This year marks the 200th anniversary since tantalum was first discovered by Anders Gusta f Ekeberg, a professor at Uppsala University in Sweden. Owing to the extreme difficulty he had decomposing the mineral in acids he named it tantalum - after Tantalus, who was condemned by Zeus to stand up to his neck in water. Each time Tantalus stooped to drink, the water receded, while above him hung succulent fruits that the wind would blow just out of reach, this eternal frustration being punishment for killing his son and serving him to the gods as a stew.
The metal oxide discovered by Ekeberg was obtained from minerals taken from pegmatite (an igneous rock of course grain size) at Ytterby, Sweden, and Kimoto, Finland. Over the following decades several scientists discovered other facets of the new oxide, but it was not until 1844 that Heinrich Rose, who had studied under Berzelius, who in turn had studied under Ekeberg, was able to determine that the oxide contained two elements, tantalum and a second element that he named niobium, Niobe being the daughter of Tantalus.
Tantalum itself is a heavy (specific gravity of 16.6) blue-grey metallic element with a melting point of 2,996°C. It has excellent corrosion resistance, good ductility and is resistant to most acids. It displays a number of desirable physical properties - in electronics, it forms the basis of high-performance capacitors used in electrical goods, and when alloyed with iron, imparts excellent corrosion resistance. Consequently it is used in corrosive environments such as oil and gas pipelines. In aluminium alloys, it prevents oxidation, enabling lighter components to be used safely and, because of its high melting point, it is also used in cementing tungsten carbide in machine tools and in the alloys found in jet-engine turbine blades.
Applications of Tantalum
Capacitors and Other Electronics
Recently tantalum has generated much interest because of its use in capacitors in electronic equipment. Capacitors perform a vital function, storing electricity for a short period of time and ensuring that the current supplied stays within narrowly defined parameters - particularly useful in low-voltage applications such as mobile phones and PDAs, in which these tolerances can be very tight. The advantage of tantalum in capacitors is its high volumetric efficiency, which enables miniaturisation, high reliability and stability over a wide temperature range (-55°C to 125°C), attributes not matched by other types of capacitor material, such as ceramics. Such is the use of tantalum in capacitors that in 2001 1.6 million pounds (mlb) of a total of 3.4 mlb or approximately 50% of the global consumption of tantalum, went to capacitor production.
In addition to electronics, consumption has increased in metal alloying, chemicals, carbides and machined metal uses. Metal alloys containing tantalum (at levels between 2%-12%) are used in aircraft engines and in the static turbines used in power generation between 1993 and 2001 consumption in this sector increased four-fold to more than 301,000 lbs. Overall tantalum consumption has risen from around 2.2 mlb to more than 4.7 mlb during the period 1993-2000, equivalent to an increase of 13°/ per annum, outstripping most other mined products, although in the period 2000-2001, the total fell as the cycle in customer goods declined.
Sources of Tantalum
Tantalum occurs in a number of oxide minerals associated with granite and other alkali igneous rocks. There is no shortage of tantalum in the world’s geological inventory and although relatively rare, known reserves can more than meet foreseeable demand. However, many of the easiest to work resources, such as residues and high-grade deposits, have been depleted.
Tantalum from Tin-Smelting
In the 1980s most tantalum originated as a by-product of tin smelting. Thailand and Malaysia accounted for nearly 40% of the world’s production of 236,000 tonnes. The tin alluvials of Malaysia and Thailand were rich in tantalum and slags resulting from tin smelting contained between 10-15% tantalum. But by 1994, only 20% was derived from this source, and it has decreased further as other sources have been developed.
Tantalum Sources in Australia
Pegmatites continue to be the largest source of tantalum. They generally occur as numerous ‘stringers’ of quartz and other minerals containing incompatible elements such as tin, tantalum and rare earth elements. The Greenbushes pegmatite near Perth in Western Australia is one of the world’s largest resources, and is mined by the Australian company, Sons of Gwalia. It is the world’s largest producer of tantalum, a position maintained by exploration and expanded production at Greenbushes and development of the Wodgina mine near Port Headland. In 2002 estimated production should reach 2 mlbs. These mines are open pit hard rock mining operations using modern mechanised equipment, and they account for more than one third of world mined production. Reserve grades are quoted as 230 and 414 ppm respectively.
Tantalum Sources in Africa
Another important, albeit variable, source of tantalum is Africa, where artisanal miners recover tantalum minerals from mainly alluvial resources. These contain elevated concentrations and can easily be upgraded into saleable concentrates by simple techniques such as panning. This informal sector causes uncertainty in both reserve and production calculations as these resources are often brought into production when prices rise. This recently occurred when ‘coltan shops’ were established in East Africa, when traders bought concentrates from Rwanda, Burundi and the Congo. Concern and action by the United Nations and Dianne Fosse Foundation reduced the trade in these concentrates as the proceeds were being used to fund the on-going civil war in the region.
