Electrochemistry Sulfuric acid stripping cell PSU

[BAMGOLD]

Butcher, thanks for almost copying my post word for word, lol.

I know I'm over thinking it, but it's the one thing I've read on this forum where I feel comfortable doing so.... I've messed with electronics/computers since I as 12, now 27. I'm just an experimenter or "Hacker" as it were... I make things better, this is one place where I think it can be made better, but in the end my main question really is...

What is more important, from Most important to Least important

Cell Temp
Cell Voltage
Cell Voltage waveform

My assumption after reading a bit more is that I just wrote them in the correct order, but Voltage is directly related to Temp

Waveform and duration *could* help the Temp, POSSIBLY minimally so...

What is the *BEST* temp for the sulfuric acid? Cold as possible?? What temp does it start attacking base metals?

I do think to gain any noticeable effect of cooling, I would STILL need a method to cool the solution, I'm thinking something like a metal box with a few of those frozen ice packs you keep in the freezer for a cooler, or some version of that, and this may be enough to cool it I just don't know...

My mind is still stuck on 50% duty cycle, now square or sine shaped is the next question on my mind...

As for the Peltier coolers, I've looked into the numerous times before, never actually bought any, I was actually going to make power from them instead of use their cooling abilities, just as an experiment. :mrgreen:

I actually have some Aluminum blocks that have been milled out and welded back together, they have 2 fittings on them for coolant to be ran through them. They keep our IGBT's in the wind turbines cool, when they blow up, we strip them down. I have some SSR's mounted to one of these blocks, as I run a Burst Fire controller for my Electric Meat Smoker, I constantly run the SSR at 10-15amps and run water through the block, they never get even warm... Speaking of that... I should sell it, I sold my smoker.. It CAN go up to 75 amps, and used for Resistive loads only, Inductive loads... well... I have a 1500watt controller for that too... ok.. now I'm just rambling as I remember I have this stuff. Oh and a Freq drive... :mrgreen:

 

[publius]

My thoughts on cooling a sulfuric cell:

1) Use dry ice (frozen CO2)

2) Crushed ice with salt (NaCl) that your cell floats on but with heavy poly plastic that covers the ice so that if any of the acid spills or your cell cracks it will not be dumped into the water.

3) A large aluminum block to set the cell on top of.

 

[Golddigger Greg]

Golddigger Greg,
If we are discussing a gold stripping cell using concentrated sulfuric acid, 10 amp battery charger will be large enough, as long as you build your cell similar in size to those you will see in the forum.

I was actually referring to the variable transformer, but I assume the same would apply. Thanks!

 

[butcher]

Golddigger Greg, the alternating current variable transformer (variac) will come in handy to be able to adjust the AC power to the DC power supply or battery charger, this will give you more control of the DC voltage output.

The variable transformer is adjustable to change the alternating current voltage, (you need direct current DC to power the cell), the variac would allow you to change the voltage output of the battery charger which is normally around 14.5 volts DC, so that you can adjust the DC voltage from 0 volts to even a little higher than the normal 14.5 volts.

 

[dcorley001]

There are a few ways to do this, but I have an Arduino and SSR's... You could go 555 Timer route, or other ways..

Bamgold, I'm really interested if you persue this avenue. The Arduino could also be utilized to monitor cell temp and change cycles, control fans for ventilation of the gases, monitor cell conditions and control safety functions and so much more. Best of all, Arduinos and their accessories are cheap. A vast number of learning tools and the libraries are available free. I've already purchased a Duemilanove an Uno and a number of other accessories to begin my personal journey. What's sad is that this would have been the perfect avenue to begin the journey with. As stated let me know if you decide to give these a try. I will warn you I'm just beginning to learn so it's extremely doubtful that I'll be of any/much help! Thank you so very much for planting this seed and wringing a few drops of moisture over it!!!

 

[BAMGOLD]

There are a few ways to do this, but I have an Arduino and SSR's... You could go 555 Timer route, or other ways..

Bamgold, I'm really interested if you persue this avenue. The Arduino could also be utilized to monitor cell temp and change cycles, control fans for ventilation of the gases, monitor cell conditions and control safety functions and so much more. Best of all, Arduinos and their accessories are cheap. A vast number of learning tools and the libraries are available free. I've already purchased a Duemilanove an Uno and a number of other accessories to begin my personal journey. What's sad is that this would have been the perfect avenue to begin the journey with. As stated let me know if you decide to give these a try. I will warn you I'm just beginning to learn so it's extremely doubtful that I'll be of any/much help! Thank you so very much for planting this seed and wringing a few drops of moisture over it!!!

