Question

why pure metal always collected at cathode during electrolytic refining

Answer 1

Dear user,

In general, the polarity of cathode and anode is decided on the basis of the
device used for different purposes.
In electrolytic cell, cathode is taken as negative electrode while anode is taken
as positive electrode.
The two types of ions in refining are cations and anions. Cations carry pure metal while the
anions carry the impurity.
And since cations always possess positive charge therefore they are attracted towards
cathode as they are negatively charged (unlike charges attract each other) while the anions carry
negative charge hence they get attracted towards anode.
Hence pure metal is always collected at the cathode.