Pt? is there graphite?

clays?

Ca effects on partical surfaces?

Yes, there is about +/- 1.5% Pt in the final dore as well as +/- 1.5% Ni.

I do not know about graphite.  We are doing toll elution so I haven't seen the ore firsthand.  There are some clays, but the pores of the carbon do not appear to be blocked with clay or calcium.

The leaching agent is very similar to Goldix.  We had one good elution, but we are unable to replicate the results.  

Your problem is with the leach system, not your stripping circuit.

The Goldex and similar formulations will solubilise many metals, unlike cyanide which is predominantly a lixiviant for gold, silver and copper.

What you get adsorbed on the carbon is a large quantity of base and other metals which either are not soluble in caustic cyanide or are occluded from the strip solution.

The only way to remove the metals from the carbon is with a long term leach in 10 - 20% HCl, put the carbon into plastic drums, keep covered with the acid. Hotter and longer is better, this will take at least weeks if not months.

You will find that the sellers of the leach formulations will take no responsibility for the problems you are encountering.

If your clients want to persist with these leaches my advice is to refuse to attempt stripping their carbon and explain nicely why you cannot do so without a long term leach of the carbon, this is not a method you want to be doing on a continuous basis.

Based on the information you provided, the alternative reagent to cyanide is called GoldMax. My suggestion is to consider the AARL elution process (more temperature, more pressure). In this kind of elution, electrowinning is performed on the complete batch of eluate produced by a single pass through the elution column. Open-circuit AARL systems will generate seven to eight bed volumes of eluate,which will mix by recirculation to a relatively steady head grade. Split AARL systems will concentrate the gold at higher concentrations into a smaller volume of approximately five bed volumes.

Thanks for your replies Deano and Jorge.  Deano, any thoughts on the AARL?

We've achieved one highly satisfactory strip although it was not without difficulty...We first performed a non-alcohol zadra strip which produced a goopy mess in the EW cell as well as mercury build up on the cathodes (the ore is artisinal tailings) with such little gild recovery after 36 hours that we decided to shut the system down.

After that, we completey replaced the eluate and used a 15% alcohol solution.  We then stripped the carbon and achieved greater than 90% recovery and thought our problem was solved.

However, we have been unable to repeat this success while the head ore and leaching procedures remain the same.  

If it wasn't for that one successful elution we would have given up by now.  Every elution cycle since then points to the direction of Deano's comments in that we recover some gold plus a mess of other unknown as if the carbon pores are blocked.  That being said, the carbon in question is still effectively adsorbing gold from the leach circuit.

That one good strip cycle leaves us scratching our heads.

I have done a lot of strips of different types on these forms of leach carbons.

None of them were remotely what I could say was successful.

I ran the temperatures and NaOH and CN levels up to very excessive levels in all types just to see if there was any possibility of getting a reasonable strip but with no success.

I simply could not get any reasonable level of gold in the eluate.

In the end I approached the problem as a straight scientific puzzle and, having exhausted all of the possibilities of standard type strips and variations thereof, I looked at running exhaustive pretreatments.

I ended up with a long line of plastic 200 litre tubs with batches of half ton carbon splits from a bulk sample I wished I had never seen or started playing with.

I ran a series of chelates in some of the drums and various acids in others.

The best pretreatment by a long way was HCl as a long term pre - leachant.

When I tried ashing the carbon and aqua regia digesting to get gold grades from the test carbons I had an eerily close correlation between the gold grades and the efficacy of the strip from the various pretreatments.

It appeared that the gold had not only loaded onto the carbon but had also been reduced on the base metals which were also loaded onto the carbon. Further loading of these base metals occluded the gold almost completely.

Out of personal interest I contacted sellers of these leach formulations. It appeared that all of the formulations were variations on a theme where the variations were applied without rhyme or reason.

All of the sellers claimed that because all orebodies were different they took no responsibility for the results of the leaches, most definitely no responsibility in regard to the recovery of precious metals from any adsorbent used.

Their attitude was along the line of "I have sold you an environmentally benign leach and you will have to work out how to best use it for your ore".

If you looked carefully at the leach components and the recommended leach conditions the environmentally benign aspect was very dubious.

Best of luck, if you find anything I missed I would appreciate hearing about it.

The elution problem is part of a research work, for that reason I suggested  to evaluate the AARL process. If someone made some tests using similar conditions to the AARL elution process and the results were not positive, it is good to know it. 

The technical data associated to the leaching reagent makes only reference to the dissolution of gold, but it is not mentioned the effect of the reagent on the elution process, electrowinning and Merrill-Crowe. There is a pending research work on this matter. 

HCL acid washing will be critical to getting a faster strip and low barrens on your carbon, but you need to remove both kinetically fast and slow desorbing species. Pre treat any carbon with a 3% solution in plug flow for at least half an hour and.the. Soak to get rid of kinetically slow species, then rinse extensively.

Your problem is both with the adsorption circuit (lack of cyanide) and with the strip circuit. Unlike AARL, you don’t need a presoak with a zadra but some levels of residual cyanide are needed for an effective strip. And temperature and pressure is essential. You can run a zadra strip at temperatures above 130C with no residual cyanide at all if you came from a traditional cyanide adsorption circuit. Without it, you will need at least 0.2% and about 2% caustic.

I have performed successful non cyanide strips with Bromo Chloro processes but you need also to pressurise the cell for that to work.

Sean