AU699127B2 - Recovery of nickel and cobalt from laterite ores - Google Patents

Description

Recovery of Nickel and Cobalt

From Laterite Ores

Field of Invention

This invention relates to the hydrometallurgical processing of nickeliferous oxide ores and, in particular, to acid leaching of nickeliferous oxide ores selected from the group consisting of limonite and saprolite, which jointly are called laterites.

Background Of The Invention

It is known that nickeliferous oxide ores, e.g., limonite and saprolite, are the world's largest potential sources of nickel and cobalt.

The ability to beneficiate these ores by conventional techniques has placed these ores at an economic

disadvantage in that these ores cannot be concentrated by magnetic separation or by froth flotation as compared to nickeliferotis sulfide ores which can be easily

concentrated to substantially high levels of nickel by well known methods, such as froth flotation and matte smelting.

One process for recovering nickel and cobalt is the well known Moa Bay process involving acid leaching at elevated temperatures and pressures at which iron oxide and aluminum oxysulfate are substantially insoluble.

In the Moa Bay process, limonitic ore at minus 20 mesh (95% passing 325 mesh U.S. Standard) is pulped to approximately 45% solids and the nickel and cobalt

selectively leached with sufficient sulfuric acid at elevated temperature and pressure

(e.g. 230 C to 250 C and 405 to 580 psia) to solubilize about 95% each of nickel and cobalt in about 60 to 90 minutes. After pressure let down, the leached pulp is washed by countercurrent decantation with the washed pulp going to tailings. The leach solution pH, which is quite low (e.g., between 0 and 0.5), is then neutralized with coral mud to a pH of about 2.4 in a series of four tanks at a total retention time of about 20 minutes and the thus-treated product liquor (containing about 5.65 gpl Ni, 0.8 gpl Fe and 2.3 gpl A1), after solid-liquid separation, is then subjected to sulfide precipitation. The leach liquor is preheated and the sulfide precipitation carried out using H2S as the precipitating reagent in an autoclave at about 120ºC (250ºF) and a pressure of about 150 psig.

In the original scheme for treating the mixed

sulfides,, the sulfide precipitate was washed and

thickened to a solids content of 65%. It was then

oxidized in an autoclave at about 177-C (350ºF) and a pressure of about 700 psig.

The solution containing nickel and cobalt was then neutralized with ammonia to a pH (5.35) sufficient to precipitate any residual iron, aluminum, and chromium present using air as an oxidizing agent.

The precipitate was thereafter separated from the solution and the nickel and cobalt solution then adjusted to a pH of about 1.5. H2S was added to precipitate

selectively any copper, lead and zinc present. The precipitate was separated from the solution by filtration and the nickel recovered by various methods, one method comprised treating the nickel-containing solution with hydrogen at elevated temperature and pressure to produce nickel powder.

The aforementioned process is similar to that

described in "the state of the prior art" set forth in U.S. Patent No. 4,097,575, the disclosure of which is incorporated herein by reference.

The aforementioned method had certain economic disadvantages. The conversion of mixed nickel-cobalt sulfide into salable separate nickel and cobalt products was very expensive and there was no market for mixed sulfide precipitates.

It has now been discovered that a novel combination of operational steps can be employed to separate nickel from cobalt and produce nickel metal directly from a leach solution produced from a nickel oxide ore, e.g., laterite ore, without going through an intermediate step of

producing a nickel-cobalt sulfide concentrate or matte, the refining of which to recover nickel is cost-intensive.

The hydrometallurgical process employed involves the use of a chelating ion exchange resins in which nickel is preferentially separated from cobalt and impurities typically obtained in the sulfuric acid leaching of laterite ores. While chelating ion exchange resins are known for extracting nickel from solutions, it was not known that, under relatively high acidic conditions, nickel can be separated from cobalt present in laterite leach solutions and provide an eluate with a substantially high Ni to Co ratio, e.g., at least about 50:1 suitable for recovery of substantially pure nickel by electrolysis.

In this connection, reference is made to an article directed to Process Developments in the Cobalt

Purification Circuit employed at CHAMBISHI RLE COBALT PLANT of Z.C.C.M, Zambia (copyright 1993 by the Minerals, Metals & Material Society).

Reference is also made to a paper entitled

"Separation of Nickel From Cobalt in Sulphate Medium Ion Exchange" presented by L. Rosato et. al. at the AIME

Annual Meeting of February 14-18, 1982, in Dallas, Texas.

The use of an ion-exchange chelating resin, such as XFS 4195, for separating nickel from a concentrated aqueous solution of cobaltous sulfate is disclosed in U.S. Patent No. 4,320,099 (March 16, 1982). Objects Of The Invention

It is thus an object of the present invention to provide a hydrometallurgical process for recovering nickel and cobalt separately from nickel oxide ores, in

particular, limonite and saprolite ores.

Another object is to provide a process for

economically recovering both nickel and cobalt.

These and other objects will more clearly appear when taken in conjunction with the following disclosure, the accompanying drawings and the appended claims.

Brief Description Of The Drawings

Fig. 1 is a flowsheet illustrating the process as applied to nickel laterite ores;

Fig. 2 depicts two curves published by Dow Chemical showing the absorption characteristics for each of nickel and cobalt using a Dow ion exchange composition identified by the trade designation XFS-4195 in which an active ingredient thereof is comprised of bis-picolylamine;

Fig. 3 is a curve depicting the absorption

selectivity of Dow resin XFS-4195 as a function of

solution pH;

Fig. 4 is illustrative of cumulative loading of nickel and

cobalt as a function of bed volumes of feed solution passed

through a column of XFS-4195 resin;

Fig.5 depicts generally an ISEP configuration in the form

of a carousel for carrying out the ion-exchange

extractions of nickel and cobalt;

Figs. 5A and 5B are schematics shown as flow sheets illustrating the use of said ISEP carousel configuration in carrying out the ion-exchange extraction of nickel from solution using the resin XFS-4915; Fig. 6 is illustrative of cobalt and nickel loading at room temperature as a function of the number of bed volumes (BVS/hr) passed through a column of XFS-4195 resin;

Fig. 7 depicts curves illustrating the selective stripping of cobalt from the resin employed in extracting the cobalt;

Fig. 8 is a simplified schematic illustrating the counterflow operation of the ISEP configuration through a series of columns;

Fig. 9 illustrates the use of the ISEP configuration for carrying out the Ni + Co IX (i.e. nickel plus cobalt ion exchange); and

Fig. 10 is a flow sheet based on the use of a Recoflo apparatus in recovering the nickel from the pregnant leach liquor, Fig. 10A being a continuation of Fig. 10.

Summary of The Invention

Generally speaking, laterite ores (e.g. limonite and saprolite) contain Ni, Co, Fe, Al, Mg, Mn, Cr, SiO₂ and a variety of impurity elements along with free and

crystalline water, some of which elements and the water are lost when the ore is heated.

