Leach Process Models - American Chemical Society

18 Leach Process Models IVAN V. KLUMPAR Downloaded by NANYANG TECHNOLOGICAL UNIV on October 12, 2017 | http://pubs.acs.org Publication Date: May 30, 1980 | doi: 10.1021/bk-1980-0124.ch018

Kennecott Copper Corp., Lexington, MA 02173

Chemical processes involving multicomponent multistage leaching were modeled in the following way depending on the process type and complexity: • Steady state counter-current leaching and washing with specified solid compositions in each phase and a specified material balance of the remaining process units were simulated with simultaneous linear non-differential equations. The model can calculate the material balance including wash and makeup water, losses, number of stages and solute buildup in two recycles. The corresponding ready-to-use computer program can be applied to any process. • The material balance of steady state leaching and washing units of any configuration integrated with a number of other process units was modeled using iterative simulation. The method is particularly useful if multiple nested and intersecting recycles are involved. The model is applicable if each physical separation is defined by distribution coefficients, and each chemical reaction by stoichiometry and conversion. The corresponding computer program is again general and ready to use. • Kinetics and mass transfer were simulated for steady and non-steady state cocurrent or cross- c u r r e n t leaching of moving or stationary solids. The model can handle any number of parallel or consecutive reactions. The method is applicable to complex processes that include leaching of desirable and undesirable species, side reactions of a non-leach character, losses, product separation and recovery, lixiviant recycling, etc. While the main-line program is general, specific sub-routines for the individual process steps have to be written. 0-8412-0549-3/80/47-124-327$05.00/0 © 1980 American Chemical Society Squires and Reklaitis; Computer Applications to Chemical Engineering ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

COMPUTER APPLICATIONS T O CHEMICAL ENGINEERING

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Downloaded by NANYANG TECHNOLOGICAL UNIV on October 12, 2017 | http://pubs.acs.org Publication Date: May 30, 1980 | doi: 10.1021/bk-1980-0124.ch018

L i n e a r Equation

Model

A t y p i c a l h y d r o m e t a l l u r g i c a l p r o c e s s (1) i n c l u d e s : • L e a c h i n g and washing, r e p r e s e n t e d in F i g u r e 1 by a s e r i e s o f mixers w i t h i n t e r s t a g e l i q u i d - s o l i d s e p a r a t i o n in t h i c k e n e r s . • P r o d u c t s e p a r a t i o n , such as l i q u i d i o n exchange (LIX). • P r o d u c t r e c o v e r y , such as e l e c t r o w i n n i n g . • Waste d i s p o s a l , such as a t a i l i n g s pond. The b a r r e n l i q u o r s from t h e p r o d u c t s e p a r a t i o n o r r e c o v e r y s e c t i o n s , and t h e waste d i s p o s a l f a c i l i t y may be r e c y c l e d as wash l i q u o r t o t h e l a s t s t a g e o f t h e leach-wash system a f t e r a p p r o p r i a t e t r e a t m e n t . The p r o c e s s may i n c l u d e o t h e r streams such as an i n l e t o f l i x i v i a n t o r a d d i t i o n a l wash water, and a f i c t i c i o u s e x i t stream r e p r e s e n t i n g l o s s e s . An example o f this type o f c o n f i g u r a t i o n is t h e A r b i t e r P r o c e s s (2) f o r ammoniacal l e a c h i n g o f copper concentrates. The l i x i v i a n t c o n s i s t s o f aqueous ammonia f l o w i n g c o u n t e r - c u r r e n t l y and oxygen sparged crosscurrently. Depending on t h e c o n c e n t r a t e n a t u r e , t h e f o l l o w i n g t h r e e and o t h e r r e a c t i o n s may o c c u r : + +

2

#

CuFeS +2.25 0 +4 NH^ = C u ( N H ^ ) 4 ^ Ο ~ + 0 ^ 2

S

2°3~

2

+

2

°2

+ 2

N H

2

3

+ H

2°

=

2

S 0

4~

+ 2

N H

4

F e

( 1 )

2°3 (

2

)

Cu AsS +8.75 0 +15 NH +2.5 H 0 = 3

4

2

3

2

2+

2

= 3 C u ( N H ) + N H H A s 0 + 4 S0 "+2 NH* 3

4

2

4

(3)

