I
PB85-200038
Removal and Recovery of Fluoborates and
Metal Ions from Electroplating Wastewater
New Jersey Inst. of Tech., Newark
Prepared for
Environmental Protection Agency, Cincinnati, OH
May 85
DJS.
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EB85-20Q038
EPA/600/2-85/054
Hay 1985
REMOVAL AND RECOVERY OF FLUOBORATES AND METAL IONS FROM
ELECTROPLATING HASTEWATER
by
John W. Liskowltz, Vincent N. Cagnatl,
Terrance Hunter and Ray Haralson
New Jersey Institute of Technology
Newark, NJ 07102
Grant No. R 804710
Projec* Officer
Mary K. Stinson
Organic and Inorganic Chemicals and Products Branch
Hazardous Waste Engineering Research Laboratory
Cincinnati, Ohio 45268
HAZARDOUS WASTE ENGINEERING RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
"NATIONAL TECHNICAL
INFORMATION SERVICE
Of CO*«8CI
o. »*. am
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TECHNICAL REPORT DATA
(Rear ma Imurucnont on rt« rrvtnt t*lort compttnnfi
•E»ORT NO.
EPA/600/2-85/054
3 "'NT
. TI , LE -NO SUBTITLE
REMOVAL AND RECOVERY OF FLUOBORATES AND METAL
IONS FROM ELECTROPLATING WASTEUATER
t. REPORT OATE
Mav 1985
•. PERFORMING ORGANIZATION CODE
7 AUTHORlS)
John W. Liskowitz, Vincent N. Cagnatl,
Terrance Hunter and Ray Haralson
t. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION '.-MS ANO AOOREU
NEW JERSEY INSTITUTE OF TECHNOLOGY
323 HIGH STREET
NEWARK, NEW JERSEY 07102
10. PROGRAM cLcMENT NO.
1BB610
II. CONTRACT CRANT NO.
R 804710
12 <1»ONSO«»ING AGENCY NAME ANO ADDRESS
HAZARDOUS WASTE ENGINEERING RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OH A5268
13. TYPE OP REPORT ANO PERIOD COVERED
FINAL
14. SPONSORING AGENCY CODE
EPA/600/12
is. SUPPLEMENTARY NOTES
16. ABSTRACT
Two separate methods for the treatment of fluoborate wastewater frost the electron
plating of tin. solder, copper and nickel stripping were investigated. These involved!
specific ion flotation and electrodialysis to treat dilute waste streams from single
tank rinsing or concentrated ^astewaters fron counter-current or series rinsing,
respectively.
The fluoborate ion was found to bind with an alkylamine acetate by displacement
of the acetate group and can be removed from dilute waste stream either by air flo-
tation or ultrafiltration. Ultrafiltration provided greater rates of removal than air
flotation. The surfactant can be recovered for reuse hy electrolysis.
A new high density low porosity graphite anode that is resistant to the corrosive
properties of fluoboric acid electrolyte was developed for electrodialysis treatment
of the tin, solder and copper fluoborate containing wastewaters. Fluoboric acid
electrolyte was used to rrevent contamination of the products with sulfate ion. Re-
coveries of the metal ions were in excess of 902 with the stannous ion being preferen-
tially concentrated in the product and with the stannic ion remaining preferentially
in the feed. In general , recoveries of the fluoborate ions were in excess of 80*.-
KEY WORDS ANO DOCUMENT ANALYSIS
DESCRIPTORS
b.lOENTIFISRS/OPEN ENDED TERMS Ic. COSAT* Field/Croup
specific ion flotation, electrolysis,
ultrafiltration, electrodialysis
fluoborates, surfactants,
copper, nickel, tin, and
solder fluoborate plat-
ing wastewaters
13 B
13 DISTRIBUTION STATEMENT
Release to Public
19 SECURITY CLASS iTha Rtforti
Unclassified
21 NO. Of "AGES
90
2O. SECUR'TY CLASS iTtia pagll
Unclassified
IPA Form 2220-1
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DISCLAIMER
The Information In this document has been funded wholly or 1n part by
the United States Environmental Protection Agency under Grant No. 804710
to the Kew Jersey Institute of Technology. It has been subject to the
Agency's peer and administrative review, and it has been approved for publi-
cation as an EPA document. Mention ,of trade names or commercial products
does not constitute an endorsement or recommendation for use.
ii
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FOREWORD
Today's rapidly developing and changing technologies and Industrial
products and practices frequently carry with them the increased generation
of solid and hazardous wastes. These materials, if improperly dealt with,
can threaten both,public health and the environment. Abandoned waste sites
a.nd accidental releases of toxic and hazardous substances to the environment
also have important environmental and public health implications. The
Hazardous Waste Engineering Research Laboratory assists in providing an
authoritative and defensible engineering basis for assessing' and solving
these problems. Its products support the policies, programs and regulations
of the Environmental Protection Agency, the permitting and other responsi-
bilities of State and local governments and the needs of both large and
small businesses in handling their wastes responsibly and economically.
This report describes a laboratory process to remove and recover
fluoborates and metals from platinu rinsewaters. Several methods were
investigated including specific ion flotation, ultrafiltration, electrolysis,
and electrodialysis. The results indicate that each method has value
depending on the particular requirements in any specific case. This report
will be useful to EPA's regulatory program (Effluent Guidelines Division) and
to the industry itself in arriving.at meaningful and achievable discharge
levels. For further information, please contact the Alternative Technologies
Division of the Hazardous Waste Engineering Research Laboratory.
David G. Stephan, Director
Hazardous Waste Engineering Research Laboratory
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ABSTRACT
The study conducted at the New Jersey Institute of Technology, Newark,
New Jersey was concerned with development of two separate methods for
treatment of fluoborate-containIng wastewater from electroplating of tin,
solder, copper and nickel stripping.
The first method was based on the specific ion flotation principle
which involves the removal of specific ions from dilute wastewater through
binding with a surfactant, followed by flotation or ultrafiltration. This
part of the investigation involved the evaluation of structurally different
commercially available surfactants to determine the type, structure,
mechanism and conditions which govern the formation of a fluoborate-
surfactant complex. Also, air flotation and ultrafiltration were
evaluated for removal of the complex from the wastewater. Methods for
recovery of the surfactant were examined.
The fluoborate was found to bind with a commercially available alkyl-
amine acetate type surfactant which reduces the fluoborate concentration In
rinse wastewaters from 100 mg/1 of fluoborate to 7-15 mg/1 of fluo-
borate. Actual plating operation rinse wastewaters containing 100 mg/1 of
fluoborate were used in the study. Dltrafiltration followed by electro-
lysis provided the shortest treatment time with' recovery of the
surfactant.
The second method was electrodiaiysis. Here t/e major effort was to
find a suitable anode. Electrodialysis was found feasible for treatment
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of wasCestrearns containing plating chemical concentrations s* 1000 mg/1
using a high density low porosity graphite anode. Electrodialysis can
reduce the plating chemical concentrations in the wastestreams to about
100 mg/1.
The specific ion flotation process either used separately or in the
combination with electrodialysis caa be useful and effective for closed
loop treatment 'of fluoborate-containing vastewaters from electroplating
operations,. Reagent recovery in speciclc ion flotation and fluo bo rate and
metals recoveries in electrodialysis can be achieved in addition to pollu-
tion control. However, both methods need further development to make them
commercially suitable for treatment of fluoborate-containing wastestreams.
This report was submitted in fulfillment of Grant No. R - 804710 by
the New Jersey Institute of Technology under sponsorship of the U.S.
Environmental Protection Agency. This report covers the period October 1,
1976 to December 1, 1979 and wo-k was completed as of October, 1979.
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CONTENTS
Page
FOREWORD ill
ABSTRACT lv
CONTENTS vl
FIGURES vlil
TABLES x
I. INTRODUCTION' 1
Ion Flotation 4
Electrodialysis 6
II. CONCLUSIONS 10
Specific Ion Flotation 10
Electrodialysis 11
III. RECOMMENDATIONS 13
IV. EXPERIMENTAL 15
Ion Flotation 15
Surfactants 15
Equipment and Procedures ,16
Fluoborate Analysis 19
Micelle Formation, 19
Ultrafiltration 19
Simple Cell 19
High Volume Cassette 22
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Page
Breaking the Fluoborate-Surfactant Complex . , 25
Addition of Excess Acetic Acid 25
Electrolysis 25
Electrodialysis 27
V. RESULTS AND DISCUSSION 33
Ion Flotation 33
Factors Influencing the Removal of Fluoborate
by the Surfactant 34
Process Parameters 44
Removal of Fluoborate from Plating Rinse-Waters .... 45
Recovery of Surfactant 47
Ultrafiltration '47
Electrodialysis 52
Evaluation of Different Types of Anodes 54
Electrodialysis Result 57
Treatment of Tin Fluoborate Rinse-Waters 57
Treatment of Solder Fluoborate Rinse-Waters 61
Treatment of Copper Fluoborate Rinse-Waters 69
Rates of Mass Transfer 75
Analysis of Electrolyte 76
VI. REFERENCES 78
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FIGURES
Number
1 A Schematic of A Simple Electrodlalysls Cell 7
2 Flotation Apparatus 17
3 Schematic of A Simple Ultrafiltration Cell 20
4 Single Pass Flow System 23
5 Recirculating Flow System 24
6 Schematic of Electrolysis Set-Up ' 26
7 Schematic of an Electrodlalysls Stack 28
8 Spacer on Graphite Anode to Define S Shaped Flow Pattern . 30
9 Electrodlalysls Unit Feed Reservoir and
Electrolyte Reserv6ir 31
10 Treatment of Dilute Sodium Fluoborate Solution
with Avmac C 35
11 Fluoborate Removal from Solder Rinse-Water
Dependence on Surfactant Molecular Size 41
12 Fluoborate Removal from Solder Rinse-Water
Dependence on Surfactant Degree of Saturation 42
13 Time Reaction of Fluoborate with Surfactant 43
14 Removal of Fluoborate from Plating Bath
Rinse-Waters Using Armac T 46
15 Electrolysis of Surfactant Fluoborate Concentrated
Solution from Treatment of Solder Bath Rinse-Water .... 49
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Number Page
16 Photograph of Corroded Platinized Titanium Anode 53
17 Photograph of Corroded Nickel Anode 56
18 Electrodialysis Treatment of Tin Fluoborate
Rinse-Waters, Feed Cation Concentration 58
19 Treatment of Tin Fluoborate
Rinse-Waters, Feed Anion Concentration 60
20 Electrodialysis Treatment of Tin Fluoborate
Rinse-Water, Product Cation Concentration . . 62
21 ..lectrodialysis Treatment of Tin Fluoborate
Rinse-Water, Product Anicn Concentration 63
22 Electrodialysis Treatment of Solder Fluoborate
Rinse-Waters, Feed Cation Concentration 66
23 Electrodialysis Treatment of Solder fluoborate
Rinse-Waters, Feed Anion Concentration 67
2A Electrodialysis Treatment of Solder Fluoborate
Rinse-Waters, Product Ion Concentration 68
25 Electrodialysis Treatment of Copper Fluoborate
Rinse-Waters, Fejd Anion Concentration 72
26 Electrodialysis Treatment of Copper Fluoborate
Rinse-Waters, Feed Anion Concentration 73
27 Electrodialysis Treatment of Copper Fluoborate
Rinse-Waters, Product Ion Concentration 74
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TABLES
Number Page
1 Effects of pH Removal en Fluoborate Ion 37
2 Fluoborate Removal Using Stepwise Addition of
Armac C Surfactant to Sodium Fluoborate 39
3 Removal of Surfactant with Low Through-Put
Ultrafiltration Experiment 50
4 Results of Recycled Retentate Experiment,
Millipore Cassette • 31
5 Changes in Percent Stannous Cation in the Feed
and Product with Time During the Electrodialysis
Treatment of Tin Fluoborate. Rinse-Mater 64
6 Changes in the Percent Stannous Ion in Feed
and Product with Time During the Electrodialysis
Treatment of Solder Fluoborate Rinse-Water 70
7 Rate of Mass Transport of Cations and Fluoborate
from Tin, Solder, Copper Fluoborate Rinse-Water 77
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I. IHTRODUCTIOH
A recognition of the detrimental effects of Industrial pollution on our
environment has surfaced in recent years. Along with this awareness came
federal regulations calling for reduction of industrial discharges into the
environment. The metal finishing Industry is an example of an industry,
which will need to develop new technology in order to meet the discharge
requirements under these regulations.
