Electromotive Series

[goldsilverpro]

This is a short electromotive series list that only contains the common metals. The list could be expanded to contain every element and alloy.

The rule is that a metal will drop out of solution any metal below it in the list. The metal used also must be soluble in that particular solution. The metal used actually trades places with the metal(s) that it is dropping. It dissolves into the solution and the other metals drop out, as metal powders, usually. The metal will not drop out any metal above it or, itself. The general dropping out process is called cementation.

For example, you have an HCl solution containing copper, nickel, gold, and palladium. You can first drop out the gold and palladium using metallic copper. The copper will not drop the dissolved nickel or copper. After collecting the gold and palladium, you can use aluminum or iron (steel) to drop out the nickel and copper, as metallic powder. The end result is much less toxic.

The greater the surface area of the metal, the faster the other metals will drop out of solution.

Sometimes, the metal doing the dropping gets completely covered with the metals being dropped and, the reaction slows down. Scrap it to expose fresh metal.

If you drop silver from a nitric acid solution containing excess nitric acid, using copper, the excess acid will, at first, only dissolve copper. When the excess acid is used up, the copper will start cementing silver.

Here's a simplistic way of looking at the EM series. The metals at the bottom want to be metals. The metals at the top don't want to be metals - they want to be metallic compounds. In nature, gold is often found in metallic form, copper is sometimes found in metallic form, and aluminum is never found in metallic form. A long time ago, aluminum metal was more valuable than gold because no one could reduce aluminum compounds to aluminum metal, except in small quantities, at great expense. They used such super powerful things as metallic potassium to do this. It was so valuable that some king or queen (British, I think) had a crown made from aluminum.

http://en.wikipedia.org/wiki/Aluminum



Magnesium
Aluminum
Zinc
Chromium
Iron
Cadmium
Nickel
Tin
Lead
Hydrogen
Copper
Silver
Palladium
Mercury
Platinum
Gold

 

[LeftyTheBandit]

Magnesium
Aluminum
Zinc
Chromium
Iron
Cadmium
Nickel
Tin
Lead
Hydrogen
Copper
Silver
Palladium
Mercury
Platinum
Gold

Does this mean I could selectively drop metals this way...

Platinum to cement gold
Palladium to cement platinum
silver to cement palladium
copper to cement silver
lead to cement copper
tin to cement lead
nickel to cement tin
iron to cement nickel
zinc to cement iron
Aluminum to cement zinc?

So I could recover all my metals from a solution selectively step by step?
If so, this would make refining and recovery quite selective if you followed each cementation?

 

[qst42know]

GSP. The metal used also must be soluble in that particular solution.

Lefty, I think this rule would cause some note worthy breaks in laddering down your metals.

 

[LeftyTheBandit]

My interest in this is dealing with a solution that would contain many elements such as a leach from ground eDust. Especially finding a way to drop more noble elements before, say tin, which is troublesome, not to mention Mercury.

 

[Anonymous]

GSP, would not all metals that are above hydrogen replace it in solution, forming the oxide for that metal?
Example, nickel is quite a few steps above hydrogen, so if you used to to replace say copper, the copper would cement out, thats great
they use use zinc which is even higher, the zinc replaces nickel and the nickel replaces hydrogen?

I just wandered because I had read somewhere that you can not produce iron powder in an aquious solution.

thanks
jim

 

[Irons]

It gets even more complicated when you have a solution of elements that can exist at multiple REDOX potentials.

Connect a chart recorder to ORP and reference electrodes, and you can watch the ions get reduced in a stairstep fashion as you slowly add the reducing agent. If you know at what potential the ion of interest gets reduced, the reaction can be stopped. pH, temperature and other factors will affect the reaction. It can get pretty complicated.
Oxidation reactions can be monitored as well.

Here's a good primer on the subject:

http://www.chemguide.co.uk/physical/redoxeqia/introduction.html#top

 

[butcher]

I have nothing to back this up except my observations, but seems to me that several metals in solution can also form colloids, plating to one another in solution, concentration, type of metals involved Ph and metal salt content seem to be factors,
this leads to problems such as dragdown of unwanted metals, problems filtering, sticking to side of jar, trouble precipitating and other troubles.
no wonder it is so important to remove the base metals, and keep certain metals out of the soup if possible. the electromotive series works but chemistry is not a perfect world, especially if you did not eliminate the base metals.

