WO2002008477A1

WO2002008477A1 - Method for recovering nickel and cobalt from laterite ores

Info

Publication number: WO2002008477A1
Application number: PCT/CA2000/000858
Authority: WO
Inventors: Jean-Marc Lalancette
Original assignee: Nichromet Extraction Inc
Current assignee: Nichromet Extraction Inc
Priority date: 2000-07-21
Filing date: 2000-07-21
Publication date: 2002-01-31
Anticipated expiration: 2003-01-21
Also published as: AU2000262567A1

Abstract

A method for the recovery of nickel, cobalt, iron, chromium and magnesium species from laterite ores by a series of steps which include grinding the ore to produce granules; chlorinating the ore by first subjecting them to gaseous hydrochloric acid and secondly, by curing them with concentrated HCI to form water soluble salts of nickel, cobalt, iron, chromium and magnesium, filtering the solution; selectively recovering nickel and cobalt by a process selected from the group of processes consisting of electrowinning, solvent extraction, specific ion-exchange resins and sulfide precipitation. In one preferred embodiment the values of nickel and cobalt are first isolated from a head solution composed of the chloride salts of nickel, cobalt, iron, chromium and magnesium followed by the isolation of the values of iron and chromium as their respective oxides (Fe2O3 and Cr2O3) and finally by the isolation of the magnesium values as basis magnesium carbonate. In a second preferred embodiment the values of iron and chromium are first extracted as their respective oxides (Fe2O3 and Cr2O3) from the head solution composed of the chloride salts of nickel, cobalt, iron, chromium and magnesium by a thermal treatment at a temperature range of 100-200 °C, followed by the extraction of the values of nickel and cobalt and then finally by the isolation of the magnesium values as basic magnesium carbonate.

Description

TITLE OF THE INVENTION

Method for recovering nickel and cobalt from laterite ores.

FIELD OF THE INVENTION The present invention pertains to a method for the recovery of nickel and cobalt from laterite ores containing nickel, cobalt as well as iron, chromium and magnesium. It also relates to a method to recover most of these values in useful forms.

BACKGROUND OF THE INVENTION

Laterites are porous clay-like rocks largely impregnated with ferric hydroxide. It is a residual weathering product of such rocks as basalts, granites and shales. Laterites occur widely in India, East Indies, Australia, in the equatorial regions of Africa and in various parts of South America and Cuba and contain more than 50% of hydrated ferruginous matters and some alumina, magnesium oxide, silica and many other elements such as chromium, cobalt, nickel and manganese. It may incorporate traces of platinum and other metals of the platinum group along with gold. For that reason, several techniques have been developed in order to extract the valuable species from the laterites.

In US patent 4,548,794 issued to Lowenhaupt et al. on October 22, 1985, Lowenhaupt et al. describe a method of recovery of nickel, cobalt and other metals from laterite ores by leaching the high magnesium fraction of the ore with hot sulfuric acid, under pressure, the excess acid being neutralized by low temperature contact with a low magnesium fraction of the starting ore.

In an other process described in US Patent 3,644,114 issued to Lowenhaupt et al. on February 22, 1972, the laterite ore is reduced by an appropriate agent such as water gas and then leached for such a period of time to allow reprecipitation of initially dissolved magnesium compounds.

Gandon et al., in US Patent 3,661 , 564,issued on February 5, 1980, describe a method of recovery of nickel and cobalt from laterite with the elimination of iron, a minor portion of the ore being treated by HCI and then slurried with the major portion of the ore to give chlorides of cobalt and nickel by heating, said chlorides being leached while ferric chloride remains in the residue. The chlorides of nickel and cobalt are then separated by ion exchange resins.

Nickel and magnesia can be recovered from laterite ores, according to US Patent 4,125,588 issued to Hansen et al. on November 14, 1978, by grinding the ore and preparing a slurry with concentrated sulfuric acid, the heat produced by further addition of water giving a solution of magnesium and nickel sulfates.

Sauter reports in US Patent 4,187,281 issued on February 5, 1980 the recovery of nickel from ores by reductive treatment or roasting at 500-900 °C followed by ammonia/ammonium chloride leaching.

In US Patent 3,953,200 issued to Im et al. on April 27, 1976, nickel is obtained from low grade ores by simultaneous grinding and leaching with aqueous ammonia.

