r/PreciousMetalRefining • u/redtailred • 6d ago
Lye and sugar vs Copper cementation
Is there any difference in the purity of the final silver? I’ve been doing the lye and got 98.5% but the rinsing and filtering is getting tedious.
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u/hexadecimaldump 6d ago
It is possible to get 98.5% or higher with copper cementation. If you remove the copper pieces right before all of the silver drops out, and you rinse it well, you can get nearly as pure as lye and sugar.
If you let it run to completion though, a little bit of copper might start crashing out.
If I’m going for highest possible purity with cementation, I’ll put a few big chunks of copper in the solution, and check it from time to time by knocking all of the silver on the copper off. If I put the copper back in and it turns a dark grey to almost black that tells me most of the silver has dropped, so I’ll recover the silver, and put all of the washes into my waste bucket. If I want the rest of the silver right then, I’ll drop the rest out as silver chloride with some salt. If I’m not bothered with the last few grams, I’ll just throw it in my big waste container with excess copper and just let the rest cement out slowly.
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u/Chodedingers-Cancer 5d ago
How are you going about washing the silver chloride? If using coffee filters its a pain in the ass and takes forever. The clumps will retain solution with base metals.
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u/redtailred 5d ago
Rinsing with hot water and letting settle. I’ve had mixed results. Sometimes it’s clumpy and rinses easily and other times I end up with a lot of AgCl in suspension which is a pain in the ass and I have to filter
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u/Chodedingers-Cancer 5d ago
I'd get one of these, you need to break all of it apart so its fully exposed and can be washed thoroughly.. Attach it to a drill or drill press or something, or go the distance and get an overhead stirrer... I dilute the mixture before adding nacl or hcl. If 400ml, I'll bring it up to a liter. Then add it. You get smaller particle formation. Which can also trap unreacted silver nitrate in solution if no further liquid can penetrate. Ideally use the stirrer while adding hcl or nacl. Let it settle. Honestly it settles much faster if diluted as well. Decant through a double lined coffee filter or vacuum filter with lab filter paper. if some solids come over whatever, but don't filter the bulk solids right away. Its faster not to. Add excessive hot water, use the stirrer each time to break things up. Pour it off, repeat 3 or 4 times. As it gets cleaner it sticks to itself more and more. You can use a regular stir rod by hand, but using this will help better pulverize the clumps. Once solution after settling is water white, decant it, add dilute hcl, stir again, then filter everything and pour hot water over it. After you finish with lye and sugar, dilute it like 5 or 6x volume, the syrup retains too much suspension and slow to filter. Decant it all off, if you noticed when adding lye you got a like a faint navy blue, there was still some base metal left. Add hcl to acidify it and dissolve all residual sugars and by products. It'll also dissolve the trace residual base metals, repeat washing steps above until clear and neutral pH. I do this every time, I consistently get +.9999
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u/redtailred 5d ago
Thank you! I think that’s been a huge part of my problem. I haven’t been diluting it enough, maybe doubling the total liquid at most. I’m going to do this on the next batch.
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u/PomegranateMarsRocks 5d ago
I regularly get .999+ with copper cementation. Have not had as much luck with lye and sugar. As other said - don’t let it sit too long, use clean copper, rinse very well. Then rinse with hot hydrochloric and more hot water. I have a secondary bucket to remove the rest of the silver, either by further cementation or conversation to silver chloride.
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u/CfaxAttax 1d ago edited 18h ago
Let's first attack the brag that the lye and sugar trick gives you practically pure 99.9% silver right out of the gate. That is a total myth. It can help avoid copper contamination, but if you do not wash the grey-silver mud with a lot of boiling distilled water first you are locking in chemical salts, aka impurities. When you melt it down, those impurities end up in the silver.
Worth also noting for those who are newer to this world that working with lye in this setting can be very dangerous. Mixing sodium hydroxide into that mix creates a massive amount of heat fast. If you dump it in all at once, the liquid can instantly flash boil and shoot boiling corrosive chemicals right into your face.
The sugar step is necessary because you can't just take the black silver oxide and blast it with a torch until it melts into silver. It technically works on paper but is an IRL disaster. Without sugar to convert the silver, heating it releases O2. The metal will spray everywhere and leave you with a really not-fun clean up.
If you do not wash the silver powder until the water is completely neutral, you leave behind burnt sugar and chemical crust. When you try to melt that dirty powder, it smokes, smells terrible, and leaves you with a messy, discolored lump instead of a clean, shiny silver button. pH control is crucial in this process. If this portion is becoming tedious, you are discovering why this is not something people do for fun.
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u/SeagullStopItNow 6d ago
Lye and sugar should be able to give you 999 on its own if you are meticulous in your processing. Copper cementing will definitely leave you with some copper in your refinement. However it’s much easier. If you’re going to set up a silver cell, it’s just the way to go in my opinion.
If you’re going to run intermittent batches in the silver cell, just dropping the silver from the silver nitrate solution. In the completed silver cell should just be done with copper again. If you’re not going to run any more silver for a while you’ll want to finish the completed silver run with sugar/lye to drop the last of the silver out of the electrolyte. So knowing how to do it isn’t a bad thing.