The metal finishing Industry in the United States includes approxi-
mately twenty thousand facilities, the majority of which are associated with
the automotive, electronic and jewelry industries. These facilities en-
compass both job-and captive-shops. The major operations performed at
metal finishing facilities Include cleaning and pickling, annealing, case
hardening, polishing, buffing, immersion plating, electroplating, phosphatlng,
conversion coating, oxidizing, painting, electropainting and anodizing.
The wastewater produced in metal finishing operations is mainly generated
in two ways. Concentrated wastes come from the dumping of solutions
which have become used or fouled. This Is especially true of cleaning,
stripping, passivating and anodizing solutions. The dilute wastes, which
are the larger volume wastes, come from the rinse-waters. These rinses wash
off the process solution that has adhered to the surface or was entrapped
in crevices due to the shape of the processed piece.
Presently, the most common used procedure for treating metal finishing
wastewaters include the following operations:
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. Separation of Oil and Grease
. Oxldatlve Destruction of Cyanides
. Reduction of Chrcmatea
. Neutralization of Acids and Alkalies
. Precipitation of Metal Hydroxides
. Disposal of Sludge
Problems arise mainly with the disposal of sludge because the precipitates
present a potential leaching problem when they are disposed of on land.
Alternatives to the precipitation process is the recovery and recycle of
wastes from their point of generation, or the substitution of toxic process
chemicals with less objectionable ones.
Among the more attractive recovery techniques are reverse osmosis, ion
exchange, evaporation, ultraflltration and electrodialysis. 'In specific
areas, these processes have been applied to the recovery of metals from
plating rinse-waters, or the concentration of the rinse-waters for the reuse
In the plating bath (1).
Substitution of process chemicals is practical only when the replacement
does not compromise the quality of the finished product. One such substition
Is the use of fluoborate to replace cyanides as a conducting salt in plating
baths. Fluoborate has been found to be an excellent carrier ion which gives
a uniform, bright, well-thrown covering. Also, fluoborate is much less
toxic than cyanide, and therefore, provides for a safer plating room. For
these reasons, many platers of cadmium, zinc, tin, lead, solder, copper,
nickel and iron are replacing their cyanide baths with fluoborate b-ths.
Commercial fluoborate solutions are presently available for the plating
of copper, indium, iron, lead, nickel, tin and their alloys. Also, fluoboric
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acid Is used in various pretreatnent operations, such as stripping and clean-
ing. The concentration of these rinse-waters is variable, depending upon
the rinsing technique which is employed. Dilute rinses would be typical of
single tank rinsing, while the concentrated rinse-water would be attributed
to multiple tank countercurrent or series rinsing.
The fluoborate ion is an ion in which boron is covalently saturated by
fluorine. This ion forms salts in which there is a true cation with no co-
valent bonding to the anion. Fluoborate is a very small, tightly bound
tetrahedron with a uniform charge. It apparently does not polarize (2).
Fluoborate by Itself Is relatively non-hazardous. However, it will
hydrolize (3) in water yielding boric acid and fluoride in accordance with
the following equilibrium reaction:
HBF4 + 3H20 -^ B(OH)3 + 4HF
The presence of this resulting fluoride in our receiving waters is un-
desirable.
There are presently no specific discharge limitations on fluoborate.
However, when a wastestream is analyzed for fluoride by the approved method
(BelLack Distillation), any fluoborate present will be hydrolized yielding
Inflated fluoride concentrations. For each fluoborate ion present in a
sample the test will show four fluoride ions. This gives a false Indication
.of fluoride concentration and can show a National Pollution Discharge
Elimination System Permit (NPDES) violation where none exists.
Few processes are known for the removal of fluoborate from plating
rinse-wa-.ers. It is a small tight molecule and is not easily rejected by
membrane processes such as reverse osmosis. Presently, there is no known ion
exchange resin which will efficiently remove fluoborate frontsolution. Battele
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Memorial Institute in their January 1974 draft of the Development Document
for Limitations for>Electroplating Point Sources, suggested the hydrolysis
of the fluoborate to fluoride, followed by lime precipitation as a possible
treatment. This however, results in the production of a sludge that must
be disposed in secure landfills.
Vaccum evaporation is currently being used as a means of recycling
stannous fluoborate rinse waters back into the plating tank as make-up
solution. Although it provides a closed-loop treatment system, problem*.
such as precipitation of stannic oxide which inhibits the evaporation are
encountered during the evaporation process. It is also an energy intensive
operation.
Since suitable technology for the treatment of rinse-water from
fluoborate plating baths is lacking, this investigation was undertaken.
Two separate processes, ion flotation and electrodrolysis, were investigated
as a possible close-loop treatment of the dilute and concentrated fluoborate
containing wastestresms from the electroplating industry.
Ion Flotation
Flotation processes for use in separation of solid particles frrji
liquids is an old, well-established process in waste removal (4,5) as rell
as in the process industries (6). For waste removal tr flotation, the
mechanism is to add a surface active agent to the wastewater and mix it
well. This allows the surfactant to adhere to the particles in the water.
Foaming through the introduction of air brings tne surfactant-solids
combination to the surface even though they are more dense than water.
When an air bubble contacts the surfactant-particle combination, the
weight of the particle is balanced by the buoyancy of the affixed air
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bubbles, and the particle floats.
Ion flotation is a relatively recent process. The field has been
explored by Sebba (7) in South Africa and Grieves (8) in the United
States. The concept of ion flotation is different from particle flotation in
that a complex is formed between the surfactant and the dissolved ion. In
participate flotation, the surfactant adheres to the particle, but In waste
streams such as from metal finishing operations, there are no particles.
The surfactant, therefore, must chemically react with the ion which is to
be removed.
Most of the work done in the ion flotation field has been concerned
with removing metal cations from solution with anionic surfactants.
However, Grieves (9) has investigated the use of ion flotation for the
removal of the anionic chromate ion, but' there has been no research into
the removal of the fluoborate ion using this process. Thus, the use of
specific ion flotation for the treatment of fluoborate plating bath
rinse-waters containing dilute concentration of fluoborate was
investigated.
The part of the investigation dealing with dilute fluoborate rinse-waters
was concerned with 1) determining the type and structure of the surfactant
that favors the binding of the fluoborate ion with the surfactant, 2) under-
standing the mechanism of binding and those parameters such as pH, ratio of
the amount of surfactant to fluoborate ion, and contact time which can
influence the binding of the fluoborate ion to the surfactant, 3) identifying
those process parameters such as air feed rate, air bubble size, rir diffuser
location, inlet feed direction and mixing time which can Influence the optimum
removal of fluoborate ion, and 4} evaluating this technology for the removal
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of fluoborate ion from the rinse-waters resulting from nickel stripping,
solder plating, tin plating and copper plating operations.
Also, the means to recover the surfactant and fluoborate ion for reuse
in the treatment process and plating baths, respectively, was examined.
Ultrafiltration was evaluated, as an alternate to flotation for rapid
separation of Che fluoborate-surfactant complex from the rinse-waters.
ElecCrodialysis
Eleccrodialysis is a membrane process which can be used for the separa-
tion, removal or concentration of ionized species in aqueous soluCions. The
above is accomplished by using an electromotive force to selectively trans-
port ions Chrough an ion-exchange membrane. These ion-exchange membranes
are permeable Co either cations or an ions,1 but not to both. The membranes
are thin sheets of ion-exchange material reinforced by a synthetic fabric
backing. The resin matrix is usually copolymerized styrene divinylbenzene,
the exchange capacity being imparted by sulfonic acid groups for cation ux-
1 change niemoranes and quaternary ammonium groups for anion exchange membranes.
A simple electrodialysis system consists of an anode and a cathode,
separated by an anion permeable membrane near the anode and a cation
permeable membrane near the cathode. Thus a cathode chamber, an anode
chamber, and a center chamber are formed. When the electric charge is
applied, anions pass from the center chamber to the anode chamber while
cations pass from the center chamber to the cathode chamber. Therefore,
the concentration of salt in the center chamber is decreased. The appli-
cation of a simple electrodialysis cell in the separation of a potassiutc
sulfate solution is shown in Figure 1.
