Is it possible to pay a part of the amount due to the retiring partner and the balance transferred to his loan account?

Yes

Disposal of Amount Due to Retiring Partner-
The outgoing partner’s account is settled as per the terms of the partnership deed i.e., in lumpsum immediately or in various installments with or without interest as agreed or partly in cash immediately and partly in installment at the agreed intervals.
The total amount due to the retiring partner which is ascertained after all adjustments have been made to be paid immediately to the retiring partner. In case the firm is not in a position to make the payment immediately, the amount due is transferred to the retiring Partner’s Loan Account, and as and when the amount is paid it is debited to his account.