Apparatus for removing a component from solution

Spent solution from photographic processors are fed into a conduit (18) to which subsequently are added precipitating agents from a first source (22) and flocculating agents from a second source (28); so that, well grown or ripened clumps of flocculated solids are formed along the conduit before being emptied into a gravity collecting vessel and shipping container (38) from which clarified liquids are displaced by a mass (50) of accumulated flocculated solids, typically through a filter (58, 142, 150, 158, 162, 166, 220) for removal of any unsettled fines.

TECHNICAL FIELD 
The invention concerns apparatus and methods for removing unwanted or 
valuable components from solutions. More particularly, the invention 
relates to removal of silver from spent solutions used to process or 
develop photographic film. 
BACKGROUND ART 
Processing or developing photographic film and paper products and other 
imaging products requires the use of a variety of known types of 
processing solutions. During use, the processing solutions gradually lose 
their effectiveness and must be replaced with fresh solutions. 
Photographic processors and film manufacturers for many years have been 
concerned with how to properly dispose of the spent or waste solutions. 
The spent solutions may contain precious metals such as silver which often 
have been recovered as an economic measure. Also, government regulations 
on discharge to the environment of solutions containing such metals 
typically have required that virtually all of the metals be removed before 
the remaining liquid may be discharged to the sewer. Certain ingredients 
in such spent solutions have been reacted with precipitating and 
flocculating agents to form solid precipitates containing the metal or 
other ingredient to be removed. The precipitates have been filtered from 
the solution and the remaining liquid has been discharged. Some film 
processors have separated the precipitates by centrifuging. Others have 
separated the precipitates by simple settling and decanting. Various 
techniques of these sons are described in commonly assigned U.S. Pat. No. 
3,832,453 and by Thomas W. Bober and Austin C. Cooley in "The Filter Press 
for Filtration of Insoluble Photographic Processing Wastes," Photographic 
Science and Engineering, Vol. 16, No. 2, March-April 1972. 
More recently, recovery of silver from spent solutions has been made 
simpler due to introduction of metal salts, most commonly the trisodium 
salt of trimercapto-S-triazine or TMT, as the metal precipitating agent. 
Other cationic salts of TMT also can be used as precipitating agents, such 
as the potassium, ammonium or lithium salt. TMT can be used for primary or 
secondary recovery of silver; however, many film processors have reported 
that TMT is very useful and most economical for secondary treatment of 
spent solutions which have previously had most of the silver removed by 
metal exchange or electrolysis, for example. In one known method, the 
spent solution and TMT were mechanically mixed for as long as an hour in a 
large settling vessel, typically a round-bottomed or cone-bottomed vessel. 
The resultant mixture was left to settle overnight or for as long as 
twenty hours. Then, much of the liquid above the settled solids was 
decanted and the settled solids were passed out of the bottom of the 
vessel into a bag filter. Some work has been reported in the literature in 
which a polymeric flocculant has been added to the mixture prior to 
settling. Methods of the latter type were described by Nathan Spears and 
Robert Sentell in a paper entitled "Silver Recovery from Photographic 
Waste Processing Solutions by Using the Trisodium Salt of 
2,4,6-Trimercapto-S-Triazine," presented at the Seventh International 
Symposium on Photofinishing Technology in San Francisco, Calif. 3 to 5 
Feb. 1992. 
Those skilled in the photographic processing technologies will understand 
that various other types of components have been removed from spent 
processing solutions by precipitation, such as Prussian blue (iron 
ferrocyanide), calcium sulfate, various coupling agents, chromium 
hydroxide from bleach and systems cleaners, aluminum salts and many 
others. Some of these precipitated materials tend to form rather 
gelatinous solids that will quickly clog or blind most filters. Others 
produce a very large amount of suspended fine particles that tend to 
remain suspended in the liquid even after rather long settling times. 
While such known methods for removing components from waste photoprocessing 
solutions have proven relatively effective at recovery of precipitated 
solids, a number of problems have remained. Considerable care has been 
required when decanting the last portions of the liquid in the zone 
closest to the settled solids in the bottom of the settling vessel, since 
the solids tend to stir up and carry out with the liquid, potentially 
requiring a further filtering operation or return of the liquid and fines 
from that zone to the vessel for processing with the next batch of spent 
solutions. 
Another problem may exist when solids already settled on the bottom of the 
settling vessel are disturbed when a valve is opened at the bottom of the 
vessel to dump the moist solids for further processing. If no liquid 
remains in the vessel when the valve is opened, difficulty may be 
encountered with getting the settled solids to flow completely out of the 
vessel without subsequent scraping or other manual handling. So, enough 
liquid often has been left in the vessel to permit the solids to be 
discharged as a slurry for easy conveyance. 
Similarly, there may occur times when it is desired to remove solids from 
the settling vessel while a considerable volume of liquid remains above 
the settled solids. In such situations, when the solids are disturbed by 
opening the bottom valve, some solids, particularly fines, are stirred up 
and resuspended in the liquid layer for a considerable period of time 
until the entire contents of the vessel are quiescent for a long enough 
period to allow the fines to settle again. But, if the liquid must be 
decanted before the fines have resettled, the fines are carried out and a 
further filtering may be needed to achieve the desired level of purity of 
the discharged liquid. 
SUMMARY OF THE INVENTION 
The primary objective of the invention is to provide simple, compact and 
inexpensive apparatus and methods for removing a component from a 
solution, such as spent photo-processing solution, by treating the 
solution to form settleable solids, passing the solids into a collecting 
vessel and allowing the remaining liquid to flow from the collecting 
vessel. 
A further objective of the invention is to provide such apparatus and 
methods in which the collecting vessel is readily removable and suitable 
for use as a shipping container to transport the solids to another 
location for further processing, such as to a precious metals refiner. 
Another objective of the invention is to provide such apparatus and methods 
in which waste solutions from a film processing machine can be taken 
directly from the machine and treated in a reliable, repeatable manner 
while maintaining clean surroundings, essentially without requiring 
frequent intervention by the operator of the machine. 
Still another objective of the invention is to provide such apparatus and 
methods in which removal of the collecting vessel causes minimal 
disturbance to the operation of the rest of the apparatus or method. 
Yet another objective of the invention is to accomplish separation of 
solids and liquids in a controlled manner in the shortest possible time 
for greatest efficiency while minimizing any stirring up and resuspending 
of already settled solids and thus minimizing any need for additional 
settling time. 
A still further objective of the invention is to accomplish separation of 
solids and liquids in a reproducible manner and to such a degree that the 
clarified liquid will meet regulatory requirements for discharge or will 
be suitable for reuse or reclamation. 
Another objective of the invention is to accomplish such separation while 
decreasing the flow velocity of the solids and liquids as they move 
through the apparatus thus enhancing the tendency of the solids to 
agglomerate into clumps which will settle read fly. 
These objectives are given only by way of illustrative examples; thus other 
deskable objectives and advantages inherently achieved by the disclosed 
invention may occur or become apparent to those skilled in the an. 
Nonetheless, the scope of the invention is to be limited only by the 
appended claims. 
The invention is defined by the appended claims. In one embodiment, the 
apparatus is particularly suited for continuously or intermittently 
removing a component from solution. Means are included for providing a 
solution containing a component to be removed. Conduit means define a 
mixing path having an inlet end and an outlet end, for receiving and 
passing the solution. The mixing path may be a closed conduit such as a 
length of tubing through which the solution is pumped; however, an open 
flow channel also may be used in accordance with the invention. First 
means, such as gravity feed or a peristaltic or bellows pump, is provided 
for delivering the solution into the inlet end of the mixing path. Second 
means, such as gravity feed or a suitable pump, is provided downstream of 
the first means for delivering into the conduit means a precipitating 
agent for the component. The spent solution and precipitating agent also 
may be delivered to the conduit means in the reverse order or essentially 
simultaneously, provided the proper ratios are maintained. In some 
embodiments of the invention, the spent solution and precipitating agent 
may be mixed in a separate vessel and the mixture delivered into the 
conduit means. Third means, again such as gravity feed or a suitable pump, 
is provided downstream of the second means for delivering into the conduit 
means a flocculating agent for the precipitate. The second and third means 
are separated by a first distance chosen to provide a first residence time 
sufficient for mixing of the solution and the precipitating agent and for 
forming a precipitate well suited for flocculation. That is, the residence 
time between the second and third means is long enough to enable the 
crystals of precipitate to grow or ripen to a point at which addition of a 
flocculating agent will cause formation of flocculated particles which 
tend to agglomerate readily into clumps. In some applications, however, 
the residence time for precipitation may be very short. The outlet end of 
the conduit means is located downstream of the third means, at a second 
distance chosen to provide a second residence time sufficient for forming 
larger, more ripened clumps of flocculated particles of the precipitate. A 
collecting vessel having an inlet, releasably connected to the outlet end 
of the conduit means, is provided for receiving the flocculated solids and 
any remaining liquid and for permitting the flocculated solids to settle 
to a bottom of the vessel and the remaining liquid to move toward an 
outlet of the vessel. As a result, the settled flocculated solids 
gradually will substantially fill the vessel while at least a substantial 
pan of the remaining liquid gradually will pass from the vessel, thereby 
permitting a filled collecting vessel to be disconnected from the outlet 
end of the conduit means. The flow area of the collecting vessel 
preferably is substantially larger than that of the conduit means, thereby 
causing the solution velocity to decrease and the solids to settle more 
readily in the collecting vessel. The collecting vessel may be used as a 
shipping container for the settled solids. 
One embodiment of the method of the invention is suited for continuously or 
intermittently removing a component from solution. A solution containing a 
component to be removed is provided, either from a holding vessel or 
directly from a photo-processing machine. A mixing path such as an 
elongated tube is defined having an inlet end and an outlet end for 
receiving and passing the solution and the solution is delivered into the 
inlet end. Downstream of the point of delivery of the solution, a 
precipitating agent for the component is delivered into the mixing path. 
