United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
EPA-600/2-79-204
November 1979
Research and Development
Coagulation and
Precipitation of Selected
Metal Ions from
Aqueous Solutions

-------
                  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 INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded  under the 17-agency Federal  Energy/Environment  Research and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations  include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects;  assessments of, and development of, control technologies for energy
systems; and integrated assessments of a wide range of energy-related environ-
mental issues.
                        EPA REVIEW NOTICE
This report has been reviewed by the participating Federal Agencies, and approved
for  publication. Approval does not signify that the contents necessarily reflect
the  views and policies of the Government, nor does mention of trade names or
commercial products  constitute endorsement or recommendation for use.

This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.

-------
                                    EPA-600/2-79-204

                                        November 1979
Coagulation and Precipitation
      of Selected  Metal Ions
    from  Aqueous Solutions
                      by

             C.W. Westbrook and P.M. Grohse

               Research Triangle Institute
                  P.O. Box 12194
         Research Triangle Park, North Carolina 27709


               Contract No. 68-02-2612
                  Task No. 103
              Program Element No. IBB610


          EPA Project Officer: John S. Ruppersberger
         Industrial Environmental Research Laboratory
      Office of Environmental Engineering and Technology
            Research Triangle Park, NC 27711
                   Prepared for

        U.S. ENVIRONMENTAL PROTECTION AGENCY
           Office of Research and Development
               Washington, DC 20460

-------
                                  ABSTRACT

     Laboratory jar tests were conducted to develop data on the removal
from aqueous solution of 12 metal ions of environmental concern.  The
project, which was of very limited scope, provides initial screening
data only.  Thus, coagulants were evaluated at only two dose levels (1.1
and 1.5 stoichiometric), no combinations of metals or coagulants were
evaluated, and no attempt was made to optimize precipitation conditions.
The metal ions tested were:   Al+3, Be+2, Bi+3, Cr"1"3, Mo+3, Sb+3, V+3,
  +2    +3    +4    +3    +5
Zn  , Ti  , Se  , As  , As  .  Treatment chemicals used were:  lime
(Ca(OH)2), sodium sulfide (Na2S), alum (A1K(S04)2), and ferrous sulfate
(FeS04).
     Chromium, aluminum, and titanium concentrations were reduced to
below 0.5 mg/2. at pH 8 by lime addition.  Alum was effective for titanium
removal (probably due to pH effects) and marginally effective for vanadium
and arsenic (+5).  Beryllium, bismuth, zinc, and titanium were reduced
to below 1 mg/a by sodium sulfide treatment.  Ferrous sulfate was not
effective in removing antimony, selenium, or arsenic (+5).
     Additional treatment with a flocculent-coagulant, i.e., organic
polymer, may be required for the consistent removal of the fine suspension
formed by some of the metal ion-coagulant systems tested.
                                      in

-------
                                  CONTENTS

Abstract	i'11
Tables	v
Acknowledgement	V1*
   1.0  Introduction 	  1
   2.0  Summary and Conclusions	2
   3.0  Background Information 	  6
   4.0  Test Data.	8
            4.1  Reagents and Solutions	8
            4.2  Coagulant Dosage Calculations 	  9
            4.3  Test Procedures	10
            4.4  Atomic Absorption Analysis	10
            4.5  Test Results	11
                                     iv

-------
                                   TABLES

Number                                                                Page
  1.  Summary of Results	4
  2.  Test Results	;	12

-------
                               ACKNOWLEDGEMENT

     This report has been submitted by Research Triangle Institute in partial
fulfillment of the requirements of EPA Contract No.  68-02-2612,  Task 103.
The authors are grateful to Mr. John Ruppersberger for his advice and assis-
tance.  RTI also wishes to express its appreciation  to Mr. Jack  Robertson of
Catalytic, Inc. and to J. M. Cohen of EPA - Cincinnati for their comments
and suggestions on the work.
                                       vi

