FhP- 437
RECOVERY OF METAL VALUES FROM METAL-FINISHING HYDROXIDE SLUDGES
BY PHOSPHATE PRECIPITATION
L. G. Twidwell, D. R. Dahnke, B. W. Arthur, S. M. Nordwick
Department o f M e t a l l u r g y and M i n e r a l Processing Engineering
Montana College o f M i n e r a l Science and Technology
Butte, Montana 59701
ABSTRACT
A process f o r s e l e c t i v e l y r e c o v e r i n g t r i v a l e n t c a t i o n s from e l e c t r o p l a t i n g hydroxide
The process i s based on phosphate p r e c i p i t a t i o n .
sludge m a t e r i a l s has been developed.
The advantages o f t h e process are:
'simple s e l e c t i v e p r e c i p i t a t i o n
'easy s o l i d / l i q u i d s e p a r a t i o n
' e f f e c t i v e conversion o f t h e p r e c i p i t a t e d phosphates t o o t h e r products w i t h t h e
regeneration o f phosphate reagent.
A p p l i c a t i o n o f t h e process t o mixed metal hydroxide sludges w i l l be discussed.
Experimental r e s u l t s i l l u s t r a t i n g s e l e c t i v e separation, f i l t e r a b i l i t y r a t e s , and
conversion p o s s i b i l i t i e s w i l l a l s o be presented.
INTRODUCTION
Metal bearing hydroxide sludge
m a t e r i a l i s generated by t h e metal
f i n i s h i n g industry.
Environmental impact
and resource conservation c o n s i d e r a t i o n s
have i n r e c e n t years promoted development
o f a l t e r n a t i v e s t o d i s p o s i n g of these
hydroxide m a t e r i a l s i n t o hazardous waste
containment s i t e s .
Separation and
p r o d u c t i o n o f pure m e t a l s a l t s from mixed
In
metal sludges i s one such a l t e r n a t i v e .
many cases s y n t h e s i s o f these metal s a l t s
i s v e r y a t t r a c t i v e economically, w i t h
p u r i f i e d forms demanding h i g h market value.
I n o t h e r instances, metal compounds can be
produced f o r reuse i n t h e metal f i n i s h i n g
c i r c u it.
P r e l i m i n a r y work on developing a
series o f selective precipitations f o r the
s e p a r a t i o n and recovery o f s o l u b l e metal
components common t o e l e c t r o p l a t i n g sludges
has been completed.
As a p a r t o f t h i s work,
flowsheets were developed f o r s e p a r a t i o n o f
iron, copper, zinc, chromium and n i c k e l , and
t h e v a r i o u s u n i t o p e r a t i o n s o f t h e flowsheets were t e s t e d a t a f l o w r a t e o f 200
l i t e r s p e r day. Although t h i s treatment and
recovery system performed s a t i s f a c t o r i l y t h e
chromium e x t r a c t i o n phase i n v o l v e d t h e v e r y
c o s t l y step o f chromium o x i d a t i o n .
Use o f a
phosphate p r e c i p i t a t i o n system, however, may
o f f e r t h e advantages o f a l l o w i n g s e l e c t i v e
- - p r e c i p i t a t i o n o f metal phosphates, producing
p r e c i p i t a t e s w i t h b e t t e r f i l t e r a b i l i t y chara c t e r i s t i c s than hydroxide o r s u l f a t e sol i d s , and e l i m i n a t i n g t h e chromium o x i d a t i o n
step.
The p r e c i p i t a t i o n s may be accomplished by e x p l o i t i n g t h e s e l e c t i v e s o l u b i l i t y as
a f u n c t i o n o f pH and s o l u t i o n temperature of
v a r i o u s metal phosphates.
Typically, t r i v a l e n t metal phosphates are v e r y much l e s s
s o l u b l e than d i v a l e n t metal phosphates.
Metals such as i r o n o r chromium can be rap i d l y and c l e a n l y separated from s o l u t i o n s
c o n t a i n i n g many grams p e r l i t e r ( g / l i t e r ) of
n i c k e l . z i n c o r cadmium. These i r o n and
chromium phosphates form as dense, s p h e r i c a l
p a r t i c l e s and y i e l d e x c e l l e n t f i l t e r a b i l i t y
and washing c h a r a c t e r i s t i c s .
338
A p r o j e c t i s c u r r e n t l y i n progress a t
Montana College o f M i n e r a l Science and
Technology t o pursue t h e f i n a l development
o f t h i s process i n terms o f long-term
o p e r a t i o n and i n t e g r a t i o n w i t h other, more
t r a d i t i o n a l hydrometallurgical u n i t
w h i t e p r e c i p i t a t e , gypsum, formed d u r i n g
t h e leach operation. T h i s process r e j e c t e d
approximately 88% o f t h e t o t a l calcium from
t h e leach s o l u t i o n . Data i n Table 7 represents t h e a n a l y s i s o f t h e sludge m a t e r i a l
w h i l e data i n Table 2 g i v e s t h e a n a l y s i s o f
t h e leach s o l u t i o n .
