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- Feb 25, 2007
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I processed floor sweeps, filters and polishing wastes together. After incineration, the glass filter material readily crumbles to dust. After screening and removing any large pieces for processing by inquartation, or discarding magnetic pieces (to the stock pot----which was where I sent saw blades after incineration and mulling in a mortar). That way if there are traces of values on the surfaces, they are not discarded.
Once I had the material screened, it was given a boil in HCl and water. I used a roughly 50/50 mix, using tap water. Cover the material by a couple inches. You have to be vigilant to keep stirring the material as it heats, so you don't get localized drying. The material will readily stick and bake on to the beaker if you don't keep it in suspension. Once that happens, you get a hot area that cracks when you stir the container again. Because the material can be difficult to stir, and will often break a large glass stirring rod, I used a fiber glass rod instead. It seems to work well, but I didn't leave it in the solution. It was used then removed each time to avoid subjecting it to boiling acid for a prolonged period of time.
Be advised that this process puts some bad miles on your vessel. They get severely scratched from the abrasives included, and eventually fail from abrasion, but you can run a large number of batches before the beaker is lost. Also, don't use a beaker that has been through this process for precipitation. The roughed up surface of the beaker will make recovery of the precipitated gold very difficult. It tends to adhere doggedly to any scratches or other rough spots in the beaker when it is precipitated.
After you have boiled the material for a given amount of time (I usually gave it about 15 minutes), it was removed from the burner, then the container filled with tap water and stirred well. It should be allowed to settle well because you are dealing with extremely fine particles of gold, which may not settle immediately.
When the solution has settled well (next day is good), decant using a hose, then fill the container with tap water and stir well, then allow to settle once again. I did this routine until the rinse water was fairly clear of color. Often just one water rinse after the digest will be enough.
When the final rinse has been decanted, add AR to the lot, using one ounce of nitric and 4 ounces of HCl for each ounce of gold you expect to recover. The color of the material is a fair indicator of concentration, but it can be deceiving as well.
When you add the AR, you should see an instant change in color, from pink/purple to a creamy yellow color. That is a sign that you are dissolving the gold, so you can use that as a guide to needing more acid. A small excess is advised, and a low boil is also advised, so if any filings have found their way to your polishing wastes, they'll be dissolved as well. Even karat gold will cooperate, due to the small size. By the time enough hard silver chloride might form, the acid has penetrated the entire particle, so all of the gold should be liberated.
Add a little water after the boil, stir, then allow solids to solution to settle. Your solution should be a rich orange/yellow color.
After it has settled, decant the pregnant solution, then add more water and stir well once again. You can repeat this process until the rinse comes off testing barren. Get the remains in a filter, using a fast paper (I liked S&S Sharkskin), removing the last traces of fluid.
The remaining dirt will still contain values. It will contain silver, and it may even contain tiny bits of un-dissolved gold, although it should not. It likely will contain traces of platinum if any was included in the lot. I saved it for future processing in cyanide, then it was sold. Even after two processes, it still had value. It's hard to get everything from so much dirt, so you will spend only the amount of time you feel appropriate.
This process should recover the vast majority of the values.
As for bench sweeps, I'm assuming you're discussing filings and other material that accumulates in the pan.
Such material was incinerated, then screened. Large pieces of value were removed and inquarted for separate processing. Filings were cleaned with a magnet, then they were given a prolonged boil in dilute nitric. I used 70% nitric and used it at roughly 50/50 with tap water. I was not concerned about creating traces of silver chloride. If you are, use distilled or purified water instead of tap water.
This process will dissolve some of the silver contained in the filings, but it may not dissolve all of it. The filings will be much cleaner after the boil, but certainly not clean. Because the solution from this process tends to be very dirty, it is the once case where I produced silver chloride instead of cementing the silver with copper. You may choose a different course. There is no right or wrong method in this case. User's choice.
After you've rinsed the filings (until the rinse is clear), dissolve the material using AR at the same ratio as above. Again, use an ounce of nitric for each ounce of gold you expect to recover. Heat until everything is in solution (you should expect to see particles of abrasive, which will not dissolve). Finish up by the method of your choosing. I evaporated, using a button of gold to consume any free nitric acid. That it got reduced in size was evidence that I had not left any gold behind.
Gold from filings tends to be quite dirty after the first refining. You should find your now barren solution quite dirty, colored anywhere from a dark green to a dark blue color. Test it for platinum metals before discarding.
I found no problems from processing materials that included either borax or boric acid. The only big problem you may experience is if you try to filter the wash solutions. It is for that reason I suggest decanting (using a small hose). Most of these solutions are very difficult to filter, and there's no good reason you should have to.
