Silver recovery system

A silver recovery system includes a novel power supply and a novel structure for a cell used in the recovery system. The power supply monitors the conductivity of the electrolyte of the silver recovery system and automatically sets power to the operating or standby modes depending on the magnitude of the conductivity. Thus, the system is capable of unattended operation. The cell consists of a canister which is a hollow cylinder having an open top end and a closed bottom end. The anode is an elongated rod and extends into the canister centrally thereof, and the cathode is a partial cylinder which surrounds the anode.

The invention relates to a power supply for a silver recovery system. More 
specifically, the invention relates to such a power supply which monitors 
the conductivity of the electrolyte of the silver recovery system and 
automatically provides either operating or standby power depending on the 
magnitude of the conductivity, whereby to render the system capable of 
unattended operation. 
The invention also relates to a structure for a cell for the silver 
recovery system. 
The invention also relates to a silver recovery system incorporating the 
novel power supply, or the novel cell structure, or both. 
Silver recovery systems are known in the art as illustrated in the 
following patents: U.S. Pat. No. 3,418,225, Wick et al, U.S. Pat. No. 
3,551,318, Snook et al, U.S. Pat. No. 3,616,412, Gnage, U.S. Pat. No. 
3,616,435, Favell et a1, U.S. Pat. No. 3,705,716, Hendrickson, U.S. Pat. 
No. 3,751,355, Manroian, U.S. Pat. No. 3,875,032, Thompson, U.S. Pat. No. 
3,980,538, Higgins, U.S. Pat. No. 4,127,465, Higgins, U.S. Pat. No. 
4,186,067, Blake et al, and U.S. Pat. No. 4,263,108, Berg et al. 
U.S. Pat. No. 3,418,225 teaches a silver reclaiming process wherein the 
amount of film entering into the electrolytic solution is counted. The 
apparatus continues the operation of the reclaiming process until the 
count is exhausted. U.S. Pat. No. 3,551,318 uses a separate detecting 
electrolytic cell 15 to control plating current. In U.S. Pat. No. 
3,616,412, a coulometric device is used to determine the concentration of 
silver in a solution in a silver reclaiming apparatus and process. In U.S. 
Pat. No. 3,616,435, quiescent silver content is determined by measuring 
the film motion, and reclaiming current to said proportional to this 
content. 
The apparatus as taught in U.S. Pat. No. 3,705,716 monitors effluent from a 
silver recovery unit to determine if the unit is still functioning 
efficiently. Thompson U.S. Pat. No. 3,875,032, teaches an apparatus which 
monitors threshold voltage required to induce flow of current at 0 silver 
content. Thompson uses a control cathode and electrode. 
The teachings in U.S. Pat. Nos. 3,980,538 and 4,127,465 are similar in that 
the two patents are divisionals of the same application. The apparatus of 
both of these patents monitors the rate of input of film and increases 
plating current as the rate is increased. It also decreases plating 
current as the rate is decreased. 
There is the implicit assumption that as the rate of input of film is 
increased, the silver content in solution increases, and vice versa. 
The apparatus in U.S. Pat. No. 4,186,067 monitors the level of a reducing 
agent added to the silver solution to automatically add more agent when 
the level falls below a predetermined level and to automatically stop when 
the level exceeds a predetermined level. In U.S. Pat. No. 4,263,108, 
plating current is controlled as a function of cell voltage in the absence 
of plating current. 
In the apparatus illustrated in U.S. Pat. No. 3,751,355, a sensing terminal 
44 is connected to the negative terminal 46 of an electrolytic recovery 
cell to measure the conductivity of the electrolyte. The plating 
parameters of voltage and current are controlled as a function of the 
conductivity. As can be seen from FIG. 3, as the conductivity increases 
(resistance decreases) the current increases. Thus, the apparatus of this 
patent teaches a system wherein the parameters are varied in the light of 
conductivity measurements. However, it does not teach a system which can 
continue to operate unattended by putting the power in standby position 
when the silver content of the electrolyte becomes too low. In addition, 
the apparatus of the '355 patent requires that a probe be placed in the 
electrolyte. Such a probe provides its own problems, so that such a system 
could advantageously be improved on. 
It is therefore an object of the invention to provide a power supply for a 
silver recovery system which overcomes the disadvantages of the prior art. 
It is a further object of the invention to provide a structure for a cell 
for the silver recovery system. 
