# Method for recovering silver from photo chemicals



## Ignatz61

Hi all,

I am trying to learn how to recover silver from darkroom chemicals.

Hoke gives three ways:

1. add sodium suphide silver drops as a black silver sulphide

2. Add zinc powder. This she says results in cleaner silver but is slower.

lastly, She describes a silver stripping cell that uses low voltage but huge amperage.

I have tried the zinc but after sitting overnight nothing seems to be happening. The solution is very basic when tested with litmus paper it comes up a nice blue.
Do I need to add acid to the solution to drop the ph? If so, What would be the acid of choice, or does it matter?

Am I going the wrong way with this? Any help would appreciated as I think I have a continous source of these chemicals for free.
Thanks,
JOHN


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## Lino1406

Silver solution in a fixer?


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## Ignatz61

It's a mix of fixer and developer, they dump all the day's chemicals into a container.
it is very alkaline, The zinc I added isn't doing anything.
I am wondering if I could add HCL to it to make it acidic or if electroplating is the best solution?

I know silver is cheap and this won't replace my salary but the solution is free so anything I get out of it is profit (Less chemnicals etc.). Plus I find all the refining/recovery procedures facinating. I am a concrete learner so I have to do something inoder for it to totally make sense. Thats why I have posts in so many different places, I am trying as many things as possible. Platinum in O2 sensors/spark plugs, gold plate in a stripping cell, Photo/xray film in oxalic acid.....


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## Lino1406

That it contains a fixer and if
it's really very basic then 
take a sample and add
some formaldehyde


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## Ignatz61

Thanks,
I am looking for some formaldehyde, in the meantime i put a small amount in a test tube and added some HCL.

The solution turned from dark to an off white kind of ivory color, No notesable fumes. after a day it turned clear with a black percipatate that coated the sides and formed a fairly solid disk on the bottom. It held it's shape when I pulled it out with a small spatula.

Is this black precipataion the silver?
if it is what now? melt and put in parting cell?
Is till have a jug full and more on the way.
Is there an advantage to having them put the developer and fixer in separate containers?


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## Lino1406

Only the fixer is useful
You should have Ammonium smell 
To test silver, dissolve in HNO3 - should be kind of yellow
and add some K2Cr2O7 solution - should be red
Now you know all I know


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## Juan Manuel Arcos Frank

Here are the J Series

Manuel


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## Juan Manuel Arcos Frank

The J215 and J217

Manuel


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## Juan Manuel Arcos Frank

Ignatz 61:

Well,you have asked for help,so here it is:

The first thing you have to do is reading all the "J Series" from Eastman Kodak that I have posted for you... here the theory of silver recovering from photo processes is magisterially exposed.

The second thing that you have to be able to do is measuring the silver content of your spent fixers,I assume that you do not know how to do it,do not worry,here is a method created by me which is cheap,easy and fast:Get a copper wire,take off its plastic cover and dip it into your spent fixers,if they have silver the wire will get silvered according with the silver concentration:

If the wire gets silvered in ------- Silver Concentration

1 second-------------- 12 gr/lt
2 seconds------------- 10 gr/lt
3 seconds------------- 6 gr/lt
4 seconds------------- 3 gr/lt
5 seconds------------- 1.5 gr/lt

To use the zinc recovery method you have to down the pH of your spent fixers to a 5 level,you can do this adding a 5% solution of sulphuric acid (H2SO4) .To prepare this solution you have to deal with concentrated acid,this is a risk and you have to use gloves,apron and eye protective lenses because H2SO4 is very dangerous and could produce severe burns.

In a plastic container add 19 lt. of tap water,CAREFULLY and SLOWLY andd 1 lt of H2SO4 concentrated,let the acid flow through the container`s wall,NEVER add water to the acid,if you do that the acid will spatter and cause you severe burns.Stirr gentely.

The rest is easy..check your silver content,add 1 lt of 5% H2SO4 solution to each 5 lt. of spent fixer to adjust the pH and add the same weight of zinc that you have of silver (i.e. if you have a silver concentration of 3gr/lt,20 lt. of spent fixer then your silver content is (3gr/lt)(20lt.)=60 gr of silver,so add 60 gr. of zinc....and 4 lt. of 5%H2SO4 solution) stirr for 5 minutes,you will see that a black precipitate is formed,this black precipitate is pure silver,so let it settle down,pour off the liquid,filter the black mud and put it into a container,add some hydrocloric acid to dissolve the zinc,you will see that the mud starts bubbling,when the bubbling stops that means that the zinc is completely dissolved.Let settle down,pour off the liquid,wash with tap water,filter the black mud and melt it with a mixure of borax and nitro salt,you will get a pretty fine silver.