From the teachings of US Patent 3,903,241 issued to Stevens et al. on September 2, 1975, nickel can be recovered from a reduced ore at 750- 900 °C by acid leaching. Nickeliferous laterite ores are best treated by high pressure sulfuric acid by first scalping the ore so as to obtain a nickel-rich fraction according to US Patent 4,044,096 issued to Queneau on August 23, 1977.

Hatch and Dunn indicate in US Patent 4,410,498 issued on October 18, 1983, that nickel and cobalt extraction from serpentinic laterites is much improved by sulfuric acid leaching in the presence of a reducing agent. Sefton et al. in US Patent 3,860,689 issued on January 14, 1975 have reported that the nickel extraction from roasted high magnesium nickeliferous laterites by an ammonia ammonium carbonate solution is much improved by attrition of the roasted material prior to leaching.

In US Patent 4,328,192 issued on May 4, 1982, Tolley and Corral indicate that the nickel leaching of laterites is improved by addition of hydrogen halide during the reductive roasting.

It is reported in US Patent 3,892,639 issued to Leavenworth et al. on July 1, 1975 that nickel, chromium, manganese, iron and cobalt can be obtained by volatilization of chlorides in the presence of hydrochloric acid gas, in a fluidized bed, chromium being retained in the bed. Subsequent electrolytic/chemical treatments allow the recovery of metals.

In US Patent 5,571,308 issued on November 5, 1996, Duyvesteyn et al. report the leaching of nickel from high magnesium-containing lateritic ores by leaching with a mineral acid, sulfuric acid or nitric acid, HCI being preferred, and circulating the resulting solution on a resin specific to nickel, the resulting ferric chloride and magnesium chloride solution being decomposed to the corresponding oxides by heat treatment.

Leaching the ore with an acid, such as in US Patent 5,571,308 seems attractive but the recovery of nickel and cobalt is relatively low, of the order of 65% from our tests, and less than five percent of the available chromium is found in the pregnant solution.

Also, it was found that several of the teachings of Duyvesteyn et al. in US Patent 5,571,308 are not operational. The digestion with HCI of a material containing about 60% of Fe₂0₃ and 10% of magnesium oxide will give predominantly a lixiviate of ferrous chlorides with a minor amount of magnesium chloride. If such a mixture is pyro-hydrolyzed as described by Duyvesteyn et al., there will be an important production of magnesium oxychloride rather than MgO, because of the relatively high temperature of hydrolysis of MgCI₂ in the presence of important amounts of HCI from the decomposition of predominant FeC^, according the following equation:

2MgCI₂ + H₂O — _► Mg₂OCI₂ + 2HCI

This formation of magnesium oxychloride should have been expected from several sources of chemical literature such as Grosvernor and Miller in US Patent 2,206,399 (page 1 column 2, lines 26 to 32) and H. Remy, Treatise on Inorganic Chemistry, Elsevier, 1956; Vol. 1 page 267.

Besides removing the availability of MgO to act as a neutralizing agent, this unforeseen formation of magnesium oxychloride prevents the efficient neutralization of the excess acid in the lixiviate, prior to contacting with ion exchange resins, since Fe₂0₃ alone has a low basicity and a small specific area when calcinated at the temperature required to hydrolyze MgCI₂.

Also, heap leaching with hydrochloric acid is not compatible with environmental regulations since even at low concentration, where the leaching capabilities of the acid is much reduced, hydrochloric acid liberates acidic vapors. Heap leaching is only possible with a non volatile acid, such as sulfuric acid and then, it is not possible to recycle the acid by a simple method such as spray roasting (US Patent 5,911 ,967) used with chlorides.

Therefore, because of faulty circuit, relatively low yields of recovery of nickel, absence of data on the recovery of cobalt, magnesium and chromium and long contact times, the process described by US Patent 5,571,306 is not attractive to gain access to Ni, Co, Mg and Cr values found in laterites.

Treatment of the laterites in a stream of hydrochloric acid (US Patent 3,392,639) calls for rather high temperatures, in the range of 600 °C to make sure that all the nickel and cobalt are carried with the predominant amounts of iron chlorides. The operation of such a system is complex and very costly, due to the corrosive action of HCI gas at high temperatures.

High pressure and high temperature leaching with sulfuric acid calls for the use of autoclaves with a high resistance to corrosion (US 4,548,794 and US 4,044,096). Titanium or special alloys can be used, with the corresponding elevated capital cost and a batch rather than continuous process.

