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今日外刊原文
标题：经济学人 | 城市垃圾堆里有大量的黄金
背景：
正文：
Gold mining can be a dirty business. Even with relatively rich deposits, usually found in remote areas, you need giant excavators, huge crushing machines, lots of water and highly toxic chemicals, like acids and cyanide, to extract just ten grams of gold from a single tonne of ore (there are 31 grams in a troy ounce). At current rates, that is worth over $800.
A different sort of pay dirt, however, offers the prospect of a much greater return for urban miners: the printed circuit boards (PCBs) found in rapidly growing mountains of electronic waste. Estimates vary, but a tonne of PCBs could contain 150 grams or more of pure gold, which, because it does not tarnish, produces stable electrical connections. There are also other valuable materials used alongside gold, including silver, palladium and copper, which, if recovered, could push the total haul to well above $20,000 per tonne.
According to the UN, some 62m tonnes of electrical items, ranging from domestic goods to computers and mobile phones, were disposed of globally in 2022. Less than a quarter is reckoned to be recycled, at least in any formal way. Typically, the PCBs are removed and crushed before being either burned in a furnace to melt out metals or treated with chemical solvents, like strong acids. As these processes produce large carbon emissions and have poisonous by-products that are difficult to clear up, companies are developing a number of cleaner recycling methods. One of the more intriguing employs bacteria to do the actual extraction of metals.
