United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/S2-86/031 May 1986
Project Summary
Selenium Oxidation and
Removal by
Ion Exchange
Joan V. Boegel and Dennis A. Clifford
Strong-base anion exchange was
evaluated as a process for the removal of
trace quantities of selenium from ground-
water. The efficiency of the process was
found to depend on the oxidation state of
selenium, with the selenate anion, Se(VI),
having a greater affinity for the anion-
exchange resin than selenite or biselenrte
anions, Se(IV). Bench-scale experiments
with an Ion-exchange column compared
the effluent concentration histories for
synthetic groundwater solutions con-
taminated with 100 ppb of either Se(IV)
or Se(VI). The resin bed capacity for
selenium removal was 55% greater with
Se(VI). Since Se(IV) is less preferred than
the major groundwater anion, sulfate, it
was eluted from the column with a
chromatographic concentration peak 5.4
times its feed concentration. Se(VI) con-
centration in the effluent never exceeded
its feed concentration.
An analytical method was developed to
measure the concentrations of Se(IV) and
Se(VI) (i.e., to determine the speciation of
selenium) at trace concentration in
groundwater. This method uses anion
exchange at pH 1.5 to separate un-
dissociated selenious acid (Se[IVl), which
passes through the column, from selenate
and biselenate anions (Se[VI]), which are
retained by the resin. Graphite furnace
atomic absorption spectroscopy (GFAAS)
is used to measure total selenium in an ali-
quot of the original groundwater sample
and Se(IV) in the anion-exchange column
effluent. Se(VI) is determined by
difference.
Using this new analytical method as a
tool, the oxidation of Se(IV) to SE(VI) at
trace concentration in groundwater was
studied. The study found that free chlorine
can oxidize Se(IV) to Se(VI) in ground-
water. In synthetic groundwater contain-
ing sulfate, chloride, and bicarbonate at pH
8.3, the reaction is first order in both
Se(IV) and free chlorine concentrations,
and it can be described by the following
rate expression:
—rge = — dCse/dt =
(0.21 L/(min-mgCI2))(CC|)(CSe)
The pH dependence of the reaction was
examined in the pH range of 5 to 10. A pH
optimum exists between 6.5 and 7.5 in
which nearly 70% of the Se(IV) is con-
verted to Se(VI) within 5 min with a
chlorine dosage of 5 mg/L. Oxygen was
completely ineffective as an oxidant for
Se(IV), and potassium permanganate and
hydrogen peroxide were much less effec-
tive than chlorine.
This Project Summary was developed
by EPA's Water Engineering Research
Laboratory, Cincinnati, OH. to announce
key findings of the research project that
are fully documented in a separate report
of the same title (see Project Report order-
ing information at back).
Introduction
The U.S. Environmental Protection
Agency (EPA) National Primary Drinking
Water Regulations of 1976 established
maximum contaminant levels (MCL's) for
10 inorganic contaminants: barium, cad-
mium, chromium, lead, mercury, silver,
fluoride, nitrate, arsenic, and selenium.
Public drinking water supplies con-
taminated with any one of these
substances in excess of the MCL must be
-------
treated to remove the contaminant or
abandoned.
The MCL for selenium was set at a very
low level (0.01 mg/L) because of
selenium's suspected carcinogenicity.
Selenium contamination of groundwater
is fairly common in some regions of the
United States, but its removal from these
water supplies is not yet practiced. Thus
a continuing need exists for research to
evaluate treatment processes for selenium
removal. This study is based on an
understanding of selenium chemistry and
complements the work of previous re-
searchers. The study focuses on the
following two-step process for removal of
selenium from groundwater:
1. Oxidation of all aqueous selenium
to selenate anion, Se(VI), and
2. Strong-base anion-exchange remov-
al of the selenate anion.
Experimental Details
The study described in this report in-
cluded three phases: (1) evaluation of
anion exchange for removal of both Se(IV)
and Se(VI) from groundwater, (2) develop-
ment of a method for the separate analysis
of Se(IV) and Se(VI) at trace concentra-
tion in groundwater, and (3) determination
of the preferred oxidant and optimum
reaction conditions for the oxidation of
Se(IV) to Se(VI).
