184 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
,0175 v d 0
P,min
Z 3
2
t
v
=c m (1)
where σZ is the tensile strength and ρ is the density of
the material. Quite obvious, the various materials in an
ore body have different tensile strength and densities. So,
if particles are classified into narrow fractions, there may
be a velocity range, where particles of one material already
break, while particles of other materials do not. Such a
scheme is indicated in Figure 4. The curves resulting from
the calculation of the minimum impact speed acc. to eq.
(1) are indicated for the various ores and gangue materials
found in the deposit with the particle size on the main axis.
Tests conducted earlier already indicated, that a speed of
40 m/s would result in a good selectivity. This can be con-
firmed by the calculated minimum impact speed for Test
point 1 (Figure 4). This test point is drawn at an average
particle size of the fraction of d =20 mm. It is below the
calculated critical speed of gangue materials 1–5, just above
the curves for Ore 1 (magnetite) and Gangue Materials
6–7, and far higher than the critical speeds calculated for
the chlorite and sulfide ores (Ore 4+5). It is to be expected,
that the latter two ores, in particular the cassiterite and
sphalerite contained, would preferably report to finer frac-
tions while the magnetite as well as the gangue materials
are hardly crushed. The fraction, of course, is rather wide
(10…30 mm). So the selectivity may be somehow veiled by
increased comminution of gangue material.
Similar considerations can be made for the coarser
material (fraction 30…60 mm). The impact speed lies
above the critical impact speed of all different materials
for the whole fraction. Nevertheless, also here it can be
Figure 3. Thin sections of skarn wall rock (gangue, Hämmerlein deposit, magnification: 16x)
Table 2. Results of the Quantitative Microstructure Analysis (QMA) for the skarn gangue material (Hämmerlein, Saxony),
(NDP: non-differentiated faces)
Mode
Phase Related
Characteristics
Rock Related
Characteristics
Phases Cluster NDP ∑ Microbodies
Content Volumetric portion [%]19 81 100
Fabric
Texture
Size Mean diameter [mm] 1,615 — 1.1615
Deviation [-]0.244 — 0.244
Grain surface Specific surface [mm2/mm3] 4.850 — 4.850
Shape Elongation [-]1.155 — 1.155
Flatness [-]2.012 — 2.012
Roughness Degree of roughness [%]36 — 36
Structure
Orientation Degree of linear orientation [%]7 — 7
Degree of areal orientation [%]34 — 34
Degree of isotropic orientation [%]59 — 59
Distribution Degree of clustering [%]0 — 0
Space filling Degree of space filling [%]— — 100
,0175 v d 0
P,min
Z 3
2
t
v
=c m (1)
where σZ is the tensile strength and ρ is the density of
the material. Quite obvious, the various materials in an
ore body have different tensile strength and densities. So,
if particles are classified into narrow fractions, there may
be a velocity range, where particles of one material already
break, while particles of other materials do not. Such a
scheme is indicated in Figure 4. The curves resulting from
the calculation of the minimum impact speed acc. to eq.
(1) are indicated for the various ores and gangue materials
found in the deposit with the particle size on the main axis.
Tests conducted earlier already indicated, that a speed of
40 m/s would result in a good selectivity. This can be con-
firmed by the calculated minimum impact speed for Test
point 1 (Figure 4). This test point is drawn at an average
particle size of the fraction of d =20 mm. It is below the
calculated critical speed of gangue materials 1–5, just above
the curves for Ore 1 (magnetite) and Gangue Materials
6–7, and far higher than the critical speeds calculated for
the chlorite and sulfide ores (Ore 4+5). It is to be expected,
that the latter two ores, in particular the cassiterite and
sphalerite contained, would preferably report to finer frac-
tions while the magnetite as well as the gangue materials
are hardly crushed. The fraction, of course, is rather wide
(10…30 mm). So the selectivity may be somehow veiled by
increased comminution of gangue material.
Similar considerations can be made for the coarser
material (fraction 30…60 mm). The impact speed lies
above the critical impact speed of all different materials
for the whole fraction. Nevertheless, also here it can be
Figure 3. Thin sections of skarn wall rock (gangue, Hämmerlein deposit, magnification: 16x)
Table 2. Results of the Quantitative Microstructure Analysis (QMA) for the skarn gangue material (Hämmerlein, Saxony),
(NDP: non-differentiated faces)
Mode
Phase Related
Characteristics
Rock Related
Characteristics
Phases Cluster NDP ∑ Microbodies
Content Volumetric portion [%]19 81 100
Fabric
Texture
Size Mean diameter [mm] 1,615 — 1.1615
Deviation [-]0.244 — 0.244
Grain surface Specific surface [mm2/mm3] 4.850 — 4.850
Shape Elongation [-]1.155 — 1.155
Flatness [-]2.012 — 2.012
Roughness Degree of roughness [%]36 — 36
Structure
Orientation Degree of linear orientation [%]7 — 7
Degree of areal orientation [%]34 — 34
Degree of isotropic orientation [%]59 — 59
Distribution Degree of clustering [%]0 — 0
Space filling Degree of space filling [%]— — 100