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How Are Precious Metals Refined?

Updated on June 5, 2017

Fine Gold Casting Grains

Fine Gold Casting Grains available for purchase.  Wouldn't you like to own some of these?  I checked the JM Bullion website, but did not see them listed for sale.
Fine Gold Casting Grains available for purchase. Wouldn't you like to own some of these? I checked the JM Bullion website, but did not see them listed for sale. | Source

About Precious Metals

What exactly are "Precious Metals", and why are they so important to us?

These metallic elements exist on our planet naturally. They are considered valuable to us as they have several redeeming properties. The most obvious is their lustre, or the way the sunlight or artificial light reflects off the surface of the metal. Their lustre makes them very shiny and sparkly to the eye. They are considered precious as these metals are rare in comparison to other naturally occurring metal elements, like iron. Our planet is full of iron. In fact, our planet's core is made up of both solid and liquid iron, nickel, and sulfur.

Our history shows, mostly through the discoveries of ancient coinage, that we humans have almost always placed a value on these metals. The ancient civilizations that produced coinage did so to use in trade for commodities. The coinage metals that were used in ancient times were a combination of metals cast together with an anvil and hammer. The earliest coins were made of "electrum" which is a combination of gold ,silver, and copper. The early Romans also used bronze. It is important to remember that coins are normally made of an alloy, or combination of metallic elements to give the coin more durability.

The metals we consider rare and precious are palladium, platinum, gold and silver. Gold and silver are most popular with coin, jewelry, and art manufacturing. They also have a very sought after property of conduction. They are able to conduct heat and electricity very well. Due to this
added benefit, these metals are also used heavily in industrial manufacturing. Think about the film used in everyday X-Rays. That film contains silver bromide, Other types of film contains this too. It is the element used to capture light for photography.

In addition to coin currency, jewelry, art, and industry, another popular use for precious metals is investments. Since the monetary value of these rare precious metals fluctuate by demand, institutional and individual investors will purchase forms of these metals when the price is low and sell them when the price is high. The metals are normally minted in various shapes, but they will be as pure as possible to maintain a high retail value. The most common forms found on the market are bullion bars and rounds, and round currency coins.

The Touch Stone Method

"The touch stone is a smooth fine grained, slightly abrasive black stone, usually quartz or jasper. It was used as the first method of assaying gold and was used at least as early as 500 BC."
"The touch stone is a smooth fine grained, slightly abrasive black stone, usually quartz or jasper. It was used as the first method of assaying gold and was used at least as early as 500 BC." | Source

The Refining Processes

The term Refining as described by wikipedia is a process that:

"consists of purifying an impure material, in this case a metal. It is to be distinguished from other processes such as smelting and calcining in that those two involve a chemical change to the raw material, whereas in refining, the final material is usually identical chemically to the original one, only it is purer."

So the refining of precious metals does NOT involve processes where chemical changes are a result to the original metal element.

Here are some examples of processes used:

1. Extracting Silver from Lead: Cupellation - this process involved melting the lead in a bone ash and blowing air across the surface. This separated the lead form the silver.

2. Purifying Copper: Copper Smelting involved the repeated process of melting down the copper to remove, or skim off, impurities.

3. Precious Metals: Hydrometallurgy: leaching, concentration and purification, precipitation, and electrolysis.

  1. Leaching is a method involving the use of an aqueous solution with various ph balance, temperature manipulation, and oxidation to extract the precious metal from the sample.
  2. Concentration and Purification is the next step used after leaching. The precious metal ions are normally concentrated and prepared for removal. Other, non-precious metal ions, are removed during this process to help facilitate purification of the resulting element.
  3. Precipitation is a method involving the chemical precipitation, or evaporation, caused by manipulating the temperature of the metallic element.
  4. Electrolysis is a method used involving a direct electric current sent through the sample metallic element to separate the elements.

These are described in more detail in the following section and training videos.

If you are interested in testing your precious metals for their purity at home, here is a link to Precious Metal Testing Kits on ebay.

The International Precious Metals Institute

The IPMI logo taken from their website.
The IPMI logo taken from their website. | Source

The International Precious Metals Institute

The International Precious Metals Institute (IPMI) is the worlds largest association of precious metal industry related groups. These groups include the public and private sector financial investors and merchants, and the material side producers, refiners, and manufacturers.

IPMI is a non-profit organization that seeks to be the primary resource for all things related to precious metals.

Their goals are to provide their members with technical, economic, environmental, and educational services. As part of their focus on the environment, they promote more environmentally and efficient uses for precious metals.

As part of their educational goal, they have provided the public several YouTube videos for education on the process to refine precious metals.

One of those videos training sessions provides more detail on the precious metal refining process and methods. This is a 4 - part series as described in the following:
First -
How to Refine Precious Metals - Hydrometallurgy: Part 1- Leaching
Second -
How to Refine Precious Metals- Hydrometallurgy: Part 2 Concentration and Purification
Third -
How to Refine Precious Metals - Precipitation: Hydrometallurgy Part 3
Fourth -
How to Refine Precious Metals - Electrolysis: Hydrometallurgy Part 4

Here is the link to the videos and other educational training = https://www.ipmi.org/

Also note: the IPMI training video on the Mining for Precious Metals explained...is located at the end of this article.

Collector or Consumer Precious Metal Poll

Do You Own Any Precious Metal Products (Coins, Bullion, Jewelry)?

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Examples of Metal Refineries in the United States

Refinery
Refinery
Refinery
Arch Enterprises
HI-Tech Precious Metals & Refinery
NTR Metals
David H. Fell & Company
Johnson Matthey Refining
Precious Metals Reclaiming
Doral Refining Corporation
Metal Refinery
Sims Recycling
Geib refining Corp
Mid States Recyling
Specialty Metals
General Refinery
Midwest Refineries
United Precious Metal Refining
Great American Mint & Refinery
Norman's Precious Metal Refiners
US Gold Refinery
This table provides several examples of Metal Refineries in the United States. This list is by far not a complete compilation, but it does provide you with valid resources.

Mining for Precious Metals Explained

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