Taking a great idea and applying modern techniques

Gold Refining Forum

Help Support Gold Refining Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

anachronism

Well-known member
Joined
May 31, 2016
Messages
3,095
For a few months now people have been asking me how I've applied Dean's electrowin cell to refining. Following calls and emails with senior members and moderators, I thought it would be good to throw out there some of the work that's being done.

Whilst the concept and chemistry that Dean so kindly shared with the members is a given, only the practical presentation and structural design can really be improved utilising current technology. The end goal being a cell that anyone can use. Repeatedly, and with a minimum of consumables. I would strongly recommend that anybody who has not read Dean's missives does so post haste. Why? Because the information held in these is revolutionary in terms of bringing processes both up to the modern age, and allowing a home refiner to process product that he/she would have originally thought beyond their reach.

For those who have yet to read the thread written by Deano, you can find it here http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=21526

The design, prototyping, materials technology, equipment, and engineering to do this is costly both financially and in sheer time however I hope members will agree that it's a worthwhile exercise.

The pics below detail some of the basic interior cathode carriers. Moving the cathode closer to the anode reduces the [stt]current[/stt] voltage (see posts below) required to operate the cell efficiently thereby allowing more than one cell to operate on one power supply. Allowance has to be made for the cathode increasing in thickness whilst making changing it quickly and efficiently a priority.

The print shown in process is using a rough detail and ABS. The actual material used will be different. I'd welcome any comments or questions that anyone may have.

Jon
 

Attachments

  • Centre prod.png
    Centre prod.png
    937.3 KB · Views: 1,078
  • Centre ext.png
    Centre ext.png
    443.2 KB · Views: 1,078
  • Centre.png
    Centre.png
    315.2 KB · Views: 1,078
Moving the cathode closer to the anode reduces the current required to operate the cell efficiently thereby allowing more than one cell to operate on one power supply.
I must admit that I have not read Deano's threads. I will, since your post has interested me in them. In the meantime, let me comment on your above statement.

Moving the electrodes closer together will lower the resistance between them and will thus require less voltage for the same amount of current. The amount of metal deposited is directly proportional to the current applied to the cathode. In your statement, if you reduced the current, you would plate less metal. I can't see how you would gain by reducing the current.

Hypothetically, let's say you have a cell with a 12" spacing between the electrodes. Let's say you are plating 100A @ 6V, using a 100A, 9V rectifier. You decide to move the electrodes closer, to 3" apart. At the same 100A, you are now only using 3V, let's say. Therefore, using the same rectifier, you are now able to add 2 more identical cells, in series. Each cell will run 100A at 3V. The rectifier will read 100A and 9V. This will triple your production using the same power supply. In a series circuit, the amperage is constant and the voltage is additive.
 
Chris you're correct but there is one factor that needs to be considered.

You're using carbon felt as a cathode with a surface area exponentially greater than any other cathode.
 
That's ingenious to 3d-print the electrode apartment. I really like it! :)

Chris is correct in that the distance between electrodes affects the voltage in the cell, not the current efficiency. That is a fundamental concept of electrolytic cells.
The cell voltage depends on a number of factors, the chemical reaction at the electrodes (practically a fixed voltage depending on the chemistry), electrode polarization (heavily depending on electrode area, concentration of chemicals, current density, temperature and convection) and electrolyte resistance (depending on electrode distance and concentration of ions in the electrolyte).

Current efficiency is defined as the amount of metal produced compared to the theoretical maximum and can as most be 100 percent. Losses comes from side reactions, for example splitting water into oxygen and hydrogen but also from other reactions driven by the current at the electrodes.
https://en.wikipedia.org/wiki/Faraday_efficiency

Power efficiency on the other hand is increased with lower electrode distance as the voltage drops and the cell uses less wattage of power.

Where do you find the carbon felt that you are using for the electrode?

Thanks for sharing! Looking forward to the rest of this thread.

Göran
 
Jon I know you have been working hard on using Deano,s teachings and it's good to see the proof of concept and the effort of all your hard work and study, I have seen other versions of the same concept that were very very expensive but worked really well on stripping all metals from acidic and base solutions.
With the environmental controls now in place all over the modern world many industries need to strip waste solutions before discharge meets the rules, from the tests I saw the discharged waste was cleaner than the water ways it was going into including harmful metals, as for refining if members can grasp the science behimd this and adapt it to their needs and processes it really can be a game changer from recovering values to stripping waste solutions making disposal very easy and legal.
As you have suggested and I have already posted about read and understand Deano,s posts they contain some real gems of knowledge which can be applied to most members processing.
 
