A SECOND billion-pound slice of student loan debt is to be sold off to the private sector. N. M. Rothschild and Sons will advise the Department for Education and Employment on the sale to be launched next month and completed by next March. Twenty international finance companies qualified for the auction of the first tranche, worth Pounds 1.02 billion, sold in March this year to NatWest Markets who are interested in the second tranche. After the second sale approximately Pounds 1.5 billion of debt will remain.