# Precipitating Silver Chloride with Zinc Oxide Powder



## unclephester (Sep 7, 2016)

Hello All,

I am a home amateur refiner and new to this forum. I am comfortable and experienced with cementing silver with copper, then creating shot for the silver cell to get 999. 

I just recently ran a few batches of silver chloride using Lye and Sugar, and as I understand it, this is supposed to be 999 without using the silver cell? Can anyone confirm this? (I haven't smelted and tested yet, as it's still drying).

I recently saw a video on YouTube showing the instant precipitation of fine powder (Sponge) from silver chloride using Zinc powder 99% and sulfuric acid.

YouTube link: https://www.youtube.com/watch?v=_EDclVVJBKU&index=2&list=LLwBP72ZHRI0ZYydY1_g8wyw

I have not seen this method before, and was curious if anyone had more information on this subject, as I have been unable to find any reading material on this so far. The claim is that you get very pure silver using this method.

Not being a chemist, I am admittedly weak in my chemical relationship's aptitude, although I am willing to learn if I can find information, but I have been unsuccessful so far. Therefore, I have come here in hopes of a more experienced person who might be able to share any insights... 

My questions are:
(1) what volume of zinc oxide to silver chloride should be used or how to calculate?
(2) what volume of sulfuric acid to silver chloride should be used or how to calculate?
(3) is this truly a viable way to get 999 silver without a phase 2 silver cell? _(after adding HCI to dispose of the zinc, and then washed well)._

any help is surely appreciated.


----------



## nickvc (Sep 7, 2016)

Welcome to the forum.
There is a search box, in fact two top right of your screen, if you wish to search for topics.
I used to use zinc dust mixed into the silver chloride and then add a little dilute sulphuric as my main method to convert it to elemental silver and it works well but as with all methods of conversion from chloride to elemental silver you need to mix the material thoroughly for complete conversion, you can also use old iron for the same purpose but again agitation and mixing is needed for complete conversion.
The trick with silver chloride is to wash it thoroughly before and after the process and if done right 999 silver is achievable, in other words if you leave copper or any other metal in your solution before conversion it too will convert to elemental metal spoiling the purity of your silver, in honesty converting silver chloride into silver is easy with small volumes whichever method you choose but it can become troublesome in larger volumes.
The beauty of using zinc and sulphuric is that the sulphuric will dissolve the zinc and possibly a little silver but leave a very clean product to melt, same with iron but you can remove the iron using a magnet or simply picking the pieces out.
I can't remember the exact ratios but try a small volume and experiment.
Good luck and let us know how you get on.


----------



## Lino1406 (Sep 9, 2016)

Theoretically for 100g silver you need 30.3g zinc. However use a little more


----------



## unclephester (Sep 10, 2016)

nickvc said:


> There is a search box, in fact two top right of your screen, if you wish to search for topics.



I actually used the search boxes first, but was unable to find any good info on zinc powder with silver. My results came back with pages and pages of hits, but none mentioning specifics of this process that I could find. Perhaps my search criteria was not well enough defined. is there a certain process name I should look up? I know the copper transfer method is known as "cementing", but is there a name for the zinc powder/sulpher method I should look up?



nickvc said:


> The trick with silver chloride is to wash it thoroughly before and after the process and if done right 999 silver is achievable, in other words if you leave copper or any other metal in your solution before conversion it too will convert to elemental metal spoiling the purity of your silver



I always rinse the silver chloride extremely well ( I believe), and do not move past the rinsing until the rinse water is absolutely clear like drinking water (this usually takes a several washes). Thank you for that advice.



nickvc said:


> I used to use zinc dust mixed into the silver chloride and then add a little dilute sulphuric as my main method to convert it to elemental silver and it works



Thanks for that. I was not aware that the sulpheric acid needed to be dilute. I have 2 forms of sulpheric acid, (1) is from battery acid bought at the auto store, which i understand to be somewhere between 32-40%, and I have Rooto Professional drain cleaner, which I understand is 99% sulphuric acid. I assume the battery acid would be the better option if i understand you correctly?