E q u a t i o n 3 is an example o f an u n d e s i r a b l e r e a c t i o n because o f t h e s o l u b i l i z a t i o n o f a r s e n i c . Fortunately, most o f it p r e c i p i t a t e s s u b s e q u e n t l y as an i r o n a r s e n a t e . The ( N H ) S 0 4 r i c h wash l i q u o r p a s s e d t o a r e g e n e r a t i o n p l a n t c o n s t i t u t e s t h e e x i t stream in F i g u r e 1. Regenerated ammonia is t h e i n l e t stream. Regeneration is not shown in F i g u r e 1. N e i t h e r a r e o t h e r s e c t i o n s such as p r e g n a n t s o l u t i o n f i l t r a t i o n , t a i l i n g s f l o t a t i o n and r e c y c l e t r e a t m e n t . In d e v e l o p i n g t h e model, t h e f o l l o w i n g b a s i c assumptions have been made: • The s o l i d phase c o m p o s i t i o n in each s t a t e is specified. • The major c o n s t i t u e n t o f t h e s o l i d phase is an inert solid. 4

2

Squires and Reklaitis; Computer Applications to Chemical Engineering ACS Symposium Series; American Chemical Society: Washington, DC, 1980.


Ρ ·

PRODUCT-

Y

1

B

H

Y

j-1 j-1 SX I

MIXER SETTLER

I EXTRACTION

L

E

IY,

N

T

"!

Figure 1.

BjYj SX:

-HIM ll'h

CELL

ELECTROWINNING

EYc

EXIT

STAGE j

Simple leach process

ELECTROLYTE

STRIPPING

ORGANIC

LIQUID ION EXCHANGE

B

1 1 SX

STAGE 1

PREGNANT LIQUOR

FEED

D +

Y

J+1 J+1

SOLVENT I MAKEUP TAILINGS LIQUOR RECYCLE _

D

STAGE J

RAFINATE RECYCLE p D ^

+

j 1 j 1 Y

MULITSTAGE COUNTERCURRENT LEACHING AND WASHING


COMPUTER

330

APPLICATIONS TO CHEMICAL

• L i q u i d phase c o m p o s i t i o n s o f the o v e r f l o w underflow l i q u o r are equal.

ENGINEERING

and


The model a l g o r i t h m is based on the f o l l o w i n g r e l a t i o n s h i p s (symbols a r e l i s t e d at the e n d ) : D

j+1

+

D

j 1

Y

+

S

+

j 1 +

1

=

+

SX

D

0

+

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I

j Y

+

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D

Y

I - 1 1

+

B

Y

j j

+

S

X

j

+

E Y

( 5 )

E

E q u a t i o n s 4 and 5 a r e the o v e r a l l and component m a t e r i a l b a l a n c e s , r e s p e c t i v e l y , f o r the f i r s t j s t a g e s . S i m i l a r r e l a t i o n s h i p s have been d e v e l o p e d f o r the o t h e r s t a g e s and combined i n t o a system o f s i m u l t a n e o u s l i n e a r e q u a t i o n s (3). The c o r r e s p o n d i n g computer p r o gram has about 250 FORTRAN s t a t e m e n t s . In a d d i t i o n t o the s o l i d phase c o m p o s i t i o n f o r each s t a g e and the ine r t s o l i d f l o w r a t e , the u s e r must always s p e c i f y the c o m p o s i t i o n o f one i n l e t o r e x i t stream.

la. lb.

2. 3. 4.

5.

The computer program c a l c u l a t e s the f o l l o w i n g : L i q u i d phase c o m p o s i t i o n s f o r each s t a g e from the corresponding flowrates of overflows; or L i q u i d f l o w r a t e s f o r each s t a g e based on the concentration of • one component in each s t a g e , • a n o t h e r component in pregnant l i q u o r , wash l i q u o r , and l a s t s t a g e underflow; A l l r e m a i n i n g c o n c e n t r a t i o n s are a l s o c a l c u l a t e d . Requirements f o r makeup s o l v e n t . Number o f s t a g e s t o a t t a i n a s p e c i f i e d p r o d u c t l o s s in the r e s i d u e ( o p t i o n a l ) . B u i l d u p o f any s o l u t e in the wash l i q u o r based on s p e c i f i e d f r a c t i o n s , p and q, r e c y c l e d from p r e g nant l i q u o r and r e s i d u e l i q u o r , r e s p e c t i v e l y (optional). E f f i c i e n c i e s o f l e a c h i n g , washing and the e n t i r e leach-wash system ( o p t i o n a l ) .

The model is c o m p a t i b l e w i t h the p r e s e n c e o f a gas w h i l e n o t a c c o u n t i n g f o r it in the l e a c h a l g o r i t h m . L e t us l o o k at E q u a t i o n s 1, 2 and 3. R e l a t i v e convers i o n s o f the non-gaseous components are f i x e d i n d e p e n d e n t l y o f oxygen as l o n g as t h e r e is an 0 excess. T h i s is the case in most i n d u s t r i a l a p p l i c a t i o n s . Washing is n o t a f f e c t e d by oxygen in any c a s e . 2


18.

