Preserving miners’ health & the environment

Sep 10, 2017 AFC Column, Features / Columnists

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The Guyana Geology and Mines Commission (GGMC) staged its annual Mining Week from August 20 to 26 last under the theme “Mining Clean, Living Green”. In keeping with the most talked-about topic among the world’s leading environmentalists, green energy, climate change and deforestation specialists, Guyana’s Mining Week 2017 had as its primary focus the removal of Mercury from the gold recovery cycle.
The symposia, tours and other events also focused on improving worker safety at the operations of small and medium scale miners. This issue of safety will remain under the microscope until every single miner operates his/her gold and diamond extraction in compliance with human safety regulations and the tenets of environmental preservation.
Miners, porkknockers up to medium scale precious metal extraction operators have been utilizing elemental mercury to ‘collect’ gold in the field for all the years that gold has been mined in Guyana.
Generally, Mercury is mixed with gold-containing ore from the ground or river bed forming a mercury-gold amalgam which is then heated to vaporize the mercury then obtain the gold.
This process can be very dangerous, and it causes miners and the people living nearby the camp to be exposed to the Mercury-tainted air and water which then lead to health issues particularly in children. Ridding the global environment of Mercury has occupied the attention of global environmentalists since before the 1980’s, and countless studies and recommendations have been conducted and tabled, even in Guyana. (Recall former Minister Robeson Benn leading a charge in the 2000’s to encourage miners to utilize alternative gold retrieval methods).
These environmental and health concerns, the wish to clean up or avoid the use of bad gases and chemicals around the globe have formed the axis for the new Minamata Convention on Mercury. This Convention is a global agreement among a large number of nations to reduce and eliminate the prevalence of mercury pollution. The agreement was formally put in force on 16 August 2017, and the 75 member countries will have their first Meeting of the Parties to the Minamata Convention on Mercury (COP1) from 24 to 29 September 2017 at the International Conference Centre, Geneva, Switzerland.
The theme is “Make Mercury History”, and among the Convention’s objectives is to amplify the benefits of Mercury-free mining techniques that are safer for miners and local communities, and which ultimately lessen the market prices for gold and other mined minerals.
Today we present the first set of gold recovery techniques that do not require the use of Mercury:-
Concentration Methods
Concentration means increasing the amount of gold in the ore or sediment by removing lighter particles. Before concentration can begin, the ore must be crushed or milled to liberate gold particles from rock and to decrease grain size. Concentration works best when the grain size of the milled material or sediment is relatively consistent, i.e. most particles are of similar size. Appropriate grain size can be achieved using screens or sieves.
Most concentration methods rely on the high density of gold relative to other minerals in the ore or alluvium mixture. These are referred to as Gravity Methods. Each mining operation is unique. You can select which Concentration Method best suits your operations by assessing the type of ore or sediment, i.e. finding out what other minerals are present in the soil, determining the gold particle size, and the availability of water and electricity.
There are several Gravity Concentration Methods
Panning
Panning uses water to separate heavy gold particles from other lighter particles within a medium sized pan. In this process, sediment or ore containing gold is placed in a wide, curved pan along with water. The miner moves the pan in a series of motions designed to eject lighter sediments. The high density of gold keeps it on the bottom of the pan as the lighter materials float up to be ejected into the surrounding water. After a series of repeats, the gold would be exposed for the miner to recover.
Panning works best when the gold particles are coarse. For amalgamation, miners can employ direct smelting.
Panning offers miners a low-cost method of gold recovery but it requires time and skill. One of the major drawbacks is the small amounts of ore that can be handled at any one time. In addition, panning is done after other methods of gravity concentration such as sluicing have completed.
Sluicing
Sluices use water to wash ore or alluvium down a series of angled platforms. As water washes sediment down the sluice, gold particles sink and are captured by the carpet-like lining at the bottom of the sluice. Sluices are usually inclined at 5 to 15 degrees. The moving water generates greater force as it travels which keeps gold particles from sinking easily. In this way, most of the gold is captured at the first part of the sluice. Carpets or other devices on the bottom of sluices could be removed after the process and washed to recover captured denser materials.
The design of the Sluice can yield higher gold recovery, e.g. if the force of the water traveling through the sluice is decreased, or if you construct the sluice with a series of riffles to help break the water flow. A zig-zag sluice also raises your recovery if a drop is installed between the first and second platforms. This drop disrupts the velocity of the water as it travels down the sluice.
A consistent supply of water is necessary for a well-functioning sluice since the constant flow of water is better than a bucket-driven flow which is interrupted.
On the downside, while sluices are good for concentrating large amounts of ore and sediment in a relatively short time, but they may not yield high amounts of gold concentrate. Plus, the recovered concentrate would have to go through at least 2 other processes, i.e. panning and amalgamation.
(To be continued with shaking tables, spiral tables, and more)

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