V
V
United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
">- ,,v"
>M*
Research and Development
EPA/600/S2-85/054 June 1985
Project Summary
Removal and Recovery of
Fluoborates and Metal Ions from
Electroplating Wastewater
John W. Liskowitz, Vincent N. Cagnati, Terrance Hunter, and Ray Haralson
The study conducted at the New Jer-
sey Institute of Technology, Newark,
New Jersey, was concerned with devel-
opment 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 removing specific ions from
dilute wastewater through binding with
a surfactant, followed by flotation or
ultrafiltration. This part of the investiga-
tion involved the evaluation of structur-
ally different commercially available
surfactants to determine the type, struc-
ture, 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 waste-
water. Methods for recovery of the sur-
factant 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/l of
fluoborate to 7-15 mg/l of fluoborate.
Actual plating operation rinse waste-
waters containing 100 mg/l of fluobo-
rate were used in the study. Ultrafiltra-
tion followed by electrolysis provided
the shortest treatment time with recov-
ery of the surfactant.
The second method was electrodialy-
sis. Here, the major effort was to find a
suitable anode. Electrodialysis was
found feasible for treatment of waste-
streams containing plating chemical
concentrations > 1000 mg/l using a
high density low porosity graphite
anode. Electrodialysis can reduce the
plating chemical concentrations in the
wastestream to about 100 mg/l.
The specific ion flotation process
either used separately or in the combi-
nation with electrodialysis can be useful
and effective for closed-loop treatment
of fluoborate-containing wastewaters
from electroplating operations. Reagent
recovery in specific ion flotation and
fluoborate and metals recoveries in
electrodialysis can be achieved in addi-
tion to pollution control. However, both
methods need further development to
make them commercially suitable for
treatment of fluoborate-containing
wastestreams.
This Project Summary was developed
by EPA's Hazardous Waste Engineering
Research Laboratory, Cincinnati. OH.
to announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
A recognition of the detrimental effects
of industrial pollution on our environment
has surfaced in recent years. One of the
industries contributing to this pollution is
the metal finishing industry.
The wastewater produced in metal fin-
ishing operations contains toxic cation
and anions. Concentrated wastestreams
are generated by cleaning, stripping, pas-
sivating, and anodizing operations when
the spent process solutions are discarded.
The larger volume dilute streams come
-------
from the rinsewaters that are contami-
nated with the process solution that has
adhered to the surface or is entrapped in
crevices due to the shape of the pro-
cessed piece.
Presently, the most commonly used
procedure for treating metal finishing
wastestreams involves precipitation of
the heavy metals and anions to form a
sludge.
Problems arise mainly with the dispos-
al of sludge because the precipitates
present a potential leaching problem in
landfills. Alternatives to the precipitation
process are the recovery and recycle of
plating chemicals from the wastestreams
at their point of generation, or the substi-
tution of toxic process chemicals with
less objectional ones.
Substitution of process chemicals is
practical only when the substitute does
not compromise the quality of the fin-
ished product. One such substitution is
the use of fluoborate to replace cyanides
as a conducting salt in plating baths.
Commercial fluoborate solutions are pres-
ently available for the plating of copper,
indium, iron, lead, nickel, tin, and their
alloys. Also, fluoboric acid is used in var-
ious pretreatment operations, such as
stripping and cleaning. Fluoborate has
been found to be an excellent carrier ion
which gives uniform, bright, well-thrown
covering. Also, fluoborate is much less
toxic than cyanide, and therefore pro-
vides for a safer plating room.
There are presently no specific dis-
charge limitations on fluoborate. How-
ever, when a wastestream is analyzed for
fluoride by the approved method (Bellack
Distillation), any fluoborate present will
be hydrolyzed yielding inflated fluoride
concentrations. For each fluoborate ion
present in a sample the test will show
four fluoride ions. This gives a false indi-
cation of fluoride concentration and can
show a National Pollution Discharge
Elimination System Permit (NPDES) vio-
lation where none exists.