Evaluation of Anion Exchange
for Removal of Selenite and
Selenate
Ion chromatography (1C) was used to
provide a rapid determination of the posi-
tions of selenite and selenate anions in the
selectivity sequence of a strong-base
anion-exchange resin. A Dionex Model 16
Ion Chromatograph * (Dionex Corporation,
Sunnyvale, California) was used for all 1C
work. The eluent used was the standard
carbonate buffer consisting of 0.003 N
NaHCO3 and 0.0024 N Na2C03 with pH
10.4. Standard anion solutions were
prepared from reagent-grade sodium salts
of the anions fluoride, chloride, bromide,
nitrite, nitrate, phosphate, sulfite, sulfate,
selenite, and selenate.
Ion-exchange column runs were used to
generate experimental breakthrough
curves for selenite and selenate in a
background of highly saline synthetic
groundwater. Figure 1 shows the ap-
Metering Pump,
0.9 mL/min
Ion-
Exchange
Column
Feed Reservoir
1.0L
1
\
4.5-mL Resin
5.33-mm I.D.
Fraction
Collector
Figure 1. Experimental set-up for the ion-exchange column runs.
'Mention of trade names or commercial products does
not constitute endorsement or recommendation for
use.
paratus used. A variable-speed positive
displacement pump (Milton Roy) was used
to pump the feed water at 0.9 mL/min
from a glass reservoir bottle through a col-
umn packed with Rohm and Haas IRA-458
strong-base, acrylic anion-exchange resin.
The column was constructed from
6.35-mm (0.25-in.) O.D. stainless steel
tubing with an I.D. of 5.33 mm (0.21 in.).
The resin bed volume was 4.5 mL and the
empty bed contact time (EBCT) was 5.0
min. Effluent from the column was col-
lected in glass test tubes held in the
carousel of an Eldex universal fraction
collector.
The multicomponent, ion-exchange col-
umn runs required chemical analyses for
pH, bicarbonate, chloride, sulfate, selenite,
and selenate. Methods used for these
analyses were pH electrode, Beckman in-
frared TOC analyzer (inorganic carbon
channel) for bicarbonate, potentiometric
titration with AgNO3 for chloride, ion
chromatography for sulfate, and GFAAS
for both selenite and selenate.
Development of Method for
Se(/V/Se(VV Separation and
Analysis
The method developed to determine the
speciation of selenium in groundwater
uses ion exchange for the separation of
Se(IV) from Se(VI) at low pH and GFAAS
for analysis of selenium in both the original
sample and the ion-exchange column ef-
fluent. Determination of optimum pH for
the ion-exchange separation involved a
series of separation experiments at dif-
ferent pH's within the range of 0 to 2.5.
Figure 2 shows the apparatus used for
ion-exchange separation of Se(IV) and
125-mL Separatory Funnel
100-mL Sample
Gum-Rubber Tubing
Resin Column
0.8-cm I.D. x 11.5-cm Length
10-cm Resin Bed Depth
S.O-mL Resin
Press Fit Cap With Porous Pye Frit
Gum-Rubber Tubing
Flow-Restricting Capillary
0.20-mm I.D. x 3.5-cm Length
125-mL
Polyethylene Bottle
Figure 2. Ion-exchange apparatus for
separation ofSe/IV) from Se/VI).
Se(VI). The ion-exchange separation col-
umn was a glass tube filled with 5 mL
(wet, settled volume) of IRA-458 anion-
exchange resin in chloride form. Before
using a fresh or freshly regenerated resin
-------
, column, an HCI solution of the desired
separation pH was passed through the col-
umn at about 10 mL/min to adjust column
pH. After each separation test, the column
was regenerated with 1.0 N NaCI or 0.5
N HCI.
For each experiment, three 5-mL ion-
exchange columns were adjusted to the
specified pH, and test solutions (adjusted
to the same specified pH by dropwise ad-
dition of HCI) were passed through each
column. The three test solutions, desig-
nated A, B, and C, were standard solutions
of selenate or selenite or both in a
383-mg/L IDS synthetic groundwater
containing 1 meq/L (58.5 mg/L) sodium
chloride, 1 meq/L (72 mg/L) sodium sul-
fate, and 3 meq/L (252 mg/L) sodium
bicarbonate. Test solution A contained 100
ppb Se(IV), B contained 100 ppb Se(VI),
and C contained 50 ppb Se(IV) and 50 ppb
Se(VI). Column effluents were collected,
preserved with 5 mL concentrated nitric
acid per 100 mL of sample, and analyzed
for selenium by GFAAS.
A Perkin Elmer model 5000 atomic ab-
sorption spectrophotometer equipped
with a graphite furnace, a model 400
graphite furnace programmer, and Zeeman
background correction was used for all
selenium analyses. A selenium electrode-
less discharge lamp was the light source.