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Leach

Process

Modeh

331

I t e r a t i v e S i m u l a t i o n Model A c o n s i d e r a b l y more complex p r o c e s s is shown in F i g u r e 2. I t includes: • F o u r - s t a g e c o u n t e r c u r r e n t m i n e r a l l e a c h i n g and washing w i t h waste d i s p o s a l (M,W,D) • Two s e p a r a t i o n and r e c o v e r y c i r c u i t s f o r two d i f f e r e n t p r o d u c t s . Each c o n s i s t s o f c r y s t a l l i z a t i o n intermediate product l e a c h i n g , f i n a l product r e c o v e r y and e x t r a c t a n t r e g e n e r a t i o n (C,I,P,R). • Reagent p r e p a r a t i o n c o m p r i s i n g a b s o r p t i o n and s t r i p p i n g (A,S). The p r o c e s s i n c l u d e s a number o f r e c y c l e s t h a t can be i n t e r p r e t e d as 18 i n t e r s e c t i n g and n e s t e d l o o p s of a f i r s t through f i f t h o r d e r . I t is i m p o s s i b l e o r i m p r a c t i c a l to model p r o c e s s e s o f this type w i t h s i m u l t a n e o u s e q u a t i o n s . Rather, i t e r a t i v e s i m u l a t i o n is used (£). The a v a i l a b l e computer programs, however, have the f o l l o w i n g disadvantages : • They a r e l a r g e and e x p e n s i v e because they were developed f o r r e g u l a r process d e s i g n , • Becoming w e l l a c q u a i n t e d w i t h t h e program is time consuming, • Most c a s e s r e q u i r e w r i t i n g o f s p e c i f i c s u b r o u t i n e s . There is a need f o r a s i m p l e model l i m i t e d t o m a t e r i a l b a l a n c e s t h a t c o u l d be used f o r p r e l i m i nary c a l c u l a t i o n s when t h e r e a r e n o t enough d a t a o r time a v a i l a b l e f o r r i g o r o u s p r o c e s s d e s i g n . The p r o posed model is p a r t i c u l a r l y u s e f u l f o r p r o c e s s e s t h a t a r e c o n t r o l l e d by m a t e r i a l b a l a n c e r e l a t e d parameters r a t h e r than by t h e t h e r m a l and k i n e t i c n a t u r e o f t h e system. Many l e a c h p r o c e s s e s f a l l w i t h i n this c a t e gory b e i n g s e n s i t i v e t o o v e r s a t u r a t i o n , pH, o v e r a l l water b a l a n c e , d i s t r i b u t i o n o f i m p u r i t i e s , e t c . Any c h e m i c a l p r o c e s s can be broken down i n t o a number o f modules o f the f o l l o w i n g f o u r types ( 5 ) : (a) A d d i t i o n o f two o r more streams, (b) B r a n c h i n g o f an i n l e t stream i n t o two o u t l e t s o f t h e same c o m p o s i t i o n , (c) C o n v e r s i o n o f a stream by a c h e m i c a l r e a c t i o n i n t o another stream o f a d i f f e r e n t c o m p o s i t i o n , (d) D i s t r i b u t i o n o f an i n l e t stream i n t o two o u t l e t s of d i f f e r e n t composition. Each r e c y c l e is d e f i n e d by a module o f a f i f t h type ("e" f o r e n c i r c l i n g t o keep t h e symbols meaningful) .


#


Squires and Reklaitis; Computer Applications to Chemical Engineering ACS Symposium Series; American Chemical Society: Washington, DC, 1980. Figure 2. Complex leach process



18.

