Simply heating silver chloride will not 'drive off chlorine'
I have done this with an oxy-propane torch and ended up with fine
silver but the heat required is quite high and dealing with the
liberated chlorine without an industrial scale ventilation system is
a real problem.
James Binnion
@James_Binnion
James Binnion Metal Arts
360-756-6550
I used to do my own refining, when acid prices were reasonable. Now
it is more economical to send it away.
But as a theoretical point, the silver chloride can be melted safely
if one combines powdered activated charcoal with borax. Charcoal will
absorb all the gases emitted during melting process. That is how the
gas mask works. Installing charcoal filter on the exhaust hood, will
make 100% environmentally safe.
Remaining solution after precipitation of the silver is also easy to
handle. Just add enough baking soda to neutralize acid completely (
until all fizzing stops and then some more to be sure ). What you
have
at this point is a harmless salt solution. ( No need to write out
reaction ).
Leonid Surpin
after dropping out the silver with salt solution (or hydrochloric acid if you like)
I’ve seen reference to using hydrochloric acid like this before, but
my chemist friend tells me this won’t work. Anyone have another
opinion?
John, as others have by now pointed out, this is a bad idea. I tried it once. Filled a studio with acrid blue chlorine fumes.
Actually, the first time I read this thread my thought was “Send it
to a refiner”. As I recall the ingot in question is 5 pounds or
something - large, anyway. Setting up a refinery somewhere and
buying the chemicals to handle that is pretty out there. I just
posted that for chemical curiosity reasons, and I’m happy to have
people tell me/us their own experiences with it. You could also deal
with chlorine by simply bubbling it through water - gives HCl, but
that’s better than gassing the neighborhood. But then, again, you
run into much more of everything in effort and cost than just
sending it to the pros.
But as a theoretical point, the silver chloride can be melted safely if one combines powdered activated charcoal with borax. Charcoal will absorb all the gases emitted during melting process. That is how the gas mask works. Installing charcoal filter on the exhaust hood, will make 100% environmentally safe.
You would need a charcoal filter the size of a small room to handle
the volume and velocity of the ventilation system necessary for
this. And your sugestion of adding charcoal to the flux will not work
as again not enough volume of charcoal to capture all the chlorine.
Remaining solution after precipitation of the silver is also easy to handle. Just add enough baking soda to neutralize acid completely ( until all fizzing stops and then some more to be sure ). What you have at this point is a harmless salt solution. ( No need to write out reaction ).
Depending on where your shop is located the neutralized acid can be
considered a hazardous waste (metals content) and require “proper”
disposal. If this is the case and you are in business and were to
pour it down the drain and get caught, The fines would be quite
serious. In California many of the larger cities have sewer
departments that actually monitor and analyze the waste water in the
sewer and have cited small manufacturers for things like pouring
tumbling effluent down the drain because it has metals content. The
metal messes with the waste treatment facilities. This was the point
I was trying to make. Yes it is no problem to neutralize the acid
waste but you still have a solution that may be regulated as to how
you dispose of it. Just because it is no longer an acid doesn’t mean
it is not considered hazardous waste.
James Binnion
@James_Binnion
James Binnion Metal Arts
360-756-6550
G’day; When I was into very high vacuum systems (long time ago) we
sometimes used melted silver chloride to use as a non-outgassing
sealant. I never experienced any evolution of chlorine during the
melting. Maybe I didn’t heat it strongly enough to break the bond.
As someone else mentioned, silver chloride heated strongly on a
charcoal block produced a silver button with no chlorine.
But I used to silver glass and non conductive materials by adding
ammonia to the silver chloride suspension until it just dissolved.
The addition of a sugar or some sort - I used sucrose - and warming,
resulted in a perfect silver mirror on any very smooth surface. Only
one problem. If one allowed the ammonia-silver solution to dry out,
crystals of silver azide were produced. This is a shock sensitive
powerful explosive, as one of our lab folk discovered - accidentally!
The boss happened to be out; just as well. Young Henry would have got
the boot!
I've seen reference to using hydrochloric acid like this before, but my chemist friend tells me this won't work.
