Reminder: Always add acid slowly

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RMcFadden94

New member
Joined
Jun 13, 2017
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2
Hey all,
So I have started refining sterling Silver recently as a new hobby/business venture. It has been going swell, but I got a little cocky the other day.

I learned the hard way and was reminded that surface area means everything when dissolving silver with nitric acid.

400g of Sterling silver ware vs 400g of Sterling silver jewelry needs to be handled entirely differently.

I was doing the jewelry outside during a sunny dayand had my standard Amy of nitric ready to go. Well because of the extra warmth from the sun and all the nooks and crannies of the jewelry the reaction fired up ALOT faster then the prior evening's silverware and I had a boil over. BIG TIME. Luckily I had gloves, but forgot the capture dish. I spent my afternoon trying to remove nitric acid/silver nitrate solution from my work table. Even with gloves it got EVERYWHERE. I had to answer a lot of questions from the kids on my son's tball team why my hands were so "dirty".

Needless to say I relearned my lesson. SLOW addition of acid in increments always is the best approach.

I hope this helps any readers of this thread.

Happy Refining!

~Greg
 
Greg

Yes - sometimes we learn our lessons the hard way - but I have to somewhat disagree with the - "Always add acid slowly" (though as a *general rule* that is good advice)

The fact is that *sometimes" adding all the acid at once can be to your advantage - but - one important factor when doing so (especially if the metal you are dissolving has a LOT of surface area) is to *be sure* to leave *plenty* of head room in the vessel (beaker etc.) to allow for excessive foaming

For one thing - in the case of nitric - you can dissolve more metal - with less acid - if you add ALL the acid at once --- especially if the metal has a lot of surface area

Example - normally - it takes *about* 1 ml of 67 - 70% nitric along with 1 ml of distilled water to dissolve 1 gram of silver (pure) --- BUT - you can actually dissolve MORE then 1 gram silver per 1 ml nitric - I do it *all the time* when I make my electrolyte for my silver cell - for which I dissolve silver crystals from the cell - which means there is a LOT of surface area so the reaction gets VERY violent with LOTS of foaming at the peak of the reaction

When I make my electrolyte - I dissolve 500 grams silver crystals - BUT - only need to use 300 ml of 67% nitric (so *about* 200 ml less nitric then is normally figured)

There are a couple tricks to doing this (dissolve *more* metal with *less* acid)

1) you MUST leave *plenty* of head room in the vessel to allow for excessive foaming at the peak of the reaction

2) though you use less acid - you MUST use more water

3) the reaction MUST take place in a *closed* vessel

1) I start by putting the 500 grams silver crystals in a 4000 ml beaker - that means there is 3/4 head room in the vessel for foaming --- & you need it because at the peak of the reaction it will foam up to between 3000 ml & 3500 ml depending on how fine (amount of surface area) the crystals are

2) normally you would figure you need 500 ml nitric & 500 ml D-water to dissolve the 500 grams silver - but instead - I put in 600 ml D-water & ONLY 300 ml nitric (67%) & I add ALL the nitric "at once"

3) as soon as I have dumped the nitric in - I put a watch glass on top of the beaker --- & I should add that you want a beaker with a "small" pour spout & a nice round top so the watch glass makes a nice tight fit - the tighter the better --- the reason for that is you want the NOx fumes to stay inside the beaker as much as possible

The reason this works (dissolving more metal with less acid) is because you get more of the full potential use of the nitric - which comes from the NOx fumes - by keeping them in the vessel - & - having enough water to start with to re-absorb the NOx - thereby increasing &/or extending the working potential of the nitric

You can look at it this way --- if you run your reaction in a reaction vessel set up with a vacuum scrubber that vacuums the NOx out of the reaction vessel - & the first chamber of the scrubber is filled with water (instead of NaOH) the result will be a week (or dilute) nitric forming in the water chamber as the NOx fumes pass through the water

So - instead - if you can keep those NOx fumes in the reaction vessel - along with enough water to re-absorb the NOx - you will keep more of the working potential of the nitric in the vessel & thereby dissolve more metal with less acid --- & you want to add ALL your acid at once so you don't have to take the lid (watch glass) off to add more acid & end up losing NOx

I apply this same principle when doing larger batches whether its dissolving the base metal of plated pins or silver contactor points or sterling or etc. - which I often do in 3 gallon &/or 5 gallon stainless steel pots

I would rather use 3 or 4 or 5 vessels (leaving *plenty* head room for foaming) & less acid --- then use less vessels & more acid --- & I should add that you will dissolve your metal in less time as well - especially if you put your vessel on the hot plate once the reaction dies down

Kurt
 
Kurt,

Thank you for your post and taking the time to write the steps above. This will be extremely useful as I graduate to larger lots of material. Nitric acid is crazy expensive and will be a burden as I attempt to grow my business.

Much appreciated!

~Greg
 
Hi Greg

If you're registering as a business then Nitric isn't a great hardship to buy at the right money over there. Pop a search in the box on the top right and you'll see a few threads on it.

Jon
 
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