Hi guys
I have new refining "tutorial" here. If there would be positive feedback, I´ll find some time and try to post some more of my refining ventures.
For now: batch of 1080g metal case transistors, gold plated from outside and inside, with plated legs as well. These originate from post-soviet countries and around 1/4 of the batch were USSR made. Espetially these are very thick plated and rich, averaging more than 12g/kg. TESLA branded ones, manufactured in Czechoslovakia averaged around 8g/kg for mixed batches, but small ones or metal-cased ICs are richer than regular ones. Legs, espetially from USSR ones are extremely rich, solely legs assayed give more than 30g/kg Au - so it is important to consider the batch also based on how these were collected. If someone de-soldered them from boards, it is much better in your perspective than just cut-outs or ones just torn from boards missing legs completely.
Casing of these transistors is most often made from basically pure nickel, many times whole piece is dipped in tin to ensure air-tight seal. Some top lids could be cut off with pliers, but ones, which are dip-tinned are very difficult to decap. So I do not bother with doing this, and just processing them as whole pieces. Legs are made of kovar. Worth to note - some types, espetially from USSR boards, are often covered in transparent varnish (whole assembled board is dipped into varnish). This should be removed before processing - as it is fairly acid-resistant and many times acid cannot reach the metal and these are left undissolved. I use dichloromethane (DCM) to swell the varnish, which upon stirring flakes off and enable the access of the acid. I am sure other conventional "hard" solvents like MEK or acetone would swell it also.
Processing: I do not apply nitrosulfuric processing route here, as it is very tedious, slow and unefficient. I go straight AR with these, as gold resulting from this material is fairly heavy and relatively cleaner in comparison with gold from regular Cu material as eg pins.
De-varnished transistors were weighed, and transfered to cut HDPE canister - used as reaction vessel. Than, 2,5 L of tech grade HCL were heated to around 45°C on the hotplate in 5L beaker - to facilitate onset of the reaction. This was poured in, followed by 1/3 of expected nitric acid required - which was roughly 250 mL of 65% HNO3 (expected ammount for 1kg of Cu based material is around 750 mL, so this was my empirical reference). Reaction start in couple of minutes, and as nickel is much less noble metal than copper, quite a bit of heat is evolved. Actually, this one addition of nitric is capable to bring the whole pot near boiling point. After the reaction dies down, another 2L of HCL are added (to pass required 4L/kg ammount) and rest of the nitric acid is added in a way that it maintain steady reaction rate and minimal evaporation of HCL = no white steamy fumes are produced, just NOx gasses. With nickel material, reduction of nitric during the reaction is very deep. In some points, practically colourless outgas is produced, which does not turn to appreciable NO2 when came into contact with air - meaning that quite a bit of nitric is reduced even to nitrous oxide or N2 gas.
Be careful when adding fresh nitric to hot AR reaction, which died down completely - sometimes, solution tend to react extremely vigorously and emmit NOx gasses and create boil-over. I was fascinated by this fact - why it is happening. Clearly, HNO3 does not even reach the metal on the bottom and solution foams like crazy. My hypothesis is that dissolved metals in the solution somehow complex NO and NO2 forming nitroso and nitrito complexes, which are then somehow broken down by the addition of nitric acid, suddently releasing quite a bit of NOx gasses. Anyway, carefully adding few 5-10 mL portions of nitric manage to kickstart the reaction again, and from there, nitric can be added relatively smoothly to maintain the reaction.
Advantage of doing bigger lots like this one (more than 1kg = more than 5L of juice) is that when it heats up by the reaction, it retain the temperature for couple of hours - if you insulate the vessel with aluminium foil or something else. This retention of heat allow the nitric to fully react with material and be completely spent. Usually, I add empirical ammount of nitric and let the reaction go to completion, and then let it insulated overnight. By doing this, I give the reaction plenty of time to go to completion = nitric fully spent.
Next morning, the spent juice is poured off and leftovers inspected. Usually, some metal is left on the bottom of the vessel - juice is conveniently poured off and leftovers transfered to a beaker, where they are treated with fresh portion of HCL and nitric is dosed in small aliquots in order to fully dissolve everything metallic.
