8/8/2019 39820734 Silver Extraction From Hypo Fixer Solution

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  SILVER EXTRACTION FROM HYPO FIXER SOLUTION 

INTRODUCTION

Silver is a very precious and important metal. So recycling of silver from waste

solutions of X-ray clinics, photographers is a profitable business. Silver is a major costcomponent of photographic films. Every film either X-ray or photographic, has a thin coating of 

silver over it. During image formation, silver transfers from image portion of films and comes tothe fixing solution called 'hypo fixer'. Due to repetition of fixing process of several films in same

solution, more and more silver keeps on dissolving in hypo fixer solution. When the amount of dissolved silver reaches to saturation level, no more fixing of films can be done in such solution.

This exhausted waste solution is the basic raw material for business of extracting pure silver. 

RAW MATERIAL ( HYPO) 

The concentration of silver is hypo/fixer solution varies from process to process and

time to time. During photographic film processing, silver leaches into the fixer solution (sodium

thiosulphate) from the photographic film and forms silver thiosulphate complex ions. This ismetal displacement process. Generally hypo solution is rich in silver (6-10gm/lit.). Before

 processing the solution, the silver concentration can be checked using 'SILVER ESTIMATION

PAPER'. 

Silver testing process is very simple. A small silver estimation paper is dipped in the solution and

then the change is colour is compared with the colour chart accompanying it. By this methodsilver concentration can be determined in gms/liter within 5 seconds. Purchase price of fixer can

 be estimated accordingly. Moreover it helps to determine the profitability and reduce the risk factor. 

8/8/2019 39820734 Silver Extraction From Hypo Fixer Solution

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 EXTRACTION OF SILVER FROM HYPO 

The methods mainly used are; A) Chemical method and B) Electrolytic method. 

A) CHEMICAL METHOD: 

1) Determine gm/lit of fixer solution using silver estimation paper. 

2) Take 1 lit. solution and to it add approximate amount sodium sulphide ( Na2S) and causticsoda ( NaOH). Using common ion effect we can remove silver from it.

3) Using the proper proportion as per the upper estimation add proper amount of sodium

sulphide ( Na2S) and caustic soda ( NaOH) to all the solution. 

4) We get black residue at bottom due to reaction and the solution at the top becomes yellow in

colour. Filter the solution and retain the black residue. Dry the residue using filter paper. Get it

melted and molded into bricks by Goldsmith. While melting we can use Borax / Na2CO3 /CaCO3 etc. In this way shiny silver metal is recovered from black silver residue. 

B) ELECTROLYTIC METHOD: 

Silver can be extracted from hypo using semi automatic or fully automatic machines. The mostappropriate model of such machine can be selected according to our working and financial

capacity. 

Anode used in such machine is made up of carbon or graphite and Cathode is mostly made up of large stainless steel or other alloy plates. By filling the waste solution into the machine and

connecting to the electricity mains, machine starts working. Silver present in the solution startsdepositing over silver collecting plates. The machine should be operated till all the silver present

in the solution gets deposited on cathode plates as black flakes. The process time can beestimated by checking silver availability using silver estimation paper time to time during

operation. 

It is not essential to attend the machine continuously while operating. Machine can be operatedwith full tank / half tank /quarter tank filled. No special training, industrial process , power, load

line or license is required for this operation. 

This information is compiled by Deepak V. Doddamani,Mumbai. Email: deepbaazigar@gmail.com