In practical electrodialysis installations (10), there are ten to
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Cathode
Cation-
Pettieable
Membrau?
i
I
i
Anion-
Permeable
Membrane
H
i
>
K2S°4
30
-
Anode
FIGURE 1. A SCHEMATIC OF A SIMPLE ELECTRODIALYSIS CELL
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hundreds of compartments between one pair of electrodes. These units are
referred to as electrodialysis stacks. These stacks include specially
designed spacers to separate a cationic and anionic impermeable membrane and
allow flow between adjacent membranes. The feed solution is distributed and
the concentrate collected by two internal hydraulic Channels; one for feed and
one for concentrate. \ cell pair includes the following components:
. Cation Selective Membrane
. Feed Spacer
. Anion Selective Membrane
. Concentrate Spacer
Passing a direct current through the stack causes ions to migrate across the
permeable membranes from the feed channel and collect in the concentrate
channel.
The most frequently used application of electrodialysis is in the
desalination of brakish water (.11) . Some recent investigations relating to
the metal finishing industry include the recovery of nickel and copper from
plating rinse waters and closed-loop control of cyanide rinse-waters (11,
12). However, none have examired the use of electrodialysis as a means
of treating fluoborate plating rinse-waters.
The feasibility of using electrodialysis as a means of treating
concentrated tin, solder and copper fluoborate plating bath rinse-waters for
recovery of the metal and fluoborate ion as well as reuse of the feed as
rinse-water was investigated.
This study also involved the development and testing of an inexpensive
new anode which could be used in an electrodialysis unit and be resistant to
the corrosive properties of fluoborlc acid electrolyte. The development of
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this anode allowed fluoboric acid to be used as an electrolyte to match the
anions present in the fluoborate waste stream.
The use of the traditional anodes such as the platinized titanium
anode was unable to meet the corrosive nature of the fluoboric acid
electrolyte. The use of this anode in an electrodialysis unit would
require the use of less corrosive electrolytes such as sulfuric acid which
can result In the contamination of the product with undesirable anions;
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II. CONCLUSIONS
The specific ion flotation process used either separately or in
combination with electrodialysis appears to be feasible for the close-loop
treatment of waste rinse-waters resulting from solder, tin, nickel and copper
plating operations. The combined use of both processes provides for recovery
of plating bath chemicals at concentrations that approach plating bath
strength with a treated effluent suitable for reuse as rinse-water.
Specific Ion Flotation
1. Specific ion flotation using a commercially available alkylamine acetate
surfactant is feasible for the treatment of dilute rinse waste streams from
solder, tin, nickel and copper, plating operations to provide a product that
can be reused as rinse-water.
2. Fluoborate anion concentration in the solder, tin and nickel fluoborate
rinse wastestreams can be reduced to a concentration of 7 mg/1. Fluoborate
anion in the copper plating bath rinse waters can be reduced to a
concentration of 15 mg/1.
3. The removal of fluoborate anion by the surfactant is dependent on
replacement of the acetate group on the surfactant by the fluoborate anion.
Removals are inhibited by anions such as chloride, which fonra stronger
acids than fluoborate acid.
4. Fluoborate anion removals are enhanced by an increase in the molecular
weight of the surfactant and by acidic conditions, which increase the
ionization of acetate groups on the surfactant.
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5. Excess surfactant is required to make up for the acetate groups that are
lost to the replacement reaction because of micelle formation which occurs
at surfactant concentrations of 12 mg/1.
6. The replacement of the acetate group on the surfactant by the fluoborate
anion occurs within one minute. The rate limiting step in this process is
the mixing time required to achieve a complete mix upon addition of
surfactant to a fluoborate wastestream by the laboratory system used in
this study.
7. The fluoborate-surfactant complex can be removed from solution by
aeration. Air bubble size, air diffuser location and inlet feed direction
with respect to bubble rise, does not influence the rate of removal of the
fluoborate-surfactatit complex.
8. Increases in the air feed rate decreases the concentration of the
fluoborate-surfactant complex in the foam by removing more liquid with the
foam.
9. Ultrafiltration with recycling of the retentate provides a four times
greater rate of removal ox the fluoborate-surfactant complex from the rinse-
water than aeration.
10. Electrolysis is suitable for splitting the fluoborate-surfactant
complex to recover the surfactant. The surfactant is concentrated at the
cathode and can be dissolved from the cathode in the acetate form with
concentrated acetic acid.
Electrodialysis
1. Electrodialysis appears to be feasible for the treatment of concentrated
fluoborate-containing rinse waste waters. It provides a product that appro-
aches plating bath chemical concentrations and an effluent that can be
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further treated by the specific ion flotation process.
2. The use of a high density, low porosity graphite anode in an
electrodialys:.s unit provides greater resistance to chemical corrosion and
a greater cuixent density for a given applied voltage than the more
commonly usfed platinized titanium anode.
3. The graphite anode's resistance to chemical corrosion permitted the
highlv corrosive fluoboric acid to be used as an electrolyte tu match the
anion in the feed.
4. The rate of transfer of stannous ion and lead ion from the feed to the
concentrate is significantly greater than the rate of transfer of stannic
ion from the feed to the concentrate. This difference in the rate of
transfer of the cations minimizes the build-up of undesirable stannic ion
in the plating baths from reuse of the electrodialysls product.
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III. RECOMMENDATIONS
The recovery of placing bath chemicals and the closed-loop treatment
using electrodlalysls with newly developed graphite anode and specific
ion flotation of rinsewater containing fluoborate anlons from solder, tin,
copper and nickel plating operations has been shown to be feasible. There are
a number of advantages in using electrodialysls and specific ion flotatir.. for
the,treatment of rinsewater containing fluoborate. Electrolysis treatment
preferentially concentrates the desirable stannous ions in the product
stream from a mixture of stannous and stannic cations usually present in
the rinsewaters. The product contains cation and anion concentrations
that approach plating bath strength. The development of the graphite anode
which is resistant to the corrosive nature of fluoboric acid provides an
anode which Is approximately one-fortieth the cost of the commonly used
platinized titanium anode and allows the fluoborate electrolyte to be used
to match the fluoborate anions present in the rinsewaters. The use of an
electrolyte in the electrodialysls unit containing anions> that match the
anlons in the feed is preferred to avoid contamination of the product
produced from electrodialysis treatment. In addition, the surfactant used
in the specific ion flotation treatment of rinsewaters containing low
concentrations of fluoborate can be recovered along with the fluoborate
anion by electrolysis.
In view of the above, the commercial feasibility of using electro-
dialysis in combination with specific ion flotation to> provide a closed-
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loop treatment system should be established on a pilot scale. The
engineering parameters and costs associated with the design, assembly and
operation of both systems must be det ermine •!. Also, this pilot scale
effort should identify the methodology that will allow rapid mixing of the
fluoborate rinse-waters with the alkylamine acetate surfactant solutions at
concentrations that do not favor miceUeformation. In addition, the long
tena stability of electrodialysis membranes (longer than 60 hours) toward
the fluoboric acid electrolyte should be evaluated since frequent replace-
ment of these membranes can lead to unacceptable operating costs. The
substitution of the graphite anode after a period of time should not
significantly contribute to the operating costs of the electrodialysis
unit since Its replacement cost is approximately one-fortieth of that
required to restore the'commonly used platinized titanium anode.
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IV. EXPERIMENTAL
Ion Flotation
Surfactants
A number of different type surfactants were evaluated in this
investigation. A literature search revealed that there were a number of
different type surfactants that may bind to the fluoborate anion'.
However, there was no Information to indicate the type of structure that
would allow the surfactant fluoborate complex to be removed from
solution either by air flotation or ultrafiltration and that would
readily allow the surfactant to be separated from the anion for reuse.
A number of cacionic surfactants were sslected that differed in
size, degree of saturation and structure. The cationic surfactants
were evaluated because of the attraction that could be expected in
solution between a positively charged surfactant molecule and a
negatively charged fluoborate ion. Several non-ionic and anionic
surfactants were investigated to determine if it would be possible to
bind both the metal and the fluoborate to the surfactants for removal
from solution.
The cationic surfactants evaluated were Amine 0, Amlne C, Amine S,
Amlne T, Ammonyx 220, Ammoayx T, Armac C, Armac T, Armac 180, Armac H,
Armac 8D, Duomac T, Atlas G-3634A and Finazoline T. The Clba-Geigy Amlne 0,
Amine C, Amine S and Amlne T surfactants are heterocyclic tertiary amines.
-15-
-------
The Ammonyx 220 and Ammonyx T obtained from Onyx are an alkyl dimethyl
benzyl ammonium chloride and a cetyl dimethyl benzyl ammonium chloride,
respectively. The Armac C, Armac T, Armac 18D, Armac HI, and Doumac T
i
surfactants which were obtained from Armak are an alkylamine acetate
(12-15 carbon atoms), an alkylamine acetate (16-18 carbon atoms), a
distilled octadecane amine acetate (18 carbon atoms), a hydrogenated
alkylamine acetate (16-18 car,bon atoms), and an alkylamine diacetate,
respectively. The Atlas G-3634A surfactant obtained from Id is a
quaternary ammonium derivative. The Finetex surfactant, Tinazoline T,
is an amlnoethylimldazolene.
The nonionlc surfactants used in this study, AmmonyxCDO, Onyxol 336
and Neutronyx, were obtained from Onyx and are an alkyl amido propyl
dimethyl amine oxide, a lauric acid and an alkjlphenol polyglycol ether
with etbylene oxide, respectively.
The anionic organic phosphate surfactants used in this study were
Dextrol OC-60, Dextrol OC-80, Dextrol OC-90, Oextrol OC-105 and Dextrol
OC-110 and were obtained from Dexter.
Equipment and Procedures
The specific ion flotation experiments were 'carried out in a modified
recirculation bath system (see Figure 2) designed to simulate an actual
treatment process. The recirculation was required because the length of
time required for the removal of the surfactant by air flotation was much
longer than could be accomodated in a single flow-through tank. The
equipment consisted of an eight liter holding tank, a two liter reaction
vessel, an eighty liter per hour recirculation pump, and a twelve liter
foam collector. The air for flotation was introduced through a porous
-16-
-------
Foam Collector
Reactor
Air Diffuser
Level Control
Air In
/
Surfactant
_v
Holding
Tank
FIGURE 2. FLOTATION APPARATUS
-17-
-------
stone diffuser, the air was controlled by a Brooks R-2-15 rotometrer.
The surfactant was introduced into the suction line of the pump using
a tventy milliliter hypodermic syringe after fluoborate plating bath
solutions were added and thoroughly mixed in the system. The syringe
was used because even slow mixing in the pump caused foam to be
generated in the holding tank during the makeup.
