# Mesh size of gold drop?



## Dorcas Nimrod (Mar 18, 2022)

Does anyone know the range of particle sizes you get when you drop gold? I understand temperature and purity of solution will affect particle size, as well as whether you precipitate with SMB, SO2, ascorbic acid, and so forth.
I have searched the forum, to no avail.
It's a great forum, and I've learned a lot, and appreciate the effort people put in to documenting their various projects.


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## nickvc (Mar 18, 2022)

Not sure too many members will know or care as our primary interest is to ensure we recover all the gold in solution, I’m guessing that there are too many variables to give a definitive reply.


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## cejohnsonsr1 (Mar 19, 2022)

If you’re talking about the gold that drops out of solution when you precipitate with something like SMB, there’s no mesh size. The gold is in elemental form. It’s literally just small clusters of atoms of gold.


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## Dorcas Nimrod (Mar 19, 2022)

Alright, well thanks for taking a stab at it guys.


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## orvi (Mar 19, 2022)

cejohnsonsr1 said:


> If you’re talking about the gold that drops out of solution when you precipitate with something like SMB, there’s no mesh size. The gold is in elemental form. It’s literally just small clusters of atoms of gold.


Pretty much true. When dropping gold, very very small nanocrystals could form, which then clump together to form aggregates and settle down. Very variable, there is no definite answer to former question.
One photo how standardized 100 nm gold nanoparticles look like under SEM


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## Lino1406 (Mar 19, 2022)

Brown chocolate gold - 0.5 micron and above. 0.1 micron - violet blue. Over 10 microns, as with oxalic acid reduction - golden


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## orvi (Mar 19, 2022)

Lino1406 said:


> Brown chocolate gold - 0.5 micron and above. 0.1 micron - violet blue. Over 10 microns, as with oxalic acid reduction - golden


Thanks for the input, very interesting information. Yes, it goes with particle size - that small particles with ability to bend the light, you get darker colours. But it also depends from concentration in the solution.
When dealing with highly polluted solutions, full of copper, dissolved polymeric junk and organics, they could act as some sort of "stabilizers", blocking the gold nanoparticles from the possibility to clump together.
Manufacturers of gold and silver nanoparticles take advantage of this phenomena, for us, refiners, it is the worst nightmare


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## Dorcas Nimrod (Mar 19, 2022)

Thanks for everybody's input, that's tremendously helpful, and thanks cejohnsonsr1, I overlooked your last sentence, it didn't register at the time. So it's not really particles, but clusters of atoms.
The main reason I was curious is to see if my recovered product was viable for use in a DIY "PMC" product. Precious Metal Clay is a malleable clay product which can be kiln fired into solid sintered jewelry and parts. The finer the particles, the lower the temperature needed to fire and the less shrinkage. I've seen people make DIY silver clay, but was wondering if gold would be possible.
You guys are awesome.


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## nickvc (Mar 20, 2022)

The problem I can see in using your precipitates for jewellery clay is that you will be using fine gold which is extremely soft and pliable and expensive compared to karat gold items.


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## kurtak (Mar 20, 2022)

Dorcas Nimrod said:


> and thanks cejohnsonsr1, I overlooked your last sentence, it didn't register at the time. *So it's not really particles,* but clusters of atoms.


Per the bold print - close but not quite (fully) true --- in other words - though there is some truth - it's not the whole story so just not fully true

Though a particle can be just one atom in size (so that is true) --- but a particle can also be a "cluster" of things (atoms, molecules, etc.) clumped (or clustered) tight enough together to form an aggregate

So a particle can be just one atom in size - or - be formed (as an aggregate of atoms) packed tight enough together to make a particle several &/or MANY atoms in size

one atom of gold (actual gold) is 0.1441 nanometer in size 

A nanometer is 1 billionth of a meter --- whereas a micron is 1 millionth of a meter --- so it takes 1000 nanometers to make a particle 1 micron in size

therefore - a 1 nanometer gold "particle" is about 7 gold atoms 

technically speaking - when we reduce gold chloride - the reduction happens at the atomic level

however - if gold simply &/or only reduced at the atomic lever - it would never precipitate 

The definition of precipitate is --- to fall out - or to settle out --- so the gold atoms need to aggregate together enough to form a particle size heavy enough to "precipitate"

If the gold does not aggregate to particles large enough to precipitate they are called colloids - which are particles of gold larger then an atom (also a particle) but not large enough to fall out or settle out - so they stay in suspension

Gold "particles" in the range of 100 nanometers & smaller will produce colloid gold (gold particles in suspension) that is pink to red in color - particles larger then 100 nanometers will produce colloid gold particles in the blue to purple color (think stannous test) --- so particles plus/minus 700 atoms in size

We want our gold to actually precipitate - for that to happen we need the atoms to aggregate together to form "particles" that are at least "approaching" 1 micron in size (they can be "a bit" under a micron - but need to be headed to that size for precipitation to happen)

To put microns in perspective - a single particle of cigarette smoke is about 2 microns in size --- also - a particle needs to be over 40 microns in size before it can be seen by the human eye

So what happens when we add SMB to a solution of gold chloride - the very first thing we see is gold being reduced at the atomic level & we see a black cloud appear - that black cloud is nanogold particles forming - black being nano particles a bit above purple - but then that black cloud (very quickly) shifts to a brown smoke like color - that is because the black nano particles are aggregating into particles approaching &/or surpassing micron size - those brown smoke like particles soon aggregate into particles you can see falling to the bottom of your beaker - so those are particles greater then 40 microns in size 

So yes - though a precipitated gold particle is made up of MANY gold atoms - that particle is just many single atom particles - aggregated together to form a larger particle --- in other words - when enough atoms aggregate together - it forms a particle large enough to fall (or precipitate) out allowing your gold to settle from solution

For precipitation - particle size matters - we want the particle size to be big enough so that the gold particles "fall out" --- that means we are shooting for particles in the micron range - not particles in the nano range & we would never get our gold back if all we could do is reduce it at the atomic level --- though yes it is true that the atomic level is where reduction "starts" --- particles need to grow - by way of aggregation - to precipitate

The particles we "see" falling are 40 plus microns in size - the particles that take a bit longer to settle (near end of precipitation) are 1 plus micron in size (we only see them because there are A LOT of them so we see a cloud) - the particles that take a looooong time to settle (after precipitation) are 0.5 - 1 micron in size (& again we only see them because there are A LOT of them) 

Kurt


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## kurtak (Mar 20, 2022)

As an added note & to put it a bit more in perspective --- gold particles that actually precipitate will range from around 0.5 micron (maybe "a bit" smaller) to "over" 40 microns --- & "everything" between

it's just that at the 0.5 particle size it may take days for the particle(s) to settle - whereas particles 40 plus microns in size will drop like a rock (& everything in between)

which is why we see gold settle in phases - it's particles size & particle size matters

Kurt


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## kurtak (Mar 20, 2022)

cejohnsonsr1 said:


> If you’re talking about the gold that drops out of solution when you precipitate with something like SMB, there’s no mesh size. The gold is in elemental form. It’s literally just small clusters of atoms of gold.


