EPA-670/2-75-055
June 1975
Environmental Protection Technology Series
REMOVAL OF CHROMIUM FROM
PLATING RINSE WATER USING
ACTIVATED CARBON
National Environmental Research Center
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
-------
EPA-670/2-75-055
June 1975
REMOVAL OF CHROMIUM FROM
PLATING RINSE WATER USING
ACTIVATED CARBON
By
Richard B. Landrigan and J. B. Hallowell
Battelle Memorial Institute
Columbus Laboratories
Columbus, Ohio 43201
EPA Grant No. S802113
Program Element No. 1BB036
Project Officers
Donald Wilson (Cincinnati) and John Ciancia (Edison)
Industrial Waste Treatment Research Laboratory
Edison, New Jersey 08817
NATIONAL ENVIRONMENTAL RESEARCH CENTER
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
-------
REVIEW NOTICE
The National Environmental Research Center - Cincinnati has reviewed
this report and approved its publication. Approval does not signify
that the contents necessarily reflect the views and policies of the
U. S. Environmental Protection Agency, nor does mention of trade
names or commercial products constitute endorsement or recommendation
for use.
ii
-------
FOREWORD
Man and his environment must be protected from the adverse effects
of pesticides, radiation, noise, and other forms of pollution, and
the unwise management of solid waste. Efforts to protect the environ-
ment require a focus that recognizes the interplay between the com-
ponents of our physical environment—air, water, and land. The
National Environmental Research Centers provide this multidisciplinary
focus through programs engaged in
• studies on the effects of environmental contaminants
on man and the biosphere, and
• a search for ways to prevent contamination and to
recycle valuable resources.
As part of these activities, the efforts on this study have been
directed toward an assessment of techniques for regenerating activated
carbon used in removing chromium from metal finishers' wastewater.
This assessment has been a part of continuing efforts to develop more
economical and simpler methods for treating the wastewater from small
metal finishing establishments.
A. W. Breidenbach, Ph.D.
Director
National Environmental
Research Center, Cincinnati
111
-------
ABSTRACT
Activated carbon is highly effective in adsorbing chromium from the
rinse water, and leaves no detectable chromium in the water until the
carbon is "saturated" with chromium to its upper limit. Thus, it is
necessary to "regenerate" the carbon by removing the chromium from it,
after which the carbon can be used for another adsorption cycle.
These studies were conducted (1) on a laboratory scale to determine the
effects of basic and acidic media regeneration of chromium-loaded
activated carbon especially as it affects adsorption capacity of the
carbon after repeated cycling and (2) in a small pilot-plant unit on
the basis of the best results of the laboratory-scale work. In the
latter case, studies were conducted on the unit operation for eight
adsorption-desorption cycles.
In the initial laboratory work, experiments were performed to evaluate
the use of acidic or basic solutions for removal of chromium from the
carbon. Since the basic solution (NaOH) proved more effective, further
work was done using caustic. Further work with the basic solutions
included a study of adding chelating agents to improve the effective-
ness of the regeneration.
Laboratory experiments involving regeneration of chromium-loaded
activated carbon in the basic media were conducted in (1) a 5 percent
Na-CCL solution, (2) a 20 percent NaOH solution, and (3) a 20 percent
NaOH solution containing disodium salt of ethylenediaminetetraacetic
acid (EDTA) chelating agent. Chelating agent in amounts ranging from
0.25 g/1 to 10 g/1 were used in the regenerants. Results of these
tests indicated that Na_CO« was not as good a regenerating agent as
20 percent NaOH solution, and that 20 percent NaOH containing chelating
agent was a better regenerating agent than 20 percent NaOH when used
alone. A regeneration solution of 20 percent NaOH containing 500 mg/1
EDTA was selected for use in the pilot-plant runs.
In the pilot plant experiments the capacity of the carbon to adsorb
chromium from rinse water varied in the first five cycles but appeared
to stabilize in the fifth to eighth cycles. A larger number of cycles
would be needed to determine longer-term behavior. During the pilot
plant work, it was found that an aeration step more than doubled the
effectiveness of the caustic solution for the removal of the chromium
from the carbon.
This report was submitted by Battelle's Columbus Laboratories in ful-
fillment of U. S. Environmental Protection Agency Grant S802113 to Metal
Finishers' Foundation. Work was completed as of February 28, 1974.
iv
-------
CONTENTS
Page
Abstract iv
List of Figures vi
List of Tables vii
Acknowledgements viii
Sections
I Conclusions 1
II Recommendations 2
III Introduction 4
IV Experimental Work 8
V Appendixes 33
-------
FIGURES
No. Page
1 Adsorption Capacity for Total Chromium after Multiple 11
Cycles with Acid (5 percent H SO,) Used for Stripping
2 Adsorption Capacity for Total Chromium after Multiple 12
Cycles with Basic Stripping Media
3 Adsorption Capacity for Total Chromium after Multiple 13
Cycles with NaOH Stripping Solution (Effect of EDTA
Concentration)
4 Adsorption Capacity for Total Chromium after Multiple 14
Cycles with NaOH Stripping Solution
5 Chromium Retained on Carbon after Adsorption-Desorption 17
Cycles
6 Schematic Diagram of Activated Carbon Adsorption Unit 18
7 Results of Experiments During an Eight Cycle Operation 22
of the Pilot-Plant Unit
8 Concentration of Chromium in Wash Solutions 25
9 Chromium Loading Remaining on Carbon after Regeneration 26
A-l Standard Chromium Curve 35
vi
-------
TABLES
No. Page
1 Data from Experiment Nos0 4, 6, and 8 15
2 Capital Costs for Continuous Treatment of Chromium 29
Rinse Waters
3 Operating Cost Estimate for Continuous Chrome Removal 30
by Conventional Process
B-l. Summary of Data from Laboratory Experiments on 36
Chromium Adsorption and Regeneration Using Acid
and Basic Media
C-l Summary of Regeneration Operation Data 39
D-l Data on Results of Eight Cycles of Operation 43
in the Pilot-Plant Unit
VII
-------
ACKNOWLEDGMENTS
This project represents the cooperative effort of the U. S, Environ-
mental Protection Agency, the Metal Finishers' Foundation, and
Battelle's Columbus Laboratories. This study was performed under EPA
Grant S802113 to the Metal Finishers1 Foundation, under which were
combined the efforts of the Pollution Abatement Committee of the
Foundation, represented by E. P. Durkin, and the cooperation of the
Superior Plating Company, Columbus, Ohio, represented by James Shriver,
at which plant the chromium removal equipment was installed and oper-
ated. Experimental work was performed in the laboratory and in the
plant by Battelie-Columbus staff members including R. G. Brown, T. L.
Tewksbury, and R. B. Landrigan, with project supervision by G. R.
Smithson, Jr.
viii
-------
SECTION I
CONCLUSIONS
(1) Chromium can be adsorbed by activated carbon from rinse water
solutions up to a concentration of at least 600 mg/1.
(2) Chromium can be desorbed from activated carbon using a cycle of
(a) wetting with 20 percent NaOH-500 ppm chelating agent solution,
(b) exposing the wetted carbon to air for 18 hours, (c) washing
with 20 percent NaOH solution, (d) washing with water, (e)
washing with sulfuric acid solution.
(3) The process stabilized after eight cycles where about 6-1/2 pounds
of chromium remained on the carbon after the acid wash (see
Figure 7) and where a total loading of 16 pounds of chromium was
reached after adsorption (based on 200 pounds of activated carbon).
(4) The majority (over 90 percent) of the chromium adsorbed was
removed in the caustic-aeration and water wash steps.
(5) A maximum loading of 22 pounds of chromium (per 200 pounds of
carbon) was reached in one cycle.
(6) Under actual plant operating conditions of 20 gpm of rinse water
containing 100 ppm of hexavalent chromium, an activated carbon
system would require a capital investment of approximately
$35,800, Under these conditions, the estimated total operating
cost would amount to about $62.60 per day. This includes the cost
of disposing of the regenerant.
-------
SECTION II
RECOMMENDATIONS
In this program an evaluation of a process for treatment of chromium
rinse waters was continued. It is recommended that field tests be
conducted using the same activated carbon process and following the
same procedure outlined in this report. To realize the full potential
of this process, the data should be extended to include a large number
of cycles, at various sites having different rinse solution
compositions.
It also is recommended that a laboratory program be conducted concur-
rently with the field tests to resolve some of the basic questions
raised in the pilot-plant operation. These include:
(1) The solubility of the chromium compounds of
interest in caustic solutions varying from
0 to 20 percent NaOH at various temperatures
from 80 to 180 F
(2) The solubility of the chromium compounds of
interest in various sulfuric acid solutions
ranging from pH 1.5 to 6.5 at various
temperatures
(3) The best oxidizing agent to use. Those sug-
gested are air, hydrogen peroxide, sodium
peroxide, oxygen, ozone, etc.