The spent solution and precipitating agent also may be mixed in a separate 
vessel before delivery into the elongated tube. Downstream of the point of 
delivery of the precipitating agent at a first distance chosen to provide 
a first residence time sufficient for mixing of the solution and the 
precipitating agent and for forming a precipitate well suited to 
flocculation, a flocculating agent for the precipitate is delivered into 
the mixing path. The outlet end of the mixing path preferably is 
downstream of the point of delivery of the flocculating agent at a second 
distance chosen to provide a second residence time sufficient for forming 
larger, more ripened clumps of flocculated particles of precipitate. The 
flocculated solids and any remaining liquid are collected in a first 
vessel having an inlet, releasably connected to the outlet end of the 
mixing path, for receiving the flocculated solids and any remaining 
liquid. The flocculated solids are permitted to settle to a bottom of the 
first vessel and the remaining liquid to move toward an outlet of the 
first vessel. The settled flocculated solids gradually will substantially 
fill the first vessel while at least a substantial part of the remaining 
liquid gradually will pass through the outlet from the first vessel, 
thereby permitting a filled first vessel to be disconnected from the 
outlet end of the mixing path. When the first vessel has filled, it is 
removed from communication with the outlet end; and a second, empty vessel 
is connected to the outlet of the mixing path. 
In the previously described apparatus and method of the invention, the 
conduit means may increase in flow area from the inlet end to the outlet 
end to thereby decrease the flow velocity of the flocculated solids and 
enhance their tendency to agglomerate and separate from the liquid. An 
intermediate settling vessel may be provided for receiving the flocculated 
solids and any remaining liquid from the conduit means, the settling 
vessel having a sloped bottom wall and a bottom outlet for liquid and 
flocculated solids, the collecting vessel being releasably connected to 
the bottom outlet of the settling vessel. The settling vessel may comprise 
an internal baffle extended across the vessel, the conduit means extending 
into the settling vessel on one side of the baffle; and an outlet for 
clarified liquid on an opposite side of the baffle near an upper end of 
the settling vessel. In some applications where fine particles of 
precipitate do not settle from the settling vessel into the collecting 
vessel, a further collecting vessel may be connected to this outlet for 
clarified liquid, to remove such fines. The conduit means may include 
static mixing elements between the second and third means for delivering. 
Optionally, static mixing elements may be included downstream of the third 
means for delivering. The conduit means may be curved into a flat coil, a 
helix, a spiral, a flattened helix or spiral, undulating pattern or other 
regular or irregular patterns. 
A further embodiment of the apparatus of the invention includes means for 
providing a solution containing a component to be removed; a mixing 
vessel; and first means for delivering the solution into the mixing 
vessel. Second means are provided for delivering a precipitating agent for 
the component into the mixing vessel. Third means are provided for 
delivering a flocculating agent for the precipitate into the mixing 
vessel, whereby flocculated solids are formed by the precipitate and the 
flocculating agent. A settling vessel is included for receiving 
flocculated solids and any remaining liquid from the mixing vessel, the 
settling vessel preferably having a sloped bottom wall and a bottom outlet 
for liquid and flocculated solids. An internal baffle is extended across 
the settling vessel from an upper end of the settling vessel downward to 
near the sloped bottom wall, thereby defining an inlet passage on one side 
of the baffle within the settling vessel, the inlet passage having a 
length sufficient to provide adequate residence time for formation or 
ripening of clumps of the flocculated solids. The inlet passage also may 
be defined by a downwardly extending conduit or nest of conduits within 
the settling vessel, rather than by a baffle. An outlet for clarified 
liquid is provided on an opposite side of the baffle near an upper end of 
the settling vessel. Fourth means are provided for delivering flocculated 
solids and liquid from the mixing vessel into the inlet passage. A 
collecting vessel having an inlet, releasably connected to the bottom 
outlet of the settling vessel, preferably is provided for continuously or 
intermittently receiving the flocculated solids and any remaining liquid, 
for permitting the flocculated solids to settle to a bottom of the 
collecting vessel and the remaining liquid to move toward an outlet of the 
collecting vessel, whereby the settled flocculated solids gradually will 
fill substantially the collecting vessel while at least a substantial pan 
of the remaining liquid gradually will pass from the collecting vessel, 
thereby permitting a filled collecting vessel to be disconnected from the 
bottom outlet of the settling vessel. 
A further embodiment of the method of the invention may include the steps 
of providing a solution containing a component to be removed; providing a 
mixing vessel; delivering the solution into the mixing vessel; delivering 
a precipitating agent for the component into the mixing vessel; delivering 
a flocculating agent for the precipitate into the mixing vessel, whereby 
flocculated solids are formed by the precipitate and the flocculating 
agent; providing a settling vessel for receiving flocculated solids and 
any remaining liquid from the mixing vessel, the settling vessel 
preferably having a sloped bottom wall and a bottom outlet for liquid and 
flocculated solids; providing an internal baffle extended across the 
settling vessel from an upper end of the settling vessel downward to near 
the sloped bottom wall, thereby defining an inlet passage on one side of 
the baffle within the settling vessel, the inlet passage having a length 
sufficient to provide adequate residence time for formation or ripening of 
clumps of the flocculated solids; providing an outlet for clarified liquid 
on an opposite side of the baffle near an upper end of the settling 
vessel; delivering flocculated solids and liquid from the mixing vessel 
into the inlet passage; delivering flocculated solids and liquid from the 
settling vessel into a first collecting vessel having an inlet, releasably 
connected to the bottom outlet of the settling vessel, for receiving the 
flocculated solids and any remaining liquid; permitting the flocculated 
solids to settle to a bottom of the collecting vessel and the remaining 
liquid to move toward an outlet of the collecting vessel, whereby the 
settled flocculated solids gradually will fill substantially the 
collecting vessel while at least a substantial pan of the remaining liquid 
gradually will pass from the collecting vessel, thereby permitting a 
filled collecting vessel to be disconnected from the bottom outlet of the 
settling vessel; removing the first collecting vessel when it is filled; 
and connecting a second, empty collecting vessel to the outlet of the 
mixing path. 
In any of the previously described apparatus and methods of the invention, 
the outlet of the collecting vessel may be above the bottom of the vessel; 
and the flocculated solids and any remaining liquid may flow into the 
collecting vessel near the bottom of the vessel, whereby any remaining 
liquid flows upward through previously settled solids, thereby removing 
fines before the liquid reaches the outlet of the vessel. By "near the 
bottom of the vessel" is meant that flocculated solids and liquid are 
flowed into the collecting vessel close enough to the bottom to avoid 
undue breaking up of the clumps entering or already resting in the vessel 
or excessive stirring up of fines. The clearance to the bottom of the 
vessel may be adjusted depending on the spent solution being treated. The 
collecting vessel may comprise a filter for removing fines from liquid 
flowing through the outlet of the collecting vessel. The filter may be a 
porous bag suspended within the collecting vessel, the flocculated solids 
being captured within the bag. When a filter bag is used, the primary mode 
of separation is settling within the bag; the secondary mode of separation 
is filtration through the bag; and the tertiary mode is wicking of liquid 
by the bag. When the outlet from the collecting vessel is located above 
the bottom of the vessel, the filter may comprise an annular ring of 
filter material supported at the level of the outlet; and the inlet of the 
collecting vessel may open inside the annular ring, whereby flocculated 
solids settle to the bottom of the collecting vessel and remaining liquid 
eventually rises to flow through the annular ring to the outlet. 
Also in any of the previously described apparatus and method of the 
invention, the flocculated solids and any remaining liquid flow into the 
collecting vessel near the bottom of the collecting vessel, whereby any 
remaining liquid must flow upward through previously settled solids, 
thereby removing fines from the liquid; a filter element is positioned 
within the collecting vessel, the filter element dividing the interior of 
collecting vessel into a first chamber for receiving flocculated solids 
and liquid and a second chamber for receiving liquid passed through the 
filter element; and the outlet of the collecting vessel is connected to 
the second chamber. Preferably, the first chamber is substantially larger 
in volume than the second chamber. The filter element may extend upward 
from the bottom of the collecting vessel and may be tubular; and the 
second chamber may be surrounded by the filter element. The filter element 
may be tubular and the first chamber may be defined within the filter 
element. The filter element may be tubular and the second chamber may be 
defined within the filter element. 
In accordance with a further aspect of the invention, an apparatus for 
collecting and separating flocculated solids and liquid may include a 
collecting vessel having an interior and a bottom; an inlet for 
flocculated solids and liquid to flow into the collecting vessel near the 
bottom, whereby the liquid must flow upward through previously settled 
solids, thereby helping to remove fines from the liquid; a filter element 
positioned within the collecting vessel, the filter element dividing the 
interior into a first chamber for receiving flocculated solids and liquid 
from the inlet and a second chamber for receiving liquid passed through 
the filter element; and an outlet for the liquid to flow from the second 
chamber. 
In accordance with yet a further aspect of the invention, a method for 
collecting and separating flocculated solids and liquid may include the 
steps of providing a collecting vessel having an interior and a bottom; 
flowing flocculated solids and liquid into the collecting vessel near the 
bottom, whereby the liquid must flow upward through previously settled 
solids, thereby removing fines from the liquid; positioning a filter 
element within the collecting vessel, the filter element dividing the 
interior into a first chamber for receiving the flow of flocculated solids 
and liquid and a second chamber for receiving liquid passed through the 
filter element; and flowing the filtered liquid from the second chamber. 
In the further aspects of both the apparatus and method of the invention, 
the filter element may extend upward from the bottom and may be tubular; 
and the second chamber may be surrounded by the filter element. The filter 
element may be tubular and the first chamber may be defined within the 
filter element. The filter element may be tubular and the second chamber 
may be defined within the filter element. 
The apparatus and methods of our invention provide numerous significant 
advantages over the prior art. The apparatus is very versatile and works 
with a great variety of solutions to be treated and ingredients to be 
removed or recovered. It is clean, not messy, and eliminates direct 
handling of chemical precipitates, chemically coated filters and reaction 
chemicals. Automatic metering is used so that manual measuring of 
individual reactants for various batch sizes is not required. The 
apparatus is inexpensive to make and has a compact size requiring minimal 
floor space ("footprint") compared to prior art equipment. No large 
solution storage tanks are required since a continuous or intermittent 
method is used rather than batch. No large settling or precipitation tanks 
are needed, which in conventional systems may require from several hours 
to several weeks to accomplish satisfactory settling, depending on 
composition. The reaction conduit and collection vessels do not need to be 
open to atmosphere. Therefore, with our invention there is a minimum of 
odors and contamination of solutions, worker exposure to vapors, corrosion 
of nearby equipment and facilities or need for large ventilating systems. 