-------
                              1.0  INTRODUCTION

     The requirements of the 1977 Amendments to the Clean Water Act
emphasize the control of "Toxic" or "Priority Pollutants."  In addition
to the 13 metals designated as toxic and which are to be.controlled by
Best Available Technology Economically Achievable regulations that
industry must meet by July 1, 1984, there are other metals and non-
metals of environmental and health concern.
     Although a number of highly effective methods continue to become
available for removal of heavy metals from wastewater, chemical precipi-
tation is currently the most commonly used and practical technique and
is possibly the best approach for coping with the metals removal problem
up to and including 1984.
     The purpose of this project was to develop specific data for incor-
poration into a wastewater treatability model.  As such, the scope of
work was specific and limited.  Each metal ion was to be treated with a
specific chemical at two dose levels (1.1 and 1.5 stoichiometric) with
the final pH in the range 6-9.  RTI also evaluated some other pH's and
chemicals where these specified conditions proved to be inappropriate.
     All experiments were simple jar tests using analytical grade re-
agents and distilled water as the medium.  We recognize that the variable
chemical environment found in actual wastewater can affect the removal
of metal ions present.  However, to provide a consistent data base for
use in the model, this variability was reduced substantially by using
distilled water.
     Section 2 of this report summarizes the data obtained and conclusions
that can be drawn.  Section 3 presents some background information that was
obtained on the metal ions and coagulation methods tested.  The test proce-
dures and test results are presented "in Section 4.

-------
                        2.0  SUMMARY AND CONCLUSIONS

     Table 1 summarizes the test data obtained.  The first two columns give
the metal ion and coagulant(s) tested.  Columns three and four give the
stoichiometric ratio (see Section 3) for the coagulants and the final pH,
respectively.  The fifth column gives the concentration of metal ion remain-
ing (typically 100 mg/n initially) in the solution after filtration by a
Whatman No. 40 filter (medium porosity) which may be similar to that expect-
ed from clarification and sand filtration.  The last column gives the metal
ion concentration obtained after washing the precipitate, suspending it
(shaken by hand at infrequent intervals) in water for 24 hours, and filtering
through a 0.8 p millipore filter.  This information is useful for situations
where physical-chemical sludges generated must be washed before disposal and
as an estimate of the Teachability of the sludge.
     The data show that pH adjustment (lime addition) is effective for the
removal only of Al   , Cr  , and Ti  .  Alum is effective for the removal of
  +3
Ti  , probably due to pH effects, and marginally effective in the control of
V+3 and As+5.' Removal of Be+2, Bi+3, Zn+2, Ti+3 was effected by Na2S addi-
tions.  Ferrous sulfate was not effective for the removal of Sb  , Se   , or
As  .  Mo   , Sb   , Se  , As   , and As   were not effectively removed by the
coagulants used for  these ions (Mo   and As   were tested only with Na2S;
all coagulants were  used with the remaining three) under the conditions used.
     Aluminum hydroxide becomes more soluble as the pH is raised above 8.
Therefore, optimum control will be obtained between pH 5 and pH 7.  Several
of the test solutions, most notably AT, Cr, and Zn, appeared to be somewhat
turbid after filtration.  Some of these were reanalyzed after standing for
one day.  The original Zn solution had been discarded before we observed
that some of the solutions cleared on prolonged standing.  Duplicate experi-
ments were performed and the solution allowed to stand"3 hours before being
filtered.  In all cases a substantially lower metal concentration was obtained.

-------
This indicates that some of the precipitate formed is very finely divided.
To adequately remove the metals from solution, particularly when lime or
H&2^ is used, may require the use of an additional coagulant, i.e., organic
polymer.
     It will also be observed that a number of cases occurred where the metal
concentration was higher from the resuspended precipitate filtrate than in
the original test solution filtrate.  The effect is apparently not due to
suspended solids since the original filtrate passed through a medium porosity
filter, Whatman 40, whereas the resuspended particulate .filtrate passed
through a fine filter, 0.8 v millipore.  When the precipitate was washed, ions
present in the original test solution were removed.  Thus, one might conclude
that these ions reduce the solubility of the precipitate and/or effect the
desorption of the metal from the precipitate.  This implies that some precau-
tions should be taken in the washing and/or disposal of these sludges.

