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Susan Egan Keane’s Blog

Travels with Mercury II: Using Mercury in Small Scale Gold Mining

Susan Egan Keane

Posted June 2, 2009 in Health and the Environment

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 In my last post, I described my visit to small scale gold mining operations in Kalimantan, on the island of Borneo.  The devastation of the land was stunning, but the truth is, I didn't come to Indonesia see the effects of small scale mining on the landscape.  I came for the mercury.

Mercury is a very nasty toxin that damages the nervous system, especially the growing brains of young children.  Unfortunately, mercury is also a very common, widespread pollutant - in fact, nearly every state in the U.S. advises against fishing in one or more of its streams or rivers, because of mercury contamination. 

While mercury is a naturally occurring element, we humans contribute substantially to the mercury that circulates in the global environment.  Most of the mercury that we emit comes from burning coal (another entry in the long list of coal's many sins; see also: global warming, mountain top removal, toxic fly ash spills). However, mercury is also routinely used around the world in certain products, like batteries and lighting, and in industrial processes, including small scale gold mining.  The miners combine the mercury with gold-containing ores; the mercury reacts with the gold particles to form a mercury-gold amalgam.  The amalgam is then heated, to burn off the mercury, leaving behind only the gold.  This technique is quick and effective; it is also inexpensive, because mercury itself is very cheap.

Now, you are probably thinking, how much could these small scale miners really contribute to the overall global mercury problem? After all, they are small scale operators, by definition.  But consider that there are somewhere between 10 million to 20 million small scale gold miners working in Asia, South America and Africa.  It adds up.

A United Nations Environment Program report estimates that up to 1350 tons of mercury are used each year by these miners, making it the single largest use of mercury in the world.  And, most of the mercury they use will end up in the environment - either washed into the tailings, or emitted to the air when the amalgam is burned. 

My visit to Kalimantan, Borneo, gave me the chance to observe first hand the use of mercury in small scale gold mining.  When I  arrived at the amalgamation area, there in front of me was a good-sized bottle of mercury, about 300 grams worth (the same amount contained in about 60,000 compact fluorescent light bulbs).Mercury, in person

In person, mercury seems placid and harmless. In fact it's downright pretty.  It's shimmering and silvery, and looks like a lot of fun to play with.  One miner poured out about 100 grams of the mercury from the bottle into a bucket containing the gold ore concentrate.  Standing in a small pool built just for this process, the miner slowly poured the contents of the bucket, a little at a time, into a flat pan.  The panner carefully swirled the material around, allowing the lighter minerals to float to the top while the heavier mercury-gold amalgam sunk to the bottom. Swirling, swirling, a blob of amalgam finally plumped up from the sand at the center of pan.  Guided by the panner's finger, the blob wriggled to the edge of the pan and then plopped back into the bucket, while the waste material was washed into the pool. Mercury-gold amalgam

This process patiently continued until all of the amalgam had been collected in the bucket and all of the waste material had been washed away.  The amalgam was then filtered through a cloth - excess mercury was squeezed out and saved for later use.  The remainder was a tiny, pea-sized mercury-gold amalgam ball, which was later sold to one of the gold shops that line the main street of Karengpangi, the nearest town. The final mercury-amalgam ball

All of that work, a full day of digging, sluicing and processing, all for that tiny ball.  But imagine how much more work it would be without the mercury. The tedious and inefficient process of panning gold without the help of the mercury would undoubtedly take hours more time and yield much less gold.  In this area, the gold yield when using mercury is only about 3 to 5 grams per day; the miners can ill-afford to work all day for less than that.

It bothered me, but didn't surprise me, that the miners' attitude toward mercury was very casual.  The miners handled the mercury with ease, mixing and squeezing it with their bare hands.   A small crowd, including a few bashful children, gathered around to chat and watch the amalgamation process (and to stare at us, the foreigners), with no regard to the very hazardous material being used in front of them. Bashful children looking on  To them, it is just a tool of the trade, not a dangerous toxin that threatens their health. 

Fortunately, there are efforts underway to educate miners about the dangers of mercury, and to help them find ways to change their practices.  In my next post, I'll report on some of the successful measures taken in this community, and in others around the world, to substantially reduce the amount of mercury used and released while mining gold.

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