CA1103040A

CA1103040A - Leaching of nickeliferous oxide ores

Info

Publication number: CA1103040A
Application number: CA308,444A
Authority: CA
Inventors: Willem P.C. Duyvesteyn
Original assignee: Amax Inc
Current assignee: Cyprus Amax Minerals Co
Priority date: 1977-08-01
Filing date: 1978-07-31
Publication date: 1981-06-16
Also published as: JPS5452615A; FR2399483A1; AU3819278A; JPS6353250B2; FR2399483B1; GB2001612A; AU522966B2; GB2001612B; BR7804871A; DE2833039A1

Abstract

ABSTRACT OF THE DISCLOSURE

Water-soluble alkali metal or ammonium com-pounds are added to slurries of nickeliferous oxide ores which are leached with sulfuric acid at tempera-tures between about 230° and about 300°C. The alkali metal or ammonium compound additions improve the handling characteristics of the slurry, nickel recov-eries, settling rates and compaction rates and lower scaling rates.

Description

~ 1~3c~41~ CASE PC--887 IMPROVEMENTS IN LEACHING NICXEI~EF~US OXIDE ORES

The present invention relates to leaching nickel fr~m nickelif3rous oxlde ores and, more particularly, to the acid leaching of such ores.
A number of procesæes for leaching nickel from nickeliferous oxide ores are known. One process is des-cribed in "The Winning of Nickel" by Boldt and Queneau, published by Longman's Canada Ltd., Toronto at pages 437 to 444. The process described by Boldt and Queneau is the process used at Moa Bay for leaching nickel from nickeliferous limonites ~high iron, low magnesia oxide ores).
Raw nickeliferous limonite is slurried with water and pre-heated to between 230C and about 260~C. The preheated slurry is then fed to the firæt of a series of autoclaves along with the requisite amount o~ sulfuric acid. The acidified slurry is then flowed through the train of auto-claves by gravityO Total leaching time i9 between 1 and

2 hours. After lowering the slurry to atmospheric temp-eratures and pressures the resulting pregnant solution i9 separated from the residual solids in gtandard thickeners Although the proce~s used at Moa Bay effectively recovered nickel and cobalt from nickel;iferous limonitic ores, a number of operational problems were encountered.
For example, the pumping of raw ore slurries encountered ~ome difficulties.
In accordance with the inventian there ..
is provided a process for acid leaching nickeliferou~
oxide ores, in which a water-soluble alkali metal or ammonium compound is added to an aqueous slurry of the ore in small but effective amounts to increase nickel recovery, to increase the settling rate of solids and to lower the viscosity of the slurry to improve slurry handling characteristics.
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ThR amount of the water-soluble a~ etal c ~ ound added to the slurry is dependent upon the favorable result de-sired, the nature of the ore being treated and the leach-ing conditions employed. The slurry is generally pre-heated to a leaching temperature between about 230C. andabout 300C, and sulfuric acid is added to the preheated slurry to leach substantially all the n~ckel from the nickeliferous oxide ore.
All nickeliferous oxide ores can be treated by the process in accordance with the present invention.
However, the process of the present invention fi~ its greatest utility in treating nickeli~us silicate ores, i.e., ores having comparatively low iron contents and com-paratively high magnesia contents, often referred to as garnierites. Deep sea nodules can also be treated by the process in accordance with the present invention and are intended to fall within the term "nickeliferous oxide ores " .
Raw ore from the mine is, if necessary, crushed or ground without drying to provide a feed material that will form stable slurries and will readily react with the leaching solution. ~f the ore must be ground, it is ground to a particle size such that about 10~% pas~e~
through a 30 mesh screen ~U.S. Screen Size). The finely divided ore is then formed into an aqueous slurry con-taining between about 25% solids and about 50% sollds, and advantageously between about 35~ solids and about 45% solids. Slurries containing sollds wlthin the fore-going ranges minimize materials handling problems while insuring efficient utilization of autoclave capacity.
The slurried ore is fed to a preheating vessel in which the slurry is preheated to a leaching temp-erature between about 230C. and about 300C. Preheating can be accomplished indirectly or by in~ecting live steam into the slurry. The preheated slurry is then fed to an autoclave where sulfuric acid in an amount between about 0.15 part and 0.8 part for each part of dry ore is added. Nickelifer~us oxide ores are generally a blend of limonitic and silicate fractions, and higher iron contents up to 55% indicate increasing amounts of the ,~

