In another thread, someone asked if the sulfuric could be reused. The answer is no in the present system. The reason is because of the water dilution that is used to gather the black sludge. And, of course, if you try to strip with the diluted sulfuric, it would be worthless since, you will dissolve everything - copper, nickel, etc. It has been suggested that the water could be removed through a boiling and distillation process. I feel that this would be expensive, dangerous, and unnecessary. There is a simple way to avoid the dilution and use the concentrated sulfuric over and over again.
In the early '70's, I used this same system on a grand scale. I had a 50 gal tank and used the same solution over and over for several years. I used a mild steel tank and made the tank the cathode. I was stripping gold IC's on plating type racks (see the diagrams in the original patent - #2185858 - go to Google patents - Google/more/patents). We ran about 300 gold IC's every 20 minutes. Every few weeks, when the solution became saturated with gold, we allowed the gold to settle and then pumped the solution off the top into a second stripping tank. We then harvested the sludge in the first tank and commenced our stripping in the second tank. We could tell when the solution was saturated by observing the amperage. Normally, when the parts are finished stripping, the amperage goes to zero. When saturated, the amperage doesn't go to zero because the large amount of gold creates conductivity between anode and cathode.
Here's how I would modify your setup:
(1) When you're ready to harvest, carefully stir up the solution with a stir rod. One of the straight parts of a plastic clothes hanger works good. Use the rod to knock down the gold clinging to the sides of the container. Put something (a piece of 1" wood?) under one end of the container to tilt it. Allow the gold to settle overnight. Since the container is tilted, most of the gold will settle at the opposite end.
(2) Instead of pouring the solution into water, carefully pour the solution off of the sludge into a clean, dry container. This could be any suitable container but, it would be best to use a second stripping container. This way, you only have to pour the sulfuric once and you don't lose any stripping time. Be careful not to pour off any sludge. But, even if a little sludge gets transferred, don't fret, you'll get it next time. If the sludge gets stirred up, tilt the container again even more, let it settle, and pour it off again. The idea is to pour off as much sulfuric as possible without pouring off any sludge.
(3) Treat the sludge as normal, by putting it into water.
(4) You will lose a little strong sulfuric in the process. Top it off with a little fresh sulfuric and start stripping.
(5) If you dissolve a lot of nickel in the solution, it will, eventually, make the solution stop stripping. There is almost always nickel plating under the gold plating. To avoid dissolving the nickel (it dissolves very slowly), make sure you remove the parts as soon as the gold has finished stripping.
(6) SAFETY. Pouring strong sulfuric can be a very dangerous proposition. Pour slow and steady. If you're shaky, you shouldn't be doing this work. Don't get cocky. If you have a hangover, wait until tomorrow. Make sure your gloves and the outside of the container are dry. Wet gloves will slip. Don't allow strong sulfuric to remain on the gloves, as it will eventually attack them. When pouring, it is best to put the receiving container in a cheap plastic tray (WalMart). If fact, it would be best to get a fairly large tray, about 6" deep and perform all operations in the tray. It makes dribbles a lot easier to clean up. When pouring, pour away from you. Protect your eyes and face with, at least, a full face shield. If a splattered spec of sulfuric gets on your arm, you will immediately feel it start burning. Don't panic and drop the container. Grit your teeth and put it down carefully before running to the faucet or dipping your arm in a bucket of fresh water. Always have a lot of fresh water handy. Don't wear cotton clothing or any nice clothing. Although ugly, polyester clothing stands up the best. Think smart and look before you leap.
Although I learned every one of these safety tips the hard way, I have never been hurt, even though I operated systems as large as 200 gallons. I have no scars and I still have my sight. I have ruined a lot of Levis. Listen to me.
In the early '70's, I used this same system on a grand scale. I had a 50 gal tank and used the same solution over and over for several years. I used a mild steel tank and made the tank the cathode. I was stripping gold IC's on plating type racks (see the diagrams in the original patent - #2185858 - go to Google patents - Google/more/patents). We ran about 300 gold IC's every 20 minutes. Every few weeks, when the solution became saturated with gold, we allowed the gold to settle and then pumped the solution off the top into a second stripping tank. We then harvested the sludge in the first tank and commenced our stripping in the second tank. We could tell when the solution was saturated by observing the amperage. Normally, when the parts are finished stripping, the amperage goes to zero. When saturated, the amperage doesn't go to zero because the large amount of gold creates conductivity between anode and cathode.
Here's how I would modify your setup:
(1) When you're ready to harvest, carefully stir up the solution with a stir rod. One of the straight parts of a plastic clothes hanger works good. Use the rod to knock down the gold clinging to the sides of the container. Put something (a piece of 1" wood?) under one end of the container to tilt it. Allow the gold to settle overnight. Since the container is tilted, most of the gold will settle at the opposite end.
(2) Instead of pouring the solution into water, carefully pour the solution off of the sludge into a clean, dry container. This could be any suitable container but, it would be best to use a second stripping container. This way, you only have to pour the sulfuric once and you don't lose any stripping time. Be careful not to pour off any sludge. But, even if a little sludge gets transferred, don't fret, you'll get it next time. If the sludge gets stirred up, tilt the container again even more, let it settle, and pour it off again. The idea is to pour off as much sulfuric as possible without pouring off any sludge.
(3) Treat the sludge as normal, by putting it into water.
(4) You will lose a little strong sulfuric in the process. Top it off with a little fresh sulfuric and start stripping.
(5) If you dissolve a lot of nickel in the solution, it will, eventually, make the solution stop stripping. There is almost always nickel plating under the gold plating. To avoid dissolving the nickel (it dissolves very slowly), make sure you remove the parts as soon as the gold has finished stripping.
(6) SAFETY. Pouring strong sulfuric can be a very dangerous proposition. Pour slow and steady. If you're shaky, you shouldn't be doing this work. Don't get cocky. If you have a hangover, wait until tomorrow. Make sure your gloves and the outside of the container are dry. Wet gloves will slip. Don't allow strong sulfuric to remain on the gloves, as it will eventually attack them. When pouring, it is best to put the receiving container in a cheap plastic tray (WalMart). If fact, it would be best to get a fairly large tray, about 6" deep and perform all operations in the tray. It makes dribbles a lot easier to clean up. When pouring, pour away from you. Protect your eyes and face with, at least, a full face shield. If a splattered spec of sulfuric gets on your arm, you will immediately feel it start burning. Don't panic and drop the container. Grit your teeth and put it down carefully before running to the faucet or dipping your arm in a bucket of fresh water. Always have a lot of fresh water handy. Don't wear cotton clothing or any nice clothing. Although ugly, polyester clothing stands up the best. Think smart and look before you leap.
Although I learned every one of these safety tips the hard way, I have never been hurt, even though I operated systems as large as 200 gallons. I have no scars and I still have my sight. I have ruined a lot of Levis. Listen to me.
