United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-88/009 Apr. 1988
Project Summary
A Study of Possible Economical
Ways of Removing
Radium from Drinking Water
Richard L Valentine, Roger C. Splinter, Timothy S. Mulholland,
Jeffrey M. Baker, Thomas M. Nogaj, and Jao-Jia Horng
A study was undertaken to determine
variables that control the incidental
removal of radium observed to occur
as a consequence of treatment to
remove iron by oxidation-sand filtra-
tion. This study also evaluated the
possibility of exploiting these factors to
provide an inexpensive means of re-
moving radium using existing or mod-
ified iron removal facilities. Emphasis
was placed on the use of aeration to
oxidize soluble iron. The initial objec-
tive was to determine how water
chemistry influences 226Ra sorption to
iron oxides produced by aeration.
Studies were also conducted to eval-
uate radium sorption to hydrous man-
ganese oxides produced by perman-
ganate oxidation. A latter objective was
to evaluate the potential of exploiting
sorption to filter sand as a novel
removal technology. Batch and pilot
plant studies were conducted in the
laboratory and in the field at a city
whose supply contains excessive
radium.
Sorption of iron and manganese
oxides and filter sand appears to be
controlled primarily by the presence of
calcium and magnesium, which are
believed to compete for sorption sites.
Excessive pH values would need to be
used to obtain significant sorption to
iron oxides at concentrations typical of
natural waters. Removals obtained by
freshly precipitated hydrous manga-
nese oxides in batch studies were much
greater than those obtained in systems
containing only iron oxides or mixtures
of iron and manganese oxides produced
by the oxidation of ferrous iron by
potassium permanganate. This sug-
gests that sorption to manganese
oxides could possibly be exploited to
remove radium if iron did not interfere.
The presence of iron may limit the
utility of permanganate oxidation of
iron as a means to reduce radium.
Filter sand has a potential capacity
to sorb significant concentrations of
radium at typical hardness concentra-
tions if the capacity is maintained by
periodically rinsing the sand with a
dilute acid. Removal efficiencies of
approximately 80% to 90% could be
achieved in laboratory and field studies
using a 61-cm (2-ft) deep sand bed at
conventional loading rates when daily
rinsing with a dilute acid was practiced.
This Project Summary was devel-
oped by EPA's Water Engineering
Research Laboratory, Cincinnati, OH,
to announce key findings of the
research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering
information at back).
Introduction
Radium in drinking water is a concern
because of suspected detrimental health
effects, primarily the formation of
cancers. Concentrations exceeding the
current EPA-mandated maximum con-
taminant level (MCL) of 5 pCi/L total
radium (226Ra + 228Ra) have been
observed in several areas, the most
notable occurrences in the United States
being in Florida, North Carolina, Virginia,
the New England states, the uranium
mining areas of the mountain states, and
in the midwestern states of Iowa, Illinois,
Wisconsin, Missouri, and Minnesota.
It has been estimated that 500 munic-
ipal supplies may contain excessive
radium. Lucas reported in 1985 approx-
-------
imately 1.4 million people in a total of
177 cities in the midwest alone are
delivered a water containing 226Ra in
excess of 3 pCi/L (the 1962 U.S. Public
Health Service drinking water standard
and the value above which mandatory
analysis for 228Ra is required). Radium
concentrations in the range of 5 to 20
pCi/L are typical of the majority of these
supplies although higher levels (up to
nearly 50 pCi/L) have been reported. In
many cases removal efficiencies in the
range of 50% to 75% would be adequate
to put these waters into compliance.
Several conventional water treatment
practices bring about the removal of
radium. Sorg and Logsdon have pointed
out that the two most efficient methods
are sodium ion exchange and lime-soda
softening, each generally removing
about 85% to 95% of the influent radium.
In those processes radium removal is
only incidental to other changes in water
quality that may not be needed or even
desired. For example, sodium ion
exchange causes an increase in sodium
concentration, which has been asso-
ciated with an increased risk of heart
disease. In particular, conventional
processes are not suited to the many
small communities that have excessive
radium. Other removal technologies
have also been investigated but to date
no processes to remove radium alone are
in widespread use.
Many supplies having high radium also
have unacceptably high concentrations
of iron and sometimes manganese that
must be removed, commonly through
processes involving oxidation and sand
filtration. It has been observed that some
radium removal occurs during iron
removal treatment, presumably by sorp-
tion/coprecipitation with the hydrous
metal oxides. Radium, like other alkaline
earth metals, probably exists in water as
a divalent cation and has been shown
to sorb to many types of materials. For
example, sorption to glass is a common
sampling problem that is overcome by
acidification. An understanding of the
factors that control radium removal in
iron removal processes could possibly aid
in the development of inexpensive
radium removal methods based largely
on the use of existing facilities.
