Citigroup (C) could announce a deal to unload its student-lending subsidiary, Student Loan Corp. (STU) as early as today. SLM (SLM) and one or two other student lenders are hammering out a $500-600M offer, sources say. Citi put a for-sale sign on STU by placing it in Citi Holdings, which holds assets Citi views as ancillary. STU +5.2% premarket. C +0.8%.