oro-del-sur
Active member
I’m working on a small scale stripper for gold bearing carbon and would like to share as I go along. I also need more advice. We have a small scale mining operation in Costa Rica and are building our first lixiviation plant. I made a previous post showing my first stripper test in a Pyrex dish to see if I could elute and deposit gold onto steel wool using a 6v battery charger (which seemed to work). That thread is here: https://goldrefiningforum.com/phpBB3/viewtopic.php?f=44&t=27600&p=291363#p291363
Since then I have read a fair amount of info about Zadra and also pressurized carbon elution. I understand the theory and some basics but finding detailed information in the public domain, the actual nuts and bolts of how to set up and operate a small system is scarce. All the info I found discusses industrial scale - tonnage - sophisticated and expensive systems. Our ultimate need will be for 50-100 kg of carbon and a system I can put together myself that doesn’t cost many thousands of dollars. I will eventually hire someone with more experience to operate the system and perform carbon assays etc. but in the meantime I need to learn develop a system we can deploy.
One thing to note - given that carbon elution only considers stripping from traditional cyanide adsorption we are operating in experimental territory with a non traditional lixiviant - due to environmental restrictions our strips are from one of the cyanide derivative products called Eco-Goldex (Canada). We will leach milled head ores and also process a mountain of tailings from previous artisanal works (our own) which contain traces of mercury.
In this post I show a bit larger system I made which I will use for practice. The black steel tank and plastic EW cell shown here hold a total of 25 liters of solution - capacity for 2-3 kg of carbon. The carbon sits on a fixed screen divider in the black tank keeping it suspended inside the tank about half way up. The solution is heated in the bottom section of the tank with two 110v heating elements and maintains the temp at 70-80 C. The flow from the small mag pump is controlled with a valve, and another valve to drain the tank. The frames for the two anodes and single cathode are made of 1/4” round stainless, anodes are heavy gauge stainless mesh. The coffee filter is to catch any loose solids so they don’t pass into the EW cell.
What I’ve learned so far (non pressurize elution):
Solution makeup is 1% caustic soda and .1% - .2% cyanide
Up to 20% isopropyl alcohol addition can enhance elution but successful elution can also be achieved without alcohol.
De-mineralized water is best, calcium and magnesium from natural water sources can be problematic.
Soak / wash the carbon for a couple of hours in 3%-5% HCL is often necessary to dissolve the junk, making for a cleaner strip of the gold-cyanide complex.
A non pressurized elution strip can take up to 48 hours. Pressured systems can achieve it in less than 10 hours. Ideal flow rate is 2-3 bed volumes x hour.
Electro-winning onto a steel wool cathode is most practical, proper voltage is between 2-4 volts. Amperage is determined by actual resistance in the electro cell i.e. the solution itself and all the metal components. The 6v / 1 amp motorcycle battery charger was tested previously in 4 liters of solution with a carbon rod anode and achieved deposition of gold onto the cathode without burning up the steel wool - so I’ll use it in subsequent tests as long as the results allow it.
To harvest the gold, the steel wool is typically digested with sulfuric acid.
What I don’t know:
How to determine the amount of solution required per batch.
How much steel wool is needed per gram of gold anticipated.
Alcohol - In my previous post Deano responded and mentions that evaporation is an issue with the alcohol and elution will cease without the organic component (alcohol). But I read elsewhere that elution can be accomplished without any alcohol. So does Deano mean the elution will cease altogether or just slow down?
What is a practical method to determine the alcohol level?
What are all the important operating considerations when using alcohol (aside from the vapor hazard) ?
I just bought 5 gallons of “Mosstanol” from an industrial supply which is 60% ethanol and 40% isopropyl. I read that ethanol is more effective versus isopropyl. Is this true?
Can the carbon pre-wash be done with dilute nitric acid?
Can the steel wool be digested with nitric instead of sulfuric?
How do I determine what rectifier to get for the 50kg-100kg system ?
