Extractive metallurgy of bismuth

Bismuth, whose concentration in the earth's crust is around 0.2 g/tonne, is most often associated with other elements: its metallurgical extraction must therefore be adapted to complex materials.

The most common mineralogical forms of bismuth are native bismuth, bismuthinite, and various complex copper and lead sulfides. Bismuth is also often present in copper sulfo-antimonides and sulfo-arsenides.

Most deposits are of hydrothermal origin, but bismuth is also found in some gold porphyries, where it is associated with copper and molybdenum.

Worldwide reserves are of the order of 56,000 tonnes, resources around 350,000 tonnes, and annual production between 8,000 and 9,000 tonnes. Production and resources are held by five main producers (Bolivia, Canada, China, Mexico and Peru); China leads both in terms of resources (240,000 tonnes) and mining production (6,000 tonnes/year).

Extractive bismuth metallurgy is carried out either on wolfram- and bismuth-bearing mining concentrates, or on crude metals from primary lead, copper or tin metallurgies. In the former case, bismuth is present as simple sulfides or oxides, as complex sulfides, or as impurities. In the latter case, it is recovered as a co-product of lead or as a by-product of copper or tin.

Lead metallurgy produces 90% of the bismuth consumed worldwide: lead de-bismuthizing takes place at the end of lead refining operations. Bismuth production from tin and copper metallurgy is much lower. Tin metallurgy provides raw tin from which bismuth is extracted by slagging; another route is the hot hydro-metallurgical treatment of cassiterite concentrates with hydrochloric acid. Copper metallurgy produces a crude copper refined by electrolysis: bismuth is found both in the electrolysis solution and in the anode sludge; it also generates dust and leaching solutions from which bismuth can be extracted by hydro-metallurgical means.

Crude bismuth is refined thermally or electrolytically, reaching grades of over 99% Bi.

Bismuth's uses break down as follows: 57.2% for chemicals and pharmaceuticals, 26.4% for alloy composition, 8.8% for metallurgical additives and 7.6% for miscellaneous uses.

It can only be recycled from alloy scraps, other uses being too dispersive.

Bismuth substitutes have been studied, notably for use in pharmaceuticals and safety system alloys.

Environmental pollution by bismuth results from its use in fungicides and fertilizers, but is negligible. For humans, bismuth is considered the least toxic of the heavy metals, but it can cause irritation through inhalation and intoxication through ingestion.