Reduction of the ore followed by leaching is recommended by several patents (US 4,187,281; US 3,953,200; US 3,860,689). This technique is implemented industrially but 20 to 30 % of the nickel and as much as 50% of the cobalt is left in the tailings. And no chromium and magnesium are recovered.

A critical assessment of this patent literature indicated that a process allowing the recovery from laterites of the iron, nickel, cobalt, magnesium and chromium values by a simple and economical circuit remained to be established. OBJECTAND STATEMENT OF THE INVENTION

It is an object of the present invention to recover in useful forms most of the metals from laterites which are iron-rich metamorphic rocks containing oxides such as CoO, NiO, MgO, Cr₂0₃ and Fe₂0₃. This is achieved by a method which consists of a series of steps including:

(a) grinding the laterite ores to yield granules;

(b) subjecting the granules to gaseous HCI to achieve adsorption of gaseous HCI onto the granules and wherein excess HCI is recycled to produce a concentrated HCI solution; (c) curing acid adsorbed ores in concentrated HCI to obtain a lixiviate containing water soluble nickel, cobalt, iron, chromium and magnesium chlorides and an insoluble residue;

(d) filtering the lixiviate from the insoluble residue to produce a head solution; and (e) selectively recovering nickel and cobalt by a process selected from the group of processes consisting of electrowinning, solvent extraction, specific ion-exchange resins and sulfide precipitation.

Hence, in one form of the invention, the ore is ground and digested in hot hydrochloric acid. The insoluble fraction, about 30% or less of the weight of the starting ore, is a chromium enriched solid amendable to chromate production. The soluble fraction contains at least 90% of the cobalt and nickel along with 85% of the magnesium, 85% of the iron and 25% of the chromium, initially present in the starting ore, as chlorides. This solution is evaporated and treated by heat in the presence of oxygen and steam, at

450-600 °C, after addition of KCI. Under such conditions, the iron chloride and magnesium are hydrolyzed to the corresponding oxides. By water extraction, the soluble chlorides of Co and Ni are separated from the insoluble chromium and iron products. The potassium chloride and the hydrochloric acid are recycled. Cobalt and nickel can be recovered as metals by known technologies and magnesium is recovered as magnesium hydroxide or carbonate. In another form of the invention, the values of iron and chromium are first extracted as their respective oxides (Fe₂O₃ and Cr₂0₃) from the head solution composed of the chloride salts of nickel, cobalt, iron, chromium and magnesium by a thermal treatment at a temperature range of 100-200 °C, followed by the extraction of the values of nickel and cobalt and then finally by the isolation of the magnesium values as basic magnesium carbonate.

Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that this detailed description, while indicating preferred embodiments of the invention, is given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.

DESCRIPTION OF THE DRAWINGS

Figure 1 is a block diagram illustrating the various steps of one embodiment of the method according to the present invention; and

Figure 2 is a block diagram illustrating the various steps of a second embodiment of the method according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Starting from standard reactions, the following steps have been tested and optimized. The actual combination of these steps with specific operation conditions allows for the recovery of the four most valuable elements present at significant levels in laterites, namely cobalt, nickel, chromium and magnesium. In reference to figure 1 , these steps are as follows. CONDITIONING OF THE ORE

Cobalt, nickel, magnesium and chromium exist in laterites as oxides combined with silica, alumina or alumino silicates. Weathering and metamorphic changes render this material very complex.

In order to make the material more amendable to digestion and to open-up the structure, a reductive roasting in the range of 400 to 750 °C is sometimes practiced with some processes.

Applicant has noted that, with reduced laterites, such as the tailings of the ammonia/ammonium salts extraction technology, the time required to leach out the base metals with hydrochloric acid was of the order of 15 minutes at 100 °C. With non reduced material, a longer time of digestion is required, of the order of one to three hours; but then, the only required conditioning of the ore prior to lixiviation is size reduction to particles of one millimeter in diameter or less, thus avoiding the elaborate operation of reductive roasting. Therefore, in the present technology, the conditioning of the ore consists in grinding and screening operations that bring the size of the particles to one millimeter or less.

ACID LEACHING

The acid selected for leaching is hydrochloric acid. With chlorides, the selective decomposition of the corresponding salts is possible under appropriate conditions and permits separation of the four metals sought into two distinct categories namely cobalt-nickel and iron-chromium- magnesium respectively; and, most of the acid can be recycled after the extraction of Ni, Co and Mg.

