United States
             Environmental Protection
             Agency
             Industrial Environmental
             Research Laboratory
             Cincinnati OH 45268
EPA-600/2-78-040
March 1978
             Research and Development
&EPA
FBI Reverse Osmosis
Membrane for
Chromium Plating
Rinse Water

Environmental Protection
Technology Series

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                 RESEARCH REPORTING SERIES

 Research reports of the Office of Research and Development, U.S. Environmental
 Protection Agency, have been grouped into nine series. These nine broad cate-
 gories were established to facilitate further development and application of en-
 vironmental technology. Elimination  of traditional grouping  was  consciously
 planned to foster technology transfer and a maximum interface in related fields.
 The nine series are:

       1.  Environmental Health Effects Research
      2.  Environmental Protection Technology
      3.  Ecological Research
      4.  Environmental Monitoring
      5.  Socioeconomic Environmental Studies
      6.  Scientific and Technical  Assessment Reports (STAR)
      7.  Interagency Energy-Environment Research and  Development
      8.  "Special" Reports
      9.  Miscellaneous Reports

 This report has been assigned to the ENVIRONMENTAL  PROTECTION TECH-
 NOLOGY series. This series describes research performed to develop and dem-
 onstrate instrumentation, equipment,  and methodology to repair or prevent en-
 vironmental degradation from point and non-point sources  of pollution. This work
 provides the new or improved technology required for the control and treatment
 of pollution sources to  meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia  22161.

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                                                 EPA-600/2-78-040
                                                 March 1978
            FBI REVERSE OSMOSIS MEMBRANE
         FOR CHROMIUM PLATING RINSE WATER
                            by

                      Howard J. Davis
                      Frank S. Model
                       Joseph R. Leal
                Celanese Research Company
                  Summit,  New Jersey 07091

                           for

      THE AMERICAN ELECTROPLATERS1 SOCIETY
                   Winter Park,  Florida 32789
                     Grant No. R-803620
                        Project Officer
                      Mary K. Stinson
            Industrial Pollution Control Division
       Industrial Environmental Research Laboratory
                   Edison, New Jersey 08817
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
       OFFICE OF RESEARCH AND DEVELOPMENT
      U.S. ENVIRONMENTAL PROTECTION AGENCY
                 CINCINNATI, OHIO 45268

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                               DISCLAIMER
    This report has been reviewed by the Industrial Environmental
Research Laboratory - Cincinnati,  U. S. Environmental Protection Agency
and approved for 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.
                                    11

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                                  FOREWORD
     When energy and material resources are extracted, processed,  con-
verted, and used, the related pollutional impacts on our environment and
even on our health often require that new and increasingly more efficient
pollution control methods be used.  The Industrial Environmental Research
Laboratory - Cincinnati (IERL-CI) assists in developing and demonstrating
new and improved methodologies that will meet these needs both efficiently
and economically.

     This report is a product of the above efforts.  It was a laboratory
scale research study to assess the potential utility of recently developed
polybenzimidazole membranes in a reverse osmosis system for the treatment
of chromium plating rinse waters.  Feasibility studies had demonstrated
that FBI possessed the requisite chemical stability to withstand long-term
contact with chromic acid waste streams where other, earlier membranes,
such as cellulose acetate and polyamides, have failed.  The results of the
report are of value to R & D programs concerned with the treatment of
wastewaters from various metal finishing, nonferrous metal, steel, in-
organic and other industries.  Further information concerning the  subject
can be obtained by contacting the Metals and Inorganic Chemicals Branch
of the Industrial Pollution Control Division.
                                       David G.  Stephan
                                          Director
                        Industrial Environmental Research Laboratory
                                        Cincinnati
                                     111

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                                ABSTRACT

     The objective of this laboratory research study was to develop a high
 temperature,  oxidation-resistant  reverse osmosis (RO) membrane for the
 treatment of metal finishing effluents.  Specifically, the study was directed
 to the selection and optimization of a flat polybenzimidazole (PBI) mem-
 brane to treat chromium plating rinse water.

     Important  variables  in casting PBI films and subsequent heat treatment
 were investigated to assess their  effects on membrane RO properties in
 this application.  Membranes were tested on a high pressure circulating
 flow system in flat film  test cells.  Membrane screening tests  were carried
 out by pretesting them with sodium chloride feed solution at 5,000 ppm con-
 centration.  Membranes with optimum properties were then tested with a
 simulated rinse water containing 200 ppm chromic acid or with authentic
 plating bath solution diluted to 200 ppm chromic acid.

     PBI RO membranes  were found to be resistant to attack by chromic
 acid.  After pretesting with dilute  sodium chloride solution, the membranes
 showed  a short-term effective level of rejection with chromic acid.   Upon
 retesting with sodium chloride, the same membranes exhibited high salt
 rejections, thereby demonstrating that they had not been chemically
 attacked by chromic acid.

     A significant improvement in long-term rejection of chromic acid was
 obtained when the membranes were pretreated with 5, 000 ppm sodium
 tungstate solution.   The  continuous addition of sodium tungstate to the feed
 solution further improved chromic acid  rejection.   However, this approach
 to long-term high level rejection of chromic acid is not acceptable in
 practice because of the possible contamination of the plating bath by
 tungstate ions.

    Another approach to  long-term high  level chromic acid rejection in-
 volves pH adjustment. In this case, no  pretreatment or preconditioning
 of the membrane is required.  When the pH of the feed was  raised from
 2.9  to 4. 0 with sodium hydroxide,  an 80% chromic acid rejection resulted.
 Adjustment of  the pH to 5. 7 with ammonium hydroxide increased the
 chromium rejection level to 95%.   Again,  this approach turned out to be un-
 acceptable in practice because of the possible introduction of extraneous
 ions into the working bath.   The project failed to develop an acceptable PBI
 RO membrane  for treating  chromium plating rinse water.

    This report was submitted in fulfillment of Grant No.  R-803620 by the
American Electroplaters' Society under the sponsorship of the U.S.  Envir-
onmental Protection Agency.  The report covers work performed in the
period between March 15, 1975 and December 15,  1976.

