Method for nickel and cobalt recovery from laterite ores by combination of atmospheric and moderate pressure leaching

Abstract

A process for leaching laterite ores containing limonite and saprolite. Sufficient mineral acid is added to a slurry of limonite which is leached at atmospheric pressure to dissolve most of the soluble non-ferrous metals and soluble iron. After adding saprolite the slurry is further leached at a temperature above the normal boiling point and at a pressure above atmospheric pressure for a time sufficient to leach most of the contained nickel in the saprolite and to precipitate most of the iron in solution. The pressure of the slurry is then reduced, and nickel and / or cobalt is subsequently recovered from the leach solution by solvent extraction, resin-in-pulp or other ion exchange, sulfide or hydroxide precipitation, or other recovery method.

Description

CROSS REFERENCE TO RELATED APPLICATION [0001] This application claims the benefit of U.S. provisional patent application No. 60 / 592,375 filed on Aug. 2, 2004, the disclosure of which is hereby incorporated herein by reference.FIELD OF THE INVENTION [0002] The present invention relates to the hydrometallurgical processing of nickeliferous laterite ore, and in particular to a method for acid leaching both the limonite fraction and the saprolite fraction of such ores in a single process. BACKGROUND OF THE INVENTION [0003] Laterite ores are formed by the in-situ weathering of nickel-bearing ultramafic rocks near or at the surface of the earth in tropical environments by the action of naturally acidic meteoric waters over geologic time. They consist of a variety of clay, oxide and silicate minerals, some enriched in nickel and / or cobalt, and this distinguishes them from the other major class of nickel ores, the sulfide ores. The latter consist typically of sulfide minerals of iron, nicke...

AI Technical Summary

Benefits of technology

[0029] The present invention provides a process for the efficient leaching of nickel and cobalt from limonite and saprolite ores in two stages, the first stage consisting of mixing and reacting a slurry of the limonite ore with concentrated mineral acid at atmospheric pressure, and the second stage consisting of adding saprolite ore to the resulting leach slurry and then leaching at a moderately elevated temperature and pressure. Iron is efficiently separated from nickel and cobalt in the solid leach residue primarily as an oxide and / or hydroxide of ferric iron other than jarosite.

[0031] In the saprolite leaching stage, the temperature should be high enough to achieve a rapid rate of reaction and satisfactory nickel (and cobalt) extraction, but low enough that the resulting working pressure is within the tolerance of a simple, low cost autoclave. The working pressure of the autoclave is approximately equal to the pressure of saturated steam at the working temperature employed. This pressure increases very rapidly with increasing temperature, especially much above about 150° C. To avoid the complexity and difficulty of operating at excessive pressures, an appropriate range of temperature for carrying out the second stage of leaching in the present invention is from about 120 to 160° C., and the temperature should be kept as low as reasonably possible consistent with good process performance. It has been found that excellent results are achieved, for example, at 150° C. The associated pressure at this temperature (approximately 70 psi) is low enough to enable a simple autoclave system to be used for carrying out the leach.

[0034] The laterite leaching method of the present invention can surprisingly achieve high levels of nickel extraction while avoiding the high cost of high-pressure autoclaves, and avoiding the production of environmentally unfriendly, high-acid consuming jarosite compounds. While the process does require an autoclave, the operating conditions are relatively benign compared to the high pressure acid leaching processes (nearly ten times or more the operating pressure required for the latter autoclave processes). Consequently, the process of this invention permits much simpler equipment design, and operations and maintenance are also easier than in high pressure acid leach processes. In addition, the saprolite leach and iron precipitation reactions occur much faster at moderately elevated temperature and a much shorter leach retention time, compared to the previously described atmospheric leach processes, is required. Thus, the autoclave required to carry out the process of the current invention is much smaller than the atmospheric leach reactors required for the processes of U.S. Pat. Nos. 6,261,527 B1 and 6,680,035 B2 and WO 03 / 093517 A1. In addition, the process of the current invention achieves higher nickel extraction than can be achieved with the aforementioned atmospheric leach processes.

Problems solved by technology

A challenging aspect of nickel recovery from laterite ores is that the nickel values typically can not be concentrated substantially by physical means, that is, so-called ore dressing techniques, prior to chemical processing to separate the metal values.

This renders the processing of laterites expensive, and means to lower the costs of processing laterites have been sought for many decades.

Also, because of the distinct mineralogical and chemical composition of limonite and saprolite ores, these ores usually are not amenable to processing by the same process technique.

A major disadvantage of the HPAL process is that it requires sophisticated high-temperature, high-pressure autoclaves and associated equipment which are expensive, both to install and to maintain.

The latter proton (acid) is therefore not utilized fully for leaching and results in excess sulfuric acid which must be neutralized, for example with limestone.

Another disadvantage of the HPAL process is that it is limited to treating largely limonite-type feeds because the presence of saprolite will cause a large, and often uneconomic, increase in sulfuric acid consumption due to the leaching of magnesium from saprolite.

Disadvantages of the process are that it still requires the use of expensive autoclaves for leaching limonite, and it requires a roasting process for saprolite ore, which is expensive both in capital and operating cost terms.

However, this process still requires the use of expensive autoclaves.

While this process overcomes the disadvantages of pressure leaching, it has other disadvantages.

First, the precipitation of iron is as a jarosite compound, which is a thermodynamically unstable compound of iron that decomposes over time to release sulfuric acid, thus causing environmental problems.

Jarosite contains two moles of sulfate for every three moles of iron and thus this compound represents substantial excess consumption of sulfuric acid to provide the necessary sulfate ions.

Second, the nickel extractions from the ore were apparently relatively low.

Fourth, there is a need to add relatively expensive iron precipitating agents such as potassium carbonate, sodium carbonate or the like.

This process also has the disadvantage of producing jarosite.

Another disadvantage of the processes described in U.S. Pat. Nos. 6,261,527 B1 and 6,680,035 B2 and WO 03 / 093517 A1 is that the leach process is slow.

Thus, many large leach reactors are required to carry out the process and this increases the capital and operating costs of the process compared to a leach process which has a much shorter retention time.

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