It is important to know the composition of the solution we are
talking about.
But let’s assume that it is AgNO3 + H2O ( standard product of one of
the refining stage ) without any residual acid.
Adding hydrochloric acid or HCl theoretically would result in the
reaction AgNO3 + HCl = AgCl + HNO3, giving us silver chloride (AgCl)
which was the goal.
But I said theoretically, because even if reaction is possible on
paper, the real world is different and your friend may be right.
Sometime for reaction to take place a catalyst is required. This may
be the case. I simply do not know.
From practical point of view, it is never done in practice because
hydrochloric acid much more expensive that a table salt. So whether
reaction works or not is of no practical significance.
Leonid Surpin.
You would need a charcoal filter the size of a small room to handle the volume and velocity of the ventilation system necessary for this. And your sugestion of adding charcoal to the flux will not work as again not enough volume of charcoal to capture all the chlorine.
With all due respect, this is not a theory but practice as old as
the trade itself.
But let’s me address your concerns factually:
Let us say we are melting 200 grams of silver chloride. How much
chlorine is in there?
The mole of silver chloride is : Ag atomic weight is 108, Cl atomic
weight is 35.5, so the mole of AgCl = 108 + 35.5 = 143.5 grams. We
have 200 grams so 143.5 relates to 35.5 as 200 relates to X, and
therefore X = (200 * 35.5)/143.5 = 49.477 approximated to 49.5 grams
of chlorine.
Chlorine density is 2.6 times of the air. Since air density is
0.00128 grams / mili Liter ( gr/mL ), the chlorine density is
0.003328 gr/mL That means that 1 liter of chlorine weighs 3.328 grams
and, in our case, 49.5 grams of chlorine would occupy 14.8737 liters,
or let’s round to 14.9 liters.
How much charcoal do we need to absorb 14.9 liters of chlorine?
Without doing any more calculations I will use empirical
observation. Average human breathes 15 times a minute and uses 45 to
60 liters of air every minute. A gas mask filter, which is simply a
container filled with activated charcoal, will keep wearer alive for
many hours filtering air from pollutants. The size of the gas mask
filter, I do not have in front of me, but I am sure not larger then 8
X 4 X 2 inches, or somewhere in that area.
This small container has capacity of filtering thousands liters of
air, so your assertion that we would need filter of the size of a
small room, does not stand up under the examination.
As far as using charcoal as flux additive you are wrong again. A
single gram of activated charcoal has a surface area of 400 square
meter to 1500 square meter, so volume is not a problem at all.
I am wondering if I mentioned in the original post that activated
charcoal should be used. If I did not, then it would explaine the
confusion. I assumed that my mentioning of gas mask would be
self-explanatory.
Leonid Surpin.
As someone else mentioned, silver chloride heated strongly on a charcoal block produced a silver button with no chlorine.
You are correct. The chlorine will be absorbed by the charcoal
block.
Leonid Surpin
my chemist friend tells me this won't work. Anyone have another opinion?
I’m hoping that at this point this whole thread is moot, and the
ingot’s on the way to the refiner… Anyway, just out of curiousity,
I looked around a bit in Wikipedia. Seems if you treat a solution of
silver nitrate with NaOH you’ll get silver oxide, also insoluble,
which decomposes at 200c. Just for interest, it could have potential.
Or, one could just use Helen’s and other’s way of copper - me, I’d
send it out…As Jim said long ago, just having 25 gallons of HNO3
around to do that big of a job is bad enough…
G’day;
I've seen reference to using hydrochloric acid like this before, but my chemist friend tells me this won't work.
Sorry about your chemist friend but adding HCl to the collection of
student discards from experiments really did work.
My wife and I performed the reclaiming of silver many times using
HCl to precipitate the silver as chloride with no trouble. We used
HCl because it was to hand and very cheap in bulk. So why should we
spend extra time dissolving salt? We were both very busy people. And
it worked well.
Cheers for now,
JohnB of NZ
G’day.
People are still on about large volumes of chlorine being evolved
when silver chloride is heated. I melted silver chloride quite a few
times to use as a high vacuum sealer, and certainly never even smelt
a trace chlorine - and I assure you, I am sensitive to the smell!