Laterites are very rich in iron, Fe₂O₃ representing more than 60% of the weight of this mineral. Acid digestion will therefore dissolve large amounts of this iron, typically about 85% of the total amount of Fe present. This dissolving of such a large amount of the starting material explains the high yields of extraction observed: the structure of the starting ore is more or less completely broken down, giving access to the trace elements present, such as cobalt.

The conditions of leaching are of paramount importance to achieve the complete recovery of the values in laterites. The hydrochloric acid used is in the form of gaseous HCI, obtained from the roasting of the chlorides. This HCI stream which contains some water vapor and air from the operation of the roaster is directed to a rotary tubular reactor and the starting ore is circulated countercurrent to the stream of HCI. The ore containing a moisture content of 30-70% is circulated through the reactor, this moisture acting as a captor of HCI. In this fashion, the acid solution generated in situ, at the surface of the particles is very concentrated and continually refurbished in HCI as the formation of chlorides proceeds. As the HCI stream leaves the reactor, a significant amount of the HCI has been adsorbed by the starting ore. The remainder of HCI in gaseous state is then scrubbed with water in a countercurrent fashion so as to obtain an acid with a concentration of 20 to 25% HCI. During the contacting of the ore with the hydrochloric acid stream, heat is evolved from the adsorption of HCI by water and the reaction of hydrochloric acid with the ore. These reactions liberate enough heat to raise the temperature of the partly chlorinated ore at the exit of the reactor to 50-70 °C.

The acid saturated and partly reacted ore is then transferred to a second rotary tubular reactor for the purpose of completing the reaction. This is achieved by heating at around 90-100 °C the partly reacted mass and by adding to said mass the concentrated hydrochloric acid (20-25%) stripped from the first reactor at the outlet of the gas stream. The duration of this contact is adjusted so as to complete the extraction of the values to more than 90% for nickel and cobalt and around 80% of iron and magnesium. The amount of HCI required to achieve such yields is 125% of the theoretical amount required to convert the iron to FeCI₂ ,the magnesium to MgCI₂, the nickel to NiCI₂, the cobalt to CoCI₂. Chromium reacts only to an extent of about 35 to 45% and is found as CrCI₃. It is complexed and solubilized in the presence of the large amount of chloride ions in the reacted mass. The duration of contact can vary from 15 minutes to three hours, pending on materials.

After contacting for an appropriate duration at around 100 °C, the reacted material is slurried with enough water to insure the solubilization of the chlorides and the phases are separated by an appropriate means, such as a belt filter or a centrifuge. Three displacements of the retained volume of liquid are made with water in order to reclaim all soluble material from the cake. The filtrate and washings are combined so as to produce the head solution. The insoluble fraction which may represent from 20 to 40% of the weight of the starting ore contains about 66% of the chromium initially present in the starting ore. This chromium is highly insoluble and cannot leach out of the residual solid by action of atmospheric agents. Since its content of chromium is about twice the content of chromium in the starting ore, it could be used as a starting material for the production of chromates or bichromates.

RECOVERY OF NICKEL AND COBALT

The nickel and cobalt in the head solution can be recovered by a variety of means such as electrowinning, solvent extraction, specific ion exchange resins, sulfide precipitation and other processes known to those familiar in the art. It could be advantageous at this stage to isolate in a complete or partial fashion the nickel and the cobalt so as to have a simplified road for the production of pure metals further on. After this recovery of nickel and cobalt, the solution contains iron (FeCI₂), magnesium (MgCI₂) and chromium (CrCI₃) along with the excess acid used for digestion. RECYCLING OF HYDROCHLORIC ACID AND RECOVERY OF OXIDES OF MAGNESIUM AND IRON

It is known that iron chlorides can be decomposed by heat, in the presence of steam and oxygen to give the corresponding ferric oxide and hydrochloric acid (for example US Patent 3,658,483). This decomposition is currently practiced by spray roasting at 700-800 °C and leads to a ferric oxide. Such a spray roasting or pyro-hydrolysis has the disadvantage of transforming the magnesium chloride into magnesium oxychloride in the presence of large amounts of FeCI₂ if appropriate conditions are not used.

Applicant has found that if the lixiviate obtained from step two is evaporated and then treated with air and steam at 450-475 °C, the iron chloride is essentially completely decomposed while the chloride of magnesium is not decomposed.

