Rotary furnaces and processes for heat treating a workpiece generally include an external shell wall and a refractory lining abutting the shell wall to define a substantially cylindrically shaped interior chamber for treating one or more workpieces; an opening in the an external shell wall and a refractory lining for loading and unloading the workpieces; a rotatable hearth for receiving and rotating the workpieces within the substantially cylindrically shaped interior chamber; and a plurality of thermal isolation walls, wherein adjacent thermal isolation walls define a space effective to accommodate and thermally shield each one of the workpieces to be treated and have a height at least equal to a height of the workpiece. The presence of the thermal isolation walls substantially prevents heat transfer between the workpieces being treated.