US3791816A

US3791816A - Production of nickel from nickel-bearing materials

Info

Publication number: US3791816A
Application number: US00239454A
Authority: US
Inventors: R Israel
Original assignee: Kaiser Aluminum and Chemical Corp
Current assignee: Kaiser Aluminum and Chemical Corp
Priority date: 1972-03-30
Filing date: 1972-03-30
Publication date: 1974-02-12
Anticipated expiration: 1991-02-12

Abstract

A process for producing nickel of high purity and with high recovery from nickel-bearing materials containing nickel and less noble metals including cobalt and iron, such as ores and alloys. A molten slag phase and molten metal phase is provided in a furnace having an elongated flow path in which the nickel of high purity is removed at a point near one end of the furnace while molten slag highly impoverished with respect to nickel oxide is removed at a point near the other end. A metal purification zone and a slag treating zone are established in the vicinity of the molten metal removal point and the molten slag removal point, respectively. An intermediate zone is located between the metal purification zone and the slag treating zone, and a countercurrent movement between the slag and metal phases is induced, the said slag phase flows from the metal purification zone through the intermediate zone to the slag treating zone while the metal phase flows from the slag treating zone through the intermediate zone to the metal purification zone. Oxidation of the metal phase in the metal purification zone provides the nickel in high purity, while treatment of the slag in the slag treating zone with a reducing agent effects a high recovery. Interphase contact and intraphase mixing between the slag and metal phases is promoted during their flows. At least periodically, a portion of the metal present in the metal phase in the intermediate zone, which is rich in cobalt, is removed.

Description

United States Patent [1 1 Israel Feb. 12, 1974 1 PRODUCTION OF NICKEL FROM NICKEL-BEARING MATERIALS Robert D. Israel, Oakland, Calif.

[73] Assignee: KaiserAluminum & Chemical Corporation, Oakland, Calif.

[22] Filed: Mar. 30, 1972 21 Appl.No.:239,454

Related U.S. Application Data [63] Continuation-impart of Ser. No. 22,755, March 26,

1970, abandoned.

[75] Inventor:

Primary Examiner-L. Dewayne Rutledge Assistant Examiner-M. .l. Andrews Attorney, Agent, or FirmPaul E. Calrow 57 ABSTRACT A process for producing nickel of high purity and with METAL [PURIFICATION k INTERMEDIATE ZONE -i high recovery from nickel-bearing materials containing nickel and less noble metals including cobalt and iron, such as ores and alloys. A molten slag phase and molten metal phase is provided in a furnace having an elongated flow path in which the nickel of high purity is removed at a point near one end of the furnace while molten slag highly impoverished with respect to nickel oxide is removed at a point near the other end. A metal purification zone and a slag treating zone are established in thevicinity of the molten metal removal point and the molten slag removal point, respectively.

An intermediate zone is located between the metal purification zone and the slag treating zone, and a countercurrent movement between the slag and metal phases is induced, the said slag phase flows from the metal purification zone through the intermediate zone to the slag treating zonewhile the metal phase flows from the slag treating zone through the intermediate zone to the metal purification zone. Oxidation of the metal phase in the metal purification zone provides the nickel in high purity, while treatment of the slag in the slag treating zone with a reducing agent effects a high recovery. Interphase contact and intraphase mixing between the slag and metal phases is promoted during their flows. At least periodically, a portion of the metal present in the metal phase in the intermediate zone, which is rich in cobalt, is removed.

4 Claims, 4 Drawing Figures SLAG I TREATING TAPPING END STATIONS FOR TAPPING COBALT-RICH ALLOY PAIENTEUFEBIZW 3.791.816

SHiET 1 BF 4 o E n. n.

END

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FIG. 4

PRODUCTION OF NICKEL FROM NICKEL-BEARING MATERIALS CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part application of co-pending United States application Ser. No. 22,755 filed Mar. 26, 1970, and entitled, Production of Nickel from Nickel Bearing Materials, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to the production of nickel in high purity and high yield from nickel-bearing materials; More particularly, it relates to the separation and recovery of nickel metal from a nickel-bearing material, such as ores, concentrates and alloys, containing cobalt and other less noble metals and nonmetallic impurities. The process involves separation of metallic nickel from other constituents, including cobalt, in a furnace having an elongated flow path, wherein the nickel-bearing material is subjected to both oxidation and reduction. These treatments result in the formation of a two-phase system consisting of an upper layer of slag and a lower layer of metal. Semi-continuous or continuous tapping of the upper layer and the lower layer at predetermined locations in the furnace provide for a countercurrent flow of these layers relative to each other and allow the production of metallic nickel in high yield and purity.

It has been proposed heretofore to treat, for example, relatively low grade nickel-bearing ores, such as laterites, garnierites and serpentines by reduction in a blast furnace, electric arc furnaces, or in rotary kilns. Such practice results in the formation of nickel alloys, usually iron'rich alloys, which must be subjected to further metallurgical treatments to recover the nickel constituerits. Such treatments include selective chloridization of the nickel or iron constituents, which not only results in low nickel recovery, but also creates severe operation conditions due to the corrosive nature of the chlorine treating agent. Another method of treating oxidic nickel ores is by the Caron'process or modifications thereof. The ore is dried, ground, and selectively reduced to convert some of its iron content and all of its nickel and cobalt content to the metallic state. The nickel and cobalt are dissolved with ammonium carbonate solution in the presence of air to repress the dis solution of the iron. The nickel and cobalt containing solution is then treated to remove the cobalt and many other minor constituents before the nickel is finally reduced to the metallic state by high pressure hydrogen. This process requires a high capital investment and many delicate costly process steps to produce a salable nickel product. The complexity of the process renders it uneconomical except for very large plants.

