Direct Smelting: An Alternative to Mercury Use in Gold Mining

In over 80 developing countries in the world, mercury is the artisanal gold miner’s go-to for separating gold from concentrated ore. Due to a lack of resources and available alternatives, mercury is often handled with bare hands, and in the effort to amalgamate gold, much of it escapes into waterways and soil where it enters the food chain. Most dangerously, the amalgamate is burned, and mercury is converted into a vapor that enters the atmosphere to cause widespread pollution. Improper handling has led to small-scale mining being listed as the single largest contributor to global mercury emissions, and cases of acute mercury poisoning continue to rise.

There are other methods that can be used to isolate gold from concentrated ore, and one of the more accessible alternatives is direct smelting. Smelting completely replaces the need for mercury and eliminates all of the attendant health and environmental dangers it can pose. What’s more, smelting is a process familiar to small-scale miners, who are used to burning the mercury from gold.

Direct smelting has been shown to be more effective as well. It has the ability to collect unliberated gold that remains trapped/attached to rock as well as the super fine gold particulate that escapes when mercury amalgam is squeezed and condensed. Field experiments conducted in 2009 showed that the mercury method recovers about 88% of gold, whereas direct smelting yielded recoveries of 95%.

This means that mercury is not only a danger to health and the environment, but it isn’t as effective as less toxic methods. On the downside, mercury is familiar and available to an impoverished set of the population that often has no recourse to support their families. Mercury poisoning is a phantom threat, and even miners aware of its danger choose to risk it rather than have their families face starvation.

In order for smelting to be successful in developing countries where small-scale mining takes place, it must be introduced in a wide-sweeping campaign. Smelting materials would have to be locally available at a reasonable cost, and miners would need to be educated about the dangers of mercury use. Most importantly, smelting would need to fit into the equation that provides the same daily income they achieve by using mercury.

In an effort to make direct smelting a more visible process, MBMM has undertaken a series of direct smelting experiments which showcase the process from start-to-finish. They can be viewed on our Youtube Channel or on our website under Direct Smelting.

References: Direct smelting of gold concentrates, a safer alternative to mercury amalgamation in small-scale gold mining operations (*Abbey, Nartey, Al-Hassan, and *Amankwah 2010). Report available at http://www.iasir.net/