XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3919
commodities (e.g., base metals, gold, platinum). Instead,
each mine has a unique average rough diamond value in
US $/ct that is incorporated with yearly carat production
over the life of mine into a ‘Tier Structure’ which under-
pins the value rating for global diamond deposits (de Wit et
al., 2016 Kjarsgaard et al., 2022). The successful liberation
of large, high-value (undamaged) stones is key to ensur-
ing the diamond value chain. Critically, optimization of the
comminution process by ensuring diamonds are liberated
effectively and with minimal damage has generated up to a
~14% improvement in US $/ton revenue (e.g., Rider and
Roodt, 2003).
Mechanical diamond breakage typically occurs dur-
ing crushing and scrubbing and through material trans-
port (e.g., the pumping of milled product, drop heights
within storage bins and transfer chutes, and the pneumatic
conveying of free diamonds, e.g., Chele, 2021 Figure 1)
within a diamond processing plant. The inherent mecha-
nisms for breakage include impact, shear (abrasion/attri-
tion) and compressional stresses which exceed the tensile
strength of the stone. This highlights the contrary brittle-
ness of diamond, a function of the high covalent bond
strength between carbon atoms in the crystal structure
which are unable to accommodate excessive energy applied
though strain, making them prone to shatter (or chipping)
and cleavage (fracture along inherent planes of weakness
such as twin planes). Breakages induced by excessive force
may result in further blemishes such as percussion marks,
stress-matched abrasion features, and internal rainbow
colours (Newton’s Rings) that result from the interference
of light waves through the diamond (Mountain Province
Diamonds Inc., internal report). Conventionally, mechani-
cal breakage is categorized by increasing fragmentation or
severity of diamond breakage (Figure 2), where stones can
range from ‘perfect’ unbroken crystals to chipped crystals
(10% loss), half-crystals (lightly broken ~25% loss), rem-
nant crystal faces (heavily broken ~50% loss) and finally,
fragments (unknown primary morphology 75% loss).
Recently, however, diamond processing plants have
implemented new technologies to curb breakage based on
the results of diamond simulant studies and diamond size
frequency distribution curves together with rudimentary
breakage descriptions (Chele, 2021). One such technology,
which has revolutionized the diamond circuit, is HPGR—
High Pressure Grinding Rolls, which employ a compres-
sional action where size reduction and liberation is attained
through the abrasion and attrition of similar sized particles
(i.e., friction). Ideally, the frictional shear stresses applied
Figure 1. A historical diamond processing flowsheet
commodities (e.g., base metals, gold, platinum). Instead,
each mine has a unique average rough diamond value in
US $/ct that is incorporated with yearly carat production
over the life of mine into a ‘Tier Structure’ which under-
pins the value rating for global diamond deposits (de Wit et
al., 2016 Kjarsgaard et al., 2022). The successful liberation
of large, high-value (undamaged) stones is key to ensur-
ing the diamond value chain. Critically, optimization of the
comminution process by ensuring diamonds are liberated
effectively and with minimal damage has generated up to a
~14% improvement in US $/ton revenue (e.g., Rider and
Roodt, 2003).
Mechanical diamond breakage typically occurs dur-
ing crushing and scrubbing and through material trans-
port (e.g., the pumping of milled product, drop heights
within storage bins and transfer chutes, and the pneumatic
conveying of free diamonds, e.g., Chele, 2021 Figure 1)
within a diamond processing plant. The inherent mecha-
nisms for breakage include impact, shear (abrasion/attri-
tion) and compressional stresses which exceed the tensile
strength of the stone. This highlights the contrary brittle-
ness of diamond, a function of the high covalent bond
strength between carbon atoms in the crystal structure
which are unable to accommodate excessive energy applied
though strain, making them prone to shatter (or chipping)
and cleavage (fracture along inherent planes of weakness
such as twin planes). Breakages induced by excessive force
may result in further blemishes such as percussion marks,
stress-matched abrasion features, and internal rainbow
colours (Newton’s Rings) that result from the interference
of light waves through the diamond (Mountain Province
Diamonds Inc., internal report). Conventionally, mechani-
cal breakage is categorized by increasing fragmentation or
severity of diamond breakage (Figure 2), where stones can
range from ‘perfect’ unbroken crystals to chipped crystals
(10% loss), half-crystals (lightly broken ~25% loss), rem-
nant crystal faces (heavily broken ~50% loss) and finally,
fragments (unknown primary morphology 75% loss).
Recently, however, diamond processing plants have
implemented new technologies to curb breakage based on
the results of diamond simulant studies and diamond size
frequency distribution curves together with rudimentary
breakage descriptions (Chele, 2021). One such technology,
which has revolutionized the diamond circuit, is HPGR—
High Pressure Grinding Rolls, which employ a compres-
sional action where size reduction and liberation is attained
through the abrasion and attrition of similar sized particles
(i.e., friction). Ideally, the frictional shear stresses applied
Figure 1. A historical diamond processing flowsheet