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Carbon Elution (9 replies)
Yes, it is possible. I have seen some plants using only NaOH with good results, however it does not seems to have a "name" usually is a modified AARL or a ZADRA. Other elution process that is commonly used (mainly in Brazil) is the extraction by alcohol, this process born as a "re-extraction" process following the ZADRA system but the true is that in some cases it is used alone (with no cyanide) and also reporting good results.
Page 314, chapter 7.1.3.2 of 'Chemistry of Gold Extraction' by Marden and House states ' the presence of free cyanide throughout the desorption process is not a requirement for effective elution and several procedures have been developed that use a cyanide presoak step followed by deionized water elution'. Cyanide appears to benefit the elution process but perhaps is not absolutely necessary.
This has been done using the Zadra process. Barney's Canyon (RT-Kennecott) used this. The cycle time was longer.
It is the exact answer i was searching for. I think it wouldn't be incorrect if i call that type "cyanide-free elution" in my project.
Zadra(pressure atmospheric)
AARL
Alcohol
Micron
Cyanide-free
Have done carbon elution without cyanide on both, ZADRA and AARL. Zadra pressure strip (at 145C) does not show any difference with or without cyanide.
In atmospheric pressure (up to 120C) is somehow different. If you have good quality water then no problem, both, AARL and ZADRA will perform well without cyanide. The drawback is that you may not be able to recycle the spent solution for re-use in the elution.
With a Zadra strip, if you acid wash prior to strip it is necessary to have some free cyanide. Normally with Zadra the base solution is 1% caustic and 0.1% cyanide to start and adjustments, primarily to caustic, occur with different ore bodies. You can strip without but as above says it will lengthen the strip.
It is possible. But I have some questions:
Is there any difference with using or not cyanide on the gold elution efficiency?
If I decide have a gold strip without cyanide, could I reach the minimum gold elution efficiency? For example: Not lower than 95%
If I decide have a gold strip without cyanide, what about the gold content on the desorbed carbon?
For example: The gold content is lower or greater than 40 ppm
I think, that in AARL, and ZADRA process, caustic and cyanide both are necessary to get a high gold elution.
I have operated a plant were we never used cyanide as part of the stripping electrolyte in the zadra process and it was very efficient achieving above 96%stripping efficiency. It is my opinion that the operating temperatures render it not necessary. However I think the question we ought to be asking is why was its presence in the electrolyte considered in the first place, I personally believe it should be mineral specific especially the copper containing ores where the GAC is loaded with also di-cyano copper cyanide complex which maybe could be stripped by soaking the loaded GAC with cyanide containing electrolyte. I assume the role of the cyanide in this particular case would be to form the tri- and/or tetra -cyano copper complex which has a poor affinity for attaching to the GAC and ultimately desorbing from GAC.
Is it possible to do the carbon elution using a solution contains only caustic soda and no cyanide? If it is possible and known, is there any name of this process?