Q.Which of the ores mentioned in Table 6.1 can be concentrated by magnetic separation method?

Magnetic separation works when either the ore particles or the gangue particles are magnetic, so that a moving belt over magnetic rollers deflects the magnetic component away from the non-magnetic one. Among the common ores in Table 6.1 (oxides/sulphides/carbonates of Fe, Al, Cu, Zn), magnetite ($Fe_3O_4$) is ferromagnetic and is readily separated from its non-magnetic gangue this way.

Step 1 – Principle of magnetic separation

This physical concentration method is used when either the ore or the impurity (gangue) is magnetic while the other is not. The crushed ore is fed onto a conveyor belt running over two rollers, one of which is magnetic. The magnetic component is attracted and falls closer to the magnetic roller, while the non-magnetic component is flung farther off, separating the two.

Step 2 – Survey the ores in the table

Table 6.1 lists common ores of iron, aluminium, copper and zinc — e.g., haematite ($Fe_2O_3$), magnetite ($Fe_3O_4$), iron pyrites ($FeS_2$), bauxite ($Al_2O_3.2H_2O$), copper pyrites ($CuFeS_2$), copper glance ($Cu_2S$), zinc blende ($ZnS$), etc. Of these, magnetite stands out as ferromagnetic — it is strongly attracted to a magnet, unlike the siliceous/earthy gangue associated with it.

Step 3 – Conclusion

Because magnetite is intrinsically magnetic, it is the ore in the table that is amenable to magnetic separation, allowing the magnetic ore particles to be mechanically separated from the non-magnetic gangue.

Recall that magnetic separation requires either the ore or the gangue to be magnetic; scan the listed ores for one that is intrinsically magnetic — that is magnetite ($Fe_3O_4$).

• Assuming any iron ore (e.g. haematite $Fe_2O_3$) is magnetic — haematite is only weakly/paramagnetic and is not the textbook example; magnetite specifically is ferromagnetic.
• Confusing magnetic separation (a purely physical concentration step) with a chemical process such as roasting.