How do I refine precious metal?
There are many kinds of materials that, when refined, yield pure gold, platinum or silver. Refining them yourself is pretty easy (though the first time you do anything, it's usually a little intimidating).
What kinds of materials can you refine yourself?
- Circuit boards and electronic scrap ("e-scrap")
- Jewelry, both regular jewelry and gold plated
- Gold nuggets, black sand and flour
- Catalytic converters, which contain platinum group metals (platinum, palladium, and rhodium)
- Jeweler's waste, including: grindings, bench sweeps, polishing sweeps, floor sweeps, etc.
- X-ray film, which contains silver
There are many reasons to refine these materials yourself, but the most common reasons are: a desire for independence, and to ensure that you're not cheated out of your gold by refining companies (a common complaint we hear from customers). Commonly, if you refine things such as circuit boards yourself, you get about 8-10 times as much gold as selling the material to a refining company.
Here's an overview of how to refine:
- With gold and platinum, there are two basic methods: working with saltwater and working with acid. Both work equally as well, but for a variety of reasons (safety, cost and the kind of material that you are refining) you may choose to use one method or the other. Each method has its advantages and its pitfalls.
- With silver, there are also two methods: chemical and electrolytic. Regardless of the method, you will have to use dilute nitric acid. Sorry, no way around that. However, if you choose to refine using the electrolytic way instead of purely chemically, then the nitric acid will be very dilute and the fumes will be relatively minor.
You can refine both gold and platinum group metals with this process. Silver is recoverable using this process but it will not refine the silver. After working with people who have refined using this method, we've carefully perfected this method through the Simplicity Refining System to make it simple for individuals and companies.
Refining gold with saltwater
The process is very simple. Hang your metal on a wire that is connected to a car battery charger and then immerse the metal in saltwater in the Simplicity unit. When you turn on the battery charger, an electric current runs through the metal causing it to dissolve at a rate of about 1 ounce per hour. When all the metal is dissolved, add a selective precipitant, called "Quadratic," to the solution. Only pure gold will turn back into solid metal. For all the other metals, the impurities will remain dissolved. The resulting gold is at least 99.95% pure gold.
The losses of gold left dissolved in the solution will be less than 4 parts of gold per million parts of saltwater.
Refining platinum group metals with saltwater
The platinum group metals (or PGM's) metals include platinum, palladium, rhodium, iridium, osmium and ruthenium. Platinum, palladium and rhodium are commonly used in industry and jewelry. However, the saltwater process will recover and refine all the platinum metals and will separate each platinum group metal from the other and providing a purity of at least 99.95+% pure (99.99% purity is common). At the present time, this is the only known method of refining mixed PGMs easily, the only known method of consistently achieving this degree of purity, and the only known method of refining PGMs with a minimum of hazard.
So how are platinum group metals refined in saltwater?
It's actually pretty simple. Melt your metal with a base metal, such as tin or ASR Alloy and pour into an ingot mold to make a bar. Hang it on a wire in the Simplicity Refining System and connect the other end of the wire to a battery charger. When you turn on the battery charger, the base metal in the ingot starts to dissolve and the platinum group metals are converted into platinum group chlorides. When the ingot finishes disintegrating (which takes about one hour per ounce), use water to rinse the platinum group chloride you made. Dissolve them in ammonia and add a selective precipitant for platinum group metals. Each platinum group metal will precipitant in a different time frame, with about 1/2 hour between the conclusion of each precipitation from the start of the next. By simply recovering the precipitated metal between each precipitation, you can achieve a purity of at least 99.95+ purity for each platinum group metal.
Refining gold with acid
The traditional method called "aqua regia" (Latin for "Royal Water"), dates back thousands of years. This method requires the use of both nitric and hydrochloric acids. Because of the nitric acid, the fumes produced by this process (nitric oxides) are very, very corrosive; they will rust high grade stainless steel with less than 1 second of exposure.
To correct this issue, we've developed a non-corrosive, pelletized substitute for nitric acid called SubZero. While there are still fumes when using SubZero, they are limited to ordinary muriatic acid fumes (muriatic acid can be obtained in most paint and hardware stores). Additionally, if you use the Shor SubZero Refining System, it is a sealed unit with an integrated scrubbing system to even eliminate the muriatic acid fumes. It also scrubs the fumes if you want to work with nitric acid based aqua regia.
Why work with acid when you can use saltwater instead?
For two reasons. First, some materials, like circuit boards and jeweler's polishing sweeps, are much more easily refined using the process. Secondly, you may want to refine out of doors, where there is plenty of ventilation. You can set up your own system, using the SubZero Starter Package and a few other things, such as plastic buckets, for less than $100.
How do I refine using aqua regia?