Although not really untrue - not fully true ether

Particles don't need to be a single atom to be considered a particle - atoms can be bonded together tight enough to form a particle made of many atoms - when they (atoms) bond together by electrical charge it is called an aggregate particle 

in other words - a particle is not restricted to it's smallest denominator (the atom) - rather - the size of a particles is determined by the number of atoms bound together in the particle 

so a particle could be anything from 1 atom in size to several thousand atoms in size

therefore - a gold "particle" could most certainly be mesh in size

Example; - a 400 mesh gold particle is about 40 microns in size --- or a gold particle about 280,000 atoms in size

you can/will see gold *particles* - that size & bigger drop when you precipitate gold - they are the *gold particles* that fall instantly to the bottom of the beaker & stay there 

That is because a HUGE number of gold atoms have aggregated together to form a very large gold particle

Kurt


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## cejohnsonsr1 (Mar 21, 2022)

kurtak said:


> Although not really untrue - not fully true ether
> 
> Particles don't need to be a single atom to be considered a particle - atoms can be bonded together tight enough to form a particle made of many atoms - when they (atoms) bond together by electrical charge it is called an aggregate particle
> 
> ...


Clumps form, but but the beginning of the process is the exchange of electrons in individual atoms. The clumps never really reach a size that could be classified by mesh size. Even larger clumps that form when drying are easily reduced back into powder that would pass through the smallest mesh. My only real point was that classification by mesh isn’t a viable method of measurement.


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## orvi (Mar 21, 2022)

There is a lot going on phase interfaces. The attraction forces for single atoms of gold formed by reduction are extreme. Tendency to clump together is very natural. It could be computed by some not very pleasant-looking equations tho  But tuning the conditions in solution, adding additives which have stronger bonding ability with particles, than particles with other particles, could stabilize nano-suspensions. You can also strenghten the binding forces between particles by adding flocculants, or physically flocculate particles on some "sticky" polymers. Very difficult and useful subject


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## Dorcas Nimrod (Mar 22, 2022)

I was going to ask if it was Van Der Waals forces which are holding the agglomeration together, but I already know the answer would be over my head.
In my limited experience, temperature and dilution have an effect on how fine the precipitate is, and ascorbic acid can produce a very fine precipitate as well.
As for jewelry, I think some would argue the durability issue of 24k is a bit overstated. At any rate, Mitsubishi came out with the gold version of PMC right before the mass transfer of wealth in 2008, when gold prices shot up, and the product was swiftly discontinued. It was eventually replaced by a slip-like product used for painting gold highlights/accents onto silver pieces, in effect producing Keum Boo-like gold highlights. If I recall, 4000 mesh is needed, which would be about 3 microns(?), so I guess that would require some experimenting. Maybe sonication? Stick the beaker in an ultrasound bath while precipitating?
Thanks again, everyone's replies have been fascinating. It's a privilege to pick your brains.


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## kurtak (Mar 22, 2022)

cejohnsonsr1 said:


> Clumps form, but but the beginning of the process is the exchange of electrons in individual atoms. The clumps never really reach a size that could be classified by mesh size. Even larger clumps that form when drying are easily reduced back into powder that would pass through the smallest mesh. My only real point was that classification by mesh isn’t a viable method of measurement.


Again somewhat true but not entirely true



cejohnsonsr1 said:


> but the beginning of the process is the exchange of electrons in individual atoms.


This part is true --- For dissolved gold (Gold in a state of oxidation - or Au+) to be reduced back to elemental gold (Au) the plus (+) electrons need to be stripped/knocked off --- that indeed does happen at the "individual" atomic level

However - generally speaking &/or for the most part (at least when talking about "dropping" our gold) the rest of your post simply is not true



cejohnsonsr1 said:


> The clumps never really reach a size that could be classified by mesh size.


As I said - when precipitating our gold - particle size matters

that's because particles size makes a difference in all the other steps we do with those particles before our final end product (button/bar/round)

In other words - particle size matters in the steps of settling - filtering - washing & "going to melt"

When we precipitate our gold - the larger we can get those particles to form - the better each of those steps go

Therefore - as a matter of fact - we want those particle to form in size that can indeed be measured in mesh size

As a reminder to putting particle size in perspective --- a (single) particle that is 40 microns in size (which is "about" 400 mesh) can not be seen by the average human eye

Therefore for a single particle to be (clearly) seen - it actually needs to be "much" larger then 400 mesh

When we precipitate our gold - the vast majority of the gold particles we drop - are (or at least should be) large enough that we can "see" them as individual particles

Example; - (& putting it in perspective) when you drop your gold - you will almost always - if not always get a few particles that are floaters (particles that float on top of the solution) those are "individual" particles you can see with your eye & therefore MUCH larger then 400 mesh

If you are doing a good job in dropping your gold - much - if not most of the particles that drop to the bottom of the beaker are &/or should be even MUCH larger then those floaters --- even as large as 1 - 2 mm in size

That is our goal when precipitating our gold --- to form particles "as large" as possible - in order to make all steps after precipitation go better

Therefore - when precipitating our gold - it is our goal to form particles that most certainly can be measured in mesh size 


cejohnsonsr1 said:


> Even larger clumps that form when drying are easily reduced back into powder that would pass through the smallest mesh.



