Note: Descriptions are shown in the official language in which they were submitted.
~AC~GROU~'D OF T~E I~ ;TION
__ _ _
The present invention relates to a liquid-liquid
extraction ~rocess and, more particularly, to an improved '
method of preventing losses of valuable ions used in
liquid organic extraction processes.
~lany processes for utilizing liquid extraction techni-
ques in treating process solutions to separate one metal
value from another metal value exist. Although such liqùid-
liquid extraction processes are highly effective in separa-
ting one metal value fro~ another metal value, the loss of
expensive reagents to tne raffinate and/or to the stripping
solution has made the liquid-liquid extraction techni~ues
less attractive economically. Reagent costs associated
~ with the recovery of metal values from both the loaded
- 15 extractant and the rafrinate have also made these processes
less attractive on a co~mercial basis. Losses of v~lua~le
or~anic extractant components and the non-regenerative uses
o~her reagents have made liquid extraction processes
less com2etitive wlth al,ernative methods for separating
~n and/or recovering metal values from aqueous process solu-
~iOI~ S .
.
t2)
.. . .
~RIEF SUMMARY OF THE INVENTION
- The present invention relates generally to a process
for minimizing losses of thiocyanate ions used in solven~
extraction processes to aqueous process solutions. Mineral
acid is added to the aqucous process solution to aepress
substantially completely ionization of the thiocyanate and
to form hydrogen thiocyanate and the aqueous process solu-
tion is contacted with a liquid organic solvent to extract
the hydrogen thiocyanate.
In one embodiment, an acidic process solution contain-
ing two metal values, one of which is complexible by thio-
cyanate ions, is contacted with a liquid organic extractant
of hydrogen thiocyanate dissolved in a water-immiscible
organic solvent to load the extractant with the complexible
metal and to produce a raffinate containing the other metal,
the loaded extractant is contacted with a sufficiently con-
centrated mineral aci~ to strip the complexible metal there-
from without dissolving significant amounts of hydrogen
thiocyanate in the mineral acid solution. The complexible
metal value is recovered by crystallization which also
regenerates a concentrated mineral acid solution for further
stripping. The acidity of the raffinate is increased to
depress the ionization of any hydrogen thiocyanate dissolved
therein, and the raffinate is contacted with the stripped
extractant to scavenge the hydrogen thiocyanate. The other
metal value is recovered by crystallization which regenerates
a concentrated acid solution which is recycled to increase
the acidity of further amounts of the raf~inate.
(3)
,;, , ~
More particularly, the invention resides in a process
for extracting cobalt from an aqueous process solution contain-
ing nickel which comprises extracting cobalt from the aqueous
solution by contacting the aqueous solution with an organic
extractant of a water-immiscible organic solvent of at least
one member selected from the group consisting of ketones,
esters and alcohols having hydrogen thiocyanate dissolved
therein to produce a nickel-containing raffinate and an
organic extractant loaded with cobalt, and contacting the
loaded extractant with an aqueous solution of a mineral acid
having a concentration of at least about 16 N whereby cobalt
is recovered as a salt of the mineral acid and the organic
extractant is regenerated with minimal thiocyanate losses.
DESCRIPTION OF THE DRAWING
.
Figure 1 is a flowsheet of a process incorporating
the process in accordance with the present invention; and
- 3a -
~L ~ P r . `J S~ ~J ;-3
~`igur~ ~ is ~ flowsheet of an alternative embodiment
of the pr~sent in~rention.
DET~IL~D ~F~CRIPTION
Th~ process in accordance with the present invention
5 can be employed in any process employing solvent extracti~,n
in which thiocyanate complexes are formed to provide the
reauisite solubility t~ifferentials. However, the present
invention will be described in conjunction with the separa-
tion of cobalt from nickel-containing aciQic pr~cess solu-
1~ tions by use of liquid organic extractants containing hydrogen
thioc~anate. Other examples of metal separation that can be
effected by practice of the present invent~on include
beryllium from aluminum and hafnium from zirconium.
Nickel process solutions having acid strengths up to
a~o~t S normal (N) can be treated by the process in ac~or-
dance with the present invention to separate cobalt from
the nickel process solution. A typical nonlimiting example
of an a~ueous nickel process solution is a leach so~ution
having a pH value of about 3.5 and containin~ 40 grams per
liter tt~pl) nic~el and between 2 and 20 gpl co~alt.
