Inorganic ion-exchange membranes and their application to electrodialysis

INORGANiC AND THEIR K. S.

ION-EXCHANGE

APPLICATION

MEMBRANES

TO ELECTRODIALYSIS

RAJAN. D. B. BOIES. k J. CASOLO

AND J. I_ BREGMAN

IiT Research fnstit~fe, Chicago, III. (U.S.A.) (Rmiwd

August 16, 1966)

Inorganic ion-cxcbangc membranes were prepared by using the phosphates of tin. titanium. and zirconium and the mixed hydroxides of thorium with Mg2 +.Ca2 +. UO$ +, Al3 +, Cr3 +. es’. Ce*+. and Sn4 l. Potfinylidene fluoride was used as the binder. The membranes thus obtained bad transfcrence numbers of 0.88 to 0.9s (in 0.05 to 0.10 M KCl) and resistancesof 2 to 10 ohmscm‘. For the first time. inorgznic cation- and aniontxchangeo were used in the multicompartment ekctrodialjsis of brackish **ata. Polarization studies wwc made on NaCl and KC1 brines conraining 3000 ppm total disokd solids. Salt t-cmo~& adicvcd WI-C 57.5 and -W.60,‘, for Nat3 and KC1 brines, rcspnztivcly. ‘phe effect of HCOI. SOi-. Mg’ +, and Ca’+ ions in NaCI fozd solutions on the desalting performance of inorganic efcctrodialjris stacks *as invatigalcd. The performances of inorganic and commercial organic membrane units UCT=compared under different conditions of temperature

and fouling and in long-term tests.

IN-t-RODU~tON

In continuing studies of new cIasses of inorganic ion-exchange membranes (I-31, the preparation of a number of such membranes for use in electrodialysis operations was investigated. In addition, the performance of zirconium phosphate and thorium hydrous oxide membranes in a multicompartment ckctrodialysis unit was examined by using NaCl and KC1 brines. Preliminary data are reponed. ESPERIMEXTAL

WORK

Materials used as cation-exchangers in the preparation of ion-exchange membranes included the phosphates of zirconium, titanium, and tin. Pure zirconium phosphate was obtained from Bio Rad Laboratories, Calif., and the phosphates of tin and titanium from the SxiCtC d’Etude de Recherches et d’Application pour l’industrie, Brussels, Belgium. The anion exchangers consisted of rhe hydrous oxides of thorium, zirconium, and titanium as well as the mixed hydroxides of thorium with Mg2+, Ca*+, tJOf+, Al’+, Cr’+, Zr’+. Ce4’, and SnJ+. Reagent-grade salts of thorium and the other metal ions were obtained from Fischer Scientific Company. Binder. A 2@% solution of po‘iyvinylidene fluoride in dimethyl acetamide (Kynar) was used as the binding agent. Kynar was obtained from Pennsalt Chemical Corporation, Philadelphia, Penna. 231 Desahiratfon, 1 (1966) 231-246

232

IC. S. RAJAS,

D.

B. bOlEi,

A.

J.

CASOLO

APiD

J.

1. BREGMAN

casting process was used to make 8 x 16 in. samples For cation-exchange membranes, a mixture containing one part by weight of Kynar and three parts by weight of finely powdered exchanger (-200 mesh) was spread with a doctor blade on a glass plate. For anion-exchange membranes. the hydrous oxides were incorporated on the binder matrix by an in situ procedure. Details of the preparation procedure have been described previously (2). Eleciricaf properties. Ektrical resistances of the membranes were measured by using a small standard cell with a cross-section area of 5 cm2 and a General Radio conductance bridge. The procedure consisted of placing the equilibrated membrane in the ceil, filling the ceil with the 0.5 .I/ NaCI, and measuring the resistance with the conductance bridge. Membrane resistance was taken as the difference in the cell resistance with and without the membrane, in terms of area rcsistancc, ohms-cm’. Membrane transference numbers reported here are the transference numbers of potassium or chloride ions through the membranes. The method used to obtain transference numbers was essentially that dcscribcd in the “Office of Saline Water Test Manual for Permselective klembranes” (i). Electrodial_wis cell. The clectrodialysis unit consists of six diluting and five concentrating compartments, in addition to the two electrode compartments. The main cell feed solution is introduced by means of passageways of expanded plastic spacers in two streams that feed alternate compartments, the diluting and the concentrating streams. The anode and cathode compartments arc fed by separate streams. The diluting and concentrating compartments are 0.040-in. thick and contain -IO-mil expanded-plastic-mesh screens, which keep the membranes parallel and aiso increase the turbulence in the compartments. The active area of each membrane is 0.22 sq ft. The electrodes arc platinized titanium. Figure I is a schematic of the flow system of the clectrodiaiysis unit. Feed to the cell is by gravity from a constant head system and is controlled by valves and measured by variable-area flowmeters. Provisions are made for sampling the feed solution and the various effluent streams. The feed solution, the concentrating and diluting emuents, and the anode and cathode sweep streams were analyzed for pH, conductivity. and cation and anion contents_ The electrical characteristics of the cell were obtained by measuring the current and voltage. .~!embrme sr_trthesis. A simple