I understand the correct spacing is 1.5” more or less between the anodes and cathodes but I notice that “hairs” on the steel wool make contact with the ss mesh anode. To solve this I was thinking to wrap the steel wool cathode in a cloth mesh (mosquito netting). I assume this will not affect anything (?). Is there a better way?
Thanks in advance!
Since then I have read a fair amount of info about Zadra and also pressurized carbon elution. I understand the theory and some basics but finding detailed information in the public domain, the actual nuts and bolts of how to set up and operate a small system is scarce. All the info I found discusses industrial scale - tonnage - sophisticated and expensive systems. Our ultimate need will be for 50-100 kg of carbon and a system I can put together myself that doesn’t cost many thousands of dollars. I will eventually hire someone with more experience to operate the system and perform carbon assays etc. but in the meantime I need to learn develop a system we can deploy.
One thing to note - given that carbon elution only considers stripping from traditional cyanide adsorption we are operating in experimental territory with a non traditional lixiviant - due to environmental restrictions our strips are from one of the cyanide derivative products called Eco-Goldex (Canada). We will leach milled head ores and also process a mountain of tailings from previous artisanal works (our own) which contain traces of mercury.
In this post I show a bit larger system I made which I will use for practice. The black steel tank and plastic EW cell shown here hold a total of 25 liters of solution - capacity for 2-3 kg of carbon. The carbon sits on a fixed screen divider in the black tank keeping it suspended inside the tank about half way up. The solution is heated in the bottom section of the tank with two 110v heating elements and maintains the temp at 70-80 C. The flow from the small mag pump is controlled with a valve, and another valve to drain the tank. The frames for the two anodes and single cathode are made of 1/4” round stainless, anodes are heavy gauge stainless mesh. The coffee filter is to catch any loose solids so they don’t pass into the EW cell.
What I’ve learned so far (non pressurize elution):
Solution makeup is 1% caustic soda and .1% - .2% cyanide
Up to 20% isopropyl alcohol addition can enhance elution but successful elution can also be achieved without alcohol.
De-mineralized water is best, calcium and magnesium from natural water sources can be problematic.
Soak / wash the carbon for a couple of hours in 3%-5% HCL is often necessary to dissolve the junk, making for a cleaner strip of the gold-cyanide complex.
A non pressurized elution strip can take up to 48 hours. Pressured systems can achieve it in less than 10 hours. Ideal flow rate is 2-3 bed volumes x hour.
Electro-winning onto a steel wool cathode is most practical, proper voltage is between 2-4 volts. Amperage is determined by actual resistance in the electro cell i.e. the solution itself and all the metal components. The 6v / 1 amp motorcycle battery charger was tested previously in 4 liters of solution with a carbon rod anode and achieved deposition of gold onto the cathode without burning up the steel wool - so I’ll use it in subsequent tests as long as the results allow it.
To harvest the gold, the steel wool is typically digested with sulfuric acid.
What I don’t know:
How to determine the amount of solution required per batch.
How much steel wool is needed per gram of gold anticipated.
Alcohol - In my previous post Deano responded and mentions that evaporation is an issue with the alcohol and elution will cease without the organic component (alcohol). But I read elsewhere that elution can be accomplished without any alcohol. So does Deano mean the elution will cease altogether or just slow down?
What is a practical method to determine the alcohol level?
What are all the important operating considerations when using alcohol (aside from the vapor hazard) ?
I just bought 5 gallons of “Mosstanol” from an industrial supply which is 60% ethanol and 40% isopropyl. I read that ethanol is more effective versus isopropyl. Is this true?
Can the carbon pre-wash be done with dilute nitric acid?
Can the steel wool be digested with nitric instead of sulfuric?
How do I determine what rectifier to get for the 50kg-100kg system ?
I understand the correct spacing is 1.5” more or less between the anodes and cathodes but I notice that “hairs” on the steel wool make contact with the ss mesh anode. To solve this I was thinking to wrap the steel wool cathode in a cloth mesh (mosquito netting). I assume this will not affect anything (?). Is there a better way?
Thanks in advance!