Exercise 5-2 Multi-stage flotation plant
This exercise will use the same feed material as was used in exercise 5-1 and also the same rougher stage. Therefore open the existing saved job from exercise 5-1. Edit the flowsheet and add a scavenger cell to take the tailings from the rougher and a cleaner cell to take the concentrate from the rougher. Add concentrate and tailings streams from these cells but at this stage DO NOT CONNECT THE RECYCLES. Flotation plants can be tricky to calculate when they have recycles and you should run a few simulations with the open-circuit configuration until you are satisfied that the various units in the flowsheet are behaving as expected.
You should also add water to the concentrate launder of the rougher cell. Recall that you specified a rougher concentrate at 55% solids in exercise 5-1. This would be too dense to serve as the feed to the cleaner cell so it must be diluted. You can add a water stream directly to the concentrate launder of the rougher cell as shown here.
Accept the flowsheet and this is a good time to change the job name.
Edit the system data to register the new flowsheet structure and to specify the water flowrate in the rougher launder. Specify that this should dilute the concentrate to 25% solids which will make a satisfactory feed to the cleaner.
Edit the unit model parameters and choose model KLIM for each stage in the circuit. Specify one cell of 10 m^3 for the scavenger and one cell of 2 m^3 for the cleaner.The kinetic constant should be set to the values shown in Table 1. It is not possible to specify accurately the ultimate recoveries in the scavenger and cleaner cells. Most of the sulfide minerals that gets to the scavenger is non-floating since it consists of all of the non-floatable fraction in the rougher as well as the unrecovered portion of the floatable fraction. Almost all of the sulfide mineral in the cleaner is floatable since the only non-floatable material that gets to the cleaner is by entrainment into the rougher froth. It is impossible to know these amounts before the simulation is done so the ultimate recoveries must be estimated for the scavenger and cleaner cells. Use the values given in Table 2.
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| Silicates |
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| Pyrite |
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| Chalcopyrite |
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Table 2 Assumed ultimate recoveries in scavenger and cleaner.
This difficulty in specifying the ultimate recoveries is made even worse when the plant includes recycle streams and makes the Klimpel model unsuitable for any but the most approximate simulations. MODSIM has a better method that is based on the distributed rate constant model and you will investigate this in exercise 5-3.
Run the simulation to check that all parameters have been set up correctly.
When you are satisfied that all three cells are operating properly you are ready to close the recycle loops. To do this you need to insert a mixer in the feed stream ahead of the rougher cell. Close the recycle from the scavenger concentrate and run the simulation. If this is satisfactory, close the recycle from the cleaner tailing. This should produce a final concentrate containing 27% Cu at 69% recovery. The advantage of multistage operation is immediately apparent by comparison with the results from a single rougher stage in exercise 5-1.