                                   iv

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                            CONTENTS







 Foreword	jlii




 Abstract	iv




 Figures	vi




 Tables	vi




 Acknowledgment	 .vii




 I   Introduction	1




 II   Conclusions	4




III   Recommendations	5




IV   Experimental	6




 V   Results and Discussion	9




VI   References	27

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                              FIGURES
Number

    1
    2
Experimental Reverse Osmosis Test System	7
RO Properties of PBI Membranes in Sequential
    Feed Changes	16
Effects of Different Membrane Treatments and Feed
    pH on Chromic Acid Rejection	  26
                              TABLES
Number                                                          Page

    1     Effect of Casting ancl Annealing Conditions on Membrane
             RO Properties	10
    2     Long-term RO Properties with Sodium Chloride and
             Chromic Acid Feed Solutions	12
    3     RO Properties of Unconditioned Membranes	13
    4     Effect of Sequential Feed Changes on Membrane RO
             Properties. .	14
    5     RO Properties of Tung state-Treated Membranes	17
    6     RO Properties of Molybdate-Treated Membranes	19
    7     RO Properties of Tung state-Treated Membranes	 20
    8     RO Properties of Membranes  Coagulated in Tungstate
         Solution	21
    9     Effect of Tungstate Addition to Chromic  Acid Feed
         Solution on Membrane RO Properties	23
   10     RO Properties of Fluo silicate-Treated Membranes	24
   11     RO Properties of Crosslinked Membranes	25
                                 VI

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                           ACKNOWLEDGMENT

    Throughout this laboratory study,  valuable guidance and suggestions were
offered by the members of the American Electroplaters1 Society Project 37
Committee.  Particular recognition is given to Mssrs. Lawrence J. Durney
and O. Gardner Faulke, AES.  The EPA project officer, Mary K. Stinson,
also contributed significantly to the program.

    Financial support for this laboratory research study from the Office of
Research and Development of EPA and from the  American Electroplaters'
Society is gratefully acknowledged.
                                   VII

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                           I.  INTRODUCTION

GENERAL

    Electroplating and metal finishing waste streams are significant con-
tributors to stream pollution.  This occurs either directly, owing to the
content in the effluents of such toxic and corrosive materials as cyanides,
acids and metals, or indirectly, as a result of the  deleterious effects these
compounds exert on sewage treatment systems.  Effective waste treatment
methods are needed by the metal processing industries to meet the  strin-
gent effluent guidelines for 1977  and the more  stringent guidelines proposed
for 1983 and 1985.  Satisfactory methods exist for the removal and recove-
ry, if warranted,  of most metals from plating  waste waters,  but chromium
remains a problem.

    Chromium can be removed from waste or  rinse water by a number of
methods  -- chemical treatment, evaporation or ion exchange.  Chemical
treatments methods are commonly practiced.   These include the reduction
of hexavalent chromium to trivalent chromium by reagents  such as  sulfur
dioxide, sodium bisulfite or ferrous sulfate,  followed by neutralization to
precipitate the metal; precipitation of hexavalent chromium by barium
chloride or sodium hydroxide; neutralization by sodium hydroxide,  lime-
stone,  sodium carbonate,  etc.  Chemical treatment methods, however,
pose the vexing problem of sludge and liquid waste disposal.  Moreover,
there is an economic loss of valuable chromium.  It would be preferable
to recover and recycle the chromium as well as the purified water.

PRINCIPLES  OF REVERSE OSMOSIS

    Reverse osmosis, a relatively new membrane process discovered
about 17 years ago  and originally aimed at providing potable water from
brackish water, has aroused great interest in major industries, such as
food,  textiles, chemical, metal processing, etc.  It involves the pressure-
activated transport of.water through a semipermeable membrane by a
selective solubility process in which water dissolves and is subsequently
transmitted to an extent much greater than that for dissolved solutes.
Pressure, in  excess of the solution's osmotic pressure, acts preferentially
to enhance the selective permeation of water;  solute-flux is essentially
pressure-insensitive.

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    The equations describing the transport of water and solute through a
 membrane are:
                        J1=    A ( A P  - A IT )
                        J2 =    D2K     A C
                                         A X
 where J^ and J2 are water and solute fluxes.  A P is the pressure differ-
 ence across the membrane; ATT  is osmotic  pressure difference and A is
 a membrane constant related to the diffusion coefficient and solubility of
 water in the membrane.   D2 is the solute diffusion coefficient; K is the dis-
 tribution coefficient for the solute between membrane and solution; AC  is
 the  concentration difference on the two sides of the membrane; and AX  is
 the  effective membrane thickness.

 APPLICATION OF  REVERSE  OSMOSIS TO METAL FINISHING WASTE
 TREATMENT

     Reverse osmosis offers the potential for achieving closed loop control
 for  treating metal finishing waste waters.  Previous studies have  shown
 that RO is both technically and economically feasible for some plating
 waste streams.  Particular advantages of RO over other recovery proces-
 ses  include:

            Low capital cost.  The modular nature of RO units
            make them particularly well-suited for small-scale
            installations.

            Low energy cost.  Only power for pumping is required.

            Low labor cost.  The process  is simple to operate
            since it involves primarily the pumping of liquids.

            Low space requirements.  RO equipment is compact
            and operates continuously,  requiring minimal tankage.

            No sludge.   There are only two exit streams:  purified
            water return to the rinse bath, and concentrated me-
            tal solution return to the finishing bath.

   On the basis of pilot plant  investigations  sponsored by the Environmen-
tal Protection Agency and the  American Electroplaters' Society,  reverse
osmosis appears to be attractive for treating rinse waters from Watts
nickel,  nickel sulfate (acid copper),  copper pyrophosphate,  zinc  chloride,
and copper-zinc and cadmium  cyanide  baths, as well as total plant effluents.
However, the technique has not yet been found workable for chromium
wastes which need more chemically stable membranes.

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FBI REVERSE OSMOSIS MEMBRANES

    The potential of the polybenzimidazole (FBI) polymer, poly-^2, 2'-
(m-phenylene)-5, 5!-bibenzimidazole,  prepared as described by Concia-
tor.i et al* ',  as  a reverse osmosis membrane was explored several years
ago.  RO properties of flat FBI membranes were  found to be comparable
to cellulose acetate at ambient conditions and significantly superior at ele-
vated temperature.   The polymer is known to possess outstanding thermal,
physical and chemical stability over a wide pH range and a high affinity for
water.  Its solubility in N, N' -dimethylacetamide (DMAc) permits  easy con-
version of polymer  to fiber or flat film.

     In a series of research studies concerned with morphological  anil
transport characteristics, PBI membranes were found to possess useful,
long-term RO  properties in both  hollow fiber and  flat film configurations
(2, 3, 4, 5).  FBI's oxidative resistance to,  and stability in,  high levels of
chlorination in the seawater desalination study  ' ' and its resistance to
strong acid made it an attractive RO candidate for chromium plating rinse
water application where earlier membranes,  including cellulose acetate
and polyamides, cannot be used.

