All of us know that recovering silver from used X-Ray fixer is regulated by local, state, and federal wastewater regulators. Silver is not toxic to humans but it becomes hazardous when it seeps into rivers, streams, ground water, and alters the ecological food chain. Once silver is in the environment, it can kill micro organisms (which are needed in sewer treatment plants) as well as fish eggs and minnows, which larger animals depend on for survival. Therefore, very strict regulations exist for the disposal of silver concentrations exceeding 5 ppm (part per million). There is still great potential for huge fines, penalties, and legal fees for improper disposal of silver waste.

Calculating The Silver Potential

Now that you know the basics of the how’s and why’s of silver recovery, do you know how much silver is available to collect? This information is extremely important when selecting the proper when selecting the proper type silver recovery collector. If you know how much silver you generate, you can tailor a recovery program and calculate your profit potential. Every gallon of used fixer contains on average, approximately 0.25 troy ounces of silver (This average will vary depending on the type of film that is processed, single or double emulsion). If you use 10 gallons of fixer on your processor per month, you would multiply 0.25 x 10=2.5 troy ounces, which would show you that this processor has 2.5 ounces of silver available per month. Then take the 2.5 troy ounces times 12 months, which will give an annual silver total of 30 troy ounces. If the current silver spot price is $5.00 per troy ounce this processor is generating $150.00 in silver annually. Knowing how to calculate the silver potential is a great way to educate yourself on what type of profits you should be receiving from the current silver usage volume.

Learning The Silver Recovery Process

Silver recovery equipment, the operation, servicing, and refining of the silver is just a matter of education. The process of silver recovery is not difficult . There are several methods for recovering silver from the fixer solutions, but two are predominate. The first method is known as metallic exchange. It refers to the replacement of the silver with iron. Any steel wool bucket or iron mesh cartridge (also referred to as a canister) are metallic exchange and consist of iron material within the unit. When an x-ray film is processed, the silver is released into the fixer solution. When that solution is discharged from the processor, it is routed to the cartridge where the sliver then exchanges with the iron within the cartridge, the silver is captured and the dissolved iron leaves the unit with the fixer solution. This process is the most common and economical method for reducing silver discharge to as low as 5 ppm and almost requires no service other than installation and removal of the cartridge. (ST-WDC recommended.  see page 75).  If you use this method, installing two cartridges in series is recommended to ensure compliance. Refining of these units is also extremely simple: the unit should be rinsed with water, drained and then can be put in a box and shipped UPS to your refiner. Both profits are ongoing. Cartridges need replacement on a regular basis (approximately 150-200 gallons of fixer a year or 1 year which ever comes first). Installing and removal of the cartridges is usually done by your service technician when he is doing his P.M. on the processor.  The second method for recovering silver is known as electrolytic recovery. This process is done by passing an electrical current between two electrodes in the solution.

The almost pure silver is collected at the negatively charged electrode, called the cathode. There are two types of electrolytic systems. The first is known as a terminal system, and the second is a recirculating system. With the terminal type of recovery, the silver-laden fixer solution passes through the electrolytic recovery equipment on its way to the drain. While within the terminal system, the silver is being electrolytically removed and will plate itself on the cathode. This system, if sized properly, can remove 90% of all available silver. The silver is from 85% to 96% pure. The recirculating electrolytic system has now become the most popular type of recovery for facilities that want to be in total compliance with their silver discharge regulations. The recirculating unit is installed in-line with the fixer recirculation pump.  The fixer within the processor’s fixer tank is then circulated from the tank to the re-circulating electrolytic unit where the silver is gently removed, and then returns back to the processor tank. The fixer does eventually discharge through the processor overflow as normal. 

The advantage to a recirculation system is two fold. With the silver within the fixer tank dramatically reduced, the silver does not carry over to the wash water tank when the film goes to the wash tank.  Wash water on a typical processor has up to 20 ppm of silver if a re-circulation unit is not being used. That same wash tank, if a recirculating system is used, may now only have 2 ppm. As you can see , using a recirculating system is far better for obtaining total silver compliance. The other advantage a recirculating system offers is the optional fixer reduction of up to 50% for medium to high volume processors. With the recirculation system removing silver from the fixer tank, the fixer within that tank now has a longer usable life span. Fixer reduction is achieved by simply reducing the processor’s replenishment rates. The recirculation system collects 98% of all the processor’s available silver and the purity is from 92% to 98%. Electroyltic systems, by design, cannot collect 100% of your silver. When using any electolytic system, metallic exchange cartridges must also be used to meet silver discharge regulations. 

Refining of the silver (silver flake) that is collected from the electrolytic units is also easy and profitable. When the silver from a terminal or recirculation system is harvested, it is done on one of two ways, depending on the system. If the system has a permanent cathode, the silver flake must be carefully scraped off the cathode. If the system has a disposable cathode, the cathode is simply un-screwed from the unit and a replacement cathode screwed on. The silver flake from both units can then be rinsed with water, dried, and sent to your refiner by UPS.

Most small volume single doctor offices do not generate a profit from the silver collection process, but should break even plus allow the facility to meet EPA compliance. The silver profits of the replacement cathode or metallic exchange cartridges, and the refining are ongoing. Scraping the cathode and replacement of the disposable cathode is normally done every three months to a year, during the processor’s P.M.

A simple reliable test for the silver content of X-Ray chemicals effluent solutions below 5 parts per million (the E.P.A. threshold limit), this simple test takes only minutes and is required for E.P.A. compliance purposes. Ordinary Silver test paper strips only detect silver concentrations as low as .5g/l (500 parts per million). Silver indicating strips clearly test positive for silver content above 2 ppm and negative below 2 ppm. Call for Details. Silver Estimating Test Kits available.