KLUMPAR

Leach

Process

Models

333

F i g u r e 3 shows t h e f l o w s h e e t o f F i g u r e 2 e x p r e s s e d in terms o f t h e f i v e modules. Lower case l e t t e r s a r e used t o d i s t i n g u i s h modules from p l a n t s e c t i o n s which a r e denoted by c a p i t a l s . Some modules a r e i d e n t i c a l w i t h equipment u n i t s , e.g. f i l t e r s and t h i c k e n e r s a r e d i s t r i b u t i o n modules. I n o t h e r c a s e s , one p i e c e o f equipment is s i m u l a t e d by two o r more modules. For example, a b s o r b e r A is r e p r e s e n t e d by a, c, d and b modules. The u s e r has to s p e c i f y a s p l i t r a t i o f o r each b r a n c h i n g module and a d i s t r i b u t i o n c o e f f i c i e n t f o r each component e n t e r i n g a d i s t r i b u t i o n module. The c o n v e r s i o n module r e q u i r e s a s t o i c h i o m e t r i c c o e f f i c i e n t f o r each component i n v o l v e d and the f r a c t i o n a l c o n v e r s i o n o f a s e l e c t e d key component. Each r e c y c l e has t o be d e f i n e d by the o r i g i n a t i n g and d e s t i n a t i o n modules, c o m p u t a t i o n a l sequence, and convergence t o l e r a n c e o f a key component. A f t e r a l l modules a r e s p e c i f i e d , the computer p r o gram c a l c u l a t e s f l o w r a t e s and c o m p o s i t i o n s o f a l l ins i d e and o u t l e t streams based on known i n l e t streams. I n l e t and o u t l e t streams a r e t h o s e which do not o r i g i n a t e o r end in a module, r e s p e c t i v e l y . The o t h e r s a r e i n s i d e streams. The program has o n l y 250 FORTRAN statements. K i n e t i c s and Mass T r a n s f e r Model R e a c t i o n k i n e t i c s and mass t r a n s f e r a s s o c i a t e d w i t h l e a c h i n g can be e x p r e s s e d u s i n g a m o d i f i e d s h r i n k i n g c o r e model (6). L e t us a g a i n use the A r b i t e r P r o c e s s as an example. The i n t e r a c t i o n o f ammonia and oxygen w i t h a c h a l c o p y r i t e p a r t i c l e can be v i s u a l i z e d as c o n s i s t i n g o f the f o l l o w i n g elements (see F i g u r e 4 which is a s e c t i o n o f the t h r e e phase s y s t e m ) : 1. Oxygen d i s s o l u t i o n at the l i q u i d i n t e r f a c e , 2. Ammonia and O 2 t r a n s f e r t o the r e a c t e d p a r t i c l e shell, 3. Aqueous NH^ and 0 d i f f u s i o n t o the u n r e a c t e d p a r t i c l e core, 4. R e a c t i o n (Eq. 1) at the c o r e s u r f a c e , 5. D i f f u s i o n of r e a c t i o n products across the s h e l l , 6. T h e i r t r a n s f e r to the bulk l i q u i d . Each element r e p r e s e n t s a r e s i s t a n c e . I f one r e s i s t a n c e is c o n t r o l l i n g , a s i m p l e r a t e e q u a t i o n may be derived. F o r example, i f the s h e l l d i s i n t e g r a t e s and the l i q u i d is v i g o r o u s l y a g i t a t e d , l e a c h i n g can be r e p r e s e n t e d by the s u r f a c e r e a c t i o n r a t e e q u a t i o n , 2


COMPUTER APPLICATIONS TO CHEMICAL ENGINEERING


334

CO

Ο

s

s .ο J§ "5

•S

ε c6

< a *·.



18.

KLUMPAR

Leach

Process

Figure 4.

Modeh

Shrinking-core model


335

COMPUTER

336


r

= -(dN /dt)/V

M

M

= 4 π R

2

APPLICATIONS TO CHEMICAL

ENGINEERING

η ksC /V Q

(6)

As t h e r i g h t - h a n d s i d e e x p r e s s i o n is based on t h e mean p a r t i c l e d i a m e t e r , it has t h e advantage o f e l i m i n a t i n g shape f a c t o r s . S i m i l a r r a t e e q u a t i o n s can be d e v e l o p e d f o r t h e p a r a l l e l l e a c h i n g o f o t h e r m i n e r a l s (see Eq. 3 ) . The o x i d a t i o n o f i n t e r m e d i a t e s u l f u r compounds t o s u l f a t e s such as Eq. 2 is a c o n s e c u t i v e r e a c t i o n t o m i n e r a l leaching. Other r e a c t i o n s a r e v i r t u a l l y i n s t a n t a n e o u s , e.g., p r e c i p i t a t i o n o f i n s o l u b l e f e r r i c a r s e n a t e s from s o l u b l e N H 4 H 2 A S O 4 which is c o n s e c u t i v e t o Eq. 3. On t h e o t h e r hand, t h e i n s t a n t a n e o u s s h i f t in t h e amonia ammonium e q u i l i b r i u m , NH

3

+ H 0*NH 2

+ 4

+ OH"

(7)

can n o t be a s s o c i a t e d w i t h t h e l e a c h i n g o r p r e c i p i t a t i o n o f any p a r t i c u l a r s p e c i e s . Instantaneous r e a c t i o n s a r e f i x e d by t h e i r e q u i l i b r i u m r e l a t i o n s h i p s , e.g., C

A

»

C

C

U H

/

V

Leach Process Models - American Chemical Society

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