432:. This process used the different melting points of the metals in the solution in order to separate them out. Through fractional crystallization, the metals silver, copper and bismuth can be separated out of the lead in one step. However, this process is not very effective at removing bismuth because of how close the melting points of lead and bismuth are to each other.
70:
with a higher melting point, which then can be skimmed off of the surface. This process leaves behind lead with less than 0.01 percent bismuth by weight. The process is crucial to cheap industrial lead smelting and offers significant advantages over more expensive processes like the
404:. When the centrifuge is spun, the molten lead separates out of the dross more completely than just waiting for the dross to float to the top. This process also removes the need to hydraulically press the dross after extraction because very little lead ends up trapped in the dross.
332:
can be added to the solution. Once in the mixture at high temperature, electrodes can be used to decompose the salts into the metal and oxygen gas, so the calcium and magnesium are free to form alloys in the solution. For calcium oxide, the reaction that occurs is:
752:
103:
The key to the
Betterton–Kroll process is adding calcium and magnesium metal to molten lead bullion. The metals react with impurities in the lead and form a solid film on the surface, which can be easily removed, leaving behind much purer lead.
600:
117:
point (the lowest temperature that the alloy is completely liquid), which around 320-380 °C. At the lower temperature, the calcium and magnesium react with bismuth and antimony in the lead bullion in the following way:
112:
The
Betterton–Kroll process begins by heating lead bullion to around 500 °C. A calcium-magnesium alloy is added to the solution, which melts into the bullion in 15–20 minutes. The lead mixture is then cooled to the
391:
Because the calcium is produced by a reaction and doesn't spend time exposed to air, method prevents loss from oxidation. Another advantage of this method is that salts of calcium are often cheaper than calcium metal.
283:
200:
387:
416:
is used. However, due to the significant energy and equipment requirements of the Betts process, the
Betterton–Kroll process is preferable if that high level of purity is not needed.
320:
Although the
Betterton–Kroll process is the most widely used method, it has variations and alternatives that can provide advantages for specific use cases.
312:
of the calcium-magnesium-bismuth alloy. In the chlorination process, chlorine reacts with other metals in the dross and leaves behind high-purity bismuth.
300:
in order to squeeze out any remaining lead. Through this process, the bismuth in solution can be reduced to under 0.01 wt. %(percent by weight).
66:
are added to the molten lead at temperatures around 380 °C. The calcium and magnesium react with the bismuth and antimony in the bullion to form
425:
76:
95:
improved the process by adding magnesium to the process, which decreased the total amount of metal required in order to refine the lead.
400:
Instead of skimming the dross off the top of the molten bullion, the calcium and magnesium can be combined with the lead bullion in a
750:, Li, Rui-Qing & Harris, Ralph, "Process for bismuth recovery from lead-bismuth dross", issued 2003-09-12
412:
The
Betterton–Kroll process can only reduce the bismuth concertation to about 0.01% by mass. If higher purity is required, the
206:
123:
91:
developed a process for removing bismuth from lead by the addition of calcium. However, it was not commercially viable until
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413:
72:
328:
Instead of calcium and magnesium metal being added directly to the mixture, oxides of the metals mixed with other
338:
308:
After the dross is skimmed off, it can be treated to recover the bismuth. The most common process for this is
296:, on the surface that can be skimmed off. Molten lead can remain trapped in the dross, so the dross is often
292:
The alloys produced have a melting point greater than the rest of the metal, so they form a solid film, or
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43:
598:, Oatman, Betterton Jesse, "Process for removal of bismuth from lead", issued 1932-04-12
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Electrochemical processes within the slimes layer of lead anodes during Betts electrorefining
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from lead bullion (lead that still contains significant amounts of impurities). Developed by
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remain. The
Betterton–Kroll process is used to remove these impurities. In the process,
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547:"Analysis of the Kroll-Betterton Process: The Removal of Bismuth from Lead Bullion"
441:
50:. After gold, copper, and silver are removed from the lead, significant amounts of
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in 1922, the
Betterton–Kroll process is one of the final steps in conventional
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768:"Calcium–magnesium exchange reactions in lead alloys under molten salt"
619:"Behaviour of copper in refining of lead by fractional crystallization"
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51:
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Montagna, D; Ruppert, J. A; United States; Bureau of Mines (1977).
