Silver Extraction

2011-10-02T06:28:00.000-07:00

Silver extraction or silver recovery is a high profitable business. Silver extraction means remove the silver from the used film, photograph and other silver content materials.

Every film and photograph is coated with a thin layer of silver. During image formation, silver transfers from image portion of film to fixing solution (fixer). After some time fixer solution becomes saturated and stops working.

Silver concentration in fixer reaches around 5-10 grams per litre. This waste solution is the basic raw material for our business, which can be procured from all X-ray Clinics, Photographers etc.

While purchasing and processing the fixer/hypo solution, the silver concentration in solution can be estimated in grams per litre with the help of Silver Estimation Papers.

Before you start this silver extraction business you need to read:

Silver Concentration in Solution: The Affected Factors

2011-09-28T01:05:00.000-07:00

Before you start your silver recovery process, you need to know the silver concentration in the solution. This step is most important to know whether silver recovery is profitable or not.

There are many factors affect silver concentration in solution.

1) Type of Film Being Processed:

The silver content of x-ray film or photographic emulsions varies with the type of film. For example, the thin-emulsion films used in the graphic arts industry contain less silver than double coated x-ray films and therefore will yield less recoverable silver.

In processing color films, all of the silver is removed by the fixer to yield a dye image, and so nearly all of the silver is available for recovery.

2) Exposure Level:

In processing black-and-white materials, the ratio of exposed and developed silver to soluble silver halide has a considerable influence on the amount of recoverable silver in the fixing bath. This ratio depends largely on subject matter. For example, it negatives of a line drawing on white paper are processed, the emulsion contains a large proportion of exposed and developed silver and a small proportion of soluble silver halide.

On the other hand, if positives of the same drawing are processed, the emulsion contains a small proportion of exposed and developed silver and a high proportion of soluble silver halide. The positive line image, therefore, yields much more recoverable silver than the negative image since less silver is retained in the film.

3) Processing Work Load:

The quantity of material processed in a solution is a major factor affecting the amount of silver in that solution. Processing work loads vary considerably in many operations, and the load often peaks at certain periods during the working day.

If the flow rate at these periods is greater than the recovery unit can handle, silver will be lost to the drain.

4) Replenishment Rate:

In processing systems that require replenishment, always observe the recommended replenishment rates. Over replenishment dilutes the silver bearing solution going to the recovery cartridge and so results in a lower silver yield than expected. The cartridge becomes exhausted by the passage of solution with a low silver content. Silver is not lost by over replenishment, but the cartridge requires more frequent replacement and replenisher solution is wasted as well.

5) Solution Carryout:

Varying amounts of silver-bearing solution are carried out of the processing tank on the surfaces of the photographic material. This solution is not available for silver recovery by the cartridge.

Factors that affect solution carryout are machine speed and film area, as well as the incorrect adjustment or absence of squeegees and drive belts. Under normal circumstances, the volume of solution that may be carried out varies between 3 percent and 15 percent of the replenishment rate. Use of squeegees is an effective means of minimizing solution carryout.

6) Obstruction of Solution Flow:

If the solution going to the cartridge contains an abnormal amount of solid precipitates or gelatinous matter, the steel-wool filler acts as a filter and eventually obstructs the passage of solution. The solution is then diverted through the bypass loop of the circulating unit and is discharged to the drain untreated.

By known these factors, you can analyze your silver concentration in your solution before you start silver recovery process.

Source: Technical Documents

Related Articles:

Silver Recovery Equipment, Which One is Best for You?

2011-09-27T01:11:00.000-07:00

That best silver recovery equipment for you depends on the following factors:

1) Your processing volume, whether or not you want to reuse your fixer or bleach-fix, and environmental concerns, such as strict limits on effluent discharge.

2) The training and technical knowledge of your personnel,

3) The price of silver,

4) The operating and refining costs.

The cost of silver recovery equipment is closely related to the volume of materials you process. If your volume is low, chemical recovery cartridges are a reasonable choice for silver recovery.

If your processing volume is high, you probably don't want to make frequent cartridge replacements or provide a large storage area for spent and replacement chemical recovery cartridges.

Although initial capital investment for electrolytic silver recovery cells is higher than for chemical recovery cartridges, you don't have the recurring cost of equipment replacement. If you use an electrolytic cell, your refining costs for the recovered silver will be much lower than with other methods, because the silver you recover is usually more than %95 pure.

For a large-volume operation, in-situ ion exchange is also an option. You can use this method for primary treatment, or use it to tail an electrolytic unit if you dilute the discharge from the electrolytic cell with wash water. This method will let you recover the maximum amount of silver and minimize the amount of silver discharged. It requires a greater capital investment and more chemical handling than chemical recovery cartridges or electrolytic cells.

