Potassium is chemically similar to sodium. As described in the history of that element, the compounds of both elements were regarded as the same in antiquity. During the 18th century, though, chemists were getting different results from experiments on these supposed same substances. For example, crystals of (sodium) saltpeter derived from salt are cubic; crystals of (potassium) saltpeter from plants are prismatic. Chemist Humphry Davy settled the question in 1807 by using electrolysis to extract both metals. They were clearly different.
Mining and Production
Potassium is rather common on the Earth's surface. It is found in rocks such as feldspars and granite. More importantly, it forms many water-soluble compounds and has therefore been concentrated in ancient seabeds. Another source of potassium is guano, the accumulated excrement of birds or bats found in isolated locations. The significance of guano is attested by the Spain-Peru-Chile war that began in 1864 for control of guano-bearing islands off the coast of Peru.
About 850 thousand tonnes of potash and equivalent minerals were mined in the United States in 2014, down about 10% from recent years. (On the right, potash settling ponds.) The world total was 35 million tonnes, with Canada being the largest producer at 28%. Potassium is also found in other minerals that are mined, such as feldspars and granite, but these are not selected for their potassium content.
Properties and Uses
Potassium is a very lightweight metal that is easily cut. It is silvery when pure but tarnishes rapidly in dry air. It reacts explosively in water, liberating hydrogen that also burns. Potassium must therefore be handled very carefully and stored under mineral oil or inert gas.
Potassium burns with a lilac color as distinct from the yellow color of sodium. It forms compounds with most of the elements on the right side of the periodic table other than the inert gases. Several of these have useful applications.
Potassium is essential to both animals and plants. Most commercial potassium is used as a fertilizer; see potash. In animals, potassium ions regulate nerve impulses, water balance, and muscle contraction.
Potassium hydroxide is a powerful alkali used to manufacture soap and as an industrial cleaner. Potassium nitrate is one of the three components of gunpowder. Potassium chloride is sold as a substitute for table salt (sodium chloride).