Tungsten W · 74

The metal with the highest melting point of them all — you can heat it to 3,400 C before it turns liquid.

なぜ重要なのか

Tungsten carbide is what cuts, drills and mills every other metal. Industrial capacity depends on it in a way that is easy to overlook.

Where it is in the Earth

Tungsten does not spread itself evenly through the crust. It concentrates into economic deposits through a specific set of geological circumstances, most of which involve heat and chemistry working together over long timescales. The most important setting is the contact zone between a cooling granite intrusion and the surrounding limestone or carbonate rock. As the intrusion cools, hot fluids carrying dissolved tungsten, calcium and other elements migrate outward and react with the carbonate. The result is a skarn — a zone of chemically altered rock — in which the mineral scheelite (calcium tungstate) crystallises in quantities large enough to mine. Skarns account for much of the world's tungsten output.

The other principal deposit type forms when tungsten-bearing hydrothermal fluids — essentially hot, mineralised water circulating through fractures in the rock — cool and deposit the mineral wolframite along veins. Wolframite is an iron-manganese tungstate and tends to form in and around granite bodies, often alongside tin, molybdenum and bismuth. These vein deposits can be narrow but rich, and they are the classic form of tungsten mineralisation associated with the granites of southern China, the Iberian Peninsula and parts of Southeast Asia. The geographical pattern of tungsten deposits around the world therefore follows the distribution of old granitic terranes and the limestone sequences that surround them, which is why China, with its enormous extent of such geology, holds reserves far larger than any other country.

A useful distinction to carry through the rest of this page: scheelite tends to show up in skarns associated with calc-silicate metamorphic belts, while wolframite is more typical of high-temperature hydrothermal veins. Both are tungstates — salts of tungstic acid — but they respond differently to processing, which matters when the ore leaves the mine.

Getting it out

Because tungsten ore bodies are often steep, irregular and relatively small in lateral extent, underground mining is the dominant extraction method. Miners follow the vein or skarn body downward, using methods such as stoping — excavating the ore in a controlled sequence of rooms or slices — while leaving enough intact rock to support the surrounding ground. The ore itself makes up only a small fraction of the total rock that must be handled; the rest, called waste or gangue, is moved and stored. This ratio of waste to ore, called the strip ratio in open-pit operations or expressed as dilution underground, is a central economic variable at any tungsten mine.

Ore grade matters enormously because tungsten concentrations are reported in units of WO₃ — tungsten trioxide equivalent by weight — per tonne of rock. Economic grades are typically low by the standards of base metals; the ore contains a small proportion of tungsten mineral surrounded by a large volume of unremarkable rock. Moving and processing that surrounding rock has a cost, and when ore grades fall below a threshold that varies with the price of tungsten concentrate, mines close. This sensitivity explains why capacity outside China has been prone to care-and-maintenance closures during periods of low prices. Some scheelite is also recovered as a by-product of mining for other metals, particularly tin and copper, which changes the economics considerably: the tungsten recovery cost is shared with the primary product.

Open-pit mining does occur where ore bodies are wide enough and shallow enough to make it practical, though this is less common than in commodities such as iron ore or copper. In either configuration, the extracted ore must be crushed and processed promptly, since there is no value in stockpiling low-grade rock indefinitely. The mining method is therefore chosen primarily by the geometry and depth of the deposit, and only secondarily by other considerations.

What pulls on it

The single largest use of tungsten worldwide is in cutting and wear-resistant tooling, where it appears as tungsten carbide — a compound of tungsten and carbon that is extraordinarily hard. Cemented carbide, sometimes called hardmetal, binds tungsten carbide grains together with a metal binder, usually cobalt, to produce inserts, drills, end mills and other cutting tools used to machine steel, aluminium and other materials. Without these tools, manufacturing as it is currently practised would not function. Almost every metal component that requires a precise shape passes through a cutting tool at some stage, and tungsten carbide is the material those tools are most commonly made from.

Beyond cutting tools, tungsten appears in a range of demanding applications where its extreme density or melting point is specifically required. In defence, its density makes it suitable for kinetic energy penetrators — projectiles that rely on mass rather than explosive force. In aerospace and other precision applications, small tungsten alloy components serve as counterweights and vibration dampers. The semiconductor industry uses tungsten in contacts and vias — the tiny conducting pathways that connect layers within a microchip — because tungsten can be deposited uniformly into very small features and withstands the high temperatures of chip fabrication.

