RE:RE:Gold trial 6th wave has recently partnered with Rio 2 to test their gold recovery technology. I wanted to better understand the conventional heap leach process, and the potential benefits that 6th. Wave’s technology may provide to the mining industry. Here are my findings.
Heap leaching originated in Spain in 1752 on the banks of the Rio Tinto River.
With respect to gold collection, the chemical properties of Cyanide serve to dissolve gold that is contained in ore stockpiles. This chemical reaction with Gold is governed by Eisner’s Equation.
Gold (duh), Cyanide, Oxygen and Water are required for the reaction.
A leach pond is specially constructed to prevent the cyanide solution from seeping into the soil resulting in cyanide environmental contamination and gold loss.
Ore is placed on the leach pad/pond and sprinkled with cyanide solution.
Lime or caustic soda is added to keep the pH of the solution high in the range of 9-11 so as to prevent the cyanide from decomposing by interaction with carbon dioxide.
The solution percolates through the ore, dissolving gold. The leach pad may simply "gravity feed" pregnant cyanide solution to a collection tank.
Once complete, waste can be removed from the pad and the process can repeat.
This is a sensitive chemical reaction that can be greatly affected by a wide variety of factors, including the presence of whatever specific chemicals may be found in the ore body along with the gold.
Heap leaching is therefore only successful in certain scenarios. The gold particles must be exposed to the cyanide solution for good recovery rates. Often, a crusher is required for this exposure.
The successful leach test conducted by rio2 is an extremely important factor to take into consideration in the evaluation of the project. Not only does the test demonstrate that a rock crusher is not needed, but it also lays to rest many other factors which could have had a negative impact on the recovery rates. These factors include the presence of impurities in the ore body, size of gold particles, etc. The leach test can also give indications as to how much alkali material (lime or caustic soda) or cyanide is required in the process. Rio2 also came in under their estimates with respect to consumption of these costly materials; Lime 2.95 kg/t vs 4 kg/t PFS and Cyanide .18 kg/t vs .4 kg/t PFS.
Given the size of the 5M ounce deposit, positive leach test results can result in significant benefits over the life of the project. Higher recovery rates, and a requirement for less alkali and cyanide materials and absence of a rock crusher all benefit future earnings reports.
Heading back to our cyanide solution, the solution, once it absorbs the gold, is processed by activated carbon. Conventionally, this was performed by trickling the pregnant cyanide solution through columns of activated carbon. This process of passing the solution through the carbon can be repeated until the gold extraction rate drops off.
1 ton of carbon may hold upwards of 800 ounces of gold. For a typical lower grade heap leach project, 200 ounces is typical. The carbon absorption process can also be important for recovery rates as carbon can also absorb unwanted particles such as calcium, copper, nickel, mercury and iron which may be present in the cyanide solution and reduce recovery.
Recovery of gold from the carbon can occur by simply smelting the carbon/gold residue. But, the carbon can be reused if the gold is desorbed from the carbon. One example is called the Zadra desorption process.
Now, understand that I am no geologist or mine operator and most of the above discussion is from a 43 year old technical document. Many improvements in the heap leach process have likely occurred. The point is to give you a basic understanding of heap leaching.
Now that we have (hopefully, I tried my best) a basic understanding of heap leaching and the role of carbon in gold recovery, we will take a look at 6th Wave Innovations' use of nanoparticles to replace carbon in heap leach gold absorption.
6th. Wave attempts to use molecularly imprinted polymer beads (MIP) to function the same way as carbon in the absorption process. These are small particles in the nanometer range.
The question you may have at this point is, “why use this complex MIP when carbon works perfectly fine”. After all, carbon is the basic building block of life on planet earth and one of the most prevalent compounds.
