I did something very similar in a 120 gallon tank with a 30 gallon sump.
Make sure you use a chemical pump resistant to copper II chloride.
I used a gravity filter, made of plexi that originally was intended for salt water reef tanks. I have many of them laying around. They usually look something like this:
Basically, the way the pre-works is by gravity. The solution falling down the backside to the sump tank, pulls solution out of the big tank you have your material in.
I use polypropylene sponge filters, also borrowed tech from salt water tank enthusiasts. The nice thing about using polypropylene is that you can put your entire sponge in an AR solution, and the sponge/filter will not dissolve, but the gold foil will.
So I use two sponge filters, one in the pre-filter and one in the sump. I adjust the tank so that the water breaks up as it flows down the tube. I do this to break the electrical connection through the flow of the solution into the sump. I plate the copper out in the sump using a method very similar to the same one on this website/page.
http://www.docbrown.info/page01/ExIndChem/electrochemistry06.htm
Plating the copper as it's being dissolved makes this system works more effectively, and with far less hassle.
From the chemical pump up to the 120 tank I use PCP pipe, and divided the pipes so that they distribute the solution going back into the tank, in several places. Heating, and then flattening the pipes on the end ensure that the pressure is increased as it exits the pipe in the tank solution, agitating it. I designed this system so the exit points can be moved slightly, to ensure that they can be directed against the material I put into the tank for processing. This helps to agitate the foils from the material, thus increasing the efficiency, and decreasing somewhat, the time required to de-foil the material.
I am using processing boards this way, so I use a shower curtain rod, with plastic shower curtain loops and polypropylene string. Two rods running the length of the tank. I simply drill two holes in the boards, and clip them to the poly string. As the boards de-foil I move them from one end of the tank to the other, pulling out the boards on one end, and entering them into solution at the other. In this way I ensure that the boards are subjected to different nozzles ( the pipe ends I slightly flattened ) and thus different angles and directions, helping with the de-foiling process.
At any given time, when there is enough gold foil captured by a poly filter, I remove and replace the filter with a clean one and never stop the process. Having a poly filter in the pre-filter, and sump, ensures I capture most of the gold foils easily, using a large cell sponge in the pre-filter, and finer ones in the sump. Also, if any gold foil does flow over the sponges due to not removing them soon enough and being too loaded with gold foil, the gold foils then re-circulate into the tank with no harm or loss.
Using this method the only real requirement is adding a small amount of HCl when the reaction discontinues removing the gold foil. Small additions of DI water are sometimes required due to evaporation. Also, another benefit to the pre-filter is that it adds a lot of oxygen to the solution as it is agitated. I purposefully created my pre-filter so that it has a slight angle as the water falls out of the tank into the filter because this also adds oxygen. I also use another piece of equipment intended for fish tanks, an air pump with tubes entering the main tank that have air stones on the ends. It does not matter where in the tank you place the stones as the solution is constantly moving through the tank.
When the sponges are removed for processing, I simply enter them into a reaction vessel, add AR and dissolve the foils directly into solution. No more filtering is required prior to this step.
You can easily come by this equipment used, I am fortunate in that I already have large salt water aquariums, and have the equipment on hand. But I have seen equipment like this sell for very little at good will type stores, Craigslist, garage sales, etc. The only real expense is the chemical pump, but well worth the investment. Many times, people who re-market equipment have these types of pumps and sell them for reasonable prices, or you might also find them on ebay. If you do use a used pump, ensure it is either refurbished or that you have it refurbished prior to using the pump, even then make sure you flush it well prior to use as some people do not flush them after using them. If you do not flush them you may be adding something in the pump to your copper II chloride solution that could have an adverse reaction.
I made a simple fume extraction hood out of scrap polypropylene plastic I purchased at TAP Plastics, connected to an exit tube and squirrel fan that exits outside the building. If you do not use some type of ventilation I would strongly suggest operating equipment like this in an open space, not enclosed. It does produce some small amounts of hydrogen gas, and other gases if you add the electrolytic process to your sump.
All in all, if you are smart about it, and take your time obtaining used equipment you can build a system that is similar very inexpensively.
I am not posting pictures of my own system, as I am trying to get the entire process patented. But I would be more than happy to answer any questions, and take suggestions on how to improve my own system.
Scott