Pyrolytically coated graphite tubes with
Lvov platforms were used, and all sample
injections were 20 uL followed by 20 ^L
of NiNO3 matrix modifier (1000 ppm Ni).
Study of Se(IV) Oxidation
The test solution for all oxidation ex-
periments was the previously described
383 mg/L TDS synthetic groundwater,
with an initial pH of 8.3 and spiked with
100 ppb Se(IV). The Se(IV) stock solution
was made up from sodium selenite (99%)
from Aldrich Chemical Company. Rea-
gents used for oxidation experiments were
sodium hypochlorite solution prepared by
dilution of Clorox bleach, oxygen gas,
hydrogen peroxide solution prepared by
dilution of 30% H202, potassium per-
manganate, and ammonium hydroxide. All
chemicals were reagent grade unless
otherwise noted.
For all oxidation reaction experiments in-
volving liquid-form oxidizing agents,
100-mL aliquots of the test solution were
placed in 250-mL Pyrex Erlenmeyer flasks
and stirred with Teflon-coated magnetic
stirring bars on a six-position stirring plate.
A pre-measured aliquot of the oxidant
solution was injected into each test solu-
tion flask with a graduated glass pipette.
Quenching agents were added at predeter-
mined times in the same manner. The new
ion-exchange separation/GFAAS method
was used to determine the concentration
of Se(IV) remaining in solution after each
oxidation experiment.
In the test of oxygen as an oxidizing
agent for Se(IV), pure oxygen at a supply
pressure of 20 psi was bubbled into 200
mL of the test solution in an open 500-mL
Erlenmeyer flask through a porous gas-
diffusing stone made of fused crystalline
alumina with an average pore size of 60 p.
The temperature was between 21 ° and
24.5°C for all tests. For the study of pH
dependence of selenium oxidation by free
chlorine, the pH of the test solution was
adjusted in the range of 5 to 10 by the
dropwise addition of either NaOH or HCI.
Results and Discussion
Evaluation of Anion-Exchange
Removal of Selenite and
Selenate
Figure 3 shows the multicomponent ion
chromatogram for a dilute aqueous mix-
ture of anions, including selenate and
selenite. The anion corresponding to each
peak is noted on this chromatogram, along
with its observed retention time. The least
preferred anion has the shortest retention
time and appears first in the effluent,
whereas the most preferred anion has the
longest retention time and is eluted last.
The selectivity sequence from most
preferred to least preferred at the eluent
pH of 10.5 is as follows:
The most-preferred-ion status of
selenate is significant in consideration of
an ion-exchange process to remove trace
amounts of selenium from groundwater
containing much larger concentrations of
sulfate. Based on this chromatogram, and
regardless of their relative concentrations,
selenate is expected to break through after
sulfate with no chromatographic peak elu-
tion of selenate. Furthermore, the break-
through capacity of the ion-exchange
column for selenate is expected to be
much greater than it would be if the major
I
I
Time, Minutes
Figure 3. Ion chromatogram for selenium species in the presence of common anions. Eluent -
0.003 M /VaHCOa/O.0024 M NaiCOa. pH = 10.5.
-------
anion, sulfate, were preferred over
selenate. Selenite's low position in the
selectivity sequence suggests that ion ex-
change is unfavorable for the removal of
selenium in the +4 oxidation state.
Experimental breakthrough curves for
selenite and selenate in a highly mineral-
ized (712 mg/L TDS) synthetic ground-
water verified the predictions of the ion
chromatogram. Rgure 4, the breakthrough
curve for Se(IV), shows selenium concen-
tration reaching the 10 ppb MCL at about
152 bed volumes (BV's) throughput and
peaking to 540 ppb (5.4 times the feed
concentration) at 237 BV's. The column
is completely exhausted at 265 BV's,
where the most-preferred sulfate anion
has reached its influent concentration.
Figure 5, the breakthrough curve for
Se(VI), shows selenium concentration
reaching the MCL at 235 BV's with a
gradual, presumably mass-transfer-
controlled increase to feed concentration
at about 385 BV's. As expected from the
1C selectivity sequence, selenate broke
through after sulfate, and the Se(VI) con-
centration in the effluent never exceeded
the feed concentration of 100 ppb. A very
significant improvement (55% in this
case) exists in ion-exchange removal of
selenium when it is in the selenate rather
than the selenite form. In less saline
groundwaters with lower sulfate concen-
trations (e.g., 50 mg/L sulfate), run lengths
exceeding 1000 BV's to Se(VI)
breakthrough may be expected.