True - but only to a point - & somewhat dependent on whether the formation of the "original" (larger) particle is tight bonded - or loose bonded when forming

so again - one of our goals in refining is to form "tight" bonded particles (that don't easily fall apart) - as large as possible & the larger the better

That is something we hope to achieve in the washing process - to get already large particles (large enough to see) to aggregate into even larger particles - that don't easily fall apart after drying - so that particles don't blow away when putting the torch to them when going to melt

Personally - it is my goal - to achieve particles - after the washing & drying - that are at the very least half a millimeter (500 microns) to 1 - 2 mm in size &/or even some particles (tight bonded) as large as half a cm (5 mm) ---- Edit to add; - or at least a large number of particles as described here

That is what I like to see - in particle size - when I dump my dried gold in my melting dish

In other words - it is my goal - in refining - to create - the largest (tight bonded) particles possible - from the point of first precipitation - to the point of melting --- because in refining - particle size matters

And the larger the particles - from the point of precipitation - to the point of melt - the better

Therefore - the goal is in fact to create (tight bonded) particles - that are indeed measured by mesh in size

Bottom line - in refining - if you are not achieving the largest particles possible (as described above) you are ether doing something wrong on the path to melt - or - deliberately trying to create small particles

Granted - you will always have some "very small" particles - but your goal should be the most as well as the largest particles possible 

Kurt


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## cejohnsonsr1 (Mar 23, 2022)

Elements don’t form particles. Particles are the subatomic components of an element. All precipitation is the breaking of chemical bonds to release the objective element from the solute. The clumps that form are nothing more than the result of accretion. No matter how small a clump is, it can be reduced further. No matter what the size of the clumps, when melted it’s all the same. Just in metallic form.


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## kurtak (Mar 23, 2022)

Dorcas Nimrod said:


> In my limited experience, temperature and dilution have an effect on how fine the precipitate is, and ascorbic acid can produce a very fine precipitate as well.


Interesting - so you want to deliberately precipitate ultra fine particles (which is the opposite of our goal when refining wherein we want to precipitate the largest particles possible)

There are many factors that can/will determine particles size during precipitation with temperature & dilution being two of those factors - other metals &/or organics in solution (contamination) can be another factor in particle size during precipitation - another factor can be the precipitant itself that is used for precipitation (and there are other factors)

Therefore - taking those factors into consideration we can throw dirty solutions out the door as we can assume you intend to work with clean solutions - so ----

Dilution - yes - A dilute solution will precipitate smaller particles then a concentrated solution - therefore - yes - to deliberately form smaller particles diluting the solution would be one path to smaller particles - the more dilute the smaller

Precipitants - with the concentration of the solution(s) being equal - (& as examples) copperas will precipitate larger particles then SMB - & as you say - ascorbic acid will precipitate finer (much finer) particles then copperas or SMB

Another precipitate that will precipitate even smaller particles is stannous chloride

The problem with using stannous chloride as a precipitant is that in as much as it can create ultra fine particles that will precipitate - it can (& likely will) produce colloid particles that do not precipitate but rather stay in suspension

This is all the time I have for today

Kurt


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## kurtak (Mar 23, 2022)

cejohnsonsr1 said:


> Elements don’t form particles.


simply NOT true


cejohnsonsr1 said:


> Particles are the subatomic components of an element.



only PARTLY true

Thats all I have time for today

Kurt


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## Yggdrasil (Mar 23, 2022)

Before this gets out of hand, there is an element of semantics here.
Particle as defined in physics are electrons, atoms and smaller things like photons, quarks and so on.

In the world of refining i do not think going past molecules make sense in practical terms. 
On the theoretical term one can discuss ions and those can be "smaller" than atoms.
Not very important for our day to day practical work.

My two cents, lets get back to refining shall we?


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## cejohnsonsr1 (Mar 24, 2022)

I would only add that when precipitating you really want the objective element as finely divided as possible in order to facilitate the removal of anything else, which would be considered a contaminant.


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## kurtak (Mar 24, 2022)

Yggdrasil said:


> Before this gets out of hand, there is an element of semantics here.


semantics for sure 

semantics being the "context" within which we discuss something 


Yggdrasil said:


> Particle as defined in physics are electrons, atoms and smaller things like photons, quarks and so on.


So yes - if we are/were to discuss particles "in the context" of physics - then yes - we would discuss particle size in the context of their smallest denominator (molecules, atoms & even subatomic size)

However - this is not a physics discussion forum (although physics is indeed PART of the discussion)

Because this is a discussion forum about refining - & part of that discussion is indeed about precipitation chemistry - & therefore particle size of the precipitate needs to be discussed in the context of forming particles larger then molecules, atoms & even subatomic size (much larger) 


Yggdrasil said:


> In the world of refining i do not think going past molecules make sense in practical terms.


The fact of the matter - is that in precipitation chemistry - & for all practical terms - forming LARGE particles is our goal --- other wise we would never get our gold/silver/PGMs to precipitate

Or as I have said - in precipitation chemistry - particles size matters


Yggdrasil said:


> lets get back to refining shall we?


Therefore - IMO - in the context of precipitation chemistry (& the context of this thread) refining is what we are discussing 

As a matter of fact - as a result of cejohnsonsr1 insisting that particles are defined by their smallest denominator (atomic - subatomic) - it has caused me to do a "great deal" of research "on particles"

I think "one" (of several) days of research I had something like 12 - 15 tabs open

I will post links to "some" of that info concerning "particles" 

Kurt 
​


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## kurtak (Mar 24, 2022)

cejohnsonsr1

In as much as I will agree - that a particle can be defined by it's smallest denominator (atomic or even subatomic) that does not mean thing larger are not also particles

Granted - though large particles can also be referred to as clumps, aggregates, etc. etc. etc. does not make them less a particle

The FACT of the matter is that the "size" of a particle is determined by the amount of clumping, aggregating. etc. etc. etc. that happens in forming THE particle & what the size of THAT particle is

AND - those clumps, aggregates etc. etc. etc. are in deed referred to as particle - whether it be in the real world or the world of precipitation chemistry

To put it in context - here are just a "few" links to "particles"

Theory and Practice of Precipitation Gravimetry: Controlling Particle Size 

Note that in this link it talks about controlling "*particle*" size in precipitation 









