# Solvent Extraction Tutorial.



## HAuCl4 (Oct 28, 2010)

I'm teaching myself to Sx metals to high purity in as few steps as possible.

This will be a "developing tutorial thread" for those interested to contribute knowledge, specific processes or documents.

I'll probably end up posting to myself most of the time, since these processes are still regarded as "secrets" or protected by patents or both.

The initial material to "process" are chloride solutions of Au, Pt, Pd, Ag, with maybe traces of Rh, Ir and base metals Cu, Ni, Pb, Zn, other as they are encountered in the processing of jewellery and/or platinum scrap.

1-The initial broad stroke process proposed includes the digestion in aqua regia of the above mix, and separation of AgCl and other insolubles by filtration.

2-The liquid is then extracted with BDG according to the process described by Ferro to isolate gold in high purity form. (see attached .pdf)

2-b Optional. To treat the aqueous solution after BDG extraction with an ammonium oxalate solution, to effect complete removal of gold after filtration, before going to the next step.

3-The remaining aqueous solution is then extracted with n-octyl sulfide or other suitable alkyle sulfide diluted in kerosene or other, with the purpose of extracting palladium from the remaining aqueous solution of other PGMs and base metals. An sketch of the process is available free online, with some references to other patents.

http://www.patentgenius.com/patent/5266727.html
*****
BACKGROUND OF THE INVENTION

The present invention lies in the art of refining platinum group metals (PGM's) through solvent extraction. More specifically, the invention relates to a process for purifying alkyl sulfide extractant for use in extracting palladium from amixture of palladium and other PGM's. In particular, the process is directed to the removal of organosulfur compounds from alkyl sulfide extractant, as they interfere with the recovery of palladium.

Solvent extraction of aqueous solutions containing precious metals derived from ores and their subsequent products is gaining in use due to its advantages over the classical precipitation and redissolution methods. Advantages of solventextraction include a reduced cycle time, higher purity, and often higher yields. With proper selection of solvents and process conditions, extraction can be highly specific for a particular metal species, resulting in recovery of a high purity product. Typically, the required purity of PGM's is up to about 99.995%. To achieve this level of purification using precipitation and redissolution procedures requires multiple repeat processing and thus considerable time. Solvent extraction shortens the timefor purification many fold, while yielding a higher purity product.

Solvent extraction is carried out by contacting an aqueous phase solution of one or more extractable metals with an organic phase containing the extractant. The extractable metal or metals form complex compounds, with the extractant acting asthe complexing agent or ligand. Each of the extractable metals can form one or more complexes with different atomic or molecular entities occupying ligand positions in the coordination spheres of the complexes. These ligands can be anions (chloride andother halides, sulfate, nitrite), cations (nitrosyl, NO.sup.+), neutral species (H.sub.2 O, NH.sub.3) or organic compounds (ethers and other oxygenated compounds, amines, sulfides). For those metals exhibiting more than one valence state, some of whichcan be easily reduced (e.g. Au(III), Pd(IV) and Ir(IV)), care must be taken in achieving the desired chemistry for extraction and stripping. Large differences in rates of reduction and ligand substitution reactions result in separation between metalspecies. Sequential extractions using different extractant enables separation of a plurality of metal species from a single solution.

For recovery of palladium (Pd) from ores containing Pd and other PGM's, various alkyl sulfides have been used as extractant. For such an example, see U.S. Pat. No. 3,985,552 issued Oct. 12, 1972 to Edwards. In a typical extraction, a diluentsuch as a paraffinic or aromatic liquid is combined With the alkyl sulfide to form an organic phase. An aqueous phase, usually an aqueous acidic chloride solution containing Pd and other metals extracted from the ore, is contacted with the organicphase. The Pd in the aqueous phase forms a complex with the extractant and, due to its high solubility in the organic phase, the Pd complex is almost completely partitioned into the organic phase. Using n-octylsulfide (NOS) as the extractant, forexample, the equation for extraction is:

