Why is there so much zinc?

[chemist]

Why is there so much zinc in my button?
I finally had my first gold button assayed and it turned out to be 0.8% zinc. All of the other contaminants were less than 0.05%. The button was processed from fingers and boards (some with solder) using Hoke's method (nitric to remove the base metals and then processing using AR and precipitation with SMB). What part of the process should have removed the zinc?

 

[lazersteve]

A good boil in HCl after the gold is precipitated should remove any zinc.

Steve

 

[nickvc]

This is why Harold V advises washing procedures that should always be followed.Gold from a contaminated source such as electronic scrap is notoriously hard to get to industry standards until you have the procedure down to a fine art,some of our members seem to have done that.A re refining of your button will improve the quality to acceptable standards but again use the washing technique as described by Harold.Dont get disheartened to produce your own button you have learnt a lot already its now just a bit of fine tuning in your processes you need now 8)

 

[machiavelli976]

normally to much zinc is comming from brass(golden pins from boards?) how does zinc passed the AR process? contamination along the steps maybe

 

[Harold_V]

normally to much zinc is comming from brass(golden pins from boards?) how does zinc passed the AR process? contamination along the steps maybe

Simple drag down. It is very important to chemically wash precipitated gold if purity is desired.

Harold

 

[chemist]

Yes, it is probably simple drag down that I didn't wash out. It was my first button and I know that my cleaning process for the powder was not up to the standards of the experts here. I am not discouraged. 98.8% on the first try isn't that bad.

 

[nickvc]

Yes, it is probably simple drag down that I didn't wash out. It was my first button and I know that my cleaning process for the powder was not up to the standards of the experts here. I am not discouraged. 98.8% on the first try isn't that bad.

Well the good news is if your following Harold V s methods which includes using a button to consume excess nitric it will be top notch Au 999 next time round 8) and im with you 98.8% is a good first effort,better than mine many years ago