Although laterite ores already provide a significant proportion of the
world's nickel and cobalt production it is anticipated that they will surpass
sulphide ores as a source of nickel in the next century. The most recent period of greenfield nickel project construction was
during the 1970s when it was notable that all of the eight new plants were
based on treating laterite ores. This was because of the relatively large
selection of available high grade laterite ore deposits amenable to cheap
open cast mining and a paucity of high grade sulphide ore prospect
alternatives. Of the three processing options for treating laterite ores: 1. smelting for the lower horizon saprolite ore,
2. ammonia; and 3. acid leach for the upper horizon limonite ore, smelting currently accounts for about 80 per cent of nickel production. In
the future, as saprolite ore grades decline because of relatively high
exploitation rates, the incentive to process the large untapped reserves of
limonite ore will increase. The high cobalt content of limonite ore also
makes it ideally suited to processing by a hydrometallurgical rather than
smelting route. With only two exceptions, all saprolite smelting operations have a
Class 2 nickel end product (largely ferronickel) and do not produce a
cobalt by-product. As a result of technological advances, the modified
ammonia leach process for limonite and transition ore as undertaken at
Yabulu, now allows the production of pure nickel metal as a Class 1
product, along with significant tonnages of cobalt by-product. The mixed
Ni-Co sulphide intermediate product of the pressure acid leach processing
of limonite ore at Mon is converted to Class 1 nickel and cobalt metal at
Fort Saskatchewan, Canada.