Any toxic or dangerous gases such as ammonia which might be encountered 
are typically retained within the system. The collection vessel is 
inexpensive and also acts as the shipping vessel for precipitated solids. 
The method greatly extends the life of the filter used since settling is 
the primary mode of solids separation and filtration is only a secondary 
mode, even though done in the same vessel. Therefore a much greater 
quantity of solution may be passed through this system compared to 
conventional filtration. The apparatus is simple, having very few moving 
parts and easily replaceable components and therefore requires minimal 
maintenance and downtime. The method and apparatus provide real-time 
treatment of solution by simultaneous treatment steps at various zones in 
the system; therefore, each increment of solution receives essentially the 
same treatment regardless of when it enters the system. The method is 
highly reproducible for a given composition of solution. Use of the method 
may simplify compliance with certain hazardous chemical storage 
regulations by minimizing the amount and duration of storage of such 
hazardous materials. 
Other advantages are provided by our invention. The apparatus is easy to 
use by operators unskilled in chemical technology. The apparatus is 
portable, easily transportable between sites by one person, and not 
dependent on fixed supporting utilities except for an electric source. It 
can be taken to the photographic or other process as needed and returned 
to storage when not needed. The apparatus provides totally automatic 
operation, is able to operate unattended at all hours including overnight, 
and starts and stops automatically as necessary. The apparatus and method 
provide extremely safe operation due to relative lack of chemical spills 
and splashes since all reactants and products are contained. Only small 
quantities are being processed at a given time which precludes disastrous 
spills. All components are commercially available and readily purchased 
off the shelf without long lead times. The invention provides an 
inexpensive method, including materials and labor, of separating and 
transporting solids compared to existing techniques. The apparatus 
minimizes the potential to generate fine solid particles which normally 
tend to confound conventional settling and filtration methods. The 
invention features a built-in dewatering step which promotes compaction of 
the flocculated solids and concentration of the recovered silver to 
eliminate unwanted water, which thereby decreases shipping and recovery or 
treatment costs. The collecting/shipping vessel is totally combustible, 
making refining of recovered metals less complicated and therefore less 
costly. The apparatus permits better estimates of the recovered silver in 
the shipping container by the equipment user, due to transparency of the 
vessel, consistency of collected product, and improved ability to estimate 
value of contents from weight, thereby ensuring that user will get a fair 
price from the refiner. The apparatus and method effectively operate over 
all typical effluent ranges of silver typically encountered in 
photographic processing wastes, from milligrams per liter to tens of grams 
per liter, using a single apparatus. This is compared to other 
conventional recovery systems which may require two or more systems in 
tandem, one for primary recovery to recover economically higher levels and 
the second for secondary recovery to reduce residuals to environmentally 
acceptable low levels. The invention permits flocculated solids, once 
collected, to remain undisturbed after collection, thereby eliminating 
separate secondary recovery operations. The apparatus can be operated by 
gravity flow if desired thereby saving costs of pumps and electricity. 
Therefore, the apparatus could readily be adapted for use in remote 
locations that do not have electricity. 
Still other advantages are provided by our invention. The ready 
releasability and changeover of collecting vessels minimizes downtime and 
complexity of operation. The invention permits easy handling of reagents 
and collection vessels because of the relatively small sizes involved and 
the sealed nature of the collection vessels. The apparatus typically 
produces higher density flocculated solids in a given time than in 
conventional clarifiers because of the solids agglomeration or compaction 
mechanism inherent to the method. The reaction conduit is easily visually 
observable in operation to immediately discern and correct any operational 
problems. Since many applications of the invention will be in a retail 
environment, the apparatus can be enclosed easily in a simple and 
clean-appearing housing, which does not suggest an industrial treatment 
process. The simplicity and small number of components of the apparatus 
permit arrangement of the components in a wide variety of external 
geometries for different user circumstances. Batches of photographic 
processing or other solutions containing a variety of concentrations of 
silver or other ingredients are homogenized to a considerable degree and 
their concentrations damped out to more uniform concentrations, for more 
uniform treatment and greater reagent cost savings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The following is a detailed description of the preferred embodiments of the 
invention, reference being made to the drawings in which the same 
reference numerals identify the same elements of structure in each of the 
several Figures. 
FIG. 1 illustrates an apparatus 10 which functions in accordance with one 
embodiment of the method of the invention. The apparatus is useful for 
removing a variety of components from solutions, but is particularly 
useful for primary or secondary removal of silver from spent 
photo-processor solutions. An infeed conduit 12 is provided to deliver 
spent photo-processor solutions from a holding tank, not illustrated, or 
directly from a photo-processing machine. The solutions are drawn through 
conduit 12 by a first pump 14 for delivering the solutions to the inlet 
end 16 of a reaction conduit means 18 which defines a mixing path. In some 
applications of the invention, pump 14 may be eliminated and the spent 
solution may be delivered from a tank, not illustrated, positioned to 
provide an adequate gravity head for flow into conduit 12. Conduit means 
18 may be conventional flexible tubing such as transparent plastic tubing 
or the like and may be formed as illustrated into a helical coil to 
enhance mixing and to provide a compact arrangement. The axis of the coil 
may be generally vertical, as illustrated, or horizontal or at any 
intermediate orientation. The coil may be open or flattened and its 
perimeter may have any regular or irregular shape. A check valve 20 
optionally may be provided at the outlet of pump 14. A source 22 of a 
suitable precipitating agent, such as a solution of TMT for removal of 
silver, is connected to a second pump 24 for delivering the precipitating 
agent into conduit means 18 at a point just downstream of inlet end 16 and 
check valve 20. The spent solution and precipitating agent also may be 
delivered to the conduit means in the reverse order or essentially 
simultaneously, provided the proper ratios are maintained. A check valve 
26 optionally may be provided downstream of pump 24 at an inlet 27 to the 
conduit means. A source 28 of flocculating agent is connected to a third 
pump 30 for delivering the flocculating agent into conduit means 18. A 
suitable flocculating agent for removal of silver is a cationic copolymer 
of acrylamide and acryloyloxyethyl trimethyl ammonium chloride available 
from the Calgon Corporation as Product No. POL-E-Z-2406. A check valve 32 
optionally may be provided downstream of pump 30 at an inlet 33 to the 
conduit means. 
The flow from pump 30 is delivered into conduit means 18 downstream from 
inlet 27 from pump 24 at a distance chosen to provide a residence time 
sufficient for mixing the spent solutions and the precipitating agent and 
for forming a precipitate well suited for flocculation. That is, the 
residence time is long enough to enable crystals of precipitate to grow or 
ripen to a point at which addition of a flocculating agent will cause 
formation of flocculated particles which tend to agglomerate into clumps. 
Different spent solutions may require different residence times. The 
length of conduit can be readily determined experhnentally for various 
spent solutions by those skilled in the art. Once the residence time has 
been determined for a given spent solution, reproducible results can be 
achieved in accordance with the invention. Conventional static mixing 
elements, such as those disclosed in U.S. Pat. 3,286,992, may be installed 
in conduit means 18 upstream or downstream, or both, of inlet 33 to 
facilitate good mixing. However, in many applications ordinary turbulent 
flow of spent solutions and precipitating agent will provide adequate 
mixing without static mixing elements. In the illustrated embodiment, 
pumps 14, 24 and 30 may be conventional peristaltic, diaphragm or bellows 
pumps or the like and may be driven by a common motor 34 to synchronize 
the pulses of liquid into conduit 18, thus potentially eliminating any 
need for check valves 20, 26, 32. Alternatively, if there is sufficient 
difference in elevation among reaction conduit means 18 and sources 22, 28 
to provide adequate gravity head for flow into reaction conduit means 18 
to produce suitable mixing of spent solution, precipitating agent and 
flocculating agent, then pumps 24, 30 may be eliminated without departing 
from the scope of the invention. Also, the downward direction of flow 
through conduit means 18 illustrated in FIG. 1 may be reversed to upward 
flow, as will be discussed further with regard to FIG. 4. 
The outlet end 36 of conduit means 18 preferably is downstream from inlet 
33 from pump 30 at a distance chosen to provide a residence time 
sufficient for forming or ripening clumps of flocculated particles of the 
precipitate. Those skilled in the art will appreciate that various 
combinations and concentrations of spent solutions, precipitating agent 
and flocculating agent will produce flocculated solids having different 
characteristics and requiring different residence times to form clumps 
which will settle properly. As in the case of residence time for mixing of 
spent solution and precipitating agent, the length of conduit required for 
formation of such clumps can be readily determined experimentally for 
various anticipated combinations, after which reproducible results can be 
achieved. 
The flocculated solids and remaining liquid flow from outlet end 36 into a 
preferably enclosed collecting vessel 38 in accordance with the invention. 