This time, to my surprise, quite a bit of unreacted metal was found to be on the bottom, so I used like 0,75L of HCL and dosed nitric to dissolve everything. It took few hours of mild heating, but eventually all of it was gone. It is important to decant this spent juice and do one more leach with fairly nitric-rich AR in order to dissolve also pieces of legs which are imbedded in glass bottoms of the resistors. Otherwise, gold will precipitate here and quite a bit of it will be lost.
All leach solutions were then combined, filtered through kitchen strainer to remove bigger undissolved pieces of silicone, plastic or some other junk, and halved into 2 5L beakers. I then heat them on the hotplate and insert copper (in my case springs from big breakers) to precipitate gold and also de-nox the solution. I found out, espetially with Ni-rich material, that denoxing with sulfamic acid is rather slow and very tedious. Sometimes, it took hours and overwhelming ammount of sulfamic acid just to find out that some gasses still escape from the solution. Again, my hypothesis is that NOx gasses are complexed with nickel cations and bind strongly - so sulfamic acid has hard time to react with them. So by ensuring I do not use unhealthy excess of nitric, I use copper as de-noxing agent - and when the solution heats up to around 80°C, copper start to react vividly, emmiting NOx gasses. It could be nicely paired with additions of sulfamic to stop re-adsorption and oxidation of NO by oxygen, disrupting the creation of in-situ nitric acid. It is clearly visible that gold is dropped on the copper (gold "bleeding" from the wire) but quickly redissolved in solution. But in certain point the solution will start to get more cloudy, and eventually all effervescence dies down and gold drop down. Quick stirring and heating for couple dozen minutes result in complete drop of gold, which is farily heavy, coagulated and easily decanted. By XRF measuring, it is usually more than 98,5% pure - if the material did not contained silver or palladium.
So I filtered the gold precipitate, stannous negative on the solution. This filtered gold mud was then redissolved in HCL with small additions of H2O2. I found this old technique very beneficial over classic AR route due to simple fact - there is no need of de-noxing to be done before dropping the gold. Just remove watchglass from the beaker for a minute or two and let the small residual chlorine to escape. So, if you have access to 30% H2O2, I recommend to try it out - if you didn´t already done this before. Anyway, volume was doubled by addition of water and ice and solution was filtered through Buchner funnel to obtain clear yellow-orange pay-liquid
Gold drop was accomplished with SO2 gas bubbled through the solution. In other posts, I disclosed why it is (according to me and my point of view) beneficial to use SO2 rather than SMB or other sulfites, and I sticked to this method for final purification of gold - because it gave very nice, easy settled, heavy gold precipitate with superior purity.
Result: 8,93 9,65 g of gold. Meaning material was around 8,3g 8,93g/kg. There are small leftovers of gold from filtrations of the leaching liquors, decants from washings of gold powders etc. I assume like 0,1-0,3g of gold is still to be recovered. This will move the figure closer to 9 g/kg.
This yield on lower side of the spectrum will reflect the fact that most of the best yielding USSR transistors and ICs were just torn from the boards and missing those 30g/kg legs. I reflected that on purchase, and advised the seller to remove the components properly next time, so we will see how he will cope with this
That´s it for today.
Orvi
(edited yields after re-weighing and realizing I messed the numbers)
Transistors weighed and poured to the reaction vessel.
Onset of the reaction. Top piece of the canister is used like DIY "watchglass" to cut down the effervescence loss and heat loss during the reaction. Insides of the inverted top of the canister could be filled with water and act as pro-forma cooler, if needed. Pieces of PE tubing on the sides prevent whole thing falling inside the canister Big plastic bowl used as catchpan if reaction does not want to cooperate and boil over
Remains of glass bottoms and silicon dies of the transistors at final digestion stage with fresh AR solution. This should be held hot for some time in order to fully dissolve the remains of the legs inside the glass.
Dropping the gold and de-noxing with thick copper wire inserted into the solution. Unfortunately, it can´t be seen on the photo, but it actually sticks out of the solution in both beakers - enabling to easily pull it off after completion of the reaction.