Particle - Wikipedia







en.wikipedia.org





Note that in this link "particles" can be subatomic/atomic in size to MUCH larger - or - to macroscopic particles like powders and other granular materials. --- in other words "particles" seen by the human eye









Particle aggregation - Wikipedia







en.wikipedia.org





this link talks about forming "large particles









Flocculation - Wikipedia







en.wikipedia.org





Again a link to forming "large particles" as well as other terms/words used to describe what "a particle" is

All I have time for today

Kurt


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## kurtak (Mar 24, 2022)

Here is one more link - note under the heading nucleation it says ---------
Nucleation​An important stage of the precipitation process is the onset of nucleation. The creation of a solid *particle*









Precipitation (chemistry) - Wikipedia







en.wikipedia.org





Kurt


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## orvi (Mar 24, 2022)

kurtak said:


> Here is one more link - note under the heading nucleation it says ---------
> Nucleation​An important stage of the precipitation process is the onset of nucleation. The creation of a solid *particle*
> 
> 
> ...


As I studied chemistry, I am familiar also with physical chemistry. Just to some extent, as it is insanely deep and difficult to catch on and really understand what is going on.
Nucleation is one of the key factors that could help to ruin your gold drop. It could be disclosed similarly to crystallization - if you do the filtration diligently, and do not "overdisturbed" the solution = number of nucleation sites is lower = so there will be fewer, but bigger particles.
On the other hand, if you have AgCl cloudy solution, there is immense number of nucleation sites that start to grow much more particles = particles are smaller and more "floaty".

Just to add my perspective to the particles. From physical chemistry point of view, aggregates of particles are different from say well defined gold nanoparticles or gold filings. They could have similar size, but one have defined crystal structure, while aggregates doesn´t.
From gold refiner´s perspective - it does not matter. Forces that hold together the agglomerated particles are so strong, that you cannot "tear" them apart by mixing or while filtering. You can obviously rip apart some chunky inquarted gold sponge, but only to certain level.


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## kurtak (Mar 25, 2022)

cejohnsonsr1 said:


> I would only add that when precipitating you really want the objective element as finely divided as possible in order to facilitate the removal of anything else, which would be considered a contaminant.


Just simply & flat out not true

you do not need your precipitate to be "finely" divided in order to facilitate removal of contamination

you can remove contamination from very large & very solid objects by implementing kinetic energy (energy that it possesses due to its motion)

Boiling is an example of using kinetic energy to remove contamination from large & even solid objects

Example; - processing tungsten/silver contact points - if you put W/Ag contact points in a beaker with nitric acid even with some heat (but not boiling) you will not dissolve those points due to the silver being in a matrix of sintered tungsten

However - if you bring the nitric to a boil - the kinetic energy of boiling - will allow you to leach the silver out of the sintered tungsten matrix

We use the same principle in washing the contamination out of our gold sponge (large particles of precipitated gold) when we do the washing of the sponge by doing a simmer/boiling of the sponge with water & HCl washes

I have added a pic of washed gold sponge (contamination removed --- note that the size of some of those sponge "particles" are "about" a centimeter in size - the contamination was removed using kinetic energy

Kurt


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## orvi (Mar 25, 2022)

kurtak said:


> Just simply & flat out not true
> 
> you do not need your precipitate to be "finely" divided in order to facilitate removal of contamination
> 
> ...


I will just add, that when "boil-washing", there is synergic effect of two major physical processes - convection (or that "kinetic" factor) and diffusion. As temperature goes up, viscosity of the liquid is going down sharply. This allow more rapid movement of the liquid in these extremely small cavities and spaces in agglomerated particles.

This is also thing why washing AgCl powder work the best with boiling hot water. With regular cold water from tap, system will be equilibrating for much longer.

Diffusion is also increased with temperature, as enthropy of the system goes up = molecules are "shaking" more, enabling quicker transport of ions in solution via concentration gradient. This is very important.

When washing the gold drop with HCL, usually copper and silver contamination is partly locked up in agglomerates. So inside the particles, there is high concentration of say Ag+ or Cu2+. Outside solution contain no contaminants (if you wash with clean HCL). In accordance with basic physical laws, system want to attain the lowest energy level = all of the Cu/Ag ions evenly distributed in solution. You start heating the gold agglomerates and you synergically combine better diffusion, lower viscosity and also kinetic mixing-or convection mixing. You will probably achieve the same result also at room temperature, but it will took much much longer to get there.


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## cejohnsonsr1 (Mar 26, 2022)

orvi said:


> As I studied chemistry, I am familiar also with physical chemistry. Just to some extent, as it is insanely deep and difficult to catch on and really understand what is going on.
> Nucleation is one of the key factors that could help to ruin your gold drop. It could be disclosed similarly to crystallization - if you do the filtration diligently, and do not "overdisturbed" the solution = number of nucleation sites is lower = so there will be fewer, but bigger particles.
> On the other hand, if you have AgCl cloudy solution, there is immense number of nucleation sites that start to grow much more particles = particles are smaller and more "floaty".
> 
> ...


No. That’s just wrong in the first couple of sentences. You’re entitled to your opinion, but that’s just not right.


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## Yggdrasil (Mar 26, 2022)

cejohnsonsr1 said:


> No. Thats just wrong in the first couple of sentences. You’re entitled to your opinion, but that’s just not right.


Can you please enlighten us then, how to easy calculate the forces that drive agglomeration.

I'm not much in favour of blatant statements in most situations and certainly not in complicated matters.