Collecting vessel 38 preferably is small enough to be handled manually, 
sealed and shipped when full of flocculated solids and some liquid. A one 
to ten gallon (3.785 to 37.85 L) container will suffice for most 
applications. Collecting vessel 38 typically will be cylindrical but may 
have many shapes including a bottom 40, side wall(s) 42 and a preferably 
sealed top 44. A removable, threaded cap or closure 46 is provided to 
manually, releasably connect conduit means 18 to vessel 38. Closure 46 has 
a through passage to which conduit means 18 is connected in any convenient 
manner, such as those to be discussed subsequently. Within vessel 38, a 
conduit 48 preferably extends below closure 46 to deliver the flocculated 
solids and liquid to a location near bottom 40. Thus, as the flocculated 
solids and liquid flow into the vessel, a mass 50 of solids collects on 
the bottom and a layer or volume 52 of separated liquid collects above 
mass 50. By "near the bottom of the vessel" is meant that flocculated 
solids and liquid are flowed into the collecting vessel close enough to 
the bottom to avoid undue breaking up of the clumps entering or already 
resting in the vessel or excessive stirring up of frees. The clearance to 
the bottom of the vessel may be adjusted depending on the spent solution 
being treated. When a sufficient mass 50 has accumulated on bottom 40 to 
rise above the lower end of conduit 48, the subsequently discharged 
flocculated solids and liquid will be forced to flow into mass 50, where 
the flocculated solids and much of the fines will be caught due to the 
self-filtering effect of mass 50. Liquid will rise through mass 50 without 
much disturbing the settled flocculated solids. The level of the clarified 
liquid rises to increasingly higher levels until the liquid begins to 
leave the vessel through another passage in closure 46, which may be 
connected to an optional check valve 54 provided just downstream of 
closure 46 in a discharge conduit 56. A final filter 58 may be provided in 
conduit 56 if necessary to remove additional fines before the liquid is 
discharged from the apparatus, such as to the sewer. FIGS. 14 to 31 
illustrate alternate embodiments of collecting vessel 38 and modes for its 
attachment to receive flocculated solids and liquid. As can be understood 
from FIGS. 1 and 14 to 31 and their associated descriptive passages in 
this specification, collecting and shipping vessel 38 is closed, other 
than at the means for manually, releasably connecting the conduit for 
incoming liquid and solids and the port or conduit for outgoing liquid. As 
illustrated, while the collecting and shipping vessel is connected to the 
overall apparatus, the vessel's being closed in this manner effectively 
prevents removal of settled flocculated solids from locations within the 
vessel which are below the level of the liquid in the vessel. As a result 
of this arrangement, the settled flocculated solids progressively 
accumulate, agglomerate and compact, expelling entrapped liquid and 
forcing the liquid upward from the agglomerated mass 50 toward the outlet 
of the vessel. 
Use of collecting vessel 38 is preferred in accordance with the invention 
to provide optimum assurance that flocculated solids, once formed and 
ripened within conduit means 18, will be able to settle to a location 
where they subsequently will be disturbed very little and will be able to 
agglomerate into mass 50. As the higher specific gravity mass 50 forms and 
agglomerates on bottom 40, the lower specific gravity liquid which entered 
with the flocculated solids is gradually displaced upward in the vessel 
until it reaches discharge conduit 56. Then, when vessel 38 is full, 
incoming flow is stopped in any of the manners to be discussed shortly. 
The vessel is removed, sealed and replaced by an identical empty vessel. 
The full vessel may then be shipped away for further processing, such as 
to a refiner for recovery of precious metal. 
EXAMPLE 1 
A fixer/bleach-fixer/stabilizer/low-flow wash mixture from the KODAK 
Flexicolor film process C-41 and KODAK Ektacolor paper process RA-4, 
containing 3 grams/liter silver, was used as the feed solution in the 
apparatus shown in FIG. 1. Reaction conduit means 18 was a horizontal, 
flattened helix configuration having a generally oval shape. A 15% by 
weight solution of TMT (TMT-15) at a concentration of 305 gm/L in water 
was the precipitating agent in source 22. American Cyanamid Magnifloc 846 
A at a concentration of 1.0 gm/L in water was used as the flocculating 
agent in source 28. The total flow of solutions was as follows: 308 ml/min 
of spent solutions from pump 14, 6.15 ml/min of precipitating agent from 
pump 24, and 6.15 ml/min of flocculating agent from pump 30. Conduit 18 
was a flattened helical coil of flexible transparent polyvinyl chloride 
tubing having a 0.375 inch (9.53 mm) inside diameter. Pumps 14, 24 and 30 
were peristaltic pumps operated simultaneously on a common shaft by a 
100-rpm motor 34. Collecting vessel 38 was a commercial 5-gallon (18.93 L) 
seeded polyethylene can for liquid shipment with top openings, of a 
translucent nature which allowed the operation and contents to be observed 
as the can filled with solids and liquid. Optional check valves 20, 26 and 
32 were not used. Spent solution was injected into inlet end 16 at the 
side leg of a nylon tee, with precipitating agent injected into inlet 27 
at an end leg of the same tee. The tee exited into conduit 18 containing a 
static mixer section immediately downstream of inlet 27. Initially, the 
static mixer section was tested at 24 inches (610 mm) in length, but 
experimentation for this particular combination of spent solutions and 
precipitating agent established an optimum length in this trial to be 8 
inches (203 mm). A residence time downstream of the static mixing section 
sufficient for forming the silver-TMT precipitate initially was provided 
by a further conduit length of 26 inches (660 mm) downstream of the static 
mixer section; but further experimentation established this length to be 
more optimum at 20 inches (508 mm). Flocculating agent from source 28 was 
then injected through a second nylon tee into conduit 18 at inlet 33 from 
pump 30, the point of injection being approximately 28 inches (711 mm) 
downstream of inlet end 16. A second static mixer section, first tested at 
8 inches (203 mm) long and later optimized at 4.5 inches (114 mm) long was 
placed in conduit 18 immediately downstream of inlet 33. A residence time 
downstream of the second static mixer section sufficient for forming 
clumps of particles of precipitate was provided by a further conduit 
length of about 58 inches (1473 mm) which provided approximately 2 minutes 
residence time for growth or ripening of clumps. The flocculated solids 
formed in conduit 18 became pea-sized clumps of yellow material with a 
mucoid consistency. These clumps were discharged into collecting vessel 38 
through a 0.250 inch (6.35 mm) conduit 48 which ended about 0.5 inch (12.7 
mm) above bottom 40. The mass of solids 50 which gradually built up around 
the end of conduit 48 served as a filtering medium to remove residual 
fines. Liquid effluent from vessel 38 passed through a bag filter 58 as a 
final polishing filter which removed any remaining fines in the liquid. 
The apparatus was permitted to operate intermittently for several days, to 
simulate actual operating conditions in a photographic processing 
laboratory. As the mass of material sat undisturbed in the collecting 
vessel for several weeks, small pockets of liquid that had still been 
entrapped in the settled solids were expelled upward, until the bottom 
solids were a relatively homogeneous solid yellow mass. The final silver 
concentration in the clarified liquid was less than 1 mg/L. 
FIG. 2 illustrates an alternate embodiment of conduit means 18. Rather than 
the simple helical coil of conduit as in FIG. 1 or the flattened helix of 
Example 1, conduit means 18 can be arranged in an undulating, back and 
forth, rather sinusoidal pattern in which straight spans 60 of conduit are 
essentially horizontal between the connecting turns or curved portions 62. 
The changes of direction of the flow help to promote proper mixing. If 
desired for faster or more thorough mixing, conventional static mixing 
elements 64 of the type previously mentioned, may be installed in conduit 
means 18 between the inlet for precipitating agent and the inlet for 
flocculating agent, as indicated schematically by the cross-hatched areas. 
In some cases, static mixing elements may also be used after inlet 33 for 
flocculating agent. FIG. 3 illustrates another alternate embodiment of 
conduit means 18 in which the conduit is arranged in an undulating, up and 
down, rather sinusoidal pattern in which the straight spans 66 of conduit 
are essentially vertical between the connecting turns or curved portions 
68. FIG. 4 illustrates still another alternate embodiment of conduit means 
18 in which the conduit is arranged in a spiral whose radius decreases 
between inlet 16 and outlet 36. An increasing radius from inlet to outlet 
would provide more gentle turns for the growing clumps of flocculated 
solids. The axis of the spiral may be horizontal, vertical or at any 
intermediate orientation. The spiral may be open or flattened. In the 
embodiment of FIG. 4, the spent solution, precipitating agents and 
flocculating agent flow upwardly in the conduit, which helps to improve 
growth of the clumps of flocculated solids, particularly in intermittently 
operated systems. Upward flow also may be used in the other embodiments of 
conduit means 18. FIGS. 5 and 6 illustrate yet another alternate 
embodiment of conduit means 18 in which the conduit is coiled into a flat 
coil with conventional T-fittings 70 for connecting adjacent sections of 
conduit and delivering precipitating and flocculating agents to the 
conduit. The embodiments of FIGS. 3 to 6 also may include static mixing 
elements located as in the embodiment of FIG. 2 and in Example 1. Those 
skilled in the an will appreciate that conduit means 18 may be formed into 
a wide variety of regular or irregular geometric shapes including ovals, 
figure-eights, triangular or rectangular coils, flattened helixes and 
spirals and the like, without departing from the scope of the invention. 
FIG. 7 illustrates another embodiment of the apparatus of the invention in 
which conduit means 18 increases in flow area between inlet end 16 and 
outlet end 36. The increase in flow area may be stepwise, as illustrated, 
or gradual without departing from the scope of the invention. The 
increasing flow area permits the precipitate and the flocculated solids to 
grow or ripen more fully as they move progressively more slowly along the 
conduit, thereby reducing the percentage of fines delivered to collecting 
vessel 38. Such a reduction in the fines reaching the collecting vessel 
has been observed visually as the clumps of flocculated solids grow during 
movement along the conduit and as the percentage of silver-TMT fines 
decreases in the clarified liquid. Also, calculated residence times in the 
conduit correlate with reduction in fines; that is, longer residence times 
lead to reduced fines. An initial section 72 of conduit means 18 receives 
a mixture of spent solution and flocculating agent and preferably includes 
static mixing elements 64. 
EXAMPLE 2 
For example, with a flow rate of spent solution in the range of 175 to 400 
ml/min and a flow rate of precipitating agent (TMT-15) in the range of 3 
to 8 ml/min, tubing having an internal diameter in the range of 0.250 to 
0.375 inch (6.35 to 9.53 mm) and a length in the range of 0.5 to 3.0 inch 
(12.7 to 76.2 mm) as was suitable for section 72. More than 500 gallons 
(1893 L) of such spent solutions were processed. As the mixture flowed 
along section 72, the spent solution and the precipitating agent mixed 
thoroughly and particles of precipitate formed and grew. At the downstream 
end of section 72, the flocculating agent (American Cyanamid Magnifloc 846 
A) was delivered into the conduit at T-fitting 70 at a flow rate with 
range of 5 to 25 ml/min. The mixture of liquid, precipitate, flocculant 
and flocculated solids then flowed into a section 74 of conduit means 18 
having an internal diameter in the range of 0.375 to 0.625 inch (9.53 to 
15.88 mm) and a length in the range of 18 to 30 inches (457 to 762 mm). As 
the mixture flowed at lower speed along section 74, the precipitate 
gradually formed or ripened into larger and larger clumps of flocculated 
solids. The mixture then flowed into a section 76 of conduit means 18 
having an internal diameter in the range of 0.75 to 1.0 inch (19.1 to 25.4 
mm) and a length in the range of 18 to 30 inch (457 to 762 mm). As the 
mixture flowed at still lower speed along section 76, the clumps of 
flocculated solids continued to grow. The mixture then flowed into a 
section 78 of conduit means 18 having an internal diameter in the range of 
1.25 to 1.75 inch (31.8 to 44.5 mm) and a length in the range of 74 to 78 
inches (1880 to 1982 mm). As the mixture flowed even more slowly along 
section 78, the clumps of flocculated solids continued to grow and reached 
substantially their maximum size when the mixture reached outlet end 36. 