 

[LeftyTheBandit]

I'm working on the assumption that before having the items ground into eDust that all high yield items have been harvested.

The eDust is the remaining low yield items all ground up. I am trying to see if I can make at least an attempt to break up the separate metal groups in less than pure form to sell as un-pure forms of that metal and at least remove the dangerous metals and their salts from the solution for disposal.

I am looking at soaking the eDust in a dilute HNO3 Nitric Acid for a long period of time in a stainless steel tank with ultra-sonic agitation. Then rinse well and then apply a HCL & CL soak in a Polyethylene tank with ultra sonic agitation to hopefully recover Au. (not sure if ultra-sonic work on polyethylene)

What I'm concerned about is mercury and other dangerous metal/salts like beryllium being left in solution or left in the cemented metals after my 1st HNO3 soak. (I guess Aluminum would drop almost everything as it appears so low but I would like to have the base metals some what separated.)

I have seen a youtube video showing that after incineration they created anodes of the metal left after incineration and soaked them in a bath to electrowin gold and pgm's, then move to different tanks to recover other base metals.

Question #1 :Is there any benefit to soaking this eDust as outlined or is incineration right away the best method. (Proper incineration methods shall be applied)

Question #2 Even if incineration is hands down best way, what metal would you use in order to cement out the separate metals and the solution required?

Question #3: If incinerated and anodes made from slag metals, what would the order of the electrowinning systems you would apply?
(Please indicate cathode material and solution used in the bath.)

 

[lazersteve]

I can answer your first two questions.

1. Proper incineration would be the best route in my opinion.

This breaks the bulky organics down into carbon and carbon dioxide ultimately. It also converts many of the base metals into their more soluble oxides if performed below their melting points in an oxygen rich atmosphere. The base metal oxides can them be removed with the cheaper acids like HCl or H2SO4.

2. The best approach to cementing the metals out from solutions would be to start with copper as the added metal.

This forces all the precious metals out of the solution as a group which can processed and separated without having the troubles caused by base metals in the solution.

Maybe GSP or someone with plating experience can answer your third question.


Steve

 

[Anonymous]

Hi there.
If you use copper sulfate it will remove base metals that are above it like nickel, cobalt, chromium, iron. they can then be rinsed from the pulp. The pulp will not be enriched with copper that replaced the base metals and if you incinerate the copper will act as a collector for the precious metals.
Then you can refine this however you like.
I would also try to concentrate the ground material by density first even if you can only cut the pulp by 1/2 that would be a big advantage to you. But I think if all the particles are the same size you could get it down to less than 1/8 th of the pulb contaminating the metals. then incinerate with even less bad fumes.

Jim

 

[lunker]

Ok,
So I have incinerated fifty pounds of e-waste. The result is 28 lbs of material. I ball milled this and ended up with 12 lbs of pulp material.The balance being metallic solids.

My plan is to leatch the pulp with h2so4 to remove base metals.
would this remove the silver as a sulphate?
Also, I read a post from harold that mentioned that palladium can be oxidized at high temps. Would that also be leached from the pulp.
Can I then soak in aqua regia to convert the balance of the pgm's and gold from the pulp?

If not what would be a better process?
Thanks!

 

[Anonymous]

Not sure h2so4 is a good choice most sulfates will gum up the works. It would be much better to use hcl, then hcl and peroxide.
Or copper sulfate, then nitric, then your choice of gold leach.
There are several ways to skin this cat so you will most likely get several suggestions.
jim

 

[Irons]

Pd will dissolve in Sufuric. The Oxide will also dissolve in Con HCl and is easier to recover by cementation with Copper.

If you heat PdO above 600 deg C., it will disassociate into Pd and Oxygen.

