From your figures. At 1000A, at 85% efficiency, with 95% Ag anodes, it would take about 13.6 hours of operation, daily, to get 1500 oz of Ag crystal. During that time, you would add about 83 oz of Cu/Zn to the solution. This would displace 83 x 3.4 = 282 oz of silver. It would take at least 81 Moles of HNO3 (about 5 liters of 70% HNO3) to provide enough NO3- to make up for the NO3- lost by the 83 oz of Cu/Zn added to the solution.
If the silver content is only 95%, I feel that, mathematically, a goal of 95% efficiency (approx. 3.82 g of Ag/A-hr) is an impossibility. I feel that 85% is about as high as you could possibly hope to achieve, mathematically. In essence, that 85% is, in your situation, 100%. The fly in the ointment is that pesky 5% base metals in the anodes and the corresponding amount of nitric that must be added to make up for the NO3- used up to put those base metals in solution.
Instead of adding acid, you could add 282 oz of pre-dissolved Ag to the cell daily. At worst (using an open top dissolving vessel), that would require about 3 gallons of 70% HNO3. If you did this, you might dissolve the 95% material. Then, if you want to keep the base metals in the bath at a lower level, you could cement out the silver with copper, clean it up, and then re-dissolve it to add back to the tank. This would allow you to raise the apparent efficiency of the bath. This would be an illusion, however, when you consider the hassle and the expense required to provide Ag solution to add daily to the tank. You could also remove solution from the cell daily, cement the Ag from it using copper bars, re-dissolve the Ag, and add it to the tank. You could also remove some solution from the tank, add a chelating agent that would only chelate the base metals, and cement the Ag out with copper or drop it out as a chloride. The problem with this is that a chelated metal solution is almost impossible to treat economically.
If you could figure a way to continually remove base metals from the bath without adding anything foreign that would build up and inevitably cause problems, you could, theoretically, run the same bath forever without changing it. There was a patent in the 70s by a guy name Hunter that used solvent extraction (I'm thinking) to do this. Or, one could probably use an ion exchange column or electrolytical ion-exchange membranes.
A neat thing about silver cells is that everything can be almost perfectly predicted by knowing the anode composition. Within this box you're forced into by your parameters, though, there are a lot of different ways to skin the same cat. However, in order to improve the apparent efficiency, I think you would have to set a system external to the cell, rather than doing something to the cell internally.
A question that keeps nagging me. Why, oh why, do you want to improve the efficiency, anyhow? If you want to do this to increase production, there are better ways.
(1) Get another cell, maybe a simple 30 gallon Thum cell, or two. Two would give about 600oz in 13.5 hours. Simple and cheap to build yourself. Build one from lumber in half a day and then have it coated with "chopped on" PVC. No drilling anodes, just snug them next to each other in the tray. No dismantling anything to harvest crystal. Thum cells take up more floor space but it looks like you have plenty of space. The way your cell is set up takes a lot more floor space than normal.
(2) Since you're now running at only 2-3 volts, you might be able to jack the current up 10% with no problems.
By the way, where are you located - city and state? PM me if you want to keep that confidential.
If the silver content is only 95%, I feel that, mathematically, a goal of 95% efficiency (approx. 3.82 g of Ag/A-hr) is an impossibility. I feel that 85% is about as high as you could possibly hope to achieve, mathematically. In essence, that 85% is, in your situation, 100%. The fly in the ointment is that pesky 5% base metals in the anodes and the corresponding amount of nitric that must be added to make up for the NO3- used up to put those base metals in solution.
Instead of adding acid, you could add 282 oz of pre-dissolved Ag to the cell daily. At worst (using an open top dissolving vessel), that would require about 3 gallons of 70% HNO3. If you did this, you might dissolve the 95% material. Then, if you want to keep the base metals in the bath at a lower level, you could cement out the silver with copper, clean it up, and then re-dissolve it to add back to the tank. This would allow you to raise the apparent efficiency of the bath. This would be an illusion, however, when you consider the hassle and the expense required to provide Ag solution to add daily to the tank. You could also remove solution from the cell daily, cement the Ag from it using copper bars, re-dissolve the Ag, and add it to the tank. You could also remove some solution from the tank, add a chelating agent that would only chelate the base metals, and cement the Ag out with copper or drop it out as a chloride. The problem with this is that a chelated metal solution is almost impossible to treat economically.
If you could figure a way to continually remove base metals from the bath without adding anything foreign that would build up and inevitably cause problems, you could, theoretically, run the same bath forever without changing it. There was a patent in the 70s by a guy name Hunter that used solvent extraction (I'm thinking) to do this. Or, one could probably use an ion exchange column or electrolytical ion-exchange membranes.
A neat thing about silver cells is that everything can be almost perfectly predicted by knowing the anode composition. Within this box you're forced into by your parameters, though, there are a lot of different ways to skin the same cat. However, in order to improve the apparent efficiency, I think you would have to set a system external to the cell, rather than doing something to the cell internally.
A question that keeps nagging me. Why, oh why, do you want to improve the efficiency, anyhow? If you want to do this to increase production, there are better ways.
(1) Get another cell, maybe a simple 30 gallon Thum cell, or two. Two would give about 600oz in 13.5 hours. Simple and cheap to build yourself. Build one from lumber in half a day and then have it coated with "chopped on" PVC. No drilling anodes, just snug them next to each other in the tray. No dismantling anything to harvest crystal. Thum cells take up more floor space but it looks like you have plenty of space. The way your cell is set up takes a lot more floor space than normal.
(2) Since you're now running at only 2-3 volts, you might be able to jack the current up 10% with no problems.
By the way, where are you located - city and state? PM me if you want to keep that confidential.
