Dryden 1987 Aquacultural-Engineering

7/28/2019 Dryden 1987 Aquacultural-Engineering

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Aquacultural En gineering 6 (1987) 51-68

A q u a c u l t u r e W a te r T r e a tm e n t b y I o n -E x c h a n g e :I I. S e l e c t i v i t y S t u d i e s w i th C l i n o p t i lo l i te a t 0 . 0 1 NH . T . D r y d e n t a n d L . R . W e a t h e r l e y

Department of Chemical and Process Engineering, Heriot-Watt University,Chambers Street, Edinburgh EH1 1HX, UK

A B S T R A C TThe se lec ti v it y beha viour o f c l inopt i lo l i te in the presence o f the ion icspec ies Na K + , Ca 2 a nd M g 2 w as de term ined fo r each ion re la ti ve tothe am m o n iu m ion N i l +~at a to ta l so lu t ion concentra t ion o f O 'O1 u . Wi tht h e e x c ep t io n o f t h e N H 4 / K e x c h an g e e a ch o f th e b i n a ry e x c h a n g esys tem s exh ibi te d a degree of i rrevers ibil ity an d par t ial exchange. Thes e lec ti v it y s equence K > N H +~> N a > C a 2 > M g 2 w as de t e r m i nedan d is cons is tent wi th the low c hang e den s i ty s tructure of c l inopt ilol ite .Co mp ariso n wi th oth er data fo r cl inopt i lol i te sugges ts s igni f icant var iationsi n the s e lec ti v it y behav i our o f the z eo li te w h i ch m ay de pend upo n t hesource o f the minera l. The i so therm data fo r the sys tem NH+~/Na +con f i rm t he po t en t i a l o f c l inop t il o li te a s an am m o n i a r em ov a l t echn i quefor fi sh farm water t rea tment .

1. INTRODUCTIONT h e r e l a ti v e c h a r a c t e r i s ti c s o f b i o l o g ic a l f i lt r a ti o n a n d i o n - e x c h a n g e a sw a t e r t r e a t m e n t t o o l s i n t h e c o n t e x t o f a q u a c u l t u r e w e r e d i s c u s s e d i n a ne a r li er p a p e r (D r y d e n a n d W e a th e r le y , 1 9 8 7 ) . R e m o v a l o f a m m o n i a a sa m m o n i u m i o n s i s t h e p r i m a r y r o l e o f a n i o n - e x c h a n g e s y s t e m i n t h i sc o n t e x t a n d t h u s s e le c t iv e r e m o v a l o f N H ] c o m p a r e d w i t h o t h e r c a ti o n sp r e s e n t i s r e q u i r e d .I n c l o s e d c y c l e i n t e n s i v e a q u a c u l t u r e s y s t e m s w h e r e t h e w a t e ri n v e n t o r y i s e s s e n t i a l l y f i x e d , t h e u s e o f i o n - e x c h a n g e c o u l d s e r i o u s l ya f f e c t t h e b a l a n c e o f i o n c o n c e n t r a t i o n s p r e s e n t , t h u s a d v e r s e l y i n f l u e n c -+Present address: Dryden Aquaculture Ltd, Abbeymount Techbase, 2 Easter Road,Edinburgh EH7 5AN. UK.

51Aquacultural Engineering 0144-8609/87/S03.50- Elsevier Applied SciencePublishers Ltd. England. 1987. Printed in Great Britain


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5 2 H o T . D r y d e n , L . R . W e a t h e r l e y .i n g cu l t u r e c o n d i t i o n s . T h e zeo l i te c l i n o p t i l o l i te h as ag a i n b een s e l ec tedf o r s t u d y a s a c h e a p a n d r e a d i ly a v a il a b le io n - e x c h a n g e r f o r a p p l i c a t io nin th i s con tex t .T h e o b j e c t iv e o f t h e e x p e r i m e n t a l w o r k p r e s e n t e d w a s t o i n v e st ig a tet h e s e l ec ti v it y o f c l i n o p t i l o l i t e f o r p o t a s s i u m , s o d i u m , m ag n es i u m ,c a l c iu m a n d a m m o n i u m i o n s a t a t o t a l s o l u t io n c o n c e n t r a t i o n o f 0 .0 1 N.Pr ev i o u s p u b l i s h ed w o r k w i t h c l i n o p t i l o l it e h as s h o w n t h a t t h e s e lec t i-v i ty ch a r ac t e r i s t i c s can b e s u cces s fu l ly d e t e r m i n ed b y b a t ch eq u i l i b r i u mex p er i m en t s .

