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SKIM-AIR FLASH FLOTATION LABORATORY PROCEDURE
The aim of the flash flotation process is to recover liberated
free ground valuable minerals which because of their relatively
higher specific gravity are returned to the grinding circuit by a
hydrocyclone whereby they are further reduced in size. The
installation of a Skim Air flash flotation cell allows these
minerals to be removed from the grinding circuit thereby reducing
overgrinding and loss of recovery. The purpose of laboratory
testwork using a conventional laboratory cell is to obtain
flotation kinetic data on the suitability of the material to the
flash flotation process. Results of site testwork should be
forwarded to Outotec Pty Ltd for evaluation. Pilotscale testwork
should only be undertaken in a pilotscale cell that has been
approved by Outotec. The following Laboratory procedure should be
used : Equipment Standard Laboratory Flotation Cell. (2.5 Litre
cell) Sampling Procedure Flash Flotation Procedure at 45% Solids 1.
Sample Collection. From the Grinding Circuit take multiple cyclone
U/F samples from
different cyclones in the same Cyclone Cluster over a half hour
period using a proper metallurgical sample cutter. Please ensure
that when you take the sample that you cut across the entire stream
and avoid having the sampler overflow. Use a 20 litre bucket and
fill with Cyclone Underflow sample till it is approximately three
quarters full. At the same time obtain 2 x 20 litre buckets of mill
circuit water for use during the wet screening process and for
make-up water during the flotation kinetic tests. Take all samples
to the Plant Laboratory for processing.
2. Wet Screening Sample. Wet Screen the Cyclone underflow sample
at 600 micron or
nearest screen size available to prevent damage to the
laboratory cell. Use the following procedure to screen sample. Fill
another 20 litre bucket three quarters full of mill water and use
this water and container together with the 600m screen to wet
screen sample. Refer to Video step 1.
3. Decanting and Filtering of Fines. Once screening is completed
decant off slimes and
filter. Leave coarse sand in bottom of bucket. Collect filtrate
water and reuse again during the flotation tests. Do not add any
other water other than process water
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obtained from the milling circuit when the samples were taken.
This is to ensure that you do not change the pH or Eh during the
sample preparation stage as this will affect the flotation
results.
NB: Only filter the fines that have been decanted off to save
time in filtering. Leave the coarse sand in the bucket. Take the
+600 micron fraction that has been placed into trays during Step 2,
label and place in oven to dry. When the sample is dry record dry
weight and submit for assay. Refer to Video Step 2.
4. Systematic sampling of Wet Sample. Place the minus 600 micron
coarse fraction left
in the bucket onto the bench with the plastic sheet spread out.
Once the minus 600 micron slimes have filtered, remove cake from
filter and place in tray. Quickly overturn the bucket with the
minus 600 micron coarse fraction and place sample onto the plastic
sheet. Add the filtered slimes on top of the coarse fraction and
mix sample thoroughly before cutting out samples using a systematic
sampling method. Then weigh out 8 samples of 1,980 gm (wet) if
using 2.5 litre flotation cell and select one of the samples at
random for Head Sample. Add 500 ml of water to all samples to keep
solids under water as soon as possible to prevent oxidation. NB:
Steps 1, 2 and 3 must be all completed together and done as quickly
as possible. Refer to Video Step 3.
5. Flotation Kinetic tests. Transfer sample from bucket to the
Laboratory Cell carefully
to ensure that no solids are left behind. Add dilution water to
make up cell volume to about 30mm from top of froth lip with
agitator running.
Run flotation machine at 1200 rpm to keep coarse particles in
suspension if the cell is
an Agitair Cell. If the Lab Cell is a Denver self aspirating
Cell then increase speed to 1800 - 2000 rpm to avoid sanding. Also,
raise the mechanism 2 notches off the bottom as this will increase
the mixing. Add make up water during each Flotation Test to
maintain the pulp level as required. Add reagents and begin
flotation immediately without any conditioning. Remove concentrate
from cell by continuously raking froth using a paddle in a
consistent and repeatable manner. Collect concentrate samples at
30/60/90 and 120 seconds (cumulative time). Refer to Video Step
4.
6. Chemical Analyses. Assay Head Sample, Concentrate Samples and
Flotation tail
samples for each Flotation Test. Always discuss with the Client
what elements should be assayed. i.e. Cu, Au, Fe & Sulphur as
an example. Record all dry weights.