Firstly, the amount of gold a specific amount of an MIP can absorb is around six times greater than that of carbon. This is due to the MIP being highly selective to the target molecule. In percentage terms, while carbon has a selectivity to gold of around 22%, an MIP is 95%. Carbon also readily absorbs not just gold, but many nasty chemicals that could be present in the ore body, including, of great importance, mercury tetracyanide. Time is also a benefit of using an MIP. It can take nearly 50 hours for carbon to complete the absorption of gold. An MIP can perform this task in around 2 hours and at far lower temperatures (20C vs 95C). The use of MIP can thus result in more efficient absorption, less foreign particles, faster absorption, etc.
These MIP’s can also be used upwards of 30 times.
But what about a cost benefit analysis? MIP’s can be comparable in cost to conventional carbon. Their benefits may result in improved gold production and lower processing cost which can benefit those quarterly gold production results. Extraction can increase by 3-5% and cost can be reduced by as much as 60%.
Those actually familiar with the day-to-day operations of a gold mine can hopefully obtain a far better grasp of the cost benefits of MIPs given the above listed data.
MIPs are particles that are adapted to absorb specific materials called “target molecules”. For our discussion, our target molecule is the gold from the heap leach process.
These target molecules function as a template to define a specific shape or size in a polymerized matrix. Essentially, the MIP is a lock that fits the key of the target molecule (gold), increasing absorption rates.
Conventionally, the MIP is modified by the very presence of the material it is being trained to target. When dealing with gold, this presents a drawback. Gold itself must be used as the target molecule which can significantly raise cost with respect to the supply of the target molecule and its handling. Large amounts of gold are required to train a volume of MIP at the scales required for a heap leach project.
6th. Wave sought to develop a MIP that did not require use of the actual target molecule during the development process. Essentially, they sought to advance the use of MIP’s in gold recovery from a glorified laboratory experiment to profitable use in mining.
Instead of using gold itself as the target material, 6th wave uses a surrogate. While the use of a surrogate is not as accurate as using gold itself, they still offer the benefits over conventional carbon. Pregnant cyanide solution and surrogates, MIPs, oh my, the technical jargon!
6th. Wave has identified specific surrogate chemical compositions which closely resemble the molecular structure of gold and which are low cost and can be supplied in larger volumes to generate enough MIP material to process a pregnant cyanide solution from a heap leach pad. Phew!
The marriage of gold and technology is quite wonderful. No, I don’t mean bitcoin! MIP’s and mining and heap leaching! Time will tell as to whether this technology has a future in the mining industry. You can bet that if things do “pan out”, the mining industry will take note and Rio’s reputation as an innovator in the mining space will be cemented. Remember, this is the company focusing on one project, getting it up and running quickly and efficiently; even constructing off-site while permitting is pending.
So it was not surprising to learn that Rio2 had reached out to 6th. Wave showing interest in this technology. From Rio2's perspective, there is practically 0 risk for them to agree to a test. Meanwhile, what better place for 6th. Wave to put their technology to the test than a massive, simple heap leach project like Rio2?
This testing will allow Rio2 to directly compare cost and recoveries of conventional carbon to MIPs for consideration of deployment when production at the mine is expanded beyond the initial startup.
Personally, it is exciting to see this level of innovation in a tech that evolved out of the Rio Tinto River in 1752 put to test by another Rio; Rio 2. Given the success and wealth of knowledge displayed by this team in developing Rio 1.0 into a billion dollar project, and thus far their initial success with Rio 2, I am optimistic and happy to come along on the journey as a shareholder. And seeing what 6th Wave is doing with their MIP technology, I am excited to see the results.
Best of luck to both companies.
Thanks for reading!
-Gold River
Disclaimer: I have a background in Patent Law and experience in a variety of technical disciplines including ME, EE, Chemistry and Microfabrication. None of the above should be considered investment or legal advice and while I shall rename nameless and anonymous, none of the above comments should reflect on any possible employer of mine or organization or corporation that I may be affiliated with.
Sources: Processing Gold Ores Using Heap Leach-Carbon Adsorption Methods, Bureau of Mines 1978 and 6th Wave U.S. Patent Publication 20180214845 A1 (Gluckman et al.), U.S, Patent number 10,814,306 assigned to 6th Wave Innovations Corp.