Category Archives: Gold - Chemical Element

The Gold Production and Refining Process

With the state of the current economy, the world’s financial systems have come into the spotlight recently. As stocks have dropped and companies have become unstable, gold has also been a source of much attention as the price of gold has skyrocketed. People want to have a tangible indicator of wealth and nothing serves that purpose like gold.

Since earliest recorded history, gold has been the most highly prized precious metal. Its malleability, corrosion-resistance, and rarity, have made it a valuable commodity. But where does gold come from?

Gold is a chemical element found as nuggets or grains in veins or alluvial deposits in the earth. South Africa, the United States, and Australia are the world’s top three gold producing nations. Most gold in the U.S. is mined in open pit mines. Scientists use technology like satellite surveys and geochemistry to locate a gold ore deposit. The deposit is measured and the mine is carefully designed. Samples of the ore are then taken to measure the grade of the ore as well as its metallurgical properties.

The ore is then mined and separated into low grade ore and high grade ore. The low grade ore is dissolved and collected. The high grade ore is ground and pulverized into powder. That ore is then separated into three different processes, depending on the characteristics of the ore. Refractory ore containing carbon is roasted and burnt down to oxide ore. Oxide ore is sent to a leaching circuit where it is dissolved in cyanide. Sulfide refractory ore without carbon is oxidized in an autoclave to remove the gold from the minerals and then it is sent to a leaching circuit.

Once the leaching process is finished, the gold is collected out of the solution and onto activated carbon. It is then loaded into a vessel and the gold is chemically stripped from the carbon. Using chemical substitution called the electrolytic process, the gold is precipitated from the solution and it is finally in its pure form. This pure gold is then melted into bars called “dore” bars that contain up to 90% gold. These bars are then sent to precious metal refiners for further refining until the bars of gold are up to 99.9% pure gold.

There are two main methods for refining gold: the Wohlwill process and Miller process. After refining, these bars can then be kept and used in financial dealings or melted down and used in thousands of other applications like jewelry, watches, coins, dentistry, medicine, industry and many other applications.

Tarnished Gold, What Makes it Happen?

Many people that have an interest in gold jewelry and coins often will claim that tarnished gold doesn’t exist, however, that’s the furthest thing from the truth. Pure gold will not tarnish, but it is rare to find jewelry that contains this pure element. When pure gold is added to alloyed gold, such as 18 carat or higher, this will also lessen the risk of tarnishing, with the exception of a few conditions. Tarnishing is generally only seen in smaller carats, depending on the base metals and the elements that each one is exposed to. For example, if a 10 carat gold piece has a decent amount of copper in it, it can oxidize, creating a red or black tarnish. Silver also exposed to the elements when combined with gold produces black tarnish.

So what causes tarnished gold? When gold is mixed with these base metals, as it almost always is, exposure to environmental factors that are going to have an effect on the metals. Moisture, organic vapors, oxygen and sulphur compounds in the atmosphere, and even human sweat and oil from human touch can make gold tarnish if it is mixed with a high amount of base metals. Surprisingly, perfumes and deodorants with certain chemicals in them can also affect gold to a point that it will tarnish.

One of the most surprising offenders that cause gold to tarnish is certain food products. Pickles, fruit juices, onions, and other items with high acidity or sulphur compounds are likely to create a tarnishing affect on gold that is less than pure.

Sometimes the way a piece of jewelry or something made of gold is manufactured can have an effect on its susceptibility to tarnishing. Items that are cast by lost wax casting and other methods that leave a micro-porous surface can actually cause the jewelry to trap various acids, compounds, and other elements which will cause a form of local tarnishing wherever the foreign impurities gets trapped.

Jewelry can be kept from tarnishing by storing it in a pouch or bag in a dry atmosphere. You should also polish your jewelry regularly to remove contaminants and other inconsistencies. You can even have the item electroplated with pure 24 carat gold which will prevent tarnish for awhile, but will eventually wear through with use and age. Some countries such as India and the Middle Eastern countries do experience a blackening of higher carat gold pieces, and no one seems to know the cause. Generally, it is related to a different lifestyle and condition or environment, since the problem doesn’t occur elsewhere in the world, but no one knows for sure.

When it comes to coin collecting, many consider a bit of tarnishing, or toning as it is called in collecting circles, to be highly desirable. Gold coins rarely tarnish because of their purity, but some exceptional toned coins exist and this toning makes them all the more valuable. You may want to clean your jewelry to have it restored to its original shine, but all coin collectors know to never, ever clean the tarnish off their coins. In fact it is a general rule to not clean your coins in any way. Collectors desire the antique look of an old coin and want that look preserved. Cleaning highly collectible gold coins can ruin their value.

Just remember it is perfectly okay to clean tarnish off of your beautiful jewelry, but never clean the tone off of valuable old gold coins. Stick by these rules and keep your gold valuables of any kind in the best condition and highest valuable possible.