Process for the separation and recovery of metals from metal alloys 

(Debismuthising of lead [21] & Deantimonising of tin alloys)

This table shows that Kroll assigned his German inventions to industrial companies, against up-front payments rather than keeping the property of the patents and granting licences.

“Then I discovered that aluminum can be used to deantimonise and dearsenise tin alloys, especially solder. This process was put to practice by Th. Goldschmidt Co. Essen, to which I sold this idea.”

Refined lead is consumed in a number of end-uses, of which lead batteries constitute by far the most important market, accounting for 60% of total lead consumption.

Still at university, Kroll filed patent applications on the debismuthising of lead (later known as “Betterton-Kroll process”).

“Als ich die Technische Hochschule Charlottenburg im Jahre 1918 verließ und bei einem deutschen Metallunternehmen Anstellung nahm, schrieb ich meinem Chef über die Möglichkeit, Blei mit Kalzium vom Wismut zu befreien, ein wichtiges Problem, da Wismut in geringsten Mengen Bleiweiß braun färbt. Mein Vorgesetzter war nun ganz erbost über diese Dreistigkeit und er empfahl mir, nachdem er mich vorgeladen hatte, mir erst einmal zwanzig Jahre Bleihütten-Praxis anzueignen, ehe ich in solchen Dingen mitreden könnte. Nun, er war im Unrecht, denn meine Erfindung als «Grüner» wird heute auf 15% der Weltbleierzeugung angewandt.”

Czochralski, to whom Kroll refers as “mein Vorgesetzter”, was recruited by M&M in June 1917 shortly before Kroll took up his appointment with the company. Kroll made the proposal to Czochralski to further develop the debismuthising process but the latter refused. [22]

The “Betterton-Kroll” process made it possible to remove bismuth from lead and thereby to refine lead for industrial use. Kroll’s patent rights were bought by the company « American Smelting and Refining Co » around 1923 [23], suggesting that Kroll received at the time a substantial payment.


At the end of 1919 Kroll departed for Vienna to prepare for his new job in Hungary.

“After about one year spent in the lead plant in Call, to get under way the production of Ca/Ba bearing alloy, I accepted a mission to go to Vienna in 1919 to study a process whereby tin, silver and gold were extracted from antimonial copper tin residues, originating from church bells. With this knowledge I went to Hungary where I spent the years of 1920 and 1921 on behalf of the Hungarian Government and two other associated companies …” 

In a contribution to the L’Echo des naturalistes of 1962 [23], Kroll further explained:

“Un jour vers la fin de l’année 1919, quand on chantait encore dans les dancings "Yes we have we have no bananas", je travaillais humblement dans une pauvre usine à plomb de l’Eifel allemande. Je reçus alors inopinément la visite d’un grand chef d’entreprise qui me tint a peu près le langage suivant: "Nous désirons que vous alliez entreprendre tout de suite pour nous la construction et la direction d’une usine a Csepel, près de Budapest, pour y récupérer de l’étain et des métaux précieux contenus dans des résidus de traitement de cloches, appartenant au gouvernement hongrois. - Moi? dis-je tout étonné. Il doit y avoir erreur! Car je suis a peine sorti d’université. Je n’ai pas la moindre expérience prati­que - et je n’ai jamais dirigé une usine." Mais le grand chef insista, me disant que sa compagnie avait pleine confiance en mes talents et que, d’ailleurs, il n’y avait personne d’autre pour cette noble tâche.Ceci naturellement me flattait énormément et je ne pus, hélas! résister à la tentation. Si seulement j’avais su, en ce moment, ce qui se préparait pour moi!“


In October 1920, Kroll moved from Vienna to Budapest and on New Years’ Eve of 1920 he moved from Budapest to the «Manfred Weiss» industrial complex in Csepel where he stayed for 2 years.

In his contribution to the publication L’Echo des naturalistes of 1962, Kroll reflects on his stay in Hungary but does not mention any particular research work or any inventions that he may have made at the time. [24]

From a French patent that was granted to Kroll in 1920, we learn that he had been working, as of 1917, on a process for preparing alkaline-earth metal alloys.


[21] d’Lëtzeburger Land, 1956, No 10, page 3

[22] Helmut Maier, 100 Jahre Deutsche Gesellschaft für Materialkunde (2019), p. 12

[23] L’Echo des Naturalistes, No 3, 31 December 1962, pages 2-5

[24] to be further investigated