It has been known for some time that certain alkali granites and related rocks contained tantalum and niobium in large quantities, albeit at low concentrations. Modern mechanised open pit mining can make recovery of metals at very low concentrations economic. Gwalia is now mining profitably tantalum ore grades of 200-400 ppm. Furthermore, these tantalum-containing granites often contain reserves that are factorially greater than those occurring in pegmatites.
Granite is a generic term for intrusive acid igneous rocks rich in quartz and feldspar. There are many varieties and they are ubiquitous throughout the geological record, occurring in large masses making up a significant proportion of the continental crust. Although most of them are not mineralised, a rare granite termed apogranite contains tantalum and other incompatible elements such as tin and niobium. Because of the large scale of these intrusions, reserves based on apogranites are also large, despite grades averaging around 200 ppm of tantalum.
A particularly large apogranite resource exploited for tin is the giant Pitinga deposit in Amazonia, operated by the Brazilian company Paranapanema. Recently its weathered ore reserves have been depleted and a new hard rock mine, Sa Rocha, is being developed. As well as tin, Paranapanema is producing tantalum and niobium (apogranites contain both elements in a ratio of approximately 1:10) and the company is reported to have signed a 80,000 lbs per year contract with a US processor.
Saudi Arabia as Source of Tantalum
Another apogranite resource being considered for production is in the northwest of Saudi Arabia. This is the Ghurayyah deposit, initially investigated in the 1970s as a source of uranium. Today a British company Tertiary Minerals plc, is undertaking a feasibility study to recover tantalum from the granite.
Changes to Local Laws
The Saudi government has recently proclaimed the mineral sector as a development priority and has set ambitious growth targets. Apart from the drafting of a new Mining Code, a number of other legislative changes have been made during the past two years with the objective of increasing foreign investor interest in Saudi Arabia’s mining sector. In April 2000, a new Foreign Investment Law was issued, under which foreign investors can own 100% of a business with no local partner required.
Size of the Deposit
The Ghurayyah deposit is reportedly the world’s largest single accumulation of tantalum metal. With an estimated inferred mineral resource of more than 385 million tonnes to a depth of 250 metres, the deposit, which is graded as 245 g/t Ta2O5 and 2,840 g/t Nb2O5, contains more than 208 mlbs of tantalum pentoxide. Tertiary has been awarded a five-year exclusive exploration licence for the deposit, which is renewable for up to nine years and gives Tertiary the right to acquire a 50-year mining lease on the 47 km2 license area.
Ghurayyah is estimated to contain more tantalum than the combined published reserves at the Greenbushes and Wodgina mines in Western Australia, the two largest tantalum mines in the world, which currently account for around 30% of world tantalum minerals output. The grade of mineralisation at Ghurayyah is similar to the weighted average grade of the published reserves and resources of the two mines.
Development of the Saudi Arabian Resource
Tertiary has been conducting metallurgical test work on the deposit. Previous work done in 1978 defined at least one possible flowsheet, which achieved overall recoveries of 77% of tantalum and 80% of niobium into separate purified and marketable products. These tests also indicated that higher recoveries should be possible with process refinement and flowsheet optimisation.
Since this work was undertaken, significant advances have been made in the recovery of fine-grained tantalum and niobium minerals. Tertiary is using these advances and has retained Lakefield Research Inc to carry out work on bulk samples from Ghurayyah.
Preliminary concentration tests using the industry-standard flotation technique and magnetic separation of zircon have achieved a fifty-fold upgrading of the tantalum and niobium contained in the rock and a preliminary concentrate grading of approximately 13% niobium and tantalum. The test results also suggest that commercially acceptable recoveries of tantalum and niobium might be achieved using flotation.
Optimisation is in progress and will be followed by further upgrading test work. Once the test work programme is complete Tertiary plans a preliminary economic scoping study.
The company regards development of Ghurayyah as a medium-term objective that will complement its much smaller Rosendal project in Finland (1.3 million tonnes, at a grading of 289 g/t tantalum pentoxide), which could be brought into production within two years. Recent test work on Rosendal ore has shown that a marketable tantalum product could be recovered by simple gravity processing.
Financing the Project
New projects in Saudi Arabia can benefit from the availability of project financing through various offset programmes. For example, Tertiary’s Ghurayyah project is currently receiving both logistical and financial support from the British Offset programme, a joint initiative between the UK Government and BAE, and in future this could be a significant factor in project funding. Tertiary estimates that it may need to equity fund as little as 12.5% of the project’s capital costs.
In the 200 years since its first discovery, tantalum has been a laboratory curiosity, a filament for some of the earliest light bulbs, and now the enabler of the mobile communications revolution. Its increasing use looks set to continue.