That's an excellent suggestion Björn. Your wish is my command.
Dave
Dave
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Testwork carried out on the ashing of carbon with low levels of adsorbed gold
Over the years I have carried out many ashings of activated carbon which had been used to adsorb gold from a liquor.
Early tests I did many years ago indicated that when using an electric furnace with the door just cracked for air access a temperature of 600C was suitable.
The carbon was always ashed in porcelain dishes 100mm diameter and 40mm deep, claimed capacity of 150 ml.
I thought that it was time to run a series of tests and define the best conditions for ashing carbon in these crucibles.
I loaded 10 micrograms of gold as gold chloride onto replicate batches of dust free virgin activated carbon of various brands.
The batches varied in quantity from 1 to 20 grams in weight with the 20 gram samples having a bed depth of 15mm.
Due to the difficulty of getting complete ashing using carbon which had been used to adsorbed gold from solutions containing large quantities of base metals I have always used a maximum of 20g of carbon giving the bed depth of 15mm.
If larger quantities of carbon are used in these dishes then several episodes of rabbling the carbon during the ashing will be needed to achieve full ashing.
I ran the batches of carbon for 8 hours at temperatures of 400C, 500C, 600C, 700C and 800C.
All of the 400C batches failed to ash completely.
The 500C batches containing less than 5 grams of carbon ashed completely but the 10, 15 and 20g batches failed to ash completely unless rabbled several times.
All of the 600C, 700C and 800C batches ashed completely without rabbling.
All of the 600C batches returned the full 10 micrograms of gold.
All of the 700C batches returned 9 micrograms of gold.
All of the 800C batches returned between 6 and 7 micrograms of gold.
The above results indicate that although the temperatures in the furnace did not reach even the temperature at which gold melts there is still substantial volatilization of the finely divided gold at 800C.
Overall ashing of carbon should be conducted at 600C to minimize gold losses but still be done in an 8 hour time frame.
Deano
Over the years I have carried out many ashings of activated carbon which had been used to adsorb gold from a liquor.
Early tests I did many years ago indicated that when using an electric furnace with the door just cracked for air access a temperature of 600C was suitable.
The carbon was always ashed in porcelain dishes 100mm diameter and 40mm deep, claimed capacity of 150 ml.
I thought that it was time to run a series of tests and define the best conditions for ashing carbon in these crucibles.
I loaded 10 micrograms of gold as gold chloride onto replicate batches of dust free virgin activated carbon of various brands.
The batches varied in quantity from 1 to 20 grams in weight with the 20 gram samples having a bed depth of 15mm.
Due to the difficulty of getting complete ashing using carbon which had been used to adsorbed gold from solutions containing large quantities of base metals I have always used a maximum of 20g of carbon giving the bed depth of 15mm.
If larger quantities of carbon are used in these dishes then several episodes of rabbling the carbon during the ashing will be needed to achieve full ashing.
I ran the batches of carbon for 8 hours at temperatures of 400C, 500C, 600C, 700C and 800C.
All of the 400C batches failed to ash completely.
The 500C batches containing less than 5 grams of carbon ashed completely but the 10, 15 and 20g batches failed to ash completely unless rabbled several times.
All of the 600C, 700C and 800C batches ashed completely without rabbling.
All of the 600C batches returned the full 10 micrograms of gold.
All of the 700C batches returned 9 micrograms of gold.
All of the 800C batches returned between 6 and 7 micrograms of gold.
The above results indicate that although the temperatures in the furnace did not reach even the temperature at which gold melts there is still substantial volatilization of the finely divided gold at 800C.
Overall ashing of carbon should be conducted at 600C to minimize gold losses but still be done in an 8 hour time frame.
Deano
Research135
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Maybe carbon ashing with concentrated sulphuric acid will work better and faster?. 8 hours is a full day's work. Losses should be less than 1/10000 (0.01%). It is a beautiful solution for used filters. Much better than incineration.
edit: I failed to read that you loaded Gold Chloride, instead of gold. Please disregard my post. IMHO it's the gold chloride that volatilizes, not the gold. It happens even at 80 degC.
edit: I failed to read that you loaded Gold Chloride, instead of gold. Please disregard my post. IMHO it's the gold chloride that volatilizes, not the gold. It happens even at 80 degC.