In typical commercial practice, the organic phase is first washed with a dilute HCL solution to remove entrained raffinate comprising other PGM's and small amounts of other metals, such as iron and copper, which are extracted to a low level. Thewashed, loaded organic phase, containing less contaminant metals, is then stripped using aqueous ammonia The Pd complexes with the ammonia to form Pd(NH.sub.3).sub.4.sup.2+ ion in aqueous solution. The extractant is then recycled for reuse. The aqueousPd solution, which also contains excess NH.sub.3 and Cl, is then carefully acidified to precipitate the sparingly soluble salt Cl.sub.2 Pd(NH.sub.3).sub.2. Conversion to the metal results by its ignition at high temperature (e.q., about 900.degree. C.)to form "Pd sponge."

The extraction and stripping of PGM's using alkyl sulfides is affected by organosulfur impurities such as mercaptans and disulfides present in the alkyl sulfides. During stripping the organosulfur impurities readily react with palladium andother PGM's to form a solid emulsion-like "crud" phase which disrupts the complete recovery of Pd. For example, sulfur compounds, such as mercaptans, are undesirable in the alkyl sulfide as they can tie up metals as the mercaptides and can subsequentlycause problems in the stripping step. These problems can be overcome by using highly purified alkyl sulfides, but at considerable added materials cost.

There is a need for a process for conveniently and efficiently purifying the alkyl sulfides which are used for purifying palladium and other PGM's, of the unwanted impurities. This need is met by the present invention.

*****

3-b Optional. To treat the aqueous solution after Pd extraction with a small amount of DMG, to effect complete removal of Pd after filtration, before going to the next step.

4-The remaining aqueous solution is then extracted with Tri-n-butyl phosphate or other suitable solvent, with the purpose of extracting platinum and Iridium from the remaining aqueous solution of Rh and remaining PGMs and base metals.

[Insert relevant patents or processes here]

An sketch of the above Sx process was obtained initially from:

http://www.halwachs.de/solvent-extraction.htm

I believe Halwachs was one of the first pioneers of Solvent Extraction.

Feel free to further these process with specifics and details!. 8) 

After we nail this down completely, we can explore Sx to produce pure forms of other interesting metals like U and Pu!. Save the flames and contribute if you can! :shock:


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## HAuCl4 (Oct 28, 2010)

Nickel Sx:

http://www.freepatentsonline.com/4162296.html


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## HAuCl4 (Oct 28, 2010)

Lead-Zinc extraction of silver and gold, for lead purification:

http://en.wikipedia.org/wiki/Parkes_process

The Parkes process is a pyrometallurgical industrial process for removing silver from lead, during the production of bullion. It is an example of liquid-liquid extraction.

The process takes advantage of two liquid-state properties of zinc. The first is that zinc is immiscible with lead, and the other is that silver is 300 times more soluble in zinc than it is in lead. Hence when zinc is added to liquid lead that contains silver as a contaminant, the silver preferentially migrates into the zinc. Because the zinc remains in a separate layer, it is easily removed. The zinc-silver solution is then heated until the zinc volatilizes, leaving nearly pure silver. If gold is present in the liquid lead, it can also be removed and isolated by the same process.[1] The process[2] was patented by Alexander Parkes in 1850.


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## lazersteve (Oct 28, 2010)

Here's some of my posts on the use of Dibutly Carbitol to extract gold:

DBC Posts

Steve


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## lazersteve (Oct 28, 2010)

Here's a nice flowchart from a book that include Sx for many precious metals:

Solvent Extraction Scheme for Ore

Go to page 1771 in the link above to see the flow chart. The text describes the process.

I have a nice SX flowchart diagram somewhere if I can find it I will post it here.

Steve


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## HAuCl4 (Oct 29, 2010)

lazersteve said:


> Here's a nice flowchart from a book that include Sx for many precious metals:
> 
> Solvent Extraction Scheme for Ore
> 
> ...



Excellent diagram and resource. Looks like a book worth getting. Thanks Steve!. 8)


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## HAuCl4 (Oct 29, 2010)

HAuCl4 said:



> Lead-Zinc extraction of silver and gold, for lead purification:
> 
> http://en.wikipedia.org/wiki/Parkes_process
> 
> ...



