Note: Descriptions are shown in the official language in which they were submitted.
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3~1l5
This invention relates to the hydr~dynamic recycle
of seed material, e.g., metallic sulfide seed, under pres-
sure i~ the precipitation of precipitatio~-forming ions
from solutions thereof, for example, the precipitation of
5 nickel and cobalt ions as sulfides ~rom dilute solutions
~tai~ed ~n ~he hydrometa~llurgical recov~ry of n~ckel
and cobalt from lateritic ores.
Precipitation of nickel and cobalt as sulfides
from either ammoniacal or acidic leach solutions i~ ~ c~m-
1~ monly used commercial method. The Moa Bay pla~t in Cubais one of the few commercial operations where nickel and
cobalt are precipitated rom acidic leach solutions.
Briefly, the process consists of neutralizi~g the leach
llquor ~pressure leaching of lateritic ores wi~ sul~uric
15 acid~ with lime (coral mud) and decanting the ~eutralized
liquor which is the~ treated with hydrogen sulfide gas.
T~e ~ulide precipitation is carried out in a ser~es o~
hlgh pressure autoclaves at a temperature of about 120C.
and a total pressure of about 150 psig. A choke controls
20 the ~low of the slurry from a high pressure autoclave to
a flash tank. A large amount of H2S gas is dissolved i~
the solution at the high pressure prevalent i~ the auto-
c}aves and is released in the flash tank. This released
gas, which is several times the amount actually consumed
25 during precipitation, is washed, dried and compressed hy
a compressor to high pressure prior to its recycle to
the autoclaves. ~he slurry from the flash tank goes ts
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a solid~liquld separation step ~thickener~. About two-
third~ of the ~ickel sulflde leaving the reactor is
returned back to the process for recycl~ng and the
remai~ing one-third leaves as the product concentrates.
5 The amo~nt of solid recycle is proportio~ed to give about
20 gpl solids in the fee~ slurry.
The Moa Bay acid leaching proce~s is d}sclosed
in an article entitled "Acid Leaching Moa Bay-Nickel"
by E.T. Carlson and C.SO Si~ons (Journal of Metals,
10 March, 1~6~, pp 206-213~
Another sulfide precipitation method is dis-
closed in U.S. Patent NoO 2,722,480 (November 1, 1955~.
The method is particularly applicable in the treatment
of nlckel solutions resulting from the leaching o~
15 later~tic ore, such solutions generally contain~ng 3 to
13 grams per liter ~gpl) of n~ckel, 0O2 to 0.7 gpl Co,
Q.5 to 2.0 gpl Fe , 2 to 8 gpl Al, 1 to 5 gpl Mn, n . 5
to 2~0 gpl Mg, and about 15 to 30 gpl H2SO4. The method
comprîses adjust}ng the free acid content of the solution
to a p~ of about 1 to 3, adding to the adjusted solution
a~out Q~03 to about 10 gpl of finely divided metallic
po~der selected from the group consisting of Fe, Ni, and
Co and mixtures thereof, confining the solution at a
temperature of about 60C. to 90Cn under a positlve
25 over-pressure of hydrogen sulfide gas and contl~uing
the treatment with agitation until sulfide precipitat~n
su~stantially ceases According to the patent, sub-
sta~tially all of the nickel (eOgO, 98 to 99~ i9 pre-
clp~tated by this method in about 1 to 2 hour~e
3~ In U~SO Patent No 4,110,400, which issu~d on
August 29, 1978, a method is disclosed for efficiently
pxec~pitating nickel sulfide from an acidic nickel sulfate
solution having a p~ ~etween 1O5 and 4, containing about
1 to 4Q gpl nickel, optionally containing cobalt, and
35 containing sufficient inert soluble sulfate salt to
buffer the solution during the precipitation of nickel
sulfide at relatively low temperature and pressure. As
in the Moa Bay process, the precipitation is carried out
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under pressure ~n a series of autoclaves, the ~-olution
with the precLpitate ~iOe~ the slurry~ ls flashed to
ordi~ary pressure, and the flashed solution is then
passed to a thickener ~here the slurry is elutriated to
5 recover the product, a portlon of the product being re-
cycled as se~d material to the autocla~es as a precip~ta-
tion aid.
