3818 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
grinding bodies in free fall. According to Rosa (2013), the
grinding bodies used can be made of different shapes (bars,
balls, cylinders, cylpebs, etc.) and materials (steel, cast iron,
ceramics, etc.).
Currently the chromium ore comminution circuit is
carried out in jaw crushers, bar, and ball mills (Figure 1).
Primary crushing is carried out in a 120×40 Blake-type jaw
crusher from the former FAÇO. For the secondary, a C96
jaw crusher from Metso is used, in a closed circuit with
vibrating screens (what is retained on the screen is sent to an
80×50 jaw crusher from FAÇO). Tertiary crushing is car-
ried out in a 45×35 jaw crusher from FAÇO, with APA set
at 2,” while quaternary crushing uses a Symons Nordberg
4¼’ Standard cone crusher model 60TS. Primary grinding
(bars) and secondary grinding (balls) are carried out in mills
measuring 1,500 mm in diameter and 3,000 mm in length.
One option for bar mills has been high pressure roll-
ers, known as High Pressure Grinding Rolls (HPGR).
Developed by Professor Dr Klaus Schonert, from the
Technical University of Clausthal, located in Germany.
These machines have high efficiency in mineral breakdown,
mainly due to the mechanism for understanding individ-
ual particles. In this way, the energy efficiency resulting
from the breaking of a mineral bed under compression is
clearly higher than that obtained in revolving tubular mills
(Pedrosa 2019). Also noteworthy is the ease of granulomet-
ric control of the HPGR product by adjusting the pressure
applied to the rollers and the possibility of simplifying the
grinding circuits (Pedrosa 2017 Pedrosa 2019). Therefore,
the present work presents a study aiming at the adoption of
an HPGR as a viable alternative to the grinding of chrome
ore currently adopted by FERBASA.
MATERIALS AND METHODS
Samples of chrome ore from the Ipueira mine with an aver-
age content of 38% Cr2O3 were collected at two points in
the mineral processing plant: feeding the tertiary crushing
plant (100% passing through the 40 mm sieve) and at the
bar mill discharge (100% through 1 mm sieve). Between
the sample collection points, the chrome ore is currently
subjected to fragmentation in a jaw crusher, a conical
crusher and three bar mills (which operate in parallel).
The samples were sent to the Metso-Outotec testing cen-
ter, located in Sorocaba-SP, where they were homogenized,
quartered, granulometrically analyzed and subjected to
tests to determine Bond (Ai) and Macon (AI) abrasiveness,
Macon crushability (Br), Bond Work Index (Wi), and tests
on a bench-scale HPGR, model HRC D1000 from Metso,
which operates with 1,000 mm diameter rolls. The operat-
ing conditions of the Metso HRC D1000 are presented in
Table 2.
Ore Wi was determined using standard Bond Wi test
methodology in a ball mill with a 0.150 mm control mesh.
The Ai test was performed according to the methodology
available in the literature (Peres et al 2017). To determine
the AI index, a sample of ore (500 g with particle size
-¾”+½”) was placed in a cylinder (drum) 12” in diameter
and 4.5” deep, which contains a concentric rotor in its inte-
rior is 4.5” in diameter. A steel plate with high friction resis-
tance (hardness from 110 to 121 HB), with dimensions 25
× 50 × 5 mm and known initial weight (m1), is fixed to the
rotor. The rotor is then subjected to 70 rpm for 15 minutes,
and the final weight of the plate is measured (m2). The AI
(expressed in g/t) is represented by the mass reduction of
the steel plate at the end of the test and calculated as shown
in equation 1.
.5 AI
m
0
1000^m
1 2 =
-h (1)
To determine the Macon crushability (Br), the plate is
kept in motion for 5 minutes. After this time, the drum
was emptied and the tested ore was sieved using a 1.6 mm
square mesh. The Macon crushability of the sample is rep-
resented by the relationship between the total mass of the
sample (mt) and the mass retained in 1.6 mm after the test
(mr), as shown in equation 2.
Table 1. Mineralogical characterization by x-ray diffraction of ore from the Ipueira/BA mine
Mineral Chemical Formula Abundance
Chromite (Mg0.43Fe0.58)8(Cr1.19Al0.77Ti0.03)8O32 Average
Talc Mg3(OH)2Si4O10 Average
Bulk lizardite serpentine Mg
3 (Si
2 O
5 (OH)
4 )Average
Clinochlore Mg
4.54 A
l0.97 Fe
0.46 Mn
0.03 (Si
2.85 Al
1.15 O
10 )(OH)
8 Low
Biotite K(Mg1.48Fe1.28Ti0.24)(Al1.2Si2.8O10)(OH)1.4F0.32O0.28 Trace
Pyrrhotite Fe7S8 Trace
Pentlandite FeNiS
2 Trace
Chalcopyrite CuFeS
2 Trace
Calcite CaCO3 Trace
grinding bodies in free fall. According to Rosa (2013), the
grinding bodies used can be made of different shapes (bars,
balls, cylinders, cylpebs, etc.) and materials (steel, cast iron,
ceramics, etc.).
