Precious metals are so called partly because of their rarity; it is said that all the platinum ever produced would only cover our ankles in one Olympic-sized swimming pool. But we choose them for their properties, such as durability, low chemical reactivity and resistance to corrosion. Besides their aesthetic qualities so prized in jewellery, they have applications in industry and other fields, which encourages their mining. But just as in the past, when the extraction of luxury materials such as gold or diamonds spared no resources, cost or damage because of their high market price, so today the demands of sustainability, environmental friendliness and ethics extend to even the wealthiest consumers. Thus it is pertinent to ask: are precious metals sustainable? Are some more so than others?
The category of precious metals (not to be confused with rare earths, which are often distinguished by their electrical and magnetic properties) has no single definition, but includes those with an ISO 4217 currency code on the international market: gold, silver, platinum and palladium. Also commonly included are those known as the platinum group in the periodic table, with similar properties: ruthenium, rhodium, osmium and iridium.
Some metals have changed status over time. For example, aluminium, despite its abundance, was once considered a more valuable precious metal than gold because of the difficulty of extracting it from its ore; it was used in jewellery, and Napoleon III of France honoured his most illustrious guests with aluminium cutlery instead of silver. This changed in the late 19th century, with the development of separation on an industrial scale.
From cost to applications
The king of them all is undoubtedly gold, the precious metal par excellence, which deserves its own chapter. But it is not the most expensive: platinum has often surpassed it in price, although today the most valuable is rhodium. Palladium and iridium are also among the most sought-after. Apart from their use in jewellery, platinum, palladium and rhodium are mainly used in catalytic converters for cars. Ruthenium is used in electrical contacts, industrial chemical reactions and alloys. Palladium is also used in electronics, medicine and fuel cells, while iridium is used in spark plug contacts, industrial catalysis and in alloy with osmium for the tips of fountain pens and compasses. This is one of the few uses of osmium, which is distinguished by the fact that it is the densest element, twice as dense as lead.
Unlike gold and contrary to what it might seem, jewellery is a minority use for the other precious metals: only 27-35% of platinum and 21-26% of silver (depending on sources) are used for jewellery, and only 2% of palladium, with industrial applications absorbing the rest of the production.
The biggest problem with metals is their procurement. As with all mining, and although the industry is trying to adopt more sustainable practices, the extraction and purification of these materials is environmentally damaging and generates greenhouse gases (GHG), not to mention the human exploitation that often surrounds these activities. Of all the precious metals, gold emits the most GHGs due to its higher production volume. But in terms of relative emissions, platinum is far more polluting: 40,000 kg of CO2 per kilo of metal, compared to just 16,300 kg for gold. By comparison, the climate impact of silver is minimal, at 104 kilos per kilo. Translating the emissions into a finished product, a ring of the same size (but with different weights depending on the metal) produces 0.3 kg of CO2 if it is silver, 64 kg if it is gold and 236 kg if it is platinum.
This higher environmental cost of platinum and its group is due, according to experts, to the fact that these metals are found in extremely low concentrations in the ore, in parts per million, so a large amount of material has to be collected and processed in expensive and complex refineries that often use proprietary technology.
Alternatives and solutions to the environmental impact
The solution to this is recycling: the emissions from recycled platinum are only 5% those of mining, and 14% in the case of silver. Going back to the ring example, the recycled platinum ring emits only about 12 kg of CO2, and the silver ring just 42 grams. But recycling is still in the minority: only 26% of platinum produced is recycled, and even less for silver (17%), even though silver production is almost 125 times higher than platinum production. These rates still fall short of the jewellery demand: platinum recycling generates about 59 tonnes, compared to 63 tonnes for jewellery manufacturing; for silver, recycling covers 4,800 tonnes of the nearly 6,000 tonnes absorbed by jewellery.
Mining is highly unlikely to disappear. That is why, as University of Alberta earth scientist Jeremy Richards points out, metals should be treated as irreplaceable: if international agreements were to raise the price of mined materials, this would stimulate the consumption of recycled metals, whose recovery is improved by new processes. In industry, for example in catalysis, there are projects that seek to replace precious metals with combinations of other more abundant metals, such as copper, iron or manganese. And for consumers, the most responsible option is to look for jewellery brands that offer recycled metal.
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