Recovery of Gold and Silver

The high concentration of copper might interfere with the selective recovery of gold and silver. The use of ion exchange resins or activated carbon has been advocated to remove the copper ion (Cu+). Either cementation or electrolysis is adopted to recover the gold from the purified solution. The major reactions of the cementation process are the cathodic deposition of gold and anodic corrosion of zinc, which occur at the surface of zinc particles.

In practice, if the cyanide concentration is reduced too much, a passivating layer of zinc hydroxide may form on the surface of the zinc particles. It is reported that cementation of gold is practically constant over the pH range 8–11. However, impurities such as lead,copper, nickel, arsenic, antimony, and sulfur are most deleterious for gold cementation. The poisoning effect of the sulfide ion is thought to be due to the precipitation of insoluble zinc sulfide on the surface of zinc particles.

The electrolysis method has been used in concentrated solutions in electrochemical reactors with planar electrodes. However, with dilute solutions, efficiency is low. Works reported in the literature have shown that high surface area increases efficiency when used in dilute solutions.

Cyanide Leaching in the Mining Industries

Cyanide leaching has been used by the mining industries for more than 100 years to extract noble metals. Minerals from which most of the noble metals are obtained are increasingly poorer, so the leaching solution from these processes contain substantial quantities of silver and copper along with gold. In most cases the copper ion concentration is over 100 times higher than the other two metals.The dissolution of gold in cyanide solution is essentially an electrochemical process. The overall reaction is accompanied by the cathodic reduction of oxygen at the surface of the gold particle.

The remarkable success of cyanide as lixiviant for gold is due to the enormous stability of the dicyanoaurate ion. This allows gold to be leached efficiently at a very low concentration of cyanide (<0.01 mole dm-3), and the dicyanoaurate complex remains in alkaline solution even when the free cyanide concentration falls to zero. This contributes to the selectivity of the process.

Another advantage of cyanide is that the reaction takes place in an alkaline environment. The dissolution of gold requires cyanide to be present as the free cyanide ion (CN–). Therefore, the composition of cyanide solution is determined by the hydrolysis reaction.

Hence, it is very obvious that the high alkalinity suppresses the forward reaction, leading to higher cyanide ion concentration in the system. A high pH is also necessary for safety and economic reasons, as HCN is a volatile and poisonous gas that is purged from the leach slurry during vigorous air agitation. An electrochemical study by Dorin and Woods4 has shown a maximum dissolution of gold, silver,palladium, and platinum in cyanide solution at pH 10–10.5.Cyanide loss is very low at pH 11.5, as it mostly eliminates the loss of cyanide through HCN formation. It is 0.1 kg/t NaCN in the 10–10.5 pH range as compared to 2–3 kg at 9.5 pH.4,5 An important advantage of leaching under alkaline conditions is that the dissolution of base metals is substantially reduced, resulting in clearer effluents than those generally produced in an acidic leaching system.The noncorrosive nature of alkaline cyanide solution also means that cheaper materials can be used for the construction of a gold recovery plant.

Gold is Used for Electroplating of Connectors

In electronic components, gold is used for electroplating of connectors and contacts because it has excellent corrosion resistance and high electricalconductivity. In addition, gold is used in hybrid links and solders.

As the number of electronic products in use increases, so does the need to dispose of defective and obsolete equipment including printed circuit boards. Thus, the gold content from electronic components has become a candidate for recovery.

The Metals are Found in Many Electronic Components

In general, electronic scrap is composed of plastics (~30%), refractory oxides (~30%), and metals (~40%).

The metals are found in many electronic components such as edge connectors, integrated circuits, and transistors with the following compositions: Au 0.1%, Ag 0.2%, Pd 0.005%, Cu 20%, Ni 2%, Sn 4%, and Pb 2%. The physical forms of these precious metals maybe plated gold or palladium on copper laminate and plated gold or silver on nickel or iron. Thus, the main economic driving force for the recycling of electronic scrap is the recovery of precious metals, particularly gold.

However, environmental considerations are also important in electronic scrap recycling. The disposal of obsolete electronic equipment is a problem of considerable magnitude. Additionally, the waste solution and other scrap from manufacturing plants should be rendered harmless before they are discharged into the environment.