An additional method of separating the nickel from other constituents present in nickel-bearing ores involves acid leach of the ores, which when properly conducted allows recovery of a major amount of nickel present in the ores. However, the leach solution which contains the nickel, will always be contaminated with other metallic impurities and further purification steps must be employed to recover substantially pure nickel. This prior art method of nickel recovery is restricted to ores low in acid-consuming species, such as magnesia and alumina. Since these ores have a relatively low nickel content, the acid leach process plants are very expensive and the process can only be used in very special circumstances.

To overcome the difficulties presented by the aforementioned processes, it was suggested to admix nickelbearing ores in finely divided state with a fuel oil followed by reductive combustion in a tumbling ore bed. This method recovers nickel in high yield, usually about percent, based on the nickel content of the nickel-bearing ore; however, the product of this reduction is an iron-nickel alloy, e.g., ferronic kel, where the nickel content of the alloy is about 25 percent. The ferronickel, although eminently suitable for many purposes, must be further treated to obtain pure nickel free of iron and cobalt.

The metallurgical processes utilized to treat the ironnickel alloy most commonly involve partial oxidation of the iron constituent in a batch-type operation, followed by electrolytic refining or vapo-metallurgical refining of the resultant nickel-enriched alloy. These operations not only result in 'low nickel recovery rates but require extensive refining facilities with correspondingly high operating costs.

A particular problem existing heretofore relates to nickel-bearing oxidic ores wherein the ratio of nickel to cobalt is rarely less than to 1 and can commonly be as low as 10 to 1, especially where nickel content of the ore is under about 1.5 percent, such as in the socalled nickel laterites. In such instances, the prior art processes produce iron-nickel-cobalt alloys of low nickel to cobalt ratios. These alloys have a limited usefulness due to their high cobalt content which makes them unsuitable for use if the final product may be used in nuclear radiation areas. There is a close family relationship between nickel and cobalt as shown in the Periodic Table and as evidenced by their occurrence together in nature. As the relative affinities for oxygen of cobalt and nickel are relatively close, a reduction process for obtaining nickel from a nickel-bearing ore will inherently include a significant amount of reduced cobalt in the product, e.g., ferronickel. The separation of the cobalt from the product is not easily accomplished and, heretofore, has entailed a series of complex treatments, usually involving a series of chemical processing steps and/or'electrolysis.

Accordingly, the present invention is directed to a pyrometallurgical process for the production of nickel in high purity and high yield from nickel-bearing mate- I rials containing cobalt which heretofore could not be refined in an efficient and economical manner.

BRIEF SUMMARY OF INVENTION This invention broadly comprises the production of nickel in high purity and high yield from nickel-bearing material, such as ores, alloys, concentrates and combinations thereof, containing nickel and other less noble metals including cobalt.

By the expression less noble metals as used herein is meant those metal elements present in the nickelbearing material which are more easily oxidized than nickel, for example, cobalt and iron.

The process of the invention utilizes a furnace having an elongated flow path having a metal purification zone, a slag treating zone, and an intermediate zone. The metal purification zone is located in the vicinity of one end of the flow path while the slag treating zone is located in the vicinity of the other end of the flow path. The intermediate zone extends from the metal purification zone to the slag treating zone. A layer of molten slag phase and a layer of molten metal phase extends throughout the elongated flow path. The slag phase generally consists essentially of nickel oxides and oxides of the less noble metals, while the metal phase consists essentially of metallic elements, one of which is the desired nickel metal to be produced. In certain instances, it may be desirable to add a flux material, such as silica (Si lime (Ca0), or limestone (CaCO to the slag in the metal purification zone to assist in giving a better separation between the slag and metal phases.

The nickel-bearing material is introduced into the elongated flow path. The nickel-bearing material is selected from the group consisting of ores, concentrates, alloys and combinations thereof.

A countercurrent movement between the slag and metal layers is induced by removing slag at least at one slag tapping station located in the vicinity of the slag treating zone and by removing'metal at least at one metal tapping station located in the vicinity of the metal purification zone. Interphase contact and intraphase mixing between the slag and metal phases is promoted as these phases flow in countercurrent relationship in the elongated flow path. The interphase contact and intraphase mixing achieves a high degree of efficiency for the process and effects a progressive increase of the nickel metal content of the molten metal phase as it proceeds from the slag treating zone to the sure a slag composition rich inthe nickel oxide. Al-

though a relatively substantial amount of the desired metal is oxidized, this results in the unexpectedly high purity of the desired nickel product. I

In the slag treating zone, the loss of nickel with the slag is controlled by reducing and causing to be incorporated in the metal phase substantially all of the nickel oxide in the slag treating zone.

The removal of a cobalt-rich alloy from the metal phase of the refining furnace is essential to the smooth controlled operation of the unit. If cobalt is not removed at least periodically from the furnace, the concentration of cobalt in the metal and slag will increase until the cobalt separating capability of the furnace is exceeded. The cobalt will then leave the furnace with Y the nickel reducing its purity, or with the slag as a loss of valuable material, or with both slag and metal simultaneously. The concentration of cobalt in the furnace can be controlled at any predetermined level by selecting the rate of withdrawal of the cobalt-rich alloy. This has the desirable result of increasing the stability of operation, decreasing the cobalt content of the prodnet, and giving as a by-product a salable metal alloy of cobalt and nickel.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic sketch of an elongated flow path and showing the essential features in which nickelbearing materials may be treated according to the invention.