A disadvantage of the foreg~lng methods i5 the
requir~ment for pumps for maintainlng recirculation
10 throughout the autoclave system, particularly in the re-
cycling of seed or solld catalysts In the case o~
metallic sulfide precipitation, a ma~or problem is the
transport, reslurry and the general handling of der~se,
abraslve metal sulfide seed which can result in pump
15 break-down and ther~by adversely affect the overall
efficiency of the systemO
It would be desirable to have a precipitation
system which does not require the need for a plurality of
pumps for mo~ing leach liquor and seed through the auto-
20 claves during the precipitation cycle
In accordance with the invention there is pro-
vided a process for continuously precipitating precLpltate-
forming ions under elevated temperature and pressure from
a solution of said ions using recycle precipltate seed as
25 a precipitation aid which comprises,
establishing a solution of said precipitation-
f~rming ionsl,
feeding said solutlon at an elevated temperature and
pressure through an autoclave having one or a series o~
30 precipitation compartments~
adding a precipitation agent to said solutiorl while
it is maintained under said elevated temperature and
pressure to form a precipitate of said precipitation-
forming ions in the form of a slurry,
and causing said slurry to flow out of said auto-
clave by virtue of the prevalllng pressure in the sys~em
to a serially co~nected solids-liquid separator i~
pjressure commu~ication with said autoclave,
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said separator having a lower, den~e ~luidized slurry
column and being dLsposed at an elevatlon relative ~o said
autoclave to ~rovide a hydrostatic head of said ~it~dra~n
slurry ~.n gravity-flow relationship to said autocla~e,
said hydrostat~c head being sufficient to provide
pressure d~fferential to cause flow of the dense fluldized
slurry to said autoclave as seed.
The solids-liquid separatoL ~e.g., classifyi~g
thickener~ may have an elutriation column the precipitate
1~ slurry being continuously elutriated in the column under
the prevailing pressure so as to provide a dense fluidized
slurry havi~g an upper portion of precipitate fines and a
lower portio~ of product concentrate and the upper poxtlon
of precipitate flnes being caused to flow by gravity
15 ~hydros~atically] as seed material to the autocla~e while
the product concentrate is collected at the lower port~o~
of the elutriating columnO
A~ important advantage of the invent;on resides
in recycling the precipitate seed under system pressure
20 without requiring the use of pumps. In the case of metal
sulfide precipitate, such as nickel sulfide, the slurry
of metal sulfide particles in the liquid substantlally
barren of metal values flows to a solids-liquid separa~or
~e.g., a thickener~ characterized by a long vertical
25 colum~ or pipe~ The dense solids are caused in one
embodiment to flow by gravity to the vertical p~pe
sectio~ of the separator where the sollds are fluidized
~y wash water such as to exhibit the properties of a
liquid of high density (e.gO, 2 grams~c.c ~ A head of
3~ slurry is developed in the vertical column or pipe of
a~out three or four feet, which head is su~tained by the
pressure in the system, the head being more than the head
lost in discharging the dilute reaction slurry to the
higher elevation of the solids-liquid separator ~including
35 friction loss in the discharge piping)~ As a result ~f
this imbalance in head, seed solids are a~Le to flow from
a point i~ the dense slurry column directly into the
pressurized reactor or into the clear liquid feed line
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leading to the reactor~ The decant barren Liquid from the
separator is throttled to atmospheric pressure ~or the next
process step of further clarificatlon.
In a demonstration of this technique in the metal
sulflde precipitation reaction, the dense slurry column was
an elutriation and wash column fluidized by wash water~
The relati~ely coarse bottom slurry was withdrawn as a pro-
duct while the finer particles were returned to the reaction
vessel or autoclave as seed. The fluidizing wash water dis-
places the acid reaction product from the recycle slurry9thus minimizing the circulating acid load to the reactor
In one embodiment of the inventionr the recycle
seed slurry was intxoduced through a jet in the clear l~quid
feed to the reactor. This variation wa~ used to take into
account limited headroom for the elevation of the sollds-
liquid separator above the reaction autoclave.
In a particular system in which this lnvention
was demonstrated, four agitation tanks and four trou~le-
prone slurry pumps ~ere eliminated. The operating
e~ficiency for the system increased from ~9 to 99 percent.
Mechanical reliability was also enhanced in
that the bulk of the coarse slurry did not pass through
the pressure let-down system.
The invention is particularly applicable to the
continuous precipitation of metal sulfide under elevated
temperature and pressure fxom an aqueous solution of
sulfide-forming metal ions, such as nickel and/or cobalt,
using recycle nickel sulfide seed as a precipitation aid.
