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Metal Profile: Antimony

What is antimony?

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Antimony is a hard, brittle metalloid that is used as an alloying agent in lead-acid batteries, Babbitt bearings and pewter. In its chemical forms, antimony is valued as a flame-retardant and catalyst material.

Properties:

  • Atomic Symbol: Sb
  • Atomic Number: 51
  • Element Category: Metalloid
  • Density: 6.697g/cm3
  • Melting Point: 1167.13°F (630.63°C)
  • Boiling Point: 2889°F (1587°C)
  • Moh’s Hardness: 3

Characteristics:
Antimony is technically classified as a metalloid, or semi-metal, meaning that it possesses both some properties of metals and some of non-metals.

In its pure metal form, antimony is hard and brittle. Its silver appearance is similar to that of zinc, but this quickly tarnishes to grey in air, forming a layer of antimony trioxide on the metal's surface.

Antimony has very low thermal and electrical conductivity.  Metallic antimony expands as it solidifies, making it useful as an alloying material in precision-cast alloys.

While antimony metal is relatively stable and safe, compounds of the element are considered toxic.

History:
Unlike many minor metals, antimony has been used by humans for millennia.

Early Egyptians used forms of antimony in cosmetics and medicines around 5000 years ago. Ancient Greek doctors prescribed antimony powders for the treatment of skin disorders, and during the Middle Ages antimony was of interest to alchemist who gave the element its own symbol. It has even been suggested that Mozart's death in 1791 was a result of excessive consumption of antimony-based medicines.

According to some of the first metallurgy books published in Europe, crude methods for isolating antimony metal were likely known by Italian chemists over 600 years ago.

One of antimony's earliest metallic uses came in the mid-15th century when it was added as a hardening agent in cast metal printing type used by Johannes Gutenberg's first printing presses.

By the 1500s, antimony was reportedly being added to alloys used to produce church bells because it resulted in a pleasant tone when struck.

In the mid-17th century, antimony was first added as a hardening agent to... (Read more about the History of Antimony).

Production:
Antimony is most often extracted from the sulphide ore stibnite, but can also be produced from a number of oxide and sulphide-type ores, including jamesonite and valentinite.

Mined as both a principal material as well as a by-product of other metals, a variety of extraction methods are used to isolate antimony depending upon the content, form and purity of the raw ore.

Lower purity sulfide ores and concentrates are first roasted with charcoal in a roaster or shaft furnace. Once the sulfur combines with oxygen, burning off as gas, low-grade antimony oxide can be recovered.

Higher purity oxide and sulfide ores are often smelted in a blast furnace, which produces crude antimony metal. Liquation can also be used to convert higher-grade sulfide ores in metal or oxide forms. This requires the ore to be heated in reducing environment to between 550-600°C (1022-1112°F).

Oxide ores are either reduced in blast furnaces to crude metal, or reduced and refined to commercial-grade metal in rotary or reverberatory furnaces with charcoal. This extraction method can be used in the production of 99% grade antimony metal.

Commercial-grade antimony oxides are finally produced via the revolatilization of impure oxide or the volatilization of antimony metal.

Crude antimony, produced via smelting, liquation, reduction or other methods, must be further refined to create commercial purity metal. Steps to lower iron and copper impurities often use stibnite or sodium sulfate and charcoal, while arsenic and sulfur impurities are removed by covering molten metal with an oxidizing flux.

According to US Geological Survey (USGS) statistics, China currently accounts for nearly 90 percent of global antimony mine-production. In 2011, an estimated 169,000 metric tonnes of antimony was mined worldwide.

Large Chinese producers include Hsikwangshan Twinkling Star Co., Liuzhou China Tin Group and Hunan Chenzhou Mining. Many large antimony mines outside of China are also owned by Chinese companies, including Beaver Brook Mine in Newfoundland, Canada (Hunan Nonferrous Metals) and Consolidated Murchison in South Africa (Metorex, a subsidiary of Jinchuan Group).

Although there is some recycling of antimony, this is limited to antimonial-lead, extracted from lead batteries. For the most part, this is refined at secondary lead smelters and re-used in lead-acid batteries.

Applications:
Up to 80 percent of all antimony consumed annually is used in chemical forms, particularly antimony trioxide, for its flame-retardant and catalytic properties. The greatest demand for antimony metal alloys comes from the lead-acid battery industry.

Grid plates in lead-acid batteries are alloyed with between 0.6 and 1.6 percent antimony in order to strengthen the metal, as well as increase corrosion and creep resistance.

Antimony is often alloyed with lead, zinc or tin as a means of strengthening and hardening these metals.

Babbitt metal is a common example such as alloy. Babbitt can contain anywhere from between 6 to 18 percent antimony and is used in the production of Babbitt bearing, which are used for their low friction resistance, low wear, good run-in properties. Babbitt bearings are mostly found in high-speed rotating equipment, such as compressors, turbines, chillers, electric motors and gear drives.

Antimony is also used as a dopant in tin-lead solders to improve thermal fatigue resistance and strength, as well as to stop grey tin transformation at low temperatures. Tin-lead solders with melt temperatures below 662°F (350°C) contain between 0.05-0.50% antimony, whereas tin-lead-antimony solders can contain up to 3.0% antimony.

Antimony-containing lead alloys are also used to produce:

  • Lead-alloy shot and bullets (~2% Sb)
  • Cable sheathing alloys (~1% Sb)
  • Rolled and extruded alloys for flashing, gutters, tank-linings, pipes and roofing (2-8% Sb)
  • Casting metals, including pewter, Britannia metal and type metal

Demand for high purity antimony metal (99.99% minimum) has grown in recent years with the development of DVD, semiconductor and photovoltaic technologies that make use of antimony's conductive properties, however, such applications only account for a very small portion of total demand.

As mentioned, the majority of all antimony produced and consumed each year is in the form of chemicals. Antimony trioxide is used as to produce antimony-halogen flame retardant materials that are used in the production of plastics, rubbers and textiles.

Antimony-based chemicals are also used as:

  • Stabilizers in the production of PVC plastic
  • Catalysts in the production of PET plastic
  • Decolorants and fining agents in glass production
  • Pigments for paints
  • Phosphors in fluorescent lamps
  • A vulcanizing agent in red rubber production
  • Reactants in organic chemistry reaction (e.g. producing freons)

Sources:
USGS. Mineral Commodity Summaries: Antimony. 
URL: http://minerals.usgs.gov/minerals/pubs/commodity/antimony/
Butterman, WC and JF Carlin Jr. USGS. Mineral Commodity Profile: Antimony. 2004.
URL: http://pubs.usgs.gov/of/2003/of03-019/of03-019.pdf
US Antimony Corp. Processing of Antimony Ores. Metallurgy.
URL: http://www.usantimony.com/metallurgy.htm
Vulcan, Tom. Antimony: A Metal? February 18, 2009. HardAssetInvestor.com
URL: http://www.mmta.co.uk/uploaded_files/HArd%20Assets,%20Antimony.pdf

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