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Coarse Gangue Rejection by Selective Comminution
Holger Lieberwirth
TU Bergakademie Freiberg
ABSTRACT: Diminishing ore grades and rising metal demand call for more efficient mineral processing
solutions. Coarse gangue rejection by selective comminution is a comparably simple way to foster sustainability
in processing and reduce mass specific energy expenses in comminution by exploiting differing comminution
characteristics of ore and gangue minerals. A pilot test with ore from a mine nearby Freiberg, Germany, processed
on an impact crusher in a tertiary comminution stage is presented. Even a rather gentle impact stressing led to
the majority of the zinc bearing sphalerite reporting to the –1 mm fraction. Coarse rejection can be affected by
simple vibrating screening of the crusher product.
INTRODUCTION
Background on Selective Comminution
The global upward trend in resource consumption, which is
mainly caused by the rising standard of living of a growing
world population, but also by energy transition approaches,
is not interrupted (Krausmann et al. 2009 European
Commission 2016 IEA International Energy Agency
2021). Newly discovered ore deposits, however, show a gen-
eral downward trend in ore grades (Schodde 2010, 2023).
As a result, increasing amounts of lower quality ores have to
be mined and processed to ensure the supply of the increas-
ing amounts of valuable materials. New societal trends such
as the large scale use of wind turbines for renewable energy
generation or battery driven cars accelerate the demand
increase (Steinbach 2019) (Marscheider-Weidemann et al.
2016 Hertwich et al. 2020). Emissions from raw mate-
rial production as a share of global greenhouse gases rose
from 15% in 1995 to 23% in 2015 (Hertwich et al. 2020),
respectively. Since comminution processes with their high
energy consumption contribute substantially to those emis-
sions, the need for more efficient comminution methods is
obvious (Ballantyne und Powell 2014).
Energy saving size reduction technologies, such as
Selective Comminution, that have already successfully
proven their effectiveness, productivity and durability in
certain fields need to be further investigated, with regard
to a wider application in new areas. The term “Selective
Comminution” describes the behavior of various com-
ponents of an ore, a mixture or composite material, to
respond differently to external loads in a comminution pro-
cess. Selective Comminution is a system characteristic that
depends on the material being stressed and the machine,
which produces those stresses (Hesse 2017). It allows, for
example, to prepare a pre-concentrate just by sieving, if
valuable components and gangue material report to differ-
ent size fractions after crushing. Particles of the valuable
or the gangue material are often found already enriched at
rather coarse fractions. In combination with the various
advances in coarse sorting an unnecessary energy intensive
milling of gangue material can be avoided as well as prod-
uct losses by overgrinding of the valuable component.
The technology has been used in industry for a long
time, preferably in connection with impact comminution
(Puffe 1955, 1960). The current level of understanding
of the „system response“ of material and comminution,
Coarse Gangue Rejection by Selective Comminution
Holger Lieberwirth
TU Bergakademie Freiberg
ABSTRACT: Diminishing ore grades and rising metal demand call for more efficient mineral processing
solutions. Coarse gangue rejection by selective comminution is a comparably simple way to foster sustainability
in processing and reduce mass specific energy expenses in comminution by exploiting differing comminution
characteristics of ore and gangue minerals. A pilot test with ore from a mine nearby Freiberg, Germany, processed
on an impact crusher in a tertiary comminution stage is presented. Even a rather gentle impact stressing led to
the majority of the zinc bearing sphalerite reporting to the –1 mm fraction. Coarse rejection can be affected by
simple vibrating screening of the crusher product.
INTRODUCTION
Background on Selective Comminution
The global upward trend in resource consumption, which is
mainly caused by the rising standard of living of a growing
world population, but also by energy transition approaches,
is not interrupted (Krausmann et al. 2009 European
Commission 2016 IEA International Energy Agency
2021). Newly discovered ore deposits, however, show a gen-
eral downward trend in ore grades (Schodde 2010, 2023).
As a result, increasing amounts of lower quality ores have to
be mined and processed to ensure the supply of the increas-
ing amounts of valuable materials. New societal trends such
as the large scale use of wind turbines for renewable energy
generation or battery driven cars accelerate the demand
increase (Steinbach 2019) (Marscheider-Weidemann et al.
2016 Hertwich et al. 2020). Emissions from raw mate-
rial production as a share of global greenhouse gases rose
from 15% in 1995 to 23% in 2015 (Hertwich et al. 2020),
respectively. Since comminution processes with their high
energy consumption contribute substantially to those emis-
sions, the need for more efficient comminution methods is
obvious (Ballantyne und Powell 2014).
Energy saving size reduction technologies, such as
Selective Comminution, that have already successfully
proven their effectiveness, productivity and durability in
certain fields need to be further investigated, with regard
to a wider application in new areas. The term “Selective
Comminution” describes the behavior of various com-
ponents of an ore, a mixture or composite material, to
respond differently to external loads in a comminution pro-
cess. Selective Comminution is a system characteristic that
depends on the material being stressed and the machine,
which produces those stresses (Hesse 2017). It allows, for
example, to prepare a pre-concentrate just by sieving, if
valuable components and gangue material report to differ-
ent size fractions after crushing. Particles of the valuable
or the gangue material are often found already enriched at
rather coarse fractions. In combination with the various
advances in coarse sorting an unnecessary energy intensive
milling of gangue material can be avoided as well as prod-
uct losses by overgrinding of the valuable component.
The technology has been used in industry for a long
time, preferably in connection with impact comminution
(Puffe 1955, 1960). The current level of understanding
of the „system response“ of material and comminution,