An example of a limonite ore is one containing by weight 1.72% Ni, 0.14% Co, 41% Fe, 2.5% Al, 1.58% Mg, 0.8% Mn, 2.05% Cr, 12.1% SiO₂ and 11.3% LOI (Loss on Ignition).

When speaking generally of laterite ores, the

important elements of interest are nickel and cobalt.

Such ores will generally contain by weight about 0.5% to 3% nickel and about .005 to 0.5% cobalt.

Restating it with regard to all of the constituents present, the oxide ores to which the invention is applied may contain by weight about 0.5% to 3% nickel, about

0.005% to 1% cobalt, about 10% to 55% Fe, about 0.2% to 10% Al, about 0.5% to 15% Mg, about 0.1% to 5% Mn, about 1% to 5% Cr, about 1% to 25% Si0₂ and the balance loss-on-ignition constituents ranging up to about 20%.

In its broad aspects, the invention is directed to a process for the recovery of nickel from particulate nickel oxide ores, such as saprolites and limonites, by sulfuric acid leaching said ores to form a pregnant solution of metal values, e.g., nickel and cobalt, which are recovered directly by ionexchange. The ore may be either

atmospherically leached or pressure leached.

In a preferred embodiment, sulfuric acid leaching is carried out at a relatively high temperature and pressure, e.g., 270° and 810 psi. The advantage of employing the sulfuric acid pressure leaching process in an autoclave is that iron is separated from the nickel by dissolving and then reprecipitating from solution as hematite, while the nickel remains in solution. Any iron left in the leach liquor is usually in the ferrous state.

Another embodiment of the process comprises forming an aqueous slurry in the form of a pulp of particulate oxide ore containing by weight about 1.5% Ni and about

0.15% Co and leaching the ore in the presence of sulfuric acid solution at a pH of less than about 0.5. The leaching may be carried out by either atmospheric or pressure leaching. The amount of sulfuric acid solution is at least stoichiometrically sufficient to dissolve

substantially the nickel and cobalt present. In a

preferred embodiment, the pulp is subjected to pressure leaching following injection of sulfuric acid at an elevated temperature of about 150ºC to 300ºC at a pressure ranging from about 150 psig to 1,000 psig to solubilize at least 80% nickel and at least about 80% of the cobalt present in the ore. A typical time of leaching may range from about 15 minutes to 120 minutes.

Following completion of the leaching, a pregnant liquor is obtained containing said nickel and cobalt as sulfates and residual other elements and undissolved residue as tailings.

The acid in the pregnant solution is adjusted to or provided at a pH of about 0.5 to 4 following which the slurry is subjected to countercurrent decantation to separate the pregnant nickel and cobalt solution from said tailings.

The acid in the tailings is neutralized with lime or other base to a pH of about 9 and the tailings disposed of.

The pregnant nickel sulfate solution with the

contained cobalt is contacted with an ion exchange resin under pH conditions selective to the absorption of nickel, while providing a raffinate containing cobalt. The raffinate is thereafter prepared for the removal of cobalt plus any nickel remaining therein by an ion exchange resin under conditions selective to the absorption of cobalt and nickel.

Thus, in essence, the invention provides a process for selectively recovering nickel by ion exchange

absorption from a Ni/Co sulfuric acid feed solution containing nickel in the range of about 0.5 to 40 gpl and cobalt in the range of about 0.01 to 2 gpl as sulfates. The process comprises contacting the nickelcontaining acid solution at a pH ranging from about 0.3 to 6 with a bed of protonated ion exchange resin in which protons associated with said resin are exchangeable with nickel ions in the solution. The protonated resin selectively extracts the nickel in preference to cobalt from the solution at a pH of less than about 2. The low pH is generally achieved by proton ions entering the solution as the nickel ions are absorbed by the resin. The absorbed nickel is then stripped from the resin with sulfuric acid to form a nickel sulfate solution characterized by a nickel to cobalt ratio of at least about 50:1 suitable for the recover of substantially pure nickel by electrolysis. In a preferred embodiment, the pregnant nickel solution is passed serially through a plurality of moving columns of the resin which move countercurrently to the flow of the pregnant solution entering the first column and exiting through the last column thereof with the bulk of the nickel removed in the initial columns and the nickel-impoverished solution containing cobalt thereafter passing through the last column. In one embodiment, the ISEP^® continuous contactor manufactured by Advanced

Separation Technologies, Inc. of Lakeland, Florida of the carousel type is employed.

In another embodiment, the pregnant nickel solution may be passed serially through two stationary columns of resin in a Recoflo^® ion exchange system produced by Eco-Tec Inc. of Pickering, Ontario, Canada. When nickel starts to "break through" the second column, the feed solution is stopped and the first column only is stripped of the loaded nickel with sulfuric acid solution. After stripping, the feed solution is again passed through the two columns serially, except the second column now becomes the "lead" column for feeding the pregnant liquor. When nickel begins to break through the first column, now the "lag" column, the feed solution is stopped and the second column is stripped. Then feeding commences once again with the first column as the lead column. This is

equivalent to the counterflow ISEP^® process.

The nickel absorbed by the resin is stripped with sulfuric acid to provide a pregnant solution from which substantially pure nickel is recovered, such as by

electrowinning.

Similarly, the cobalt plus the remaining nickel absorbed in a second ion exchange step is recovered by stripping with a sulfuric acid solution and the mixed cobalt nickel solution then sent to nickel/cobalt

recovery. An important economic advantage of the invention is that sulfide precipitation of nickel and cobalt is

completely avoided, as well as the necessity of recovering said metals by pressure leaching the sulfide precipitate and refining the resultant solution which is cost

intensive.

The invention, on the other hand, takes a more simple and economic route in that following the leaching of the nickel oxide ore, e.g., pressure leaching in the

autoclave, the nickel is directly recovered in

substantially the pure state, by passing the pregnant solution through an ion exchange resin under conditions selective to the absorption of nickel in preference to cobalt following separation of the leach residue from the nickel leach liquor by, for example, countercurrent decantation of the pregnant nickel solution from the washed residue or tailings.

Details Of The Invention

One method of carrying the invention into practice is disclosed in the flowsheet of Fig. 1 as applied to nickel- containing oxide ores, such as limonite.

The limonite ore contained by weight 1.7% Ni, 0.15% Co, 40% Fe, 4% Al, 2% Mg, 2% Mn, 2% Cr, 10% SiO₂ and 15% LOI (Loss On Ignition).

