Exercise 4-2. Dense-medium cyclone - two stage

Open the job saved in exercise 4-1. Change the job name to Exercise4-2.

Edit the flowsheet and add a second dense-medium cyclone to receive the underflow (sink fraction) from the first stage. Note that it is necessary to process the underflow in order to make a heavy concentrate with minimum silica content.

At this stage do not attempt to simulate closed-circuit operation. Your flowsheet should look similar to Figure 1

Because the flowsheet has changed, the system data must be edited to register the changes. You can take this opportunity to name any of the intermediate streams. Check that MODSIM has recognized all the new streams that were added.

Edit the unit parameters and set the second stage medium density at 2.8.

Run the simulation and view the flowsheet note the silica content of the second-stage underflow. You can now run several simulations with varying medium density in the second-stage cyclone. You should easily find the medium density that minimizes the silica content of the second stage underflow. You should also look at the data output file to check the recovery of the valuable mineral nagnesite.

You are now in a position to simulate closed-circuit operation. Edit the flowsheet. Delete the second stage overflow stream and add a new stream from the second stage overflow and mix it with the fresh feed to the first stage. Remember to use a mixer or sump to mix the recycle with the feed. If you do not know how to insert a mixer into an existing stream, watch the appropriate viewlet in the Trainer. Your flowsheet should look similar to Figure 2.

Run the simulation and note that the silica content of the second stage underflow inevitably increases but the recovery of the magnesite increases significantly.

To complete this exercise you should plot a series of grade recovery curves using the two medium densities as the control variables. To accumulate the grade-recovery data you should copy and paste the appropriate data from the simulation results screen into a spreadsheet program from which you can plot the grade recovery curves. A sample spreadhseet can be downloaded or viewed.

This simple exercise has introduced you to dense-medium circuits and has shown you how to generate grade-recovery curves quickly and easily for a concentration plant with recycle.

Figure 1 Two-stage open circuit configuration. TOP

Figure 2 Two-stage closed circuit configuration. BACK