Waste related Problem

[Harold_V]

After cementing the Silver the solution is never blue in color as suggested.
It stays dark green, but the Salt solution test shows that there is no more Silver in it.

Because silver plated items are not always made of pure copper, the remaining solution contains other elements, likely to include nickel, and most assuredly zinc. That may well be why it isn't blue after the silver has been recovered. So long as you get no silver chloride when testing with a drop of HCl or a crystal of salt, you have done your work well. I would advise you to have on hand some stannous chloride for testing for other elements, however. It's possible you have traces of palladium present, although where it may have come from I do not know. Testing will eliminate the possibility. Please note that you can also test for palladium with DMG (dimethylglioxime). It is a very conclusive test, and can also be used to test for the presence of nickel. Hoke discusses testing with DMG.

I am then raising the Ph with Sodium Carbonate to 2,5
but when I add my Iron no Copper falls out of Solution.
Just the Iron gets a red Copper coating.

You likely have more than one problem. What you're seeing is copper being cemented, but it may be building a solid sheet that becomes impervious to any further cementation. That may be because of a highly concentrated solution, or even because the pH is wrong. I suggest you use a lot more scrap steel, and dilute the solution. I wouldn't take the pH up so far, either. Some free acid is very desirable for the cementation process. So long as the solution isn't emitting the dreaded brown fumes, just leave it as it is.

How does the Copper look that has to precipitate?

It can resemble cemented silver, although the color will be the familiar copper red. It can also yield a solid surface, which you are experiencing. It's important that it not do that--otherwise it eventually stops working because the solution is isolated from the scrap steel.

I am using Iron that is galvanised with Zink. Can this be the problem?

It shouldn't be a problem. Zinc, too, will work, and it does so much faster than steel. However, if it is getting plated, you face the same problem we've been discussing. The cemented copper must be loosely attached, so it constantly sheds. Leaving the pH low should assist in solving this problem.

Hope some of this helps. Let us know if you solve the riddle.

Harold

 

[mikelugg]

Thank you to all the members who share their Ideas.
I understand that further experiments are necessary with the
waste problem.
As to the question whether my operation is financially viable, it depends for
how much you can buy the spoons and forks.
Big companys here with us buy the silverplated cuttlery which is stamped to contain 70 gramms of silver
per kg for up to 32 Euros and they make a profit.
At 32 euros it is not so feasible for me anymore.
I also resell my spent spoons as Copper scrap and I think it pays.

 

[mikelugg]

I had my Spoons tested, they contain Copper, Zinc and Nickel as Base materials.
So my Solution is full of theese. -
I have made a test where I added NaOH Solution to my Copper-Zinc-Nickel Nitarte Solution which gave off a
precipitate which settled nicely to the floor of the container. The liqiud above was very much see trough
with a bit of green, but as I said with a lot of material precipitating out of solution.
I may be not totallly wrong if I said that when I filter this off for further disposal as solid waste, the liquid should be
pretty clean.
Someone please correct me but the metalls have converted to their oxides and are removed from solution.
So can someone confirm that this is a way of dealing with the waste?

 

[butcher]

mikelugg
"Someone please correct me but the metals have converted to their oxides and are removed from solution.
So can someone confirm that this is a way of dealing with the waste?"

Mike, I do not know that I can help you, but this is the way I see it, metals dissolved in acid become a salt of that metal, copper + nitric acid become copper nitrate,
3Cu + 8HNO3 --> 3Cu(NO3)2 + 2NO + 4H2O, the copper lost an electron(oxidation), the nitric gained electron (reduction), copper is being positive ions, and nitrate being negative ions, both in solution, giving us a blue color solution, note it is the copper metal ions giving us the blue color.
When we add hydroxide, or a strong base we do make oxides and hydroxide of these copper Ions, and depending on the solubility of these ion's, the pH of our solutions and other conditions (like air exposure forming copper carbonates) would determine the color of our solution, but here we are talking pure copper and acid and hydroxide solution,.
Which as we know many times we are dealing with a wide variety of metals, some even soluble as hydroxides and these also give color to solutions.
Say I have a copper and iron in chloride solution, I may not be able to tell the difference even if these metals were in two different test tubes as both are green (iron will usually show rust ring at surface,
Now say we have both these copper and iron ions mixed in the same test tube and add some sodium hydroxide till most of the copper precipitates and our solution contained some copper hydroxide and Iron, my solution may stay green, now I add more hydroxide my Iron may change to iron oxide or hydroxide and solution changes yellowish to tea looking (the iron hydroxide somewhat water soluble still giving a color to my solution).
Now we may have other metals in this solution also they may be higher in the reactivity series and be very soluble in a hydroxide solution.
The metals at the top of the reactivity chart are so reactive that the pure metals dissolve in water to form hydroxide of that metal (some will dissolve so fast they explode into metal hydroxides when water is added, these metals you will always have in your waste solutions).

Color of a solution is not much of an indicator as to what is in there, but sometimes it does give us clues.

In this metal chemistry we may say add this chemical and precipitate this metal from the other metals in solution. Remember with chemistry many times it may not be black and white (may actually be gray), my meaning here many times there is no definite line where all of this metal will precipitate from others in solution (we can still have some in solution) or where adding extra of the chemical may precipitate both metals from solution, we may speak about this being black and white when actually it is a bit gray.

Read up on the post dealing with waste, I believe it was flagged; it will help you understand better than I could.