of membranes.

RESULTS

ASD

DISCUSSION

Inorganic ion-e_wlrmge ntembrunes

After the inorganic cation- and anion-exchange membranes had been prepared in accordance with the casting technique described above, the electrochemical properties of the membranes were evaluated. The data (Table I) indicated that inorganic membranes show electrical resistances comparable to those of commercial organic membranes and that their transference numbers are somewhat below those of organic membranes_ With further modifications in exchanger-binder combinations, membrane Desahution, I (1966) 231-246

ISORC;ANIC

CONSThH\ HEAD

TAP \

ME~~BRANES

ION-EXCCIASCE

233

WATER

f-1

I FLOWMETERS FEE0 SAMPLER,

> 1,

rr

DILUTING STREAM

SOLUTION

CONCENTRATED DILUTED CENTAl

EFFLUENT EFFLUENT

TO

-

AND

SAMPLI

ING

ANALYT

IC,

SYSTEM

FUGAL

PUMP

Ftg. I. Schemwc of ckztrodial>Gs cell flow system.

TABLE

S?cmbrane thicknti: 7 to 8 mils. Weight ratio of c.xchanger to bin&r:

I

3 for cation membranes;

1.6 for anion mcmbrancs

TronS,erence number in O.OS,O.I Al KCI

3 lembrune

Zirconium phosphate Tin phosphate Titanium phosphate Zirconium IungsMc Ammonium molybdophosphate Commercial organic Thorium hydrous oxide Zirconium hydroxide Titanium hydroxide Thorium-cakium hydroxide Thorium-magnesium hydroxide Thorium-aluminum hydroxide Thorium-chromium hydroxide Thorium-zirconium hydroxide Thorium-cerium hydroxide Thorium-tin hydroxide Commctial organic

Cationic Cationic Cationic Cationic C3rionic Cationic

Anionic Anionic Anionic Anionic Anionic Anionic Anionic Anionic Anionic Anionic Anionic

8.0 5.6 9.6 4.0 19.0 4-1 I 2.0 4.0 2.5 3.0 2.5 z*‘: 3:o 2.0 2.5 5-21 Desaharion,

0.91 0.90

0.85

0.9s 0.87 0.99 0.91 0.75 0.74 0.83 0.90 0.82 0.86 0.86 0.93 ::z

1 (1966) 23 I-246

IC. S. WAN,

234

D. B. BOIES, A. J. CASOLD AND J. E. BREGMAN

pores, other rele-rant electrochemical parameters, it should be possible to obtain inorganic membranes with transference numbers close to unity.

Reinforced inorganic membranes In order to increase the ion-exchanger to binder ratio and at the same time maintain the physical stability of the membranes, reinforced membranes were prepared by using nylon mesh. Zirconium phosphate and thorium hydrous oxide membranes were cast by incorporating increased amounts of exchanger (representing a 30% increase over that contained in the formulations reported in TabIe I). Ion transference and resistance measurements were made on a few reinforced membranes (Table II). All the membranes exhibited excellent physical stability. The electrochemical properties were not greatly improved except in the case of zirconium phosphate membrane. TABLE II JXECTRICAL PROPFRTIES

OF RElNFOR(ID

Afembrane

ISORGAMC!

Erpertim -

ME!bfBRAhTS=

Ruis&vue

ohmr-cllI2

Zirconium phosphate

Cationic

:

z

Thorium

Anionic

: 5

d

hydrous oxide

-Reinforced

on nylon screen

4

Transference

num&cr 0.96 0.90 0.91

0.90

0.89

of 7 mil thickness.

