Electrochemistry Electrolytic cell questions

[bswartzwelder]

I built an electrolytic cell some time ago, but never used it until this weekend. I seem to have several problems.

1. The power supply I purchased new was supposed to be able to output 30 VDC at 10 amps. However, after using it for about 10 to 15 minutes, the current dropped off to 0.3 amps. Unplugged one of the leads for a 10 minute "rest" period and when I plugged it back in, the current went back up to 7.6 amps and started dropping slowly. After a few minutes, the cell quit fizzing and I noticed the current had once again dropped to 0.3 amps. Evidently this wonderful power supply from China can not live up to its rated output. I used a second power supply for the rest of the day with no problems except that it didn't have an ammeter connected to it. I can always put an ammeter in line with one of the leads next time I try it out.

2. The solution turned black. I put the used solution into a separatory funnel overnight and now (24 hours later) the solution is still black. I used a copper basket made from copper mesh I bought from LaserSteve and the cathode is a sheet of lead purchased from an online distributor. It is supposed to be pure lead, so I don't know what could be causing the acid to turn black aside from the gold that was deplated from the parts in the cell. How long does it take for the gold to drop once the solution has been put into the separatory funnel? Perhaps I just need to wait a while longer.

3. I know I saw somewhere that the temperature of the cell needs to be monitored. I believe the maximum temperature need to be limited to 105 degrees Fahrenheit, but I have searched the forum (and LaserSteves site) and do not see the temperature limits. Other than these minor problems, the items I put into the cell came out without their original gold plating, so I must be doing something right. What am I doing wrong?

The power supply I purchased from China was not an el cheapo model, so I am puzzled by the way it worked. If anyone is interested, it's a MASTECH DC Power Supply HY3010E. Strange how the name MASTECH almost sounds like MISTAKE>

Bert

 

[goldsilverpro]

As the gold strips, the amperage will drop. This is normal. Assuming the solution temperature has not been allowed to get too high (above about 110F), when all the gold has stripped the amperage should read zero or very close to zero.

To keep the solution temperature low, I would not run more than about 6 amps per gallon of solution, at any point in the stripping cycle.

Here's how I do it. Let's assume I have a 1 gallon tank. I start with the voltage/amperage at zero and then bring up the amperage to 6 amps. The voltage will be quite low at this point, maybe only 1 or 2 volts. Shortly, the amps will start dropping. I then adjust the amps back up to 6. The voltage will increase somewhat. I repeat this procedure several times. At some point, the voltage will be maxed and the amps will be at 6 or below. At that point, I do no more adjusting. Eventually, the amps will read zero or very close to it. This tells me that the parts are completely stripped and it's time to take them out.

I might mention that 30 volts is pretty high. If it were me, I would do the same as above except I wouldn't run the voltage over 15-20V.

This procedure will keep the amps at a high level without overheating the solution. If the solution overheats, all sorts of bad things will happen. For one, copper will start to dissolve and contaminate the solution. Overheating may be the reason you have the black material that won't settle.

I once had a large 50 gallon sulfuric stripping tank. The rectifier I used was 12V, 250A. That's 5 amps/gallon. I used the same exact solution all day, every day for at least 2 years. When the black gold powder built up to the point that it was creating a partial short and, therefore, the amps wouldn't go to zero when the gold was completely stripped, I knew it was time to harvest the gold. I harvested about every 2 weeks, or so. The parts I was stripping (old side-braze IC's) were mounted using piano wire spring contacts on ladder shaped racks made of bare (uncoated) 1/4" square yellow brass stock. The 2 sided racks held about 200-300 IC's. The same racks were used for about 2 years with no attack on the brass. Also, the tank was made of mild steel which was used as the cathode. Here again, there was no attack on the steel after 2 years. To me, the #1 secret of using the sulfuric stripper in a trouble free manner is to not allow the solution to get too hot from excessive amperage.

 

[bswartzwelder]

GSP,

Thank you so much for the response. I looked at the funnel yesterday afternoon from about 5 or 6 feet away and did not see any change. Last evening as I was closing up shop for the evening, I looked over and really didn't see any change. However, when I got up close and looked, there was some change. Starting at the bottom of the funnel, there was about 1.5 inches of black sediment. I think I found my gold. Above the top of the sediment, there was an area about 1.5 inches high where the acid was relatively clear. Above that, the color faded from the clear to the black color. I don't know if the amperage affects the size of the gold particles. If the gold particles are of different sizes, then possibly the smallest of them are still floating around suspended in the acid giving the black color.

