Sunday, June 3, 2012

Concentration of Gold Ores - a Key to Reducing Mercury Use in Artisanal and Small Scale Gold Mining

In artisanal gold mining, mercury is essentially used to concentrate the gold. It does this by bonding with the gold to form a heavy amalgam that is then easily separated from the other minerals. It follows therefore, that if mercury is used as a mechanism of concentration, producing concentrates of gold ores through other means can enable reduction or even elimination of mercury use. In other words, a good process of concentration can replace mercury and lead to big environmental and health improvements.

Concentrating gold ores before applying mercury greatly reduces the mass of material that comes into contact with mercury. This reduces the amount of material that becomes contaminated and also the amount of mercury that is required to be applied. And of course, if concentration is done with sufficient sophistication and knowledge, mercury is not needed at all.

As an important first step along the way to eliminating mercury, concentrating avoids a worst practice called whole-ore-amalgamation, where mercury is brought into contact with 100% or the ore and losses of mercury to the environment can be very high - as high as 50 parts mercury for every part gold produced (more often ranging from 20:1 to 4:1). Simple concentration methods reduce the amount of mercury required for amalgamation to roughly 1 part mercury per 1 part of gold recovered. A vast improvement. Better yet, almost all of the mercury that is applied to a good concentrate ends up in the gold-mercury amalgam and if this mercury is recycled, for example by using a retort, losses can be further decreased by an additional 95%. Operating in this way, only 1 part mercury is used for each 20 parts of gold produced. 

That is hundreds of times less mercury used and lost to the environment

Common methods of concentration that are, to a variable degree, accessible to artisanal and small scale gold miners are: panning, magnets, sluicing, spirals, vortexes, centrifuges, shaking tables, and flotation - in increasing order of complexity and cost.

Choosing a technology to produce a concentrate depends on the type of ore, access to capital, and having the knowledge and organisational skills with which to acquire and operate the equipment. Access to capital and expertise is often affected by legal status – with illegal or informal status being a significant barrier for miners to acquire and operate better equipment, and by extension a barrier to eliminate the use of mercury.

There is no doubt that helping artisanal miners gain access to the equipment and knowledge required to adequately concentrate their gold ores will help them reduce and ultimately eliminate the use of mercury. Technically speaking, replacing mercury with other processes of concentration can certainly be done. It is in fact, exactly what the large scale mining sector has done over the last decades. 

They used to use mercury and now they don't - and they get more gold without it 

With some innovation, finance, and most importantly, some political will, the same can be true for artisanal gold miners.

Wednesday, May 16, 2012

Is Borax the Miracle Chemical that Will Replace Mercury in Artisanal Gold Mining?

The Myth of a Miracle Cure

Can borax replace mercury in artisanal gold mining? – or is it better concentration that can replace mercury? Does Borax really have anything to do with it?

Is Borax a Miracle Chemical?

Those promoting borax as a replacement for mercury in small scale gold mining are overselling it and risk giving the impression that there is a miracle cure. They may be well intentioned but they are misleading the world by claiming that borax is a direct replacement for mercury. This is simply not true.

The bar of gold shown here was entirely produced using borax. It was also entirely produced using mercury. How can that be if the word going around is that borax is a replacement for mercury?

It is not. Borax is used in every Artisanal and Small Scale Mining gold shop in the world and has been for a hundred years. It has been used in pottery glazes for centuries for the same reason. It is a flux.

Background: if a miner has 10 kilograms of sand that contains 10 grams of gold, that is 0.1% gold or 1/1000 th. So she needs to concentrate by 1000 times to end up with the gold. How can she separate the gold from the sand? She adds mercury to the 10 kilograms of sand which dissolves the gold and is then easily separated from the sand as a heavy liquid. Then she evaporates the mercury and is left with the gold plus about 10% impurities - grains of sand for example. It is at this stage that borax is used in gold shops - for melting and removing the impurities in 10 grams of gold - not for concentrating the gold in 10 kilograms of sand by 1000 times. Borax is only used to assist in removing the impurities.

Everybody has always used borax (and other fluxes) to melt gold concentrates. It makes some impurities – tiny bits of other minerals – melt at a lower temperature and become thinner so that the mineral melt, a molten glass slag, and the molten gold can be separated easily. That is what fluxes do.

It doesn’t matter if you have a 25% gold, 75% sand mixture or a 90% pure piece of sponge gold (the porous product of mercury amalgamation), you’re going to use borax to melt it.

