TCCA (Trichloroisocyanuric acid - pool chlorine tablets)

[haveagojoe]

I'm planning to use the HCl-TCCA (pool chlorine tablets) method to dissolve my next lot of escrap foils over the holidays. Previously I have used Sodium Hypochlorite bleach but I can't find any locally any more which doesn't contain fragrance and other additives. I'm curious to try TCCA as it seems the Chlorine is released into the solution in a more controlled manner, and I've read that it also avoids the potential problem of bleach neutralizing the HCl. When I've done it with bleach, while successful, it seemed like the Chlorine left the solution rapidly and I have been obliged to add more HCl to complete the dissolution, resulting in a large volume and low concentration of gold in solution.

I have read everything I can find on the forum about the method, it seems that the ideal approach is to drip HCl onto the TCCA in a flask and bubble the resulting Chlorine gas into the metal reaction vessel via a tube. I have seen @kadriver Sreetips do it that way some years ago on Youtube and a few other times since.

Unfortunately I don't have the right glassware to do it that way, but it seems that alternatively TCCA can be added directly to the foils in HCl. So I plan to do that; first crushing the tablet to powder and adding it in small doses while stirring, allowing time inbetween additions for the Chlorine to react. I'm wondering if perhaps it would be better to use small chunks rather than crushing the tablet to powder? Maybe that would help to slow down the rate of Chlorine production?

I'm considering possibly covering the beaker and stirrer loosely with clingfilm which I'm thinking might help to keep the gas in the beaker while still allowing me to stir it. After allowing the Chlorine to off-gas I plan to cement the gold out of solution with copper before refining.

Since most of the threads on this topic are several years old I was wondering if anyone had any updates or tips to share regarding this process? I understand @Yggdrasil favours this method, alongside HCl-H2O2- sadly though even H2O2 is becoming more difficult to obtain here in the UK, apparently 12% is the maximum available now and the pharmacy may ask you to complete a questionnaire

I was not able to find any specfic information regarding waste handling for this process but I understand that it produces cyanuric acid, which Wikipedia tells me is classifed as "essentially nontoxic" and "a component of urine" which is somewhat reassuring but I want to maintain caution since this is a new method for me.

Maybe I'm overthinking it but better safe than sorry, so any comments would be much valued.

 

[Yggdrasil]

I'm planning to use the HCl-TCCA (pool chlorine tablets) method to dissolve my next lot of escrap foils over the holidays. Previously I have used Sodium Hypochlorite bleach but I can't find any locally any more which doesn't contain fragrance and other additives. I'm curious to try TCCA as it seems the Chlorine is released into the solution in a more controlled manner, and I've read that it also avoids the potential problem of bleach neutralizing the HCl. When I've done it with bleach, while successful, it seemed like the Chlorine left the solution rapidly and I have been obliged to add more HCl to complete the dissolution, resulting in a large volume and low concentration of gold in solution.

I have read everything I can find on the forum about the method, it seems that the ideal approach is to drip HCl onto the TCCA in a flask and bubble the resulting Chlorine gas into the metal reaction vessel via a tube. I have seen @kadriver Sreetips do it that way some years ago on Youtube and a few other times since.

Unfortunately I don't have the right glassware to do it that way, but it seems that alternatively TCCA can be added directly to the foils in HCl. So I plan to do that; first crushing the tablet to powder and adding it in small doses while stirring, allowing time inbetween additions for the Chlorine to react. I'm wondering if perhaps it would be better to use small chunks rather than crushing the tablet to powder? Maybe that would help to slow down the rate of Chlorine production?

I'm considering possibly covering the beaker and stirrer loosely with clingfilm which I'm thinking might help to keep the gas in the beaker while still allowing me to stir it. After allowing the Chlorine to off-gas I plan to cement the gold out of solution with copper before refining.

Since most of the threads on this topic are several years old I was wondering if anyone had any updates or tips to share regarding this process? I understand @Yggdrasil favours this method, alongside HCl-H2O2- sadly though even H2O2 is becoming more difficult to obtain here in the UK, apparently 12% is the maximum available now and the pharmacy may ask you to complete a questionnaire

I was not able to find any specfic information regarding waste handling for this process but I understand that it produces cyanuric acid, which Wikipedia tells me is classifed as "essentially nontoxic" and "a component of urine" which is somewhat reassuring but I want to maintain caution since this is a new method for me.

Maybe I'm overthinking it but better safe than sorry, so any comments would be much valued.

I favor the use of Peroxide.
I found some old 30% that I used.
I can buy 49% but only in 20L cans.
When I used TCCA I ground it up and drizzled it into the HCl.
Quite effective this way since the Chlorine is released slowly.

 

[haveagojoe]

I've just finished dissolving my gold foils this way and I must say, it is far superior to bleach. Doing it outside with a gentle breeze, the escaping chlorine was barely noticable compared to the stench that bleach creates. The foils dissolved easily with about 10 minutes of stirring, much more straightforwardly than beach which can require an extra addition of HCl.

In 250ml of HCl at 10% I used about 10g of powdered pool tablet (half a tablet) which I think was far too much, as there are undissolved clumps of it remaining at the bottom of the beaker even after all the foils have been dissolved. I'm expecting less than 5g of gold so it was definitely overkill, 5g of tablet powder would have been plenty.

My idea of leaving some of the tablet in chunks was not a good one, even though they were small. Next time I will make sure it's crushed down as finely as possible as the chlorine stays in the solution more than adequately. I elongated the solution afterwards with 100ml of water, I'm hoping this will give the remaining bits of tablet some space to dissolve completely. I think it will take several days and then perhaps some gentle heating to drive off the chlorine before I add a few drops of sulfuric and then filter it- I was hoping to do the drop on Christmas day but I think that might be too soon. Overall though I was very impressed by the action of the tablet and will do it this way from now on.

 

[haveagojoe]

After settling there seems to be a lot of white sediment, I think there must be some kind of filler in the tablet which doesn't dissolve in the HCl, or perhaps just very slowly. So I decided to go ahead and filter the solution, I figure that should help with releasing the chlorine too. I'll just run it through once to get the bulk of the solids out, then add the sulfuric drops before filtering twice through a fresh filter. If I try to double filter it through the first filter it will take forever. Then I'll put the first filter inside the second filter and rinse through with water.