Method for Sef/V)/SefVI)
Separation and Analysis
The basis for the ion-exchange separ-
ation of Se(IV) and Se(VI) is the difference
in acid strength of selenious (Se[IV]> and
selenic (Se[VI]( acids. The dissociation
equations and constants for the two acids
are as follows:
Se(IV) Selenious Acid
H2Se03 = H+ + HSe03-
HSe03- = H+ + Se03=
Time. Mrs.
Se(VI) Selenic Acid
H2Se04 = H+ + HSe04-
HSe04~ = H+ + Se04=
pK, = 2.55
pK2 = 8.15
pK, = -3.0
pK2 = 1.66
Below its pK1 of 2.55, the weaker
selenious acid exists predominantly as the
undissociated acid that has no charge and
therefore no electrostatic attraction to the
positively charged quarternary ammonium
sites of a strong-base anion-exchange
resin. Selenic acid is a much stronger acid,
comparable to sulfuric acid. Above a pH
of -3, Se(VI) exists predominantly as a
4
I
I
6
I
§
o
Q.
;o.o
8.0
6.0
4.0
2.0
JO
—i—
20 .
30
40
SeflVlRun
Resin: IRA-458
EBCT: 5 minutes
TDS: 712 mg/L
Ion
~SeflVJ
cr
HCOa
Effluent Feed
Cone. Cone.
100 ppb
3.0 meq/L
3.0 meq/L
4.0 meq/L
8.3
600
50 100 150 200 250 300 350 400 450 500 550
Bed Volumes Throughout, BV
400
300
200
700
0
\
vj
a
Figure 4.
Breakthrough curves for Run No. 1 —synthetic groundwater feed contaminated with
lOOppbSef/V).
100 ppb
3.0 meq/L
3.0 meq/L
4.0 meq/L
8.3
Resin: IRA -458
EBCT: 5 minutes
TDS: 712 mg/L
Figure 5.
50 100 150 200 250 300 350 400 450 500 550
Bed Volume Throughput, BV
Breakthrough curves for Run No. 2—synthetic groundwater feed contaminated with
lOOppbSefVI).
negatively charged ion, and Se(VI) anions
will be attracted and held by strong-base
anion-exchange resins. Because of their
acid dissociation equilibria, most Se (IV)
will pass through an ion-exchange column,
and most Se (VI) will be retained in the
same column at any pH between -3
(pK, of selenic acid) and + 2.55 (pK2 of t
-------
selenious acid). Based on acid dissociation
equilibria alone, the optimum separation of
Se(IV) and Se(VI) would be expected at
the midpoint of this range, pH 0.225.
Table 1 presents results of separation
experiments at five pH's: 0.6, 1.0,1.1,1.5,
and 2.1. Figure 6 plots the percentage of
recovery of selenium in the column ef-
fluent (i.e., passage of selenium through
the column) as a function of separation pH
for test solutions A and B, prepared with
pure Se(IV) and pure Se(VI), respectively.
The experimental passage is compared
with that predicted by the acid dissocia-
tion constants for Se(IV) and Se(VI). The
best correlation of experimental results to
predicted % recovery occurred at a pH
equal to or greater than 1.5, and the max-
imum separation of Se(IV) from Se(VI)
was observed at pH 1.5.
At lower pH, a very significant, unex-
pected recovery of Se(VI) occurred in the
column effluent. This passage of Se(VI) at
low pH could have resulted either from
reduction of Se(VI) to Se(IV) in the
presence of strong HCI, or unfavorable
competition between the low concentra-
tions of Se(VI) anions and the very high
chloride concentration, e.g. 8900 mg/L
Cr at pH 0.6.
Based on the pH screening experiments,
an optimum separation pH of 1.5 was
identified, and the following procedure
was adopted for the analytical technique:
1. Collect a 200-mL water sample.
2. Oivide'the sample into two 100-ml
aliquots — one (A) for total Se
analysis and the other (B) for Se (IV)
analysis.
3. Adjust pH of sample B to 1.5 by drop-
wise addition of 1.5 N hydrochloric
acid.
4. Pass acidified sample B through a
small (5-mL) column of chloride-
form, strong-base anion-exchange
resin at a flowrate of 1.5 mL/min.
Collect the effluent and then pass 25
ml of deionized water through the
same column at 10 mL/min and col-
lect the rinse effluent. Theoretical-
ly, 91.8% of the Se(IV) and 0% of
the Se(VI) from the original sample
will be recovered in the effluent and
rinse.
