Continuous Electrolytic Treatment of Complex Meb!$8$!&!s With a Rotating Barrel Plater As the Cathode

And a Packed Bed as the Anode 8=88304

P 4\ a7324

By C.-D. Zhou and D.-T, Chin

A continuous electrolytic process consisting of a plating barrel cathode and a packed-bed anode was used to recover metals and to destroy cyanide in waste silver, copper and cadmium cyanide solutions. The experi- ments were carried out with and without the addition of NaCl to the feed solutions. The effluent concentrations of total cyanide, free cyanide and metal Ions were examined for various cell currents, solution tempera- tures, solution feed rates, solution reclrculation rates, barrel rotation speeds, and barrel loadlngs. The total cyanide concentration was reduced from 520 ppm to fewer than 10 ppm, and metal concentrations from 225-486 ppm to less than 1 ppm. The average energy consumption per kilogram of total cyanide destroyed was: 80 to 490 kWh for silver cyanide, 80 to 520 kWh for copper cyanide, and 50 to 330 kWh for cadmium cyanide.

he sources of metal and cyanide wastes and their characteristics are listed in the literature.'$ Because of toxicity, these wastes must be adequately treated T before discharge from the process plant. In a previous

paper, the authors described a batch electrolytic process to recover copper and destroy cyanide using a plating barrel cathode and a packed-bed anode.3 The total cyanide concen- tration was reduced from 580 ppm to fewer than 10 ppm. The process was more cost effective than the conventional alkaline chlorination method.* It also had a cost advantage over a commercial carbon fiber electrolytic process because of a lower capital investment.

For dilute solutions, such as plating rinsewater, electrolytic recovery of metal and destruction of cyanide Is diff icult because of mass transfer limitation and low reaction rate per unit electrode area. A number of electrolytic cells have been de- signed with the electrodes that either enhance mass transfer rate or have a large surface area. Some of these designs are: porous ele~trode,~ concentric cylinder: rotating ~ylinder,~ packed-bed?efluidized-bed,'+ll and carbon fiber.12 The porous electrode, packed-bed and carbon fiber designs provide a large surface area, whereas the concentric and rotating cylinders have a high mass transfer rate. The fluidized-bed offers a large surface area and a high mass transfer rate; however, it has a nigh electric resistivity because electrode particles lose contact with their current collector during the fluidization movement. The tumbling bed, such as a plating barrel, is agood choice for the treatment of dilute waste solutions. The particles in the tumbling bed possess a large surface area, and the tumbling motion of electrode particles improves mass transfer without losing electric contact with the current collector. Several pat- ents describe the use of tumbling beds to treat wastewater.1515 Oehr used a plating barrel to destroy cyanide.lB Tison used a

* Based on 1992 US. dollars, the cost per kllogram of cyanide destroyed was estimated at: $71.81 for the chlorination method; $14.54 for the carbon fiber electrolytic method; and $12.52 for the electrolytic treatment using a plating barrel cathode and a packed-bed anode.s

Table 1-Test'Solutions

tumbling bed to recover copper from a dilute copper sulfate s o I u t i ~ n . ~ ~ ' ~ ~ He found that the tumbling bed had a more uniform current and metal distribution than the packed-bed.

In this study, a continuous electrolytic process, using a plating barrel cathode and a packed-bed anode to recover metals and destroy cyanide simultaneously in waste plating solutions, was examined. Silver cyanide, copper cyanide, and cadmium cyanide solutions were used in the experiments. The effect of temperature, cell current, solution feed rate, NaCl concentration, barrel rotation speed, barrel loading, and solu- tion recirculation rate on the effluent cyanide and metal concen- trations and energy consumption was studied.

Experimental Program Test Solutions Experiments were carried out with acontinuousflow cell to treat silver cyanide, copper cyanide, and cadmium cyanide solu- tions. The copper cyanide and cadmium cyanide experiments were carried out with the addition of NaCI. Table 1 lists the com- position and temperature of test solutions used in the study.