The system was 'cleaned by washing all tanks and tubing, and
thoroughly rinsing them with delonlzed water after each experiment. The
system was then charged with eight liters of deionized water. The
desired quantity of sodium fluoborate or plating bath solutions was added
to the deionized water and the solution recirculated for 36 minutes to
assure thorough mixing. A series of tests in which the resulting dilute
rinse-waters solutions were circulated through the system for different
lengths of time up to 24 hours indicated that the test solutions were
completely mixed within 36 minutes. The desired amount of surfactant,
which had been dissolved in 200 ml of deionized water, was injected into
the system at a rate of 8 ml per minute. The system was again
recirculated for another 36 minutes to insure complete mixing of surfactant
solution with the fluoborate solutions. Air was applied, and the
solutions were .recirculated continuously unti. there was no further
generation of foam at the liquid surface in the reactor. The foam was then
removed as formed.
-18-
-------
Fluoborate Analysis
Analysis of the solution for the fluoborate ion was carried out using
the series 92 and series 93 Orion fluoborate specific ion probes. The 93
series, which was determined to be the more sensitive probe, was used to
analyze the solutions that contained no surfactants. The surfactant was
observed to have an adverse effect on the probe's membrane. Therefore, the
(
series 92 probe was used to measure the fluoborate concentration in the
presence of the surfactant because its membranes could be replaced. It was
determined that the membrane in the 92 series probe had to be replaced after
the measurement of 10 solutions containing fluoborate ion and surfactant.
Micelle Formation
The critical micelle concentration was determined by conductivity
measurement. A sharp decrease in the plot of conductance -versus the square
root of the surfactant concentration indicated the concentrations at which
micelles begin to form.
Ultrafiltration
a. Simple Cell
The equipment used for initial evaluation of ultrafiltration for removal
of the fluoborate surfactant complex from solutions was the Millipore
t
Corporation's 47 mm stirred cell, catalogue number XX 42 047 10. The
membranes were Milliporefs Pellicon membranes, PSAC type.
The two membranes evaluated were the 1,000 and 10,000 nominal molecular
weight limit (nmwl) membranes. The rnnwl is a rough guide to the size above
which mrst molecules are efficiently retained by that membrane.
The siaple, stirred cell, which is depicted in Figure 3, is a cylindrical
plastic unit designed to hold membrane discs for the ultrafiltratlon of small
-19-
-------
Pressure = 238 cm. of Hg.
Feed Solution
I Stirring Bar
Magnetic
Stirrer
Teflon Ring
Membrane
•Perforated Spacer
Filtrate-
FIGURE 3. SCHEMATIC OF A SIMPLE ULTRAFILTRATION CELL
-20-
-------
fluid volumes. The cell barrell is polycarbonate with silicone 0-rings
for seals at the base and cap. The capacity of the cell is 80 ml, the cell
f\
takec a 47 mm membrane disc which has a filtration area of 10.5 cm .
In the evaluation of the two different membranes, the set-up
that is shown in Figure 3 was used. Seventy-five millillters of solution
was placed in the cell. The pressure applied to the feed solution was
maintained at 238 cm. of Hg. The cell was mounted on a magnetic stirrer
and stirred by means of a magnetic stirring bar inside the cell. This
minimizes polarization occurring at the membrane. The filtrate was
collected in test tubes from the plastic tube which was inserted in the
base of the cell.
Initial experiments were run using a solution of 1500 mg/1 of alkyl-
amine acetate surfactant and 100 mg/1 of fluoboratj anion. During the
evaluation of the 10,000 and 1,000 nmwl membrane a dye test was used to
Indicate the presence of alkylamine acetate surfactant in the filtrate.
The dye test provided qualitative evidence of the presence or absence of
alkylamine acetate in the filtrate solution by visual inspection.
Bromophenol blue, which was the dye that was used, gave a rough
quantitative indication of the surfactant In solution. When the surfactant
was present, a blue color was' formed in the solution. When no surfactant
was present the solution remained clear and colorless. The deepness of
the blue Increased as the concentration of surfactant increased. There-
fore, the dye test was a good preliminary indication of the passage of the
surfactant fluoborate complex through the ultrafiltration membrane.
-21-
-------
The surfactant concentration in the ultrafiltratlon filtrate solution
was analyzed using a Dorhmann Envirotech DC-52D Carbon Analyzer. The
presence of fluoborate was observed to have no effect on this analysis.
b. High Volume Cassette
Further evaluation of ultrafiltration for the removal of the fluoborate-
surfactant complex from solutions was carried out using the 100 nomimal
molecular weight limit membrane in a Millipore High Volume Cassette System.
The cassette system is 25 cm wide x 23 on. deep x 30 cm. high. Membranes for
this system have a filtration area of 465 cm2.
The systec 'vas run utilizing a variable speed tubing pump to transport
pressurized solution to the cassette's feed port. Pressure at the feed
port was regulated by the pump speed. A needle valve was placed at the
retcntate port in order to maintain pressure over the entire sesahrane area.
Using this system, two types of experiments were run: they were single pass
flow and recirculating flow as depicted in Figures 4 and 5, respectively.
During both experiments the same feed solution containing 1500 mg/1 of
alkylamlne acetate surfactant and 100 mg/1 of fluoborate was used.
Operating pressures were maintained at 155 en of Hg at the feed port
and 109 cm of Hg at the retentate port, during the single pass flow experi-
ment. Due to the viscosity of the feed solution, only 5.7 ml of filtrate vas
collected per liter of feed. In order to remove more fluid from the sample
than can be accomplished in one pass, the recirculating flow system was
investigated.
During the recirculating flow experiment the retentate was run back
into the sample vessel. The sample vessel was mounted on a magnetic stirrer
and the solution was stirred to maintain a homogeneous feed. The pressures
-22-
-------
Pump
Valve
Sample Retentate
Filtrate
FIGURE 4. SINGLE PASS FLOW SYSTEM
-------
Pump
Cassette -
Sample
Filtrate
FIGURE 5. RECIRCULATING FLOW SYSTEM
-------
were maintained at 155 cm. of Hg at the feed port and 114 on. of Hg at the
retentate port.
The filtrates from both the single pass flow and the recirculating flow
experiments were analyzed for TOG to determine the surfactant-fluoborate
complex removal.
Breaking the Fluoborate-Surfactant Complex
a. Addition of Excess Acetic Acid
In an attempt to reverse the equilibrium of the surfactant-fluoborate
complex and break the complex, the addition of excess acetic acid was
examined. A one liter solution of 100 mg/1 of fluoborate and 1500 mg/1
of alkylamine acetate surfactant was used. Concentrated acetic acid was
pipeted into this solution at an initial volume of 0.5ml. The solution was
stirred utilizing a magnetic stirrer. The concentrated acetic acid was added
in increments of 0.5 ml. After each addition of acid, the concentration
of fluoborate anion was monitored using the Orion 92 series electrode
system.
b. Electrolysis
Electrolysis was also investigated as a means for separating the
surfactant-fluoborate complex. A simple electrolysis cell was set up as
shown in Figure 6. The components were a pyrex beaker, a spiraled platinum
anode, a copper cathode, and a direct current (D.C.) power supply.
The D.C. power supply was kept constant at 45 volts (12 ripple). This
^
provided a current density at the cathode of approximately .004 Amps/cm .
A surfactant-fluoborate solution of 1500 mg/1 of alkylamine surfactant
and 100 mg/1 of fluoborate anion was added to the system and then the power
supply was turned on. Using the 92 series fluoborate specific ion electrode,
-25-
-------
Platinum
Anode
Copper
Cathode
Surfactant-Fluoborate
Solution
FIGUKE 6. SCHEMATIC OF ELECTROLYSIS SET-UP
-26-
-------
the fluoborate concentration was determined periodically. These concentra-
tions were then plotted versus time to determine the rate of disassoclation
of the complex.
Using the above system, disassociatlon of the following four solutions
were examined:
1. Solution A: surfactant (1500 mg/1) + sodium fluoborate (100mg/l);
stirred for 90 minutes.
2. Solution B: Same constituents as Solution A; stirred for 8 hours.
3. Solution C: surfactant (1500 mg/1) + lead and tin fluoborate,
fluoborate anion = 100 mg/1; stirred overnight.
4. Solution D: surfactant (1500 mg/1) + lead and tin fluoborate,
fluoborate anlon = 100 mg/1 + brighteners;
stirred overnight.
2. Electrodlalysis
Elrctrodialysis was investigated here as a means of concentrating
fluoborate plating rinse-waters for recycle back to the plating bath.
All plating bath rinse-waters were generated by diluting plating bath
soluticns with deionized water to desired metal cation and fluoborate
anion concentrations. A Micro Pore (Hanover, Mass.) electrodialysis stack
i
was used to carry out the electrodialysis experiments. The stack consisted
of thirteen cell pairs and was arranged as illustrated in Figure 7. Each
cell pair consisted of a Neosepta strongly acidic cation permeable (C66-5T)
and strongly basic anion permeable (AFN) membranes (Tokuyima Soda Co Ltd.,
Japan).
The size of the membranes and electrodes was 55.9 cm x 30.5 cm. Appro-
ximately 63 percent of the area of the membranes was used for ion transfer.
-27-
-------
I
N>
ncentrat
I
V
•a
1
Feed
Cathode-
L
i
f \
.. t It
p
A I C
A;
I
1
<-
P
A C
'C+
A\
i
-
*
A'
?~
Flows
Reservoir
r
A 1 C
H
\
i
<
^>
^
A"
k
L
1 f
A C
h
\
1
X
>>
A
£+
AV
1
4
^ k
r
-Anode
f7 Flows
-M
A = Anion Selec
Membrane
C = Cation Jfelec
Membrane
A = Anion
.
C = Cation
„
Electrolyte
Reservoir
I
Cell-Pair
FIGURE 7. SCHEMATIC OF KA ELECTRODIALYSIS STACK
-------
The spacers and membranes delineated an S-shaped flow pattern which incor-
porated the advantages of the more common sheet flow and tortuous path
designs (see Figure 8). Alternate cells were connected to internal feed or
product manifolds. An additional anion permeable membrane was used at the
cathodes to prevent migration of the cations into the electrolyte and being
reduced at the cathode.1 The ends of the stack were terminated with the two
i
electrodes. The cathode was stainless steel 316 while the anode which was
originally platinized titanium metal but had to be replaced because of
corrosion problem. A hydraullcally Isolated electrode rinse solution
consisting of a mixture of hydrofluoboric acid and sodium fluoborate was
recirculated from an electrolyte reservoir.