Metal complexes A few metal complexes containing one or more vacant coordination sites on the central metal atom were examined as possible ion-exchangers for membrane work. The membrane containing the 8-hydroxyquinoline complex of zirconium showed sign&ant anion-transference characteristics (Table III). The ion-exchange behavior of this zirconium complex has not been reported in the literature. TABLE

Exchanger

XIX

to binder ratio: 3 l-hi-CkIUSS

Mt-l?IbrUJlI!

Thorium&hydroxyquiline

ZirconiuaShydroxyqUnoIine

ml% complex

complex

Transference R&.SlUCC@? number& ohrns-enl2 0.05ro 0.10 M KCI

8

32

0.60

8

80

0.93

Desahhatiorr.

1 (1966) 23X-246

INORGANIC

Multiconpartnrent

IOS-EXCHANGE

MEMBRANES

235

etectrodialysis

The zirconium phosphate and thorium hydrous oxide membranes were chosen for further investigation of their possible application to the electrodialysis of brackish water. A multicompartment electrodialysis unit containing these membranes was assembled, and electrodialysis studies were conducted on NaCl and KC1 feed solutions containing 3COO ppm total dissolved solids. A parallel liquid flow system was used, and the flow rate through the cell was adjusted to 1.O and 1.1 ml/set. Complete polarization studi& were made separately for NaCl and KC1 brines (Fig. 2). Analytical data were evaluated at the point of limiting current density (Table IV). TABLE IV FLECTROD1ALI’SlS

Membranes:

cell :

OF

iiCI

ASD

Zr-phosphate (cationic) Fixe working pairs.

Xrd

SOLVnOS

WITH

ISORGA?*iC

bfE.UBRAhZS

and thorium hydrous o.tide (anionic)

membranes.

Ydues CorAitior5 Na Cl

Voltage.

v

current, amp RaisUnce. OhmS Cell Dilute &ucnt

Conccliu;lrcd CfiIucnt Feed solution

KCI

14.5

12.0

0.930

0.730

15.6 47-s 1x3 21.6

How rate, ml+c Dilute effluent Conc.cntlatcd effluent

1.05 1.00

Tanpcrature* ‘C Dilute effluent GmaxltlTjtcd etlluent

25.5 25.5

16.5

425 15.3 22.4 1.10 1.05 26.5

27.0 27.0

25.0

Feed solution Total disrolved solids, ppm Dilute e@uent Concentrated cWuent Feed solution

1512

1310 4!300 3080

E

3.7 2.9 6.7

Salt exchange,

7; Concentrated cffiuent (added) Dilute &Iucnt (rcmovcd)

- Values in parentheses

indicate

55.3 57.5 (61)-

51.0 48.6 (62)a

maximum salt removal achieved. Desahation. 1 (1966) 231-246

236

R. S. RAJAY,

D.

R. EOIES, A.

3. CA!XXO

AND

J. E. BRECiSfAN

~-__-

30,

---

1

26 ,” I 0

t

-22c

lOl-_._L__

-l____-. 2

1

RECIPROCAL 0

InOrganiC

Cell XXI

feed solulion

(30

_.____I

CURRENT. ppm).

Fig. 2 Polarization tuna

‘?

____

1

3

4

AMPSs’

InOrg;lnlC

Cc!1 KC1 fd

solution

t’%tt)

pTm)

for inorganic membnncs cc&

Irtfluence oj-other ions on the electrodialysis of N&I Sodium and chloride ions are the two major components of most brackish waters, but Ca’+. Mg”+, SOS-. and HCO; ions are also present. Since Ca2 + and Mg2+ ions can form insoluble phosphates and since SO:- and HCO; ions can adversely -.____

26r-------

!

.-.-.-_--_

-___

LIYITING CURRENT DENSITY

L-J

. .__._.-i.. ___..__.._.._.__._t._____-__A___ I

3

2 RECIPROCAL

Augmented C

NJCI

fed

180gprnSO~-,

solutions. A

CURRENT, G

56 ppm

350 ppX$-

Fig. 3. Effect cif SO; - and HCOJ ions on

4

5

AMPS-’

HCO,-. --

0

68 ppm

Typical

NsCl

the ektrodi&sis

SOi-. run

of NaCI.