-------
                     TABLE 1.  SUMMARY OF RESULTS
Metal
Al+3




4-7
Be d



, Q
Bi J



Cr+3




Mo+3
J.O
Sb+3




y+3




Coagulant
Ca(OH)2





Alum

Ca(OH)2
Na9S
c.
Na2S



Ca(OH)2




Na0S
c.
Alum

Ca(OH)2
Na2S
FeS04
Na2S

Ca(OH)2

Alum
Stoichiometric
Ratio
-
-

-
_

1.1
1.5
-
1.1

1.1
1.5
1.1
1.5
-
_

-
-
1.1

1.1
1.5
-
1.1
1.1
1.1
1.5
-
-
1.1
Final
pH
7.0
8.0

9.0
10.0

7.3
6.9
8.0
8.0

8.9
9.2
8.0
8.0
7.0
8.0

9.0
10.0
7.5

7.2
8.3
8.0
6.6
8.0
8.5
8.5
8.0
10.0
7.0
Metal
Filtrate Solubility from
mg/A Solids, mg/&
5 (0.4)*
0.4
*
31 (20)
48

> 50
16
MOO
0.3

< 0.03
< 0.03
< 0.5
2.5
10
0.6
if
12 (0.4)
0.12
No reaction

22
12
^ 50
13
10
> 50
> 50
32
27
20
< 0.1
1.1


6.4

16
21

0.2

0.05
< 0.03


< 0.1
< 0.05


< 0.05
occurred

8.4
13


.
1.7
1.6



 Value obtained after one day aging.
(Continued)
                                      4

-------
TflRI F 1
Metal
Zn+2


T1+3






SeH


As+5



As*3

Coagulant
Na2S


Alum


Na2S



Ca(OH)2
Na2S
Ca(OH)2
Alum
FeS04
Na2S

Ca(OH)2
Alum
FeS04
Na2S

Stoichiometric
Ratio
1.1
1.5
1.1
1.5
1.1
1.5
1.1
1.1
1.1
1.1
1.5
1.1
1.5
-
1.1
1.1
1.1
1.5
-
1.1
1.1
1.1
1.5
Final
PH
8.5
7.0
8.0
8.0
8.6
7.3
7.0
8.8
8.6
8.0
8.0
8.0
8.0
8.5
10.0
7.2
8.0
5.5
9.6
8.0
7.0
8.0
5.0
5.5
Filtrate
mg/2.
1.2
> 50
0.07
0.6
< 0.5
< 0.5
< 0.1
< 0.5
< 0.5
0.2
0.3
< 0.1
> 50
> 50
MOO
MOO
MOO
MOO
MOO
39
6.0
MOO
25
18
Metal
Solubility from
Solids, mg/£
0.7
1.1
5
5


0.2


0.8
0.4
< 0.1
0#








#
 Probably  indicates  no  Se  in the precipitate.

-------
                        3.0  BACKGROUND INFORMATION

     A number of literature sources, listed at the end of this section, were
consulted to determine appropriate precipitation conditions and other re-
quired information.  The data accumulated is not a complete review of the
literature available on the subject.
      ,+3
     Al
     Be3
          A1(OH)3 is amphoteric (soluble at both low and high pH).  The solu-
          bility product is about 2 x 10"33 (5 x 10"8 mg/fc Al) at pH 7.
          Aluminum sulfide cannot be prepared in aqueous solution.
     Bi+3
     Cr+3
     Sb+3
        is amphoteric.  The sulfide reportedly decomposes in
aqueous solution.  The sulfate is very water soluble.

The hydroxide is not amphoteric.  The water solubility is about
0.0014 gm/A (1.1 mg/A Bi).  The sulfide can be formed in aqueous
solution and has a solubility of about 0.00018 gm/A (0-14 mg/A).

The "hydroxide" is thought to be merely a hydrated form of the
oxide.  The compound is amphoteric dissolving in excess strong
base.  The approximate solubility is 0.00064 mg/A.  The sulfide
cannot be made in aqueous solution.  The sulfate is very water
soluble.

