CA1183690A - Chloride leaching of nickel-cobalt-iron sulphides - Google Patents

Abstract

Abstract of the Disclosure Metal values are recovered from mattes containing nickel, cobalt and iron by first suspending the mattes in water, oxygen pressure leaching and then chlorine leaching the residue from the oxygen leach.

Description

The present invention is directed to the treatment of mattes containing nickel9 cobalt and iron to recover the valuable metals and to discard ~he iron.
BACRGROUNI) OF THE INVENTION AND THE PRIOR ART
It is considered that nickel mattes rich in cohalt will be available from a number of sources, such as, for example, the recovery of metal values from sea nodules, treatment of slags to reclaim metal values from waste products generated in the nickel smelter and various residues arising in the treatment of nickel containin~ materials.
It is to be appreciated that in the normal opera-tion of the nickel converter wherein iron elimination is desired, that a large proportlon of cobalt present in the nickel matte will be oxidized along with the iron. Accord-ingly, it is to be expected that nickel mattes rich in cobalt will also contain considerable quanti~ies of iron. This factor presents difficulties in terms of potential reagent costs particularly when chlorine leaching i5 ~o be employed.
In the case oE -nickel mattes, which are u~ually poor in cobalt and iron, chlorine leaching has been demon-strated to have a number of advantages. In particular, the production of chloride solutions provides the means for ready separation of cobalt from nickel based on solvent extraction of the cobaltous chloride complex. Cobalt and nickel electro-winning may readily be conducted from all chloride electro-lytes~ In applying chlorine leaching to mixed ~ickel-cobalt mattes containing substantial iron contents, the iron will be converted to ferric chloride during the leaching repre-senting a sub~tantial loss of chlorine. This can only be ~3~

replaced by hydrolysis of the ferric ions~ When large amounts of iron are present~ th;s approach is not practical from the viewpoint of reagent cost~
The leaching of mattes, ores and concentrates with chlorine or oxygen is an established practice in hydrometal~
lurgy. In addition, simultaneous use o~ chlorine with chloride solutîons containing ~opper is known. Recently, as shown in South Africa patent No. 7A/3297, replacement of chlorine by oxygen and HCl has been suggested. Methods of removing and recycling copper in solution when leaching nickel matte have been shown in U~S. patent No. 3,880,653~ The combination of chlor;ne and ferric chloride solutions has been proposed for leaching nickel matte in U.S. patent No~
1~943r 337. A method for recycling ferric ions by means of solvent extraction has been suggested in U.S. Patent No.
4~173r520~ The use of both chlorine and oxysen as reagents in a leaching scheme for sulfides has been suggested in U.S.
patent No. 3~981,962 and has been described in a paper entitled, 'ILead-Zinc Extraction from Flotation Concentrates by Chlorine~Oxygell Leaching" at the SME Fall meeting, Salt Lake City, September 1975, preprint No. 75-B-B14 by Scheiner, Smyres and Lindstrom. In accordance with the teachings of these disclosures, oxy~en is added simultaneously with or subsequent to chlorine.
SUMMARY OF THE INVENTION
Ni kel-cobalt-iron mattes are leached by a process in wh;ch the particulate matte in aqueous suspension is first leached with oxygen under pressure and the residue rom the oxygen leach is then subJected to chlorine leaching. The products of the process include a solution containing the cobalt and nickel chlorides~ a sulfur xesidue and an iron oxide-hydroxide cakeO
DESCRIPTION OF THE DR~WXNG
~ he accom~?anying f igure depiots a flowsheet or treating nlckel-cobalt-lron ma~tes wherein the matte is first oxygen lea~hed and is ~hen chlorine leached and wherein the solid materials move coun~ercurrent ~o the solution between the leaching sta~es.
DETAILED ~ESCRIPTION OF TH~ INVENTION
In accordance with the inventi~n metal values are recovered from mattes containing nickel~ cobalt and ironr b~
first leaching the feed matte in aqueous suspension under pressurized oxygen and then chlorine leaching the matte residue from the oxygen leachr The oxygen leach is conducted in an acid chloride aqueous solution high in solubilized iron. This step solubilizes at least a portion of the base metal contenk of the matte and hydrolyzes iron in solutionO
The partially oxygen leached matte may then be a~itated with the leach solution to cement copper thereon. Thereaf ter, the oxygen leached products are subjected to solid-liquid separation and the solids are reverted to the chlorine leaching step while the pregnant ox~gen-leach liquor is purified, treated to remove cobalt, and then subjected to nickel electrowinnlng~ The spent liquor from electrowinning is reverted to the chlorine leach step~
In the chlorine leach step, the remainin~ metal values are ~issolved and elemental sulfur is obtained. The leach products from the chlorine leach are subjectea to solid-liquid separation to remove the elemental sulfur and the li~uor is cycled to the oxygen leach.