Note t h a t i f t h e t o t a l
calcium a v a i l a b l e had leached, a calcium
c o n c e n t r a t i o n o f 6.0 g / l i t e r would have
resulted.
The gypsum produced i n t h i s t e s t
was 93% pure CaS04'2H20 w i t h i r o n being t h e
major contaminant.
operations. An extensive f i n a l r e p o r t w i l l
be issued upon completion o f t h e p r o j e c t .
TREATMENT TECHNIQUES
Leaching
S u l f u r i c a c i d i s a very e f f e c t i v e
l e a c h i n g agent f o r metal-bearing hydroxide
m a t e r i a l s : one gram o f H SO i s r e q u i r e d
f o r each gram o f s o l i d s Bre4ent i n t h e
sludge.
The l e a c h i n g o p e r a t i o n i s
performed a t ambient pressure and w i t h o u t
e x t e r n a l heating.
The heat o f r e a c t i o n i s
s u f f i c i e n t t o r a i s e t h e temperature o f t h e
leach s l u r r y t o about 50°C, which
undoubtedly a i d s t h e d i s s o l u t i o n process.
R e t e n t i o n t i m e i s 30 minutes, f o l l o w e d by
s o l i d - l i q u i d separation.
The f i l t r a t e
t y p i c a l l y c o n t a i n s b e t t e r than 95% o f t h e
metal values a v a i l a b l e from t h e sludge.
A
small f r a c t i o n o f unleachable m a t e r i a l ,
u s u a l l y c o n s i s t i n g o f sand from f i l t e r s ,
wood chips, p l a s t i c , etc.. comprises t h e
f i l t e r cake.
The leach s o l u t i o n i s u s u a l l y
d i l u t e d t o y i e l d a t o t a l dissolved solids
l e v e l o f 40 g / l i t e r .
Some water may be
added d u r i n g t h e leach, w i t h t h e remainder
s u p p l i e d a f t e r s o l i d - l i q u i d separation.
F i l t e r cake wash water i s used i n t h i s
second d i l u t i o n t o enhance o v e r a l l metal
recovery.
The l e a c h i n g o p e r a t i o n produces
a feed stream w i t h a pH value of
approximately 1.5.
Calcium Removal
Copper Recovery
High l e v e l s o f copper present in+She
l e a c h s o l u t i o n preclude removal o f Fe
f e r r i c phospate p r e c i p i t a t i o n because Cu
w i l l coprecipitate with the iron.
For
those sludge m a t e r i a l s which c o n t a i n s i g n i f i c a n t f r a c t i o n s o f copper, t h e removal o f
copper from t h e leach s o l u t i o n must precede
f e r r i c phosphate p r e c i p i t a t i o n .
Hydrometal
l u r g i c a l treatment o f copper i s a w e l l
developed commercial o p e r a t i o n and these
technologies a r e r e a d i l y a p p l i c a b l e t o
copper b e a r i n g hydroxide sludge leach solutions.
By f a r t h e s i m p l e s t method f o r
copper recovery from a c i d i c , aqueous media
i s by cementation w i t h i r o n .
The cementat i o n process i s described by t h e reaction:
&
.-
Some sludge m a t e r i a l s c o n t a i n a
s i g n i f i c a n t f r a c t i o n o f Ca, present e i t h e r
from water d e i o n i z i n g system backwashing
operations, o r from CaO used i n waste water
treatment.
When s u l f u r i c a c i d i s employed
t o l e a c h a h i g h calcium bearing m a t e r i a l ,
gypsum (CaS04'2H20) w i l l s e l e c t i v e l y
precipitate.
The s o l u b i l i t y l i m i t f o r
calcium i n t h e leach l i q u o r i s
I f a minimum
approximately 0.6 g / l i t e r .
volume o f d i l u t i o n water i s added before
s o l i d - l i q u i d separation, t h e t o t a l mass o f
calcium r e j e c t e d i s increased and a f i n a l
feed s o l u t i o n bearing 0.2 t o 0.4 g / l i t e r
calcium can be produced. The gypsum
p r e c i p i t a t e enhances f i l t e r a b i l i t y o f t h e
leach residue.
The gypsum bearing f i l t e r
cake can e i t h e r be disposed, o r t r e a t e d t o
recover pure gypsum which c o u l d then be
c a l c i n e d t o produce p l a s t e r o f Paris.
I n small s c a l e o p e r a t i o n s t h e cement a t i o n process i s c a r r i e d o u t by suspendi n g a permeable basket c o n t a i n i n g i r o n
f i l i n g s i n t h e leach solution.
