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- Feb 25, 2007
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A recent inquiry by PM concerning incineration has prompted me to post on the subject.
Those of you who have read my ravings know that I endorse the process, and recommend it for almost everything you may encounter. When your material gets incinerated and why may vary, but rarely will a process not benefit by the procedure.
These are my thoughts, based on years of practice:
Hoke, in her book, talks freely of tossing on gasoline when incinerating. That, of course, is insane. Gasoline should never be used as an accelerant, especially when working indoors. The risk of a fire out of control is immense. I strongly advise against using anything when incinerating aside from the material in question. None is required.
Do not incinerate in a kiln. The most desirable condtion is one whereby the material in question can be ignited, not just heated and permitted to smolder. It's one way to limit the amount of smoke created by the roasting process. An ample supply of oxygen is required, which would be limited in a kiln. Open incineration is the answer.
If plastic items (bags containing polishing waste, for example) are incinerated, they should be monitored closely. The bulk of plastic items don't burn well, turning to oil instead when heated. However, once they reach critical temperature, they often erupt in flame much like you'd expect from burning fuel.
Do not incinerate in a hood that is flammable, nor on a countertop that has a wooden base under the burner. Prolonged heating will slowly convert the wood to charcoal, with a fire the outcome, assuming there is enough oxygen. A smoldering fire could result easily after prlonged incineration.
My method for incinerating was simple. My heat source was the same one that I used for the refining process, although when incinerating no other process was in motion because of the excessive heat.
The heat source in question was a three burner natural gas hotplate. They are relatively inexpensive (I used to pay $60), and were used as purchased, with one modification. I adjusted the valve on one position so it would be opened with greater flow, and adjusted the air full open. If natural gas is not an option, one could use propane, although with the propane tank out of doors, piping the gas inside.
A discarded fry pan serves very well as the incineration container. It should never be made of aluminum, which would melt, nor cast iron, which will be difficult to heat well, plus they will crack when heated as is necessary for proper incineration.
I found that stainless pans held up very well, and could be used for many cycles before they perforated. They do have a finite life, especially if acid bearing materials are incinerated, and that's one of the things you'll do routinely once you understand the benefits.
Second-hand stores (Goodwill, for example) are an excellent source for pans of this nature. Boy Scouts used a small pan, about 6" in diameter, which serves very well for small lots, so if you encounter one, don't pass it by.
I am assuming that the greatest interest here is the processing of E scrap. In that case, incineration may not be required until after the gold has been stripped. I would assume that the material would be stripped by a sulfuric cell, or one of the work-around methods promoted on the forum.
Once the values have been removed from the base metals, the step I would recommend is to get all of them in a filter, where they can be drained and dried. When well drained, they should be introduced to the pan, filter and all. Heat the lot until the filter combusts, then add sufficient heat to the pan to achieve a dull red heat. Apply heat to the sides and bottom of the pan, not to the material inside, and do not melt the material. A Hoke type torch, or a rose bud serves very well for the additional heating. This should remove all oils and grease and plastic bits from the material, and burn off all carbonaceous substances. Heat should be maintained until there are no glowing embers.
After incineration, crush the material well in a mortar, then screen the lot, removing anything that's magnetic, which should be added to the stock pot. It will likely carry traces of values, and they'll be recovered in the future when the stock pot is refined or furnace reduced.
The now crushed and screened material can be treated by two methods, each of which will remove unwanted substances. If nitric is your choice, the material would be boiled in nitric/water until no more fumes evolve, then the beaker filled with water. Decant when the solids have settled well, and rinse once again, using water.
If the material in question has the risk of containing tin, either from E scrap (solder) or it came from gold filled objects, which often have a soft solder bonding the gold surface, the material will benefit by a boil in HCl. This process will make for very easy filtration of the gold chloride solution that is yet to be produced.
