'\ i) P a u l ? a j u n e n , P.Eny. Eco-Tec L i m i :ed

4 \'$a 9 2 5 Brock Road S o u t h HewLett P a c k a r d 114i3 X h i n d e n Blvd -

'L\c:F"; P i c k e r i n g , O n t a r i o C a n a d a L1W 2 x 9

I n t r o d u c t i o n -. - --.-

- - _ .

Boise, I d a h o 8370.7

T h e wet c h e m i s t r y p r o c e s s o f a p r i n t e d c i r c u i t board m a n u f a c t u r i n g o p e r a t i o n c a n i n c l u d e t h e p l a t i n g of b o t h copper a n d n i c k e l . I n a d d i t i o n , a number of e t c h i n g , s t r i p p i n g , a n d a c i d c l e a n i n g s t e p s a r e r e q u i r e d b e t w e e n t h e s e p l a t i n g o p e r a t i o n s .

T h e r i n s e w a t e r s a n d b a t h dumps from t h i s process m u s t b e t r ea t ed p r i o r t o d i s c h a r g e i n o r d e r t o meet loca l e f f l u e n t d i s c h a r g e

c o n v e n t i o n a l m a n n e r s u c h as pH n e u t r a l i z a t i o n followed by s o l i d - l i q u i d s e p a r a t i o n . h o w e v e r , wou ld g e n e r a t e l a r g e q u a n t i t i e s of h a z a r d o u s metal h y d r o x i d e s l i l d g e t h a t wou ld n e e d t o b e s u b s e q u e n t l y h a u l e d fo r d i s p o s a l . T h e e s c a l a t i n g cos t s f o r s u c h d i s p o s a l , c o m b i n e d w i t h t h e l o n g - t e r m r a m i f i c a t i o n of l i a b i l i t y , c a n act a s a m o t i v a t i n g f a c t o r t o i n v e s t i g a t e a l t e r n a t i v e t r e a t m e n t s y s t e m s .

T r e a t r n e n t s y s t e m s a r e a v a i l a b l e t o h a n d l e waste streams c o n t a i n i n g c o p p e r a n d n i c k e l w i t h o u t g e n e r a t i n g waste s l u d g e . T h e s e s y s t e m s e m p l o y a d v a n c e d i o n e x c h a n g e a n d e l e c t r o w i n n i n g t e c h n o l o g i e s f o r t h e r e m o v a l o f copper a n d n i c k e l f r o m e f f l u e n t s t reams a n d t h e p r o d u c t i o n o f m e t a l l i c s h e e t s o f copper a n d n i c k e l .

) r e g u l a t i o n s . T r e a t m e n t o f t h e s e e f f l u e n t s c a n be d o n e i n t h e

T h i s c o n v e n t i o n a l t r e a t m e n t a p p r o a c h ,

i o n E x c h a n g e --- --

T h e h e a r t of t h i s t r e a t m e n t s y s t e m is comprised o f the p a t e n t e d i o n e x c h a n g e 2 r o c e s s known a s Rg~,ip,ra~b@ingF,ELo.w ' r a m E x c h a n g e l . T h i s t e c h n o l o g y h a s S e e n e m p l o y e d i n t h e metal f i n i s h i n g i n d u s t r y f o r the l a s t f i f t e e n y e a r s f o r c h e m i c a l r e c o v e r y a n d e f f l u e n t t r e a t m e n t , a n d h a s shown t o o f f e r a number of u n i q u e a n d

) s i g n i E i c a n t a d v a n t a g e s 2 o v e r c o n v e n t i o n a l i o n e x c h a n g e t e c h n o l o g y .

1

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In any operating ion exchange column, the resin near the top of the column is exhausted while the r e s i n near the bottom is in the regenerative state. At any given time, most oE the resin is

~ ~ ~ % ~ A ~ ~ & U & Q

kDChe&iL* The following design possible:

i I I

I

! . I - ! i

&QqeMtmesbimesLns: zeciprocating flow systems employ much smaller diameter ion exchange resins than other systems. This allows a faster exchange time than conventional resins thereby reduciny the length of the reaction zone and allowing the use of higher flow rates. This is particularly important f or p ~ i ~ t e ~ ~ ~ i t s U i h ~ ~ K ~ , .appT: f ca t3 i o n s w h e r e se Lec t ch4atins %Le s-"&e&M,taA be employed-., These r e s i ns have poorer kinetics and normally require utilization of slower flow rates. Rinse requirements, which are a function of diffusion kinetics, are also substantialLy less with fine mesh resins.

b) low exchanger loadings: Reciprocating flow improves performance by utilizing only those exchange. sites, near sur;Eace of the resin particles which are the most acces This is i&,marke ntrast ,to other systems which try to maximize e oadings by relying on 39"znge siTes withinwethe particle that can only be accessed by slbw &iEf usion.