Iron chloride presents a substantial vapor pressure at 450-475 °C and this volatility has to be depressed in order to prevent sublimation rather than decomposition. This control of the volatility of iron chloride is achieved by the addition of potassium chloride to the acid solution prior to thermal treatment. The amount to be added is from 10 to 30% of the weight of the starting ore, prior to acid lixiviation. This potassium chloride is added in the form of a saturated solution of about 20% by weight of KCI.

After thermal treatment at 450-475 °C in the presence of KCI, a solid is then obtained which is composed of ferric oxide, chromium oxide, magnesium chloride and potassium chloride.

The residual solution resulting from the collection of cobalt and nickel is enriched by the addition of KCI in the form of a 20% aqueous solution so as to have enough KCI present to depress the vapor pressure of FeCI₂ during pyrolysis. This KCI enriched solution is evaporated and the hydrochloric acid thus reclaimed is directed to the recycling circuit. The solid, a mixture of FeCI₂, MgCI₂ and CoCI₃ is then heated at 450-475 °C in the presence of water vapors and air in order to oxidize the iron and liberate the hydrochloric acid according to the following equation:

2FeCI₂ + 2H₂O + ¹/₂0₂ _^ Fe₂O₃ + 4HCI

Under such conditions, the chromium follows the iron to give an iron oxide of high purity containing about one percent of chromium oxide which is about 30% of the chromium present in the starting ore. This ferric oxide enriched with chromium oxide would be an interesting product for the production of ferrochrome. Under such conditions, the magnesium

^' chloride is essentially unreacted and can be leached out of the ferric oxide. Further thermal treatment at 600°C will lead to the precipitation of magnesium oxide while the KCI is not influenced by this thermal treatment and can be recycled as a solution to the process.

Alternatively, both ferrous chloride and magnesium oxide at 500 to 600 °C can be decomposed to liberate a mixture of ferric oxide along with KCI. Then, by lixiviation of MgO by CO₂ leaching, one obtains precipitated magnesium carbonate and the solution of potassium chloride. The following equation describes this preferred option:

KCI+MgCI₂+2FeCI₂+3H₂O+¹/₂O₂ — _► MgO(s)+Fe₂O₃+6HCI(g)+KCI(s)

MgO+H₂O+2CO₂ ^ Mg(HCO₃)₂ (water soluble)

Heat (100 °C) 4Mg(HCO₃)_{2 ►} 3MgCO₃ * Mg(OH)₂(s)+5CO₂+3H₂0 RECOVERED PRODUCTS

At the end of the operation, the values in the starting laterite, namely Ni, Co, Mg and Cr are recovered in the following forms:

• Nickel and cobalt, with 90% yield, as chlorides that can be readily separated by several known technologies.

• Magnesium, with a 80-85% yield, as magnesium oxide or carbonate.

• Chromium under two forms, the larger fraction (75%) as an enriched chromite ore and the minor fraction (25%) with high purity reprecipitated iron oxide, a desirable starting product for the production of ferrochrome.

Alternatively and referring to the block diagram of figure 2, the head solution can be thermally treated, with exposure to air, at temperatures ranging from 130 to 180 °C, without the addition of potassium chloride. Under such conditions, the free hydrochloric acid is carried out of the system and scrubbed. In this process, the ferrous chloride is selectively oxidized to ferric chloride and is then subsequently hydrolyzed to ferric oxide. This hydrolysis is facilitated by the continuous removal of HCI from the system. The ferric oxide obtained is insoluble under neutral or basic conditions. The other chlorides present, NiCI₂, CoCI₂₍ and MgCI₂, with the exception of CrCI₃ which is decomposed into Cr₂0₃ under these conditions, are not subject to this hydrolysis and can be obtained as soluble entities that can be separated by standard approaches. However, it is important to mention that ferric hydroxide has strong adsorptive properties and it is well known that salts of nickel are adsorbed upon precipitated iron. From this it would not be obvious to hold low concentrations of nickel and cobalt in solution while relatively large amounts of iron are removed. The recovery of NiCI₂, CoCI₂, and MgCI₂, from the insoluble Fe₂O₃ is essentially quantitative if the decomposition of FeCI₂ is done in the temperature range indicated above, that is below 200 °C. The chromium chloride also subject to the above hydrolysis forms Cr₂O₃ and is entirely contained in the Fe₂0₃.