Cu-dropped gold on the filter, ready to be purified by re-dissolution in HCL/peroxide and drop with SO2 gas.
I have new refining "tutorial" here. If there would be positive feedback, I´ll find some time and try to post some more of my refining ventures.
For now: batch of 1080g metal case transistors, gold plated from outside and inside, with plated legs as well. These originate from post-soviet countries and around 1/4 of the batch were USSR made. Espetially these are very thick plated and rich, averaging more than 12g/kg. TESLA branded ones, manufactured in Czechoslovakia averaged around 8g/kg for mixed batches, but small ones or metal-cased ICs are richer than regular ones. Legs, espetially from USSR ones are extremely rich, solely legs assayed give more than 30g/kg Au - so it is important to consider the batch also based on how these were collected. If someone de-soldered them from boards, it is much better in your perspective than just cut-outs or ones just torn from boards missing legs completely.
Casing of these transistors is most often made from basically pure nickel, many times whole piece is dipped in tin to ensure air-tight seal. Some top lids could be cut off with pliers, but ones, which are dip-tinned are very difficult to decap. So I do not bother with doing this, and just processing them as whole pieces. Legs are made of kovar. Worth to note - some types, espetially from USSR boards, are often covered in transparent varnish (whole assembled board is dipped into varnish). This should be removed before processing - as it is fairly acid-resistant and many times acid cannot reach the metal and these are left undissolved. I use dichloromethane (DCM) to swell the varnish, which upon stirring flakes off and enable the access of the acid. I am sure other conventional "hard" solvents like MEK or acetone would swell it also.
Processing: I do not apply nitrosulfuric processing route here, as it is very tedious, slow and unefficient. I go straight AR with these, as gold resulting from this material is fairly heavy and relatively cleaner in comparison with gold from regular Cu material as eg pins.
De-varnished transistors were weighed, and transfered to cut HDPE canister - used as reaction vessel. Than, 2,5 L of tech grade HCL were heated to around 45°C on the hotplate in 5L beaker - to facilitate onset of the reaction. This was poured in, followed by 1/3 of expected nitric acid required - which was roughly 250 mL of 65% HNO3 (expected ammount for 1kg of Cu based material is around 750 mL, so this was my empirical reference). Reaction start in couple of minutes, and as nickel is much less noble metal than copper, quite a bit of heat is evolved. Actually, this one addition of nitric is capable to bring the whole pot near boiling point. After the reaction dies down, another 2L of HCL are added (to pass required 4L/kg ammount) and rest of the nitric acid is added in a way that it maintain steady reaction rate and minimal evaporation of HCL = no white steamy fumes are produced, just NOx gasses. With nickel material, reduction of nitric during the reaction is very deep. In some points, practically colourless outgas is produced, which does not turn to appreciable NO2 when came into contact with air - meaning that quite a bit of nitric is reduced even to nitrous oxide or N2 gas.
Be careful when adding fresh nitric to hot AR reaction, which died down completely - sometimes, solution tend to react extremely vigorously and emmit NOx gasses and create boil-over. I was fascinated by this fact - why it is happening. Clearly, HNO3 does not even reach the metal on the bottom and solution foams like crazy. My hypothesis is that dissolved metals in the solution somehow complex NO and NO2 forming nitroso and nitrito complexes, which are then somehow broken down by the addition of nitric acid, suddently releasing quite a bit of NOx gasses. Anyway, carefully adding few 5-10 mL portions of nitric manage to kickstart the reaction again, and from there, nitric can be added relatively smoothly to maintain the reaction.
Advantage of doing bigger lots like this one (more than 1kg = more than 5L of juice) is that when it heats up by the reaction, it retain the temperature for couple of hours - if you insulate the vessel with aluminium foil or something else. This retention of heat allow the nitric to fully react with material and be completely spent. Usually, I add empirical ammount of nitric and let the reaction go to completion, and then let it insulated overnight. By doing this, I give the reaction plenty of time to go to completion = nitric fully spent.
