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Conclusions from
the trial
1.
The nickel and cobalt recoveries achieved were around 60%
and 36%, respectively
2.
Iron extraction was around 13%
3.
The ratio Fe/Ni in the leach liquor produced was 10/1, much
lower than the value of this ratio in the ore, 49/1. Thus, the selectivity of
the heap leaching technique for the phyllosilicate minerals over the iron
minerals (haematite, goethite) is apparent and is due to the difference in the
kinetics of dissolution of these minerals under the mild conditions of this
technique
4. Although
agglomeration had not been performed, the percolation was good. However, it is
believed that proper agglomeration in an agglomerator would certainly allow
for higher flowrates to be used and thus shorter leaching times
5. The
sulphuric acid consumption was around 67kg H2SO4 /kg Ni.
This is double the value that was usually obtained for many laterite samples
leached by the N.T.U.A. Research Group. This high consumption was attributed
to the high iron content of the ore chlorites and the high calcite content of
the waste ore, that was used as a bedding layer
General
Conclusions
1. The
pilot-scale heap leach test confirmed the leachability of the greek low –grade
nickel oxide ore according to the HELLAS Method
2. The main
characteristic and advantage of the HELLAS Method is the selectivity of the
nickel and cobalt leaching over iron at the mild conditions of the method
(ambient temperature, dilute sulphuric acid solution)
3. The most
significant factor affecting the leachability of the nickel oxide ore, the
recoveries of nickel and cobalt, the co- extraction of metal impurities and
the sulphuric acid consumption is, besides the leaching conditions, the
mineralogical composition of the ore. The higher the percentage of the ore
nickel in the phyllosilicate minerals, the higher the nickel recovery. Also,
the lower the iron and the magnesium contents of the phyllosilicate minerals,
the lower the sulphuric acid consumption is. This is so because most of the
iron and all of the magnesium and chromium pass into the solution from the
phyllosilicate minerals.
4. Given that
in the majority of the greek nickel deposits, nickel occurs in phyllosilicate
minerals, the HELLAS Method would allow the economic exploitation of poor
nickel oxide ore deposits with nickel grade too low to be treated by any other
method, pyrometallurgical or hydrometallurgical, whatsoever.
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