Referring to Fig. 1, the technology employed includes an ore preparation step (1) in which the coarse reject 1A thereof may be used for the neutralization of excess acid. Sulfuric acid pressure leaching (2) is carried out at about 270° C with a leaching time in the range of about 20-40 minutes and generally ranging up to 30 minutes

following injection of the acid into the autoclave. Leach discharge pulp containing the tailings without prior acid neutralization is passed through a conventional

countercurrent (CCD) decantation system which is used to wash soluble nickel plus cobalt values from the slurry. The tailings are separated from the pregnant liquor at 4 and passed on. to tailings disposal at 5. Following

tailings neutralization (5) with limestone and milk of lime, in which the pH is raised to about 9, the residue is disposed of at a tailings dam. The CCD overflow solution 6 is contacted with an ion exchange resin where only nickel (plus copper if present) and only minor quantities of cobalt are loaded (7). Because nickel replaces the proton or hydrogen ion in the active part of the resin, the pH of the solution decreases during ion exchange, whereby the nickel is extracted by the resin in preference to a cobalt at a pH of less than about 2.

The nickel is stripped from the ion exchange resin (7) with sulfuric acid. The nickel-containing solution is neutralized at (8A) with limestone and the neutralized solution subjected to solid/liquid separation with the solids recycled to neutralization (3) and the nickel solution sent to nickel electrowinning (15).

The raffinate 8 with only minor amounts of nickel plus most of the cobalt and other impurities (iron, aluminum, manganese,, magnesium, chromium, etc.), is further neutralized at (9) with limestone to a pH of about 2 to 4. The solids and liquid are separated at (10), the solids sent to tailings disposal (5) and the nickel/cobalt solution (11) sent to cobalt recovery 12 with the

raffinate 13 depleted in cobalt recycled to tailings disposal (5). The nickel/cobalt following ion exchange is substantially pure and free of the contained impurities.

The purified cobalt solution is treated for recovery of cobalt as a salable commodity, either by soda ash precipitation, sulfide precipitation or electrowinning. The nickel loaded on the resin (7) may be stripped with spent electrolyte (16) from the nickel electrowinning circuit (15). Prior to returning the stripped resin to loading, the resin is washed with water which converts the resin from the bisulfate into the sulfate form, releasing sulfuric acid which can be reused for stripping.

Tests were conducted using DOW's XFS-4195 as the resin both for nickel loading as well as cobalt/nickel loading. Other resins which may be used include Rohm and Haas IR-904, Amberlite XE-318, and DOW XFS-43084. As disclosed hereinafter, the DOW resins have picolylamines as active groups.

The DOW resins which are sold under the trade

designations XFS-4195, XFS-4196 and XFS-43084, are

macroporous resins of polystyrene/divinylbenzene

copolymers onto which weakly basic chelating picolylamine derivatives have been attached.

DOW resin XFS 4195 is a stronger and preferred completing agent for nickel than the other resins

hereinabove. The functional groups in the XFS 4195 and XFS 4196 resin are more specifically referred to as bis(2-picolyl)amine and N-(2hydroxyethyl-2-picolylamine, respectively.

The XFS 43084 resin is similar to the resins above, that is, the resin is a macroporous polystyrene copolymer with a weakly basic chelating picolylamine derivative attached, i.e., specifically N-(2-hydroxypropyl)-2-picolylamine.

With respect to the XFS-4195 resin, the following

Table 1 taken from the DOW literature shows the absorption constants of various metals.

The absorption constant is really not a constant but a function of the pH, as shown in the attached Figure 2 published by DOW chemical. A DOW Chemical publication indicates that from a practical standpoint, a resin will be loaded to 5₀% of its maximum value when K=100 and when [Me] = 0.01 M (i.e. 0.6 gpl Ni). The importance of keeping the pH low will be apparent from Figure 3. This figure clearly shows that it is advantageous to keep the pH of the pregnant solution low if one wants to

selectively remove nickel from laterite leach solutions containing nickel and cobalt. At the optimum pH of 1 the ratio of the nickel and cobalt K-factors is 8 compared to around 2 at the usual, and customary operating pH for SX or IX of 2-3. This shows an improved selectivity of about 400%.

In carrying out the novel process of the invention, it is the Ni/Co ratio in the product which is important. For example, if the Ni/Co ratio in the electro-winning of nickel is better than 50:1 and particularly better than 90:1 or 100:1,, a high quality nickel product is

obtainable.

Likewise, with respect to the electrowinning of cobalt, the Co/Ni ratios are similarly important. An example of a desirable ratio is a ratio which is at least about 50:1 preferably 80:1 or 100:1.

Previous nickel/cobalt studies on the use of DOW XFS-4195 resin were concentrated on the removal of small quantities of nickel from low acid, high grade

cobaltiferous solutions contaminated with nickel.

Generally, these solutions contain between 20 and 100 gpl Co and have a cobalt to nickel ratio of about 100 to 1.

Ion exchange treatment of these solutions extracted nickel but also a great deal of cobalt. The laterite leach solutions treated in accordance with the invention

contained about 0.5 gpl Co and have a cobalt to nickel ratio of 0.1 to 1. According to the method employed, it has been possible to "crowd off" nearly all of the cobalt from the resin during nickel absorption, while at the same time extracting substantially all of the nickel. Thus a strip solution is produced having an adequate Ni/Co ratio for direct electrowinning and for achieving high nickel recovery without additional Ni-Co separation. Thus, it is now possible to extract up to 99% of the nickel without significant coextraction of cobalt (less than about 10%).

In the present invention, much improved selectively of the chelating ion exchange resins with respect to nickel over cobalt is achieved by controlling the

conditions during resin loading to ensureθthat any cobalt loaded on the resin is displaced by nickel. Furthermore, the free acid content of the aqueous solution is also controlled to prevent cobalt loading and thus increase the Ni/Co ratio in the solution obtained by stripping the loaded resin with sulfuric acid. This is achieved by:

1) ensuring that "fresh" resin, i.e. resin

containing little or no extracted nickel or cobalt, is contacted with liquor of relatively high acid content, and (2) ensuring that "fresh" feed solution of

relatively low acid content is contacted with resin which has already loaded a substantial quantity of nickel, and further ensuring that the resin is loaded to a level close to its theoretical maximum capacity for nickel, i.e., the level which would be achieved if a quantity of resin were contacted repeatedly with fresh solution containing excess nickel.

Thus, cobalt loading can be substantially eliminated and virtually-complete nickel loading can be achieved. The best method of achieving these conditions is to contact resin with leach solution in-a true countercurrent fashion. Very few ion exchange systems, however, permit resin flow and those that do suffer from the engineering problem of resin breakage by attrition and other

mechanical forces. Two other types of equipment which allow the conditions described above to be achieved are detailed in the examples which follow. Both of these systems produced "pseudo" countercurrent flow of resin and solution, as will be described later. The first condition is met because the solution naturally acidifies as nickel is loaded onto the resin by the release of protons from the resin. Thus, even though fresh resin may load both cobalt and nickel, cobalt loading is impeded due to the high acidity (see Fig. 2). Cobalt does not load from the fresh feed solution, even though the pH may be higher, because the resin is already loaded close to its maximum capacity with nickel and therefore thermodynamically incapable for cobalt to displace nickel on the resin.