Cokalt is extracted from the nickel process solutio~
~,y contacting the process solution with an organic extractan~
of hydrogen thiocyanate dissolved in a water-immiscible
v~anic solvent. This extraction can be conducted in any
appararus that provides good liquid-liquid contact. For
e~anple, the process can be conducted in packed columns,
p~rforatod plate columns, or a series of mixer-settlersr
~ate~-im~isci~le organic sol~-ents that can be employed
i~lclu~e Xetones~ esters and alcohols. Methyl iso~utyl
3~t keto~e is ad~antageously used as it is hi~hly ef icient in
(4)
in extrac'illg co~al~ thiocyanate complexes from nickel-
containin~ aqueous solutions. Another ad~antageous water-
immiscible organic solvent is ethyl acetate.
Although it is advantageol~s to employ an organic
S extractant of hydrogen thiocyanate dissolved in a water-
im~iscihle organic solvent, cobalt can also be extracted
from nickel containing process solutions by adding water-
soluble ~hiocyanate compounds, such as calcium thiocyanate,
sodium thiocyanate, and potassium thiocyanate to the nickel-
1~ ccn~aining process solutions to form cobalt thiocyanate
complexes in the aqueous phase and then contacting ~he aqueous
phase with a water-immiscible organic solvent to extract the
cobalt thiocyanate complexes from the aqueous phase in~o
~he organic solvent. This latter embodiment is effective
1~ b~t large amounts of thiocyanate compounds must be adde~ to
the aqueous phase to c~mplex the cobalt values. When hydrogen
thiocyanate ~s dissol~ed in the organic solvent comp~ratively
small quantities of thiocyanate ions are reauired.
As noted above, it is advantageous to incorporate hydro-
gen thiocyanate in the orsanic solvent before contacting the
nickel process solution with the organic extractant. Hyd~o-
gen thiocyanate is incorporate~ in the organic solvent in
amounts between about O gpl and about 70Q gpl, advantageously,
in amounts between about 100 gpl and about 450 gpl. Organic
extractants containing hydrogen thiocyan~te within the fore~oing
ranges are highly e~fective in ~xtracting cobalt from nick~l-
containing process solutions while minimizing thiocyanate
losses to the raffinate.
'~he extraction process ~rodllces a subs~antially cobal.-
3~ free ra~finate ard a cobalt-loaded organic extr~ctant.
( ~ )
T~e raffinat2 is treated for nickel recovery, and the cobalt-
load~d or~anic ~x~ractant is stripped of its cobalt values
t~ regenera~ the organic extractant. AdvantageQusly, a
mine~al ~cid is added to the raffinate to increase the
5 C concentration of this solution to~value of at least abou~ 5 N
al~d then the raffinate is contacted with the organic extractant
regenerated in the stripping operation to recover any thio-
cyanate ions dissolved in the raffinate.
Alternatively, the ra~finate can be trea-ted with a second
organic Pxtr~ctant comprising an amine or a quaternary ammonium
cor.pound dissolved in a water-immiscible organic solvent to
recover any dissolved thiocyanate values, as aescribed more
ul y hereinzfter. -
The loaded organic extractant is advantageously scrubbed
with a weak acid solution, i.e., an aqueous mineral acid 501u-
tion having a normality of less than ~bout 5~ Contact of the
loade2 organic extractant with weak mineral acid solutions
scrubs any nickel contained in the organic extrac-ant thereby
insuring that the cobalt product obtai.led from the organic
2U extrac~ant is substantially nickel ~ree. Aci~ scrubbing of
the loade~ organic extraction is ef~cctive in removing suffi-
cie~t amounts of nickel so that the final cobalt product has
a cobalt to nickel ratio of at least about 2000:1. The
scrubb-ng solution can be recycled to the nic~el process
~5 solution to return the nickel values to the nicXel circuit.