A m e s ( 1 9 6 7 ) d e t e r m i n e d b i n a r y s e l e ct iv i ty d a t a u s i ng a m m o n i u m -b as ed c l i n o p t i l o l it e a t 2 3 C an d a t o t a l s o l u t i o n co n cen t r a t i o n o f 0 .0 1 N.T h e s e le c ti v it y s e q u e n c e d e t e r m i n e d w a s f o u n d t o b e:

K + > N H ~ > N a + > C a 2 + > M g 2+T h e r ev e r s i b i li t y o f t h e ex c h an g e r s w as n o t i n v es t ig a t ed .S k u d d e r ( 1 9 7 6 ) a l s o i n v e s t i g a t e d b i n a r y e x c h a n g e e q u i l i b r i u m i nc l in o p t i lo l i te a t a t o t a l s o l u t io n c o n c e n t r a t i o n o f 0 .1 N . T h e r e p o r t e dr es u lt s s h o w ed a s l i g h tl y d i f f e r en t se l ec ti v it y s eq u en ce f r o m t h a t o f A m es( 1 9 6 7 ) , n am e l y :

K + > N H ~ > C a 2 > N a + > M g 2~S k u d d e r p r e s e n t e d c l e a r e v i d e n c e o f i rr e v e rs i b il it y i n th e a m m o -n i u m - s o d i u m e x c h a ng e s y s te m s h o w in g ty p ic a ll y t h a t a m m o n i u m u p t a k eb y s o d i u m - b a s e d z e o l i te w a s a p p r o x i m a t e l y 8 6 % t h a t o f s o d i u m u p t a k eb y a m m o n i u m - b a s e d z e o l i te a t 0.1 N.F u r t h e r w o r k b y C r i d l a n d ( 1 9 7 9 ) o n t h e a m m o n i u m - s o d i u m s y s t e mex ch an g e a t 0 .0 1 N d em o n s t r a t ed t h a t i r r ev e r s i b i l it y is a l s o ex h i b i t ed a tt h e l o w e r c o n c e n t r a t i o n . S i m i l a r b e h a v i o u r w a s r e p o r t e d i n t h ea m m o n i u m - c a l c i u m e x c h a n g e o n c l i n o p ti l o li t e a t 0 -0 1 N.T h e r e s u l t s o f S k u d d e r a n d C r i d l a n d s u g g e s t t h a t t h e a p p a r e n t l yi r re v e r s ib l e e x c h a n g e b e h a v i o u r o f c l i n o p t il o l it e m a y b e e x p l a i n e d b yh y s t e r e s i s a n d s l o w e x c h a n g e . H o w e r y a n d T h o m a s ( 1 9 6 5 ) s u g g e s t e dt h a t p a r ti a l e x c h a n g e m a y b e a m o r e p r o b a b l e e x p l a n a t i o n i n t h e c o n t e x to f m u l t i- i o n - ex ch an g e . I n c o m m o n w i t h o t h e r zeo l it e s , c l i n o p t i l o l it e d o esn o t e x h i b i t t h e m u c h m o r e p r e d i c t a b l e b e h a v i o u r o f c o n v e n t i o n a l

s y n t h e t i c i o n - ex ch an g e r s , ev en i n s i n g le 1 :1 ex ch an g es , an d t h is u n i q u eb e h a v i o u r i s a t t r ib u t e d b o t h t o t h e n o v e l s t ru c t u r a l a n d c h e m i c a l n a t u r eo f th e zeo l i te . I t is b e l iev ed t h a t a n u m b e r o f p a r am e t e r s a s s o c i a t ed w i t ht h e s t r u c t u r e o f c l i n o p t i l o l it e i n f l u en ce s e lec ti v it y . T h es e i n c l u d e f r am e-w o r k t o p o l o g y , n u m b e r a n d p o s i t i o n o f t h e f ix ed an i o n i c si te g ro u p i n g s ,d e g r e e o f h y d r a t i o n a n d t e m p e r a t u r e .