Containment
of t h e i r o n f i l i n g s i n t h i s f a s h i o n f a c i l i t a t e s r a p i d removal o f t h e cement copper
product from t h e process s o l u t i o n a f t e r a 15
t o 30 minute r e t e n t i o n time.
Copper
cementation i s n o t w i t h o u t i t s
drawbacks:
1.
an impure copper i s produced which
must f u r t h e r be r e f i n e d by
smelting,
2.
i r o n i n s o l y j i o n i s reduced t o t h e
f e r r o u s (Fe ) s t a t e , and
t h e r e f o r e must be o x i d i z e d Q j f o r e
p r e c i p i t a t i o n as f e r r i c (Fe )
phosphate.
Cementation o f copper w i t h i r o n powder
was t e s t e d i n t h e l a b o r a t o r y t o remove copper
from a mixed-metal e l e c t r o p l a t i n g sludge
A l a r g e excess o f i r o n
leach solution(2).
= 10) was s l u r r i e d i n t o the
powder (M /M
mixed-metif s % u t i o n f o r one-half hour w i t h a
A h i g h calcium bearing e l e c t r o p l a t i n g
sludge m a t e r i a l was t r e a t e d w i t h s u l f u r i c
A heavy
a c i d t o leach t h e metal values.
339
and i s normally considered t o be a
d e l e t e r i o u s i m p u r i t y because o f i t s low
value.
Two p r e c i p i t a t i o n techniques are
c u r r e n t l y employed i n d u s t r i a l l y t o remove
i r o n from process s o l u t i o n s .
One technique
i s t h e h i g h temperature synthesis o f f e r r i c
hydroxide which y i e l d s a very h i g h surface
area s o l i d t h a t i s d i f f i c u l t t o f i l t e r and
adsorbs many i o n i c species from s o l u t i o n
r e s u l t i n g i n heavy contamination o f t h e
The second method
i r o n bearing s o l i d .
e n t a i l s t h e h i g h temperature f o r m a t i o n of a
b a s i c hydrous a l k a l i s u l f a t e o f i r o n , a
m i n e r a l named j a r o s i t e .
This process req u i r e s near b o i l i n g s o l u t i o n temperatures
f o r several hours t o promote acceptable
r e a c t i o n k i n e t i c s , and w i l l reduce t h e i r o n
c o n c e n t r a t i o n i n aqueous s o l u t i o n t o o n l y
Also, i f chromic
0.2+50 0.4 g / l i t e r .
( C r ) c a t i o n s are present, they w i l l cop r e c i p i t a t e w i t h t h e i r o n and contaminate
In
t h e j a r o s i t e w i t h a valuable metal.
s p i t e o f these drawbacks, both o f these
i r o n removal processes c u r r e n t l y are
practiced industrially.
S t a r t i n g and
s o l u t i o n temperature o f 57°C.
ending s o l u t i o n c o n c e n t r a t i o n s o f metals
a r e r e p o r t e d i n Table 3.
I r o n powder i s
o b v i o u s l y very e f f e c t i v e i n r a p i d l y removi n g copper from s o l u t i o n .
The composition
o f t h e cemented copper i s r e p o r t e d i n Table
4. The l a r g e f r a c t i o n o f i r o n contained i n
t h i s m a t e r i a l i s i n d i c a t i v e o f having used
a l a r g e excess o f i r o n f o r t h i s p a r t i c u l a r
t e s t . Copper can s u c c e s s f u l l y be cemented
from s o l u t i o n u s i n g much l e s s i r o n which
would r e s u l t i n a product w i t h h i g h e r
copper values.
Another commercially p r a c t i c e d method
of recovering copper from aqueous s o l u t i o n
i s by s o l v e n t e x t r a c t i o n . T h i s technique
invvJves t h e s e l e c t i v e t r a n s f e r o f c u p r i c
(Cu ) ions from t h e aqueous l e a c h s o l u t i o n
This
i n t o an i m m i s c i b l e organic phase.
organic phase c o n t a i n s a reagent which i s
capable of forming s t a b l e organometallic
complexes w i t h copper.
A f t e r t h e organic
i s loaded w i t h copper by c o n t a c t w i t h t h e
s l i g h t l y a c i d i c feed s o l u t i o n , i t i s
contacted w i t h a h i g h l y a c i d i c aqueous
s o l u t i o n where t h e copper i s t r a n s f e r r e d
from t h e o r g a n i c i n t o t h e a c i d i c s t r i p
Copper i s recovered from t h e s t r i p
phase.
s o l u t i o n e i t h e r by copper s u l f a t e
c r y s t a l l i z a t i o n o r electrowinning.
This
method produces a r e a d i l y s a l a b l e copper
product, b u t i s i n h e r e n t l y more complex i n
o p e r a t i o n than cementation.