Other related supplies Included pumps for both the feed and electrolyte
solution, reservoirs for 114 liters of feed and 38 liters of electrolyte
collecting vessels for the concentrated products, and an exhaust over the
electrolyte reservoir to remove electrolyte gases, a rectifier and
necessary piping and valving. The complete installation is shown in Figure 9.
Initiall>, the electrolyte was recirculated through the cathode and anode
cells at a rate of 133 1/hr., while the feed solution was recirculated
through the feed cells at a rate of 456 1/hr. The D.C. power supply was
then turned on and the current was brought up to 10 amperes by slowly
increasing the voltage across the electrodes. The flows were regulated by
gate valves to maintain a pressure of 52 cm. of Hg at both the electrolyte
and feed inlets. Also, the temperature of the solution at the feed outlet
was monitored in order to prevent possible membrane damage due to the over-
i
heating of the stack. At the end of each experiment, the flows were run for
2-3 minutes after the current was shut off. Also, between experiments the
-29-
-------
FIGURE 8. SPACER ON GRAPHITE ANODE TO DEFINE S-SHAPED FLOW PATTERN
-30-
-------
FIGURE 9. ELECTRODIALYSIS UNIT FEED RESERVOIR (tank on right)
AND ELECTROLYTE RESERVOIR (lower middle right)
-------
stack was flushed with distilled water until no metal or fluoborate could
be detected.
Feed, product and electrolyte samples were collected initially, at
regular Intervals during each run and at the completion of each run and
analyzed for metal concentrations, fluoborate concentrations and pH. The
pH was monitored to indicate whether there was a significant transfer of
hydrogen ions from the feed to the product. The electrolyte was analyzed
to detect metal ion breakthrough frons the concentrate to the electrolyte at
the cathode.
The concentration of total tin, copper and lead were analyzed after
serial dilution with fluoboric acid solutions using a Varian Techtron
Atomic Absorption Spectrometer (Model 1200). The serial dilutions were
carried out to reduce the metal ions to levels that could be measured.
Serial dilution of the samples with fluo boric acid solution at the same pH
as the samples being analyzed was found to prevent precipitation of metal
prior to analysis.
Stannous Ion concentrations were determined according to Method 155
(14) by tltration by 0.1 N and 0.01 N iodine solution to a blae iodine-
starch complex end point. The fluoborate ion concentration was calculated
using the Orion Model 93 series Pacific ion electrode.
-32-
-------
V. RESULTS AHD DISCUSSION
1. Ion Flotation
This part of the Investigation was concerned with identifylug tbe type
of surfactant which would bind to the fluoborate ion. A number of cationic,
anionlc and non-ionic surfactants were initially evaluated using sodium
fluoborate solutions. The cationic surfactants were primary, secondary and
tertiary amines attached to various organic radicals. The non-ionic surfac-
tants were the oxide of an aromatic amlne, an aliphatic acid and acyclic
ether. The anionlc surfactants were of the organic phosphate type.
Significant fluoborate removal was observed with only two of the
cationic surfactants, Duomac T and Armac C. Approximately 55 percent
removal of the fluoborate was achieved with Armac C, the better of the two
surfactants, during the Initial surfactant screening. All of the other
surfactants tested showed no significant removal of the fluoborate Ion.
The Duomac T and Armac C differ from the other surfactants examined In that
both surfactants contain acetate groups. Apparently, the presence of the
acetate group Is required for the removal of the fluoborate by specific
ion flotation.
Fluoborate ion removal could be increased from 55 to 132 percent by
Increasing the mole ratio of Armac C to fluoborate from 1.0 used in the
initial screening to 3.0. A series of tests were performed on solutions
containing different initial concentrations of sodium fluoborate and
varying the specific mole ratios of Armac C to fluoborate ion to determine
-33-
-------
the concentrations tc vhich Axmac C could reduce the fluoborate Ion. The
results indicate that At Initial fluoborate concentrations of 100 mg/1 and
below, the Armac C can reduce the fluoborate concentration to approximately
18 mg/1, using a surfactant to fluoborate mole ratio of 3:1 (see Figure 10).
When the initial fluoborate concentration is raised to 150 gm/1, the Armac
C reduced the fluoborate concentration to only 48 mg/1 using the same mole
ratio of 3:1. These reoults appear to be due to the fact that not all of the
surfactant required to provide a mole ratio of 3:1 to treat a fluoborate
concentration of 150 mg/1 can be dissolved. An extremely turbid solution
resulted. Thus, even though a 3:1 mole ratio of surfactant to fluoborate
ion was prepared not all of the surfactant was available to react with
fluoborate ion.
Factors Influencing the Removal of Fluoborate by the Surfactant
The results of the initial screening of the surfactants suggested that
the acetate group on the surfactant molecule is Involved in the removal of
fluoborate ion. In order to test this further, factors which Influence the
removal of the acetate ion from the surfactant were examined. Sodium
acetate was added to the Axmac C surfactant so as to reduce the ionization
of the acetate group. A 100 mg/1 of Armac C acetate solution when added to
the fluoborate solution to provide a 3:1 mole ratio of surfactant to fluo-
borate resulted in only 63 percent removal of fluoborate ion. When no
sodium acetate was added,an 82 percent removal of fluobcrate was obtained.
These results Indicate that the binding of the fluoborate requires the
removal of the acetate group from the surfactant through Ionization of
the surfactant to form a cation and an acetate ion.
If the above is the case, an Increase in acidic conditions should also
-34-
-------
70
60
50
eo
5
u
o
.a
§
30
20
10
Starting fluoborate concentration
£ 150 mg/1
O 100 mg/1
O 50 mg/1
25 mg/1
I
I
I
1.5 2.0 2.5 3.0
Mole ratio surfactant to fluoborate
Figure 10. TREATMENT OF DILUTE SODIUM FLUOBORATE
SOLUTION WITH ARMAC C
3.5
-35-
-------
favor the removal of fluoborate by an acetate surfactant since acidic
conditions would favor the formation of the surfactant cation through removal
of the acetate ion from solution in the i'orm of acetic acid. A reduction In
the final pH of the surfactant-fluoborate solution was found to favor tbe
removal of the fluoborate from solution by the Armac C. The use of fluoboric
acid Instead of sodium fluoborate In the mole ratio of 3:1 surfactant tc
fluoborate decreased the final pH from 6.2 down to 5.0. The removal of
fluoborate vas Increased from about 87 percent up to 92 percent (see Table 1).
The' Influence of other anions which form stronger acids than fluoboric
acid on the removal of the fluoborate by the surfactant uas examined. Hydro-
chloric acid was added to separate solutions containing the 3:1 mole ratio of
surfactant to fluoborate 'ion in amounts sufficient to provide final solutions
that contained 50 mg/1 and 100 rag/1 of hydrochloric acid. Fluoborate ion
removals of only 70 percent and 58 percent were obtained In the solutions
containing the 50 mg/1 and 100 mg/1 of hydrochloric acid, respectively. Tbjus,
the presence of anions which form stronger acids than fluoboric acid appar-
ently inhibit the removal of the fluoborate ty the surfactant.
The above results indicate that the fluoborate ion reacts with the
i
surfactant by replacing the acetate group on the surfactant since it forms a
stronger acid than acetic acid. Ho waver i maximum removal of the fluoborate
in these experiments is achieved with a surfactant to fluoborate mole ratio
of 3:1. The use of the 3:1 mole ratio Indicates that 3 acetate groups are
Involved In the removal of one fluoborate ion since each Armac C surfactant
molecule contains only one acetate group. The need for excess surfactant
suggested that all acetate groups are unavailable for replacement by the
fluoborate ion.
-36-
-------
TABLE 1. Effects of pH on Removal of Fluoborate Ion
mg/1 Fluoborate as
HBF^ NaBF4
100
75
50
40
30
25
0
0
25
50
60
70
75
100
Initial
3.7
3.8
4.1
5.4
7.1
6.7
7.4
pH
Surfactant
6.0
6.0
6.0
6.0
6.2
6.1
6.0
Final
5.0
5.6
5.8
6.2
6.2
6.1
6.3
Z Removal
92
92
89
86
83
87
87
-37-
-------
The results of three atepwlae additions, maintaining a mole ratio of 1:1
of surfactant to fluoborate remaining in the resulting solution after
removal of the surfactant-fluoborats complex reduced the amount of surfac-
tant required to remove a specific number of molecules of fluoborate.
Only 2.06 millimoles (554 mg) of total surfactant red-ices 1.15 milli-
moles of fluoborate (100 mg) in one liter to 0.21 millimoles (18 mg) by
stepwise addition of decreasing amounts of surfactant (see Table 2). The
fluoborate which reacted with the surfactant was removed by aeration after
each addition of surfactant. In contrast, a single addition of 3.45 milli-
moles (810 mg) of surfactant was required to reduce the 1.15 millimoles of
fluoborate in one liter of solution to the 18 mg.
Micelles were observed to form at surfactant concentrations above
12 mg/1. This could limit the number of surfactant acetate groups that
are available for replacement by the fluoborate. 'Since the fraction of the
total surfactant molecules in solution that exists as micelles generally
decrease as the surfactant solution becomes more dilute, the step wise
addition of decreasing amounts of surfactant to a given amount of fluo-
borate would Increase the fraction of total 'acetate available for replace-
ment by the fluoborate ion. Thus, it appears that step wise addition of very
dilute solutions of surfactants to minimize the micelle formation should
require less surfactant to react with a specific amount of fluoborate.
In order to further understand the selective fluoborate ion removals
exhibited by the surfactant containing the acetate group, surfactants similar
to Armac C but differing in carbon chain length and degree of saturation were
Investigated.
The effect of surfactant molecular size on the removal of the fluoborate
-38-
-------
TABLE 2. Fluoborate Removal Using Stepwise Addition of Anaac C Surfactant
Co Sodium Fluoborate
Concentration of
Annac-C
ag/1
310
160
84
millimoles
1.15
0.60
0.31
Concentration
of Fluoborate
ng/1
100
56
27
millimoles
-'
1.15
0.60
0.31
Fluoborate Concentration
remaining after aeration
mg/1
52
27
18
-39-
-------
ion in a solder plating bath rinse-water containing 100 mg/1 of fluoborate
ion UBS studied using Armac C (12-15 carIon atoms), Armac T (16-18 carbon
~ corns) and Armac 18D (18 carbon atoms) . The results show that as the chain
length of the surfactant is Increased from the Cjjj.is to C18» tne Percent
fluoborate removed is increased from approximately 80 percent up to 97
percent when using the surfactant to fluoborate mole ratio of 3:1 (see
Figure 11) . The treatment of the solder bath rinse-water with the surfactant
containing the 18 carbon atoms results in only .» mg/1 of the fluoborate ion
remaining in the rinse-water. Reduction of the fluoboric ion concentrations
in the solder rinse-water to below 3 mg/1 using surfactants with chain
lengths greater than 18 carbon atoms was not possible because of the marked
decrease In solubility exhibited by the surfactants with larger molecular
sizes than Armac 18C.