    In this research project,  PBI RO membranes  were evaluated in flat
film configuration with a simulated rinse water containing 200 ppm chromic
acid.  Major efforts were devoted to the optimization of membrane prop-
erties as influenced by fabrication variables and post treatment techniques,
including those based on reacting the basic -NH- groups of polybenzimi-
dazole with reactive agents to favorably alter transport properties.

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                           II.   CONCLUSIONS

    Pretreatment of PBI RO membranes with sodium tungstate significant-
 ly improves the long-term rejection of chromic acid over that of the Tin-
 treated membrane.  Newly fabricated,  untreated membranes exhibit low
 chromic acid rejection levels.   The tungstate treatment markedly increases
 the rejection which remains effective for at least nine days.  Even higher
 rejection levels are achieved when 100 ppm sodium tungstate is added to the
 chromic acid feed solution.  However,  the addition of extraneous ions,  such
 as tungstate, to chromium plating rinse water would not be acceptable in
 practice since it would not be feasible to recycle the chromium solution
 containing tungstate ions.

    Other conditioning or treatment agents tested were not as effective  as
 sodium tungstate.   With  sodium chloride, only a short-term  beneficial
 effect is observed.

    Optimum RO membrane properties are obtained from  PBI films cast
 from a dimethylacetamide solution containing 18% polymer by weight,
 coagulated in water at room temperature, and annealed in ethylene glycol
 for 10 minutes at 165°.

    PBI RO membranes are resistant to attack by chromic acid.  The in-
 trinsic RO properties are not affected by several weeks exposure to 200
 ppm chromic acid  feed solution at pH 2. 9-3. 0.  This is demonstrated by
 the high salt rejection achieved after testing with chromic acid solution.

    Adjustment of the feed pH by addition of sodium hydroxide or aqueous
 ammonia yields the highest chromic acid rejection levels  and an  increase
 in water flux, without pretreatment or preconditioning of the membrane.
 Rejection levels as high as 95% were obtained on adjusting feed pH from
 pH 2. 9 to pH 5. 7 with aqueous  ammonia. As with the tungstate addition to
 the rinse water,  pH adjustment is not acceptable in practice  because of the
 possible buildup of harmful salts in the plating solutions.

   Although membrane performance was improved by feed pH adjustment
 and membrane treatment, the project failed to develop a PBI membrane
 which  would  be acceptable or satisfactory for the treatment of chromium
plating rinse water.

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                      IE.  RECOMMENDATIONS

    In view of the demonstrated improved level of chromic acid rejection
obtained with PBI RO membranes by pretreatment with sodium tungstate
and the demonstrated polymer's resistance to chromic acid, it is recom-
mended that the study be continued on a laboratory  scale to develop a
membrane with higher long-term rejection levels without the addition of
agents to the feed solution.

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                         IV.   EXPERIMENTAL

 MEMBRANE CHARACTERIZATION

    A high pressure,  closed loop, circulating flow loop with flat film test
 cells taking 2 - inch membrane circles was assembled.  The  system was
 described in an earlier study '  '  and is shown in Figure 1.  Feed solution
 from a five-gallon feed tank was  pumped through the test cells by a positive
 displacement Lapp diaphragm pump rated for 1500 psi service at a flow
 rate of about 20 gallons per hour.  From the pump,  the feed passed to the
 manifold on which 12 cells were mounted in series.  The membrane sample,
 1. 9 inches in diameter, was placed in the cell on top of a filter paper  cir-
 cle and supported underneath by a porous steel disc. Cell diameter was
 1. 9 inches and the chamber clearance of 0 . 090 inches over the membrane
 sample resulted in a linear feed flow rate of about 65 feet/min.  Operating
 pressure was controlled by a back-pressure regulator.  Feed composition
 was maintained constant over an  extended test period by returning permeate
 to the feed tank by means of a small return pump.  The chromic acid  feed
 solution was changed about every two days because it reacted with parts of
 the metal system and slowly changed in concentration.  Percent conversion
 i.e., the ratio of product volume removed to feed volume,  was essentially
 zero since negligible volumes of  permeate were removed for  analyses.

    Flux, percent chromic acid rejection (%R) and pH of feed  and product
 were determined.  Flux is the volume  rate of flow of permeate per unit
 membrane area and was determined by timing the volume of permeate
 flowing into  a graduated cylinder.  It is expressed as gallons  per square
 foot per day (gfd).

    The percent rejection, %R, of solute is defined as:

                         %R =     C£ - Cp    x  100

                                     Cf"
    where C| = solute concentration in  the feed
          Co= solute concentrations in the product

Chromium concentration was determined by a spectrophotometric method
based on measuring the absorbance at 540 nanometers of the highly colored
cdiromium-diphenylcarbazide complex.   A Beckman  recording spectre-
photometer,  DB-GT,  was used.  Atomic absorption analyses  were also

                                    6

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    FIGURE 1  EXPERIMENTAL REVERSE OSMOSIS TEST SYSTEM
                        BACK PRESSURE
                            VALVE
                                  H.R
                               PRESSURE
                                GAUGE
        O
    L.P.
 PRESSURE
   GAUGE
    O
x—
/
FLOW
METER
                  CHECK
                  VALVE
                      FLOW
                    VOLUME
                      CELL
               u
  0*3
                 RETURN
                  PUMP
                                (MEMBRANE
                          COND.A  CELL
                           CELLV
                                    PERMEATE
                                    LINE
                            •M-
i-HXJ-
     FEED
     TANK
                          L.P.
                         SURGE
                         TANK
             FILTER
                               H.P.
                              SURGE
                              TANK
 DAMPER
 VALVE

 SOLENOID
-VALVE

BYPASS
VALVE

H.P. SAFETY
VALVE

                                           H.R PUMP
                 LTJ
                 HEAT
               EXCHANGER
                                   FEED STREAM
                                   PERMEATE STREAM

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carried out on selected samples to verify the accuracy of the spectropho-
metric method.

    Measurements of pH on feed and permeate samples were made with a
Beckman SS-2 pH meter.

    Concentrations of sodium chloride in sodium chloride feed solutions and
permeate samples were obtained by conductivity measurements with a
Radiometer conductivity meter,  Model CDM 2nd (Copenhagen, Denmark.)