Pricing Refining Services

First off, do you really know how to refine? Can you produce gold of acceptable quality? If not, accepting his material can prove to be a fatal mistake. One of my best advertisers was a friend that was slip shod in his refining techniques, and refused to change. As he supplied low quality gold to his customers, who he had pursed with vigor, they slowly quit using his services, at which time he'd give them my name. I ended up with his entire customer base because he was inept. Please keep that in mind. You must be able to walk before you can run. OK--my sermon is over----I hope it served a purpose. I charged 10% for refining bench sweeps and solids unless the yield exceeded 10 troy ounces,at which time I made an adjustment, and did the work for 8%. It is a fair fee, but there were no other hidden charges, and I DID NOT steal customer values. That's the other big mistake refiners like to make. My fee was in the way of withholding the metal. I did not accept cash payment. That insures you get paid. I refined polishing wastes and floor sweeps for a 15% fee. You earn the money on this stuff, it's labor intensive. Carpet fee was 50%----and it can be a losing proposition at that price. All depends on the carpet.

Data Security

When equipment is collected, the owner may want the data which is written on the hard drives to be disposed of. This operation can be carried out either on the collection site or on the recycling site. Even if the owner does not specifically request the data disposal, in numerous countries, the recycling centre is legally obliged to do it, in compliance with regulations on private and intellectual property. The company may communicate about the reliability of its data disposal methods, to reassure the equipment suppliers.

To remove data from a computer, the recycling centre carries out several hard drive formattings, either at the hard drive test bench, or directly on the computer. There are various software programmes on the market enabling the retrieval of data erased from the computer by the user or during the formatting. Therefore, the recycling centre must be equipped with efficient data disposal and formatting tools, and must repeat the operation several times on each hard drive to make sure that no trace of former information remains on the hard drive. There are several data disposal software products available on the market, among which the free software Root Boot, under Linux.

If hard drives are pierced to secure the data disposal, this operation should be carried out under an aspirator, as the smoke resulting from it may contain harmful substances.

Traceability

Once a piece of equipment has been tested, its track sheet must be updated,indicating its condition, the possible repairs and the name of the technician who carried them out, and lastly its next destination (i.e. the refurbishment workshop, the dismantling workshop or the sales area). If the equipment is broken up into spare parts, it is recommended to create a track sheet for these parts.

Monitor Testing

Contrary to the other components testings, monitor testing is based only on the tester’s own assessment. His job is to evaluate the quality, the brightness and the contrast of the monitors. He must also detect potential problems, such as image distortion. Therefore, the technician in charge of these tests must have a lot of experience. He may use a working computer as a point of reference.

If the monitor is in good working order, it is stored, waiting to be resold. If the case is damaged, it is sent for repair. Finally, if the monitor is out of order, it is sent for dismantling. The technician may sever the cables of faulty monitors, so that they cannot be mixed up with monitors in working order or those waiting to be tested.

RAM Testing

It is usually recommended to test the RAM modules on their original motherboard, due to important risks of incompatibility between the different models. The module testing process is similar to that implemented for hard drives. It requires the use of a functioning computer, equipped with a motherboard compatible with the modules to be tested. The technician must install these modules in the computer, switch it on and run tests thanks to the appropriate software. If the RAM modules are faulty, they are sent for dismantling. If they are fit for reuse, they are stored once their characteristics have been carefully registered.

Hard Drive Testing

It is recommended to set up a workstation devoted to hard drive testing,equipped with a computer in perfect working order. To assess the condition of hard drives (up to four at the same time), the technician must connect them to the available IDE connectors. Once connected, the technician uses specific software to test hard drives and repair them if need be. Once a hard drive has been tested, it is either sent for dismantling (if it is faulty), or stored to be used later as a spare part.

Computer Testing

Before opening the computer and individually testing its parts, the technician must try to switch the computer on. If it starts, the technician will be able to run tests directly on the machine to assess the condition and capacity of the various components. To test components such as the motherboard or the RAM, the technician will often have to use programmes specific to the brand of these components. For this reason, the entrepreneur is advised

to provide his company with a programme library, where technicians can quickly find the appropriate software.

If the equipment does not work, it is important to determine if it would be worthwhile repairing it or using it for spare parts. If it is the type of equipment often asked for by clients, its subsets should be tested either to identify the failure or to extract spare parts.

The Largest Jewelry Market in the World

The largest jewelry market in the world is India, where consumption has fluctuated roughly between 500 and 600 tonnes a year over the past decade, depending on the price. It is said that Indians hold about 15,000 tonnes of gold, mainly in the form of jewelry. A sizable portion of the demand in India comes from rural parts, where jewelry is foremost a saving instrument.

