Klosters–Patenter process
The Klosters–Patenter process is a method of purifying lead produced by roasting sulfide concentrates. This method involves treating the roasted material with salt and iron oxide and then heating it with charcoal in a crucible. The iron oxide reacts with the lead to form iron sulfate and metallic lead. The iron sulfate is removed as slag while the metallic lead is allowed to settle at the bottom of the crucible.
The name Klosters–Patenter is derived from the two inventors, Edouard L. Klosters of the United States and Bruno A. Paten of Germany, who developed the process. It was Hans Goldschmidt of Germany who first suggested the use of iron oxide to remove lead from sulfide concentrates, however it was not until the collaboration between Klosters and Paten that the process was perfected.
The first commercial applications of the process occurred in Germany in 1888 and its use soon spread around the world. In the United States, plans for a large-scale lead refining plant using the Klosters–Patenter process were put forth in 1893 by Columbia Lead Smelting and Refining Company.
The Klosters–Patenter process is relatively simple and requires relatively simple equipment, namely a fireclay or refractory-lined crucible and a furnace. The furnace can be powered by either electric or fuel heat. Most modern operations use electric furnaces as they provide more precise control over the temperature.
The process begins by roasting the lead sulfide concentrates in air to form lead oxide. The lead oxide is then mixed with salt, usually sodium chloride or sodium carbonate, and iron oxide, usually ferric oxide. The mixture is then heated in a crucible until the iron oxide and salt react with the lead and form iron sulfate and metallic lead. The iron sulfate and other impurities are then removed as slag, leaving the powdered metallic lead at the bottom of the crucible.
This lead is then cast into ingots or further processed into products such as wire or sheet lead. The quality of the lead produced by the Klosters–Patenter process is usually very high, often exceeding 99.9% purity.
The Klosters–Patenter process has been improved and modified over the years. One major variation that has been developed is the use of sulfuric acid to dissolve the iron sulfate slag, thus allowing a higher lead recovery from the concentrate. This saves time and money as the lead does not need to be further refined to remove any remaining impurities.
Even with the introduction of newer and more efficient technologies, the Klosters–Patenter process remains a reliable and cost-effective method of lead purification. It can be used on a variety of sulfide concentrates, including those containing other metals such as copper or zinc. By producing a high-purity product, the process has enabled lead to become an important industrial metal, used for everything from pipe casing to electric wiring.