(4) How the caustic wash solution should be handled
to obtain optimum desorption. For example,
a. first 30 gallons once-through, second
30 gallons recycled
b. all recycles
c. all once-through
(5) How best to prepare carbon with acid wash
a. contact with strong acid
b. contact with weak acid
c. what temperature to contact with acid
(6) What method is best for recovery of chromium
from wash solutions and its ultimate disposal.
-------
Answers to the following questions should come from the experimental
work:
(1) Can a maximum value of adsorption be attained
in each cycle? In the eight cycle operation
described here a maximum value of 22 pounds
of chromium was adsorbed on 200 pounds of
carbon.
(2) Why was the maximum loading not achieved every
time? Did the fast addition of acid change
the carbon so that more chromium was adsorbed?
(3) Can the adsorbed chromium be stripped more
effectively if the chromium is oxidized? Does
the improved stripping technique lend itself
to better adsorption capacity? To what extent
will the improved stripping and higher adsorp-
tion capacities enhance the practical and
economic feasibility of the process?
(4) What is the effect of more dilute chromium
rinse solution on adsorption and on desorption?
What effect do metals such as Ni, Cu, Zn, etc.,
have on the adsorption-desorption cycle, and
what is the maximum tolerance of the carbon-
absorption system for such contaminants?
The answers to these questions from either the laboratory or the field
should make the process more versatile so that it could cover a variety
of situations met in the small plating plants located throughout the
nation.
-------
SECTION III
INTRODUCTION
The work presented in this report represents the latest segment of a
series of studies involving the cooperative efforts of the U.S.
Environmental Protection Agency, the Metal Finishers' Foundation, and
Battelle's Columbus Laboratories. These studies have extended over
the last several years and have included, in serial order, a state-of-
the-art survey of metal finishing wastewaters, evaluation of numerous
treatment methods for various wastewaters, and laboratory work on
treatment of selected types of wastewaters, most notably those con-
taining cyanides and those containing chromium. During the evaluations
of various treatment systems, emphasis has been placed on identifying
systems applicable to smaller plating operations.
Reports of the earlier work are identifiable as:
"A State-of-the-Art Review of Metal Finishing Waste
Treatment"; U.S. Department of the Interior, Federal
Water Quality Administration; Water Pollution Control
Research Series, 12010 EIE 11/68
"An Investigation of Techniques for Removal of Chromium
from Electroplating Wastes"; U.S. Environmental Protection
Agency, 12010 EIE 03/71
"An Investigation of Techniques for Removal of Cyanide
from Electroplating Wastes", U.S. Environmental Protection
Agency, 12010 EIE 11/71.
In these earlier reports, background information including a state-of-
the-art study and current practices in small electroplating plants was
presented. Production characteristics and waste effluent volumes and
composition were discussed. In the previous experimental work noncon-
ventional methods of treatment of chromium rinse waters studied
included ion flotation, liquid-liquid extraction, activated carbon
adsorption, activated alumina adsorption, reverse osmosis and reduction
with activated carbon. A preliminary estimation of costs of the
various methods was also given.
Carbon adsorption was singled out as the most promising method to
study. As a result, experiments were performed with both acid regener-
ation and caustic regeneration. Results of the acid regeneration
experiments showed that this media was not completely effective in
stripping chromium once it had been adsorbed on the carbon.
Results of the caustic regeneration (followed by an acid wash treatment
to remove residual caustic and condition the column for subsequent
adsorption cycles) indicated that chromium adsorption capacities were
somewhat better than with acid regeneration.
-------
The results of those preliminary studies demonstrated that electro-
plating plant rinse waters could be effectively treated with activated
carbon, but that important areas existed for additional study or
refinement of the process.
The work on chromium removal methods thus has reached the stage
described in this document; namely, the operation of a carbon adsorp-
tion system for the treatment of rinse waters from a commercial
chromium plating operation. This study thus represents work on the
stage of development of the transition from laboratory bench to plant
application.
The objectives of this program were to achieve a timely assessment of
the practicability of this system within a limited program. This
included the judicious selection of operating conditions and deter-
mining the effectiveness of the system under actual operating condi-
tions in the plant. The overall timing of the program was affected
by plant operations in that a seasonal shutdown of the chromium
plating line was spanned by this program.
Report Content
The following sections of the report deal with two separate types of
work:
(1) laboratory bench studies
(2) operation of a pilot scale device in a
plating plant.
The laboratory bench studies were performed to allow the determination
of the choice of whether acid or caustic should be used to strip or
remove chromium from the activated carbon, and, once caustic was
selected, whether either stripping or the subsequent adsorption capac-
ity could be enhanced by the addition of a chelating agent to the
caustic.
The operation of the pilot-scale unit to remove chromium from rinse
waters in a plating plant was carried out to determine the effective-
ness of the unit under real plant conditions. The original concept
was to operate for 100 cycles of the adsorption-strip-reactivate
sequences to determine the effective life of the carbon and to deter-
mine carbon losses (i.e., operating and maintenance costs). Final
contract limitations and plant operating conditions combined to limit
operations to eight cycles.
Overall Description of Operating
Sequence and Explanation of Terms
The generalized sequence of operations associated with the removal of
chromium from waste waters by carbon absorption may be described as
consisting of two major sequences:
-------
(1) Adsorption - during which chromium-rinse waters are
passed over activated carbon and the chromium is
adsorbed onto the carbon. The carbon eventually
becomes loaded with chromium to some limit, whereupon
adsorption ceases, and, if flow is continued, the
effluent still contains chromium.
(2) Regeneration - during which the carbon is treated by
passing, for example, caustic (NaOH) solution over
the carbon to remove the chromium from the carbon
and restore the adsorbing capacity of the carbon.
This major cycle actually consists of the following
steps:
(a) Desorbtion - caustic is run through the
carbon to remove the adsorbed chromium
(b) Water is run through the carbon to rinse
away any residual caustic
(c) Acid is run through the carbon to restore
the carbon to the pH condition necessary
for best adsorption
(d) Water is run through the carbon to rinse
away any residual acid. The carbon is
then ready for another cycle of adsorption,
i.e., (1) above.
Thus it may be seen that the laboratory work was aimed at the refine-
ment of step 2a, whereas the pilot-plant work necessarily dealt with
all steps of the operation.
The characteristics of operation of the activated-carbon-adsorption
apparatus are that during the adsorption cycle, all the chromium is
removed from the waste rinse water put through the carbon. For
example, the plating plant rinse waters treated in this study con-
tained analyzed values of up to approximately 600 mg/1 of chromium.
After passing through the carbon, the water would contain no detect-
able concentration (< 0.05 mg/1) of chromium.
When the adsorption capacity of the carbon was reached or exceeded,
(during operations in the plant) the effluent exhibited a corresponding
change from colorless to a light yellow, or tan, or brown color charac-
teristic of this particular rinse water. This change, which was termed
"break-through", was readily detected with the unaided eye, and was
confirmed by analytical results.
The prior results focused additional efforts on the area of apparent
loss of adsorptive capacity after multiple cycles of operation with
either caustic or acid stripping to determine the reason for the loss
of adsorptive capacity and to determine how to maintain it at a high
level. A less important aspect of the process involves complete
-------
stripping of the adsorbed chromium from the carbon during the regener-
ation cycle. Incomplete stripping occurred during all runs. Whether
adsorption capacities could be increased significantly if complete
stripping were achieved remained to be established. This phase of the
operation would require further study. Since reduction of chromium
during adsorption was found to occur and since this material would be
stripped very slowly during the regeneration cycles, a chelating
reagent (EDTA*) was added in new experiments to aid in the release of
tightly bound chromium. Hence experiments were performed in BCL
laboratories on a small scale and at Superior Plating Company,
Columbus, Ohio, on a pilot scale to test the effectiveness of this
addition to improve the stripping of chromium from the carbon.
The pilot plant was operated over a 3-1/2-month period where eight
cycles of adsorption-desorption were performed on a bed of activated
carbon.
* Disodium salt of Ethylenediaminetetraacetic acid
-------
SECTION IV
EXPERIMENTAL WORK
The experimental program was divided into two areas. The first was
laboratory studies of adsorption of chromium in a stirred bed of carbon
at a fixed pH of the solution followed by the desorption of chromium
using (1) 5 percent I^SO^ solution, (2) 5 percent I^SOA plus sodium
persulfate, (3) 5 percent t^SO^ plus chelating agent, (4) 20 percent
sodium hydroxide, (5) 20 percent sodium hydroxide plus chelating agent,
and (6) 5 percent ammonium carbonate.