MEMBRANE OPTIMIZATION

    Important variables in the  film  casting operating and annealing step
which were studied included  (1) polymer concentration in the casting solu-
tion,  (2) water coagulation bath temperature, (3) film thickness and (4)
annealing conditions  (time and temperature).  The 4" x 12" films were cast
on glass plates in a laboratory film casting unit, dried 60 seconds in an
air drying chamber and then immersed in water coagulation baths.  As a
result of the operations an asymmetric film is obtained.  Polymer solutions
with 16%, 18% and 20% polymer in dimethylacetamide (DMAc)  were prepared
by diluting a 24% PBI dope to the target solids concentration with DMAc.
Coagulation temperatures of 25°C and 5°C were employed.  Film thickness
ranged from 2 mils to 5 mils.   Annealing was carried out in ethylene glycol
at 165°C and 180°C and in polyethylene glycol at 220°C.  It is  during the
annealing step that the RO properties are developed in the thin, dense sur-
face (the air side  of the film as cast onto glass plate) of the asymmetric
membrane.  This active layer, about 1 micron thick, is supported by the
open,  porous  substructure.  The films were lightly constrained during
annealing to prevent distortion but not completly constrained because
shrinkage, even though small, was  sufficient to cause tears and cracks in
the film.

    Post treatment of membranes included treating the membrane with
inorganic salts or with strong  acid  to prevent or reduce interaction between
the -NH-groups in PBI and chromic acid feed solution.
                                    8

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                    V.  RESULTS AND DISCUSSION

    The effects of film casting variables  and annealing conditions on RO
properties are summarized in Table 1.  These data were obtained with a
5, 000 ppm sodium chloride feed solution at pH 6. 4.  Duplicate samples
were tested and the values  reported are the averages.  Membrane casting
and annealing conditions for each sample are given.   These are, in the
order presented:  casting solution concentration; film coagulation tempera-
ture; annealing medium, (ethylene glycol and polyethylene  glycol); anneal-
ing temperature; and wet film thickness.

    These results indicate that the best combination of RO  properties was
obtained with films cast from 18% solutions (dopes) and annealed in ethylene
glycol at  165°C.  An annealing time of 10 minutes was adequate.  Annealing
times as  long as 30 minutes are detrimental while annealing times of less
than  5 minutes do  not develop as good RO properties.  Membrane sample
F-l, 2 is typical of these preparative conditions.  It exhibited good flux,
27.6  gfd,  and rejection, 83% after 24 hours (this would improve with time)
against 5, 000 ppm sodium chloride feed.  Flux decreases and rejection
improves with time due to pressure-induced compaction and tightening up
of the membrane.  This effect is noted for samples B, C,  G and H.  Mem-
branes from the 20% solution exhibited properties equivalent to F-l, 2.
Coagulation temperature does not appear to have any effect on  RO proper -
ties;  hence,  room  temperature  is preferred as a matter of convenience.

    Membrane thickness of 4-5  mils proved to be adequate to withstand
sustained, high pressure operation.  Film thickness less than  2. 5 mils
proved to be inadequate.  This is shown for membrane samples D and E,
Table 1,  both of which failed under pressure testing at 600 psi.

    Annealing studies in ethyjene glycol showed no real difference in mem-
brane RO properties between 165° and 180° annealing temperatures.  The
lower annealing temperature  was adopted as the standard in membrane
fabrication.  Membranes annealed at a much higher temperature, e. g.
220°C, in polyethylene glycol, exhibited poor RO properties, as shown by
the very low flux values  and low rejection levels for membrane sample
1-A in Table 1.

    Films were cast at room  temperature from 16%, 18% and 20% solutions
of PBI in  dimethylacetamide to  assess the  effect of polymer concentration

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TABLE 1  EFFECT OF FILM CASTING AND ANNEALING CONDITIONS ON
                    MEMBRANE RO PROPERTIES
Membrane Casting, Annealing
Samples Conditions*
B-l, 2

C-l, 2

D

E

F-1,2

G-l, 2

H-l, 2

1-A

A-l, 2

16%, RT, EG, 165°, 4 mils

16%, 5° C, EG, 165°
4 rails
18%, RT, EG, 165°,
21/2 mils
18%, 5° C, EG, 165° C,
21/2 mils
18%, RT.EG, 165°C,
4-5 mils
18%,RT,EG, 180° C,
4-5 mils
18%, 5°C, EG,165°C
4-5 mils
18%, RT, PEG, 220° C,
4-5 mils
20%, RT, EG, 165° C,
3 mils
Total Flux
Test gfd
Hours
24
192
24
192

(Too thin;

(Too thin;
24

24
48
24
48
75
92
192

18.8
17.2
16.9
15.2

failed)

failed)
27.6

21.3
19.7
23.0
19.5
0.4
0.3
11.4

Rejection
%
84
89
64
73




83

86
87
86
88
52
53
89


   Test Conditions: 600 psig, 25°C, 20 gal/hr, 0% conversion
   Feed Solution:  Sodium Chloride,  5, 000 ppm,  pH 6. 4

   #EG-Ethylene glycol
   PEG-Polyethylene glycol
   RT  -Room temperature
                                  10

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on film and membrane properties.  Casting solutions with 18% polymer
concentration were found to yield the best combinations of film strength,
solution viscosity, film casting speed, film thickness control and RO
properties.  This therefore was adopted as the standard solids concentra-
tion.

    Membrane samples from Table 1 were selected for long-term testing
with sodium chloride solution before proceeding to the critical testing  with
chromic acid feed solution.  Membrane samples A and B performed well
through 420 hours with sodium chloride.  This is shown in Table 2.  Re-
jection levels were 94% and 88% and flux values were 10 gfd and 17  gfd,
respectively, for samples A and B.  Samples F and H also exhibited good
RO properties with the sodium chloride feed solution.

    The feed solution was then changed at the 420th hour from dilute sodi-
um chloride to 180-200 ppm chromic acid,  as shown in Table 2.  Through
the next 72 hours, i. e., from 420 to 490 total test hours  of testing with
chromic acid, all four membrane samples  were performing effectively in
rejecting chromic acid.  The rejection values ranged from 62% to 69% and
the flux values ranged from 5 gfd to 12 gfd.  Feed pH was 2. 9-3. 0 and  pro-
duct pH was 3. 3-3.4.   However, the next 48 hours of testing with chromic
acid revealed a rapid deterioration in RO properties.  Chromic acid re-
jection values dropped sharply and after 5  days (120 hours) testing  with
chromic acid had declined to  10% and less for all four samples.  In addition,
a decline in water flux was observed over this period.  Some of the decline
in chromic acid rejection level can be attributed to the lower flux but the
total drop in rejection level far exceeds that attributed to flux  decline.