Mrs. Hoke is right about the sodium sulphide (Na2S) process,it is cheap,easy and fast...BUT if you use more Na2S than nedeed you will produce hydrosulphuric acid (H2S) which is toxic and smells like rotten eggs.To avoid this risk check first the silver content of your spent fixers,then add the same weight of Na2S than silver weight you have(i.e. if you have a 3gr/lt silver concentration,20 lt. of spent fixer then you have (3gr/lt)(20lt)=60 gr of silver,then add 60 gr. of Na2S).When you add the Na2S to the spent fixer you will see that a black mud is formed,this mud is silver sulphide (Ag2S),check the silver content with the copper wire until the wire stills clean for more than 20 seconds,this will cause to precipitate all the silver in the spent fixer.Let settle down the black mud,pour off the liquid,filtrate the mud and it is ready for the refining process,you can use the nitric acid process,this process is posted in this wonderful forum.

I hope I did not crushed you with so many information.Keep me informed about your progress.Do not quit...silver recovering from photo processes is such a good bussines.

Best Regards

Manuel


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## Ignatz61

Juan,
Wow! Thanks for all the info. I will be studying it tonight. 
I will post my results. I have 1 batch of about 3 liters done. I just added HCL to the solution and after 2 days I have a white precipitate (spongee looking). I am going to melt it tomorrow and see what happens.
I am thinking it is like filleting your first fish. It's always a hack job  but each one gets better as experience grows.

Thanks again
JOHN


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## Juan Manuel Arcos Frank

It is OK John,but try first the Ag2S method and zinc method...if you just add HCl to the spent fixers you will precipitate all kind of salts...except those that have silver..by the way..now that you know how to measure the silver content,how many silver do your fixers have?.

Have a nice day

Manuel


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## Ignatz61

Hi Juan,

I melted the sponge and got only small amounts of silver metal. I still have a jug of nasty smelling brown liquid.
I think I have this batch too messed up to get much out of it. 
My next batch I will check the silver content as you suggested and will Process with the AG2S method and will post my results.

The Kodak info in the pdf's is very informative, Thanks again for posting them. They are good reading for anyone interested in photo chemical recovery.
JOhn


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## Juan Manuel Arcos Frank

John:

Probably the silver content is low..now you know the key in this bussines in the silver content.Here I am for what you need.

Manuel


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## Daport

Good day to all! 

I have been reading about silver recovery from this wonderful forum for quite some time now and I really have to say that I have learned a lot . I have some questions regarding the silver recovery method using zinc powder from used fixer. I tried a small batch of 1 liter fixer (X-ray Fixer made by Kodak) and dropped the zinc powder directly to the solution. At that time I have no idea on how to estimate the silver content and then came up with Mr. Juan Manuel Arcos Frank's post about the copper wire test which is really genius! 

I immediately saw the fixer precipitate a black substance, drained the fixer solution and retained the sludge. washed the sludge with 15% HCL until there is no more bubbling. then rinsed it again twice with tap water. After drying the powder I melted it and got tiny balls of silver  . All of this I did without adding 5% HCL.

My question is, 

1. Do I have to check the PH of the fixer solution 
2. Is there a way to get rid of the smell from the fixer solution without loosing silver in the process?

Thank you for your time an please excuse my ignorance on the matter.

John


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## Juan Manuel Arcos Frank

Daport:

Metallic replacement reaction between zinc and silver complex is accelerated by lowering pH(near 5).Some fixers are pH 5 so there is no need to add acid to low pH but if reaction is not fast enough then you have to add acid.Checking ph from spent fixers is advisable.

Look,there is a way to get rid from fixer smelling...just do it outside and in a well ventilated area.

Kindest regards.

Manuel


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## Daport

Thank you very much for the reply Sir Manuel. 

I will decrease the Ph as sudgested. One of these days I will try your formula on how to convert silver sulfide into metallic silver. As of the moment I still have 15 gallons of fixer to run, I used a flat copper bar (about a 1/2 inch wide and 4 inches long) to test the fixer solution, soaked it for about 1 second and it instantly grayed the copper (thanks of course to Mr. Juan Manuel Arcos Frank's copper method).

