Colloid after Copper drop

Advertise with us
xelexo
Shop deals on ebay
shop deals on amazon
Gold Refining Forum

Help Support Gold Refining Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
F

frontiermetals

Member
Joined
Mar 31, 2012
Messages
20
Question for you guys: I just completed a SSN digest of an ore containing, by assay, platinum, palladium and some silver in a zinc/lead/carbonate matrix. Basically I first used an HCl leach with no oxidizer, to dispose of the carbonates, zinc, iron etc., then rinsed residue thoroughly. Residue was then digested with SSN , allowed to settle, producing an amber yellow solution devoid of suspended particles. Same color as Listerine. I placed a copper bar into a 350 ml aliquot of this solution and immediately began to get black precipitates and mild bubbling from the copper. After about 15 minutes the reaction heated up and evolved nitric fumes and the solution turned black as coffee and stayed black upon cooling. After 36 hours, no settling. By transmitted light (holding it up to the sun) the solution is ruby red. My question is this: Could the hot reactive solution have driven excess copper into solution where it precipitated out as a colloid upon cooling? There is no hint of blue or green to the solution as I would expect with copper. There is also little if any gold in this ore so doubt the ruby colloid is gold. Any experience with platinum or palladium colloids is appreciated.
Best,

Jeff
 
The colors in a solution do not necessarily mean there are colloids of a metal in solution; these colors can come from dissolved metal salts or other compounds in solution, or from metal colloids reflecting light.

Colloids are so small you will cannot be see them, they join into clumps of atoms large enough to reflect light to color, which we see as a color, How large these clumps of metal chlorides form can be determined by the metals and what formed these colloids, which also is related to the color of light reflected (by the certain size of the colloid of the particular metal).

For example gold can be reduced back to a metal as a colloid (from a gold chloride solution) by using stannous chloride (what we use to test for gold in solution with stannous chloride), the gold and tin solution form a colloidal gold solution, these colloids from a certain size of clumps of atoms of reduced gold metal, with an electrostatic charge, which will reflect light to where we see a purple color to the solution, there are other compounds that can also be used to reduce the gold to a colloid of a certain size that can produce other colors of reflective light (making colloids of gold of a certain size, and certain color, like citric acid...).

These colloids have an electrostatic charge (after the reduced gold atoms combine to grow to a certain size, that reflect a certain color of light). This static charge will not let the colloid grow larger (more reduced gold atoms contact each other and form larger clumps), this static charge causes these clumps of reduced gold atoms to repel each other (so they cannot come into contact and grow larger).

This repelling force of the static charge of these colloidal clumps of combined reduced gold atoms also keeps them in motion in solution (indefinitely unless the colloid is broken, or the static charge is removed), basically preventing them from coming into contact and forming larger clumps of reduced gold atoms that can settle in solution by gravity, the repelling force can keep them stirring each other in solution almost forever if the colloid is not broken, basically a colloid will not grow to form larger clumps visible to the eye, and will not grow large enough to precipitate.

Colloids of gold have already been reduced to metal, these atoms of gold have a full shell of electrons and do not want extra, you cannot reduce (give electrons to these gold atoms) as they are already have a full shell of electrons.

Colloids of gold or another metal cannot be precipitated by any means until the colloid is broken (the static charge removed).
Chemical precipitants Like SMB, ferrous sulfate or others, cannot give theses gold atoms another electron or reduce them back to atoms of gold electrons with a full shell of electrons (the gold has already been reduced into clumps of gold metal atoms with each gold atom having a full shell of electrons).

Colloids of gold or another metal cannot be cemented from solution by a metal higher in the reactive series of metals until the colloid is broken (static charge of the colloid is removed).
These already have all the electrons they want and are already reduced (just to colloidal form of clumps of atoms with a static charge staying in constant motion repelling each other around in solution).

You cannot test for the gold in solution (when that gold is in colloidal form) by using a reagent like stannous chloride, (stannous chloride works by reducing the gold to a certain size colloid), (colloidal gold is already reduced, so stannous chloride will not reduce it, the colloidal gold is already a certain size colloid and will not change its size in this testing method...
The gold or other metal colloid is already atoms of that metal which have been reduced (gained an electron) to atoms with all of there wanted electrons (and formed clumps of these reduced atoms with an electrostatic charge), basically the gold is already reduced, so it cannot be reduced to metal again...

Ore is complicated and many things involved can produce many colors in solutions, some metals in certain oxidation states can produce certain colors in certain solutions, but when you have many metals and non metals in solution, color may or may not be much of an indicator as to what is in solution, or in what form that metal is in.
With the complications involved with ore colors would very rarely mean a whole lot.
Testing may be the only way to determine what is in solution.

Colloids can be broken (although not easily), Heat in highly acid solutions or with electrolytic means, are the methods mostly used, sometimes complete evaporation of the solution and incineration and washing out the substance that caused the colloid to form has to be used, to break the colloid and keep it from forming again.
 
