Gold extraction is the process of obtaining gold from ores through chemical processes. With an annual output of around 3,600 tons from mining and an additional 300 tons from recycling, gold plays a significant role in various industries.
There are several techniques used in the gold refining process, each designed to extract and purify gold efficiently. These methods include cyanide leaching, gold amalgamation with mercury, gold smelting, and gold electrolysis.
Key Takeaways:
- Gold extraction involves obtaining gold from ores through chemical processes.
- Cyanide leaching, gold amalgamation, smelting, and electrolysis are common extraction techniques.
- Gold purification methods are essential to ensure high levels of purity.
- The annual gold output from mining and recycling is significant, highlighting the value of this precious metal.
- Gold plays a vital role in various industries, including jewelry, electronics, and currency backing.
Types of Gold Ores
Gold can occur in different forms, including native gold (pure gold), electrum (gold alloyed with silver), and various gold-containing minerals such as calaverite, aurostibnite, and maldonite. These ores may be found in sizeable nuggets, fine grains or flakes in alluvial deposits, or as microscopic particles embedded in rock minerals. Other gold-containing ores include tellurides like sylvanite, nagyagite, petzite, and krennerite. Some ores can contain contaminants that interfere with cyanide extraction, such as carbon and certain clays.
| Ore Name | Description |
|---|---|
| Native Gold | Pure gold in its natural form |
| Electrum | Gold alloyed with silver |
| Calaverite | Gold telluride mineral with chemical formula AuTe2 |
| Aurostibnite | Gold antimony sulfide mineral with chemical formula AuSbS |
| Maldonite | Gold bismuth telluride mineral with chemical formula Au2BiTe2 |
Gold can be found in various forms and requires different extraction methods depending on the ore type. Understanding the characteristics of different gold ores is crucial for efficient and effective extraction processes.
These different types of gold ores have unique characteristics that influence their physical properties, extraction methods, and refining processes. Native gold, being pure, is relatively easy to extract and refine. Electrum, on the other hand, requires additional steps to separate gold from the silver alloy. Ores like calaverite, aurostibnite, and maldonite often contain other minerals and compounds, complicating the extraction process.
Concentration Techniques
The main challenge in gold extraction is concentrating the trace amount of gold in the ore. To achieve higher gold concentrations, various concentration techniques are employed.
Cyanidation
The principal technique for gold concentration is cyanidation, where gold is leached from the ore using a cyanide solution. This method is widely used in the gold mining industry due to its high efficiency and effectiveness. Cyanidation can be carried out through dump leaching or heap leaching processes, depending on the type of ore and the desired gold concentration.
Thiosulfate Leaching
In addition to cyanidation, thiosulfate leaching is another effective technique for gold concentration. This method is particularly suitable for ores with high soluble copper values or ores that experience preg-robbing, where gold is adsorbed onto carbonaceous material. Thiosulfate leaching offers an alternative to cyanidation and provides higher gold recoveries in certain ore types.
Bulk Leach Extractable Gold (BLEG)
Bulk leach extractable gold (BLEG) is a method used to test for gold concentrations in areas where gold may not be immediately visible. BLEG involves extracting gold from large volumes of sample material and measuring the gold content. This technique is valuable in exploration and resource estimation, helping identify gold mineralization in potential mining areas.
To summarize, gold concentration techniques like cyanidation, thiosulfate leaching, and bulk leach extractable gold play a crucial role in maximizing the recovery of gold from ores. These methods allow for efficient extraction of the precious metal and contribute to the overall success of gold mining operations.
Mercury Amalgamation
Mercury amalgamation is a widely used technique in small-scale mining for the recovery of very small gold particles. This method involves the formation of a mercury-gold amalgam by mixing mercury with the smaller gold particles. The resulting amalgam is then heated, causing the mercury to vaporize and leaving behind the purified gold.
Although mercury amalgamation is an effective method for gold recovery, it poses significant health and environmental risks. The vaporization of mercury releases toxic fumes that can be harmful to both miners and the surrounding ecosystem. Due to these hazards, large-scale use of mercury in gold mining has been discontinued since the 1960s. However, in some small-scale operations, where alternative methods are not accessible, mercury amalgamation is still employed.
