Environmental Protection Technology Series
REMOVAL OF TOXIC METALS FROM  METAL
                 FINISHING  WASTEWATER BY
                        SOLVENT EXTRACTION
                      Industrial Environmental Research Laboratory
                           Office of Research and Development
                          U.S. Environmental Protection Agency
                                   Cincinnati, Ohio 45268

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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-600/2-78-011
                                             February 1978
          REMOVAL OF TOXIC METALS FROM

METAL FINISHING WASTEWATER BY SOLVENT EXTRACTION
                       by

               Curtis W. McDonald
            Texas Southern University
              Houston, Texas  77004
              Grant No.  R-803332-01
                 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 endorse-
ment or recommendation for use.
                                    11

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

     This report is a product of the above efforts.  These studies were
undertaken to perform a laboratory-scale investigation at Texas Southern
University to ascertain the feasibility of utilizing solvent extraction
techniques to develop economical methods for removing cadmium, chromium,
copper, nickel and zinc ions from metal finishing wastewater.

     Such information will be of value both to EPA and to the industry it-
self.  Within EPA's R§D program the information will be used as part of the
continuing program to develop and evaluate improved and less costly technol-
ogy to minimize industrial waste discharges.  Besides its direct application
to metal-finishing wastes from electroplating, this technology may find
application in the control of toxic metals generated by a host of other in-
dustries .

     For further information concerning this subject the Industrial Pollu-
tion Control Division should be contacted.
                                              David G. Stephan
                                                  Director
                                Industrial Environmental Research Laboratory
                                                 Cincinnati
                                    111

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                                 ABSTRACT

    This report describes a study on the removal of chromium, cadmium,
copper, nickel and zinc from metal finishing wastewater using the high mole-
cular weight amine Alamine 336.  The study consisted of an initial phase in
which the extraction of the metal ions of interest was studied using synthe-
tic solutions.  The second phase of the study involved extraction from
actual metal finishing wastewater samples.

    The results of the study indicated that chromium, cadmium and zinc ions
can be extracted simultaneously or selectively using a 100-to-l wastewater
to Alamine-336-xylene solution.  The simultaneous extraction procedure
appears to have some promise for adoption at the industrial scale.  Copper
and nickel could not be satisfactorily extracted using this procedure.

    Chromium, cadmium and zinc can be stripped from the organic phase with
better than 99.5 percent efficiency using 4M NaOH.  The regenerated reagent
can be recycled and reused without any loss of extraction efficiency.  The
procedures are reproducible, rapid and relatively simple.

    This report was submitted in fulfillment of Research Grant No. R-803332
by Texas Southern University under the partial sponsorship of the U.S.
Environmental Protection Agency.  This report covers the period August 1,
1974  to March 31, 1977  and work was completed as of March 31, 1977.
                                    IV

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                                 CONTENTS
Foreword	iii
Abstract	    iv
Tables	    yi
Acknowledgment	vii

    1.  Introduction  	  1
    2.  Conclusions 	  2
    3.  Recommendations	3
    4.  Materials and Methods	4
            Apparatus  	 4
            Reagents 	 4
            Metal Finishing Wastewater	5
            Sludge Samples  	  5
    5.  Results and Discussion	6
            Extraction of Chromium	6
            Extraction of Cadmium	   7
            Extraction of Zinc	   7
            Extraction of Copper and Nickel	   7
            Selective Extraction of Chromium, Cadmium and Zinc ....  8
            Simultaneous Extraction of Chromium, Cadmium and Zinc .  .   8
            Reagent Loss 	    8
            Stripping and Recycling 	  11
            Studies of Sludge  	 	   11
            Chemical Reactions and Mechanism	   11

References	14

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                                  TABLES