The hydroxide solubility is about 2 gms/A (1300 mg/A Mo+3).  The
sulfide is slightly soluble in water.

The oxide is amphoteric.  The sulfide can be formed in acid solu-
tion (up to about pH 6) and has a solubility of about 0.0018 gm/A
(1.3 mg/A Sb).  The sulfide is soluble in neutral to alkaline
                            6

-------
Zn*2
Se+4
     solutions and  in solutions containing excess alkali sulfide  (^S)-

     The  oxide is basic  (soluble  in  acid  solution) and slightly soluble
     in water.  Although  the  sulfide is insoluble in water,  it is
     soluble  in alkali sulfides.

     The  hydroxide  is amphoteric  and when formed in aqueous  solution
     forms  a  gelatinous  precipitate.  The solubility product is about
     2 x  10"14 indicating the hydroxide is slightly soluble  in water.
     The  sulfide  is white and has a  solubility  product of  about
     1 x  10"23.   ZnS(a)  has a water  solubility  of 0.0069 gm/A (4.6  rag/A
     In)  while ZnS(P) has a solubility of 0.00065 gm/£  (0.44 rag/A Zn).
     The  sulfide  is soluble at pH less than  6.

     The  oxide  is very water  soluble. The sulfide is  insoluble in  water
     but  dissolves in excess  sulfide reagent.
As+3, As+5
     The  arsenic  oxides  are quite soluble in water.  Arsenic(V) sulfide
     has  a water  solubility of 0.0014 gm/ji  (0.6 mg/£ As) and arsenic
     (III) sulfide's water solubility is  0.0005 gm/ji  (0.3  mg/ji As).
     Both sulfides are  soluble at pH's above 6  and also are  soluble in
     excess alkali  metal  sulfide  (Na2S).
Sources
     Handbook of  Chemistry and Physics, 45th Edition,  The  Chemical  Rubber
     Co., 1964.
     Fundamentals of Analytical  Chemistry, Skoog and West, Holt,  Rinehart
     and  Winston, Inc.,  1963.
     Inorganic Reactions  and  Structure, E. S.  Gould, Holt, Rinehart and
     Winston, Inc., 1962.
     Calculations of Analytical  Chemistry, Hamilton and Simpson,  McGraw-
     Hill Book Co., Inc., 1960.
     General  Chemistry,  Miller and Babor, Wm.  C. Brown  Co.,  1965.

-------
                               4.0  TEST DATA
4.1  REAGENTS AND SOLUTIONS
     All reagents used were analytical grade.  All test solutions, except
molybdenum and bismuth, were prepared containing 100 mg/£ of the metal  ion.
Lime (Ca(OH)2) and ferrous sulfate (FeSO^-7 H20) were added as dry powders.
Alum (AlK(SO^,)2i12 H20) was weighed out before each test and dissolved in
30 ml of water before addition.  A stock solution, prepared before each
series of tests, of sodium sulfide (Na,,S'9 H20) containing 10 gms/£ was added
to the test solutions using pipets.
     The test solutions were prepared as follows:
             +3
Aluminum - Al     0.1000 gm of aluminum wire was dissolved in dilute (3N) HC1
and diluted to 1 liter.
Beryllium - Be*2.  2.0758 gms of Be(N03)2-3 H20 (F.W. 187.07) was dissolved
in water and diluted to 1 liter.
Bismuth - Bi   .  0.0853 gm bismuth metal was dissolved in dilute (3N) HNO,
	                                                          o
and diluted to 1 liter.  Bi   concentration was 85.3 mg/£.
Chromium - Cr*3.  0.7695 gm Cr(N03)3'9 H20 (F.W. 400.15) dissolved in water
and diluted to 1 liter.
               J.O
Molybdenum -Mo  .  0.2 gm MoCU suspended in water for 24 hours, filtered
and analyzed by A.A.  Mo concentration was 5.0 mg/£.
Antimony - Sb*3.  0.1874 gm SbCl3  (F.W. 228.11) dissolved in dilute HC1 and
diluted to 1 liter.
Vanadium - V+3.  0.1471 gm V203 (F.W. 149.884) dissolved in dilute HN03 and
diluted to 1 liter.
Zinc - Zn*2.  0.1000 gm zinc metal dissolved in HC1 and diluted to 1 liter.
Titanium - Ti+3.  0.3220 gm TiCl3  (F.W. 154.26) dissolved in dilute HC1 and
diluted to 1 liter.
Selenium - Se  .  0.1633 gm H2Se03 (F.W. 128.97) dissolved in water and
diluted to 1 liter.