Currently I am still looking for the right chemicals to buy and is currently reading the pdf file by Mr. Juan Manuel over and over so that I cannot skip a step/procedure. because I have read in this wonderful forum that it produces toxic gasses. Sir when using your sodium/potassium method is it ok to precipitate the silver in the original container itself and just screw the cover back? I mean just to trap the harmful gasses that it produces. 

Thank you. 

John


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## MarcoP

Daport said:


> Sir when using your sodium/potassium method is it ok to precipitate the silver in the original container itself and just screw the cover back? I mean just to trap the harmful gasses that it produces.
> 
> Thank you.
> 
> John


It will create so much pressure to make the container explode.


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## Daport

Hi everyone! I successfully cemented the silver from the fixer solution using the zinc method. Unfortunately some the chemicals are banned here in my country so i was unable to use Manuel's method. 

I have a few questions. While doing the cementation I tested the fixer solution and got a ph value of 5. Then i proceeded to cement the values by droping zinc dust cp grade while agitating the solution. Whin i was about to wash the cemented silver with diluted hcl i got this white solution. 

Is this silver chloride?

Thank you


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## butcher

The zinc cemented elemental silver as a powder, by adding HCl, you turned the silver into silver chloride, (complicating your recovery), now you will need to convert it back to silver metal.


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## Barren Realms 007

butcher said:


> The zinc cemented elemental silver as a powder, by adding HCl, you turned the silver into silver chloride, (complicating your recovery), now you will need to convert it back to silver metal.



A little clarity in this statement for new members. It didn't covert the already cements silver to silver chloride just the silver that was still left in the solution that didn't convert from the addition of the zinc. When adding something to a solution like this it is always good to take a small sample and perform a test to see what you are adding will do to your solution.


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## Daport

I am a little bit confused. I got a grayish precipitate and then proceeded to dry it in an oven. Is the black precipitate (like back sand) silver chloride ir is it the white White substance floating.


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## butcher

The black could be elemental silver. Although I would expect it to look more gray. You said you dried it in an oven so black would make sense, if the gray silver powder turned black then.

Silver chloride will be white, the white silver chloride will be milky in solution and can form what looks like a white cottage cheese, which can take some time for this fluffy precipitate to settle from solution, to a white powder. If this white powder is washed free of acid and let sit in the sun (or bright light) it will darken to look like a gray, violet or even black as the sun will try to convert some of this salt to elemental silver (photography uses this principle), but you will need to use a reducing method to reduce your silver chloride to metal, as light may work on film, it will not work well with a jar of silver chloride salt, where the light has a hard time being exposed to all of the silver chloride in its crystal structure or where powders do not give good exposure to all of the silver chloride to that light...


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## Daport

Thank you for the reply.

Is it safe to use sulfuric acid then?


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## butcher

The cemented silver will be finely divided elemental silver, if this silver was cemented from solution by adjusting pH with Dilute H2SO4 and zinc, (note adding just enough zinc to precipitate the silver), then you should not have much extra zinc in the silver powders, Juan suggested using Dilute HCl to wash any extra zinc from the silver powders checking for bubbles indicating pieces of zinc.

Some of this depends on the size of zinc used, fine powders or shavings , or if larger pieces of zinc or were used, and you added more than necessary, you could have pieces that can be fished out, and removed locating them by the bubbles they form in the dilute acid. fine shavings in abundance will need to be dissolved in the acid wash.

Dilute HCl will dissolve zinc powders, larger pieces of zinc will take longer in the HCl wash which can convert a tiny bit of the fine silver to a silver chloride, normally I would suspect just the surface of some of the silver powder to begin to form a coating of silver chloride if left in the acid for a short period of time after the zinc dissolved, this normally would not be a problem if done properly as I do not think much silver chloride would be formed from a wash, without too much excess, or large pieces of zinc, or where the HCl was diluted as to not attack the silver to much of an extent, but had enough acid to dissolve the much more reactive zinc.

Using too strong of an HCl acid in the wash, leaving the silver in the acid solution for long periods of time, or heating it, the more possibility of coating some of the fine silver with a crust of silver chloride.

Dilute 10% H2SO4 could also be used to wash the zinc and dissolve it, it will also form bubbles to find pieces of zinc, the dilute sulfuric acid will not dissolve elemental silver and will not form any silver chloride.