For the silver cyanide test, a solution containing 0.0045 M AgCN, 0.01 55 M NaCN and 0.005 M Na,CO, at 25 and 65 "C was used. The total cyanide, free cyanide, and silver concen- tration in the solution was 520 ppm, 286 ppm and 486 ppm, respectively.

For the copper cyanide test, a solution containing 0.005 M CuCN, 0.015 M NaCN and 0.1 M NaOH was used. The composition corresponded to a concentration of 520 ppm of total cyanide, 1 12 ppm of free cyanide and 31 8 ppm of copper. The test was performed without NaCl as well as with 0.2, 0.4 and 0.6 M NaCl at 25 "C and 65 "C.

1

70 P18fhg and Surface Finlshlng

z

electrolyte in recirculation-

ai I I

waste solution

tank

)de I ' metering t--'O Pump

and sampling port

t n effluent I -7 1 s;;;;on 1

drain cathode anode compartment compartment

Fig. 1-Schematic of cell sef-up.

For the cadmium cyanide test, a solution containing 0.002 M CdO, 0.02 M NaCN, 0.1 M NaOH and 0 - 0.6 M NaCl at 25 OC and 65 "C was used. The concentrations of total cyanide, free cyanide and cadmium were 520 ppm, 380 ppm, and 225 ppm, respectively.

Cell Set-up The continuous flow cell used in the experiment is shown schematically in Fig. 1. The system consisted of an electro- chemical cell having a packed-bed anode and a plating barrel cathode of 6.4 cm, inside diameter, by 10 cm in length," a solution feed tank, an effluent solution tank, and two metering pumps. These components were connected together by poly- ethylene and Tygon tubes.

The electrochemical cell was made of Plexiglasm sheets 1.25cminthickness,withdimensionsof 18cmxl5cmx25cm(lwh).

The cell was divided into a cathode and an anode compartment as shown in Fig. 1. The plating barrel loaded with metal particles was placed in the cathode compartment. A copper cylinder 0.6 cm in diameter by 1.2 cm in length was used as the dangler contact in the barrel. The packed-bed anode was located below the plating barrel to serve as a partition between the cathode and anode compartments. It had dimensions of 13 x 10 x 9 cm (Iwh), and was loaded with 5009 of activated carbon pellets, 0.2 cm in diameter by 0.5 cm in thickness. A 1.25-cm thick piece of graphite felt, inserted through the anode compartment, was used as the anode current collector. The solution temperature in the cell was controlled by a quartz heater and a temperature controller.b

a Model Snap LockrH, Singleton Company, Cleveland, OH Model 21 57, Cole-Parmer, Chicago, IL

0.05 v I I / I 50% Immersion 50% loading. 11 = 15 rpm Racirculallon rate = 4 mVsec

, 0 5 10 15 20 25 30 35 40 i S

Dlmenslonless cell current, I'

Fig. &Dimensionless effluent total cyanide concentration vs. dltnensionileJ cell current for treatment of silver, copper, and cadmium cyanide solution$

I ilver Cyanide Solution without Addition of NaCI*

C.E. kWh/kg CN

0.014 8.9 0.018 3 6.2 , 247

Two 5-gallon polyethylene tanks were used as the feed and effluent solution tanks. A metering pump" with a flow range of 0.02 to 2.1 mUsec was used to pump the test solution from the feed tank to the plating barrel. The solution flowed from the plating barrel through the packed-bed anode to the anode compartment and overflowed to the effluent tank as shown in Fig. 1. A second metering pumpd with a flow range of 0.05 to 4.7 mUsec was used to recirculate the solution from the anode compartment to the topof the plating barrel. Ad-cpower supply" was used for the electrolysis; a digital multimeter' was used to measure the anode-to-cathode cell voltage.

For the copper cyanide and silver cyanide tests, copper chips with a diameter of 0.1 to 0.3 cm were used in the plating barrel to recover metals. For the cadmium cyanide test, steel rings withan insidediameterof 0.7cm,anoutsidediameterof 1.4cm, and a thickness of 0.1 cm were used as the cathode material. The cyanide ion released by the electrodeposition of complex metal cyanide ion at the barrel cathode was transported by the solution flow to the packed-bed anode, where it was oxidized to nontoxic N, gas and HCO; ion.

