BENEFICIATION OF NICKELIFERROUS LATERITE BY PHYSICAL AND CHEMICAL PROCESSES

5th International Scientific Conference - SGEM2005, www.sgem.org, SGEM2005 Conference Proceedings/ ISBN: 954-918181-2, June 13-17, 2005, 3- 14pp

ABSTRACT

Nickeliferrous laterite is a source of ferronickel alloy extracted by a pyro-metallurgical
process. Laterite deposits found in Greece are mainly secondary depositions and their nickel
content is about 1%. Beneficiation of the run of mine ore is limited to the +1 mm fraction by
magnetic or gravitational processes and its effect is rather unsatisfactory due to the
insufficient liberation of the nickel bearing minerals.
The mineralogical structure of the ore consists mainly of hematite nodules (pissoids)
and quartz grains cemented together with a softer material made also of hematite and quartz
as well as nickel bearing magnesium silicate minerals of very fine grain size. The hematite
nodules themselves are not pure hematite but they contain inclusions of quartz, nickel bearing
magnesium silicate minerals and some chromite that are also found in the cement material.
This mineralogical structure makes the beneficiation of laterites a low efficiency process
that results to a low grade feed for the pyro-metallurgical plant that produces ferronickel
alloy. The production cost depends mainly on the feed grade and there is always an interest
for a higher grade feed material.
Initially the present work examines the selective grinding between the hematite nodules
and the softer cement material the result of which is the enrichment of nickel in the slimes.
Consequently it examines the liberation of the material at fine sizes below the size of
the nodules by mineralogical analysis. Physical methods like magnetic separation, centrifugal
separation and froth flotation are used for the beneficiation of the deslimed fine material with
limited results.
Finally acid leaching is used for the recovery of nickel from the deslimed fine material
with much better results than the ones obtained by physical separation processes. There is an obvious selectivity in leaching between nickel bearing magnesium silicate minerals like
chlorite or serpentine and the iron bearing minerals like hematite.
Selective grinding can produce a high-grade solid concentrate of slimes that after
pelletizing can be used as feed material to the existing pyro-metallurgical plant for the
production of ferronickel alloy. Hydro-metallurgical treatment of the low-grade sand material
can be considered as a new development in the existing system.
The combination of physical and chemical processes gives a better overall recovery than
chemical treatment of the whole material and ensures a higher grade feed material to the
existing high cost pyro-metallurgical plant.