Going from nitric to HCl presents a serious risk of dissolving values prematurely. To get around the problem, once again, the material should be incinerated. Once well heated, all nitric would have been expelled. Once again, crush the material well in a mortar, then place it back in a beaker. There should be no need to screen after the first time. Cover the material with 50/50 HCl and tap water and bring to a boil, holding there for several minutes. Remove the beaker from the heat source, and add water. Allow to settle well, then decant. Rinse with water, stirring well, then allowing the material to settle. None of these processes require distilled water. Tap water should be more than adequate.
After decanting, the material is ready to be dissolved to extract the gold. The resulting solution should be various shades of yellow, depending on the level of concentration. For the most part, the base metals will have been eliminated because of the acid washes. That serves to provide much cleaner gold.
All of these operations may sound like they are labor intensive, but they are routine-----easily accomplished, and paying huge benefits in the overall quality of gold recovered, plus ease in handling of the gold solution. Another benefit is you won't experience floating of precipitated gold, assuming you keep your vessels well washed, and don't get finger prints on the insides of beakers that are used in precipitation.
If you are involved in refining wastes from the jeweler's bench, the only material that doesn't require incineration is large pieces of karat gold, which would be inquarted, thus freed of oils when they are melted.
Something to ponder.
Regardless of how much you may wash filters when filtering your gold chloride solutions, traces of values will usually remain. If you do not wish to spend the time, and prefer to not dilute your solutions by rinsing, do not discard the filter when finished with filtration and a fast rinse with water (I always used tap water). They should be dried, then incinerated, with the resulting ashes stored. By incinerating, any free acids are eliminated, limiting the amount of rust you'll experience in your work area.
Don't discard anything that is in the filter. Everything should be stored for future processing by furnace. There is often silver chloride included, along with traces of other metals. They will serve to act as a collector when the material is processed, so they provide a valuable function.
The bottom line here is that incineration should be a part of your refining processes. The benefits far outweigh the results of avoiding the process.
Contrary to the belief of some, incineration does nothing to degrade the quality of gold, nor does it complicate refining. Yes, it is ugly from heating, but otherwise not changed. Incineration will not complicate the refining process, and the washing process will restore the bulk of luster to the material.
Harold
Those of you who have read my ravings know that I endorse the process, and recommend it for almost everything you may encounter. When your material gets incinerated and why may vary, but rarely will a process not benefit by the procedure.
These are my thoughts, based on years of practice:
Hoke, in her book, talks freely of tossing on gasoline when incinerating. That, of course, is insane. Gasoline should never be used as an accelerant, especially when working indoors. The risk of a fire out of control is immense. I strongly advise against using anything when incinerating aside from the material in question. None is required.
Do not incinerate in a kiln. The most desirable condtion is one whereby the material in question can be ignited, not just heated and permitted to smolder. It's one way to limit the amount of smoke created by the roasting process. An ample supply of oxygen is required, which would be limited in a kiln. Open incineration is the answer.
If plastic items (bags containing polishing waste, for example) are incinerated, they should be monitored closely. The bulk of plastic items don't burn well, turning to oil instead when heated. However, once they reach critical temperature, they often erupt in flame much like you'd expect from burning fuel.
Do not incinerate in a hood that is flammable, nor on a countertop that has a wooden base under the burner. Prolonged heating will slowly convert the wood to charcoal, with a fire the outcome, assuming there is enough oxygen. A smoldering fire could result easily after prlonged incineration.
My method for incinerating was simple. My heat source was the same one that I used for the refining process, although when incinerating no other process was in motion because of the excessive heat.
The heat source in question was a three burner natural gas hotplate. They are relatively inexpensive (I used to pay $60), and were used as purchased, with one modification. I adjusted the valve on one position so it would be opened with greater flow, and adjusted the air full open. If natural gas is not an option, one could use propane, although with the propane tank out of doors, piping the gas inside.
A discarded fry pan serves very well as the incineration container. It should never be made of aluminum, which would melt, nor cast iron, which will be difficult to heat well, plus they will crack when heated as is necessary for proper incineration.