The second was pilot-plant studies of the adsorption of chromium on
activated carbon, the desorption of the chromium with 20 percent NaOH-
chelating agent (500 ppm) solution, and the reactivation of the carbon
with H2SO, solution.
Laboratory Experimental Work
The initial conditions selected for laboratory studies were based on
the findings of previous work in which various grades of carbon were
evaluated and various conditions, such as optimum pH of the carbon,
were determined(1*2,3)a These prior studies established the basis for
the selection of Pittsburgh OL activated carbon (denoted as a granular-
type carbon with a particle size of 20 x 50 mesh). Similarly, maximum
chromium-removal was achieved in the prior work using carbon treated
to a pH of 3.
The chromium-containing rinse water used in the laboratory experiments
was obtained from the rinse-water tank of the same plating shop where
the pilot-plant work was to be done. This solution ranged in total-
chromium content from 0.234 g/1 to 0.315 g/1 during the experiments
(see Table B-l, Appendix B). The chromium-rinse water obtained from
the plant consisted of make-up water from the local municipal supply
plus constituents introduced by chromium-plate-rinse operations.
Rinse waters from other (e.g., brass-) plating operations were ex-
cluded from this work.
Laboratory experiments were conducted wherein acid and basic solutions
with and without chelating agent were used to determine the best
desorption agent. The experiments were conducted in five or more
cycles. The procedure included washing a 5-gram sample of carbon with
acid to adjust the pH to 3.0 prior to adsorption.
The carbon was then stirred for 1 hour in one liter of chromium-plating
rinse water. The pH was adjusted by the addition of H2SO^ to maintain
a value of 3.0 during adsorption. The mixture was filtered and the
filtrate analyzed for hexavalent and total chromium. The methods of
analyses are outlined in Appendix A. The filtered carbon was regener-
ated in one liter of stripping solution by stirring for 1 hour. (This
ratio of carbon to solution was much smaller than in the subsequent
pilot-plant operations, 5 g/1 versus 200 pounds/30 gallons = 1140 g/1.)
The mixture was filtered and the filtrate analyzed. The results of
these experiments are tabulated in Appendix B.
8
-------
Three regeneration experiments were conducted using an acid solution
and eight regeneration experiments were conducted using a basic solu-
tion as listed below.
Experiment
1
2
3
4
5
6
7
8
9
10
11
Stripping Solution
5 percent
5 percent t^SO, + 10 g/1
EDTA
5 percent
persulfate
+ 10 g/1 ammonium
*
20 percent NaOH
5 percent (NH ) CO,
U 2 J
20 percent NaOH + 10 g/1 EDTA
20 percent NaOH + 5 g/1 EDTA*
20 percent NaOH + 1 g/1 EDTA*
20 percent NaOH + 0.5 g/1 EDTA*
20 percent NaOH + 0.25 g/1 EDTA
20 percent NaOH +0.1 g/1 EDTA*
The results of these experiments are shown graphically in Figures 1, 2,
3, and 4.
Discussion of Results of Laboratory Experiments
Results of the first three experiments (details listed in Appendix B)
indicate that the quantity of chromium adsorbed decreased as the number
of cyclers increased, suggesting that the carbon would be spent and
require rejuvenation or replacement after only a few additional cycles.
It can be se^n from the graphs in Figure 1 that the use of the oxidant
ammonium persulfate in the acid stripping solution resulted in a rela-
tively faster decline in absorptive capacity of the carbon. The data
for the sixth through ninth cycles of Experiment 2 show anomalous
behavior, which is tentatively attributed to varying storage times
applicable to the latter cycles.
The results using a basic solution for stripping indicate that the 5
percent ammonium carbonate causes rapid degeneration of the adsorption
capacity of the carbon after five cycles, as shown graphically in
Figure 2 (Experiment 5). Whether the adsorption capacity could be
recovered in subsequent cycles was not determined. In any event, the
use of ammonium carbonate would be no better than caustic solution.
* Disodium salt of ethylenediaminetetraacetic acid
9
-------
Results of experiments with addition of chelating agent to the caustic
stripping medium show, by a comparison of Figures 2, 3, and 4, that the
highest total chromium adsorbed after five cycles was 0.045 g/g carbon
when 10 g/1 of EDTA was used (Experiment No. 6) and the lowest total
chromium adsorbed after five cycles was 0.038 g/g carbon when 1 g/1 of
EDTA was used (Experiment No. 8). Total chromium adsorption values for
carbon stripped with 20 percent caustic solution containing in the
range of 0.1 g/1 to 5 g/1 EDTA fall within a value of 8 percent above
the lowest total adsorption values. It was concluded that the effec-
tiveness of chelating agent in removing proportionate quantities of
chromium dropped as the quantity of chelating agent increased. Effec-
tiveness is based on the ratio of EDTA and quantity of chromium removed
In excess of that removed in caustic solution alone. A comparison of
Experiments 4, 6, and 8, presented in Table l} suggests the trends
noted in the data, i.e., the adsorption capacity of the carbon appeared
to be better sustained with 10 g/1 of EDTA (Experiment 6) while the
residual chromium appeared to be simultaneously higher. These data
appeared to indicate some benefit from the addition of EDTA. The cumu-
lative chromium retained on the carbon after each cycle for each
experiment is presented graphically in Figure 5, showing the effects
of stripping and regeneration. These data again suggest some benefit
from the addition of intermediate amounts of EDTA, although the effect
is not totally decisive.
For example, the values for percent of chromium adsorbed given show
higher sustained values at the five cycle point for Experiment 6
(10 g/1 EDTA) than for experiments with smaller amounts of EDTA.
Similarly, the data plotted in Figure 5 show a striking difference of
behavior between Experiment 8 (1 g/1 EDTA) and Experiment 1 (no EDTA)
beyond the five-cycle point.
Pilot-Scale Work
Before discussing the actual experiments and data accumulated in the
pilot-plant work a description of the facility and the general proce-
dure followed is presented.
Design of Equipment
The experimental unit (a Standard Ion Exchange package purchased from
the Illinois Water Treatment Company) was essentially as shown in
Figure 6. The major equipment items are (1) a 30-gallon galvanized
rinse tank sump, (2) two 1000-gallon rubber-lined storage tanks,
(3) two 30-gallon polyethylene makeup tanks, and (4) two 12-inch-
diameter by 6-feet high rubber-lined adsorption columns, each contain-
ing 100 pounds of activated carbon. All the piping and valves are
polyethylene.
The liquids are transported through the system by four chemical-
resistant centrifugal pumps. The rinse-water pump delivers the rinse
water from the overflow rinse tank (sump) to the storage tank. This
pump is activated and deactivated by a microswitch attached to a float
in the sump tank. The stored rinse water is recycled in the storage
10
-------
c
o
«
o
00
00
•I
0)
i-H
U
0)
P-.
•a
ai
•8
o
0)
•g
O
CJ
0.10
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
LEGEND
Experiment No. 1 (no EDTA)
D Experiment No. 2 (10 g/1 EDTA)
V Experiment No. 3 (10 g/1 ammonium persulfate)
Note:
all solutions contained 5% H^SO,
0.01
2 3
Operating Cycles
FIGURE 1. ADSORPTION CAPACITY FOR TOTAL CHROMIUM AFTER MULTIPLE CYCLES
WITH ACID (5 PERCENT H0SO.) USED FOR STRIPPING
2 A
11
-------
o
,0
o
00
00
•t
a>
iH
U
O
o
in
I
O
O
H
0.10
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
LEGEND
A Experiment No. 4 [200 g/1 NaOH]
+ Experiment No. 5 [5 percent (NH.) CO ]
<* Experiment No. 6 [200 gpl NaOH + 10 g/1 EDTA]
2 34
Operating Cycles
8 9
FIGURE 2. ADSORPTION CAPACITY FOR TOTAL CHROMIUM AFTER MULTIPLE
CYCLES WITH BASIC STRIPPING MEDIA
12
-------
cl
o
(J
tB
O
DC
60
•t
111
tH
O
U
t-l
(X,
•o
-------
c
o
.0
o
00
00
M
01
I-l
o
o
(U
a,
•o
01
•s
o
0)
e
o
6
r-!
O
H
0.10
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
FIGURE 4.
