Rhodax® interparticle crusher maximizes chloride slag

PORTAL, J. Rhodax® interparticle crusher maximizes chloride slag production with a minimum generation of fines. The 6th International Heavy Minerals
Conference ‘Back to Basics’, The Southern African Institute of Mining and Metallurgy, 2007.
Rhodax® interparticle crusher maximizes chloride slag
production with a minimum generation of fines
J. PORTAL
Research Centre, FCB.ciment, France
One of the key products produced by the mineral sands industry is the titanium dioxide slag, a
process that requires grinding of a coarse product down to a valuable saleable product. Traditional
methods have included the vertical roller mill in tandem with dynamic air classifiers and,
alternatively, two-stage grinding and crushing through an AG mill in closed circuit with a
dynamic classifier and secondary gyradisc crushers.
The products produced, commonly known as chloride and sulphate slag, are differentiated by
the particle size distribution of the final product. The more valuable chloride slag must, by
specification, be a product sized in the range between 850 and 100 microns—the more fines
generated in the grinding process, the less higher valuable final chloride slag is produced.
This paper will explore a technology that is new to both the mineral sands and to other mineral
processing industries. Inter particle communition, or IPC as it is known, has been applied in the
cement industry to improve the performance of clinker grinding mills. The principle is to create a
process of material on material comminution under high pressure that fractures the material along
the grain boundaries rather than breaking it smaller than a gap setting in the crusher.
The process is now looked at for the TiO2 slag producers because of the potential benefits of
energy savings and with a minimal generation of minus 100-micron fines.
Discussions will revolve around the design and functionality of the Rhodax® both from a
process and maintenance perspective, a typical test regime and results on slag grinding. The
development of the flowsheet necessary for the process will be examined, the ancillary equipment
required and finally the scale-up from the test to an industrial plant will be investigated.
Full-scale results of an operating plant will also be given showing the benefits that can be
realized.
A promising new flowsheet with fines reintroduction to the Rhodax® crusher will be presented.
Rhodax principle
Rhodax ®
is an inertial cone crusher. The bowl subassembly (bowl) consists of a frame supporting the bowl
liner. The cone sub-assembly (cone) consists of a structure
supporting a vertical shaft and the cone (head), protected by
the mantle. The cone is suspended from the bowl by means
of tie rods and ball joints. The bowl is supported by elastic
suspensions to minimize the transmission of vibrations to
the environment. No extensive foundations are required for
the installation of the Rhodax. (see Figure 1)
The driven part of the Rhodax is the bowl while the cone
sub-assembly is suspended via tie rods and allowed to
deflect as a result of the applied grinding force. The mantle
(cone liner) is free to rotate around the centre shaft.
The bowl describes a horizontal circular motion caused
by the rotation of peripheral unbalanced masses (Figure 2).
The masses are synchronized and create a perfectly
controlled force. The controlled inertia force makes the
Rhodax® insensitive to non-crushable material, unlike the
direct mechanical force in conventional equipment.
Rhodax is a multi-compression bed machine. In
operation, the horizontal circular motion generates a cycle
in which both parts of the crushing chamber move towards
and away from each other. During each cycle, the material
undergoes the breaking force, followed by a separation
phase when the material can move lower in the chamber
until the next compression cycle (Figure 3).
While moving downwards by gravity through the
chamber, the material is subjected to a series of 3 to 6
compression cycles. This slows down the progression of the
material and a material bed is formed in the lower part of
the crushing chamber, where the nominal pressure is
applied.
The following three parameters can be adjusted on the
Rhodax:
• the gap opening between mantle and bowl liner
• the rotation speed of the unbalanced masses
• the phasing of the unbalanced masses.
The gap controls mainly the flow of material through the
unit, and indirectly controls the power. The gap is
controlled hydraulically by adjusting the vertical position of
the mantle sub-assembly mounted on sliding sleeves. This
system also allows the operator to compensate for liner
wear when the machine is in operation. Finally, the
crushing surfaces have steep angles at the bottom of the
chamber and the large release stroke allows easy removal of
large tramp pieces.
