RHODAX® INTERPARTICLE CRUSHER MAXIMIZES CHLORIDE SLAG PRODUCTION 63

Rhodax principleRhodax® is an inertial cone crusher. The bowl sub-assembly (bowl) consists of a frame supporting the bowlliner. The cone sub-assembly (cone) consists of a structuresupporting a vertical shaft and the cone (head), protected bythe mantle. The cone is suspended from the bowl by meansof tie rods and ball joints. The bowl is supported by elasticsuspensions to minimize the transmission of vibrations tothe environment. No extensive foundations are required forthe installation of the Rhodax. (see Figure 1)

The driven part of the Rhodax is the bowl while the conesub-assembly is suspended via tie rods and allowed todeflect 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 causedby the rotation of peripheral unbalanced masses (Figure 2).The masses are synchronized and create a perfectlycontrolled force. The controlled inertia force makes theRhodax® insensitive to non-crushable material, unlike thedirect mechanical force in conventional equipment.

Rhodax is a multi-compression bed machine. Inoperation, the horizontal circular motion generates a cyclein which both parts of the crushing chamber move towardsand away from each other. During each cycle, the materialundergoes the breaking force, followed by a separation

phase when the material can move lower in the chamberuntil the next compression cycle (Figure 3).

While moving downwards by gravity through thechamber, the material is subjected to a series of 3 to 6compression cycles. This slows down the progression of thematerial and a material bed is formed in the lower part ofthe crushing chamber, where the nominal pressure isapplied.

The following three parameters can be adjusted on theRhodax:

• 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 theunit, and indirectly controls the power. The gap iscontrolled hydraulically by adjusting the vertical position ofthe mantle sub-assembly mounted on sliding sleeves. Thissystem also allows the operator to compensate for linerwear when the machine is in operation. Finally, thecrushing surfaces have steep angles at the bottom of thechamber and the large release stroke allows easy removal oflarge tramp pieces.

The rotation speed and the phasing of the unbalancedmasses impose the breaking force, control the product sizedistribution and therefore the power absorbed by the

PORTAL, J. Rhodax® interparticle crusher maximizes chloride slag production with a minimum generation of fines. The 6th International Heavy MineralsConference ‘Back to Basics’, The Southern African Institute of Mining and Metallurgy, 2007.

Rhodax® interparticle crusher maximizes chloride slagproduction with a minimum generation of fines

J. PORTALResearch Centre, FCB.ciment, France

One of the key products produced by the mineral sands industry is the titanium dioxide slag, aprocess that requires grinding of a coarse product down to a valuable saleable product. Traditionalmethods 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 adynamic classifier and secondary gyradisc crushers.

The products produced, commonly known as chloride and sulphate slag, are differentiated bythe particle size distribution of the final product. The more valuable chloride slag must, byspecification, be a product sized in the range between 850 and 100 microns—the more finesgenerated 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 mineralprocessing industries. Inter particle communition, or IPC as it is known, has been applied in thecement industry to improve the performance of clinker grinding mills. The principle is to create aprocess of material on material comminution under high pressure that fractures the material alongthe 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 ofenergy savings and with a minimal generation of minus 100-micron fines.

Discussions will revolve around the design and functionality of the Rhodax® both from aprocess and maintenance perspective, a typical test regime and results on slag grinding. Thedevelopment of the flowsheet necessary for the process will be examined, the ancillary equipmentrequired 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 berealized.

A promising new flowsheet with fines reintroduction to the Rhodax® crusher will be presented.

HEAVY MINERALS 200764

machine. The speed is adjusted for each application. Whenmaximum 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 theproduction of material with a minimum of fines), the speedwill be as low as possible, compatible with processstability. The phasing of the masses can also be adjusted byremote control by means of hydraulic rotating jacks tomaintain the grinding force at the optimum for the process.

The combination of these two items results in cracks thatare formed along the natural grain boundaries, instead of ashattering across the natural grain (Figure 4).

Rhodax on titanium slag resutlsThere is a world-wide trend towards the use of thechlorination process (CP) for the production of titaniumdioxide. Titanium slag is produced by a smelting process.The slag (100% < 100 μm) must then be milled to producea 100–850 μm fraction. The minus 100 μm fraction must beas small as possible. Finer products can be treated using amost costly sulphate process (SP).

Figure 1. Rhodax sectional view

Figure 2. Rhodax operating principle

Figure 3. Rhodax grinding principle

Horizontal circular oscillation

Maximum compressionMinimum gap opening

FORCE

Material beingground

Material movingdownwards

Mantle

Peripheralunbalance masses

Bowl liner

Timingbelt

Figure 4. Rhodax compressive grinding advantages

Large accessible surfaces

Ore recovered

Cubicalparticles

Fine and flakyparticles

Ore broken

Little accessible surface

RHODAX® INTERPARTICLE CRUSHER MAXIMIZES CHLORIDE SLAG PRODUCTION 65

One plant equipped with one Rhodax 1000 LP (LowPressure) is in operation in Norway. For this application(minimum of fines), the speed of rotation of the Rhodax isextremely low and the circulating load is 400 to 600% toreduce the production of the minus 100 μm fraction andincrease 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 conventionalcrusher offers 60–65% recovery. The CP slag flow is about30 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 infcb.ciment laboratories on a Rhodax 300 test rig. Theresults obtained on the test rig help to design the industrialplant. The fcb.ciment test rig replicates the industrialconditions and produces grain size equivalent to theindustrial Rhodax (see Figure 8). The capacity scaling-upfactor between the pilot machine (Rhodax® 300) and theindustrial machine (Rhodax® 1000) is about 20.