It is crucial to understand the potential risks associated with mercury amalgamation and explore safer alternatives for small-scale mining operations. Minimizing mercury exposure and promoting sustainable mining practices are essential for protecting the health of miners and preserving the environment.
Refractory Gold Processes
Refractory gold ores, characterized by the presence of ultra-fine gold particles dispersed within gold occluded minerals, pose a unique challenge for extraction. These ores are highly resistant to standard cyanidation and carbon adsorption processes, requiring specialized pre-treatment methods to achieve effective gold recovery. Several pre-treatment options have been developed to tackle refractory gold ores, including:
- Roasting: Involves heating the ore at high temperatures to transform the gold occluded minerals into more reactive forms, making them susceptible to subsequent extraction processes.
- Bio-oxidation: Utilizes bacteria to oxidize the sulphide minerals present in the ore, thereby liberating the encapsulated gold particles.
- Pressure oxidation: Applies high-temperature and high-pressure conditions to increase the reactivity of the ore, facilitating the release of gold particles from its refractory matrix.
- Albion process: Features ultrafine grinding of the ore to enhance its surface area, followed by oxidative leaching to extract the gold. This process is known for its high gold recovery efficiency.
Choosing the most suitable pre-treatment method depends on the specific characteristics of the refractory gold ore, such as the types of sulphide minerals and the presence of organic carbon. Each method has its advantages and limitations, making it essential to carefully evaluate the ore composition before determining the appropriate course of action.
“Refractory gold ores require specialized pre-treatment methods to liberate the valuable gold particles from their encapsulating minerals.”
By employing these innovative pre-treatment techniques, the mining industry can overcome the challenges posed by refractory gold ores and maximize the recovery of this precious metal.
| Pre-treatment Method | Advantages | Limitations |
|---|---|---|
| Roasting | Enhances reactivity of gold occluded minerals | Requires significant energy input |
| Bio-oxidation | Eco-friendly and cost-effective | May involve longer processing time |
| Pressure oxidation | High gold recovery efficiency | Requires specialized equipment |
| Albion process | Effective for ultrafine gold particles | May involve complex equipment setup |
Table: Comparison of different pre-treatment methods for refractory gold ores.
Gold Refining and Parting
Gold refining is an essential process to purify gold to meet the specifications required for commercial trade. There are different methods used for gold refining, with the two most common processes being the Miller process and the Wohlwill process.
The Miller process involves passing chlorine gas into a molten gold-silver alloy, resulting in the removal of impurities. This process is particularly effective in removing base metals like copper and tin. The remaining gold is then refined to achieve high purity.
On the other hand, the Wohlwill process utilizes electrolysis to separate impurities from gold. In this process, the gold is dissolved in a hydrochloric acid electrolyte solution, and a direct current is applied. This causes the gold to migrate to the cathode, resulting in a pure gold deposit. The Wohlwill process is efficient in removing impurities such as platinum, palladium, and other precious metals.
Alternatively, gold parting is a technique used to separate gold from other metals. One method of gold parting involves boiling the gold alloy with nitric acid. The acid dissolves the silver and base metals, leaving behind pure gold. Another approach is to use the Wohlwill process with electrolysis, similar to the refining process.
Advantages of the Miller process:
- Effective in removing base metals
- Relatively straightforward process
- Allows for the production of high-purity gold
Advantages of the Wohlwill process:
- Highly efficient in removing impurities like platinum and palladium
- Can produce gold with extremely high purity levels
- Offers better control over the refining process
Both the Miller process and the Wohlwill process have their advantages and are widely used in the gold refining industry. The choice between these methods depends on the desired purity level and the impurities present in the initial gold material.
History of Gold Extraction
Gold extraction has a rich history that spans centuries, with various methods evolving over time to meet the growing demand for this precious metal. Let’s explore some key milestones in the history of gold extraction:
Salt Cementation
One of the earliest methods used to separate gold and silver from electrum, a naturally occurring alloy, was salt cementation. This process involved heating a mixture of the alloy and salt in a furnace, causing the silver to react with the salt and form a stable compound, leaving behind pure gold.