5. Preserve all samples with 5 ml con-
centrated nitric acid per 100 ml of
sample.
6. Analyze the original water sample. A,
and the IX column effluent and rinse,
B, for Se by GFAAS.
Table 1. Results of pH Screening Experiments
% Selenium Recovered (% Passage)H
PH
0.6
0.6
0.6
1.0
1.0
1.0
1.1
1.1
1.1
1.5
1.5
1.5
1.5
1.5
1.5
2.1
2.1
2.1
Flow Hate
(mL/min)
10.3
9.9
8.5
1.5
1.5
1.4
9.1
11.0
9.1
11.6
11.9
12.6
1.5
1.6
1.7
11.0
11.0
11.O
Test
Solution"
Se(IV)
Se(VI)
SellWVI)
Se(IV)
Se(Vt)
Se(IV/VI)
Se(IV)
SetVI)
Se(IV/VI>
SetIV)
SetVI)
Se(IV/V/)
Se(IV)
SetVI)
SetlV/VI)
SetIV)
SetVI)
SellV/VI)
Predicted
96.91
.02
48.45
95.31
<0.01
47.65
94.64
<0.01
47.32
89.98
<0.01
44.99
89.98
<0.01
44.99
72.3
<0.01
36.15
Experimental
78.7
66.9
72.9
97.4
40.5
70.2
95.5
13.1
48.6
93.5
8.5
54.9
85.6
2.0
52.0
70.3
6.8
36.5
*AII test solutions were prepared with synthetic groundwater containing 3 meq/L NaHCOg,
1 meq/L NaCI, and 1 meq/L Na2SO4. Test solution Se(IV) contained 100 ppb Se(IV); Se(VI)
contained 100 ppb Se(VI); and SetlV/VI) contained 50 ppb Se(IV) and 50 ppb Se(VI).
+ The desired selenium passages are Se(IV) = 100%, Se(VI) = 0%, and SetlV/VI) = 50%.
it
t. CD
-S! ^.
0) _„
CO C
100
90
80
70
60
50
40
30
20
10
Optimum Separation at pH 1.5
Predicted
SeflV)
Experimental
SeflV}
Experimental
SefVH
0.5
1.0
1.5
pH
2.0
2.5 3.0
Figure 6.
SeflV) and Se(VI) passage through ion-exchange separation columns as a function
ofpH.
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7. Calculate the concentrations of total
Se, Se(IV), and Se(VI) as follows:
Total Se(mg/L) is determined direct-
ly by GFAAS analysis of sample A.
Se(IV)(mg/L) = (1/0.91 8) x (total mg
Se measured in the combined IX col-
umn effluent and rinse from sample
B)/(0.100 L original sample B). Se(VI)
concentration is determined by dif-
ference — that is, total Se concen-
tration minus Se(IV) concentration.
The accuracy of this technique with the
separation pH of 1.5 is verified in Table 2,
which shows a slight tendency toward
Se(VI) leakage. This leakage results in
slightly high values for the reported Se(IV)
concentration. Nevertheless, the method
proved to be of adequate precision and ac-
curacy for this research.
Se(/V) Oxidation Study
Experiments proved ammonia to be a
satisfactory quenching agent for the ox-
idation of Se(IV) by free chlorine in syn-
thetic groundwater. When added to a test
solution at a dosage 10 times the chlorine
dosage, ammonia completely and instan-
taneously destroyed the free chlorine. The
product of this reaction was chloramine,
which had no tendency to react with
either Se(IV) or Se(VI), and did not inter-
fere with the ion-exchange separation/
GFAAS technique used to monitor the
progress of the oxidation reaction.
With ammonia as a quenching agent,
kinetic data were obtained for the oxida-
tion of Se(IV) by free chlorine. The results
are plotted in Figure 7. The experimental
rate expression for the reaction is as
follows:
-rse = -
(0.21 L/(min-mg CI2))(CC|)(CSe),
where the chlorine concentration is given
in mg/L and the Se(IV) concentration,
CSe, is arbitrary.
The pH dependence of the oxidation
was examined in the range of pH 5 to 10.
Results are plotted in Figure 8. The op-
timum pH is clearly between 6.5 and 7.5.
The reaction becomes very slow at both
extremes, with less than 10% of the
Se(IV) converted to Se(VI) in 5 min at pH
5 and at pH 10.