China has recently moved into second place globally in terms of gold jewelry consumption,after recent growth lifted demand in 2007 to just over 300 tonnes. In contrast, the recent economic and financial crises in the United States, on top of structural change, have meant poor demand for luxury products like jewelry, pushing the United States to third place as demand fell to only about 260 tonnes in 2007. The remaining two in the top five consumers are Turkey and Saudi Arabia. In Turkey, the earthquake of 1999 and the banking crisis of 2001 had adversely impacted domestic demand till 2002. Recovery of the Turkish lira, along with far greater economic and financial stability, has since aided the revival of demand.

If we review global ranking in terms of where the jewelry is produced, the top two stay unchanged,but Turkey moves up to third place while Italy claims fourth. The latter used to be number two, but structural change and market share loss (mostly to Turkey and south-east Asian countries) for its exports in the United States have seriously undermined its output. Fifth place again goes to Saudi Arabia.

Jewelry consumption is critical to the overall gold market as it is the single largest physical user of the yellow metal, typically accounting for about two-thirds of the total demand for gold. Despite this fact, jewelry often plays second fiddle to investment (and on occasion other elements of supply and demand) as the most important determinant of the gold price due to its price sensitivity. Jewelry is best seen as a price taker rather than a price maker, tending to expand or contract depending on the price of gold and therefore acting as a “cushion” for the other supply and demand variables.

Fine Jewelry and Costume Jewelry

In recent years, the lines have blurred between what is considered fine jewelry and costume jewelry. In the past, something like a gold pendant, for example, would be featured only with a gold chain. In today’s more informal times, however, the piece could be found on a leather or silk cord.

This process has been extended further by recently high prices such that a predominantly steel or brass item might carry a small gold accent, weighing a fraction of a gram.A common theme to Western markets is the shift from plain gold to pieces with stones and the move to branded or high-fashion designs. All these carry much higher markups over the value of contained gold, and this is important as the trend for sales in terms of total value, number of pieces,or weight of pure gold can go in opposite directions. 

These trends are also spreading to developing world markets, in particular China where 18-karat gold is gaining market share.These trends are also important as, in industrialized markets, consumers within the overall jewelry segment devote ever more expenditure proportionately to other materials, such as diamonds, or to the perceived value of design and branding, all of which cuts the amount of money being spent on gold. In addition, all jewelry has been losing market share to other discretionary areas, such as foreign vacations or technology goods (such as cell phones), both of which typically enjoy far greater advertising budgets. This has culminated in the weight of gold sold in jewelry form declining steadily in the industrialized world over the past decade or so.

Gold in Jewelry

The use of gold in jewelry can take many forms but, for the purpose of statistics, it is typically measured only when in “karat” form. This specifically excludes an article of costume jewelry made from, say, brass to which a gold plating has been applied. A karat is a measure of purity of gold,defined as parts per 24. Some jewelry, such as that in China, exists in 24-karat form (essentially pure gold), but the highest caratage typically sold is 22-karat (the norm in India) as other metals such as copper and silver are added to bring sufficient strength to the alloy. Just beneath that sits 21-karat, the norm for many Middle East markets. Purchase of these high-karat grades is often motivated by investment considerations. For this to work, the pieces can carry only a small amount of labor or markup over the value of the contained metal.

The main driver for the purchase of the remaining types of gold jewelry is adornment or fashion.Within this, the next major grade is 18-karat jewelry, the norm in areas such as southern Europe.This is the standard typically used in high-quality pieces, especially those carrying precious stones such as diamonds, because at this concentration of gold, the alloy is sufficiently hard to hold stones and color on an effectively permanent basis. This is also the grade at which “white gold” appears gold to which a silver-colored metal such as palladium or nickel has been added in sufficient quantity to mask the yellow of the pure gold and render the piece “white” (industry jargon for silver colored). Beneath that is 14-karat gold, the last grade commercially available in which the majority of the alloy is gold; 8, 9, and 10 karat follow. These qualities are the various norms in northern Europe and North America, and in some markets, the United Kingdom, for example, there is legislation to enforce these standards.

Jewelry Dominating Old Scrap

With jewelry dominating old scrap, it should come as little surprise that volumes should be greatest in those countries making or buying jewelry. Volumes also tend to be greater in the developing world as pieces there typically have lower markups over the price of the contained gold and as a result of the unsentimental investment motive behind initial purchase. Such pieces are also more likely to be plain, in other words not carry precious or semiprecious stones and be of higher caratage. In industrialized markets, jewelry is more likely to carry stones and be of medium/lower caratage, be branded, and be bought as a gift for adornment—which will lower the propensity for remelt—and the consequent high markups over the contained gold mean a profit can rarely be made. Nonetheless, scrap can still prove significant through the liquidation of poorly selling merchandise or through the previously noted selling of stylistically dated pieces.