The scrubbed, loaded extractant is contacted with an
aqueous mineral acid solution having a normality greater than
about 16. ~dvanta~eously, the loaded extractant is contacted
~7ith sul,uric acid solutions at concentration between about
N and about 21 N. Upon contact wi~h concentrated sul~uric
acid7 cob~lt is back e~tracted into the sulfuric acid
sol~Lion and ~ile organic extractan-t is rec,en~rated for reuse
~)
~ ~ i
in ~he extrclctiorl stage Stripping with concentrated
aq~e~us solutions of mineral acids is an advantageous feature
of the present invention. Stripping with concentrated mineral
aciA solutions minimizes losses of thiocyanate to the stripping
solution.
Co~alt contained in the stripping solution is advanta-
geou,ly recovered by crystallization. For exam~le, cobalt
can be crystallized from the stripping solution by increasing
the acid concentration thereof to diminish cobalt solubility
1~ or by the combination of increasing the acid concentration
whil_ lowering th~ temperature of the solution to again lower
cobalt ~olubility. Crystallization can also be accomplished by
heatin~ the stripping solution to vaporize water which increases
the acid concentrations to the point that cobalt is precipi~ated.
Cr~stallization by hea.ing has the advantage of also vaporizing
any organic solvent which can be recovered and recycled to the
proces3. Crystallization of cobalt from the stripping solu-
tion regenerates a concentrated mineral acid solution which can
be recycled to the stripping operation. Thus, the only mineral
acid ~hat has to be added to the system is an amount equivalent
to that xemove~ by crystallization.
As noted hereinbefore, the raffinate is treated for
nic~el recov~ry. Advantageously, sufficient mineral acid is
added to the raffinate to increase its acid concentration
^'S to at leæst about ~.5 N, and advantageously between about
4.5 ~T and 14 N. The raffinate with its aci~ content so
adjusted is contarted with the regenerated orqanic extractant
Irom, the stripping operation whereby any thiocyanate contain-
ed in the -affinate is reccvered in the regenerated or~anic
3~ extractant. The treatment of the raffinate with mineral acid
~nd subs~quen~ coniact with the resenerated organic extractant
along with the stripping with _oncent~ated ~ineral acids
minimizes 1GSS of the metal complexing constituents.
The raffinate after ~.eing treated for thiocyanate
reco~ery is trea.ed for metal value recovery. ~ickel is
also advantageously recovered by crystallization. Crystalli-
~ation of nickel from the raffinate ~roduces concentrated
S mineral acid which can be recycled to condition the raffina~e
~ro~l the extraction stage for scavenging any dissolved thio-
cyanate ~alues.
Thiocyanate values dissolved in th~ raffinate can alter-
nat vely be recovered by contacting the rafinate with an
lC organic extractant of an amine or a quaternary ammonium com-
pound dissolved in a water-irnmiscible organic solvent. The
~mine should be water-insoluble and can be a prin~ary, secondary
or terLiary amine. The quaternary a~nonium cornpound should ;
also be water insoluble. Although primary and secondary amine3
extract thiocyanate from the raffinate reasonably well, ter- j
tiary amines are more effective in scavenging metal complexing
constituents contained in the raffinate solutions.
More specifically, among the s-litable amines are includea
x-he~tylamines, x-dodecylamines, didodecylamine, ~ri-x-pro-
~0 pylamine, trî-x-butylamines, tri(2-ethlyhexyl)amine, ~ri-
isooc~ylamine, tertiary amines which are derivatives of styrene
oa~ide such ~s di(2-hydroxy-Z-phenylethyl3 ethylamine and ter-
tiary amines which are polyglycolamines, such as tripropylene-
glycolamine. The use OL X hereinabove as in the term "x-
2~ he~tylamines'i is intended to refer to any structural isorners,
as l-n-heptvlarnine, 2-n-heptylamine, etc.
Examples of quaterI-ary ammonium compounds that are use-
rul in scaven-~ing thiocyar;ate from the raffinate includ~
c~.ialk~l di methyl ammonium chloride in which the two al~
3i~ gr~ups eac~ ha~re a ca~bon chaill lenq~h va-iriny from e;ght to
eiyhto--n and a~eraqing about tt~elve and monomethyl trial~yl
quatern~ry ammonium chloride in t`'hich each al~yl chaitl e?~ch
;. . ` ' 1
contains bfef~ween eight and ten carbon atoms. The ff~mines or f
quaternary a~lonium compounds are f-issolved in a water-im~is~
cible organic solvent. Examples o_ such solvents include - 3
~ r foJ6~f~e
me~hyl isobutyl ketone, benzene, ko'uenc, xylene, water-
S immiscible alcohols, mixtures of sucn alcohols with ketones
` or xylene and esthers. The amines or qua.ernary ammonium
~ - . - i
compounds are present in the organic solve~t in amounts suffi-
cient to insure scavenging of the m-tal complexing constituent
from ~he raffinate. In most instances, efficient scavenging
~10 is realized if the organic extractfffnt contains a~fout 20%, by
weight, of the amine or the quaternary ammonium compound.