1

c )-,caunter-cucr,.en genera-tion: A significant improvement in uptake, regene on, and rinsing efEiciency is made 2ossible by the use of counter-current regeneration (waste water flow is downward - regeneration flow is upward). The entire regeneration sequence takes only 4 - 5 minutes in contrast to a conventional system which can typically take 1.5 - 3 hours. The conventional method would then require the use of two exchange columns -"one in service while the other is regenerating. The ability to employ counter-current regeneration due to the short height column and fine mesh resin allows the production of a better quality effluent and a more concentrated product than co-current regeneration.

1 .

d ) b&mm~opef8Y?PymslyQItfS3 The-ma jar" C%.f?or- most, ion exchange h-'e**regenertant= acid": Count e r -c u r r en t r eg ene r a t ion

allows the"recipr0 ng flow ion exchange process to signif icantLy.',redu hemical consumption. ..

* 2 :

2

bed i n a convention Lts in . , apprec iab le

the re is m&sret F2w?Jkhhk&&es&he

t imes both i n s e r v i c e and r e g e n e r a t i o n , For a p r i n t e d c i r c u i t processing a p p l i c a t i o n , the ~ t s ~ e s t ~ s & w i ~ e . ~ & s typic.+ 2Qxm & b w e & ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ s ~ r ~ ~ e ~ a t=i o n sequ~nce~cxE~.5 mrnukes. T h i s is i n marked c o n t r a s t t o o the r systems which a r e out of s e r v i c e for s e v e r a l hours f o r regenera t ion .

g ) m e t z . E "analysis tQI-.izL~~P8tecIz~er;ler,Bti~a T h e r ec ip roca t ing f Low ion exchange des ign lends i t s e l f t o fine-tuned monitoring c o n t r o l . For the example of copper metal , an analyzer can cont inuously monitor the e f f l u e n t copper concent ra t ion and i n i t i a t e regenera t ion a t t h e des i r ed . s e tpo in t . T h i s f u r t h e r enhances the chemical e f f i c i e n c y of the system. Copper ana lyzers a re a v a i l a b l e which can d e t e c t the metal a s low as 0 . 2 ppm concen t r a t ion .

These above f e a t u r e s t r a n s l a t e i n t o a number of advantages w h i c h a r e a t t r a c t i v e t o the p r in t ed c i r c u i t board manufacturer. These advantages include:

p$"-w*-, /, - reduced equipment--size' - S p a ' f C r e q m e m k s a r e lessened due t o the small column s i z e and assoc ia ted regenerant inakeup tanks and flow equa l i za t ion tanks.

- l o 9 s r s t a L t u p .CQS~S - These systems a r e preassembled, skid-mounted, and p r e - t e s t e d . Costs a s s o c i a t e d w i t h f r e i g h t , i n s t a l l a t i o n , and commissioning a re a l l e v i a t e d .

- lower opera t ing c o s t s - Counter-currenk regenera t ion and t h e var ious o t h e r f e a t u r e s cm2loyed. allow t h e sign.iEican,t. reduct ion o f r chemicaE.cransumprion.

- longer' r e s . i n . l i € e a The r ec ip roca t ing flow technique can reduce the impact of the th ree major f a c t o r s a f f e c t i n g r e s in l i f e ; namely, phys ica l a t t r i t i o n , o rganic fou l ing , and chemical ox ida t ion . Fine mesh r e s i n s a r e much l e s s prone to f r a c t u r e r e s u l t i n g from the con t r ac t ion and expansion caused b y changing ion ic form and osmotic shock. Short s e rv i ce cyc le s minimize organic s o r b t i o n and f i n e r e s i n s f a c i l i t a t e desorb t ion. A l s o , t.he-she>.r t - ~ o r r @ a c t - t ~ m ~ s " c h ~ r ~ ~ ~ ~ . ~ s ~ ~ ~ ~ f r echpraca t i-ng- ~ ~ ~ ~ . r ~ . n - - e x ~ ~ ~ ~ ~ - e ~ " " E e ~ ~ ~ ~ ~ ~ ~ ~ o n g . - ~ r e ~ ~ ~ ~ e ,

-9 x-id,king. , , c;randitians...--

3

. .