I am running a new batch of about 8-9 oz now. I plan to use the zinc powder/sulpheric process on this. I will let you know how that turns out.

thanks for the help, I really do appreciate it!


----------



## unclephester (Sep 10, 2016)

Lino1406 said:


> Theoretically for 100g silver you need 30.3g zinc. However use a little more



Wow, so it sounds like the conversion is about 3:1 just like copper conversion?

I was not aware of that. I had bought a 2 oz bottle (57 grams to be precise) for checking this method out, but it looks like I will need quite a bit more  

Any suggestions on how much dilute sulphuric acid to add for a 8 oz batch? I was thinking something like 5ML maybe? but to be honest, I really have no idea what the calculation should be.

is there a calculation similar to the 3:1 ratio recommended above for the amount of dilute sulphuric acid to add?

thanks to all for the friendly advice!!


----------



## nickvc (Sep 11, 2016)

From memory you do not need much it's basically to kick start the reaction, add a small amount mix well and if the whole lot starts to bubble, produce heat and fume you are good, once it stops add a little more and stir again if you get no reaction it's done, you need to mix the zinc dust well into the chloride and make sure it reaches all the chloride for complete conversion and a little extra sulphuric will do little harm but will remove any left over zinc, you may create a little silver sulphide but you can recover this.


----------



## Geraldo (Sep 11, 2016)

Not to get too nitpicky, but both your title and the first question referenced "zinc oxide." Zinc oxide (ZnO) won't reduce silver chloride to silver metal. It is metallic zinc (typically zinc dust or powder) that will cement silver.

Yes, metallic zinc powder will have a microscopically thin layer of zinc oxide on the surface of the powder as zinc is extremely reactive with oxygen, and that is why you need some small amount of acid in the system for fast precipitation (you essentially dissolve the zinc oxide from the metallic zinc surface) but it isn't technically correct to refer to metallic zinc as "zinc oxide" - these are two very different things. 

Also, by "small amount of acid" I do mean very small - in the zinc industry zinc dust purification of solution (for Ni and Co) is done at "neutral" pH, which for a concentrated zinc sulfate solution is still around 5 and still has traces of free acid (<<1g/l). We avoid really acidic solutions because you can then get hydrogen evolution (and with arsenic bearing solutions, deadly toxic arsine gas).

Sorry for the picking of nits.

Good luck with it!

Geraldo


----------



## mls26cwru (Sep 12, 2016)

I was interested when i read the original post so I decided to look into it... C.W. Ammen covers it in his book in case you need a reference.


----------



## unclephester (Sep 14, 2016)

Geraldo said:


> Not to get too nitpicky, but both your title and the first question referenced "zinc oxide." Zinc oxide (ZnO) won't reduce silver chloride to silver metal. It is metallic zinc (typically zinc dust or powder) that will cement silver.
> 
> Yes, metallic zinc powder will have a microscopically thin layer of zinc oxide on the surface of the powder as zinc is extremely reactive with oxygen, and that is why you need some small amount of acid in the system for fast precipitation (you essentially dissolve the zinc oxide from the metallic zinc surface) but it isn't technically correct to refer to metallic zinc as "zinc oxide" - these are two very different things.
> 
> ...



OMG, Thank you so much for that clarification!! I never even realized when I saw that video that it was Zn powder, and not ZnO. although I did think it odd that the ZnO powder was white, and not dark charcoal looking like in the video.... 

Luckily for me, it was too windy this weekend to work on this, so I escaped being a complete and utter NUB by trying this with no results to speak of....so I remain still a partial NUB though for (1) not noticing that, and (2) not knowing better :roll: 

I really appreciate your attention to detail in catching that, and your willingness to call it out. It is by far better to be embarrassed and learn, than to stay ignorant and be stupid!

Thanks.


----------



## unclephester (Sep 14, 2016)

mls26cwru said:


> I was interested when i read the original post so I decided to look into it... C.W. Ammen covers it in his book in case you need a reference.



Thanks for that information, I was able to find the book online, and ordered it today.


----------