5 10 1 S x t ? B 3 0

DlmenslonlrB cell current, 1.

. 0.011 ' , 6.3

0.0079 4.3

0.01 3 ,'iT ;,12.6

0.0088 6.3

83.

205

< 2 ,

Fig. 4-Dimensionless metal concentratlon vs. dimensionless cell current for treatment of silver, copper, and cadmium cyanide solutions.

ba&l loading 01 ' 50% barrel volume.

Experimental Procedures For each run, a known amount of metal particles was placed in the plating barrel, which was then immersed in the cell filled with the test solution at a constant temperature. The solution feed and recirculation pumps were turned on and the plating barrel began to rotate at aconstant speed. A constant current from the d-c power supply was applied to the cell. The cell voltage and solution pH were monitored during the electrolysis.

The effluent concentration was analyzed by taking 50 mL of a solution sample every one to two hours from the effluent overflow port until the steady-state was reached. Free cyanide concentration was measured with a cyanide ion-selective electrodeg and a double junction Ag/AgCI reference electrode. Afterward, the sample was acidified in a distillation devicen

Model A161-61S, Walchem Co, Holliston, MA Masterflex US, Cole-Parmer, Chicago, IL Model 62748, Hewlett-Packard, Albany, NY Model 178, Keithley Co, Cleveland, OH

0 Model 94-06, Orion Research Inc., Cambridge, MA, with a sensitivity of 0.03 ppm for CN-

50% Immersion, T P 65 ' C 50% loading. il I 15 rpm Recirculalion rale. 4 mllsec

Capper cyanide

. O 5 10 15 20 25 30 35 40

Dlmenelonlees cell current, I'

Fig. %Energy consumption/kg of total cyanide destroyed vs. dimensionless cell current for treatment of silver, copper, and cadmium cyanide solutions.

72 Plating and Surface Finishing

Ta ible

Control Variable

NaCl

Conc.

Temp.

Barrel,

Speed

Barrel ; Load

' z

Rec. Rate

s .

(with 50 mL of 6M H,SO, for the copper cyanide and cadmium cyanidesampleorwith 50 mLof 1 -M HN0,forthe silvercyanide sample). The gaseous HCN liberated was absorbed in a glass flask containing 100 mL of 135-M NaOH solution. The total cyanide absorbed in the NaOH solution was determined with the cyanide ion-selective electrode. The sample left in the distillation flask was used to determine the metal ion concentration with a silver,h copper! or cadmium! ion-selec- tive electrode. For the copper and cadmium cyanide solu- tions coataining MaCI, a small amoljni of A g W , was added to precipitate CI- before the copper or cadmium ion-selective electrode was used to analyze the metal concentration. The accuracy of the cyanide and metal selective electrodes was f-10 percent.

A run was terminated when the effluent total cyanide, free cyanide and metal concentrations no longer changed with time.

Model 94-16, Orion Research Inc., Cambridge, MA, wlth a sensitivity of 0.001 ppm for Age

' Model 94-29, Orion Research Inc., Cambridge, MA, with asensitivity of 0.0006 ppm tor Cu**.

I Model 94-48, Orion Research Inc., Cambridge, MA, with a sensitivity of 0.01 ppm tor Cd'?

Depending upon solution feed rates and cell currents, it took approximately 8 to 16 hr to reach the steady state.

Results and Discussion A mathematical model, based on a continuously stirred tank reactor,21e22 was made for analysis of the effluent concentra- tions of metal, free cyanide and total cyanide ions for continu- ous electrolysis of a waste cyanide solution. Several dimen- sionless variables were identified from the analysis:

Dimensionless Cell Current

I 1 I* E- 'a' Q C , inlet

= f hc# I*)

Dimensionless Effluent Metal Ion Concentration c*, = CM

C , inkt

Dimensionless Effluent Free Cyanide Concentration

= fh,, qa> I*) c*,, = ' C N

C , inlet (3)

June 1994 73

0.03 o'O)l \

DlmenSlOnleS8 Cell Current, I'

7. 7-Dimensionless effluent copper concentration vs. dimensionless cell

0.02 -

0.01 -

. . .

