A B757-200 IN CLB AT 17500 FT DECLARED AN EMER AND DIVERTED DUE TO R ENG FAILURE. CAUSE OF FAILURE UNKNOWN.

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THIS WAS ON FLT ABCD FROM FLL-JFK. (16 PAX; CREW 6; FUEL 26900 LBS; GROSS WT 163900 LBS.) START AND TAXI OUT WERE NORMAL. TKOF NORMAL WITH EXCEPTION THAT THE R ENG WAS SLIGHTLY SLOWER TO SPOOL UP ON RWY; BUT CERTAINLY NOTHING DRASTIC. SO; TKOF AND CLBOUT WERE NORMAL; WITH ME (THE FO) FLYING. WE THEN HEARD A LOUD BANG; HAD A SIGNIFICANT YAW AND LOSS OF PWR NOTED ON ALL R ENG GAUGES. (NO EGT EXCEEDENCE WAS NOTED.) I LEVELED OFF (17500 FT); THE CAPT DECLARED AN EMER WITH AN IMMEDIATE TURN BACK TO FLL. THE CAPT GOT OUT THE QRH TO READ THE APPROPRIATE 'NON-NORMAL' CHKLIST. BUT MY EFIS DISPLAY BLANKED OUT SEVERAL TIMES DUE TO LOSS OF GENERATOR PWR AND WE DECIDED ON A SWITCH OF ROLES. CAPT TOOK CTL OF THE FLYING AND I RAN THE APPROPRIATE CHKLISTS. WE LET THE FLT ATTENDANTS AND THE PAX KNOW EVERYTHING WAS 'UNDER CTL' AND WE WERE RETURNING TO FLL WITH AN ENG OUT. WE THEN REQUESTED THE FIRE EQUIP TO STAND BY FOR A STRAIGHT-IN LNDG ON RWY 27R. LNDG; TAXI IN; AND SHUTDOWN WERE NORMAL. A POSTFLT EXAMINATION OF THE ENG SHOWED ALL BLADES INTACT; BUT 'FROZEN' AND SMALL BITS OF METAL IN THE TAIL SECTION. (OUR FLT ATTENDANTS DID RPT SEEING A LARGE BALL OF FLAME EXIT THE ENG AROUND THE TIME OF ENG FAILURE; BUT NO FIRE WAS OBSERVED OR INDICATED IN COCKPIT.) CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED A REQUEST WAS MADE TO MAINT TO ADVISE THE CREW OF THE CAUSE OF THE ENG FAILURE BUT HAVE RECEIVED NO MAINT REPLY. THE RPTR SAID IT RESULTED IN AN ENG CHANGE DUE TO THE FAN ROTOR BEING LOCKED UP AND THE PRESENCE OF TURBINE BLADE DEBRIS IN THE TAILPIPE.