The silver chloride could have been precipitated from solution as the milky solution, with the addition of HCl (by the way this is a good way to test a small portion of the solution for silver).

With as much milky solution as you show in your photo that is a good possibility, I was assuming you were washing the silver powders, and had already decanted them from the original solution they were cemented from, in which case you would not be precipitating silver chloride from that original solution, as that original solution would have been removed from the silver powder, and the powders washed with water before adding the dilute HCl solution to dissolve the little zinc left in the silver powders.

If you are only washing the silver powder, where you did not have silver in solution, the silver chloride was formed with too strong of an HCl acid wash on the finely divided silver powder.

If you had a solution with silver ions left in it, you would precipitate silver from solution as silver chloride.

I would not expect such a milky solution if you used dilute HCl to wash silver powders just to remove a little zinc, but I did not expect you were washing the silver powder with a solution that still contained silver ions either.

But you obviously did form a lot of silver chloride...


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## Daport

Thank you sir for the reply.

I was washing the cemented silver at the time with HCL, and I was using 15 percent HCL 50cc to 1 liter of distilled water. Sir, how can I dilute the battery acid to use as a wash for the excess zinc? or can I just add boiling water to wash the excess zinc?

Sincerely,

John


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## butcher

Hot water will dissolve many salts of metals, but it will not dissolve zinc metal, zinc is a very reactive meta,l and will dissolve in dilute acids easily, the dilute acid containing large amount of water can hold this newly formed, salt of the metal and acid, (such as zinc sulfate).

As far as diluting the sulfuric acid I am sure there are formulas, but I was never concerned with them (unless I need a certain molar solution), I would just get close to the dilution of the acid I wanted, I also normally use heat in most every process, and this has many benefits, like if I get the acid to diluted, the heat just concentrates it as water is vapored off...

Say I am using a sulfuric battery acid which is about 32% I may just use two more parts its volume of water.
Example two parts water one part 32% acid, if I was using concentrated acid I may go with nine parts water and one part acid with a little heat, and stirring.

Other members may have better advice, methods or formulas to get a better percentage of acid (dilution of the acid) concentration than I will normally use, or can give advice on.
I do not think an exact dilution was that important here, as long as it is very dilute, and not very concentrated.

volume percentage = volume of solute/total volume of solution X 100 (to get percentage)...

Concentrated sulfuric especially if heated could form some silver sulfate, silver is such an unreactive metal as long as the sulfuric acid is dilute it will not be attacked by the dilute sulfuric acid...

Note: With sulfuric acid always add the acid to the water.
NEVER ADD WATER TO THE ACID.

Concentrated sulfuric acid is especially dangerous if you do not follow the above rule, the water hitting the concentrated acid makes a steam explosion as the water flash boils, that can splash the concentrated acid all over you giving any uncovered skin terribly acid burns...


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## Daport

Hi everyone! I tried to melt the cemented silver using the zinc method and here are the results. 

I have some few questions. When I was melting the cemented silver using the zinc method, I got this metal that is hard to melt, but i did maage to melt some silver though. Is this hard to melt metal the left over zinc?

I guess the next step for me is to refine the silver using nitric acid and puting copper to ceent the silver out again. But i have a worry though. I found something in youtube about nitric acid and powdered zinc combined which burst into flames! 

Any comments anyone?

Thank you

John


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## rickbb

If it was done properly you shouldn't have any "left over zinc". 

The zinc will dissolve and replace the silver in the fixer, unless you use way to much, then you can have some zinc in with the precipitated silver.

One thing I've learned about you tube videos, unless they were made by one of the forum members here, they aren't worth watching.


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## Erceg

I'm bit confused now. At the start Ignatz61 said that he has mixture of fixer and developer and it seams to me that people have forgotten that as they only mention fixer in their advices. The mixture was alkaline so maybe that fixer was in fact blix. I'm wondering now is there a difference in processing (chemically or electrolytically) pure fix or blix in contrast to fix/blix mixed with developer. I have learned quite a lot about pure fix/blix processing from this forum but I can't find anything about daily spend chemical mixture processing.


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## rickbb

Photo processers do not mix the developer and fix, maybe someone who didn't quite understand the process dumped them in together. 

Blix is used in processing color film/prints and it stands for bleach/fix, (not the same kind of bleach you have at home), and also does not, (normally), contain developer.

Spent developer does not contain any silver, none, and is of no value. Mixing it in with fix only complicates things and makes a stink and it can release a form of chlorine gas if you have more developer than fixer.

