Flue dusts, arsenical

Figure 7.6 Flowsheet of SMITE stabilization of arsenical flue dust.

SYNS ARSENICAL FLUE DUST FLUE DUST, ARSENIC CONTAINING... 

During copper and lead smelting, arsenic (mostly as arsenic trioxide) vaporizes and condenses in the ductwork to form flue dust. Arsenical flue dust is a commercial source of arsenic. 

Similarly, finely divided mixed metals undergo electrochemical reactions in contact with one another, sometimes with sufficient heat to ignite surrounding combustible materials or with a dangerous depletion of surrounding oxygen in confined spaces, o Lead dross (mostly lead sulphate) is acidic, o Arsenical flue dust and other metal by-products are toxic, o Residues may be mixed with other compounds and metals such as lead, cadmium, mercury, and uranium. 

Arsenical Dust (Arsenical Flue Dust). Consists of smelter dust containing large proportions of arsenic. These dusts are hazardous due their toxic characteristics. lATA App. A... 

Cashman A high-pressure process for extracting gold from arsenic-bearing ores, concentrates, and flue dusts. 

Today, most arsenic is recovered as a by-product from the smelting of nickel, copper, iron, and tin. It is also recovered from the flue dust of copper- and lead-smelting furnaces. 

It may also be obtained by fusion of a mixture of arsenic and arsenious sulphide 8 in the calculated proportions. A fiery red product is formed by melting arsenious oxide or arsenic pentoxide with sodium thiosulphate.9 The red sulphide has also been found mixed with other sulphides in the flue dusts obtained during the roasting of arsenical ores.10... 

The principal ore of arsenic (5 x 10 % of earth s crust) is arsenical pyrites, FeAsS, but the element occurs commonly with nickel, copper and tin As40g is recovered from flue-dusts collected during the extraction of these metals. Sublimation in the presence of galena, which prevents the formation of arsenites, purifies the oxide this is reduced to arsenic with carbon in a cast iron retort. The element itself has few uses about 0.5% added to lead increases the surface tension of the molten metal and allows spherical lead-shot to be produced. The principal commercial form is the so-called white arsenic, As Og. Arsenic compounds are used mainly for their toxicity arsenical insecticides have been much used. 

Derivation Flue dust of copper and lead smelters from which it is obtained as white arsenic (arsenic trioxide) in varying degrees of purity. This is reduced with charcoal. The commercial grade is not made in the U.S. 

The principal source of As is FeAs8, and the element is extracted by heating (equation 14.2) and condensing the As sublimate. An additional method is air-oxidation of arsenic sulfide ores to give AS2O3 which is then reduced by C AS2O3 is also recovered on a large scale from flue dusts in Cu and Pb smelters. 

To quantify the elements deposited on the catalyst surface as a function of exposure time in the flue gas duct, their relative atomic fractions x were recorded with exposure time (Fig. 4). An increase in sulfur and arsenic contents with exposure time can be observed. Both elements were first detected after 48 h. Depending on exposure time, these elements cover increasingly large areas, 10% after 96 h, 20% after 3270 h. At the same time, all samples were observed to determine whether the detected Xjj decreases with exposure time (Fig. 5). This reduction is particularly pronounced between 24 h and 48 h. After about 400 h of exposure time, the titanium fraction has decreased to about one third of its initial value. Since it does not change after this time, it is assumed that the catalyst surface contamination process is completed. From this time on, a constant balance should be achieved between abrasion and contamination. Surprisingly, this does not hold for sulfur and arsenic. It is assumed that the modified catalyst surface involved in this abrasion/contamination balance forms a further reactive component for these elements. There is other interesting evidence that the arsenic deposited originates, at least from that point on, exclusively in the gas phase, since the arsenic entrained by the flue dust would otherwise result in an increase in Xgj. 

---