Method for nickel and cobalt recovery from laterite ores by reaction with concentrated acid and water leaching

Abstract

A process for leaching laterite ores containing limonite and saprolite in a two stage process. The first stage consisting of mixing and reacting the ore with concentrated mineral acid, and the second stage consisting of preparing a slurry of the acid / ore mixture in water and leaching the mixture to dissolve nickel and cobalt. Iron is efficiently separated from nickel and cobalt in the solid leach residue primarily as an oxide or hydroxide of ferric iron other than jarosite.

Description

CROSS REFERENCE TO RELATED APPLICATION [0001] This application claims the benefit of U.S. provisional patent application No. 60 / 583243 filed Jun. 28, 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, nickel a...

AI Technical Summary

Benefits of technology

[0032] The present invention provides a process for the efficient leaching of nickel and cobalt from limonite and saprolite ore, such as could be produced by bulk mining of a typical nickel laterite deposit, in a two stage process, the first stage consisting of mixing and reacting the ore with concentrated mineral acid, and the second stage consisting of preparing a slurry of the acid / ore mixture in water and leaching the mixture to dissolve nickel and cobalt. Iron is efficiently separated from nickel and cobalt in the solid leach residue primarily as an oxide or hydroxide of ferric iron other than jarosite.

[0036] Advantageously, a reductant, such as sulfur dioxide, hydrogen sulfide, soluble bisulfite and sulfite compounds, or soluble ferrous iron compounds, is added during the water leaching to enhance dissolution of cobalt.

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 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 would be 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 disadvantages of producing jarosite, requiring separate mining and preparation of the limonite and saprolite fractions of the ore, and being limited to a narrow range of saprolite to limonite ratios.

The latter disadvantage is due to the fact that the quantity of saprolite that can be leached effectively is determined by the quantity of ferric iron in the limonite leach solution.

Subsequent water leaching results in high extraction of nickel and cobalt and low extraction of iron to solution.

The primary disadvantage is that it requires an expensive roasting step.

However, the process also has significant disadvantages.

One disadvantage is that the ore used should contain no more than 1% moisture, which means that in most cases the ore must be dried, as in-situ moisture contents of laterite ores are usually 20% or more.

A second disadvantage is that the process does not provide selective dissolution of nickel over iron, as illustrated in all of the examples cited in the patent (>90% iron extraction).

The separation of nickel from iron in solution usually results in additional nickel losses.

In addition, this process is only applicable to ores containing “large amounts of magnesia and silica,” i.e. the saprolitic or garnieritic ores.

Moreover, acid consumption is very high in this process, from about 0.9 to 1.1 tonnes of sulfuric acid per tonne of ore.

As with various processes described above, the requirement for a high temperature roasting step is a significant disadvantage in this process.

The baking step is a significant disadvantage because it requires substantial heat energy to evaporate the contained water in the ore / acid mixture.

Nickel extraction can reportedly be increased by adding additional sulfuric acid to the first stage residue and carrying out a second sulfation and water leaching step, but this adds complexity to the process and will not improve the iron / nickel separation achieved in the process.

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