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Aquaculture water treatment by ion-exchange -- H 532 . E X P E R I M E N T A L

T h e o b j e c t i v e o f t h e e x p e r i m e n t s w a s t o d e t e r m i n e t h e b i n a r y i o n -e x c h a n g e e q u i li b ri u m f o r t h e f ol lo w i ng i o n p a ir s: N H 4 / N a , N H ] / K ~ ,N H ] / C a 2+, N H ] / M g 2+ , N a + / K +, N a + / C a 2 a t a t o t a l co n cen t r a t i o n o f0 .0 1 N an d i n t h e p r e s en c e o f ch l o r i d e i o n .A b a t c h e q u i l i b r i u m t e c h n i q u e w a s u s e d t o d e t e r m i n e e q u i l i b r i u mi s o t h e r m s s t a r t i n g , f o r each p a i r o f i o n s , w i t h h o m o - i o n i c s am p l es o fzeo l i te a t eac h en d o f t h e co m p o s i t i o n r an g e . Eq u i l i b r ia w er e e s t ab l i s h eda t d i s c r e t e co m p o s i t i o n s b y b r i n g i n g a s am p l e o f c l in o p t i l o li t e o f k n o w nw e i g h t an d co m p o s i t i o n t o eq u i l i b r iu m w i t h a s p ec if ic v o l u m e o f aq u e o u ss o l u t i o n o f k n o w n n o r m a l i t y a n d i o n i c c o m p o s i t i o n . E x p e r i m e n t a ld e t a i ls a r e s u m m ar i s ed i n Tab l e 1.

T A B L E 1Experimental Details of Binary Ion-ExchangeWeight of clinoptiloliteParticle sizeTotal so lution normalityTemperatureEquilibrium periodEquilibrium solution volume

0"500 g0"60-0"85 mm0"0118-21C7 days150 ml

Tw o t y p es o f c l i n o p t il o l it e f r o m t h e H e c t o r d ep o s i t w er e s e l ec t ed f o rs tu d y . T h e s e a r e d e s i g n a t ed A an d B , b e i n g d i s t in g u i s h ed b y d i f f e r en tco l o r a t i o n s , w h i t e an d g r een r e s p ec t iv e l y .T h e i n it ia l s am p l es o f c li n o p t i lo l i te w e r e o b t a i n ed a s d e t a i led e a r l i e r( D r y d en , 1 9 8 4 ) , b y co l u m n e l u t i o n i n t o p u r e s o d i u m , p o t a s s i u m ,c a lc iu m , m a g n e s i u m a n d a m m o n i u m f o rm s . T ra c e s o f c o n d i t i o n in gs o l u t i o n w e r e r e m o v e d b y v i g o r o u s w a s h i n g w i t h d e i o n i s e d w a t e r . T h em i x t u r e s o f c l i n o p t i l o l i t e an d s o l u t i o n w er e a l l o w ed t o eq u i l i b r a t e a t2 0 C f o r a p e r i o d o f s ev en d ay s , a f t e r w h i ch n d d i s ce r n i b l e ch an g e i ns o l u ti o n c o m p o s i ti o n w a s m e a s u r e d .

T h e c o m p o s i t i o n s o f e a c h p h a s e w e r e d e t e r m i n e d b y a n a l y s i s o f t h eaq u e o u s p h a s e f o r each ca t i o n i c s p ec i e s p r e s en t .A m m o n i u m i o n a n a l y s is w a s c o n d u c t e d b y a d d i t io n o f N e s s l e rr e a g e n t f o l l o w e d b y s p e c t r o p h o t o m e t r i c d e t e r m i n a t i o n . P o t a s s i u m a n ds o d i u m w e r e d e t e r m i n e d b y f la m e p h o t o m e t r y a n d c a l c iu m a n dm a g n e s i u m b y a ti tr o m e t r ic t e c h n i q u e g i v en b y M a c k e r e t h et al. (1978) .