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823:"Synthesis of Pb–Ca alloys by electrolysis of CaO in molten salts"
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67:
728:. Washington, D.C.: U.S. Dept. of the Interior, Bureau of Mines.
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680:. Proceedings of the Fourth European Lead Battery Conference.
674:"Advances in the refining and alloying of low-bismuth lead"
617:
Qiu, K.; Chen, Q.; Winkler, P.; Krüger, J. (April 2001).
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164:
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Removing bismuth from lead with a submersible centrifuge
672:
Hibbins, S. G.; Closset, B.; Bray, M. (1 January 1995).
499:
González Domínguez, José Alberto; Alberto, José (2011).
278:{\displaystyle {\ce {Ca + 2Mg + 2Sb -> CaMg2Sb2(s)}}}
195:{\displaystyle {\ce {Ca + 2Mg + 2Bi -> CaMg2Bi2(s)}}}
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27:Industrial process for removing bismuth from lead
424:Another way to separate the bullion is through
766:Freidina, E. B.; Fray, D. J. (1 August 2003).
545:Mallaley, K.; Morris, D. R. (1 January 1990).
8:
827:Mineral Processing and Extractive Metallurgy
821:Freydina, E. B.; Fray, D. J. (August 2002).
772:Mineral Processing and Extractive Metallurgy
623:Mineral Processing and Extractive Metallurgy
382:{\displaystyle {\ce {CaO -> Ca + 1/2O2}}}
505:(Thesis). University of British Columbia.
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472:"Lead processing - Refining"
316:Variations and Alternatives
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792:10.1179/037195503225002709
426:fractional crystallization
420:Fractional Crystallization
414:Betts Electrolytic process
408:Betts Electrolytic Process
77:fractional crystallization
73:Betts Electrolytic process
847:10.1179/mpm.2002.111.2.79
643:10.1179/mpm.2001.110.1.60
678:Journal of Power Sources
571:10.1179/cmq.1990.29.1.67
476:Encyclopedia Britannica
32:Betterton-Kroll Process
18:Betterton-Kroll process
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93:Jesse Oatman Betterton
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324:Molten Salt Reactions
298:hydraulically pressed
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38:process for refining
883:Industrial processes
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89:William Justin Kroll
87:In the early 1920s,
44:William Justin Kroll
839:2002MPEM..111...79F
784:2003MPEM..112..135F
690:1995JPS....53...75H
635:2001MPEM..110...60Q
563:1990CaMQ...29...67M
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479:. Retrieved
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442:Lead smelter
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330:molten salts
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310:chlorination
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83:Development
877:Categories
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596:US1853539A
519:2429/30919
481:21 October
453:References
402:centrifuge
855:0371-9553
800:0371-9553
706:0378-7753
659:137570796
651:0371-9553
579:0008-4433
527:753010310
347:⟶
235:⟶
152:⟶
64:magnesium
863:97304441
808:95435976
436:See also
428:and the
115:liquidus
56:antimony
888:Bismuth
835:Bibcode
780:Bibcode
686:Bibcode
631:Bibcode
559:Bibcode
60:calcium
52:bismuth
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68:alloys
859:S2CID
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294:dross
34:is a
893:Lead
851:ISSN
796:ISSN
730:OCLC
702:ISSN
647:ISSN
575:ISSN
523:OCLC
483:2021
239:CaMg
156:CaMg
75:and
62:and
54:and
40:lead
30:The
843:doi
831:111
788:doi
776:112
694:doi
639:doi
627:110
567:doi
515:hdl
507:doi
344:CaO
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350:Ca
252:Sb
232:Sb
222:Mg
212:Ca
169:Bi
149:Bi
139:Mg
129:Ca
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