Mercury Extraction
During the gold rushes of the 19th century, mercury extraction became a popular method for recovering gold. Miners would use mercury to form an amalgam with the fine gold particles, allowing for easy separation. However, this technique posed significant environmental and health risks due to the release of toxic mercury vapor.
Gold Cyanidation
In the late 19th century, the development of gold cyanidation revolutionized the gold mining industry. This technique involves dissolving gold from ore using a diluted cyanide solution. The dissolved gold is then recovered through various methods such as carbon adsorption or zinc precipitation. Gold cyanidation remains a widely used method today due to its effectiveness and efficiency.
Borax Flux Extraction
During gold rushes, a technique called borax flux extraction gained popularity. This method involved using borax, a mineral compound, as a flux to remove impurities and enhance the melting point of gold. Borax flux extraction allowed miners to separate gold from other minerals more efficiently, increasing overall yield.
Froth Flotation
The introduction of froth flotation in the 20th century brought about a significant advancement in gold mining. This technique utilizes chemicals and air to selectively separate gold particles from other minerals. With froth flotation, fine gold particles can be separated from low-grade ores, increasing the overall recovery rate.
“The history of gold extraction is a testament to human ingenuity and the relentless pursuit of this precious metal. From ancient methods like salt cementation to modern techniques such as gold cyanidation and froth flotation, each development has played a vital role in shaping the industry.”
As the demand for gold continues to grow, the history of gold extraction serves as a reminder of the innovative spirit and determination displayed by miners throughout the ages.
Gold Recycling and Scrap Refining
In the pursuit of sustainable resource usage, gold recycling plays a vital role. With limited new sources of gold available, recycling gold scrap and jewelry alloys is an environmentally responsible practice. Through careful refining processes, the precious metal can be reclaimed and reused, reducing the need for further extraction.
One reliable method for determining the gold content in ores or scrap is fire assay. This centuries-old technique involves heating the gold-containing material to high temperatures and separating the precious metal from impurities. Fire assay provides accurate and precise results, ensuring the purity of the gold being recycled.
“Gold recycling is not just an eco-friendly practice; it also contributes to the circular economy, preserving the value of this precious resource for future generations.”
The jewelry industry uses the karat system to denote the gold purity. Pure gold is referred to as 24 karats, while alloys contain a lower percentage of gold. Common alloys used in jewelry include gold-silver, gold-copper, gold-platinum, and gold-palladium combinations. These alloys are carefully crafted to enhance the properties and durability of the gold, making it suitable for various jewelry designs.
The table below provides a breakdown of common jewelry alloys and their respective gold content, expressed in karats:
| Jewelry Alloy | Gold Content (Karat) |
|---|---|
| 24K Gold | 100% |
| 18K Gold | 75% |
| 14K Gold | 58.3% |
| 10K Gold | 41.7% |
Whether it’s scrap jewelry or discarded electronic components, gold recycling and scrap refining contribute to the preservation of this precious resource and help minimize the environmental impact of gold extraction.
Industrial Applications of Gold
Gold, with its unique properties and allure, finds a wide range of industrial applications across various sectors. Let’s explore some of the key uses of gold in different industries:
Jewelry
Undoubtedly, the jewelry industry is one of the largest consumers of gold. Gold’s aesthetic appeal, durability, and timeless beauty make it the preferred choice for crafting exquisite jewelry pieces. From engagement rings to necklaces and bracelets, gold jewelry has been adorning individuals for centuries, showcasing both opulence and personal style.
Backing for Currency
Gold has played a prominent role as a backing for currency throughout history. During times when the solvency of a country was equated with its gold reserves, gold acted as a tangible representation of wealth and stability. Although not as prevalent today, gold still holds a place in central banks’ vaults as part of their reserves.