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5 4 H. T. Dryden, L. R. WeatherleyA l l s o l u t i o n s w e r e p r e p a r e d f r o m a n a l y t i c a l - g r a d e r e a g e n t s o f t h eap p r o p r i a t e ch l o r i d e s a lt . T h e t o t a l s o l u t i o n n o r m a l i t ie s w e r e ch eck ed b y

ch l o r i d e i o n an a l y s is . T h e zeo l i te p h as e co m p o s i t i o n s w er e t h en ca l cu -l a t ed b y m as s b a l an ce .P a r t i cu l a r ca r e w as t ak en d u r i n g t h e ex p e r i m en t s t o en s u r e t h a t t h eb o t t l e s i n w h i ch eq u i l i b r a t i o n w as co n d u c t ed w er e c l ean an d s t e r i l e , t oav o i d t h e e f f ec t s o f p o s s i b l e b ac t e r i a l o x i d a t i o n o f am m o n i u m i o n s.T h e b i n a r y e x c h a n g e s i n v o lv i n g a m m o n i u m , p o t a s s i u m a n d s o d i u mi o n s w e r e c o n d u c t e d a c r o s s t h e w h o l e c o m p o s i t i o n r a n g e s t a r t i n g w i t hh o m o - i o n i c s am p l es o f c li n o p t i lo l i te i n t h e ap p r o p r i a t e f o r m . I n th es y s te m s i n v o lv i n g c a l c iu m a n d m a g n e s i u m i o n s h o m o - i o n i c f o r m s o fzeo l i t e w er e u n ach i ev ab l e ; s ee t h e ea r l i e r m eas u r em en t s o f cap ac i t y( D r y d e n , 1 9 8 4 ). T h e c o n d i t i o n i n g p r o c e d u r e a d o p t e d h e r e m e a n t t h a t a tm a x i m u m c a l c iu m o r m a g n e s i u m i o n lo a d i n g a s ig n i fi c an t a m o u n t o fa m m o n i u m i o n w a s p r e s e n t o n t h e z e o li te . A s a c o n s e q u e n c e o f th is th ei s o t h e r m d a t a w e r e c a l c u l a t e d o n t h e b a s i s t h a t a m m o n i u m , p o t a s s i u man d s o d i u m i o n s h ad acces s t o a l l ex ch an g e s i t e s an d t h a t ca l c i u m an dm a g n e s i u m h a d a c c e s s to a p r o p o r t i o n o f t h e s it es in a c c o r d a n c e w i t h t h ev a l u es o f t o t a l cap ac i t y f o r t h es e i o n s.

3. E X P E R I M E N T A L R E S U L T ST h e s o l u t i o n c o n c e n t r a t i o n s b e f o r e a n d a f t e r e q u i l i b r a t i o n w e r e u s e d i nt h e u s u a l w ay t o ca l cu l a t e t h e n e t t r an s f e r o f io n s f r o m s o l u t i o n to zeo l i t e

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Aquacul ture water t reatment b y on-exchange - - 11 55o r v i c e v e r sa . T h e f i n a l z e o l i t e p h a s e i o n f r a c t io n o f , sa y, a m m o n i u m i o nw a s c a l c u l a t e d f r o m t h e i n i t i a l z e o l i t e c o m p o s i t i o n a n d w e i g h t a n d t h en e t t r a n s f e r o f a m m o n i u m i o n s c a l c u l a t e d f r o m t h e c h a n g e i n s o l u t i o np h a s e c o m p o s i t i o n . T h e t o ta l i n it ia l i o n i c c o m p o s i t i o n o f th e z e o l i te w a sc a l c u l a te d o n t h e b a s is o f t h e t o t a l c a p a c i t y m e a s u r e d f o r e a c h p a r t ic u la ri o n . T h u s t h e i o n f r a c t i o n s o f a m m o n i u m i o n ( o r o t h e r io n ) in z e o l i te a n ds o l u t i o n p h a s e s a t e q u i li b r iu m w e r e c a l c u l a t ed . T h e r e s u lt s a r e p l o tt e d i nF i g s 1 - 1 0 a s i o n f r a c t io n i n z e o l i t e p h a s e v e r s u s i o n fr a c t io n in so l u t i o np h a s e .It w a s i m m e d i a te l y e v i d e n t f r o m a l l b u t th e a m m o n i u m - p o t a s s i u me x c h a n g e t h a t o n l y p a r t i a l e x c h a n g e w a s a c h i e v e d w h e n h o m o - i o n i c

