In the Bayer Process, the Purpose of Filtration After the Ore

In the Bayer process, the purpose of filtration after the ore has been digested in concentrated sodium hydroxide is .

A) to remove the sodium ions from the sodium hydroxide solution
B) to separate the soluble aluminum complex from the insoluble iron impurities
C) to remove the anode sludge
D) to separate the insoluble aluminum oxide from the soluble iron impurity
E) to separate the aluminum metal from the hydroxide ions