A s i g n i f i c a n t , r e c e n t development i n
i r o n removal technology i s t h e p r e c i p i t a t i o n
o f f e r r i c phosphate.
F e r r i c phosphate prec i p i t a t i o n p r e v a i l s over t h e inadequacies o f
t h e p r e s e n t l y employed i n d u s t r i a l techniques.
Rapid f o r m a t i o n o f f e r r i c phosphate
occurs i n a c i d i c aqueous media a t room temperature, r e q u i r i n g an hour o r l e s s t o reduce several grams per l i t e r o f i r o n t o l e s s
The p r e c i p i t a t e d s o l i d s
-than 0.1 g / l it e r .
a r e spherical, which i s t h e geometric shape
w i t h t h e lowest s p e c i f i c s u r f a c e area, and,
t h e r e f o r e , t h e tendency t o adsorb contamina t i n g i o n s from s o l u t i o n i s much reduced.
T h i s p a r t i c l e morphology a l s o promotes
e x c e l l e n t f i l t e r a b i l i t y and easy washing o f
t h e s o l i d s t o remove entrapped s o l u t i o n .
F e r r i c phosphate o f remarkable p u r i t y , i.e.,
b e t t e r than 99% FeP04'2H 0 can be p r e c i p i t a t e d from a s o l u t i o n c o 6 t a i n i n g several
grams p e r l i t e r each o f a x t r i e t J 2 0 f o$Qer
, Cr
i o g j c specjes inc]udinq,Ni
,-fn
Cd , SO4 , NO
, C 1 CrO+ , etc. A i t e r
t h e i r o n phosphdte has been i l t e r e d from
s o l u t i o n and washed, conversion t o f e r r i c
hydroxide i s r e a d i l y accomplished by s l u r r y i n g t h e f e r r i c phosphate i n t o a h i g h pH,
aqueous s o l u t i o n t h a t i s s l i g h t l y e l e v a t e d
i n temperature.
Conversion i s complete i n
one t o one-and-one-half
hours. T h i s process
recovers t h e v a l u a b l e phosphate reagent i n a
form usable f o r pH c o n t r o l and phosphate
a d d i t i o n i n t h e l e a c h l i q u o r treatment c i r cuit.
F e r r i c hydroxide produced i n t h i s
manner f i1t e r s reasonably we1 1, much b e t t e r
Extensive d a t a has a l s o been c o l l e c t e d
on removing copper from mixed-metal
e l e c t r o p l a t i n g hydroxide sludge l e a c h
A Bell
s o l u t i o n s by s o l v e n t extraction.(3)
Engineering l a b o r a t o r y s i z e continuous s o l vent e x t r a c t i o n system was s e t up w i t h
A
t h r e e e x t r a c t i o n and two s t r i p c e l l s .
s o l u t i o n w i t h 15 volume p e r c e n t LIX-622
d i s s o l v e d i n Kermac 470-B kerosene was used
IS t h e o r g a n i c e x t r a c t i o n agent i n t h i s
t e s t work.
S t r i p l i q u o r was a s o l u t i o n o f
200 g j l i t e r s u l f u r i c a c i d and 30 t o 40
g / l i t e r copper.
T h i s system was operated
through eleven, 40 l i t e r batches o f mixedmetal leach s o l u t i o n s .
Results o f extract i o n e f f i c i e n c i e s from t h i s s e r i e s o f t e s t s
a r e presented i n Table 5 and i n d i c a t e v e r y
good e x t r a c t i o n o f copper.
Iron Precipitation
An extremely i m p o r t a n t aspect o f t h i s
treatment scheme as a whole i s t h e ease o f
i r o n removal v i a p r e c i p i t a t i o n w i t h
I r o n i s a common c o n s t i t u e n t o f
phosphate.
many h y d r o m e t a l l u r g i c a l process streams,
340
t h e r e s u l t i n g recovery o f phosphate i n t h e
The chromic hyvery a l k a l i n e solution.
d r o x i d e can be c a l c i n e d t o produce h i g h
value chromic o x i d e ($5.50/lb.).(7)
than does f e r r i c hydroxide which i s
p r e c i p i t a t e d d i r e c t l y from s o l u t i o n .
Extensive data have been c o l l e c t e d on
t h e p r e c i p i t a t i o n o f f e r r i c phosphate from
a wide v a r i e t y o f process s o l u t i o n s and
under a wide range o f conditions.
Details
o f these experiments are presented i n o t h e r
publications.(2,4)
A summary o f t h e solub i l i t y o f f e r r i c phosphate as a f u n c t i o n of
pH i s presented i n F i g u r e 1 ( t h e s o l i d l i n e s
represent the s o l u b i l i t y o f s o l i d f e r r i c
phosphate and f e r r i c hydroxide).
