Is it necessary that we have to use only chiral column for enantiomeric separation. Is there any mobile phase to be used in chiral separation which may separate enantiomers on achiral column?
You certainly can perform chiral separations without a "chiral" HPLC column. One of the most common examples involves the use of an additive (cyclodextrin) to the mobile phase. To learn more, try a simple keyword search using any popular search engine. The time you invest in researching a topic is all part of the learning experience.
Enantiomers have the same chemical and physical behaviour (apart the different interaction with polarized light). So if you want to separate it by chromatography you need to transform the two enantiomers in diastereomers. So depending to the molecules you have you can think to transform it employing a chiral synthon. I can't suggest you anything without more information, sorry.