Abstract: In a process and apparatus for producing an expanded particulate product in a rotary tubular kiln presenting an essentially linear product conveying and treating region free of lateral offset, in which a burner at the discharge end of the kiln operates to introduce heat into the conveying and treating region, raw material is introduced into the conveying and treating region via the charging end and is conveyed through a preheating zone following the charging end in order to dry and heat that material, the material is then conveyed into an expansion zone following and preheating zone to produce the expanded product, and the expanded product is discharged via the discharge end, additional heat is supplied to the raw material by means of at least one additional burner, preferably a mantle burner, located in the conveying and treating region between the first-mentioned burner and the charging end.