Desahation.

1 (1966)

231-246

lXc‘O%iAX;1C iOS-EXCllA~GE

6j tP---

0

--

1 _--.

L.-.-

_.__.___A_

I

REC Torat Jirrokcd 7

sof:t$s. 3095 ppm

*:.

3tzo

__ _ __

2

I PROCI\L prrn

m

Ty$cJ

L_ -_.__ 3

CURRENT, ppm

HCO>-h a

Cl30 P&ml soy-,.

--

LlEMBIUSES

^___ _-._-.--__-__

-.-

,

237

._-I

.I, ..-. 4

5

AMPS-’ 0

3x10 ppm

28iO

ppm

(350 *pm

468 pptn

S0:-).

SOi-).

S;rCI run m*th 3000 ppm fc:d

nffkct the anion-exchange behavior of thoria membranes, influence of these ions on the desalting perfotmancc of inorganic membrane cells was investigated. Separate ckctrodialysis runs were made at n constant liquid flow fete of 1 ml/sea Polarization data and percent salt removal were obtained for the SOi- and HCO; augmented NaCI brines (Figs. 3 and 4). Analytical results evaluated at the point of limiting current density for the SOi- and HCO; augmented NaCI brines are presented in Table V and those for the cases of Ca2 + ar?d Mg’+ in Table V1. The data showed that the overall stack resistances of the SOi- augmented brines were lower than those obtained for the pure NaCI run. For the HCO;, Ms2+, and Ca2+ augmented brines, the limiting current densities were lower and the overall stack resistances were higher than those for the pure NaCl run. However, the percent salt removal achieved for edch of the augmented brines was only slightly smaller than that achieved in pure NaCl elt~trodialysis. Stability ad high-temperatureperformawe

In order to test the stability, high-temperature performance, and resistance to fouling of inorganic membranes and to compare the results with those from similar tests on organic membranes, ektrodialysis runs were made separately on small inorganic and commercial organic membrane units. Eact unit consists of six working pairs of membranes to give six diluting and six concentrating compartments, in addition to two ektrode compartments. The efkctive flow area is 6 sq in. per membrane. Dedination,

1

(1966) 331-246

238

K. s. RUAN,

D. B. BOLES, A. J. CASOLO

AND

J. I. BREGMAN

TABLE v AND soi-

cation- and anion-pcmxab!e

Iblanbcanc~:

Inorganic

cell:

FM sotking pairs,

Voltage,

v

current, amp Resktance, Gil

rWuent cowmtXltcdcfikcnr Fe& solution L?zzE CoacernTatcdetffualt TanrYerrWre. “C Dilute &l-t c33llamtrsicd e!Euenr Feed solution

10.9

11.0

11.1

Il.0

O.slO

0.710

0.840

0.790

21.3 40.5 16.0 23.5

15.5 45.7 17.0 27.0

$i

13.9 z.90

21:7

24:o

IS.6 47.5 13.5 2i.6

1.00 0.96

0.94

E

1.08 1.00

1.os 1m

24 24 24

26 26 27

2S 2

26 26 25

1980

1310

Feed soIution PH

DiIutt ctll~t CoWntrated diIu< Fad solution

salt con:cnt, % Concentrated effiuent (added)

Dilute &iuClQ(rUEoVWU

in parentheses

24 E

solids, ppm

Dilute dikxnt ?Lxlcatrated efsucnt

0 Values

membraues.

14.5 0.930

o&s

Dilute

Total diikd

roxs

indicate

1653 4362 3120

6.6 62 7.7

47(5;(1 40 (48)

1.02

1460

Exm

42So 2870

437s 3095

4.0

3::

E

3.7

z

6.7

618

;;

40t0 SC)60

49.t(63.8) 4S.O
MS0

SS.3@8.~ S7.S(61)

the maximumsalt mmokalachicvzd.