 

[mikelugg]

Thank you Butcher,
your Post was helpfull indeed!
I was looking up as much as I could in the Chemistry section about Metal Hydroxides.
What I found out is that they are water insoluble which is what I need for my purpose,
to get rid of them - out of the water.
I will use this way for now to clean up my waste, so that I can seperate the water from the metals.
The metalhydroxides I collect, in order to dispose them seperate from the water.

 

[Dr. Poe]

Raising the pH of a nitric solution too high converts the nitric to ammonia. Ammonia then redissolves the copper oxides turning the solution blue. So I don't recommend that method. Using scrap junk steel to cement the copper works great (On the acidic side of pH). The copper adheres loosely and falls off with physical shock, vibration. The steel scrap can continue to be used again. A single nail dipped into a copper solution turns red if copper ions are still in solution. Salt water kills plants and ruins the land until enough rain disperses it. Iron hydrolyzes at pH 7, producing ferrous ions and ferrous oxide hydrates.
Ferrous hydroxide has a natural pH of 9, so completely precipitates at pH9. Gathering the goop and separating it from the sodium nitrate solution, makes a good starting point for making ferrous sulfate, the preferred reduction reagent for precipitation of metallic gold from gold chloride solutions. Ammonia is good for plants, but bad for humans.
Stick to cementation. Just my opinion. :| Dr. Poe

 

[4metals]

Commercial refiners often use urea to kill off excess nitric but again ammonia is formed in an alkaline solution necessary to drop metals as hydroxides. The ammonia re-dissolves some of the copper hydroxide and makes meeting discharge standards difficult.

I agree with Dr Poe, cementation is preferable. Adding a small quantity of sodium thiosulfate helps create an easily dislodged copper to make collection easier.

 

[Westerngs]

pH adjustment should work fine for precipitating metals as hydroxides and neutralizing acids. It is not necessary to cement out the copper first.

Get a pH meter, it is necessary in order to stay below pH 10 and avoid redissolving metals. Since you have mostly copper, you want to stay at about pH 8.2. You will be fine up to pH 9.5

I would suggest you use lime to neutralize your waste as the sludge will be more manageable versus sodium hydroxide sludges.

Make sure you stir the solution very well as you add the lime - or any other neutralizing chemical - if you don't, it is easy to overshoot the desired pH range.

Slow down the chemical additions once you reach pH 5,as the closer you get to pH 7 the chemical additions will have a greater effect on pH.

 

[niteliteone]

It is not necessary to cement out the copper first.

Are you saying it is better to poison the environment with the copper :?:

Tom C.

 

[butcher]

For me the cementing process is very important.
I first use copper metal to treat solutions, (this may be in bar form (or copper powders from previous waste treatment process) to treat solutions (cementing values that may have been missed, or were just traces left in solutions).

Then using iron to cement copper (produces copper powders used above), and this also removes the metals from solution that are dangerous.

Discarding improperly treated waste you not only are creating a very dangerous environment for yourself, and others, but you will also be fined, or loose your freedom (jail, prison time) when caught by authorities having jurisdiction, when these authority’s do give you a visit to see what your doing with these chemicals you purchased, or a visit for some other reason like your neighbor smelled funny smell and you were working with some type of chemicals that they suspected was a drug lab, being able to show them what you are doing and that you are responsible with your waste and understand how to treat them and dispose of them in a safe manner (this alone can save you), also it is not difficult to learn how to properly treat waste, and spending time learning and doing that keeps you, your family and neighbors safe, can also mean the difference between profit or loss of what you have worked so hard for in your life, and even your freedom.

Study a very good and interesting topic, where you can learn how to treat waste properly, we are very lucky here on the forum to have members knowledgeable in this area to teach us, and help us to do it the right way, please do not dishonor them by not taking their advice, and put yourself and others in danger by disregarding their advice

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=47&t=1300

 

[4metals]

Most commercial refiners simply raise the pH to 9.5 and drop out the metal hydroxides. It takes quite a bit of sodium hydroxide to raise the pH and it gets quite hot. The waste liquor is very salty water.

When copper hit $3 a pound a refining client of mine wanted to be paid for copper, burning crushing and sifting the hydroxides from the filter press to ship them as a copper bearing sweep was labor intensive but it was done to recover the gold platinum and palladium in the waste stream.

Then we started cementing, mostly to recover the precious metals and then ship the hydroxides (with no PM value) as a listed waste. Labor was much less but the waste still required a lot of caustic, and it cost him to haul it away as a waste.

So we added scrap iron to recover the copper. Refining 4500 ounces of karat gold per week, this refiner saved about 150 pounds a week of copper which could be melted and sold for about $24,000 a year as copper scrap.

Plus he was able to get rid of the ferric chloride liquid which was left to a local steel plant for use as a pickling liquor.

 

[Westerngs]

Niteliteone. I did not intend to say that you can poison the environment with copper hydroxide. After pH adjustment and precipitation of the copper hydroxide, you can collect the copper hydroxide and melt it into a copper bar.

4metals, question for you. Why was the copper hydroxide a listed waste? Was it from a plating shop? If it was from a plating shop then, yes it would be a listed waste.

In my experience, copper hydroxide resulting from wastewater treatment of silver refining operations would not be a listed waste. It could potentially be a characteristic waste if it fails TCLP. But even if it does fail TCLP, if it is a byproduct and is being reclaimed then it is not a solid waste and therefore cannot be a hazardous waste. See 40 CFR part 261 table 1. I was unable to copy and paste in a readable form.