I found that stainless pans held up very well, and could be used for many cycles before they perforated. They do have a finite life, especially if acid bearing materials are incinerated, and that's one of the things you'll do routinely once you understand the benefits.
Second-hand stores (Goodwill, for example) are an excellent source for pans of this nature. Boy Scouts used a small pan, about 6" in diameter, which serves very well for small lots, so if you encounter one, don't pass it by.
I am assuming that the greatest interest here is the processing of E scrap. In that case, incineration may not be required until after the gold has been stripped. I would assume that the material would be stripped by a sulfuric cell, or one of the work-around methods promoted on the forum.
Once the values have been removed from the base metals, the step I would recommend is to get all of them in a filter, where they can be drained and dried. When well drained, they should be introduced to the pan, filter and all. Heat the lot until the filter combusts, then add sufficient heat to the pan to achieve a dull red heat. Apply heat to the sides and bottom of the pan, not to the material inside, and do not melt the material. A Hoke type torch, or a rose bud serves very well for the additional heating. This should remove all oils and grease and plastic bits from the material, and burn off all carbonaceous substances. Heat should be maintained until there are no glowing embers.
After incineration, crush the material well in a mortar, then screen the lot, removing anything that's magnetic, which should be added to the stock pot. It will likely carry traces of values, and they'll be recovered in the future when the stock pot is refined or furnace reduced.
The now crushed and screened material can be treated by two methods, each of which will remove unwanted substances. If nitric is your choice, the material would be boiled in nitric/water until no more fumes evolve, then the beaker filled with water. Decant when the solids have settled well, and rinse once again, using water.
If the material in question has the risk of containing tin, either from E scrap (solder) or it came from gold filled objects, which often have a soft solder bonding the gold surface, the material will benefit by a boil in HCl. This process will make for very easy filtration of the gold chloride solution that is yet to be produced.
Going from nitric to HCl presents a serious risk of dissolving values prematurely. To get around the problem, once again, the material should be incinerated. Once well heated, all nitric would have been expelled. Once again, crush the material well in a mortar, then place it back in a beaker. There should be no need to screen after the first time. Cover the material with 50/50 HCl and tap water and bring to a boil, holding there for several minutes. Remove the beaker from the heat source, and add water. Allow to settle well, then decant. Rinse with water, stirring well, then allowing the material to settle. None of these processes require distilled water. Tap water should be more than adequate.
After decanting, the material is ready to be dissolved to extract the gold. The resulting solution should be various shades of yellow, depending on the level of concentration. For the most part, the base metals will have been eliminated because of the acid washes. That serves to provide much cleaner gold.
All of these operations may sound like they are labor intensive, but they are routine-----easily accomplished, and paying huge benefits in the overall quality of gold recovered, plus ease in handling of the gold solution. Another benefit is you won't experience floating of precipitated gold, assuming you keep your vessels well washed, and don't get finger prints on the insides of beakers that are used in precipitation.
If you are involved in refining wastes from the jeweler's bench, the only material that doesn't require incineration is large pieces of karat gold, which would be inquarted, thus freed of oils when they are melted.
Something to ponder.
Regardless of how much you may wash filters when filtering your gold chloride solutions, traces of values will usually remain. If you do not wish to spend the time, and prefer to not dilute your solutions by rinsing, do not discard the filter when finished with filtration and a fast rinse with water (I always used tap water). They should be dried, then incinerated, with the resulting ashes stored. By incinerating, any free acids are eliminated, limiting the amount of rust you'll experience in your work area.
Don't discard anything that is in the filter. Everything should be stored for future processing by furnace. There is often silver chloride included, along with traces of other metals. They will serve to act as a collector when the material is processed, so they provide a valuable function.
The bottom line here is that incineration should be a part of your refining processes. The benefits far outweigh the results of avoiding the process.
Contrary to the belief of some, incineration does nothing to degrade the quality of gold, nor does it complicate refining. Yes, it is ugly from heating, but otherwise not changed. Incineration will not complicate the refining process, and the washing process will restore the bulk of luster to the material.
Harold