The established aqueous solution may in this instance be a
leach liquor obtained in the leaching of nickel lateritic
ores. The process comprises feeding the solution or leach
liquor at an elevated temperature and pressure through at
least one autoclave having a series of precipitation com-
partments, adding a sulfide-precipitation agent, e.gO,
H2S, to the solution while maintaining it under elevated
temperature and pressure to precipitate the metal sulfide
and thus form a sulfide slurry, causing the slurry to flow
out of the autoclave by virtue of the prevailing pressure
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in the system to a serially connected solids-liquid
separator (e.g., classifying thickener) in pressure com-
municat~on with the autoclav~, the separator being char-
acterized by an elutriation column and being disposed at an
elevation relative to the autoclave to provide a hydrostatic
head of the withdrawn slurry so as to effect recycle gravity
flow to the autoclave, continuously elutriating the sulfide
slurry in the elutriation column while under the prevailing
pressure so as to provide an upper slurry portion of sulfide
fines in the elutriation column and a lower portion of pro-
duct concentrate, and then causing the upper fines portion
of the metal sulfide fines to flow by gravity (hydro-
statically~ as seed material to the autoclave while
collecting the product concentrate at the lower portion of
the elutriating column.
The details of the invention will be clearly
apparent by referring to the drawing which shows a
hydrometallurgical system for precipitating nickel sulfide
using H2S as the precipitant, the system comprising an
autoclave 10 having a series of compartments A to F, each
compartment having a stirrer 11.
Clear liquid feed 12, e.g , pregnant leach
liquor, is fed to the autoclave where it is maintained under
pressure (for example, 150 psig) as it passes through the
autoclave. After pH adjustment in the known manner, H2S
xeagent 13 is injected under pressure into the autoclave to
precipitate the metal sulfide (for example, at a solution
temperature of about 1209C.). The dilute slurry 14 formed
is caused to leave the autoclave by virtue of the pressure
in the system and enter the upper end of the solids-liquid
separator at 15A which is characterized by a vertical
column 16 having a reduce~ lower portion 17, the separator
communicating with the autoclave under the prevailing
pressure in the system.
As will be noted, the dense slurry 18 is caused to
maintain a substantial head above the autoclave. Wash water
19 is injected into the bottom of the column as shown to
fluidize the precipitate under conditions such khat the
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coarse particles are allowed to settle at the lower column
portion 17 for removal as product 21 by means of valve 20.
The finer particles are maintained fluidized at the upper
end of the column and, by means of the hydrostatic head,
are recycled as seed material by gravity flow via valve 22
into clear liquid feed line 12 entering the autoclave. In
the alternative, the seed may enter the autoclave directly.
As is clearly apparent, a process is provided for
continuously precipitating metal values from solution in
which part of the precipitate is recycled as seed material
while the total system is under pressure~ the seed recycle
being accomplished by maintaining a hydrostatic head of the
slurry in the solids-liquid separator while under the
pressura prevailing in the system. Because of the lmproved
technique employed for effecting recycling of seed material,
pumps need not be used in this phase of the process~
The invention is applicable to any high pressure
precipitation system in which recycle seed materials is
employed as a precipitation aid. However, the invention is
particularly applicable to the recovery of nickel and/or
cobalt from pregnant leach liquor obtained in the leaching
of nickel lateritic ore. As illustrative of the invention,
the following typical example is given.
XAMPLE
In the sulfuric acid leaching of nickel laterites,
the nickel concentration in the pregnant liquor usually
ranges from about 3 to 15 gpl. However, depending upon the
starting feed material, e.g~, the addition of alloy scrap,
the pregnant liquor concentration may broadly range from
about 1 to 40 gpl, an~ optionally cobalt, the cobalt, when
present, ranging up to about 5 gpl (e.g., 1 or 2 gpl)O The
pH is adjusted to a range of about 1.5 to 4, e.gO, 2.5,
following which the solution is subjected to sulfide pre-
cipitation with H2S at a pressure ranging from about 5 to 50
psig and a temperature ranging from about 65 tv 110C~ while
vigorously agitating the solution in the presence of seed
material, for example, at least about 75 gpl of seed
material, until substantially complete precipitation obtains.
The seed concentration is at least about 40 gpl may range
from about 40 to 300 gpl,
In a specific embodiment, reference being made
to the clrawing, clear liquid feed 12 containing about 6 gpl
nickel clS nickel sulfate and having an adjusted pH of about
2.5 is fed to autoclave 10 as shown maintained under a
circuit pressure (autoclave and solids-liquid separator 15)
of about 20 psig and a temperature of about 95C.
Dilute slurry 14 is withdrawn under pressure and
pa~sed to solids-liquid separator lS where the precipitate
is fluidized by flowing wash water 19 upwardly in column
16-17 to provide a dense slurry of fines 18 and a coarse
product 21 which is withdrawn from the bottom of column 17
via valve 20. The fines are recycled to the autoclave via
valve 22 through clear liquid feed line 12, the amount of
fines xecycled being sufficient to provide a seeds content
in the autoclave of about 150 gpl.
The precipitation cycle is continued untll all o
the pregnant liquor has been processed.
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