Whats the use of Hydrazine Hydrate in GOLD FACTORY?

Method to precipitate the Gold with Hydrazine Hydrate : 
Recovere all gold from working area then dissolve all into Aqua Regia Solution. Leave this solution for 10 -12 hrs to complete precipitation, then Filter it out. And addition of Hydrazine hydrate 64 or 85% (liquid)  works well  to precipitate gold from  acid gold plating baths which contain HAuCl4 solution.
 

After addition of Hydrazine Hydrate you can practically see big brown spongy ball like gold getting precipitated & once all the gold in the solution has precipitated the solution at the top has lot of white foam, which indicates the end of precipitation. Finally neutralise the solution with 25% urea solution.
This will give you the necessary result in recovering pure gold.
 

We let the solution stand overnight to settle down & recover gold from it by washing it with water.

Hydrazine Hydrate also used in GOLD purifiaction factory.  Remember Hydrazine Hydrate does not work well with alkaline solution.
NOTE : You use hydrazine hydrate for gold precipitation. Don't add urea in gold chloride solution.
You can also dilute hydrazine hydrate with five parts of water, that is 1:5. Then you add it in your gold chloride solution. You can get exact value by checking your pH level of gold chloride.
Hydrazine Hydrate Reaction can be easily understand by this reaction :::

PtCl4+N2H4=Pt+N2+4HCl
4AuCl3+3N2H4=4Au+3N2+12HCl
4AgNO3+N2H4=4Ag+N2+4HNO3.