The silver concentration that can be discharged to a treatment plant or to a receiving body of water is often regulated even though silver in photographic effluent is in a form that is not harmful. Therefore, cost may not be the primary consideration in choosing your silver recovery method. If you do not know the code limits for silver, check with your local regulatory agency. You may need to consider a method that will reduce the silver to an acceptable level. In some cases a regulatory agency may take into account the non-toxic nature of the silver in photographic effluent and allow a variance.

Chemical recovery cartridges can achieve silver recovery efficiencies greater than %90. However, it is difficult to maintain this level of recovery, so cartridges are an unreliable choice if you need to observe low discharge limits. Another problem with chemical recovery cartridges is that as silver is recovered, the steel wool becomes soluble, producing iron levels in the effluent as high as 3000 mg/L. Iron is regulated to levels well below those concentrations by many sewer codes.

It is also difficult to maintain very low silver concentrations in effluents with electrolytic recovery cells. The concentration depends on how low the current density can be set with your unit. As the silver concentration gets lower, the current density must be set lower to prevent silver sulfide from forming. With low current densities, a large cathode area is needed to achieve the necessary recovery rate. If your electrolytic cell is not capable of reducing the silver concentration in the effluent to the level required, you can simply feed the effluent from the electrolytic cell through chemical recovery cartridges to recover additional silver.

The greatest recovery efficiency is possible with an ion exchange recovery method. In-situ precipitation ion exchange can reduce silver concentrations in the effluent to a level as low as 0.1 mg/L. However, it is critical that you dilute the concentrate with the proper amount of wash water before treatment; too high a thiosulfate concentration in the solution will cause silver to leak through the column.

You need to do small study to know which silver recovery equipment is the best for you.

Source: Technical Documents

Silver Recovery Methods

2011-09-26T03:30:00.000-07:00

There are three methods of silver recovery from waste fixer solution and other silver-rich processing solutions. These methods are:

Electrolytic
Metallic replacement
Precipitation

1) Electrolytic Recovery

Electrolytic recovery is the most widely used silver recovery method for fixer solution and photographic processing solution. The silver is recovered from solution by electroplating it onto a cathode. A controlled, direct electrical current is passed between two electrodes suspended in the silver-bearing solution. Silver is deposited on the cathode in the form of nearly pure silver plate. The cathodes are removed periodically and the silver is stripped off for sale or reuse.

There are two basic types of electrolytic equipment: one in which the cathode rotates in the solution and the other in which the solution is pumped around a stationary cathode. Either type is capable of recovering more that 90% of the silver from silver-rich solutions.

2) Metallic Replacement

Metallic replacement is a process where elemental iron undergoes an oxidation-reduction reaction with the silver thiosulfate to produce ferrous ions and metallic silver. The exchange reaction is very rapid, but dependent on the contact of the silver-thiosulfate complex with the iron surface. Flow rate, iron surface area, contact time, and the pH of the solution are the major variables influencing recovery efficiency.

To ensure effective and controlled contact, metallic replacement is accomplished by metering silver-rich solutions at a controlled rate through a container of steel wool, iron particles or an iron-impregnated resin. These containers are generally referred to as metallic replacement cartridges, chemical recovery Cartridges, or silver recovery cartridges. As the recovery cartridge is used, the active surface area is reduced and small channels will begin to develop in the iron substrate.

A properly designed and maintained Metallic Replacement CRC is capable of recovering more than 95% of the silver from silver-rich solutions when used in accordance with manufacturer specified flow rates.

3) Precipitation Method

Precipitation method involves metering silver-rich solutions or washes water into a reaction vessel and adding a precipitant to separate the silver from the solution. The chemical TMT (trimercapto-s-triazine, trisodium salt) is used as a precipitating agent.

TMT is a chemical that causes silver to settle out of photographic liquids. The rate of this settling is astonishing. When TMT is introduced into silver bearing solutions, settled silver can be seen and measured in a mixing graduate within minutes.

The cost of operating a Precipitation TMT silver recovery system is somewhat higher than other silver recovery technologies. Precipitation chemicals and filtration costs will account for about 25% of the recovered silver for a large lab. However, Precipitation TMT is so reliable that silver concentrations can be easily predicted and compliance can be consistently met. Often, this will justify the additional cost.

The TMT sludge is not considered hazardous material in most states, and can be shipped without a manifest. If you are having a difficult time meeting your present or future environmental regulations, TMT is worth considering.

