Boron B · 5

An element that makes glass resist thermal shock, fibreglass strong, and — with iron and neodymium — the strongest magnets known.

なぜ重要なのか

Borosilicate glass, glass fibre for wind blades, agricultural micronutrients and NdFeB magnets all start here, from very few deposits.

Where it is in the Earth

Boron does not form metal deposits in the way that copper or iron do. Instead, it concentrates through evaporation. The process begins when boron-rich hydrothermal fluids — hot water carrying dissolved minerals up through volcanic rock — discharge into enclosed, arid basins. As the water evaporates under a dry climate, the dissolved material crystallises out in layers on the basin floor, building up sequences of borate minerals over geological time. The most important of these minerals is borax, a hydrated sodium borate, though dozens of other borate species can occur depending on the chemistry of the brines and the temperature at which they crystallise. The resulting deposits are called evaporites, because evaporation is the engine that made them.

This process explains why the world's major boron deposits cluster in specific geological settings: the volcanic arcs and high-altitude closed basins of the Andes in South America, the great endorheic basins of Central Asia and the Tibetan plateau, and — most importantly — the Neogene sedimentary basins of western Turkey. Turkey's deposits, particularly those in the Kütahya-Eskişehir region, formed in lake basins associated with Miocene-age volcanism and rifting, and they accumulated to exceptional thickness and purity. The reserve figures in the table above make this concentration stark: Turkey holds reserves vastly larger than any other country, which is unusual even by the standards of mineral commodities, where production is often geographically concentrated but reserves are more widely spread.

The Atacama and other South American salars represent a related but distinct setting. Here the boron occurs dissolved in brines beneath the surface of salt flats at high altitude, rather than as solid mineral layers. The brine has accumulated over millions of years in structurally closed basins — basins with no outlet to the sea — where inflow from volcanic springs exceeds evaporation loss of water, but the salts themselves build up steadily. Whether the deposit takes the form of a solid evaporite bed or a subsurface brine depends largely on how far evaporation has proceeded since the brine formed, and on the age and thermal history of the basin.

Getting it out

Because boron deposits are mostly soft sedimentary evaporites, the dominant extraction method is open-pit mining. The ore — typically borax or a related borate mineral — sits in horizontal or gently dipping beds that are accessible from surface with standard earth-moving equipment. The overburden, meaning the rock and soil above the ore that must be removed first, is stripped away to expose the ore body. The ratio of waste moved to ore recovered varies with the geometry of the deposit and the thickness of the borate layers, but borate ore bodies tend to be thick and relatively close to surface, which generally makes them more economical to mine by open pit than many metal ores.

Grade, in this context, refers to the concentration of boron oxide (B₂O₃) in the ore expressed as a percentage by weight. This matters because a higher-grade ore requires less energy and fewer processing steps to produce a tonne of sellable product. Borate deposits can be quite high grade relative to many industrial minerals, which is part of what makes large-scale open-pit extraction economic at the prices the market has historically supported. That said, within any deposit there will be zones of varying grade, and miners selectively work higher-grade material when conditions allow.

The South American salar operations, such as those at the Salar de Atacama in Chile, use a fundamentally different method: brine pumping and solar evaporation. The boron-bearing brine is pumped from wells into a series of large, shallow ponds. The sun does most of the concentration work, evaporating water and progressively enriching the remaining liquid in dissolved salts. The boron is eventually recovered from the concentrated brine through further processing. This approach uses far less mechanical energy than conventional mining but depends on the right climate — abundant sunshine and very low rainfall — and takes considerably more surface area than an equivalent solid-ore operation.

What pulls on it

Boron reaches most of its markets in the form of borosilicate glass, glass fibre, or agricultural micronutrients, rather than as a metal or pure element. Borosilicate glass — the kind used in laboratory equipment, cookware, and pharmaceutical packaging — contains boron oxide as a network modifier that lowers the thermal expansion coefficient, meaning the glass expands and contracts far less when heated or cooled than ordinary soda-lime glass does. This property is what allows a borosilicate dish to go from a cold refrigerator to a hot oven without cracking. Glass fibre, produced by drawing molten glass into very fine filaments, uses boron to control the viscosity and crystallisation behaviour of the melt, and the resulting fibres are the reinforcement in fibreglass composites used in wind turbine blades, printed circuit boards, and construction panels.

Agriculture consumes a meaningful share of boron supply as a micronutrient. Plants require boron in small amounts for cell wall formation and reproductive development, and soils in many parts of the world are deficient in it. Boron-deficient crops show characteristic symptoms — hollow stems in brassicas, corky patches in apples — and yield losses can be substantial. The correction is applied either through foliar sprays or soil amendments using borax or boric acid. Demand from agriculture tracks closely with arable land use and crop intensification, and it tends to be fairly stable year to year.

The end markets table on this page lists nuclear power and wind power as distinct demand segments. In nuclear pressurised-water reactors, boron is dissolved in the coolant water and incorporated into control rods because boron-10, one of its naturally occurring isotopes, is exceptionally good at absorbing neutrons — the particles that sustain the fission chain reaction. In wind power, the connection is more indirect: boron is one of the three elements in neodymium-iron-boron (NdFeB) permanent magnets, which are the magnet type used in the direct-drive generators of many offshore turbines. The material-intensity figures in the table show how much boron is embedded per unit of each application. For demand to shift sharply downward in glass fibre, an alternative reinforcing material would need to achieve equivalent stiffness and fatigue resistance at comparable cost — carbon fibre can do this technically but is substantially more expensive. For the magnet application, alternative magnet types exist but none currently match NdFeB in energy density at room temperature.