BENEFICIATION OF PHOTOGRAPHIC WASTES
Frederick Nelson, Chemist
Kurt A. Kraus, Chemist
Oak Ridge National Laboratory
Oak Ridge, Tennessee 37830
J. S. Gilbert, Graduate Student
Department of Environmental Engineering
University of Tennessee
Knoxville, Tennessee 37916
INTRODUCTION
This chapter deals with examination of several techniques which might find use in
treatment of photographic wastes to avoid discharge of silver, for which very low discharge limits are being placed, and also perhaps to permit reuse of the water.   Of particular interest were the large volumes of wastes which are generated during washing of
photographic materials after they passed through the fixer bath.
In the treatment of these photographic wash waters, one normally deals with very
dilute silver solutions which, in addition to some other toxic metals such as cadmium and
mercury, contain less toxic "additives" and, of course, the important complexing agent,
thiosulfate.   Though emphasis was on highly dilute solutions with their special problems,
it is hoped that some of the techniques to be described can be adapted to silver recovery
from more concentrated sources.
Three techniques for beneficiation of the water have been examined.   In two of these
the silver (as well as other toxic metals) would be removed from the water while it still
contains thiosulfate and the other relatively nontoxic sulfur-containing species.   The third
technique searches for a method which would remove silver and the sulfur-containing
species and allow recycle of a significant fraction of the wash waters.   If silver is first
removed and recycle desired, destruction of the sulfur-containing species will have to be
carried out in a second step.
The first method discussed involves adsorption of silver on insoluble sulfides and particularly on carbons filled with insoluble sulfides.   It was assumed that thiosulfates remain
in the wash during adsorption.   The results of this work are described in detail in
Chapter 95 [ 1).   Here, some of the results are merely summarized.
The second technique explored involves adsorption of silver from dilute thiosulfate
solutions on organic quaternary amine anion exchangers.   In an attempt to establish the
range of applicability of the technique, adsorption functions for the silver-thiosulfate system were established over a broad range of thiosulfate concentration and, in addition,
adsorntion functions of a number of other elements of possible interest in photographic
waste treatment were determined. Some features of this anion exchange technique were
explored with column experiments, fluidized bed experiments, and with the axial filter
operated in the stirred-tank mode.   Also, a technique was developed for regeneration of
the resin to make it reusable in repetitive cycles.
Finally, a technique of silver removal was examined which combines destruction of
the complexing agent by oxidation followed by axial filtration for removal of the precipitated silver halides.
Each of these techniques has promise for application to the photographic waste problem. Not enough information has been obtained to allow decisions regarding which technique is best under which circumstances.
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