Two VERY COOL experiments, to be performed CAREFULLY, by any wannabe metallurgist/alchemist:

1-Melt about 2 Oz of jewellery yellow scrap, 10 Oz of pure lead, and 1 Oz of charcoal in a clay crucible covered with a clay cover with a very small vent hole on top. Do this in a muffle or electrical kiln. Bring temperature to 1,100 C, and then start lowering the temperature about 25 degrees every 5 minutes till it is below 950 C. After this you can set the furnace temperature to 450-500 C and allow it to cool. Then you can open the crucible and with an iron "spoon" or thick wire skim the slag on top of the still barely molten lead. This "dross" consists of crystallized copper, nickel, iron, cobalt, and zinc, and whatever that literally floats to the top of the molten lead as the temperature is slowly dropped below the copper melting point.

Silver, with about the same density as lead and very soluble in it, stays with the lead, same as any gold which is heavier and stays with the silver and lead.

This experiment is similar to cupellation in a fire assay, but there is no oxygen to oxidize the base metals, that float and crystallize above the molten lead.

2-Experiment 2 consists of allowing the above crucible cool to room temperature, after "skimming" the dross. Then one adds about 10 Oz of pure zinc metal, and another 1 Oz of charcoal. Place the crucible cover with very small vent hole, and this time clamp the crucible and cover with an iron or other clamp. Place in furnace and bring temperature to 850 C (never surpass 900 C !). At this point you can plug the vent hole with an iron nail, grab the crucible with an appropiate set of tongs, and shake it vigorously for about a minute, as if you were mixing a cocktail.

Now place it again inside the furnace for a few minutes at 800-850 C and let the temperature slowly drop by letting the crucible cool inside the furnace (shut off electricity to the furnace and let crucible cool inside).

When at room temperature, break the crucible, and you will see the metal layered in 2 parts, the zinc on top and the lead on the bottom. The surprise is that almost all gold and silver will have migrated to the zinc, and you will have effected a liquid-liquid extraction at pyrometallurgical temperatures!. This experiment illustrates the Parkes process.

Disclaimer: These two experiments involve lead and zinc, which when molten and exposed to air can and will produce dangerous fumes. These dangers are forever present, but can be minimized by the added charcoal, and of course by having a good draft with a scrubber or fume hood. Always do these type of experiments with good ventilation and/or on an open physical space.

For me, this is one of the coolest experiments to be done with lead. Now you know why lead was so popular with alchemists!. 8)

There is a third experiment, which I have never done, which consists of "distilling" the zinc from experiment 2 in a closed vaccuum circuit. This allows the separation of pure zinc in the condensing chamber, and leaves a residue of almost pure gold and silver. 

Instead of experiment 3, and to recover the gold and silver, simply dissolve the zinc of experiment 2 in H2SO4 or HNO3, and the residue is gold mud as in inquarting/parting, and you can recover the silver from the liquid adding salt which precipitates the AgCl. There'll be very little, if any copper present, but maybe some lead if you aren't careful!. 8)


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## HAuCl4 (Oct 31, 2010)

TBP as extractant for Silver.


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## HAuCl4 (Nov 27, 2010)

Brief summary of R. Gilchrist professional life, sketches of some of his PGM procedures, and references.


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## g_axelsson (Jan 7, 2014)

Thanks for the collection of solvent extraction documents. It surely deserves a bump!

Göran


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## sharkhook (Jan 8, 2014)

I have a 40Lb commercial pot for melting lead that has a variable temperature control that I use for fishing sinkers and bullets . I have lowered the temperature slowly to "clean" the lead for other projects. Never thought about using it in some of the ways described here. I am not sure how hot it will get, but it will melt 20lb lots of silver solder easily. And with 20# lots of dirty lead it will burn the zinc and other lower metals out of the lead. Now I am wondering if some of the "slag" I have thrown away over the years was silver? I once did a melt of silver bearing solder that consisted of 80, 1# rolls.


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