Number                                                                 Page



   1.  Selective Extraction of Chromium, Cadmium and Zinc	9



   2.  Simultaneous Extraction of Chromium, Cadmium and Zinc	10



   3.  Stripping Studies	12
                                     VI

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                             ACKNOWLEDGMENT
     The author wishes to thank Mr. Frank Rudman of the Dixie Metal Finish-
ing Company for supplying the wastewater.  He also wishes to thank Ms. Orbie
S. Cowling, Mr. Ta-Sheng Lin, Mr. Mohammed Mahayni and Mr. Hossein Pahlavan
for their technical assistance.  Special appreciation goes to the Industrial
Environmental Research Laboratory of the U.S. Environmental Protection .Agen-
cy, particularly Mr. J. Ciancia, Mr. R. Tabakin and Ms. M. Stinson, who mon-
itered the project and to the Minority Institution Research Support program
of EPA which financed the research.
                                   vn

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                                SECTION I

                              INTRODUCTION

     As a result of our increased awareness in recent years of the import-
ance of protecting and improving the quality of our water, there has been
considerable interest in treating polluted waters generated by various in-
dustrial processes.  Due to this concern, new technology has been developed
and is currently available to remove toxic materials from polluted water
at reasonable cost for many industrial processes; thereby preventing the
pollution of our rivers, streams and municipal sewer systems.

     The metal-finishing industry is one in which sufficient technology is
not generally available for the economic removal of toxic materials from
the wastewater it generates.  There are more than 15,000 metal-finishing
facilities in the United States.  Of these, more than 10,000 can be
classified as small shops.  Ample technology is available at reasonable
costs for huge operations such as large independent plants and captive
facilities.  The captive facilities are generally subsidiaries of auto-
mobile, home appliance, or plumbing manufacturing companies.  The technology
currently available to remove toxic metals from metal-finishing wastewater
requires a capital outlay that poses a financial burden for equipment on
the small shops.  Since the vast majority of the metal-finishing facilities
are in the small shop category and are generally concentrated in industrial
areas within cities, they pose a serious pollution problem for municipal
sewer systems.

     This report describes the use of solvent extraction procedures using
high-molecular-weight amines to detoxify metal-finishing wastewater.  Sol-
vent extraction methods using high-molecular-weight amines for the removal
from aqueous solutions of the toxic metal ions generally found in metal-
finishing wastewater, such as cadmium, chromium, copper, nickel, and zinc,
have been extensively investigated (1-10).  Some extraction processes have
been recommended for utilization by various industries for water detoxifi-
cation (11»13).  Several industrial processes utilizing solvent extraction
procedures have recently been employed in Europe (14).  The Gullspang pro-
cess utilizes the high-molecular-weight amine Alamine 336 to remove moly-
bdenum, tungsten, chromium, iron, cobalt, and nickel from solid waste such
as scrap lathe turnings, and mill shavings.  The Soderfors process is
used to recover metals and acids from a stainless steel pickling bath,
The Valberg process is currently being used to recover zinc from effluent
water generated by the manufacture of rayon.  All of these processes
utilize solvent extraction procedures on an industrial scale.

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                                SECTION 2

                               CONCLUSIONS
1.  Chromium, cadmium and zinc ions can be extracted simultaneously from
    metal finishing wastewater using a 25 percent Alamine-336-xylene sol-
    ution.  Using a 100 to 1 wastewater to Alamine-336 ratio,  90 percent
    of the chromium, 98 percent of the cadmium and 83 percent  of the zinc
    can be removed with a single extraction.

2.  Chromium, cadmium and zinc ions can be extracted somewhat  selectively
    from metal-finishing wastewater using the 25 percent Alamine-336-xylene
    solution by carefully controlling the hydrochloric acid concentration.
    Using the 100 to 1 wastewater to extractant ratio, 89.8 percent of
    chromium can be extracted without removing any cadmium, zinc, copper
    or nickel.  At higher hydrochloric acid concentrations, cadmium and
    zinc can be removed successively.

3.  Neither copper nor nickel can be efficiently extracted from the metal
    finishing wastewater using 25 percent Alamine-336-xylene solution.

4.  The high molecular weight amines, Alamine-336, Aliquat-336-S, Primene
    JMT, Primene SIR and Amberlite LAI proved unsatisfactory as extractants
    for removing chromium, cadmium, copper, nickel and zinc from metal
    finishing sludge.

