ABSTRACT
Potassium (atomic weight = 39.098) is an alkaline metal, as revealed by the etymology of its symbol (K) which derives from the Latin word “kalium” and from the Arabic word “qali” (alkali). K is thus strongly electropositive and always occurs as a monovalent cation. Consequently, its physic-chemistry and speciation are rather simple. K is an abundant alkaline metal cation, reaching a concentration of 26 g kg–1 in the Earth’s crust. It is a major nutrient for all living organisms.