LEGEND
0 Experiment No. 9 (0.5 g/1 EDTA)
0 Experiment No. 10 (0.25 g/1 EDTA)
± Experiment No. 11 (0.1 g/1 EDTA)
Note: All solutions contained 200 g/1 NaOH
1 2 3 456789
Operating Cycles
ADSORPTION CAPACITY FOR TOTAL CHROMIUM AFTER MULTIPLE CYCLES
WITH NaOH STRIPPING SOLUTION (EFFECT OF EDTA CONCENTRATION)
-------
TABLE 1. DATA FROM EXPERIMENT NOS. 4, 6, and 8
Cycle
1
2
3
4
5
6
7
8
9
10
Experiment
Total Chromium
Adsorbed from
Rinse Water,
percent
79
74
73
70
64
65
63
--
--
--
No, 4 (stripping solution
207= NaOH, no EDTA)
Chromium
Remaining on Carbon
(cumulative total),
grams total Cr/grams carbon
0.006
0.01
0.02
0.01
0.01
0,02
0.02
--
--
—
Cycle
]
2
3
4
5
6
7
9
10
Experiment
207=
Total Chromium
Adsorbed from
Rinse Water,
percent
79
75
73
73
72
—
--
__
_ „
No. 6 (stripping solution
NaOH, 10 g/1 EDTA)
Chromium
Remaining on Carbon
(cumulative total),
grams total Cr/grams carbon
0.01
0.02
0.03
0.03
0.03
--
--
__
^ —
15
-------
TABLE 1. CONTINUED
Cycle
1
2
3
4
5
6
7
8
9
10
Experiment No. 8
20% NaOH,
Total Chromium
Adsorbed from
Rinse Water,
percent
75
72
67
68
67
59
63
60
61
55
(stripping solution
1 e/1 EDTA)
Chromium
Remaining on Carbon
(cumulative total)
grams total Cr/grams
0.01
0.009
0.006
0.01
0.01
0.006
-0.004
-0.006
-0.006
-0.007
9
carbon
16
-------
0.04
§
•8
t-l
oo
OJ
o.
UJ
I
1-1
00
(1)
C
•H
U
nj
E
o
0.03
0.02
0.01
LEGEND
Exp. No
34567
Operating Cycles
EDTA
None
10 g/1
5 g/1
1 g/1
0.5 g/1
0.25 g/1
0.1 g/1
10
FIGURE 5. CHROMIUM RETAINED ON CARBON AFTER ADSORPTION-DESORPTION
CYCLES
17
-------
Rinse Water Pump
20% NaOH-
500 ppm
Chelating
Agent
I
iConc.
IH SO
1 J r
t t f
MAKE-UP
TANK
(30 gal)
t
-i
STORAGE TANK '
(1000 gal)
i
— g-
Jr
Feed Pump (.'.) fc
1
1
1
[—*-
i
STORAGE TANK
(1000 gal)
20% NaOH-
500 ppm
Chelating
Agent
Cone.
1 1
t t
' 1
COLUMN,
ACTIVATED
CARBON
x J
<
To Sewer
}
^7 ^
H2.
p •
P
T
1
1
1
1
t
MAKE-UP
TANK
(30 gal)
\
t
; Recycle f
r Pump r
COLUMN,
ACTIVATED
CARBON
i 1
•\ Water Meters
' 0 0
1JLX
y
1
To Recvcle
p
k
d
L.
Portable
Pump
FIGURE 6. SCHEMATIC DIAGRAM OF ACTIVATED CARBON ADSORPTION
UNIT
18
-------
tanks and/or fed to the top of the activated carbon adsorption towers
where the chromium is removed. The clean metered effluent water is
returned to the rinse uanks for reuse. When the activated carbon is
loaded with chromium compounds, as revealed by the discoloration and
pH change of effluents at breakthrough, the adsorption is terminated
and regeneration begins. Regenerating solutions and wash solutions
are cycled through the columns in an upward direction via the recycle
pump. Spent regeneration solutions and wash solutions are transferred
from the makeup tank to the sewer or neutralizing/settling vessel via
the portable pump.
The two-column design allowed for an optional procedure of regenerating
one column while the other was being used for absorbing chromium.
Since chromium-rinse operations were non-continuous, this mode of oper-
ation was not considered appropriate.
The sump tank serves to catch and transfer rinse water overflowing from
the chrome-rinse bath, which was, in this particular case, operated as
a running-water rinse, i.e., tap water was allowed to run into the tank
continuously while the plating line was operating. This flow was
varied by the plating line operators depending on production conditions.
The liquid level control points in the 30-gallon sump were set at any
convenient levels which would avoid overflow and avoid running the pump
when there was no solution in the sump. The sump allowed the automatic
collection of rinse water in the storage tanks until sufficient supply
was available to justify an adsorption cycle.
The feed pump was used to mix the accumulated solutions (by pumping
from both back into both) in order to more nearly equalize the feed to
the columns during this experimental work.
In the particular work described, regenerating solutions were made up
sequentially in the makeup tanks, i.e., the caustic solution was pre-
pared, circulated through the columns, and then drained away, then
acid solution made up and drained away, e'ic.
Any installation for long-term operation should naturally incorporate
chemical supply or storage tanks.
Procedure
The carbon when first put in the columns is prepared for an adsorption
cycle by treating with sulfuric acid solution until a pH of 3 is
reached. This is accomplished by adding concentrateI sulfuric &cid at
the rate of 200 ml/'min to 30 gallons of water which is cycling through
the activated crr»-bon column in series with the make-up tank. When a pK
of 3 is reached, the acid is recycled for a period of 50 minucet. anc
then drained from the column into the sewer or neutralizing vessel.
The acid volume is measured and a sample of the solution analyzed for
chromium. The remaining acid is blown out of the column and into the
makeup tank with air entering the top of the column. The column is
ready now for the next adsorption run.
19
-------
Each column is flushed with 30 gallons of water and the effluent is
analyzed for chromium. Plating rinse water containing 200-700 mg/1
chromium is pumped through the activated carbon column in a downflow
direction at a rate of 2 to 3 gallons/minute/column. The two columns
are operated in parallel and effluent flowing from the column is moni-
tored with water meters reading in gallons. Spot checks are made to
maintain approximately equal rinse water flow rates through each
column. When a breakthrough of the column is observed as evidenced by
pH of the effluent rising above 6 or the color changing to a pale
yellow, the adsorption phase of the cycle is terminated.
The column is drained and the regeneration is begun. The activated
carbon is washed with 30 gallons of 20 percent caustic solution con-
taining 500 mg/1 chelating agent by cycling the solution (in an upflow
direction) through the column and makeup tank in series. After cycling
the caustic solution for one hour, the column is drained completely in-
to the makeup tank and held for further washing after an air treatment.
Air is blown slowly through the column in a downflow direction for 18
hours (overnight). The used 20 percent caustic solution is then
returned to the activated column and recycled for an additional wash
for one hour.
The caustic solution is removed from the systam; the volume measured,
and the effluent analyzed for chromium.
Each column is washed for one hour with 30 gallons of recycling tap
water (in an upflow direction); the effluent is collected, the volume
measured, and the solution analyzed for chromium.
The column is again prepared for adsorption by acid washing and the
cycle repeated.
A chromium balance of the feed material versus that recovered in the
various effluents and/or lost is made.
The sequence of operations may be summarized in chart form as follows:
Operation
Acid Wash
Drain
Water Rinse
Drain
Cr Adsorption
Drain
Caustic Strip
Drain
Aerate
Caustic Strip
Water Rinse
Drain
Volume
30 gallons
30 gallons
Variable
30 gallons
(Reuse above)
30 gallons
Chemical Content
57, H2S04
Tap Water
200-600 mg/1 Cr
207o NaOH+500 mg/1 EDTA
Tap Water
Time
1 hour
1 hour
11-3/4- 19-1/2
1 hour
18 hours
1 hour
1 hour
20
-------
The chromium adsorption cycle is dependent on the concentration of
chromium in the rinse water. The adsorption may be expressed in terms
of 8 to 9 pounds (the value in 4 of the eight runs) of chromium
adsorbed on the 200 pounds of carbon. For example, at a pumping speed
of 2 gpm (7.6 1/m), a solution containing 200 mg/1 of chromium would
be equivalent to 8 pounds of chromium in approximately 40 hours; a
solution with 600 mg/1 of chromium would be equivalent to 8 pounds of
chromium in 1/3 of that time (i.e., 13-1/3 hours).
In the case of the higher concentration (600 mg/1), the volume of rinse
water involved would be approximately 1600 gallons, i.e., the 8 pounds
of chromium would be transferred from 1600 gallons of rinse water (all
of which would be fit for recycle or discharge) to 120 gallons of
regenerating and rinse solution, which could be treated for recovery
or disposal.
In the above listing, the 18 hours for aeration reflect a convenient,
overnight cycle length, and might well be reduced. This and other
areas of potential improvement are listed in the Recommendations
section of this report.
