Abstract: A method and apparatus for production of cement clinker uses fragmented metallurgical slag, such as from blast furnace production of iron or steel, introduced into a rotary kiln at an infeed located between the kiln front feed end and the rear outlet end. The metallurgical slag combines with predominantly limestone feedstock material flowing inwardly from the feed end toward a burner pipe at the outlet end and intimately blends with the limestone material to become transformed into cement clinker as the blended materials progress through the kiln. Preferably, the metallurgical slag is introduced into the kiln through a kiln dust infeed apparatus present in many rotary kilns at a mid location.