~#;~ 3~

The solid material from the oxygen leach comprising a mixed residue of par~ially leached and cemented matte with iron hydroxides may be treated to separate and reject the iron hydroxides.
Mattes to be treated in accordance with the present invention may contain, in weight percent, about 10 to about 40~ nickel, about 1 to about 20% co~alt, about 20 to about 7~ iron, up to about 20% copper and about 5 to about 30~
sulfurO The sulfur content will usually be sufficlent to sulfidize the iron and cobalt contents sto.ichiometrically.
Reference to the accompanying figure o~ drawing will make the invention more readily comprehensible~ As shown in the drawing, the feed matte is first leached with oxygen in an intermediate high iron liquor coming from the chlorine leach. This step simultaneously leaches part of the base met:als in the matte and hydrolyzes the iron in solution. Following this, the oxygen leach slurry may be immediately filtered yielding a comparatively iron-free solution containing a major proportion of the copper in addition to cobalt and nickel. Copper may ~e separated from ~.his solution by, for example, precipitation as sulfide.
Alternately, the oxygen in the leach reactor atmosphere is released and the slurry of hydrolyzed iron and partially leach d matte stirred for a further period during which soluble copper is cemented onto the partially leached matte ~ielding a comparatively copper- and ironfree solution.
Cobalt can be extracte~ from the copper- and ironfree solu-tion by solvent extraction or ion exchange~ then nickel can be recovered by electrowinning.

~ 3~

The oxygen leach residue comprises a mixture of iron hydroxides and partially leached ma~e~ These components can be separated by flotation or, if ~he matte particles are large enought by screeniny/ elu~riationg or hydrocloning.
If the matte residue contains a substantial proportion of cemented copper~ it is desirable to remove a portion of the matte residue for separate copper recovery.
The matte residue i 5 then further leached in spent electrowinning electrolyte with chlorine, to pxoduce a high sulfur residue and an intermediate liquor which is cycled t~
the oxygen leach. In preparation ~or the oxygen leach r the matte feed will usually be granulated or ground to pxovide a particle si~e of less than about 8 meshO The ~iquor fed to the oxygen leach will contain about 100 to about 180 grams per liter (gpl) o~ nickel, abouk 1 to about 50 gpl of cobalt, up to about 50 gpl of copper, and about 25 ~o about 150 gpl of iron as chlorides with up to 10 gpl sulfate.
Oxygen leaching is conducted at a temperature in the range of about 60 to abou~ 105C, at a pressure of about atmospheric to about 400 lbs/in~. The p~I durin~ oxygen leach;ng will be about ~1 to about 3. Condition.s leaching to sulfate formation are avoided.
The liquor fed to the chlorine leach will be essen-tially devoid of cobalt, copper and iron and may contain about 60 to about 100 gpl o~ nickel. Chlorine is employed in the leach at a rate of about 0.1 to about 0.8 kilograms of chlorine per kilogram of oxygen leach residue feed to the leach. Chlorlne leaching is conducted in the pH range of about 1 to about -1, and may be conducted at ambient tempera-ture and pressure.