0.00

Dlmenelonlerr cell current, Io fig. 6-Dimensionless effluent total cyanide concentration vs. dimensionless cell current for treatment of copper cyenide solution with four different NaCl concentrations.

Dimensionless Effluent Total Cyanide Concentration

' * E N = c, hbl (4)

where I is the cell current (A): n, is the number of electrons transferred forthe oxidation of cyanide (2etgmol); Fis Faraday's constant (96,500 C/eq); Q is the solution feed rate (Usec); CM,iniel and CTCN,lniei are the inlet concentrations of metal and total cyanide (mol/L), respectively: CM is the effluent metal concen- tration (mol/L); CcN is the effluent free cyanide concentration (mol/L); C,, is the effluent total cyanide concentration (mol/L); qc is the cathodic current eff iciency; and q, is the anodic current efficiency. The values of qc and q, are calculated from the following equations:

(5)

I' 7.8 "- Cadmium cy-

o! . . . . . . . . . , . . . . . . . . . 0.0 -- 0.4

0.6 . . - ' . * - 1

NsCl concontntlon, moVL

O.005M CuCN + 0.015M NaCN + 0.1M NnOH T - 25 *C, 50% immerdon , 5wc loading I2 I 15 rpm RBCirculalion rate: 4 m u m

where nc is the number of electrons transferred in the cathodic electrodeposition reaction (1 eq/mol for silver and copper cyanide solutions and 2 eq/mol for cadmium cyanide solution). - The energy consumption per kilogram of total cyanide d i - stroyed is:

where E,,, is the anode-to-cathode cell voltage (V); and M is the molecular weight of cyanide (26 g/mol).

The dimensionless metal concentration depends only on the cathodic current efficiency and dimensionless cell current, whereas the dimensionless free cyanide concentration de- pends on the dimensionless current and anodic and cathodic current efficiencies. The anodic and cathodic current efficien- cies, q, and qc, vary with the operating conditions, such as cell current, solution temperature, feed rate, NaCl concentration, barrel rotation speed, barrel loading, and solution recirculation rate. These variables need to be determined by experimental investigation.

Ir Copper cyanide

= Q 2 0

O r" r 150 4 Cadmium cyanide

.- s 5

100 2

" n

Enerpy

c 0.0)

0.03 5

50

0.MM NaCi. T /. 25 'C

0.00

Barrel rotatlon sDeed. rom

Ir Copper cyanide

= Q 2 0

O r" r 150 4 Cadmium cyanide

.- s 5

100 2 e

" n

h

.- s Enerpy

c 0.0) 2 0

5 L 0.03

50

0.MM NaCi. T /. 25 'C SO% Immersion. I. = 15.5

6 e 6

0.00

Barrel rotatlon sDeed. rom

74 Platlng and Surface Nnlshlng

I

:eed Cell late Current nw (A)

1.5 3.05

3

1.025 3

1.5

3

1.025 3

1.5

0.05 .

)r

Table 4-Results for Continuous Treatment of Cadmium Cyanide Solution with 50% Barrel Immersion Level

EHluenl Tolal CN Effluent Free CN Effluent Cadmium I CN I' Conc. ! Conc. ~ C.E. Energy

7.8 192 I 0037 9 1 C018 9 3 I ~ D ~ ' 12..

15.5 13.5 1 0026 6 1 0012 6 3 0028 6 5

31.1 9 4 1 0018 3 9 00076 4 6 002 3 2

7.8 124 0024 I 6 1 I 0012 , 6 7 0029 i 1 2 6 82

15.5 8 2 0016 ~ 2 1 ' 00041 j 2 7 0014 6 3 1%

31.1 3'3

7.8 , 8 1 1 0016 ~ 4 1 00079 , 4 4 , 0019 12'

- . _____ ._ -_ - .__-.

