Abstract: An apparatus for treating a water solution of a waste material containing a salt with smelt-water explosion characteristics comprises an open-bottomed incinerator and a gas-liquid separator disposed beneath the incinerator in fluid-flow communication therewith. The waste solution is sprayed into the incinerator and heated therein so that the salt in the solution is fused, water vaporized and organic components of the solution burned. The combustion gases and water vapor flow downwardly into the separator, while the fused salt forms a deposit on the inner surface of the incinerator and flows downwardly into the separator. At the junction between the incinerator and separator, cooling water is fed to the fused salt so that the deposit of salt is solidified and cracked into separate masses which fall together with the cooling water onto an inclined baffle member disposed in the separator and roll downwardly on the baffle member.