An apparatus includes a reactor vessel containing a carbonaceous bed and having means for establishing an elevated temperature within the carbonaceous bed; and the reactor vessel also having one or more feed material inlets above the carbonaceous bed for depositing process material from outside the vessel onto the carbonaceous bed, one or more gas exhaust ports above the bed for exit of gaseous products from the vessel, and one or more slag ports at the bottom of the carbonaceous bed for exit of molten and vitreous material from the vessel; wherein the carbonaceous bed comprises bricks that contain carbon and are of varied size and shape of which at least 25% of the total carbon content of the bed comprises spent pot liner material from aluminum processing, and wherein the bricks further comprise at least one of: Portland cement, potassium silicate cement, or aluminum silicate cement.