You didn't say which form of gold chloride you used to load the samples. I assume you used HAuCl4 as that would be what we get when leaching gold.
Then I suggest that the reactions while ashing the carbon would be...
1. When heated (haven't found the temperature yet) HCl is removed.
2. Further heating breaks down the gold tri chloride above 160 °C and takes away 2/3 of the remaining chloride.
3. At yet higher temperatures (>420 °C) the remaining gold mono chloride reacts and creates metallic gold and gold tri chloride, which probably goes off as a gas.
This could explain why you see about 2/3 of the gold remaining in the ash and 1/3 going off as gas.
Ref:
Wikipedia : Chloroauric acid
Wikipedia : Gold(III) chloride
Göran
Then I suggest that the reactions while ashing the carbon would be...
1. When heated (haven't found the temperature yet) HCl is removed.
2. Further heating breaks down the gold tri chloride above 160 °C and takes away 2/3 of the remaining chloride.
3. At yet higher temperatures (>420 °C) the remaining gold mono chloride reacts and creates metallic gold and gold tri chloride, which probably goes off as a gas.
This could explain why you see about 2/3 of the gold remaining in the ash and 1/3 going off as gas.
Ref:
Wikipedia : Chloroauric acid
Wikipedia : Gold(III) chloride
Göran
Gold was in the form of tetrachloroauric acid standard from Merck, Germany.
The standard interpretation of reactions during the ashing of the carbon is as you have shown and should lead to gold losses at all of the temperatures used in the test regimes.
The reason I posted the results is that there were no losses at all until the temperature reached 700C.
The indication is that the conventional expectations for gold loss do not occur in the expected manner and that further testwork is required to ascertain what is actually happening.
This is a secondary result separate from the fact that 600C is probably near optimal for carbon ashing.
Deano
The standard interpretation of reactions during the ashing of the carbon is as you have shown and should lead to gold losses at all of the temperatures used in the test regimes.
The reason I posted the results is that there were no losses at all until the temperature reached 700C.
The indication is that the conventional expectations for gold loss do not occur in the expected manner and that further testwork is required to ascertain what is actually happening.
This is a secondary result separate from the fact that 600C is probably near optimal for carbon ashing.
Deano
Further on the ashing of carbon.
I re-ran the ashing tests under both cold start furnace and steady temperature furnace conditions for all tests.
All results were identical with the previously reported numbers.
This indicates that furnace temperature ramp up conditions play no part in the gold losses.
I then took dishes containing carbon which had been ashed at 600C and subjected half of them to furnacing at 700C and the other half at 800C for 8 hours.
I also subjected some of these 600C ashings to aqua regia digest to confirm that the gold levels were indeed the same as previously reported, they were, no losses.
The ashings subjected to the higher temperature furnacings returned identical results to the original higher temperature ashings.
This indicates that the losses are solely due to the finely divided gold being kept in the higher temperature furnacing conditions.
They are not due to volatilisation of gold chlorides as such.
Deano
I re-ran the ashing tests under both cold start furnace and steady temperature furnace conditions for all tests.
All results were identical with the previously reported numbers.
This indicates that furnace temperature ramp up conditions play no part in the gold losses.
I then took dishes containing carbon which had been ashed at 600C and subjected half of them to furnacing at 700C and the other half at 800C for 8 hours.
I also subjected some of these 600C ashings to aqua regia digest to confirm that the gold levels were indeed the same as previously reported, they were, no losses.
The ashings subjected to the higher temperature furnacings returned identical results to the original higher temperature ashings.
This indicates that the losses are solely due to the finely divided gold being kept in the higher temperature furnacing conditions.
They are not due to volatilisation of gold chlorides as such.
Deano
By accident I placed some activated carbon blanks in a furnace which has become contaminated with gold from smelts.
Normally this furnace is now only used for smelts, certainly not for precise analytical work.
To my surprise the carbon blanks all registered high levels of gold.
Repeating this test at various temperatures from 600C to 900C showed gold from all samples, the lowest temperature samples registering the highest gold values.
I repeated the tests but only placed empty dishes in the furnace, no carbon.
There were no gold values registered from the empty dishes at any temperatures.
I took dishes containing ash from carbon blanks which had been ashed in a clean furnace and placed half of them in the contaminated furnace at the various temperatures.
