2016
IN ASSOCIATION WITH
CONCENTRATION
Dr D.R. Nagaraj
Flotation chemicals constitute a most
powerful tool in enhancing mineral
separation performance, affecting
overall economic and environmental
impacts of the process. Dr D.R.
Nagaraj (Nag) has more than 35 years
of outstanding and innovative
achievements in the design,
development and commercialisation of
numerous families of novel flotation reagents
(collectors, depressants, dispersants, etc.) and in
advancing the art and science of flotation agents for
sulphide and non-sulphide mineral separations. His
seminal 1987 paper[1] titled The chemistry and
application of chelating or complexing agents in
minerals separations formally introduced the
donor-acceptor model, which paved the way for
rational design of flotation reagents. During his
entire career he has been involved in a bridge
building exercise between academic research and
practical applications.
However, his persistence at requiring knowledge to
be useful has made him sought after by both
communities. His holistic approach[2] to reagent
selection and flotation optimisation is one example
of his devising a rational and practical scheme for
dealing with real, complex ores. His pioneering work
in the use of SIMS surface analytical technique[3],[4]
for determining the disposition of collectorsMinCa
on 26
mineral surfaces started a trend in the academic
community and is an example of the high quality
work for which he is known.
In addition to devising schemes to optimise chemical
usage, Nag has developed and patented many
organic and polymeric materials for flotation and
toxic metal removal. Here are a few examples:
• Alkyl and Aryl monothiophosphates as acid
circuit sulphide collectors: Nag pioneered the use
of alkyl and aryl monothiophosphates (modifications
of existing dithiophosphates) as acid circuit sulphide
collectors[5]. Under alkaline conditions the monothiophosphates are excellent collectors for precious metals
such as Au and Ag. The largest mines in North
America and Asia currently use the monothiophosphates to improve their gold and silver recoveries.
• Synthetic functionalised polymers as
depressants in sulphide flotation:[6] Using insights
from his donor-acceptor model, Nagaraj et al
conceptualised and synthesised polymeric
depressants containing mineral-specific functional
groups for use in enhancing sulphide flotation. The
most important application for these depressants
has been for Cu-Mo separation, where they can
greatly reduce the use of inorganic Cu sulphide
depressants such as NaSH, Na2S, and Nokes.
These inorganic reagents are known to have serious
safety, health and environmental (SHE) concerns
such as stench and H2S formation. Mitigation of
those SHE issues through the use of polymeric
depressants protects operators and also improves
economics and logistics as a result of greater
reagent efficiency. A number of mines around the
world currently use these depressants.
• Alkoxycarbonyl thionocarbamates as
collectors for mildly alkaline circuits:[7] A major
gangue mineral present in sulphide copper ores is
pyrite, which readily responds to sulphide collectors
at pH <10, resulting in results in significant grade
dilution of the concentrate. In order to deal with this
problem, plants typically use large amounts of lime
to raise the pH to greater than 10.5 to depress
pyrite. Lime consumptions can be quite high, and
most plants run multiple lime kilns in order to
generate enough lime, even though they are
notoriously energy inefficient. The collectors
developed by Nag allow for the flotation of copper
ores at pH 9.5, resulting in significant energy
savings. These reagents, now in use at multiple
mining operations around the world, also brought
unprecedented dose-efficiency, leading to
significantly reduced reagent footprint at mining
operations. Plants in Africa are known to use as little
as 1ppm of this family of reagents to achieve
desired performance, as compared to 20-30ppm of
other reagents.
• New Collectors for PGMs and gold: Nag
developed a new family of modified
dithiocarbamates[8]. When using these reagents by
themselves, the recovery of metallics improved
considerably, and in combination with existing
reagents, overall Au and sulphide recovery could be
improved. As a result these reagents are now in use
at multiple Au operations around the world.
Nagaraj’s productive career has been characterised
by the application of good fundamentals to the
solution of practical problems in flotation, elevating
both the academic and industrial communities.