Pilot-Plant Experimental Work
During a 3-1/2-month period the pilot-scale adsorption unit was oper-
ated in the open-loop fashion for eight cycles at Superior Plating
Company in Columbus, Ohio, with one exception of three hours when the
unit was operated in a closed loop. The general procedure followed in
most runs was (1) an acid wash to prepare the carbon bed for adsorp-
tion, (2) an adsorption cycle, (3) a short-time 20 percent NaOH-500 ppm
chelating agent wash, (4) an aeration of the wetted bed, (5) a short-
time wash with the caustic solution used in (3), and (6) a water wash.
In three runs the acid wash was followed by a water wash.
The experimental conditions and results of these eight cycles are shown
in Appendix C. Some of the results also are shown graphically in
Figure 7.
In the acid wash, the carbon was prepared for the adsorption step.
Experience in previous runs indicated a pH of 2.8 to 3.2 of the wetted
carbon was desirable for good adsorption. The acid was added rapidly
to the circulating solution in the first four runs and slowly in the
last four runs. Initially it was assumed that the rate of acid addi-
tion had no affect on the adsorption capacity of the carbon., However,
the results of the first four acid additions suggested that there is
an effect on adsorption capacity, especially in cycle 4 where 16 per-
cent chromium was adsorbed (see Figure 7).
Plating rinse solutions used in the experiments were uncontaminated
chromium-rinse (i.e., rinses used only on chromium-plated work, in
contrast to zinc-plated work, for example) solutions containing a total
chromium content in the range of 254 ppm to 608 ppm. The adsorption
rate was faster with the more highly loaded solution; however, the
total loading changed only slightly with feed chromium concentration.
21
-------
CO
1
o
p.
e
o
Si
u
o
4J
X
•H
Ol
26
24
22
20
18
16
14
12
10
LEGEND
Total Loading
Chromium Adsorbed
Chromium Recovered
Chromium Recovered in NaOH
Chromium Recovered in Water
Chromium Recovered in Acid
456
Cycle Number
10
FIGURE 7. RESULTS OF EXPERIMENTS DURING AN EIGHT CYCLE
OPERATION OF THE PILOT-PLANT UNIT
22
-------
The quantity adsorbed per cycle and the total loading of the carbon
are shown in Appendix D and Figure 7.
It may be noted that the amount of chromium recovered is higher than
the weight absorbed for cycles 5, 6, and 8 in Table D-l (Appendix D).
This is related to the recovery of chromium not stripped in previous
cycles. A recovery rate less than 100 percent in the earlier cycles
reflects an accumulation of chromium on the carbon, part of which is
apparently recovered in later cycles.
The adsorbed chromium was desorbed from the carbon in three washes
interspersed with an aeration of the NaOH wetted bed. The loaded bed
was washed with 20 percent NaOH solution containing 500 ppm of EDTA
chelating agent for periods of 1/4 to 100 hours (see Appendix C). The
drained bed was aerated for 14 to 72 hours followed by a continuation
of the first wash using the same solution. The aeration step allowed
additional chromium to be removed in the NaOH solution.
The caustic wash was followed by a water wash which removed additional
chromium.
The water wash was followed by a repeat of the cycle with the acid
wash wherein additional chromium was removed.
Results
In the first cycle only 40.5 percent of the adsorbed chromium was
removed in two caustic-solution washings. The first wash removed
about 18 percent of the adsorbed chromium in 100 hours of washing,
which was the same quantity in solution after 1/2-hour of washing.
The extra 99-1/2 hours of washing were unnecessary. In a second wash
with fresh caustic solution another 22.5 percent of the adsorbed
chromium was removed in a 72-hour wash. The remaining chromium was
removed by an acid wash followed by a water wash. The water wash
removed 51 percent of the chromium adsorbed. Slightly over 50 percent
of the adsorbed chromium was recovered. This low desorption value
indicated the caustic solution was not performing as expected and for
this reason the procedure was changed in subsequent cycles. The change
was made based on review of the experimental data.
After the experimental work was completed it was noted that, in a few
experiments, a sample of activated carbon left on a filter overnight,
exposed to air and wetted with caustic solution (not yet washed with
water), showed a greater desorption of chromium than a sample of acti-
vated carbon which was processed immediately. The air exposure was
not controlled nor was the increased desorption expected. When the
benefits of aeration were realized, an aeration step was incorporated
in the pilot-scale-desorption procedure.
In the second cycle slightly less chromium was adsorbed and slightly
less chromium recovered than in the first cycle. However, the amount
of chromium recovered in the caustic solution had increased in weight
and the amount of chromium recovered in the water wash had increased
23
-------
in weight. The combined caustic and water wash in this run accounted
for 85 percent of the recovered chromium—35.3 percent in the NaOH
solution and 49.5 percent in the water. The rest of the chromium was
recovered in the acid wash and a water wash that followed - 9 percent
in the acid solution and 6.5 percent in the rinse water.
In the third cycle both the quantity of chromium adsorbed and the quan-
tity of chromium recovered increased. The quantity of chromium
adsorbed amounted to almost twice that in Cycle 1. The combined
caustic wash and water wash accounted for 93 percent of the total
chromium recovered, with the remaining 7 percent recovered in the acid
solution. The weight of chromium in the caustic wash was about twice
that in the water wash. Repeated alternate washing and aeration with
the same solution indicated that the maximum chromium was removed after
the first aeration period. A prolonged treatment was not beneficial
for chromium removal (see Appendix C). The greater adsorption power
of the carbon is though to be due to the manner in which the acid is
added - fast or slow.
In Cycle 4 an increased quantity of chromium was adsorbed equal to a
loading of .115 g Cr/g carbon. This was the maximum loading of the
carbon in these cycles. The combined caustic wash and water wash
removed 92 percent of the adsorbed chromium. Additional desorption
may be possible because the caustic solution and the water solution
apparently reached their saturation point for this operation.
In Run 5, much less chromium was adsorbed than in the previous cycles.
This was due either to channeling or the residual loading from previous
runs, not because of the saturation limits alluded to in the previous
cycles. In this cycle, 3.91 pounds of the chromium left on the carbon
from the previous cycle was removed in addition to the 4.16 pounds
adsorbed during this cycle (100 percent recovery). During the desorp-
tion treatment, the chelating agent concentration was increased 8 times
without any change in total recovery.
In Run 6, the chromium adsorbed increased, but not to the level of
Cycle 4, probably because of the milder acid pretreatment (dropwise
addition). Again all the adsorbed chromium from this run was recovered
plus 1.46 pounds from previous runs. The combined caustic-solution
wash and the water wash accounted for 98 percent of the chromium re-
covered. The concentration of the caustic solution was 25,374 ppm of
Cr and the water wash concentration was 11,226 ppm of Cr. Both these
concentrations are close to the maximum concentration of 29,500 ppm Cr
and 13,400 ppm Cr for caustic and water solutions, respectively,
encountered in the eight cycles of regeneration (see Figure 8).
In Runs 7 and 8, the operation stabilized with 98 percent of the
adsorbed chromium recovered (59 percent in the caustic - 39 percent in
the water wash). The chromium remaining in the 200 pounds of carbon
stabilized to 6.82 pounds (see Figure 9).
These data suggest that a large number of cycles could be repeated
before the carbon is spent.
24
-------
3000
B
IX
o.
§
V
u
e
o
u
§
•a
o
1-1
2000
1000
Caustic
Solution
Water
Wash
456
Cycle Number
10
FIGURE 8. CONCENTRATION OF CHROMIUM IN WASH SOLUTIONS
25
-------
22
20
18
16
CO
•o
§ 14
o
ex
5 12
|
6 10
-------
During Cycle 8 the effluent was recycled to the rinse tanks for several
hours without injury or damage to the plated products.
The adsorption portion of the cycle was routine. The condition found
most detrimental to successful operation was bubble formation in the
column. This caused channeling and led to premature termination of
the adsorption. For this reason upflow filling of the column is sug-
gested. The quantity of chromium adsorbed during these runs appeared
to be dependent on the manner acid additions were made, i.e., slow
additions suggest a low adsorption and fast additions suggest a high
adsorption.
Ideally whatever is adsorbed is desorbed. However, the forces involved
in the two operations work in an opposite manner and so the adsorption
bonding force must be broken to desorb. In this system it was found
that aeration after wetting of the chromium with caustic was helpful in
achieving desorption. However, as the chromium was removed in an up-
flow direction (opposite to adsorption, which was in a downflow direc-
tion) , it was put back (recycled) into the bottom of the column where
it might be readsorbed. This suggests a once-through washing of the
column at least for the first portion of the caustic regeneration cycle.
