# Precipitating with Zinc dust and Zinc Turnings - Comparison



## kadriver (Jul 15, 2012)

Hello:

Yesterday, I recoverd some Platinum Group pregnant solutions from Catalytic Converter beads - 3 liters total.

I course filtered using 4 coffee filters - took all day because the beads were very dirty with combustion residue.

The beaker on the left has been course filtered once and fine filtered once - still a slight bit of cloudiness.

The beaker on the right has been course filtered one time through that strainer and 4 coffee filters.

I ran it all back through the vac filter with fine filter paper and the solution came out clear and bright.

I then put all of the solution into one beaker to mix properly, then divided the liquid equally between two beakers.


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## kadriver (Jul 15, 2012)

My plan was to add some sodium carbonate to reduce the acidity (increase pH).

It only took two spoons of pH increase in each beaker - I can tell by the reaction how much sodium carbonate to use.

Then I used zinc turnings to precipitate the beaker on the left, and fine zinc powder (3000 mesh) to precipitate the beaker on the right.


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## kadriver (Jul 15, 2012)

After about 1/2 hour the black PGMs begin to be pushed out of the solutions by the zinc.

The zinc goes into solution and the Platinum Group Metals come out of solution.

Notice that the beaker on the right appears to have more black PGMs that the beaker on the left.

The fine zinc powder precipitates the PGMs faster than the turnings.

But the beaker with the turnings has far less finely suspended black powders - note it's greay color while the right side appears black.

This black is finely divided black PGMs suspended in the soluiotn - it may take longer to get this fine black powder from the solution.


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## kadriver (Jul 16, 2012)

After about 1 and 1/2 hours the precipitations are done.

The reaction in the right beaker completely used all the zinc powder, there is no more bubbling.

The beaker on the left continues to react because there are still turnings of zinc left undissolved - I probably put in too many zinc turnings.

A test with stannous chloride (not shown) confirms that no more PGMs are in the solution.


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## kadriver (Jul 16, 2012)

I ended up having to fish out the remaining zinc pieces from the beaker on the left.

After removing the pieces of undissolved zinc, I poured off the liquid into another 2 liter beaker and added some of the undissolved zinc back into that solution.

I then rinsed the precipitated black powders that were left in the bottom of the large beaker with cold tap water and allowed the black powder to settle.

This is a photo of the beaker with zinc turnings looking up from under the beaker.


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## kadriver (Jul 16, 2012)

The beaker on the right as viewed from under the beaker looking up.

There was no zinc left in this beaker. The precipitation had consumed all of it.

I poured off the black liquid into another 2 liter beaker.

To this 2 liter beaker I added sodium carbonate until no more reaction - this will ensure that the suspended black powder will not go back into solution.

It will be allowed to settle (last one took two days to settle completely). Then wash and store the settled balck powder.


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## kadriver (Jul 16, 2012)

Here is the final result.


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## Noxx (Jul 16, 2012)

Thank you for the comparison.


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## kadriver (Jul 16, 2012)

Edited for spelling 

I prefered the zinc powder over the turnings for now.

I did not like having to fish the pieces of undissolved zinc out of the beaker with the zinc turnings.

The beaker which used the powder had no left over zinc to be removed (that I could see).

The zinc powder did produce a greater volume of finely divided suspended black PGM powder that will take a long time to settle.

The turnings did not have as much of this fine black powder suspended.

The zinc powder was faster then the turnings.

In the photo below the beaker on the left was the poured off liquid from the zinc turnings.

The beaker on the right was the poured off liquid from the zinc powder beaker.

I put some of the undissolved turnings back into the beaker on the left - this zinc is still reacting

The beaker on the right is being treated with sodium carbonate to neutralize all the acid to keep the suspended black powders from going back into solution.

There will be more black powder from each of these beakers tomorrow.

This is only about the third or fourth time doing this.

If anyone spots a mistake with my procedure, then please let me know.

Thank you,

kadriver


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## sena (Jul 16, 2012)

Kadriver , your post are very neat, 8)


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## ericrm (Jul 16, 2012)

it was suposed to be a comparison between both zinc method, but in fact you just have created the best tutorial i have read so far on platinum recovery via cementation with zinc . you realy did a fantastic job 8)


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## goldenchild (Jul 16, 2012)

I just wanted to add that if you use a "Charmin plug" anywhere in your processing you can actually put it on a vacuum. You just have to make sure the funnel is snug in the rubber stopper. It saves alot of time!


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## kadriver (Jul 16, 2012)

Mario:

I have never used a charmin plug.