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                                SECTION 3

                             RECOMMENDATIONS
1.  The Alamine-336-xylene system for simultaneously removing chromium,
    cadmium and zinc merits further investigation.  A pilot plant scale
    study is needed to determine the economic feasibility of the process.

2.  Fundamental research needs to be undertaken on the utilization of
    commercially available high molecular weight amines in the relatively
    new foam and liquid membrane separational techniques to ascertain
    the potential of using these new methods for removing toxic metal
    ions from metal finishing wastewater.

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                                 SECTION 4

                          MATERIALS  AND METHODS
Apparatus

     ANal(Tl) well  type  scintillation  counter,  1.75 x  2.0  inches,  consist-
ing o£ a high voltage power supply,  a discriminator and a tinier  sealer was
used for gamma counting.

     A Perkin Elmer  Model 360 atomic absorption  spectropnotometer equipped
with digital display and  a Houston Instruments OmniScribe recorder  was
used to analyze both phases for the  metals. Dry  air and acetylene gases
were used for the flame.

     A Dorhmann Model DC-50 Total Organic Carbon Analyzer was used  to
analyze the aqueous  phases for loss  of  reagent from the organic  phases
during the extraction processes.

     A Sargent Welch Model 119NX digital pH meter was used  to make  the pH
measurements.

     High speed motors equipped with glass paddle stirrers were  used to mix
the phases.

     A clinical centrifuge with 50 ml heavy walled glass centrifuge tubes
was used for phase separation.

Reagents

     Primene JM-T is a mixture of primary amines, principally in the CIR
range.  Primene 81-R is a  mixture of primary amines principally  in  the   ^
C12-14  ranSe-  Amberlite LA-1 (impure n-dodecenyltrialkylmethyl amine)  is  a
secondary amine.  Amberlite LA-1 and the primary amines listed above are
available from Rohm  and Haas Chemical Company, Philadelphia, Pennsylvania.

     Alamine 336 (impure tricaprylmethylamrnonium chloride) is a  quarternary
ammonium salt, available from General Mills.

     Extractant solutions were made  of  the high-molecular-weight amines by
dissolving the appropriate quantities in xylene.

     Aqueous standards (1000 ppm)  for atomic absorption spectrophotometric
analysis were  obtained from Curtin-Matheson Company.   The appropriate organo-

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metallic compound was purchased from Curtin-Matheson and dissolved in xylene
for use as standards for the nonaqueous phase analysis.

     All of the aqueous solutions were prepared using deionized water.

Metal Finishing Wastewater

     The metal finishing wastewater was obtained from the Dixie Metal Fin-
ishing Plant, Houston, Texas.  It is a medium sized plant which generates
between 40,000 and 50,000 gallons of wastewater a day.  The plant is di-
versified, utilizing many metal finishing procedures.  The wastewater from
the various processes after appropriate pH adjustments is combined to leave
the plant at a single outlet and then treated by an ion exchange system.

     Samples of the untreated wastewater were collected for investigation.
They contained all of the metallic ions of interest; cadmium, chromium,
copper, nickel and zinc.  Their composition varied widely depending on
when the sample was taken.  This apparently depended on the metal finishing
process which was taking place at the time of the sampling operation.
Generally, the wastewater content was; chromium 12 to 60 ppm, cadmium
2 to 8 ppm, copper 0.5 to 5 ppm, zinc 2 to 14 ppm, and nickel 2.2 to 2.5
ppm.  The pH usually ranged between 4 to 5.  The water was somewhat turbid
and a brown gelatinous sludge formed in the bottom of the vessel on settl-
ing.

Sludge Samples

     Sludge Samples were obtained through the U.S. EPA from a job plating
company in Iowa.

Method

     Screening studies were performed on synthetic solutions of cadmium,
chromium, copper, nickel and zinc using Primene 81-R, Amberlite LA-1,
Alamine 336 and Aliquat 336-S as extractants.  In a typical screening study,
5 ml of a 5 percent solution of the high-molecular-weight amine in xylene
was placed in a 50 ml heavy wall centrifuge tube with an equal volume of
10 ppm nietal ion solution.  The phases were mixed for 3 minutes using a
small motor stirrer equipped with a glass paddle.  The phases were separat-
ed using a clinical centrifuge.  After phase separation, each was analyzed
for its metaj. content using an atomic absorption spectrophotometer.   In
some cases the cadmium and zinc were analyzed using a gamma scintillation
counter with cadmium-109 and zinc-65 as tracers.