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5 6 H. T. Dryden, L. R. Weatherley

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samples of zeol i te were equi l ibrated with solut ions containing a secondco u n t e r- i o n . Fo r exam p l e , th e cas e o f t h e am m o n i u m - s o d i u m ex ch an gein cl inopt i lo l i te ' ? / , shown in Fig . 2 , shows that s tar t ing with homo-ionicam m on ium -for m c l inop ti lo l it e success ive equ i l ib ra t ions a long theco m p o s i t i o n cu r v e t o th e p u r e s o d i u m f o r m can n o t b e ach i eved .A number o f au thors a re agreed tha t a conven ien t way to dea l wi thsuch sys tems i s to express the equ i l ib r ium i so therms in t e rms o f the t ruerever s ib le exchange capac i ty fo r the pa i r o f ions p resen t . Sher ry (1966 ,1 9 6 8) a n d B a r r e r e t a l . ( 1966 , 1973) deve lop a norm al i sa t ion p roce durewhic h involves def in ing a f ract ional ex chang e c apac i ty factor , fn, whe re:

Revers ib le exchange capac i tyf n ~ M ax i m u m h o m o - i o n i c ex ch an g e cap ac i t y


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T h u s t h e f r ac t io n a l ex ch an g e c ap ac i t y f ac to r w i l l v a r y f r o m s y s t em t os y s t e m . T h e v a l u e s o f f r a c t i o n a l e x c h a n g e c a p a c i t y w e r e d e t e r m i n e d i nt w o w ay s . F i r s tl y , w i t h r e f e r en ce t o F i g s 1 - 1 0 , t h e eq u i l i b r iu m i s o t h e r m sw er e ex t r ap o l a t ed . Th e i s o t h e r m s s t a r t i n g a t ( I , 1 ) w er e ex t r ap o l a t ed t ocu t t he y -ax i s a t x -- 0 , and the i so therm s s t a r t ing f rom (0 , 0) ex t rapo la t edto cu t t he y -ax i s a t x -- 1. T he va lues o f cu t -o f f on ea ch y -ax i s i nd ica t e thel i m i t o f ex ch an g e ach i ev ab l e i n t h a t d i r ec t i o n f o r t h e zeo l i t e i n co n t ac twi th so lu t ion co n ta in ing a s ing le spec ies o f coun ter - io n a t 0 -01 N.A m o r e co n v en i en t an d u s e f u l ap p r o ach w as t o ca l cu l a t e an e f f ec t i v er ev e r s i b l e ex ch an g e cap ac i t y , u n i q u e f o r each b i n a r y s y s tem . Th i s w asach i ev ed o n a t r i a l - an d - e r r o r b as i s b y f i n d i n g t h e v a l u e o f ex ch an g ecap ac i t y w h i ch w o u l d r e s u l t i n t h e ca l cu l a t ed i s o t h e r m p o i n t s b e i n g


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Aquacul ture water treatment by ion-exchange -- H 5 9

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co i n c i d en t o n a s i n g l e l i n e ac r o s s t h e x -y d i a g r a m . E x c h a n g e c a p a c i t yca l cu l a t ed i n t h is w a y is r e f e r r ed t o a s th e n o r m a l i s ed ex ch a n g e cap ac i ty .I s o t h e r m s ca l cu l a t ed f r o m t h e ex p e r i m en t a l d a t a o n t h i s b as i s a r e a l s os h o w n . T h e r e s u l t i n g x -y d a t a w er e f i t t ed t o a p o l y n o m i a l eq u a t i o ni n d ic a t e d o n e a c h F i g u r e .A c o m p a r i s o n o f t h e fo r w a r d a n d r e v e rs e e x c h a n g e c a p a c it ie so b t a i n e d b y e x t r a p o l a t i o n o f t h e u n n o r m a l i s e d i s o t h e r m d a t a w i t h t h en o r m a l is e d e x c h a n g e c a p a c i t ie s i s s h o w n i n T a b l e 2 . I n o r d e r t o m a k e aqual i t a t ive app ra i sa l o f t he se l ec t iv i ty o r de r o f t he ions re l a t ive toam m o n i u m , v a l u es o f s ep a r a t i o n f ac t o r a , d e f i n ed i n eq n ( 1 ) , w er eca l cu l a t ed a t a s o l u t i o n i o n f r ac t i o n o f 0 "5 . T h e s e d a t a , t o g e t h e r w i th a