Generally, scrap is reused in the markets in which it is generated. However, during times of peak supply (such as after Egypt’s currency crisis), amounts surplus to local industry requirements would invariably be exported, often to the major Swiss refineries, where the metal reenters the supply

chain.

Process Scrap and Old Scrap

The recycling of gold takes two forms—so-called process scrap and old scrap. The former concerns gold that never ends up in a finished product and returns unused to a refinery for remelt. This includes areas such as the edgings to a sheet of metal once coins have been stamped out or the filings recovered from the polishing or engraving of jewelry. Because this effectively forms part of a continuous loop, it is of no interest to an economist and is excluded from analysis. Old scrap, in contrast, is the metal recovered from finished items containing gold. The vast bulk comes from jewelry, although small amounts are also received from other areas such as electronic goods or dental alloys.

Old scrap is typically the second largest source of supply after mine production, accounting for approximately a quarter of total supply each year. The amount, however, can prove quite volatile, surging, for example, to a then record of about 1,100 tonnes in 1998 on the back of the East Asian economic crisis before slumping to about 600 tonnes the following year.

Selling by individuals during a time of financial crisis is but one reason for dishoarding. However,perhaps the greatest determinant is changes in the price of gold. One example of this would be the increases in scrap seen emerging from the Middle East at times of high gold prices. Other factors nonetheless mean old scrap does not always track changes in the price. A recession, for example, could trigger an increase in scrap as manufacturers, wholesalers, and retailers remelt unsold jewelry inventory. Changing fashion can even influence scrap, as we are seeing increases in scrap in western Europe as inherited jewelry pieces—considered too dated to be worn by their new owners—are remelted.

Gold Once Presided as the Dominant Asset in the Reserves of Central Banks

For governments, gold once presided as the dominant asset in the reserves of central banks (commonly referred to as the official sector) and against which all paper currencies were backed. However, with the suspension of the gold standard in 1932 and later dismantling of the Bretton Woods System in the early 1970s, gold’s link to the dollar and the majority of world currencies was severed and the metal’s price was allowed to float freely and be determined by the market. The metal still plays valuable roles for central banks, however, such as reserve diversification, instilling public confidence in the central bank, and economic security. It can also generate income through the lending of its bullion.

As of the end of 2007, total official sector gold holdings stood at just under 30,000 tonnes. The largest holdings are in the Western world, with the United States, Germany, France, Italy, and Switzerland making up the top five and mostly for whom gold is far larger in value than other currency reserves. Japan, China, and Taiwan come in respectively at numbers six, eight, and ten, but the value of their gold holdings is tiny compared to their other reserves.

The official sector has been a net supplier of gold to the market for nearly two decades, providing as much as 18% of total annual supply. The bulk of recent sales has come from European banks. These disposals have been conducted under the Central Bank Gold Agreement, which became effective in September 1999 and was renewed in 2004. A key reason behind these five-year agreements was to add an element of certainty to the market. Purchases by central banks have occurred in recent years, such as those by Russia and China but to date their scale remains limited.

ABOVEGROUND STOCKS

In addition to newly mined metal, gold can also be sourced from aboveground stocks, either through the recycling of fabricated products (see section that follows on scrap) or the mobilization of bullion stocks. The latter comprises central bank sales (see following); disinvestment by individuals (covered in the section on investment); and advance sales—the hedging described previously—by mining companies. During the past decade, supply from aboveground stocks has typically accounted for about a third of annual supply.

GFMS estimates put aboveground stocks of gold at the end of 2007 at 161,000 tonnes (the equivalent of over 60 years of current mine production) [1]. It is the sheer scale of these aboveground stocks that sets the yellow metal apart from other commodities. The reason for this buildup is primarily the virtual indestructibility of the metal—almost all of the gold mined throughout history still exists in some form. The metal’s durability also allowed gold to become a highly suitable store of value and form of money over the ages, for individuals and state bodies.