Suitable connectors 80 were used to join sections 74, 76 and 78. From 
outlet end 36, the mixture of liquid and ripened flocculated solids flowed 
through downcomer 48 into collecting vessel 38, where the flocculated 
solids agglomerated to form mass 50 and the liquid rose toward the outlet 
of the collecting vessel. Total silver content in the liquid effluent was 
in the range of 0.17 to 0.6 mg/L. 
In each of sections 74, 76 and 78, the diameter and length should be chosen 
to facilitate formation of clumps of flocculated solids and permit the 
largest clumps of flocculated solids to pass readily without being broken 
up too much. However, the diameter and geometry or layout of each section 
should not be so constricted that the clumps may settle in low spots 
during prolonged idle periods and block the flow or so large as to permit 
the clumps to be easily short circuited by the liquid. Those skilled in 
the art will appreciate that such diameters will vary depending on factors 
such as the concentrations of the spent solution, precipitating agent and 
flocculating agent; and the flow rate through the conduit. 
FIG. 8 illustrates a particular, more compact embodiment of the conduit 
means 18 of FIG. 7. In this case, the conduit may be formed readily as a 
panel of two sheets of thermoplastic which have been suitably 
thermmoformed or from plate stock of suitable material which has been 
conventionally machined or injection molded or formed by any convenient 
manufacturing process. A pair of sheets 82 of thermoplastic material such 
as polyvinyl chloride or acrylonitrile-butadiene-styrene may be 
thermoformed and sandwiched together to define conduit means 18. For ease 
of observation, one of such sheets may be transparent or translucent. An 
initial mixing and ripening section for spent solution and precipitating 
agent is defined between the inlet from check valve 26 and the inlet from 
check valve 32. 
EXAMPLE 3 
For infeed conditions of the type described for Example 2, the initial 
mixing section had an internal diameter of about 0.5 inch (12.7 mm) and a 
length of about 32 inches (813 mm). Depending on the particular spent 
solution and precipitating agent, static mixers 64 could be provided in 
this initial mixing section. Downstream of the inlet for flocculating 
agent through valve 32, a second mixing and ripening section began with an 
internal diameter of about 0.5 inch (12.7 mm) over a length of about 16 
inches (407 mm); then extended through a smooth transition portion 84 into 
a section having an internal diameter of about 0.875 inch (22.23 mm) over 
a length of about 32 inches (813 mm); and finally extended through a 
smooth transition portion 86 into a section having an internal diameter of 
about 1.25 inch (31.8 mm) over a length of about 48 inches (1219 mm) 
terminating at a smooth portion 88 which opened through outlet end 36. If 
desired, mounting pockets for check valves 20, 26 and 32 could be 
incorporated between the thermoplastic sheets. In the embodiment of FIG. 
8, the straight runs of conduit means 18 preferably were arranged 
vertically in operation. Based on laboratory tests, during operation 
clumps of flocculated solids formed and grew or ripened as they passed up 
and down through the conduit, with the clumps agglomerating to form 
progressively larger and larger masses of flocculated solids and the 
liquid acting to drive the mixture through the conduit. The growing masses 
of flocculated solids tend to entrap fines moving along in the liquid. 
Total silver content in the liquid effluent was less than 1.0 mg/L, after 
the polishing filter. Those skilled in the art will appreciate that the 
conduit means for FIG. 7 may be foraged from a series of two or more 
connected panels of conduits, without departing from the scope of our 
invention. Parallel panels also could be used. 
For some spent solutions and in continuous rather high volume applications, 
addition of the precipitating agent may generate a high percentage of fine 
particles which are relatively slow to agglomerate even after addition of 
the flocculating agent. The modification of FIG. 9 is configured to reduce 
the number of such fines. A further improvement in fines reduction will be 
discussed with regard to FIG. 25. A generally cylindrical settling vessel 
90 is provided for receiving the effluent of flocculated solids, fines and 
liquid from conduit means 18. Vessel 90 comprises a sloped or concave 
bottom 92 having an outlet opening 94 at its lowest point. A valve 96 
optionally may be included to control the flow of solids and liquids, as 
described in more detail with regard to FIGS. 21 to 29. Within vessel 90 a 
baffle plate or wall 98 extends across a chord of the cross section of the 
vessel and terminates at a lower edge 99 near to bottom 92. Solids and 
liquid flowing in conduit means 18 are discharged through outlet end 36 
into the open upper end of an enclosed inlet passage or downcomer 100 on 
one side of baffle plate 98. Alternatively, a downcomer tube may be used 
rather than baffle plate 98. See also the discussion of the embodiment of 
FIG. 11. As fines, clumps of flocculated solids and liquid flow downward 
in passage 100, the clumps continue to agglomerate and fines continue to 
adhere to each other and to existing clumps. On the opposite side of 
baffle plate 98 near the upper end of vessel 90, an outlet opening 102 is 
provided for clarified liquid rising within the vessel. At the bottom of 
the settling vessel, rather than forming a thick accumulation for later 
removal in the manner of the prior art, flocculated solids settle 
continuously or intermittently through normally open valve 96 into 
collecting vessel 38 in the manner previously described. Thus, once the 
flocculated solids settle to the bottom of vessel 38, they essentially are 
not again disturbed. Liquid that enters collecting vessel 38 may be 
removed in the manner described with regard to FIG. 1. Alternatively, the 
liquid simply may be displaced upward gradually within the collecting 
vessel until the liquid actually flows slowly back into settling vessel 
90, in the opposite direction of the solids passing downward through valve 
96, and eventually leaves through outlet 102. When the collecting vessel 
is full, valve 96 is simply closed and vessel 38 is removed and replaced 
without any need to disturb again the solids already settled therein. 
Since a small amount of liquid and solids may remain in the short length of 
tubing below valve 96 but above collecting vessel 38, the arrangement of 
FIG. 10 may be used to provide a convenient way to avoid spilling. An 
outlet 104 for liquid is provided in or near the top of the collecting 
vessel and is connected via a suitable conduit 106, which optionally may 
include a filter for fines, to an overflow collection vessel 108 for 
clarified liquid. Then, after valve 96 has been closed, outlet 104 may be 
opened and connected to conduit 106 to allow the small amount of liquid 
and solids to drain into the collecting vessel and displace liquid through 
opening 104 to collection vessel 108. Vessel 38 may be tilted slightly for 
decanting, if necessary. When the small amount has drained from below 
valve 96, outlet 104 may be closed and the liquid in vessel 108 may be 
returned to settling vessel 90, for instance. 
FIG. 11 illustrates an embodiment of the invention in which the flat 
reactor coil of FIGS. 5 and 6 has been combined with the settling vessel 
of the apparatus of FIG. 9. A standpipe or downcomer 110 of somewhat 
larger diameter than conduit means 18 at outlet end 36 may be attached to 
conduit means 18 and extended downward through inlet passage 100 toward 
bottom 92. Thus, flocculated solids and fines passing downward through 
standpipe 110 will experience minimal additional shearing action and will 
have additional time to grow or ripen before flowing out into the still 
larger inlet passage 100 and on toward the bottom of settling vessel 90. 
Because standpipe 110 ends well above the lower edge 99 of baffle 98, any 
buoyant particles leaving standpipe 110 will tend to rise within passage 
100 and have still more tinge to precipitate, agglomerate and settle. 
Thus, settling time for fine particles is extended in this embodiment. At 
the stone time, the clumps of flocculated solids will settle to bottom 92 
and move on through outlet opening 94 into the collecting vessel. 
FIG. 12 illustrates another embodiment in which sources 22 and 28 and a 
holding tank 111 for spent solutions respectively deliver precipitating 
agents, flocculating agents and spent solutions into a rigid conduit means 
18 extended downward into inlet passage 100 next to baffle 98. If desired, 
conduit means 18 may be attached to or formed within baffle 98. For 
applications in which particularly effective flocculation is achieved 
within conduit means 18, baffle 98 may be omitted. Preferably, the conduit 
includes static mixer elements 64 upstream of the point of delivery of the 
flocculating agent. Depending on the degree of mixing of spent solutions 
and precipitating agent needed to ensure adequate precipitation, the 
length of conduit including optional static mixing elements can vary and 
flocculating agent from source 28 can be delivered into conduit means 18 
at any point along a span 112 of the conduit. If necessary to permit 
further growth of the clumps of flocculated solids, an extension conduit 
114 can be added to lengthen conduit means 18. A polishing filter 116 may 
be connected to outlet 102 if necessary for removal of fines. 
In operation of the embodiment of FIG. 12, spent solutions are pumped out 
of holding tank 111 directly into conduit means 18. Precipitating agent is 
pumped from source 22 into the conduit just after entry of the spent 
solution and the two are mixed vigorously by mixer elements 64. After 
sufficient mixing of these solutions has been achieved, the flocculating 
agent is introduced along span 112. No further mixer elements are used 
after introduction of the flocculating agent, to avoid breaking up the 
clumps of flocculated solids as they move along conduit means 18. Those 
skilled in the an will appreciate that the precise point for introduction 
of the flocculating agent in this and other embodiments of our invention 
can be determined empirically and will depend on the number and type of 
mixer elements needed, the compositions and concentrations of the spent 
solutions and the precipitating agents, the type and concentration of the 
flocculating agent, the viscosity of the overall mixture, the pressures 
and flow rates of the various liquids and related factors. 
