U.S. patent number 3,767,572 [Application Number 05/196,770] was granted by the patent office on 1973-10-23 for destruction of edta by alkaline chlorination.
Invention is credited to Thomas W. Bober, Thomas J. Dagon, Idalee Slovonsky.
United States Patent |
3,767,572 |
Bober , et al. |
October 23, 1973 |
DESTRUCTION OF EDTA BY ALKALINE CHLORINATION
Abstract
Waste photographic processing solutions which contain
ethylenediaminetetraacetate (hereinafter EDTA), such as exhausted
ammonium iron EDTA bleaching or bleach-fixing solutions, are
chlorinated to destroy EDTA and thereby increase the
biodegradability of the solution. Chlorination can be effected by
introduction of chlorine gas or by the use of hypochlorite
solution. Since EDTA and complexes thereof account for a large
portion of the oxygen consuming material present in photographic
processing effluent, a significant source of water pollution is
substantially eliminated by this method.
Inventors: |
Bober; Thomas W. (Rochester,
NY), Dagon; Thomas J. (Rochester, NY), Slovonsky;
Idalee (Rochester, NY) |
Family
ID: |
22726750 |
Appl.
No.: |
05/196,770 |
Filed: |
November 8, 1971 |
Current U.S.
Class: |
210/721;
210/756 |
Current CPC
Class: |
C02F
1/76 (20130101); Y02W 10/37 (20150501) |
Current International
Class: |
C02F
1/76 (20060101); C02b 001/36 () |
Field of
Search: |
;96/6R,6BF
;210/42,48,50,59,62 ;252/188 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Zaharna; Samih N.
Assistant Examiner: Wyse; Thomas G.
Claims
I claim:
1. A method of treating a waste photographic processing solution
containing an iron complex of EDTA to reduce the oxygen demand of
said solution so as to minimize water pollution resulting from
disposal thereof, said method comprising the step of chlorinating
said solution under alkaline conditions to destroy EDTA.
2. The method of claim 1 wherein said chlorination is carried out
with said solution at a pH of greater than 10.
3. The method as described in claim 1 wherein said chlorination is
carried out with said solution at a pH of about 11.5.
4. The method described in claim 1 wherein said chlorination is
effected by introducing chlorine gas into said solution.
5. The method as described in claim 1 wherein said chlorination is
effected by mixing said solution with hypochlorite solution.
6. A method for treating an exhausted ferric ammonium EDTA
bleaching solution to precipitate iron therefrom and to reduce its
oxygen demand so as to minimize water pollution resulting from
disposal thereof, said method comprising the steps of
a. introducing sodium hydroxide into said solution to precipitate
iron hydroxide which can be separated and
b. introducing a member selected from the group consisting of
chlorine and hypochlorite into said solution to destroy EDTA.
7. The method of claim 6 wherein said steps (a) and (b) are
performed simultaneously.
Description
This invention relates in general to the photographic art and in
particular to the treatment of waste photographic processing
solutions. More specifically, this invention relates to treating
waste photographic processing solutions which contain EDTA
complexes or free EDTA, such as exhausted ammonium ferric EDTA
bleach solutions, to convert the residual EDTA to innocuous
reaction products so as to reduce water pollution resulting from
disposal of the waste solution.
Until recently one of the most common class of bleaches comprised
alkali metal ferricyanides, especially potassium ferricyanide. Much
research has been performed to define substitutes for these
materials in view of the potentially relatively high toxicity of
the ferrocyanide compounds which form the bulk of the waste
discharged after bleaching in view of the reaction products formed
by such waste upon exposure of same to sunlight in streams, etc. If
waste processing solutions containing hexacyanoferrate ion (the
products of ferricyanide bleaching) are discharged to the sewer
without treatment, these ions are slowly oxidized in the presence
of ultraviolet radiation to cyanide ions, which are probably the
most toxic to fish and other aquatic life of any of the chemicals
discharged from photographic processes. A valuable substitute for
the ferricyanide bleaches which is well known to those skilled in
the photographic art are the ferric EDTA complexes, for example
ferric ammonium EDTA or tetrasodium EDTA which, while producing
excellent bleaching effects, do not yield the potentially toxic
ferrocyanides of earlier ferricyanide systems. Thus, the most
commonly used bleaching agent is rapidly becoming ferric ammonium
EDTA which avoids the potential toxicity problems of the
ferricyanide and demonstrates excellent bleaching properties, but
which has been found to result in the discharge of materials
requiring high chemical oxygen demand.