Small hose: I used a short length of 3/8" ID vinyl tubing. It's easy to rinse, and is flexible enough to allow easy use. I used 1/8" wall thickness to avoid collapse of the tubing when making bends. You can prime the hose with water to begin transfer. Do not suck on the end with your mouth! :wink:
Hope this helps.
Harold
Once I had the material screened, it was given a boil in HCl and water. I used a roughly 50/50 mix, using tap water. Cover the material by a couple inches. You have to be vigilant to keep stirring the material as it heats, so you don't get localized drying. The material will readily stick and bake on to the beaker if you don't keep it in suspension. Once that happens, you get a hot area that cracks when you stir the container again. Because the material can be difficult to stir, and will often break a large glass stirring rod, I used a fiber glass rod instead. It seems to work well, but I didn't leave it in the solution. It was used then removed each time to avoid subjecting it to boiling acid for a prolonged period of time.
Be advised that this process puts some bad miles on your vessel. They get severely scratched from the abrasives included, and eventually fail from abrasion, but you can run a large number of batches before the beaker is lost. Also, don't use a beaker that has been through this process for precipitation. The roughed up surface of the beaker will make recovery of the precipitated gold very difficult. It tends to adhere doggedly to any scratches or other rough spots in the beaker when it is precipitated.
After you have boiled the material for a given amount of time (I usually gave it about 15 minutes), it was removed from the burner, then the container filled with tap water and stirred well. It should be allowed to settle well because you are dealing with extremely fine particles of gold, which may not settle immediately.
When the solution has settled well (next day is good), decant using a hose, then fill the container with tap water and stir well, then allow to settle once again. I did this routine until the rinse water was fairly clear of color. Often just one water rinse after the digest will be enough.
When the final rinse has been decanted, add AR to the lot, using one ounce of nitric and 4 ounces of HCl for each ounce of gold you expect to recover. The color of the material is a fair indicator of concentration, but it can be deceiving as well.
When you add the AR, you should see an instant change in color, from pink/purple to a creamy yellow color. That is a sign that you are dissolving the gold, so you can use that as a guide to needing more acid. A small excess is advised, and a low boil is also advised, so if any filings have found their way to your polishing wastes, they'll be dissolved as well. Even karat gold will cooperate, due to the small size. By the time enough hard silver chloride might form, the acid has penetrated the entire particle, so all of the gold should be liberated.
Add a little water after the boil, stir, then allow solids to solution to settle. Your solution should be a rich orange/yellow color.
After it has settled, decant the pregnant solution, then add more water and stir well once again. You can repeat this process until the rinse comes off testing barren. Get the remains in a filter, using a fast paper (I liked S&S Sharkskin), removing the last traces of fluid.
The remaining dirt will still contain values. It will contain silver, and it may even contain tiny bits of un-dissolved gold, although it should not. It likely will contain traces of platinum if any was included in the lot. I saved it for future processing in cyanide, then it was sold. Even after two processes, it still had value. It's hard to get everything from so much dirt, so you will spend only the amount of time you feel appropriate.
This process should recover the vast majority of the values.
As for bench sweeps, I'm assuming you're discussing filings and other material that accumulates in the pan.
Such material was incinerated, then screened. Large pieces of value were removed and inquarted for separate processing. Filings were cleaned with a magnet, then they were given a prolonged boil in dilute nitric. I used 70% nitric and used it at roughly 50/50 with tap water. I was not concerned about creating traces of silver chloride. If you are, use distilled or purified water instead of tap water.
This process will dissolve some of the silver contained in the filings, but it may not dissolve all of it. The filings will be much cleaner after the boil, but certainly not clean. Because the solution from this process tends to be very dirty, it is the once case where I produced silver chloride instead of cementing the silver with copper. You may choose a different course. There is no right or wrong method in this case. User's choice.
After you've rinsed the filings (until the rinse is clear), dissolve the material using AR at the same ratio as above. Again, use an ounce of nitric for each ounce of gold you expect to recover. Heat until everything is in solution (you should expect to see particles of abrasive, which will not dissolve). Finish up by the method of your choosing. I evaporated, using a button of gold to consume any free nitric acid. That it got reduced in size was evidence that I had not left any gold behind.
Gold from filings tends to be quite dirty after the first refining. You should find your now barren solution quite dirty, colored anywhere from a dark green to a dark blue color. Test it for platinum metals before discarding.
I found no problems from processing materials that included either borax or boric acid. The only big problem you may experience is if you try to filter the wash solutions. It is for that reason I suggest decanting (using a small hose). Most of these solutions are very difficult to filter, and there's no good reason you should have to.
Small hose: I used a short length of 3/8" ID vinyl tubing. It's easy to rinse, and is flexible enough to allow easy use. I used 1/8" wall thickness to avoid collapse of the tubing when making bends. You can prime the hose with water to begin transfer. Do not suck on the end with your mouth! :wink:
Hope this helps.
Harold