- low e€fluent : c o n c e n t r a t i o n s - T h e c o m b i n a t i o n of f i n e mesh n t r e g e n e r a t i o n r e s u l t s i n low

aL. t y p i c a l l y , much l e s s t h a n L ppm f o r

r e c i p r o c a t i n g f l o w . . i on e x c h a n g e c a n p r o c e s s l i q u i d s w i t h m i n i m a l d i l u t i o n a n d a c h i e v e h i g h r e g e n e r a t i o n e f f i c i e n c y , i t is i d e a l l y s u i t e d t o p r i n t e d c i r c u i t board a p p l i c a t i o n s ~ ~ a ~ ~ s n ~ ~ ~ ~ ~ e ~ ~ ~ ~ ~ a t $ o ~ ~ ~ m ~ s ~ ~ ~ ~ ~ ~ e i t t e d . c ~ n e r m . .war i o u s &&di@rrPEmpS.

W h i l e t h e a d v a n t a g e s of r e c i p r o c a t i n g f l o w a p p l y t o a n y i o n e x c h a n g e r e s i n o r a p p l i c a t i o n , t h e r e a r e cases w h e r e t h e r e l a t i v e a d v a n t a g e is more p r o n o u n c e d , s u c h as :

- v&.ere-~expensive ''

- where"""~he"'""We'neti.~s of the r e s i n a r e very slow

c i a l t r s e l e c t b e c h e . 1 ~ t i n g . z e s i n s a r e r;gcpi+red

- when t i g h t e f f l u e n t l imi t s m u s t be met a n d water c o n s e r v a t i o n m e a s u r e s a re e n f o r c e d r e s u l t i n g i n t h e n e e d f o r r e l a t i v e l y c o n c e n t r a t e d s o l u t i o n s t o b e t r e a t e d

E 1 ec t row i n n i n z - )

The smal l , c o n c e n t r a t e d v o l u m e o f r e g e n e r a n t s o l u t i o n f r o m t h e r e c i p r o c a t i n g f l o w i o n e x c h a n g e u n i t l e n d s i t s e l f q u i t e n i c e l y t o m e t a l r e c o v e r y b y e l e c t r o w i n n i n g . T h e t r a d i t i o n a l e l e c t r o w i n n i n g c e l l d e s i g n , h o w e v e r , is n o t e n t i r e l y c o n d u c i v e t o t h e t r e a t m e n t o f low metal c o n c e n t r a t i o n s . S o l u t i o n metal c o n c e n t r a t i o n s i n c o n v e n t i o n a l e l e c t r o w i n n i n g o p e r a t i o n s a r e u s u a l l y i n t h e order o f 30 - 5 0 g / L w h i l e r e c i p r o c a t i n g f l o w i o n e x c h a n g e c o n c e n t r a t e s c o n t a i n a p p r o x i m a t e l y 1 0 - 20 g/L c o p p e r .

For t h e most p a r t , e l e c t r o w i n n i n g c e l l s u t i l i z e a b a s i c d e s i g n c o m p r i s e d of a l t e r n a t i n g f l a t shee t cathodes a n d a n o d e s . T h e metal i n s o l u t i o n is depos i t ed o n t o t h e cathode b l a n k s by a p p l i c a t i o n of a d i r e c t e l e c t r i c a l c u r r e n t . s i m u l t a n e o u s l y f r o m i n s o l u b l e a n o d e s w h i c h a r e f r e q u e n t l y made f r o m lead a l l o y s .

As metal is p l a t e d o n t o t h e c a t h o d e , t h e s t a g n a n t l i q u i d f i l m a d j a c e n t t o t h e c a t h o d e s u r f a c e t e n d s t o become d e p l e t e d i n m e t a l . T h e c u r r e n t d e n s i t y , w h i c h d e t e r m i n e s t h e r a t e of me ta l d e p o s i t i o n , m u s t n o t e x c e e d t h e r a t e a t w h i c h meta l i o n s d i f f u s e t h o r u g h t h i s f i l m t o t h e c a t h o d e . If t h e c u r r e n t d e n s i t y is too h i g h , t h e c o n c e n t r a t i o n o f meta l ions i n t h e d i f f u s i o n f i l m w i l l

Oxygen e v o l v e s

L ' .

4

. . , .. .. . . .. .

be e x c e s s i v e l y dep le t ed p r o d u c i n g a I

" c o n c e n t r a t i o n p o l a r i z a t i o n " , T h i s ces o n t h e c u r r e n t e f f i c i e n c y as w e l l as d u e t o h y d r o g e n e v o l u t i o n ,

One a p p r o a c h t o e x t e n d i n g t h e oparat t h e e l e c t r o w i n n i n g process a n d t h u s ma l o w - l e v e l meta l c o n c e n t r a t i o n s is t o i c u r r e n t d e n s i t y by r e d u c i n g t h e t h i c

K e n n e c o t t C o p p e r , a t o n e time t h e l a rges t ,U.S. copper p r o d u c e r , d e v e l o p e d a u n i q u e e l e c t r o w i n n i n g c e l l d e s i g n based upon a n a i r a g i t a t i o n scheme t h a t e f f e c t v e l y r e d u c e s t h e c a t h o d e f i l m t h i c k n e s s . The p a t e n t e d c e 1 1 3 i n c r e a s e s t h e e l e c t r o w i n n i n g c a p a b i l i t y i n d e x t o 3 - 5 ASF/g/L w h i l e a t t h e sane time m a i n t a i n s a b a s i c s i m i l a r i t y to t h e t r a d i t i o n a l e l e c t r o w i n n i n g d e s i g n .

