Report on Test work conducted on the Fisher Air Separator
Considering the water limitations at Leqhobong, and previous exposure to the Fisher Air Separator a
trial was undertaken in Lephalale (Ellisras) to consider the effectiveness of the separator in the
removal of ultra-fines from a kimberlitic feed.
The installed air separator is currently being used for the supply of aggregate and crusher dust for
the Medupi power station. A sample of material was transported to Lephalale for the trial. Due to
excessive rain in the area over the December period the sample was spread out to dry and covered
at night. As a result the percentage moisture was lower than what would have been preferred.
Principle of operation
The principle of operation is simple and the unit has minimal moving parts
The operation involves introducing the feed material into a vertically rotating chamber. The outer
wall of the chamber is so constructed that a counter current air stream can pass from the outside
inwards. The rotation of the chamber also acts as a fan, generating the counter current air flow.
.
As the air passes though the chamber it comes into contact with the feed, which due to centrifugal
force is moving outward in the chamber. The air flow passes though the feed and in so doing
removes all fines present in it. The fines with the air flow are circulated and deposited on the outer
wall of the discharge cone. Coarse material moves through the rotating chamber and is discharged
via an inner cone.
General operation of the unit produces minimal dust, however at the start of operation the unit
generates a fair amount of dust for a few minutes.
Test Work
The test work was done in two stages.
Primary feed was fed into the unit and a mass reduction calculated based on the units feed tons.
Fines from the test were sampled and then discarded.
The primary coarse product was retained and then used as a feed in a second separation stage. It is
common practice to use two separators in series.
Results
As can be seen the sample contained a high degree of fines which can be attributed to the handling
and drying.
The feed moisture was 4% which was lower than what would have been preferred. The machine is
capable of operating at 10% moisture with higher yields.
The resulting yields are tabulated below
Primary yield 64.2 %
Second Yield 78.7%
Overall yield 50.5%
The overall reduction of fines is impressive. Unlike a screening operation the cut point is determined
by the velocity of the air stream. It is thus possible to change the cut point by increasing or
decreasing the air velocity.
Considering the distributions above, the reduction in fines from the feed to the primary product is
very evident. The second reduction appears to be far less but due to no screen sizes being available
in the fine ranges the product curves have been skewed. What in effect has happened is that the
second separation curve has moved down in the finer fractions. During the test work it is clear that
the second pass cut point was lower than in the first pass and this would be in agreement with the
comment above.
A size distribution on the fines fraction will be conducted to confirm the cut point.
It is also clear from the test work that the unit removes fines below 2mm with the bulk of the
reduction being effected at 1.5mm
1st
pass product (coarse)
1st
and 2nd
pass ultra-fines.
Conclusion
From the test work it is clear that the unit is capable in the separation of fines using a dry
application.
Given the water and slimes dam constraints at Leqhobong as well as the associated costs building
slimes dams, this would certainly be a route to pursue.
I do not see that the unit would entirely replace scrubbers in the process. There will always be a
combination of both. It may also be possible to utilise the unit in the process during the dry winter
months when water is at a premium.
RK Prentice
II ̂ A T' RO CAST F?TiI?il:'IVIA I- CIVIL ENG. LABORATORY SERVICES -
Reg.No.: 2000/030983107 - VAT. Reg.No.: 4130197405
a SANAS Accredited Testing Laboratory, No. TO24S4 HMrcT CLOSE , BRACKENDUST . 7560P.O BOX 1106 , BRACKENFELL
TEST RESULTSKElTH PRENTICE
Attention: MR K. PRENTICE
Tel. : 021 9815558Fax :021 9816724Email : [email protected]
Project : LESOTHO MINING MATERTAL
Your RefOur RefDate Reported
' :37824
:20.04.2011
S a m p l e N o . : C 0 6 1 9
Ho le No . : -
Depth : -
Liquid Limit (%) : 19
Plasticity lndex : 5
Linear Shrinkage (%) : 3.0
Pl of Whole Sample : 5
P.R.A, Classification : A-4(2)
Unified Soil Classificatior: SM-SC
Activity : 1.00
Heave Classification : LOW
Grading Modulus : 0.59
Percentage (<0.002) : 5.0
Moisture Content (%) : 3.8
FOUNDATION INDICATOR (ASTMz D4221Material Description : DARK OLIVE SILTY SAND
ACTIVITY DIAGRAM1 . 0
0.70.60.5
-9q.
Ec'o-go
=od
10 20 30 40 50 60 70Percentage (<0.002)
Clav (%) sitt (%) Sand (%) Gravel (% ClassificationJenninqs 9.6 21.0 67.8 1 . 6 SILTY SANDAstm 9.6 35.8 54.5 0.0 S]LTY SANDBritish Standard 4.8 28.2 65.4 1 . 6 SILTY SAND
CASAGMNDE PLASTICITY CHART
x(l,Ec
F(-,olgo-
1
0d 10 20 30 40 50 60 70 80 90 100Liquid Limit (%)
1PARTICLE SIZE DISTRIBUTION
Lr,l
u.lo(9=oan
o-
sIIJ
If=:)o
90
80
70
60
50
40
30
20
1 0
JENN CLAY GRAVEL
ASTM CLAYFINESAND
MEDIUMSAND GRAVEL
BS CLAYFINESILT
MEDIUMSILT
COARSESILT
F INESAND
MEDIUMSAND
COARSESAND
FINEGRAVEL
MEDIUMGRAVEL
COARSEGRAVEL
Remarks : SAMPLED AND DELTVERED By CUSTOMER
FORM: A6 3.3R (06.10.2010) Technical Signatory: Raymond van Niekerk
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