-------
Arsenic - As  .   100 ml of arsenic A.A. standard (1000 mg/£) diluted to
1 liter.
Arsenic - As*3.   0.1320 gm As203 (F.W. 197.84) dissolved in dilute HC1 and
diluted to 1 liter.
4.2  COAGULANT DOSAGE CALCULATIONS
     Below are representative calculations of the coagulant dosage required
for each coagulant used (except lime which was used for pH adjustment only).
Alum.  Calculations were based on the assumption that the metal sulfate  is
formed simply to provide a consistent technique for alum addition.  The
assumption is not necessarily valid since metal ion removal probably takes
                                                                    +2
place by adsorption on the aluminum hydroxide floe that forms.  2 Be   +
A1K(S04)2 ->• 2 BeS04.  500 ml of a 100 mg/i Be"1"2 solution contains 50 mg  Be"1"  .
50 mg * 9.012 gms/raole Be"1"2 = 5.548 millimoles/500 ml.  Since the stoichio-
                                                         +2
metric requirement is 0.5 millimole alum per millimole Be  , 5.548/2 =
2.774 millimoles alum required for stoichiometric addition.  Therefore,  for
a 1.1 stoichiometric addition, 1.1 x 2.774 = 3.051 millimoles are required.
Since alum has a formular weight of 474.39, one millimole is 0.4744 gm.
3.051 millimoles alum is 1.4476 gms.
     The complete calculation is:
     ((50 mg * 9.012 mg/millimole) * 2) x 1.1 x 0.4744 gm/millimole =
     1.4476 gms.
Na^S.  Calculations are based on the assumption the metal sulfide is formed.
Bi 3 + 1.5 Na2S-9 H20 ->• 1/2 Bi2S3.  500 ml of an 85.3 mg/J. Bi3 solution  con-
tains 0.2058 millimole.  Since 1.5 millimoles of the sulfide are required per
millimole of Bi   and one millimole of Na,,S'9 H20 is 0.24018 gm, the sulfide
dosage required for 1.1 stoichiometry is (1.1)(1.5)(0.2058)(0.24018) = 0.0816
gm.  The sulfide stock solution (10 gms/100 ml) contains 0.1 gm/ml.  Thus
0.816 ml is required for the test.
Ferrous Sulfate.  The calculations assume the sulfate is formed  (to provide
a consistent basis for addition) although metal ion removal may actually
occur by adsorption on the ferrous (-ic) hydroxide floe formed.  Sb   +
1.5 FeS04-7 H20 -> 1/2 Sb2(S04)3.  500 ml of a 100 mg/£ Sb+3 solution contains
0.4107 millimole.  Since 1.5 millimoles of FeS04 7 H20 weighing 0.2781 gm per