The degree of saturation of the surfactant does not appear to effect the
removals of the fluoborate ion. The removals of fluoborate ion in solder
bath rinse-water achieved with Armac HT whose percent saturation is 97
percent is comparable ".o that achieved with Armac T whose percent saturation
is only 58 percent. This Is observed for the range of surfactant to fluo-
borate ion mole ratios studied (see Figure 12).
The reaction of the fluoborate ion with the surfactant occurs within
a relatively short period of time. The mixing of Armac C with fluoborate in
mole ratio of 3:1 resulted in the reduction of fluoborate ion from 87 mg/1
to 18 mg/1 within 1 minute (see Figure 13). These results indicate that
a contact time of one minute between the surfactant and fluoborate is
required for the replacement of the surfactants' acetate group by the
fluoborate ion prior to removal by aeration.
-40-
-------
100
Q Armac-18D (Cjg)
O Armac-T
A Annac-C
1234
' Molar Ratio of Surfactant to Fluoborate
FIGURE 11. FLUOBOKATE REMOVAL FROM SOLDER RINSE-WATER
DEPENDENCE Oil SURFACTANT MOLECULAR SIZE
-------
100
90
O
£~ 80
-------
90
80
70
60
§.
o.
•o
41
u
U
a
ai
M
3
Vi
O
Jl
20
1
n
5 10
Time (Minutes)
15
FTCTRE 13. TIME OF REACTION OF FLDOBORATE WITH SURFACTANT
••43-
-------
Process Parameters
Changes in air feed rate, air bubble size, air diffuser location, Inlet
feed direction, and mixing time on the removal of the surfactant-fluoborate
complex from solution by aeration were investigated because these factors can
Influence the performance of bubble columns (15, 16).
Varying the air feed rate from 4 cc/sec. to 30 cc/sec. using a 3:1. mole
ratio of Armac C to fluoborate did not improve the rate of removals of
fluoborate and surfactant from solution. In both cases, time in excess of
20 hours was required to remove all of the surfactant. However, an Increase
in the air feed ratios does augment the amount of solution that is carried
over in the foam. This results in a wetter foam and a reduction in the
concentration of the surfactant-fluoborate complex in the foam. For example,
twa foaming operations were carried out at air feed rates of 15 cc/sec. and
30 cc/sec. were used. The lower air feed rate provided a resulting foam with
a surfactant-fluoborate complex concentration of 4000 mg/1 whereas the higher
air feed rate provided a foam with surfactant-fluoborate complex
concentration of less than 1000 mg/1.
Neither changes in bubble size, air diffuser location nor inlet feed
directions with respect to the rising air bubbles were observed to
influence the removal of the surfactant-fluoborate molecule in the bubble
column. Separate experiments using 3:1 mole ratio of Armac C to fluoborate
ion In which 1) initial air bubble diameters of 0.003 and 0.007 were
i
generated in the column, 2) positioning the air diffuser location at 10 cm.
and 30 cm. below the surface of the liquid In the columns to increase the
contact time between the bubble and the solution, and 3) introducing the feed
into the column counter-current as well as perpendicular to the rising air
-44-
-------
bubble did not Improve ths rate of removals of the surfactant-fluoborate
complex. Times in excess of 20 hours were required to remove ail of the
surfactant for each of the above experiments. However, these results
Indicate that significant variation can occur in the bubble size, and
contact time between the air bubble and the solution without influencing the
rate of removal of the fluoborate-surfactant complex.
Removal of Fluoborate from Plating Rinse-Waters
A series of tests were performed on rinse-water containing 100 mg/1 of
fluoborate ion by adding different amounts of Anaac T to different rinse-
waters that are representative of that obtained from solder plating, tin
plating, nickel stripping, and copper plating operations. Armac T rather
than Armac 18D which provided greater removals of fluoborate Ion was used for
these studies because it is far less expensive. It was felt that in practice
the slightly better removals achieved earlier with Armac 18D did not warrant
the additional expense.
The results indicate that Armac T can reduce the fluoborate concentra~
tlon from 100 mg/1 to approximately 7 mg/1 in the solder, tin and nickel
stripping rinse-water using a surfactant to mole ratio of 3:1. The
fluoborate Ion in the copper plating rinse-water is only reduced to
approximately 15 mg/1 (see Figure 14). This Is probably due to the fact that
the pH of the copper plating rinse-waters is less acidic than the other
plating bath rinse-water.
The above results are significant in that they Indicate that the removal
of fluoborate with surfactant is comparable with that which can be achieved
with li>e precipitation of fluoride in wastestreams. The widely used lime
precipitation of fluoride In uastestreams results in a fluoride ion residual
-45-
-------
70
ao
g
O
i
1
SO
SO
30
2Q
10
O Solder Rinse Waters
O Tin Rinse Water
O Nickel Stripping Rinse Water
Copper Rinse Water
_L
JL
312345
Mole ratios of surfactant to fluoborate
FIGURE 14. REMOVAL OF FLUOBORATE FROM PLATING BATH
RINSE WATERS WITH ARMAC T
-46-
i 0'. r".2E
F- - .-B7 :c
-------
of about 8 mg/1 in the wastestream (17). Thus, where fluoride concen-
trations of
-------
alternate more rapid process for removing the surfactant-fluoborate complex.
Evaluation of the ultrafiltration membranes utilized a low through-put
pressure cell. In the cell, experiments were run with 10,000 and 1,000 molecular
weight cut-off membranes. Experiments with the 10,000 molecular weight cut-
off membrane were unsuccessful. The solution passed right through the
membrane.
The 1,000 molecular weight cut-off membrane was effective in filtering
a solution of plating rinse-water containing fluoborate ions complexed with
the Armac T surfactant. Removals of Approximately 79 percent were achieved
(see Table 3) in the low through-put cell as determined by total organic
carbon measurements.
Although the molecular weight of Armac T surfactant is approximately
330, it was determined from conductivity that the Armac T forms micelles
at concentrations greater than 12 ppm. Therefore, at the concentration of
surfactant that is required to complex the fluoborate, it will exhibit an
apparent molecular weight much greater than 330.
Experiments utilizing the 1,000 molecular weight cut-off membrane by
recycling the retentate in a Millipore Cassette ultrafiltration apparatus
showed favorable results. Recycling the retentate back into the ultrafil-
tration cassette resulted in a removal of surfactant of 85 percent (see Table
4).
These ultrafiltration experiments produced the same results as air
flotation. However, times In excess of 20 hours were required to achieve
maximum removal of the surfactant-fluoborate complex from solution using
air flotation. The recycled ultrafiltration experiments achieved this
separation in approximately 5 hours. The ion flotation time cannot be
-48-
-------
FIGURE 15. ELECTROLYSIS OF SURFACTANT FLIJOBORATE
CONCENTRATED SOLUTION FROM TREATMENT
OF SOLDER BATH RINSE-HATER
-49-
-------
TABLE 3. Removal of Surfactant with a Low Through-Put Ultraflltration
Experiment
Solution
Initial
1st filtrate collected
2nd filtrate collected
3rd filtrate collected
4th filtrate collected
5th filtrate collected
Total
Z Surfactant fluoborate
Volume (ml)
75
1.2
2.6
10.6
43.0
2.4
59.8
initial cone.
I
TOC (rag)
80
0.13
0.56
2.12
10.06
0.54
13.5
- filtrate cone. .„ ..
retained by membrane initial cone.
-50-
-------
TABLE 4. Results of Recycled Retentate Experiment, Hlllipore Cassette
Solution
Initial
1st filtrate collected
2nd filtrate collected
3rd filtrate collected
4th filtrate collected
Total
% surfactant fluoborate
Volume (ml)
1,000
20
50
10
50
130
initial cone.
TOG (ing)
1,073
1.72
8.65
1.65
9.25
21.3
- filtrate cone. lofl „ a.
retained by membrane initial cone.
-51-
-------
reduced by Industrial scale-up; however, the time required for ultrafUtratlon
can be minimized by Increasing the number of membranes used In the ultra-
filtration unit.
Electrodlalysls
Countercurrent or series rinsing of products from fluoborate plating
operations can lead to fluoborate concentrations equal to or in excess of
1000 mg/1. For these highly concentrated wastewaters ion flotation
treatment is not suitable. Thus, electrodialysis was investigated as a means
to pretreat these concentrated rinse-waters to recover and reuse the plating
reagents lost to rinse-waters and reduce the plating chemicals in the
effluent to levels suitable for ion flotation treatment.
Application of electrodialysis for treatment of rinse-water containing
high concentration of plating reagents required modification of an existing
electrodialysis unit. Rapid deterioration of the commonly used platinized
titanium anode was encountered when fluoboric acid is used as the electrolyte.
Although this anode has been successfully used with nickel sulfate plating
bath rinse-waters and a sulfuric acid electrolyte, it quickly turns black,
cracks, and peels from the titanium metal backing when voltage is applied in
the presence of fluoboric acid electrolyte (see Figure 16, Photograph of
Corroded Platinum Anode). Apparently, the smaller fluoborate ion can
penetrate the porous platinum coating and corrode the metal bond between
the platinum and the titanium.
The matching of the an ion in the electrolyte with that in the rinse-
waters is preferred to using another anion such as sulfuric acid electrolyte
which is non-corrosive to the platinized titanium anode. The sulfuric acid
i
electrolyte would result In introduction of undesirable sulfate anion Into
-52-
-------
FIGURE 16. PHOTOGRAPH OF CORRODED PLATINIZED TITANIUM ANODE
-53-
-------
the concentrate stream and ultimately the plating bath.
Evaluation of Different Types of Anodes
Several different approaches were considered to obtain an anode that
would not corrode In presence of fluoboric acid electrolyte. These were
1) to Increase the thickness of the platinum plated on the platinized
titanium anode, 2) to plate a less porous metal such as gold on nickel
backing and 3) examine the use of inexpensive conducting materials such
as low porcslty high density graphite to which voltage could be applied
directly.