The maximum concentration of desorbed chromium in the caustic solution
encountered in the eight cycles was 29,500 ppm (see Figure 8). This
suggests that a limit may have been reached, and also suggests that a
second caustic wash with fresh solution may have removed additional
chromium in Cycle 4 (see Figure 9).
The water wash following the 20 percent caustic wash removed about half
as much chromium as the caustic wash. This suggests that the concen-
tration of caustic may have a considerable effect on chromium desorp-
tion. Chromium concentration in the water wash as shown graphically in
Figure 8 indicates that the solubility limit was reached.
The acid wash is a complicated step in the operation and although only
a small portion of the chromium adsorbed is removed in this step, the
change from a pH of 11.5 to 3.0 is accompanied by changes in the solu-
tion. As the pH decreases, first the color of the solution changes
from yellow to orange; next, at pH 8.3, a precipitate appears. At
lower pH (6.1) the precipitate disappears and an orange solution
appears accompanied at a lower pH by a green precipitate.
With regard to the behavior of the carbon, no detectable loss of carbon
occurred during the pilot-plant operations. All solutions run through
the carbon were sampled, tested, or analyzed at various times. No
carbon particles were detected visually in any of the samples or on
filter paper catches. It was concluded that carbon losses were so
small as to be undetectable in terms of the 200-pound charge, the
residual chromium, and the effects of moisture content pick-up which
would occur during any removal and handling of the carbon.
27
-------
Capital and Operating Cost Estimates for the Removal
of Hexavalent Chromium from Plating Rinse Waters
For the removal of chromium from rinse water via
adsorption process the following conditions have
Flow rate of waste rinse water
Hexavalent chromium concentration
Loading of activated carbon
Number of cycles possible before discard
Bulk density of carbon
Carbon required for 1 day's operation
Size of column of activated carbon
required for above
Assumed dimensions of column total
Number of columns (1 working, 1 polishing,
1 on regeneration)
Total weight of carbon in columns
Additional tankage
Equalizing tank
Discharge tank
NaOH tank for regeneration
Pumps
Feed pump to columns
Circulating pump for regeneration
Circulating pump for discharge tank
Treatment tank for Na0CrO. solution
2 4
the activated carbon
been assumed:
20 gpm
100 ppm
4% by weight
50
30 lbs/ft2
600 Ibs
20 cu. ft.
2.50' dia. x 6'
1800 Ibs
600 gallons
600 gallons
250 gallons
1 hp
1 hp
1 hp
250 gallons
Capital and operating costs based on these assumptions are shown in
Tables 2 and 3, respectively.
It further is assumed that the regenerant containing the chromium will
be removed on a scheduled basis by an industrial waste disposal con-
tractor. Preliminary estimates indicate that the cost of disposal in
this manner will amount to about $17.50 per day. This will increase
the daily operating cost to about $62.60.
28
-------
VD
TABLE 2. CAPITAL COSTS FOR ACTIVATED CARBON PROCESS
r
No.
3
Items of Equipment
Absorption Towers
\
Specifications Unit Cost
2.5' dia. x 8' overall, rubber
Estimated Costs
$25,0001
2 Auxiliary Tanks
1 Caustic Feed Tank
1 Treatment Tank for
3 Pumps
3 Pump Motors
Miscellaneous Piping
Miscellaneous Electrical
TOTAL
lined, fitted with distri-
butor's piping valves
gauging. Charged with carbon
Installed
Feed and discharge 600 gallons, installed
250 gallons, installed
250 gallons, installed
14 p each, installed
650
150
4,000
700
700
1,950
450
2,000
1.000
$35,800
1 Informal estimate, not quotation from information in manufacturer's literature.
-------
TABLE 3, ESTIMATED OPERATING COSTS FOR CARBON ADSORPTION PROCESS
Basis
u>
o
Unit Cost,
dollars
Direct Costs
Reagents
Sulfuric Acid
Sodium Hydroxide
Carbon Losses
Labor
Maintenance
Plant Supplies
Utilities, Power, etc.
Direct Cost/Day
Fixed Costs
Depreciation, Taxes, Insurance
Direct plus Fixed Costs
100 Ibs/day
150 Ibs/day
12 Ibs/day
2 mans/hours/day
57o of fixed capital cost
157,, of above
0.03
0.06
0.30
4.00
Daily Costs,
dollars '
$ 3.00,
9.00.
3.60-
8.00'
5.00
1.00
2.50
$32.10
1 Assuming the Na-CrO, is used in the plating plant, e.g., anodizing, or hauled away by a
chemical reclaimer at no cost.
2 NaOH in regenerating solution.
3 Assumes complete replacement of carbon is necessary every 50 cycles. 60 lbs/50 = 12 Ibs/day.
4 Includes labor required for operation of adsorption unit regeneration.
-------
References
(1) "A State-of-the-Art Review of Metal Finishing Waste Treatment",
U.S. Department of the Interior, Federal Water Quality Adminis-
tration, Water Pollution Control Research Series, 12020 EIE
11/68, Washington, D.C.
(2) "An Investigation of Techniques for Removal of Chromium from
Electroplating Wastes", U.S. Environmental Protection Agency,
12010 EIE 03/71, Washington, D.C.
(3) "An Investigation of Techniques for Removal of Cyanide from
Electroplating Wastes", U.S. Environmental Protection Agency,
12010 EIE 11/71, Washington, D.C.
31
-------
SECTION V
APPENDIXES
Page
A. Methods Used for Control Analyses 33
B. Summary Data from Laboratory Experiments 36
C. Summary of Regeneration Operation Data 39
D. Data on Results of Eight Cycles on Operation of the 4-3
Pilot-Plant Unit
32
-------
APPENDIX A
METHODS USED FOR CONTROL ANALYSES
Simplified Test for Hexavalent Chromium
(1) Transfer a 50-ml sample, containing no more than 1.25 ppm of
hexavalent chromium (predilute if necessary) to a 100-ml Erlen-
meyer flask.
(2) Add 0.1 gram of solid reagent mixture made by grinding together
0.25 gram of 1,5 diphenylcarbohydrazide and 9.75 grams of tartaric
acid.
(3) Shake vigorously until all the reagent is dissolved.
(4) Let stand 5 minutes to develop full color and measure the absor-
bance in a spectrophotometer at 540 m wavelength.
(5) Determine the hexavalent chromium concentration of the solution by
comparison with a standard calibration curve (see Figure A-l).
(6) The color also may be compared against a set of permanent standards
prepared in steps of 0.5 ppm by mixing together various proportions
of cyrstal violet and safrinin.
This simplified test was taken from the reference "Simplified Test for
Hexavalent Chromium" by B. L. Goodman in Water and Sewage Works, Feb-
ruary, 1961, (page 80). It may be noted that the referenced publication
makes no mention of the maximum time of standing [cf (4) above] before
before the fading of the color. In the performance of these analyses
on this program good practice was observed in all aspects of analytical
procedure. For example, blanks of tap water and analytical standards
were run in association with analyses of chrome-rinse waters. Checks
among the blanks and standards were so close as to indicate no inter-
ference or variance other than routine. An examination of the refer-
enced publication would indicate this method gives a precision of 11
parts in 1000 parts at a chromium concentration of one ppm and had an
average accuracy within 2 percent of the complete Standard Method as
given in "Standard Methods for the Examination of Water, Sewage, and
Industrial Wastes", APHA, AWWA 6= WPCF, New York, 10th ed., 1955.
Examination of the publication describing the simplified method shows
that the article states that the "permanent standards are absolutely
stable", in. terms of checks against spectrophototnetric analyses over
a period of a year and a half.
All determinations of pH were made using commercial bench-type pH
meters for research work, with the meters standardized before each use
and periodically calibrated against National Bureau of Standards
standards according to BCL's routine instrument calibration schedules
and procedures. All sampling and handling techniques were in accordance
33
-------
with the "Standard Methods" referenced above or in accordance with
analytical procedures developed by BCL depending on which would give
better results on this program.
Titrlmetric Method for Total Chromium
A control procedure for total chromium also was developed. This method
involved the oxidation of chromium by ammonium persulfate in the
presence of silver nitrate and titration of the chromium by the conven-
tional ferrous sulfate-permanganate titration.
34
-------
100
90
80
70
60
50
B
g 40
P
01
o.
8
cd
-------
10
APPENDIX B
TABLE B-l. SUMMARY OF DATA FROM LABORATORY EXPERIMENTS ON CHROMIUM ADSORPTION
AND REGENERATION USING ACID AND BASIC MEDIA
\
\
Exper-
iment
No.
