Roasting, of lead

Fume rxillection from smelter gases 1790 Roasting of lead ores in a hearth furnace... 

In the selective flotation of zinc-lead sulfide ores, cadmium is distributed between ZnS and PbS concentrates. When heated to high enough temperature (1100°C), as is the case during roasting of lead concentrates, CdS volatiHzes without decomposition and is found in the dust collected in bag filters or in electrostatic precipitators. Dur-... 

The principal ore of lead is galena, PbS. Although there are some galena deposits in Great Britain, much of this country s requirements must be imported. In the extraction of lead, the sulphide ore is first roasted together with quartz in a current of air ... 

Thallium occurs in crooksite, lorandite, and hutchinsonite. It is also present in pyrites and is recovered from the roasting of this ore in connection with the production of sulfuric acid. It is also obtained from the smelting of lead and zinc ores. Extraction is somewhat complex and depends on the source of the thallium. Manganese nodules, found on the ocean floor, contain thallium. 

Process. The QSL process (14) is a continuous single-step process having great flexibiUty in regard to the composition of the raw materials. In this process the highly exothermic complete oxidation, ie, the roasting reaction, can be avoided to some extent in favor of a weakly exothermic partial oxidation directly producing metallic lead. However, the yield of lead as metal is incomplete due to partial oxidation of lead to lead oxide. 

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. 

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). 

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. 

Blei-rhodanid, n, lead thiocyanate, -rohr, n., -rShre, /. lead tube or pipe, -rostprozess, m. lead roasting, -rot, n. red lead, minium, -safran, m. orange lead, -salbe, /. (Pharm.) lead ointment, cerate of lead subacetate, -salpeter, m. lead nitrate, -salz, n. lead salt, specif, lead acetate, -sammler, m. lead accumulator lead storage battery. 

When galena, a lead ore (composed of lead sulfide) is roasted in a well-ventilated, open furnace, part of the lead is oxidized by air oxygen to lead oxide and the sulfur to sulfur dioxide, which is released into the atmosphere (see Textbox 33) ... 

Lead is commonly obtained by roasting galena (PbS) with carbon in an oxygen-rich environment to convert sulfide ores to oxides and by then reducing the oxide to metallic lead. Sulfur dioxide gas is produced as a waste product. Large amounts of lead are also recovered by recycling lead products, such as automobile lead-acid electric storage batteries. About one-third of all lead used in the United States has been recycled. 

Cadmium is obtained as a byproduct in zinc recovery processes. The metal volatdizes during roasting of zinc concentrates and collected as dust or fume in bag houses or electrostatic precipitators. The dusts are mixed with coal (or coke) and zinc chloride and calcined. The cadmium chloride formed volatihzes upon calcination and thus separates out from zinc. The chloride then is treated with sulfuric acid in the presence of an oxidizing agent. This converts lead, present as impurity in cadmium ore, to lead sulfate which precipitates out. Cadmium is finally separated from copper by the addition of zinc dust and... 

Cadmium also may be recovered from zinc ores and separated from other metals present as impurities by fractional distillation. Alternatively, the cadmium dust obtained from the roasting of zinc ore is mixed with sulfuric acid. Zinc dust is added in small quantities to precipitate out copper and other impurities. The metal impurities are removed by filtration. An excess amount of zinc dust is added to the solution. A spongy cadmium-rich precipitate is formed which may he oxidized and dissolved in dilute sulfuric acid. Cadmium sulfate solution is then electrolyzed using aluminum cathodes and lead anodes. The metal is deposited at the cathode, stripped out regularly, washed and melted in an iron retort in the presence of caustic soda, and drawn into desired shapes. More than half of the world s production of cadmium is obtained by elecrolytic processes. 

Determining the Equivalent of Lead. Roast a clean porcelain bowl in a muffle furnace at 4C0-450 °C, and after cooling it in a desiccator, weigh it with an accuracy up to 0.01 g. Put about 0.5 g of granulated lead in the bowl and weigh it with the same accuracy. Pour 10 ml of a 40% nitric acid solution onto the metal, cover the bowl with a watch glass, and place it in a water bath. See what happens. Write the equation of the reaction. 

Transfer the bowl into a muffle furnace and roast the precipitate at 400-450 °C during one hour. Cool the bowl with the substance to room temperature in a desiccator and weigh it. Use the found value of the equivalent and the approximate value of the atomic mass of lead to determine its valence. Calculate a more accurate value of the atomic mass of lead from the obtained data, compare your result with the value of the atomic mass of this element given in Mendeleev s periodic table, and establish the magnitude of the error in per cent. 

Preparation of Lead. a. Thoroughly mix 5 g of lead(II) oxide and 0.5 g of finely ground charcoal. The lead(II) oxide must be preliminarily dried in a drying cabinet at 100 °C, and the charcoal roasted in an iron crucible covered with a lid. Put the mixture into a porcelain crucible, spill charcoal over it, and roast it in a muffle furnace at 800 °C. After 10 or 15 minutes, mix the contents of the crucible with a carbon rod and again roast them during 30 minutes. Pour out the molten lead onto a chamotte dish. Cool the metal bead and keep it for following experiments. Calculate the yield in per cent. Write the equations of the reactions. 

Preparation of Lead(n) Oxide (Yellow and Red Modifications). Fill two small boats with lead carbonate and roast them in a stream of dry nitrogen, one at 490 °C and the other at 650 °C until carbon... 

Roast 2-3 g of lead carbonate at 450-500 °C in a porcelain bowl. When decomposition of the salt terminates, roast the substance at the same temperature for another two or three hours. Next transfer the product into a beaker and boil it several times with a lead acetate solution. Pour off the solution from the precipitate, filter off the latter, wash it with hot water, and dry it in a drying cabinet at... 

The principal objection to this method of assay is the largo amount of lead which is produced for cupellation, since pure iron pyrites affords, when thus treated, eight and a half partB of lead, whilst sulphate-of antimony and grey copper ore yield from six to seven parts. This inconvenience, as well as the trouble of roasting, may be avoided by the cautious and gradual addition of nitrate of potassa, which effects the partial oxidation of the mineral, and enables tho skilful assayer to pro-... 

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