I started out operating the cell as I should have and when the temperature approached 105 degrees, I shut it down and put the acid into the funnel. Then I dumped the plated items into a bucket of water and started over with fresh plated item and fresh acid. I did this a total of 3 times and each time, there was fizzing at the lead and the gold. All three times the acid turned black. At no time did I allow the acid to go above 107 degrees.

I am in no hurry, and with the top of the funnel capped off, no moisture from the air will be getting into the acid. When I am ready to harvest the gold, I'll place a graduated cylinder (500 ml) with about 100 ml water below the stopcock and drain the gold sediment into the cylinder.

I never used 30 volts while doing this. Only once did I go up to 13.8 volts which is about what a fully charged battery can put out. The 30 volts I mentioned was only the rating on the power supply. I really think I may have a power supply which isn't living up to what the manufacturer said it could do. It really appeared to me that the unit was cycling off for some reason and if I disconnected one lead for a couple of minutes and then reconnected it, the current would go from zero (disconnected) to about 7.5 amps (connected), drop off very slowly to about 6 amps, then jump down to the 0.3 to 0.4 amp range. That jump was almost instantaneous and adding a little more gold plated items to it didn't cause the amperage to go back up. The only way to get it back up was to disconnect one lead and then reconnect it after a rest period.

I really enjoy hearing how the other members have processed their material and the success they have had. I try to duplicate their methods when practical and hope to duplicate their results.

Thanks again,
Bert

 

[goldsilverpro]

The solution, itself, in some cases, will get dark from use. Put a flashlight behind the solution and you should be able to see things better.

What is the source of the sulfuric you're using?

 

[Geo]

There is a way to clean the carbon from the sulfuric acid but it's dangerous because it entails diluting and evaporating the acid itself.

 

[bswartzwelder]

I purchased my sulphuric acid from a store online. I thought it was hvchemicals, but when I click on it, I don't seem to be able to get there. The label says it's strength is 98.1%. It was thick, almost syrupy when I poured it from the bottle.

As far as the black color, I'm not certain it's carbon. It may be gold that is just taking its good old time dropping. Strange, there is an area above the black sediment which is fairly clear. To me, that would indicate that whatever is causing the black color is something suspended in the acid and not dissolved into it. I'm in no hurry, so I'll keep an eye on it for the next couple of days. Alternatively, I could drain the sediment very slowly without disturbing the acid above it too much and see if this black stuff is still settling out. It's hard to see a slight increase in the height of the sediment and measurements would not be very accurate. The thick, syrupy composition of the acid might also be a contributing factor as to why this is taking so long to settle out.

I sure wish there was an easy method to keep everything cool. Having said that, I see so many people on the forum jumping into things without doing their mandatory studying. I know that if there was an easy way to do this, you guys would have found it and shared it with us. I'm working outside with the ambient temperature reaching close to 90 degrees Fahrenheit, so that doesn't leave much before the acid hits the 105 degree limit I have set. I'm using an IR thermometer which one of my sons gave me as a Christmas gift.

Thanks again, guys.

 

[goldsilverpro]

98% is too strong. Did you dilute it? Some dilution with help it strip more efficiently and will somewhat thin it out so it will probably settle faster. I would suggest diluting it with 5% water, by volume. Measure out the water, put it it a container, and slowly add the sulfuric to the water. Use gloves and a full face shield. It will get hot. When all has been added, stir it slowly and carefully, but well. If not mixed completely, you will see a wavy motion in the solution. Let it cool before using.

 

[bswartzwelder]

Yesterday I drained 100 ml of the acid into a beaker. It sat there, undisturbed for several hours. At that time, it looked like a black soup. I then added 300 ml to 400 ml water to it. Within 1 hour, the gold had either settled to the bottom or was floating on top. A slight amount of agitation and the gold floating on top quickly settled to the bottom. I'm not about to dilute the rest of the 2 liters just to get to the gold in suspension. Perhaps it will settle on its own over time. If not perhaps the addition of 5% distilled water will help the process. Not really concerned because I know where it is.

Thanks for the tip on diluting the H2SO4. I have been under the impression that the stronger it is, the better it works and that below 90% it is almost useless.

Sincere thanks,
Bert

 

[FrugalRefiner]

Yesterday I drained 100 ml of the acid into a beaker. It sat there, undisturbed for several hours. At that time, it looked like a black soup. I then added 300 ml to 400 ml water to it.