FIG. 13 illustrates still another embodiment of the invention in which the 
various solutions are mixed in a vessel rather than in a continuous 
conduit. A valve 118 and a valve 120, respectively, are used to control 
gravity flow of precipitating agent and flocculating agent into a mixing 
vessel 122. Within holding tank 111, a float switch 124 is used to 
indicate the presence of a sufficient volume of spent solution to warrant 
operating the system. A valve 125 may be closed to stop flow from holding 
tank 111. Pump 14 delivers the spent solution into mixing vessel 122 where 
a float switch 126 is used to indicate the presence of a sufficient volume 
of all three solutions. Mixing in vessel 122 may result simply from 
turbulence of the liquids as they are introduced into the vessel or from 
use of a conventional prop mixer, not illustrated. A valve 128 may be 
closed to prevent back flow to the inlet of pump 14. A valve 130 may be 
closed to prevent flow toward a pump 132 used to deliver a mixture of 
liquids, precipitates and growing or ripening clumps of flocculated solids 
into the upper end of conduit 110 within settling vessel 90. Pump 132 
preferably is a bellows pump or similar pump with low shearing tendencies 
to minimize any tendency to break up clumps of flocculated solids. As the 
clumps move downward in conduit 110, they continue to grow or ripen. A 
conventional programmable controller, not illustrated, may be used to 
govern to operation of the various pumps and valves. 
The system of FIG. 13 preferably functions in a sort of continuous batch 
mode in which batches of liquids are pumped through periodically. However, 
those skilled in the an will appreciate that continuous operation also can 
be achieved in accordance with the invention, except for brief shutdown 
periods to exchange collecting vessels 38, to replenish sources 22 and 28 
or to change filters. In a continuous batch mode, spent solutions from 
photoprocessing systems are added to holding tank 111, either by manual 
dumps or by hoses or pipes from the photoprocessing system. Valves 118, 
120, 125, 128 and 130 are closed. When the level of spent solutions 
reaches a predetermined level, float switch 124 signals the controller to 
open valve 125 and turn on pump 14 to deliver spent solution to mixing 
tank 122. As spent solution is pumped into mixing vessel 122, valve 118 is 
opened by the controller to deliver a predetermined quantity of 
precipitating agent which mixes turbulently with the incoming spent 
solution. When the level of solutions reaches a predetermined level, as 
determined by a timer in the controller or by float switch 126, the 
controller closes valve 125 to stop the flow of spent solutions from tank 
111, opens valve 128 to drain vessel 122 to the inlet of pump 14 and 
closes valve 118 to stop the delivery of precipitating agent. Pump 14 
continues to operate, at the same or a lower speed, to circulate the 
mixture of spent solution, precipitating agent and ripening precipitate 
from vessel 122 through valve 128 to pump 14 and back to vessel 122. After 
sufficient time has passed for adequate mixing, valve 120 is opened by the 
controller to deliver a predetermined quantity of flocculating agent into 
mixing vessel 122 and then closed. Circulation of the mixture continues at 
the same or lower speed until sufficient mixing has occurred to form a 
satisfactory flocculated precipitate. Pump 14 then is stopped; valve 128 
is closed; valve 130 is opened; and pump 132 is turned on to deliver 
liquids, precipitates and flocculated solids to the inlet of conduit 110 
within settling vessel 90. Though two pumps 14 and 132 are illustrated, 
those skilled in the art will appreciate that these functions can be 
performed with a single pump and suitable valving and piping. 
Within conduit 110, the flocculated solids grow or ripen as they settle 
toward the bottom of vessel 90. At the lower end of baffle 98, most of the 
liquid and some of the fines separate from the clumps of flocculated 
solids and flow upward, eventually leaving through outlet 102 and filter 
116 where any remaining fines are removed. The liquid discharged from 
filter 116 may be discarded. At the same time, most of the flocculated 
solids flow downward through valve 96 into collecting vessel 38. When 
vessel 38 has filled with flocculated solids and some liquid, valve 96 is 
closed manually to permit the full vessel to be removed and replaced with 
an empty one. Any liquid between valve 96 and collecting vessel may be 
collected manually and returned to settling vessel 90 or holding tank 111. 
Vessel 38 of course may be removed and replaced at any time, whether full 
or not. 
FIGS. 14 to 20, 30 and 31 illustrate alternative forms of collecting vessel 
38 in accordance with the invention, which include various types of 
built-in filters to remove fines from the clarified liquid. In each of 
these collecting vessels, the liquid and clumps of agglomerated solids 
flow into a first chamber of larger flow area than that of the inlet 
conduit to the vessel, so that the flow velocity decreases and the clumps 
are permitted to settle, predominantly due to gravity effect, to the 
bottom of the vessel, before the liquid encounters the filter element. 
Thus, the life of the filter element is extended since most of the 
incoming solids do not encounter the filter before settling. Preferably, 
when metals are to be removed from the flocculated solid, all materials of 
the collecting vessel should be combustible to enable a refiner to place 
the entire container in a refining furnace. 
These collecting vessels may be used for primary collection and filtration 
as in the systems of FIGS. 1 to 8, where the flocculated solids are 
settled directly in the vessel without any presetting. Typically, this 
would mean that all liquid undergoing treatment eventually would pass 
through the collecting vessel. Such an arrangement is appropriate where 
the flocculated or precipitated solids tend to settle quickly; however, 
buoyant or pasty solids might tend to blind or clog the filter rather 
quickly. Alternatively, such collecting vessels can be used for secondary 
settling and filtration, as in the systems of FIGS. 9 to 13, where much of 
the clarified liquid is removed from the settling vessel 90 and the solids 
are presettled in settling vessel 90 before passing into collecting vessel 
38. In such secondary applications, the outlet from collecting vessel can 
be closed much of the time, making settling the primary mechanism of 
separation of liquid and solids, and can be opened only when necessary to 
remove accumulated liquid. A tertiary use of such collecting vessels would 
be as receivers for liquid flowing from settling vessel 90 through outlet 
102 where a small amount of residual fines may be present. 
Except for the embodiments of FIGS. 30 and 31, each vessel 38 comprises a 
simple pail or bucket 134 which preferably is partially or fully 
transparent or translucent to permit visual observation of mass 50 of 
flocculated solids on the bottom of the vessel. The vessel is closed by a 
preferably sealed lid or closure 136 so that, once filled, the vessel may 
be capped and used as a shipping container. In the embodiment of FIG. 14, 
an inlet conduit 138, which may be nested within another solid or 
perforated cylindrical baffle 139, extends downward from the underside of 
closure 136 and preferably extends near to the bottom of bucket 134, not 
illustrated. Thus, as previously described, flocculated solids will tend 
to settle around the lower end of the inlet conduit and force incoming 
liquid and solids to flow into and through previously settled solids to 
remove fines and improve growth of the clumps of flocculated solids. 
Generally, the smaller the diameter of bucket 134, the more the solids 
will tend to stir up in the bottom as more liquid and flocculated solids 
are introduced. For flow rates into the bucket in the range of 50 to 1000 
ml/min, an internal diameter in the range of 4 to 30 inches (102 to 762 
mm) would be expected to give good results. A filter support disk 140 
extends radially around the inlet conduit and provides a support for the 
upper edge of an annular filter element 142, such as a ring of pleated 
paper filter material. An annular filter support ring 144 supports the 
lower edge of filter element 142. Thus, liquid and any fines flowing 
upward through mass 50 of flocculated solids move toward filter element 
142 where the fines are removed. The clarified liquid then passes through 
a radial and axial clearance 146 surrounding the filter and above support 
disk 140, and leaves the vessel through a top outlet 148. 
In the embodiment of FIG. 15, filter element 142 is replaced by a bag 
filter 150 of suitable porosity. Preferably, inlet conduit 138 extends 
close to the bottom of the bucket, not illustrated. The edge of the mouth 
of filter 150 is supported at the periphery of support disk 140. The 
clarified liquid then flows through the bag filter and leaves through a 
top outlet 152. The bag filter also helps to wick liquid out of mass 50. 
When the filter is full, vessel 38 is removed and replaced. In the 
embodiment of FIG. 16, support disk 140 has been replaced by an annular 
filter support ring 154 mounted on the underside of closure 136; and a 
side outlet 156 is provided through the wall of the bucket. 
In the embodiments of FIGS. 17 to 20, conventional cylindrical, pleated 
paper filter cartridges are used to remove fines. In the embodiment of 
FIG. 17, the axis of a filter cartridge 158 is set horizontally to allow 
the clarified liquid to pass from the interior of the filter through 
outlet 156. In the embodiment of FIG. 18, inlet conduit 138 extends toward 
the bottom of the bucket at an off-center location. A baffle wall 160 
extends across the width of the bucket to stop solids from short 
circuiting to the filter, thus allowing fines more time to agglomerate and 
clumps of solids more time to settle into mass 50. A filter cartridge 162 
is set horizontally on the opposite side of baffle wall 160 from inlet 
conduit 138, to allow the clarified liquid to pass through a centrally 
located top outlet 164. In the embodiment of FIG. 19, the positions of 
inlet conduit 138 and outlet 164 are reversed from those of FIG. 17; and a 
filter cartridge 166 is set vertically. In the embodiment of FIG. 20, the 
positions of inlet conduit 138 and outlet 164 are reversed from those of 
FIG. 18. A restriction may be provided in outlets 156 and 164 to control 
the flow rate through collecting vessel 38 and reduce the chances of 
stirring up fines from mass 50. 
Normal density differences between the flocculated solids and the liquid 
should allow the solids to settle into vessel 38 and the liquids to rise 
back into settling vessel 90 for discharge through outlet 102 or to rise 
within vessel 38 for discharge through outlet 56, 148, 152, 156 or 164. 
When the collecting vessel first begins to fill, entry of solids and 
liquid naturally will cause convection currents, coupled with Brownian and 
displacement movement of the solids. In the collecting vessels of FIGS. 1, 
14 to 20, 30 and 31, these currents and disturbances are confined to the 
interior of the vessel. If the liquids and solids are discharged from 
conduit 138 a substantial distance above the bottom of the vessel, the 
height through which the solids must settle will decrease as the vessel 
fills and mass 50 accumulates, which will tend to reduce such currents and 
disturbances. However, as previously discussed, preferably the flocculated 
solids and liquids are discharged near the bottom of the collecting vessel 
to take advantage of the filtering effect of mass 50. For the collecting 
vessels of FIGS. 1 and 14 to 20, the vessels eventually will be 
substantially full of settled solids, plus a rather thin covering layer of 
liquid and some liquid held interstitially within mass 50. At that time, 
the full vessel is removed and replaced. 