FIG. 2 is a longitudinal elevation, in section, ofa furnace having an elongated flow path which is suitable for practicing the invention, particularly'inregard to the refining of ferronickel alloys.

FIG. 3 is a view in sectional transverse elevation taken on the line 3-3 of FIG. 2.

FIG. 4 is a longitudinal elevation, in section, of a furnace embodiment having an elongated flow path in which nickel-bearing materials may be treated according to the invention, particularly ores, concentrates and the like. I

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the preparation of nickel from nickel-bearing materials, such as nickel alloys, nickel concentrates and nickel-bearing ores. It utilizes a furnace having a substantially long flow path wherein the nickel-containing materials are subjected toboth oxidative and reductive treatments to produce a two-phase system, an upper layer of slag and a lower metallic layer containing nickel. In order to induce a countercurrent flow in the furnace of the two layers relative to each other along the long path treating area and thereby effect refining and separation, both the slag layer and the metal layer are tapped at points separated from each other along the long path of the furnace, as-shown in FIG. 1 along the longitudinal axis. The process of the invention provides an efficient method whereby metallic nickel is recovered in high yield and purity regardless-of the starting materials shown above.

Due to the differing chemical nature of nickelbearing materials encompassed within the scope of the present invention, the process steps involved may be utilized in-a different degree and in different locations within the refining furnace. Regardless, however, of the nature of the nickel-containing materials, the process of the invention in every case involves both an oxidative and reductive treatment in the furnace and the utilization of countercurrent flow and interphase contact and intraphase mixing ofthe slag and metal layers. The slag and metal phases must move at a velocity great enough to prevent homogenization along the axis of the furnace by intraphase mixing or diffusion. This can be accomplished by making the furnace very long compared to its cross section or by restricting the cross section of the liquid phases at intervals along the length of the furnace.

In the production of nickel within the scope of this invention, an elongated furnace is utilized which comprises a metal purification zone, aslag treating zone,

and an intermediate zone. These zones are interconnected in the following order; the metal purification zone is located in the vicinity of one end of the furnace and is in open communication with the intermediate zone which generally occupies a major portion of the furnace. The intermediate refining zone at its other extremity communicates with the slag treating zone, which is in the vicinity'of the other end of the furnace. The extent of these zones is determined by the metallurgical treatments accomplished in the furnace and also by the nature of the feed introduced into the furnace.

The drawings, FIGS. 2, 3 and 4, in which the same references are used to indicate like or corresponding parts or features, shown advantageous furnace embodiments for practice of the invention. These drawings are for illustrative purposes for describing the invention, and it is not to be construed that the invention is limited to the specific furnace embodiments depicted in FIGS. 2, 3 and 4.

With particular reference to FIGS. 2 and 3, there is shown an elongated refining furnace having an elongated flow path which is substantially greater in length than width as shown in comparing the sectional transverse elevation view of FIG. 3 with the longitudinal elevation view of FIG. 2. Disposed within the elongated flow path are a layer of molten slag 18 and a layer of. molten metal 16. The molten slag layer 18 is superimposed on and is contiguous with the molten metal layer 16. Both of the layers extend throughout the flow path of the furnace 20, and the countercurrent movement of slag layer 18 and metal layer 16 relative to each other is indicated by arrows. The metal purification zone is indicated by 10, the slag treating zone by 14 and the intermediate zone, which is between the metal purification zone and slag treating zone, by the numeral 12. Furnace 20 has a metal tapping spout 22 and a slag tapping spout 24. The feed material for refining, such as a crude nickel alloy, e.g., ferronickel, can be introduced into the furnace by a suitable mechanism, such as hopper 30, which is located in proximity to the slag treating zone 14. A water-cooled oxygen lance 26 is located in the metal purification zone 10. The lance is shown as mounted vertically through the top of the furnace and as having its tip or lower extremity submerged beneath the upper surface of the slag layer 18 but above the metal layer 16. It has been found that this is an advantageous way to operate; however, there may be instances where it may be advantageous in operating with the tip or lower extremity of the lance above the upper surface of the slag layer 18. A water-cooled lance 28 mounted vertically through the top of the furnace is shown for introducing a reducing gas into the slag layer 18 in the slag treating zone 14. Auxiliary gas burners 32 are shown, one located in the intermediate zone 12 and the other in the slag treating zone 14. These may be used to add additional heat to the bath if required and also to create stirring and mixing, particularly in the intermediate zone. The burners 32 are shown disposed vertically through the roof of the furnace 20. However, they be tilted at an angle, preferably slanted towards the flow of the slag layer 18, to create the desired flow and mixing. Although the oxygen gas from the lance is used substantially in its entirety in forming nickel oxide in the metal purification zone 10, there is the possibility of the reductant or reducing gas having unreacted components (e.g., hydrogen, carbon monoxide, methane, etc.), as well as products of combustion (such as H 0 and CO which are released into the furnace atmosphere. In this event, unreacted components would be burned in the furnace atmosphere above the intermediate zone 12, thereby adding needed heat to slag and/or metal layers. A gas exhaust 34 is provided for removal of the products of combustion, such as CO H O, etc. Also, a gas exhaust 35 is provided in the vicinity of the metal purification zone if needed for withdrawing any gases in the furnace atmosphere at that point. To preclude the reverse flow of reducing gases and oxidizing gases, a barrier 36 (shown in phantom) may be provided in the furnace.