The composition of aboveground stocks is also important because it determines the speed and likelihood of the return of the metal to the marketplace. Gold as bullion (usually in bar form) typically comes back the most readily, and stocks in this form stood at about 55,500 tonnes. Just over half of this bullion is held by central banks and other official sector bodies, with the balance being held by private individuals and institutions. More, however, just over half of the total, is held as jewelry items. Lastly, about 19,000 tonnes have been absorbed by other types of fabrication (such as electronics), the least likely area to get recycled back into the market. Just under 4,000 tonnes cannot be accounted for and can be considered irretrievably lost or as true consumption. This would include manufactured items containing gold that have gone to landfill, any metal lost at sea, and so forth.

Producer Hedging

A hedge is a transaction that acts to manage the risk of adverse price movements in an asset such as gold. Gold producers typically enter into hedging contracts for one of three reasons. The first is in order to secure a forward premium in price. The second reason is to seek to protect revenues against falling gold prices, while the third is as part of the terms of a financing package. The simplest method of hedging is the forward sale, whereby a producer enters into a contract in which it can receive a fixed payment for a certain amount of gold at a predetermined date in the future. Regardless of any price movement between entering into the contract and its expiration, the producer will realize this guaranteed price on delivery.

There are three main parties involved in a basic gold hedge contract: the producer; the bullion bank, which acts as the producer’s dealer; and a central bank. To place a hedge, the producer advises its dealer that it wishes to forward sell, for example, 1 tonne of metal. The dealer then immediately borrows this amount from a central bank (paying a leasing fee), which it immediately sells into the spot market, agreeing to return the 1 tonne by a certain date. The proceeds from this sale are then placed in a high-yielding cash account (subtracting the dealer’s fee and the leasing fee on the borrowed gold), usually generating a premium for the producer. The producer is obliged to return 1 tonne of gold to the bullion bank by the preagreed date. At the time of implementation, the action of the bullion bank of borrowing gold and selling it into the spot market increases the supply of gold to the market. However, when the gold is returned, usually by delivering mine production from the producer’s account, supply reaching the market is correspondingly constrained. Hedging activity therefore represents an acceleration of supply to the market, but the overall balance of supply and demand is maintained over the lifetime of the transaction.

Hedging and de-hedging activities are thus important in the wider gold market. To give a historical perspective, the 1990s were largely characterized by unrelenting downward pressure on the gold price, which led to steadily increasing levels of hedging undertaken by producers who were seeking revenue protection from further declines. In 1995, hedging had a particularly noticeable impact, reaching 475 tonnes and thus accounting for about 13% of total supply. By September 1999,however, the gold price had made an abrupt change of direction and started to climb. Many hedged producers were caught off-guard and were unable to take advantage of soaring spot prices. On the back of this crisis, the year 2000 was the first year since the late 1970s when the global producer hedge book did not expand. There has since been a protracted period of de-hedging, in which producers have both delivered into and also prematurely closed out their hedge contracts. This is accomplished either by bullion purchases from the market, delivered to the bullion bank,or through delivering their own production into contracts before they mature. De-hedging posted a record level of 447 tonnes in 2007, representing just over 11% of total gold demand. Expectations for higher gold prices and investors’ associated anti-hedging sentiment were the chief reasons for this.

It can be seen that, pre-1999, producer hedging activity was a significant supply component in the gold market, whereas post-1999, hedging activity became a significant demand component of the market. Today, many more exotic and complex financial derivatives and option structures exist, in addition to the humble forward sale, through which producers can hedge. The effect of these more complicated contracts is, however, ultimately the same: hedging activity by gold producers affects the timing of mine supply reaching the market.

China is the World’s Leading GOLD Producer

China has now become the world’s leading GOLD producer, overtaking South Africa in 2007. Market liberalization has had a dramatic impact on China’s gold mining sector, and one of the most important changes has been the end to official purchases in 2003, with producers no longer forced to sell all of their production to the People’s Bank of China at regulated prices. 

A further impact of deregulation has been increased participation from foreign investors. Chinese mine production has also shown a remarkable ability to quickly respond to rising gold prices and has risen accordingly with the price. From delivering around 72 tonnes in 1987, it increased production almost fourfold by 2007, when it produced 281 tonnes. Asian production has also been boosted by the contribution from Grasberg in Indonesia, the other of the two largest mines in the world.

“Big Four” of Gold Producing Countries

“Big Four” of gold producing countries—South Africa, the United States,Australia, and Canada. For over a century, South Africa was the world’s largest gold producer. Its peak output reached 1,000 tonnes in 1970, which accounted for about two-thirds of total global production in that year. In 2007, however, it produced 270 tonnes, representing 11% of the world total of 2,476 tonnes. One of the main reasons for the country’s declining production is due to the maturity of many core South African operations; after over a century of intensive mining, shallow deposits have been exploited and mines have become progressively deeper and in many cases seen a fall in ore grades.