T h i s e l e c t r o w i n n i n g ce1.L i n c o r p o r a t e s a number o f f e a t u r e s 4 w h i c h i m p r o v e t h e p e r f o r m a n c e a n d f e a s i b i l i t y of e l e c t r o w i n n i n g f o r waste water a p p l i c a t i o n s . T h e s e f e a t u r e s are:

a ) c o n v e c t i v e b u b b l e c u r t a i n a g i t a t i o n : T h e t h i c k n e s s o f t h e d i f f u s i o n l a y e r o f l i q u i d a d j a c e n t t o t h e cathode i s r e d u c e d by d i r e c t i n g a u n i f o r m c u r t a i n of a i r b u b b l e s across t h e f a c e of t h e c a t h o d e . T h i s d r a m a t i c a l l y i n c r e a s e s t h e r a t e of mass t r a n s p o r t t o t h e c a t h o d e f r o m t h e b u l k l i q u i d . As a r e s u l t , t h e meta l c a n b e d e p o s i t e d a t c u r r e n t d e n s i t i e s w h i c h a r e h i g h i n r e l a t i o n t o t h e meta l c o n c e n t r a t i o n w h i l e p r o d u c i n g metal of h i g h q u a l i t y a n d p u r i t y . T h i s simple t e c h n i q u e h a s p r o v e n i t s e l f t o b e m u c h more e f f e c t i v e a n d e n e r g y e f f i c i e n t t h a n s i m p l e a i r s p a r g i n y o r m e c h a n i c a l a g i t a t i o n . A l s o , t h i s i m p r o v e d a g i t a t i o n l e s s e n s t h e t e n d e n c y t o o c c l u d e a n o d e c o r r o s i o n p r d u c t s i n t h e metal d e p o s i t .

b ) c l o s e a n o d e / c a t h o d e s p a c i n g : Close a n o d e / c a t h o d e s p a c i n g o n t h e o r d e r o f o n e i n c h r e d u c e s t h e v o l t a g e d rop ac ross t h e c e l l r e s u l t i n g i n lower e n e r g y c o n s u m p t i o n a n d r e d u c e s t h e o v e r a l l s i z e of t h e c e l l €o r a g i v e n ca thode a rea r e q u i r e m e n t .

c ) c u r r e n t s h a d o w i n g : T h e d e s i g n o f t h e c e l l is s u c h t h a t t h e c u r r e n t d e n s i t y is r e d u c e d t o w a r d s t h e e d g e s of t h e c a t h o d e . T h i s " f e a t h e r i n g " e f f e c t m e a n s t h a t n o n - c o n d u c t i v e e d g e s t r i p p i n g i s n o t r e q u i r e d t o p r e v e n t t h e e d g e s o f t h e d e p o s i t o n e a c h c a t h o d e f ace f r o m j o i n i n g . T h e c a t h o d e s a r e made f r o m s t a i n l e s s s t e e l from w h i c h t h e metal c a n be e a s i l y s t r i p p e d . Spec ia l t r e a t m e n t o f t h e cathode b l a n k s u r f a c e w i t h p a r t i n g a g e n t s i s a l s o n o t r e q u i r e d .

d ) s p e c i a l a l l o y a n o d e s : The a n o d e i.s comprised of a p a t e n t e d l e a d / c a l c i u m a l l o y s . S i n c e o c c l u s i o n of a n o d e c o r r o s i o n p r o d u c t s a r e a major c o n t r i b u t o r t o c a t h o d e lead i m p u r i t i e s , t h e use of t h e s e more s t a b l e a n o d e s r e s u l t s i n t h e p r o d u c t i o n of p u r e r metal .