; The organic extractant loaded -ff~ith thiocyanate i8 then
! treated ~or the recovery thereof. The loaded extractant is -
ad~antageously treated with a base, such as soda ash or ammonium
~15 hydroxide,-to produce an aqueous thiocyana.e solution. The ~
aqueous thiocyanate solution is reoycled to the stripping~cir
cui~ where the aqueous thiocyanate solution and the loaded
extrac~ant are contacted whereby thiocyanate in the aqueous
phase is transfer~ed to the organic ~hase.~ Advantageously, ~;
~0 the aqueous thiocyanate solution is recycled to the scrub stag2,
Y ~ when such a scrubfbfing operation is e.. ployed, and thiocyanate in
- the aqueous phase is transferred to ~he organic phaseff. ~ -
Referring now to Figure 1 there is disclosed one embo~iment
of the present invention. Cobalt confained in nickel process
f~S solution 1 is extracted by contacting process solution 1 with an
f~ ~ organic extractant which contains b~'ween~about 100 gpl and
about 450 gpl hydrogen thiocyanate cissolved in methyl isobutyl
f ketone in co~alt extraction stage 2. The produffcts from this
~ f xtraction operation include nic~el-containir.g raffinate 15
and cobalt-loaded extractant 5. The cobalf~-loaded extractant 5
.
(9)
... . . . . ~ . . ....
is scrub~ed o. its nickel content by an a~ueous solution or
5 N sulf~ric acic7, stream 7. The aqueous scrubbed sol.ution
3 CGntainii~g nic~el is recycled to cobalt extraction stage 2
or is al,ernatively combined wi.th the feed solution 1. The
S scrubbed cobalt-loadecl organic extractant 8 is then stripped
of its cobalt content in stripping stage 9 by contact with
concentrated sulfuric acid. The su~furic acid solution con-.
taining cobalt is treated by crystallizing cobalt in c~balt
crystallization stage 11 and the acid generated in stage 11
lC is returned ~o the cobalt strippi.ng stage 9. Stripping of
cobalt from the scrubbed cobalt loaded organic extrac~ant 8 ;~
regenerates the organic ex-~ractant 14. Nickel-containing
raffinate 15 i.~ conditicned by the addition of sulfuric acid
and is then contacted with regenerated organic extractant 14
in thiocyan~t~ scavenging stage 16 .to recover,any thiocyanate
~ontained in nickel-containing raffinate 15. The thus recon-
stitute~ organic extractant 4 is recycled cobalt extraction ,
stage 2. Nickel-containing raffinate lg from which thiocya-
nate has been removed is treated to ~rystallize nickel in
niclcel crystallization stage 20 and to regenerate 65% sulfuric
~cid- which is recycled to thiocyanate scavenging stage 16.
From the description of this embodiment it is apparent t~.at
both acid consumption and thiocyanate losses to the aqueous
p~ases are ~.inimized.
1~he use of a second organic extractant comprising an
~nine or quaternary ammonium compound is dissolved in a water- I
imm,iscible orsanic sol~ent is disclosed in Figure 2. ~ic'.~el- ` -
and cobalt-containing p~ocess solution 1 is ~ed to cobalt
extraction stage 2 ~7here the soll~tion is contacted with an
:iC orsanic extractant c,~omprisins h~drocJen thiocyanate dissolvPd
i.~ me~hyl i~obuty.~ ketone. The cobalt-loaded organic extract-
ant S is trans~err~d to the nickel scrubbing stage 6 where the
organic e~tractant is contacted with a 3 ~T sulfuric acid solu- ,
tion 7. The nickel-containing scrubbing solution ~rom stage 6 '.