1
1
1
1
1
2
2
2
2
2
2
2
2
2
3
3
3
3
3
4*
4
4
4
4
Stripping
Solution
5% H.SO.
2 4
5% H0SO. +
2 tf
10 g/l EDTA
5% H so +
10 g/l
ammonium
persulfate
20% NaOH
Cycle
1
2
3
4
5
1
2
3
4
5
6
7
8
9
1
2
3
4
5
1
2
3
4
5
Initial
Solution
Total Cr,
grams
0.234
0.234
0.234
0.297
0.297
0.297
0.297
0.297
0.297
0.297
0.315
0.315
0.310
0.310
0.297
0.297
0.297
0.297
0.297
0.297
0.297
0.297
0.297
0.297
Adsorbed
Total Cr,
grams
0.194
0.168
0.141
0.151
0.142
0.236
0.218
0.225
0.200
0.163
0.113
0.141
0.066
0.130
0.241
0.146
0.101
0.083
0.085
0.234
0.219
0.217
0.207
0.189
Adsorbed
Total Cr,
percent
82.9
71.8
60.3
50.8
47.8
79.4
73.4
74.8
67.3
54.9
35.9
44.8
21.3
42.0
81.1
49.1
34.0
27.9
28.6
78.7
73.8
73.1
69.7
63.6
Total Chromium
Adsorbed,
grams Cr/gram carbon
0.0388
0.0336
0.0282
0.0302
0.0284
0.0472
0.0436
0.0450
0.0400
0.0326
0.0226
0.0282
0.0132
0.0260
0.0482
0.0292
0.0202
0.0166
0.0170
0.0468
0.0438
0.0434
0.0414
0.0378
Total Chromium
Remaining on Carbon,
cumulative
grams Cr/gram carbon
0.0120
0.0230
0.0200
0.0260
0.0275
0.0108
0.0182
0.0388
0.0388
0.0582
0.0616
0.0780
0.0568
0.0698
0.0235
0.0304
0.0334
0.0348
0.0382
0.0065
0.0095
0.0167
0.0132
0.0115
-------
TABLE B-l. (Continued)
Exper-
iment
No.
5
5
5
5
5
6
6
6
6
6
7
7
7
7
7
8*
8
8
8
8
9
9
9
9
Stripping
Solution
5% (HH. )2CO
20%
NaOH +
10g/l EDTA
20% NaOH
+ 5g/l EDTA
20% NaOH
+ 1 g/1 EDTA
20% NaOH
Cycle
^ 1
•3 2
3
4
5
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
1
+0.5 g/1 EDTA 2
3
4
Initial
Solution
Total Cr,
grams
0.297
0.297
0.312
0.312
0.312
0.312
0.312
0.312
0.312
0.312
0.305
0.305
0.305
0.305
0.305
0.305
0.305
0.305
0.305
0.305
0.315
0.315
0.315
0.315
Adsorbed
Total Cr,
grams
0.236
0.208
0.211
0.194
0.114
0.246
0.232
0.227
0.226
0.224
0.239
0.198
0.213
0.206
0.204
0.230
0.218
0.203
0.208
0.203
0.274
0.214
0.194
0.200
Adsorbed
Total Cr,
percent
79.4
70.0
67.6
62.2
36.5
78.8
74.4
72.8
72.5
71.8
78.4
64.9
69.8
67.5
66.9
75.4
71.5
66.6
68.2
66.6
86.9
67.4
61.6
63.4
Total Chromium
Adsorbed,
grams Cr/gram carbon
0.0472
0.0416
0.0422
0.0388
0.0228
0.0482
0.0464
0.0454
0.0452
0.0448
0.0478
0.0396
0.0426
0.0412
0.0408
0.0460
0.0436
0.0406
0.0416
0.0406
0.0547
0.0425
0.0388
0.0399
Total Chromium
Remaining on Carbon,
cumulative
grams Cr/gram carbon
0.0213
Oo0305
0.0345
0.0351
0.0354
0.0149
0.0175
0.0289
0.0318
0.0300
0.0181
0.0121
0.0218
0.0204
0.0202
0.0111
0.0086
0.0063
0.0099
0.0112
0.0112
0.0161
0.0161
0.0195
-------
TABLE B-l. (Continued)
LO
00
Exper-
iment
No.
10
10
10
10
10
11
11
11
11
11
Stripping
Solution
20% NaOH
+0.25 g/1
EDTA
20% NaOH
+ 0.1 g/1
EDTA
Cycle
1
2
3
4
5
1
2
3
4
5
Initial
Solution
Total Cr,
grains
0.315
0.315
0.315
0.315
0.315
0.315
0.315
0.315
0.315
0.315
Adsorbed
Total Cr,
grams
0.274
0.205
0.207
0.177
0.201
0.251
0.232
0.220
0.208
0.200
Adsorbed
Total Cr,
percent
86.9
65.0
65.6
56.2
63.8
79.8
73.8
69.9
66.0
63.6
Total Chromium
Adsorbed ,
grams Cr/gram carbon
0.0547
0.0410
0.0413
0.0354
0,0402
0.0502
0.0465
0.0441
0.0416
0.0400
Total Chromium
Remaining on Carbon.
cumulative
grams Cr/gram carbon
0.0042
0.0039
0.0117
0.0131
0.229
0.0071
0.0163
0.0097
0.0109
0.0135
* See Table 1 for additional cycles.
-------
APPENDIX C
TABLE C-l. SUMMARY OF REGENERATION OPERATION DATA
PPM PPM
Hexa Total
Operation Chromium Chromium
Cycle 1
(1) First caustic solution 1/2 hour after 3,300 4,052
cycling
(2) First caustic solution 100 hours 4,250 5,255
after cycling
(3) Second caustic solution 1/4 hour 1,731
after cycling
(4) Second caustic solution 72 hours 2,550 2,845
after cycling
Ditto 1,675 1,862
(5) Wash water solution 2 hours after 160
after cycling
(6) Wash water solution 3 hours after 325
after cycling
(7) l^SO^ wash 1 hour after cycling
(8) h^SO^ wash 72 hours after cycling
pH 2.3
(9) H20 wash 2 hours a.fter cycling
(10) H20 wash and acid pH adjustment
Cycle 2
(1) Caustic solution 24 hour recycle
(2) Aerate for 24 hours
(3) Caustic solution drained after 6,200 6,311
1 hour cycle
(4) Water wash 1 hour recycle 8,750 8,891
(5) Acid wash 22 hour recycle (pH 1.8 1,807
adjust to 3.0 with NaOH)
(6) Water wash 1 hour recycle 1,166
Cycle 3
(2) Aerate for 18 hours
(3) Caustic solution 1/4 hour recycle 27,417
(4) Caustic solution continued for 8 25,331
hours
Actual Estimated
Actual Estimated Weight of Weight of
Volume, Volume, Chromium, Chromium, *
gallons gallons pounds pounds Cononents
30 -- 1.01 Chromium removed in first 1/2 hour
22.5 -- 0.987 — Additional 4 days no help
37.5 0.54
12.5 0.296 -- Little chromium removed by second caustic wash
60 -- 0.932
9 -- 0.013
30 0.009
30 -- 0.53
7.5 0.457
60 2 .73 Most of chromium removed in water wash after pH adjustment
34 0.063
30 -- 1.58 -- Good removal after aeration. Air must oxidize chromium.
30 — 2 .22 Good removal with water wash
26 0.39
30 0.29
-- 30 -~ 3 90
30 6.86
30 6.34
* Note: All caustic solutions contain 20% NaOH plus 500 ppm EDTA unless otherwise noted.
-------
TABLE C-l. (Continued)
*»
o
(5)
(6)
; (7)
(8)
'(9)
(10)
(11)
(12)
Cycle
(1)
(2)
(3)
(4)
(5)
(6)
Cycle
(1)
(2)
(3)
W
(5)
(6)
(7)
Operation
Aerate over weekend (72 hours)
Caustic solution 1/4 hour recycle
Continued caustic solution 9 hour
recycle
Aerate 16 hours
Caustic solution 1/4 hour recycle
Water wash 2 hour recycle
Acid wash 6 hour recycle pH 3.4
Water wash
_4
Caustic solution 1/2 hour recycle,
drain
Aerate for 24 hours
Water wash 1/2 hour recycle
Added water and I^SO^ slow addition
pH 3.0
Water wash 1 hour
_5
Caustic solution 4-1/2 hours
recycling
Aerate overnight
Caustic solution 1/2 hour recycle
Added 480 grams EDTA-4 percent
recycle 1/2 hour
Caustic solution 1/2 hour recycle
Water wash once through left column
Water wash recirculating right column
Acid wash - right column pH 3.1
Acid wash - left column pH 2.4
PPM PPM Acutal Estimated
Hexa Total Volume, Volume,
Chromium Chromium gallons gallons
..
