The Betterton–Kroll process is an industrial process for removing bismuth from lead. The process was developed by William Justin Kroll and patented in 1922. Further improvements were developed by Jesse Oatman Betterton in the 1930s.
Calcium and magnesium are added to a molten lead-bismuth bath. The resulting bismuth compounds have higher melting points and lower densities than the lead, and can be removed as dross. The compounds are treated with chlorine to free up the bismuth. Temperature used in the process is about 380–500 °C(572–932 °F) . The other major processes for separating the two metals are by fractional crystallization and by the Betts electrolytic process.
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