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How to Gold Refining, Emakmakina.com

How  to Gold Refining
How to Refine Gold Scrap
 
1- )The silver proportion in gold scrap is checked. It should be less than 8%. 
 
2- ) The thin parts are put into the titanium boiler. The thicker parts however should be melted first and put into water in order to obtain thinner parts. The parts are made thinner by pressing the in scrap cylinder.
 
3- ) 1 lt HNO3 (nitric acid) is calculated for 1000 gr Scrap. HCl (hydrochloric acid) is calculated 3 times as much as the total amount of nitric acid. 
 
4- ) First the whole amount of hydrochloric acid and water (same amount of nitric acid) are put into the boiler. Then nitric acid is added slowly, 1 lt every time, checking the reaction. When the reaction speed slows down, the boiler is put on a heater and the acid is boiled.
 
5- ) The acid vapor is observed. The mixture is boiled until the red vapor becomes white.
 
6- ) Acid is cooled thoroughly by adding a lot of water into the boiler. 
 
7- ) The remaining nitric acid in the boiler should be eliminated. Therefore H2NCONH2 (Urea) is added slowly into the boiler until there isn?t any red vapor coming out. 
 
8-) The boiler is opened, and the liquid is put on the filter with vacuum or using a pot. If the silver amount is high, and if some silver chloride has passed through the filter, the liquid is filtered through a cartridge filter.
 
9- ) The remaining on the filters is washed thoroughly, if possible with hot water, until the yellow color disappears.
 
10-) FeSO4 (iron sulphate) or NaSO4 (sodium sulphate) or Na2S2O5 (sodiummeta bisulphate) or N2H5OH (hydroxonium hydroxide) is added to the filtered gold liquid in order to precipitate gold.
 
11-)The liquid with precipitated gold is put onto a second filter and the gold is washed thoroughly with hot water on the filter. The acidity of the washing liquid is checked with the tip of the tongue (liquid is taken with a clean tip of finger and is tasted to check if there is still sourness left) and so the process is finished.
 
12-) In case there is still some gold left in the liquid in very small particulars, the liquid is once more filtered through a cartridge filter.
 
13-) The liquid is taken into another barrel. In case there is still some gold left in the liquid, some zinc powder, or zinc tablets, or aluminum tablets are put into the liquid. Thus the copper in the liquid precipitates and the last possible amount of the remaining gold is taken back.
 
14-) The remaining liquid is put into a barrel containing some iron material and the whole amount of copper is taken back. Thus the liquid is disposed in a completely secure way.
 
15-) Scrap containing silver more than 8% are melted adding copper or gold to have the desired proportion. If gold proportion has become less than 35%, gold is first reacted with only nitric acid and the excess amount of gold is melted in nitric acid. The remaining high grade gold is purified with aqua ragia. 
 
16-) Silver chloride is precipitated as white precipitate by adding salty water to nitric acid. It is washed thoroughly with hot water, as it had been done to the silver chloride which remained on the filter after aqua ragia was applied, and taken to another pot. Some water is added to dilute it, and it is thoroughly mixed by adding zinc powder. The excess zinc is removed from silver by adding hydrochloride acid. The remaining metallic powder is washed on the filter until there is no more acid left and then it is melted.

Reference : Gold Refining
Reference : How to refine gold scrap Gold Refining Forum