Bismuth refining

Georgius Agricola, a German scientist of the sixteenth century, was the first to mention bismuth detailing the melting of bismuth from ore (1). It was ia the sixteenth century that bismuth compounds were first discovered to have a soothing effect on stomach disorders. Bismuth compounds are stiU widely used ia preparations to reheve this condition. Not until the 1800s was bismuth refined and proven to be an element. Until that time, bismuth was usually referred to as one of the other elements with which it is associated ia ores such as antimony, silver, lead, and tin. 

The washed slime is dried and melted to produce slag and metal. The slag is usually purified by selective reduction and smelted to produce antimonial lead. The metal is treated ia the molten state by selective oxidation for the removal of arsenic, antimony, and some of the lead. It is then transferred to a cupel furnace, where the oxidation is continued until only the silver—gold alloy (dorn) remains. The bismuth-rich cupel slags are cmshed, mixed with a small amount of sulfur, and reduced with carbon to a copper matte and impure bismuth metal the latter is transferred to the bismuth refining plant. 

The crude bismuth from the pyro or hydrometallurgy smelting need further refining to obtain the pure bismuth. Refining can be adapt fire or electrolysis process just... 

The most important ores are bismuthinite or bismuth glance and bismite. Peru, Japan, Mexico, Bolivia, and Canada are major bismuth producers. Much of the bismuth produced in the U.S. is obtained as a by-product in refining lead, copper, tin, silver, and gold ores. 

The pyrometaHurgical processes, ie, furnace-kettle refining, are based on (/) the higher oxidation potentials of the impurities such as antimony, arsenic, and tin, ia comparison to that of lead and (2) the formation of iasoluble iatermetaUic compounds by reaction of metallic reagents such as 2iac with the impurities, gold, silver and copper, and calcium and magnesium with bismuth (Fig. 12). 

Bismuth concentrates in the dorn until the last stages of cupeUation, when it is oxidized and removed with the Htharge. After the last Htharge has been removed, it is often necessary to add bars of refined lead to provide more Htharge to carry off the last traces of bismuth. The dorn metal is then cast into bars for marketing. 

Electrolytic Eefming. Electrolytic refining (26,27), used by Cominco Ltd. (Trad, B.C., Canada) and Cerro de Pasco Corp. (La Oroya, Pern), as weU as by several refineries in Europe and Japan, removes impurities in one step as slimes. The impurities must then be separated and purified. Before the development of the Betterton-KroU process, electrolytic refining was the only practical method of reducing bismuth to the required concentrations. 

Low bismuth, low silver, pure lead Refined pure lead Pure lead Chemical copper—lead... 

Iron, copper, arsenic, and antimony can be readily removed by the above pyrometaHurgical processes or variations of these (3). However, for the removal of large quantities of lead or bismuth, either separately or together, conventional electrolysis or a newly developed vacuum-refining process is used. The latter is now in use in Austraha, BoHvia, Mexico, and the CIS (5). 

The bismuth that is found in the lead ore accompanies the lead through the smelting operation right up to the last refining steps. The removal of bismuth then requires special techniques, the most common being the Betterton-KioU and the Betts processes (5). 

This bismuth—calcium—magnesium dross also contains lead that must be removed. The dross is heated in a ketde to free any entrapped lead that melts and forms a pool under the dross. This lead is cast and returned to the bismuth separation cycle. The dross is then melted and treated with chlorine and/or lead chloride to remove the calcium and magnesium. The resulting molten metal is an alloy of bismuth and lead, high in bismuth which is then treated to produce refined bismuth metal. 

Recovery of Bismuth from Tin Concentrates. Bismuth is leached from roasted tin concentrates and other bismuth-beating materials by means of hydrochloric acid. The acid leach Hquor is clarified by settling or filtration, and the bismuth is precipitated as bismuth oxychloride [7787-59-9] BiOCl, when the Hquors are diluted usiag large volumes of water. The impure bismuth oxychloride is usually redissolved ia hydrochloric acid and reprecipitated by diluting several times. It is then dried, mixed with soda ash and carbon, and reduced to metal. The wet bismuth oxychloride may also be reduced to metal by means of iron or 2iac ia the presence of hydrochloric acid. The metallic bismuth produced by the oxychloride method requites additional refining. 

Refining. The alloy of bismuth and lead from the separation procedures is treated with molten caustic soda to remove traces of such acidic elements as arsenic and teUutium (4). It is then subjected to the Parkes desilverization process to remove the silver and gold present. This process is also used to remove these elements from lead. 

The desilverized alloy now contains bismuth as well as lead and ziac. To remove the lead and ziac, advantage is taken of the fact that ziac and lead chlorides are formed before bismuth chloride [7787-60-2J, BiCl, when the alloy is treated at 500°C with chlorine gas. Ziac chloride [7646-85-7] ZnCl, forms first, and after its removal lead chloride [7758-95-4], PbCl2, forms preferentially. This process is continued until the desired level of lead removal has been reached. The bismuth is given a final oxidation with air and caustic soda the refined product has a purity of 99.999%. 

Although some changes occur in the melting furnace, cathode impurities are usually reflected directly in the final quaUty of electrorefined copper. It is commonly accepted that armealabiUty of copper is unfavorably affected by teUurium, selenium, bismuth, antimony, and arsenic, in decreasing order of adverse effect. Silver in cathodes represents a nonrecoverable loss of silver to the refiner. If the copper content of electrolyte is maintained at the normal level of 40—50 g/L, and the appropriate ratio of arsenic to antimony and bismuth (29) is present, these elements do not codeposit on the cathode. 

A nonprofit international association of companies engaged in the mining, smelting and refining of bismuth. 

Of the elements commonly found in lead alloys, zinc and bismuth aggravate corrosion in most circumstances, while additions of copper, tellurium, antimony, nickel, silver, tin, arsenic and calcium may reduce corrosion resistance only slightly, or even improve it depending on the service conditions. Alloying elements that are of increasing importance are calcium especially in maintenance-free battery alloys and selenium, or sulphur combined with copper as nucleants in low antimony battery alloys. Other elements of interest are indium in anodesaluminium in batteries and selenium in chemical lead as a grain refiner ". 

V. H. Aprahamian and D. G. Demopoulos, The Solution Chemistry and Solvent Extraction Behaviour of copper, iron, nickel, zinc, lead, tin, Ag, arsenic, antimony, bismuth, selenium and tellurium in Acid Chloride Solutions Reviewed from the Standpoint of PGM Refining, Mineral Processing and Extractive Metallurgy Review, Vol. 14, p. 143,1995. 

Electrolytic copper refining Blister copper Process wastewater Slimes containing impurities such as gold, silver, antimony, arsenic, bismuth, iron, lead, nickel, selenium, sulfur, and zinc... 

Refining operations have two principal wastestreams, waste electrolyte and cathode and anode washwater. Spent electrolyte is normally recycled. A bleed stream is treated to reduce copper and impurity concentration. Varying degrees of treatment are necessary because of the differences in the anode copper. Anode impurities, including nickel, arsenic, and traces of antimony and bismuth, may be present in the effluent if the spent electrolyte bleed stream is discharged. Tables 3.14 and 3.15 present classical and toxic pollutant data for raw wastewater in this subcategory. 

The United States gets most of its bismuth as a by-product from smelting ores of lead, silver, copper, and gold. It is also recovered from the refining of tin and tungsten ores. 

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