All of the samples registered no gold, thus the ash plays no part in the adsorption of gold in the contaminated furnace.
In summary, a dish containing blank carbon ashed in the contaminated furnace registered gold values.
An empty dish placed in the contaminated furnace registered no gold values.
A dish containing ash from a previous ashing in a clean furnace registered no gold values after being subject to the same temperature regimes in the contaminated furnace.
All furnacings were carried out for 8 hours.
Unless activated carbon is present in the dishes in the contaminated furnace there are no gold values registered from these dishes.
It appears that the activated carbon is capable of adsorbing volatilised gold values from the furnace atmosphere until such time as the activated carbon is completely ashed.
This most likely is the mechanism by which gold losses as gold chloride during carbon ashing are eliminated.
It appears that any gold volatilised as gold chloride is adsorbed on the carbon, this effect is repeated until the furnace temperature is high enough to convert the gold chloride to metallic gold.
At this stage there is still enough un-ashed carbon present to stop any volatilisation losses.
Once the gold chloride has been converted to gold particulates then the volatilisation of these particulates will continue in the closed cycle until all of the carbon present has been ashed.
At this stage any volatilisation of the particulate gold will lead to gold losses.
As the 800C ashing is completed in a much shorter time than the 700C ashing there is a longer time for volatilisation to occur when all ashings are conducted for 8 hours.
The 600C ashing is completed just short of the 8 hours and so very little time is available for free volatilisation of the particulate gold.
All of the above fits with there being no gold losses for the 600C ashings, a small loss for the 700C ashings and a larger loss for the 800C ashings.
If you wish to minimise any losses you should keep a close watch on any ashings and turn the heat off as soon as ashing is complete.
Deano
Normally this furnace is now only used for smelts, certainly not for precise analytical work.
To my surprise the carbon blanks all registered high levels of gold.
Repeating this test at various temperatures from 600C to 900C showed gold from all samples, the lowest temperature samples registering the highest gold values.
I repeated the tests but only placed empty dishes in the furnace, no carbon.
There were no gold values registered from the empty dishes at any temperatures.
I took dishes containing ash from carbon blanks which had been ashed in a clean furnace and placed half of them in the contaminated furnace at the various temperatures.
All of the samples registered no gold, thus the ash plays no part in the adsorption of gold in the contaminated furnace.
In summary, a dish containing blank carbon ashed in the contaminated furnace registered gold values.
An empty dish placed in the contaminated furnace registered no gold values.
A dish containing ash from a previous ashing in a clean furnace registered no gold values after being subject to the same temperature regimes in the contaminated furnace.
All furnacings were carried out for 8 hours.
Unless activated carbon is present in the dishes in the contaminated furnace there are no gold values registered from these dishes.
It appears that the activated carbon is capable of adsorbing volatilised gold values from the furnace atmosphere until such time as the activated carbon is completely ashed.
This most likely is the mechanism by which gold losses as gold chloride during carbon ashing are eliminated.
It appears that any gold volatilised as gold chloride is adsorbed on the carbon, this effect is repeated until the furnace temperature is high enough to convert the gold chloride to metallic gold.
At this stage there is still enough un-ashed carbon present to stop any volatilisation losses.
Once the gold chloride has been converted to gold particulates then the volatilisation of these particulates will continue in the closed cycle until all of the carbon present has been ashed.
At this stage any volatilisation of the particulate gold will lead to gold losses.
As the 800C ashing is completed in a much shorter time than the 700C ashing there is a longer time for volatilisation to occur when all ashings are conducted for 8 hours.
The 600C ashing is completed just short of the 8 hours and so very little time is available for free volatilisation of the particulate gold.
All of the above fits with there being no gold losses for the 600C ashings, a small loss for the 700C ashings and a larger loss for the 800C ashings.
If you wish to minimise any losses you should keep a close watch on any ashings and turn the heat off as soon as ashing is complete.
Deano
mkamalahmadi
New member
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My name is Mahmoud Ahmadi, and I am a PhD student in Chemical engineering at State University of New York (SUNY) at Buffalo.we developed a new technology (patent app in process) for tuning a metal scavenging chemistry to cost effectively capture high value metals in low ppm and ppb concentrations from aqueous solution (gold, palladium).