I purchased my Duemilanove right when they came out, also bought about 100$ in accessories and books, I read them all and played around with it for awhile, then lost interest, it's still in the drawer... Your right about monitoring things, I actually forgot about that, as I mostly bought it for PWM more than anything... now you got me thinking again.... Thank You!!! :mrgreen:

So.. #1 thing is Cooling, meaning if you can control the temp to a "certain degree" (still looking for that temp???) then you can raise the voltage..
Here are my thoughts: (Lets pretend the current source is capable of 25amps)

12vdc heats the solution to 100*F in 10min
24vdc heats the solution to 100*F in 5min
48vdc heats the solution to 100*F in 2.5min

Lets guess that 100*F is the MAX temp you would want to see in your Cell.

Now if 48vdc can strip your gold 4times faster than 12vdc can, then I see no reason not to use 48vdc.
If 48vdc can't strip it 4x faster, but lets say 3x faster, then it may still be the best voltage to use if you can control the temp to 100*F, as you may only need to actually cool the solution for 1-2min, that means you could use any number of cooling means as again it's only 1-2min you need to cool.

I think people MAY be having cooling issues with 12volts as it takes so long (in my theory) to De-plate that the cooling method has a hard time keeping up.

lets say I have 3lbs of Aluminum heat-sink attached, and I just pulled it out of the freezer, so it's at 0*F, I put it under my 12v solution to help cool, well after 10min, most of the cooling of the aluminum was lost to the ambient temp of the room, where as you put it under the 48v cell and it's so fast at heating that the "cold" from the aluminum will be used on the solution and not the ambient room temperature.. (of course I understand that heat transfers, not cold, hope you understand what I mean)

In the end... I still haven't made a cell but am hoping to hear some useful advice I haven't yet read/heard.

 

[goldsilverpro]

I have been using the sulfuric stripper, on and off, for 42 years. I have used many different volumes of this stripper, ranging from 1 liter to 250 gallons in size.

In the early 70s, I ran a 50 gal (actually, 2 - see below) sulfuric stripper all day, every day, for about 2 years and never had to make up a fresh solution. I attribute that longevity to maintaining the temperature at a level below 100F and, maybe, an occasional 105-110F. I had a 18V, 250A rectifier, so it was run at a maximum of 5A/gallon of solution. The rectangular tank was made from 1/4" mild steel and it acted as the cathode. I mainly ran 2 items in this tank, 40 lead all-gold side braze IC packages (exactly the same parts as the photos in the link below) and the lids that had been removed from these packages. The packages were run on racks made of 1/4" square yellow brass stock (uncoated) and were held on the racks with springs made from stainless piano wire mounted with stainless screws. A rack held about 300 packages and they were stripped completely in 20 minutes. The lids were run in a PP barrel plater (tumbler). After 2 years, there was no visible attack on the tanks, racks, screws or springs.
http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=58&t=14665&p=149014&hilit=mostek#p149014

The PS was a standard common plating rectifier with 1 continuously variable control knob, an ammeter, a voltmeter, and 2 fuses, one in the front for the ammeter and one in the back for the whole unit. Except for the electrode terminals, that was it.

The rack was placed in the solution with the control knob turned all the way off. Then, I carefully turned up the voltage. At first, the amperage was near its maximum with only 1 or 2 volts. As the gold stripped, the amps dropped and the voltage increased. I would then raise the voltage to increase the amps as much as possible without blowing the ammeter fuse. At some point, I was able to max the voltage with the amps somewhat below 250. I could then take a break. When all the gold was stripped, the amps normally fell to zero. The only time they didn't fall to zero was when there so much gold sludge in the tank that it partially shorted the electrodes. At that point (about once a week), I knew it was time to harvest the gold. I then switched the production to a second tank and harvested the first one.

The plating rectifier, as described above, is the only type of PS I will ever use for any electrolytic system. I don't like digital readouts because I like to visually see changes and meters give me a better feel for an overall picture what's happening. Things like constant current or voltage would be worthless with the stripper.

To me, the whole trick is to NEVER get the solution hot during the stripping operation. Anything higher than about 105-110F will start dissolving and depositing base metals and this causes big problems. It eats baskets, decreases the stripping efficiency, slows the settling, and shortens the life of the bath. Also, the sludge that formed in my tank had a high gold percentage and, after collecting it, I simply diluted it, filtered it, dissolved it in AR, and dropped it.

Cooling is one way to overcome these problems. Other ways are to run fewer parts, get a proper PS that gives you total control, don't exceed 8 amps per gallon of solution, or get a bigger tank. And, of course, get a thermometer.

