Arsenic recovery

The soil samples were first heated to fumes with a mixture of nitric and sulphuric acids. This method gave appreciably higher arsenic recoveries (95-102%) than fusion with potassium pyrosulphate and was considerably more rapid than fusion with a mixture of nitric and perchloric acids. 

Arsenic recoveries from the zinc column in the range 0.1-5pg ml-1 arsenic exceeded 97%. The concentrations at which certain elements interfere are shown in Table 12.16. Various other elements [A1 m, B m, Ca II, Cd II, Co II, Cr VI, Fe III, K I, Li I, Mg II, Mn H, Na I, Ni II, Pb II, S VI, Sn II and Zn II] showed no significant interference at the 500pg level. Only low senium concentrations in extracts can be tolerated. However, few environmental samples contain appreciable amounts of selenium. As selenium is not reduced to hydrogen selenide on the column, selenium will not interfere in the final determination step, but probably suppresses either arsenic reduction or arsine formation. Selenium appears to suppress arsine generation at high arsenic concentrations but causes a slight enhancement at low arsenic concentrations (around O.lpg), which could not be traced to arsenic impurities in the selenium standard used. 

The recoveries of known additions of arsenic in various forms taken through the entire recommended procedure are shown in Table 13.3. With additions in the range 5-10g of arsenic, recoveries of 92-97% were obtained and in all cases recoveries were better than 90%. 

Itakura, T., Sasai, R. and Itoh, H. (2006) Arsenic recovery from water containing arsenic ions by hydrothermal mineralization. Chemistry Letters, 35(11), 1270-71. 

Grabinski [12] spiked 0.500pg of each of the four arsenic species into filtered (0.45pM) lake water and distilled and deionised water. Arsenic recoveries for the entire procedure averaged 104%, 100% and 97% and 99% for As(III), monomethylarsonate,... 

The application of SPE has partially eliminated the above problems, particularly in the case of arsenic concentration in water samples [123]. SPE delivers better selectivity than LEE because it can be used to sequentially elute compounds from the activated carbon bed, and to separate inorganic compounds of As(III) and As (V), as well as the phenyl (PAS) and dimethyl (DMA) derivatives of arsenic (V) acid [124]. The extraction process is short, which is why it is possible to directly coimect the SPE module with the ICP MS detector [125]. Whenever modified silica is used, arsenic recovery is low (even below 50 %) owing to the formation of hydrogen bonds between the substances being separated and silanol groups [114, 126, 127]. 

The percentage recoveries obtained by the above digestion followed by atomic absorption spectrometric determination are given in Table 1. The recoveries obtained by the same method when applied to arsenic spiked water samples are shown in Table 2. Figure 1 shows the effect of ultra-violet irradiation as a function of time for triphenylarsine oxide, disodium methanearsonate and dimethylarsinic acid. The extent of arsenic recovery using... 

The method described above gives good results with arsenic recoveries ranging from 98.5 to 104.9%. The same method when applied to primary settled raw sewage gave arsenic recoveries ranging from 89.1 to 96.0%. 

Arsenic recoveries of 89.4 to 104.4% were experienced from an activated sludge effluent sample. Employing the high-sensitivity arsenic analysis by atomic absorption resulted in arsenic recoveries of 99.2-100.8%. 

The hydrogen peroxide-sulphuric acid digestion seemed to provide the most consistent and complete recoveries of any of the wet digestive procedures examined, and coupled with the silver diethyldithiocarbamate colorimetric analysis resulted in quantitative arsenic recoveries from waste water samples. 

Probably the most frequently used method of digestion incorporates the use of nitric and sulphuric acids. Kopp and Bandemar used this method and experienced 91 to 114% recovery of arsenic trioxide added to de-ionized water and 86 to 100% recovery of the compound added to river water. Evens and Bandemar recovered 87% of the arsenic trioxide added to eggs. By modifying the method by the addition of perchloric acid, and Caldwell and coworkers observed 80 to 90% arsenic recovery with o-nitrobenzene-arsonic acid, 85 to 94% with o-arsanilic acid and 76.7% with disodium methylarsenate. 

Odanaka and coworkers have reported that the combination of gas chromatography with a multiple ion detection system is useful for the quantitative determination of inorganic, mono-, di- and trimethylarsenic oxide compounds, and this approach is applicable to the analysis of environmental and biological samples. The limit of detection for a 50-ml sample was 0.2-0.4ngmU of arsenic. Recoveries of all four arsenic species from river water ranged from 85% to 100% (Table 17). 

Grabinski has described an ion-exchange method for the separation of four arsenic species on a single column containing both cation and anion exchange resins. Flameless atomic absorption spectrometry with a deuterium arc background correction is used as the detection system because of its linear response and lack of specificity for these compounds combined with its resistance to matrix bias in this tyjw of analysis. Arsenic recoveries ranged from 97% to 104% for typical lake water samples while 96% to 107% were obtained from arsenic-contaminated sediment interstitial water. The detection limit was 10 p.p.b. for each individual arsenic species. 

Arsenic recovery also presents a problem since nearly all of the arsenic resulting from DAVINCH operations is in dust, on munition fragments, or on the walls of the inner vessel. Although most of the arsenic on the vessel walls can be scraped off, some may remain in microcracks in the vessel wall that result from the detonations. Because removal of this arsenic is difficult, it is not routinely removed. 

Table 5.II. Confirmation of Quantitative Arsenic Recovery by Neutron Activation...

An interesting feature of the Russian process is the two-step method employed for the complete recovery of arsenic from solution waste-streams. In the first step, which is similar to the recovery method used in the Thylox process, the solution is heated to 70°C (158 F), and arsenic sulfide is precipitated by the addition of 75% sulfuric acid. The precipitate is separated from the liquid by filtration, dissolved in aqueous sodium carbonate, and returned to the circulating solution-stream. The clear liquid is then passed to the second step where it is made alkaline with sodium carbonate solution and treated with a solution of ferric sulfate. In this operation the small amount of arsenic remaining in the solution after the first step is fixed and precipitated as ferric arsenite and arsenate. The precipitate is finally removed by filtration, and the filtrate, which contains about 10 to 20 ppm of arsenic, is either discarded or processed for recovery of thiosulfate. Wooden tanks lined with acid-resistant materials are used in both steps of the arsenic-recovery operation. Each tank is sized for a solution residence time of 4 hr and provided with a mechanical agitator. 

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