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Hydrogen peroxide (H2O2) is an oxidizer used in different instances of refining. It is a colorless liquid and is usually sold as a weakly acidic water solution (pH 4).
Measure of strength
The strength of hydrogen peroxide is usually measured in percent. Common strength are 3%, 6%, 15% or 35%. Stronger concentrations are available to industrial customers but not needed for refining purposes.
Sometimes the strength is measured in "volume". This is based on how big volume of oxygen is released when the hydrogen peroxide decomposes. A 1% concentration releases 3.3 times the volume of oxygen so a 3% solution is the same as 10-volume strength.
Oxidizer in leaches
Copper chloride leach
In copper chloride leach there is a need to add an oxidizer. Usually that is done by bubbling air through the solution but sometimes people use hydrogen peroxide instead. It is commonly used to start a leach if there isn't any old copper chloride around.
The risk of using hydrogen peroxide is that it will dissolve some gold too. Later on the gold will cement onto base metals as a fine black powder.
As a reducer
Hydrogen peroxide can also work as a reducer in basic solutions.
Hydrogen peroxide can be distilled to increase strength but it has it's dangers. Highly concentrated hydrogen peroxide can explode. High strength hydrogen peroxide is used in rocket engines.
Silver will break down hydrogen peroxide into water and oxygen while releasing large amounts of heat. That is the basis of many liquid propellant rockets.
A safe way to increase the concentration of hydrogen peroxide is to partially freeze it. The lower in temperature the more concentrated is the part that doesn't freeze.
- GRF : Acid peroxide thread
- GRF : Silver oxide reduction with hydrogen peroxide
- Wikipedia : Hydrogen peroxide
- Sciencemadness : Freezing H2O2 to concentrate it
- Akzo Nobel : AkzoNobel hydrogen peroxide product information manual December 2015 (pdf)