Direct nickel electrowinning from laterite leach solutions as obtained is not generally feasible because of the impurities present in the solution. In particular, chromium, aluminum and iron present a problem. In the nickel plating industry, hexavalent chromium has to be limited to less than 10 ppm to maintain a good quality deposit. On the one hand, XFS-4195 has a disadvantage in that it has a very high affinity for hexavalent chromium

(it does not load trivalent Cr). Sulfuric acid strips the hexavalent chromium which normally contaminates the electrolyte. Thus, it is important to keep the amount of hexavalent Cr in the IX feed to a minimum. XFS-4195 is also selective for copper. Laterite leach solutions have up to about 50 ppm Cu and up to 300 ppm total chromium, of which about 10% or more may be present as hexavalent Cr. A pretreatment step for removing both Cu and hexavalent Cr can be included as a preferred embodiment of the

processing invention. This pretreatment step can either be a metal cementation step using iron, zinc or even nickel to reduce hexavalent Cr to the trivalent state and to cement copper. Alternatively, an ion exchange column may be included that is specifically used to load both hexavalent Cr and Cu from the leach solution. After this treatment, the leach solution can then be treated by the ion exchange approach discussed herein. Another

alternative approach is the removal of the copper and hexavalent chromium from the pregnant electrolyte after ion exchange. In carrying out the invention, the best results were obtained with a system operating under hot and acidic conditions. Both conditions are met by pressure leaching and ion exchange which provides hot and acidic solutions. Because of the natural pH of about 1 of the autoclave discharge solution,, an efficient Ix separation of Ni and Co obtains. Thus, the neutralization step 3 of Fig. 1 can be omitted. In addition, ion exchange with XFS 4195 can be carried out at temperatures up to at least the normal boiling point of the leach liquor; whereas, in the case of solvent extraction of nickel, it is generally advised to keep the temperatures lower than 50 degrees Celsius and that the pH be greater than 2. The effect of the bisulfate and sulfate equilibrium will clearly appear from the following.

Nickel Ion Exchange Combined With

Pressure Sulfuric Acid Leaching

A novel aspect of the invention is the fact that the XFS4195 resin has the ability of being converted from the sulfate to the bisulfate form by taking up sulfuric acid as follows:

[R-H⁺.1/2SO₄ ^2-] + 1/2H₂so₄ = [R-H⁺.HSO₄ ^-1 (1) wherein R is the bis-picolylamine group and the bracket indicates a species in the resin phase. Alternatively, if the resin is in the bisulfate form, a sulfuric acid

solution can be generated when the resin is stripped with water. (Equation 1 shifts then to the left. This ability of the resin to extract sulfuric acid allows nickel loading onto XFS-4195 from an acidic solution because conversion of the resin from sulfate to bisulfate form during nickel loading prevents the solution pH from being lowered further, thus maintaining a relatively high nickel absorption constant. This is illustrated by reaction (2):

2[R-H⁺.1/2SO₄ ^2-] + Ni²⁺ + SO₄ ^2- = [R₂-Ni²⁺. (HSO₄-)₂] (2) The sulfuric acid loaded on the resin at the same time can be stripped from it by water washing. This is clearly advantageous since laterite leach solutions tend to have a high acidity, which normally would have to be neutralized prior to nickel recovery. A further advantage of using acid-bearing leach solution is that Co loading can be virtually eliminated because the solution pH is always too low to load any appreciable amount of cobalt.

Another feature for the combined approach of the invention is the advantages of pressure leaching with its high solution temperatures. There are presently liquid organic compounds available that can extract nickel and cobalt from laterite leach solutions. However, solution cooling is required since solvent extraction does not operate efficiently at temperatures higher than say 50ºC. Ion exchange resins, on the other hand, can be

beneficially used at higher temperatures in that the loading kinetics are favorably affected. Using naturally hot leach solution saves on solution cooling and even improves the ion exchange efficiency. Another embodiment of the invention is the use of a hot resin-in-pulp (RIP) process. Solid/liquid separation can be quite cost intensive when processing chemically treated ores and this can be avoided by employing resin directly in the leach slurry. One example of the RIP route is illustrated by one of the following examples:

The higher temperatures have an impact on the

sulfate/ bisulfate equilibrium. Sulfuric acid

disassociates as follows:

H₂SO₄ - - - - > H⁺ + HSO₄ ^-1 (3)

H₂SO₄ - - - - > H⁺ + SO₄ ^-2 (4)

Equation (3) shifts completely to the right under all conditions of the acid leaching process. Equation (4), however, shifts only to the sulfate side at higher pH and lower temperatures. The bisulfate to sulfate ratio as a function of the temperature and pH is calculated as

follows in Table 2.

It has been recommended that the IX system be

operated at a feed pH in the order of about 2 or that the raffinate has a pH of about 1. At room temperature, this will provide an HSO4/SO4 ratio of 1.0. This means that, for a solution with 50 gpl total sulfate, 50% of the sulfur or 25 gpl is present as bisulfate and 25 gpl as sulfate. One preferred method of carrying out the

invention is hot with about 25 gpl free acid in the leach solution. This translates into an HSO₄/SO₄ ratio of about 50. In such a case, 98% of the sulfate is present as bisulfate with only 2% as sulfate. Thus, with a 50 gpl total sulfate solution, this indicates that 49 grams are

represented as bisulfate and only 1 gram as sulfate. In other words, the ion exchange process can tolerate more free acid in solution as the process temperature is raised.

In the flowsheet for processing lateritic ore, the kinetics of nickel loading on the resin are rather slow at room temperature. It is not economically advisable to heat the solution to improve reaction kinetics. However, with respect to the invention, the leach discharge is generally near its boiling point and an advantage is obtained since the nickel loading will be done hot without the need for additional heating. The improved kinetics usually result in a significant increase in resin capacity in that, in carrying out the invention, the resin is capable of being loaded at a rate of at 30 Bed Volumes (BV) per hour while conventionally the maximum is about 5 BV/hr.

It has been noted that there may be a problem with respect to both chromium and aluminum as possible

contaminants in the electrolyte. This might occur if the ion exchange resin is not washed efficiently prior to nickel stripping. Both aluminum and chromium (III) must be prevented from entering the nickel electrowinning circuit. Efficient resin washing ensures they do not contaminate the electrolyte because Cr (III) and Al do not load on the resin. The nickel sulfate feed to the

electrowinning cell generally should be at a pH of 2.5 to 3.5 to obtain the best deposition characteristics. Test work in the laboratory has shown that raising the pH of the eluate going to the electrolytic cell not to 2.5-3.5, but to 4.5 to 5.5, removes any aluminum and chromium which pass through the ion exchange system, down to less than about 10 ppm levels. Little nickel will precipitate at this pH. However, in order to provide the optimum cell feed compositions, it is necessary to re-acidify the cell feed with acid to the required lower pH.

