Nickel laterite mineralogy

The mineralogy of nickel-bearing laterite deposits is poorly understood, with conflicting structural models for their nature and co-ordination.

Currently there is a simple three-fold classification for nickel-bearing laterites, based on largely empirical criteria:

  • hydrous Mg-Ni silicates (serpentine, talc, chlorite and sepiolite)
  • smectites (e.g. nontronite, saponite, beidellite, montmorillonite)
  • oxides/oxy-hydroxides (e.g. goethite, hematite, asbolane, heterogenite)

There are conflicting structural models for the nature and co-ordination of nickel within both layer silicates and iron oxy-hydroxides. 

In laterite oxide zones the bulk of nickel is accommodated in variably crystalline goethite, where the Fe3+-for-Ni2+ substitution in goethite must be accompanied by a mechanism to compensate the charge imbalance. 

Nickel substitution is probably accompanied by hydroxylation, however it is also possible that co-substitution on Ni2+ with other polyvalent ions such as Mn and Cr may be the cause.