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## kurtak (Mar 26, 2022)

orvi said:


> . You start heating the gold agglomerates and you synergically combine better diffusion, lower viscosity and also kinetic mixing-or convection mixing. *You will probably achieve the same result also at room temperature, but it will took much much longer to get there.*


Orvi - thank you for joining in on this discussion - I was actually hoping you would do so at some point as you most certainly have a great deal more knowledge about chemistry from its in depth technical aspect then I (having been a big part of your life story) whereas my understanding/knowledge comes from the more simple practical application of make a living refining PMs

I actually FLUNKED chemistry in high school --- if my chemistry teacher could see me now - LOL

Anyway - per the bold print - yesterday I gave the example of leaching the silver from W/Ag contact points & though yes it may/could be possible to leach the silver from the W/Ag points - at room temp - it would likely take a year or more for the acid to get to the core of the points & leach out "all" the silver - whereas by implementing kinetic energy (boiling) we are able to leach out (& recover) that silver in a day

Which is/was my point to cejohnsonsr1 - we most certainly do not need our gold drop to be "finely divided" in order to rid it of contamination - & his saying so is in fact mis-information

cejohnsonsr1 - in order to show you how/why some of the things you are posting are in fact mis-information (in other words - though they are not exactly wrong &/or completely untrue - they most certainly are NOT absolute truths & therefore mis-information)

To put it in perspective (gold needing to be finely divided to facilitate contamination removal) here is a pic of a gold ring I was given once to refine

This ring was a gold/copper (alloy) ring --- it was a 6 karat ring - so 25% gold 75% copper - copper being the contaminating metal that needed to be removed to "refine" the gold

So - knowing it was 6K - knowing the process of inquartation - & knowing the process of leaching silver from W/Ag contact points - I opted to do a nitric leach rather then dissolve the ring in AR

So I put the ring in a beaker - added my nitric/water & put it on the hot plate & brought the acid up to a boil & let it (the acid) boil for "the day" & this is the result

in this picture - you will see that after a day of boiling it in nitric acid - which indeed removed the copper (contamination) there was still enough tight bonding of the gold that the gold was able to hold the original shape of the ring

Not only was the ring boiled in nitric to remove (dissolve/leach) the copper out of the ring - it also went though several "boiling" water washes to remove the copper nitrate out of the pours of what was now pure gold sponge - gold sponge - tight enough bonded that the (gold) sponge was able to maintain the original shape of the ring

You will notice that there is a gap in that (gold sponge) ring - that gap is because a jeweler "up sized" the ring so he cut the ring - added a piece of copper in the gap & then gold plated the ring - so I ended up with a gold foil in the beaker where the piece of copper was added in the gap

In other words cejohnsonsr1 - what you see in this pic - is pure gold sponge - that was originally a gold/copper alloy

My point cejohnsonsr1 being that if you can remove a contaminating element from a sold piece of actual alloyed metal - then you can most certainly remove contamination from gold sponge (from the precipitation process) without it being finely divided (in other words *LARGE* particles of gold sponge)



cejohnsonsr1 said:


> I would only add that when precipitating* you really want the objective element as finely divided* *as possible* in order to facilitate the removal of anything else, which would be considered a contaminant.


So - per the bold print - not only is that mis-information - it is in fact bad advice - VERY bad advice

Why ?

because telling our members to intentionally precipitate their gold as finely divided as possible will lead them down a path of problems with every step in the process after precipitate - those problems being --- a problem with settling - problems with filtration - problems with washing - & problems with melting (the problem in melting being "finely divided " particles of gold blowing out of your melting dish when you put the torch to it to melt it)

Do you understand ??? 

Kurt


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## kurtak (Mar 26, 2022)

Yggdrasil said:


> Can you please enlighten us then, how to easy calculate the forces that drive agglomeration.
> 
> I'm not much in favour of blatant statements in most situations and certainly not in complicated matters.


I agree !!!!

Kurt


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## kurtak (Mar 26, 2022)

cejohnsonsr1 said:


> No. That’s just wrong in the first couple of sentences. You’re entitled to your opinion, but that’s just not right.


Please explain - otherwise all you have done is post an opinion without backing that opinion (your opinion) up

Kurt


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## orvi (Mar 26, 2022)

cejohnsonsr1 said:


> No. That’s just wrong in the first couple of sentences. You’re entitled to your opinion, but that’s just not right.


Citing from Wikipedia on "Nucleation":

"Nucleation is often very sensitive to impurities in the system. These impurities may be too small to be seen by the naked eye, but still can control the rate of nucleation. Because of this, it is often important to distinguish between heterogeneous nucleation and homogeneous nucleation. Heterogeneous nucleation occurs at _nucleation sites_ on surfaces in the system.[1] Homogeneous nucleation occurs away from a surface."

We can argue about it, but it isn´t my point here. I just pinpointed one variable out on my previous post - *one that we can largely affect by filtration and elimination of impurities before dropping the gold. *

There is *second very important variable* which could affect the drop, but you *usually have no good means of contolling it - presence of colloid-stabilizing compounds.* This is completely unintentional from our perspective - we don´t want this to happen. Most of the times, it is some leached organic matter from the boards, or decomposed fillers/lubricants/paints etc. 
When made on purpose (synthesizing gold NP), commonly additives like tetraoctylammonium salts, dialkylthiols or disulfides, citrate salts or various organic solvents like DMF etc are added to cut the growth of the particles in certain stage and simultaneously bind with formed particles strongly enough, they do not want to agglomerate with each other.

This is thoroughly studied subject. Gold nanoparticles are extraordinarily useful for so many things, that we have hundreds of methods that can produce evenly shaped particles with defined diameter EVERYTIME. From immense number of applications, I just mention one, which could be very familiar to everybody after 2 COVID years - COVID antigen rapid-tests... They use colloidal (or nano-gold) particles as part of sensoring mechanism for the presence of specific antigens of COVID-19. Everything is in the literature for precipitating gold in whatever form you want.

To your point, you are certainly right in way that you wash 0,1 micron gold drop much more quickly than inquarted sponge. That´s for sure. But settling it out and filtering will be such a pain in the... you just don´t want to go that way  we all know that inquartation work. Also washing the inquarted gold work. Also leaching the silver from sintered Ag/C motor brushes, or as kurtak said from Ag/W contacts.

After washing the finest precipitate so quickly, you will need that saved time to figure how to efficiently scavenge your values. Filter paper will be no way how to catch them. Using flocculants have it´s own downsides lowering the purity etc. But I do not want to dive into this any deeper


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## orvi (Mar 26, 2022)

kurtak said:


> Orvi - thank you for joining in on this discussion - I was actually hoping you would do so at some point as you most certainly have a great deal more knowledge about chemistry from its in depth technical aspect then I (having been a big part of your life story) whereas my understanding/knowledge comes from the more simple practical application of make a living refining PMs
> 
> I actually FLUNKED chemistry in high school --- if my chemistry teacher could see me now - LOL
> 
> ...


