# Membrane Systems



## goldsilverpro (Jan 26, 2015)

I moved the posts I made on Ralph's membrane thread here. His cell is really neat and well-made and I hijacked his thread. Sorry, Ralph


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## goldsilverpro (Jan 26, 2015)

If anyone recalls, I promised a write-up on a nitric making cell about 5 years ago. Better late than never, I guess.

Your tank is basically the same configuration as the tanks I built in the early 80s - one was about 100 gallons. How did you secure the membrane to make it leakproof? If the materials used can withstand nitric and sodium hydroxide, you can use a 3 cell system with 2 ion-exchange membranes to make HNO3 and NaOH at the same time using sodium nitrate.

From left to right:

- 300 series SS Anode (+) at far left - 304L is probably best
- Weak nitric solution (say, 2%) in left cell to make the solution conductive and get it started
- Anodic membrane (will only pass anions - those with a minus sign like NO3-)
- Sodium nitrate solution in middle cell
- Cathodic membrane (only pass cations - like Na+)
- Weak NaOH in right cell
- SS cathode at far right (-)

Use distilled water in each cell.

Here's what happens:

When you turn the current on, all the (-) ions are attracted to the left to the anode (+) and all the (+) ions are attracted to the right to the cathode (-). Unlike charges attract.

At the same time, water is split at both electrodes. At the anode, oxygen is given off as a gas and H+ ion enters the solution in the left cell. At the cathode, hydrogen gas comes off and the OH- ion enters the cell on the right.

NO3- (middle cell) and OH- (right cell) are both attracted to the left towards the anode. The NO3- passes through the anodic membrane into the left cell. The OH-, however, stays in the right cell because it won't pass through the cathodic membrane. In the same vein, the H+ stays in the left cell (it is blocked by the anionic membrane) and the Na+ passes through the cathodic membrane from the middle cell to the right cell.

The result is that H+ and NO3- (HNO3) build up in the left cell, Na+ and OH- (NaOH) build up in the right cell, and the Na+ and NO3- (sodium nitrate) becomes depleted in the middle cell. You just add NaNO3 to the middle cell periodically and bail out the left and right cells periodically.

If you want to make HCL and NaOH, you use NaCl in the middle cell, although that might not work too well due to Cl2 coming off as gas at the anode. To make H2SO4 and NaOH, you use sodium sulfate in the middle cell.

A problem with the nitric is that I haven't found an anionic membrane that will stand up to nitric in excess of about 20%. Dupont makes a teflon cathodic membrane but not an anionic one. I think someone makes them, though. 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. There are also bipolar membranes (they work a bit differently) that can be used to make the acids/NaOH (or, whatever you want to make).

Ion-exchange membranes are sometimes called ion traffic controllers.


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## goldsilverpro (Jan 26, 2015)

When I started working with membranes, I was able to get free samples (usually about 6"X6") from the companies that sold them. Some membranes (Ionics, for one) have to be stored in water because they will crack when dried out.

I spent about 2 years playing with membranes. I used to fill notebooks with sketches (similar to the drawing above) of the 100s (literally) of interesting things you could try doing with membranes. I had an AA with most every lamp and lots of titration stuff to monitor ion transference in the various cells. All this became an addiction!

_____________________________________________________________________

This is hard to explain without a drawing, but I'll try. 

For experimental purposes, I obtained a bunch of about 250ml open top, square, tall boxes (say, 2"x2"x4" tall) made from a very rigid, hard clear plastic (Styrene? Acrylic? I don't remember). Each box was an individual cell.

In the above 3 cell example, I cut 1 window (say, 1" x 2") centered on one side of the left and right boxes and 2 windows in the middle box, one on each side, using a Dremel tool. The windows were all the same size and were in identical positions on each box. The membranes were about 1/4" larger than the window on all 4 sides.

I then applied grease (silicone? or teflon?) to the 1/4 border (only!) on both sides of the membranes. The membranes were then positioned over the windows and the 3 cells were lined up perfectly. To hold the 3 cells together, I used a couple of heavy rubber bands. The grease sealed the membranes around the windows and prevented leaking.