Few processes are suitable for the
removal of fluoborate from plating rinse-
waters. It is a small ion and is not easily
rejected by membrane processes such as
reverse osmosis. Presently, there is no
known ion exchange resin which will
remove fluoborate from solution efficient-
ly. Battelle Memorial Institute in their
January 1974 Draft of the Development
Document for Limitations for Electroplat-
ing Point Sources, suggested the hydrol-
ysis of the fluoborate to fluoride followed
by lime precipitation as a possible treat-
ment. This, however, results in the pro-
duction of a sludge that must be disposed
in secure landfills.
Vacuum evaporation is currently being
used as a means of recycling tin fluobo-
rate rinsewaters back into the plating
tank as a makeup solution. Although it
provides closed-loop treatment, problems
such as precipitation of stannic oxide
which inhibits the evaporation are en-
countered during the evaporation pro-
cess. It is also an energy intensive
operation.
Since suitable technology for the treat-
ment of rinsewater from fluoborate plat-
ing baths is lacking, this investigation
was undertaken.
Two separate processes, ion flotation
and electrodialysis, were investigated for
the treatment of dilute and concentrated
fluoborate wastestreams, respectively
from the electroplating industry. Specific
ion flotation has been investigated for the
removal of metal cations and the anionic
chromate from solutions, but it has not
been explored for the removal of fluobo-
rate ion from dilute wastestreams result-
ing from single tank rinsing.
The specific ion flotation investigation
involved the identification of the type and
structure of the surfactants that would
provide maximum removal of the fluobo-
rate ion, in dilute rinsewaters. This was
followed by a series of studies to under-
stand the mechanism involved in the
removal of the fluoborate ion and the
parameters that would influence its re-
moval from the wastestream. Also, meth-
ods for recovering the surfactant and
fluoborate anions for reuse were studied.
The second method involved the inves-
tigation of electrodialysis for the recovery
and reuse of plating chemicals in concen-
trated rinse wastewater generated by
multiple tank counter-current and series
rinsing operations. Electrodialysis has
been applied to the recovery of nickel and
copper from plating rinsewaters and
closed-loop control of cyanide rinse-
waters. However, electrodialysis has not
been employed in the treatment of fluob-
orate plating rinsewaters.
The use of electrodialysis treatment for
the wastestreams containing copper fluo-
borate, tin fluoborate, and solder fluobo-
rate required the development of a new
anode that would resist the corrosive
properties of the fluoboric acid electro-
lyte. Fluoboric acid which is extremely
corrosive toward the commonly used plat-
inized metal anodes was employed in-
stead of sulfuric acid as the electrolyte to
avoid contamination of the product with
undesirable sulfate anions.
Results
Specific Ion Flotation
A number of different commercially
available surfactants were examined.
Only alkylamine acetate type surfactants
provided significant removals of fluobo-
rate ion from solution. The removal of the
fluoborate ion was found to be dependent
upon its binding to the surfactant through
displacement of the acetate group on the
surfactant. Kinetic studies of the displace-
ment reaction revealed that optimum
binding of the fluoborate ion to the surfac-
tant occurred within one minute. Acidic
conditions that favor the formation of the
acetic acid from the displaced acetate ion
improve the removal of the fluoborate ion
by the surfactant. The presence of other
anions in solution that form stronger
acids than fluoboric acid tend to inhibit
the removal of the fluoborate ion by the
surfactant.
The molecular weight of the surfactant
was observed to have a pronouneed effect
on the fluoborate ion removed. An in-
crease in the size of the surfactant con-
taining from 12-15 carbon atoms up to 18
carbon atoms increased the percent of
fluoborate ion removed from 80 percent
up to 97 percent. The degree of saturation
did not have an effect on the amount of
the fluoborate ion removed.