It i s
imperative t o note t h a t t h i s s o l u b i l i t y
f u n c t i o n f o r f e r r i c phosphate i s b u t l i t t l e
a f f e c t e d by a wide v a r i a t i o n i n s o l u t i o n
compositions o r temperatures.
F e r r i c phosphate p r e c i p i t a t e s e q u a l l y w e l l from s u l f a t e ,
c h l o r i d e , o r n i t r a t e systems, and t h e solub i l i t y i s n o t s i g n i f i c a n t l y a f f e c t e d by
s o l u t i o n temperature. (5)
Work t h u s f a r performed on c o n v e r t i n g
f e r r i c phosphate t o f e r r i c hydroxide sugg e s t s t h a t h i g h pH and moderate s o l u t i o n
temperatures a r e r e q u i r e d t o achieve c o w
A summary o f p r e l i m i n a r y
p l e t e conversion.
data i s presented i n F i g u r e 2.(6)
Chromium Treatment
T r i v a l e n t chromium i s removed from
s o l u t i o n by phosphate p r e c i p i t a t i o n i n a
manner v e r y s i m i l a r t o i r o n removal. Unl i k e t h e s o l u b i l i t y o f f e r r i c phosphate,
however, t h e s o l u b i l i t y o f chromium phosphate e x h i b i t s a s t r o n g dependence on solut i o n temperature, w i t h i n c r e a s i n g temperat u r e s promoting reduced s o l u b i l i t i e s .
This
p r o p e r t y i f 3 e x p l o i t e q 3 t o achieve a separaA t ambient tempert i o n o f Fe
from C-r
atures, i.e., 20°C. f e r r i c phosphate w i 11
p r e c i p i t a t e c l e a n l y i n t h e presence o f
chromic c a t i o n s through t h e pH range 1.5 t o
2.1.
A f t e r f e r r i c phosphate i s f i l t e r e d
from s o l u t i o n , chromic phosphate can be
made t o p r e c i p i t a t e through approximately
t h e same pH range by h e a t i n g t h e s o l u t i o n
t o 50 t o 60°C. The i n d i v i d u a l chromium
phosphate p a r t i c l e s a r e s p h e r i c a l i n shape
which r e s u l t s i n e x c e l l e n t f i l t e r a b i l i t y
and minimum s u r f a c e a d s o r p t i o n o f o t h e r
i o n i c species.
.
Some hydroxide sludge m a t e r i a l s
c o n t a i n chromium i n t h e hexavalent state:
sludge produced b y electrochemical machini n g i s one such example.
I n t h i s case, i t
i s economically advantageous t o recover
chromium i n i t s o x i d i z e d chromate state.
This i s e a s i l y accomplished by p r e c i p i t a t i o n o f l e a d chromate from m i l d l y a c i d i c
Lead chromate
s o l u t i o n s , i.e.,
pH > 4.0.
f i l t e r s w e l l and can be leached w i t h s u l f u r i c a c i d t o produce l e a d s u l f a t e and
chromic acid. The l e a d s u l f a t e so produced
can be r e t u r n e d t o t h e l e a c h l i q u o r t r e a t ment c i r c u i t f o r recovery o f a d d i t i o n a l
chromate. Chromic a c i d produced by t h i s
methodology can be r e t u r n e d t o a p l a t i n g
bath.
S u f f i c i e n t data has thus f a r been
generated t o c h a r a c t e r i z e chromium phosphate
precipitation.(4)
S o l u b i l i t y data f o r
chromium phosphate p r e c i p i t a t i o n i s summari z e d i n t h e s t a b i l i t y diagram presented i n
F i g u r e 3.
S o l u b i l i t y data as a f u n c t i o n o f
s o l u t i o n temperature i s presented i n F i g u r e
4 and c l e a r l y shows t h e i n v e r s e r e l a t i o n
It i s
between s o l u b i l i t y and temperature.
e v i d e n t t h a t several grams p e r l i t e r chromium can be maintained i n s o l u t i o n t o pH
l e v e l s g r e a t e r than four, w i t h low s o l u t i o n
'temperature.
P r e c i p i t a t i o n o f l e a d chromate has been t e s t e d f o r removing chromate
Because o f t h e g r e a t
i o n s from s o l u t i o n .
s o l u b i l i t y o f chromate as a f u n c t i o n o f pH,
t h i s i s u s u a l l y t h e l a s t i o n t o be removed
i n t h e leach s o l u t i o n t r e a t m e n t scheme. A
leach s o l u t i o n produced from electrochemic a l machining sludge was t r e a t e d for+Eetal
value recovery, w i t h 1.59 g / l i t e r C r
remaining i n s o l u t i o n a f t e r f e r r i c
phosphate and n i c k e l hydroxide p r e c i p i t a tion.