5

I

e ) m e t a l a n a l y z e r con t ro l . : I n order t o o p t i m i z e e l e c t r i c a l e f f i c i e n c y as t h e metal c o n c e n t r a t i o n is r e d u c e d , t h e r e c t i f i e r c u r r e n t can be s t e p p e d down a u t o m a t i c a l l y b y a n a l y z i n g , fo r example, t h e copper c o n c e n t r a t i o n of t h e e l e c t r o l y t e . F l u c t u a t i o n s i n t h e c o p p e r c o n c e n t r a t i o n f e d t o t h e c e l l c a n t h u s . be a c c o u n t e d for a n d c o n t r o l l e d ,

Despi te t h e h i g h e r c u c x e n t d e n s i t i e s e m p l o y e d w i t h t h e c e l l , t h e c e l l v o l t a g e is n o t s i g n i f i c a n t l y d i f f e r e n t t h a n t h a t €or c o n v e n t i o n a l e l e c t r o w i n n i n g . However , t h e e n e r g y r e q u i r e d fo r a i r a g i t a t i o n is n o t apprec iab le compard t o t h e e lectrochemical e n e r g y r e q u i r e m e n t s . As a r e s u l t , d e s p i t e t h e h i g h e r p e r f o r m a n c e o f t h i s c e l l , i t s e n e r g y r e q u i r e m e n t s a r e n o t s i g n i f i c a n t l y d i f f e r e n t t h a n a c o n v e n t i o n a l e l e c t r o w i n n i n g c e l l .

The c u m u l a t i v e e f f e c t of t h e a b o v e f e a t u r e s i s t o p r o v i d e t h i s d e s i g n o f e l e c t r o w i n n i n g c e l l w i t h a number of d i s t i n c t b e n e f i t s s u c h as:

- a metal p r o d u c t r e c o v e r e d i n a r e a d i l y m a r k e t a b l e f o r m

- a h i g h p u r i t y m e t a l p r o d u c t

- low e n e r g y c o n s u m p t i o n

- a n e a s i l y h a r v e s t e d metal p r o d u c t

- s i m p l e a n d r e l i a b l e e q u i p m e n t d e s i g n

- smal l space r e q u i r e m e n t s

Hewlett P a c k a r d Case S t a - -.---I--

The c o m b i a a t i o r r . of - r e c i p r o c a t i n g flow i o n e x c h a n g e a n d t h e p a t e n t e d ‘ e l e c t r o w i n n i n g s y s t e m o f f e r s t h e p r i n t e d c i r c u i t b o a r d m a n u f a c t u r e r a p r o v e n m e t h o d of m a i n t a i n i n g e f f l u e n t c o m p l i a n c e w h i l e a v o i d i n g t h e costs a n d l i a b i l i t i e s assoc ia ted w i t h t h e p r o d u c t i o n of h a z a r d o u s meta l h y d r o x i d e s l u d g e . H e w l e t t P a c k a r d , P r T n t e d ” C ‘ i r c u i e ^ D i v i s i o n , ^a€ Boise, I d a h o , h a s b e e n a b l e t o t ake a d v a n t a g e of t h e s e a d v a n c e m e n t s .

A new t r e a t m e n t system was i n s t a l l e d i n J u l y , 1 9 8 6 , t o process waste streams c o n t a i n i n g copper a n d n i c k e l w i t h o u t g e n e r a t i n g waste s l u d g e . T h e t r e a t m e n t s y s t e m e m p l o y e d t h e a b o v e a d v a n c e d i o n e x c h a n g e a n d e l e c t r o w i n n i n g t e c h n o l o g i e s f o r t h e ~ m ~ h o f u .

@ppetWand&%&sk from e f f l u e n t streams a n d t h e p r o d u c t i o n of metal l ic s h e e t s of’ copper a n d n i c k e l . U t i l i z a t i o n of these t e c h n i q u e s h a s r e s u l t e d i n lower o p e , r a t i n g costs t h a n t h e p r e v i o u s l y u s e d c o n v e n t i o n a l waste t r e a t m e n t s y s t e m .

Figure 1 schematical ly i l l u s t r a t e s t h e which t r e a t s r insewate a m.

The average flow of &8,A.gpq and c o n t a i n i c g ~ g e r f lows t o a c o l l e c t i o n tank. FK' waste stream overflows t o a second tank removal ion exchange u n i t a t a ~ H . Q E employs the r ec ip roca t ing flow i of a ca t ion exchanqe resin, calum automat ic v a l v i n g a n d controls l , mounted on a s t nless steel fTame. (30 . i n c h diameter, 6 i n c h h e i g h t ) , disso lved copper from the waste water i s exchanged f o r hydrogen on the r e s i n , TPie-unit

es b a - 6 l o w ~Of"wtlp ' " ~ o ' " ~ E ) l l l l ) ? r C O f f ~ ~ ~ ~ ~ f f ~ ~ ~ 5 0 " r ~ 1 5 ~ ~ mg/L.. of ariC""pro-&vces..a f i.na.1 effluents " m e ~-**~o~.-d-i.sso-~tred "c~pper. r r -

e f f r u e n P ? s - o f t e n '6eIo"w'the"~";B5 m p 1 antls,,atami c abso r p tl. i o n ' s pe'ctropho tometer

rtc.&dp.'apr&-Eirte r ,

As the waste water is pumped through t h e cesi

The e f f l u e n t leaving the ion exchanger flows t o a f i n a l pH adjustment tank where c a u s t i c soda is added t o r a i s e t h e f i n a l pH t o n e u t r a l €or f i n a l d i s c h a r g e . An i n - l i n e flow t o t a l i z e r on the ion exchanger measures the volume of waste water processed and i n i t i a t e s a n automatic regenera t ion sequence once 1 5 0 0 g a l l o n s has been processed Upow- regemerati>on,*"the, cupperz_& t h i s ""1-500 ' g a r i o n s is concentcaked intop, apEroximate a one hundred fold volume reduct ion.