The primary objective of this study was
to determine what factors control the
incidental removal of radium occurring
in iron removal plants typical of those
operating in the midwest utilizing aer-
ation and sand filtration. The study also
evaluated the possibility of exploiting
these factors as an inexpensive means
of removing radium from drinking water
using existing iron removal facilities. The
initial focus was on modification of the
water chemistry expected to affect
sorption to iron oxides produced by
aeration. Studies were also conducted to
evaluate radium sorption to hydrous
manganese oxides produced by perman-
ganate oxidation. A latter objective was
to evaluate the potential of exploiting
sorption to filter sand as a novel removal
technology.
Tasks included (1) batch studies of the
effect of variable water chemistry on
sorption of 226Ra to hydrous iron and
manganese oxides, mixtures of iron and
manganese oxides coproduced by per-
manganate oxidation of ferrous ion, and
sorption to filter sand; (2) evaluation of
radium removal occurring in a laboratory
pilot plant simulating an aeration-sand
filtration iron removal process under
various operating conditions including
regeneration of the filter sand using a
dilute acid rinse to maintain radium
sorption; and (3) field evaluation at
Oxford, IA, of the use of a regenerable
sand filter to sorb naturally occurring
radium.
Materials and Methods
Waters Used
Batch studies were conducted using
synthetic groundwaters and ground-
waters obtained from Oxford, IA, and
Eldon, IA. A hardness-free synthetic
water was prepared by mixing 5 mM
NaHC03, 1 mM Na2SO4, and 1mM NaCI
to deionized water. Calcium and/or
magnesium sulfate were added to vary
hardness. Finished waters were obtained
from Oxford and Eldon and were filtered
through a 0.45 /urn filter prior to use.
Oxford water had a hardness and alka-
linity of approximately 1300 mg/L and
300 mg/L as CaCOs, respectively. Eldon
water had a total hardness and alkalinity
of approximately 300 mg/L and 200
mg/L as CaC03, respectively. Oxford and
Eldon water contained approximately 10
and 50 pCi/L of natural 226Ra, respec-
tively. Radium concentrations were
generally increased by adding additional
226Ra.
Laboratory pilot plant studies were
conducted using the tap water obtained
at the University of Iowa Hygienic
Laboratory, which had a total hardness
of approximately 150 mg/L as CaCOs and
an alkalinity of approximately 300 mg/L
as CaCOs. Field studies at Oxford used
water from the existing sand filter
effluent (iron floe removed) or water from
an existing aeration/flow equalization
tank (containing iron floe).
Batch Studies
Batch studies were conducted using
2-L beakers thermostatted to 25°C and
stirred with a Birds and Phipps* gang
stirrer. Mixtures of varying carbon
dioxide-air composition were bubbled
through to provide pH control although
in several experiments pH was adjusted
by addition of concentrated sulfuric acid
or sodium hydroxide.
Solutions containing pure iron oxides
were generally prepared by first deaer-
ating the water by purging with nitrogen
gas, adjusting pH to approximately 6.5
by bubbling pure carbon dioxide, then
adding ferrous sulfate and 226Ra. The
solutions were then aerated to approx-
imately pH 8 with normal air to oxidize
the iron, and the pH adjusted to the
desired value by bubbling buffer gas (or
acid/base addition) followed by aging for
1 hr. Solutions of pure manganese oxides
were prepared similarly except using
stoichiometric amounts of permanga-
nate to oxidize added manganous ion.
Mixtures of iron and manganese oxides
were prepared by addition of enough
permanganate to oxidize 90% of the
initial added ferrous ion in deaerated
solutions followed by aeration to oxidize
the remaining iron and then aging for
1 hr at the desired pH. Sorption onto acid-
washed and deionized-water-rinsed 0.5
mm filter sand (effective size) was
studied using the same apparatus.
After aging, an aliquot was withdrawn
and filtered through a 0.45 fjm filter and
the filtrate acidified for later analyses. In
some cases the apparatus and beakers
were rinsed with 0.1 N nitric acid and
the rinses analyzed for radium to ensure
that significant quantities of radium were
not sorbing to these components.
Pilot Plant Studies
Laboratory pilot studies were con-
ducted at the University of Iowa Hygienic
Laboratory using an iron aeration-sand
filtration pilot plant (Figure 1). The 10.2-
cm diameter (4-in.) pressure filter was
filled with 61 cm (2 ft) of filter sand and
equipped for water backwashing and
periodic rinsing with dilute acid. 226Ra
and ferrous iron could be added to the
*Mention of trade names or commercial products
does not constitute endorsement or recommenda-
tion for use.
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metering pumps
ffa Fe
flow
control tank
A
tu
feed pomp
flow
meter
contact tank
dechlorinated
~ process
water
aeration
air tank
compressor
to-» r-
waste
-*
h feed
ank backwash
pump 4
sand
filter
U &
flow controller
flow
meter
31
to
waste
filter feed
pump
finished water
Figure 1. Schematic diagram of pilot plant used in laboratory studies.
water, which was maintained at pH 6.5
prior to aeration by bubbling carbon
dioxide through it. Aeration to approxi-
mately pH 7.5 was accomplished in a
tank having a 10-min hydraulic residence
time. Filter influent was withdrawn from
a small tank used to moderate flow. Flow
rate through the filter was controlled
using a small, constant-head tank
equipped with a flow control float and
valve. Automatic samplers were used to
obtain discrete and composite samples.