Chromate c o n c e n t r a t i o n was reduced
t o 0.3 p a r t s per m i l l i o n by adding a s l i g h t
s t o i c h i o m e t r i c excess o f l e a d n i t r a t e and
p r e c i p i t a t i n g a t a s o l u t i o n pH o f 6.1.
Aluminum P r e c i p i t a t i o n
The s o l u b i l i t y o f t r i v a l e n t aluminum
i n aqueous s o l u t i o n i s e s s e n t i a l l y
i d e n t i c a l t o t h a t o f chromium.
Separation
o f i r o n from an aluminum-chromium b e a r i n g
s o l u t i o n can be accomplished by p r e c i p i t a t i o n o f f e r r i c phosphate a t low temperature.
Heating t h e s o l u t i o n , a f t e r s o l i d l i q u i d s e p a r a t i o n t o remove f e r r i c phosphate
A market f o r chromic phosphate e x i s t s
i n t h e pigment i n d u s t r y . T h i s market may
v e r y w e l l be e x p l o i t e d t o consume t h e chromic phosphate produced from hydroxide
sludge m a t e r i a l s .
An a t t r a c t i v e a l t e r n a t i v e t o t h e s a l e o f chromic phosphate i s
t h e conversion t o chromic hydroxide w i t h
341
s o l i d s , r e s u l t s i n c o p r e c i p i t a t i o n o f aluminum and chromic phosphates. These two
metals can be separated by leaching t h e
mixed-metal phosphate, o x i d i z a t i o n o f chromic c a t i o n s t o chromate anions, and reprec i p i t a t i o n o f aluminum phosphate: t h i s t i m e
w i t h o u t contamination by chromium.
The
chromate bearing f i l t r a t e which r e s u l t s
from f i l t r a t i o n t o remove aluminum phosphate can be t r e a t e d by lead chromate prec i p i t a t i o n f o l l o w e d by chromic a c i d and
lead s u l f a t e production.
Separations by Valence
t h e normal realm o f waste water treatment
methods.
A l l p r e c i p i t a t i o n s used i n t h e
f o r e g o i n g metal recovery scheme r e q u i r e proper reagent a d d i t i o n , pH c o n t r o l , and c o n t r o l
o f s o l u t i o n temperature.
Indeed, these a r e
c r i t e r i a v e r y common i n waste water
treatment.
The p r e c i p i t a t i o n techniques described
h e r e i n a r e n o t equipment i n t e n s i v e . A s e r i e s
o f s t i r r e d vessels w i t h a p p r o p r i a t e h e a t i n g
c a p a b i l i t i e s , pH sensors and reagent a d d i t i o n
equipment, coupled w i t h a f i l t r a t i o n system,
i s e s s e n t i a l l y a l l t h a t i s r e q u i r e d t s implement t h i s technology on an i n d u s t r i a l scale.
These types o f equipment a r e p r e v a l e n t i n t h e
It i s certainly
water treatment i n d u s t r y .
f e a s i b l e t h a t some sludge generators can
s u c c e s s f u l l y implement a t l e a s t some o f these
p r e c i p i t a t i o n techniques w i t h v e r y l i t t l e
o p e r a t i o n a l o r equipment change and minimal
equipment a c q u i s i t i o n . The r e t u r n on i n vestment can begin immediately, because t h e
volume o f sludge r e q u i r i n g hazardous waste
greatly
h a n d l i n g and d i s p o s a l can be v e r y
reduced, reagents can be regenerated f o r use
i n t h e process l i n e r e s u l t i n g i n reduced
expenditure f o r raw m a t e r i a l s , o r marketable
metal s a l t s can be produced.
This, o f
course, i s a l l i n a d d i t i o n t o t h e
c o n s e r v a t i o n o f nonrenewable resources.
The preceeding d i s c u s s i o n has f9cuseQ3
on s e p t 3 a t i n g t r i v a l e n t c a t i o n s (Fe , C r
and A1 ) from each @her qpd from v a r i o u s
d i v a l e n t c a t i o n s (Zn , N i ). C e r t a i n
instances a r i s e where t h e i s o l a t i o n o f each
individual t r i v a l e n t cation i s not desirable.
Instead, o n l y removal o f contaminati n g t r i v a l e n t c a t i o n s from a predominately
d i v a l e n t specie bearing s o l u % i o n i s d e s i r able.
I n t h i s case, i r o n , chromium, and
aluminum can be made t o c o p r e c i p i t a t e as
phosphates by e l e v a t i n g t h e s o l u t i o n temp e r a t u r e t o 50 t o 60°C.