The rotation speed and the phasing of the unbalanced
masses impose the breaking force, control the product size
distribution and therefore the power absorbed by the
RHODAX® INTERPARTICLE CRUSHER MAXIMIZES CHLORIDE SLAG PRODUCTION
63
Figure 1. Rhodax sectional view
Horizontal circular oscillation
Peripheral
unbalance masses
Timing
belt
Maximum compression
Minimum gap opening
FORCE
Mantle
Material being
ground
Bowl liner
Material moving
downwards
Figure 2. Rhodax operating principle
The combination of these two items results in cracks that
are formed along the natural grain boundaries, instead of a
shattering across the natural grain (Figure 4).
Rhodax on titanium slag resutls
There is a world-wide trend towards the use of the
chlorination process (CP) for the production of titanium
dioxide. Titanium slag is produced by a smelting process.
The slag (100% < 100 μm) must then be milled to produce
a 100–850 μm fraction. The minus 100 μm fraction must be
as small as possible. Finer products can be treated using a
most costly sulphate process (SP).
Figure 3. Rhodax grinding principle
Fine and flaky
particles
machine. The speed is adjusted for each application. When
maximum pressure on the bed is required (up to 50 MPa),
the Rhodax® is operated at maximum speed. Alternatively,
if the process must operate at low pressure (i.e. for the
production of material with a minimum of fines), the speed
will be as low as possible, compatible with process
stability. The phasing of the masses can also be adjusted by
remote control by means of hydraulic rotating jacks to
maintain the grinding force at the optimum for the process.
64
Ore broken
Cubical
particles
Ore recovered
Little accessible surface
Large accessible surfaces
Figure 4. Rhodax compressive grinding advantages
HEAVY MINERALS 2007
One plant equipped with one Rhodax 1000 LP (Low
Pressure) is in operation in Norway. For this application
(minimum of fines), the speed of rotation of the Rhodax is
extremely low and the circulating load is 400 to 600% to
reduce the production of the minus 100 μm fraction and
increase the titanium recovery rate.
The process flow diagram is given in Figure 6.
A simplified flow chart is represented in Figure 7.
The CP quality production is approximately 70–80% of
the raw material, depending on the fine quantity (<100 μm)
in the raw product. The classic solution with conventional
crusher offers 60–65% recovery. The CP slag flow is about
30 t/h for 40 t/h of raw material.
The main characteristics of the raw material are:
• Bond work index = 6.8 kWh/ton @ 400 μm
• Abrasiveness YGP = 140 mg/kg.
The titanium oxide raw material has been tested in
fcb.ciment laboratories on a Rhodax 300 test rig. The
results obtained on the test rig help to design the industrial
plant. The fcb.ciment test rig replicates the industrial
conditions and produces grain size equivalent to the
industrial Rhodax (see Figure 8). The capacity scaling-up
factor between the pilot machine (Rhodax® 300) and the
industrial machine (Rhodax® 1000) is about 20.
It is worth noting that the Rhodax produces a very small
amount of fines, with 200 t/h of feeding material (0–20
mm, D50=10 mm virtually no particles finer than 100 μm),
the crushed material is a 0–15 mm D50=2.8 mm with only
2% finer than 100 μm (see Figure 9). This does not change
with product quality changes, thanks to adjusting
parameters of the Rhodax (opening gap, rotation speed,
phasing adjustment).