To validate our technology we need to get input from industry experts. Since gold electroplating and refinery cause gradual loss of gold in waste effluent , I wanted to ask if it would be possible for experts to get back to me at [email protected] to share their thoughts and advice regarding where our technology might fit in.
Thank you for the time and help,
Regards,
Mahmoud
To validate our technology we need to get input from industry experts. Since gold electroplating and refinery cause gradual loss of gold in waste effluent , I wanted to ask if it would be possible for experts to get back to me at [email protected] to share their thoughts and advice regarding where our technology might fit in.
Thank you for the time and help,
Regards,
Mahmoud
Mahmoud,
This is an public forum, we discuss topics openly and get input from the broad spectrum of our members. We welcome you to discuss your process openly on the forum but to seek private email conversation does little to benefit the forum. This is why your post was reported as it is seen as spamming the board.
If your process is worthy, it should be aired publicly.
This is an public forum, we discuss topics openly and get input from the broad spectrum of our members. We welcome you to discuss your process openly on the forum but to seek private email conversation does little to benefit the forum. This is why your post was reported as it is seen as spamming the board.
If your process is worthy, it should be aired publicly.
There has previously been substantial posting regarding hypochlorite leaching.
This post is an attempt to pull all of the previous work into a single post and also to incorporate further work not mentioned in the earlier threads.
Hypochlorite in solution in its generic sense exists in three forms depending on solution pH.
Below pH 3.5 it exists as chlorine gas.
Between pH 3.5 and pH 7.5 it exists as hypochlorous acid.
Above pH 7.5 it exists as the hypochlorite ion.
At all pH levels there will be some of all of the above forms present.
Thus at pH 10 there will not only be hypochlorite ions present but there will be some hypochlorous acid and some gaseous chlorine present.
In the above example the main form present will be the hypochlorite ion with minor levels of the other forms. You can smell the free chlorine gas present when you open a bottle of bleach even though the pH is above 10.
The pH only controls what dominant species will be present, it does not allow only that species to be present.
If leaching is carried out as a chlorine leach at a pH below 3.5 the chlorine will offgas and be lost to the process unless the reaction is carried out in a sealed vessel.
It is only when the sealed vessel is pressurised that enough of the chlorine will stay in solution and be available for leaching with.
If leaching is carried out as a hypochlorous acid leach it is most efficiently carried out at a pH between 6 and 7.
This is because you are operating in the part of the hypochlorous acid leaching zone which is furtherest away from the free chlorine gas zone and so there is less loss of free chlorine gas.
If leaching is carried out as a hypochlorite leach it is best carries out at pH near 8.
This is because it is operating close to the hypochlorous acid leach zone and will have a fairly large component of hypochlorous acid present.
How can you improve the operation of a hypochlorite system.
Very simply, add salt.
Gold chloride is very enthusiastic about adsorbing onto quartz and sulfides as well as other ore components.
This adsorption can be minimised by adding salt, sodium chloride, to the leach.
About 20% by weight is a good working level of salt addition.
Technically, apart from minimising adsorption of gold chloride complexes onto ore components the presence of the salt stabilises the gold chloride complexes and allows leaching to occur at higher pH levels and lower Eh levels.
Generally pH levels should be kept under 9 even with the salt additions.
The maximum salt addition level theoretically is around 36%, practically it is around 30%.
Care must be taken that evaporation does not cause the salt level to rise to the level where salt starts to crystallise in the leach solution, apart from the operational problems this can cause there will be gold losses from co-precipitation.
What are the benefits of leaching with hypochlorite.
Near neutral pH conditions.
Very little attack on iron complexes at these pH's.
Rapid adsorption of gold complexes onto activated carbon.
Rapid leaching.
Will attack sulfides thus allowing leaching of gold values from sulfides.
Disadvantages of leaching with hypochlorite
Health and safety, chlorine is a cumulative poison and should only be used where all safety gear is being used.
If used around pH 7 the offgassing of chlorine is minimised but is not stopped.
Always keep in mind that chlorine is effective enough as a chemical warfare agent to have been used as such in world war 1.
Plant must be constructed of non-metallic parts, a slow attack on iron complexes does not mean no attack.
A close check must be kept on carbon loadings, if loadings are allowed to get too high there will be loss of gold by attrition from the carbon.
This loss also indicates that the gold should be stripped in the loading canister rather than be transferred to a specialist stripping column, there will be losses during the transfer.