    Fresh,  unconditioned membranes were then tested against chromic acid
first,  followed by sodium chloride feed solution to determine whether or
not the membranes were irreversibly attacked by  chromic acid. A pre-
liminary indication that the membranes were not attacked  by chromic acid
was available from the flux data in Table 2.  The fact that the  product
flux did not increase as the chromic acid rejection dropped sharply,
strongly suggested that the membranes  were not attacked.  Table 3 shows
rejection/flux data for fresh membranes, including one (J) which was
cross-linked with perfluoroglutaric acid in an attempt to prevent the basic
imidazole nitrogens in PBI from reacting with chromic acid.  All three
membranes exhibited very low rejections of chromic acid.  After 72 hours,
the rejection values for samples J and L were less than 10%.   Surprisingly,
Sample K showed a slight increase in rejection during the  72 hours test
period.  This behavior is typical of RO  membranes in which pressure-
induced compaction results in a tightening  of the membrane and a conse-
quent increase in rejection.

    Additional long-term testing was carried out to assess the effects of

                                    11

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   TABLE 2.  LONG-TERM RO PROPERTIES WITH SODIUM CHLORIDE
                       AND CHROMIC ACID FEED SOLUTIONS
Membrane Sample
A
Test
Feed Hours
NaCl 24
48
145
170
240
392
420
Cr03 440

492
518
542
Reject.
93
94
94
95
95
93
94
62
70
65
21
3
Flux
gfd
15.0
14.5
12.5
12.5
12.0
10.5
10.0
5.5
5.0
5.2
5.0
4.0
B F H
Reject.
84
87
88
88
89
88
88
66
74
62
25
11
Flux Reject.
gfd %
18.5
17.5
16.0
16.0
15.0
17.0 82
17.0 83
11. 5 69
10. 0 77
11. 0 65
9.3 27
7.5 10
Flux Reject. Flux
gfd % gfd





26.5 86 23
89 19-0
17.0 69 13.0
14. 0 75 11. 5
12.0 63 10.3
10.0 29 8.7
9.0 3 10.3
Test Conditions: 600 psig; 25°C; 20 gal/hr; 0% Conversion.

Feed Solutions;  NaCl,  5, 000 ppm, pH 6. 4.
                CrO3,  180-200 ppm, pH 2. 8-3.0.
                                12

-------
      TABLE 3.   RO PROPERTIES OF UNCONDITIONED
                             MEMBRANES
Membrane Sample
J
Test Reject. Flux
Feed Hours % gfd
CrO3 20 13 10.5
44 4 6.2
72 4 5.3
Nad 92 61 5. 5
116 64 5.0
140 66 5. 5
230 65 5.0
K
L
Reject. Flux Reject.
% gfd %
15 2.8
15 2.0
22 1.5
83 2.0
87 1.8
88 2.0
93 1.8
9
3
6
54
53
56
55
Flux
gfd
13.5
6.8
4.7
5.0
4.5
5.0
4.5
Test Conditions:  600 psig; 25°C; 20 gal/hr; 0% conversion.

Feed Solutions:   NaCl; 5, 000 ppm; pH 6.4.
                 CrO3; 200 ppm; pH 2.8.
                             13

-------
 membrane pretreatment,  pH adjustment and annealing conditions on RO
 properties.  Test results are given in  Table 4.

    It is concluded from these test data that neither the chemical nor phy-
 sical integrity of the FBI membrane is affected by long-term exposure to
 dilute chromic acid.  This is  substantiated by the high rejection levels -
 80% with chromic acid adjusted to pH 4. 0 and 96% with sodium chloride -
 achieved in subsequent testing with these feed solutions.  The beneficial
 effect of pfl adjustment is striking, with rejection of hexavalent  chromium
 increasing from 20% to about  80%.  This is presumable due to the forma-
 tion of sodium dichromate salt upon addition of sodium hydroxide to adjust
 the pH.

    The membranes in Table 4 were cast from 18% polymer solutions,  and
 all,  except sample 2A, were annealed in ethylene glycol at 165°C.  Sample
 2A was annealed in polyethylene glycol at 220°C, which resulted in poor
 RO properties.  Very low flux values, 0.4-0. 5 gfd, were obtained.   Mem-
 branes IB and 2A were pretreated with 10% sulfuric acid before testing in
 an attempt to improve the RO properties.  No significant effect was  noted,
 however.

    Following the feed pH adjustment  which sharply increased the rejection
 of chromium (+6),  and changing back  to 5, 000 ppm sodium  chloride feed,
 the membranes exhibited excellent salt rejection.  Rejections of 93% and
 better were obtained,  thereby demonstrating that PBI is resistant to attack
 by chromic acid.  Upon replacing the sodium chloride test  feed with 200
 ppm chromic acid feed, these membranes again  exhibited a sharp drop in
 chromic acid rejection.  The  sequential test results in Table 4 are  pre-
 sented in Figure 2 for a convenient overview of RO properties obtained with
 the different feed solutions and membrane treatments.

    The RO properties of PBI membranes  were improved when the mem-
 branes were pretreated with sodium tungstate.  The objective was to form
 a complex ol the anion with the reactive,  basic NH groups in  the polymer
 in order to prevent their interaction with chromic acid. However, to be
 effective,  the resultant PBI-tungstate complex must be sufficiently  stable
 and non-leachable when exposed to dilute chromic acid solution.  The mem-
 brane samples from Table 4,  were, therefore, conditioned with sodium
 tungstate solution by exposing them to a 5, 000 ppm sodium tungstate feed
 solution for 48 hours in the high pressure  flow loop.  At the end of this per-
 iod,  the membranes we re then tested again with  chromic acid.  The results
 are presented in Table 5.

   A significant improvement in long-term chromic acid rejection  was ob-
tained.  After  9 days testing against 200 ppm chromic acid feed, the re-
jections levelled off,  ranging from 42% to  55% for three samples.   This was

                                   14

-------
       TABLE 4.  EFFECT OF SEQUENTIAL FEED CHANGES ON
                          MEMBRANE RO PROPERTIES





1
Reject.
Feed
NaCl

CrO3



Adjust
pH to
4.0



NaCl
CrO3




Hours
75
96
112
132
156
225
250
275
300
395
420
448
525
545
582
606
630
707
%
90
92
74
41
19
16
57
73
75
78
78
81
95
68
36
14
22
24


Membrane Sample
IB* 2A*
Flux Reject,
gfd
11.0
10.1
2.3
2.0
2.2
2.0
1.9
1.8
- -
1.6
1.6
1.7
3.1
1.4
1.2
1.3
1.4
1.1
%
86
88
76
43
19
20
58
74
77
81
81
84
93
69
37
18
20
25

3##
. Flux Reject Flux Reject Flux
gfd % gfd
9.5 83 1.6
8.9 85 1.4
2.6 97 0.5
2.4 64 0.4
2.6 30 0.4
2.4 33 0.4
2.1 52 0.5
1. 9 (Removed)
- -
1.7
1.7
1.6
2.8
1.6
1.3
1.2
1.4
1.0
% gfd









76
76 5.1
78 4.4
96 9.2
70 4.8
37 3.9
14 4.1
19 4.5
22 3.4

 *Pretreated with sulfuric acid.
**Same membrane as 1, but without NaCl conditioning.
 Test Conditions: 600 psig; 25°C; 20 gal/hr; 0% conversion.
 Feed Solutions:  NaCl; 5, 000 ppm; pH 6.4.
                 CrO3; 200 ppm; pH 2. 8.