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                                SECTION 5

                         RESULTS AND DISCUSSION
Extraction of Chromium

     The screening studies indicated that Alamine 336 and Aliquat 336-S
showed promise as satisfactory extractants for chromium.  Generally, Alamine
was effective in acid media and Aliquat 336-S effective in slightly alkaline
solution.  Both removed more than 99 percent of the metal with a single ex-
traction when carried out under optimum conditions.  Alamine 336 was chosen
for further investigations, since the pH of the wastewater was usually be-
tween 4 and 5.  In addition, raising the pH will cause some of the metals
to precipitate out as the hydrous oxides and cause unwanted sludge.

     Attempts were initially made to extract the chromium from the waste-
water as received from the plants by vigorously shaking the water and ana-
lyzing rapidly.  This proved unsuccesful due to the clogging of the aspira-
tion system of the spectrophotometer and the frequent necessity for clean-
ing the burner liead.  Clogging problems were also encountered when the
mother liquor from settled wastewater was used.  Filtered wastewater samples
were used in all subsequent investigations.

     The pH was generally in the range of 4 to 5 when received from the
plant.  If the pH was higher than 5, it was lowered prior to filtration to
prevent loss of the metals as hydrous oxides.

     A high aqueous phase to organic phase ratio is desirable in order to
concentrate the chromium into a small volume.  Ratios up to 100 to 1 proved
satisfactory.  Higher ratios increased settling time due to formation of
emulsions.  The high aqueous to organic phase ratios caused a need for a
higher Alamine 336 concentration than was used in the screening studies.
The 5 percent Alamine 336 solution did remove the chromium efficiently with
a single extraction, but on standing, the solutions turned green, and the
chromium content of the aqueous phase increased.  This situation did not
arise if a 25 percent reagent solution is used.

     At a chloride ion concentration of 2 x 10"% (as hydrochloric acid) or
higher, 90 percent of the chromium can be removed from the wastewater.  The
pH of the 2 x 10"^ chloride solution varied from about 2.5 to 3.0 depend-
ing on the initial pH and composition of the samples.  Some waste water
samples showed considerable buffering actions presumably due to phosphates
and/or borates used in the plating operations.  Improving the extraction
efficiency substantially above 90 percent was difficult.  Increasing the

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Alamine 336 concentration or reducing the aqueous to organic phase ratio
did not materially improve the degree of extraction.  Carrying out a second
extraction on the raffinate from the first extraction removed only one to
two percent of the remaining chromium.  It appears that only about 90 per-
cent of the chromium is in the hexavalent state under the conditions of the
extraction.  The remaining 8 to 10 percent appears as trivalent chromium
which cannot be extracted into the organic phase.  In the screening studies
in which I^CrO^ was used as the source of chromium, 99 percent of the chro-
mium was removed under the same conditions.  The Chromium III was oxidized
to chromium VI by acidifying the wastewater, adding potassium permanganate
and heating.  On extracting the oxidized wastewater, more than 99 percent
of the chromium was removed.

     Further studies indicated that chromium can be extracted selectively
(about 90 percent of the chromium) by controlling the chloride ion con-
centration.  At a chloride ion concentration of 2 x 10~3M, no detectable
quantities of cadmium, copper, nickel, or zinc are extracted, when the
extractions are carried out with 25 percent Alamine 336 in an aqueous to
organic phase ratio of 100 to 1.

Extraction of Cadmium

     Screening studies indicated that Primene JM-T, Alamine 336, Aliquat
336-S can remove more than 95 percent of the cadmium from synthetic solu-
tions with a single extraction.  Of the three reagents, Alamine 336 appear-
ed to be superior and was chosen for further investigations.  If sufficient
hydrochloric acid is added to the metal finishing wastewater sample (after
removing the chromium) to make the solution 0.03M in chloride ions, more
than 90 percent of the cadmium can be removed from the solution.  This
extraction is again carried out using 25 percent Alamine 336 and an aqueous
phase to organic phase ratio of 100 to 1.  Unfortunately, about one per-
cent chromium and about 8 percent zinc is also extracted.  No copper or
nickel was extracted under these conditions.