D u r i ng r eg e ne r a t i 0 n , camcerI ' tT~a~e~"~SU% )"""TGTf'u r?c **xci-d, is i n j ec ted b y .a-'meZerl'ng pump into. a- Elow 0 5 wa\tea-.passina,--,thr,ough the r e s i n coIumii. exchanging copper c a t i o n s from the r e s i n for t he hydrogen c a t i o n s of t h e a c id . ( 1 5 - 2 0 g /L) copper s t ream w h i c h t h e ~ , ' € l o w s ~ . " ' f r o m . t h ~ r e s i n column t o a s to rage tank feeding am ,~Lec*erowinnina-.systerrP; flow of water then r i n s e s the excess ac id ou t of t h e r e s i n column which prepares the column fo r t reatment O E f u r t h e r waste water. T h i s r e s in r i n s e water flows t o t h e system c o l l e c t i o n tank for subsequent processing. ion exchange i n i t s ope ra t ion .

The' r e s u l t i n g 9 % acid. regemerates t h e ,resin by

T h i s produces about 1 5 ga l lons of a concentrated

A

As a r e s u l t , no waste is produced by the

7

I ' I '

Copper E l e c t row i n n

The concentrated copper s u l f a t e s o l u t i o n produced by t h e ion exchanger flows t o an e leva ted holding tank, t h e n .cascades by g r a v i t y through a se r i e s of four 1 2 0 ga l lon electrowinning c e l l s each conta in ing about 1 3 2 square Eect of cathode a rea . A s i n g l e r e c t i f i e r provides c u r r e n t t o a l l €our c e l l s w i t h t h e f i r s t c e l l connected e l e c t r i c a l l y i n s e r i e s w i t h the th ree subsequent c e l l s w h i c h a r e connnected i n p a r a l l e l . T h i s provides the f i r s t c e l l w i t h a c u r r e n t t h r e e times h i g h e r than the o the r t h r e e . A s copper s u l f a t e s o l u t i o n flows through t h e four c e l l s , copper is p la ted ou t onto 20" x 24" s t a i n l e s s s t e e l cathode s h e e t s .

A copper concent ra t ion of 1 0 0 0 my/L leaving the f i n a l c e l l i s maintained by a n analyzer w h i c h c o n t r o l s the output of the r e c t i f i e r . T h e 1000 mg/L copper stream leaving the l a s t c e l l i s c o l l e c t e d and t r a n s f e r r e d back t o the f r o n t of the system t o combine w i t h the incoming waste r insewater . T h i s e f f e c t i v e l y c l o s e s t h e loop o n t h e copper. Continuous closed loop opera t ion i n t h i s manner r e s u l t s i n t h e b u i l d u p over time of o ther metals ( n i c k e l , z inc , i r o n , c a l c i u m ) , which could u l t ima te ly a f f e c t copper e lectrowinning. I n order t o maintain these m e t a l l i c contaminants a t an acceptably low l e v e l ( l e s s than 1 0 0 0 m g / L ) , about f i v e g a l l o n s per day of the stream Leaving the l a s t electrowinning c e l l is d ive r t ed for batch t reatment .

Nickel Removal System

I ,~~ .I+- * * ' . The Nickef a 1 System t r e a t s e l e c t r o l y t i c . mickel pfating, (Wat t s b a t te;*s. and electroless n i c k e l p l a t ing r insewater d bath dumps from nickel=. Bksci pl;oductLon. Watts n i c k water a t an average flow of Wqpm and containing do"' mg/L of nickel- "fLows EKQIQ. u.aprfeede-karrk t o the n i cke l removal ion exchange u n i t (Figure 2 ) .

