Cosmetics, Alchemy , Fire and Electricity
Antimony sulphide (stibnite) was used as a cosmetic as long ago as 3,000BC, in Sumer (today’s south-central Iraq) and Egypt. The sulphide was finely ground and generally applied to the eyes and eyelashes. Much later its use as a cosmetic spread to many countries and it became known in Hebrew and Arabic as kohl. In other languages kohl was spelt “alcool” or “alkohol” and up until the Middle Ages “alcohol” referred to anything in the form of a fine powder.
A number of references state that a vase dated at around 3,000BC was discovered at Tello, Chaldera (in Sumer) that was cast in “metallic” antimony. References are also made to antimony plated objects in Egypt at around the same time.
Antimony was integral to the practice of alchemy, particularly in its later stages during the 17th century. One of the most important practitioners at that time was Isaac Newton, of subsequent gravitational fame. Antimony was part of a process that was thought would ultimately lead to discovery of the “philosophers’ stone”, an agent for the transformation of elements (such as the fabled transmutation of lead into gold).
Although the philosophers’ stone has never been discovered, the late 17th century alchemy is fascinating and is described briefly here. First stibnite (antimony sulphide) was reduced to the “metallic” antimony at high temperature in the presence of iron, then allowed to cool slowly beneath the iron flux. This formed visible, star-like crystals of antimony, known as the star regulus of antimony.
The antimony was then fused with silver (or sometimes copper) and the subsequent alloy amalgamated with mercury, to become “sophic” mercury. Gold could be “dissolved” in the resulting amalgam where it formed branching forms that were thought to be akin to vegetation, that is, the gold had been transformed. This led to the belief that sophic mercury was the key to producing the philosophers’ stone.
So antimony has a long and varied history. I should mention in passing that it has also been used as a medicine and as a poison.
Within the periodic table of the elements, there is a continuum from non-metals to metals. Antimony lies somewhere within the middle of the range and is often referred to as a metalloid; that is, it is metallic looking, brittle and able to alloy with metals. Related elements are boron, silicon, germanium, arsenic and tellurium.
Metalloids or their compounds can all be used as semiconductors. For example, with regard to antimony, gallium antimonide is used in infrared detectors, LED’s and thermophotovoltaics and indium antimonide is used in thermal imaging sensors.
Antimony is a silvery grey colour that can exist in nature as the metal, but almost always occurs as the sulphide, stibnite (Sb2S3). Stibnite looks a little like lead and historically has often been misidentified as such. Antimony can exist as four allotropes, that is as four different elemental structures. By way of comparison, two of the allotropes of carbon are diamond and graphite.
There are dozens of antimony compounds in industrial use today. However the vast majority of antimony is consumed as antimony trioxide (“ATO”), antimony metal, secondary antimonial lead and sodium antimonate.
ATO is an important component of flame retardants, of which the vast majority is used in electronics and plastics and the remainder in fabrics such as clothing and upholstery. Flame retardants account for about 50% of the world’s antimony consumption, and market share continues to grow.
Flame retardants are primarily composed of chlorinated or brominated (halogenated) hydrocarbons with less than 10% ATO. To simplify, when subject to heat, halogenated flame retardants breakdown and the breakdown products prevent the direct reaction of hydrogen and oxygen. This reduces and eventually suppresses the supply of flammable gases, thus “putting out the flame”. ATO is a synergist, which is to say it that it effectively speeds up and improves the retardant process.
Around 25% of world antimony consumption is in lead acid batteries; the antimony is sourced from new metal supply and from secondary antimonial lead from the recycling of batteries. Antimony is added to strengthen and harden the lead. The weight percent of antimony in a lead acid battery is in continuous decline and antimony metal use will also be impacted by alternative battery technologies. However demand is holding up for now because of the sharp increase in world automotive production.
Antimony metal is used in a number of other lead alloys. For example, it is important in bullets as it allows the correct expansion of the bullet into the rifling, thus improving accuracy and range. In general, more antimony is used in higher speed projectiles.
Sodium antimonate is used as a high temperature oxidant, in fire proofing, and in glass refining and decolourising. Antimony compounds are also used in paints and pigments.
Substitutes & Recycling
Antimony can be readily substituted for in batteries and in paints and pigments. Some hydrocarbons and hydrate aluminium oxide are already used to reduce the usage of ATO in flame retardants. Antimony is traditionally recycled from batteries but not flame retardants, although when plastic is recycled so is the antimony, if inadvertently.