As illustrative of the invention, the following example is given: Example 1

Particulate lateritic oxide ore is formed into a pulp with water and screened at 28 mesh (U.S. Standard). The composition is comprised of 1.5% Ni, 0.14% Co, 4% Al, 0.8% Mg and the balance substantially iron, i.e., 42% Fe, present as oxides or hydroxides.

The coarse fraction (approximately +20 mesh) is separated from the ore and may be used for atmospheric leaching by

including this step in the flowsheet of Fig. 1 and the nickelcontaining solution thereof joining the pregnant leach solution at the acid neutralization station.

Preferably, the fines fraction of the ore, which is passed to pressure leaching 2 of the flowsheet, is first pulped with water or an aqueous solution to a pulp density of about 35%. Sulfuric acid is added to provide an acid to ore ratio of 0.2:1 to 0.3:1 based on weight of

concentrated sulfuric acid and the dry weight of the ore.

The pulp is pressure leached in an autoclave at a temperature of about 270ºC under a total pressure of about 810 psia, the sulfuric acid being added to the pulp in the autoclave by injection.

Under these conditions, the ore is leached in about 15 to 60 minutes and the nickel extracted to about 95% based on the amount of nickel in the ore.

At this temperature, the iron and aluminum in the solution are substantially rejected and appear in the tailings as basic aluminum sulfate (alunite) and hematite (Fe₂O₃).

Following leaching, the pregnant nickel solution is passed on to acid neutralization at (3). The solution is neutralized with limestone to a pH of about 2, after which the neutralized slurry is subjected to solids/liquid separation at (4). In a preferred embodiment, the

neutralization step (3) may be omitted. The separated solution is passed to an ion-exchange apparatus (7) containing an ion-exchange resin specific to the

extraction of nickel.

In some tests, a commercially available ion exchange apparatus (Note Figs. 5, 5A and 5B) referred to as an "ISEP" apparatus was employed in carrying out the

extraction of nickel. In other tests, the commercially available apparatus known as "Recoflo" was used.

The ratio of nickel in the feed solution to the quantity of resin employed is such as to provide 95% of resin loading capacity while extracting 95% of the nickel. This helps to ensure complete "crowding" off of cobalt, that is, the preferential loading of nickel over that of cobalt.

As stated herein, a particularly advantageous ion exchange resin is one identified as DOW XFS 4195 in which the active ingredient is bis-picolylamine.

Following selective removal of nickel at (7) , the raffinate remaining is subjected to acid neutralization at (9) with limestone to a pH of about 2 to 4.5, following which the slurry from acid neutralization is passed to solid-liquid separation at (10) and the solution

containing cobalt and the remaining nickel is passed on to cobalt recovery.

Reference is made to the schematic of Fig. 8 which is a simplified illustration of the general operation of the ISEP configuration.

Fig. 8 is a schematic of Figs. 5, 5A and 5B,

illustrating the use of a carousel, as one embodiment, comprising a series of resin-loaded columns 1, 2, 3 and ranging up to the Nth column, arranged and adapted to provide a serial pathway for the solution 5 from the first column to the Nth column, the interruption in the system at 4 indicating that other resinloaded columns may be present in the system between the 3rd and Nth columns.

The rotational arrangement of the columns shown in Fig. 5 is such that the flow direction 6 of the resin loaded columns of Fig. 8 (i.e., the direction of travel of the resin columns) is counter to the flow direction of the nickel pregnant solution through the columns as shown, i.e., countercurrent flow) whereby the resins of each succeeding column remove the nickel from solution with the raffinate solution 7 containing cobalt flowing out of the system for the subsequent recovery of said cobalt.

A more detailed schematic is shown in Figs. 5A and 5B to be discussed later.

In recovering the nickel from the pregnant solution, the acid pH is preferably maintained at a level selective to the absorption of nickel, the pH being such that the nickel crowds off or substantially inhibits the absorption of cobalt. The nickel to cobalt ratio in the resin following substantially complete recovery of nickel is at least about 50:1 or at least 90:1 or higher.

The cobalt-containing raffinate solution

substantially impoverished in nickel may then be treated after a pH adjustment, if necessary, to recover the cobalt using a resin and conditions selective to the absorption of cobalt, e.g., DOW FXS 4195.

Additional examples illustrating the novel process are as follows:

Example 2

Ion exchange tests were conducted on a nickel

sulfate/cobalt sulfate solution having a Ni/Co ratio corresponding generally to that produced by leaching a typical limonite ore. The solution contained 12.5 gpl Ni and 1 gpl Co and had a pH of 3. The solution had a

temperature of about 25ºC and was passed through a column of diameter 1 3/16 inches containing 200 ml of DOW XFS 4195 at a flow rate of 13.3 ml/min corresponding to 4 BV/hr (bed volumes/hr.). Each 100 ml of the column effuent was collected as a separate sample and assayed for Ni and Co. From the this data, the cumulative percentage loading of Ni and Co contained in the feed solution was calculated and plotted as a function of the solution volume passed as shown in Fig. 4.

The curves in Fig. 4 demonstrate some selectivity for Ni over Co. However, the data also show that very low Co loading, say <20%, cannot be achieved while maintaining very high Ni loading, say >90%, in a single column. For example, after passing approximately 7.5 bed volumes of feed solution through the resin column, around 20% Co loading and only around 50% Ni loading were achieved. It is apparent from this example that it would be difficult to achieve the degree of separation desired from a single column.

From the data of Example 1 and the selectivity data of Fig. 3, the advantages of the present invention are quite apparent. In such a system, fresh resin would be contacted with a solution already depleted in nickel because a portion of the nickel would already be loaded on the resin further "upstream". This depleted nickel solution would contain a higher sulfuric acid

concentration than the feed solution because acid is produced by the ion exchange reaction as follows:

[ 2 (RH⁺) (SO₄ ^2- ) _1/2] + Ni²⁺ - - - - > [ (R₂Ni₂₊) (SO₄ ^2-) ] +2H⁺

Thus, cobalt loading on the fresh resin would be suppressed due to the lower pH environment (see Figs. 2 and 3), despite the fact that fresh resin normally loads both Ni and Co (see Fig. 4 at a low number of bed volumes feed passed). At the solution feed inlet of the "loading zone," partially loaded resin is contacted with fresh Ni and Co bearing solution at a higher pH. At this

condition, Co loading is suppressed because the resin is already loaded with substantial nickel which cannot be easily exchanged for Co, even at the higher pH of the feed solution.

