# Help needed in precipitating silver sulfide



## iqbalaloha (Jan 21, 2015)

Hello everybody and warm greetings to all the members of this wonderful family. I am new to this forum and my English is not so good. So, I request all the kindhearted members to forgive me if I make any mistake in my posts or replies.I am Iqbal, from a small state called Assam in India. I have a bit knowledge of chemicals and now taking interest in PM. I feel blessed and proud to be a member of this remarkable and mind blowing forum where there are members with amazing degree of knowledge and unbelievable amount of practical experience. Hats off to them. However, I am sharing my first experience.

I bought 2 batches of used x ray fixer- one of 10 liters and the other of 20 liters. I mixed 50 gms of sodium hydroxide and then same amount of sodium sulfide to the first batch of 10 litres .The fixer immediately turned black and after 15 hrs I filtered the ppt . I took a small amount of the sludge ( half a spoon after drying) and got it melted by a jeweler with sodium nitrate, soda ash and borax and got a small white metallic ball which the jeweller told to be silver. I am drying the rest. I have read here the post of one of the geniuses, Juan Manuel Arcos Frank, to use KNO3 for melting but I dont have that salt now. Can I use sodium nitrate? I mixed caustic soda to the fixer because I have read somewhere that it prevents formation of hydrogen sulfide gas. Is that correct?
My problem arose with the second batch of 20 ltrs. I mixed 75 grms sodium hydroxide and stirred for sometime. Then I mixed 75 gms of sodium sulfide and stirred. The solution immediately turned black but even after 3 days there is no ppt though it is still black. I got only little ppt. Why this happens? I tried to find its solution using the search button created by respectable Lazersteve but could not find. How can I get the silver sulfide ppt now? I tested the presence of silver in the black solution using silver estimation paper and it indicated the presence of Silver around 3 to 5 gm/ ltr.
I did an experiment with the black solution. I took about 200 ml of the liquid and boiled for sometime in an aluminium pan and after cooling put in a plastic container . Then I added little dil. sulphuric acid ( Battery acid). The solution immediately turned yellowish white with foam on top. I removed the foam and added little sodium sulfide, stirred and then added sodium hydroxide pieces ( pallets) one by one with constant stirrig. The solution turned dark grey and ppt appeared. I kept it and after a few hours there was dark grey ppt with clear light yellow liquid at the top. Is that silver sulfide ppt or something else? please help to fix my problem.

Warm regards
Iqbal


----------



## rickbb (Jan 21, 2015)

Before you start anything you should check to see if/how much silver there is in the fix. 

Use a bright piece of copper wire and hold in solution, if it silvers quickly, within a few seconds, then lots of silver. If after 30 seconds there is barely any silver on the wire, don't waste your time on it.

It could be that the second batch did not have any or very little silver in it, hence, no precipitation.


----------



## Juan Manuel Arcos Frank (Jan 21, 2015)

Iqbal:

Welcome to the Forum!!!!!.

Rickbb is right,probably the second fixer contains less silver then the first so it is very important to check silver content with that copper wire BEFORE processing.

Anyway,if the black mud does not settle down then you can boil the solution for a while.Silver sulphide tends to form a colloidal solution which never precipitates so you have to break down that colloidal solution by boiling or changing pH.

About the greyish mud that you have obtained it is hard to say if it was silver sulphide or not,but melt it with sodium/potassium nitrate and if it contains some silver then you will see a nice little ball of silver.You can use NaNO3 instead of KNO3,I prefer the last one because it is a common fertilizer.

Keep us posted about your progress.

Kindest regards.

Manuel


----------



## iqbalaloha (Jan 22, 2015)

Thank you rickbb. Thank you Manuel for your kind advice. OK I will boil the solution. If I want to change the ph, how can I do it? Should I add dil. sulphuric acid or a base. What should be the required ph?

I will let you know if there is silver in the grey mud after melting it.

Warm regards
Iqbal


----------



## jungle_Dave (Jan 22, 2015)

Hi Iqbal, Welcome to the forum!

Im doing small batches of fixer and also new here.
I like you are doing it the hard way, thats how you learn. In my case I am learning from your experiences.

I used the zinc method, please have a look at this post
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=50&t=3558
Juan Manuel explains it perfectly.
I've followed his instructions, the result was perfect, thanks again Dr.!

Learn the silver content test he describes, get ph test strips as it will save you so much time and guessing.

Your fixer should be Ph 5, the small amounts I have done mostly were but 1 was not.
If its too alkaline (more likely then not) you need to acidify with 5% sulfuric acid.

Please let us know how it goes,

Best of luck,

Dave


----------



## iqbalaloha (Jan 23, 2015)

Thank you very much Dave. I' ll keep posting of my progress.

Warm regards
Iqbal


----------

