Flue-dust collection

After the unsuccessful inspection of hundreds of samples with highly sensitive techniques attempts were made to improve the sensitivity of such searches by enrichment of superheavy elements from very large quantities. The extreme case [47] was a search for element 114 in flue dust collected during the industrial processing of 103 to 104 tons of galena. Eka-lead should be more volatile than lead and, hence, be enriched in flue dust. After further concentration by chemical and mass separations, the final samples were exposed to neutrons but no fission events were found with track detectors. The deduced concentration limit of 10-19 to 10 23 g/g is the lowest ever achieved in searches in Nature. 

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. 

Silicon (not of high purity) is extracted from sihca, Si02, by heating with C or CaC2 in an electric furnace. Impure Ge can be obtained from flue dusts collected during the extraction of zinc from its ores, or by reducing Ge02 with H2 or C. For use in the electronic and semiconductor... 

The combined flue dust from waste heat boiler and electrostatic precipitator, including dust from the ventilation system, is collected in a bin and recirculated to the mixing and pelletizing step, where it is used as a binding reagent. 

Production and Economic Aspects. Thallium is obtained commercially as a by-product in the roasting of zinc, copper, and lead ores. The thallium is collected in the flue dust in the form of oxide or sulfate with other by-product metals, eg, cadmium, indium, germanium, selenium, and tellurium. The thallium content of the flue dust is low and further enrichment steps are required. If the thallium compounds present are soluble, ie, as oxides or sulfates, direct leaching with water or dilute acid separates them from the other insoluble metals. Otherwise, the thallium compound is solubilized with oxidizing roasts, by sulfatization, or by treatment with alkaU. The thallium precipitates from these solutions as thaUium(I) chloride [7791 -12-0]. Electrolysis of the thaUium(I) sulfate [7446-18-6] solution affords thallium metal in high purity (5,6). The sulfate solution must be acidified with sulfuric acid to avoid cathodic separation of zinc and anodic deposition of thaUium(III) oxide [1314-32-5]. The metal deposited on the cathode is removed, kneaded into lumps, and dried. It is then compressed into blocks, melted under hydrogen, and cast into sticks. 

Preparation. Rhenium is extracted commonly as a by-product from molybdenum smelter flue dust. The volatile Re207 is collected, converted to NH4Re07 which is reduced in a stream of hydrogen. 

In most countries, solid waste containing metals such as neutralization sludge from the plating industry and flue dust from the metal and steel industries is currently collected and dumped in landfill, where it constitutes a perpetual toxic threat to the environment and a waste of resources. The alternatives to this landfill disposal are either to reduce the rate of discharge at source by an individually designed recovery process or to separate and recover the metals from the collected waste in a centrally located facility. A presumption for a centrally located facility would be that companies with metals in their effluents require treatment of their total wastewater streams. This could be accomplished through the relatively simple process of neutralization, which requires minor investment in sedimentation tanks and dewatering equipment and involves relatively modest operation costs. 

C Extraction. The major source of T1 is flue dusts from the roasting of Zn, Cu, and Pb ores. Many T1 compounds are much more volatile that those of other elements, and as a result, they collect in the flues, particularly TI2O and TI2SO4. Since both of these compounds are soluble in water, they may be leached out of the dusts to give solutions of TlOH and TI2SO4, leaving behind most impurites as insoluble residue. 

The rotary furnace lends itself very well to the use of oxygen-assisted combustion. The reduced flue gas volume provides for a longer residence time of the hot combustion gases in the furnace thus allowing more heat to be transferred to the charge material. Also, because of the reduced flue gas velocity, less lines are carried into the dust collection system. 

Flue dusts and fumes collected from sinter plant and smelter gases can contain concentrations of volatile metals as well as lead and zinc. Elements which tend to concentrate in sinter plant dusts are... 

Chlorine from PVC separators forms volatile lead chloride, which vaporises in the lower shaft and condenses in the upper shaft, forming a recycle loop as well as wall accretions. Some lead chloride reports to flue dusts, again causing accretions in the gas handling system, and collected dusts must be leached for removal of chlorine before recycling to the furnace feed. 

Electrostatic precipitators can also be used for dust collection from flue gases. 

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