-------
millimole are required per millimole  of  Sb+3,  (1.1)(1.5)  x  (0.4107)(0.2781)  =
0.1885 gm FeS04'7 H20 are required  for a 1.1 stoichiometric  dosage.
4.3  TEST PROCEDURES
     One liter of the metal  ion  solution was prepared  as  previously described.
The solution was equally divided and  placed in  two  1 liter  flasks.  A magnet-
ic stirrer and a pH measuring  electrode  were also placed  in  the  flask.  The
initial pH was measured and  adjusted  as  necessary using appropriate strength
NaOH or HC1.  The selected coagulant  was then added and the  solution rapidly
agitated for about one minute.   The pH was measured and adjusted as required.
Stirring was then reduced to that required to  keep  the precipitate in suspen-
sion and maintained for 14 minutes.  The suspension was then filtered through
Whatman No. 40 filter paper.  The filtrate was  retained for  atomic adsorption
analysis.  The solids collected  were  thoroughly washed with  distilled water
and resuspended  (shaken by hand  at infrequent  intervals)  in  about TOO ml of
distilled water.  After 24 hours, this suspension was  filtered through a
0.8 y millipore  filter and the filtrate  retained for A.A. analysis.
     Table 2 shows that the  initial pH's were  generally quite low compared
to typical wastewater values.  Operating in this manner,  precipitates of
A1(OH)3 and Fe(OH)2 did not  form immediately when alum and  ferrous sulfate
were added.  Since these compounds were  soluble, they  were  completely mixed
into the solution before the pH  was raised to  develop  the floe.  This
technique could  not be used  with Na,,S because  the H2S  which  would be formed
would escape from the solution.
     Only the  sulfide solution (and lime, of course) had  any measurable
effect on the  initial pH.  Addition of HC1 was  required to  control the pH
rise caused by the addition  of this strong caustic  solution.
4.4  ATOMIC ABSORPTION ANALYSIS
     All analyses were completed on a Perkins-Elmer Model 603 atomic absorp-
tion instrument  which has background  correction. Air/acetylene  or N20/acety-
lene flames were used as appropriate. A model  2100 Heated  Graphite  Furnace
accessory was  used for Ti, Mo  as well as those  metals  having a concentration
below 0.5 mg/£,.  Electrodeless discharge lamps  were used  for As, Se, Sb, and
Bi.  Hollow Cathode lamps were used for  other  metals.  Concentrations of the
                                     10

-------
metals in the test solutions were determined by comparison with known concen-
trations of the metals.  In addition, the method of standard additions (adding
a known amount of the test metal to the solution) was used to check the ana-
lytical results.
4.5  TEST RESULTS
     Table 2 gives the test results and a comment on the precipitate formed.
Unless otherwise indicated, the initial concentration of metal ion was 100
mg/a.
                                      11

-------
                                 TABLE 2.  TEST  RESULTS
Metal
Sb«
Sb*3
Be+2
Be*2
T1+3
T1+3
C/3
Cr+3
Al+3
Al+3
B1+3
Bi+3
Set4
Se+4
_i_O
V"1"3
As+5
As*5
Coagulant
Type Dose
Alum
Alum
Alum
Alum
Alum
Alum
Lime
Lime
Lime
Lime
Na2S
Na?S
c~
Na2S
Na2S
Na2S
Na9S
£
1.5
1.1
1.1
1.5
1.1
1.5
M
-
_
_
1.1
1.5
1.1
1.5
1.1
1.5
1.1
1.5
pH at pH after
Test Start Addition
1.5
1.5
3.3
3.3
2.4
2.4
3.2
3.2
1.5
1.5
6.1
5.8
6.2
5.7
6.1
6.2
5.6
7.4
1.6
1.1
3.3
3.6
2.5
2.6
10.0
8.0
8.0
10.0
8.9
9.2
8.0
8.5
7.6
8.0
6.4
9.6
Final
PH
8.3
7.2
7.3
6.9
8.6
7.3
10.0
8.0
8.0
10.0
8.9
9.2
8.0
8.5
8.5
8.5
5.5
9.6
Filtrate
Cone . ,
mg/Ji
12
22
> 50
16
< 0.5
< 0.5
0.12
0.06
0.4
48
< 0.03*
< 0.03*
> 50
> 50
> 50
> 50
'vlOO
'vlOO
Washed
Filter
Cone . ,
13
8.4
16
21


< 0.05
< 0.05
1.1
6.4
0.05
< 0.03
0
0
1.7
1.6
-
_
Comment
Fine white needles
formed on addition.
Solids form at
pH 4.5.
Light blue solids
form on addition.
Turbid at pH 5.7
fine dispersed
solids.

