Understanding AR

[Moo]

Hi guys n girls

Im reviewing instructions on sams website about processing ceramics in AR, it mentions this.
"The vessel is now placed on a heat source such as hot plate or a mantle and the solution temperature is raised to 176-194 F (80-90 C)."
I do not have a tempreture probe and my hotplates lowest setting it still comes to a boil. Is a higher tempreture ok? If so and the soulution is constantly boiling how am I going to be able to tell when the reaction from adding the sodium nitrate had stopped?

 

[butcher]

What type of hotplate?

Electric you can add a light dimmer in series (make sure it can handle load.

I am assuming you have a gas burner you could add a heat sink in between your reaction vessel and the flame metal plate and a sand bath in large pot to sit your vessel in.

Or use something else to heat the solution like the electric burner from an automatic coffee maker, or some other appliance that you have better control of the temperature.

You do not want to boil your solutions and lose that gold you are working so hard to get.

 

[Moo]

Sorry butcher its an electric hotplate much like this one but with only 3 dials
http://www.breville.com.au/cooking/hot-plates/single-hot-plate.html
I suppose cheapest bet would be to fill a stainless pot with sand and add it to that? I can get a gas burner but with all my recent failures lately buying something else is not an option.
Great idea on the dimmer might go that route.

 

[kurt]

Is the "boiling" the result of an actual boiling temp caused by the hot plate - or - is it the result of the acid reacting with the metal being dissolved?

I am betting once your AR becomes "warm" on the hot plate & starts to "react" with the metal - the boiling is the reaction of the acid on the metal. --- Keep in mind that when acid reacts with metal it generates its own heat - enough heat to "self boil"

Thats why a sand bath is recomended - the sand acts as a heat sink there by giving you a lower more even heat compared to direct heat.

Reguardless of your heat source - you need to keep an eye on your reaction. the heat is ment to "warm" the acid enough to get the reaction going - once you have a good reaction going you can turn the heat down &/or off as the reaction will generate its own heat - then when the reaction slows down you can turn the heat back on or up to finish the reaction.

With less reactive metals (like gold & PGMs) it may take several times of turning the heat up & down to get the complete reaction job done.

Be sure to keep a watch glass on top of your reaction vessel durring the reaction process.

Kurt

 

[Moo]

thanks kurt, it definitly boils enough to beb of a bp result I placed a aluminum top from an old psu and let that heat for a while can hear it is boiling on the bottom now but only a few mediumish size bubbles come into play, kinda like its just about to simmer.

 

[maynman1751]

I placed a aluminum top

Aluminum and acid do not agree with each other! I would use glass or even plastic.

 

[kurt]

A "good" simmer reaction is what you want to see - lots of "tiny" bubbles but not "boiling"

Part of it is learning how your particular hot plate works

What are you using for a reaction vessel?

Kurt

 

[Moo]

Sorry for the confusion, I placed the sheet between the hotplate and flask. nothing aluminum on top

 

[Moo]

Kurt for the setup I am using nerdrages setup for hcl generation and having the trap with some washing soda in it and the recieving cylinder at the end of line with the same solution as well. the reac ion vessel however is a erlenmeyer not filtration with tubing through a hole stopper is covered in teflon

[youtube]http://www.youtube.com/watch?v=YGjd7xxTuZw[/youtube]

 

[Moo]

errrm guys n girls.... my completed AR solution tests positive for gold but its light green in colour

 

[maynman1751]

errrm guys n girls.... my completed AR solution tests positive for gold but its light green in colour

No matter! There is contaminants in solution. Just filter your solution, making sure to rinse any solid material well, and drop the gold with the precipitant of your choice. I would then do an incineration of the powders to remove any nitrates and oxidize contaminants. Then do the proper washing procedures with HCl, water and ammonia. The resulting gold powder will have to be re-refined anyhow. That's how I would do it. You may want to wait for others advice. John.

 

[Geo]

Moo, keep in mind that AR is considered a refining process and not a recovery process. even though it can be used for that, its always better to remove as much base metal as you can first by other means. theres certain instances that you will use AR as a recovery process (CPU's, chips). if you digest karat gold, your solution will almost always be some shade of green. the only time your solution will not be green is when you dissolve gold that has already had the base metal removed.

 

[Moo]

thanks Geo, I decanted and started fresh solution a few times so explains light shade of green... can AR be used for mixed jewellery scrap example. GP Bangles GF watch band GP necklace?

 

[Palladium]

thanks Geo, I decanted and started fresh solution a few times so explains light shade of green... can AR be used for mixed jewellery scrap example. GP Bangles GF watch band GP necklace?

No! those items are about 99% base metals. Those require pretreatments and different processes to refine.

 

[Moo]

So dissolve in lots of nitric and retrieve foils?

 

[Palladium]

It's all according to what you have. The G.F. you can use nitric. If it's plated you can look at using a stripping cell instead of nitric. Some people use nitric acid on plated but it can cause problems not to mention consume large amounts of acid. There again it all according to what you have.