Cheers for now,
JohnB of NZ
Many catalysts are produced by coating aluminum oxide- 0r similar
carrier with a metal chloride solution and reducing this to the pure
metal with hydrogen. This produces HCl vapor ( about as noxious as
chlorine). This isn’t an artist studio or kitchen table technique.
Another way to reduce silver chloride is add sodium carbonate (
washing soda) and heat to about 650C. the silver ends up as pure
particles and sodium chloride (table salt) which is washed out with
water.
I am a little familiar with the catalyst production and regeneration
method using hydrogen.( been a while). but not the other one.
jesse
Adding hydrochloric acid or HCl theoretically would result in the reaction AgNO3 + HCl = AgCl + HNO3, giving us silver chloride (AgCl) which was the goal.
Couldn’t find this original yesterday – Nope, ain’t ever gonna
happen, catalyst or not.
How much charcoal do we need to absorb 14.9 liters of chlorine?
Even though all that Leonid says is correct on paper, I’ll point out
that 14.9 liters of pure chlorine is a LOT of gas. I’m sure his
method of using activated charcoal is correct, I’m not disputing it
at all, haven’t done it, not gonna. Just for those who are following
this thread, as Jim said about this whole process: What Leonid
didn’t figure was how much space that much gas will fill at a lethal
level if you do something wrong. I won’t bother with actually doing
that because it’s pedantic, but it would certainly sterilize a large
basement, since Cl is considerably heavier than air - it hugs the
ground. I would hope that those who don’t have a lot of resources
will consider this thread as I do - an interesting bit of
mental/chemical gymnastics and no more. For all the effort and
hazard that this process involves, Leonid’s example will yield 4.84
oz. of fine silver at 100% efficiency, or $67.37 at today’s market.
Send it to the refiner…
Boy! The chemistry in this thread just escapes me.
but my 2c worth
I’d wonder why this guy who apparently knows enough to process the
silver somewhat, is willing to sell to you when he could scrap the
stuff himself. I’d also wonder how much of a discount from market
price I would need considering the risks and costs involved.
Risk…it may not be silver at all or some lower count silver. This
was, after all, some guy in his garage melting stuff.
Cost…It should be refined before you can use it or you risk(hehe)
inferior product after whatever labor (more cost) you supplied. Do
you want to specula te that the metal is good enough as is? This
was, after all, some guy in his garage melting stuff.
I melted silver chloride quite a few times to use as a high vacuum sealer, and certainly never even smelt a trace chlorine - and I assure you, I am sensitive to the smell!
Hi John from NZ. I have no practical experience with this - I feel a
little responsible because it was I who brought up the process to
begin with, and I have no doubt that you did what you said - perhaps
you mean literally that you melted it to liquid. But if you reach
the point where you break the bond and get silver metal, as Jim said
he did (once!), then you WILL get chlorine. whether you didn’t go
that far or you had something else happening, like Leonid’s carbon
thing, I don’t know. But if you get silver metal from AgCl, you will
also get chlorine. Fundamental stuff.
Adding hydrochloric acid or HCl theoretically would result in the
reaction AgNO3 + HCl = AgCl + HNO3, giving us silver chloride
(AgCl) which was the goal.
Nope, ain't ever gonna happen, catalyst or not.
There are many thousands, probably millions of reactions that look
good on paper but won’t necessarily work in reality. There are also
many ways to skin a cat or recover silver from silver nitrate. Some
people have said do such and such rather than buying large quantities
of hazardous nitric acid, but the person who asked the last question
on this subject has said that he already has a large amount of silver
already dissolved in nitric acid which has then been diluted with
distilled water. He therefore doesn’t need to buy any nitric acid.
It’s a no brainer really, just use the very simple adding copper
metal displacement method. Sacrifice some cheap copper in an
essentially safe (or much safer than other quoted methods) method to
reclaim valuable silver metal. It’s safe (relatively), it’s fun and
it’s cheap (considering he already has it in nitric acid). He also
has copper apparently.
Helen
UK