Where to start with old plating solutions?

[upcyclist]

A quick description of the problem: I'm in charge of the shop at a local lapidary guild in the Midatlantic coast area (US). Our current shop has a frightening amount of old plating solutions laying around--some we inherited, the balance due to the guild just buying more supplies instead of figuring out if the old stuff is still any good or not. We haven't done much plating in quite a few years, so that puts the age of these materials at anywhere from 10 to 50 years old.

We're talking about roughly 5 dozen bottles in the pint/quart/gallon range. Some of it is labeled, and most of the labeled gold solutions are cyanide-based. I'm guessing from the color that a lot of the unlabeled bottles are simply old nickel solutions, but I'm unsure of the chemistry (also cyanide?).

What are my options?

Scaring the bejesus out of my local county dump on hazmat day doesn't sound like the best plan, and they're more likely to treat the cyanide problem and not worry about the gold, a horrible loss in my opinion. That's if they'll even accept the waste, since most are unlabeled and the rest are labeled "cyanide".

The more likely options are try to get the materials to a recovery specialist or take the DIY route.

The Board might prefer the former (recovery specialist), but I'd still need to figure out what state to get those materials in--I'm guessing the USPS is a big fat NO, and even a local refiner probably doesn't want to deal in cyanide plating solutions. Would ion exchange resin be something to try in this vein?

The latter DIY option would be far more interesting: test what I can and determine content (stannous chloride, etc.), and take my time recovering the gold & other precious metals, mitigate the nickel, etc. I've a fair mind for chemistry, but honestly haven't done a whole lot since AP Chem in high school. So I'd need to do a bunch of reading, get the right equipment, figure out safety, etc. I promise not to throw acid in the cyanide, I swear

In a few hours of reading (and I'm glad I found this forum!), including a quick scan of Hoke, I've figured out that for the gold/cyanide solutions at least, I could use zinc powder to precipitate out the gold, and possibly even stabilize the remaining solution into ferrocyanide or even Prussian blue. Am I on the right path here?

 

[butcher]

Studying Hokes will help to put you on the right path.
Studying the forum will also help you on your path.
Keep studying before working with your solutions.

Zinc will displace the metals from solution, if it is cyanide based, zinc will even displace the metals from an acid base solution.

Do a search of the reactivity series of metals.
Zinc will also displace nickle from solution notice its place in the reactivity series of metals.
Zinc is above iron in series, so making ferrocyanide with that solution would not be easily done.

 

[upcyclist]

Thanks--the first bit of your advice (study, study, study) was a given. I just wasn't sure about the plating solutions since this board (well, almost all interest in PM refining these days) seems pretty centered around e-waste.

Do a search of the reactivity series of metals.
Zinc will also displace nickle from solution notice its place in the reactivity series of metals.
Zinc is above iron in series, so making ferrocyanide with that solution would not be easily done.

Ahhh, so that's how stannous chloride works--it's all slowly coming back, hehe. I'll do some looking and see how iron might work instead of zinc, and see if I can kill two birds with one stone.

One question on my initial post, though: what would be a decent channel for simply handing off the old solutions to someone, preferably having them bought from the guild rather than us having to pay to dispose of it? Knowing the answer to that will help advise the rest of the board on a good course of action (i.e., would we be able to sell the waste--if not, their best option might be to let me take it off their hands and learn on it).

 

[kurtak]

Try this company :arrow: http://www.advchem.com/index.php

They are in Warwick RI & they handle waste solutions & pay out on the gold

Kurt

 

[butcher]

Using a metal to displace metals in solution, like using zinc to recover metals below zinc in the reactivity series of metals from a solution, zinc a reactive metal, gives up electrons to the metal ions in solution that are more reactive than zinc, these metal ions gaining the electrons become metal atoms which join to become clusters of elemental metal atoms which grow to large enough clusters to precipitate from solution as metal powders.
The zinc is oxidized (lose of electrons)to zinc ions, while the metal ions in solution are reduced (gain of electrons).

Using a metal reagent like stannous chloride, to test for values (gold, silver, palladium, platinum, in an acidic chloride solution, the stannous chloride is oxidized to a higher state stannic chloride, as the gold is reduced to a colloid of gold, here the gold ions are reduced, but the reduced gold atoms only combine to a certain point, these clusters of atoms do not combine to maturity of size to become a precipitant, they develop a charge of all the same polarity, and cannot combine to grow larger, same charges repel (like magnets) these small clusters push each other around in solution forever (unless the colloid is broken) reflecting light (as a certain color) because of there size, the colloid (when using stannous to form these colloids gives gold colloids of a certain size (that reflects the light) to give the violet color (a certain wave length) we see. colloids of other sizes would give different colors of reflected light.
This is also an oxidation-reduction reaction.
But different from the one of displacing metals from solution using a metal like zinc above.

Do not confuse displacing metals from solution with a metal higher in series, with the reaction of the stannous chloride to test for metals in solution, these are different reactions.

Note stannous chloride (made from acid) can be an acid (kept acidic to keep tin in solution as the stannous ion), mixing acid with cyanide can produce deadly gases, even though this test is normally done in very small quantity's, the gas would be produced from the reaction.

