How is ore-dressing of iron done?

Ores obtained from the Earth’s crust are always pure.

Which of the following is not a suitable ore for extracting iron?

In invar, what is the composition of iron and nickel?

Which of the following ores cannot be concentrated by hydraulic washing?

Which of the following ores are concentrated by froth flotation?

Where are the magnetic particles collected in concentration by electromagnetic separation?

What is the net reaction in Hall-Heroult process?