Chris/Goran

Yes I got my terminology completely incorrect regarding the current. Closing the distance between the anode and cathode lowers the voltage required to draw enough current to deposit the metal. Effectively lowering the wattage and running cost of the cell.

Something to bear in mind on this cell is that an over current is required to keep the deposition rate above the loss rate otherwise you can end up in a situation whereby have an equilibrium where metal is being lost to the liquor as fast as it is being deposited. The current required to deposit depends upon the tenor of the liquor. Now the challenge in building this for a home user is as follows:

The ideal situation is to run the cell in conjunction with an AA. The liquor would be sampled at point of entry and point of return (after passing through the cathode) to ensure that the current is high enough, and removing gold from your solution. This isn't ideal for a home user since the cost of an AA is likely to be prohibitive. As such the cell needs to be robust enough to run at a relatively high over current to ensure your metals are being deposited without the need to check the tenor of the solution using an AA.

Then again, running it far too high would shred your anode quicker than normal, so again you need to weigh up the cost/benefit of either using high grade carbon or low grade carbon for the anode or even using a platinised Titanium anode.

These are considerations that have required investigating and the respective options are undergoing test. It's all about trade offs because for each benefit there is a cost somewhere else in the system. Determining the healthy balance is the challenge.

Jon
 
Concept print of the internals. Printed in low detail high speed in cheap material to produce a physical model of the unit whilst allowing improvement and development.

Even whilst this was printing a further 8 design alterations were being made. There's a lot to do to ensure correct fluid flow and ease of use. The cell is scale-able- this is a miniature one.
 

Attachments

  • Concept print.jpg
    Concept print.jpg
    309.1 KB · Views: 965
The circle around the base is where a plastic pipe is attached to form the liquid holding reservoir? The carbon felt you use comes in square sheets, is the slot on the outer circle where the ends of the sheet start and end up to assure all liquid has to pass through the felt fabric? Very nice design so far.

I think a re-posting of the image you had posted in a previous thread of your original system before you started with the 3 D printed version would be helpful to show where this is all leading, albeit in a more efficient improved version.
 
The ideal situation is to run the cell in conjunction with an AA.

What are the ranges of gold concentration you expect to see before passing through the cell in grams per liter? The reason I ask is there is an analytical method using concentrated sulfuric acid added to the solution, which is carried out in a properly exhausted lab hood, that has been used for years to analyze gold cyanide plating solutions gravimetrically. If the concentrations are sufficient for detection, it is possible an AA is not necessary for a small shop. This could go a long way into opening up this methodology to smaller refining operations.
 
4metals said:
The circle around the base is where a plastic pipe is attached to form the liquid holding reservoir? The carbon felt you use comes in square sheets, is the slot on the outer circle where the ends of the sheet start and end up to assure all liquid has to pass through the felt fabric? Very nice design so far.

Yes and yes. That's completely correct.

I think a re-posting of the image you had posted in a previous thread of your original system before you started with the 3 D printed version would be helpful to show where this is all leading, albeit in a more efficient improved version.

Thanks 4 metals, certainly please see below. This was made using standard readily available items for the hardware, and fabricated with plastic welding. The proof of concept worked well.
 

Attachments

  • Orig cell 1.JPG
    Orig cell 1.JPG
    76.6 KB · Views: 926
4metals said:
The ideal situation is to run the cell in conjunction with an AA.

What are the ranges of gold concentration you expect to see before passing through the cell in grams per liter? The reason I ask is there is an analytical method using concentrated sulfuric acid added to the solution, which is carried out in a properly exhausted lab hood, that has been used for years to analyze gold cyanide plating solutions gravimetrically. If the concentrations are sufficient for detection, it is possible an AA is not necessary for a small shop. This could go a long way into opening up this methodology to smaller refining operations.

You're running the cell with the express aim of operating a recirculating leach. i.e. The leach liquor is drawn out of the leach tank and fed into the cell where it is stripped of metals before being passed back into the leach tank.

Given that a leach such as any derivative of CN- loads best at low tenors the concept is that this cell keeps the tenors low constantly, thereby allowing the user to strip at maximum capacity using the minimum of CN-. In non technobabble, the less metal in your leach solution, the faster it strips gold and that's where you want to keep it. As such you do not want grammes per litre concentrations of gold flowing around the circuit.

You therefore need to know that the liquor coming back into the leach has less gold in it than the liquor going into the cell. Can I ask if that method you mentioned would enable that information to be obtained?

Edits for context and spelling.
 
With very low loaded solutions I do not think the method 4metals alluded to would work as the amount of gold would be almost negligible if the system is working correctly, I stand to be corrected by the experts in this view because if it is indeed possible, as 4metals said, it could be a game changer for many.
 