Platinum electrodes, 6 sq in. in area, are used. Figure 5 is a photograph of the multiple test facility consisting of two separate units. The high-temperature performances of the inorgnnic and organic membrane units were tested by carrying out demineralization experiments on NaCl solution (Moo ppm) at 25 and 60°C. Polarization and saIt removal data were obtained (Figs. 6 and 7), and analytical data were collected at the point of limiting current density (Table VII). At 25°C the inorganic unit showed a current efficiency of 88.5 %, compared with the 94.5% achieved by the commercial organic unit. The relatiycly lower sait removal effected by the inorganic unit (Fig. 7 and Table VII9 could presumably be attributed to its lower current density. The acidic pH’s of the e@uent D-n, 1 (1966) 231-246

INORGANIC

ION-EXCHAXGE TABLE

ELECIRODIALYSIS

Membranes: Cclt :

239

Vi

+ AND

SUz+

AUGMENTED

BRINE

inorgsnic

five working pairs. CoRdif ions

volrilgq

OF Cd

hlEh4BRAh’ES

v

15.0

Current. amp

0.670

Resistulcc, ohms CA Dilute el?lucn: CocKentratcd et%Icnt Fad solution Flow r;itc, mlisee Dilute efhcnt Conocr.ttatcd dcucnt Tem~turc. ‘C Dilute &uent Concectntcd effluent Fad solution Total dissolwxl solids, ppm Dilute cfIiusr~t coRccntratcd etiiuent Fad solution

PH

Dilute effluent Conantmtrd &lucnt Feed solution

wtucrhans. % Concentrated &ucnt Dilute cfhcnt

NaCI with 67 ppm Cd+

(added) (removed)

22_4 47.0 15.9 23.0

1.00 0.98

60 ppm ,Ugr +

Pvre NaCI

12.2

14.5

NaCI wirh

0.410

29.8 38.2 17.5 23.7

1.00 0.98

0.930

15.6 47.5 13.5 21.6

1.05 1.00

25 25 25

25 25 25

26 26 25

1476 4502 3157

1674 4029 3023

1310 4800

4.5 3.5 6.7

43.0 53.5

6.8 3.1 6.7

33.0 45.0

3.7 2.9 6.7

55.3 57.5

streams of the inorganic unit will be of potential value in the electrodialysis of hard waters. Comparison of the results of the inorganic membrane unit at 25 and 60°C showed that operation at 60°C resulted in a 31 oA decrease in the overall stack resistance and a 30% increase in the salt removal with a lower power input. The current efficiency was satisfactory and was not greatly affected by temperature. Although the high-temperature performance of the organic membrane unit was better than that of the inorganic unit, the hydraulic tlow condition of the former the organic membranes were badly distorted. The deteriorated considerably: inorganic aembrane unit showed no signs of deterioration of the hydraulic flow Desabation,

1 (1966) 231-246

240

K. S.

RAJAS,

D.

R. BOIFmS, A. J.

CASOLO

Fig. 5. ~MuItiple ekctmdiaI~6s

AND J.

1. BREGMAN

test fadlitg. Ded~tion,

I (1966) 2X-246

241

:

I

6

12 RECIPROCAL

Cl

0

.--

1. .._ 6

-

I_ _ ._ _ 12

RECIPROC4L

1..

i4

-:-Ii

AMPS-”

CURRE%T.

1. --.

ia

.

I..

_

24

Fig. 7. Dcmincnlintion

__...L_._._.--r--i 30

CURREIVT,

HaI diuol\xd solids = 3WO ppm. FIow T;IIC = 0.1 ml,scc. Ino~~~ic mcmbrxxr (25’0. rpanic -brana @OX 3

_

30

36

AMPS-’ 0 I

Ckxnic membranes (?.YC). Inor&mic mcmbrarus (60’0.

at 25 and 6O’C. Desahation.

1 (1966) 231-246

K. S. RAJAN,

242

D. E. BOBS,

A. J. CASOLO AND J. I. BREGMAN

TABLE -cP

Of

TEW’ERAlWRf

ON

VII

Et_E~OOIALYStS

OF

?2ad

Vdtaffi

v

8.5

6.9

cuimlt.

amp

0.170

0.160

50.0 1

43.0 a 265.0 12.0 24.5

Resislma, ohms Cell Dilute ctlluent Conantrated effluen: Feed solution

139.0 12.9 23.2

Flow rate, mI/sec Dilure etil*uent Conantrated etment Total dissohed solids, Dilute effluent G.wlantlatcd muent Feed solution

0.23

0.22

!XXUllOSS~

11.1

0.122 90.0 50.0

15.0 23.2

0.2 I 0.19

0.20 0’1

8.8 0.14O 62.5 61.0 15.3 24.5 0.24 0.28

ppm

PH Dilute eHucnt Collantntcd cwaKnt Feed solution Salt exchmge, % Dilute efiluenl (removed) Conanuated effluent (added)