Whether using nitric acid based aqua regia or SubZero-based aqua regia, the process is very simple. The metal is first dissolved in the aqua regia. When all the metal is dissolved, urea (a harmless chemical: CO(NH2)2) is added to remove any free nitrogen in solution. With nitric-acid-based aqua regia, a large amount of urea is generally required. With SubZero based aqua regia, usually only a pinch is required. The purpose of the urea is to prevent gold from re-dissolving after it has been precipitated. If urea is not added and some free nitrogen remains dissolved in solution, some gold may be re-dissolved. At this point, the gold is selectively precipitated out of solution. There are a variety of precipitants that can be used: Quadratic, Storm Precipitant, sulfur dioxide gas, sodium bisulfite and ferrous sulfate are among the most common. Most of these precipitants produce very unpleasant fumes or odors and have other negative side effects. Some people prefer Quadratic Precipitant, since it's odorless, fumeless, produces large particles that are easily rinsed, and has an unlimited shelf life. Regardless of the precipitant used, the resultant gold is typically at least 99.95% pure. At this point, the solution is checked with gold detection liquid to ensure that there are no losses. The gold detection test is sensitive to around 4 parts of gold per million parts of solution--the maximum loss of metal left dissolved in solution.
Refining platinum in acid
When platinum group metals are mixed, it is very complicated and difficult to refine them using aqua regia. However, when they are not mixed, the aqua regia method is not hard. The procedure is very similar to refining gold in aqua regia, but the precipitant used will be different. There are several standard precipitants, different precipitants for different platinum group metals. Refining by this method is tricky and the purity of the resultant platinum group metal is often below normal standards. Refining of platinum metals is best done by the saltwater method.
The chemical process requires no equipment, just a few buckets. It's a very simple process but the fumes are quite corrosive. To refine silver by the acid method, first dissolve the silver in nitric acid. After the silver is dissolved, it can be precipitated out of solution by adding ordinary table salt. The salt precipitates silver chloride. The white silver chloride is then oxidized by adding sodium hydroxide (also called caustic soda or lye). This blackens it and turns it into silver oxide. The addition of sugar water turns the silver oxide into pure silver. A simpler process of refining silver is electrolytic. In this process, silver is hung in an electrolytic bag and immersed in a very dilute nitric acid solution. The silver is connected to a "rectifier," which supplies a highly-filtered DC current. The silver dissolves and the impurities fall into the electrolytic bag. Meanwhile, the pure silver plates out onto a cathode in other electrolytic bag in solution. This simple process can run 24 hours a day, 7 days a week, with minimal fumes. Electrolytic silver refining requires a starting purity of at least 92% for sterling silver.
How do these methods compare?
|Method||Speed||Materials typically refined||Fumes||Ease of use||Costs||Comments|
|Gold Refining with Nitric-acid-based Aqua Regia||1-2 hours per batch||e-scrap, jewelry, black sands, jewelers sweeps||very highly corrosive||simple||setup costs can be as low as $100, depending upon capacity and sophisitication about $1-$2 per ounce to operate||silver content can slow the process significantly|
|Gold Refining with SubZero-based Aqua Regia||1-2 hours per batch||e-scrap, jewelry, black sands, jewelers sweeps||corrosive||simple||setup costs can be as low as $100, depending upon capacity and sophisitication||silver content can slow the process significantly|
|Gold Refining with Saltwater||1 hour per ounce of scrap||jewelry, gold bars or ingots||very mildly corrosive (saltwater)||simple||about $600 to set up. About $1-$2 per ounce to operate||silver content above 6% can slow the process|
|Platinum Refining with Nitric-acid-based Aqua Regia||varies||catalytic converters, e-scrap, jewelry||very, very highly corrosive||very complicated||varies widely depending upon the metal content||the acid has to be boiled to dissolve the platinum|
|Platinum Refining with SubZero-based Aqua Regia||varies||catalytic converters, e-scrap, jewelry||very corrosive||very complicated||varies widely depending upon the metal content||the acid has to be boiled to dissolve the platinum|
|Platinum Refining with Saltwater||about 1-2 hours per ounce||jewelry, bars or ingots||very mildly corrosive||simple||About $600 to set up. About $5 per ounce to operate||when working with catalytic converters, the PGM's are usually recovered first by heating the converters first in a solution of lye and water (dissolving the ceramic)|
|Silver Refining in Nitric Acid||about 3-4 hours per batch||jewelry, silverware, x-ray film, etc.||very highly corrosive||simple||consumable costs about $1 per ounce||almost no setup costs if done outdoors|
|Silver Refining by Electrolytic Method||about 1 hour per ounce||jewelry, silverware, ingots (bars)||somewhat corrosive||very simple||about $500; consumable cost of a few dollars per day||requires a starting purity of at least 93% (sterling silver)|
When in doubt, let us help
If you follow our instructions, typically you will get a purity of at least 99.95% with no loss.
Shor can help you refine all these materials, providing you with full, no charge, online instructions as well as free, unlimited tech support. We ask that you purchase the supplies and equipment from us, but we don't require that. Even if you purchase your supplies and equipment elsewhere, we will still provide full tech support at no charge. It's the way we help people and the way we've helped amateur and professional refiners for nearly 100 years.