Exercise 2-3 Data for multicomponent ore.

This exercise will demonstrate the specification of data when the ore contains more than one mineral component. The problem studied in exercises 2-1 and 2-2 will be used but now the material to be processed is an iron ore consisting of 48% magnetite by mass in silica. To keep things simple assume that 80% of the silica is completely liberated and 75% of the magnetite is completely liberated. The remainder of the ore is unliberated and for simplicity assume that all incompletely liberated particles have the same composition or grade. (You will examine the correct way to get accurate representations of unliberated ore in Module 7). Sections 2.5 - 2.7 in the text book will be useful.

Load the previous job from Exercise 2-2 if this is not your current job. Change the job name to Exercise 2-3 and save this job. Open the flowsheet editor to check that you have got the correct flowsheet and if so Accept the flowsheet to register the new job name on the flowsheet. Edit the system data. Change the number of minerals to 2, select "Specific gravity by mineral " and add magnetite of specific gravity 5.2. Change the number of grade classes to 3, one for liberated silica, one for incompletely liberated particles and one for liberated magnetite. It is now necessary to specify the composition of the particles in each grade class. Click on "Set up grade classes". This brings up a form that enables the grade of each particle type to be specified. Note that the default composition of the unliberated particles is 50% silica and 50% gangue. This must be changed in this example according to the following calculation.

Calculate distribution over G-classes

Consider 100 mass units of ore:

Units of liberated silica = 52 x 0.8 = 41.60

Units of liberated magnetite = 48 x 0.75 = 36.00

Units of unliberated ore = 100 - 41.60 - 36.00 = 22.40

Units of silica in unliberated portion = 52 - 41.60 = 10.40

Units of magnetite in unliberated portion = 48 - 36.00 = 12.00

Average silica grade in unliberated particles = 10.40/22.40 = 0.4643

Average magnetite in unliberated particles = 12.00/22.40 = 0.5357.

Change the composition of grade-class 2 to 0.4643 0.5357. Note that you cannot change the specific gravity of the unliberated particles. MODSIM will calculate this for you because you previously specified that specific gravities are to be specified by mineral. The easiest way to get the calculation done is to select "Default" in the "Data set" box and then immediately reselect "New" which will show the new data with the specific gravity calculated. You can now accept this data.

It is now necessary to specify how the particles in the feed population are distributed over these three grade classes. To do this double click on the feed stream in the "Feed streams" box on the system data editing form. This will bring up the particle-size distribution form for the feed stream. NOTE THAT THE "Specify grade distributions" BOX IS GREYED OUT in this example. This is because MODSIM remembers that the current data was inherited from the previous exercise which did not require G-classes. To register the new data click "Accept" which takes you back one form and immediately double click on the feed stream. This time the particle size distribution form opens with the "Specify grade distributions" button enabled. You will keep the size distribution used in the previous exercise so click on the "Specify grade distribution" button. This opens the form to specify the distribution of particles among the grade classes. From the calculation given above the mass fraction of the particles in G-class 1 is 0.4160, in G-class 2 (the unliberated particles) it is 0.2240 and in G-class 3 it is 0.3600. Clear the default data and enter these values.

Accept this data and the particle size data and the system data (Click three Accept buttons in succession). This will take you back to the main page. Take a quick look at the unit parameters to make sure everything is OK and you are ready to run the simulation. Run it and then view the flowsheet to see the results.

We expect that the hydrocyclone should show an upgrading of the heavier mineral in the underflow and it is interesting to check this. A convenient way to do this is to show the Fe content of each stream in the vacant quadrant of each flyout. This is done using the output format facility so cancel the flowsheet and edit the output format.

Select your preferred units for the solid and water flowrates. Enter Fe into the first field under "Metals or elements". This will tell MODSIM that you want to keep track of iron in the flowsheet streams. Because MODSIM does all calculations using the individual minerals you must specify how much Fe is in each mineral that is listed - 0% in silica and 72.4% in magnetite (enter 0.724). To display the Fe content in each stream check the "Recovery and grade of individual metals" in the "Select quantities to display" frame. While your cursor is in the neighborhood, check the "Recovery and grade of individual minerals" because you will need this information shortly. Check the "Display latest output data" box and accept the form.The results from the simulation are displayed in a formatted file which you can examine. This file is most often used to insert simulation data into a report. Close this form. View the flowsheet and notice that the iron content of each stream is displayed in the 4th quadrant of the flyouts. Note the upgrading of the heavy mineral in the underflow.

Right click on the overflow and underflow streams and note the d80 size for each stream.

Right click on the hydrocyclone icon and open its report file. Scroll down and check the d50c sizes for each G-class. Note that these decrease from G-class 1 to G-class 3. Why? Note also that d50c for silica is smaller now than in exercise 2-2. Why? (Here is another 2 point bonus to any for-credit student who can post an explanation on the bulletin board before any not-for-credit student).

One final piece of information should be checked before you start investigating possible parameter changes. Recall that we never specified that the magnetite content of the feed should be 48%. MODSIM had to reconstruct this from the G-class information. To check this, View the simulation results from the main View menu. Because the grade and recovery of the minerals was selected in the output format these are displayed in the table. The grade of magnetite in the feed is correctly calculated as 48%.

This concludes the exercises for module 2.

These jobs for exercises 2-1, 2-2 and 2-3 can be loaded into MODSIM from the Internet if you do not succeed in setting them up correctly yourself.