500

zt

250 6100 2925

4.5 3.1 4.5

4.3 3.1 4.7

91.5 +99

SO.0 56.5

65.0 51.5

96.5 +99

538.5 80.5

89.6 83.0

6.1 3.0 4.5

6.3 3.0 4.7

32.6 92.7

1317 4700 3010

Curmnt efficiency, % Diluiing ails Conantmting

945 cells

99.0

Data colkcted below tti Point of limiting current density. ’ Stack dintznsions: 6 all pairs, 13 membranes; flow aura = sq in./rnembr;ine.

l

condition. Samples of both membranes used in the 4O’C experiments are shown in Fig. 8. The stability and demineraliting performance of the inorganic unit were investigated by making an intermittent electrodialysis run on NaCi (3000 ppm) for a total of 105 hr. For comparison, a similar run was made with organic membnne unit. Data on salt removal, currcnt efficiency, hydraulic flow condition, and overall stack resistance were obtained (Table VIII). The data showed that the inorganic unit gave a steady sait removal of 55 to 59% from the diluting stream and operated at a satis-

factory current efficiency and overa. stack resistance. The liquid flow conditions Dcsa&a!bl, 1 (1966) 231-246

INORGANIC

XON-EXCHANGE

TABLE LOSG-TERMlXst5 A%z

Temperature: Stack dimensions: Inorganic uni: : Organic unit:

VIII

25°C: duration: 105 hr. 6 cell pairs, 13 membranes; flow area: 6 sq in./membrane thoria and zirconium phosphate mtmbranc commercial organic membranes

oganic IOU?

Inorganic wit

Initial

v

9.7

0.155

current. amp Ekcwxal

243

OH THE EUX-IRODULYSIS OF NaCl BY ISORGANIC cOMS4ERClAL ORCAWC LWbfBRANE UNSY3

Con&lions

Voltage.

MEMBRANES

resistance. ohms

62.5

Flow rate, ml/set Dilute stnzun Concentrated stream Anode stream Cathode stream

0.30 0.27 ::z

Fml

Initicl

14.5 0.155

9.0

8.4

0.150

0.140

60.@

93.1 0.23

0.28

ii-iii

0.27 0.32 0.38

0.45-0.48

Fd

60.0

0.26 0.27 0.44 0.21

Sal1 exchange, “I: Dilute strum (removed) Concentrated strum (added)

55 63

69

61 68

72 72

Current efFicicncy, :d

80

63-73

85

84-91

59

remained steady. The saIt exchange achieved in the inorganic unit was nearly equivalent to that achieved in the organic unit. The relatively lower current e5ciency and salt removal of the inorganic unit as compared with those of the organic unit can be attributed to the lower transference numbers of the inorganic membranes, i.e., 0.84 to 0.91. At the end of the 105hr electrodialysis operation, the electrochemical properties of the inorganic membranes were measured. A decrease in the transference numbers of 1 to 504 and a resistance increase of 5 to 30% were noted. The largest variations were shown by the membranes closest to the cathode compartment where the ekctrolyte showed an alkaline pH. These variations could be obviated by adequate equilibrations of the membranes and by the use of acidic cathode rinse. All the inorganic membranes showed excellent physical stability. Efict

of dodecyl benzene sufinate

(DBS)

In order to study the effect of DBS on the performance of the inorganic membrane unit, a long-term electrodialysis test was carried out on DEE-augmented NaCl. An acidified solution (pH = 2.5) was used as the cathode rinse in the inorganic membrane unit. For comparison, a similar test was carried out on an organic unit (Table IX). The inorganic unit was run for only 36 hr because the hydraulic flow, electrical Demhatian.

1 (1966) 231-246

K.

S. RASAS,

D.

