US3503734A - Beneficiation of nickel-containing lateritic ores - Google Patents

Description

United States Patent 3,503,734 BENEFICIATION OF NICKEL-CONTAINING LATERITIC ORES James Alexander Evert Bell, Toronto, Ontario, Canada, assignor to The International Nickel Company, Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Dec. 6, 1967, Ser. No. 688,317 Claims priority, application Canada, Mar. 6, 1967,

,486 Int. Cl. C21b 1/10 U.S. Cl. 751 18 Claims ABSTRACT OF THE DISCLOSURE Ores containing a metal value at least as reducible as iron oxide are formed into oxide pellets containing the metal value and the pellets are then heated to above their softening but below about 1400 C. in a reducing atmosphere in the presence of a non-fiuxing refractory oxide to coalesce the metal values into recoverable forms and to form on the surfaces of the oxide pellets an oxide solid solution which has a higher softening point than the oxide pellets and which minimizes sticking of the oxide pellets.

The present invention relates to treatment of complex oxide ores to concentrate metal values contained therein, and more particularly to the pyrometallurgical concentration of metal values, such as nickel, contained in complex oxide ores.

It has been proposed to selectively reduce nickel values contained in lateritic ores and then to concentrate the reduced nickel values by magnetic separation techniques. High recoveries by such techniques require that the selectively reduced ore contain nickel-enriched particles which are larger than about microns. Since the nickel values are highly disseminated throughout the ore, the selectively reduced ore must be heated to high temperatures to provide particles of the required size by diffusion of the reduced nickel values. Diffusion of the nickel values is promoted when the heated ore begins to soften, i.e., the viscosity of the ore is lowered, and, in fact, most proposed processes treat the selectively reduced ore so that the ore passes through the softening point. Some processes have relied solely on high temperatures to reach the softening point while others have relied on a combination of relatively expensive chemical reagents, such as sodium sulfate, and elevated temperatures. Regardless of the techniques employed in reaching the softening temperature processes heretofore proposed have encountered operational difficulties due to the tendency of the softened ore to agglomerate or stick on the furnace interior whether a shaft furnace or a rotary kiln type furnace is employed. Elaborate furnaces have been developed to avoid the problems of sticking and agglomeration but such furnaces involve large capital expenditures. Other processes have treated lateritic ores with relatively expensive chemicals such as sodium sulfate so that the ore softened at lower temperatures and the problems associated with sticking and agglomeration could be avoided by employing conventional techniques such as introducing a mechanically interfering phase of lime or dolomite. The use of a mechanically interfering phase such as lime or dolomite works reasonably well at lower temperatures but at such lower temperatures expensive reagents must be employed. The use of expensive reagents can be eliminated by employing high temperatures, but at higher temperatures lime and dolomite are ineffective as mechanical interfering phases and can, in fact, increase the problems of sticking and agglomeration. Although many attempts were made to overcome the foregoing difficulties and other difficulties,

Patented Mar. 31, 1970 "ice none, as far as I am aware, was entirely successful when carried into practice commercially on an industrial scale.

It has now been discovered that nickel-containing lateritic ores can be concentrated by selective reduction at high temperatures and subsequent magnetic separation while avoiding or minimizing the problems associated with high temperature treatment of complex oxide ores.

It is an object of the present invention to provide a process for treating complex oxide ores at elevated temperatures while minimizing the problems associated with sticking and agglomeration.

Another object of the invention is to provide an improved process for concentrating nickel values contained in lateritic ore by selectively reducing the nickel values and subsequently magnetically separating the reduced nickel values.

The invention also contemplates providing a process for enhancing the concentration of nickel values contained in lateritic ores by the addition of relatively inexpensive chemical reagents.

Broadly stated, the present invention contemplates heat ing a pelletized complex oxide ore which can contain at least one metal value from the group consisting of iron, nickel and cobalt to a temperature above its softening point but below about 1400 C. in an atmosphere reducing to at least one metal value in said ore and in the presence of a nonfiuxing refractory oxide and reacting the oxide ore with the refractory oxide to form on the surface of the oxide ore pellets an oxide solid solution which has a softening point higher than the oxide ore and which minimizes sticking of the ore pellets to each other. Advantageously, at least one metal value is substantially completely reduced during the heating step in the reducing atmosphere and is then, after at least partially reacting the ore with the refractory oxide, coalesced into particles of suflicient size to enable recovery of the reduced metal values. After the aforedescribed treatment, the pelletized ore can be crushed and the coalesced reduced metal values can be recovered therefrom by concentrating techniques such as magnetic separation or flotation.