It also indicates that gold loadings during CIP operations should be closely monitored so as to not overload the carbon.
Attack of sulfides by the leach will cause a drop in pH, this needs to be closely monitored during the leach cycle.
Best conditions for running a hypochlorite leach.
My preference is for pH 7, 200 grams per litre plain salt, calcium hypochlorite starting at 1 gram per litre.
The lower you can keep the hypochlorite levels the less attack on metals apart from gold.
This also makes a good silver leach if the solution is circulated through a cannister of activated carbon so that the silver level in solution is always kept low.
The silver will load on the carbon to the point where it can actually be burnished, similarly to gold.
Recover the precious metals by ashing the carbon after drying.
Deano
This post is an attempt to pull all of the previous work into a single post and also to incorporate further work not mentioned in the earlier threads.
Hypochlorite in solution in its generic sense exists in three forms depending on solution pH.
Below pH 3.5 it exists as chlorine gas.
Between pH 3.5 and pH 7.5 it exists as hypochlorous acid.
Above pH 7.5 it exists as the hypochlorite ion.
At all pH levels there will be some of all of the above forms present.
Thus at pH 10 there will not only be hypochlorite ions present but there will be some hypochlorous acid and some gaseous chlorine present.
In the above example the main form present will be the hypochlorite ion with minor levels of the other forms. You can smell the free chlorine gas present when you open a bottle of bleach even though the pH is above 10.
The pH only controls what dominant species will be present, it does not allow only that species to be present.
If leaching is carried out as a chlorine leach at a pH below 3.5 the chlorine will offgas and be lost to the process unless the reaction is carried out in a sealed vessel.
It is only when the sealed vessel is pressurised that enough of the chlorine will stay in solution and be available for leaching with.
If leaching is carried out as a hypochlorous acid leach it is most efficiently carried out at a pH between 6 and 7.
This is because you are operating in the part of the hypochlorous acid leaching zone which is furtherest away from the free chlorine gas zone and so there is less loss of free chlorine gas.
If leaching is carried out as a hypochlorite leach it is best carries out at pH near 8.
This is because it is operating close to the hypochlorous acid leach zone and will have a fairly large component of hypochlorous acid present.
How can you improve the operation of a hypochlorite system.
Very simply, add salt.
Gold chloride is very enthusiastic about adsorbing onto quartz and sulfides as well as other ore components.
This adsorption can be minimised by adding salt, sodium chloride, to the leach.
About 20% by weight is a good working level of salt addition.
Technically, apart from minimising adsorption of gold chloride complexes onto ore components the presence of the salt stabilises the gold chloride complexes and allows leaching to occur at higher pH levels and lower Eh levels.
Generally pH levels should be kept under 9 even with the salt additions.
The maximum salt addition level theoretically is around 36%, practically it is around 30%.
Care must be taken that evaporation does not cause the salt level to rise to the level where salt starts to crystallise in the leach solution, apart from the operational problems this can cause there will be gold losses from co-precipitation.
What are the benefits of leaching with hypochlorite.
Near neutral pH conditions.
Very little attack on iron complexes at these pH's.
Rapid adsorption of gold complexes onto activated carbon.
Rapid leaching.
Will attack sulfides thus allowing leaching of gold values from sulfides.
Disadvantages of leaching with hypochlorite
Health and safety, chlorine is a cumulative poison and should only be used where all safety gear is being used.
If used around pH 7 the offgassing of chlorine is minimised but is not stopped.
Always keep in mind that chlorine is effective enough as a chemical warfare agent to have been used as such in world war 1.
Plant must be constructed of non-metallic parts, a slow attack on iron complexes does not mean no attack.
A close check must be kept on carbon loadings, if loadings are allowed to get too high there will be loss of gold by attrition from the carbon.
This loss also indicates that the gold should be stripped in the loading canister rather than be transferred to a specialist stripping column, there will be losses during the transfer.
It also indicates that gold loadings during CIP operations should be closely monitored so as to not overload the carbon.
Attack of sulfides by the leach will cause a drop in pH, this needs to be closely monitored during the leach cycle.
Best conditions for running a hypochlorite leach.
My preference is for pH 7, 200 grams per litre plain salt, calcium hypochlorite starting at 1 gram per litre.
The lower you can keep the hypochlorite levels the less attack on metals apart from gold.