Experiments were designed to compare
the effectiveness of three other oxidizing
agents commonly used in water treatment
— oxygen, permanganate, and hydrogen
peroxide — with that of chlorine. The
dosages of permanganate and hydrogen
l*g Se in
Se(IV)
10.0
0.0
5.0
1.0
2.0
Sample
Se(VI)
0.0
10.0
5.0
2.0
1.0
Total
M0 Se(IV)
Passage
9.27
0.36
4.57
1.04
1.82
pg Se(IV)
Reported
10.1
0.4
5.0
1.1
2.0
Apparent*
Se(IV)
Recovery<%)
101
100
110
100
Apparent*
Se(VI)
Leakagel%l
4
0
5
0
*The apparent values are based on the observed total Se passage and a calculation that
presumes 91.8% Se(IV) passage.
Chlorine Dosage
1 mg/L C/2
2 mg/L C/2
5 mg/L C/2
Symbol
O
A
D
10 20 30 40 50 60
Figure 7. Kinetics of Se(IV) oxidation by free chlorine at pH 8.3 in simulated groundwater.
peroxide were chosen to be equivalent to
2 mg/L free chlorine, a dosage that pro-
duced easily measurable Set IV) remaining
after 5- and 30-min contact times. Table
3 lists the experimental results. No
quenching other than pH reduction to 1.5
before separation was used in the non-
chlorine oxidation experiments. Thus the
nonchlorine oxidations indicated in Table
3 may be greater than actually achieved
in the indicated contact time. Oxygen ap-
pears to be completely ineffective in the
oxidation of Se(IV). Neither permanganate
nor hydrogen peroxide is as effective as
chlorine at near-neutral pH.
Conclusions and
Recommendations
The two-step process of oxidation with
free chlorine followed by anion exchange
appears to be technically feasible and
should be considered for removal of
selenium to produce potable water from
selenium-contaminated groundwater. Fur-
ther research and development is recom-
mended to develop the optimum process
and to adapt the process for optimum
operation at specific sites.
Some problems that must be addressed
in the next phase of process development
6
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100
2 ppm C/s
NH3 Quench
After 5 min
Simulated Groundwater
(Before pH Adjusted)
HCOs 3 meq/L
Cr 1 meq/L
SOl' 1 meq/L
I
10
11
56789
pH
Figure 8. Effect of pH on Se(IV) oxidation at 23°C in pH-adjusted, simulated groundwater.
Table 3. Comparison of Oxidizing Agents*
Oxidizing Se(IV)
Agent pH Time(min) Remaining 1%)
02
KMnO4
KMnO4
H202
H202
NaOCI
NaOCI
NaOCI
8.3
7.5
7.5
7.5
7.5
7.5
8.3
8.3
60
5
30
5
30
5
5
30
101.9
72.1
63.5
97.4
89.8
32.0
63.5
7.0
*AII oxidant concentrations are equivalent to
2.0 ppm chlorine — that is, a 22-fold
stoichiometric excess for the 100 ppb Se(IV)
initially present.
and Se(VI) in actual groundwaters that are
contaminated with selenium. However, the
analytical technique should be refined by
optimizing the acid used and the sample
flow rate.
The full report was submitted in fulfill-
ment of Cooperative Research Agreement
No. CR-807939 by the University of
Houston-University Park under the spon-
sorship of the U.S. Environmental Protec-
tion Agency.
include determining the effects of tem-
perature and the presence of other
chlorine demands such as TOC, Fe2+,
Mn2+, and S2~ on oxidation kinetics,
countering the effects of residual chlorine
from the oxidation process on the anion-
exchange resin, determining the optimum
anion-exchange resin type and empty bed
contact time (EBCT), developing a process
control scheme that includes some means
(possibly pH changes) of detecting
selenium breakthrough, and disposing of
spent regenerant.
The analytical method developed to
determine the speciation of selenium in
groundwater proved to be a useful tool for
the study of Se(IV) oxidation and is recom-
mended for measurement of both Se(IV)
•&U. S. GOVERNMENT PRINTING OFFICE:1986/646-l 16/20846
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Joan V. Boegelis now with Metcalf and Eddy. Inc., Boston. MA 02114; and Dennis
Clifford is with the University of Houston-University Park, Houston, TX 77004.
Thomas J. Sorg is the EPA Project Officer (see below).
The complete report, entitled "Selenium Oxidation andlRemoval by Ion Exchange,"
(Order No. PB 86-171 428/AS; Cost: $11.95, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S2-86/031
0000329 PS
U S ENVIR PROTECTION AGENCY
REGION 5 LIBRARY
230 S DEARBORN STREET
CHICAGO IL 60604
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