An increase In the thickness of the platinum plated on the titanium
anode from 1.5 micrometers to 3.9 micrometers did not improve the anode's
ability to withstand the corrosive properties of the fluoboric acid
electrolyte. The platinum cracked and peeled away from the anode within
an hour after voltage was applied to the anode ir. the presence of the
fluoboric acid electrolyte.
Gold when plated on nickel and heated under controlled conditions can
form a solid solution at the interface between the gold and nickel. This
concept was utilized to achieve a bond between the gold and nickel backing
at the Interface. It was anticipated that the solid solution at the inter-
face would resist the peeling and cracking that was encountered with the
platinized titanium anode in the presence of the flueboric acid electrolyte.
A series of experiments were carried out in which gold was plated on
nickel strips and heated for 30 minutes and 45 minutes at temperatures of
1GOQ°F, 1250°F and 1500°F, under a reducing atmosphere of'hydrogen. Micro-
probe scan of the Interface between the nickel and gold revealed that
heating the anode at 1250°F for 45 minutes resulted In the nickel just
-54-
-------
completely diffusing through the gold to the outer gold surface, whereas a
heating time of 30 minutes resulted In the nickelforming a solid solution
through 80 percent of the gold layer. This latter strip was selected to be
evaluated for Its resistance to corrosion by the fluoboric acid electrolyte
because only the' gold surface would be exposed to the fluoboric acid
electrolyte.
Application of a voltage to this gold nickel anode strip to achieve a
current density of .07 amps/cm^ while Immersed in the fluoboric acid
electrolyte resulted in the gold layer peeling from the nickel backing
(see Figure 17). Apparently, the solid solution between the gold and
nickel at the Interface does not resist the corrosive properties of fluo-
boric acid electrolyte.
Two graphite anode strips obtained from Union Carbide, Carbon Products
Division, Chicago, Illinois, Grade AGXC and Stackpole, St. Mary, Pa. Grade
LXB were evaluated to determine if they are resistant to the corrosive
properties of fluoboric acid electrolyte under an applied voltage. Visual
Inspection revealed that neither graphite strips exhibited any deterioration
when Immersed in fluoboric acid electrolyte under applied voltage to provide
a current density of .07 amps/cm2. As a result, two anodes were fabricated
for use In the electrodialysis unit and their performance evaluated under
actual operational conditions.
The Union Carbide anode was observed to exhibit appreciable leakage of
the fluoboric acid electrolyte from its sides. Encasement of this anode In
a plastic coating did not prevent this leakage.
The use of the Stackpole high density low porosity graphite anode of the
electrodialysis unit proved to be successful. There was no leakage of
-55-
-------
'• r
~
r -* r"9
- •
-••*» -*
FIGURE 17. PHOTOGRAPH OF CORRODED NICKEL ANODE
-56-
-------
fluoboric acid electrolyte fron the anode and a greater current was achieved
for a given applied voltage than that obtained with the widely used platinized
titanium anode. The use of the graphite anode In the electrodlalysis unit
containing 13 Ion pairs of membranes produce 10 amperes of current with an
applied voltage of 10 volts. In contrast, the use of the platinized titanium
anode in the electrodialysls unit containing the 13 ion pairs of membranes
required 15 volts to produce the same 10 amperes of current.
Electrodialysls Result
In the treatment of concentrated rinse-waters prepared by diluting tin,
solder and copper fluoborate plating bath solutions was carried out in the
electrodialysis unit containing the Stackpole high density low porosity gra-
phite anode and 13 ion pair membranes. The voltage across the anode and
cathode was adjusted to maintain 10 amperes of current for all the experi-
ments. The effectiveness of electrodialysis was evaluated for reducing the
concentrations of metal and fluoborate ions In the rinse-water to levels
which would allow the effluent to be treated using the ion flotation process,
while providing a product with concentrations of metal and fluoborate ions
that would approach that needed in the plating baths.
Treatment of Tin Fluoborate Rinse-Waters
A volume of 114 liters of tin fluoborate rinse-water containing 2400 mg/1
of stamous ion, 525 mg/1 stannic ion and 6500 mg/1 of fluoborate ion was
treated by electrodialysis. After 12 hours of operation using 13 ion pair
membranes at .012 amperes/on^ current density, the stannous ion concentration
in the feed was below measurable levels,- The stannic ion was reduced to 75 ng/1
and the fluoborate ion was reduced to concentrations below 150 mg/1 (see
Figure 18). The stannous ion is reduced to concentration levels approaching
-57-
-------
i,
T)
I
6 8
Time (hours)
10
12
FIGURE 18. ELECTRODIALYSIS TREATMENT OF TIN FLUOBORATE HINSE-WATERS,
FEED CATION CONCENTRATION
-------
zero within 8 hours. The stannic ion on the other hand Is removed at a much
slower rate than the stannous Ion from the feed over the initial 8 hours.
The rate of removal of stannic ion Increases after removal of Che stannous
ion.
The most rapid decrease in fluoborate concentration in the feed appears
to occur within the initial 8 hours of operation. During this period the
fluoborate ion concentration is reduced from 6500'mg/1 down to about 500 mg/1
(see Figure 19). This amounts to a removal of about 92 percent. The last
four hours of operating the electrodLalysis unit reduces the fluoborate
concentration from 500 mg/1 down to below 150 mg/1.
The above results are of interest because the; Indicate that the
plating chemicals in the feed can be reduced to levels acceptable for ion
flotation treatment. Also, the stannous ion which is the desirable ion in
plating baths is preferentially removed from the feed. Thus, the product from
the electrodlalysis unit should be enriched with stannous ion.
The analysis of the initial product from the electrodialysis unit
shows a 30 fold increase in the stannous and fluoboiate ions concentration.
I
The stannous ion in the Initial product collected is about 73,000 mg/1 after
2 hours of operation and decreases to 17,500 mg/1 (see Figure 20} as the
concentration of stannous ion in the feed is further depleted. The fluoborate
anion in the initial product is about 200,000 mg/1 and decrease to 100,000
mg/1 in six hours of operation (see Figure 21). This .decrease is expected
since the concentration of a specific ion in the product is reported (13)
to be proportional to that in the feed. The stannic ion concentration in
the initial product is about 7500 mg/1 and decreases to about 5000 mg/1
within six hours due to reduction in stannic Ion in the feed from 565 mg/1
-59-
-------
10
12
FIGURE 19.
Time (hours)
TREATMENT OF TIN FUJOBORATE RINSB-WATERS,
FEED ANION CONCENTRATION
-60-
-------
down to 500 Dg/1.
The percent stannous ion in the product is observed to remain essen-
tially well above 80 percent even though the stacnous ion in the feed has
been reduced from 83 percent down to 23 percent (see Table S).
These results reflect the greater rate of removal of the stannous ion
from the feed than the stannic ion.
The total amount of product generated in six hours from the treatment
of 114 liters of feed was roughly 4.3 liters. This amounts to a volume
ratio of product to feed of about 1:27. The concentration of tin and fluo-
borate in the product was 45 gm/1 of stannous ion, 6.7 gm/1 of stannic ion,
and 140 gm/1 of fluoborate ion. The stannous and fluohorate ions in the
product represent approximately one-half and one-third, respectively, of the
concentration of stannous and fluoborate ions required for plating bath
strength. The product collected in the initial six hours of operation
represent a recovery of 95 percent of the stannous ions, 48 percent of the
stannic Ion and 70 percent of the fluoborate ion originally present.
Treatment of Solder Fluoborate Rinse-Waters
The treatment of solder fluoborate plating bath which contains stannous,
staialc, lead and fluoboric ions in Its rinse-waters was carried out under
the same conditions employed for the treatment of the tin fluoborate plating
bath rinse-waters. Greater than 97 percent reductions in the stannous ion
and lead ions in the feed was achieved in eight hours. The time of operation
was not extended beyond these 8 hours because it was shown earlier that the
stannic ion and fluoborate ion concentration in the feed could be reduced to
levels acceptable for treatment by ion flotation.
The stannous ion is again observed to be preferentially removed from the
-61-
-------
s
X
o
Q)
U
0
Time (hours)
FIGURE 20. ELECT80DIAL7SIS TBEATKENT OF TIM FLUOBORATE.
RINSE-WATER, PRODUCT CATION CONCENTRATION
-62-
-------
in
o
e
o
41
4J
a
o
1
O
4)
u
1.5
0.5
Time (hours)
FIGURE 21. ELECTRODIALJfSIS TREATMENT OF TIN FLUOBORATE
RINSE-WATER, PRODUCT ANION CONCENTRATION
-63-
-------
TABLE 5. Changes In Percent Stannous Cation in the Feed and Product with Time
During the Electrodlalysls Treatment of Tin Fluoborate Rinse-Water
42 4-2
Time (hours) ZSn feed ZSn product
0 83
0.5 83 85
1.5 70 86
2.75 67 87
3.75 45 89
4.75 39 89
6.00 23 72
-64-
-------
feed. After eight hours of operation, the stannous ion is reduced from about
275 mg/1 to below 5 mg/1, whereas, the stannic ion concentration in the feed
was reduced from about 185 mg/1 to only about 165 mg/1 (see Figure 22).
Reductions in the lead ion are comparable to the stannous ion. The lead ion
concentration in the feed was reduced from about 190 mg/1 to below 5 mg/1.
Significant reductions in the concentration of fluoborate ion in the
feed was also observed. During eight hours of operation, the fluoborate Ion
was reduced from 1920 n>s/l to about 220 mg/1 (see Figure 23). This reductica
represents a removal of 90 percent of the fluoborate ion in the feed. Since
the stannous ion is again observed to be removed at a much faster rate from
the feed than the stannic Ion, the concentration of stannous ion In the
product should be significantly higher than the stannic.
Analysis of the Initial product collected after the first hour of
operation reveals the stannous ion concentration to be about 1300 mg/1
whereas, the stannic ion is found to be only 1800 mg/1 (see Figure 24). A 50
fold Increase In the stannous ion concentration in the product is achieved
over that originally present In the feed. The Increase in the stannic Ion
concentration In the product represents only a 10 fold increase over that
originally present in the feed. This Is the same Increase as encountered In
the treatment of the tin fluoborate rinse. This greater rate of removal of
i
the stannous ion produces a product where most of the total tin is in the
form of stannous ion. The stannous ion in the product averages above 80
percent even though the percent stannous ion in the initial feed is only
62 percent (see Table 6).