Further testwork was conducted to demonstrate that high Ni loading and very low Co loading on the resin could be achieved in a countercurrent system. For this purpose. two commercially available ion exchange contactors were employed to carry out the invention, one apparatus,

(similar to Fig. 5) called an "ISEP", is manufactured by Advanced Separation Technologies Inc. of Lakeland,

Florida. It consists of a carousel of 30 ion exchange columns connected to a rotary valve arrangement at the top and bottom of the carousel as means for providing serial, flow through the columns of resin. Each rotary valve consists of a rotating disc attached to the columns and a stationary disc attached to reservoirs of the various process solutions. Each stationary disc has 20 internal ports. Each column on the carousel is connected to a port on the rotating disc at the top and the bottom of the carousel. (There are 30 columns and 30 ports in each rotating disc.) The carousel and rotating disc portions of.the top and bottom valve rotate continuously and the ports in the rotating disc are connected to the ports of the stationary disc in sequence. Thus, the solution pumped continuously into a port or ports of the stationary disc flows serially through each column in sequence as the carousel rotates. A countercurrent flow of solution and resin can thus be effected in this apparatus by the aforementioned indexing means.

A second ion exchange system for carrying out the novel aspects of the invention is referred to as the

Recoflo (trademark) system manufactured by Eco-Tec Inc. of Pickering, Ontario, Canada. In this system, two beds of resin are employed. A cyclic process is used (note Fig. 10) to provide in effect a partial countercurrent flow resin and solution. As will be clearly apparent from Fig. 10, there are eight distinct steps in each cycle,

following which the cycle is repeated.

In step 1, feed solution is passed through beds I and 2 in series. Bed 1 has already been partially loaded with nickel in the preceding step while bed 2 contains fresh resin because it was stripped and washed in the preceding steps. Thus, fresh feed solution is contacted with partially loaded resin and fresh resin is contacted with partially depleted and acidified solution as occurs in the ISEP contactor.

Example 3

The stationary ports of the ISEP apparatus are illustrated in the configuration shown in Fig. 5A. The carousel, containing thirty 1 3/8 inch diameter by lm high columns of Dow XFS 4195 resin, was rotated at 0.2

revolutions per hour. The direction of rotation was such that each column was connected to each numbered port in decreasing number sequence. For example, each column entered the nickel loading portion of the process at port 12, thus effecting a partial countercurrent flow of solution and resin. (Note the simplified schematic of Fig. 8). As can be seen from Fig. 5A, the complete ion

exchange process consisted of four steps:

1. Loading - ports 4-12 in a 3/3 series/parallel configuration;

2. Load wash - ports 2-3 in series;

3. Elution - ports 16-20 all in parallel; and

4. Elution wash - ports 14-15 in series.

In addition, air was passed through ports 1 and 13 to drain out as much solution as possible between the loading and elution zones. The load wash was required to remove impurities in entrained feed solution from each column prior to entering the elution zone. The elution wash was required to remove entrained Ni from each column and prevent its recycle to the loading zone and also to recover sulfuric acid loaded on the resin during elution. All feed, wash and strip solutions were heated to 65ºC prior to entering the ISEP and each column of resin was insulated. The solution flowrates were as follows:

The compositions of the various solution streams after 15 hours of continuous operation in grams/liter were as follows:

There was little change in the assays of each stream with time after 15 hours of operation, indicating a close approach to steady-state.

Based on the raffinate and feed compositions and measured flow rates, the Ni and Co extractions from feed solution were 95% and 13%, respectively, producing a Ni/Co ratio in the eluate of >300:1. Based on the feed solution composition of 6.6 g/L Mg and the eluate composition of 0.2 g/L Mg, only 1.8% of the Mg in the feed was passed to the eluate by solution entrainment, indicating >98% washing efficiency in the load wash stage. The other impurities, including Al and Mn, behaved similarly to Mg.

An examination of the free sulfuric acid assays illustrates the loading and stripping of sulfuric acid which occurs in the elution and elution wash stages, respectively. Elution of divalent metals, such as Ni, requires theoretically 1 mole of sulfuric acid per mole of metal. Thus, 21.9 g/L Ni in the eluate corresponds to a theoretical acid consumption of about 37 g/L H₂SO₄. The actual consumption of acid was approximately 108-20 = 88 g/L H₂SO₄, indicating substantial loading of sulfuric acid. This occurs due to reaction (1). The high level of sulfuric acid (93 g/L) in the elution wash stream

indicates that the loaded acid is stripped from the resin in this section by reversal of reaction (1). This is important in order to achieve efficient utilization of sulfuric acid in the elution stage and to ensure that the resin is in the "sulfate form" when it enters the loading zone. If the resin entered the loading zone in the

"bisulfate form", additional sulfuric acid would be liberated during loading and this would impede maximum nickel loading.

The foregoing illustrates the benefits of employing countercurrent flow of resin and feed solution to achieve efficient Ni recovery and an efficient separation of Ni and Co in the feed stream. The Ni/Co ratio of 310 in the eluate is sufficient for direct electrowinning of good quality Ni cathodes, although not of so-called Class I quality (Ni/Co 1670:1). These cathodes would certainly be usable for stainless steel manufacture as the main source of Ni for the production of stainless steel is ferronickel, which typically has a Ni/Co ratio of only 30-40:1.

Example 4

The test configuration and flow rates in this test were exactly the same as in Example 2 except all solutions were maintained at ambient temperature, around 20ºC. The various solution analyses after 9 hours running were as follows:

In this test, Ni and Co extractions were

approximately 74% and 6%, respectively. The advantage of higher solution temperatures is clearly seen by comparing this result with the result of Example 3. Example 5

The configuration of the ISEP for this test was only slightly different from Examples 3 and 4, as shown in Fig. 5B. The main difference is that the acidity of the feed solution was 25 g/L H₂SO₄, which is about the natural acidity expected for high pressure acid leach solution. Also, the strip solution was a "synthetic" spent

electrolyte, as normally produced by electrowinning Ni directly from neutralized eluate, as shown in Fig. 1.

The solution flowrates were as follows:

The results of this test after 14 hours of operating time are given below:

Ni and Co extractions in this test were approximately 86% and 0.4%, respectively. Surprisingly, very good Ni extraction was achieved despite the high acidity of the feed solution.

Nickel and sulfuric acid mass balances using the above data show that in the loading section net production of H₂SO₄ was only 0.5 moles per mole of Ni loaded on the resin. This indicates that some sulfuric acid liberated by Ni loading actually reloads on the resin via reaction (1), thus limiting the free acid content of the raffinate and permitting substantial Ni loading despite the high acidity of the feed solution.

The other significant advantage apparent from this example is that Co loading is virtually prevented by maintaining relatively high acidity throughout the loading zone. Thus it is possible to produce an extremely high Ni/Co ratio in the eluate by this technique. The Ni/Co ratio of 263 achieved in Example 4 was limited due to the presence of Co in the synthetic nickel spent electrolyte used for elution.

From the foregoing example, it is obvious that high quality Ni cathodes could be produced by neutralizing the eluate and feeding this solution to a conventional Ni electrowinning cell.

