Membrane Systems

[METLMASHER]

Thanks, GSP. It looks like a very do - all program. I left the page blank, inviolate, pristine. I will get into it very soon, and practice a lot.

 

[solar_plasma]

Today I got an anion exchanger membrane and a cation exchanger membrane from Fumatech as a free sample, both 20cmx30cm Very nice people!

I will take the time needed to read everything again, so I know exactly what and how to do before starting. Would be a shame to destroy them by stupidity.

I think I have a plan with my membranes:

waste sulfate solutions containing cobber, nickel, zinc, traces of impurities possible:
carbonate precipitation, clear solution (witch I can test and might contain mg of heavy metals) is titrated to neutral by H2SO4, put into the middle cell, left H20 and a litlle NaOH, right H2O and a little H2SO4. I get new NaOH and new H2SO4 in a technical grade that can be concentrated and reused. Continiously waste NaSO4 is replaced in the middle chamber and while NaOH and H2SO4 are partly removed and replaced with H2O.

The idea is to have a closed cycle for most of the waste volume, so the mg trace of metal ions do not leave the loop. The carbonate residues are stored wet and finally go to a professional recycler.

Comparable settings for nitrate or chloride I still need to investigate. Precipitation, propper distilling off nitric or hydrochloric and leaving sodium sulfate for further processing in the membrane cell might be a better choice, than to use them in membrane cells directly, since I have no need for chlorine and as GSP said, there are problems regarding durablity with nitric.

I would like to use only one big clean easy maintained recyling cell with a high durablity. No nasty coloured salts, precipitates or floating metal powders in my clean cell.

The concentrations in the left and right chamber are monitored by two araeometers. It should be save to leave the process, though an internet cam might be an option. If this works like I dream of, I could let our regional safety inspector look at it, to be on the safe side, if this should be applied as a continous waste treatment at my school.

This method competes with a resin system. I have to find out, if this would be a better choice to clean waste sodium chlorides, sulfates and nitrates from any problematic cations. It would be easier and more handy. On the other hand it is more expensive and nothing is recycled for reuse.

Does this sound like a plan or did I miss anything?

 

[solar_plasma]

Still thinking over experiments with my membranes. Before I try anything, I want to be sure, what exactly I want to do.

Since yesterday one idea just doesn't let me find peace:

Purpose: dissolve lowgrade silver scrap that shows high corrosion resistance and recovery of the silver as chloride with least waste and effort

Setup:
A cell with a cation permeable membrane.
Anode 5% silver, rest Cu, Ni, Zn
Cathode inert material like steel or graphite
Electrolyte ZnCl2

Expected reactions:
Most Ag will precipitate as AgCl. Some of it will stay dissolved as AgCl₂^-. Both of them will not pass the membrane and AgCl₂^-will be attracted by the anode.
Cu will partly do the CuCl₂-CuCl₂^- twist at the anode and dissolve the anode.
Ni and Zn (and some Cu) will be oxidized and attracted by the cathode, pass the membrane and build up moss and lumps at the cathode.
Nascending chlorine is developed at the anode, dissolves it directly and feeds the CuCl₂ circle. It does not leave the system as gas (I tried this with copper).
Since this cell would be used with overvoltage, some hydrogen gas would be generated at the cathode. This side of the cell, or easier the whole cell, should be closed i a way that the expelled gas can be filtered or washed before leaving since it would contain a lot of heavy metal aerosole.

With the precipitated AgCl a stoichiometric amount of chloride will leave the system and has to be replaced.

Do you think this is worth to think over it further or will it just be another impasse?

 

[Research135]

Japanese companies make a big variety of interesting membranes. One is a membrane that will only pass +1 ions (by Asahi Glass, I seem to remember). Separate Ag+ from Cu++ and other higher charged positive ions.

Nice thread. I 'd like to learn more about the specific subject quoted. Thanks.

Specifically thinking about separating Ag+ from the Pt(II) and Pd(II).!

 

[Research135]

perrhenic acid

Sounds like a super-acid. Will PTFE be enough to contain that?.

 

[solar_plasma]

As far as I understand this matter, you will be able to collect pure Ag, but you will have problems getting the last Ag traces out of the electrolyte by electrolysis. On the other hand, the more Ag is removed at first hand, the less Pt can be draged down, when precipitating AgCl.

I think the benefit regarding Pt would be marginal, since the converted AgCl would go to the silver cell anyways and all Pt will end in the anode slimes. Pd is another story since over time it contaminates the silver cell electrolyte.

 

[Research135]

As far as I understand this matter, you will be able to collect pure Ag, but you will have problems getting the last Ag traces out of the electrolyte by electrolysis. On the other hand, the more Ag is removed at first hand, the less Pt can be draged down, when precipitating AgCl.

I think the benefit regarding Pt would be marginal, since the converted AgCl would go to the silver cell anyways and all Pt will end in the anode slimes. Pd is another story since over time it contaminates the silver cell electrolyte.

Think large conventional silver cell, plus an Ag+ only membrane. AgCl is cumbersome, even in less than kilo quantities. I always try to avoid it. A membrane would eliminate the need for DMG treatment for Pd too.

 

[MarcoP]

Think large conventional silver cell, plus an Ag+ only membrane. AgCl is cumbersome, even in less than kilo quantities. I always try to avoid it. A membrane would eliminate the need for DMG treatment for Pd too.

But wouldn't PD still be in the anolyte? Will it deposit it self or DMG will be still needed even in the anolyte? Sure will eliminate any co-deposition.

 

[solar_plasma]

I see. Sounds ingenious.

I do not think Pd in the anolyte would cause any greater problems, it just can't go anywhere you don't want to have it. The catholyte stays clean and only the anolyte has to get removed when and if the cell becomes too ineffective.

 

[Research135]

I see. Sounds ingenious.

I do not think Pd in the anolyte would cause any greater problems, it just can't go anywhere you don't want to have it. The catholyte stays clean and only the anolyte has to get removed when and if the cell becomes too ineffective.

How about this?

An electrified Buchner filter with an anode on the top half (filled with liquid nitrates of everything), a cathode in the bottom half (filled with Ag+, and ???), and the Ag+ only membrane acting as the filter in the middle. Controlled flowrate keeps both halves of filter full of liquids. Looks easy to setup and test.

 

[Research135]

sssssshhhhh!