The 23-year-old, who arrived at Glanford Park in January, was supposed to join on a free transfer at the time, but had already played for two other clubs this season - Watford and Stevenage - and under FIFA rules the switch had to be completed as an emergency loan.
Walker, who will sign a one-year deal, has made 18 appearances for the Iron, scoring his only goal in the win at Chesterfield last month.
Meanwhile, the club have also offered a one-year contract to youth team skipper Callum Howe.
The 18-year-old central defender is the only second-year trainee at Glanford Park to be handed a deal.