Figure 5. View of the Rhodax® installed in Norway
Figure 6. Process flow diagram
RHODAX® INTERPARTICLE CRUSHER MAXIMIZES CHLORIDE SLAG PRODUCTION
65
13 tph
-106 μm
# 106 μm
87 tph
+106 μm -8 mm
# 12 mm
100 tph
-8 mm
135 tph
-12 mm
HGG
120 tph
+120 mm
# 90 μm
# 850 μm
35 tph
-12 + 8 mm
27 tph
+106 m -850 μm
215 tph
-30 mm
40 tph
-150 mm
85 tph
-106 μm
5 tph
+106 -850 μm
607 tph
+850 μm -8 mm
8 tph
32 tph
80% yield @ 106 μm
Figure 7. Simplified process flow diagram
99.90%
99.00%
Passing through (%w)
90.00%
80.00%
70.00%
60.00%
50.00%
40.00%
30.00%
20.00%
10.00%
1.00%
400
10
200
150
100
60 50
μm (mesh)
28
14
1000
10
8
6
4
3
10000
Figure 8. PSD of the Rhodax products
The future process
The Tinfos flowsheet was made by screening specialists
and the bed interparticle crushing knowledge was poor at
that stage. The Rhodax was used to apply the minimum
force onto the material but we then discovered that it was
possible to reduce even more the production of fines and
increase the yield in producing some specific grain size
fractions.
Regarding specifically at the ilmenite slag problem, the
production of -850 μm +106 μm versus -106 μm. In other
words, we need to increase the grinding slope of the final
product (-850 μm), as shown in Figure 10.
66
To increase the grinding slope, one must look at what the
in-bed compressive theory says. In this theory, the
compactness (bulk density/S.G.) of the bed of material
increases with the pressure applied on it. The compactness
evolution is due to the grain size modifications. For given
material characteristics, this law is as shown in Figure 11.
The PSD slope is linked to these trends. If the trend shifts
to the left (e.g. moist material), the slope will be less. The
way to increase the slope is to shift the trend to the right
side. One of the easiest ways is to increase the initial
compactness (e.g. get more fines in the interparticle crusher
feed).
HEAVY MINERALS 2007
Rhodax Titanium Slag results
99.90%
Passing through (%w)
99.00%
90.00%
80.00%
70.00%
60.00%
50.00%
40.00%
30.00%
20.00%
10.00%
1.00%
150
100
60
50
28
14
1000
μm (mesh)
10
8
6
4
3
10000
Figure 9. PSD of the inlet and outlet products
99.90%
Passing through (%w)
99.00%
90.00%
80.00%
70.00%
60.00%
50.00%
40.00%
30.00%
20.00%
10.00%
1.00%
400
200
150
100
μm (mesh)
100
60
50
28
1000
Figure 10. Required slope increase of final product to get a 15% yield
100
90
Standard dry material
Dry material with fines
Moist material
80
Pressure (MPa)
70
60
50
40
30
20
10
0
0,5
0,55
0,6
0,65
0,7
Compactness (-)
0,75
0,8
Figure 11. Compactness evolution with pressure for different material characteristics
RHODAX® INTERPARTICLE CRUSHER MAXIMIZES CHLORIDE SLAG PRODUCTION
67
Fresh
Feed
RHODAX®
First stage
Screen
(-850 + 106 μm)
TSV™
1-x
x
(-106 μm)
Figure 12. RHODAX® Flow diagram with fines re-circulation
The best way to get more fines in the crusher feed is not
to increase fines contents from the previous crushing stages.
We can indeed reintroduce a certain portion of the fines
produced by the Rhodax itself. This new crusher feed will
lead to a new steady state where the fines generation is less
and coarse fraction production increases (see. process
Figure 12).
Conclusion
The Rhodax offers the unique possibility to perfectly
controlling the grinding force, and continuously to adapt it
to the variations of the characteristics of the titanium slag
because of the several adjusting parameters of the Rhodax.
• the gap opening between mantle and bowl liner
• the rotation speed of the unbalanced masses
• the phasing of the unbalanced masses.
Fines production (<100 μm) is drastically reduced in the
Rhodax crusher; only 2% of fines are produced against
5–10% in the concurrent solutions (cone crusher, hammer
crusher, roller crusher…). Whatever the slag quality is, the
Rhodax parameters are adjusted to limit fines production
and to enhance the titanium oxide recovery. Rhodax
increases by 20% the recovery against classic crushing
systems.
Latest comprehensive developments in interparticle
crushing and grinding show that reintroduction of fines in
the process should even lead to better and optimized yields.
FCB has successfully installed two HOROMILL® mills
working in such process in calcium carbonate industry.
68
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HEAVY MINERALS 2007