Antimony: The Flame Fighter the United States Imports

Antimony (element 51, symbol Sb) is a brittle, silvery-white semimetal that conducts heat poorly. Its best-known compound, antimony trioxide (Sb₂O₃), is used widely in plastics, rubber, paints and textiles — from industrial safety suits to some children's clothing — to slow the spread of flames. Another, sodium antimonate (NaSbO₃), goes into the high-quality glass found in mobile phones.

An ancient mineral

People have known stibnite (Sb₂S₃), a lead-grey antimony sulfide, since antiquity. Egyptians ground it into black eye make-up for their distinctive look. The first-century Greek physician Pedanius Dioscorides recommended it for skin complaints, and 17th-century French and German doctors prescribed antimony mixtures to make patients vomit. Antimony was later recognised as a strong skin irritant and a deadly poison, especially when swallowed.

The scholar Constantinus Africanus used the word antimonium in the 11th century, but the metal itself was not isolated until the 16th century, by the Italian metallurgist Vannoccio Biringuccio. In the early 18th century the chemist Jöns Jacob Berzelius gave it the symbol Sb, from stibium, the Latin name for stibnite. Antimony occurs naturally in more than 260 minerals, and, like water, it expands when it freezes.

What it is used for

• Flame retardants take most of the world's antimony. Powdered trioxide is chemically bonded or blended into many materials, textiles included. On its own it does not stop fire, but combined with halogens such as bromine in polymers, the mixture suppresses, reduces and delays the spread of flames.
• Batteries. Antimony-lead alloys improve batteries' electrical properties: electrodes coated with them recharge more efficiently and can be fully drained many times without losing performance. Many mobile phones use antimony-bearing batteries, and research into replacements for lithium-ion batteries has produced antimony nanocrystals for future high-energy-density batteries.
• Ammunition. The same alloys make ammunition harder, enough to penetrate some armour.
• Plastics and glass. It is used in making plastics such as PET, the material of soda bottles, and sodium antimonate removes bubbles and traces of iron from high-quality glass and makes it resistant to sunlight.

Where it comes from

Antimony occurs worldwide in many kinds of deposits, but two types supply 80 percent of it:

In carbonate-replacement deposits, stibnite — the commonest antimony mineral — fills veins in carbonate rocks such as limestone, sometimes as lenses of almost pure stibnite tens of metres long, which makes very rich ore. In gold-antimony epithermal deposits the ore is also in veins, but less concentrated; the veins link up in three-dimensional networks to form low-grade, high-tonnage deposits that can be mined from open pits, in host rocks from shale, limestone and quartzite to granite, calc-silicate rocks and volcanic rocks. The open pit at Yellow Pine once produced a great deal of gold, antimony and tungsten.

Supply and demand

World production could meet consumption in the near term, but might fall short if consumption rises sharply and no new sources are developed. China leads the world in production, but its mine output in 2013 was about 20 percent below 2011's. In 2013 the United States imported 85 percent of the antimony it used, 71 percent of that from China.

No U.S. antimony mine was operating in 2013, though a smelter in Montana produced antimony from imported concentrates and oxides. The Sunshine Mine, in the Coeur d'Alene district of northern Idaho, was the only domestic producer from the late 1990s to early 2001. As of 2015 there was renewed interest in mining Yellow Pine, and the tripling of antimony prices between 2009 and 2014 may encourage mines to open.

Securing future supply

U.S. defence, energy and manufacturing industries depend on foreign antimony and could suffer as world supply declines. Substitutes exist but work less well and cost more, so domestic sources are being explored and stockpiling is planned.

• The Stibnite mining district of central Idaho, which includes Yellow Pine, holds an estimated 41,000 metric tons of antimony — the largest domestic resource.
• The Coeur d'Alene district of northern Idaho, with a quartz-stibnite vein deposit that produced significant antimony in the past, ranks second.

To predict where future supplies might lie, USGS scientists study how and where antimony is concentrated in the Earth's crust and use that to judge how likely undiscovered deposits are in an area — methods developed to support the stewardship of federal lands and to assess mineral availability worldwide. The USGS also compiles statistics on world antimony supply, demand and flow to inform U.S. policymakers.

Sources

• Wintzer, N.E., and Guberman, D.E., 2015, Antimony — A flame fighter: U.S. Geological Survey Fact Sheet 2015–3021, USGS Mineral Resources Program. https://pubs.usgs.gov/publication/fs20153021
• Photo: Stephen Box, U.S. Geological Survey, from the fact sheet's PDF. The sheet's other photographs — a burn test (Thor), the bust of Nefertiti (Egyptian Museum of Berlin) and a stibnite specimen (Robert Lavinsky collection) — are not federal and are left out.
• Corrected: the sheet spells the chemist's name "Jons Jakob Berzelius"; he was Jöns Jacob Berzelius.
• Rewritten in hubnx's own words.