It is worth noting that the Rhodax produces a very smallamount of fines, with 200 t/h of feeding material (0–20mm, 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 changewith product quality changes, thanks to adjustingparameters of the Rhodax (opening gap, rotation speed,phasing adjustment).

Figure 5. View of the Rhodax® installed in Norway

Figure 6. Process flow diagram

HEAVY MINERALS 200766

The future processThe Tinfos flowsheet was made by screening specialistsand the bed interparticle crushing knowledge was poor atthat stage. The Rhodax was used to apply the minimumforce onto the material but we then discovered that it waspossible to reduce even more the production of fines andincrease the yield in producing some specific grain sizefractions.

Regarding specifically at the ilmenite slag problem, theproduction of -850 μm +106 μm versus -106 μm. In otherwords, we need to increase the grinding slope of the finalproduct (-850 μm), as shown in Figure 10.

To increase the grinding slope, one must look at what thein-bed compressive theory says. In this theory, thecompactness (bulk density/S.G.) of the bed of materialincreases with the pressure applied on it. The compactnessevolution is due to the grain size modifications. For givenmaterial characteristics, this law is as shown in Figure 11.

The PSD slope is linked to these trends. If the trend shiftsto the left (e.g. moist material), the slope will be less. Theway to increase the slope is to shift the trend to the rightside. One of the easiest ways is to increase the initialcompactness (e.g. get more fines in the interparticle crusherfeed).

Figure 8. PSD of the Rhodax products

Figure 7. Simplified process flow diagram

80% yield @ 106 μm

32 tph 8 tph215 tph-30 mm

40 tph-150 mm

120 tph+120 mm

35 tph-12 + 8 mm

135 tph-12 mm

100 tph-8 mm

13 tph-106 μm

87 tph+106 μm -8 mm

607 tph+850 μm -8 mm

HGG

5 tph

+106 -850 μm

85 tph

-106 μm

27 tph+106 m -850 μm

# 12 mm

# 106 μm

# 850 μm# 90 μm

99.90%

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 60 50 28 14 10 8 6 4 3

10 100 1000 10000μm (mesh)

Pas

sin

g t

hro

ug

h (

%w

)

RHODAX® INTERPARTICLE CRUSHER MAXIMIZES CHLORIDE SLAG PRODUCTION 67

Figure 9. PSD of the inlet and outlet products

Figure 10. Required slope increase of final product to get a 15% yield

Figure 11. Compactness evolution with pressure for different material characteristics

99.90%

99.00%

90.00%

80.00%70.00%60.00%50.00%40.00%

30.00%

20.00%

10.00%

1.00%150 60 50 28 14 10 8 6 4 3100 1000 10000

μm (mesh)

99.90%

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 60 50 28

100 100 1000μm (mesh)

100

90

80

70

60

50

40

30

20

10

00,5 0,55 0,6 0,65 0,7 0,75 0,8

Compactness (-)

Standard dry material

Dry material with fines

Moist material

Rhodax Titanium Slag results

Pass

ing

thro

ugh

(%w)

Pass

ing

thro

ugh

(%w)

Pres

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(MPa

)

HEAVY MINERALS 200768

The best way to get more fines in the crusher feed is notto increase fines contents from the previous crushing stages.We can indeed reintroduce a certain portion of the finesproduced by the Rhodax itself. This new crusher feed willlead to a new steady state where the fines generation is lessand coarse fraction production increases (see. process Figure 12).

ConclusionThe Rhodax offers the unique possibility to perfectlycontrolling the grinding force, and continuously to adapt itto the variations of the characteristics of the titanium slagbecause 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 theRhodax crusher; only 2% of fines are produced against5–10% in the concurrent solutions (cone crusher, hammercrusher, roller crusher…). Whatever the slag quality is, theRhodax parameters are adjusted to limit fines productionand to enhance the titanium oxide recovery. Rhodaxincreases by 20% the recovery against classic crushingsystems.

Latest comprehensive developments in interparticlecrushing and grinding show that reintroduction of fines inthe process should even lead to better and optimized yields.FCB has successfully installed two HOROMILL® millsworking in such process in calcium carbonate industry.

References

1. PORTAL, J. Achieving optimal power control andmachine use through the successful implementation ofdaily mine processes, 8th Annual Crushing andGrinding in Mining Conference, Johannesburg, RSA,June 2007.

2. PORTAL, J. Introducing new technologies incrushing and grinding equipment developed byFCB.Ciment in France, 7th Annual Crushing andGrinding in Mining Conference, Johannesburg, RSA,February 2005.

3. CORDONNIER, A. and BRUNELLI, G. The dailygrind, International Cement Review, January 1999.

4. CORDONNIER, A., EVRARD, R., and OBRY, C.New compression grinding technologies, XIXInternational Mineral Processing Congress, SanFrancisco, 1995.

5. EVRARD, R. and CORDONNIER, A. Rhodax®, anew generation of cone grinders, SRBIIFragmentation committee, Grinding and preliminarygrinding study day, France, March 1995.

6. EVRARD, R. and DIEUDONNÉ, V. Industrialminerals grinding—Three key developments, 2ndIndustrial Minerals Processing Conference, NewOrleans, USA, April 1997.

Figure 12. RHODAX® Flow diagram with fines re-circulation

(-850 + 106 μm)First stageScreenRHODAX®

(-106 μm)

TSV™FreshFeed

1 - x x