Urban Mining for Precious Metals - Waste Not Want Not
Some cities are said to be paved with gold and this is taken literally by people known as "urban miners", who collect tiny fragments of gold and gemstone chips in dirt from the jewelry districts of cities all over the world.
Although gold and jewelry workers try their best to collect every scrap of material, by taking measures such as collecting fragments of gold from water used to wash hands, tiny pieces manage to escape and make their way into the city streets. Precious fragments may be washed down the drains by the rain, flushed down the toilet, or taken away in rubbish bins. Yet some rich pickings get into the cracks in the roads and pavements where they settle in the dirt.
In order to recover the gold and gemstone chips, several methods can be employed. Sewage sludge (the product that remains after sewage treatment) is processed in Nagano Prefecture of Japan. The Suwa Treatment Facility extracts gold from molten fly ash. The yield is said to be higher than that of the Hishikari Mine in Japan. This could be due to the amount of precision equipment manufacturers in the area. In the USA, scientists from Arizona State University surveyed sewage sludge samples from 32 different states and stated the possible value of the metals found in biosolids from a community of 1 million people to be up to US13 million per year.
A more crude operation takes place in cities such as Bangkok, Baghdad and Kolkata, where in the early hours of the day, people gather sludge from the drains, sewers and canals of jewelry districts and either use a panning technique to painstakingly extract the gold themselves or sell the sludge to others. Some of the urban entrepreneurs who do this are impoverished people from rural villages. In some cases, they are able to collect enough gold to return to their homes with a brighter future.
Precious metals can also be extracted from scrap such as IT products. Such valuable materials are extracted from discarded electrical appliances, such as computer and mobile phone circuit boards, that are found in rubbish dumps outside cities in Japan. It is said that a ton of recycled mobile phones can produce more gold than the average ton of ore from a gold mine. The gold and other metals can be separated, melted down and then sold to jewelers. Gold is used in circuit boards because of its electrical conductivity.
Belgian recycling facility worker, Thierry Van Kerckoven is a buyer of scrap in Antwerp, where his company, Umicore, extracts 16 different metals from waste, including rhodium and gold. In addition to precious metals, increasing scarcity of rare earths has caused their value to rise. The recycling of metals would enable countries without their own supply of rare earths freedom from relying on imports from countries such as China. One problem with the recycling of metals is the low numbers of old mobile phones that are currently being handed in to recycling facilities despite the fact that people purchase new mobile phones often.
Extracting gold from sewage sludge or circuit boards may be worthwhile, but is a little labor intensive. An easier way for the average man on the street to try urban mining is to follow the example of New Yorker and freelance diamond setter, Raffi Stephanian, who collects precious metals and even cut and polished gemstones from the streets of Manhattan's diamond trading district. Mr Stephanian claims to have collected $819 worth of gold in just six days. He uses tweezers, a butter knife, a bowl and a strainer to harvest the dirt and then sift through it.
The next time you walk the streets of your home town, throw away an old mobile phone, or even flush the toilet, spare a thought for the precious materials that you may be passing by!
- First Published: May-20-2015
- Last Updated: January-24-2019
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