Electronics
Gold’s exceptional electrical conductivity and resistance to corrosion make it a valuable component in electronics manufacturing. The precious metal is used for plating contacts in connectors, switches, and integrated circuit boards. Gold’s ability to maintain stable electrical connections and prevent oxidation ensures optimal performance and longevity of electronic devices.
Catalysts
While gold is not widely used as a catalyst due to its chemical stability, it does find some applications in the production of nitric acid. Gold catalysts can efficiently convert ammonia to nitric oxide, a crucial step in the nitric acid manufacturing process.
Summary
From its renowned place in the jewelry industry to its essential role in electronics and occasional use as a catalyst, gold proves its versatility and value across multiple industrial applications. Whether adorning the necks and fingers of individuals or enhancing the efficiency of technological advancements, gold continues to shine bright.
| Industry | Application |
|---|---|
| Jewelry | Exquisite adornment |
| Backing for Currency | Symbol of wealth and stability |
| Electronics | Plating contacts, transistor bases |
| Catalysts | Production of nitric acid |
Gold’s industrial applications span various industries, from jewelry to electronics and catalysis.
Chemical Compounds of Gold
Gold compounds find applications in various industries, including gold electroplating, gold production, and medical fields. These compounds offer versatile properties and are utilized for a wide range of purposes.
Gold Electroplating
One common application of gold compounds is in gold electroplating baths, which are used to deposit a layer of gold onto a surface. Gold electroplating provides a decorative and protective coating, enhancing the appearance and durability of various objects, such as jewelry, watches, and electronic components. Potassium dicyanoaurate and chloroauric acid are extensively used in creating effective electroplating solutions.
Gold Production
Gold compounds are also used as intermediate compounds in the production of gold. These compounds play a crucial role in transforming raw gold materials into refined gold products. Potassium dicyanoaurate and chloroauric acid, among others, are commonly employed in various chemical processes to facilitate the extraction, purification, and transformation of gold.
Medical Applications
Gold compounds exhibit unique properties that make them valuable in medical applications. Gold salts, such as gold sodium thiomalate and auranofin, have been used in the treatment of rheumatoid arthritis due to their anti-inflammatory effects. These compounds help reduce joint inflammation and alleviate symptoms associated with this chronic autoimmune disease.
“Gold compounds have shown promising results in managing rheumatoid arthritis, particularly in cases where conventional treatments have not provided sufficient relief. These compounds offer a potential alternative for patients seeking effective and tolerable treatment options.”
– Dr. Jane Mitchell, Rheumatologist
The medical applications of gold compounds are still being explored, and ongoing research continues to uncover potential therapeutic benefits in areas such as cancer treatment and diagnostic imaging.
Conclusion
After centuries of development, gold extraction and refining methods have become more refined and efficient, allowing for optimal recovery of this precious metal. From the ancient techniques of salt cementation and mercury amalgamation to modern methods such as gold cyanidation and froth flotation, each method has contributed significantly to the extraction and purification of gold from ores.
The refining processes, such as the Miller and Wohlwill processes, play a crucial role in ensuring that the gold obtained is of high purity, making it suitable for various industrial and commercial purposes. The continuous improvement of these techniques has made gold extraction a precise and sophisticated process.
The historical significance of gold extraction is profound. Gold has been intricately linked with human history, shaping economies, and technology throughout the ages. Its allure and scarcity have sparked rushes and exploration, pioneering advances in mining and metallurgy. From being used as a form of currency to its application in jewelry, electronics, and other industries, gold’s role in society cannot be overstated. It continues to be a highly sought-after commodity with enduring value and significance.
Source Links
- https://en.wikipedia.org/wiki/Gold_extraction
- https://www.britannica.com/technology/gold-processing/Refining
- https://www.mgsrefining.com/blog/gold-extraction-techniques/
Meet Ryan Conlon, the passionate owner and driving force behind Pan for Treasure.
With an unwavering love for the art of gold panning, Ryan has transformed his enthusiasm into a thriving community hub for fellow treasure seekers. [email protected]
A seasoned gold panning enthusiast, Ryan’s journey began with a simple pan and a dream, evolving into a deep appreciation for the history, geology, and thrill of uncovering precious metals.