You should not add water to concentrated sulfuric acid. The heat created can cause the acid to boil and spatter. Always add the acid to the water slowly, with plenty of stirring.

Dave

 

[pgms4me]

Just as a point of interest on the power supply. Some of the newer power supply circuitry is complex and can cause problems with loads such as these cells.
#1: If the power supply was designed to charge batteries it may have a circuit that detects the type of load a battery should present. if it doesnt "see" that " it can shut down automatically
#2: If it has a peak current limting circuit built in,it could be that your cell load caused it to briefly exceed 10 amps when you first started it, which would trigger the protection circuit to shut it down. when you turned it on the second time,it probably had stripped some gold so the current didnt go as high as the first time and it stayed running for you.... Just some things to keep in mind. Glad you are making progress. When I have that fine black above the sediment black i leave it there until I am finally done with all the runs for that batch of acid in the cell, then I just dilute it and it falls

 

[bswartzwelder]

To avoid having to move the acid from one container to another more times than necessary, I added water to it one or two drop at a time using a glass syringe. It seemed to take forever, but my future dilutions will be much less water so I will definitely be adding the acid to the water.

The power supply used was/is a laboratory type power supply and not a battery charger. At no time did the current exceed 10 amps which is the current the manufacturer stated it was capable of supplying. Later on, in the afternoon, the current was holding steady at about 2.1 amps when the power supply decided to shut itself down to the 0.3 amps or 0.4 amps which it stayed at until I disconnected one of the leads from the cell. after a short rest period, I reconnected the lead and the current immediately jumped up to the value it was at before dropping out.

I have an automotive type headlight which I'll connect to it the next time I have everything out and see if the current drops off or not. It could be the load from the cell is greater than I had originally suspected and that maybe the resistance of the cell is much less than I had suspected. At any rate, considering the size of my cell, I should most likely be operating it at about 2.0 amps instead of a higher current. Cooler weather is coming this weekend, so I'll play with it at that time. Thanks for the input.

 

[goldsilverpro]

You have 2 liters, a little over 1/2 gallon. I wouldn't use over 3.5 amps.

If you put bare copper in the cell, the amps jump up but will soon go to zero. When voltage is applied, I believe this oxidizes the surface of the nickel or copper, makes it passive, and, therefore, it doesn't pull any current and dissolve. When you turn off the PS, the acid dissolves the oxide film. Therefore, when the PS is turned back on, the amperage will jump back up but will decrease as the oxide film is recreated. I noticed the same thing when I ran my cell. So far, nothing you've said about the PS indicates it is faulty, at least in my mind.

 

[bswartzwelder]

I had the opportunity to have the garage door open yesterday and looked at the separatory funnel. Much to my surprise, there was another small pile of sediment in the bottom and the acid was almost clear. Certainly things appear to be more correct. I'll work with it more hopefully this weekend.

 

[richoc]

You need to pour off the clear acid it is still good.
You are not using your acid to what it can do.
Keep going in the same acid until you get small shorts.
Then let it sit to separate pour off the clear acid as most you can.
Reuse this, only add water to the black Goo when your done.
Distilled it distilled water 5: 1 there will be a extreme heat reaction now.
This solution is where your gold alloy drops out.
Let set for 24 hours, then remove the clear liquid, pouring it off without any black.
Repeat this rinse again to make sure acid is used up.
Your gold alloy is the black mud you can now pour it through a filter.
Pour off the clear liquid and not your golden black mud.
This is still an alloy and you can choose to turn to a gold bead at the point or refine farther.

You just trying to skip steps.

 

[yar]

Question concerning diluting 98% sulfuric acid..... GSP recommends adding 5% H2O, Lazersteve adds Glycerine in his video, others say no glycerine and in other posts there is no mention of diluting the acid at all. Is there a definative answer as to if the acid should be diluted or not?

I have just started running a small stripping cell for pins and do not dilute my acid. The positive of diluting would be a faster settling of the stripped gold but would that cause the cell to eventually not work as well?

 

[goldsilverpro]

It actually works better and faster with a little water in it. When using 98% sulfuric, I usually added 5% by volume. Add the acid to the water, not the other way around. The original patent used about 15% water, which I wouldn't recommend. The purpose of the patent was to strip bad plating off of parts so they could be replated. They weren't interested in recovering the gold.

When the forum started, most used some.glycerin, including Lazersteve. Steve stopped using it when he found it wasn't necessary.

 

[yar]

Thanks GSP, I will give the 5% H2O a try next time.