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limonitic fractionO Acid additions are keyed to the nature of the ore being treated. Sulfuric acid is added in amounts between about 0.15 part and about 0.3 parts for each part of dry ore and between about 0.45 part and about 0.8 part for each part of dry ore for limonitic and silicate ores, respecti~ely, and for ores that are blends of limonites and sillcates the acid additions are adjusted in accordance with the relative proportions of limonites and sllicates in the particular blend. For most oxi~e ores which are a blend of limonites and silicates, acid additions in amounts between about 0.1 part and about 0.4 part per part of dry ore are generally sufficient. The autoclave is maintained at a temperature between about 230C. and about 300C. to leach about at least 90% of nickel contained in the feed material. Advantageously, the process i~ conducted on a continuous basis by employing a train of autoclaves and feeding the preheated slurry to the first autoclave and transferring slurry from one autoclave to another by gravity or by employing a single ~utoclave having a series of baffles that permit contlnuous operation.
~gain, the requisite amount of acld is added to the autoclave to insure that at least about 90% of the nickel is extracted from the ore.
The sulfuric acid can be added to the preheated slurry either as a single additlon or incrementally to the autoclave or autoclaves to maintain the aluminum content of the aqueous solution at a value of less than 3 grams per liter. When using incremental additions, between 5% and 75%, preferably between 40% and 70%, of the total acid is initially added to the autoclave or the first autoclave in a train and the remainder of acid is then added in at least two equal stages or in substantially equal amounts to each of the autoclaves in the train.
When the leaching reactions are completed, the reacted slurry can be cooled to below its boiling point, let down to atmospheric pressure and then neutralized with fresh ore, such as a high magnesia nickeliferous oxide, or other suitable neutralizing reagent.

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~ 4--Advantageously, the reacted slurry is first neutralized with fresh ore before being cooled to below its boillng point in atmospheric pre~sure in order to improve the kinetics of the neutralizing reactions at the elevated S temperatures. The neutralized slurry is then sub-jected to conventional liquid-solid separation tech-niques to provide a pregnant ~olution containing nickel and any cobalt and a spent residue that i~ sent to waste.
An important feature of the present invention is the addition of a water-soluble alkali metal or ammonium compound to the slurry to accomplish any one or all of the following advantages: improvement of the handling characteristics of the slurry, improved nickel recoveries, decreased scaling rates, increased settling rates or increased compaction of the solids upon liquid-solid separatlon. The water-soluble alkali metals or ammonium compound has its greatest effect on silicate ores and while there is less L~prove~ent in these propertles when treating limonitic ores, the improvement is still significant. Depending upon the objectives to be achieved by the addition of the alkali metal or ammonium compounds, the addition can be made to the slurry immediately prior to that stage of the process where the particular ob~ective is to be realized. Because the alkali metal and ammonium cations react with solubilized iron and aluminum to ~orm hlghly insoluble ~pecies of ~arosites and alun~tes whlch con-sume the cations, it is advantageous to add the c~mpounds when leaching is more than half complete. Of course, if the compound is added to improve the handling characteristics, the compound is added as the ore is being pulped with water. Additional quantities of the alkali metal compounds can be added during the leaching stage as well.
The nature of the ore as well as the ob~ective to be achieved by the addition of the water-soluble alkali metal or ammonium compound will determine the amount of the compound added to the slurry. For example, if it is desired to improve the handling characteristics, i.e.

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lowering the viscosity of the slurry of a given ore, in-creasing amounts of the alkali or ammonium metal com-pound are added to the slurry un~il no further lowering of the viscosity is observed. From an operational standpoint, it is rarely necessary tc use amounts of the alkali metal or ammonium compound in excess of amounts equivalent to an anhydrous sodium sulfate addition of about 5%, based on the dry weight of the ore. All of the advantages can usually be achieved for most ores when the alkali metal or ammonium compound is added to the slurry in amounts equivalent to anhydrous sodium sulfate additions between about 0.5% and about 2.5%, based on the dry weight of the ore, and advantageously in amounts between about 1.5% and about 2.5%.
Any water-soluble compound of an alkali metal or ammonium can be used for treating the slurry.
Examples of such water-soluble compounds include sodium sulphate, sodium chloride, sodium nitrate, sodium bi-sulphate, sodium hydroxide, sodium carbonate, sodium 20 bicarbonate, sodium phosphate, sodium silicate, ammonium sulphate, ammonium chloride, ammonium nitrate, ammonium bisulphate, ammonium hydroxide, ammonium phosphate, potassium sulphate, potassium chloride, potassium nitrate, potassium phosphate, potassium silicate and 25 potassium bisulphate. Compounds of other alkali metals are equally e~fective, but because o~ their cost it is preferred to employ the more common alkali metal com-pounds. From the standpoint of cost and avallability, sodium sulphate i~ the pre~erred compound.
In order to give those skilled in the art a better understanding o~ the present invention, the following illustrative examples are given:

A garnieritic ore containing 3.1% nickel was 35 pulped with water to provide a slurry containing 35~
solids. The slurry was preheated to 270C. and sulfuric acid in an amount of 0069 part for each part of the dry ore was incrementally added to the preheated slurry as the slu ~ was oonveyed by gravity through a series of three auto-.: ~
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claves which were maintalned at 270Cr A solution of sodium sulfate in an amount equivalent to 78 pounds of anhydrous sodium sulfate per ton of ore was added to the slurry midway thrGugh the traln of autoclaves. Upon flashing and subsequent liquid-solid separation in a counter-current decantation system, the first thickener provided an underflow residue containing 34% solids.
Analysis showed that 94.5~ of the nickel contained in the ore had been extracted.
A similar test was conducted for comparative purposes without a sodium sulfate addition. In this test, the underflow contained only 22% solids and the nickel extraction was on~y 92~5%. Thus, the sodium sulfate addition lowered the residual nickel in the leach residue by 27% and increased solids content in the underflow by 54.4%.
EXAMPLE II
. __ A nickeliferous oxide ore containing equal fractions of garnierite and limonite and having an overall nickel content of 2.1% was treated in the same manner as deYcribed in Example I except that a lower acid addition of 0.46 part per part of dry ore was employed because of the hlgher iron content of the overall ore and the sodium sulfate addition was equi-valent to an anhydrous sodium sulfate addition of 24pounds per ton of dry oreO The underflow ~rom the first thickener from the counter-current decantation circuit contained 51~ solids, when 0.42 pounds of a poly-acrylamide based flocculant was used per ton of solids in the residue, and analyses show that 96.8% of the nickel had been extractedc A comparative test without the sodium sulfate addition provided a nickel extraction of 94.2% and an underflow residue containing 41% solids with 1.23 pounds of flocculant. Thus, the sodium sulfate additions lowered the nickel content in the resldue by 45%, in-creased the ~olids content of the underflow by 25% and reduced the flocculant consumption by 65%.
EXAMPLE II~
A nickeliferous oxide ore having a nickel content .
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of 1.8~ was slurried with water to provide a slurry containing 45% solids. Sodium sulfate in an amount equivalent to 50 part of anhydrous sodium sulfate per ton of dry ore was added to the slurry.
The ore was preheated to 270C. and then fed to a train of gravity fed autoclaves maintained at 270C. Sulfuric acid was incrementally fed to the slurry as the slurry progressed from one autoclave to another in a total amount of 0.26 part for each part of ore.
Upon leaving the final autoclave the slurry was flashed and cooled to ambient temperatures. Liquid-solids separation produced an underflow re~idue containing 57% solids, and analyses showed that about 95.2% of the nickel contained in the ore had been extracted.
A comparative test without the sodium sulfate addition was run. The underflow from liquid-solid~
separation had a solids content of 47% and analyses ~howed that nickel extractions were only 94.1%.
EXAMPLE IV
This example coneirms that the addition of water-soluble alkali metal or ammonium compounds to the slurry i9 effective ln lowering the scaling rates generally encountered in the high temperature leaching of these ore~.
A nickel~fer~us oxide was slurried wlth water, preheated to 270C. and fed through a train of S auto-claves into the first three of which sulfurlc acid was incrementally added. In one test, no water-soluble alkali metal or ammonium compound was added to the slurry while in the other test sodium ~ulfate in an amount equivalent to anhydrous sodium sulfate of 14.3 kilograms per metric ton of ore was added to the fourth autoclave in the train. During the tests samples of the leach liquor in the fourth and fifth autoclave were taken and analyzed for their aluminum content, aluminum being the mo3t significant factor in causing ~caling.
The results are shown in the following Table I. When the test runs were completed, the autoclavès were opened and the scale buildup measured. From the thickness ~i~3~