This also makes a good silver leach if the solution is circulated through a cannister of activated carbon so that the silver level in solution is always kept low.
The silver will load on the carbon to the point where it can actually be burnished, similarly to gold.
Recover the precious metals by ashing the carbon after drying.
Deano
Good write up. I hope I will get an opportunity to test this leach some day.
Is temperature affecting the leach in any major way? I guess higher temperature gives higher leach rates but also increases evaporation.
What is typical leach times? I understand that it depends a lot of ore chemistry and how fine the ore has been milled, but are we talking hours, days or weeks here?
I has probably been mentioned before but what is the maximum loading of gold on carbon?
Göran
Is temperature affecting the leach in any major way? I guess higher temperature gives higher leach rates but also increases evaporation.
What is typical leach times? I understand that it depends a lot of ore chemistry and how fine the ore has been milled, but are we talking hours, days or weeks here?
I has probably been mentioned before but what is the maximum loading of gold on carbon?
Göran
The hypochlorite leach rate is between cyanide and aqua regia.
For an ore comparison, generally hypochlorite is around 3 times as fast as cyanide but can be sped up by having more hypochlorite present.
This usually means leach times in hours rather than days.
The leach rate is controlled by the rate at which the oxidant can access the gold so some form of agitation is usual.
The agitation can be applied by stirring or by pumping the liquor, the former for ores and the latter for component leaching.
As you stated, the leach rate increases with temperature as does the evaporation rate.
The maximum loading of gold onto carbon is dependent on both the form of the gold complexes and the tenor of the gold liquor( think concentration of gold in the liquor).
The higher the gold tenor the greater the loading possible.
Gold chloride will load to a higher level and do so faster than gold cyanide.
The gold cyanide loading is an adsorption system whereas the gold chloride is mainly a reduction mechanism.
This means that gold chloride will reduce to gold metal on activated carbon and will do so to levels where the gold particles will fall off the carbon. Great care must be taken with carbon loaded from gold chloride not to get to this stage.
The maximum gold loading levels onto carbon are also very dependent on the levels of other metal species present in the leach liquors as these other metals will take up sites on the carbon and prevent gold from loading on these sites.
Temperature and pH are also among the major loading controllers.
In CIP circuits the gold loadings are anywhere from 2,000 to 20,000 ppm on the carbon depending on the mine conditions.
In artificial laboratory conditions under acid pH and low temperature gold loadings over 200,000 ppm have been achieved.
Note that gold cyanide complexes are stable under acid conditions, it is only when the acid conditions are strongly oxidising that the cyanide complex is degraded.
Deano
For an ore comparison, generally hypochlorite is around 3 times as fast as cyanide but can be sped up by having more hypochlorite present.
This usually means leach times in hours rather than days.
The leach rate is controlled by the rate at which the oxidant can access the gold so some form of agitation is usual.
The agitation can be applied by stirring or by pumping the liquor, the former for ores and the latter for component leaching.
As you stated, the leach rate increases with temperature as does the evaporation rate.
The maximum loading of gold onto carbon is dependent on both the form of the gold complexes and the tenor of the gold liquor( think concentration of gold in the liquor).
The higher the gold tenor the greater the loading possible.
Gold chloride will load to a higher level and do so faster than gold cyanide.
The gold cyanide loading is an adsorption system whereas the gold chloride is mainly a reduction mechanism.
This means that gold chloride will reduce to gold metal on activated carbon and will do so to levels where the gold particles will fall off the carbon. Great care must be taken with carbon loaded from gold chloride not to get to this stage.
The maximum gold loading levels onto carbon are also very dependent on the levels of other metal species present in the leach liquors as these other metals will take up sites on the carbon and prevent gold from loading on these sites.
Temperature and pH are also among the major loading controllers.
In CIP circuits the gold loadings are anywhere from 2,000 to 20,000 ppm on the carbon depending on the mine conditions.
In artificial laboratory conditions under acid pH and low temperature gold loadings over 200,000 ppm have been achieved.
Note that gold cyanide complexes are stable under acid conditions, it is only when the acid conditions are strongly oxidising that the cyanide complex is degraded.
