In decision precipitates in aqua regia solution that has been contained gold metal content is required several stages.And eventually precipitated from these precipitates can be dissolved to be made in a metallic gold.
Some stages are used in the decision are as follows :
- To neutralize the residual HNO, add urea [CO (NH2) 2] to the Aqua Regia which has been filtered.
it will get a reaction :
6 HNO3 + 5CO(NH2 ) 2 = 8N2 + 5CO2 + 13H2O
The trick Urea enter little by little until the reaction finished white bubbles. From this reaction would make nitric acid to neutral pH conditions and changed from 0.1 to pH 1.0.
- After the reaction is complete then Enter Sodium Bisulphite and observe the reaction.In theory, every single gram of gold requires 1.89 grams of Sodium Bisulphite. However, it should be added more, about 1.5 times longer.
Then the reaction is :
2HAuCl 4 + 2NaHSO3 = 2Au + 4HCl + Na2 SO4 + SO2
- Wait about 30 minutes, until no precipitate (sludge) that appear brownish-black color. And then dispose of the liquid solution slowly to the remaining precipitate only way destilled filtered and then rinsed with water. Sodium Bisulfide If not then there are several alternative reagents that can be used as a substitute such as Sodium Sodium Bisulphite Metabisulfide (SMB), oxalic acid, sulfur, and Sulphur Dioxide or Copperas (Ferrous Sulphate)
- Then pour it gently - the land of ammonia solution (30 ml Aqua ammonia has been dissolved into 100 ml mineral water) to precipitate until the pH reached 8.It will get a Gold Fulminating sediment.Remember fulminant sediment is very dangerous, not to dry because it has the nature of the High Explosive.
- Wash the precipitate to remove excess ammonia. Wash several times until the pH reaches close to 7
- Then rinse the sediment precipitates made in one and then in the process of melting metal to form gold.
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READ MORE >>> Gold Precipitation Methods
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