Example 6

A test was carried out with a Recoflo apparatus comprised of two 2 inch diameter columns 12 inches high containing DOW XFS 4195 resin. The two columns were connected in series and operated cyclically as illustrated in Fig. 10. The solution flow rates were maintained at about 0.4 L/min and each solution was heated to 70ºC. The feed solution contained 9.75 g/L Ni, 0.94 g/L Co, 2.1 g/L Al, 5.5 g/L Mg, 2.05 g/L Mn and had a pH of about 2. The strip solution contained 100 g/L H₂SO₄. A steady state condition was achieved after 10 complete cycles of

operation with the following results.

The eluate was collected as two separate fractions, the first fraction consisting mainly of displaced wash water.

In practice. Wash 1 and Eluate 1 would be recycled to the feed solution, whereas. Wash 2 would be used to make up fresh strip solution. Based on raffinate and Eluate 2 compositions, about 99% of Ni extraction and about 10% Co extraction to the product stream (Eluate 2), were obtained in which' -"the product exhibits a Ni/Co ration of about 110.

Example 7

Referring to the ISEP configuration, the stationary ports were arranged as shown in Fig. 9. The carousel was rotating at 0.13 revolutions per hour. All feed, wash and strip solutions were heated to 20ºC prior to being fed to the ISEP apparatus. The flow rates of each solution were as follows:

After 8 hours of operation, the following solution assays were obtained:

Based on the eluate flowrate and composition, 96% of Ni recovery, 93% Co recovery, and <<1% Mg recovery were achieved to the product stream. 0.45 moles Ni + Co were loaded per liter of resin in the loading step.

This example illustrates the ability of the ion exchange system to load both nickel and cobalt under conditions of relatively low acidity (<15 g/L H2so4) and a resin loading less than the resin maximum capacity (-0.65 moles Ni+Co per liter resin). A pure cobalt plus nickel solution is obtained which can be treated for cobalt recovery via methods apparent to those skilled in the art.

Example 8

A resin-in-pulp test was carried on a pregnant leach liquor produced as follows:

A sample of limonite of 30% solids was batch leached with concentrated sulfuric acid in an autoclave at 270ºC to produce a leach slurry. The pH of one liter of leach slurry was adjusted to 3.7 with calcium carbonate and the slurry was then mixed with 200 mL of Dow XFS 4195 resin for 2 hours at room temperature. The resin was recovered from the slurry by screening over a 50 mesh screen. The leach solution before and after treatment with the resin assayed as follows:

The pH of the solution during ion exchange, decreased to about 2. Based on the raffinate composition Ni and Co recoveries were estimated at 96% and 88%, respectively. Iron and zinc were also extracted. It should be noted, however, that iron dissolution during leaching can be prevented by careful control of leaching conditions.

Thus, a substantially pure Ni and Co solution can be produced for further processing to recover pure cobalt and pure nickel.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are

considered to be within the purview and scope of the invention and appended claims.

Claims (27)

WHAT IS CLAIMED IS:

1. A process for selectively recovering nickel by ion exchange absorption from a Ni/Co sulfuric acid feed solution containing nickel in the range of about 0.5 to 40 gpl and cobalt in the range of about 0.01 to 2 gpl as sulfates which comprises:

contacting said acid solution at a pH ranging from about 0.3 to 6 with a bed of protonated ion exchange resin in

which protons thereof are exchangeable with nickel ions in said solution

during ion exchange, selectively extracting said nickel in preference to cobalt from said

solution at a pH of less than about 2, and forming a raffinate containing

said cobalt; and then stripping the absorbed nickel from said resin with sulfuric acid-to form a nickel sulfate solution

characterized by a nickel to cobalt

ratio of at least about 50:1 suitable for the recover of substantially pure nickel by electrolysis.

2. The process of claim 1,

wherein said resin is confined as beds in a series of columns ranging from a first column to an Nth column, said series of columns being adapted

by means to allow pregnant solution to flow serially from said first column to and through said Nth column while said columns of resins are caused to move countercurrent to the flow of said nickel-containing solution

through said columns.

3. The process of claim 2,

wherein said columns of resins are provided in a carousel type

configuration, and wherein said

carousel is caused to rotate

countercurrent to the serial flow of the pregnant solution through said columns of resin.

4. The process of claim 2,

wherein the raffinate containing

cobalt is sent to cobalt recovery

5. The process of claim 4,

wherein the absorption of nickel by the resin is conducted at a

temperature ranging from about 40 ºC to

80'C.

6. The process of claim 1, wherein the resin comprises as an active ingredient bis-picolylamine selective to the absorption of nickel in preference to cobalt at a pH of less than about 2.

7. The process of claim 1,

wherein said resin is comprised of a

first bed and a second bed serially arranged one with respect to the

other, wherein said beds are adapted to allow

fresh nickel-containing feed solution to flow serially and partially

countercurrently therethrough by

cyclically employing a plurality of

steps, wherein during cycle operation of the ion exchange process, the first bed is partially loaded with nickel from a

preceding step and wherein said second bed is comprised of fresh resin

produced when the nickel is stripped therefrom with sulfuric acid and the resin washed, the plurality of steps employed being such that fresh feed solution is

contacted with partially loaded resin, and form a partially depleted

acidified feed solution, the partially depleted acidified feed solution being-then contacted with a bed of fresh resin, thereby extracting substantial amounts of nickel from said feed solution.

8. A hydrometallurgical sulfuric acid leaching process for recovering nickel from particulate nickel oxide ore containing by weight at least about 0.5% Ni and at least about 0.005% Co which comprises:

providing an aqueous pulp of said

particulate ore. leaching said ore at an elevated

temperature and pressure with an addition of an amount of sulfuric acid at least sufficient stoichiometrically to effect the leaching of contained nickel and cobalt and thereby provide a pregnant solution of nickel sulfate and cobalt sulfate and tailings of said ore, separating said pregnant solution from said tailings, contacting the pregnant solution at a pH ranging from about 0.3 to 6 with an ion- exchange resin selective to the absorption of nickel, extracting said nickel at a pH of less than about 2 by moving the resin countercurrent to the flow of pregnant solution through said resin,

[whereby] such that said nickel is

selectively absorbed by said resin at said pH of less than about 2 in preference to said cobalt,

[and] whereby a raffinate is produced deficient in nickel and containing cobalt.

9. The process of claim 8,

wherein said resin is confined in a series of columns ranging from a first column to an Nth column. said series of columns being adapted by

means for the pregnant solution to flow serially from said first column to and through said Nth column (while) under conditions of countercurrent flow of said pregnant solution with respect to said column of resins.

10. The process of claim 9 wherein said columns of resins are provided in a carousel type configuration, and wherein said carousel rotates countercurrent to the serial flow of the pregnant solution through said columns of resin.

11. The process of claim 9,

wherein the raffinate containing cobalt is sent to cobalt recovery.

12. The process of claim 11, wherein the absorption of nickel by the resin is conducted at a temperature ranging from about 40ºC to 80ºC.

13. The process of claim 8,

wherein the resin comprises as an active

ingredient bis-picolylamine selective to

the absorption of nickel relative to cobalt at a pH of less than about 2.

