Tungsten, meaning heavy stone in Swedish has the highest melting point of any element, and is extremely hard wearing and corrosion resistant, making it one of the world’s strategic metals.
A tough, hard-wearing, corrosion and heat-resistant metal, tungsten is challenging to transform from its ores, scheelite and wolframite into an export-ready concentrate, or the elemental metal. New paths in metallurgy could unlock New Zealand tungsten for use in automotive and aerospace, in hard-metal tools, counterweights, speciality steel alloys, the chemicals industry, and in electronics.
Within the Otago Schist belt are lenses containing the mineral, calcium tungstate, or scheelite, a heavy variant of limestone or marble. When scheelite occurs in association with gold, the challenge is to win both the gold and the tungsten.
Adding ammonia to scheelite produces the commercially traded intermediate material, ammonium paratungstate or APT. If this can be made to be commercially viable, New Zealand will have a new export product.
The Elusive Heavy Stone
Swedish chemist Carl Scheele produced in 1781 an oxide of tungsten, the existence of which was earlier deduced by an Irish contemporary, Peter Woulfe. His name for the metal, wolfram, is recalled today in the chemical symbol, W, while the element was first isolated by the de Elhuyar brothers of Spain in 1783. Long hidden in rocks, the challenge for better metallurgical processes for tungsten ore continues today.