A

B. BOB,

A. I.

CASOLO

A?r‘D 8. I. BREGblAS

I3

Fig. 8, Phyzical condition of the ion-exchange ntembnnes aft,t eiectrodhlysis A. Organic membrane. 33. Inorganic membrane_

at 60%.

conditions, salt exchange, and current cffrcicncies were constant throughout this period. The organic unit was run for 92 hr since considerable variations were observed from the very beginning of the operation. The data (TabIe IX) indicated that a current efficiency of SOS; and a salt removal of 68:; were achieved by the inorgnnic unit. Although the o\.erall stack resistmce of the inoqanic unit was relati-rely higher, it remained constant. Comparison of the data on DBS-augmented NaCl with that on pure NaCl showed the introduction of DBS did not affect the percent salt exchanged or the current cffic:enq. ffowcver. an increase in the overall stack resistance did result. In the case of the nrpnic unit, however, the presence of DBS brought about the deterioration of the h:;drauIic flow conditions of the dilute effluent and the cathode streams. ln addition, the Fercent saft exchanged and the current ellkiencies of the diluting and concentrating strerims showed wide and erratic variations throughout the test.

ISORGASIC

ICN-ESCHASGE

TABLE ISFLUEXE Tcmpcrature:

FIXI sufution: DBS:

‘76 C. 3009 ppm. 3.0 ppm.

OF

total dissokd

~85

0s

v

Current.

amp

RaistancT.

THE

&it cxchanee. T6 Dilute stem (rcmowd) Conccntntcd stream (addcdd) Current eflicirncy. Pi

stem

OF

sac-r

Inorganic rrniru

Inilial

FinaI

13.0

13.0

0.096

Flo\\ rate, ml/se Dilute &iucnt Conccntratcd efflucot :\ncde stnzam Cathode stream

Dilute

E~_EcTRoDIALY~~S

sofids.

ohms

Concentntcd

2-u

IX

Condifiofs

Voltage.

MEMSRANES

stream

135

0.096 135

5.3

6.8

0.120

0.068

4-t

0.20

0.20

0.22 0.40 1.10~

0.22 0.X) I .05<

0.18 0.23 0.X 0.39

96

0.10 0.11 0.35 0.25

68 65

6S 65

59 75

95 30

80 75

80 83

90 93

93 58

- Duration of the‘ccctrodialysis run ~‘3s 36 hr. b Duration of the ekctrodial~sis run ws 92 hr.

c Acid cathode rinse. pH = 2.5.

Although the inorganic ion-exchange membranes are in the early stages of development their electrical propertics. overal! stabilities, and electrodialysis unit performance show that they have promise for application to brackish water conversion. Inorganic membranes show electrical resistances comparable to those of commercial ormanic membranes, but their transference numbers are somewhat below those of organic membranes. With further modifications based 0x1 exchangerbinder combinations, membrane pores, and other electrochemical considerations, it should be possible to improve the transference properties. Preliminary data indicate that the performance of the inorganic membranes in electrodialysis units is satisfactory. Salt removals of 50”,/, and current efficiencies of 80”/, have been obtained. inorganic units have also shown steady and satisfactory performance under conditions of fouling and in long-term electrodialysis tests. At elevated temperature, they are quite stable and show greatly improved desalting performance. The organic membrane electrodialysis unit showed deterioration of Desaharion,

1 (1966) 23 l-246

K.

246

S. WAN,

D.

8.

LWIES, A. J. CASOLO AND

hydraulic flow conditions in high-temperature units exhibited remarkable s:ability. The

relatively

!ower

limiting current density

some of the aspects research on inorganic under way.

current

efficiency,

and fouling lower

percent

tests, but the inorganic salt removal,

and lower Grganic unit represent closer examination and improvement. Detailed development and ekctrodialysis performance is

of the inorganic unit as compared

that need membrane

2. I. BREGMAN

with

The authors are indebted to the Office of Mine Water, U.S. Department of the Interior, Washington, D-C., for its support of this work and for its permission to publish this paper. We are also grateful to H. P. Gregor, A. Cleat-field, R. S. Braman, and James Shackelford

for their advice during

the course of this study.

REFERENCES 1. 3, 3. 4.

A.

J. I. BRECMAS.Chrm. fig. New. 39 (l%l). J. 1. B~~EGWAS, Proc. Ann. Purer Sowres CUJI$. !6(1%2)4-6. J. I. BRU;MA!I AND R. S. BUMAN. J. Colloki Sci.. 20.9 (1965) 913-922. OfIke of &line Water, “Test Manual (Tentative) for Pemuektke Membraac”, Research & Dedopment F’rogus No. 77 (Jan. 1964). pp. 12, 156. 162 ~AVS~EKS

AND

A. DRA~MEK~,D. B. BOIESAND

Dcsafinafion.

1 (1966)

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