Arsenic roasting

Mushrooms Austria 1995 near arsenic roasting facility in operation for about 500 years and closed for about 100 years soil had 730 mg total As/kg DW Collybia maculata ... 

Germany near former arsenic roasting facility total As Ants, Formica sp. whole 12.6 DW 62... 

Before this treatment, the cassiterite content of the ore is increased by removing impurities such as clay, by washing and by roasting which drives off oxides of arsenic and sulphur. The crude tin obtained is often contaminated with iron and other metals. It is, therefore, remelted on an inclined hearth the easily fusible tin melts away, leaving behind the less fusible impurities. The molten tin is finally stirred to bring it into intimate contact with air. Any remaining metal impurities are thereby oxidised to form a scum tin dross ) on the surface and this can be skimmed off Very pure tin can be obtained by zone refining. 

A process has been developed to recover antimony and arsenic from speiss and other materials (11). The speiss is roasted along with a source of sohd sulfur and coal or coke at a temperature of 482—704 °C for a sufficient time to volatilise arsenic and antimony oxides. The arsenic can then be separated from the antimony through careful control of the off-gas temperature and oxygen potential (12). 

Minor quantities of arsenic trioxide have been obtained from the roasting of arsenopyrite, but the presence of copious amounts of SO2 iu the gas and vapor stream requires the use of lead-lined kitchens (9). 

Arsenic trioxide may be made by burning arsenic in air or by the hydrolysis of an arsenic trihaUde. Commercially, it is obtained by roasting arsenopyrite [1303-18-0] FeAsS. It dissolves in water to a slight extent (1.7 g/100 g water at 25°C) to form a weaMy acidic solution which probably contains the species H AsO, orthoarsenous acid [36465-76-6]. The oxide is amphoteric and hence soluble in acids and bases. It is frequendy used as a primary analytical standard in oxidimetry because it is readily attainable in a high state of purity and is quantitatively oxidized by many reagents commonly used in volumetric analysis, eg, dichromate, nitric acid, hypochlorite, and inon(III). 

Roasting. Rotary kilns are used for oxidizing and driving off sulfur and arsenic from various ores, including gold, silver, iron, etc. Temperatures employed will vaiy from 800 to 1600 K. 

Gold and silver (o) chloridizing roast of gold-silver ore, and (b) removal of arsenic... 

Lead The production of lead from lead sulphide minerals, principally galena, PbS, is considerably more complicated than the production of zinc because tire roasting of the sulphide to prepare the oxide for reduction produces PbO which is a relatively volatile oxide, and therefore the temperature of roasting is limited. The products of roasting also contain unoxidized galena as well as die oxide, some lead basic sulphate, and impurities such as zinc, iron, arsenic and antimony. 

The production of cobalt is usually subsidiary to that of copper or nickel and the methods employed differ widely, depending on which of these it is associated with. In general the ore is subjected to appropriate roasting treatment so as to remove gangue material as a slag and produce a speiss of mixed metal and oxides. In the case of arsenical ores, AS2O6 is condensed and provides a valuable byproduct. In the case of copper ores, the primary process... 

Gold ores can be concentrated by froth flotation, the resulting concentrate being roasted at 600-800°C to oxidize off sulphur and arsenic as their oxides. The product is extracted with cyanide under oxidizing conditions (using either peroxide or air itself) before displacement with powdered zinc. More reactive metals (silver etc.) can be removed by chlorination of molten gold. 

As seen in the above equations, the aqueous oxidation processes convert sulfur in the feed to dissolved sulfate, while arsenic is oxidized and precipitated as ferric arsenate compounds. So, problems of the emission of sulfur and arsenic oxides caused by roasting are avoided in the aqueous oxidation processes. The two different industrial methods which achieve the oxidation reactions are pressure oxidation and biological oxidation. 

Sulfide ores usually contain small amounts of mercury, arsenic, selenium, and tellurium, and these impurities volatilize during the ore treatment. All the volatilized impurities, with the exception of mercury, are collected in the dust recovery systems. On account of its being present in low concentrations, mercury is not removed by such a system and passes out with the exit gases. The problem of mercury contamination is particularly pertinent to zinc plants since the sulfidic ores of zinc contain traces of mercury (20-300 ppm). The mercury traces in zinc sulfide concentrates volatilize during roasting and contaminate the sulfuric acid that is made from the sulfur dioxide produced. If the acid is then used to produce phosphatic fertilizers, this may lead to mercury entering the food chain as a contaminant. Several processes have been developed for the removal of mercury, but these are not yet widely adopted. 

Roasting arsenic sulfide in air produces the oxide, and the element is obtained from the oxide by reduction with carbon. 

The arsenic in beer incident has led to the rule that all food ingredients must be food grade, as must any food contact materials or materials used in the process. This rule can have the consequence that a material such as coke must be food grade. If a food is to be roasted over coke then that coke must be food grade. A non-food grade coke might, possibly, contain a substance such as arsenic. 

Several examples of arsenic speciation in wastes resulting from pressure oxidation, roasting and smelting, and impacted soil are given in this manuscript with the overall goal to promote further research in this area. 

Prior to gold extraction by cyanidation, refractory gold ores are either roasted or pressure oxidized to liberate the gold contained as submicroscopic particles or in solid solution in arsenopyrite and arsenic-rich pyrite. Gold extraction from such ores require roasting or pressure oxidation or bacterial oxidation prior to cyanidation to destroy the sulfide structure. 

In the case of roasting, the pretreatment process destroys the sulfide matrix by driving off sulfur from the structure. This results in the formation of iron oxide particles that are made of concentrically zoned and porous hematite and maghemite (Paktunc et al. 2006). Arsenic is volatilized as As203 and oxidised to... 

Walker, S.W. Jamieson, H.E., Lanzirotti, A., Andrade, C.F. 2005. Determining arsenic speciation in iron oxides derived from a gold-roasting operation Application of... 

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