In cyanide (a basic solution) the iron may also form iron oxides or hydroxides, it oxidizes easily to other oxidation states, zinc would be a better choice here to replace values (as well as other metals from solution),as a method of recovery of the valuable metals, because of the zinc metals reactivity. Here I think recovering the metals from solution is more important than trying to kill two birds with one stone.

 

[4metals]

The scary part is the price you will pay for a "lab pack" service to come in and remove these chemicals safely. If it were me, I would be separating the solutions by pH and gleaning any information on the labels and making a detailed list. You will likely end up with a cyanide section, some with precious metals and some without, and an acid section which probably will not have as much in terms of gold and silver.

In any event it is easy to remove the values from a cyanide solution. Do some segregation and make the list and come back here with details and we can likely aid you in the consolidation process.

 

[upcyclist]

The scary part is the price you will pay for a "lab pack" service to come in and remove these chemicals safely.

That's my biggest worry, 4metals. We're a Not-For-Profit, which is good, cuz we don't have much money

If it were me, I would be separating the solutions by pH and gleaning any information on the labels and making a detailed list. You will likely end up with a cyanide section, some with precious metals and some without, and an acid section which probably will not have as much in terms of gold and silver.

In any event it is easy to remove the values from a cyanide solution. Do some segregation and make the list and come back here with details and we can likely aid you in the consolidation process.

That's my plan. And as long as I can save a few bucks by disposing of the chemicals (or at least render them safer) myself, I may as well go the whole 9 yards and get the metals out.

I probably need to start by finding some basic testing materials (like pH, metals). Is there a relatively painless way (like an indicator paper or stain) to detect KCN? And yes, other than adding some acid and seeing if I can smell bitter almonds Otherwise, would it work to assume that any basic solution is a cyanide solution?

 

[4metals]

Cyanide test papers

http://www.ctlscientific.com/cgi/display.cgi?item_num=90604

pH papers

http://www.ctlscientific.com/cgi/display.cgi?item_num=92110

 

[upcyclist]

In any event it is easy to remove the values from a cyanide solution. Do some segregation and make the list and come back here with details and we can likely aid you in the consolidation process.

I did go through and catalog everything. 60 containers, including at least 10 lbs. of NaCN salts, about 25% are unlabeled (lovely). Most of the labeled stuff is plating solutions (primarily cyanide-base, except one or two newer bottles of plating solution, and a few small bottles of Rhodium plating solution in acid) or electro-strip solutions. At some point I'll get around to posting the list, or at least the unique entries.

I've also started going through and testing everything with litmus paper--I've finished the general solutions and need to move on to the remaining ~40% which includes the labeled PM plating solutions. As mentioned in another post, for safety's sake, I'll assume the pH-basic solutions are cyanide-based until proven otherwise, and will treat neutral solutions as possible NaCN solutions (cuz they're old).

I've purchased tin sinkers (yay Walmart) & HCl to make stannous chloride, so the next step will be to find/make some Schwerter's and start testing (outside). I'll probably start with the acids--less dangerous, anything without PMs can just be neutralized.

 

[upcyclist]

An update:

I've mostly been reading (here & Hoke, primarily) and accumulating reagents (HCL, Ca(OH)₂, SMB, Copperas, etc.). Still haven't [tried that hard] to obtain any nitric acid. A couple cold calls to local refineries led nowhere (unless I want to order at least 15 gallons of the stuff).

I have performed a couple familiarization experiments. Since I can't test the stannous chloride without a gold standard, I tried to dissolve some alloy (14K rose) in HCl/Cl. That failed, so I'll work on getting some NaNO₃ for Poor Man's AR.

I did decide to work on the cyanide solutions first (checking pH often), since I'd rather get them out of the way and out of my life, but haven't tried anything major yet. I did try dropping gold with copperas, but no love. On the upside, I definitely got some Prussian Blue. On the downside, of course, it made a murky mess to filter, and my suspicions were confirmed: ferrocyanates formed, but there's so little gold in the solution, apparently none of it dropped. That's one filter paper for the burn pile. I tried cementation with iron, again no love, possibly because both the gold content and my trial size (20 mL) were so low. So I ordered up some zinc dust and will drop it that way, and destroy the cyanates with bleach/chlorine. Eventually.

Again, thanks for all the help, guys--even if most of it is me just finding what you already wrote!

 

[rickbb]

You can get small bottles of nitric online, The Science Company has a web site you can order from if can have it delivered to a place of business. (They will call the place to see if you really do work/hang out there and actually are who you say you are.)

Another place to order online is Amazon, Allied Chem in TX will ship a liter of so to your house.

 

[upcyclist]

I don't see any listings in Amazon from Allied Chem (or anyone on Amazon with Nitric Acid), but I'll give them a call and see what I can find out. I'll also check out the list of chem suppliers here on the forum. Thanks!

While I might be able to get away with Poor Man's AR, I'd rather have the real thing. And sometimes ya just need Nitric.

 

[upcyclist]

As an update, I finally got some pregnant solutions--most have been barren.

silverprecip by Eric, on Flickr

The spoon in the foreground contains some of the zinc dust. Alas, this solution is probably silver--the label was pretty much obliterated, but I did make out something about "pure silver anode", so it looks like it was a silver plating solution. The solution was dirty and the precipitate is still settling, hence the murky fluid.

It smelled like they used ammonium hydroxide in that sucker--is that to dissolve any silver fulminate that forms? (If so, then "plating solution that smells like ammonia" = probably silver?)