That opens up a great discussion point Nick. Do you think our resident professionals could help us with a non AA method of determining a quantifiable difference in gold loading between solutions?

Yes you could probably do it with Stannous Chloride by seeing how dark the solution goes but is there another way? As you say it would open a lot of doors.
 
Thanks for posting the photo, it makes it easier to envision the entire process. Is the peristaltic on the left of the photo bringing in loaded solution? And the overflow above it where untreated solution returns to the reservoir? This would assure the outer layer of solution is always full and the flow through flow rate (ie. how many liters per hour you process) is determined by the flow rate of the peristaltic pump on the right.

I have to look up the analytical method for gold cyanide solutions but it clearly will drop all of the gold so it can be collected and weighed. Trouble is if you were to be running around 1 gram/liter, the standard sample size would require you to be weighing about 25 milligrams which may be too little to do accurately. It is possible to increase the sample size to increase the metal you weigh at the end but before we go that route, do you think you ever approach 1 g/l?

When I get back to my book collection I will look up and post the method.
 
The photo with the pump on the left. This was actually altered so that the inflow pump was fitted to the top pipe, making the lower left hand pipe the overflow back to the tank. Otherwise you could have been in a situation where you had a head of excess fluid in the even of needing to change the pump.

Yes as you stated the theory is that you always have a constant full level in the cell which is replenishing, so even if your cell fails/or the outlet pump fails you cannot overflow.
 
Gold strike solutions run 0.5 to 1.5 g/l and they are analyzed successfully with this method.

Note of caution; This method requires acidification of cyanide solutions with concentrated sulfuric acid. It must be done in a good fume hood. This is not the type of warning you want to blow off.

Sample size 20 ml

Add 25 ml of concentrated H2SO4 to the sample and heat to the evolution of white fumes.
Cool the solution and add 10 ml of 30 percent H2O2 and heat to evolution of white fumes.
Continue the additions of H2O2 and heating until the gold coagulates and the solution clears.
Add 100 ml of H2O and heat to 140º F for 5 minutes
Filter through a tared Gooch filter and dry in a 110º C oven. Cool in a dessicator and weigh the gold.
 
4metals said:
So with the inflow into the center section and the overflow high enough to maintain a fill level, you only need 1 peristaltic pump?

On the input side yes. One on the output side is required to draw the stripped liquor out and return to the leach tank. As an improvement the new cell is optionally able to be gravity fed from a header tank using a valve to control the flow. Less components to buy and fit, and given the built in self levelling system that pump therefore becomes redundant.

This is an important modification because larger systems will require multiple cells operating in parallel.
 
I have always found that having 2 pumps paired up to fill and drain a system in tandem eventually results in either a dry tank or a flood because it is impossible to get them flowing exactly at the flow you want. I would be flowing out with gravity to a sump below so only one pump controlled the cell levels and flow rate. I learned these lessons the hard way, fortunately with aquariums (not fortunately if you happened to be a fish!) rather than with chemicals holding values. But the same basic laws of plumbing still apply.

I also understand the value of a header tank but question why the cell cannot be sized to recover the volume of leachate in a timely manner, say overnight, and come morning you will have recovered the entire batch. If you are doing an entire field of mining ore I can see needing extra cells, but for e-scrap where you have to pay each customer it is nice to know you have all of the value from one batch in a single cell.

You say the goal is to strip the values in a single pass but do you send the stripped solution back to strip more values or is there a replenishment step to adjust the CN-concentration?
 
You can't have the outflow using gravity, because the outflow is what is actually controlling the speed of the liquor through the cathode. You use the inflow to create a reservoir of pregnant liquor outside the cathode layer and the outflow draws the liquor through it. It's this flow that is varied depending on the leach liquor and whether the required stripping is being achieved.

You have two self regulating reservoirs- the one that is the header tank and the one around the cathode. A simple switch that works on current detection will turn the cell off if it runs dry.

The header tank has two purposes- the one you have mentioned, but also to feed liquor from its overflow back into the leach tank and plunge it into the solution thereby aerating it. There's no oxidant required in the set up, as this constant flow provides all the oxygen required.

To answer your question as to why the cell cannot be resized to utilise a faster flow and thereby larger volumes. The simple answer is that it can. :D

You are not necessarily looking to single pass strip everything, you are looking to strip enough of the metals to keep the tenor low enough to stay operating at peak leach rates. This liquor is passed back into the leach tank to replenish the load. You can monitor the effectiveness of the leach and top up your preferred reagent as required. Once your batch is stripped completely then flow rates will be adjusted to single pass strip everything, and a valve can divert the completely stripped solution to another holding tank for either storage or destruction by passing through the cell with reversed polarity.
 
Back
Top