Deano
solar_plasma
Well-known member
While reading discussions about recovering gold from carbon, I often wondered, if nickel will be of greater concern, since finely devided nickel reacts with CO at 50-100 °C to nickel tetracarbonyl ("liquid death" or "Nickel carbonyl is one of the most toxic substances encountered in industrial processes"), - though it will be decomposed at 180-200°C.
At 100°C or below the reaction of carbon to CO is minimal, even though it exists. So, is it correct to assume, that we are save (regarding nickel tetracarbonyl), when heating let say 100g nickel contaminated carbon to 600°C in a muffel furnace?
At 100°C or below the reaction of carbon to CO is minimal, even though it exists. So, is it correct to assume, that we are save (regarding nickel tetracarbonyl), when heating let say 100g nickel contaminated carbon to 600°C in a muffel furnace?
Regarding the ashing of carbon containing nickel I ran a quick series of ashing tests using carbon loaded with nickel chloride, carbon loaded with nickel cyanide and carbon loaded with nickel chloride reduced to nickel metal with hydrazine.
A fourth dish had only the reduced nickel present, no carbon.
After ashing the ash was digested in aqua regia and the nickel losses were calculated.
There were no nickel losses for any of the dishes where carbon was present.
There was a loss of 20 micrograms of nickel from 100 micrograms from the dish where no carbon was present.
The above indicates that the carbon acts as an adsorbent for any nickel volatilised during the ashing stage, similarly to how it acted for gold.
It is only when all of the carbon has been ashed that volatilisation of the nickel and associated losses occurs.
It appears that the nickel carbonyl does not present a threat during the ashing of carbon.
Deano
A fourth dish had only the reduced nickel present, no carbon.
After ashing the ash was digested in aqua regia and the nickel losses were calculated.
There were no nickel losses for any of the dishes where carbon was present.
There was a loss of 20 micrograms of nickel from 100 micrograms from the dish where no carbon was present.
The above indicates that the carbon acts as an adsorbent for any nickel volatilised during the ashing stage, similarly to how it acted for gold.
It is only when all of the carbon has been ashed that volatilisation of the nickel and associated losses occurs.
It appears that the nickel carbonyl does not present a threat during the ashing of carbon.
Deano
solar_plasma
Well-known member
wow! Thanks a lot!
A
Anonymous
Guest
Well......
Having invested a lot of time and a fair bit of money building the cell Deano recommended, I can confirm that it does exactly what Deano said that it would and I would strongly recommend that people look at building one.
Thanks Dean.
Jon
Having invested a lot of time and a fair bit of money building the cell Deano recommended, I can confirm that it does exactly what Deano said that it would and I would strongly recommend that people look at building one.
Thanks Dean.
Jon
Jon,
Might you post some photo's of your system?
Might you post some photo's of your system?
A
Anonymous
Guest
Looking good mate have you had it on trial ?
A
Anonymous
Guest
Oh yes.
Strips like a dream. That cell is too big for a home refiner though. The felt will take many Kg of gold and I don't have that much at a time so I'll be cutting the cell down by at least 3/4 and building in lots of improvements. I loaded around half an ounce on to the bottom quarter of the felt and apart from a visible colour change it was patently apparent that much much larger quantities would be needed to even make a dent in the capacity of the cathode.
This was very much a proof of concept build. By that I mean proof of concept to me as opposed to proving that Dean's theory worked!
Gentlemen I would strongly suggest and recommend that you read Dean's offerings again, and again. There are nuggets (sorry I couldn't resist) of information in his posts that can be used by everyone who is prepared to apply them. On this project alone I have learned so much it's incredible, and although sometimes frustrating I have benefited greatly from the experience.
Strips like a dream. That cell is too big for a home refiner though. The felt will take many Kg of gold and I don't have that much at a time so I'll be cutting the cell down by at least 3/4 and building in lots of improvements. I loaded around half an ounce on to the bottom quarter of the felt and apart from a visible colour change it was patently apparent that much much larger quantities would be needed to even make a dent in the capacity of the cathode.
This was very much a proof of concept build. By that I mean proof of concept to me as opposed to proving that Dean's theory worked!
Gentlemen I would strongly suggest and recommend that you read Dean's offerings again, and again. There are nuggets (sorry I couldn't resist) of information in his posts that can be used by everyone who is prepared to apply them. On this project alone I have learned so much it's incredible, and although sometimes frustrating I have benefited greatly from the experience.