The process of the present invention is most advantageously conducted in iron-containing oxide ores which also contain other valuable constituents such as nickel and/ or cobalt. The iron-containing oxide ore is selectively reduced to metallize a controlled portion of the iron and substantially all of the other metal values and is then heated above its softening point to coalesce the metallized values. After selective reduction and coalescence of the metallized values, the ore is comminuted and the coalesced metallized portion is recovered by magnetic separation to concentrate the metal values. Ores which can be treated in this manner are generally referred to as lateritic ores, i.e., the weathered portion of serpentine deposits, and contain, by weight, at least about 15% or 20% to about 45% iron, up to about 3% nickel, from about 1% to about 30% magnesia, from about 2% to about 40% silica as silicates, up to about 10% alumina and the balance essentially water as moisture andas chemically bound water.

At the temperatures required for coalescence, the lateritic ore softens and becomes sticky, thus presenting a difficult materials handling problem. Whether reduction is conducted in a rotary-type furnace or a stationary furnace such stickiness can cause ringing and/ or the bulidup of accretions on the furnace walls which lower the capacity of the furnace and can result in complete stoppage of operation. The undesirable effects caused by the sticky nature of the ore at elevated temperatures can be avoided or minimized by heating the pelletized ore in the presence of, e.g., by mixing the pellets with or by coating the pellets with, a non-fluxing refractory oxide which has a softening point above the softening point of the ore. The nonfiuxing refractory oxide reacts with the sticky ore to form an oxide solid solution which also has a softening point above that of the ore. A particularly advantageous refractory oxide in terms of both cost and effectiveness has been found to be unweathered serpentine underlying the lateritic ore being treated. When the reducing operation is conducted in a rotary-type furnace, the unweathered serpentine is ground to a particle size of at least about 90% minus 4 mesh and is fed to the rotary furnace at a rate of about 33%, e.g., about 15% to about 50%, by weight of the ore. After passing through the furnace the unweathered serpentine can be separated from the selectively reduced pellets and then recycled to the rotary furnace. Unweathered serpentine which contains less than about iron, at least about 40% silica, at least about 30% magnesia, at least about 1% alumina, and the balance essentially water can be employed. Other refractory oxides which function in this manner, e.g., floaters, are alumina, magnesia, titania and naturally-occurring complex oxide minerals, such as olivine, asbestos and peridotite, which contain less than about 7% iron and have low calcium oxide contents. The term non-fluxing refractory oxides as used herein refers to the hereinbefore enumerated oxides and other oxides which increase the viscosity of the ore at the pellet surfaces upon solution therein and which also display softening points above the coalescing temperatures, e.g., above about 1320" C., together with chemical stability such that the oxides are irreducible by carbon at the coalescing temperatures. Furthermore, the nature of the non-fluxing refractory oxides is such that, when added to the reduced ore mixture'in small amounts, the melting or softening point of the ore is raised. A wide variety of refractory oxides can be employed as long as they are non-fluxing to the already sticky ore at reducing temperatures. Thus, calcium oxide-bearing materials such as lime cannot be employed as floaters since calcium oxide has a tendency to flux the lateritic ore which only increases the problems associatedwith stickiness. For similar reasons silica-containing materials cannot be utilized. It might be noted that minor amounts of calcium oxide and silica can be present in the refractory oxide if they are present in amounts and in a form which will not flux the lateritic ore. The non-fluxing refractory oxide particles adhere to ore pellets and at the coalescing temperatures react therewith to form an oxide solid solution over substantial portions of the pellet surfaces and since the resulting oxide solid solution has a softening point above the coalescing temperatures, sticking between ore pellets is minimized or completely avoided. The non-fluxing refractory oxide must be added in an amount of at least about by weight of the ore, to minimize or avoid sticking and can be added in amounts as high as about 100% or higher, but for reasons of economy the amount is generally limited to about 50%.