FIGS. 21 to 29 illustrate various alternative features of the invention 
which can be used to connect and disconnect vessel 38 from the overall 
system. Whether or not vessel 38 includes an outlet for liquid, a quick 
disconnect fitting, such as a conventional Banjo fitting, may be provided 
in the conduit leading into vessel 38. Suitable conventional quick 
disconnect fittings are available from Terra Products, Inc. of 
Crawfordsville, Ind. The female end 168 of such a fitting cooperates in 
the known manner with the male end 170 and the fitting may be oriented as 
illustrated in FIG. 21 or FIG. 22. In the arrangement of FIG. 22, liquid 
and solids draining from male end 170 tend to flow into the open cavity 
176 of female end 168, thus reducing chances of spillage. Below the 
fitting, a standpipe 172 extends upward from a screw-on cap 174 suitably 
mounted to vessel 38. Thus, when the flow of liquids and solids is 
stopped, such as by closing valve 96, and fitting 168/170 is disconnected, 
a small amount of liquids and solids will remain in standpipe 172. Vessel 
38 simply may be tipped to pour off this small amount, after which cap 174 
and standpipe 172 are removed and replaced with a plain screw on cap. Cap 
174 and standpipe 172 are then mounted to an empty collection vessel and 
fitting 168/170 is reconnected to permit continued operation of the 
system. If the flocculated solids have a rather mucoid consistency, such 
as flocculated silver TMT precipitate, the flow areas through the valve 
and quick disconnect fitting and into vessel 38 must be large enough to 
permit solids to move downward and liquid to move upward, such as in the 
embodiments of FIGS. 12 and 13. For example, a flow area approximately 
0.75 to 3.0 inch (19.1 to 76.2 mm) in diameter has been found to be 
effective for flocculated silver TMT precipitate. To aid with drainage 
into vessel 38, valve 96 may be a three-way valve 178 of the general type 
illustrated in FIGS. 23 and 24. A vent conduit 180 is connected to one 
port of valve 178; so that, with the valve closed as in FIG. 24, liquid 
and solids flow readily downward through the quick disconnect fitting 
168/170. 
Where the density of the flocculated solids is close to that of the 
remaining liquids and there is a tendency for fines to be generated, 
operation of collecting vessel 38 can be improved by providing one path 
into the vessel for downward moving flocculated solids and liquids and 
another, separate path from the vessel for clarified liquids. Such an 
arrangement also helps to prevent fines from short circuiting the 
collecting vessel. FIGS. 25 to 29 illustrate various embodiments of such 
separate paths. 
In the embodiment of FIG. 25, an extension conduit 182 is provided from the 
outlet end 36 of conduit means 18 downward in settling vessel 90, through 
outlet 94 and into collecting vessel 38. Due to this arrangement, 
clarified liquids rising from vessel 38 can pass upward through opening 94 
without disturbing or being disturbed by the downward flow in conduit 182. 
A baffle plate 184 extends across settling vessel 90 opposite outlet 102; 
so that, a portion of any fines rising into the settling vessel will have 
an opportunity to agglomerate and settle downwardly through outlet 94. A 
potential drawback of the embodiment of FIG. 25 is the lack of a valve 
between the settling vessel and the collecting vessel, which can 
complicate removal and replacement of the collecting vessel. One 
alternative arrangement which eliminates this drawback is illustrated in 
FIG. 26. Here, in parallel with standpipe 172, vessel 38 is provided with 
a top outlet 186 which is connected to a valve 188 by a suitable conduit 
190. Thus, clarified liquid can be withdrawn through conduit 190 and 
returned to settling vessel 90, if a settling vessel is used, or 
discharged from the system. 
Another alternative arrangement is illustrated in FIG. 27. The inlet 
conduit 48 for flocculated solids and liquid extends into vessel 38 
through a fitting 192 which positions conduit 48 concentrically within an 
outlet conduit 194 for clarified liquid. The flow area of conduit 48 
preferably is considerably larger than that of conduit 194, to allow easy 
passage of clumps of flocculated solids. Fitting 192 preferably is 
threaded for removal from vessel 38. Valve 188 functions as in the 
embodiment of FIG. 26. Quick disconnect fittings would be provided below 
both of valves 96 and 188. FIG. 28 illustrates a variation of the 
embodiment of FIG. 27 in which the two valves share a common actuator 196. 
In the embodiments of FIGS. 26 and 27, the inlet and outlet conduits could 
be arranged side by side rather than concentrically. FIG. 29 illustrates 
another alternative arrangement in which a combined inlet and outlet 
conduit 198 comprises a central divider wall 200 to define such side by 
side conduits. A ball valve 202 is provided with a divided flow passage 
for simultaneously opening and closing the two conduits. 
FIG. 30 illustrates still another embodiment of collecting vessel 38 which 
is particularly useful in accordance with the invention. A cylinder 210, 
preferably transparent or translucent and preferably but not necessarily 
circular in cross section, is made from any suitable material such as 
clear plastic. A top end cap 212 and a bottom end cap 214 are provided 
with central bosses 216, 218 which extend into the interior of cylinder 
210 and support between them a conventional tubular, pleated paper filter 
element 220. The filter element preferably should be a single pass filter 
made from totally combustible materials, should have a nominal porosity 
less than 0.5 microns and should have sufficient structural rigidity to 
withstand operating pressure differentials. Although filter element 220 as 
illustrated extends from bottom end cap 214 to top end cap 212, a shorter 
filter element which terminates below top end cap 212, or above bottom end 
cap 214, or both, may also be used without departing from the invention. 
An upwardly extending annular collecting chamber 222 is separated by 
filter element 220 from an upwardly extending liquid discharge chamber 224 
defined within the filter element. Although a tubular pleated filter 
element is preferred to define chambers 222 and 224, those skilled in the 
an will appreciate that any filter element could be used, such as a flat 
filter extended across a chord of cylinder 210, which divides the interior 
of the cylinder into parallel, upwardly extending collecting and discharge 
chambers. At the bottom of chamber 222, an inlet 226 is provided for 
flocculated solids mad liquid; however, a suitable downcomer conduit could 
also be used to introduce the solids new the bottom of chamber 222, in a 
manner similar to conduit 48 of the embodiment of FIG. 1. The solids and 
liquid could also be introduced through the side wall of cylinder 210 near 
the bottom of chamber 222. At the bottom of chamber 224, an outlet 228 is 
provided for clarified liquid which has passed through filter element 220. 
In one actual embodiment of this collecting vessel, cylinder 210 had an 
inside diameter of about 6.0 inches (152 mm) and a length of about 20 
inches (508 mm). Filter element 220 was assembled from a pair of 
commercially available Harmsco filter elements No. 801-0.35, manufactured 
by Harmsco, Inc. of Noah Palm Beach, Fla. The filter elements were placed 
end-to-end mad had a nominal porosity of about 0.35 microns, an inner 
diameter of about 1.0 inch (25.4 mm) and an outer diameter of about 2.375 
inch (60.33 mm). 
During use of the collecting vessel of FIG. 30, clumps of flocculated 
solids accumulate on the bottom of chamber 222 to form mass 50 and liquid 
flows through filter element 220 to outlet 228. As mass 50 rises around 
filter element 220, the lower portion of the filter element gradually 
becomes partially obstructed due to the presence of mass 50. However, the 
liquid which rises out of mass 50 continues to flow through a fresh or 
relatively unobstructed portion of the filter element. As filter element 
220 becomes more or less blocked by the progressive rise of mass 50, the 
effective outlet from chamber 22 moves upward along the filter element. 
Thus, even when the collecting vessel essentially is full of flocculated 
solids, there continues to be a percentage of the filter through which the 
liquid can pass. Since the liquid and solids are introduced near the 
bottom of chamber 222, many fines tend to be filtered out within mass 50, 
which further reduces the burden on the filter element, though increased 
inlet pressure may be needed to force the liquid and solids into mass 50 
at the end of a run. 
FIG. 31 illustrates an alternative embodiment of the collecting vessel of 
FIG. 30. Cylinder 210 and end caps 212, 214 have been replaced by a molded 
shell or housing 211 having domed ends 213, 214 rather like a common 
container for carbonated beverages. The domed ends permit pressurization 
of the container without much concern for loosening or leaking of end 
caps. A closure plug 219 extends upwardly into housing 211 to support 
filter element 220. A suitable threaded connection 221 secures plug 219 to 
housing 211. Inlet 226 and outlet 228 extend through plug 219. 
Alternatively, inlet 226 may be provided through the wall of housing 211 
near the bottom of chamber 222, not illustrated. Suitable plugs, not 
illustrated, are used to close inlet 226 and outlet 228 for shipment of a 
full collecting vessel. In the collecting vessels of FIGS. 30 and 31, 
chamber 222 may be provided with a one way vent valve, not illustrated, to 
admit air to the chamber to prevent formation of a vacuum and to 
facilitate drainage through outlet 228. 
FIG. 32 illustrates schematically an apparatus or system according to the 
invention which comprises the collecting vessels of FIG. 30 or 31. Many of 
the components of the embodiment of FIG. 1 are included. Holding tank 111 
is provided with a low level shut-off float switch 230 and a high level 
shut-off float switch 232. Low level switch 230 is positioned to provide a 
control signal when the volume of spent solutions falls to a residual 
volume needed for blending with subsequently added spent solutions to damp 
out differences in composition and concentration of spent solutions 
introduced into conduit means 18. Those skilled in the art will appreciate 
that a holding tank embodying such a low level switch and residual volume 
also could be used for delivery of spent solutions in the embodiments of 
FIGS. 1 to 13. The discharge of precipitating agent from pump 24 passes 
into conduit means 18 at inlet 27 just upstream of an inlet end of a 
section of conduit means 18 comprising optional static mixer elements 64. 