7. Assumptions. For these Flotation Laboratory Tests it has been
assumed that the
moisture content of the material in Step 3 is approx. 20% for
weighing out the samples. It does not matter if this is not exactly
true. This will give approximately 45% solids in the flotation
tests and this simulates what is happening at the top of the Skim
Air. The actual reagent addition rates can be corrected later once
the actual dry weights are known.
8. Wet Samples. Never place the Cyclone Underflow wet samples in
the oven to dry as
you will change the flotation kinetics. These tests must be done
wet so that is why we
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have assumed 20% moisture in all of the Cyclone Underflow wet
samples once they have been decanted and the filtered fines added..
All testing must be completed on the same day or the samples must
be discarded and the work repeated.
9. Flotation Testwork Procedure
a) Make up fresh reagents for the Flotation Tests in the
laboratory do not use plant samples. The type of reagents used will
vary depending on what minerals are involved. You must add reagents
separately and as quickly as possible. Conditioning time should not
exceed 5-10 seconds in total when adding the Flotation Frother and
Collector. Liaise with plant personnel to determine suitable
reagents and addition rates for these Kinetic Tests. The normal
Laboratory Conditioning step must not be carried out under any
circumstances as this will affect the flotation results. Please
remember we are only interested in the speed of flotation. i.e.
Flotation Kinetics. After adding all of the reagents when you turn
on the air supply the froth should start to form immediately.
b) Make a series of tests using a normal reagent mix. Do not try
to optimise reagent
additions until you have completed at least 3 tests with similar
performance. Results can be scattered particularly on gold at the
same reagent addition rate. If you are floating free gold then
please ensure that the filter papers are not discarded and that all
solids are removed from the filter papers when dry. Also, when
placing samples in the oven to dry make certain that the oven
temperature is not set above 80 degrees Celsius or you will burn
off sulphur. The Concentrate samples must always be placed at the
bottom of the oven and the Tail samples at the top of the oven to
avoid contamination. This is of particular importance if there is
free gold present in the samples.
c) At the beginning you should determine whether materials are
free floating, e.g. Add
frother only and determine percentage free floating. Second test
should involve only frother and one collector. Reagent mixes can
then be scaled up once these basic tests are done.
Results Dried concentrate samples are weighed and assayed. Based
on the assays, weights, retention times, reagent consumption and
visual observation, it can be evaluated, if flash flotation by
SKIMAIR machine is suitable and an estimate of concentrate grade
can be given.
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NB: Overall Recovery Since the sample tested to assess the
flotation kinetics has been taken from the Recirculating Load where
there is no actual Skim air operating then the feed grade could be
an order of magnitude higher than in practice, and, consequently
the test results need to be corrected. As a general rule we use a
safety factor of 2.0 for scale up. For a more accurate assessment
of recovery we recommend pilotscale testing from an accredited
testing laboratory approved by Outotec Where Pilotscale Skim airs
are used it is of absolute importance that the device has the
correct lip length and free froth surface area for the duty
specified. If in doubt please check with an Outotec Flotation TSG
member. PETER. BOURKE PRINCIPAL METALLURGIST - FLOTATION PERTH
OFFICE SEAP. OUOTEC PTY LTD Updated 8th January, 2012.
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APPENDIX 1: PHOTOGRAPHS OF LAB PROCEDURE STEPS
Step 1: Sample collection (CUF and Process Water) and delivery
to lab
Step 2a: Wet screening using 600 micron sieve.
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Step 2b: Collected +600 micron fraction from wet screening for
drying in oven (Note: not used in float tests or metallurgical
recovery calculations does not float at full scale).
Step 3a: Filtration of decanted fines from bucket (-600 micron
fraction).
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Step 3b: Remaining coarse in bucket (-600 micron fraction).
Step 4a: Recombining all -600 micron fractions (coarse &
filtered fines).
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Step 4b: Rolling and splitting of -600 micron fractions (coarse
and filtered fines).
Step 5a: Weighing out 1980g wet weight for each flotation test.
Add Process water (500 mL) immediately after weighing to repulp
sample.
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Step 5b: Preparation for Float Test (reagents, water (Process
Water), scrapers, trays, etc)
Step 6: Concentrate samples collected, weighed, dried (at 80C to
preserve sulfides), weighed dry and analyzed for elements of
interest. Contact Outotec for results interpretation and
discussion.