of the scale buildup and the length of the test runs scaling rates, which are reported in the following Table I, were calculated.
TABLE I
5 Test Fourth Vessel Fifth Ves6el Scaling Al, Scaling Al, Rate, in~mo gpl Rate, in~mo gpl No Na2S04 Addition 0.07 0.5 0.03 0.4 14.3KgNa S0 per 0.00 <0.1 0.00 <0.1 metric ~on40f ore The results shown in Table I confirm that the addition of alkali metal or ammonium compounds lower the aluminum conten~ of the solution dramatically and reduce the scaling.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a process for recovering nickel from nickeli-ferous oxide ores containing less than about 35% iron in which the ore is slurried with water, the slurry is pre-heated to a leaching temperature between about 230°C. and about 300°C., sulfuric acid in an amount between about 0.15 part and about 0.8 part for each part of dry ore is added to the preheated slurry to leach the nickel values from the nickeliferous oxide ores, the leached slurry is neutralized and the neutralized slurry is subjected to a liquids-solids separation operation, the improvement which comprises: adding at least one water-soluble com-pound selected from the group consisting of alkali metal or ammonium compounds to the slurry when the leaching re-actions are more than half complete in small but effective amounts to minimize dissolution of silica, whereby the set-tling rate of the neutralized slurry is improved.

2. The process as described in claim 1, wherein a high magnesia nickeliferous oxide ore is added to the slurry at the leaching temperature after the leaching reactions are complete to neutralize most of the free acid contained in the leach liquor and to recover a substantial portion of the nickel contained in the high magnesia containing ore.

3. The process as described in claim 1, wherein the leached slurry is cooled and let down to atmospheric pressure and neutralized with fresh high magnesia nickeli-ferous oxide ore and the residue from neutralization is fed to the leach slurry at the leaching temperature after the leaching reactions are completed.

4. The process as described in claim 1, wherein the amount of water-soluble compound added to the slurry is up to about 5%, based on the dry weight of the ore.

5. The process as described in claim 4, wherein the water-soluble compound is added in amounts between about 0.5% and about 2.5%, based on the dry weight of the ore.

6. The process as described in claim 5, wherein the water-soluble compound is added in amounts between about 1.5% and about 2.5%, based on the dry weight of the ore.

7. The process as described in claim 6, wherein the water-soluble compound is at least one member selected from a group consisting of sodium sulfate, sodium chloride, sodium nitrate, sodium bisulfate, sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium phosphate, sodium silicate, ammonium sulfate, ammonium chloride, ammonium nitrate, ammonium bisulfate, ammonium hydroxide, ammonium phosphate, potassium sulfate, potassium chloride, potas-sium nitrate, potassium phosphate, potassium silicate and potassium bisulfate.

8. The process as described in claim 7, wherein the water-soluble compound is sodium sulfate.

9. In a process for recovering nickel from nickeli-ferous oxide ores containing about 37.1% iron in which the ore is slurried with water, the slurry is preheated to leaching temperature between about 230°C. and about 300°C., sulfuric acid in an amount between about 0.15 part and about 0.8 part for each part of dry ore is incrementally added to the preheated slurry to maintain the aluminum content of the slurry at a value of less than about 3 grams per liter to leach the nickel values from the nickeliferous oxide ores, the leached slurry is neutralized and the neutralized slurry is subjected to liquid-solids separation, the improvement which comprises: adding at least one water-soluble compound selected from the group consisting of alkali metal or am-monium compounds to the slurry when the leaching reactions are more than 50% complete in small but effective amounts to minimize dissolution of silica whereby the settling rates of the neutralized slurry is improved.

10. In a process for recovering nickel from nickeli-ferous oxide ores containing less than about 35% iron in which the ore is slurried with water, the slurry is preheated to leaching temperature between about 230°C. and about 300°C., sulfuric acid in an amount between about 0.15 part and about 0.8 part for each part of dry ore is added to the preheated slurry to leach the nickel values from the nickeli-ferous oxide ores, the leached slurry is neutralized and the neutralized slurry is subjected to a liquid-solid separation operation, the improvement which comprises: adding at least one water-soluble compound selected from the group consisting of alkali metal or ammonium compounds to the slurry when the leaching reactions are more than about 50% complete in small but effective amounts to minimized dissolution of silica whereby the settling rates of the neutralized slurry is improved.

11. The process as described in claims 9 or 10, where-in the amount of water-soluble compound added to the slurry is up to about 5%, based on the dry weight of the ore.

12. The process as described in claim 9 or 10, where-in the water-soluble compound is added in amounts between about 0.5% and about 2.5% based on the dry weight of the slurry.

13. The process as described in claims 9 or 10, where-in the water-soluble slurry compound is sodium sulfate.