IRON CHEMISTRY IN LATERITIC SAPROLITE LEACHING WITH CONCENTRATED MgCl2
BRINES
Douglass Duffy,a Michael Carlos,a Boyd Davis,b and Vladimiros Papangelakisa
a
Department of Chemical Engineering and Applied Chemistry,
University of Toronto, 200 College Street, Toronto, ON, M5S 3E5, Canada
b
Kingston Process Metallurgy, 759 Progress Ave, Kingston, ON, K7M 6N6, Canada
douglass.duffy@mail.utoronto.ca, vladimiros.papangelakis@utoronto.ca
ABSTRACT
The processing of lateritic saprolite in hyper-concentrated magnesium chloride brines offers several
potential advantages for the hydrometallurgical production of nickel. An aggressive HCl-MgCl2 leach at
atmospheric pressure can significantly reduce magnesium dissolution, and offers the ability to recover HCl
and MgO by a less energy intensive process than conventional techniques via the formation of magnesium
hydroxychlorides. Inevitably, the high chloride concentration renders iron fully soluble during leaching and
thus requires subsequent iron control and disposal steps. Experimental measurements coupled with OLITM
modelling were conducted to investigate the behaviour of iron in concentrated magnesium chloride brines,
in terms of chemistry (nature of iron species) and solubility limits. The solubility of ferric chloride in
magnesium chloride solutions of concentrations and temperatures relevant to this process was controlled
by a previously unreported solid phase: 2.5FeCl3·MgCl2·7.5H2O. Iron precipitation tests on synthetic leach
solutions without seeding indicate a metastable akaganeite precipitate which transitions to hematite upon
equilibration. Magnesium chloride solubility in ferric chloride solutions was also investigated to allow the
simulation of a ternary phase diagram for the MgCl2-FeCl3-H2O system, in order to determine process
conditions that avoid unwanted chloride precipitation.
KEYWORDS
Ferric chloride, saprolite, nickel, laterite, HCl recovery, magnesium chloride
COM2016 – IMPC2016
4th International Symposium on Iron Control in Hydrometallurgy
Quebec City, Canada
September 2016