Supply and Demand
World mine production of antimony metal in 2010 is estimated at 167,000 tonnes1. China supplied 90% of this total (including “unofficial” production), of which 60% was from Chinese mines and the balance derived from imported metal concentrates. The minor producers are Bolivia, Russia, South Africa, Tajikistan and Turkey.
Much of China’s antimony exports are as ATO rather than the metal. China itself is a large antimony consumer through both domestic consumption and export of antimony in manufactured products. Antimony, along with rare earths and tungsten, is a strategic metal for China and is therefore subject to export quota. This, along with mine closures for environmental and depletion reasons, and forced smelter consolidations, has significantly tightened supply since 2007.
The first spike in the antimony price was during the First World War, because of the extreme consumption of bullets and related ammunition. Prices and production quadrupled before settling back to pre-war levels at the cessation of hostilities. Similar spikes were also seen during the Korean and Second World Wars.
During the 1980’s until the early 1990’s China increased production until it was again supplying around 90% of the world’s market, as it had during the First World War. This supressed the antimony price, which stagnated until around 1999. For China, which was then running a trade balance deficit, antimony (and many other commodities) earned valuable foreign exchange reserves. For other countries, the depressed price led to declining production and cessation of exploration.
By 2000 the price of refined antimony had fallen to around UDS $1,500 per tonne, its lowest level since 1970. This made much Chinese production unprofitable, so the Chinese government took several steps to reduce the production and export of antimony. This worked and along with the world’s expanding consumption of commodities, the price had risen to $5,000 per tonne by 2007.
But the real price action was just around the corner. The price of antimony soared to a peak of around $17,000 per tonne in 2011. The price has drifted since then, in part due to inventory build-up, and is around $13,000 per tonne at the time of writing.
Antimony is one of the least common elements in the Earth’s crust, less common than the rare earths but more common than gold, platinum and palladium. It mostly occurs as stibnite and also occurs in minerals associated with metals such as copper, lead, zinc, silver and gold.
In 2011 the United States Geological Survey (“USGS”) estimated world reserves of 1.8 million tonnes of antimony metal. China hosted over 50% of this reserve, Bolivia and Russia with about 20% each and the balance in other countries. These figures are somewhat uncertain with regard to China.
These reserves do not include resources (that is mineralisation that is less well defined and not necessarily economic to exploit). The USGS suggest resources could be in the 4 to 6 million tonne range. There are significant antimony resources in Bolivia, China, Mexico, Mexico, Russia, South Africa and Australia. In addition, there are significant quantities of recoverable antimony as a by-product in concentrates of other metals such as lead and zinc.
In sum, the world’s reserves of antimony are small, perhaps enough for 10 to 15 year’s consumption at current rates. However, the situation may not be as dire as it seems. Production from resources, new discoveries and by-product antimony could fill the gap for a time. Finally, if the price remains high then substitution will definitely reduce antimony demand.
Antimony deposits generally occur as relatively small lenses, lodes or veins. This can lead to high mining costs and lower mined grades because of wall rock contamination. The metallurgy can be somewhat complex which can lead to processing complications, lower recoveries and higher costs.
The biggest issue is the toxicity of antimony. Antimony occurs naturally in water and on land and passes relatively quickly through an animal. However, antimony toxicity is a complex area as some antimony compounds are much more toxic than others. Antimony is often found, both in nature and industry, in combination with other potentially toxic compounds, which can make it difficult to determine the actual cause of poisoning.
There have been a number of antimony poisoning scares over the past 20 years, that while unjustified, have given antimony a bad rep. For example, in the early 1990’s research purported to show that ATO in fireproofed cot bedding was primarily responsible for Sudden Infant Death Syndrome (“SIDS”). While the role of antimony in SIDS was scientifically discredited, doubts no doubt remain in the mind of the layman.
Poor mining and processing practices in developing countries have led to antimony poisoning and environmental degradation at mines and in factories. China is well on top of this issue and practices are already showing great improvement. Environmental concerns are significant in developed economies and are an important factor in any proposed exploration or development of antimony resources.
Antimony is truly a strategic metal. Its availability is extraordinarily dependent upon China and while efforts are underway to increase production in other countries, this will take some years to bear fruit. Worldwide reserves are small and many years will elapse before exploration and development leads to any significant increase.
Against this antimony deposits are typically small and can be metallurgically complex. However the main risk, at least in the developed world, is environmental opposition to the development of antimony mining and processing. In fact in Australia there is even opposition to exploration drilling for antimony.
A great, useful and strategic metal with a bad rep.