~ he sequential leaching steps involvin~ first oxygen leaching and then chlorlne leaching~ in accordance with the present invention~ provide a process having a large measure of self-regula~lonO Accordingly, c~Lose con~rol of the quantity of chlorine added during leaching ~ase~ on ma~te assayf is not required. Only suffiien~ chlorine to combine with the nickel and ~obalt contents of the mat~e ~eing le~ched is consumed and any excess consump~io~ is readily indicated, The reason for this is ~hat slnce the ma~te is firs~ treated with ~xygen and then with chlorine~ the exces~ chlorine consumption can only occur through chlorine lusses i.n the off~gas or by sulfur oxidation. Both o~ these conditions are readily detectable~ and can be prevented.
Some examples will now be given.
EXAMPLE I

~ ' Feed for the described tests was a high co~alt matte corresponding to that expected from back reduction of slag from a nickel converter:
Ni Cu Fe Co S
-(wt. ~) 30.3 0.93 30.3 1]..5 25~4 240g of this matte was charged into a 1 li.tre titanium autoclave together with 0.6 litres o~ liquor antici-pated from stage II (CL2 leach~: (g~ i 130, Fe 50, Co 20, Cu 5~ The sLurry was preheated to g5~, with the usual àgitation and then 2 (300 psi~ admittedO Consumption of Oz was rapid, and the test was terminated after 33 minutes;
temperature was maintained at 95~C throughout~ The slurry was ~emoved from the autoclave, and the coarse particles separated by screening ~325 mesh sGreen)~ The fine particles were removed by filtration, leaving a filtrate which had a Fe content of only 0.1 g/l, and the pH o~ which had risen from -0~3 to 2.00 Ni Cu Co Fe S

Feed Solution ~0 r 6Q) .L30 S 2Q 50 -- (g/~-) Final Solution ~0~6Q) 184 6 37 Ool ~~
Feed Matte (240 g) 30~3 0.9 11~5 30,325.4 (%~
Leached Matte (165 g) ~1.3 1.6 9.125.8 31~4 Fine ppt (115 g~ 2~8 0.5 0.5 41.51~8 ~ he coarse residue corresponding to the leached matte was then C12 leached in a glass reactor at atmospheric pressure with a solution containing 80 Ni, 5 Cu. The progress of this test i5 shown below:
501ution .~ S
~ime ~ Redox S0!~ g/l Residue 0 ~.5 380 0.7 310 ~
3~ 0~0 350 3.0 __ ~5 -0.3 350 3.9 --120 ~ lo~ 570 Y.2 ~ 63 ~35 ~1.0 650 14.0 --lS0 -1.0 72~ 21~0 73 ~i Cu Co Fe S
Final Residue (wt. ~ 0 1.3 2.5 5.3 79 ~12 g) The assay of this final residue corresponds to 97%
Ni extraction (and g5% Co extraction). The improvement in residue after 1~0 minutes is marginal, and the optimum end point would probably come at this time or before.
This test demonstrates the possibility of producing residues (S and Fe cake) low in Ni, whilst generating low Fe pxegnant solutions.

3~

A second batch of 240g matte w~s leached in the same manner as before with 300 psi 2 at 95C. The 0 5 6~
solution used as tha~ produced by ~he C12 leach of Example 1, in accordance with Figure 1~ In this tes~, the 2 addition .
was terminated a~ 60 minutes and ~he 0~ atmospher~ releasea, without cooling down the slurry which was stirred for an additional 15 minutes. ~he purpose of this period was to allow the Cu in solutlon ko cement out on the partially leached makte.
At the end of the oxidation periodO the solution assayed (g/13 Cu 500t Fe 3.6~ At the conclusion of the test ~15 minutes later) the ~olution assay ~7as ~u 0~2, Fe 5Ø
The residues were again separated by screening (325 mesh) to produce a matte residue and Fe cake:

Ni Cu Co Fe Matte Residue 20.6 3.32 9.02 21.0 155 g Fe Cake 1029 ~.16 OD40 50.S 119 g The loss o~ cobalt and nickel to the iron cake was approximately 2~ of eedO The final filtrate assayed (g~l) Ni 180~ Co 36r Fe 5t CU 0~2.
The advankages of the invention, especially in terms of ease of control, are emphasized by comparison to a scheme whereby a s;milar material is treated first by chlorine leaching and then ~or simultaneously~ by oxygen leaching.
In such a case~ there is no means of detecting excess chlorine addition and chlorine may be added in amount sufficient to dissolve all khe metals includ7ng iron. Recourse to calculated addik.ions of chlorine based on ~eed assay would rarel~ be satisfactory~ Any FeC13 formed in the leaching represents a loss of chlorine, which can only be replaced ~y hydroly~is of ferriG ions, an imprac~ical process where large amounts of ferr.ic chloride is present~ The present invention permits utilization o~ the matte i~self as base and iron is hydrol~æed in oxygen lea::hing~ The invention also provides automatic correction in that the amoun-t oE feed dissolved in oxyyen leaching is a function of the iron content of the chlorine leach spent ~olution reverted thereto; ~hereas the more feed dissolved in oxyyen leaching~ the les5 iron will be available when the residue therefrom is chlorine ieached.
~ lthou~h the present invention has been described in conjunction with preferred embodiments, it is to be under-~tood that modifications and variations may be ~esorted to without departing from the spirit and ssope of the inventionr as those sk:illed in the art will xeadily understand~ Such modificatlolls and variations are considered to be within the purview and scope of the invention and appended claims.

Claims (9)

WE CLAIM:

1. A process for recovering metal values from mattes containing the base metals nickel, cobalt and iron com-prising the steps of first leaching an aqueous slurry of feed matte under pressurized oxygen in an acid chloride aqueous solution high in iron to solubilize at least a portion of the base metal content of said matte and to hy-drolyze iron, subjecting the oxygen leach products to solid-liquid separation to provide a pregnant liquor containing dissolved nickel and cobalt and a solid residue, chlorine leaching said solid oxygen leach residue in an aqueous acid liquor to produce a high sulfur residue and an intermediate liquor, cycling said intermediate liquor to said oxygen leach, treating the pregnant oxygen-leach liquor to remove cobalt and then electrowinning nickel therefrom, and cycling spent electrolyte from said nickel electrowinning to said chlorine leaching step.

2. A process in accordance with claim 1 wherein the solids from the oxygen leach are treated to separate matte residues from iron hydroxides and the iron hydroxides are discarded.

3. A process in accordance with claim 1 wherein the matte feed contains about 10% to about 40% nickel, about 1%
to about 20% cobalt, about 20% to about 70% iron, up to about 20% copper and about 5% to about 30% sulfur.

4. A process in accordance with any of the claims 1, 2 or 3 wherein the liquor fed to the oxygen leach contains, in grams per liter, about 100 to about 180 of nickel, about 1 to about 50 of cobalt, up to about 50 of copper, and about 25 to about 150 of iron as chlorides, with up to about 10 of sulfate.

5. A process in accordance with any of claims 1, 2 or 3 wherein oxygen leaching is conducted at about 60 to about 105°C, at an oxygen pressure of up to about 400 psi and a pH
of about -1 to about 3.

6. A process in accordance with any of claims 1, 2 or 3 wherein the liquor fed to the chlorine leach contains about 60 to about 100 gpl of nickel as chloride and is essentially devoid of cobalt, copper and iron.

7. A process in accordance with any of claims 1, 2 or 3 wherein the liquor from oxygen leaching is treated to remove cobalt.

8. A process in accordance with any of claims 1, 2 or 3 wherein chlorine leaching is conducted at a pH in the range of about 1 to about -1.

9. A process in accordance with any of claims 1, 2 or 3 wherein chlorine is fed to the chlorine leach in amount to dissolve essentially all of the metals in the oxygen leach residue fed to chlorine leaching.