# Sel-Rex Information



## Onthespot (Oct 31, 2012)

I am looking for information on some old (NOS) Sel-Rex products that were in a box from an estate sale. It appears from my search that the Sel-Rex Company is no longer in business. Two of the bottles are labeled Pyr-AU-bond with a gold content of 1 oz troy, one of the bottle is labeled Autronex and gold content of 1 oz troy and two of the bottles are labeled pyr au bond op. Any information would be appreiciated on what I have and what I can do with it. Thanks in advance.


----------



## etack (Oct 31, 2012)

Sel-Rex products is sold by this company. http://www.enthone.com/

http://www.enthone.com/en/Industries/Jewelry/Technology_Selector/Products/SEL-REX_AU.aspx

Eric


----------



## goldsilverpro (Oct 31, 2012)

At one point, I was senior chemist for the Sel-Rex West Coast operation.

Unless the bottles have been opened and gold salts have been added to them for some strange reason (unlikely), I'm positive the 2 "B" units on the left contain only the non-gold chemicals needed to replenish the bath - no gold. They likely contain potassium citrate, citric acid, potassium phosphate, or combinations of these. The other 3 on the right, when new and sealed (2 of the 3 appear to be sealed), each contained one troy oz of gold as potassium gold cyanide (PGC - 68.3% gold) plus small additions of other chemicals. For example, the Autronex bottle possibly contains some cobalt or nickel, which would give the salts a pink or green color.

To treat the 3 bottles on the right (assuming there is a total of 3 oz of gold):
(1) Dissolve all 3 in a total of about 1/2 - 3/4 gallon of warm water. In this case, it is best to do this in a 4 liter beaker since you will be able to better observe the zinc precipitation reaction.
(2) While stirring, add (and sir to dissolve) only enough sodium hydroxide to adjust the pH of the solution to about 12. Try not to add an excess. Add in increments and keep checking the pH. It doesn't take much.
(3) Add about 60 grams of sodium or potassium cyanide. Stir until dissolved.
(4) With constant stirring, add 325 mesh zinc dust to precipitate the gold as a powder. If the zinc dust has clumped, break up the clumps before adding. It will usually take about 1 to 1.5 times as much zinc, weight wise, as there is gold. Add the zinc in increments. At first, you will see a brown powder forming, which is the gold. At some point, you will see the powder start to turn a gray color. When the powder is a full gray color, with no visible brown, stop adding zinc. The gray color tells you that you have excess zinc and that all of the gold is precipitated.
(5) Filter the solution and rinse the gold several times with hot water. You must rinse well enough to remove the cyanide solution. The next step uses acid and, if any cyanide remains, a very poisonous gas (HCN) will be emitted.
(6) Transfer the filter paper and the gold/zinc powder to a container. I usually use a plastic bucket but a large 4 liter beaker will work well.
(7) Place the container under a fume hood, mainly in case all of the cyanide hasn't been rinsed out. Also, toxic NOx fumes will be generated.
(8) Add enough water to cover the powder and paper.
(9) Add a few ml of nitric acid. It will immediately react vigorously with the zinc and will produce toxic red-brown NOx fumes. Allow the reaction to visually die down, give it a gentle stir and add a few more ml of nitric. Repeat until an addition of nitric produces no reaction. At this point, most all of the excess zinc has been dissolved and you're left with the brown gold powder. To make sure, though, add about 25 ml of extra nitric, cover, and heat to a little below below the boiling point for about 20 minutes.
(10) Allow to cool a bit and add enough water to triple the volume.
(11) Filter and rinse very well. At this point, you could dry and melt the gold powder. However, if you want it purer, dissolve in aqua regia, using the methods outlined on the forum, and precipitate the gold with SMB.

This is about the only way that works completely and efficiently. After adding the hydroxide and cyanide, you could plate the gold out but, other problems are created and it is very difficult to get all of the gold in this manner. Whatever you do, never add acid to the gold salts, whether they are as a solid or in solution. Poisonous HCN will be emitted. Also, the PGC salts will convert to the yellow salt, gold cyanide (AuCN), which is not soluble in acids. You could rinse well and redissolve them in cyanide solution but you would then be back where you started from, with a gold cyanide solution.


----------



## ericrm (Nov 1, 2012)

that was very interesting, how would someone discard the spend cyanide solution??


----------



## rshartjr (Nov 1, 2012)

ericrm said:


> that was very interesting, how would someone discard the spend cyanide solution??



↑↑ What he said... ↑↑

Scott


----------



## Onthespot (Nov 1, 2012)

Thanks for the information goldsilverpro. That process is beyond my expertise and equipment. Should I now try and find someone that is in the gold plating business that could possibly use it? (if I can find one) I am not a big fan of anything that has the skull and crossbones on the label. I would imagine that is because of the cyanide content you mentioned. Thanks again


----------



## goldsilverpro (Nov 1, 2012)

ericrm said:


> that was very interesting, how would someone discard the spend cyanide solution??



Read 4metals' posts on this thread.
http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=5404


----------

