Printech Archive, April, 1999: Re: Silver Recovery

Re: Silver Recovery

Judy (
Wed, 17 Mar 1999 11:27:00 -0500


Perhaps you would consider referring the person who asked this silver
recovery question to the Silver Council (<> or the old
fashioned way at 202-793-8124). The industry guide to the Code of Management
Practice for Silver Dischargers would be a very useful document for this

Judy Zaczkowski
Envision Compliance Ltd.
124 Connie Crescent, Unit #1
Concord, ON L4K 1L7
Voice: 905-760-1638
Fax: 905-760-1642

>Subject: Silver Recovery
>Date: Wed, Mar 17, 1999, 8:30

>To All:
>I forgot to post the original question to the answer I gave yesterday on
>silver recovery. Therefore, I am reposting the question along with the
>Gary Jones
>On behalf of one of our newspaper members, what equipment needs to be
>installed to meet a silver discharge limit of 0.86 ppm? What do they have
>to do to get into compliance with the regulation? At the present time,
>have a silver recycling unit and a tailing unit.
>Secondly, is there a list of silver recovery equipment manufacturers
>and vendors?
>It is not clear from your email address as to where the 0.86 ppm silver
>discharge limit is being applied at the processor or at the sewer connect.
>This is critical as it does make a difference. I do not think it is
>to treat the silver bearing wastes to achieve a 0.86 ppm limit at the
>processor, but meeting it at the sewer connect can usually be achieved.
>limits for discharges are enforced at the sewer connect (e.g., where the
>printers sewer line meets the POTW's sewer line).
>In terms of silver recovery, the best approach for tight limits would be to
>focus on both the fix and the wash water. The type of silver recovery needs
>be matched to both the concentration and flow of silver bearing wastes.
>recovery is influenced by pH and residence time. For an operation that does
>not have low flow the use of in-line recovery units is the best choice. The
>two principal silver bearing streams for black and white operations are the
>fix and washwater. Operations with low flows are best handled via a batch
>approach. It is important to note that batch processing of silver bearing
>waste streams could be subject to permits as hazardous waste treatment
>this approach does not meet the "closed looped" exemption requirements.
>treatment should be performed by using an electrodepositon unit followed by
>one or two chemical recovery cartridges (AKA polishing units or steel wool
>buckets). It is also critical to note that in low flow or batch
>the chemical recovery cartridges are subject to channeling and will not be
>efficient. For facilities with moderate flow, the first step for fix is to
>an electrodepositon unit followed by one or two chemical recovery
>(AKA polishing units). If additional silver recovery is desired, then the
>solution can be passed through an ion exchange unit. Since washwater
>about 3-5 ppm, using an ion exchange unit will reduce the silver from this
>wastestream as well.
>Since residence time and pH are important factors, it may be prudent to
>collect the fix and washwater, especially the fix, in holding tanks prior
>silver recovery. The silver bearing solutions can then be metered via small
>pumps at a slower rate into the recovery system to allow for maximum
>time. The metering rate will depend upon the manufacturer's recommendation.
>Since silver recovery is reported to be more efficient at a pH of 8, the pH
>the fix can be also be raised to allow for more recovery. This can be
>accomplished in the holding tank. In the systems I have seen, pH adjustment
>usually not needed and the metering will accomplish the goal of reducing
>silver concentrations.
>The other option to consider is to install either a fix and/or washwater
>recycling unit. These units are equipped with silver recovery and will
>both the amount of silver and solution being discharged.
>Another option would be to collect the solutions and send them off-site for
>treatment. This is the most expensive option and the fix would have to be
>under a hazardous waste manifest. The weight of fix would be counted
>the generator status of the facility and would most likely cause them to be
>classified as either a small or large quantity generator.
>The other option would be to have the local POTW adopt the Code of
>Practice. This is a performance based standard that eliminates the need for
>numeric standard. It is based on the total monthly flow of silver bearing
>waste streams and the recovery is either 90, 95 or 99%. If you want more
>information about this program, let me know and I will send a book on it.
>I do not have a list of silver recovery vendors, but have made a request
>one. I will forward if I get one.
>Gary Jones



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