Analysis for the lead ion in the products reveals that its concentration
is comparable to that found for the stannous ion (see Figure 24). These
-------
5
8
Time (hours)
FIGURE 22. ELECTRODIALVSIS TREATMENT OF SOLDER FLUOBORATE RINSE-MATER, FEED CATION CONCENTRATION
-------
Time (hours)
FIGURE 23. ELECTRODIALYSIS TREATMENT OF SOLDER FLUOBORATE RINSE-WATER, FEED.ANION CONCENTRATION
-------
20000
012345 678
Time (hours)
FIGURE 2A. ELECTRODIALYSIS TREATMENT OT SOLDER FLUOBORATE RINSE-WATER, PRODUCT ION CONCENTRATIOH
-------
results are expected since the removal of lead from the solder rinse-water
feed as a function of time is comparable to that achieved with the stannous
ion.
The fluoborate ion concentration in the product collected within the
first hour of operation was found to be about 16,000 mg/1. This represents
only a 10 fold Increase in the fluoborate ion found in the product over
that present in the Initial feed. Treatment of the tin fluoborate rinse-
water resulted in a 30 fold increase in the concentration of,f1uoborate
anion in product over that found in the feed. The reason for smaller
fluoborate anion concentration effect obtained in the product from the
treatment of the solder rinse-water is not clear at this time.
The electrodialysia treatment of approximately 114 liters of solder
rlnae-water over a period of eight hours produced roughly 3.2 '.iters of
product. This amounts to a volume ratio of product to feed of about 1:36.
The concentration of stannous ion, stannic ion, lead ion and fluoborate ion
in this product was found to be 6.5 gm/1, Q.6 gm/1, 5.9 gm/1 and 11 gm/1,
respectively. The concentrations of stannous ion and lead ion in the. product
are about half of the concentrations of stannous and lead ions commonly used
in the solder plating bath. The concentrations of fluoborate ions in the
product represents about one 40th o£ the fluoborate ion used in the plating
baths. These results represent a 97 percent recovery of stannous Ion and
lead ion,. 88 percent of the fluoborate ion and 11 percent of the stannic ion.
Treatment of Copper Fluoborate Rinse-Waters
The electrodlalysis treatment of the copper fluoborate rinse- waters were
carried out under the same experimental conditions as the tin and solder
rinse-waters. The copper ion in the feed was reduced from initially
-69-
-------
TABLE 6. Changes in Percent Stannous Ion in Feed and Product with Time
During Electrodialysis Treatment of Solder Fluoborate Rinse-Water
Time (hours) ZSn"1"2 feed ZSn"*"2 product
0 62
1 44 89
3 32 36
4 15 79
5 8 83
6 6 70
-70-
-------
2500 mg/1 to less Chan 40 mg/1 lii approximately three hours (see Figure 25).
This represents about a 97 percent reduction In copper Ion concentration in
the feed in three hours. In comparison, a 97 percent reduction in tbe
stannous ion in the tin fluoborate rinse-water and the solder rinse-water
required 6 hours and 8 hours, respectively. A V7 percent reduction in the
solder rinse-water feed also required 8 hours.
The 'greatest reduction in the fluoborate ion concentration in the
treatment of the copper fluoborate rinse feed was encountered in the initial
four hours of operation. The concentration of the fluoborate ion in the
feed was reduced from 7500 mg/1 to 650 mg/1 during this period (see Figure
26). This reductiou amounts to 90 percent removal of the fluoborate ion in
the feed. In comparison, the electrodlalysis treatment of both the tin and
solder fluoborate rinse-waters required 8 hours to achieve the -same removal
percentages. Apparently, the presence of stannic ion in the feed of the tin
and solder rinse-water which is removed at a. much slower rate than the
stannous and lead ions may inhibit the removal of the fluoborate ion.
The analysis of the products collected from the electrodialysis of
copper fluoborate rinse-water after about I's hours of operation showed a 20
fold increase In cupric and fluoborate ion over their initial concentration.
The cupric and fluoborate ion In the product va's about 53,000 mg/1 and
160,000 mg/1, respectively after l*s hours of operation (see Figure 27).
In comparison, the initial stannous and fluoborate ion product concen-
tration collected from the electrodlalysis of the tin fluoborate rinse-water
showed a .J fold increase over that present in the initial feed. The initial
stannous and lead ion product concentration from electrodialysis of the
solder hath rinse-water showed about a 50 fold increase whereas the initial
-71-
-------
3000
2500
Time (hours)
FIGURE 25. ELECTRODIALYSIS TREATMENT OF COPPER
FLDOBORATE RINSE-WATER, FEED
ANION CONCENTRATION
-72-
-------
123 4
Time (hours)
FIGURE 26. ELECTRODIALYSIS TREATMENT 07 COPPER FLBOBORATE
RINSE-WATER, FEED ANION CONCENTRATION
-73-
-------
18
16
14
<=>
BO
e -
10
o
01
u
O
u
Time (hours)
FIGURE 27. ELECTRODIAIYSIS TREATMENT OF COPPER FLUOBORATE
RINSE-WATER, PRODUCT ION CONCENTRATION
-74-
-------
fluoborate Ion product concentration showed only a 10 fold Increase.
The electrodialysls of the copper fluoborate rinse-water over a period
of slightly less tnan 6 hours produced roughly 7 liters of product. This
amounts to a volume ratio of product to feed of 1:17. The concentratlou of
cupric Ion and fluoborate ion present ;ln this product was found to be about
40 gm/1 and 120 gm/1 respectively. The cupric concentration In the product
is about 3 times more concentrated than plating bath strength and the fluo-
borate Ion concentration Is about one-third that generally used in a
copper plating bath.
Rates of Mass Transfer
The results of the treatment of the fluoborate plating bath rinse-
vaters indicate that the rate of mass transfer of the ions actoss a square
centimeter of membrane surface from the feed to the concentrate Is dependent
upon the cations In the rinse-waters and plating bath rinse-water that is
being treated. The rate of mass transport across one square centimeter of
membrane'surface for the stannous ions from both the tin and solder rinse-
water feed, respectively are comparable (see Table 7). The lead ion in the
solder rinse-water feed is also removed at approximately the same rate
(1.4 mg/hr. on2) as the stannous ion (1.7 mg/hr. cm2, 1.9 mg/hr. cm ). The
stannic Ion on the other hand shous a mass transport rate that is some 10
times slower than the rates obtained with the stannous and lead tons. These
results cannot be explained at this time because the charge on the cation
does not appear to influence the mass rate of transfer. The stannic cations
with a +4 charge would be expected to move across the membrane at a greater
rate than a cation with a +2 charge. Yet the copper ion has the same +2
charge as the stannous and lead Ions, but exhibits a 20 tilmes faster rate of
-75-
-------
transport (41 mg/hr. on2) then either the stannous or lead ions.
The rate of mass transfer of the fluoborate anlon also appears to be
dependent upon the plating rinse-water. The rate of mass transport exhibi-
ted by the fluoborate anlon in the copper bath rinse-water is significantly
higher than that encountered in either, the tin or solder bath rinse-water
<*
(see Table 7). The rate of mass transport is 94 mg/hr. cm in the copper
rinse-water following in decreasing order by 28 mg/hr. cm2 and 12 mg/hr. cm2
in the tin and solder rinse-water, respectively. The difference in mass
rate of transport between the fluoborate anlon in the treatment of the tin
and solder rinse-waters cannot be explained at this time. Since the rate of
mass transport for the stannous and stannic ions between the tin and solder
rinse-waters are comparable, one would expect the rate of mass transport for
the fluoborace anlon to be similar.
Analysis of Electrolyte
The electrolysis or hydrolysis of the electrolyte as evidenced by
changes of pH and fluoborate concentration was not observed. Both the pH
and fluoborate concentration in the -electrolyte remained constant during
the electrodialysls treatment of the tin, solder and copper fluoborate
rinse-waters.
-76-
-------
TABLE 7. Rate of Mass Transport of Cations and Fluoborate from the Tin, Solder,
Copper Fluoborate Rinse-Waters
Plating Bath Finse-Vaters
Rate of Mass Transport,.
(mg/hr. cm*)
Ions Tin fluoborate Solder fluoborate Copper fluoborate
Sn*2 1.7 1.9
Sn"** .19 .14
Pb+2 1.4
Cu+2 41
BF.~ 28 12 94
4
-77-
-------
VI. REFERENCES
1. "Waste Treatment - Upgrading Metal Finishing Facilities to Reduce
Pollution", EPA Technology Transfer Seminar Publication, January, 1974.
2. Sharp, D.W.A., "Fluoboric Acids and Their Derivatives", London, England:
Bullersworth, 1960, pp. 69-80.
3. Cagnatl, V.N., R. Haralson, G. Hunter, J.W. Llskoultz, A. Perna, and
R. Trattner, "Removal of Fluoborate From Plating Wastewater: Technique
and Mechanism", Water - 1977, American Institute of Chemical Engineers,
pp. 309-315.
4. Eckenfleder, W.W., Jr., "Industrial Pollution Control", McGraw-Hill
Book Company, New York, New York, 1966.
5. Fair, G.M., J.C. Geyer, and D.A. Okum, "Water and Waste Water
Engineering", Vol. 2, John Wiley & Sons, New York, New York, 1968.
6. Shneve, R.N., "Chemical Process Industries", 3rd Edition, McGraw-Hill
Book Company, New York, New York, 1967.
7. Sebba, F., "Ion Flotation", Elsevler Publishing Co., 1962
8. Grieves, R.B.and G.A. Ettelt, "Continuous Dissolved Air Flotation of
Hexlvalent Chromium", A.I.Ch.E Vol. 13, No.6, November 1967.
9 Grieves, R.B., "Foam Separation of Anlons from Aequous Solutions,
Selectivity of Cationlc Surfactants", Separation Science, 19(1), 1975.
10. Cohan, H.J., "Electrodlalysls Equipment and Membranes", Chem. Eng. Prog.,
Vol. 52, No. 2, 1961
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11. Birkett, J.D.."Electrodlalysis - An Overview", Industrial Hater
Engineering, September, 1977, pp. 6-10.
12. Eisenmann, J.L., "Recovery of Nickel From Plating Bath Rinse Waters
by Electrodlalysis", Plating and Surface Finishing, November, 1977,
pp. 34-38.
4
13. Twiner, S.B., "Investigation of Treating Elnctroplaters Cyanide Waste
by Electrodialysis", EPA-R2-73-287, December, 1973.
14. Langford, K.E., and G.E. Parker, "Method 155, Analysis of Electro-
plating and Related Solutions", Teddington and Draper Publishing Co.,
1971.
15. Easa, H.S., and K. Scfaugerl, "Holdup and Backmixing Investigations in
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