The water supply was usually 18°C ±
3°C. Field studies at Oxford utilized a
similar pressure filter equipped for
rinsing with a dilute acid in addition to
water backwashing. Water temperature
was usually 15°C ± 3°C.
Analyses
226Ra concentration was determined
using precipitation with BaS04 and
counting of the radioactivity. Iron con-
centrations were routinely determined
using Hach Chemical Kit ISR-18. Iron
was also measured in several experi-
ments by the phenanthroline colorimet-
ric method. Hardness ions were deter-
mined by EDTA titration, and alkalinity
by acidiometric titration.
Results and Discussion
Sorption to Hydrous Iron
Oxides
Removals in a hardness-free synthetic
groundwater by oxides produced by
oxidation of 10 mg/L Fe increased with
pH from approximately zero at a pH of
about 5.5 to over 90% above pH 9.0 and
25°C (Figure 2). A linear isotherm,
q = kd [226Ra]
where q is the amount of radium sorbed
per unit mass of iron, and kd is a
distribution coefficient, and [226Ra] is the
concentration of radium remaining in
solution, could be used to adequately
describe sorption to iron oxides (Figure
3). As a consequence of a linear iso-
therm, percent removals do not depend
on the initial radium concentration and
can be equated to,
percent removed = 100 kd [Fe]/(1 + kd
[Fe])
where [Fe] is the total iron concentration.
Sorption was significantly reduced by
the presence of calcium, magnesium,
and barium and was a strong function
of pH over the range of 5 to 9. Distribution
coefficients characterizing sorption at
25°C and at approximately pH 8.0,
decreased from about 0.3 L/mg obtained
in the absence of hardness or barium to
approximately 1 /10 this value when the
calcium was increased to approximately
3mM (300 mg/L as CaCO3) or when 1
mg/L of barium was present in a syn-
thetic groundwater. Above this hardness
level little further reduction in the
distribution coefficient was observed.
This is consistent with the observation
that removals were similar in both Oxford
and Eldon water (approximately 10% to
20% in the presence of 10 mg/L Fe)
despite a large difference in hardness.
Based on measured distribution coeffi-
cients, radium reduction due to sorption
to iron oxides is not expected to exceed
10% to 20% in typical groundwaters with
iron concentrations of approximately 2
to 5 mg/L and hardness in excess of
approximately 300 mg/L as CaC03. The
pH would need to exceed at least 10 to
obtain significantly better removals in
natural waters at typical iron concentra-
tions. Radium removals obtained in
laboratory pilot studies designed to
simulate an iron oxidation (aeration)-
sand filtration plant generally supported
the findings anticipated from batch
studies.
Sorption to Hydrous
Manganese and Iron/
Manganese Mixtures
Sorption to freshly formed manganese
oxides was significantly greater than that
to iron oxides of comparable molar
concentration and does not appear to be
sensitive to either pH or hardness.
Removals of approximately 80% were
obtained in synthetic groundwater con-
taining up to 3 mM Ca (300 mg/L as
CaCO3) and 1 mg/L of freshly formed
MnO2. Removals of 40% to 70% were
obtained over the pH range of 5 to 9 by
1 mg/L MnO2 in Oxford water and Oxford
water diluted in half with deionized water
(Figure 4).
Removals of 226Ra in mixed manga-
nese/iron oxides prepared by the oxida-
tion of Fe+2by KMnO4were much greater
than by aeration produced iron oxides
alone but were less than obtained by
comparable concentrations of pure
manganese oxides. Again, removals
were less in Oxford water than in a
hardness-free synthetic groundwater. In
synthetic hardness-free groundwater,
removals increased from approximately
75% at pH 7 to nearly 100% near pH 9
when 1 mg/L Fe was oxidized by KMnO«
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Figure 4. Radium removal by freshly precipitated MnOz in Oxford water and 50% Oxford
water. Ra - 32 pCi/L.
100 -
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Figure 5. Radium removal by freshly precipitated (coproduced) iron and manganese oxides
in Oxford water. Manganese oxides produced by addition of permanganate
sufficient to oxidize 90% of the initial ferrous iron. Removal by 7.5 mg/L as Fe
pure iron oxides shown for comparison. Ra = 32 pd/L.
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RichardL. Valentine, Roger C. Splinter, Timothy S. Mulholland. Jeffrey M. Baker.
Thomas M. Nogaj, and Jao-Jia Horng are with the University of Iowa, Iowa
City, IA 52242.
Richard P. Lauch is the EPA Project Officer (see below).
The complete report, entitled "A Study of Possible Economical Ways of Removing
Radium from Drinking Water,"(Order No. PB 88-158 464/AS; Cost: $19.95,
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 Officer can be contacted at:
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
10
U.S. GOVERNMENT PRINTING OFFICE: 1983/543-158/67097
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