METHOD OF RECOVERING METAL VALUES FROM ORES

FIELD OF THE INVENTION

The present invention relates to a method for processing of metal-containing ores, particularly for recovering of nickel and other metals, and more particularly to methods for recovery of iron, nickel, cobalt, magnesium, aluminum, chromium, and other valuable constituents of saprolite and limonite ores.

BACKGROUND OF THE INVENTION

The compositions of ores vary tremendously, even when taken from the same mining site. Limonite and saprolite ores usually contain iron, nickel, cobalt, magnesium, manganese, chromium, and/or aluminum. Known processes for treating high magnesium saprolite ores or high-iron limonite type ores are generally high cost processes, whereas the present invention is an improved, cost-effective process which can handle a full range of ores, including transitional ores. The term "ores" as used herein is intended to mean oxide and sulfide ores, metallurgical wastes, and metal-bearing materials, it being understood that metals can be combined with other elements.

SUMMARY OF THE INVENTION

The invention is a method for processing of nickel-bearing saprolite and limonite ores to recover the valuable minerals contained therein. The process acts on any oxide

or sulfide ores, metallurgical wastes, and metal-bearing materials, it being understood that in such materials, metals can be combined with other elements. The ores may be ground or comminuted, if desired, or may be blended with other metal-bearing materials. The ores are leached with nitric acid, then the iron is precipitated by thermal hydrolysis or pH balancing. Optionally, aluminum is recovered by precipitation or crystalline recovery.

Magnesium hydroxide is added to the solution, and a pH balance is effected to form nickel and cobalt hydroxides which are recovered as precipitates.

Advantageously, the nitric acid for the leach is provided by the process described in US Patent Number 6,264,909, entitled Nitric Acid Production and Recycle, which issued on July 24, 2001, and which is incorporated herein by reference.

The present invention is particularly useful for recovery of nickel, cobalt, aluminum, iron, chromium, manganese, and magnesium.

OBJECTS OF THE INVENTION

The principal object of the present invention is to provide an improved method of recovering nickel and cobalt from saprolite and limonite ores.

Another object of this invention is to provide a method of recovering metal values from ores, metallurgical wastes, and other metal-bearing materials.

Another object of the invention is to provide a method of producing nitrate salts, such as ammonium, sodium, potassium, calcium, or magnesium nitrates.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects will become more readily apparent by referring to the following detailed description and the appended drawing in which:

Figure 1 is a schematic flowsheet of the invented process in its most basic form.

DETAILED DESCRIPTION

Referring now to the drawing, Figure 1 shows the invented process in its basic form. The process starts with run of the mine saprolite or limonite ores 10 or other metal bearing materials.

The ore is leached with HNO ₃ for a sufficient time to form a slurry. Although the ore may be crushed, it is not necessary to do so as the nitric acid will act efficiently regardless of the size of the ore particles. The ore is leached 18 with nitric acid 20 at a temperature of less than 160C, generally from about 7OC to 130C, but preferably about 120 C for a period of time of about 30 minutes to about 3 hours. The acid can be a 10 to

90% (weight percent) nitric acid solution, but is preferably about 30 to 67% nitric acid, and optimally is about a 45 to 55 % acid solution.

The nitric acid 20 for the leaching process is preferably obtained from a nitric acid recycle process in accordance with US Patent 6,264,909, referred to above.

The temperature of the leach solution is raised by heating 22 to a temperature in the range of about 125 to 200C, preferably to about 165 C, to form a liquid/solid residue in which the nickel, cobalt and magnesium are in solution, and the iron, manganese, and aluminum are solid residues in oxide form. The heating is carried out Ln an enclosure from which the evolved gases (principally NOJ are recovered for further treatment. The leaching and heating steps can be carried out is the same vessel, or in separate vessels.

Iron is precipitated at 22 as Fe ₂ O ₃ , either by thermal hydrolysis or pH balancing of the solution to effect the precipitation.

The slurry undergoes a solid-liquid separation, the gangue materials being removed as solids. The remaining liquid solution is heated, the iron being precipitated as Fe ₂ O ₃ , either by thermal hydrolysis or pH balancing of the solution to effect the precipitation.

The Fe ₂ O ₃ is removed as a solid by liquid - solid separation (filtration), leaving a solution containing aluminum, nickel and cobalt values.

Aluminum is removed at 24 by precipitation. Alternatively, crystallization of the aluminum as a nitrate allows separation by filtration or by centrifuge. In either event, it leaves a nickel-cobalt solution.

Mg(OH) ₂ is mixed with the nickel-cobalt solution, which then undergoes a pH balance (shift) to form Ni(OH) ₂ and Co(OH) ₂ in solid form which is removed as a precipitate (by filtration) at 26. The nickel and cobalt values can also be removed from solution by solvent extraction.

The filtrate is concentrated, usually in multiple effect evaporation until the remaining Mg(NO ₃ ) ₂ is almost anhydrous. The magnesium nitrate is then thermally decomposed at 28 to form MgO, HNO ₃ and NO _x , and the nitric acid and nitric oxides are recycled. The resulting MgO can be used elsewhere in the invented process.

The NO _x containing gases are reformed at 30 into nitric acid utilizing the nitric recycle process described in US Patent Number 6,264,909.

Shifting of the pH of the solution is accomplished by adding or removing nitric acid, or by adding alkaline earths to the solution.

Precipitation of iron is usually accomplished at a pH of 2 to 3; Precipitation of alumina is usually accomplished at a pH of 4-5; Precipitation of nickel is usually accomplished at a pH of 6-7;

Precipitation of Manganese is usually accomplished at a pH of 8-9; Precipitation of MgO is usually accomplished at a pH of 10-1 1 ; Precipitation of Ca is usually accomplished at a pH of 12-13.

Precipitates are removed by filtration, or may be separated by other known methods such as centrifuging.

In any place throughout the process where nitric acid or oxide is removed, it may be recycled to the nitric acid recycle process for further use.

SUMMARY OF THE ACHIEVEMENT

OF THE OBJECTS OF THE INVENTION

From the foregoing, it is readily apparent that we have invented an improved method of recovering nickel and cobalt from saprolite and limonite ores, and for recovering metal values from ores, metallurgical wastes, and other metal-bearing materials, more economically than heretofore has been possible.

It is to be understood that the foregoing description and specific embodiments are merely illustrative of the best mode of the invention and the principles thereof, and that various modifications and additions may be made to the apparatus by those skilled in the art, without departing from the spirit and scope of this invention, which is therefore understood to be limited only by the scope of the appended claims.