is recycled cobalt extraction stage 2. The scrubbed cobalt-
loaded organic extractant is stripped of its cobalt content in
strip?ins stage 9 by the addition of 55~ suluric acid in stream
~ The resulting cobalt sulfate solution 10 is trea'ed ;.n
cobalt crystallization stage 11 to crystallize cobalt as cobalt
sulfate 12. Suluric acid resulting from stage 11 is combined
wi.h fresh 55~ suluric acid and recycled to cobalt stripping
s.a~e 9. Nickel-containing raf~inate 16 from co~alt extr~ction
st'-age 2 is treated with an organic extractant of a terti~ry
amine dissolved in kerosene to sca~enge any thiocyanate dissolved
in ra~.inate 16. Thiocyanate-loaded organic extractant 21 is
t~eated with a 1~% ammonium hydroxide solution to regenerate
the thiocyanate scavenging organic extractant 18 and to producQ
an ~queous thiocyanate solution 24 which is recycled to ~ nickel
scrubbing stage 6. After any thiocyanate is scavenged from the
raff~nate 15 nickel is reoovered from the sul~ate solution by
conventional tec~n.iques.
. For the purpose of giving those skilled in the art a better
understanding o the present invention the following illustrative
examples are given:
':~ EXAMEL
A nickel process solution containing 46.9 gpl nick~l and
4.01 g~l cobalt (i.e, a nickel to cokalt ratio of ahout 10:1)
was concurrently contacted with an organic e~tractant comprising
~e~hyl .iso~u-t~l ketone in which 150 grams per liter o thiocya-
nz~e were dissolved. The volumetric ratio of organic extrac~ant
.... . . ..
. .
t~ ~he aqueous ~hase was about 1.4:1. The cobalt content of
the nickel-containing solution was lowered to 0.003 gpl. The
cobalt-loaded orga~ic extractant containing 3.82 gpl cobalt
and 0.2 gpl nic~el was fed to a nickel scrubbing operation in
which the loaded extractant was contacted with 5 N sulfuric
a~id in a volumetric ratio of organic ~o aqueous of about 10
The nickel scrubbing operation produced a scrubbing solution
containing 1.38 gpl nickel and 15.2 grams per liter cobalt,
whlch was recycled to the cobalt extraction stage, and a scrubbed
orga~ic extractant which contained less than 0.003 gpl nickel
and 2.58 gpl cobal~.
T~e organic extractant scr-lbbed of its nickel content was
then treated with an aqueous solution of 55.5~ sulfuric acid at
a vclumetric ratio of organic to aqueous of about 6:1, The
1~ stripping operation produced a cobalt sulfate solution h~ving
co~a~t to nickel ratio greater than 2800:1 and containing
a~ou 0~5% gpl thiocyanate~ Cobalt was recovered from the
cobalt sulfate solution by crystallization which produce~ a
co~centrated sulfuric acid solution containing 3.4 gpl cohalt
~'~ an~ 0.~7 gpl nickel. The concentrated sulfuric acid solution
d~ri~ed from the cobalt crystallization stage was recycled to
the cobalt stripping operation.
The nickel-containing raffinate from the cobalt extraction
sra~e containing 36.5 gpl nickel and 0.009 gpl cobalt was treat-
~5 ed in a scavenging stage to reco~er thiocyanate dissolved there-
in. The nic~el-containing raffinate was conditioned for thio-
cyanate recovery by the addition of 65~ sulfuric acid at a
volu~2tric ratio of raffinate to aqueous sulfuric acid solution
o about 1.6:1. The acid conditioned raffinate ~a~ then contact~
~0 with the re~enerated organic extractant fro~ t~Le cob~lt s~ripping
tl2)
~, . . . . .. . . . . . . .. . . . . . .. .. .. . .. . .. ..... . . . ..
o~eration to recover any thiocyanal:e dissolved in the raffina.e
an~ the organic e~tractant containing the recovered thiocyanate
is recycled to the cobalt extraction stage.
The nickel-containing raffinate from which the thiocyanate
was recovered was then treated fo~ nickel recovery by crystalli-
zation. Crystallization of nickel sul~ate from the raffinate
~roduces a 65~ sulfuric acid solution, about 10~ of which was
bled off and the remainder recycled to condition the raffi~ate
for thiocyanate recovery. The nickel product of the crystalli-
lC zation process had a nickel to cobalt ratio of 7700~ . the
nickel to cobalt ratio in the product was improved 770 tim~s
over t~at in the ~eed material.