I remember having as many as 7 of these boxes (cells) ganged together, with different solutions in most of the cells, for certain wild experiments. Usually, everything happened as per my sketch predictions.


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## Palladium (Jan 26, 2015)

I've ordered some sample pieces. This is a whole new field for me that i think i am going to try. This is something we don't discuss much and looks like science fun!


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## Palladium (Jan 26, 2015)

These are the samples i ordered. Will they work Chris?


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## goldsilverpro (Jan 26, 2015)

One time I tried to create a solution whose total charges were out of balance - where the total positive charge was more or less than the total negative charge. A new fuel maybe. I think I used 7 cells in a row. However, nature wouldn't let me do it although the setup I had was correct. At the bottom of each of the 6 membranes, which were not conductive!, I could see the bubbles from water splitting. This provided enough of the missing ions to keep all the charges in balance. In no other experiment did the water split anywhere but on the electrodes.


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## goldsilverpro (Jan 26, 2015)

Palladium said:


> These are the samples i ordered. Will they work Chris?


Did you mean to post a link?


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## Palladium (Jan 26, 2015)

goldsilverpro said:


> Palladium said:
> 
> 
> > These are the samples i ordered. Will they work Chris?
> ...



I'm getting old. lol
http://www.membranesinternational.com/


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## goldsilverpro (Jan 26, 2015)

Palladium said:


> goldsilverpro said:
> 
> 
> > Palladium said:
> ...


They sound OK but I don't know There are probably 100 more companies making these now than 35 years ago when I was messing with them. Back then, it seemed like each company's products were made of different materials.

Were it me, I would get on the phone and start begging for samples. Get their prices in square feet and in volume. A business name and address would very likely help. After all, you will need a lot of these in the future and you're surely not going to buy from them if their product doesn't work. I used to be the king of getting free samples.

To me, the most important thing is what they are made out of and will they withstand the chemicals I want to use. It would be great if they were all made of Teflon or other fluorocarbon, but they're not. The only ones I know of are the Dupont Nafion Cationic membranes. If they also made Teflon Anionic membranes, the nitric cell problem would be solved.


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## solar_plasma (Jan 27, 2015)

I just came to wonder, if sodium silicate and heavy metal salts could give a useful cation selective membrane. Think of the chemical garden experiment. 

maybe...glas fiber cloth soaked with sodium silicate and sprayed with an appropriate heavy metal salt....

anion selective would be quite another story, though....


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## goldsilverpro (Jan 27, 2015)

solar_plasma said:


> I just came to wonder, if sodium silicate and heavy metal salts could give a useful cation selective membrane. Think of the chemical garden experiment.
> 
> maybe...glas fiber cloth soaked with sodium silicate and sprayed with an appropriate heavy metal salt....
> 
> anion selective would be quite another story, though....


I know there is a lot of information out there on making membranes, including a lot of patents, but I never really studied that part of the literature.

There are also a lot of patents, mostly from the 70s and 80s, that utilize membranes in PM recovery schemes. I run into them every so often when I'm researching patents. At that time, membranes were new to most people. They were a hot item and it seemed that most refineries were experimenting with them.

The widely available bipolar membranes are very interesting, in that they can do wild things that the regular membranes cannot do. I would certainly research them. I have not used them.


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## goldsilverpro (Jan 27, 2015)

Here's a schematic on the small plastic box-cell arrangement mentioned above. You just assemble the cells as shown, clamp the whole thing together with big rubber bands and put an electrode in each end. The holes (windows) should be relatively bigger, though. The more membrane surface area, the lower the voltage will be for a given amount of current. I might improve the drawing and re-post it.


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## Palladium (Jan 27, 2015)

The more i read the more i can see the applications for this technology! 
I'm liking it!