Borax does not replace mercury. It is not used at the same stage of the process as mercury. 

Mercury is applied to a big pile of sand containing a tiny bit of gold.

Borax is applied to a tiny pile of gold containing a tiny bit of sand. 

Therefore, the so-called borax method is nothing more than a method of better concentration that then uses borax as it has always been used. So there is no “borax method”. There is simply better concentration. Just ask any gold shop owner or his grandfather about borax... Its been around for a long time.

Borax is not a miracle chemical that can solve the mercury problem in Artisanal Gold Mining. For the millions of artisanal gold miners and the governments working with them to reduce mercury use, proclamations of borax miracles should be replaced by a proper explanation: If you can make a 25% gold concentrate, you don't need mercury. It is better concentration that can eliminate mercury, not borax. And better concentration usually requires a higher level of organisation.

Tuesday, February 28, 2012

Health and Artisanal Gold Mining

By Dr. Paleah Moher, Human and Ecosystem Health, AGC

Artisanal and Small-scale Gold Mining (ASGM) presents a complex development and health-impact situation. On one hand it provides livelihoods to tens of millions people in the developing world while contributing significantly to the global supply of gold.  On the other hand ASGM is accompanied by serious environmental, social and health concerns. Here we discuss the health concerns and their solutions.

Generally sustainable solutions support the ASGM sector’s economy while also addressing the associated health problems. This can be realized through inexpensive safer mining practices that come along with increasing degrees of education and formalisation. Fortunately there are often economic incentives to drive such improvements.

Mercury is one of the main health concerns of ASGM. The use of mercury to amalgamate and extract metals from rock has been in practice for over 5000 years , mainly because it is a simple, expedient, and relatively inexpensive method. Today mercury-free extraction processes are readily available, as are simple mercury reduction technologies

The release of mercury into the environment from ASGM is not only a serious health issue for the local people but it also contributes towards global health problems.  When mercury is released into the air, it may travel long distances before it is deposited into waterways and soils. When this occurs, bacteria can convert mercury into an even more toxic form called methyl-mercury, which can bio-accumulate up the food-web. This results in predatory fish, such as tuna and marlin, having high mercury concentrations.

Mercury is a well known neurotoxin. When mercury enters the brain it causes permanent brain damage resulting in dizziness, difficulty in concentration, muscle twitching, poor muscle coordination, memory loss, blurred vision, and numbness in the hands and feet.  These symptoms become much more pronounced when mercury exposure occurs in a child or fetus because the developing brain is still forming and therefore more vulnerable to mercury toxicity. 

The degree of mercury toxicity depends on the level of mercury exposure, as shown here in order of decreasing seriousness:

·      Permanent overt brain damage
·      Seizures
·      Vision and hearing loss
·      Delayed childhood development
·      Language disorders
·      Deficits in fine motor functions
·      Memory issues
Often children in ASGM communities will develop mercury poisoning symptoms long before  adults, even when their exposure is lower. Children may be exposed to mercury when mercury amalgamation and burning occurs in a home or near a village or worse when they are directly involved in amalgamation.  If mercury-free processing is not available, mercury releases into the air can be minimized with the use of mercury-catching retorts.  What is particularly important however, is for children and pregnant women to stay far away from mercury-related ASGM activities and to minimize their exposure to the toxic substance.

Although mercury gets a lot of attention due its global reach, ASGM is also associated with occupational safety concerns, poor respiratory health, and infectious diseases.  Occupational health hazards such as shaft collapses and dust related lung diseases can be addressed through improved mining engineering and personal protective equipment. These safety measures can often be implemented by the leaders of ASGM sites and are therefore most readily implemented when there is a significant degree of organization and formalization. Fortunately, increasing organisation and formalisation also often results in increased gold recoveries and so there can be powerful economic drivers to contribute to improving health and making these improvements sustainable.

Some of the health issues of ASGM communities are related to the socio-economic conditions of the population rather than the mining activities themselves.  For example malaria, HIV/AIDS, tuberculosis, malnutrition, inadequate access to clean water and sanitation are often associated with ASGM communities.  Education and awareness, activities that also can come with increased organisation, are key methods in addressing such problems.  

The health issues surrounding ASGM must be holistically addressed in order to create sustainable changes within the sector. Such actions are a part of the mission of the Artisanal Gold Council and require continued collaboration between members of artisanal mining communities, governments, health care providers, and all of the other stakeholders involved in this global industry.