Also provided in the furnace 20 are tapping stations 19 in the intermediate zone 12 which are for the purpose of periodically removing a cobalt-rich alloy, thereby insuring a high purity nickel product.

FIG. 4 is a further embodiment of a furnace for practice of the invention and shows a feeding mechanism 40 located in the intermediate zone 12 of the elongated furnace 20. This feeding mechanism is particularly advantageous when processing ore in the furnace. The ore is fed through the feeding mechanism 40 into the slag layer 18, wherein it is incorporated and flows to the slag treating zone 14 where it is reduced by any suitable means, such as the lance 28, wherein a suitable reductant gas, such as CO, methane, hydrogen, etc, or mixtures thereof is introduced. A suitable gas removal means 42 is located near the slag treating zone 14. All of the other features of the furnace depicted in FIG. 4 are similar or identical to those in FIGS. 2 and 3 and are adequately discussed previously.

As it was mentioned hereinbefore, the elongated flow path of the furnace contains a layer of molten slag and a layer of molten metal. The molten slag is superimposed on and is contiguous with the molten metal and both layers extend throughout the flow path. During the refining countercurrent movement of these two layers relative to each other is induced by at least intermittent tapping of either of the two layers or both. This will assure that refined metal will flow into the metal purification zone and slag will flow into the slag treating zone.

Considering the function of the refining, metal purification and slag treating zones, the major amount of refining or metal separation takes place in the intermediate zone. High purity of the nickel metal product is obtained by oxidizing the remaining minor amount of the less noble metals entering the metal purification zone.

These less noble metals are removed from the molten metal phase into the molten slag phase by maintaining a high concentration of nickel oxide in the slag of the metal purification zone. The nickel oxide content of this slag should be at least as high as that level which would be in equilibrium with nickel having the desired degree of purity. High recovery of the nickel metal is obtained by reducing the minor amount of the nickel oxide that passes unreacted through the intermediate zone and enters the slag treating zone in the molten slag phase. This remaining nickel oxide is reduced into the molten metal phase by maintaining in the molten metal in that zone a high concentration of the less noble metals. The concentration of the less noble metals in the metal phase should be at least as high as those concentrations which could be in equilibrium with a slag having the desired degree of impoverishment with respect to nickel.

The process of the present invention is particularly suitable for the recovery of nickel from alloys which contain iron and particularly cobalt, which by prior art methods, could not be separated without special techniques, expensive equipment and considerable expense. In the present process, such separation is accomplished with ease, resulting in added advantages.

As referred to above, iron-nickel-cobalt alloys are one family of alloys which can be refined by the process with excellent results. These iron-nickel-cobalt alloys,

TABLE I Composition of a-Commercial Ferronickel Alloy Constituent Weight Nickel 25 .0 Iron 74.4 Cobalt 0.6

Total 100.0%

For purposes of further discussion, this commercial ferronickel may be subjected to the treatment of the present invention in an elongated furnace, such as that shown in FIG. 2, comprising a metal purification, a slag treating zone and an intermediate zone. There is maintained in the furnace a molten metal layer in the bottom of the elongated flow path and a molten slag layer above the molten metal layer and contiguous therewith. The alloy can be introduced in molten form into the furnace, or if desired, added in particulate form, usually in small lumps and melted in the furnace. Pig and ingot can also be supplied as feed.

Oxidation of the iron and other less noble components is achieved by the introduction of an oxidation agent, such as gaseous oxygen, air, mixtures of oxygen and air, carbon dioxide, steam and other well-known gaseous oxidants. Solid oxidants, such as nickel oxide, can also be utilized.

The reducing agents utilized in the process of the present invention include :gaseous reducing agents, such as hydrogen, methane, CO, mixtures of these and hydrocarbons, whether gaseous or liquid. Liquid reductants, such as molten iron, may be used or solid reductants, such as carbon,can also be employed. The nickel alloy from which the nickel is to be separated can also be utilized as the reducing agent. In this instance, the fresh alloy charge is introduced into the slag treating zone and the iron content of the alloy will act as a reducing agent removing nickel oxide from the slag' through the oxidation of the iron component.

The oxidation reaction which takes place in the intermediate zone selectively oxidizes the iron constituent since its affinity for oxygen is relatively great. As the iron is oxidized, the formed iron oxide due to its lower density will rise and be incorporated in the slag layer. A major'amount of the iron present in the metal layer in this zone is oxidized in the intermediate refining zone. In order to achieve a high degree of oxidation, and also a good separation of the oxides from the metal layer, it is advantageous to obtain a good mixing action in the intermediate zone. The mixing will enhance interphase contact and intraphase mixing of the slag and metal phases. This mixing effect can be obtained in several ways, e.g., by shaping the furnace geometry in a manner to form pools in a refining zone, blowing a gas-. eous agent with high velocity either onto the surface or below the surface of the slag or by the use of auxiliary burners to supply heat to selected portions of'the metal and slag in the refining zone to create movement and mixing of the metal and slag layers. Mechanical mixing can also be used, or, for example, if the refining furnace is induction heated, the eddy currents generated by the heating coils can also provide mixing. Combinations of these can also be employed with the main purpose to obtain the desired intimate mixing.

Due to the countercurrent movement of the slag layer relative'to the metal layer, the slag produced in the metal purification zone will flow hack to the intermediate zone. The slag layer will contain nickel oxide resulting from the purification treatment, and this nickel oxide can act as oxidant for the iron in the metal layer.