The equations describing this approach are the following:

2 FeCI₂ + 2 HCI + A 0₂ ► 2 FeCI₃ + H₂0

2 FeCI₃ + 3 H₂0 ^ Fe₂0₃(s) + 6 HCI(g)

2 CrCI₃ + 3 H₂0 _► Cr₂0₃(s) + 6 HCI(g)

The overall equation of this process is:

2 CrCI₃ + 2 FeCI₂ + 5 H₂O + V₂ O₂ ► Fe₂O₃.Cr₂0₃(s) + 10 HCI(g)

The steps of the method illustrated in figure 2 which are common to those shown in figure 1 are identical and need not be described again: these steps include the grinding, adsorption, curing, lixiviation and filtration procedures leading to the formation of the head solution; the isolation of nickel and cobalt; the steps leading to the isolation of basic magnesium carbonate from MgCI₂.

As depicted in figure 2, the so obtained head solution is then heated in the presence of air at a temperature range of 100-200 °C to selectively oxidize FeCI₂ into Fe₂O₃ and decompose CrCI₃ into Cr₂O₃ while not affecting the chloride salts of nickel (NiCI₂), cobalt (CoCI₂) and magnesium (MgCI₂). It is essential that the heating is done in the temperature range indicated above, that is below 200 °C, to avoid decomposition of NiCI₂, CoCI₂ and MgCI₂. This in turn allows for an essentially quantitative recovery of the chloride salts of nickel, cobalt and magnesium.

Heating the head solution in the presence of air at the desired temperature range, leads to the formation of a residue that is composed of Fe₂0₃, Cr₂O₃, NiCI₂, CoCI₂ and MgCI₂ and to the evaporation of HCI which is reclaimed and redirected to the recycling circuit. Lixiviation of the residue with water leads to the extraction of the soluble chloride salts of nickel, cobalt and magnesium and to the isolation by filtration of an insoluble residue composed of Fe₂O₃ and Cr₂O₃.

EXAMPLES

Using Nicaro laterites from Cuba as starting materials, applicant has performed a series of tests in order to determine optimal operating conditions in terms of yields of recovery and operational cost.

EXAMPLE I

A 25 g sample of tailings from Nicaro mines in Cuba (ammonium salts extraction after reduction) containing 10.02g Fe, 0.023g Co, 0.0925g Ni, 0.4635g Cr and 1.012g Mg, the residual material being made of alumino silicates was digested in accordance with the steps illustrated in figure 1, with contact of one hour at 100 °C. The reaction mixture was then filtered and the filtrate washed with water (3 washings). The insoluble fraction, after drying at 100 °C for 16 hrs weighed 7.31 g. The chemical analysis indicated that 85% of the iron, 87% of the magnesium, 91% of the cobalt, 93% of the nickel and 23% of the chromium in the starting sample had been dissolved by the hydrochloric acid.

EXAMPLE II A 25g sample of raw laterite containing 12.88g of Fe; 0.027g of Co; 0.275g of Ni; 0.530g of Cr, and 0.08g of Mg was treated with 120ml of 20% HCI at reflux temperature for one hour. The reaction mixture was then filtered and the insoluble cake was rinsed with water (3 displacements). The dry cake weighed 2.3g after drying at 100 °C for 16 hrs and contained 0.58 g of Fe, 0.0017g of Co; 0.007g of Ni; 0.326g of Cr and 0.062g of Mg. The acid solution contained 12.3g of Fe (95%); 0.0253g of Co (93%); 0.268g of Ni (97%); 0.204g of Cr (38%) and 0.02g of Mg (24%).

The solution was treated as in Example I and essentially all the values of Co and Ni were recovered as sulfides.

Example III

A 30g sample of overburden material from the Pinares mine in Cuba containing 49% Fe, 0.03% Co, 0.51% Ni and 1.71% Cr was treated at 100 °C with 80 ml of HCI 32% and 20 ml of water for a period of two hours. The residual material was then filtered and had a dry weight of 0.85g and contained 14% Cr. The solution corresponded to an extraction of 99% of the nickel, 96% of the cobalt and 78% of the chromium present in the starting sample.

This solution was evaporated to dryness with access of air at 175 °C to carry away the hydrochloric acid vapors that were condensed and titrated with caustic. The titration indicated a recovery of 96% of the hydrochloric acid initially used.

The precipitated ferric oxide and chromium oxide was rinsed with water. The solution extracted, essentially on a quantitative basis, the values of nickel and cobalt initially present in the head solution.

