There are a few different methods that can be used for separating the copper from zinc in brass. I will be specifically covering the muriatic acid method. I will not be covering any safety measures because if you choose to work with these materials, you need to have the proper knowledge and safety procedures in place before starting. A good place to start is an MSDS for each chemical involved and also basic lab safety procedures. Disclaimer: I hold no liability for anything resulting from your use of the information or lack of information contained within this instructable. You have been warned!
1. Hydrochloric Acid (C.A.S # : 7647-01-0)
2. Water (yes it is considered a chemical) (C.A.S#: 7732-18-5 IUPAC Name: Oxidane)
3. Copper (C.A.S#: 7440-50-8)
4. Zinc (C.A.S#: 7440-66-6)
5. Graphite (C.A.S#: 7440-44-0)
Intermediate Chemicals (produced from the reactions):
1. Copper(I) Chloride (C.A.S#: 7758-89-6)
2. Copper (II) Chloride (C.A.S#: 7447-39-4)
3. Zinc Chloride (C.A.S#: 7646-85-7)
Possible Side Products (from impurities or otherwise):
1. Hydrogen (C.A.S#: 1333-74-0)
2. Chlorine (C.A.S#: 7782-50-5)
3. Oxygen (C.A.S#: 7782-44-7)
4. Nickel(II) Chloride (C.A.S#: 7718-54-9)
5. Ferric Chloride (C.A.S#: 7705-08-0)
6. Ferrous Chloride (C.A.S#: 7758-94-3)
7. Stannous Chloride (C.A.S#: 7772-99-8)
8. Stannic Chloride (C.A.S#: 7646-78-8)
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Step 1: Gather Your Materials
1. Distilled Water
2. Muriatic Acid (Hydrochloric Acid)(31.45%)
3. Carbon Electrode (Graphite)
5. Filter papers
6. A Funnel
7. Power Source (‘D’ size battery or anything between 0.4-1.7 volts that can handle a higher amperage)
8. Volt Meter (always handy but not necessary)
9. Random Bits of Wire
10. Containers for filtering and holding liquids
11. Small Clamps
Step 2: Mix the Acid
Mix the water and acid in a ratio of 1:1 by volume in a well ventilated area. This step is just to ensure that that the solution doesn’t fume. Straight hydrochloric acid can be used but there will be significant fuming and HCl fumes corrode just about every metal on the face of the planet except for noble metals such as platinum and gold; and carbon.
Step 3: Hook Everything Up
Attach the brass electrode to the positive (+) and the carbon to the negative (-) and dip them into the solution.
Step 4: Go Have Some Coffee
This can be quite a lengthy process. I did a total of 5 runs that totaled 20hrs or 4hrs each.
The working voltage should stay between 0.5 and 1.7 volts if it gets much higher than this, you'll likely just plate out the brass that you started with.
Selective electrodeposition (not quite sure what it's actually called but the name fits) is a lot like fractional distillation where the voltage determines the metal that plates out. I did an experiment a few years ago where I mixed chlorides of copper, nickel, and iron and tried to separate them and I found that the copper comes out at around 0.45-0.55 volts, the nickel at 0.65-0.7 volts and the iron came out at above 0.75. It is important that the solution is depleted of the lower voltage metal before moving to the next one or it will be an alloy that plates out just as raising the temperature in a fractional distillation run before the solution is depleted of a lower boiling point solvent will result in a mixture of the solvents instead of the pure product.
It is important to wash the copper throughly, immediately after removing it from the solution since the acid will not only catalyze the oxidation of the copper, but it will also eat through the filter paper given enough time as shown in the images.
It is suggested to use graphite for the negative electrode considering that the copper doesn't really stick to it and just falls off to the bottom of the container.
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