                                 15

-------
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2  80
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   20
5,000 ppm NaCI
       200 ppm Ci
       I  pH 2.9
   15

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                           ADJUST pH
                            I  TO 4.0
                                                5,000 ppm NaCI

                                                        200 ppm 003
             100
                       200
                         300
400
500
600
700
                                 _L
                                           ±
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                       200
                         300       400
                             HOURS
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          600
          700
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-------
      TABLE 5.  RO PROPERTIES OF TUNGST ATE-TREATED
                             MEMBRANES
Membrane Sample
Test
Feed Hours
Na2WO4 24
48
Cr03 48
72
96
125
194
218
242*
266
1
Reject.
98
98
-
90
60
48
44
46
47
45

Flux
gfd
8.2
7.3
-
3.9
1.7
1.3
1.3
1.2
1.4
1.1
2
Reject.
98
99
-
90
77
53
51
50
51
55

Flux
gfd
7.1
6.5
-
?.9
1.6
1.4
1.3
1.4
2.0
1.4

Reject
98
98
-
90
60
50
46
49
45
42
3
Flux
gfd
13
12
-
7.2
2.6
2.6
2.8
2.7
4.1
2.9
Test Conditions:  600 psig,  25°C, 20 gal/hr, 0% Conversion.

Feed Solutions:   Sodium tungstate, Na2WO4; 5, 000 ppm, pH 7. 3.
                 Chromic acid, CrO3; 200 ppm, pH 2.8-3.0.

*Raised pressure to 750 psig for 6 hours.
                                17

-------
 significantly better than the 22%-25% rejections for the same membranes
 at the end of the chromic acid test cycle reported in Table 4.  Product
 fluxes for the three membranes in Table 5 ranged from 1.2 to 2. 9 gfd.  It
 is worth noting that during the conditioning period with 5, 000 ppm sodium
 tungstate (pH 7. 3), rejections as high as 98%-99% were obtained along with
 product flux ranging  from 6. 5 to 12 gfd.  These results again show that the
 intrinsic  RO properties of  PBI membranes are not affected by long-term
 exposure to chromic acid rinse  water.

    Molybdate,  another large oxygenated anion, was investigated as a con-
 ditioning  agent  for PBI membranes.  Following the procedure used in the
 tungstate treatment,  membranes were conditioned for 48 hours in the high
 pressure (600 psi) test loop with 5, 000 ppm sodium molybdate solution,
 after which they were tested with 200 ppm chromic  acid feed plus  2 ppm
 sulfuric acid.   The results are reported in Table 6.

    After 234 total test hours -  - the last 186 hours  or nearly eight days
 against chromic acid - - chromic acid rejections for the four membranes
 levelled off at about  30%.   This  is a significantly lower level of rejection
 than was  achieved with the tungstate-treated membranes.  Product flux
 values were similar, ranging from 1.4 gfd to 2. 3 gfd.  Again, as was ob-
 served in the tungstate treatment, very high solute  rejections, ranging from
 90% to 98%,  were obtained in the conditioning period after 48 hours.

    In order to  obtain test data which more closely reflect  actual plating
 operation conditions, an authentic chromium plating bath solution
 (33 oz/gal) was obtained and diluted down to a rinse water concentration of
 200 ppm CrO3.   All  subsequent membrane test results to be discussed be-
 low were obtained with the diluted plating solution.  New membranes were
 prepared from the parent batch  of 18% polymer solution.

    The tungstate treatment was repeated and the treated membranes were
 tested against the diluted plating bath solution.  Test results are given in
 Table 7 and very closely approximate those in Table 6 obtained with the
 simulated rinse water.  Chromic acid rejection values for the four samples
 levelled off and after 8 days ranged from 42% to 60%.   Product flux ranged
 from 1. 3 to 2.1  gfd.

   A modification of the tungstate treatment was investigated in an effort
 to obtain higher chromic acid rejection.  This consisted of coagulating the
 freshly cast film in a 5% aqueous solution of sodium tungstate, instead of
 water  alone, to entrain tungstate in the film.   Annealing was then carried
 out in  the manner previously described.  On testing these membranes with
 dilute  plating bath  solution, the  chromic acid rejection values were slightly
lower  than those obtained with the tungstate treated membranes in Tables
 5 and 7.   Test results  are  given in Table 8.  The RO properties are

                                    18

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       TABLE 6. RO PROPERTIES OF MOLYBD ATE-TREATED
                            MEMBRANES
Membrane Sample


Feed
Na2MoO4

CrO3







Test
Hours
24
48
48
72
96
120
144
168
234
C
Reject .
%
81
90
-
32
23
31
32
24
27
-1
Flux
Kfd
10.0
6.6
-
2.9
2.7
1.8
1.8
2.3
2.3
C-2
Reject.
%
98
98
-
68
57
50
53
22
34

Flux
gfd
10.3
9.2
-
1.6
1.6
1.5
1.5
2.4
1.9
C
Reject .
%
96
96
-
72
52
48
47
24
34
-3
Flux
gfd
8*9
7.6
-
1.4
1.4
1.4
1.3
2.0
1.6
C
Reject.
%
98
98
-
84
67
59
60
22
34
-4
Flux
gfd
8.2
8.1
-
1.1
1.2
1.4
1.1
1.9
1.4
Test Conditions:  600 psig, 25°C,  20 gal/hr, 0% Conversion

Feed Solutions:   Sodium molybdate, Na2MoO4>  5, 000 ppm, pH 7. 6
                 Chromic acid, CrO   200 ppm + 2 ppm sulfuric acid,
                 pH 2. 9.
                                  19

-------
       TABLE 7.   RO PROPERTIES OF TUNGST ATE-TREATED
                             MEMBRANES
                                     Membrane Sample
Feed
Na2WO4

CrO3



Test
Hours
24
48
48
72
96
168
A-l
Reject
%
98
98
-
69
49
45

Flux
gfd
6.8
5.4
-
2.1
1.9
1.1
A-
Reject.
%
99
99
-
87
71
62
2
Flux
gfd
5.6
4.2
-
1.4
1.3
1.2
A-
Reject.
%
97
98
-
74
53
47
3
Flux
gfd
5.1
4.2
-
1.7
1.5
1.6
A-4
Reject.
%
99
99
-
66
48
47
Flux
gfd
6.8
5.6
_
1.8
1.7
1.8
         238      42     2.1    60    1.3     43     1.6    43     1.9
Test Conditions: 600 psig, 25°C, 20 gal/hr,  0% Conversion