Although the invention has been described above with respect to two specific forms, it will be evident to a person skilled in the art that it may be modified and refined in various ways. It is therefore wished to have it understood that the present invention should not be limited in scope, except by the terms of the following claims.

Claims

1. A method for the recovery of nickel and cobalt from laterite ores containing nickel, cobalt, iron, chromium and magnesium, comprising the steps of:

(a) grinding the laterite ores to yield granules;

(b) subjecting said granules to gaseous HCI to achieve adsorption of gaseous HCI onto said granules and wherein excess HCI is recycled to produce a concentrated HCI solution;

(c) curing acid adsorbed ores in concentrated HCI to obtain a lixiviate containing water soluble nickel, cobalt, iron, chromium and magnesium chlorides and an insoluble residue;

(d) filtering said lixiviate from said insoluble residue to produce a head solution; and

(e) selectively recovering from said head solution nickel and cobalt by a process selected from the group of processes consisting of electrowinning, solvent extraction, specific ion-exchange resins and sulfide precipitation.

2. A method as defined in claim 1 wherein HCI and water are evaporated, in the presence of a saturated KCI solution, from said head solution stripped of nickel and cobalt, leaving a second residue composed of FeCI₂, CrCI₃, MgCI₂ and KCI.

3. A method as defined in claim 2 wherein said second residue is roasted in the presence of air and steam to selectively oxidize said FeCI₂ to Fe₂O₃ and decompose said CrCI₃ to Cr₂O₃ respectively, wherein gaseous HCI is evolved and recycled to said adsorption step and wherein a roasted residue and an insoluble residue composed of Fe₂O₃, Cr₂0₃ are obtained.

4. A method as defined in claim 3 wherein said roasted residue is lixiviated to extract MgCI₂ and KCI from said insoluble residue composed of Fe₂O₃ and Cr₂O₃ to obtain a second lixiviate.

5. A method as defined in claim 4 wherein said insoluble residue composed of Fe₂0₃ and Cr₂O₃ is recovered by filtration to obtain a filtered lixiviate.

6. A method as defined in claim 5 wherein said filtered lixiviate is evaporated leaving a further residue composed of MgCI₂ and KCI.

7. A method as defined in claim 6 wherein said further residue is roasted in the presence of air and steam to selectively decompose MgCI₂ to MgO and wherein gaseous HCI is evolved and recycled to said adsorption.

8. A method as defined in claim 7 wherein said MgO is lixiviated in the presence of CO₂ and water to obtain another lixiviate and wherein said other lixiviate is heated to obtain a precipitate of basic magnesium carbonate (3 MgCO₃.Mg(OH)₂)..

9. A method as defined in claim 8 wherein said basic magnesium carbonate (3 MgC0₃.Mg(OH)₂) is recovered by filtration.

10. A method as defined in claim 1 wherein acid adsorbed granules are cured in a tubular reactor and combined with concentrated HCI of about 20-25% at temperatures ranging from 90-100 °C over a period of 15 minutes to 3 hours, to obtain water soluble chloride salts of nickel (NiCI₂), cobalt (CoCI₂), iron (FeCI₂), chromium (CrCI₃) and magnesium (MgCI₂).

11. A method as defined in claim 10 wherein said water soluble chloride salts are lixiviated with water to obtain said lixiviate and said insoluble residue embodying about 66 % of the chromium content initially present in the laterite ore.

12. A method as defined in claim 11 wherein said insoluble residue is recovered by filtration to obtain a filtered lixiviate and a filtered residue.

13. A method as defined in claim 12 wherein said filtered residue is extracted with water to produce washings and wherein said washings are combined with said filtered lixiviate to obtain said head solution.

14. A method as defined in claim 13 wherein nickel and cobalt are recovered from said head solution to produce a leftover solution.

15. A method as defined in claim 14 wherein is added to said leftover solution a saturated aqueous solution of KCI which is then evaporated to obtain a second residue composed of FeCI₂, CrCI₃, MgCI₂ and KCI.

16. A method as defined in claim 15 wherein said second residue is roasted in the presence of air and steam at temperatures ranging from 450 to 475 °C, to selectively oxidize said FeCI₂ into Fe₂0₃ and decompose said CrCI₃ into Cr₂O₃ and wherein gaseous HCI is produced which is recycled to said adsorption and wherein a roasted residue and an insoluble second residue composed of Fe₂O₃ and Cr₂O₃ are obtained.

