haveagojoe
Well-known member
- Joined
- Aug 1, 2014
- Messages
- 83
As Copper Chloride users will know, one of the drawbacks we encounter when releasing gold foils from escrap is that the solution becomes saturated with copper and eventually the etching process will slow down, and white crystals of Copper (I) Chloride will begin to accumulate in at the bottom of the reaction vessel.
Using an air bubbler to replenish the oxygen level in the solution will help to keep the Copper in solution as Copper (II) Chloride, which is what gives it the characteristic green colour. However after prolonged use the solution will turn very dark as it becomes competely saturated and the white crystals will form anyway.
The common approaches to dealing with saturation are either to decant the solution and allow Copper (I) Chloride crystals to form, after which they can be removed by further decanting or by filtering; or alternatively the solution can be elongated by adding more Hydrochloric acid to dissolve the crystals back into solution. Neither of these approaches are entirely satisfactory, since the former produces solution which is still close to saturation, and the latter produces a larger volume of solution, which in time accumulates as an ever-growing volume which consumes more and more Hydrochloric acid at not-insignificant expense.
A further issue is encountered when dealing with iron-bearing escrap, since when Iron is dissolved into the the solution it forms Ferrous Chloride. While Ferrous Chloride is not a major problem in the first instance since it also dissolves copper, it does so at a slower pace, the solution cannot be maintained by bubbling oxygen through it and the Iron does not drop out as chloride crystals as Copper does. Commonly this is addressed by using a magnet to sort Iron-bearing scrap from non-Iron bearing, and using a different method where Iron is present. However other metals may also be present in the scrap material, such as Nickel, Tin, Cobalt, Lead, etc which cannot be sorted with a magnet. Some - such a myself - opt to skip the extra step of sorting with a magnet, instead simply accepting that the solution will become fouled by this type of scrap. Doing so is uneconomical and results in an accumulation of "spent" acids which require treatment before they can be discarded.
Having accumulated a number of bottles of spent solution, and unwilling to discard them, I was interested to read a suggestion from Shark that metals could be removed from the spent solution using electrolysis:
https://goldrefiningforum.com/threa...p-processing-circuit-boards.34718/post-374650
Intrigued, I did some research and discovered that not only copper but also other contaminant metal salts can be removed from solution by forming an electrolytic cell to plate them out as solid metal, leaving behind relatively clean Hydrochloric acid suitable for reuse. This raised the possibility that the Ferric Chloride issue could be effectively addressed.
The reaction which takes place when current is applied reduces the aqueous metal salts (such as Copper Chloride) to metal on the cathode (negative electrode), and releases Chlorine gas at the anode (positive electrode) by oxidation.
Since Chlorine gas is noxious, I decided to perform my first experiment at a very small scale: 150ml of saturated Copper Chloride solution in a beaker, using two graphite pencil leads as electrodes with a spacing of around 15mm. The voltage required is low, since the reduction potential of copper is just 0.34V+, though for practical purposes in a real-life scenario between 2V and 3V is optimal. I used my bench power supply set at 2.5V, and as the reaction started the current draw was around 100mA.
Even at such a small scale, the production of Chlorine gas was noticable, rising as a continuous stream of fine bubbles from the pencil lead anode and giving off a distinctive pungent smell. However, after just a few minutes Copper metal deposits became visible on the cathode, and after 4 hours the solution was noticably clearer and the pencil lead was encrusted with a thick, uneven layer of copper with a remarkable appearance:
The deposited copper weighed just over 0.5g.
When I briefly increased the voltage to 5V, the cathode instantly turned black as other contaminant metals such as Iron and Tin were co-deposited along with the copper. They have higher reduction potentials, so at the lower voltage only copper would be deposited until the solution became almost copper-free, after which the other metals will be deposited in ascending order of reduction potential.
Deeming the initial experiment a success, I decided to set up a slightly larger one, using a piece of flattened copper pipe as the cathode and a graphite artist's drawing stick about 8mm in diameter as the anode. I had read that Stainless Steel could be used for the anode but since it may cause Chromium to be introduced into solution I decided against it, since Chromium is toxic.
