Radium of radium Curie used the residues after extraction of uranium from pitchblende. The uranium had been extracted by dissolution in sulfuric acid leaving radium sulfate, which is similar to barium sulfate but even less soluble in the residues. The residues also contained rather substantial amounts of barium sulfate which thus acted as a carrier for the radium sulfate. The first steps of the radium extraction process involved boiling with sodium hydroxide followed by hydrochloric acid treatment to remove as much as possible of other compounds. The remaining residue was then treated with sodium carbonate to convert the barium sulfate into
Radium not work well with low grade ores. Small amounts of radium were still extracted from uranium ore by this method of mixed precipitation and ion exchange as late as the 1990s, but today they are extracted only from spent nuclear fuel. In 1954, the total worldwide supply of purified radium amounted to about and it is still in this range today, while the annual production of pure radium compounds is only about 100 g in total today. The chief radium-producing countries are Belgium, Canada, the Czech Republic, Slovakia, the United Kingdom, and Russia. The amounts of radium produced were and