In order to facilitate the selective reduction operation the lateritic ore is ground to a pelletizing fineness, e.g., at least about 100% minus 48 mesh. The finely ground ore is then pelletized and fed to a furnace wherein the pelletized ore is selectively reduced as pointed out hereinbefore. Advantageously, a reducing agent is incorporated in the ore during the pelletizing operation so that the pelletized ore contains amounts of the reducing agent suificient to insure the controlled metallization. Mechanical dispersion of the reducing agent in the pelletized ore increases the kinetics of the reducing reactions and provides a material saving in the amount of reductant that must be employed. Reductants such as finely divided coke, liquid hydrocarbons, coal, carbon or lignite can be employed. The amount of reductant incorporated in the pelletized ore will depend on the iron and metal value, e.g., nickel, content of the ore and is added in quantities suflicient to reduce at least about two but less than about five parts of iron for each part of the other metal value metallized. Se ective reduction of most nickel-containing lateritic ores is controlled so that the total weight of the metallized portion is about 8% to about 20%, e.g., about 10%, of the selectively reduced ore. The proportion of iron reduced to the metallic state is also an important consideration. A controlled portion, e.g., about 8% to about 30%, of the iron in the lateritic ore must not be reduced to the metallic state so that unreduced iron can act as a fluxing agent for the ore in the coalescing operation. For most nickel-containing lateritic ores the reductant will be in amounts of from about 2% to about 10% by weight of the ore and advantageously in amounts of from about 3% to about 5% by weight of the ore.

As noted hereinbefore, magnetic separation techniques are employed to concentrate the metal values contained in the metallized portion of the lateritic ore. Experience has shown that effective magnetic separation of the metallized portion of the ore requires the selectively reduced metal values be distributed throughout the pelletized ore as metallized particles which have a size of at least about 10 microns. Since metal values as nickel are highly disseminated throughout lateritic ores, even after selective reduction, the ore must be further treated in such a manner as to insure concentration of the metal values, e.g., nickel, into particles having a particle size of at least about 1 0 microns. Concentration of the reduced metal values into particles having a size of at least about 10 microns can be realized by lowering the viscosity of the ore. The viscosity of the ore can be lowered by employing elevated temperatures and by making additions of viscosity lowering reagents to the ore. Reagents which contain at least one member selected from the group consisting of silica, lime, sodium oxide, potassium oxide and compounds thereof can be added to the ore to lower the viscosity thereof. These reagents are advantageously added to the ore during or before the ore is pelletized and are added in amounts of up to about 10%, by weight of the ore, e.g., from about 2% to about 10%. The amount of metallized nickel-containing particles having a size larger than about 10 microns can also be increased by providing a source of sulfur in the pelletized ore. The source of sulfur is advantageously added to the ore before the ore is pelletized and can be added as elemental sulfur introduced per se or in the carbonaceous reductant, pyrites, pyrrhotite or in the form of a compound with one of the aforementioned viscosity lowering reagents such as calcium sulfate or sodium sulfate. Sulfur can be added to ore in amounts of up to about 5% by weight of the ore, e.g., from about 0.5% to about 5%. The test results in Table I show the effects of sulfur and sulfur plus silica additions on the coalescence of selectively reduced nickel values in a nickel-containing lateritic ore at various coalescing temperatures.

TABLE I.COALESCENCE OF REDUCED METAL VALUES 2 Approximately of Fe reduced in each test.

As shown in Table I, heating selectively reduced pellets which contain no additives to temperatures of 1260 C. and 1315 C. produces amounts of metallized particles 15 microns or larger of "0% and 30%, respectively. Coalescing selectively reduced pellets containing 0.75% sulfur at temperatures of 1260 C. and 1315 C. produces amounts of metallized particles 15 microns or larger of 50% and 89%, respectively. Reducing nickel-containing lateritic ore pellets containing 0.75% sulfur along with 4% and 8% silica and coalescing at a temperature of 1260 C. produce amounts of nickel-containing metallized particles 15 microns or larger of 65% and 88%, respectively, which confirms the improved results due to the synergistic effect of sulfur and silica. Table I also confirms that by adding 0.75 sulfur and 4% silica to the pelletized ore and by coalescing at a temperature of 1315 C., 95% of the reduced metal values can be coalesced into particles having a size of 15 microns or larger. It is apparent from the results in Table I that far greater concentration at reasonable temperatures can be realized by incorporating the aforementioned additives in pelletized nickel-containing lateritic ores.