We only discuss recovering silver from spent fixer, (or blix if it was a color process, rare now days), because that is where the silver is. The added developer will slow down recovery but he should still be able to make it work.

If you have a source for spent photo processing chemicals, only collect the fix, let them dispose of the developer according to their local regulations.


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## Erceg

Thank you rickbb for your reply. I said i have read this forum (quite thoroughly) so I know things you are saying to me. 
Now they (photo studio) are collecting all chemicals in one bucket so that is why I'm asking the above stated question. They fill machine up and it does all the job. It may not mix developer and blix in the developing process but it may do so in discarding (of chemicals) process. The thing is I don't know if developing machine has separate drain for blix and developer or just one so it would be impossible to collect blix separately.
If it is possible of course I would ask them to do so.


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## rickbb

It may be a small shop and they just drain into one bucket to simplify their disposal. (And complicate yours.)

I've not seen an automated processer that did not have separate drains for each tank. Smaller systems are known as closed systems, just a tank of each chemical with no automated way to replenish the levels. 

Larger systems with automated replenishment will have the overflow stack pipe in the fix tank separate from the others to accommodate an inline silver recovery unit. They could have placed all their overflow stacks in the one bucket again just to simplify their disposal.

You should still be able to recover, it will just have less concentration in the liquid volume as the added developer will dilute the fix/silver ratio. If they can just give you the fix you'd be better off with less volume of liquid to work with.

If you have a good relationship with them you may want to look into putting a recovery unit inline with their fix overflow. You own and service the unit and collect and recover the silver. They get to stay in compliance with their discharge permit. (If they have one, which they should.)


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## Erceg

Thank you, those were some very useful information. I'm in good relations with them so if it is technically possible they will separate the fixer. It is a small studio so it would not be profitable to put recovery unit there. They are very close to me so it is simpler to just pick up the chemicals. Thank you again for your help.


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## Erceg

Well, there was an unfortunate development. They use all purpose chemical that go in machine for developing. It is called Fujifilm CP-49E. It contains NaOH, p-Phenylendiamine derivate, Benzolc acid derivate and Ammonium hydrogen sulfate...Did anyone work with this? I have used Cu wire test and nothing. I don't know is it because there is no silver or because it is whole new mechanism of reaction.


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## rickbb

According to Fuiji this is a process for their automated mini-labs to process color print paper. Here is a link to a PDF that explains it in detail.

It still uses a bleach/fix tank so there should be some way to separate and recover just that portion of the chemistry.

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&ved=0CFoQFjAD&url=http%3A%2F%2Fwww.fujihunt.com%2Fapps%2Ffuji%2Ffujifilmnv.nsf%2Ffiles%2FFUJIFILM%2F%24file%2FAF3-0137E2%2520CP-49E%252012-2007.pdf&ei=BplzVPyNAcyuogTuk4HACw&usg=AFQjCNEeqbQS5hCJcCHDBXV2zEKquLMMgw&sig2=qrLBAcBLYBeJwt41BgGDvw


I hope that link works, looks complicated but I just googled Fujifilm CP-49E and this was one of many sites that came up.


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## Erceg

Thank you very much. Link works fine. Now lets dig into this.
I was asking If someone had first hand experience because in reality tings rarely go just like on paper


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## Ubongrex

Yea Manuel
finally, I got. I refjned my silver just okay till the final stage. Men this is cool. You guys out here on this forum: Harold and the likes....you guys rock.

Tnx Manuel, u r d bomb. 
Ok if girls take your money from you after precious metal recovery, they aint gonna take mine (laughs).Ok, I just PM you. Please come over lets talk. Thanks.


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## FrugalRefiner

Ubongrex said:


> Tnx Manuel, u r d bomb.


Ubongrex, welcome to the forum. Please do not use text lingo. It is against our forum rules. 

Dave


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## Juan Manuel Arcos Frank

Ubongrex:

INDEED!!!!!!.You are welcome.

Kindest Regards.

Manuel


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## Auful

Juan Manuel Arcos Frank said:


> Ubongrex:
> 
> INDEED!!!!!!.You are welcome.
> 
> Kindest Regards.
> 
> Manuel


Dumb question: what if the silver content of the fixer is less that 1.5 gram/L, ie the copper wire test takes, 10, or even 15 seconds. Is this fixer not worth refining? Please advise. 
Regards,

Matt


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## Juan Manuel Arcos Frank

Hi Matt.