T h i s u n i t a l s o employs the rec iproca t ing Elow ion exchange process . As t h e waste water pas ses through t h e s i x i n c h deep bed

d isso lved n i c k e l from the r insewater is exchanged f o r n the resin. The--unit' processes a' .€low? of 12. gpm ~ ~ ' ~ ~ O ~ i ' , ' ~ ~ O O ~ ~ ~ ~ ~ L ~ ~ ~ d-?ssolved-~ nic k e groduces an

e€ f+u e n Y' con t ai..n.h+le srs. t h a n I. mg,/ L. of d5 ss o 1 nizkel: %is a,.ptEL adjustment tank of t h e secondary ion

exchang.er,,se.€.el=r( o ' a s the nickel: polisher. . T h i s tank aLso L"eceive-s,..,r,insewa~er and metered bath dumps from e l e c t r o l e s s n.Cck& p l a t i n g , as' .well a s r e s i d u a l s o l u t i o n from the n i c k e l e lectrowinning ce l l (descr ibed below) . The n icke l po l i sher pH adjustment tank has provis ion t o a d j u s t the pH t o 4 . 0 . Froin t h e pH adjustment tank, the waste stream overflows t o a second t a n k tank w h i c h f eeds the n i cke l po l i she r ion exchange u n i t .

The nickel polisher is a eeciprocating :Elow :ion exchange -unit but ~ e ~ i F e s i t ~ ~ ~ E ~ ~ ~ ' ~ x ~ ~ f f ~ ~ ~ ~ ~ ~ ~ k e 1 j u n r Y ~ a ~ h ~ L ~ t ~ n g , ~ ~ ~ e ~ ~ s . --+*The

Both the primary nickel removal and n enegate automatically as initiated by a €low complete their counter-current regeneration sequence witliin-4 minutes. Upon regeneration, accomplished in a manner simikar-.ta the copper removal unit, a nickel sulfate concentrate 'ks-:produced. The concentrate from the primary unit (25 - 30 g/L) flows to electrowinning; the concentrate from the polisher unit ( 3 - 4 g / L ) flows to the feed tank of the primary unit so that it will be concentrated further prior to electrowinning.

Nickel Electrowinning --1_1_-

_I----

, . . . . .,., 6 l r ;, . I

. . , .

, ~ . .. , . , ., , , . , . : . , . . :

I , ' X

Producing a good, homogenous, stress-free nickel deposit on a flat cathode sheet is more difficult than copper electrowinning. While the exact conditions are considered proprietary, they require control of a number of factors including agitation, current density, pH, nickel concentration, and temperature, This is accomplished by continuously circulating the contents of the nickel electrowinning cell with an adjustment tank where the critical operating parameters, including pH adjustment by caustic addition, are controlled and maintained. The system operates continuously as opposed to batchwise. This ensures that the nickel concentration is always within a controlled range. For every gallon of concentrated nickel sulfate flowing to the electrowinning cell, a gallon of more dilute nickel electrowinning electrolyte is transferred to the nickel 2olisher feed tank. This "closes the loop" on the nickel.

Figures 3 and 4 graphically display the copper concentration in the copper removal system influent and effluent respectively. The data presented was taken from daily logs over a 90 day period starting during the fourth month of the system's operation.

After one year Df operation, this data continues to be representative of the system's performance. Note that influent concentrations vary from 100 to over 300 mg/L of copper, with the average being in the 150 - 200 rng/L range (Figure 3 ) . The effluent concentrations (Figure 4) average in the range of 0.04 - 0.1 mg/L with only one reading above 0.2 g / L .

c

Copper and n i c k e l p r a t e s froin t h e s t a i n l e s s s t e e l s t a r t e r cathodes have been removed. The p l a t e s have a t h i c k n e s s of up t o 1/4" and!.weFgh about 30 - 40 pounds each. To d a t e , 6 , 2 0 0 pounds of copper metal and 2 , 4 0 0 pounds of n i cke l me ta l have been reclaimed and sold a t $l.OO/lb t o a l o c a l metal s c rap d e a l e r , An assay of the copper p l a t e s i n d i c a t e s a metal p u r i t y of g r e a t e r than 99-99% coppec;

Hewlett Packard was p a r t i c u l a r l y impressed by the h i g h r e l i a b i l i t y of the system and, i n p a r t i c u l a r , the microprocessor based ion exchanger c o n t r o l s .

Minor process modi f ica t ions made a f t e r s t a r t u p included the following:

- Upgrading c e r t a i n r insewaters used by Hewlett Packard from s o f t water t o deionized water. The s o f t water s t i l l contained an unacceptable l e v e l of calcium w h i c h r e s u l t e d i n calcium s u l f a t e c r y s t a l l i z a t i o n i n the concentrated copper s u l f a t e produced by the ion exchanger upon regenera t ion . These c r y s t a l s i n t e r f e r e d w i t h electrowinning c e l l a i r a g i t a t i o n .

- Adjusting the n i c k e l electrowinning parameters t o achieve the des i r ed q u a l i t y n i cke l depos i t a t an acceptab le e l e c t r i c a l e f f i c i e n c y .

