How to Melt and Refine Scrap Gold

Written by joshua benjamin
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How to Melt and Refine Scrap Gold
Most scrap gold can be refined, but the process is a long and challenging one. (gold image by Marek Kosmal from Fotolia.com)

Refining gold sounds like it would be something that requires the use of a large smelting oven and heavy iron tools. In truth all you need to refine your scrap gold is a few heavy-gauge plastic buckets and a couple different kinds of concentrated acid. Granted, that doesn't sound too much safer than the oven, but if you are planning on melting and refining your scrap gold at home, this is the way to do it. The acids you will be working with are extremely corrosive and can do permanent damage if they come in contact with your skin. Utmost care must be taken when refining gold through this method.

Skill level:
Challenging

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Things you need

  • Two heavy-gauge plastic buckets
  • Plastic stir rod
  • Rubber gloves
  • Rubber apron
  • Safety goggles
  • Filter funnel
  • Hydrochloric acid
  • Nitric acid
  • Soda ash
  • Urea
  • Gold detector substance
  • Gold precipitant
  • Aqua ammonia
  • Water, tap and distilled
  • Measuring containers
  • Graphite crucible
  • Acetalyne torch
  • Alcohol

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Instructions

    Refining the Gold

  1. 1

    Weigh all the gold you are going to refine to determine how much acid you're going to need. For every ounce of gold, you will be adding 300ml to the bucket, so make sure the bucket is large enough to contain the gold and the acid.

  2. 2

    Dump the gold into one or more heavy-gauge plastic buckets, then put on your protective gear. Rubber gloves, apron and safety goggles are the absolute minimum protective apparel you should be wearing; the acid you are going to be using is quite strong.

  3. 3

    Take all your equipment to an open, outdoor area. The fumes from the acid you will be using are extremely corrosive---more so than the acid itself when added to metal---and will damage any metal objects they pass over. For this reason, it is vital that you perform the refining process outdoors where no possibility of damage exists.

  4. 4

    Measure out and add 30ml---2 tbsp---of nitric acid for every ounce of gold in the bucket(s). Once you have added the acid, allow it to sit for about 30 minutes. During this time, there may be a strong reaction from the acid mixed with the gold, which can result in lots of brown fumes coming up from the bucket. Do not worry, this is perfectly acceptable.

  5. 5

    Measure out and add 120ml of hydrochloric acid for every ounce of gold in the bucket(s). Once more, you may get a strong reaction as you add the acid. There is no way to predict the strength of the chemical reaction upon adding and mixing the acids. As the acids mix and begin to dissolve the gold, the mixture will become very hot. This is also normal.

  6. 6

    Stand back from the bucket and watch for heavy brown fumes to begin wafting up from the solution. Do not breathe in or pass anything through these fumes.

  7. 7

    Wait until the fumes have disappeared, then wait a minimum of one hour more for the mixture of acid to dissolve the gold. It is advised that you let the mixture sit overnight to ensure the gold is completely dissolved.

  8. 8

    Pour the acid-gold mixture through a filter funnel and into another clean heavy-gauge bucket. Be very sure that no particulates go into the new bucket, as these will cause imperfections and contaminants in the gold. At the end of the pouring, the acid should be a clear green. If the acid is murky or cloudy, refilter it until it is clear.

  9. 9

    Boil one quart of water, then add a pound of urea and mix thoroughly. Urea is a safe industrial chemical used to safely adjust the Ph balance of acid.

  10. 10

    Add the water-and-urea mixture to the acid. Do this slowly, as the acid will foam and bubble as the urea water is poured in. When the acid no longer reacts to the addition of the mixture, stop pouring. You have just neutralised the nitric acid in the acid mixture, but the hydrochloric acid is still active.

  11. 11

    Boil a quart of water and then add 28.4gr. of gold precipitant for every ounce of gold you are refining---this mixture may differ depending on the specific type of gold precipitant you are using. Always consult the instructions that come with the precipitant to determine the correct mixture.

  12. 12

    Pour the water-and-precipitant mixture very slowly into the acid. The acid will turn a muddy brown; do not worry, this is the gold that is being drawn out of the acid by the precipitant mixture.

  13. 13

    Wait for 30 minutes for the precipitant to draw all the gold out of the acid, then test the acid to make sure no gold is still dissolved. Do this by dipping the stir rod into the acid, then removing it and touching the end against a paper towel to create a damp spot. Place a drop of your gold detector substance on the wet spot. If there is still gold dissolved in the acid, the wet spot will turn a dark purple. If it turns this colour, wait another 15 minutes and perform the test again. Do this until the wet spot does not turn purple.

  14. 14

    Pour the acid into another container, filtering it as you go. Make sure you do not pour off any of the brownish mud that has sunk to the bottom of the bucket: this is the pure gold.

  15. 15

    Rinse the "mud" with tap water, adding water to the bucket and then stirring several times until it settles. Once the mud has settled, pour the water off into the container with the acid. Repeat this rinsing process four or five times.

  16. 16

    Pour soda ash into the acid-and-water mixture to neutralise the acid.

  17. 17

    Pour aqua ammonia into the bucket containing the "mud" and stir thoroughly. Aqua ammonia will clean and neutralise any acid still clinging to the gold and will also remove any leftover trace impurities.

  18. 18

    Rinse the mud one more time using distilled water, then pour off the water and the mud into a heatable container. Let the mud settle, then pour off the water. Place the container on a stove or hotplate and heat it up to dry out the mud, which will then turn into a dry powder.

    Making the "Mud" Back into Gold

  1. 1

    Wrap the "mud" in paper towels and soak the towels with alcohol, then place the whole package into a graphite crucible. You will be using the acetalyne torch to melt the gold, so make sure you are not wearing any loose clothing and are working in an area that does not contain flammable materials.

  2. 2

    Turn on the acetalyne torch and use the flame to heat the crucible from the sides and bottom so that the gas pressure from the torch does not blow away the powdered gold.

  3. 3

    Continue working the torch over the sides and bottom of the crucible until the gold melts. The melting point of gold is 1093 degrees Celsius, so this process may take a while.

  4. 4

    As the gold powder melts, it will take on the shiny appearance of metal again. Continue to apply heat until the gold has all melted. Once the gold has melted, remove the heat source and allow the gold to harden and cool. If you have followed all the steps correctly, your gold will now be about 99.995 per cent pure.

Tips and warnings

  • The fumes from the acid used in this process are EXTREMELY corrosive. Take extreme caution when working around these fumes.

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