Currently the chromium ore comminution circuit is
carried out in jaw crushers, bar, and ball mills (Figure 1).
Primary crushing is carried out in a 120×40 Blake-type jaw
crusher from the former FAÇO. For the secondary, a C96
jaw crusher from Metso is used, in a closed circuit with
vibrating screens (what is retained on the screen is sent to an
80×50 jaw crusher from FAÇO). Tertiary crushing is car-
ried out in a 45×35 jaw crusher from FAÇO, with APA set
at 2,” while quaternary crushing uses a Symons Nordberg
4¼’ Standard cone crusher model 60TS. Primary grinding
(bars) and secondary grinding (balls) are carried out in mills
measuring 1,500 mm in diameter and 3,000 mm in length.
One option for bar mills has been high pressure roll-
ers, known as High Pressure Grinding Rolls (HPGR).
Developed by Professor Dr Klaus Schonert, from the
Technical University of Clausthal, located in Germany.
These machines have high efficiency in mineral breakdown,
mainly due to the mechanism for understanding individ-
ual particles. In this way, the energy efficiency resulting
from the breaking of a mineral bed under compression is
clearly higher than that obtained in revolving tubular mills
(Pedrosa 2019). Also noteworthy is the ease of granulomet-
ric control of the HPGR product by adjusting the pressure
applied to the rollers and the possibility of simplifying the
grinding circuits (Pedrosa 2017 Pedrosa 2019). Therefore,
the present work presents a study aiming at the adoption of
an HPGR as a viable alternative to the grinding of chrome
ore currently adopted by FERBASA.
MATERIALS AND METHODS
Samples of chrome ore from the Ipueira mine with an aver-
age content of 38% Cr2O3 were collected at two points in
the mineral processing plant: feeding the tertiary crushing
plant (100% passing through the 40 mm sieve) and at the
bar mill discharge (100% through 1 mm sieve). Between
the sample collection points, the chrome ore is currently
subjected to fragmentation in a jaw crusher, a conical
crusher and three bar mills (which operate in parallel).
The samples were sent to the Metso-Outotec testing cen-
ter, located in Sorocaba-SP, where they were homogenized,
quartered, granulometrically analyzed and subjected to
tests to determine Bond (Ai) and Macon (AI) abrasiveness,
Macon crushability (Br), Bond Work Index (Wi), and tests
on a bench-scale HPGR, model HRC D1000 from Metso,
which operates with 1,000 mm diameter rolls. The operat-
ing conditions of the Metso HRC D1000 are presented in
Table 2.
Ore Wi was determined using standard Bond Wi test
methodology in a ball mill with a 0.150 mm control mesh.
The Ai test was performed according to the methodology
available in the literature (Peres et al 2017). To determine
the AI index, a sample of ore (500 g with particle size
-¾”+½”) was placed in a cylinder (drum) 12” in diameter
and 4.5” deep, which contains a concentric rotor in its inte-
rior is 4.5” in diameter. A steel plate with high friction resis-
tance (hardness from 110 to 121 HB), with dimensions 25
× 50 × 5 mm and known initial weight (m1), is fixed to the
rotor. The rotor is then subjected to 70 rpm for 15 minutes,
and the final weight of the plate is measured (m2). The AI
(expressed in g/t) is represented by the mass reduction of
the steel plate at the end of the test and calculated as shown
in equation 1.
.5 AI
m
0
1000^m
1 2 =
-h (1)
To determine the Macon crushability (Br), the plate is
kept in motion for 5 minutes. After this time, the drum
was emptied and the tested ore was sieved using a 1.6 mm
square mesh. The Macon crushability of the sample is rep-
resented by the relationship between the total mass of the
sample (mt) and the mass retained in 1.6 mm after the test
(mr), as shown in equation 2.
Table 1. Mineralogical characterization by x-ray diffraction of ore from the Ipueira/BA mine
Mineral Chemical Formula Abundance
Chromite (Mg0.43Fe0.58)8(Cr1.19Al0.77Ti0.03)8O32 Average
Talc Mg3(OH)2Si4O10 Average
Bulk lizardite serpentine Mg
3 (Si
2 O
5 (OH)
4 )Average
Clinochlore Mg
4.54 A
l0.97 Fe
0.46 Mn
0.03 (Si
2.85 Al
1.15 O
10 )(OH)
8 Low
Biotite K(Mg1.48Fe1.28Ti0.24)(Al1.2Si2.8O10)(OH)1.4F0.32O0.28 Trace
Pyrrhotite Fe7S8 Trace
Pentlandite FeNiS
2 Trace
Chalcopyrite CuFeS
2 Trace
Calcite CaCO3 Trace