It is a still further object of the invention to provide a novel silver 
recovery system incorporating the novel power supply or the novel cell 
structure, or both. 
In accordance with the invention a power supply for a silver recovery 
system monitors the conductivity of the electrolyte and sets the input 
power to the system to either an operating or a standby level depending on 
the magnitude of the conductivity. 
The cell comprises a canister which is a hollow cylinder having an open top 
end and a closed bottom end. An anode member extends longitudinally into 
the canister and a cathode member extends longitudinally into the canister 
and encircles the anode member.

Referring to FIG. 1, a silver recovery system, illustrated generally at 1, 
comprises a plurality of cells 3 which cells are in fluid communication 
with each other. Connected to the cell at the inlet end (the lefthand 
side) is an inlet pipe 5, and connected to the cell at the outlet end (the 
righthand side) is an outlet pipe 7. The pipes 5 and 7 are connected to a 
source of silver. For example, if the source of silver is the fixing 
solution of a photographic process, then the pipes 5 and 7 would be 
connected to an outlet and inlet respectively of the container for the 
fixing solution. In that case, of course, the fixing solution will 
comprise the electrolyte of the cells. As can be seen, each cell includes 
a canister 2 and a cover 4. 
A circuit box 9 contains the electronics which are illustrated in FIGS. 4 
and 5 herein. The electronics are connected to an anode common connector 
11, and cables 13 lead from the common connector 11 to each respective 
cell anode. 
Each cell includes a ground terminal 15 which, as will be described below, 
is connected to the cathode internally of the cells. Each respective 
terminal 15 includes a respective cable 16 which is connected to a ground 
point. 
Turning now to FIG. 2, as can be seen, each canister comprises a cylinder 
with an open top end and a closed bottom end, and the cylinder includes a 
screw thread 17 at the outer surface at the top end thereof, and each cap 
4 includes a mating screw thread 19 at the bottom end of the inner surface 
thereof. Anode 21, which is in the shape of an elongated rod and which 
comprises a graphite material, extends through an opening 22 in the top of 
the cap 4 into the interior of the canister. It is of course understood 
that, in FIG. 2, the cap is shown in exploded position relative to the 
canister. 
As seen in FIGS. 2 and 3, the cathode comprises an elongated cylinder which 
also extends into the canister and which encircles the anode. As seen in 
FIG. 3, the side edges of the cathode are separated by a gap 25 which 
extends for the full length of the cathode. 
Ground terminal 15 extends through a side wall in the canister and is 
connected to a bracket 27. The cathode comprises a metallic flat sheet 
which is rolled to be inserted into the canister so that when it is in the 
canister, it is in its sprung position and will force itself up against 
the inner surface of the walls of the canister. Accordingly, the bracket 
will be in good physical contact with the cathode and therefore also in 
good electrical contact therewith. In assembling the cell, the bracket is 
first inserted by lowering it on the interior of the canister and then 
pushing the ground terminal 15 outwardly through the opening in the 
canister. The cathode is then inserted in the canister. 
Turning now to FIG. 4, the power supply comprises a circulation sensing 
unit 29 having an input 29i and output 29o. In addition, power control 
unit 31 has an output terminal 31o1. The output terminal of 31 is 
connected to input terminal 35i of voltage regulator unit 35. The voltage 
regulator has a first control terminal 35c1 and a second control terminal 
35c2. It also has an output terminal 35o. The output terminal of 35 is 
connected to input terminal 37i of power output unit 37 which also has a 
first output terminal 37o1 and a second output terminal 37o2. The first 
output terminal of 37 is connected to the anode common connector and 
thereby, in parallel, to the anode of each cell in the system. 
The second output of 37 is connected to the input terminal 39i of current 
sensing unit 39 which also has an output terminal 39o. The output terminal 
of 39 is connected to one input terminal 41i1 of comparator unit 41. The 
comparator unit has a first output terminal 41o1 which is connected to 
control terminal 31c of power control unit 31 as well as to the second 
control terminal 35c2 of voltage regulator unit 35. The comparator unit 
has a second output terminal 41o2 connected to a display unit 45. Finally, 
the comparator unit has a second input terminal 41i i2 which is connected 
to the output terminal 43o of current generator unit 43. The current 
generator generates a predetermined amplitude of current as will be 
described below. 
The input terminal 21i of the processor sensing unit is connected to the 
source of silver to determine whether this source is in the processing 
state. For example, if the source of silver is a photography processing 
unit, then the processor sensing unit senses when circulation exists. 