Nice inquart 

_Hopefully, I will finish my PhD. in short time. Still laughing at myself nowdays, imagining my high school chemistry teacher staring at me thinking... Why won´t you just study more  this was in the light of competition in "chemistry" - best ones from the school were going to represent it in "county" round, and then in whole state competition. I wasn´t able to gain enough points to pass the "school round"    _

It all comes to the point of functionality. I am nowhere any basic level of "expertise" in the physical chemistry subject, that is for sure. I just had 3 quite exhaustive courses of it during my study. I can read these simplified equations, not to calculate what will happen when I dissolve some greasy gold filings in dirty AR and then drop the gold with technical SMB  but these equations and stuff can give you numerical proof of "which direction it will possibly go" when you do this and that.

And of course, you do not need to use numbers and books. Old timers figured this out without them. It just took longer, as they used trial-error methods. But they had much more time to spend on some things than we have now


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## Yggdrasil (Mar 26, 2022)

Nice ring


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## kurtak (Mar 26, 2022)

Dorcas Nimrod said:


> The main reason I was curious is to see if my recovered product was viable for use in a DIY "PMC" product. Precious Metal Clay is a malleable clay product which can be kiln fired into solid sintered jewelry and parts. The finer the particles, the lower the temperature needed to fire and the less shrinkage.


Dorcus Nimrod --- I am sorry that this thread ended up getting so far of track from the original purpose of your question(s) - but - there was/is a great deal of mis-information being posted when it comes to our goals in the general discussion of refining processes

That mis-information needed to be addressed because as mis-information it leads to "bad advice" to new members in the beginning of their learning process

So lets get down to what it is that you actually want to do - which is to deliberately make SMALL particles - rather then large particle (wherein - generally large particles is in fact our intended goal)

When it comes to creating particles - we can in fact "control" the size of the particles we create - at least to some degree

In other words - we can create particles - within a size "range" - such as particles in a colloid size range (particles so small they will not settle but stay in suspension) & we can deliberately create particles in that range --- or we can create particles in an ultrafine range - a fine range - a course range - a large range or even very large range - or a range from ultrafine to very large

The question becomes controlling the size of the particles within the size range of our intended goal

There are a number of mechanisms we can use to control particle size - I posted "a few" of those mechanisms a few days ago - such as dilution - the precipitate we use etc. 


Dorcas Nimrod said:


> I've seen people make DIY silver clay, but was wondering if gold would be possible.


Therefore - there is absolutely no reason why you can't deliberately form particle of gold small enough to make PMC with gold instead of silver --- its a matter of controlling the particle size formation

Because - as a refiner - it is always my goal to create the largest particles possible i had to do some research to see what size particles are required for making PMC



Dorcas Nimrod said:


> If I recall, 4000 mesh is needed, which would be about 3 microns


In my research - one thing I found is that the particle size does not to be that small & can in fact be as large as 20 microns (so "about" 600 mesh)

We know that ascorbic acid will precipitate gold in "much" smaller particles size the say SMB or copperas - so we can control the particle size to smaller particles using ascorbic acid

What I don't know is how much precipitating from a concentrated solution - or from a diluted solution will affect the particle size

In other words - precipitating - with ascorbic - from a concentrated solution may well form particles 20 microns & smaller in size which would be all you need for making our PMC --- or you may need to use dilution --- so you will need to play with precipitation (concentrated - or diluted) to see where you get the particles size you are looking for

If it were me - I would start with a concentrated solution - precipitate with ascorbic acid - make a small sample of clay - sinter it & see how the sintered product turns out --- & then start working on finding the right dilution ratio - ONLY if precipitating from a concentrated solution gave me particles to large for a good PMC finished product

In other words - in as much as you deliberately want to make ultrafine particles - you could go to small in particle size which could cause other problem for making the actual clay

in other words 20 microns (& smaller) is the goal - so going to 2 microns & smaller would likely lead to other problem for making the clay

Here are some links to what I found about making PMC

In this video OwlTech had the "basic" principle for making PMC right - however he did not have the actual procedure right (getting the ultrafine metal particles evenly distributed with the binders) so his end (sintered) product had cracks





__





how to make precious metal clay - Bing video







www.bing.com





In this link - I only watched the last video (the one with the finished silver scull) which show a much better mixing of the ultrafine silver particles & the binders resulting in a much better finished sintered product





__





Making Your Own Metal Clay | Metal Clay Academy


This page is all about making your own metal clay. Here you'll find DIY tips, suppliers of metal powder and other useful resources.




www.metalclayacademy.com





This is where I found the info about 20 micron & smaller particle size





__





Society of American Silversmiths - Precious Metal Clay






www.silversmithing.com





one more link about making PMC





__





Making or Modifying Metal Clay


Making Metal Clay



redwriteblue.com





Kurt


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## kurtak (Mar 26, 2022)

A number of years ago now - we had a guy that joined the forum --- the reason he joined the forum was because he was operating a LARGE scale refinery (*KILOS* of gold per day)

They were having a real problem in their refining process

That problem was particle size & the reason it was a problem was they were actually using stannous chloride for their precipitant

As we know - SC will create not just ultrafine particles - but ultra-ultrafine particles - even colloid particles

What was interesting about that thread - was that the guy insisted that - on the advice of his (refining) chemist - the right way to precipitate their gold was to do it with SC as the precipitant

It took quite a bit of convincing him - that the problem with their refining procedure was their chemist thinking SC was the right precipitant to precipitate there gold

I am not sure how to pull that thread up - so maybe Dave or 4metals (or someone) can find it & post a link to it here

It is a classic case of where particle size in refining matters

Kurt


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## orvi (Mar 26, 2022)

There are possibilities how to "tune" the precipitation process and very roughly make "larger" or "smaller" particles. One of the key factors is dilution. You simply cannot make defined nanoparticles all the way from concentrated solutions.

Kurtak mentioned guy who used stannous chloride to precipitate gold. You can very clearly see how dependent is the size of the formed particle in correlation to concentration. When testing weak Au3+ solutions, stannous will give you fainf violet colour - that is actual nano-gold (particles so small they could bend the light). If you go to test stronger Au3+ solution, you will observe black colouration. That means not only more particles are present, but actually bigger ones - as they just block light.