17. A method as defined in claim 16 wherein said roasted residue is lixiviated with water to extract unreacted MgCI₂ and KCI from said insoluble second residue composed of Fe₂O₃ and Cr₂O₃, to obtain a second lixiviate and wherein said insoluble second residue composed of Fe₂0₃ and Cr₂O₃ is recovered.

18. A method as defined in claim 17 wherein said second lixiviate is filtered to obtain a filtered second lixiviate.

19. A method as defined in claim 18 wherein said filtered second lixiviate is evaporated to obtain a residue composed of MgCI₂and KCI.

20. A method as defined in claim 19 wherein said residue composed of MgCI₂ and KCI is roasted in the presence of air and steam at temperatures of about 600 °C, to decompose said MgCI₂ into MgO and wherein gaseous HCI is produced which is recycled to said adsorption process and wherein MgO is produced.

21. A method as defined in claim 20 wherein said MgO is lixiviated with carbon dioxide (C0₂) and water to obtain a lixiviate composed of magnesium bicarbonate [Mg(HCO₃)₂].

22. A method as defined in claim 21 wherein said lixiviate composed of magnesium bicarbonate [Mg(HC0₃)₂] is heated to about 100 °C, to obtain a precipitate composed of basic magnesium carbonate [3 MgC0₃.Mg(OH)₂].

23. A method as defined in claim 22 wherein said precipitate is recovered by filtration.

24. A method as defined in claim 1 further comprising the step of thermal treatment of said head solution, in the presence of air and water, transforming FeCI₃ into Fe₂O₃ and CrCI₃ into Cr₂O₃ and wherein a second residue composed of NiCI₂, CoCI₂, MgCI₂, Fe₂O₃ and Cr₂O₃ is obtained.

25. A method as defined in claim 24 wherein said second residue is lixiviated with water to extract NiCI₂, CoCI₂ and MgCI₂ to obtain a second lixiviate and an insoluble residue composed of Fe₂0₃ and Cr₂0₃.

26. A method as defined in claim 25 wherein said insoluble residue composed of Fe₂0₃ and Cr₂O₃ is recovered by filtration to obtain a filtered lixiviate.

27. A method as defined in claim 26 wherein nickel and cobalt are recovered from said filtered lixiviate to produce a leftover lixiviate composed of MgCI₂.

28. A method as defined in claim 1 wherein said head solution is heated in the presence of air and water at temperatures ranging from 100- 200 °C to selectively oxidize FeCI₂ into Fe₂O₃ and decompose CrCI₃ into Cr₂O₃ and wherein a second residue composed of NiCI₂, CoCI₂, MgCI₂, Fe₂O₃ and Cr₂O₃ is obtained.

29. A method as defined in claim 28 wherein said second residue composed of NiCI₂, CoCI₂, MgCI₂, Fe₂O₃ and Cr₂O₃ is lixiviated with water to extract NiCI₂, CoCI₂ and MgCI₂ to obtain a second lixiviate and an insoluble residue composed of Fe₂O₃ and Cr₂O₃.

30. A method as defined in claim 29 wherein said insoluble residue composed of Fe₂O₃ and Cr₂0₃ is recovered by filtration to obtain a filtered lixiviate.

31. A method as defined in claim 30 wherein nickel and cobalt are recovered from said filtered lixiviate to produce a leftover lixiviate.

32. A method as defined in claim 31 wherein said leftover lixiviate is evaporated to produce a residue composed of MgCI₂.

33. A method as defined in claim 32 wherein said residue composed of MgCI₂ is roasted in the presence of air and steam at temperatures of about 600 °C, to decompose said MgCI₂ into MgO and wherein gaseous HCI is produced which is recycled to said adsorption process and wherein MgO is produced.

34. A method as defined in claim 33 wherein said MgO is lixiviated with carbon dioxide (CO₂) and water to obtain a lixiviate composed of magnesium bicarbonate [Mg(HCO₃)₂].

35. A method as defined in claim 34 wherein said lixiviate composed of magnesium bicarbonate [Mg(HCO₃)₂] is heated to about 100 °C, to obtain a precipitate composed of basic magnesium carbonate [3 MgC0₃.Mg(OH)₂].

36. A method as defined in claim 35 wherein said precipitate is recovered by filtration.

37. A method as defined in any one of claims 1 to 36 wherein said laterite ores are ground to yield granules of one millimeter in diameter or less.

38. A method as defined in any one of claims 1 to 37 wherein said concentrated HCI solution is obtained by scrubbing.