Instead, I just neutralize and wait for the black to settle.

This method does take more time, and I may change in the future and use the plug.

But for now, I have the time to wait - plus, after settling, I get all the black powder.

Some of the black powder seems to adhere to the plug in the videos I've seen - settling completely eliminates this.

Kevin


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## kadriver (Jul 16, 2012)

Noxx - glad you like the post

kadriver


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## kadriver (Jul 16, 2012)

Here are the two beakers that were allowed to settles overnight.

The zinc turnings are completely dissolved and gone (beaker on the left).

The beaker with zinc powder (on the right) that I neutralized has a little color to it.

Probably not enough sodium carbonate added - still some HCl present that caused some of the black powders to go back into solution.

Plus I had to wait longer as the beaker precipitated with zinc powder still had not settled completely.


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## kadriver (Jul 16, 2012)

here is a view looking up from under the zinc turnings beaker (beaker on the left in previous photo).

Surprisingly, the beaker precipitated with zinc powders (right hand from previous photo) ended up with more black powders than the one precip with turnings, even though some of the black powder had gone back into solution in the beaker on the right.

I will repeat this experiment later when I get back from vacation on 27 July 2012 to see if i get the same results.

Thanks for looking and as usual, any critical input would be greatly appreciated!

kadriver


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## goldenchild (Jul 17, 2012)

I think you won't be able to wait to get back from vacation. You're really having fun with this stuff!


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## kadriver (Jul 17, 2012)

Golden:

This is much fun - I'll even be working on my vacation.

I am going to buy some acid (15 gallon keg) on my way to my vacation destination.

I'll have to transfer the 15 gallons to some empty containers that I have so I can get my $200 container deposit back on the drive home.

Stay safe my friend.

kadriver


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## lazersteve (Jul 17, 2012)

Kadriver,

A few points to note about your observations:

1) There is no need to remove the excess zinc turnings, simply use less or add a little extra HCl to dissolve the excess after the sponge/powder is filtered. 

2) Visually comparing the volume of the resulting mixed PGM powder is not a scientific means of comparing the yields. Filtering drying, and weighing both samples is the correct way to compare the yields. 

3) The PGMs precipitated using the zinc dust are much finer in particle size than the mixed PGMs precipitated using the zinc turnings. With the turnings you can simply pour off the settled solutions, rinse, and pour off again to clean the blacks. When using zinc powder you must vaccum filter to get all of the ultrafine PGM particles. Turnings will produce a spongy type black that filters easily and doesn't stir up after it has settled.

4) The turnings reaction will be much faster if you do not neutralize the solution first with soda ash. 

5) There is no reason why two sample solutions taken from the same reaction should produce different yields of PGMs. Perhaps it's the difference the density of the precipitate, or maybe even the fine powders in the zinc dust jar actually have excess zinc powder in the mix that you can not physically see with the naked eye. As I stated above the true test of the yields is the final weight of the refined PGMs. I suspect they will be equal for both samples if properly recovered and refined.

6) Picking out the undissolved turnings also removes some of the PGMs from the reaction as the PGMs grow on the surface of the turning as it dissolves. This skews the results of the turnings yields because a portion of the PGMs are on the surface and in the coils of the turnings. Never remove undissolved turnings from the reaction when assessing yields.

7) The purity of the final melted product may also shed some light on which is the best form of zinc to use. You may find that there are contaminates in one of the two that is skewing the 'visual appearance' of the resulting mixed blacks/sponge.

Great post with good visuals. You should do the same comparison of turnings to powder when used to convert PGM salts and compare the resulting product. 

I have used both forms of zinc and hands down I prefer turnings as they are easier to handle, easier to weigh, they produce the easier to handle and settle sponge, and go a longer way towards precipitating the blacks for the same mass of zinc. 

Did you weigh the total amount of zinc turnings used verses the total amount of zinc powder used? 

If so what were those numbers?

Steve


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## kadriver (Jul 17, 2012)

Steve, you are absolutely correct.

The observations I made are from a laymans perspective.

I tried to be as objective as possible, but as you stated, there is no reason for the yields to be different (other than human error).

I did not dry and weigh the yields, I put them all together in a single container to save them up as I get them for processing later.

I hope I have not created a problem with these posts, I just enjoy taking photos of my work.

I will be more careful in the furure - thank you.

kadriver


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## Lou (Jul 17, 2012)

Kadriver,


Nice work. Do you want me to help you with this? 


