Arsenic volatilization

Frankenberger W.T. Jr. Effects of trace elements on arsenic volatilization. Soil Bio Biochem 1997 30 269-274. 

Arsenic, fused with silver, forms an alloy composed of 100 silver and 16 arsenic. It is grey, brittle, granular, and by long fusion great part of the arsenic volatilizes. It may be entirely got rid of by roasting. 

The arsenic concentrations of metamorphic rocks generally decrease with increased metamorphism (Ryan et al., 1996), 265. As temperatures increase, more arsenic volatilizes out of the rocks. Specifically, metamorphic rocks that formed at <45 km in an ancient subduction zone in California lost about 80-85 % of their arsenic as metamorphic temperatures and pressures increased from about 275 °C and. 5 kilobars (kb) to approximately 750 °C and 12 kb (Bebout et al., 1999). As discussed in Section 3.6.2, the volatilization of arsenic during metamorphism may be important in transferring the element from subduction zones back into the crust (Figure 3.2). 

Zhang, J.-Y., Ren, D.-Y., Zhong, Q. et al. (2000) Restraining of arsenic volatility using lime in coal combustion. The Journal of Fuel Chemistry and Technology, 28(3), 200. 

Vitrification technologies may be ex situ or in situ. In ex situ vitrification, any soils, sediments, or buried wastes are excavated. After possible pretreatment to reduce arsenic volatilization, the materials are placed in a furnace and melted at temperatures as high as 2000 °C. The heat may be generated by fossil fuels, electricity, plasma torches, or microwaves (US EPA), 2002a, 5.1). 

Although arsenic is less volatile during low-temperature pyrolysis than combustion, some arsenic still volatilizes during the process. The volatilization of arsenic during pyrolysis chiefly results from the reduction of As(V) to AS4O6 ( AS2O3 ) and other As(III) oxides (Helsen and Van den Bulck, 2003 Hata et al., 2003 Helsen et al., (2003)). To minimize arsenic volatilization, the characteristics of the wood must be known and pyrolysis operations must be carefully controlled at temperatures below 320 °C (Helsen and Van den Bulck, 2003). 

Arsenic volatilization is a dissipation mechanism to remove arsenic from soil and water systems. Many soil and water microorganisms are capable of mediating arsenic volatilization, largely in the form of methylated arsines. Under highly reduced conditions, arsenate can be transformed to trimethylarsine as shown in Figure 2. 

Although microorganisms are known to be involved in arsenic volatilization, many environmental factors, such as pH, redox potential, presence of other ele-... 

Hassler et al. (36) found that arsenic volatilization in retorted oil shales would occur only when a nutrient source was provided and that total soluble arsenic levels decreased with time if no nutrient source were made available. 

The presence of heavy metals and other elements may inhibit or enhance microbiological transformations of arsenic in soil systems. It was observed that presence of phosphate and selenate causes inhibition of methylated evolution of arsenic (5,46,56). Frankenberger (57) studied the effect of 21 trace elements for their activation or inhibition on methylated arsine production by a Penicillium sp. from MMAA. Metals and metalloids at an elemental concentration of 0, 0.1, 1, 10, 100, and 1000 pM were tested for their influence on arsenic volatilization by the Penicillium sp. The effect of trace elements varied considerably depending on the speciation and concentration. At the lower elemental concentrations (0.1 and 1 pM), the metals and metalloids that stimulated arsenic volatilization were... 

Table 3 Effect of Trace Elements on Arsenic Volatilization (ng ml )...

Trace element Oxidation state Arsenic volatilized at different concentrations (pM) of added trace elements ... 

Figure 4 Influence of cobalt added to a culture medium in the presence of Penicillium sp. on arsenic volatilization. Standard error of mean was calculated based on five replicates incubated for 7 days (From Ref. 57.)...

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