Non-Chemical AR filtering question

[Anonymous]

I'm new here. So I'm still a bit confused about the whole aqua regia refining process.

This is my understanding of the method so far. Pour aqua regia into a pyrex container with gold shots inside. Wait for the fumes to settle down. Filter for precipitate that might contain silver. Neutralize pH with urea, add SMB and allow mud to settle. FIlter and keep the filtrated solution and refiltrate a couple of times while washing the gold particles with distilled water and/or methanol. Dry and melt.

My questions are: I have read several methods in this site and some suggest to filter AFTER urea is added to neutralize the solution. If so, wouldn't the silver precipitate remain in the solution? Or will it get dissolved? Also, if I were to filter BEFORE urea is added what kind of filter paper do I have to use? Would standard Buchner filter paper suffice or do I have to buy some special harsh acid resistant filter paper? If so, where can I buy it?

 

[4metals]

You should filter before the urea is added. Generally paper used for filtration in a buchner funnel will work. The acid is not neutralized with the urea, it is used to eliminate the excess nitric acid. Add the urea slowly and with caution it is easy to add too much. Adding a few prills at a time in the beginning would be best until you get a feel for how much to use. When the urea prills begin to float on the acid you've added enough.