Extraction of Zinc

     If the wastewater raffinate after removal of both chromium and cadmium
is further acidified with hydrochloric acid such that the chloride concen-
tration is 0.4M, approximately 85 percent of the zinc is removed from the
solution.  The extractions were again carried out using 25 percent Alamine
336-xylene solutions and aqueous to organic phase ratio of 100 to 1.  A
single extraction was used as in the other studies.

Extraction of Copper and Nickel

     In the screening phase of the study, copper and nickel showed some
promise of being extracted with Aliquat 336-S.  The extraction efficiencies
were low except in alkaline solutions.  No detectable quantities of copper
or nickel were extracted with Alamine 336 under the optimum conditions
described for chromium, cadmium, and zinc.

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 Selective Extraction of Chromium, Cadmium and Zinc

      In a typical laboratory extraction, the metal finishing wastewater was
 filtered through a no. 1 fluted filter paper.  To one liter of the filtered
 solution was added 5.0 ml of 0.4M hydrochloric acid.  A 25 ml sample of the
 wastewater was removed and analyzed for chromium, copper, cadmium, nickel
 and  zinc with an atomic absorption spectrophotometer.  To the remaining
 solution was added 10.0 ml of 25 percent Alandne 336-xylene solution.  The
 phases were then stirred in a 2 liter beaker for three minutes using a
 motor driven stirrer.  The resulting mixture was transferred to a liter
 separatory funnel and allowed to settle for twenty minutes.  The phases
 were  then separated.  A 25 ml sample of the aqueous phase was analyzed for
 cadmium, chromium, copper, nickel and zinc.

      To the raffinate from the first extraction was added 25 ml of concen-
 trated hydrochloric acid and 10.0 ml of 25 percent Alamine 336-xylene
 solution.  The resulting mixture was again extracted and its raffinate
 analyzed for the five metals.

      To the remaining raffinate from the second extraction was added 30 ml
 of concentrated hydrochloric acid and 10.0 ml of 25 percent Alamine 336-
 xylene solution.  The resulting mixture was extracted and its raffinate
 analyzed for cadmium, chromium, copper, nickel and zinc.  The results from
 eight analyses are shown in Table 1.  No copper or nickel was extracted in
 either of the extractions.

 Simultaneous Extraction of Chromium, Cadmium and Zinc

      To a liter of the filtered metal finishing wastewater was added 33 ml
 of concentrated hydrochloric acid.  Twenty-five ml of the solution were
 removed and analyzed for chromium, cadmium, zinc, copper and nickel. To
 the remaining solution was added 10.0 ml of 25 percent Alamine 336-xylene
 solution.  The phases were mixed using a magnetic stirrer for three minutes.
 The mixture was then transferred to a one liter separatory funnel and
 allowed to settle for ten minutes.  The phases were then separated and the
 aqueous phase again analyzed for the five metals.

      To the raffinate from the first extraction was added another 10.0 ml
 of the 25 percent Alamine 336-xylene in order to carry out a second extrac-
 tion.  The results of the ten analyses of the metal finishing wastewater
 of varying composition are shown in Table 2.  No copper or nickel was ex-
 tracted in either extraction.

 Reagent Loss

     A study was carried out to determine if any Alamine 336-xylene solution
would dissolve in the aqueous phase during the extraction processes.  A
 Dorhmann Model DC-50 Total Organic Analyzer was used in the investigation.
 The total organic carbon did increase during the extraction process.  Gen-
 erally, the TOC content increased approximately 50 ppm per extraction. The
extractions were carried out using the usual 100 to 1 aqueous to organic

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TABLE 1.  SELECTIVE EXTRACTION OF CHROMIUM, CADMIUM AND ZINC

Mean %
First Extraction
0.002M Chloride 88.
Second Extraction
0.03M Chloride 0.
Third Extraction
0.4M Chloride 0.
Total Metal
Extracted
Composition of Wastewaters:




CHROMIUM
Extd. Std.
6 4
65 1
55 0
89.8
Cr - 10.0
Cd - 4.1
Zn - 5.2
Cu - 0.3
Ni - 0.4
CADMIUM
Dev. Mean % Extd. Std. Dev.
.0 0.0 0.0
.09 94.1 1.65
.87 4.8 1.3
98.9
to 56.8 ppm
to 5.9 ppm
to 9.2 ppm
to 0.5 ppm
to 0.5 ppm
ZINC
Mean % Extd. Std. Dev
0.0 0.0
8.1 2.1
80.9 3.5
89.0






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                        TABLE 2.   SIMULTANEOUS EXTRACTION OF  CHROMIUM, CADMIUM AND ZINC
o
CHROMIUM CADMIUM
Mean °n Extd. Std. Dev. Mean % Extd. Std. Dev.
First Extraction 90.6 1.2 98.0 0.11
Second Extraction 0.0 0.0 1.4 0.86
Total Metal
Extracted 90.6 99.4
ZINC
Mean % Extd. Std. Dev.
83.3 0.11
15.4 1.8

98.7
       Composition of Wastewaters:   Cr -  8.0  to 9.0 ppm




                                    Cd -  3.7  to 4.0 ppm



                                    Zn -  4.8  to 5.2 ppm



                                    Cu -  0.3  to 0.5 ppm



                                    Ni -  0.4  to 0.5 ppm

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phase ratio and 25 percent Alamine 336-xylene solution.

Stripping and Recycling

     After extracting the toxic metal ions from the metal finishing waste-
water into the organic phase it is desirable to recover the metal regen-
erating the Alamine 336-xylene solvent in order that it nay be recycled.

     This process generally called stripping is very important in develop-
ing economic cyclic industrial processes.  A series of strippants were
investigated including sulfuric acid, ethylenediamine, EDTA and sodium
hydroxide.  Of these, sodium hydroxide proved to be most effective.

     In a typical stripping experiment, to 10 ml of the organic phase
(Alamine 336-xylene) containing 3 to 5 mg/ml chromium, 0.6 to 0.8 mg/ml
cadmium, and 1.0 to 1.5 mg/ml zinc is added 3.0 ml of 4.0M sodium hydroxide
solution.  The phases are mixed for three minutes in a 50 ml beaker using
a magnetic stirrer.  The mixture is allowed to settle for 15 minutes for
phase separation.  The organic phase was then analyzed for chromium, cad-
mium and zinc.  Stripping studies were carried out on ten solutions.  The
results (Table 3) show that more than 99.5 percent of the chromium, cadmium
and zinc were removed from the organic phase in a single stripping operation.

     The regenerated Alamine 336-xylene solution was used again to extract
the metals from the wastewater without loss of any efficiency.  Fifteen
cycles were carried out using the same solvent without  loss of efficiency.
No larger number of cycles were investigated.

Studies on Sludge

     The sludge samples were pale aquamarine in color indicating  the pre-
sence of copper or chromium.  It was quite thick and had many lumps.   It
had to be stirred for several hours to get a homogeneous mixture.

     The sludge was essentially insoluble under ordinary conditions.   About
70 percent dissolved on boiling with concentrated nitric acid, concentrated
hydrochloric acid or aqua regia.  The chromium was not  extracted  with  Ala-
mine 336-xylene solution.  Apparently it was in +3 oxidation state.  After
oxidizing the sludge with potassium permanganate it could be extracted.
Use of potassium permanganate is cost prohibitive, moreover, it is pollu-
tant itself.  Attempts to remove cadmium and zinc were  also unsuccessful.
Thus, detailed studies on sludge were discontinued.

Chemical Reactions and Mechanism

     The mechanism for the extraction of cadmium and  zinc from the metal
finishing wastewater is:

                            M+2 + 4C1" * MClJ

                          + 2H+

                                    11

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                  TABLE 3.  STRIPPING STUDIES


1.
2.
3.