If you interested in any of these Silver Recovery Methods, Hallmark Refining offers these three technologies.

Estimate Amount of Silver in Photography

2011-09-22T00:15:00.000-07:00

Before you start silver recovery from film and papers, you need to know the amount of silver available. The process to estimate amount of silver available from your photographic films and papers involves the following steps:

1. You will need to estimate how much film and paper that you process at your photographic processing facility over a known period of time.

2. If you calculate the available silver to compare to the amount reported to you by your silver refining company, you will want to use an amount that represents your average processing over a specific period of time.

3. If you calculate the available silver to determine the size of silver recovery equipment that you will need, make sure that you use a peak processing amount to ensure that the equipment will always meet your needs.

4. You will need to know the amount of silver that is present in the photographic films and papers. See (Silver In Photography ).

5. For color films and papers, use the total amount of silver present to estimate the amount that is potentially recoverable. For black and white films and papers, you will need to estimate the percentage of exposure. The higher the level of exposure (dark images), the lower the amount of silver that is removed from the film or paper.

6. Once you have estimated the area of the films and papers that you process and the amount of silver that is available, you can calculate the total amount of silver.

Silver In Photography

2011-09-21T03:26:00.000-07:00

Silver in photography

The biggest sources of silver are photographic films and papers. Once processed, silver is retained in the film and paper or transferred to the photographic processing solutions. You can collect the silver in photography by using silver recovery equipment or send the solutions off site for recovery.

You can also have a refiner recover silver from some unprocessed, as well as processed, photographic films and papers. The amount of silver recovered depends on the type of film or paper, the exposure, and the type of processing used.

Understanding the amount of Silver in photography available from photographic films and papers can help you determine if it is worthwhile for your facility to recover that silver. Knowing this will assist you in selecting the proper silver recovery equipment and ensure that you maximize the return from your refiner.

Silver is found in photographic films and papers it is the element responsible for producing the photographic image. You can recover silver from unprocessed films and papers, as well as from processed black and white films and papers.

Silver content in photographic films and papers may vary from emulsion to emulsion. These manufacturing variations are designed to ensure consistent product quality in contrast and speed. Therefore, the amount of silver available for recovery in photographic films and papers may slightly increase or decrease.

Similar products made by different manufacturers may vary in the amount of silver they contain. So to know exactly how much silver in any photographic film or paper you need to contact the manufactured company.

In processing color photographic films, two potential sources of silver are often overlooked. Some color films are pre spliced to allow for long processing lengths. A piece of film is cut off and an additional piece of film is located underneath the splicing tape. Both pieces of film contain silver.

Silver in photography can be recovered by soaking the film scraps in a fixer bath and then desilvering the fixer using your silver recovery equipment.

Silver Extraction From X-Ray Film

2011-09-20T00:42:00.000-07:00

Silver extraction from x-ray film methods are simply the means that are used to get the metal (pure silver) from waste x-ray film. There are two methods that can be used to recover silver from exposed x-ray film. These methods are both very effective.

1) The first method to recover silver from x-ray film is where the metal will be stripped from the emulsion by using either chemical or mechanical means.

2) The second method is where the will be burned in an incinerator that controls the burning process and there will be some fly ash. All the ashes that will be obtained from this silver recovery method will be processed to obtain all the metal content. This is method that is very economical when a person reclamation a small amount of the metal.

Many industries will want a silvery recovery method that is not only economical but is also fast.

You can share your experience in silver extraction form x-ray film.

You may like to read: Silver Extraction From Fixer

Silver Extraction From Fixer

2011-09-20T00:29:00.000-07:00

Silver extraction from fixer methods are simply the means that are used to get the metal (pure silver) from a fixer solution. This is a project that can be economically feasible. A large percentage of the silver that will be recovered will be in the solution where the rest of it which will just be under less than 20% will be in other places.

There are three basic methods that are used for silver extraction from fixer solution:

1) The first silver recovery method is electrolysis which called (silver recovery unit) where there is current that is passed between two electrodes that have been immersed in the liquid.

2) The second method of silver recovery is the metallic replacement where the metal will be replaced with another base metal like iron, copper or zinc. The metal will accumulate on the bottom of the container by forming sludge. The sludge will then be removed and it is from here where the metal will be obtained.

3) The third method of silver extraction form fixer is chemical precipitation where by the metal is reclaimed by the addition of certain chemicals in the fixer. The metal will be precipitated out of the solution still in the form of sludge and can be recovered in its pure from through a silver recovery process of refining.

Silver extraction from fixer is a high profitable business.