Next morning, the spent juice is poured off and leftovers inspected. Usually, some metal is left on the bottom of the vessel - juice is conveniently poured off and leftovers transfered to a beaker, where they are treated with fresh portion of HCL and nitric is dosed in small aliquots in order to fully dissolve everything metallic.
This time, to my surprise, quite a bit of unreacted metal was found to be on the bottom, so I used like 0,75L of HCL and dosed nitric to dissolve everything. It took few hours of mild heating, but eventually all of it was gone. It is important to decant this spent juice and do one more leach with fairly nitric-rich AR in order to dissolve also pieces of legs which are imbedded in glass bottoms of the resistors. Otherwise, gold will precipitate here and quite a bit of it will be lost.
All leach solutions were then combined, filtered through kitchen strainer to remove bigger undissolved pieces of silicone, plastic or some other junk, and halved into 2 5L beakers. I then heat them on the hotplate and insert copper (in my case springs from big breakers) to precipitate gold and also de-nox the solution. I found out, espetially with Ni-rich material, that denoxing with sulfamic acid is rather slow and very tedious. Sometimes, it took hours and overwhelming ammount of sulfamic acid just to find out that some gasses still escape from the solution. Again, my hypothesis is that NOx gasses are complexed with nickel cations and bind strongly - so sulfamic acid has hard time to react with them. So by ensuring I do not use unhealthy excess of nitric, I use copper as de-noxing agent - and when the solution heats up to around 80°C, copper start to react vividly, emmiting NOx gasses. It could be nicely paired with additions of sulfamic to stop re-adsorption and oxidation of NO by oxygen, disrupting the creation of in-situ nitric acid. It is clearly visible that gold is dropped on the copper (gold "bleeding" from the wire) but quickly redissolved in solution. But in certain point the solution will start to get more cloudy, and eventually all effervescence dies down and gold drop down. Quick stirring and heating for couple dozen minutes result in complete drop of gold, which is farily heavy, coagulated and easily decanted. By XRF measuring, it is usually more than 98,5% pure - if the material did not contained silver or palladium.
So I filtered the gold precipitate, stannous negative on the solution. This filtered gold mud was then redissolved in HCL with small additions of H2O2. I found this old technique very beneficial over classic AR route due to simple fact - there is no need of de-noxing to be done before dropping the gold. Just remove watchglass from the beaker for a minute or two and let the small residual chlorine to escape. So, if you have access to 30% H2O2, I recommend to try it out - if you didn´t already done this before. Anyway, volume was doubled by addition of water and ice and solution was filtered through Buchner funnel to obtain clear yellow-orange pay-liquid
Gold drop was accomplished with SO2 gas bubbled through the solution. In other posts, I disclosed why it is (according to me and my point of view) beneficial to use SO2 rather than SMB or other sulfites, and I sticked to this method for final purification of gold - because it gave very nice, easy settled, heavy gold precipitate with superior purity.
Result:
This yield on lower side of the spectrum will reflect the fact that most of the best yielding USSR transistors and ICs were just torn from the boards and missing those 30g/kg legs. I reflected that on purchase, and advised the seller to remove the components properly next time, so we will see how he will cope with this
That´s it for today.
Orvi
(edited yields after re-weighing and realizing I messed the numbers)
Transistors weighed and poured to the reaction vessel.
Onset of the reaction. Top piece of the canister is used like DIY "watchglass" to cut down the effervescence loss and heat loss during the reaction. Insides of the inverted top of the canister could be filled with water and act as pro-forma cooler, if needed. Pieces of PE tubing on the sides prevent whole thing falling inside the canister
Big plastic bowl used as catchpan if reaction does not want to cooperate and boil over Remains of glass bottoms and silicon dies of the transistors at final digestion stage with fresh AR solution. This should be held hot for some time in order to fully dissolve the remains of the legs inside the glass.
Dropping the gold and de-noxing with thick copper wire inserted into the solution. Unfortunately, it can´t be seen on the photo, but it actually sticks out of the solution in both beakers - enabling to easily pull it off after completion of the reaction.
Cu-dropped gold on the filter, ready to be purified by re-dissolution in HCL/peroxide and drop with SO2 gas.
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