A series of experiments were carried
out where different concentrations of
surfactant solutions were added in a
stepwise manner to individual solutions
containing the same amount of fluobo-
rate. The results reveal that as the con-
centration of surfactant in a solution is
reduced, the amount of surfactant re-
quired to bind with a specific amount of
fluoborate becomes less. Stepwise addi-
tion of three aliquots of dilute surfactant
solution to a solution initially containing
100 mg/l of fluoborate required a ratio of
2.1 molecules of surfactant to 1 molecule
of fluoborate ion for maximum removal.
The single addition of concentrated sur-
factant solution to the solution containing
the same concentration of fluoborate as
above required a ratio of three molecules
of surfactant to one molecule of fluobo-
rate ion for the same removals. The step-
wise addition of surfactant to the fluobo-
rate solution apparently provides a more
dilute surfactant solution with less mi-
celle formation and more free surfactant
molecules to bind with the fluoborate.
The critical micelle concentration oc-
curred at a surfactant concentration of 1 2
mg/l.
Operation parameters such as changes
in air feed ratio, air bubble size, air dif-
-------
f user location, and inlet feed direction did
not appear to improve the rates of remov-
al of the surfactant-f luoborate complex by
flotation. However, increasing the air feed
rate produces a wetter foam which results
in a reduction in the concentration of the
surfactant-fluoborate complex in the
foam.
Application of the specific ion flotation
to the removal of fluoborate ion in solder
plating, tin plating, nickel stripping, and
copper plating rinsewaters containing
100 mg/l of fluoborate reduced the
fluoborate in the solder plating, tin plat-
ing, and nickel stripping rinsewaters to 7
mg/l. The fluoborate in the copper plating
rinsewaters was reduced to 15 mg/l. The
removal of the fluoborate ion from the
copper plating rinsewater by the specific
ion flotation is probably less efficient,
because this rinsewater was less acidic
than the other rinsewaters.
Although flotation was shown to be
effective in removing the surfactant-f luo-
borate complex from the plating rinse-
waters, it required foaming times in
excess of 20 hours to completely remove
the complex from solution using our
experimental system. The use of a Milli-
pore High Volume Cassette* ultra-filtra-
tion system with 1000 molecular weight
cut-off membranes resulted in removal of
the complex within 6 hours.
Two approaches were examined for the
recovery of the surfactant and the fluobo-
rate for reuse in the treatment process
and plating baths, respectively. The first
approach which considered displacing
the fluoborate from the surfactant by
adding excess amounts of concentrated
acetic acid was unsuccessful. The second
approach used electrolysis to separate
the surfactant from the fluoborate ion.
The surfactant is plated on the cathode
and can be removed from the cathode
with concentrated acetic acid to recover
the surfactant in the acetate form. Ninety
percent of the acetate surfactant was
recovered.
Electrodialysis
Application of electrodialysis for treat-
ment of rinsewater containing high con-
centration of plating reagents required
modification of an existing electrodialysis
unit. Rapid deterioration of the commonly
used platinized titanium anode was en-
countered when fluoboric acid was used
as the electrolyte. Although this anode
has been successfully used with nickel
'Mention of trademarks or commercial products does
not constitute endorsement or recommendation for
use by the U.S. Environmental Protection Agency.
sulfate plating bath rinsewaters and a
sulfuric acid electrolyte, it rapidly turns
black, cracks, and peels from the titanium
metal backing when voltage is applied in
the presence of fluoboric acid electrolyte.
Apparently, the smaller fluoborate ion
can penetrate the porous platinum coat-
ing and corrode the metal bond between
the platinum and titanium.
The matching of the anion in the elec-
trolyte with that in the rinsewaters is pre-
ferred to using another anion such as sul-
furic acid electrolyte which is non-cor-
rosive to the platinized titanium anode.
The sulfuric acid electrolyte would result
in introduction of undesirable sulfate
anion into the concentrated streams and
ultimately into the plating bath.
Evaluation of Different Types of
Anodes
Several different approaches were con-
sidered to obtain an anodethat would not
corrode in presence of fluoboric acid elec-
trolyte. These were (1) i ncrease the thick-
ness of the platinum plated on the plati-
nized titanium anode; (2) plate a less por-
ous metal such as gold on a nickel back-
ing and form a solid solution between the
gold and the nickel at the interface by
heating; and (3) examine the use of inex-
pensive conducting materials such as low
porosity high density graphite to which
voltage could be applied directly.