When treating a nickel-containing lateritic ore and after the ore is pelletized or briquetted, the pellets are fed to a furnace and heated to a temperature of at least about 1150 C. to selectively reduce the ore and to coalesce the metallized values into particles having a size of at least about 1 microns. For reasons of ease and efficiency in operation and lower capital expenses it is preferred to employ a rotary kiln. The pelletized ore is advantageously fed to a rotary kiln to form a gently tumbling bed. The pelletized ore is preheated to a temperature of at least about 800 C. in a preheating zone and is then conducted to a reducing zone wherein a temperature of at least about 1150 C., e.g., from about 115=0 C. to about 1300 C., is maintained by a burner located at the exit end of the kiln. The atmosphere within the gently tumbling bed in the reducing zone is maintained at a reducing potential equivalent to a CO:CO ratio of at least about 1:1, e.g., from about 2:1 to about 3:1, by controlling the combustion of the fuels by the burner and/ or by adding reductants such as coke, coal, lignite and liquid hydrocarbons to the gently tumbling bed in the reducing zone.

In carrying the invention into practice, it is preferred to grind a nickel-containing lateritic ore containng, by weght, about 1% to about 3% nickel, at least about 20% but not more than about 40% iron, about 5% to about 25% magnesia, about to about 35% silica, up to about 6% alumina and the balance essentially water as moisture and chemically combined water to pelletizingor briquetting fineness, e.g., about 90% minus 48 mesh. Reductants such as liquid hydrocarbons, coke, coal, carbon or lignite are added to the finely divided ore in amounts of from about 3% to about 5% by weight of the ore. Silica in amounts of up to about 10% and sulfur from about 0.5% to about 2% by weight percent of the ore being treated are also added to the finely divided ore. The finely divided lateritic ore containing the aforementioned additions is formed into pellets having a size of from about 5 millimeters to about 25 millimeters (mm.).

The pelletized ore is fed to the preheating zone of a rotary type furnace to form a gently tumbling bed and a refractory oxide such as alumina, titania, magnesia and naturally occuring complex oxide minerals containing less than about 7% iron such as forsterite, olivine, unweathered serpentine and peridotite having a particle size of less than about 4 mesh is fed with the pelletized ore to the rotary furnace at a rate of about to about 50% by weight of the ore. The gently tumbling bed is raised to a temperature of from about 1200 C. to about 1260 C. to reduce substantially all the nickel values contained in the ore together with controlled amounts of iron and to concentrate the nickel in the form of coalesced particles, about 85% of which are larger than about 10 microns. At these temperatures the refractory oxide adheres to the surface of the pelletized ore and reacts therewith to form an oxide solid solution which has a softening point above about 1320 C. over substantial portions of the pellet surfaces to thereby minimize sticking. The reduced pellets are then cooled to ambient temperature, the excess floater material is separated therefrom and the pellets are crushed and ground. The nickel values are then magnetically separated from the ground pellets as a ferronickel alloy which contains at least about 15% nickel, advantageously about 20% to about 30% nickel, with recoveries of at least about e.g., about or even higher, on the basis of contained nickel in the ore.

For the purpose of giving those skilled in the art a better appreciation of the advantages of the invention, the following illustrative examples are given.

EXAMPLE I A lateritic ore containing 1.9% nickel, 28% iron, 18% magnesia, 27% silica, 2% alumina and the balance essentially water as moisture and as chemically combined water was pelletized. An admixture of the pellets and minus 65 plus 100 mesh alumina in equal proportions was placed in a refractory crucible. The charge along with a controlled carbon addition of about 4% was heated to about 1316 C. and held at that temperature for one hour to reduce about one-third of the iron and substantially all the nickel and to coalesce the reduced metal values. Upon cooling to room temperature the pellets were free flowing and the alumina was screened from the pellets employing an 8 mesh screen. The reduced pellets contained, by weight, approximately 15% alumina as an oxide solid solution on the pellet surfaces. This example confirms that even under the most severe conditions, i.e., maintaining the pellets in a static state, the oxide solid solution on the pellet surfaces formed by the reaction of alumina and the pelletized ore minimizes sticking between pellets.

EXAMPLE II The test in Example I was repeated in a similar manner except an unweathered naturally occurring serpentine containing 7% iron, 31% magnesia, 39% silica, 1% alumina, and the balance essentially water as moisture and chemically bound water and ground to minus 14 mesh and the pelletized ore were charged into a crucible in equal proportions as an admixture. The pelletized ore was treated at 1316 C. for one hour as described in Example I. Upon cooling the pelletized ore to room temperature, it was again found that the pellets were free flowing. About 12%, by weight, of the reduced pellets consisted of dehydrated serpentine in the form of an oxide solid solution over substantial portions of the pellet surfaces.