 

[butcher]

if using H2SO4 sulfuric as primary leach,
couldn't he use H2So4/sodium nitrate as second leach,creating nitric in solution,
then nitric(H2So4/NaNO3) and HCL, for third leaches as poormans Aqua regia?
of coarse this concept could be used with others such as Hcl then HCL/H2O2 then HCL/Bleach, and so forth.
I have noticed from leaching ore I will need to do several leaches (as primary leach) as the metals from first series of leaches may only get base metals in higher series, the ones lower in series can keep these from disolving the first leach base metals, takeing sometimes days, and letting everything settle till liquid is fairly clean, colors of solution can give indicator, or clues to metals being removed from solution and their concentration, heating is a big help, but oxidizers and little more acid as heat can dissipate these, so consider there still may be metals that that lech did not get, that the acid you are using if redone may pick up next time using the same acid when my leach does not pick up metals (color and concentration as indicator) I go to the next leach or acid higher in power.to get metals lower in series.
heck hope somebody can figure out what I am trying to say, or show me where I am mistaken.

 

[Anonymous]

I do not like the h2so4 becuase it forms insoluble sulfates with silver (robs you of values), lead (pain the the arse to filter/seperate) and I also think cadmium sulfate is insoluble. For these reasons I am also not a fan of the sulfuric and nitrate substitute for nitric although it is good for removing copper.

Jim

 

[butcher]

I was thinking could get silver and others , after primary leach with the nitric solution, I see your point James. very good point.

in just H2SO4, I was under the impression silver would not sulfate, to any extent as hydrogen so much higher in series, until you made silver nitrate and then added the H2S04 to it, and poor mans can have sodium bisulfate or sodium hydrogen sulfate if excess acid used, so in situ possible some sulfuric left in equation, I am not too sure how much silver would convert to insoluble silver sulfate in such an oxidized environment, all nitrates soluble and hot even more so.
I may be dragging around a wet blanket on this, and need more advice here from a chemist, to clear up the way I am seeing this, as sometime's too many tree's in my forest, and sometimes I don't see that one tree.

Any volunteer teacher ?

 

[Irons]

I was thinking could get silver and others , after primary leach with the nitric solution, I see your point James. very good point.

in just H2SO4, I was under the impression silver would not sulfate, to any extent as hydrogen so much higher in series, until you made silver nitrate and then added the H2S04 to it, and poor mans can have sodium bisulfate or sodium hydrogen sulfate if excess acid used, so in situ possible some sulfuric left in equation, I am not too sure how much silver would convert to insoluble silver sulfate in such an oxidized environment, all nitrates soluble and hot even more so.
I may be dragging around a wet blanket on this, and need more advice here from a chemist, to clear up the way I am seeing this, as sometime's too many tree's in my forest, and sometimes I don't see that one tree.

Any volunteer teacher ?

Try very dilute Nitric with a bit of H2O2 to keep the NOx in check and make the process more efficient. Any NOx that come off is a waste of Nitric.
As long as there are any base metals undissolved, the PMs should remain in the sludge at the bottom of the tank.

The question is: Is it economical?

It all depends on the amount of PMs in the mix and the cost of recovery or disposal of the base metals.

I think you will eventually find that an pH/ORP meter/controller to regulate the addition of Nitric and H2O2 will make a big difference in your bottom line.

 

[Anonymous]

I was thinking could get silver and others , after primary leach with the nitric solution, I see your point James. very good point.

in just H2SO4, I was under the impression silver would not sulfate, to any extent as hydrogen so much higher in series, until you made silver nitrate and then added the H2S04 to it, and poor mans can have sodium bisulfate or sodium hydrogen sulfate if excess acid used, so in situ possible some sulfuric left in equation, I am not too sure how much silver would convert to insoluble silver sulfate in such an oxidized environment, all nitrates soluble and hot even more so.
I may be dragging around a wet blanket on this, and need more advice here from a chemist, to clear up the way I am seeing this, as sometime's too many tree's in my forest, and sometimes I don't see that one tree.

Any volunteer teacher ?

You may be right on the silver. My point is the first time you add h2so4 you will get lead/cadmium sulfate for sure, messing up the place and not dissolving copper or doing so very slowly, then when you add h2so4/nitrate you will get silver sulfate messing up the works.

Jim

 

[Irons]

Standard Electrode potential data

http://tinyurl.com/yho8mqm

 

[markqf1]

Excellent reference material Irons,
Now if only I can absorb it all. :lol:

Mark