Turbid at pH 6.
Dark brown solids
slow settling fines.
Cloudy yellow sus-
pension, probably
sulfur.
Dark green-brown
soln. no solids
evident.
Colorless, clear
_ _ ^ . *
                                                                                solution.
 Initial concentration 85 mg/£.
(Continued)

-------
TABLE 2.  (Continued)
Metal
+3
T1 J
Zn+2
Zn2
Se+4
Se+4
v+3
_
Sb
4-9
Be+2
+R
As
,
v+j
• o
Cr+3

Cr **
A1+3
„
Al d
Coagulant
Type Dose
Na2S 1.1
Na2S 1.5
Na2S 1.1
Na2S 1.5
Lime
Alum 1.1
Lime

Lime

Lime

Lime

Lime

Lime

Lime
Lime

Lime
pH at
Test Start
7.1
7.2
6.3
6.2
3.3
3.3
1.1

1.0

4.1

1.2

8.0

3.5

3.5
1.5

1.5
pH after
Addition
9.7
9.9
6.8
7.0
9.8
3.3
7.9

8.0

8.0

8.0

10.0

9.0

7.0
7.0

9.0
Final
pH
8.8
8.6
8.5
7.0
9.8
7.2
7.9

8.0

8.0

8.0

10.0

9.0

7.0
7.0

9.0
Washed
Filtrate Filter
Cone . , Cone . ,
mg/ & mg/ a
< 0.5
< 0.5
1.2 0.7
> 50 1.1
MOO
MOO
32

^50

MOO

39

27
H
12 (0.4)ff

10 < 0.1
5 (0.4)# < 0.1
#
31 (20)ff
Comment
White solids,
turbid suspension.
White solids,
turbid suspension.
Clear
Alum precipitate
Brown solution,
discrete particles.
Slow settling white
solids.
Light blue gelat-
inous precipitate.
Milky colored
suspension.
No precipitate
formed .
Filtered solution
turbid but clears
on prolonged stand-
ing.
Milky, clears on
standing.

#
 Concentration determined after one day settling.

(Continued)

-------
TABLE 2.  (Continued)
Coagulant
Metal
Ti
Ti+3

V
+5
As b
Zn"1"2
+2
Zn L
Mo+3
Bi+3

Bi J
Be+3
_
Sb J
_
Ti
. *%
Ti+3
Se+4
Type
Lime
Alum

Alum

Alum
Na9S
L.
Na2S
Na2S
Na?S

Na9S
C

Na9S
L.
Na9S
c.
Na9S
FeSO,
Dose

1

1

1
1

1
1
1

1
1

1

1

1
1
—
.1

.1

.1
.1

.5
.1
.1

.5
.1

.1

.1

.5
.1
pH at pH
after
Test Start Addition
2.5
2.5

1.0

1.0
6.6

5.6
5.4
5.0

4.6
3.8

4.8

5.8

5.2
3.1
8
7

7

7
9

10
8
10

10
6

Held at

Held at

Held at
3
.2
.0

.0

.0
.8

.3
.8
.5

.4
.8

7

8

8
.1
Final
pH
8.
7.

7.

7.
8.

8.
7.
8.

8.
8.

6.

8.

8.
8.
2
0

0

0
0

0
5
0

0
0

6

0

0
0
Washed
Filtrate Filter
Cone., Cone.,
mg/fc
< 0.
< 0.

2.

6.
0.

0.
5f
< 0.

2.
0.

13

0.

0.
^100
mg/K,
1 < 0.1
1 0.2

0

0
07 5

6 5

5

5
3 0.2



2 0.8

3 0.4

Comment
White solids.
Immediate solids
formation.
Brown solids,
easily settled.
Milky solution.
Fluffy blue-white
solids.

No reaction
Reddish-brown solids
easily settled.

Cloudy, poor
settling.
Orange, poor
settling.
Turbid, white
solids.

Iron hydroxide
  Initial concentration 5
 (Continued)
                                                                               precipitate.

-------








Coagulant
Metal
Sb
As
As

As
+3
+5
+3
+•?