The power control unit 31 comprises of an AC/DC converter, and the voltage 
regulator regulates the voltage in view of the fact that very low 
amplitude voltages are used in this system. For example, when the system 
is plating, the voltage is in the range of 0.8 to 1.5 volts, when the 
system is in the standby condition, the voltage is between 0.3 and 0.6 
volts, and when it is in the off mode, the voltage is 0.03 volts. In 
addition to the regulating function, the voltage regulator switches the 
output to the plating range, to the standby range and to the off mode on 
receipt of a signal from the comparator unit as will be described below. 
In addition, when it is in the plating mode, and when the current rises 
above a predetermined level, then the voltage regulator will automatically 
lower the voltage on receipt of a signal from the same comparator unit as 
will also be described below. 
The power output unit 37 senses the voltage across each cell. In view of 
the fact that such low voltages are being used, the voltage measurement is 
taken directly across the anode and cathode of a cell. Thus, voltage 
losses of the wire conductors are taken into account. The output of the 
power unit is fed back to the voltage regulator to provide a feedback 
control system to maintain the voltage at the cells at its proper level. 
The current sensing unit can comprise a high precision resistor in series 
between the power output unit 37 and the comparator 41. 
In operation, the system operates as follows: 
When the photography processing unit is first turned on, this will be 
sensed by unit 29 which will provide a signal to the voltage regulator 
unit to change the output from off mode to either plating or standby, 
depending on the current. The electrolyte is circulated through the cells 
and out through pipe 7 back to the processing system. Thus, in a 
photography system, the silver will be removed from the fixing solution 
whereupon the fixing solution can once again be used in the photography 
processing system. 
If there is a small amount of silver in the electrolyte, then the 
conductivity of the silver will be very low (the resistance will be high), 
so that only a small amount of current will be drawn by the recovery 
system. This current is sensed by the sensing unit 39 and compared in the 
comparator unit 41 with the preset values of the current generator 43. 
When the sensed current is below a first preset value of the current 
generator, the comparator will provide a signal to the voltage regulator 
35 to set it to its standby condition. At this time, the low voltage range 
(0.3 to 0.6 volts) permits further processing without harming chemicals in 
the electrolyte which would be harmed by higher voltages in the absence of 
sufficient silver in the electrolyte. 
When the amount of silver in the electrolyte increases, the conductivity of 
the electrolyte increases so that more current will be drawn by the 
recovery system. When the sensed current exceeds the first preset value, 
the comparator provides a signal to the voltage regulator unit to set to 
its plating mode. Accordingly, the voltage will be increased to the 0.8 to 
1.5 volts range. The silver in the electrolyte will now be plated onto the 
inner surface of the cathode for later recovery. 
Should the conductivity of the electrolyte exceed the current limit of the 
unit, an influx of silver in the electrolyte, the comparator unit 41 will 
provide a signal to the voltage regula tor unit to reduce the voltage. 
However, it will not reduce a voltage within the plating level of 
voltages. 
In presently available systems, when the processor unit is turned off, the 
silver recovery unit must also be turned off to avoid damaging it even 
though it could be doing useful work by recovering silver from the fixing 
solution even after the processing unit has been turned off. In accordance 
with the present power supply, the recovery system can continue operation 
until the conductivity level falls below a predetermined value. Thus, when 
the processor is turned off, the processor sensing unit will no longer be 
providing a turn on signal to the voltage regulator. 
During operation, the display unit will display the magnitude of the sensed 
current. The current generator unit, in accordance with the invention, is 
adjustable as to the first and second preset levels. When the adjustments 
are being made, the preset levels will be displayed on the display unit. 
When the unit is in off mode, the display will turn off. 
FIG. 5A, 5B, and C when combined illustrate a schematic diagram for 
implementing the block diagram of FIG. 4. The blocks enclosing the circuit 
elements bear reference numerals, and the reference numerals correspond to 
the reference numerals in FIG. 4. As will be understood, the circuit 
elements enclosed by a block are the circuit elements which are used to 
build the referenced block of FIG. 4. The operation of the schematic 
diagram, and each of the blocks within the schematic diagram, is 
self-evident and requires no further description. 
Although a particular embodiment has been illustrated, this was for the 
purpose of describing, but not limiting, the invention. Various 
modifications, which will come readily to the mind of one skilled in the 
art, are within the scope of the invention as defined in the appended 
claims.