# Hcl/Cl leach efficancy



## Pumice (May 9, 2013)

Just wondering if I can get some idea as to the % of PGM's would be recovered on the first pass of an Hcl/Cl leach of honeycombs? I know Steve says he recomends 2-3 passes. I know it will vary, but just looking for any figures from members with experience in this process.


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## lazersteve (May 9, 2013)

In extraction chemistry there is a law of diminishing returns with respect to solvent usage verses extraction results. Typically the accepted standard for extractions is three passes, thereafter subsequent extractions do not produce appreciable yields to warrant additional extractions. It's nearly impossible to quantify as a percentage the exact amount that will be extracted with each pass for a given reaction as there are too many variables without performing a true scientific analysis. There is, however, a general pattern for each subsequent extraction: each extraction will produce *roughly half* the previous extraction up to the limit of the solvent power of the solvent and the available target compound. This rule assumes you have driven each extraction to completion/saturation before proceeding to the next extraction. The amount that can be extracted in a single pass, the efficiency of your solvent to dissolve the target compound, reaction conditions, the exposure technique, and time of exposure of the solvent to the target compound.

For example: 

You start with a new catalytic converter that contains 3 grams of palladium(Pd) hypothetically. Your three extraction passes may produce 2 grams, 3/4 gram, and 1/4 gram respectively using one gallon of full strength HCl-Cl at 40C for 12 hours on a whole honeycomb with agitation every 15 minutes for each pass. The entire 3 grams of Pd would have been extracted using 3 gallons of solvent in three passes over the course of 36 hours. If the honeycomb had contained Platinum (Pt) instead of Pd, you would expect different (lower) results. If your solvent is diluted, or run at room temperature, your results would be even lower. If you extend the first soak time, you may see a higher first extraction and get the remainder of Pd in the second pass, but not all of the Pt if it were present. If the same converter were crushed, but the reaction is not stirred or circulated properly, your numbers would again be different than the other tests.

To get a more accurate answer to your question would require a very controlled analysis of the starting material before and after each extraction stage, as well as tight control and documentation of the reaction results after each pass. Once you had this data in hand, you could plot a chart that reflected the real world data from your experiment.

As an acquaintance exercise for extraction chemistry I suggest getting a tea bag from the cupboard and extracting the tea with the directed amount of hot water for each pass as per the instructions on the bag. Squeeze the bag as dry as possible between each pass. Make a note of how dark the water turns with each pass. You will find that after the third pass, your water will only slightly discolor, indicating that the limit of the extraction reaction has been reached. Additional passes may slightly discolor the water, but you will find that once the tea bag is fully leached, the color of the water will remain roughly unchanged with each new pass.

Steve


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## kkmonte (May 10, 2013)

LOL, I can see some of these newbies around here putting t-bags in their catalytic converter buckets! We'll see a post in a few days saying this:

"Hey Steve, I know you said t-bags help with pt on cats, does it work with AP and fingers?" 

HAHA


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## Pumice (May 10, 2013)

Thanks Steve that helps. I just wanted to make sure a 2nd leach would be signifigant.

We are a large salvage yard/auto recycler and are looking into investing in the equipment to do larger scale PGM recovery/refining. Having said that, do you know of any reliable sources of yeilds on cats? We get so many different opinions/answers that we are still unsure. That is why we are trying some different cats to see for ourselves.


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## solar_plasma (May 10, 2013)

Take a look on this website:


> http://www.looker.de/kat-ankauf/index.php



They have a large list of converters with different prices they pay. If you just knew the yield of one of the listes converters, you could interpolate the estimated yield on all converters on this list. When I had to decide to keep my two old mercedes converters or to sell them, I searched the net and finally guessed that they pay between 50 and 80% of spotprice, so I sold them. Well, that was long before I found this forum :lol:


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## nickvc (May 11, 2013)

We have had this topic raised several times on the forum, refining cats inhouse, and it seems to me it's better to empty the cans and save the powder until you have volume and then mix and sample and sell as is to the big boys in refining. They use huge arc furnaces and recover everything but with wet or chemical refining you always leave some in the powders or end up with large volumes of solutions with little values far from ideal in PGM refining.


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## solar_plasma (May 11, 2013)

> We are a large salvage yard/auto recycler and are *looking into investing in the equipment to do larger scale *PGM recovery/refining.





> and sell as is to the big boys in refining



..he IS a big boy


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## skippy (May 19, 2013)

solar_plasma said:


> > We are a large salvage yard/auto recycler and are *looking into investing in the equipment to do larger scale *PGM recovery/refining.
> 
> 
> 
> ...



There's big and then there's big.

The big boys are setup to process many tons of catalyst a day. They achieve very high extraction, they can negotiate favorable terms on their recovered metals. I imagine that like a steel mill they run 24/7. One scrap yard would be just one of hundreds of customers for a large plasma furnace operator. Decanning and milling might be a good way to go for a yard, but setting up their own pgm recovery operation I'll say with a very high certainty would be a losing proposition


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