T h i s accomplishes
p u r i f i c a t i o n o f t h e aqueous s o l u t i o n i n a
s i n g l e p r e c i p i t a t i o n and s o l i d - l i q u i d sepI f present i n o n l y
a r a t i o n operation.
small q u a n t i t i e s , t h e t r i v a l e n t , mixedAn EPA sponosored research program t o
metal phosphate m a t e r i a l can be converted
t e s t these p r e c i p i t a t i o n schemes on a p i l o t t o hydroxide t o recover t h e phosphate w i t h
p l a n t s c a l e i s c u r r e n t l y underway a t t h e
subsequent d i s p o s a l o f t h e hydroxides.
The
o u r i f i e d s o l u t i o n can be r e t u r n e d t o t h e
.- Montana Colleqe o f M i n e r a l Science and
Technology.
A-wide v a r i e t y o f sludge maAn example o f t h i s a p p l i plating circuit.
t e r i a l s have been c o l l e c t e d f o r treatment
c a t i o n i s t h e recovery o f pure z i n c phosA f t e r analyses o f
i n t h e t e s t system.
phate from t h e i r o n - z i n c phosphate sludge
chemical composition and m o i s t u r e content,
t h a t t y p i c a l l y forms i n phosphatizing
each sludge i s processed through t h e system
tanks.
i n a series o f r e p e t i t i v e tests.
Data on
elemental d i s t r i b u t i o n s a r e c o l l e c t e d and
A mixed-metal leach s o l u t i o n was proc a r e f u l mass balances a r e maintained.
+3
duced from electroplating+fludgT3and
Process v a r i a b l e s a r e o p t i m i z e d t o y i e l d a
t r e a t e d t o t 2 e c i p i t a t e Fe , C r , and A1
v e r y low c o n c e n t r a t i o n o f a p a r t i c u l a r metal
from t h e Zn
r i c h solution.
Data f o r t h i s
i n s o l u t i o n and s t i l l m a i n t a i n h i g h p u r i t y o f
t e s t i s presented i n Table 6 and i l l u s t h e recovered metal product.
Successful
t r a t e s e x c e l l e n t separation o f t h e
completion o f t h i s t e s t p r o j e c t should r e s u l t
t r i v a l e n t c a t i o n s from t h e d i v a l e n t zinc.
i n an industry-ready method f o r r e c o v e r i n g
metal values from metal b e a r i n g hydroxide
SUMMARY
sludge m a t e r i a l s .
A general overview f o r each o f t h e
u n i t o p e r a t i o n s employed t o recover metal
1. Biswas, A. K., Davenport, W. G.
values from e l e c t r o p l a t i n g hydroxide sludge
E x t r a c t i v e M e t a l l u r g y of Copper,
m a t e r i a l s has been given.
These o p e r a t i o n s
Pergamon Press, Oxford, 1976, p. 272.
a r e e i t h e r a p p l i c a t i o n s o f w e l l developed
commercial technology o r a r e simple
2. Dahnke, 0. R., Removal o f I r o n from
selective precipitations.
Overall the
A c i d i c Aqueous Solutions.
M. S.
technology u t i l i z e d , except maybe f o r
Thesis, Montana College o f M i n e r a l
s o l v e n t e x t r a c t i o n , does n o t extend beyond
342
Science and Technology, May 1985, p.
137.
3.
Metal Value Recovery
Twidwell, L. G.
from Metal Hdroxide Sludges, Report f o r
EPA P r o j e c t s R-80930501 and R-80173601,
Montana College o f Mtneral Science and
Techology, November 1984, p. 290.
4.
Dahnke, D. R., Twidwell, L. G.,
Robins,
S e l e c t i v e I r o n Removal from
Process S o l u t i o n s by Phosphate
P r e c t p i t a t o n , C I M 1 6 t h Annual
Hydrometa 11u r g i c a l Fleet ing, Toronto,
Canada, October 1986.
R. G.
5.
Arthur, B.
Recovery o f Metal Values
from I r o n , Chromium, N i c k e l Solutions,
M.S. Thesis, Montana College o f M i n e r a l
Science and Technology, August 1986.
6.
Nordwick, S.
Conversion o f Phosphate
S o l i d s I n t o Hydroxides, M.S. Thesis,
Montana College o f M i n e r a l Science and
Technology, August 1986.
7.
Chemical Market Reporter, January 6,
1986, Schnell P u b l i s h i n g Company, Inc.,
New York, NY.
343
TABLE 1.
ANALYSIS OF SLUDGE
-Z Compos it ion
Compound
NaOH
8.43
A1 ( O W 3
4.63
S i (OH14
2.69
5.04
p04
8.24
s04
c1
0.36
Ca(OHI2
20.49
W O H1
16.07
Fe( OH l3
5.13
Zn(OH
18.00
TABLE 2.
ANALYSIS OF LEACH SOLUTION
Compound
Concentration g/1 i t e r 1
Fe
0.660
cu
0.024
Zn
5.304
Cr
2.959
A1
1.187
Ca
0.692
P
0.883
344
TABLE 3.