It is therefore an object of the present invention to provide a
ready and relatively simple means of lowering the chemical oxygen
demand of waste photographic solutions which contain EDTA.
According to the invention described in U. S. Pat. Application Ser.
No. 851,464 of Hendrickson et al, filed, Aug. 19, 1969, and issued
July 20, 1971 as U.S. Pat. No. 3,594,157, alkaline chlorination of
waste photographic solutions containing thiosulfate ion destroyed
the thiosulfate ion and consequently reduced the oxygen demand of
the solution. It has now been discovered that a similar treatment
of solutions containing EDTA complexes, whether they include
thiosulfate or not, results in destruction of EDTA thereby greatly
decreasing the chemical oxygen demand of waste solutions containing
such compounds by converting the EDTA complexes to innocuous
oxidation products.
The method comprises chlorination of the solutions under alkaline
conditions, preferably at a pH above about 10 and advantageously at
a pH above about 11.5 and comprises treating waste photographic
processing solutions containing EDTA complexes and free of
thiosulfate ion (treatment of such solution having already been
described in the aforementioned patent) by chlorination.
An exhausted or waste EDTA bleach solution is a relatively complex
solution which may typically contain, in addition to EDTA complexes
and free EDTA, materials such as alkali metal sulfites, alkali
metal carbonates, gelatin hardening agents, acids, halides,
gelatin, etc. In some instances the bleach may contain developer
and/or developer oxidation products which are present as a result
of carry-in from the developer solution. Even more complicated
waste solutions containing EDTA complexes and free EDTA may be
formed when different effluents from the photographic processing
system are combined together before disposal, e.g. combined bleach
and fix and/or prehardener, stabilizer baths, etc, and it is
intended by use of the term "waste photographic processing
solution" to include all such compositions. Regardless of the exact
make up of the waste photographic solution, as employed herein the
term "EDTA complex" is intended to mean all compounds comprising
such materials which may be present in the waste solution, e.g.
ferric ammonium EDTA, tetrasodium EDTA, free EDTA, etc.
As previously indicated, the method of this invention is not
limited to treatment of exhausted fixing solution but is applicable
to any photographic processing solution or other effluent
containing EDTA in any of its many complexed or free forms. Thus,
it may be used on combined processing effluents as described
above.
Alkaline chlorination of waste bleach solutions can be carried out
using batch, semicontinuous or continuous techniques. A preferable
procedure is to bubble chlorine gas into the solution while adding
sodium hydroxide to the solution to maintain the desired alkaline
pH. The amount of chlorine gas used will depend upon the
concentration of EDTA in the solution, the efficiency of the
contacting procedure utilized, the extent to which residual EDTA in
the treated solution can be tolerated, and so forth. Thus, the
amount of chlorine used may vary from as little as about 1 to as
much as about 100 volumes of chlorine gas per volume of solution,
and this amount of chlorine can be provided by any combination of
flow rate and time which will permit adequate contact between the
solution and the chlorine.
Instead of effecting chlorination by introducing chlorine gas into
the waste processing solution similar, however, somewhat less
efficient EDTA destruction can be accomplished by adding
hypochlorite to the solution. Results are essentially the same
since the introduction of chlorine gas into an alkaline solution
results in the formation of hypochlorite, an example of the
reaction being as follows:
C1.sub.2 + NaOH .fwdarw. NaOCl + HCl
An advantage in employing the hypochlorite solution is that it is
less hazardous to use. However, the use of chlorine gas tends to
give a faster and more efficient reaction with EDTA.
