Wednesday, May 24, 2017

Particle Size Distribution in ASGM

Many industries such as food, beauty and pharmaceuticals rely on a specific particle size in order for their product to excel. This is also true in mining; this blog will discuss the importance of particle size as it relates to artisanal and small scale gold mining (ASGM) and how the AGC is using particle size distribution to aid their work in Peru.

In the mining industry, large particles (rocks) are taken from the ground in the form of ore. The ore is then crushed by hand to a more manageable size before it is milled by a machine. Once the ore is milled to a fine dust, the gold is liberated. The size of the dust particles can have a great impact on how much gold a miner can process from their ore.

Machines like this crush the ore

The degree of liberation of gold is measured by particle size. Particle size is measured in ‘mesh’. Screens are stacked in order to measure the whole range of particles. Very coarse screens are measured in inches and smaller particles are measured in microns.

A set of sieves/screens (see image below) can be used to measure the particle size distribution in a sample. Ex: A Chilean mill (as used by the AGC in Burkina Faso) is 74mm (74 microns). This is important to:
·         Calculate the energy required to do any further grinding;
·         Determine if liberation size is sufficient;
·         Assess the need for an additional classification process to remove oversized particles.

Particle size distribution analysis in Cholito, Peru
In Cholito, Peru, at our mercury free processing and training centre, there is approximately 20 grams of gold exhumed from 1 tonne of ore (20 gr Au/t). This means that approximately 98-99% of the ore that is processed will be tailings/waste and the remaining 1% is a valuable gold concentrate.

At Cholito we use particle size distribution analysis to:
  • ·         Separate oversized particles coming out of the secondary crushing circuit;
  • ·         Prepare the grinding load at the ball mill to reduce incoming particles at a specific size;
  • ·         Separate fine and coarse fractions at ball mill exit.

The ball mill exit separates the fine and coarse material

Particle size distribution in ASGM is an aspect of better practices that allows miners to be more efficient and reduce and plan additional classification circuits.

For additional information about particle size distribution and gold recovery, see our YouTube channel for videos on concentration, milling, and Sixto’s seminar series on the topic.

Sunday, May 14, 2017

ASGM and Public Health

The AGC helps miners improve their productivity and helps them to comply with minimal health, safety and environmental standards; this can facilitate the formalisation of their livelihoods, allowing them to increase their income in a safer way for both them and their communities. One of the ways in which the AGC does this is through educating health workers and miners on the risks of certain aspects of ASGM and providing ways to mitigate these risks, while at the same time as training miners on how to process their gold in a safer way, largely by using less or no mercury.  

For the vast majority of the millions of people who work in ASGM worldwide, labor conditions are substandard. There are multiple health risk factors that affect these populations; for example, acute accidents and injuries are common and chronic conditions resulting from exposure to toxins are prevalent, although rarely quantified. Moreover, ASGM communities typically have little to no access to education, health care or sanitation, which further increase the likelihood of health problems.

Image Credit: Natural Resource Defense Council

Both occupational and community health hazards exist for ASGM miners and their families. Because of the working conditions and the nature of the work, miners are exposed to mild, moderate and even sometimes severe and fatal injuries and often there is no emergency response system available. Long term exposure to potential toxins such as mercury and silica result in a variety of health conditions that are the cause of a short life expectancy in ASGM miners.

A major health issue in ASGM is mercury exposure. Mercury evaporates at relatively low temperatures and is often emitted into the environment in different phases of the gold recovery process in ASGM. Multiple health effects have been documented from acute and chronic exposure to mercury vapors and it is recognized that mercury in its organic form is a potent neurotoxin. Pregnant women and children are particularly vulnerable to the effects of mercury.

Another important health risk is silica exposure. When people are exposed to dust repetitively, silica particles accumulate in the lungs causing inflammation and the person can develop a disease called silicosis, an irreversible disease that begins with fatigue and shortness of breath and can lead to progressive respiratory failure.

There are many other health risks such as the chronic musculoskeletal disorders as a result of long-term heavy and non-ergonomic labor practices. In many cases the long-term exposure to noise produced by improvised engines or generators can cause noise-induce hearing loss. Further, limited education, poor hygiene and sanitary conditions can precipitate transmissible infectious diseases, and the social environment in ASGM communities may factor into other health problems such as drug or alcohol abuse, sexually transmitted diseases, anxiety from conflicts and exploitation of women and children.

Better practices like these improve health standards for miners
The AGC provides training and education to prevent several of these health problems. In its work with miners and communities, the AGC offers training for the minimization of mercury use and the use of mercury-free technologies, the proper use of masks to reduce silica dust exposure and other forms of occupational health training. Practical educational material is also offered to raise awareness on other health risks factors identified in the specific communities with which the AGC works.

Some of the training materials we have developed can be found here:
        In addition, the AGC aims to achieve public heath sustainability through the engagement of local healthcare systems and local institutions involved in the health and environment sector. In this way, the AGC may help in the collaborative development of health curricula on ASGM to be used by local technical institutions, facilitating simple mercury prevention protocols or participating in the development of preventive programs as per the need of local communities.

Pages like these help to educate miners 
         Lastly, health activities carried out by the AGC have also the intention to serve as a channel to integrate ASGM communities to the formal society. AGC’s advocacy role help incorporate local health programs, such as Malaria or TB programs, in ASGM communities. In turn, occupational protocols that serve in pilot ASGM sites may also be incorporated in formal local health programs.

     Public health improvements in ASGM are challenging but the results of our work are rewarding to many.