 

[Golddigger Greg]

I've got some digital thermometers arriving next week. All 6 are made by VEI. I'm getting 1-DT20, 3- DT15C, and 2-DT2. 8)

 

[BAMGOLD]

The PS was a standard common plating rectifier with 1 continuously variable control knob, an ammeter, a voltmeter, and 2 fuses, one in the front for the ammeter and one in the back for the whole unit. Except for the electrode terminals, that was it.

This is the info I need clarification on, did you have an Oscilloscope on it? Was the "Variable control knob" on the AC or DC side, was it a variable transformer, or phase angle (like a light switch dimmer),or?...

Did you make this power supply? Where there capacitors inside it?

I will make my final decision based on what you answer. Thanks, GREAT POST!

 

[goldsilverpro]

If you want to know how a rectifier is made or what makes it tick, I'm not the one to ask. Basically, I could care less. In the many 1000s of hours that I've used one, I can't think of one time where I would have benefited by having that knowledge. To me, it's just one of the tools, like the tanks, electrodes, cables, heaters, filters, agitators, etc., that makes the particular solution do what you want it to do when you want it to do it. Of course, you have to know how to use those tools and their limits.

The solution is what's all important. If you don't understand the solution and its variables, success will be difficult. If you run the same solution day after day, I consider the solution a living thing, in that it's constantly changing. I can describe the parameters of setup and use (temperature, electrode sizes and materials, solution composition, current densities, etc.), for almost any electrolytic solution, whether it's for plating, stripping, electrowining, electrorefining, etc., in one short paragraph. However, that's only the tip of the iceberg. With the solution constantly changing, the other 90% is troubleshooting and tips and tricks, which can only be learned hands-on, by experimentation, or by asking someone that has had the same problems. You can't find most of that stuff in the books.

Back to the PS. I must admit that I am set in my ways concerning this subject. By the same token, I hate digital watches. Most of the modern rectifiers have digital displays and are capable of constant voltage or current. There are also periodic reverse and pulse plating PSs. An o'scope would serve no purpose as I can see. Constant current can be a good feature when plating something valuable such as gold and pulse plating can reduce the porosity of a gold deposit. I am a simple and practical guy, though, and I can't think of anything simpler or more practical than a 2 meter, 1 knob PS. There's not many of these made today but, since these were durable workhorses, there are jillions of them available used. They're not cheap. Since they were used in a corrosive atmosphere (plating shops), many of the cases don't look too great. However, it is somewhat rare to find one that doesn't function properly, even if it is 40 years old. Personally, I would trust a 40 year old one made by reliable US companies like HBS, Rapid, Udylite, etc., more than a cheaper new Chinese one. My main concerns would be durability and reliability.

Here's an example of an old one on eBay. The gizmo at the lower left is an amp-hour meter, which totals the number of amp-hours run through the PS. They are usually used for things like knowing when to add brighteners to a nickel bath or when to replenish the gold in a gold bath. For stripping, I can see no value in them unless you are replenishing a commercial proprietary stripper. Or, you could just keep an amp/time logbook.
http://www.ebay.com/itm/Rapid-Rectifier-Power-Supply-plate-plating-electroplate-cleaning-line-/370570765931?pt=LH_DefaultDomain_0&hash=item5647bd266b

The least expensive rectifiers are probably the 12V ones, because they are, by far, the most common (off-the-shelf) and will work for about any electrolytic application I can think of, except for anodizing. For stripping, they would work fine (the difference in stripping time, compared with an 18V is probably only a minute or two). Anything higher than 12V, such as 18V, are usually custom orders. Often, you will see higher voltage units used for anodizing (40V, usually). They are more expensive and the extra voltage is superfluous unless you're into anodizing.

 

[BAMGOLD]

Thank you! Another Great Post!

but, I guess we aren't talking the same language here, I can make my own PSU, no problem, but that isn't what I'm asking, and through reading I'm not sure you know either, as you say "An oscilloscope is worthless" basically. When you read "DC" it doesn't mean "STRAIGHT DIRECT CURRENT" it just means "Positive Current Only", how that is "sent" to your application depends on MANY factors.

I understand what your saying, to a point, as I know what the electricity is actually doing, I'm not sure you do, sorry. Your very smart and can get the job done, but I'm trying to learn EXACTLY what your "best PSU" is doing, and the only way of knowing is with an Oscilloscope, and there is 100% no way around it.

I will keep researching when I have time, hopefully some electrical engineer may be here reading this.

 

[goldsilverpro]

http://www.pfonline.com/articles/plating-rectifiers

 

[BAMGOLD]

Thank you very much, this quote is all I needed.

Plating chromium, precious metals, alloys and certain other metals requires minimum ripple, and if ripple is too high, it’s easy to add a ripple filter that smoothes the wave. Ripple is not very important in electrocleaning, electropolishing and anodizing.