1 --- - - __

I _-_____

- -.-*- I i

I . I I

--- - I -

5.7 I 0011 1 1 9 ' 00037 , 2 1 00093 3 2 - ~ -_. _ _ I

Control NaCl T Variable 1 Conc. ("c)

' (MI I 0

0.05 I

i - 3.025 -

I

0 2 NaCl

Conc !.-I 25

I I I

1.5 7.8

3 155

I I

' 0.4

, 6 1 \ 0012 2 9 00056 3 5 ' 0016 I 127

I !

, --- I

2 5 00049 ' 1 1 00022 I 1 5 00066 6 4 : -- _______

I ! i

3

1.5

0.6

311 1 6 1 0 0 0 3 1 0 5 00018 1 0 OOl?': 7 2

78 1 6 1 I 0012 29 00056 3 5 11l):u 1' ' I -- - - . -__ _ _ - I -

i

Temp. ' 0.6

I I

1

Barrel 1 I

Speed ' 0.6

-I I

3 - -- _-

31 1 1 6 ' 00031 ' 0 9 00018 1 0 00044 3 2 3: I - I

I I

I 1 8

! I I i -

65 1 I I

Ret. i

Rate ! , 0.6

3

1.5

3

3 -- June 1994

- , - ____ ..__

155 3 6 ' 0007 1 2 00023 1 8 DOOb u: - _ _ 7.8 6.1 I 0 0 1 2 2 9 00056 3 5 1 0 0 I G 127 b,

15.5 2 5 00049 1 1 00022 1 5 100066 6 4 164

31.1 1 6 1 00031 0 9 100018 , 1 0 100044 ~ 3 2 327

1 I - --

_-_ ___ I

25

I_

15

-

lee. late nus) -

4

4

4

-

0

- 2 -

4

0.05

0.025

0.05

-

-

0.05

- 0.02L

75

0.05

~.:2::-, I' I31.1 : n I 15 tpm. rodde lon: 4 mumc .

.- s s 0.04

8 2

L

h Ermrgy - - 0

r ; 2 0 003- m - L - L

s 0.02: ToUlCN %

.- s i!

1

e 001

s

Figure 2 shows the dimensionless effluent total cyanide, free cyanide, and copper concentrations, as well as energy con- sumption vs. dimensionless cell current curves for the treat- ment of acopper cyanide solution free of NaCl at 25 "C, a barrel rotation speed of 15 rpm, a barrel immersion level of 50 percent of barrel diameter, and a barrel loading of 50 percent of barrel volume. The results indicate that the effluent dimensionless concentrations of total cyanide, free cyanide, and copper ini- tially decreased with increasing cell current, then leveled off at high current. The energy consumption per kilogram of total cyanide destroyed increased linearly with increasing cell current.

500

z : 4 5 0 0

{

1 5 -

:400

5 ssot w

Continuous Treatment of Silver, Copper, And Cadmium Cyanide Solutions Table 2 summarizes the results for continuous treatment of

1 Silver I I 1 I I Ag(CN); + e- -+AQ + 2 CN- Cyanide 7.9 x 10- 2.0 x 10" 2.5 x Ag(CN),2- + e---+ Ag + 3 CN-

~

1 0.03 3 250

-0.31 -0.51

Copper cyanide C

'3

5 0.03 Energy

E Cadmium qnnlde

z

5

8 002

; 3 5 % f 0.01

5 E 001

6

0 02

- 3

0 OBM NaCI. T = 25 "C 50% m r m . (. = 50% W w

Cu(CN); + e- -+ Cu + 2 CN- - --_-- Cu(CN);- + e- -+ Cu + 3 CN- t

11 - 15 rpm. I. = 15.5 .. .. . .. . . r.-. . .. I . . ..-. . .. . , 000 0 0 20 40 60 80 100

-0.43 -1 .o

Reclrculatlon ratelfeed rata, dimensionless

Fig. 7 7-Dimensionless ettluent total cyanide concentration and energy con- sumption vs. ratio ot recirculation to feed rate tor treatment ol copper and cadmium cyanide solutions.

was loaded with 520 g of copper chips (corresponding to 50 percent of barrel volume) and was set at a barrel rotation speed of 15 rpm, a barrel immersion level of 50 percent of diameter and a solution recirculation rate of 4 mUsec. Two solution feed rates of 0.025 and 0.05 mUsec and two cell currents of 1.5 and 3 A were used; these values corresponded to the dimension- less cell currents of 7.8, 15.5, and 31 . I , as shown in Table 2.