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## Palladium (Jan 27, 2015)

This may be the cats meow here Chris! Seems to make cathode and anode choices easier also.
http://www.astom-corp.jp/en/product/05.html


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## goldsilverpro (Jan 27, 2015)

I know enough to know that bipolar membranes are the cat's meow. I just don't know enough to intelligently discuss them. I'll learn, though. They weren't around much when I did the membranes. Just don't lock into one manufacturer. There are lots of manufacturers and lots of different membranes. Get lots of samples. 

There's an old request in the PM refining business - *Send us Bigger Samples!!!!* :lol:


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## rickbb (Jan 28, 2015)

I've seen designs that use a "salt bridge" as a membrane. They make this salt bridge out of gelatin and table salt. It's setup in a PVC tube that connects the different tanks.


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## Lou (Jan 28, 2015)

I wonder if this type of technology could be used to turn potassium perrhenate into perrhenic acid and KOH in a compartmented cell?
What do you think Chris?


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## Palladium (Jan 28, 2015)

goldsilverpro said:


> I know enough to know that bipolar membranes are the cat's meow. I just don't know enough to intelligently discuss them. I'll learn, though.



This should help. My head hurts! :arrow:

The old technology will work but the efficiency, membrane leakage (Contamination between cells), and the anodes-cathodes, are parameters that are hell to deal with. I'm looking into not only the bipolar membrane technology, but also using PWM to control the water splitting sort of like in an hho cell. This could get real interesting. I love science!


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## goldsilverpro (Jan 28, 2015)

Lou said:


> I wonder if this type of technology could be used to turn potassium perrhenate into perrhenic acid and KOH in a compartmented cell?
> What do you think Chris?


I follow you. Sounds like it will work. Essentially the same as making nitric.


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## goldsilverpro (Jan 28, 2015)

rickbb said:


> I've seen designs that use a "salt bridge" as a membrane. They make this salt bridge out of gelatin and table salt. It's setup in a PVC tube that connects the different tanks.


Salt bridges are interesting. I've read about them. I just don't know enough to discuss them. I can learn, though.


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## solar_plasma (Jan 28, 2015)

rickbb said:


> I've seen designs that use a "salt bridge" as a membrane. They make this salt bridge out of gelatin and table salt. It's setup in a PVC tube that connects the different tanks.



This sounds as something useful and easy done for school experiments. Can you remember what anions it will work for? I would have expected, that it doesn't work with NO3- or SO4--, since gelatine is a protein, which turns yellow by nitric, and sulfuric removes water from many organics. Another problem, I see, is, that gelatine slowly dissolves in water, especially when warm.

Chloride should work. At least when a chicken bone is left in HCl, only the gelatinous (don't know, if this actually IS gelatine) components will be left structural intact.


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## rickbb (Jan 29, 2015)

I ran across the salt bridge when looking up making sodium hydroxide in a cell. The various article's claim that in this process the gelatin will not dissolve.


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## Palladium (Jan 30, 2015)

I found the company who supplied the membranes for a prototype salt splitting cell for NASA that uses salts to produce chemicals while in space. I can order samples directly from them, but they think highly of the price! I would rather go with the best than miss my mark based on price though. Looks like about $200 when all is said and done for 3 pieces the size of sheets of paper. (1 cation. 1 anion. 1 bipolar membrane). It this works then i feel we have found a process to safely produce nitric acid from salts and water. They claim with this process levels of 68% can easily be reached. I'm going to make a bench top nitric acid machine! From my estimates 1 gallon 68% every 24 hours should be an easy goal.

http://www.fumatech.com/EN/Onlineshop/fumasep-for-Electro-membrane-processes/


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## rewalston (Jan 30, 2015)

now that would be interested Ralph for those of us having a hard time getting Nitric Acid.