EXAMPLE III A nickel-containing lateritic ore containing, by weight, 1.9% nickel, 28% iron, 18% magnesia, 27% silica, 2% alumina and 14% loss on ignition (LOI) was dried and crushed to minus 48 mesh. The dried ore was blended with 0.75 and 4%, by weight of the dried ore, of elemental sulfur and silica, respectively. The blended ore was mixed with 4% by weight or Bunker C oil and the mixture was formed into pellets about 12.5 millimeters in diameter. The pellets were charged into a crucible in admixture with minus 14 mesh unweathered serpentine having a composition of 0.7% nickel, 7% iron, 31% magnesia, 39% silica, 1% alumina and 14% L01 and being present in an amount of 50% by weight of the pelletized ore. The charge was heated to about 1260 C. in an inert atmosphere for about one hour to reduce substantially all the nickel and about /3 of the iron to the metallic state and to coalesce the reduced metal values. After cooling, the free flowing pellets were separated from the unweathered serpentine by screening on a 4 inch screen. The reduced pellets contained, by weight, about 5% unweathered serpentine adhered to and in the form of an oxide solid solution on the surface of the pellets. The pellets were then ground to about 80% minus 325 mesh and the ground ore was magnetically separated. Magnetic separation yielded on an undiluted basis, i.e., as if no unweathered serpentine had adhered to the pellets, the following fractions:

Wt. percent Magnetic fraction of 18% Ni 11 Middling fraction of 2% Ni 2 Tailing fraction of 0.36% Ni 87 This example confirms that a concentration of about 8 to 1 with recoveries of about 86% of the nickel contained in lateritic ores can be realized while avoiding operating difficulties caused by sticking.

EXAMPLE IV A finely divided lateritic ore containing 1.41% nickel, 37.3% iron, 2.24% chromium oxide, 11.64% silica, 7.82% alumina, 8.08% magnesia and 14.5% LOI is mixed with 0.76%, by weight, elemental sulfur and 9%, by weight, lignite containing 32.3% fixed carbon, 15.2% ash and 52.5% volatile matter which contained 21.9% water and sulfur, originally present in the lignite. The mixture of ore, sulfur and lignite briquetted into 19 mm. diameter cylindrical briquettes. The briquettes and 30%, by weight, of unweathered serpentine of the same composition recited in Example III is charged into a rotating cylinder as an admixture. An inert atmosphere of nitrogen is introduced into the thus-charged cylinder and the cylinder is then continuously rotated for an hour while being maintained at a temperature of about 1260 C. After the charge has cooled, the unweathered serpentine is easily screened from the free flowing briquettes. The selectively reduced charge is comminuted to mainly minus 325 mesh for magnetic separation. Magnetic separation of the comminuted charge yields a magnetic plus middling fraction of about 16.8%, by weight of the comminuted charge, which contains about 10.5%, by weight, nickel and a tailing fraction of about 83.2%, by weight, which contains about 0.22%, by weight, nickel. A recovery of about 90% of the nickel is thus obtained.

It is to be observed that the present invention provides in one embodiment a process for treating complex ironcontaining oxide ores containing at least one other metal value such as nickel and cobalt. The complex iron-containing oxide ore is finely ground and then pelletized. The pelletized complex iron-containing oxide ore is then heated to a temperature above its softening point but below about 1400 C. in a selectively reducing atmosphere to reduce substantially all of the other metal value and controlled amounts of iron and to coalesce the reduced metal values. During the selective reduction and coalescence of the reduced metal values, the pelletized ore is contacted with a non-fluxing refractory oxide so that the non-fluxing refractory oxide reacts with the surface of the pelletized ore to form an oxide solid solution which has a softening point higher than the iron-containing oxide ore and which minimizes sticking of the ore pellets to each other. The thus-treated pellets are then cooled and the coalesced reduced metal values are recovered therefrom.

Although the invention has been described with particular reference to the treatment of nickel-containing lateritic ores, ores containing at least one metal value which is at least as reducible as iron oxide can be treated in accordance with the present invention. Furthermore, the metal oxide does not have to be naturally occurring but can be obtained by roasting sulfide ores containing the metal value. Thus, copper can be recovered from ores containing chrysocolla, azurite, malachite, tenorite and cuprite and from roasted ores containing covellite. In a like manner, tin can be recovered from ores containing cassiterite and lead from ores containing minium, cerussite and litharge. Ores containing natively occurring metals can also be treated. Thus, ores containing native silver can be treated in accordance with the present invention to coalesce the native occurring silver particles into particles of an easily recoverable size. In a manner similar to forming oxide pellets from naturally-occurring oxide ores or from roasted sulfide ores, ores containing native or metallic values are formed into oxide pellets with the host rock serving as the oxide. Thus, nickel-containing ores, iron-containing ores and cobalt-containing ores can be treated in accordance with the invention.

