Potassium chloride

The chemical compound Potassium chloride (KCl) is a metal halide which is used in medicine, scientific applications, food processing and in judicial execution through lethal injection. It occurs naturally as the mineral sylvite and in combination with sodium chloride as sylvinite.

In a pure state it is a odourless, white to colourless vitreous crystal. It is a face-centred cubic which cleaves easily in three directions; its physical properties include a density of 1.987 g/cm³, a melting point of 776 °C, a boiling (sublimation) point of 1500 °C, and a molecular weight of 74.55. It is readily soluble in water and insoluble or only slightly soluble in alcohols.

Potassium is vital in the human body and oral potassium chloride is the common means to replenish it although it can also be diluted and given intravenously. Medically it is used in the treatment of hypokalemia and associated conditions, for digitalis poisoning, and as an electrolyte replenisher. Side effects can include gastrointestinal discomfort including nausea and vomiting, diarrhea and bleeding of the gut. Overdoses cause hyperkalemia which can lead to paresthesia, cardiac conduction blocks, fibrillation and arrhythmias, also sclerotic effects.

Orally it is toxic, but the LD50 is around 2500 mg/kg. Intravenously this is reduced to just over 100 mg/kg but of more concern are its severe effects on cardiac muscles; high doses can cause cardiac arrest and rapid death.

As sylvite it is commercially valuable as a source of potash (sometimes called muriate of potash) and of potassium for fertilizer. It is also extracted from salt water and can be manufactured by crystallization from solution, flotation or electrostatic separation from suitable minerals.