Well,it depends on the way you get spent fixer.If you get it for free then go ahead,you will have fun recovering that little amount of silver.

If you are buying it then you must keep your eyes open for making money.Low silver concentration is not a good bussines except you buy spent fixer very cheap.

All precipitation processes work pretty good with low silver concentrations.

Kindest regards

Manuel


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## Auful

Juan Manuel Arcos Frank said:


> Hi Matt.
> 
> Well,it depends on the way you get spent fixer.If you get it for free then go ahead,you will have fun recovering that little amount of silver.
> 
> If you are buying it then you must keep your eyes open for making money.Low silver concentration is not a good bussines except you buy spent fixer very cheap.
> 
> All precipitation processes work pretty good with low silver concentrations.
> 
> Kindest regards
> 
> Manuel



Manuel,

Thank you very much. I am getting it for free, so my overhead is rather low; just the cost of zinc and a bit of time. I precipitated out silver, with zinc, from 250 mL of the fixer on hand. Once washed and clean, I plan to get an estimate, from this sample, of the actual silver concentration in this fixer. Why not use iron/steel powder instead of zinc? I'm exploring ways to make disposal easier and safer, without having to precipitate the zinc later with iron. 
Matt


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## upcyclist

Auful said:


> I am getting it for free, so *my overhead is rather low; just the cost of zinc and a bit of time*. I precipitated out silver, with zinc, from 250 mL of the fixer on hand. Once washed and clean, I plan to get an estimate, from this sample, of the actual silver concentration in this fixer.


(my emphasis)

Don't forget your waste disposal time & materials. Scrap iron (or non-stainless steel) can be had for free, but you'll probably be buying something to neutralize your post-precipitation spent acid, assuming you refine what you drop. Consumable lab supplies also include things like filters & pH paper. Eventually, you'll need to figure out how much time & money it costs you to recover from a given concentration of spent fixer.

I'm basically in the same boat--starting this out as a hobby. So if I'm _mildly _in the red, it's just the cost of entertainment. But I have an eye towards making this a side income source, too, so I want to start tracking costs. Some of our costs will come down over time, both in fixed startup costs (facilities, glassware) and efficiencies (getting an electronic pH meter, probably an ORP meter too, being more accurate and conservative with acid use, better sources for materials).


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## Auful

upcyclist said:


> Don't forget your waste disposal time & materials. Scrap iron (or non-stainless steel) can be had for free, but you'll probably be buying something to neutralize your post-precipitation spent acid, assuming you refine what you drop. Consumable lab supplies also include things like filters & pH paper. Eventually, you'll need to figure out how much time & money it costs you to recover from a given concentration of spent fixer.


I agree entirely. I will never be professional at this. I look at refining as a hobby; a means to enjoy learning chemistry, etc while converting some virtually worthless paper currency and coins (that,for some reason currently have a greater perceived value than their melt value), to substances with time-tested value. I do consider this a risky hobby with many dangers, as well, so I do not disregard safety or cut corners. No hobby is worth diminished health or death. 

Back to the topic at hand: I am wondering why iron or steel powder could not be used instead of zinc to precipitate metallic silver from the fixer. Does it increase sulfide production, or is there some other undesirable side-effect I am missing?? "Steel Wool" (some form of iron) is used in the silver fixer recovery canisters, which minimizes toxins going in the drain. I know, first hand however, many silver and iron sulfides result from this process. If steel/iron could be used, would it not eliminate a step relating to disposal?


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## upcyclist

Auful said:


> Back to the topic at hand: I am wondering why iron or steel powder could not be used instead of zinc to precipitate metallic silver from the fixer.


Please don't take my word on this (no direct experience), but I would think the primary difference is that zinc is more reactive than iron, thus your process would go quicker. When I'm dropping from cyanide plating solutions I'm using zinc dust, then processing the precipitant to ditch the zinc, nickel, etc.

Many folks use two cementation stages in their waste processing, as described by 4metals: with copper to drop PMs, with iron to drop most base metals, followed by pH manipulation to drop the rest. If you are only after silver, then you can probably use any metal that is more reactive. Since zinc is more reactive than iron, it won't drop out until you neutralize your waste solution.


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## butcher

We may choose a metal to use to cement values from solution for many different reasons, like how well the metal used is dissolved or washed from the cemented metal, or like in the case of iron and silver where the iron will not alloy with silver in a melt...


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