Hazardous waste is formed into non-hazardous non-leaching aggregate by introducing the material to a rotary kiln (10) where the large solids are at least partially combusted to form a primary aggregate. Gaseous combustion by-products and waste fines from the waste materials are introduced into at least one oxidizer (26) operating at a temperature in the range of from about 1800 DEG to 2500 DEG F. Under such conditions, some of the waste fines are melted to form a slag-like material that is cooled to form the non-hazardous aggregate. The portion of the material in the oxidizer (26) that is not melted, is cooled, neutralized and subjected to a solid gas separation. The solid is reintroduced to the oxidizer with the primary aggregate where they are either melted or entrained within the molten material and become an integral part of the non-hazardous aggregate.
