Extractive metallurgy of rare earths

Although most of the rare earth metals were discovered in Sweden, the industrialisation started in the Austrian Empire. This was due to the fact that the Swedish chemist Jons Fridrik Bahr (1815–1875) from Uppsala went to Heidelberg in Germany in 1855 to analyse some rare earth minerals by the spectroscope discovered recently by chemistry professor Robert Bunsen (1811– 1899) and his colleague physicist Gustav Kirchhoff (1824–1887). Few years later Carl Auer (1858–1929) from Vienna went also to Heidelberg to study under Bunsen. He was assigned the task to separate the rare earths from these minerals. On his return home, Carl Auer took with him the remaining minerals to continue his studies at the University of Vienna. While in Heidelberg, Carl Auer had noted the remarkable light-emitting powers of the rare earth oxides when they were inserted into the flame of a Bunsen burner. In Vienna he put this observation into practice by inventing the gas mantle, a stocking made of cotton thread and soaked in a solution of the earth metal salts. After the organic matter was burned off, a skeleton of the metal oxide was left. This emitted light when heated in a laboratory Bunsen burner. In 1887, he started a factory at Atzgersdorf, a suburb of Vienna, to separate the rare earths salts necessary for preparing the soaking solution for manufacturing the gas mantles for lighting the streets in Vienna. He also sold the solutions to customers in Germany, England, and USA. The marked for gas mantle declined later when the Edison lamp was invented at the beginning of the twentieth century. The second industrial application of rare earths came when Carl Auer recalled the preparation of metallic cerium by his colleagues at Bunsen’s laboratory and the sparking of the metal when scratched or drawn over a rough surface. He conceived that this sparking action may be utilised for ignition purposes. However, cerium would be a too costly material. He, therefore, prepared a cerium–iron alloy and found out that when the alloy contained 30%Fe it gave the best sparking effect suitable for ignition of gases. The ‘Auer lighter’ soon became as famous as his incandescent mantle when it was produced on large scale in 1903. Production reached 1 000 000 kg annually in 1930; it served to prepare 500 million flints which replaced six billion boxes of matches. This work was conducted at his new factory at Treibach in Carinthia which he took possession in 1900 and which is today a successful metallurgical plant known as Treibacher Chemische Werke in Austria.