Personally, I've seen first hand Steve's turnings and like them well because it settles and rinses well.

I don't use zinc except for CN work and hanging a big bar in cementation.

Now I feel like making a thread like this, step by step.


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## rshartjr (Jul 17, 2012)

Lou said:


> Kadriver,
> 
> 
> Nice work. Do you want me to help you with this?
> ...



That would ROCK, Lou. As a newbie, the aid of just such an illustrated tutorial would be an invaluable learning tool.


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## kadriver (Jul 17, 2012)

Lou:

I'm speachless - I would consider it a privilage to have you help me.

Thank you for your consideration.

I am leaving for a week on Wed 18 July 2012.

I will be back on the 27th of July.

kadriver


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## lazersteve (Jul 17, 2012)

kadriver said:


> ...I hope I have not created a problem with these posts, I just enjoy taking photos of my work.



No problems, mate.. you are doing a wonderful job, I figured I would give you some constructive criticism is all. I wish more members would do this sort of thing.



kadriver said:


> ...I will be more careful in the furure - thank you.



Again, no harm, no foul. You are doing great! Sorry if you felt like I was upset or something, nothing could be further from the truth, I'm very pleased with your recent posts on this subject.

Steve


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## kadriver (Jul 18, 2012)

I did measure the amount of zinc used in both cases.

Weight of zinc turnings added to PGM solution on the left;

before adding: 52.4 grams
After adding: 13.6 grams
total used: 38.8 grams


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## kadriver (Jul 18, 2012)

Zinc powder 3000 mesh added to the PGM solution on the right;

Before adding: 98.6 grams
After adding: 76.7 grams
Total Used: 21.9 grams


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## kadriver (Jul 18, 2012)

Edit for spelling 

Please remember that I took some undissolved turnings out (estimate 10 grams)

But added some of the undissolved turnings back in the poured off solution and they dissolved completely by morning.

I did not think to weigh the turnings that I removed and added back in.

I guess this makes these numbers pretty much useless.

I'll get a better set of numbers if I do this again.

The zinc turnings made better black powder that was easier to settle and work with.

The zinc powder made a bunch of fine black powder that stayed suspended and was hard to settle.

The suspended fine black powder in the beaker on the right (zinc powder side) did go back into solution as indicated by the color.

The zinc turnings completely eliminated this problem. 

Viewed this way, I must confirm what you already know - the turnings are better for the reasons stated above.

kadriver


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## frontiermetals (Jul 19, 2012)

This was anice presentation on using zinc to drop the dissolved metals from cat convertors... but I have a question: How does using zinc facilitate the purification of the metals extracted, since zinc will drop copper, iron, nickel and other metals below zinc in the electrochemical series? Cats are loaded with all these base metals and it seems a waste of effort to use zinc. Zinc will drop the cerium component, so I guess that's the main contaminant, but maybe I'm missing something.


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## goldenchild (Jul 19, 2012)

frontiermetals said:


> This was anice presentation on using zinc to drop the dissolved metals from cat convertors... but I have a question: How does using zinc facilitate the purification of the metals extracted, since zinc will drop copper, iron, nickel and other metals below zinc in the electrochemical series? Cats are loaded with all these base metals and it seems a waste of effort to use zinc. Zinc will drop the cerium component, so I guess that's the main contaminant, but maybe I'm missing something.



I've never seen cat material that contained anything other than Pd, Pt, or Rh. It wouldn't make for a good catalyst if it did. The zinc is not used for facilitating purification. It's used simply to remove all the PGMs from the solution(s). If you look at kadriver's pictures in other posts you'll notice that he's using 5 gallon buckets to leach the cat material. That's because you need alot of acid to leach cat material. It would be ridiculous (and probably impossible) to drop and recover PGM salts from all these solutions. So using zinc you isolate and remove the PGMs from the solution so they can be re-digested in a much smaller and concentrated solution. I rambled a bit but I hope that makes sense.


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## frontiermetals (Jul 19, 2012)

goldenchild said:


> I've never seen cat material that contained anything other than Pd, Pt, or Rh. It wouldn't make for a good catalyst if it did. The zinc is not used for facilitating purification. It's used simply to remove all the PGMs from the solution(s). If you look at kadriver's pictures in other posts you'll notice that he's using 5 gallon buckets to leach the cat material. That's because you need alot of acid to leach cat material. It would be ridiculous (and probably impossible) to drop and recover PGM salts from all these solutions. So using zinc you isolate and remove the PGMs from the solution so they can be re-digested in a much smaller and concentrated solution. I rambled a bit but I hope that makes sense.



