Gold amalgamation with mercury.

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What is Gold Amalgamation?

Gold amalgamation, an ancient method of extracting gold from ores, involves mixing the ore with mercury to create a gold-mercury amalgam. This process chemically binds gold particles to mercury, forming a substance that can be heated to vaporize the mercury, leaving behind the extracted gold. The principle behind mercury amalgamation is that after adding mercury to the slurry, it wets the surface of gold particles, diffuses into their interior, and triggers a chemical reaction (Au+2Hg=AuHg2). The resulting solid, Au3 Hg, turns into sponge gold when heated, as the mercury volatilizes into elemental form. This technique has historically been employed in gold mining, especially in regions where gold is finely disseminated and challenging to recover through alternative methods.

What happens if mercury reacts with gold.

When mercury reacts with gold, a process known as amalgamation occurs. In this process, gold dissolves in mercury to form an alloy. This reaction is commonly used in gold mining to extract gold from ore. The amalgamation process involves mixing mercury with crushed ore to form a gold-mercury amalgam. The gold is then separated from the mercury by heating the amalgam, which causes the mercury to evaporate, leaving behind the pure gold.It’s important to note that while amalgamation is an effective method for extracting gold, it can have serious environmental and health consequences due to the release of mercury into the environment. Mercury is a toxic substance that can bioaccumulate in living organisms and pose risks to human health and the ecosystem.Therefore, it is crucial to handle mercury with care and follow proper safety protocols when using it in processes like gold extraction. Additionally, environmentally friendly alternatives to mercury-based extraction methods are being developed to minimize the negative impact of mercury on the environment and human health.

First use of gold amalgamation.

The amalgamation of gold and silver using mercury, known for centuries, has a rich historical background. The Romans were aware of gold’s amalgamation with mercury, though it remains uncertain if they applied this process for ore separation. In 1556, Agricola detailed the gold amalgamation process used in Europe, possibly first employed by the Spaniards in Peru in 1566 to separate silver from ores.

Agricola’s described process involved fine-grinding ore between rotating flat stones, akin to flour mills, and washing the pulp into three barrels with mercury. Stirred by paddles in each barrel, a continuous process facilitated the amalgamation of gold and mercury. The resulting amalgam, a lumpy grey mass, was squeezed in a chamois or fine cotton bag to remove most of the mercury, leaving behind the gold.

Amalgamation, as described by Agricola, was considered a physical process rather than a chemical one. The rapid ‘catching’ of gold occurred when liberated gold particles, wetted by mercury due to stamping, sank into the mercury because of their higher specific gravity.

During the 19th century, various methods were debated for treating gold ores, and each millman had preferred techniques. In the 1850s, Berdan pans, Chilean mills, and stampers were experimented with for crushing in Victoria and New South Wales. Stampers, in a continuous process, became the preferred method by the late 1850s, with slurry passing through mercury pools on an inclined plane. Millmen adopted empirical methods, experimenting with different equipment and techniques to deal with diverse ores.

Some used copper plates coated with mercury, while others followed Agricola’s approach, employing blankets or cow hides to catch gold. The blankets were washed regularly to collect gold and sand particles, which were then treated in an amalgamation barrel. The variability in stampers and methods highlighted the individualized approaches taken by millmen in their quest for efficient gold extraction from ores.

Mercury Amalgamation Gold Extraction: internal and external.

https://www.unido.org/sites/default/files/files/2017-11/ASGM_English%20%281%29.pdf

Mercury amalgamation is a key method in gold extraction, divided into two main types: internal mercury amalgamation and external mercury amalgamation. while both internal and external mercury amalgamation methods contribute to gold extraction, the internal method is preferred for its higher efficiency and superior gold quality. Careful control of mercury concentration and flow rates is crucial in ensuring the success of the external amalgamation process.

Internal Mercury Amalgamation: In this method, mercury is directly introduced into the ore slurry during the grinding cycle, facilitating the extraction of gold. Notably, gold mines in South Africa and the United States often employ mercury amalgamation in ramming machines, while small and medium-sized gold mines in russia favor disc rollers. In China, mercury amalgamation cylinders are commonly utilized. The internal method is recognized for its higher efficiency compared to external amalgamation, resulting in superior-quality mercury gold. The concentration of internal mercury slurry is typically maintained at 30-50%, with the mercury in a suspended state.

External Mercury Amalgamation: External mercury amalgamation involves mixing mercury to extract gold outside the ore crushing chamber. This method is frequently practiced in China, employing fixed and vibrating mercury amalgamation plates. However, the concentration of external amalgamated mercury slurry should be carefully controlled to prevent the formation of a dense slurry flow. Maintaining a moderate flow rate is essential to allow gold particles to settle onto the mercury plate effectively.

Gold mercury amalgamation process.


How to Extract Gold Using a mercury and Rocker Cradle:

  1. Crushing the Rock:
    • Use a hammer or crusher to crush the rock into powder.
    • Strike the rock with a hammer until it breaks into small, pebble-sized pieces. When using mercury sulfide for gold extraction, powdering the rocks is unnecessary.
  2. Mixing with Mercury Sulfide:
    • Mix mercury sulfide with the powdered rock using a metal rod.
    • Stir the mercury sulfide and rock powder to ensure thorough mixing. As gold melts from the rock, mercury and gold react to form a liquid amalgam.
  3. Pouring Amalgam onto Sheepskin:
    • Spread a piece of sheepskin and slowly pour the liquid gold amalgam onto the center of the leather.
    • Leave the remaining stones in the metal container, taking care not to spill any mixture outside the leather. The debris in the metal container consists of a mix of rock fragments and sulfur.
  4. Twisting the Leather to Secure the Mixture:
    • Carefully lift the side of the leather, creating a small bag around the golden amalgam.
    • Twist the top of the leather to secure it around the amalgam. The leather acts as a cake decorating tube, allowing you to extract the unreacted mercury from the bottom of the fabric.
  5. Pressing to Extract Unreacted Mercury:
    • Hold the twisted part of the leather tightly and press the raised part of the sheepskin down to expel the mercury.
    • Be cautious of any small silver mercury beads on the bottom of the leather, as mercury poses health risks; do not touch them.
  6. Pouring Mixture into an Old Pan:
    • Open the leather and pour the mixture into an old pan that will not be used for food.
    • Handle with care to avoid spills, and do not use the pan for cooking after using it for gold extraction.
  7. Covering Mixture with Potato Slices:
    • Cut a large potato into thick slices and place them on top of the golden amalgam in the pan.
    • Ensure all metallic amalgams are covered by the potato slices.
  8. Heating to Extract Mercury:
    • Heat the pan on a fire, moving it for even heating. The amalgam will melt, releasing mercury as a gas.
    • The potatoes will absorb the gases, leaving behind the gold.

Note:

  • Warning: Heating the mixture releases mercury gas, so work in a well-ventilated area and use safety equipment. While potatoes can absorb gases, handling gold amalgam remains hazardous.
  1. Additional Warning:
    • Mercury can be harmful to health, and its use may be illegal in your region. Even small amounts of mercury can be dangerous, so it is best to avoid it.
    • Cyanide can also be used for gold extraction, but it is toxic and can produce harmful fumes if not handled carefully. If you are not a professional, it is advisable to avoid cyanide.
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