The slag from the intermediate zone flows into the adjoining slag treating zone. In this zone, the purpose of which is to recover as much as possible of the nickel oxide in the slag and to incorporate the same in the form of metallic nickel into the metal layer, a reducing agent is introduced. The reducing agents which can be utilized include the well-known gaseous reductants, such as hydrogen, hydrocarbons, carbon monoxide and solid reductants such as carbon. In an advantageous embodiment, the reducing agent is the ferronickel feed, which due to the high iron content can strip the nickel values from the slag by the MD Fe FeO Ni reaction. Introduction of the reductant in the slag treating zone can result in nickel recoveries as high as 99.5 percent by weight calculated on the basis of the nickel content of the feed.

Advantageously, the quantity of the reductant employed in the slag treating zone is at least sufficient to reduce and to cause to be incorporated into the metal layer substantially all of the nickel values present in the slag in this zone. This assures a high recovery of the nickel values.

The iron will be oxidized in the furnace; however, the cobalt, unless removed from the system, will detrimentally enrich the metal layer, as-it recycles in the furnace. Cobalt and nickel have relatively close affinities for oxygen and, consequently, cobalt tends to remain with the nickel and may contaminate the nickel metal tapped. The instant process advantageously eliminates this contamination by at least periodically removing or tapping a small portion of the metal layer at a position where the cobalt has a high concentration. Suitable tapholes are indicated in FIGS. 2, 3 and 4 for removing cobalt-rich alloy from the intermediate zone. The position of removing the cobalt alloy can be selected to provide a commercially salable alloy. In general, the cobalt alloy removed contains greater than 10 percent by weight-of cobalt. A satisfactory cobalt-rich alloy is one in which the ratio of cobalt to nickel is 1:1, e,g., 40 percent cobalt, 40 percent nickel, balance iron. Due to the small quantity of cobalt in the ferronickel feed (0.6 percent by weight), the nickel removed from the system in a Ni-Co alloy is relatively small.

The temperature of the refining is usually above 1,600C. and temperatures of about l,9002,000C. are advantageously employed. Auxiliary burners can be utilized if the exothermic heat generated by the oxidative treatment in the intermediate refining and purification zones is not suffieient.

The furnace utilized for the refining treatment is usually a straight elongated furnace. However, other elongated configurations can also be utilized, provided a sufficiently long path treatment area is available. The inner walls of the refining furnace are suitably lined with a refractory resistant to the erosive and corrosive attacks of the slag at the operating temperatures. Such a refractory lining can be made, for example, from high purity magnesia. Frozen skull'technique, well known in the art of metallurgy, can also be utilized to protect the furnace lining. Also, fluid-cooled jackets may advantageously be employed in certain sections of the furnace.

In an advantageous embodiment of the invention, nickel oxide produced in the metal purification zone is utilized for the refining of the 'iron-nickel-cobalt alloy in the intermediate refining zone. The nickel oxide-rich slag which flows into the intermediate zone, exchanges its oxygen with the iron in the metal layer. This oxygen exchanger enriches the metal layer in nickel, which then flows into the purification zone. In this mode of refining, it is of great importance to provide intimate mixing in the intermediate zone. The mixing and intimate contact established between the layers, ensures substantially complete reaction. The cobalt-rich alloy removing and the slag treatment can proceed in the same manner as already described above.

To more clearly illustrate the chemical and physical processes taking place, the intermediate zone can be considered as composed of a series of interconnected regions along the length of this zone. Within each re gion, the metal and slag are each stirred vigorously so that each phase is essentially homogeneous. Between these regions, the cross section of the flow path for slag and alloy may be reduced to locally increase the velocity of these fluids along the axis of the furnace. This increased velocity serves to prevent back-mixing or concentration induced diffusion of metals or metal oxides between adjacent stirred regions. Sufficient retention time in each region is provided so that the metals present distribute themselves between slag and metal phases in ratios determined by their relative affinities for oxygen. In the case of nickel and iron, the reaction NiO Fe FeO Ni will proceed at 1,600C. until the ratio of iron oxide to nickel oxide in the slag will be about 100 times the ratio of iron to nickel in the metal. Ex-

pressed in the form of an equation, FeO/NiO l,600 100 (Fe/Ni). In the intermediate zone, the nickel alloy high in iron flowing from the slag treating zone meets slag rich in nickel oxide coming from the purification zone. If the slag contains sufficient nickel oxide to react with all the iron present in the alloy, only two or threev regions will be required to convert the alloy into one that is very high in nickel and'low in iron. Also, in the case of cobalt and nickel, the reaction NiO+Co= C00 +Ni will proceed at 1,600C. until the ratio of cobalt oxide to nickel oxide in the slag will be about 5 times the ratio of cobalt to nickel in the metal. With operating costs for raw materials. For example, when a binary alloy of iron-nickel where the ratio of iron to nickel is 3:1 is fed into the furnace, the refining operation is as follows:

At the slag tapping end, located at the slag treating zone end of the furnace, the slag will contain about 0.1 percent nickel oxide and 99.9 percent FeO. In commercial operation, the slag leaving the furnace will also contain essentially all of the minor amounts of other impurities present in the feed, such as SiO MnO, Cr O V 0 P 0 but these are omitted from the examples for simplicity of explanation. At the metal tapping end, opposite the slag tapping end, at the metal purification zone, the metal layer will contain 99.98 percent nickel and about 0.02 percent iron. The slag which is above the metal layer contains 97.86 percent nickel oxide and about 2.14 percent iron oxide. As this slag approaches the slag tapping end of the furnace, the iron oxide content increases to the 99.9 percent shown above, while the nickel-oxide content is reduced from 99.86 percent to 0.1 percent. At any given point be tween the metal tapping end and the slag tapping end of the furnace, the composition of the slag and metal layers can be ascertained, which permits economical and efficient operation of the system. The determination of the material composition during the operation is important, as it allows efficient control of the feed, oxidation and reduction rate. Table II, which follows, shows slag-metal equilibria in the refining furnace, which is divided into a metal purification, refining and slag-treating zones. In the furnace at given intervals, four regions are established. Region I is at the metal tapping end, while region 4 is at the slag tapping end. Regions 2-3 are chosen to represent equilibria regions in the refining zone. A binary alloy containing 25 percent nickel and percent iron is fed into the refining zone at region 3, where it reacts with slag entering from region 2 to give a metal pool containing 51.93 percent nickel, as shown in Table 11.

TABLE II Slag'Metal Equilibria for an Iron-Nickel Binary Alloy Having an Iron to Nickel Ratio of 3:1

If a ferronickel alloy, such as that shown in Table I, is utilized for the production of nickel, the metal layer will additionally contain cobalt. During the operation of the refining furnace, the cobalt content may accumulate to such an extent as to reduce the purity of the metallic nickel tapped at the metal tapping station. To avoid this, there must be close control of the outflowing metallic nickel purity, and when it is observed that the purity of the nickel is below that desired, removal or tapping of a cobalt-rich alloy is effected. When sufficient cobalt has been removed, the nickel purity will again reach the desired level. Alternately, the nickel cobalt alloy can be removed at a predetermined rate to ensure continuous production of nickel containing less than some desired cobalt content.

In a manner similar to the discussion provided for alloys, the following will be described in relationship to In accordance with the process the nickel bearing ores or concentrates may be directly introduced into the refining furnace in particulate form or, if desired, can be premelted in a separate vessel and charged to the furnace in molten condition. While the nickelbearing ores or concentrates can be fed directly to the furnace, it is advantageous to dry the ores and preheat them prior to introduction tothe furnace. If desired, the nickel-bearing ore can be subjected, prior to introduction into the furnace, to a beneficiation which will advantageously remove the gangue material from the ore. It is also possible to subject the nickel-bearing ore to a preliminary reduction step wherein the degree of reduction is chosen according to the economy of the entire process. Thus, for example, a beneficiated lateritic ore containing nickel and iron in a ratio of 1 part of nickel to parts of iron can be reduced to an ironnickel alloy which can then be treated according to the process steps discussed under the production of nickel from nickel'alloys. If a sulfidic nickel-bearing ore or a sulfidic nickel concentrate is the raw material for the process of the present invention, it is preferred to convert the sulfidic material to oxides. This preliminary treatment can be accomplished by simple roasting techniques wherein sulfidic material is converted to oxides.

Regardless of whether the ores and concentrates are subjected to any preliminary treatment, the process of the present invention is capable of producing nickel directly from oxidic nickel-bearing ores and oxidic nickel-bearing concentrates.

In the process of refining ores and concentrates, it is preferred to feed the ore into the intermediate zone.

The ore is subjected to a reducing-treatment in the furnace, preferably in the slag treating zone. Similar to the conditions described under the refining of alloys, the metal layer near the slag tapping end will contain a considerable quantity of iron in metallic form. Presence of this iron will serve to strip nickel oxide from the slag layer by oxygen exchange between NiO and Fe.

As described above for the purification of alloys, the purity of the metal layer entering the metal purification zone from the refining zone must be controlled. This can be conveniently achieved by controlling the amount of nickel oxidized in the purification zone and to be returned to the intermediate zone where it becomes available to oxidize iron and enrich the metal layer with nickel.

The metal phase or lower layercan be tapped either continuously or intermittently.

Control of the compositions of the slag and metal layers can be achieved in severalways fFor example, the purity can be either controlled by determining the slag or the metal composition at the metal tapping end of the furnace, the analytical results can be related back to the furnace operation, and adjustment in the rate of oxidation, reduction, tapping and feeding can be made accordingly. Analysis of the slag layer at the slag tapping end provides a tool for the efficiency of nickel recovery. Any nickel lost through the slag can be rapidly counteracted by either increasing the rate of reduction,

reducing the rate of feed or the rate of tappiri g of slag.

To further illustrate the. improvements gained through the present invention, the following examples are given. The examples are not to be construed as limiting the invention, the scope of which is defined by the appended claims.

EXAMPLE I .A ferronickel alloy containing iron 74.4 percent by weight, nickel 25.0 percent by weight and cobalt 0.6 percent by weight is melted in-a melting vessel and is introduced into a refining furnace, such as that depicted in FIG. 2 at the slag tapping end of the furnace.