Demand would shift materially only if the nature of manufacturing changed substantially. A broad move away from metal cutting — through additive manufacturing at sufficient scale and precision, for instance — could reduce tool consumption, but this transition has been gradual and incomplete. Growth in semiconductor content per device, combined with continuing demand from defence procurement, provides a counterweight to any softening in conventional machining. Neither the composition of end-use demand nor the rate of its growth is something the tables alone convey; what matters is that the uses are structurally embedded in industrial processes that do not change quickly.

Turning ore into product レベル 3

Run-of-mine tungsten ore arrives at the processing plant with an extremely low concentration of the valuable mineral. The first task — comminution — is to crush and then grind the ore fine enough that individual grains of scheelite or wolframite are liberated from the surrounding gangue minerals. Grinding consumes significant energy and is one of the major cost centres in the flowsheet. The fineness required depends on the grain size of the ore: coarser-grained deposits can be processed more cheaply, while fine-grained ore demands energy-intensive grinding before separation is possible.

Once the minerals are liberated, concentration separates them from the waste. Scheelite is amenable to froth flotation — a process in which air bubbles are used to carry hydrophobic mineral particles to the surface of a slurry, where they are collected as a froth. Wolframite, being denser than most gangue minerals, is more commonly treated by gravity separation using jigs, shaking tables or spirals. In practice, many plants use a combination of methods, and the sequence of the flowsheet must be tuned to the specific mineralogy of each deposit. Recoveries are never complete; tungsten lost to tailings represents an irreversible cost.

The concentrate leaving the mill — typically quoted as a percentage of WO₃ — is then processed hydrometallurgically to produce ammonium paratungstate, commonly referred to as APT. This is the internationally traded intermediate product. APT is made by digesting the concentrate in sodium hydroxide or hydrochloric acid, purifying the solution through solvent extraction or ion exchange, and then crystallising the ammonium salt. APT can subsequently be reduced in a hydrogen atmosphere to produce tungsten metal powder, or reacted with carbon at high temperature to produce tungsten carbide powder, which is the form most widely used in industry. Each conversion step introduces further yield losses, and the energy cost of the hydrogen reduction and carbide synthesis stages is substantial. Because China dominates both mining and APT production, the value added through downstream conversion also accrues predominantly there, which has implications for the rest of the supply chain discussed under risk.

Substitution and recycling レベル 3

For the dominant application — cemented carbide cutting tools — substitution is constrained by physics. No other combination of hardness, toughness and thermal stability available at industrial scale replicates tungsten carbide's performance in high-speed metal cutting. Ceramics, including silicon nitride and alumina, can replace carbide in certain finishing operations on specific workpiece materials, but they are more brittle and less tolerant of interrupted cuts or variable workpiece geometry. High-speed steel, the material that preceded carbide tooling, is still used where toughness matters more than cutting speed, but it removes metal more slowly and wears faster. In practice, substitutes occupy specific niches rather than offering a general replacement.

Recycling is a more significant factor than direct substitution. Cemented carbide scrap — from worn or broken cutting inserts and other tooling — can be reclaimed by chemical or zinc-based processes and returned to the carbide production cycle. The tungsten content of scrap is well above ore grades, making secondary material economically attractive when collection is organised. However, the share of demand met by recycled tungsten depends on collection infrastructure, scrap availability relative to primary production, and price differentials. A portion of tungsten in end-of-life products is dispersed in ways that make recovery uneconomical — fine wear particles from machining, for instance, end up distributed through swarf and coolant. This represents a permanent loss to the cycle. Greater recycling rates are possible in principle, but require organised reverse logistics from tool users back to processors, which is more easily achieved in large manufacturing facilities than in fragmented supply chains.

The substitution picture in non-tooling applications is similarly constrained. In penetrators and counterweights, the substitute most often discussed is depleted uranium, which matches tungsten's density but introduces different handling and political considerations. In semiconductor contacts, tungsten has faced some competition from other refractory metals and from cobalt in certain process nodes, but remains widely specified. None of these alternatives threatens to displace tungsten from its core markets across a short timeframe.