The use of an inexpensive high density
low porosity graphite anode was the only
anode that proved successful. It did not
corrode in the presence of fluoboric acid
electrolyte and it produced a greater cur-
rent density at lower voltage than the
conventional platinized titanium anode.
Treatment of Tin Fluoborate
Rinsewaters
A 114-liter reservoir of tin fluoborate
rinsewater containing 2400 mg/l of
stannous ion, 525 mg/l stannic ion and
6500 mg/l of fluoborate ion were treated
by electrodialysis. After 12 hours of opera-
tion using 13 ion pair membranes at .012
amperes/cm2 current density, the stan-
nic ion was reduced to 75 mg/l and the
fluoborate ion was reduced to concentra-
tions below 150 mg/l. The stannous ion
which isthedesirable ion in plating baths
is preferentially removed from the feed.
The stannous ion is reduced to concentra-
tion levels approaching zero within 8
hours. The stannic ion is removed at a
much slower rate than the stannous ion
from the feed. The rate of removal of
stannic ion increases after removal of the
stannous ion.
The volume ratio of product to feed for
the treatment of tin fluoborate rinse-
waters was approximately 1 :27.
The percent stannous ion in the pro-
duct is observed to remain essentially
well above 80 percent even though the
stannous ion in the feed has been reduced
from 83 percent down to 23 percent (see
Table 1).
Table 1. Changes in Percent Stannous
Cation in Feed and Product with
Time During the Electrodialysis
Treatment of Tin Fluoborate
Rinsewater
Time (hours)
Feed %SN* Product
0
0.5
1.5
2.75
3.75
4.75
6.00
83
83
70
67
45
39
23
85
86
87
89
89
72
The concentration of stannous ion,
stannic ion, and fluoborate ion in the pro-
duct was 45 gm/l, 6.7 gm/l and 140
gm/l, respectively. These concentrations
represent a 95 percent recovery of stan-
nous ion, 48 percent recovery of stannic
ion, and 70 percent recovery of fluoborate
ion originally present in the feed.
Treatment of Solder Fluoborate
Rinsewaters
The treatment of solder fluoborate plat-
ing bath which contains stannous, stan-
nic, lead, and fluoborate ions in its rinse-
waters was carried out under the same
conditions employed for the treatment of
the tin fluoborate plating bath rinse-
waters.
The stannous ion is again observed to
be preferentially removed from the feed.
After eight hours of operation, the stan-
nous ion is reduced from about 275 mg/l
to below 5 mg/l, whereas, the stannic ion
concentration in the feed was reduced
from about 185 mg/l to only 165 mg/l.
Reductions in the lead ion are compar-
able to the stannous ion. The lead con-
centration in the feed was reduced from
about 190 mg/l to below 5 mg/l. The
fluoborate ion was reduced from 1920
mg/l to about 220 mg/l
The volume ratio of product to feed for
the treatment of solder fluoborate rinse-
waters was approximately 1:36. The
stannous ion was again preferentially
concentrated in the product and averaged
above 80 percent even though the per-
-------
cent stannous ion in the initial feed is only
62 percent. The concentrations of stan-
nous ion, stannic ion, lead ion, and fluo-
borate in the product were 6.5 gm/l, 5.9
gm/l, and 11 gm/l, respectively. This
represents a 92 percent recovery of the
stannous and lead ions, 88 percent re-
covery of the fluoborate ion, and 11 per-
cent recovery of the stannic ion.
Treatment of Copper Fluoborate
Rinsewaters
The electrodialysis treatment of the
copper fluoborate rinsewaters was car-
ried out under the same experimental
condition as the tin and solder rinse-
waters. The copper ion in the feed was
reduced from initially 2500 mg/l to less
than 40 mg/l in approximately four hours.
