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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.