Feed Solutions:  Sodium tungstate, Na2WO4; 5, 000 ppm; pH 6. 8.
                Diluted plating bath solution,  175 ppm CrO-,
                pH 3.0
                                  20

-------
    TABLE.8.   RO PROPERTIES OF MEMBRANES COAGULATED
                         IN TUNGSTATE SOLUTION
Membrane Sample
E-l E-3

Feed
CrO3


Test Reject.
Hour s %
24 32
48 34
72 34
Flux Reject.
gfd %
3.2 40
3.4 43
3.0 42
Flux
gfd
3.2
3.5
2.9
E-4
Reject. Flu
% gfd
35 3.2
39 3. 3
40 2. 7
E-5
Reject. Flux
% gfd
41 2. 5
39 2,8
'41 2. 4
Test Conditions:  600 psig,  25°C,  20 gal/hr, 0% Conversion.

Feed Solutions:   Sodium tungstate,  Na2WO4; 5, 000 ppm; pH 6. 8.
                 Diluted plating bath solution,  175 ppm CrOj, pH 3. 0
                                21

-------
 significantly better, however, than those of untreated membranes,  attes-
 ting to the beneficial effect of the tungstate  anion on FBI membrane proper-
 ties.

    In yet another modification of the tungstate treatment and in a continued
 effort to achieve higher chromic acid rejections, 100 ppm sodium tungstate
 was added to the chromic acid feed solution.  The membranes were first
 pretreated in the test loop with 5, 000 ppm sodium tungstate feed solution
 as before.  Percent rejection and flux values  which were obtained in long-
 term testing are found in Table 9.  These results clearly show that mem-
 brane performance improved significantly as  a result of adding 100 ppm
 sodium tungstate to the feed.  At 210 total test hours,  168  hours with the
 200  ppm chromic acid plating solution, chromic acid rejection values had
 levelled off at 69%-74% for the  four samples.  The average value of 71%
 represents  a  significant improvement over  the approximately 50% rejection
 value from tungstate pretreatment alone (Tables 5  and 7). Product flux
 values at 210 total test hours ranged from 2. 0 to 2.9 gfd.  These fluxes are
 higher than those obtained in Tables 5 and 7 for the pretreatment alone.
 Thus, the addition of tungstate anion to the  feed raised the chromic acid re-
 jection level to  a useful,  sustained level of  70% or  more over 7 days, at
 which point the  feed pH was raised to assess the effect of pH adjustment.

    Highest rejections of hexavalent chromium were obtained when the pH
 of the feed, containing 200 ppm chromic, acid, 100 ppm sodium tungstate and
 about 10 ppm  sulfuric acid,  was raised to pH 5. 7 by addition of aqueous
 ammonia.  At 48 hours after pH adjustment, rejections of chromium (+6)
 had  risen to 95% and product flux increased substantially, ranging from 4.1
 gfd to 6. 0 gfd, as seen in Table 9.

    Other membrane treatments were investigated  but these proved ineffec-
 tive in improving chromic acid rejection.  One was the pretreatment with
 sodium fluosilicate and the other  involved ionically crosslinking the poly-
 mer with perfluoroglutaric acid,  a  strong acid.   Test results for the fluo-
 silicate treatment are given in Table 10 and in Table 11 for the crosslink-
 ing case. It is  seen that the chromic acid rejections for the fluosilicate-
 treated membranes were much lower than that achieved with the tungstate-
 treated membranes.   Even lower rejections were observed with the cross -
 linked membranes.

    The effects  of the  various membrane treatments and feed pH on chro-
mic  acid rejection are presented  in Figure  3 for convenient  comparison.
Although membrane performance was improved by feed pH adjustment and
membrane treatment, the project failed to develop a PBI  membrane which
would be acceptable in practice for the treatment of chromium plating
rinse water.
                                  22

-------
  TABLE 9.   EFFECT OF TUNGSTATE ADDITION TO CHROMIC ACID
                 FEED SOLUTION ON MEMBRANE RO PROPERTIES
Feed Hours
Na2WO4

CrO3+
Na2W04
t





24
48
48
72
96
120
168
210
234
258
Membrane
F-l F-2
Reject. Flux Reject, Flux
% gfd % gfd
99.0 13.5 99.5 13.4
99.4 11.2 - 11.0
-
84 2.8 86 2.7
78 3.0 81 2.9
74 3.1 75 2.7
74 2.9 77 2.8
74 2.8 74 2.8
91 6.7 91 6.1
95 6.0 95 5.6
Sample
F
Reject.
%
99.4
99.4
-
89
85
80
79
70
90
95

_3
Flux
gfd
12.2
9.7
-
2.5
2.1
2.5
2.4
2.4
5.3
4.8

F
Reject
%
99.0
98.9
-
89
85
80
79
69
94
94

-4
Flux
gfd
11.5
9.3
-
2. 2
2.2
2.1
2.1
2.0
4.7
4.1
Test Conditions:  600 psig,  25°C,  20 gal/hr, O% Conversion

Feed Solutions:   Sodium tungstate,  5, 000 ppm, pH 7. 2
                 Diluted plating bath solution, 200 ppm CrO3+ 100 ppm
                 sodium tungstate + 10 ppm sulfuric acid to bring to
                 pH 3.0.

-------
           TABLE 10.   RO PROPERTIES OF FLUOSILICATE
                                TREATED MEMBRANES
Membrane Sample
D-2 D-3
Reject. Flux Reject. Flux
Feed Hours % gfd % gfd
Na2SiF6 24 82 1. 7 85 1. 8
48 79 1.6 84 1.3
CrO3 48
72 55 1.1 41 1.6
96 46 0.9 42 1.1
120 39 1.0 38 1.2
192 27 1.1 29 1.2
D-4 D-6
Reject. Flux. Reject. Flux
% gfd % gfd
71 2.1 59 1.6
69 1.5 58 1.2
- - - -
31 2.3 31 2.6
17 2.3 17 2.1
19 2.2 10 2.5
15 2.6 15 2.0
Test Conditions:  600 psig,  25° C,  20 gal/hr, 0% Conversion.
Feed Solutions:   Sodium fluo silicate,  Na2SiF/, 5, 000 ppm,  pH 3. 8.
                 Chromic acid, CrO^, 200 ppm,  pH 3. 0.
                                 24