Again using my bench power supply, I ran 3V through 4 litres of saturated Copper Chloride solution with an electrode spacing of around 20mm, which drew a current of around 1A. I was surprised that very little Chlorine was produced and the deposition of Copper on the cathode was much slower. I put this down to the composition of the graphite stick I used for the anode, since it would contain clay for hardness and strength, which would reduce its current-carrying capability.
After 12 hours the solution appeared slightly clearer and had stratified somewhat, with the clearer part near the surface close to the electrodes while the lower half remained quite dark. The deposits on the cathode were much more uneven, forming "dendrites"- curious-looking growths of metal which stretch out towards the anode. This can be a result of higher current density so I learned that at 3V, 20mm spacing was a litle too close. If I had left the cell to run much longer the dendrites would have made contact with the anode, forming a short-circuit, so I ended the experiment, with partial success.
For my third experiment I decided on a smaller volume of 2 litres of solution, and rather than subjecting my bench power supply to further inhospitable conditions in my semi-outdoor workspace I made a dedicated power supply, using a 2500mA 5V wall adapter and an adjustable voltage step-down buck convertor which I set to 2.5V. Buck convertors are available very cheaply and essentially perform the function of a bench power supply, although they lack current-limiting. Again using the graphite drawing stick as the anode and a fresh piece of flattened copper pipe cathode, but this time at a wider spacing of around 60mm to avoid dendrites from short-circuiting the cell, I measured the current draw at around 150mA. Again the reaction was slow and very little Chlorine was produced, so I felt confident to leave the setup unattended. I checked after an hour to find a modest layer of Copper deposition on the cathode, which this time was more even in composition, possibly due to the lower current density due to the increased electrode spacing. With the slow production of Chlorine gas and reduced risk of dendrite short-circuiting, I am satisfied that this slow-paced reaction will be relatively safe to leave for an extended period to gradually clean the solution of contaminant metals, so I intend to leave it to run for the next few days, checking it regularly, and will add further reports of the results to this thread.
While I am tempted to purchase a larger graphite anode for a future setup to achieve faster deposition of metals, at this stage I am inclined to think that the difficulty in dealing with the increased rate of Chlorine gas production may outweigh the benefits of faster cleanup of the solution. Since the "AP" process itself is slow-paced, I think a slow cleanup of the solution might be an appropriate match in terms of demand for supervision.
Comments and suggestions are welcomed.
Using an air bubbler to replenish the oxygen level in the solution will help to keep the Copper in solution as Copper (II) Chloride, which is what gives it the characteristic green colour. However after prolonged use the solution will turn very dark as it becomes competely saturated and the white crystals will form anyway.
The common approaches to dealing with saturation are either to decant the solution and allow Copper (I) Chloride crystals to form, after which they can be removed by further decanting or by filtering; or alternatively the solution can be elongated by adding more Hydrochloric acid to dissolve the crystals back into solution. Neither of these approaches are entirely satisfactory, since the former produces solution which is still close to saturation, and the latter produces a larger volume of solution, which in time accumulates as an ever-growing volume which consumes more and more Hydrochloric acid at not-insignificant expense.
A further issue is encountered when dealing with iron-bearing escrap, since when Iron is dissolved into the the solution it forms Ferrous Chloride. While Ferrous Chloride is not a major problem in the first instance since it also dissolves copper, it does so at a slower pace, the solution cannot be maintained by bubbling oxygen through it and the Iron does not drop out as chloride crystals as Copper does. Commonly this is addressed by using a magnet to sort Iron-bearing scrap from non-Iron bearing, and using a different method where Iron is present. However other metals may also be present in the scrap material, such as Nickel, Tin, Cobalt, Lead, etc which cannot be sorted with a magnet. Some - such a myself - opt to skip the extra step of sorting with a magnet, instead simply accepting that the solution will become fouled by this type of scrap. Doing so is uneconomical and results in an accumulation of "spent" acids which require treatment before they can be discarded.
Having accumulated a number of bottles of spent solution, and unwilling to discard them, I was interested to read a suggestion from Shark that metals could be removed from the spent solution using electrolysis:
https://goldrefiningforum.com/threa...p-processing-circuit-boards.34718/post-374650
Intrigued, I did some research and discovered that not only copper but also other contaminant metal salts can be removed from solution by forming an electrolytic cell to plate them out as solid metal, leaving behind relatively clean Hydrochloric acid suitable for reuse. This raised the possibility that the Ferric Chloride issue could be effectively addressed.