Chromium
Cadmium
Zinc
Mean % Stripped
99.86
99.53
99.95
Std. Dev.
0.10
0.18
0.03
Stripping Solution:  Cr - 3 to 5 mg/ml



                     Cd - 0.6 to 0.8 mg/ml



                     Zn - 1 to 1.5 mg/ml



         Strippant - 4.0M NaOH

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The mechanism for removing the chromium is:

                2{R3N}Q + 2H+

                         Where RjN = Alamine 336

                                 M = Cd or Zn

                                 o = organic phase

                                 a = aqueous phase

     The complexes formed by cadmium, zinc and chromium with Alamine 336
are soluble in common organic solvents such as xylene, benzene and kerosene,
etc.

     The extraction parameters associated with the selective extraction of
chromium, cadmium and zinc are somewhat critical.  Chromium can generally
be removed without contamination by cadmium and zinc.  The chromium could
be  reclaimed  and returned to the plating bath.  There were some metal
finishing samples in which each of the three metals could be extracted sel-
ectively without any contamination of the other two metals.  A general
procedure with industrial potential appears unlikely for the selective ex-
traction of cadmium and zinc due to the great variation in wastewater.

     The simultaneous extraction of all three metals appears promising if
a second extraction is carried out.

     The metals can be easily stripped quantitatively from the Alamine 336-
xylene with 4  M  sodium hydroxide.   The amine solvent can be regenerated and
reused repeatedly, making the process attractive for industrial utilization.

     The reaction mechanisms for stripping with sodium hydroxide
follows :
                      207}o + 40H"?2{R3N}0

                   {CdCl,}  + 40H~;£ 2{RJO  + Cd(OH)0  + 4C1"
                  2     4 o            3, o         *•

                                                       + ZH 0

                   {ZnCl4>  + 60H~*2{iyO  + {Zn(OH) }° + 4C1
     The procedures discussed here merit further study.  Pilot plant studies
should be carried out on the processes, particularly the simultaneous ex-
traction method.  It shows promise for utilization by small metal finishing
plants.
                                    13

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                                REFERENCES
 1.  Pribil, R. and V. Vesely, The Extraction of Cadmium and Zinc and Their
     Complexemetrie Determination in the Presence of Other Elements, Collect.
     Czech, diem. Commun., 37, 13-21, 1972.

 2.  Mahlman, H., G.W. Leddicotte and F.L. Moore, Separation of Cobalt and
     Zinc by Liquid-Liquid Extraction, Anal. Chem., 26, 1939-1941, 1954.

 3.  Singh, O.V. and S.N. Tandon, Extraction of Cadmium as Chloride by High
     Molecular Weight and Quaternary Ammonium Salts, J. Inorg.  Nucl. Chem.,
     37, 609-611, 1975.

 4.  Florence, T. and J. Farrar, Liquid-Liquid Extraction of Nickel with
     Long-Chain Amines from Aqueous and Nonaqueous Halide Media, Anal.
     Chem., 40, 1200-1206, 1968.

 5.  McDonald, C.W. and T. Rhodes, Liquid-Liquid Extraction of Zinc with
     Aliquat 336-S-I from Aqueous Iodide Solutions, Anal. Chem., 46,
     300-301, 1974.

 6.  Maeck, W.J. et al, Extraction of the Elements as Quaternary Amine
     Complexes, Anal. Chem., 33, 1775-1780, 1961.

 7.  McDonald, C.W. and F.L. Moore, Liquid-Liquid Extraction of Cadmium with
     High Molecular Weight Amines from Iodide Solutions, Anal.  Chem., 45,
     983-985, 1973.

 8.  McDonald C.W. and T. Rhodes, Liquid-Liquid Extraction of Zinc with
     Aliquat 336-S-Br from Aqueous Bromide Solutions, Separ. Sci., 9,
     441-446, 1974.

 9.  McDonald, C.W. and T.S. Lin, Solvent Extraction Studies of Zinc and
     Cadmium with Aliquat 336-S in Aqueous Chloride Solutions,  Separ. Sci.,
     10, 499-505, 1975.