The feed rate is kg/hr. The temperature at the feed location of the furnace is kept at about 1,600C. by

means of one or more auxiliaryfuel burners, such as the burner 32 located in the slag treating zone 14 of the furnace in FIG. 2. The molten alloy flows through the intermediate or interaction zone and is contacted with a gaseous oxidation agent in the oxidation zone. The oxidation agent is an oxygen supplied from a watercooled lance above the surface of the molten material. The temperature in the oxidation zone is kept above l,900C. The iron-nickel alloy- (ferronickel) acts as a reductant in the slag treating zone, and, consequently, no additional reductant is required. two-layer system is formed consisting of an upper slag layer and a metallic lower layer and slag is continuously tapped from the furnace. The metallic lower layer is tapped at two locations. At the nickel-tapping end, nickel is tapped at a rate of 24.25 kg/hr. in 99.8 percent purity (0.2 percent Co impurity). A nickel-cobalt alloy is tapped from the metallic phase at a tapping station located near the center of the furnace at a rate of 1.00 -kg/hr. The composition of this alloy is nickel 49.0 percent by weight, cobalt 49 percent by weight and iron 2 percent by weight. The overall nickel recovery based on the nickel originally present in the ferronickel alloy is 98.8 percent. Vigorous interaction between the slag and metal layers is accomplished by positioning auxiliary burners in the interaction zone.

Typical concentrations within the refining furnace would be as given below.

COMPOSITION lN WEIGHT PERCENT Slag Layer Metal Layer Ni Co Fe NiO C00 FeO Slag Treating Zone 28.08 2.11 69.81 0.40 0.l5 99.45 Cobalt Drain Zone 49.00 49.00 2.00 9.92 49.60 40.48 Metal Purification Zone 99.80 0.20 0.01 98.91 0.99 0.099

13 EXAMFLE ii A lateritic oxide ore of the following compositions is subjected to the process of the present invention:

The ore is dried and calcined to remove its moisture content. The calcined ore is melted in a suitable melt ing vessel and is introduced into an elongated refining furnace similar to that depicted in FIG. 4. in the proximity of the center of the furnace, e.g., into the intermediate zone of the furnace by a suitable feeding means, such as the feeding means 40 in FIG. 4. The molten ore is fed to the furnace at the rate of 100 kg/hr. A reducing gas containing a mixture of hydrogen and carbon monoxide (50% 1-1 and 50% CO by volume) is introduced into the slag layer of the reduction or slag treating zone of the furnace by a water-cooled lance, such as lance 28, depicted in FIG. 4. The rate of reducing gas is controlled in a manner as to reduce substantially all of the nickel oxide to nickel and a portion of the iron in the slag. As the reduction proceeds, a two-layer system having a distinct interface is produced. The metal consisting of iron and nickel flows in a countercurrent fashion towards the metal tapping end of the furnace; as the metal passes through the interaction zone, nearly all of the iron in the metal phase is oxidized and incorporated into the slag phase by oxygen exchange with nickel oxide in the slag. Prior to reaching the metal tapping end ofthe furnace, oxygen is introduced to oxidize substantially all of the remaining iron present in the lower metallic nickel-containing layer and a major amount of nickel. The temperature in the furnace is maintained by auxiliary burners which provide temperatures in excess of 1,500C. in the reduction and interaction zones. Temperatures in excess of 1,950C. in the oxidation zone are obtained by the heat of oxidation of the metal. Metallic nickel is continuously tapped from the metal-tapping end in a purity of about 99.8 percent containing about 0.2 percent impurities consisting primarily of cobalt. A cobalt-nickel alloy containing 25% Co, 30% Ni and 45% Fe is tapped from the intermediate zone of the furnace at a rate of 0.32 kg/hr. The slag layer is continuously tapped at the slag tapping station located at the end of the furnace. At an ore feed rate of 100 kg/hr., the weight of nickel produced and tapped from the furnace is 1.1.4 kg/hr. The process provides a 98.8 percent recovery of the nickel value from the lateritic ore. 92 percent of the recovered nickel is in the product, and 8 percent is in the nickel-cobalt alit will be apparent to those skilled in the art that various modifications can be made without departing from the principles of the invention as disclosed herein and for that reason, it is not intended that it should be limited other than by the scope of the appended claims.

What is claimed is:

l. A process for separating and recovering nickel from a nickel-bearing material containing nickel, iron and cobalt and other metals less noble than nickel which comprises:

a. providing a furnace having an elongated flow path comprised ofa metal purification zone, a slag treating zone, and a refining zone, the refining zone being located between the metal purification and the slag treating zones, the metal purification zone being located in the vicinity of one end of the flow path, the slag treating zone'being located in the vicinity of the other end of the flow path, a layer of molten slag, superimposed on and contiguous with a layer of molten metal, said slag and metal layers extending throughout the elongated flow path, the molten slag ph'ase consisting essentially of nickel oxide and oxides of the metals less noble than nickel, while the molten metal phase consisting essentially of metallic elements, one of the elements being the nickel to be recovered;

b. introducing into the furnace maintained at a temperature of l6002000C. the nickel-bearing metallic material, said nickel-bearing material being selected from the group consisting of oxidic nickel ores and concentrates, crude nickel-bearing alloys and combinations thereof;

. inducing a countercurrent movement between the slag and metal phases by removing slag at least at one slag tapping station and by removing high purity nickel at least at one metal tapping station;

. promoting interphase contact and controlled intraphase mixing in the refining zone in a manner to prevent back-mixing along the axis of the furnace of the molten metal and slag phases thereby effecting a progressive increase of the nickel content of the molten metal phase by oxygen exchange between nickel oxide and iron as it proceeds from the slag treating zone to the metal purification zone;

. at least periodically tapping a portion of the metal phase in the refining zone at a position where the cobalt in the metal phase has reached a concentration of greater than 10 percent by weight, said portion being sufficient in amount to prevent an accumulation of cobalt in the metal phase as it progresses from the slag treating zone to the metal purification zone;

. controlling the composition of the metal phase in the metal purification zone by oxidizing and cans ing to be incorporated into the slag phase substantially all of the elements less noble than the nickel present in the metal phase in the metal purification zone to ensure a slag composition rich in nickel oxide and controlling the composition of the slag phase in the slag treating zone by reducing substantially all of the nickel present as oxide in the slag phase to provide a slag for tapping from the elon-' gated flow path which is impoverished in nickel values thereby ensuring that the metal phase in the metal purification zone is nickel metal of high purity and that the high purity nickel product tapped from the furnace is in high yield; and

g. tapping said high purity nickel metal as product.

