Why is Adani planning to raise $1 billion via loan?

I think you are referring to $1 billion loan Adani Airports will raise on behalf of Mumbai’s International Airport Ltd (MIAL). This will help MIAL to become debt free. Barclays, JP Morgan and Deutsche bank will arrange the loan. Adani Airport Holdings, a unit of Adani Enterprises, had bought 50.5% stake in MIAL from the Hyderabad based GVK group. Adani plans to build a complete airport ecosystem covering business, leisure and entertainment.