The tests for the copper cyanide solution were carried out with the addition of 0 to 0.6 M NaCl at two cell temperatures of 25 and 65 "C and a 50-percent barrel immersion level. Three barrel rotation speeds of 3, 8, and 15 rpm, and three barrel loadings of 25,50, and 75 percent of barrel volume were used. The solution recirculation rates were: 0, 3, and 4 mUsec. The tests were carried out at the dimensionless cell currents of 7.8, 15.5, and 31 .l. Table 3 summarizes the results for continuous

silver cyanide solution at 25 and 65 "C. These runs were carried out without NaCl in the feed solution. The plating barrel cathode

treatment of copper cyanide solution.

and Standard Reduction Potentials

Reduction Reaction Dissoclatlon Con~lant'~

Solution Kl 4 K3 K, V vs. SHE I

j copper 1 1 I 1 Cyanide 1.0 x log4 2.5 x 10- 5.0 x lo4'

Cadmium Cyanide 3.3 x lo4 2.5 x lo-" 6.3 x 10-l6

plex metal cyanide ion, C,is the metal ion concentration,

76 Plating and Surface Finishing

"" . .

concentration and energy consumption vs. the ratio of recircu- lation to feed rates for the treatment of cadmium cyanide and copper cyanide solutions. The results indicate that the effect of solution recirculation rate on energy consumption was small; however, the effluent total cyanide concentration decreased with increasing solution recirculation rate because of an im- provement in mass transfer at high recirculation rates.

Smithson, BattellkColumbus Laboratories, Columbus, Ot i (1971).

3. C.-D. Zhou and D.-T. Chin, Plat. andSurf.'fin., 80,69 (June, 1993).

4. K.6. Keating and J.M. Williams, ProC. 80th Annual AlChE Meeting: Boston+ MA (1975).

5. F.S. Holland, Chem. Ind., 7, 453 (1978). 6. A.K.P. Chu, M. Fleischmann and G.J. Hills, J. Appl.

Photomicrographs of Metal Deposits The surfaces of silver, copper, and cadmium deposits were bright after the experiment. The morphology of deposits ob- tained at different operating conditions were examined under a scanning electron microscope (SEM). The NaCl concentration, solution feed rate, barrel rotation speed, barrel loading, and solution recirculation rate had little effect on deposit morphol- ogy. Figures 12a and 12b show two SEM photomicrographs of copper deposits obtained at 25 "C and two cell currents of 1.5 A and 5 A, respectively. The typical photomicrographs of silver and cadmium deposits obtained at 65 "C and 1.5 A are shown in Figs. 12c and 12d, respectively. In general, the grain size for a given metal deposit increased with increasing solution tem- perature and cell current. For example, the average grain size for copper deposits increased from 1 pm at 1.5 A to 2 pm at 5 A. The average grain size for cadmium deposits increased from 1 kiln at 25 "C to 2 pm at 65 "C.

Findings A study was made of the use of a plating barrel cathode and a packed-bed anode for continuous treatment of silver, copper, and cadmium cyanide solutions. The total cyanide concentra- tion was reduced from 520 ppm to fewer than 10 ppm, and metal concentration was reduced from 225-486 ppm to less than 1 ppm. The effect of operating conditions, such as cell current, solution temperature, solution feed rate, solution recirculation rate, NaCl concentration, barrel speed, and barrel loading on the effluent total cyanide and metal concentrations and energy consumption was examined. The effluent total cyanide and metal concentrations decreased with (1) increasing cell tem- perature; (2) increasing cell current; (3) increasing NaCl con- centration; (4) increasing barrel rotation speed;and (5) increas- ing solution recirculation rate. Energy consumption decreased with decreasing cell current and with increasing cell tempera- ture. Under the same operating conditions, energy consump- tion per kilogram of total cyanide destroyed followed the order:

cadmium cyanide c silver cyanide c copper cyanide

The optimal barrel loading was 50 percent of barrel volume. The grain size of metal deposits increased with increasing cell current and solution temperature.