Deep level mining is labor and technology intensive and, therefore, costly, requiring increasingly rigorous safety measures. Furthermore, the South African industry has experienced a pressing shortage of skilled employees with labor competition from the wider extractives and construction industries.

After reaching peak production in the late 1990s, production from the United States, Australia,and Canada has also been declining. Although output rose during the early part of the decade, low gold prices during this period meant that few new operations were brought into production, as producers were left unable and unwilling to spend capital on exploration, thereby inhibiting output in the latter part of the decade. Many mines were closed as they became uneconomical to maintain. Moreover, many operations were mature by the late 1990s, so the most attractive deposits had already been extracted.

The Science and Technology of Gold

The science and technology of gold is currently going through an exciting period of its history and is leading to new industrial and medical applications of this unique metal. It is unique, not only because of its properties (it is one of only two colored metals, for example, as well as being the most noble and most malleable), but because of its history and its role in society, where it serves as a monetary asset, for adornment, as well as an industrial and decorative metal.

Gold has a unique color and has been prized throughout history for its beauty and value, but it also has an interesting science that we are just beginning to unravel and exploit. Traditional applications have centered mainly on its metallic properties, and its chemistry has been rather overlooked,but that omission is being redressed. The surprising discovery of gold’s catalytic properties in recent years and the development of its nanotechnology are leading to some exciting applications with enormous potential in industry and medicine.

The interest in the science, technology, and applications of gold has grown considerably over recent years, as evidenced by the huge increase in scientific publications in learned journals, the growth in attendance at the series of international gold conferences held since Hanau (it returned to Germany in 2009), and the expansion of readership of the sole journal dedicated to gold, Gold Bulletin. It is interesting to note that over $13 billion worth of gold was used in industrial (and medical) applications in 2007, and consumption in this sector is predicted to grow significantly, much of it in new and green applications. Gold has a significant role to play in our quality of life during the twenty-first century.

The Supply of Gold

The supply of gold comes essentially from two distinct sources, namely new mine production and previously mined metal now sitting aboveground as stocks in various forms. New mine production provides the greatest amount of gold to the market each year, typically accounting for around two-thirds of total supply. In recent decades, annual production has exploded, up from less than 1,000 tonnes in 1980 to a peak of 2,645 tonnes in 2001, although more recently, output has fallen somewhat.

The bulk of supply from aboveground stocks comes from the recycling of the metal contained in manufactured (or fabricated) products, the vast majority of which comes from jewelry. It is therefore not surprising that the supply from recycling, typically referred to as old scrap, has generally kept to a rising trend, reflecting the addition each year to the pool of available metal from that year’s jewelry production.

Other areas of supply from aboveground stocks include sales by central banks, hedging by mining companies (a form of advanced selling), and disinvestment from private holdings (which is reviewed in an upcoming section under demand as investment). Net sales by central banks have been a constant feature of the gold market since 1989, and over the past decade, these provided an average of about 500 tonnes of gold to the market each year. Central banks do purchase gold, but buying globally on a net basis has not been seen since 1988. Hedging by mining companies is, in essence, equivalent to gold producers selling their future production at current prices. Such transactions normally involve gold being borrowed and sold in today’s market with producers later delivering their production against these commitments. Hedging was a major source of supply in the late 1980s and the 1990s, but more recently, positive sentiment toward prices has resulted in producers

cutting their hedge book commitments. This in essence adds to demand and this position of “dehedging” on a net basis has been in practice since 2000.

The Metal Thallium

Thallium is a rare metal, found in small quantities in some varieties of iron and copper pyrites, and in some lithia micas. It resembles lead in appearance. Its compounds resemble the salts of the alkalies in some respects; and, in others, those of the heavy metals.

It is detected by the green colour which its salts impart to the flame. This, when examined with the spectroscope, shows only one bright green line. It is separated and estimated by dissolving in aqua regia; converting into sulphate by evaporation with sulphuric acid; separating the second group of metals with sulphuretted hydrogen in the acid solution, boiling off the excess of the gas; nearly neutralising with carbonate of soda; and precipitating the thallium with an excess of potassic iodide. On allowing the liquid to stand for some time a bright yellow precipitate of thallous iodide separates out. This is collected on a weighed filter; washed with cold water, finishing off with alcohol; dried at 100° C., and weighed. The precipitate is thallous iodide TlI, and contains 61.6 per cent. of thallium.