25,200 30
25,765 33
13,140 13,012 31
1,506 76
Combined with acid wash
18,560 -- 30
29,495 29
13,400 12,969 28
1,426 29
1,607 15
10,627 30
—
19,822 30
19,822 30
19,500 20,343 24
3,100 3,099 60
6,400 6,302 30
1,062 26.5
2,370 30.5
Actual Estimated
Weight of Weight of
Chromium, chromium,
pounds pounds Comments
--
6.30
7.09 -- About 100 percent more chromium removed with aeration
step involved
3.36 -- About 50 percent as much chromium removed in water wash
as in preceding caustic wash
0.95
4.64
7.13 -- Same comments as for Cycle 3
3.03
0.35
0.20
2.66
--
4.96
4.96 Chelating agent did not remove chromium
4.10
1.55 Note last portion of water through the column analyzed
1.58 39 ppm chromium
0.24
0.60
-------
TABLE C-l. (Continued)
Cycle
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
Cycle
(1)
(2)
(4)
(5)
(6)
(7)
(8)
(9)
PPM
Hexa
Operation Chromium
_6
Aerate 18 hours
Caustic solution 1 hour recycle
Aerate 8 hours
Caustic solution 1-1/2 hour recycle
Aerate 72 hours
Caustic solution 1/2 hour recycle
(Final)
Water wash recycle 1 hour 12.200
Acid wash recycle 2 hours (acid
addition slowly) pH 3 . 1
6 liters/80 minutes
I
Caustic solution 1 hour recycling
(with air sparging)
Aerate for 18 hours + 1/2 hour caustic
solution recycle
Aerate 28 hours
Caustic solution 1/2 hour recycle 20,000
Water wash - left column 15 gallons
5 minute recyle
- right column 15 gallons
5 minute recycle (combined and used - -
in)-- - left and right columns 8,980
30 gallons - 15 minute recycle
Water wash 1/4 hour recycle 4,060
Acid wash-acid added slowly to water-
after water added
-after 2.5 i cone, acid added (left
column only)
-after 4.5 i cone, acid adderf
-after 60 i cone, acid added-total addition
in 1 hour
Recycle acid for 5 hours and leave in
column 72 hours pH 2.7
PPM
Total
Chromium
11 711
21,080
22,121
26,459
25,374
11,226
722
10,887
17,524
18 434
20,300
11,234
20,647
9,022
4,075
1,815
739
6,011
503
Actual Estimated
Volume, Volume,
gallons gallons
30
30
30
35
25
35
30
30
30
30.5
15
15
30
34
30
30
30
26
Actual Estimated
Weight of Weight of
Chromium, Chromium,
pounds pounds Comments
2 93
5.27
5.53
6.62
7.41
2 . 34
0.21
2.73
4.39
4.61
5.17
1.40
2.58
2.11
1.15
0.45
0.19
0.02
0.11
-------
NJ
TABLE C-l. (Continued)
Cycle
(1)
(2)
(3)
(4)
(5)
Operation
8
Caustic solution wash - 15 minute
recycling
Aerate for 15 hours
Caustic solution wash - 2 hours
with sparging air-one column
-2 hours with sparging air-both
columns
Water wash 3/4 hour
Water wash - left column
- right column
PPM
Hexa
Chromium
24,750
9,933
17,200
8,000
6,270
5,250
PPM
Total
Chromium
26,806
18,001
8,137
6,558
5,517
Actual
Volume,
gallons
31.5
30
15
15
Actual
Estimated Weight of
Volume, Chromium,
gallons pounds
30
30
4.73
2.04
0.82
0.69
Estimated
Weight of
Chromium,
pounds
6.71
2.49
Comments
Green color in solution after 5 minutes
(a) One air pump not operating.
-------
APPENDIX D
TABLE D-l. DATA ON RESULTS OF EIGHT CYCLES OF OPERATION IN THE PILOT-PLANT UNIT
Number
1
2
£
it
5
6
7
8
Adsorption
hours
11-3/4
20
19-1/2
30-1/4
19-1/2
14
14-1/4
13-1/2
Weight of
Chromium
Adsorbed,
pounds
8.16
5.46
14.12
16.11
4.16<0
8.50
8.98
8.26
Weight of
Chromium
Recovered ,
pounds
5.49
4.48
11.40
10.71
8.07
9.96
8.54
8.28
Weight of
Chromium
Not
pounds
2.67
0.97
2.72
5.40
(3.91)
(1.46)
0.44
0.02
Weight of
Chromium
on Carbon
From all
Previous
pounds
2.67
3.64
6.36
11.76
7.85
6.39
6.83
6.81
Total
Weight of
Chromium
(Loading)
8.16
8.13
17.76
22.47
15.92
16.35
15.37
.
Chromium
on Carbon
After
Regenera-
tion,
percent
carbon
1.32
1.82
3.18
5.83
3.93
3.19
3.41
3.41
Chromium
on Carbon
After
percent
4.08
4.07
8.88
11.24
7.96
8.18
7.68
--
Weight of
Chromium
Removed in
Caustic
pounds
1.28
1.58
7.09
7.13
4.10
7.41
5.17
4.73
Weight of
Chromium
pounds
0.954
2.22
3.36
3.03
3.13
2.34
3.26
3.55
Weight of
Chromium
pounds
4.57
0.39
0.95
0.35
0.84
0.21
0.11
No acid
wash
Weight of
Chromium
Removed in
pounds
2.79
0.29
"
0.20
-
'
-
—
Chromium
Removed by
NaOH Wash,
recovered
23.4
35.3
62.2
66.6
50.8
74.4
60.5
57.1
Chromium
Removed by
Water Wash,
17.4
49.6
29.5
28.3
38.8
23.5
38.2
42.9
Chromium
Removed by
Acid Wash,
percent
8.32
9.0
8.0
3.3
10.4
2.1
1.3
0
Chromium
Removed
by Final
Water
Wash, Chromium
percent Not
50.9 48.6
6.5 21.6
23.8
0.7 50.4<»>
(b)
-
0.52
0.25
(a) Removed in Cycle 5.
(b) Removed in Cycle 6.
(c) Chromium broke through one column after 5 hours operation--probably channeling.
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO. 2.
EPA-670/2-75-055
4. TITLE AND SUBTITLE
REMOVAL OF CHROMIUM FROM PLATING RINSE WATER USING
ACTIVATED CARBON
7. AUTHOR(S)
Richard B. Landrigan and J. B. Hallowell.i
9. PERFORMING ORG "VNIZATION NAME AND ADDRESS
Battelle Memorial Institute
Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
12. SPONSORING AGENCY NAME AND ADDRESS
National Environmental Research Center
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
3. RECIPIENT'S ACCESSION'NO.
5. REPORT DATE
June 1975 (Issuing Date)
6. PERFORMING ORGANIZATION CODE.
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
1BB036 (ROAP 21AZO, Task 17)
11. QQamftBE/GRANT NO.
S-802113
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Chromium is a major pollutant in wastewaters from some electroplating operations. It
can be effectively removed from rinse waters by adsorption on activated carbon, which
must be regenerated when saturated with chromium to its upper limit. This study was
concerned with the best means of regenerating the carbon under conditions which would
return it as closely as possible to its original adsorptive capacity. The tests were
conducted (1) on a laboratory scale to determine the effects of basic and acidic
media on regeneration of chromium-loaded activated carbon and (2) in a small pilot
plant unit on the basis of the best results of the laboratory-scale work. In the
latter case, tests were conducted on the unit operation for eight adsorption-
desorption cycles. The overall results of this study suggest that a chromium removal
unit could be installed in many of the small plating plants, relieving the burden on
municipal sewage systems, and bringing the plating plant into compliance with local
and Federal regulations. Recommendations for improvement of the regeneration process
are given even though the process could be used in its present stage of development.
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
*Activated carbon, *Activated carbon
treatment, Adsorbents, *Adsorption,
Chemical removal (water treatment),
*Plating, *Electroplating, Industrial
wastes, Metal coatings, *Metal finishing,
*Waste recovery, *Waste treatment,
Waste water, Chromium
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
b. IDENTIFIERS/OPEN ENDED TERMS
Rinse water
19. SECURITY CLASS (This Report)
UNCLASSIFIED
20. SECURITY CLASS (This page)
UNCLASSIFIED
c. COSATI Field/Group
13B
21. NO. OF PAGES
52
22. PRICE
EPA Form 2220-1 (9-73)
44
.S.WWWWT HUNTING OFFICE 1975-657-59*/5*OI Region Ho. 5-M
------- |