2. A process according to claim 1 wherein the ratio of cobalt to nickel in the removed metal is 1:1.

3. A process for separating and recovering nickel 5 from a crude nickel-iron-cobalt alloy material which comprises:

a. providing a furnace having an elongated flow path comprised of a metal purification zone, a slag treating zone, and a refining zone, the refining zone being located between the metal purification and 15 the slag treating zones, the metal purification zone being located in the vicinity of one end of the flow 'path, the slag treating zone being located in the vicinity of the other end of the flow path, a layer of molten slag, superimposedon and contiguous with a layer of molten metal, said slag and metal layers extending throughout the elongated flow path, the molten slag phase consisting essentially of nickel oxide, iron oxide and oxides of the metals less noble than nickel, while the molten metal phase consisting essentially of metallic elements, one of the elements being the nickel to be recovered;

b. introducing into the furnace maintained at a temperature of 1,600-2,000C. the crude iron-nickelcobalt alloy;

c. inducing a countercurrent movement between the slag and metal phases by removing slag at least at one slag tapping station and by removing high purity nickel at least at one metal tapping station;

d. promoting interphase' contact and controlled intraphase mixing in the refining zone in a manner to prevent back-mixing along the axis of the furnace of the molten metal and slag phases thereby effecting a progressive increase of the nickel content of the molten metal phase by oxygen exchange between nickel oxide and iron as it proceeds from the slag treating zone to the metal purification zone;

e. at least periodically tapping a portion of the metal phase in the refining zone at a position where the cobalt in the metal phase has reached a concentration of greater than 10 percent by weight, said portion being sufficient in amount to prevent an accumulation of cobalt in the metal phase as it progresses from the'slag treating zone to the metal purification zone;

f. controlling the composition of the metal phase in the metal purification zone by oxidizing and causing to be incorporated into the slag phase substantially all of the elements less noble than the nickel present in the metal phase in the metal purification zone to ensure a slag composition rich in nickel oxide and controlling the composition of the slag phase in the slag treating zone by reducing substantially all of the nickel present as oxide in the slag phase to provide a slag for tapping from the elongated fiow path which is impoverished in nickel values thereby ensuring that the metal phase in the metal purification zone is nickel metal of high purity and that the .high purity nickel product tapped from the furnace is in high yield; and

g. tapping said high purity nickel metal as product.

4. A process according to claim 2 wherein the ratio of cobalt to nickel in the removed metal is 1:1.

Claims

2. A process according to claim 1 wherein the ratio of cobalt to nickel in the removed metal is 1:1.
3. A process for separating and recovering nickel from a crude nickel-iron-cobalt alloy material which comprises: a. providing a furnace having an elongated flow path comprised of a metal purification zone, a slag treating zone, and a refining zone, the refining zone being located between the metal purification and the slag treating zones, the metal purification zone being located in the vicinity of one end of the flow path, the slag treating zone being located in the vicinity of the other end of the flow path, a layer of molten slag, superimposed on and contiguous with a layer of molten metal, said slag and metal layers extending throughout the elongated flow path, the molten slag phase consisting essentially of nickel oxide, iron oxide and oxides of the metals less noble than nickel, while the molten metal phase consisting essentially of metallic elements, one of the elements being the nickel to be recovered; b. introducing into the furnace maintained at a temperature of 1,600*-2,000*C. the crude iron-nickel-cobalt alloy; c. inducing a countercurrent movement between the slag and metal phases by removing slag at least at one slag tapping station and by removing high purity nickel at least at one metal tapping station; d. promoting interphase contact and controlled intraphase mixing in the refining zone in a manner to prevent back-mixing along the axis of the furnace of the molten metal and slag phases thereby effecting a progressive increase of the nickel content of the molten metal phase by oxygen exchange between nickel oxide and iron as it proceeds from the slag treating zone to the metal purification zone; e. at least periodically tapping a portion of the metal phase in the refining zone at a position where the cobalt in the metal phase has reached a concentration of greater than 10 percent by weight, said portion being sufficient in amount to prevent an accumulation of cobalt in the metal phase as it progresses from the slag treating zone to the metal purification zone; f. controlling the composition of the metal phase in the metal purification zone by oxidizing and causing to be incorporated into the slag phase substantially all of the elements less noble than the nickel present in the metal phase in the metal purification zone to ensure a slag composition rich in nickel oxide and controlling the composition of the slag phase in the slag treating zone by reducing substantially all of the nickel present as oxide in the slag phase to provide a slag for tapping from the elongated flow path which is impoverished in nickel values thereby ensuring that the metal phase in the Metal purification zone is nickel metal of high purity and that the high purity nickel product tapped from the furnace is in high yield; and g. tapping said high purity nickel metal as product.
4. A process according to claim 2 wherein the ratio of cobalt to nickel in the removed metal is 1:1.