10/18

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s u m m a r y o f t h o s e p r e s e n t e d b y A m e s ( 1 9 6 7 ) a n d S k u d d e r ( 1 9 7 6 ) a t0 - 0 1 r~, a r e s h o w n i n T a b l e 3 .

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N *y s t em s N H a / C a 2+ a n d H 4 / N a in t he p r e s en c e o f c h lo r id e . C o m -p a r i s o n o f C r i d la n d ' s d a ta w i th t h o s e d e t e r m i n e d h e r e a r e s h o w n i n F ig s1 1 a n d 1 2 .


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12/18

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revers i b i l i ty in Cridland 's d a t a c o m p a r e d w i t h t h o s e m e a s u r e d h e r e . It iss i g n i f i c a n t p e r h a p s t h a t t h e c l i n o p t i l o l i t e u s e d i n C r i d l a n d ' s e x p e r i m e n tw a s p r e t r e a te d by drying a t 70C prior t o u s e a n d i t i s v e r y p o s s i b l e t h a texposure t o t h i s l e v e l o f t e m p e r a t u r e m a y a f f e c t s u b s e q u e n t behaviour.N e v e r t h e l e s s , p a r t ia l e x c h a n g e i s n o t e d i n b o t h c a s e s .Figure 12 s h o w s c o m p a r i s o n w i t h C r i d l a n d ' s d a t a f o r t h e s y s t e m+ +N H 4 / N a ; i n t h is c a s e t h e c u r r e n t d a t a s h o w a l o w e r d e g r e e o f r ev e r si -b i l ity than C r i d l and ' s .

T h e d i f f e r e n c e s b e t w e e n t h e s e t w o s e t s o f d a t a m a y i n d i c a t e v e r ys i g n i f i c a n t b a t c h - t o - b a t c h v a r i a t i o n s i n t h e p r o p e r t i e s o f c l i n o p t i l o l i t e .W h i l s t a d e g r e e o f i n h o m o g e n e i t y i s q u i t e l i k e l y t o e x i s t , a m o r e l i k e l ye x p l a n a t i o n i s t h a t t r u e t h e r m o d y n a m i c e q u i l i b r i u m h a s n o t b e e na c h i e v e d i n a n y o f t h e s e c a s e s a n d t h a t t h e p o s i t i o n o f a n y p o i n t o n t h ed i a g r a m s m a y b e t i m e - d e p e n d e n t . S k u d d e r ( 1 9 7 6 ) s u g g e s t e d t h a ta m m o n i u m e x c h a n g e o n t o s o d i u m - b a s e d c l i n o p t i l o l i t e c o u l d b e a t w o -s t a g e p r o c e s s w i t h t h e b u l k o f t h e e x c h a n g e o c c u r r i n g i n a f a i r l y r a p i dfir st s ta g e f o l lo w e d b y a v e r y s lo w a p p r o a c h t o c o m p l e t i o n .

P a r tia l e x c h a n g e i s o b s e r v e d i n a ll t h e s y s t e m s s t u d i e d w i t h t h e e x c e p -t io n o f t h e N H 4 / K e x c h a n g e a n d t h e N a + / K e x c h a n g e. In t h e se t w oc a s e s i t a p p e a r s t h a t t o t a l a n d r e v e r s ib l e e x c h a n g e i s a c h i e v a b l e ( s e e F i g s1 , 5 a n d 1 0 ). T h i s i s c o n s i s t e n t w i t h o t h e r w o r k b y L a i a n d R e e s ( 1 9 7 6 ) ,

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Documents

Dryden 1987 Aquacultural-Engineering