~he closed cycles of the cobalt stripping and cobalt crystal-
lization operation and the thiocyanate sca~enging and nic~el
crystallization cooperate to minimize thiocyanate losses as ~-ell
as acid consumption thereby rendering the overall process econo-
mically at:~ractive.
XAMPLE II
A nickel process solution containing 63.4 ~pl nickel and
1.62 spl cobalt (a nickel to cobalt`ratio of about 40~ Jas
fed to a co~al~ extraction stage where cobalt was extracted
witn an organic extractant of 150 gpl thiocyanate dissolved in
m2'hyl isoblltyl ketone in a volumetric ra~io of organic-to
aqueo~s of about 4:1. The nickel raffinate contained 48.2
gpl nickel, 0.003 gpl cobalt and about 45 gpl nickel, 0.003
gpl cobalt and 45 gpl thiocyanate which raffinate was conveyed
to the thiocyanate scavenging operation. The cobalt-load2d
extractani contained 0.02 gpl nickel and 0.309 gpl cobalt ~hich
was treate~ for cobalt recovery.
~ .
(13)
..... ..
The cobalt-loaded orqanic extractant was initially scrubbed
~i~h 3 N ~ulfuric ~cid at an organic to aqueous ~olumetric ra'io
of about 16~1. The aqueous scrub~ing solution containing l.64 t
gpl r.ickel and 0.76 gpl cobalt was recycled to the cobalt ex- '~
traction stage.
The scrubbed cobalt-loaded organic extractant was stripped
of its cobalt content by contact with an ~queous solution of 55%
sul~uric acid at a volumetric ratio of organic extractant to
aqueous phase of about 11:1. In the cobalt stripping-operation,
fresh thiocyanate was added to the aqueous phase which was then
transferr~d to the organic extractant in order to make up for
any thiocyanate ~osses in a circuit.
The cobalt-containing aqueous phase from the stripping ope~a~
tion was treated to crystallize cobalt a~ cobalt sulfate and to
generate a 55% fiulfuric acid solution. The regenerated acid
together with fresh make up sulfuric acid was recycled to the ~ -
cobalt stripping operation. -,
The nickel-containing raffinate was initially treated to
recover the thiocyanate ions dissolved therein. Thiocyanate
~0 dissolved in the raffinate was recovered by contacting the
raff~nate with an organic extractant of a tertiaxy amine dis-
solved in kerosene at an organic to aqueous volumetric ratio
of about 3:1. This thiocy~nate recovery operation lowered the
thiocyanate content of the raffinate solution to 0.05 gpl and
provided a nickel-containing solution having a nickel to cobalt
ratio o about 11,0~0:1 (i.e. the nickel to cobalt ratio in the
product solution was 790 t mes that of the feed solution).
The organic extractant containing the thiocyanate recovered
fro~. the rafrinat2 was treated with a 10~ ammonium hydroxide
solution at a volumetric ratio of organic to ammonium hydroxide
(14)
.... .. . . .. . . .. . ..... . . . .. . .... . . .... .. ....
soi~;~ion o a~out 24:1 to prGduce an aqueous thiocyanate solution
contai~inS 243 gpl. thiocyanate, 2.66 gpl nickel and 0.016 gpl
co~alt which aqueous thiocyanate solution was recycled to the
nic~el scrubbing stage whereby substantially all the thiocyanate
5 recovered ~rom the raffinate was returned to the process.
Again this example demonstrates tha' the use of concentrated
sulfuric acid to strip the cobalt from the cobalt-loaded organic
extract2nt together with the use of a second organic extractant
to recover thiocyanate in the raffinate minimizes losses of expen- ;
1~ sive thiocyanate to the system and the use of sulfuric acid.
Although the present invention has been described in con-
j~nction with advantageous embodiments, it is to be understood
that modifications and variations may be resorted to without
~.eparting from the principles and scope of the invention, a~
15 tho~e skilled in the art will readily understand Such modi~
cations and variations are considered to be within the purview
and SCOp2 of the invention and the appended claims.
(15)