The reaction which takes place when current is applied reduces the aqueous metal salts (such as Copper Chloride) to metal on the cathode (negative electrode), and releases Chlorine gas at the anode (positive electrode) by oxidation.
Since Chlorine gas is noxious, I decided to perform my first experiment at a very small scale: 150ml of saturated Copper Chloride solution in a beaker, using two graphite pencil leads as electrodes with a spacing of around 15mm. The voltage required is low, since the reduction potential of copper is just 0.34V+, though for practical purposes in a real-life scenario between 2V and 3V is optimal. I used my bench power supply set at 2.5V, and as the reaction started the current draw was around 100mA.
Even at such a small scale, the production of Chlorine gas was noticable, rising as a continuous stream of fine bubbles from the pencil lead anode and giving off a distinctive pungent smell. However, after just a few minutes Copper metal deposits became visible on the cathode, and after 4 hours the solution was noticably clearer and the pencil lead was encrusted with a thick, uneven layer of copper with a remarkable appearance:
The deposited copper weighed just over 0.5g.
When I briefly increased the voltage to 5V, the cathode instantly turned black as other contaminant metals such as Iron and Tin were co-deposited along with the copper. They have higher reduction potentials, so at the lower voltage only copper would be deposited until the solution became almost copper-free, after which the other metals will be deposited in ascending order of reduction potential.
Deeming the initial experiment a success, I decided to set up a slightly larger one, using a piece of flattened copper pipe as the cathode and a graphite artist's drawing stick about 8mm in diameter as the anode. I had read that Stainless Steel could be used for the anode but since it may cause Chromium to be introduced into solution I decided against it, since Chromium is toxic.
Again using my bench power supply, I ran 3V through 4 litres of saturated Copper Chloride solution with an electrode spacing of around 20mm, which drew a current of around 1A. I was surprised that very little Chlorine was produced and the deposition of Copper on the cathode was much slower. I put this down to the composition of the graphite stick I used for the anode, since it would contain clay for hardness and strength, which would reduce its current-carrying capability.
After 12 hours the solution appeared slightly clearer and had stratified somewhat, with the clearer part near the surface close to the electrodes while the lower half remained quite dark. The deposits on the cathode were much more uneven, forming "dendrites"- curious-looking growths of metal which stretch out towards the anode. This can be a result of higher current density so I learned that at 3V, 20mm spacing was a litle too close. If I had left the cell to run much longer the dendrites would have made contact with the anode, forming a short-circuit, so I ended the experiment, with partial success.
For my third experiment I decided on a smaller volume of 2 litres of solution, and rather than subjecting my bench power supply to further inhospitable conditions in my semi-outdoor workspace I made a dedicated power supply, using a 2500mA 5V wall adapter and an adjustable voltage step-down buck convertor which I set to 2.5V. Buck convertors are available very cheaply and essentially perform the function of a bench power supply, although they lack current-limiting. Again using the graphite drawing stick as the anode and a fresh piece of flattened copper pipe cathode, but this time at a wider spacing of around 60mm to avoid dendrites from short-circuiting the cell, I measured the current draw at around 150mA. Again the reaction was slow and very little Chlorine was produced, so I felt confident to leave the setup unattended. I checked after an hour to find a modest layer of Copper deposition on the cathode, which this time was more even in composition, possibly due to the lower current density due to the increased electrode spacing. With the slow production of Chlorine gas and reduced risk of dendrite short-circuiting, I am satisfied that this slow-paced reaction will be relatively safe to leave for an extended period to gradually clean the solution of contaminant metals, so I intend to leave it to run for the next few days, checking it regularly, and will add further reports of the results to this thread.
While I am tempted to purchase a larger graphite anode for a future setup to achieve faster deposition of metals, at this stage I am inclined to think that the difficulty in dealing with the increased rate of Chlorine gas production may outweigh the benefits of faster cleanup of the solution. Since the "AP" process itself is slow-paced, I think a slow cleanup of the solution might be an appropriate match in terms of demand for supervision.
Comments and suggestions are welcomed.