The ope ra t ing c o s t s of t h e s e m t a l removal systems were monitored b y Hewlett Packard, .These were compared w i t h the o p e r a t i n g c o s t s of the previous convent ional waste treatment system.

1

Operating c o s t s considered were:

- chemical usage for t reatment - e l e c t r i c a l requirements - sludge d i sposa l and hauling c o s t - metal byproduct values

The new system achieved a s i g n i f i c a n t decrease i n opera t ing c o s t s . The d e t a i l s of the s a v i n g s a r e considered c o n f i d e n t i a l by Hewlett Packard. ]In a d d i t i o n t o the above considered c o s t s , the new s y s t e m r equ i r e s less ope ra t ion , maintenance, and supervisory a t t e n t i o n w h i c h can? be t r a n s l a t e d i n t o fu r the r savings.

10

C o n c l u s i o n s

Hewlett P a c k a r d ' s P r i n t e d C i r c u i t D i v as b e e n able t o t a k e a d v a n t a g e of t h e r e c i p r o c a t i n g flow i a n g e a n d advanced e l e c t r o w i n n i n g t e c h n o l o g i e s t o e l i m i n r soi;rces of metal h y d r o x i d e h a z a r d o u s waste s l u d g e i n t of c i r c u i t b o a r d s . T h e s y s t e m s d e s c r i b e d n o t o n p r o d u c i n g metal l ic s h e e t s b u t also i m e f f l u e n t a t o p e r a t i n g costs s i g n i f i c w i t h a c o n v e n t i o n a l pH n e u t r a l i z a t i o s y s t e m .

R e f e r e n c e s _I_. ---.-

1.

2.

3 .

4 .

5.

R . F . H u n t e r , U.S. P a t e n t 3 , 3 8 5 , 7 8 8 ( 1 9 6 8 ) I U . S . P a t e n t 3 , 3 8 6 , 9 1 4 ( 1 9 6 8 ) (3.5. Brown, " A c i d a n d Metals R e c o v e r I b y R e c o f l o S h o r t Bed I o n E x c h a n E " , i n S e p a r a t i o n P r o c e s s e s In

--.-.-- -.-_1_-

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H y d r o m e t a l l u r g y , e d . D a v i e s , G . A . ( 1 9 8 7 ) W . W . H a r v e y , M.R. R a n d l e t t , K.L. B a n g e r s k i s , U . S . P a t e n t 3 , 8 7 5 , 0 4 1 ( 1 9 7 5 C . J . Brown, " R e c o v e r x o f Metals from E f f l u e n t s b i H i g h E f f i c i e n c x A i r A s t a t i o n ----I_.--..- Elec t rowinn%" , p r e s e n t e d a t t h e 7 3 r d A n n u a l AESF T e c h n i c a l C o n f e r e n c e a n d E x h i b i t of

--I__ -..--- .--.---. .---

S u r f a c e F i n i s h i n g , P h i l a d e l p h i a , J u n e , 1 9 8 6 A . G . Hood 111, e t a l , U . S . P a t e n t 3 , 8 5 9 , 1 8 5 ( 1 9 7 5 )

11

, . -e.

COPPER BEARING 1 I-’ (150-250 MG/L

3ES

FEED TP

)UAL 2OPPER SULFATE 4FTER- ELECTROWINNING I GIL COPPER

I I I I

RINSEWATER COPPER)

Lj ,

WATER a 1.- SULFURIC ACID

RECOFLO CATION

EXCHANGER

~

EFFLUENT (< 0.1 MG/L COPPER)

E CONCENTRATE 7-15 G/L COPPER

FIGURE 1 COPPER REMOVAL SYSTEM AT HEWLETT-PACKARD, BOISE .

YJATTS NICKEL R I N S E S I 200-300 MG/L Ni

I I WATER

FEED TANK

NICKEL SULFATE CONCENTRATE

23-30 G/L Ni

RECOFLO

EXCHANGER CATION -

ELECTROWINNING

EFFLUENT ELECTROLESS NICKEL < 1 MG/L Ni T-, c-= 150-200 MG/L Ni

BATH AND RINSES

. .

0 '- NICKEL

SULFATE

3-4 G/L Ni

CONCENTRATI t

rDJUSTMENT t-n-l FEED TANK K o a METAL

SELECTIVE II

ION EXCHANGER

H 2 S 0 4 1 1 1 1 )

WATER 0 i , I

ADJUSTMENT ELECTROWINNING

3 G/L Ni

E

FIGURE 2 NICKEL REMOVAL SYSTEM AT HEWLETT-PACKARD, BOISE

I

0

0

N

0

0 c

0

0

W a

:

3

Z 1

I

1

-1

9 0