Then after knowing this, there is second variable and that is stabilizing compounds present. One of very basic stabilizing compounds to produce gold nanoparticles is some sort of citrate or citric acid. Maybe there is some similarity with ascorbic acid (they are structurally little similar and both bear polar protic groups) - so MAYBE that is the reason ascorbic acid produce somewhat smaller particles.

These two variables (concentration and presence of some stabilizers) are major. 
When I was to produce some "smaller or bigger gold particles" I would firstly go with clean gold solution and say ascorbic acid precipitant, and try different dilutions for the drop. Size of the particles could also be very roughly judged by the colour of the precipitate. Darker meaning finer 

Hope that this maybe somewhat help you to tune the process for good results. Inform us how it´s going if you attempt some PMC experiments


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## Bruno1971 (Mar 26, 2022)

kurtak said:


> semantics for sure
> 
> semantics being the "context" within which we discuss something
> 
> ...


Hi.may i ask a dumb qustion?if i add naoh to solution will drop all salts from solution and all acids are neutrolised.after filtering all salts and than add hcl to the salts will redisolve.is that right?


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## kurtak (Mar 27, 2022)

Bruno1971 said:


> Hi.may i ask a dumb qustion?if i add *naoh*


First of all - per the bold print - if you are going to use a chemical "formula" (instead of the actual chemical name) when posting - please use the "proper" formula is it is written in chemistry --- its easier on the eyes when reading the post & gives more clarity to understanding what is being posted

Example; - sodium hydroxide (the chemical "name") the proper formula is NaOH - not naoh - which looks more like a misspelled word when reading it instead of a chemical formula 

Example; - it is more difficult to read/understand --- if i dissolve ag with hno3 then add nacl to precipitate agcl how much nacl do i need

easier to read/understand --- if I dissolve Ag with HNO3 then add NaCl to precipitate AgCl how much NaCl do I need

So please post chemical formulas as they are actually written


Bruno1971 said:


> to solution *will drop all salts from solution* and all acids are neutrolised.after filtering all salts and than add hcl to the salts will redisolve.is that right?


Per the bold print - not exactly - it depends on the metals in the solution

In as much as most metals can be dissolved with an acids (depending on the metal & the acid) "some" metals will "also" dissolve with bases (NaOH being a base) 

Not all metals - once dissolved - will precipitate at Ph 7 (neutral)

Examples; - metals like Pb, Cd, Mg - once dissolved - can stay dissolved at Ph 7 - so the Ph needs to be raised above 7 to drop them

To drop dissolved lead (Pb) you need to raise the Ph to 8.5 - 9 --- Mg (once dissolved) will stay dissolved until Ph is raised to about 11

Some metals will drop out at a Ph of less then 7 - but will then re-dissolve at Ph above 7 

So what drops out of solution & when it drops out depends somewhat on Ph

Example; - aluminum --- nitric acid does not dissolve Al but HCl does - BUT - Al will also dissolve in a base - therefore you can also dissolve Al with NaOH

Therefore - if you dissolve Al in HCL - then adjust the Ph to about 6 it will start dropping - but - at about Ph 8.5 - 9 & above it starts re-dissolving

Also - the Ph that a metal will drop out can depend on the oxidation state of the dissolved metal

Example; - iron - Fe3 will "start" to drop out at about Ph 4.5 - 5 --- but Fe2 can stay dissolved until a Ph of about 9.5 - 10.5 

In other words - the answer is NO - simply adjusting Ph to 7 will not insure that ALL dissolved metals have dropped out



Bruno1971 said:


> after filtering all salts and than add hcl to the salts will redisolve


However - to answer this part of the question - yes - whatever metals drop out with NaOH at Ph 7 (which may not be all the metals) will re-dissolve

My question is --- why would you want to do this in the first place --- why would you want to use NaOH to drop the metals as there hydroxides - just to re-dissolve them 

It makes no sense to dissolve your metals in the first place - then drop them out as there hydroxides - just so you can re-dissolve the same metals you dissolved in the first place ???

Kurt


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## kurtak (Mar 27, 2022)

orvi said:


> *When made on purpose (synthesizing gold NP)*, commonly additives like tetraoctylammonium salts, dialkylthiols or disulfides, citrate salts or various organic solvents like DMF etc are added to cut the growth of the particles in certain stage and simultaneously bind with formed particles strongly enough, they do not want to agglomerate with each other.
> 
> *This is thoroughly studied subject. Gold nanoparticles are extraordinarily useful for so many things, that we have hundreds of methods that can produce evenly shaped particles with defined diameter EVERYTIME*. From immense number of applications, I just mention one, which could be very familiar to everybody after 2 COVID years - COVID antigen rapid-tests... They use colloidal (or nano-gold) particles as part of sensoring mechanism for the presence of specific antigens of COVID-19. Everything is in the literature for precipitating gold in whatever form you want.


Per the bold print - here is an interesting read on the deliberate making of gold NP









Colloidal gold - Wikipedia







en.wikipedia.org





Gold NP is at the foundation of using stannous chloride for testing our solutions to see if we have gold in them

Testing our solutions with SC is the only time in the refining process that we actually intentionally want to forum gold NP (as you have described)  

Kurt


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## Bruno1971 (Apr 1, 2022)

kurtak said:


> First of all - per the bold print - if you are going to use a chemical "formula" (instead of the actual chemical name) when posting - please use the "proper" formula is it is written in chemistry --- its easier on the eyes when reading the post & gives more clarity to understanding what is being posted
> 
> Example; - sodium hydroxide (the chemical "name") the proper formula is NaOH - not naoh - which looks more like a misspelled word when reading it instead of a chemical formula
> 
> ...


Thanks for the answer.A lot of times we (pioners)use a lot of HNO3.Boiling the solution to get rid of that extra nitric acid its time consuming and the nitric vapors are dangerous.So if we drop all the metals out of solution using NAOH and than we redisolve with HCL than we will have the same solution just out of nitric acid.This is my first time that i post in this forum and i know that my question is dumb please forgive me for my mistakes.thanks


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## Saddiq NG (Jul 4, 2022)

I will like to ask a question bit off the topic. The question is as for us refiners does particle size affect our end result? For example you are expecting a yield of say 2grams gold but you end up with 1gram as a result of smaller colloidal or even invisible gold particles not settling.