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.

I claim:

1. A process for treating an oxide material containing iron oxide and at least one metal value from the group consisting of nickel, cobalt, copper, tin, lead and silver which comprises forming oxide pellets containing the metal value, heating the oxide pellets to a temperature above their softening point but below about 1400 C. in a reducing atmosphere to reduce substantially all of the metal value and to coalesce the reduced metal value while reacting the surface of the oxide pellets with a non-fluxing refractory oxide to form thereon an oxide solid solution having a softening point above the softening point of the oxide pellets, and recovering the coalesced metal value after cooling the oxide pellets.

2. A. process for concentrating nickel values contained in lateritic ores which comprises heating a pelletized nickel-containing lateritic ore to a temperature above its softening point but lower than about 1400 C. in a reducing atmosphere to reduce substantially all the nickel and about 2 parts to about 5 parts of iron for each part of nickel reduced and to coalesce the reduced nickel and iron values while reacting the pelletized ore with a non-fluxing refractory oxide to form an oxide solid solution on the surface of the ore pellets which has a softening point higher than the pelletized ore and recovering the reduced nickel values.

-3.A process as described in claim 2 wherein a reductant is incorporaated in the ore pellets.

4. A process as described in claim 3 wherein the reductant is selected from the group consisting of coke, liquid hydrocarbons, coal, carbon and lignite.

5. A process as described in claim 4 wherein the reductant is added in amounts of from about 2% to about 10% by weight of the ore being treated.

6. A process as described in claim 2 wherein a reagent is added to the pelletized ore to lower the viscosity of the ore at reducing temperatures.

7. A process as described in claim 6 wherein said reagent is silica.

8. A process as described in claim 7 wherein silica is added .to the ore in amounts of from about 2% to about 10% by weight of the ore being treated.

9. A process as described in claim 2 wherein sulfur is added to the pelletized ore in amounts of from about 0.5% to about 5% by weight of the ore being treated.

10. A process as described in claim 2 wherein the reduced nickel values are recovered by magnetic separation.

11. A process as described in claim 2 wherein silica and sulfur are added to the ore in amounts of from about 2% to about 10% and from about 0.5% to about 5%, respectively, by weight of the ore being treated.

12. A process as described in claim 2 wherein said nonfluxing refractory oxide contains less than about 7% iron and is selected from the group consisting of unweathered serpentine, magnesia, alumina, forsterite, titania, olivine and peridotite.

13. A process as described in claim 2 wherein the nonfluxing refractory oxide is unweathered serpentine.

14. A process as described in claim 13 wherein the unweathered serpentine contains up to about 10% iron.

15. A process as described in claim 2 wherein the nonfluxing refractory oxide is alumina.

16. A process for concentrating nickel values contained in a pelletized lateritic ore containing nickel in amounts up to about 3%, about 15% to about 45% iron, about 1% to about 28% magnesia, about 3% to about 40% silica as silicates, up to about 1% alumina and the balance essentially water as moisture and chemically bound water which comprises incorporating in said pelletized ore silica in amounts of up to about 10%, by weight of the ore, and sulfur in an amount of up to about 5%, by weight of the ore; selectively reducing the pelletized ore to reduce substantially all of the nickel values contained therein and at least about 2 parts but not more than about 5 parts of iron for each part of nickel reduced; heating the selectively reduced ore to a temperature of not more than about 1300 C. to coalesce the reduced nickel and iron values into particles having a size of at least about 10 microns while reacting the pellets with un'weathered serpentine containing up to about 10% iron to form an oxide solid solution on the surfaces of the pellets and to prevent sticking of the pellets to each other; cooling the pellts having the coalesced particles therein; comminuting the coded pellets and concentrating the coalesced metal values by magnetic separation,

References Cited UNITED STATES PATENTS 2,400,461 5/1946 Hills 75-21 2,799,752 7/1957 Holt et a1. 75 5 3,232,743 2/1966 Anna 75 1 3,318,689 5/1967 Zubryckyjetal 7582X 3,333,370 6/1968 Thumm etal 75-21X OSCAR R. VERTIZ, Primary Examiner G. O. PETERS, Assistant Examiner US. 01. X.R. 7s 5, 21