Whether chlorination is accomplished by the use of chlorine gas or
by the use of hypochlorite solution, it is preferably carried out
in accordance with this invention under alkaline conditions. The
required alkaline pH is most easily provided by the addition of a
strong base to the solution, e.g. sodium hydroxide or potassium
hydroxide, but any other suitable means of maintaining an alkaline
pH known to the art may be employed. The strong base is preferably
added simultaneously with the addition of the chlorine. While the
method is operable at any alkaline pH, it proceeds most rapidly and
efficiently at a high pH. It is, thus, preferred to carry out the
chlorination with the solution at a pH of greater than 10 and more
preferably of 11.5 or more. Chlorination may also be carried out at
slightly acid pH, however, the efficiency of the reaction is
reduced substantially.
The invention is further illustrated by the following examples of
its practice:
EXAMPLE 1
Chlorine gas is supplied from a gas cylinder into 1 liter of a 1.56
M NH.sub.4 Fe.sup.. EDTA (90 ml/1) solution at a regulated flow
rate of 0.6 liters per minute. The pH of the reacting solution is
kept above 11.0 by periodic addition of concentrated (16N) sodium
hydroxide solution. The EDTA, EDTA-complex and iron concentrations
are measured at regular intervals. The iron precipitates as the
hydroxide and is easily filtered or otherwise removed as a
precipitate by filtration after about 30 minutes. Chemical Oxygen
Demand (COD) drops from an initial value of 38,300 mg/1 to a final
value after 2.0 hours of treatment of 13,000 mg/1 and all EDTA was
destroyed as proven by analysis.
EXAMPLE 2
Treatment of a solution of Na.sub.4 EDTA (50 g/1) results in
complete destruction of EDTA after a period of about 90 minutes,
paralleling the results obtained in Example 1.
Addition of large volumes of caustic initially rather than
periodically throughout the evaluation does not speed up EDTA
degradation, however, it does provide a secondary advantage in that
nearly all of the iron hydroxide precipitate can be removed prior
to chlorination, thus avoiding plugging of the sintered
glass-dispersion tubes conventionally used to bubble the chlorine
gas into the solution by the precipitate. Further, heating the
solution prior to chlorinating, does not appear to speed up
degradation of EDTA.
Following examples are a continuation of those reported above.
Table I describes the compositions of the bleach-fix formulations
tested. The procedures utilized were as follows:
A. GASEOUS CHLORINATION
Table II is a description of the experimental conditions under
which the separate trials were run. In Experiments 3-10, 350 ml
concentrated (16N) sodium hydroxide were added to 1-liter samples
of bleach-fix initially. Iron precipitated as the hydroxide, and
the resulting solution was filtered with the aid of Analytical
Grade Celite. The supernatant was then chlorinated. Chlorine (gas),
supplied from a gas cylinder at a regulated flow rate, was bubbled
into the bleach-fix solution through a gas-dispersion tube. All pH
adjustments during chlorination were made with concentrated (16N)
sodium hydroxide added periodically in 50-ml volumes. Samples were
taken at various time intervals and analyzed for EDTA (SLM 1255,
EDTA reported as Na.sub.4 EDTA), the EDTA-complex (as Na.sub.4
EDTA), total soluble iron (SLM 1254), and in some cases COD
(Chemical Oxygen Demand), (SLM 1128). The bleach-fix sample was
titrated with a standard zinc solution to form the zinc complex
with the excess EDTA. In some instances, chlorination was
interrupted to filter the reacting solution because a precipitate,
assumed to be sodium chloride, plugged the gas-dispersion tube.
Some trials were run for shorter time periods than others, either
because of sodium chloride precipitate plugging the sparger or the
volution of chlorine gas. The reaction of chlorine with the
bleach-fix is exothermic, and maximum temperatures were always
approximately 100 C.