-------
            TABLE 11.   RO PROPERTIES OF CROSSLINKED
                                   MEMBRANES
                               Membrane Sample
                     G-l           G-2            G-3          G-4
               Reject.  Flux  Reject.  Flux   Reject  Flux  Reject Flux
Feed   Hours     %    gfd      %    gfd      %    gfd     %    gfd
CrO3     24      10   '  12    10      7.2     12    5.9    14.    5.0

          48       0    10.6    8      5.9     7.9   5.0    12     4.1
Test Conditions:  600 psig, 25°C, 20 gal/hr,  9% Conversion

Feed Solution:    Chromic acid, 200 ppm, pH 3. 0.
                                 25

-------
FIGURE 3:
EFFECTS OF DIFFERENT MEMBRANE TREATMENTS AND
       FEED pH ON CHROMIC ACID REJECTION
     100
   UJ
   
-------
                          VI.  REFERENCES
1.    Conciatori, A.B.; E.G.  Chenevey; T. C. Bohrer; and A. E. Prince, Jr.
     Polymerization and Spinning of PBI. J. Polymer Sci. , Part C.
     19:  49-64, 1969-

2.    Davis, H. J. ; F.S.  Model; M. Jaffe; M. A. Sieminski; A. A. Boom;
     and L. A.  Lee.  An Investigation of Polybenzimidazole Hollow Fiber
     Reverse Osmosis Membranes.  Final Report; Contract No. 14-30-2810,
     U. W. Department of the Interior, Office of Saline Water,  Washington,
     D.C.  July 1972.

3.    Davis, J.  J. ; J. W.  Soehngen;  and F. S. Model.  Seawater Desalination
     with PBI Hollow Fiber Reverse Osmosis Membranes.  Final  Report,
     Contract No. 14-30-3199, U.S. Department of the Interior, Office of
     Saline Water,  Washington, D. C. , February 1974.

4.    Davis, J.  J. and F. S. Model. Celanese Research Company.  PBI
     Reverse Osmosis Membrane Developement for  use in Wash Water
     Recovery at 165°F.  (Presented at 1973 Intersociety Conference on
     Environmental Systems, San Diego. July,  1973) 5 p.

5.    Poist, J. E. and F. S. Model.   Development of Improved PBI
     Membrane Systems for Wash Water Recycling at Pasteurization
     Temperatures.  Final Report, Contract No. 14-30-3112, U.S. Depart-
     ment  of the Interior,  Office of Saline Water, Washington,  D.  C.
     July 1974.

6.    Model,  F.S. ;  H. J.  Davis; A. A.  Boom; C. Hrlfgott; and L. A. Lee.
     The influence  of Hydroxyl Ratio on the Performance  of Reverse
     Osmosis Desalination Membranes.  Research and Development
     Progress  Report No. 657. U.S. Department of the Interior,  Office
     of Saline Water,  Washington,  D.C.    June 1971

7    Standard Methods for the Examination of Water  and Waste Water.
     Twelfth Edition.  New York,  American Public Health Association,
     Inc.,  1969. p. 123-124.
                                  27

-------
                                   TECHNICAL REPORT DATA
                            (Please read InsJmctionS on tne reverse before completing)
 1. REPORT NO.
   EPA-600/2-78-040
 4. TITLE AND SUBTITLE
  FBI REVERSE OSMOSIS MEMBRANE FOR CHROMIUM PLATING
  RINSE WATER
             3. RECIPIENT'S ACCESSION"NO.
             5. REPORT DATE
                March 1978 issuing date
             6. PERFORMING ORGANIZATION CODE
 7. AUTHOR(S)
  Howard  J.  Davis, Frank S. Model, Joseph  R.  Leal,
  Celanese  Research Company, Summit, N.J.   07901
             8. PERFORMING ORGANIZATION REPORT NO.
 9. PERFORMING ORGANIZATION NAME AND ADDRESS
  The American Electroplaters' Society,  Inc.
  Winter  Park, Florida  32789
             10. PROGRAM ELEMENT NO.
                  1BB610
             11. CONTRACT/GRANT NO.
                 R-803620
 12. SPONSORING AGENCY NAME AND ADDRESS
   INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY-Cin.,  OH
   CINCINNATI,  OHIO, OFFICE OF RESEARCH AND  DEVELOPMENT
   UNITED  STATES ENVIRONMENTAL PROTECTION AGENCY
   CINCINNATI,  OHIO  46268
             13. TYPE OF REPORT AND PERIOD COVERED
                  FINAL
             14. SPONSORING AGENCY CODE

                 EPA-600/12
 15. SUPPLEMENTARY NOTES
 16. ABSTRACT
     A  laboratory research study was carried  out to select and optimize polybenzimida-
  zole(PBI)  reverse osmosis(RO) membranes  for the treatment of chromium plating  rinse
  water.   The effects of important film casting and annealing variables on RO properties
  were  investigated.   Membranes were tested in high pressure flow cells with dilute
  sodium  chloride and chromic acid feed solutions.
     PBI  RO  membranes were found to be resistant to attack by chromic acid.  After
  pretesting with sodium chloride, the membranes showed a short-term effective level
  of rejection with chromic acid.  Upon retesting with sodium chloride, the same mem-
  branes  again exhibited high salt rejections,  thereby demonstrating they had not been
  chemically attacked by chromic acid.
     A  significant improvement in long-term rejection of chromic acid was obtained when
  the membranes were  pretreated with sodium tungstate solution.  The addition of sodium
  tungstate  to the feed solution further improved chromic acid rejection.  Highest
  levels  of  chromic acid rejection were obtained by adjusting the pH of the feed.
  However, neither pH adjustment nor addition of tungstate to the feed are acceptable
  in practice because of possible contamination of the plating bath by the extraneous
  ions.  T^e project  failed to develop an acceptable PBI RO membrane for treating
  chromium plating  rinse water.
                                KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
  Electroplating*
  Waste Treatment
  Chromium*
 8. DISTRIBUTION STATEMENT

     Release to Public
                                              b.lDENTIFlERS/OPEN ENDED TERMS
  Polybenzimidazole
  Polymer(PBI) membrane*
  Chrom plating bath*
  Reverse Osmosis*
  Rinse water
19. SECURITY CLASS (ThisReport}
    Unclassified
                                              20. SECURITY CLASS (Thispage)
                                                   Unclassified
                             COSATI Field/Group
 68C
 68D
21. NO. OF PAGES
      35
                           22. PRICE
EPA Form 2220-1 (9-73)
                                             28
                                                              * U.S. GOVERNMENT PRINTING OFFICE: 1978—260-880-41

-------