1):  I think it's all about stability.  Most elements do not have a full outer shell of electrons, so they want to do whatever they can in order to get that full shell and be thermodynamically stable.  Elements such as silicon and carbon and phosphorus are found as compounds because they are usually around very reactive elements which will want to react with them, thus not letting them exist as free elements.  (Silicon and carbon are usually around oxygen, as is phosphorus.  The oxygen will make it more likely that they won't be found free).

2):  Electrorefining is an attempt at purifying a metal by electroplating it onto a designate device so that only the the pure metal plates out.  The over look of the metal is not important.  Only the purity.  Electroplating is the decorative deposition of a metal onto a target object.  Generally, when electroplating you do care about how it looks and the purity is the second thing on the list of priorities.  I also think the difference between the two is the amount of metal involved.  When you electroplate, you're generally dealing with a smaller amount of metal.  When you electrorefine, you're dealing with a LOT more metal.  (For example, when you electroplate gold onto something, you generally deal with very, very, very small amounts of gold.  When you electrorefine gold metal, you're dealing with kilograms of it).

Thanks a lot I get it now

But I still have two more questions...

1.When refining metals in an electrolytic cell, why must the metal product form at the cathode?

2.In the process of refining copper metal, why is the electrode of the impure copper placed at the anode?

Thank you again for your great explanation

Can anyone teach me? Thanks!