10.  McDonald, C.W. and G.H. Pahlavan, Liquid-Liquid Extraction of Cadmium
     with Alamine 336 from Aqueous Chloride and Bromide Media,  Separ. Sci.,
     12, 271-279, 1977.

11.  Moore, F.L., Liquid-Liquid Extraction of Zinc with High Molecular
     Weight Amines from Alkaline Cyanide Solutions, Separ. Sci., 10,
     489-497, 1975.
                                    14

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12. McDonald, C.W. and R.  Bajwa,  Removal of Toxic Metal Ions  from Metal
    Finishing Wastewater by Solvent Extraction,  Separ.  Sci.,  12,  435-445,
    1977.

13. Reed, A.K., An Investigation of Techniques for the  Removal of Chromium
    and Cyanide from Electroplating Wastes, Battelle Report # G-8925-2,
    40-49, July 1970.

14.  Reinhardt, H., Solvent Extraction for Recovery of  Metal  Waste,  Chem.
     and Ind., 210-213, March, 1975.
                                    15

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                                   TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing)
 1. REPORT NO.
  EPA-600/2-78-011
                              2.
                                                           3. RECIPIENT'S ACCESSION"NO.
 4. TITLE AND SUBTITLE
   REMOVAL OF TOXIC METALS FROM METAL FINISHING WASTE-
   WATER BY SOLVENT EXTRACTION
                                                           5. REPORT DATE
                February 1978  issuing date
               6. PERFORMING ORGANIZATION CODE
 7. AUTHOR(S)
                                                           8. PERFORMING ORGANIZATION REPORT NO.
   Curtis W. McDonald
 9. PERFORMING ORGANIZATION NAME AND ADDRESS
   Texas Southern University
   Houston, Texas   77004
               10. PROGRAM ELEMENT NO.
                  1BB610
               11. CONTRACT/GRANT NO.
                                                              R803332-01
 12. SPONSORING AGENCY NAME AND ADDRESS
   Industrial Environmental Research Laboratory-Cin, OH
   Office of Research  and Development
   U.S. Environmental  Protection Agency
   Cincinnati, Ohio  45268                       	
               13. TYPE OF REPORT AND PERIOD COVERED
                  Final
               14. SPONSORING AGENCY CODE
                  EPA/600/12
 15. SUPPLEMENTARY NOTES
 16. ABSTRACT
   This report describes a study on the removal of chromium, cadmium,  copper, nickel and
   zinc from metal  finishing wastewater using the high molecular weight amine Alamine
   336.  The study  consisted of an initial phase in which the extraction of the metal
   ions of interest was studied using synthetic solutions.  The second phase of the
   study involved extraction from actual metal finishing wastewater samples.

   The results of the study indicated that chromium, cadmium and  zinc  ions can be ex-
   tracted simultaneously or selectively using a 100-to-1 wastewater to Alamine-336-
   xylene solution.   The simultaneous extraction procedure appears  to  have some pro-
   mise for adoption at the industrial scale.  Copper and nickel  could not be satis-
   factorily extracted using this procedure.

   Chromium, cadmium,and zinc can be stripped from the organic phase with better than
   99.5 percent  efficiency using 4M NaOH.  The regenerated reagent  can be recycled
   and reused without any loss of extraction efficiency.  The procedures are reprodu-
   cible, rapid  and relatively simple.
                                KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
   Wastewater, chromium, cadmium? zinc*,
   copper, nickel,  solvent extraction,
                               sludge
                                              b.lDENTIFIERS/OPEN ENDED TERMS
                             c. COSATI Field/Group
   High molecular  weight
  amines*
   Selective extraction
   Simultaneous extraction
  Stripping, electroplatinc
     68D
 3. DISTRIBUTION STATEMENT

   Release  to Public
  19. SECURITY CLASS (ThisReport)
     UNCLASSIFIED
21. NO. OF PAGES
    24
                                              20. SECURITY CLASS (Thispage)
                                                 UNCLASSIFIED
                                                                         22. PRICE
EPA Form 2220-1 (9-73)
-16-
                                                      "' S GovtltNMENT WTING OFFICE: 1978-757-140/6694 Region No. 5-11

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