SOLUTION ANALYSES FOR CEMENTATION OF COPPER
Concentrations ( g / l i t e r )
Fe
cu
Zn
Cr
Ni
A1
Ca
Na
Cd
0.847
3.596
3.365
5.606
6.848
0.038
0.232
0.576
3.604
11.141
0.032
3.257
5.397
6.943
0.037
0.236
0.652
3.518
Starting
Final
TABLE 4.
CEMENT COPPER COMPOSITION
Z Composition
Fe
cu
Zn
Cr
75.1
22.4
0.70
1.31
345
Cd
0.54
TABLE 5.
SUMMARY OF CONTINUOUS COPPER EXTRACTION: ELEVEN DAY LONG TERM O R G A N I C
EXPOSURE TEST RESULTS.
~~
Sample No.
Condition
Copper E x t r a c t i o n From Leach S o l u t i o n
Copper Concentration ( g p l )
I n i t i a1
3458
3474
Starting Solution
F i r s t Day R a f f i n a t e
2.750
3482
3493
Starting Solution
Second Day R a f f .
3.130
3501 -B
3509
Starting Solution
T h i r d Day R a f f .
2.697
3519
3533
Starting Solution
F o u r t h Day Raff.
3.332
3542
3548
S t a r t i n g S o l u t on
F i f t h Day R a f f
2.600
3552
3567
S t a r t i n g S o l u t on
S i x t h Day Raff
0.835
3606
3613
Starting Solution
Seventh Day Raff.
1.035
3619
3631
Starting Solution
E i g h t Day Raff.
2.045
3639
3643
S t a r t i n g Sol u t on
N i n t h Day R a f f
1.812
3657
3664
S t a r t i n g S o l u t on
Tenth Day R a f f .
3670
3703
S t a r t i n g Sol u t i on
Eleventh Day Raff.
Copper E x t r a c t e d
Final
0.054
98.0
0.062
98. o
0.106
96.1
0.088
97.4
0.039
98.5
0.056
93.3
0.033
96.9
0.027
98.7
0.073
97.0
2.026
0.043
96.0
2.225
0.049
97.8
--
346
(%I
TABLE 6.
SOLUTION ANALYSIS FOR PRECIPITATION OF Fe+3, Cr+3,
AND A l + 3 PHOSPHATE
Concentrations g/1 it e r
Fe
Cr
A1
Zn
P
Starting Solution
pH = 2.07
0.118
0.694
0.182
3.735
1.151
Ending S o l u t i o n
pH = 2.48
0.048
0.073
0.016
3.760
0.684
347
0
0
1
I\ '
2
3
4
5
6
7
8
9 1 0
11
I
I
I
1
I
I
I
I
1
2
3
a
0.
4
W
LI
Q
5
6
7
8
1
A
348
100
rH
=
12.
so c
:
a0
*=
11,
50oc
pH
bp
*FwPO~.~H~O
SLURRIED
(S)
IN PH
c
CONTROLLP) SYSTEM
*P
.to WT.
v)
L
0
V
tsoc
COM3ITIONS
60
0
al
>
c
= I t .
'IL SOL1115
40
20
0
0
60
120
180
Time, M i n .
349
240
300
PH
0
1
2
3
4
5
I
I
I
I
I
I '
I
I
I
I
I
I
6
7
8
9 1 0 1 1
I
I
I
I
I
I
I
I
n
a
L
u
a
FlGUR€ 3 .
O R a M I U M PHCIBRIATE STABILITY DIAGRAM
OlROMILM-PHO.CHATE.-WATliRSYSTEM.
3 50
FOR
THE
4
3
fn
t 2
U
1
0
S o l u t i o n pH
.FIGURE 4 .
INFLLlENCE OF TEWRATLIRE ON CHI?CMILIM
FROM A MIXED =TAL
PHOSPHATE PRECIPITATION
SOLVTION.
351
I
I
EPA/600/9-86/022
August 1986
LAND DISPOSAL, REMEDIAL ACTION, I N C I N E R A T I O N
AND TREATMENT OF HAZARDOUS WASTE
Proceedings o f t h e T w e l f t h Annual Research Symposium
a t C i n c i n n a t i , Ohio, A p r i l 21-23, 1986
Sponsored by t h e U.S. EPA, O f f i c e o f Research & Development
Hazardous Waste Engineering Research Laboratory
C i n c i n n a t i , OH 45268
Edison, NJ 08837
Coordinated by:
JACA Corp.
F o r t Washington, PA 19034
.-
Contract No. 68-03-3252
Project Officers :
Harry M. Freeman
N a m i P. Barkley
C i n c i n n a t i , OH 45268
HAZARDOUS WASTE ENGINEERING RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OH 45268