The discharge of flocculating agent from pump 30 passes into conduit means 
18 at inlet 33 just upstream of an inlet end of conditioning coil 242 of 
suitable tubing, in which the clumps of flocculated solids continue to 
grow or ripen before entering collecting vessel 38. If desired, a static 
mixing zone also may be included between inlet 33 and conditioning coil 
242. A pressure gage 244 near the inlet to collecting vessel 38 indicates 
the inlet pressure, which would be expected to rise as vessel 38 fills 
with flocculated solids. A pressure switch 246 senses this same pressure 
and signals a conventional programmable controller 248 when the inlet 
pressure exceeds a predetermined limit, at which point the controller 
shuts off motor 34 to stop the various pumps; and collecting vessel 38 is 
replaced. When the control signal from switch 230 indicates a low level in 
holding tank 111, controller 248 shuts off motor 34 until switch 232 
signals that a sufficient volume of spent solutions has accumulated for 
continued treatment. 
In one actual version of the system illustrated in FIG. 32, holding tank 
111 had a volume of about 20 gallons (75.71 L). Conduit means 18 was 
formed from 0.25 inch (6.35 mm) internal diameter tubing upstream of 
conditioning coil 242, which was formed from 30 feet (9.14 m) of 0.5 inch 
(12.7 mm) internal diameter tubing. The section of static mixers was about 
2 inches (51 mm) long. The tubing from sources 22 and 28 had an internal 
diameter of about 0.0625 to 0.125 inch (1.59 to 3.18 mm). Pumps 14, 24 and 
30 were peristaltic pumps operated to provide a flow from holding tank 111 
of about 200 ml/min. and flows from sources 22 and 28 of about 4 ml/min. 
When a sufficient volume of spent solutions was accumulated in holding 
tank 111, float switch 232 signaled controller 248 to start motor 34 and 
pumps 14, 24 and 30. Until the level in tank 111 reached float switch 230, 
the system continued to operate. Well-grown or ripened clumps of 
flocculated solids were delivered from conditioning coil 242 to the inlet 
of collecting vessel 38 and acceptably clarified liquid was discharged 
from the outlet of the vessel. Under continuous operating conditions, a 
collecting vessel 38 of the type and size described with regard to FIG. 30 
required replacement about every 40 hours of continuous operation. When 
float switch 230 indicated low level in tank 111 or sensor switch 246 
indicated high inlet pressure to vessel 38, controller 248 stopped motor 
34. 
EXAMPLE 4 
The spent solution contained paper process developer, paper process 
bleach-fix, paper process stabilizer, film process developer, film process 
bleach, film process fix, and film process stabilizer. Initial silver 
content of this mix of solutions was 1.7 g/L. The percentages of each of 
the spent solutions was in proportion to what would be expected in normal 
operation of a typical minilab photoprocessor. This mix of solutions was 
treated in a system similar to those described in Example 1 and shown in 
FIG. 32. The performance of the system was acceptable, but the flocculated 
solids were not as tightly bound as those seen in Example 1. The more 
loosely bound solids filled the settling filter, similar to that of FIG. 
30, more quickly. The experiment was terminated after approximately 40 
gallons (151.4 L) of solution were treated. Silver removal was excellent, 
with total (soluble plus insoluble) silver analyses of the system effluent 
in the range of 0.06 to 0.3 mg/L. 
EXAMPLE 5 
The following minilab solutions were treated in a system similar to those 
described in Example 1 and shown in FIG. 32. A settling filter as shown in 
FIG. 31 was used to separate the flocculated solids from liquid. The 
minilab mix comprised: paper process bleach fix, simulated paper process 
stabilizer, film process fix, and film process stabilizer. Silver content 
of this mixture was 2.5-3.0 g/L. The flow rates were: 5 ml/min of TMT-15, 
20 ml/minute of a 400 PPM solution of Calgon 2406 cationic polymer, and 
200 ml/min of silver bearing solution. Filter utilization was excellent, 
with over 100 gallons (379 L)of solution treated before pressure build up 
signaled the need for a filter change. Silver removal was excellent for 
this experiment, which was repeated numerous times to prove reliability. 
Total silver in effluent ranged from 0.2 to 0.96 mg/L. 
FIG. 33 illustrates an alternative embodiment of the invention in which the 
spent solutions from conduit 12 and the appropriate amount of 
precipitating agent from source 22 are combined in a mixing vessel 250 
using a propeller mixer 252 driven by a motor 254. A pump 256 delivers a 
mixture of liquid and precipitate along a conduit 258 to a point at which 
flocculating agent is delivered from source 28 upstream of conditioning 
coil 242. Otherwise, this embodiment is much the same as that of FIG. 32. 
EXAMPLE 6 
Five gallons (18.93 L) of minilab solutions were treated after primary 
electrolytic silver recovery: paper process bleach-fix, paper process 
stabilizer, film process fix, and film process stabilizer. The silver 
content after electrolytic silver recovery was measured at 220 mg/L. The 
solution was treated in the apparatus of FIG. 33. The TMT-15 precipitating 
agent (25 mm) was added in proportion to the silver in solution, with 
continuous mixing in the reaction tank. A low molecular weight, cationic 
polymer, Calgon E-2280, made up at 400 mg/L in water, was injected at 20 
ml/min. Silver removal from solution was good with this arrangement, but 
the pleated paper filter element 220 in the settling vessel blinded more 
quickly than expected. The flocculated solids were granular, with some 
fines passing through the conduit 18. Evidence of this was a yellow color 
on the wetted filter element parts, and an increasing liquid level inside 
the settling filter. Filter capacity was not determined for this mix of 
solutions. 
EXAMPLE 7 
A simulated combined minilab effluent containing paper process bleach-fix, 
paper process stabilizer, film process fix, and film process stabilizer, 
containing 2.5 to 3.0 g/L silver was used as the feed solution in the 
apparatus shown in FIG. 33. There were 2 reactors in this case. One 
reactor was tank 250 in which 400 ml of TMT-15 were added by pump 24 to 5 
gallons (18.93 L) of the silver-beating solution with good mixing provided 
by a laboratory-scale propeller mixer 254 mounted on the top of the 
reactor. The mixer speed was held at 100-200 rpm for the duration of the 
run. After 5-10 minutes reaction time, this slurry was introduced into a 
conduit 258 using a bellows pump 256 at 200 ml/minute. A 400 mg/L solution 
of Calgon Flocculant Product No. POL-E-Z-2406 was injected into conduit 
258 using bellows pump 30 through a T-fitting sized to produce turbulence 
at the point of injection. Frown there, the slurry was carried into 
conditioning coil 242, which was made from approximately 30 feet (91.44 m) 
of 0.5 inch (12.7 mm) nominal diameter flexible polyvinyl chloride tubing 
wrapped around a plastic cylinder approximately 12 inches (305 mm) in 
diameter. Flow was directed up the spiral in order to displace air bubbles 
and cause precipitated fines to encounter the growing or ripening clumps 
of flocculated solids. From coil 242 the slurry was directed to the 
settling vessel of FIG. 30. Clarified filtrate was directed to the drain 
from the settling vessel. Filter capacity was determined by monitoring the 
pressure gage 244 built into the system. Total (soluble plus insoluble) 
silver levels leaving the settling filter were analyzed at 0.3 to 0.7 mg/L 
using atomic absorption silver analyses. More than thirty-five, 
five-gallon (18.93 L) batches of silver-beating solution as described 
above were treated in this apparatus before the back pressure in the 
settling filter reached 10-12 psig (68.9-82.7 kPa), indicating the need to 
change filters. 
EXAMPLE 8 
The following minilab solutions were treated in a system similar to those 
described in Example 1 and shown in FIG. 32. A settling filter as shown in 
FIG. 31 was used to separate the flocculated solids from liquid. The 
minilab mix comprised: KODAK Process RA-4 bleach fix plus low flow wash 
which had been electrolytically desilvered. Silver content of this mixture 
was 180 mg/L. TMT-15 solution was diluted 1:10 with water. The flow rates 
were: 5 ml/min of diluted TMT-15, 20 ml/minute of a 400 mg/L solution of 
Calgon 2280 cationic polymer, and 200 ml/min of the silver bearing 
solution. Although the flocculated precipitate demonstrated a sandy or 
grainy appearance, there were no noticeable fines. Settling and subsequent 
filtration in the filter of FIG. 31 appeared normal. Silver analysis by 
atomic absorption of the filtrate was in the range of 0.6 to 0.9 mg/L. 
Those skilled in the art will appreciate from the foregoing description and 
examples that the apparatus and methods of our invention may be used to 
remove metals other than silver from other industrial spent solutions such 
as electroplating solutions, metal etching solutions and the like. For 
example, a rinse water from a catalyst-making process containing 200 mg/L 
of nickel was treated in an apparatus of the type shown in FIG. 33 by 
adding sodium hydroxide as a precipitating agent and Calgon POL-E-Z-2406 
as a flocculating agent. Clumps of agglomerated particles of flocculated 
precipitate were readily formed and collected. Those skilled in the art 
will further appreciate that the apparatus and method of our invention can 
be used readily to remove other metal species (such as iron, copper, 
cadmium, lead, mercury, chromium, barium and aluminum) by precipitation 
using known precipitating agents (such as TMT, hydroxides, sulfides, 
sulfates or organic thiols), by flocculation using known flocculating 
agents (such as those mentioned in this specification) and by collection 
in one of our collecting vessels. Persons skilled in the art also will 
appreciate that the method and apparatus of our invention can be used to 
remove other, non-metallic species, including organic and inorganic 
compounds and materials such as hexacyanoferrates, sulfates, sulfides, 
phosphates, carbonates, photographic coupling agents, sewage sludge 
micro-organisms and the like, using precipitating agents such as iron, 
calcium, carbon dioxide or similar agents, followed by an appropriate 
flocculating agent. Suitable examples of precipitating and flocculating 
agents are given in the Bober and Cooley article and the Spears and 
Sentell article previously mentioned, both of which are incorporated by 
reference into this specification. 
The method of removing silver-TMT precipitate from solution using cationic 
polymers as flocculating agents, such as Product Nos. POL-E-Z-2406 and 
E-2280 from the Calgon Corporation, is a separate invention of our 
colleague A. Richard Szembrot, which is implemented by the apparatus and 
method of our invention. 
While our invention has been shown and described with reference to 
particular embodiments thereof, those skilled in the art will understand 
that other variations in form and detail may be made without departing 
from the scope and spirit of our invention.