# Silver Stuck in Solution



## jeanpuffx (Dec 7, 2021)

After dissolving some ore in HCl/Cl2, I added saturated ammonium chloride to precipitate out most of the Pt. The resulting slurry was filtered and yellow salt was separated. The salt was dissolved in clorox solution which hydrolyzed almost all the base metals and any PGM except for silver. I can't seem to get it out. Any ideas as to why?


----------



## FrugalRefiner (Dec 7, 2021)

I guess I don't understand your questions.

How do you know there was any silver in your ore?

Why do you believe you have silver stuck in solution?

Silver is barely soluble in chloride solutions (and only if the solution is very high in Cl-), so it is unlikely you would have any silver in any of your solutions.

Dave


----------



## jeanpuffx (Dec 7, 2021)

Thanks for the response. I also agree with you. there shouldn't be any silver in my sample.
I used ICP to analyze my solution (after it was acidified and boiled for a couple of hours) and the ore dissolve. In both results, there was silver.


----------



## jeanpuffx (Dec 8, 2021)

jeanpuffx said:


> After dissolving some ore in HCl/Cl2, I added saturated ammonium chloride to precipitate out most of the Pt. The resulting slurry was filtered and yellow salt was separated. The salt was dissolved in clorox solution which hydrolyzed almost all the base metals and any PGM except for silver. I can't seem to get it out. Any ideas as to why?


edit: Pt was not hydrolyzed and stayed in solution. Silver is only thing stopping me from reducing the Pt with hydrazine.


----------



## Geo (Dec 8, 2021)

What was the percentage of silver in solution? How much solution?


----------



## orvi (Dec 8, 2021)

ore + acid = mess 
usually, treating ore this way does not produce desired results. and often leave a whole bunch of values undissolved.
but if it is pure enough (just inert "rock" like quartz), OK, why not.
ammonia+chlorine = NCl3 danger 
just saying

but this aside. assuming silver in original ore, it shouldn´t dissolve that well in the mixture - formed AgCl isn´t very soluble. in concentrated HCl to some extent, but not much. if the solution was filtered prior to NH4Cl Pt drop, majority of silver was removed. some dissolved in liquor will pass to the ammonium chloroplatinate, some will stay in the filtrate (dilution of HCl could cause Ag to precipitate, altough NH4Cl is also a chloride, so it will balance somwhere  )
all in all, quantity of Ag won´t be super high. if you are aiming to just salvage the platinum, this would produce good starting material for burn-melt-sell sequence. if you are aiming for pure metal, you will refine it anyway.


----------



## jeanpuffx (Dec 8, 2021)

orvi said:


> ore + acid = mess
> usually, treating ore this way does not produce desired results. and often leave a whole bunch of values undissolved.
> but if it is pure enough (just inert "rock" like quartz), OK, why not.
> ammonia+chlorine = NCl3 danger
> ...


Thanks for the help. I am still thinking about what to do next. Maybe another precipitation? 

Yes, i am aware of the chloramines. I made sure the reaction was done under ventilation and I added the reagent drop by drop. 

The original amount was around 2 g/l and the amount in my pt dissolved solution is 0.2 g/l. I did not filter the solution prior to the ammonium chloride drop. 

Another question I had was why it was still dissolved even after adding clorox (with a small amount of caustic to help raise the pH- i forgot to bring this up)? I am surprised it did not precipitate out.


----------



## orvi (Dec 8, 2021)

hmmm, this will be more complicated.

original ammount of what was mentioned 2g/L ? you mean silver or platinum by this number ?
with that low ammount of Pt, drop with NH4Cl wouldnt be that efficient, i suppose, but there are far more experienced PGM refiners than me  maybe i will wait for more knowledged members to discuss this.
but in terms of the good recovery, from my experience, i will try to obtain some alkylamine for precipitation. 
i once had very dilute solution of PGMs and there was a good ammount of base metals and other junk as well. very straightforward was to add n-octylamine hydrochloride to it, platinum complex with octylamine is of very low solubility in water. it is somewhat fluffy and for large quantities this could be serious pain to work with, but for small ammounts of platinum, it could scavenge it pretty well. but next step will likely be incineration of obtained complex to produce very impure sponge. but at least, you will recover and concentrate high percentage of PGMs from the pot.