Rusty


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## necromancer (Jan 30, 2015)

solar_plasma said:


> rickbb said:
> 
> 
> > I've seen designs that use a "salt bridge" as a membrane. They make this salt bridge out of gelatin and table salt. It's setup in a PVC tube that connects the different tanks.
> ...




you may be thinking of "cartilage"
http://en.wikipedia.org/wiki/Cartilage


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## necromancer (Jan 30, 2015)

rewalston said:


> now that would be interested Ralph for those of us having a hard time getting Nitric Acid.
> 
> Rusty



nitric acid is easy to get here in Ontario in large amounts, small amounts are to expensive & chemicals to make nitric without distilling are impossible to get. (Potassium Nitrate, Sodium Nitrate)

i can buy a carboy of nitric acid but it will last me way to long.


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## eastky (Jan 30, 2015)

Palladium said:


> I found the company who supplied the membranes for a prototype salt splitting cell for NASA that uses salts to produce chemicals while in space. I can order samples directly from them, but they think highly of the price! I would rather go with the best than miss my mark based on price though. Looks like about $200 when all is said and done for 3 pieces the size of sheets of paper. (1 cation. 1 anion. 1 bipolar membrane). It this works then i feel we have found a process to safely produce nitric acid from salts and water. They claim with this process levels of 68% can easily be reached. I'm going to make a bench top nitric acid machine! From my estimates 1 gallon 68% every 24 hours should be an easy goal.
> 
> http://www.fumatech.com/EN/Onlineshop/fumasep-for-Electro-membrane-processes/



I would be interested in helping out with the cost of doing a cell for nitric acid. If interested send me a pm.


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## Palladium (Jan 30, 2015)

Dam! Time for a go fund me account! :mrgreen: 

Believe it or not that's how i do a lot of my designs for clients is with experiments on a scale model. The client usually covers the cost of the equipment and i donate my time and effort. When this is said and done it will probaly cost $ 350-400 for the first model at cost and then price drops as production gets efficient. I could sell them for $1,000 and do good. This will be the third experiment i'm working on right now. The first is the fizzer cell. The second is the new design for the silver cell, and the third would be the membrane cell. I really like the membrane idea on a bench scale, it's just the science that goes into it may look simple in design, but is more complex in the build. I still have control mechanisms, anode and cathode selection and design considerations. Power design is complicated, but somewhat easy. With today's technology i can buy a board off ebay, jack it in to my computer with a usb, and program the electronics fairly easy. Theirs a few things i'm not sure of yet, but that's why i build things that can be controlled by parameters so it can be adjusted. You can do the same thing with regular membranes, but the longevity, product percentages, maintenance, energy cost, and all the other problems compound into " This thing sucks! ". I won't build or sell junk! That's what ebay is for.

Wait! I'm on Ebay. :twisted:


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## butcher (Jan 30, 2015)

I have given thought to this idea several times but never followed through with any ideas,

Salt bridges will work fine for ionic salts like sodium or nitrate and so on, but trying to move hydrogen or a gas across the bridge just wont work.

I have also thought that we might be able to use a gas evolved from say one cell and add it to another cell to chemically react to form a product in that compartment...

I have made several drawing on paper of different ideas, I tried to put one on paint program(never used it before), this Idea is using a 3 compartment cell (two separate power supplies), here the center electrode could be one common electrode if wanted.


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## Palladium (Feb 11, 2015)

Got some samples in today (6X6). It's not the bipolar membranes i need, but it's something fun i can play with to learn before i drop a couple hundred on the other ones and screw them up from inexperience! :mrgreen:


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## Lou (Feb 11, 2015)

I'm interested to see how this all develops. If Ralph can make a nice compartmented membrane cell...should be cool. This means that members can dissolve their silver, remove it with just enough chloride, waste treat the barren nitrate solution, filter, and re-use that sodium nitrate solution to make more nitric! 

I know divided membrane cells are how NaOH is now made in bulk--on 3500# containers we get in, it says "diaphragm grade". Time was when all the NaOH and chlorine made from brine was made using mercury cathodes. No longer! At least here in the US. Nice to see technology make things a little more environmentally friendly.