14. A hydrometallurgical sulfuric acid leaching process for the recovery of nickel from particulate nickel oxide ores containing at least about 0.5% of nickel and at least about 0.005% cobalt by weight which comprises:

providing an aqueous pulp of said

particulate oxide ore, charging said pulp into an autoclave, said pulp being heated to an elevated temperature sufficient to effect sulfuric acid leaching of the ore in said pulp, subjecting said pulp in the presence of sulfuric acid to leaching at said elevated temperature and elevated pressure

sufficient to effect the dissolution of nickel and cobalt in said ore and form a pregnant solution thereof and an

undissolved residue as tailings, adjusting the acid in the pregnant solution to a pH of about 0.3 to 6, subjecting the leached pulp to washing and thereby separate the pregnant solution from said tailings, contacting said pregnant solution with an ion exchange resin under pH conditions selective to the absorption of nickel in preference to cobalt and thereby remove substantial amounts of nickel from said solution. said absorption being carried out under conditions of countercurrent flow of said pregnant solution relative to said resin, stripping said nickel from said resin with an aqueous solution of sulfuric acid at a pH sufficient to recover substantially all of the nickel as a nickel sulfate solution. and form a cobalt-containing raffinate depleted in nickel, and then sending said nickel sulfate solution to nickel recovery.

15. The process of claim 14,

wherein said cobalt-containing raffinate is adjusted to a pH ranging from about 1 to 6 to provide a solids/liquid slurry containing said cobalt as a cobalt sulfate solution, wherein said cobalt-containing

solids/liquid slurry is subjected to separation to provide a solution of cobalt sulfate, wherein said cobalt sulfate solution is contacted with an ion-exchange resin under pH conditions selective to the absorption of cobalt, wherein the cobalt is stripped from said resin with a sulfuric acid solution of concentration ranging from about 10 to 100 gpl to form a cobalt sulfate solution thereof; and wherein said cobalt sulfate solution following stripping is sent to cobalt recovery.

16. The process of claim 15 wherein said nickel oxide ore is selected from the group consisting of lizonite and saprolite ores.

17. The process of claim 14, wherein the ion

exchange resin for absorbing nickel is a resin which has an active ingredient comprising bis-picolylamine selective to nickel extraction.

18. A hydrometallurgical process for the recovery of nickel from particulate nickel oxide ores selected from the group consisting of limonite and saprolite ores containing by weight at least about 0.5% of nickel and at least about 0.005% cobalt which comprises:

forming an aqueous slurry of said

particulate oxide ore to provide a pulp having a density of about 25% to 70%, charging said pulp into an autoclave, said pulp being heated to an elevated, temperature, sufficient to effect

sulfuric acid leaching of said pulp, injecting into said autoclave an amount of sulfuric acid at least stoichiometrically sufficient to effect leaching of said contained nickel as nickel sulfate and said contained cobalt as cobalt sulfate, subjecting said pulp to pressure leaching at an elevated temperature and pressure of about 240ºC to 300ºC and 200 psig to 1,000 psig sufficient to effect the dissolution of nickel in said ore and form a pregnant nickel sulfate solution containing cobalt and undissolved residue as tailings, adjusting the acid in the pregnant solution, to a pH of about 0.3 to 6, if necessary, subjecting the leached pulp to a first liquidsolid separation step and thereby separate the pregnant nickel solution from said tailings, contacting said pregnant nickel sulfate solution with a protonated ion exchange resin selective to the absorption of nickel at a pH of less than about 2 and thereby selectively remove substantial amounts of nickel from said solution in preference to cobalt, said absorption being carried out under conditions of countercurrent flow of said pregnant solution

relative to said resin, stripping said nickel from said resin with an aqueous solution of sulfuric acid of concentration about 25 to 200 gpl

sufficient to recover substantially all of said nickel as a nickel sulfate solution, and thus form a raffinate depleted in nickel and containing cobalt, passing said nickel sulfate solution to nickel recovery, adjusting the pH, if necessary, of the nickel-depleted cobalt-containing raffinate to about 1 to 6, subjecting said cobalt-containing raffinate to a second solids-liquid separation step with the solids thereof recycled to said first solid-liquid separation step and provide a cobalt sulfate solution, contacting said cobalt sulfate solution at a pH of about 1 to 6 with an ion-exchange resin selective to the extraction of cobalt, stripping said cobalt from said resin with sulfuric acid at a concentration of about

10 to 100 gpl and thereby extract said cobalt as a cobalt sulfate solution, and passing said cobalt sulfate solution to recovery.

19. The hydrometallurgical process of claim 18, wherein the recovery of said nickel is achieved by

electrolysis.

20. The hydrometallurgical process of claim 18, wherein the ion exchange resin for absorbing nickel is a resin which has an active ingredient comprising bis-picolylamine selective to the absorption of nickel.

21. The hydrometallurgical process of claims 14 or 18, wherein the ion exchange resin is confined in a plurality of columns arranged to provide a pathway for the countercurrent flow of pregnant solution from a first column to an Nth column

as the columns move countercurrent to the flow of solution passing therethrough.

22. In a process for the sulfuric acid leaching of nickel oxide ore at elevated temperature and pressure, wherein said ore contains by weight about 0.5% to 3% Ni and about 0.005% to 11 Co, wherein said ore is leached to provide a pregnant nickel solution and leached solids, wherein the pregnant nickel solution after removal of the leached solids therefrom contains about 6 gpl to about 15 gpl nickel and about 0.5 gpl to about 2 gpl cobalt,

the improvement which comprises recovering said nickel from said pregnant nickel solution by contacting said solution with a resin at an acid pH selective to the absorption of nickel in preference to cobalt, said contacting being carried out by countercurrent flow of the resin

relative to the flow of the pregnant solution through the resin, such that the nickel during resin absorption crowds off or substantially inhibits the absorption of cobalt by said resin, and recovering said nickel from said resin by stripping with sulfuric acid to provide an eluate in which the nickel to cobalt ratio is at least about 50:1 and provide a raffinate containing cobalt which is sent to cobalt recovery.

23. The process of claim 22, wherein the pH

selective to the absorption of nickel ranges from about 0.5 to less than about 2.

24. The process of claim 22, wherein the absorption of nickel by the resin is conducted at a temperature ranging from

about 40ºC to about 80ºC.

25. The process of claim 22, wherein the resin for absorbing nickel contains bis-picolylamine as an active nickel-absorbing ingredient.

26. The process of claim 22,

wherein said resin is confined in a series of columns ranging from a first column to an Nth column, said series of columns being adapted by means for the pregnant solution to flow serially from said first column to and

through said Nth column while said columns of resins are caused to move countercurrent to the flow of said nickel through said columns.

27. The process of claim 26,

wherein said columns of resins are provided in a carousel type configuration, and wherein said carousel rotates

countercurrent to the serial flow of the pregnant solution through said columns of resin.