Instructions for Refining Platinum with Aqua Regia
These instructions are for refining of platinum only, not for refining multiple platinum group metals. Refining of multiple PGM’s by aqua regia is very complicated. Refining of these metals is easily accomplished by using the Shor Simplicity Refining System.
Equipment and supplies required
- Hot plate
- 3 Pyrex jars or beakers suitable for stovetop heating (do not use oven Pyrex, these will break)
- Subzero powder
- Hydrochloric acid or muriatic acid
- Precious Metal Detection Liquid
- Paper towels
- Glass stirring rod
- Rubber apron, face protection and rubber gloves
- Ammonium chloride
- Baking soda (sodium bicarbonate)
- Quadratic Gold Precipitant (only needed if you have gold mixed with your platinum)
- Rolling mill (optional)
- Platinum melting torch (optional)
Preparation of the Metal
- If your metal is in the form of an ingot or some similarly thick form, it should be rolled out to form a strip or strips that are as thin as possible. Alternatively, you can melt it and pour into cold water to make “shot”. Small open-up granules are best.
- If your metal is in the form of grindings, then no preparation is necessary.
- If your metal is in the form of polishing sweeps, then burn the sweeps first. For details on the burning procedure, call Shor tech support.
- Put your metal into one or more glass or plastic containers. The required capacity of the containers will vary depending upon how much metal you want to refine. For every ounce of scrap metal that you are going to refine, you will need a capacity of at least 300 milliliters. For instance, if you are refining 10 ounces, you need a container with a capacity of at least 3,000 milliliters (that’s 3 liter or 3 quart). Having a little extra room is always a good idea, so we recommend a 4 quart or larger container. To the container, add 1 ounce (2 tablespoons) of SubZero for every ounce of metal in the container. So, if you have 10 ounces of metal in the container, add 10 ounces of SubZero (or 20 tablespoons).
- Now add 120 ml of hydrochloric or muriatic acid for every ounce of metal in the container. So, if you have 10 ounces of metal in the container, add 1200 ml of hydrochloric. The solution will get warm or hot as the acid reacts with the metal, dissolving it. The fumes are corrosive so you should either refine the material outdoors or you should be using a scrubber to remove the fumes.
- Heat your solution to between 200º-212º F. It generally takes about 1-3 hours for the metal to dissolve. The time required will vary, primarily, as a result of the thickness of the metal. Virtually all the base metals will dissolve. However, no silver will dissolve.
- Once all the metals have dissolved, decant the acid into another container of similar or larger size, leaving behind all solids.
- The acid will be an emerald green color if you have copper dissolved in solution. It should be clear (not murky or cloudy). If the acid is murky, it may contain particles that will contaminate your purified gold. If you have a murky solution (or, for any other reason, think there are particles floating in your solution), then let the acid sit for a while. The particles will settle to the bottom and you and decant the solution again into another container.
- Add a pinch of urea to your acid. It is unlikely to reaction. However, if it does reaction (if does, it will fizz), then wait till the fizzing stops and add some more, until it no longer fizzes. The purpose of the urea is to kill any free nitrogen ions in the solution. If you have free nitrogen ions, precious metal can re-dissolve after you have precipitated it.
- If you have gold dissolved in solution, you will want to retrieve that first. Add 1 ounce of Quadratic Precipitant for every ounce of dissolved metal (not just the gold content). If the solution is still hot, then the gold will precipitate within an hour or less. If the solution is room temperature, precipitation may take a day or longer.
- Test the solution with Precious Metal Test Liquid to ensure that all the gold is out of solution.
- When the test shows negative, decant the solution, leaving behind the pure gold. And now it’s time to drop the platinum.
- The selective precipitant you will use for the platinum is ammonium chloride. Add 1 ounce of ammonium chloride for every ounce of SubZero that you used. So, for example, if you used 10 ounces of SubZero (to dissolve 10 ounces of metal), then add 10 ounces of ammonium chloride. Put the solution aside. The platinum will complete its precipitation in about 1-3 hours.
- Test for platinum using the same detection liquid you used to test for gold.
- Decant the solution and recover the platinum salts.
- Rinse the platinum salts with water, being careful not to pour platinum off with the rinse water.
- Neutralize the acid with baking soda and then dispose of it.
- At this point, the platinum will be a compound- platinum ammonium chloride. To drive off the ammonium chloride, heat the compound in a Pyrex, or similar container, under a low flame on a stove or hot plate. Make sure the container is made for heating before you use it. This will quickly evaporate the ammonium chloride, leaving pure platinum.
Before you pour off the waste acid, you want to be absolutely sure that no gold or platinum remains dissolved in the solution. The test is easy, fast, reliable and very sensitive. It will detect as little as 4 parts of gold dissolved in 1 million parts of solution. To test, just take a drop or two of solution and put it on a paper towel. Put a drop or two of Gold Detection Liquid on top of the wet spot created by the solution drops. If the solution changes to purple, black or brown, then there is still gold dissolved in solution and you should give the precipitant more time to work. You can test as often as you like but be sure to clean the pipette, eyedropper or other implement you use after each test.