Lou


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## Palladium (Feb 11, 2015)

Membranes use to intimidate me until i got a better understanding of them. I have read stuff until my head hurts. You're right! The technology is fascinating. Advanced as the industry is today it's still a specialty market that's still in it's infancy, at least for the bipolar membranes. The problem lye's not in the science or theory, but in the manufacturing of the membranes themselves. From what i read with dealing with waste streams or multi metals solutions the problems come from fouling of the membranes. So many variables to account for in a complex system like that. For years they have used membrane technology in different types of salt splitting cells, but the problems have been drift through the membranes which leads to contamination of the final product and lower levels of solution concentrations. Anode design suffers from degradation, fouling, excess gas generation, heating, and inefficiency of electrical energy conversion. With the bipolar membrane it virtually eliminates all of that. The science behind the bipolar membrane and the physics involved are both complex...... yet simple! With a simple salt splitting cell (bipolar) using just two elements combined as a salt to generate separate solutions the longevity, durability, as well as the simplicity should be fairly easy to demonstrate for everyday use by members or anyone who needs acids on demand. Nasa had a prototype built that seems to fit the bill so i figure why not me! :mrgreen:


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## goldsilverpro (Feb 11, 2015)

Ralph,

There's a lot of PM patents using membranes. Here's a couple of searches. Electrodialysis membranes and ion-exchange membranes are essentially the same thing.
https://www.google.com/search?tbo=p&tbm=pts&hl=en&q=gold+recovery+membrane&num=10#hl=en&tbm=pts&q=gold+recovery+membrane+electrodialysis

https://www.google.com/search?tbo=p&tbm=pts&hl=en&q=gold+recovery+membrane&num=10#hl=en&tbm=pts&q=gold+recovery+membrane+ion-exchange
____________________________________________________________________

When fabricating a membrane cell, the most important part is seal them so that there is no leakage from one chamber to another. This is easier said than done. All materials used must stand up to whatever types and strengths of chemicals are in the chambers. 

During the 2 years I played with membranes, I used only 2 methods for sealing off the chambers:

*(1)* For the small (~200ml) experimental cells I discussed earlier in this thread, I cut windows in the boxes (polystyrene, I think - very rigid) and sealed the membranes between boxes with grease that was inpervious to the chemicals. Rubber bands clamped the line of boxes together. This method is easy with a fast setup and allows you to use any number of chambers that your heart desires. I mentioned that I once used 7 chambers and each was needed in the weird-ass experiment I thought up.

I once thought about building and selling a larger version of this, maybe with one gallon chambers, using a strap ratchet clamp. Besides chemical resistance, the most important thing is that the walls of the individual tanks (chambers) are rigid enough to prevent distortion of the walls when clamped. This could cause leakage.

Thick (1/2"?) plastic sheet welded into 1 gal. tanks would work. I also thought of, say, 1/8" thick stainless tanks with a plastisol coating. I used to buy a liquid plastisol by the gallon that was made for plating fixtures. I used it to dip coat small plating racks.

*(2)* Big tanks. The biggest one I made was about 100 gallons. I was dissolving superalloys in weak sulfuric anodically. A membrane divided the tank into 2 compartments and prevented the dissolved metals from contacting the cathode. Worked great except for the significant mist of sulfuric in the air caused mainly by the fizzing at the cathode. It was so bad you couldn't go in the room. We floated about 3 layers of different sized PP mist-suppression balls on top of the cathode solution and that helped considerably.

I'll make a drawing for this sooner or later. I had the tank fabricated from probably 1/4" plastic. A flat picture frame was welded up from the same plastic, using, say, 1/2" thick x 3" wide pieces. The width of the frame was such that it fit fairly snugly in the tank. Holes of a size to take a 1/2" PVC bolt were drilled every 3", or so, around the 4 sides of the frame. The frame was welded into the tank. A slightly narrower duplicate frame with matching holes was built. We used a one piece Buna-N (I'm thinking - either that or Neoprene) rubber gasket I made (with holes) between the frame and membrane. In order: Frame in tank - Buna N gasket - membrane - loose frame. We may have also used a 2nd gasket between the other side of the membrane and the loose frame. Everything was sandwiched together and mounted using 1/2" PVC bolts, nuts, and washers.
_________________________________________________________________________

If I were to get heavy into this, I would surely get a good self-contained plastic welder (about $500) and learn how to use it properly - I have a little experience in this and it seems pretty easy - just control the variables - temp and flow rate of the heated air - positioning, etc. Also, with a table saw, 4x8 sheets of plastic, and a heated sheet bender, you could make your own tanks to your own specs. Saves a lot of money and puts you in better control.


