm near the surface in the channel-fill silts (borehole 20, Fig. 2). 

Fig. 2. Solid-phase arsenic in ppm versus depth in m from a continuous core. The core consists of clayey silt to depth of 28 m, and fine sand thereafter with a silt horizon at 34 m depth. As was measured by digestion with an HCI-HNO3-H2O aqua regia solution followed by inductively coupled plasma mass spectrometry and inductively coupled plasma atomic emission spectroscopy analysis.

Thin layer chromatography was carried out on 20x20cm glass plates coated 0.25mm thick with a suitable support and dried overnight. Silica gel G, silica gel H and cellulose were examined as the solid phases for chromatography of methanearsonate, arsenite and arsenate. Several sprays for the visualization of the arsenicals on plates were tested. Three of the more successful reagents and the colour produced with final product are shown in Table 13.2. 

Fe(OH), using Mdssbauer spectroscopy, optical spectroscopy and transmission electron microscopy. Phy. Chem. Min. 22 11-20 McCreadie, H. Blowes, D.W. (2000) Influence of reduction reactions and solid-phase composition on porewater concentrations of arsenic. Environ. Sd. Tedm. 34 3159-3166 McFadden, L.D. Hendricks, D.M. (1985) Changes in the content and composition of pedogenic iron oxyhydroxides in a chronose-quence of soils in Southern Cahfomia. Quart. Res. 23 189-204... 

The speciation of trace elements in solid phases determines their mobility and toxicity. Spectroscopic techniques such as XANES and XAFS, can be used to determine directly the oxidation and structural state of elements in coal combustion byproducts. For example, Huggins et al. (2000) used these synchrotron techniques to determine that Cr and As occur predominately in the less toxic oxidation states Cr(IIl) and As(V) in CCBs. In addition, they found As, Cd, Cr, Ni, and Zn were present primarily as oxidized species (i.e., as oxides, sulphates, arsenates, etc.) in unweathered CCBs. 

The electrical conductivity of a pure arsenic crystal has been measured 3 at temperatures down to 2-42° Abs. The resistance-temperature curve is similar to those of pure metals. There is evidence of definite residual resistance being maintained at low temperatures, but arsenic does not exhibit the abnormally high residual resistance shown by bismuth, nor does it show superconductivity. The resistance is by no means proportional to the absolute temperature. It has been estimated that the electrical resistance of liquid arsenic at the melting point is about 0-4 of that of the solid phase.4... 

A study of the viseosit - of solutions of ferric oxide in aqueous arsenic acid at concentrations between 2-6 and 23-3 per cent. As2Os shows2 that two solid phases exist within these limits, the normal salt, FeAs04.rrH,0 (so about 3), which adsorbs arsenic acid, and an acid salt of composition Fe203.2Asa05.8H20, which has also been obtained by the action of excess of arsenic acid on a solution of ferric chloride. 

When mercuric oxide is treated with aqueous arsenic acid, the solid phase separates into two layers, one of which is mercuric oxide and the other a basic mercuric arsenate of composition 3Hg0.Hg3(As04)2. When ammonium arsenate solution acts on mercuric oxide, a product of composition Hg2NH2As04 is obtained.6... 

The presence of suitable reductants (or oxidants) is essential. These effects are examined here for As(III)/As(V) and Cr(III)/ Cr(VI). The redox states of trace elements affect their solubility (e.g., Cr(III)/Cr(VI)) and their affinity for binding to solid phases (e.g., arsenite and arsenate). Biological effects (e.g., uptake and toxicity) are also dependent on the redox state. 

Foster, A.L. (2003) Spectroscopic investigation of arsenic species in solid phases, in Arsenic in Ground Water (eds A.H. Welch and K.G. Stollenwerk), Kluwer Academic Publishers, Boston, MA, pp. 27-65. 

Grafe, M. and Sparks, D.L. (2006) Solid phase speciation of arsenic, in Managing Arsenic in the Environment From Soil to Human Health (eds R. Naidu, E. Smith, G. Owens et al.), CSIRO Publishing, Collingwood, pp. 75-91. 

Hutton, C., Bryce, D.W., Russeau, W. et al. (2005) Aqueous and solid-phase speciation of arsenic in Cornish soils. Mineralogical Magazine, 69(5), 577-89. 

Van Herreweghe, S., Swennen, R., Vandecasteele, C. and Cappuyns, V. (2003) Solid phase speciation of arsenic by sequential extraction in standard reference materials and industrially contaminated soil samples. Environmental Pollution, 122(3), 323-42. 

Following consumption of dissolved O2, the thermodynamically favored electron acceptor is nitrate (N03-). Nitrate reduction can be coupled to anaerobic oxidation of metal sulfides (Appelo and Postma, 1999), which may include arsenic-rich phases. The release of sorbed arsenic may also be coupled to the reduction of Mn(IV) (oxy)(hydr)oxides, such as birnessite CS-MnCb) (Scott and Morgan, 1995). The electrostatic bond between the sorbed arsenic and the host mineral is dramatically weakened by an overall decrease of net positive charge so that surface-complexed arsenic could dissolve. However, arsenic liberated by these redox reactions may reprecipitate as a mixed As(III)-Mn(II) solid phase (Toumassat et al., 2002) or resorb as surface complexes by iron (oxy)(hydr)oxides (McArthur et al., 2004). The most widespread arsenic occurrence in natural waters probably results from reduction of iron (oxy)(hydr)oxides under anoxic conditions, which are commonly associated with rapid sediment accumulation and burial (Smedley and Kinniburgh, 2002). In anoxic alluvial aquifers, iron is commonly the dominant redox-sensitive solute with concentrations as high as 30 mg L-1 (Smedley and Kinniburgh, 2002). However, the reduction of As(V) to As(III) may lag behind Fe(III) reduction (Islam et al., 2004). 

Polizzotto, M.L., Harvey, C.F., Li, G. et al. (2006) Solid-phases and desorption processes of arsenic within Bangladesh sediments. Chemical Geology, 228(Special Issue 1-3), 97-111. 

KOber, R., Daus, B., Ebert, M. et al. (2005a) Compost-based permeable reactive barriers for the source treatment of arsenic contaminations in aquifers column studies and solid-phase investigations. Environmental Science and Technology, 39(19), 7650-55. 

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