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## cejohnsonsr1 (Jul 4, 2022)

Saddiq NG said:


> I will like to ask a question bit off the topic. The question is as for us refiners does particle size affect our end result? For example you are expecting a yield of say 2grams gold but you end up with 1gram as a result of smaller colloidal or even invisible gold particles not settling.


No. If you expect 2 gr and only get 1 gr, something is wrong either with your calculations or your process. Gold is heavy and will clump. If it precipitates, it will settle, though some minuscule amount might remain suspended. That’s why you should keep a stock pot.


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## Saddiq NG (Jul 5, 2022)

cejohnsonsr1 said:


> No. If you expect 2 gr and only get 1 gr, something is wrong either with your calculations or your process. Gold is heavy and will clump. If it precipitates, it will settle, though some minuscule amount might remain suspended. That’s why you should keep a stock pot.


I think the process I use is the problem then, cos I used to:
1. Over dilute the solution with six time it's original volume with water.
2. I do not kill nitric acid but weaken it through the excess dilution.

Could this be the reason for the low yield cos there was a time I recovered 1.3 grams brown gold powder from IC chips, I decided to refine it again only to end up with a powder weighing 0.8grams.


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## Yggdrasil (Jul 5, 2022)

Saddiq NG said:


> I think the process I use is the problem then, cos I used to:
> 1. Over dilute the solution with six time it's original volume with water.
> 2. I do not kill nitric acid but weaken it through the excess dilution.
> 
> Could this be the reason for the low yield cos there was a time I recovered 1.3 grams brown gold powder from IC chips, I decided to refine it again only to end up with a powder weighing 0.8grams.


Why do you use AR on powders?
Much better HCl/Peroxide or even bleach or other chlorine source.


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## Saddiq NG (Jul 5, 2022)

Yggdrasil said:


> Why do you use AR on powders?
> Much better HCl/Peroxide or even bleach or other chlorine source.


I tried looking for hydrogen peroxide in the chemical store but can't find one. As for the bleach I don't fell comfortable with it as the bleach here in Nigeria might be different from yours


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## Yggdrasil (Jul 5, 2022)

No problem.
It is just more convenient to bypass the Nitric.
Chemists, hairdressers and such may have 12-20% hydrogen peroxide.
Which should be good enough.
It is sometimes called chlorine free bleach.
You can use chlorine tablets for swimming pools and drip HCl on them and divert the chlorine gas to the beaker. 
If your glass ware is not good this may be risky though.
Chlorine is nothing to be careless with.


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## Saddiq NG (Jul 5, 2022)

Yggdrasil said:


> No problem.
> It is just more convenient to bypass the Nitric.
> Chemists, hairdressers and such may have 12-20% hydrogen peroxide.
> Which should be good enough.
> ...


Thanks man


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## GoIdman (Jul 5, 2022)

Saddiq NG said:


> I tried looking for hydrogen peroxide in the chemical store but can't find one. As for the bleach I don't fell comfortable with it as the bleach here in Nigeria might be different from yours


Try looking in pharmacy for peroxide, i think 10% is the biggest concentration you will get, but that works just fine. You can also try beauty salon suppliers as *#Yggdrasil *has mentioned.. Beauty salons also use peroxide on different hair whitening processes.

Hope this helps.

Be safe

Pete


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## grainsofgold (Jul 5, 2022)

if your wanting small particle gold size to use in PMC , why not atomize gold ? 

There’s a fellow in NY that does this. Can’t recall his name or company at the moment.


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## cejohnsonsr1 (Jul 6, 2022)

Saddiq NG said:


> I think the process I use is the problem then, cos I used to:
> 1. Over dilute the solution with six time it's original volume with water.
> 2. I do not kill nitric acid but weaken it through the excess dilution.
> 
> Could this be the reason for the low yield cos there was a time I recovered 1.3 grams brown gold powder from IC chips, I decided to refine it again only to end up with a powder weighing 0.8grams.


Dilution won’t remove excess nitric. For that amount of gold you probably only need to add the nitric a few drops at a time so as not to have much excess. And there’s really no need for such extreme dilution. It just creates more waste. If you don’t have a significant excess of nitric, SMB will consume it during precipitation. It’s also not unusual for a 2nd refining to produce a smaller yield. How much smaller depends on how clean and pure your 1st refining was. You should also do a stannous test to make sure you actually precipitated all the gold out of solution.


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## Yggdrasil (Jul 6, 2022)

grainsofgold said:


> if your wanting small particle gold size to use in PMC , why not atomize gold ?
> 
> There’s a fellow in NY that does this. Can’t recall his name or company at the moment.


I think he is afraid he is loosing gold due to colloids.
The more concentrated, the larger the particles generally speaking.


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## Saddiq NG (Jul 6, 2022)

Yggdrasil said:


> I think he is afraid he is loosing gold due to colloids.
> The more concentrated, the larger the particles generally speaking.


That's the truth I'm I believe I'm loosing gold alot because here in Nigeria we takeg e-waste business seriously, every e-waste from cell phone, smart phone, laptop, desktop etc have a specific price. The more the gold the more the price and they always increase or decrease in price directly proportional to current gold price and the naira to dollar rate. 
So if you buy it you can calculate what you expect from it and hence any mistake that leads to lesser gold yield, will result in loss.


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## Yggdrasil (Jul 6, 2022)

Well with the diluting you do, the dropped gold will be very very fine. 
So it is easy to loose it to waste through filters and all, if you don’t have a stock pot at least.

There is NO reason to use AR for e-waste unless it is bond wires. 
Use AP aka CopperChloride etch to liberate the gold from fingers, plating and such.
Try to run concentrated HCl/Chlorine or Peroxide to dissolve the Gold, then drop with SMB as usual.
The drop will be fast and well defined.


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## Saddiq NG (Jul 6, 2022)

Yggdrasil said:


> Well with the diluting you do, the dropped gold will be very very fine.
> So it is easy to loose it to waste through filters and all, if you don’t have a stock pot at least.
> 
> There is NO reason to use AR for e-waste unless it is bond wires.
> ...


Thank you once again. And good news i have ordered hydrogen peroxide finally. I expect it to reach me in one week time.


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