The extracts I've done and precipitated with sodium borohydride have all shown very high levels of cerium and lesser amounts of iron and nickel in addition to the PGM's. Zinc precips have shown no cerium but same amounts of iron and nickel and some other base metals along with PGM's.


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## Palladium (Jul 19, 2012)

Do you remember what those percentages were compared to pgm content?


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## goldenchild (Jul 20, 2012)

frontiermetals said:


> goldenchild said:
> 
> 
> > I've never seen cat material that contained anything other than Pd, Pt, or Rh. It wouldn't make for a good catalyst if it did. The zinc is not used for facilitating purification. It's used simply to remove all the PGMs from the solution(s). If you look at kadriver's pictures in other posts you'll notice that he's using 5 gallon buckets to leach the cat material. That's because you need alot of acid to leach cat material. It would be ridiculous (and probably impossible) to drop and recover PGM salts from all these solutions. So using zinc you isolate and remove the PGMs from the solution so they can be re-digested in a much smaller and concentrated solution. I rambled a bit but I hope that makes sense.
> ...



What is your typical source material? Is it cut out of cats?


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## rusty (Aug 4, 2012)

zinc.


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## goldenchild (Aug 4, 2012)

Rusty,

Are you still selling those bars?


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## kurt (Aug 5, 2012)

goldenchild said:


> frontiermetals said:
> 
> 
> > This was anice presentation on using zinc to drop the dissolved metals from cat convertors... but I have a question: How does using zinc facilitate the purification of the metals extracted, since zinc will drop copper, iron, nickel and other metals below zinc in the electrochemical series? Cats are loaded with all these base metals and it seems a waste of effort to use zinc. Zinc will drop the cerium component, so I guess that's the main contaminant, but maybe I'm missing something.
> ...




Here is a bit about other metals used in CATs (from Wiki) 2.The washcoat. A washcoat is a carrier for the catalytic materials and is used to disperse the materials over a high surface area. Aluminum oxide, titanium dioxide, silicon dioxide, or a mixture of silica and alumina can be used. The catalytic materials are suspended in the washcoat prior to applying to the core. Washcoat materials are selected to form a rough, irregular surface, which greatly increases the surface area compared to the smooth surface of the bare substrate. This in turn maximizes the catalytically active surface available to react with the engine exhaust. The coat must retain its surface area and prevent sintering of the catalytic metal particles even at high temperatures (1000 °C).[13]
3.The catalyst itself is most often a precious metal. Platinum is the most active catalyst and is widely used, but is not suitable for all applications because of unwanted additional reactions[vague] and high cost. Palladium and rhodium are two other precious metals used. Rhodium is used as a reduction catalyst, palladium is used as an oxidation catalyst, and platinum is used both for reduction and oxidation. Cerium, iron, manganese and nickel are also used, although each has its own limitations. Nickel is not legal for use in the European Union (because of its reaction with carbon monoxide into nickel tetracarbonyl). Copper can be used everywhere except North America,[clarification needed] where its use is illegal because of the formation of dioxin.


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## Marcel (Oct 7, 2012)

Nice and informative work, kadriver. 
I think another point for the hobbist might be, that powders as precipitant dont develop some much chlorfumes. The reactivity with the large surface of the powder keeps the acidions "busy", while with the comparatly small surface of a bar, pellets or a sheet of metal, these nasty gases, can wander around evrywhere and escape to the surface. Some powders such as my fine copperpowder even stays on the surface until beeing cemented and therefor to heavy.
But let me tell you my best observation:
I use both! I doesnt harm and you have the best of both worlds.
I prepare asecond vessel with some copper sheet f.i. and then pour the solution into that vessel.
That way, if I underdose the powder, there is still enough material to finish the rest overnight and I dont have a second go, but I also dont need to fish the powder out again, because it was more than needed.
I just poure it back into the oher vessel after shaking it ab bit.
The problem with the powder is to find the right dosis. the problem with solid precipitants is that the reaction is slow due to the limited size. Take the powder as starterfuel and chlorgassurpressing and then let the rest be done by the pellets etc without the need for rerpeating..
Just what I found out for myself.


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## etack (Oct 8, 2012)

goldenchild said:


> Rusty,
> 
> Are you still selling those bars?