In Experiments 3-7, the initial solution was a fresh bleach-fix. In
Experiments 8-10, the initial solution was a formulation simulating
the overflow to a silver recovery cartridge in a conventional
bleach-fix process. Because chlorination also results in silver
recovery, with silver in the spent bleach-fix precipitating as
silver sulfide, chlorination can be used as a tailing operation.
The concentration of EDTA is higher in the spent bleach-fix.
Formulas are given in Table I.
B. ADDITION OF SODIUM HYPOCHLORITE SOLUTION
Two experiments were run in which concentrated Sunny Sol (analyzed
at 16% sodium hypochlorite) was added to a 100-ml volume of spent
bleach-fix and stirred. Volumes of Sunny Sol added were 380 ml in
Experiment 9 and 760 ml in Experiment 10. Although the temperature
did rise upon the addition of Sunny Sol, it never reached 100 C as
occurred in gaseous chlorination. No pH adjustments were made. All
iron did not immediately precipitate as the hydroxide as it did in
gaseous chlorination, although a large percentage did form a
precipitate. Samples were taken initially; immediately after
addition; and after 1 hour, 24 hours, and 48 hours. They were
analyzed immediately for EDTA, the EDTA-complex, and total soluble
iron.
The results for all of these Examples are shown in Table III.
TABLE I
FORMULATIONS OF SOLUTIONS CHLORINATED
Fresh Bleach-Fix:
FeEDTA 91 ml/l 60% (NH.sub.4).sub.2 S.sub.2 0.sub.3 125 ml/l
Na.sub.2 SO.sub.3 12 g/l Spent Bleach-Fix to Silver Recovery
Cartridge: FeEDTA 134 ml/l 60% (NH.sub.4).sub.2 S.sub.2 O.sub.3 110
ml/l Na.sub.2 SO.sub.3 5 g/l ##SPC1##
TABLE III
GASEOUS CHLORINATION -- COD REDUCTIONS
Example 3 Sample COD (mg/l) Overall Reduction = 99% After Filter
60,000 30 min 13,238 60 min 9,265 90 min 885 120 min 500 150 min
385 Example 4 Sample COD (mg/l) Overall Reduction = 99% After
Filter 58,100 30 min 35,200 60 min 20,000 90 min 4,600 120 min
2,800 150 min 1,450 180 min 760 Example 5 Sample COD (mg/l) Overall
Reduction = 86% After Filter 61,500 30 min 47,100 60 min 26,700 90
min 8,800 Example 6 Sample COD (mg/l) Overall Reduction = 84% After
Filter 59,650 30 min 54,950 60 min 41,300 90 min 9,550 Example 7
Sample COD (mg/l) Overall Reduction = 88% After Filter 66,932 30
min 54,177 60 min 31,152 90 min 8,645 Example 8 Sample COD (mg/l)
Overall Reduction = 88% After Filter 61,250 30 min 28,541 60 min
7,381 Example 9 Sample COD (mg/l) After Filter -- 30 min 44,960 60
min 49,344 90 min 25,215
It should be noted, however, that the amount of chlorine or
hypochlorite utilized to achieve chlorination of EDTA will vary
considerably depending upon the make up of the particular waste
photographic solution being treated since many other materials
present in such compositions may tend to utilize the chlorine in
preference to the EDTA and therefore require the addition of
significantly more chlorine.
As also demonstrated from the foregoing Examples, if the EDTA
containing solution also happens to have iron, a compound alluded
to as a polluter in some circles, present therein, as in the case
of a major portion of the newest bleach materials which contain
ferric ammonium EDTA, this compound is precipitated and easily
removed from the effluent by filtration for safe disposal
elsewhere.
The invention has been described in detail with particular
reference to preferred embodiments thereof; however, it will be
understood that variations and modifications can be effected within
the spirit and scope of the invention.
* * * * *