I notice that article is dumb'd down quite a bit, almost to the point of it not making sense, but I got it....

The best thing to do for the non electrical person would be to wire it up like this.

Battery Charger > Battery > Fuse > AMP meter > Switch > Gold Cell

Great Thread!

 

[goldsilverpro]

The best thing to do for the non electrical person would be to wire it up like this.

Battery Charger > Battery > Fuse > AMP meter > Switch > Gold Cell

Great Thread!

Where is the voltage control in this scheme? To me, you must to be able to control it to get the right results. Using a battery would provide straight DC and, thereby, reduce the ripple to zero but, since the ripple is TOTALLY unimportant when using the sulfuric stripper or most other things, why complicate it with a battery? To me, it would be much simpler to just plug the charger (non-automatic type only, I think Lazersteve said) into a Variac and control it with that.

Here's a rectifier article with a little more meat (maybe) from the 2002 Metal Finishing Guidebook. The best I've found is in my 1971 copy of Electroplating Engineering Handbook. It's old but good. If I get around to scanning it, I'll post it.

 

[BAMGOLD]

That isn't how I'm going to do mine, that was a "simple" scheme that would work.... As alot of people simply use ONLY a battery charger w/ internal amp meter, I went one better for that scenario, not by any means "the best", I have yet to make that....

I have many tools/electronics at my disposal, I know what needs to be done, now it's figuring out the best way for ME to do it. After it's done I will share what I have done, but more than likely people don't have the things I have laying around.

My main 2 questions were already answered.
#1 - Voltage type (I knew DC, but what type of DC is what I was looking for)
#2 - Cooling


Thanks again! I'll read that article soon!!! :mrgreen:

 

[kjavanb123]

All,

This is my very first experience with sulfuric cell, processed gold plated pins from PCI slots, memory slots, and other related components from 2 Chinese made motherboards. It's really amazing stuff, the time to dissolve, filter, dry and drop the gold using this cell is cut in 1/10 compare to acid methods.

Here are some pics, I could't find copper mesh here in middle east, so I used stainless steel 316 instead and it seem to be working fine.

the cell


the cell operating on PCI slot pins, the gold extraction was in matter of seconds.


and the PCI slot pins after being processed in the cell, most of the gold plating was gone.


The cell solution after couple of runs with different type of pins.


Your comments are appreciated.


Thanks to Steve and Harold and other members who came up with this cell system.
Kevin

 

[element47.5]

BAMGOLD, as far as I know, NONE of this is any real concern. There certainly isn't any need for a lab-grade, filtered, regulated PSU. A battery charger ~~10 amps is fine, a little more powerful is better, but as you'll see when you go to buy them, they start to cost more above that range. Some folks like meters..but you typically don't get meters except on more expensive chargers, and they aren't especially accurate meters.

Personally, I like the idea of finding a 25 amp Lambda 5 volt supply on ebay, a real 35 lb NASA-quality brick, and buying a cheapo $15 DVM that you can use elsewhere that's lots more accurate than front-panel meters on all but expensive supplies. That way you get metering, but it's much more accurate metering and since it's digital, you can read (and write down) trends over time. Your typical battery charger meter is no great shakes when it comes to remembering where the meter was last time you looked.

http://www.ebay.com/itm/Lambda-LMS-7018-Regulated-Power-Supply-0-18-Vdc-450-Watts-/280969394788?pt=LH_DefaultDomain_0&hash=item416b14ba64 Would be a doozy of a supply!

Brick: http://www.ebay.com/itm/LAMBDA-REGULATED-POWER-SUPPLY-0-14vdc-12vdc-13vdc-adjustable-/180980541127?pt=US_CB_Radios&hash=item2a2347e6c7

 

[Marcel]

How about the fumes, when using the cell (in general). What are they made of? Sulfurdioxide? Are they corrosive ? toxic ? Any safety advices regarding them?
What I dont like is the handling of the wet material. This will surely release acid drops when removing the basket maybe even PMs. Any ideas ?

 

[kjavanb123]

How long do I have to wait for any black powder to settle after the cell operation? It's has been 12 hrs since I ran the cell with some low grade pins from slots, and the cell solution still dark / brown.

thanks
Kevin

 

[goldsilverpro]

How about the fumes, when using the cell (in general). What are they made of? Sulfurdioxide? Are they corrosive ? toxic ? Any safety advices regarding them?
What I dont like is the handling of the wet material. This will surely release acid drops when removing the basket maybe even PMs. Any ideas ?

To collect drips, I always hold whatever I'm transferring over a bucket lid. Also, if I'm dipping out solution with, say, a Pyrex measuring cup, I do it over a bucket lid. When finished, the bucket lid is rinsed off with a squirt bottle. Never lost a drop.