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## solar_plasma (Apr 1, 2015)

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.


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## goldsilverpro (Apr 1, 2015)

Richard,

In your sketch, you can accomplish exactly the same thing by using just one power supply across the 2 outer electrodes and eliminate the 2 inner electrodes. I would also use NaNO3 instead of NH4NO3. That way, there would be no ammonia coming off although I'm not sure it would come off as in your sketch. Sometimes the chemical reactions at the electrodes are not that easy to predict. Actually, I like your setup (but with only 1 PS) for nitric better than the one I gave earlier, although it might be harder to control.

Instead of Paint, download Inkscape. It's probably the best free drawing program. I use Adobe Illustrator (AI), which is not free, but you can do about anything with Inkscape that you can with AI. After downloading, go to Help in the menu. You will find an Inkscape manual and some good tutorials. Any of these drawing programs need practice.

https://inkscape.org/en/


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## FrugalRefiner (Apr 1, 2015)

Thanks for the recommendation GSP! I've been needing a new drawing program. This one looks like it should keep me busy learning it for a while.

Dave


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## goldsilverpro (Apr 1, 2015)

Now that you have Inkscape, you might download Gimp (free), which is a pixel manipulation program like Photoshop. I haven't used it but it looks simpler than PS.

http://www.gimp.org/downloads/


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## FrugalRefiner (Apr 1, 2015)

I already have GIMP, thanks. I'm sure I've only scratched the surface of its abilities, but I accomplished what I needed to do. If you want full featured software, you have to be prepared for a steep learning curve. I just started on the Inkscape tutorial.

Thanks again for the recommendations,
Dave


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## MarcoP (Apr 1, 2015)

Yeah GIMP is ok, specially because is cross platform, but at the beginning you'll have some issues even for easy tasks. For example there is not a tool for straight lines, press SHIFT, click and draw but sometimes this is great because you don't have to change tools so often.


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## Sucho (Apr 1, 2015)

Hi guys!

Its a long time ago i wrote something here, but this topic is very interesting for me and corresponds with my ideas.
It touches my field partially, i am working on solid phase extractants based on ionic liquids for heavy and radioactive metal separation.

my pium desiderium is to apply solid phase membranes or liquid surfactant membranes in refining cells.

The key elements for electrolytic cell containing various metals in electrolyte would be the kinetics of sorption/desorption on an membrane - includes surface, hydrophobicity/hydrophilicty of the membrane, in a case of fixed extractants- washing out extracting agents on each site of membrane and selectivity, of course.

The problem would be speciation of desired membrane-transported metal ion on each site of the membrane according to the direction of current in cell.

i am really curious for updates in this topic !


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## METLMASHER (Apr 1, 2015)

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.


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## solar_plasma (Apr 11, 2015)

solar_plasma said:


> 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?


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## solar_plasma (Jul 28, 2015)

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?


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## Research135 (Jul 28, 2015)

goldsilverpro said:


> 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).!


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## Research135 (Jul 28, 2015)

Lou said:


> perrhenic acid


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


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## solar_plasma (Jul 28, 2015)

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.


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## Research135 (Jul 28, 2015)

solar_plasma said:


> 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.


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## MarcoP (Jul 28, 2015)

Research135 said:


> 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.


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## solar_plasma (Jul 28, 2015)

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.


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## Research135 (Jul 28, 2015)

solar_plasma said:


> 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.


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## Research135 (Jul 31, 2015)

sssssshhhhh!


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