Thank you Butcher for all the information on colloids. A real pain to deal with but that's part of the game.

So I guess at least part of my question remains... has anyone experienced formation of copper colloids when dropping PM's with copper from a dirty solution of SSN?

Jeff
 
Colloids of metals normally form as something in solution gives up electrons to the metal ions in solution, we will say gold just for this conversation, but it could be another metal.

The gold dissolved in solution does not have all of the electrons in the atoms of gold (these atoms of gold are now basically ions of gold and are not called atoms),(the electrons being taken from the gold atoms were taken by the acid and oxidizer) these gold ions can take electrons from another metal higher in the reactivity series of metal, or from something else in solution that acts as a reducer, or reducing agent, willing to give up electrons to the gold atoms, and in doing so it is itself oxidized (lose of electrons), these ions of gold now receiving electrons from the reducing agent are now atoms of gold in solution, but still invisible to the eye.
Basically elemental gold metal atoms with a full shell of electrons, these tiny atoms floating around in solution begin to bump into each other and stick together into clumps of atoms of elemental gold.

Growing larger as they bump and stick more atoms together, (if this process continued without interference they would grow large enough to where you could begin to see them, and heavy enough that they will begin to precipitate from solution).

But where the colloid forms is before these clumps of atoms grow to that size. The substance in solution that causes the colloid to form (like tin does with gold), stunts the growth of these tiny gold atoms from combining more, or to grow to larger clumps, usually at a certain size, the tin in solution with gold polarizes these clumps of gold atoms with a charge, all these clumps of gold atoms with the same polarity of static charge, now these small clumps of gold atoms all with that same static charge begin to repel each other, not coming into contact, and like many small magnets of the same polarity, begin shoving each other around in solution so the will not come into contact, or stick together to from large enough clumps to be seen with the naked eye, they will not grow large enough to settle and will not because they are too busy constantly shoving each other around in solution, not able to come into contact with another clump, to break the colloid you have to remove this static charge.

Colloids of metals will reflect light (normally we see as certain colors), with a metal like gold the certain size of the colloids appear to our eyes as certain colors) gold colloids can come in many colors depending on the size of the colloids formed, with gold they can make these colloids experimentally on purpose with certain things to form the colloids of certain sizes, giving certain colors to solution.

Colloids could form with many metals if there is something in the mix, and with a dirty solution, or with many substances in solution they are more likely to form. I do not know if what you have is a colloidal solution or not, read about the tyndall effect, you may be able to use it to see if that may be the case.


https://www.google.com/search?hl=en&q=tyndall+effect&gbv=2&sa=X&as_q=&spell=1&ei=KgWxU_enDpbqoASApYK4Aw&ved=0CBEQBSgA
 
Why do you think you have a colloidal solution and not only a simple mixture of various salts in solution?

A simple test would be to take a small sample and add a tiny part nitric acid. The added acid would form aqua regia with the chloride ions already in solution and would dissolve any colloidal solution you have. If the color doesn't change it isn't caused by a colloidal solution, at least not a metallic colloidal solution.
The resulting liquid could be tested in normal ways with stannous for dissolved precious metals.

Göran
 
Irrespective of how interesting colloidal chemistry is, I suspect, like Göran, that the answer is probably more straight-forward.

I'd start, as already mentioned, with a stannous test; this can show the presence of not only gold but also platinum and palladium, but I suspect you'll get a negative result. In this case check the ORP/Eh (Oxidation Reduction Potential); I'd guess the reading will be too low to dissolve gold.

Freshly mixed SSN will generally show an Eh in excess of 900 mV and quickly drop from the chemical reactions occurring in a mixed ore. Even from just standing, I usually see it drop to around 700 mV after 24 hours. Gold requires approx 850 mV, platinum 680 mV and palladium 380 mV to dissolve in acidic chloride media. Any gold that dissolved when the SSN Eh was high enough will plate out as the Eh drops. Similarly with platinum and palladium, but at lower Eh's.
 
Thank you for the input guys. I see the problem now. There's a considerable amount of tin in the ore, about 20 ounces per ton, so as the values drop from the copper they are driven to colloids by the dissolved tin. I can work around the tin by using chelation resin in pulp. Thanks all.
 
I was going to share the fact that there is something else besides finger grease that causes the gold to float... But it look like Butcher has already researched and explained.

I washed all my equipment thoroughly - very very thoroughly and dried very well - while wearing latex gloves with Harold's recommended Bonami scratchless powder cleaner and still had floating gold. Then I found Butchers explanation. Once again very informative.

I try not to worry too much about the floaters... They get caught by the filter anyway. 99% of the yield is 18x's heavier than water and settles easily.

The only thing I can say now is at least I've got a bunch filters to process one day. 8)
 

Latest posts

Back
Top