Found some that look pretty cheap
http://www.rotometals.com/product-p/zinccastrods.htm

Eric


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## lazersteve (Oct 8, 2012)

Cementing with bars is not only slow, but makes recovering the PGMs difficult as they form a slimy black layer on the surface of the bar that gets lodged in the pits and crevasses of the zinc. Scraping and washing gets a good portion of the slimy PGMs, but will not get it all. When the bar is fully dissolved the PGMs will be all that remain. I prefer turnings as they dissolve faster and don't lock up any of the PGM blacks.

Steve


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## HAuCl4 (Oct 10, 2012)

kadriver said:


> Instead, I just neutralize and wait for the black to settle.
> 
> This method does take more time, and I may change in the future and use the plug.


Try with a strong alnico or Neodymium magnet outside the beaker and be surprised!. :shock: 

Very neat presentation and photos!. 8)


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## rusty (Feb 16, 2013)

lazersteve said:


> Cementing with bars is not only slow, but makes recovering the PGMs difficult as they form a slimy black layer on the surface of the bar that gets lodged in the pits and crevasses of the zinc. Scraping and washing gets a good portion of the slimy PGMs, but will not get it all. When the bar is fully dissolved the PGMs will be all that remain. I prefer turnings as they dissolve faster and don't lock up any of the PGM blacks.
> 
> Steve



Steve what color will my zinc solution be once the precious metals (PGM's ) from cats are completely cemented out. Thanks

Edit to add, 
Went out and had a look at my pails which have had zinc bars in them since last summer, a few pails have clear liquid while two others are still working away.


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## etack (Feb 17, 2013)

lazersteve said:


> Cementing with bars is not only slow, but makes recovering the PGMs difficult as they form a slimy black layer on the surface of the bar that gets lodged in the pits and crevasses of the zinc. Scraping and washing gets a good portion of the slimy PGMs, but will not get it all. When the bar is fully dissolved the PGMs will be all that remain. I prefer turnings as they dissolve faster and don't lock up any of the PGM blacks.
> 
> Steve




Steve I have found this to be very true. I have a PMG solution that is slowly cementing away at a snails pace. I have found that if you wash the bars with HCl you can remove the PMG black and it speeds it up. The only reason I used the bars was because I couldn't find turnings. I think I will buy some powder off the ebay just to speed it up. Its only 1-3Oz of Pd in the solution. I don't know the exact amount it came from some slip rings I was working with it was mixed in with silver as an alloy.

Eric


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## Marcel (Feb 17, 2013)

Hmm, I found that as long as you still have PMs cementing on the surface of the bar, the drop is still unfinsihed.
Wait some more time, once teh drop is through the remaining acid will start dissolving the zinc/copper etc. and give you a clean piece of metal.
I is helpful to clean the bar using an ultrasonic bath (with simple water in it) from time to time, to support this process. Occational Tapping on the bar can also help.
We know that the dopping is a replacement process, where the more precious metal is discarded by the acid in favour of a less "fancy" metal. So if there is no more precious metal in solution that can be dropped, the process will go on by eating up the remaining base metal. This will lead to a clean surface over time. This may take a while and stirring, tapping or ultrasonic will support it, but this is the next stage of the reaction and it will come sooner or later.


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## skippy (Feb 18, 2013)

Rusty, I've found that nickel doesn't really like to cement out of solution for me. So sometimes nickel will be present in enough quantity to tinge the solution a faint green. I know though that a nearly/mostly reduced platinum solution is also supposed to be faint green, because that's the colour of pt(ii) compounds in solution, so can anyone tell me if stannous shows pt (ii) salts in solution?

I've made zinc turnings before and they work quite well. I've also used steel roofing flashing and ducting (clean it first for any oil). I just recently tried using some transformer lamination, and it the steel was very smooth. I don't know if it was the purity of the iron or the surface or maybe there was some copper or something in the solution in addition to cat pgms, but the cemented product was a foil like substance that adhered to the iron pretty tightly. It could still be rubbed off very easily with a finger, but it was still bad enough to stop the cementation, whereas I have not had this problem with the steel from flashing or ducting. 

When I used ssn I was able to avoid having to de nox the solution by dropping the metals quickly from the dillute ssn with a sufficient amount of steel and quickly pouring off the solution after sufficient settling. The key is not to let the cementation slow down. If the metal forms an adherent layer that slows down cementation, some of the cemented metal starts redissolving and you get fine metals that don't settle fast enough and you lose values. If you have excess steel I find the pgms rinse nearly completely off the steel after a short treatment with hcl. Also after you find with stannous testing that you have cemented all the metals out pour or siphon off as much of the solution as possible as quickly as you can, and then get the cemented metals rinsed so they don't start redissolving.


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