In this period of time, the concentration of
the fluoborate ion in the feed was reduced
from 7500 mg/l to 65 mg/l.
The volume ratio of product to feed for
the treatment of copper fluoborate rinse-
waters was approximately 1:17. The con-
centration of copper and fluoborate ions
in the product was 40 gm/l and 120
gm/l, respectively. These product con-
centrations represent a 97 percent and a
90 percent recovery of the copper and
fluoborate, respectively, originally pres-
ent in the feed.
Rates of Mass Transfer
The rate of mass transfer of the ions
across a square centimeter of membrane
surface from the feed to the concentrate
is dependent upon the cations in the rinse-
waters and the plating bath rinsewater
that is being treated. Comparable rates of
mass transport across one square cen-
timeter of membrane surface were ob-
tained for the stannous ions from both the
tin and solder rinsewater feed, respec-
tively (see Table 2). The solder rinsewater
feed is also removed at approximately the
Table 2. Rate of Mass Transport of
Cations and Fluoborate from the
Tin, Solder, Copper, Fluoborate
Rinsewaters
Plating Bath Rinsewaters
Rate of Mass Transport
(mg/hr. cm2)
Tin Solder Copper
Ions Fluoborate Fluoborate Fluoborate
Sn+*
Sn"
Pb*
C
-------
sistance to chemical corrosion and
greater current density for a given
applied voltage than the more com-
monly used platinized titanium
anode.
3. The graphite anode's resistance to
chemical corrosion permitted the
highly corrosive fluoboric acid to be
used as an electrolyte to 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 concen-
trate. 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 electrodialysis product.
Recommendations
The recovery of plating bath chemicals
and the closed-loop treatment using elec-
trodialysis with newly developed graphite
anode and specific ion flotation of rinse-
water containing fluoborate anions from
solder, tin, copper, and nickel plating
operations has been shown to be feas-
ible. There are a number of advantages in
using electrodialysis and specific ion flo-
tation for the treatment of rinsewater
containing fluoborate. Electrolysis treat-
ment preferentially concentrates the de-
sirable stannous ions in the product
stream from a mixture of stannous and
stannic cations commonly 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 pro-
vides 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 electrodialysis unit containing
anions that match the anions in the feed
is desirable to avoid contamination of the
product produced from electrodialysis
treatment. I n addition, the surfactant used
in the specific ion flotation treatment of
rinsewaters containing low concentra-
tions of fluoborate can be recovered along
with the fluoborate anion by electrolysis.
In view of the above, the commercial
feasibility of using electrodialysis in com-
bination with specific ion flotation to pro-
vide a closed-loop treatment system
should be established on a pilot scale. The
engineering parameters and costs asso-
ciated with the design, assembly, and
operation of both systems must be de-
termined. Also, this pilot-scale effort
should identify the methodology that will
allow rapid mixing of the fluoborate rinse-
waters with the alkylamine acetate sur-
factant solutions at concentrations that
do not favor micelle formation. In addi-
tion, the long-term stability of electrodial-
ysis membranes (longer than 60 hours)
toward the fluoboric acid electrolyte
should be evaluated since frequent re-
placement of these membranes can lead
to unacceptable operating costs. The
replacement 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 replace the commonly used
platinized titanium anode.
The full report was submitted in fulfill-
ment 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 work was completed as of
October 1979.
John W. Liskowitz. Vincent N. Cagnati, Terrance Hunter, and Ray Haralson are
with the New Jersey Institute of Technology, Newark, NJ 07102.
Mary K. Stinson is the EPA Project Officer (see below).
The complete report, entitled "Removal and Recovery of Fluoborates and Metal
Ions from Electroplating Wastewater," (Order No. PB 85-200 038/AS; Cost:
$ 11.50. subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
•&U. S. GOVERNMENT PRINTING OFFICE: 1985/559-111/20608
-------
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
OCOr329 PS
U 3 6NVIR PROTECTION AGENCY
REGION 5 LIBRARY
£30 S DEARBORN $TRE£T
CHICAGO IL 60*04
------- |