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-

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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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                               '	!  5 mg/L MnOz. Oxford water
                               C)  JO mg/L MnOz, Oxford water
                               •  / mg/L MnOz. 50% Oxford water, 50% dis. water
                   56789
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Figure 4.    Radium removal by freshly precipitated MnOz in Oxford water and 50% Oxford
            water. Ra - 32 pCi/L.
   100 -
             7.5 mg/L Fe
             2.0 mg/L Fe + 0.8 mg/L MnOz
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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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