# Info on HCl/Cl leach recovery



## chemgal68 (Sep 29, 2012)

We are leaching ore with HCl/Cl with fairly good results. Now we need to recovery the dissolved metal. We are currently using resin beads. Just wondering if anyone has any experience to add. We are planning on rinsing loaded beads with borohydride to change PGM's to neutral state while still on the beads and then doing a dilute acid rinse to remove any excess base metals that might be still there. The initial process will be to them fume the beads off to recover the PGM metal powder. Question - can this powder be processed directly by a refiner at this point and if not, why not and what might be the next step?


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## steyr223 (Sep 30, 2012)

Have you hade an assay done
What other Pgm's or base metals
are you getting from your ore

I'm new. And unfamiliar with your process
but I believe these and many other questions
will need be answered before any one can help

Steyr223. Rob


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## butcher (Sep 30, 2012)

Have you tested the leach for dissolved values, if not how do you know what is in the leach, and what is left behind.

After testing your leach solution if it did have values, I would consider cementing the values from solution using a metal like copper, if all you have leached are the base metals in the ore, I would look more into the material that was leached for where the values are, as with ore usually you will leach base metals and leave the values behind, testing the solution will tell you where the values are and if they are going into solution or not.

If oxidizers or chlorine is still in solution these will need removed before being able to test solution for values.


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## chemgal68 (Sep 30, 2012)

Okay, I have a laboratory and we have verified values on not only the head ore, but also the leachates and the tailings left behind after the leaching process is finished. We know we have around 25 ppm Au, 55-70 ppm Pt and 50-70 ppm Pd. There are also smaller values of Rh present and minimal amount of Ag. We are not really interested in recoverying the Rh and Ag at this point and are mainly focusing on the Au and Pt (assuming that the Pd will most likely precip out with the Pt). One of the reasons we started working with the resin beads is they are purported to be selective for PGM metals only and the base metals will not attach. The base metals we know we have are Fe, Mn and small amounts of Ni. I would assume there may also be small amounts of As and Se in these ores based upon their origin and other geology present in the same area. 

I guess my main question would be if anyone has tried this type of process before with success. Our first thought process was that if the borohydride will convert the PGM's on the loaded resin to a neutral species and we fume off the beads, we will have an ash product that mainly consists of PGM metals in a powder form. I am wondering what kind of problems we might encounter if we try to heat this up and melt it down in this form - someone 
I spoke with voiced concerns about doing this in an oxygen environment if there was any Osmium present and the volatile nature of these metals. 

Anyway, if anyone sees this and has any additional info for me I would greatly appreciate your comments.


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## chemgal68 (Oct 2, 2012)

Returning to my previous question and process - the leachate I am dealing with is at a pH of around 1.0 and can easily be buffered with baking soda. However, the ORP is around +900 as there is a lot of excess Cl. Does anyone know of a method of ppt the PGMs directly from this solution (we are mainly after the Au and Pt) and is there a chemical way of discharging the excess Cl (heating large quantities of this leachate just is not practical on large scale). Will SMB do the trick for recovering both the Pt and the Au or should I be looking at a 2-stage ppt process, 1 for the Au and 1 for the Pt? 

I have read through Hoke's book yet again and she seems to deal mainly with recovering specific metals, not combinations. Forgive me if I have missed something and feel free to direct me to the answer if it has already been answered on this site.

Thanks for the input in advance.


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## butcher (Oct 4, 2012)

Sodium thiosulfate is used to remove chlorine from pools, but if you used too much with the HCl acid it can form SO2 gas and sulfur and precipitate the gold from solution.

Gold and silver chloride can form thiosulfate compounds but this is usually at a pH of around 4 to 9.
http://en.wikipedia.org/wiki/Sodium_thiosulfate

I have never tried lowering the chlorine in a gold chloride solution with thiosulfate so I cannot say how well it would work.

It does not take much heat to remove chlorine from solution sitting in the sun can do it (as long as there is not some chemical generating chlorine in solution un-reacted or in excess).
I would look into cementing the values out of solution onto copper for the recovery stage and then refining the cemented powders.

Sodium metabisulfite would precipitate gold after the excess chlorine was removed, but would not precipitate much platinum (using it as we normally do).

Yes Hokes is concerned with selectively recovering specific metals as she is dealing with refining of the metals, She also eliminates other metals as much as possible before putting the valuable metal in solution, otherwise it becomes more difficult to separate the valuable metal from the not so valuable base metals in solution, too much base metals in solution can make precipitating with chemicals troublesome.

Do you understand the reactivity series of metals and how to use this in recovery or refining? From understanding this you can see how a leach will prefer to put base metals into solution before valuable metals, and how the base metal can cement the values out of solution. If not then Google the reactivity series of metals and get an understanding of the principles involved.


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## chemgal68 (Oct 11, 2012)

I just have to post the latest update. We fumed 2 batches of resin beads from the HCl/Cl leach yesterday and sent it over to the refinery. They saw trace quantities of gold. We did not give them enough sample to test for the Pt, however, the resin we used to get the Au pulls all PGM's out so I am fairly confident that we also have Pt and Pd.

The other sample we sent over was from a Cu cementation experiment. It also showed trace amounts of Au, but yet again we need to process a larger quantity or ore so the refinery has something to process.

We have identified a loading problem with the resin and that is too much free chlorine, we seem to have been able to take care of this with very small amounts of Sodium Thiosulfate, drops the ORP below 400 and lowers the pH to around 2.

Question for anyone reading this, we are currently experimenting with Dowex 21K XLT, does anyone else have experience with a different resin and contact information so that we can obtain several different ones to run a bench test on what will work best in this recovery process? Resin requirements would include presence of Cl ions, and a lower acidic pH.

Thanks.


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