with pH rise above 7, silver wouldnt be that happy in solution. too high pH and platinum will start to drop from the solution too. but in chloride solutions, silver will be still somewhat soluble despite the pH rise. 
there is a method for refining PGMs - bromate hydrolysis. look it up here on the forum, very useful and expert opinions and procedures were given.

with the next batch, i could advise filtering the solution after dissolving the ore. i cant imagine that being clear solution with all kinds of mixed stuff in the juice 
or maybe find more viable way of concentrating the values by means of gravitational separation (sluice/pan), and then smelting the actual ore to get the metal dore. with clean metal, all this would be much more easy and straightforward
also look up "platinosis", wikipedia should be enough. if you didn´t already done this  
stay safe and wear good gloves with platinum


----------



## jeanpuffx (Dec 9, 2021)

Geo said:


> What was the percentage of silver in solution? How much solution?


Hi the original amount of Ag was around 2 g/l and the Ag in my pt dissolved solution is 0.2 g/l. Sorry for the lack of clarification.


----------



## jeanpuffx (Dec 9, 2021)

jeanpuffx said:


> Thanks for the help. I am still thinking about what to do next. Maybe another precipitation?
> 
> Yes, i am aware of the chloramines. I made sure the reaction was done under ventilation and I added the reagent drop by drop.
> 
> ...


I wanted to touch upon the chloramine issue. I ran a few experiments a while back on whether chloramine formed rapidly when sat. ammonium chloride was added to bleach (~12%) and vice versa. When I conducted it at room temp and dumped 100 mL of bleach into 200 ml sat ammonium chloride while stirring, nothing really happened, same when added in reverse. When done again but heated to around 60 C, 5-10 small bubbles formed and then stopped. FYI I did this all under ventilation and wore proper PPE! 

Interestingly, I got a good amount of foaming when I added clorox to a slurry of Pt yellow + water (pH ~ 2-3). 

I do know that ammonia and bleach forms chloramine. My guess is the foaming was mostly caused by chlorine gas, not chloramine? Any clorox will readily produce chlorine at a low pH. But ammonium ion seems to be different and safer? 

The ion is in equilibrium: 
NH4+ <-> NH3 + H+ 
and does form ammonia when the pH is high- heating up sat ammonium chloride at pH > 8 will turn my pH paper blue (basic) when exposed to its vapors. At low pH, the pH paper will not change color when exposed to the vapors.


----------



## jeanpuffx (Dec 9, 2021)

orvi said:


> hmmm, this will be more complicated.
> 
> original ammount of what was mentioned 2g/L ? you mean silver or platinum by this number ?
> with that low ammount of Pt, drop with NH4Cl wouldnt be that efficient, i suppose, but there are far more experienced PGM refiners than me  maybe i will wait for more knowledged members to discuss this.
> ...


yes I am taking a lot of precautions to avoid platinosis. 

The original amount of silver was ~2 g/L and after precipitation, it was 0.2 g/L. The platinum concentration was around 10 g/L I believe. 

I did read about bromate hydrolysis. Bromate is somewhat expensive and I did not have it readily available. 

Thanks for the advice!


----------



## orvi (Dec 9, 2021)

when the precipitate is formed, which is of large surface area, it has a tendency to "drag" other substences with it. silver chloride could possibly stick to the vast surface of ammonium chloroplatinate. being of that low solubility, it dont wash away very easily. filtering the solution before the drop could reduce this ammount. chilling down the solution also help silver to come out of solution as insoluble AgCl. dilution too, but for next platinum drop step, it is not the best approach, as it will impair recovery.
now when i know the supposed concentration of platinum in the liquid, i take back the word about using octylamine to scavenge it  with this quantity, it will be very painful recovery method.


----------