Type
FeS04
FeSO.
*t
c.
Na9S
Dose
1.1
1.1
1.1

1.5


PH
Test
5
5
4

3


at
Start
.0
.1
.5

.5 Held


pH


after
Addition
5
8
10

at
.0
.0


6


Final
pH
8.0
8.0
5.0

5.5

Filtrate
Cone . ,
mg/fc
10
MOO
25

18
Washed
Filter
Cone . ,
mg/& Comment








Cloudy, yellow
solution,
settling.
poor


-------
                                TECHNICAL REPORT DATA
                          (Please read Instructions on the reverse before completing}
1. REPORT NO.
  EPA-600/2-79-204
                                                      3. RECIPIENTS ACCESSION NO.
4. TITLE AND SUBTITLE
Coagulation and Precipitation of Selected Metal Ions
 from Aqueous Solutions
                                                      S. REPORT DATE
                                                      November 1979
                                                      6. PERFORMING ORGANIZATION CODE
7. AUTHOH(S)
C.W. Westbrook and P.M. Grohse
                                                      8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Research Triangle Institute
P.O. Box 12194
Research Triangle Park, North Carolina
                                                      10. PROGRAM ELEMENT NO.
                                                      1BB610
                                                      11. CONTRACT/GRANT NO.

                                                      68-02-2612,  Task 103
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC  27711
15. SUPPLEMENTARY NOTES

62, 919/541-2733.
                                                       13. TYPE OF REPORT AND PERIOD COVERED
                                                       Task Final; 6-10/79	
                                                       14. SPONSORING AGENCY CODE
                                                        EPA/600/13
                                                        •••^••^•••^^••^•••••^^•^•^••••••i
                              project officer is John S. Ruppersberger, Mail Drop
 16. ABSTRACT
           The report gives results of laboratory jar tests to develop data on the re-
moval from aqueous solution of 12 metal ions of environmental concern. The project,
of very limited scope, provides initial screening data only: coagulants were evaluated
at only two dose levels (1.1 and 1. 5 stoichiometric), no combinations of metals or
coagulants were evaluated, and no attempt was made to optimize precipitation condi-
tions. The 12 metal ions were: Al(+3), Be(+2), Bi(+3), Cr(+3), Mo(+3), Sb(+3),
V(+3), Zn(+2), Ti(+3), Se(+4), As (+3),  and As(+5). Treatment chemicals used were
lime, sodium sulfide,  alum, and ferrous suliate.  Cr(+3), Al(+3),  and Ti(+3) concen-
trations were reduced to below 0. 5 mg/1 at pH 8 by lime  addition.  Alum was effective
for Ti(+3) removal (probably due to pH effects) and marginally effective for V(+3)
and As(+ 5).  Be(+ 2), Bi(+ 3), Zn(+ 2), and Ti(+ 3) were reduced to below 1 mg/1 by
sodium sulfide treatment. Ferrous sulfate was not effective in removing Sb(+3),
Se(+4),  or As(+5).  Additional treatment with a flocculent-coagulant (e.g. , organic
polymer) may be required for the consistent removal of the fine suspension formed
by some of the metal ion-coagulent systems tested.
17.
                             KEY WORDS AND DOCUMENT ANALYSIS
                 DESCRIPTORS
                                          b.lDENTIFIERS/OPEN ENDED TERMS
                                                                  c. COS AT i Field/Group
 Pollution
 Metals
 Ions
 Solutions
 Precipitation
 Coagulants
                    Calcium Hydroxides
                    Alums
                    Iron Sulfate
                    Flocculents
Pollution Control
Stationary Sources
Metal Ions
Aqueous Solutions
Sodium Sulfide
13B      07B
11F,07B
07D,20H
                                                                  06O,11G
13. DISTRIBUTION STATEMENT

 Release to Public
                                          19. SECURITY CLASS (ThisReport)
                                          Unclassified
                                                                   21. NO. OF PAGES
                                          20. SECURITY CLASS (Thispage)
                                          Unclassified
                                                                  22. PRICE
EPA form 2220-1 (9-73)

-------