A pumpable slurry of shredded scrap solid carbonaceous plastic-containing material that contains associated inorganic matter in admixture with a comminuted aluminosilicate-containing material having noncombustible constituents is reacted by partial oxidation to produce synthesis gas, reducing gas, or fuel gas. The noncombustible constituents in the aluminosilicate-containing material captures the inorganic matter in the scrap solid carbonaceous plastic-containing material while in the reducing atmosphere of the gasifier to produce nontoxic, nonleachable slag. The slurrying medium is water, liquid hydrocarbonaceous fuel, or mixtures thereof. Scrap plastics may be disposed of by the subject process without polluting the nation's environment.