White salt dropping out of poor mans AR as it cools

Gold Refining Forum

Help Support Gold Refining Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

raa

Member
Joined
Jan 30, 2017
Messages
14
Location
South-West England
So I am attempting my second ever refining session. My first involved gold fingers in Copper Chloride and produced the gold button in my avatar photo thanks to some guidance from the forum.

Now I am tackling 400g of gold plated material from motherboards, HDDs and wire wrap LAN sockets. I made up a sulphuric cell which worked OK (will do a write up later) and I am now working on refining the black sediment from the cell.

For whatever reason I was having trouble getting this material to dissolve using HCL/Bleach so I am trying poor mans AR for the first time using food grade Potassium Nitrate crystals.

My HCl/bleach process and subsequent attempts to drop with SMB got completely messed up and I ended up transferring everything to a bucket with some copper sheet. After a week or so I collected up the cemented sediment for another try, this time with the KNO3.

Before dissolving this material I took some initial steps of hot washes in HCL and distilled water to remove most of the base metals.

I made the classic rookie error of over adding the nitrate salt. I made this mistake because there was some insoluble non-metallic particles which I thought was undissolved Au :oops: !

Anyway, once I realised my mistake I started evaporating down the solution according to the denoxing method described by Hoke, I also decided to sacrifice my first (and only) gold button for the cause and dropped it in to help with using up the excess nitric.

Here's the mystery: because I don't own an electric hotplate, I'm using a gas stove along with a sand bath. To avoid having to stand over the process I was heating the solution to just below boiling then turning off the gas and leaving it unattended. The sand holds lots of heat so the process continues for a good 25 minutes. I had to repeat this several times over 2 days.

Anyway sometimes I would end up leaving it for long enough to cool down completely and I noticed there were plenty of white crystals all over the bottom of the beaker . The crystals would go back into solution once it was re-heated and stirred.

I initially thought it was simply the KNO3 however on the last time I heated it all back up to redissolve the white crystals, my gold button was no longer reacting so I guess it might not have been KNO3. Could the white salt have been Potassium Chloride?

The button in my avatar was 1.5g and after being in the poor mans AR for several hours it is now 0.4g and no longer looks pretty!

How does over a gram of gold compare to what is normally required to denox AR? I am thinking I must have added a serious excess of KNO3.

Suffice to say i'll be a lot more careful with the Nitrate additions in future...
 
raa said:
I initially thought it was simply the KNO3 however on the last time I heated it all back up to redissolve the white crystals, my gold button was no longer reacting so I guess it might not have been KNO3. Could the white salt have been Potassium Chloride?
Most likely.

How does over a gram of gold compare to what is normally required to denox AR? I am thinking I must have added a serious excess of KNO3.
It depend on how much excess nitrate was added. If you only dissolved 1 gram of your button, you didn't overshoot all that terribly.

In the future, when you run into bits that don't want to dissolve, first decant the pregnant solution, then add a bit of fresh acid to the undissolved bits. The fresh acid will be stronger. Then test with stannous to see if any more gold dissolved.

Dave
 
Unfortunately almost everything has a white salt, so it can be very difficult to pinpoint what exactly you have.
The solubility of Lead Chloride varies dramatically with temperature, so that is a possibility.
 
Back
Top