Bring 4 cups water to a boil in a medium saucepan. Add tea bags and mint to pan; steep 10 minutes. Remove and discard tea bags and mint.
Combine sugar and juice in a glass measuring cup. Add 1/2 cup hot tea mixture; stir until sugar dissolves. Pour sugar mixture into a 2-quart pitcher. Pour the remaining hot tea mixture into pitcher. Add 4 cups cold water; stir. Serve over ice. Garnish with lemon slices and mint sprigs, if desired.