Acknowledgment The work described in this paper was supported by AESF Research Project 78. The authors wish to thank the project supervisor, Dr. Peter Bratin of ECI Technology for his assis- tance in the course of this study.

References 1. S.A.K. Palmer, M.A. Breton, T.J. Nunno and D.M. Sullivan,

Metallcyanide-Containing Wastes Treatment Technologies, Noyes Data Corp., Park Ridge, NJ, 1988; pp. 11-40.

2. Report on Project No. 12010 EIE, "An Investigation of Tech- niques for Removal of Cyanide from Electroplating Wastes," A.K. Reed, J.F. Shea, T.L. Tewksbury, R.H. Cherry and G.R.

. . Electrochem., 4, 323 (1 974).

1976). 7. D.-T. Chin and B. Eckert, Plat. and Surf. Fin., 63, 38 (Oct.,

8. S.P. Ho, Y.Y. Wang and C.C. Wan, Water Res., 24, 1317

9. G. Van der Heiden, C.M.S. Raats and H.F. Boon, Chem. Ing.

10. B.D. Barker and B.A. Plunkett, Trans. Inst. Met. Fin., 54, 104

11. A.G. Tyson, Plat. and Surf. f in . , 71,44 (Dec.. 1984). 12. D.T. Vachon et al., Plat. and Surf. Fin., 73, 68 (Apr.. 1986) 13. 0. Schab, H.-J. Lange and I(. Hein, DO-Pat. 114623 (19i'St. 14. A. Kirchhof, K. Heir1 and D. Schab, DD-Pat. 231585 (1986). 15. R. Kammel and H.W. Liber, US. patent 4,123,340 (1978). 16. K.H. Oehr, Proc. Electrochem. Soc. Meeting, Seattle, WA,

17. R.P. Tison, J. Electrochem. Soc., 128, 317 (1981). 18. R.P. Tison, Environ. Prog., 2, 70 (1983). 19. R.P. Tison and B.J. Howie, Plat. and Surf. Fin., 71, 54 (Sept.,

1984). 20. "Standard Methods for the Examination of Water and Waste-

water," 14th ed., pp. 360-375, American Public Health Asso- ciation, Washington, DC (1975).

21. J.M. Smith, Chemical Engineering Kinetics, 3rd ed., McGraw- Hill Book Co., New York, NY, 1981,

22. D.-T. Chin, and C.-Y. Cheng, in Techniques of Electroorganic Synthesis, Part Ill: Scale-up and Engineering Aspects, N.L. Weinberg and B.V. Tilak, Eds., John Wiley 8, Sons, New York,

23. Lange's Handbook ofchemistry, 13th ed., McGraw-Hill Book Co., New York, NY, 1985; pp. 5-71 to 5-76, 6-5 to 6-19.

24. F.A. Lowenheim, Electroplating, McGraw-Hill Book Co., New York, NY, 1978; pp. 373-374.

(1 990).

Tech., 51, 651 (1979).

(1976).

May 21-26 (1978); Paper S79.

NY, 1982; pp. 1-80.

Zhol! Chic

I About the Authors C. -0. Zhou IS a doctoralcandidate in chemical engineering at Clarkson University, Potsdam, NY 13699-5705. She received 6s and MS degrees in chemical engineering from the East China University of Chemical Technology.

Or. Der- Tau Chin is professor of chemical engineering, Clarkson University, Potsdam, NY 13699. He has more than 20years'research experience in electroplating, corrosion, electrochemical energy con- version, andindustrial electrolytic processes. Prior to joining Clarkson, he was a seniorresearch engineer in the Electrochemistry Department of General Motors Research Laboratories. Or. Chin received his PhD from the University of Pennsylvania.

I

Plating and Surface finishing 78