Abstract: A process for producing a chlorine-free hydrochloric acid low in AOX from crude gases containing hydrogen chloride and organic impurities has been found. The crude gases wer subjected to a thermal treatment at 800.degree. to 1600.degree. in a reducing atmosphere. The hydrochloric acid obtained after absorption of the hydrogen chloride is chlorine-free and contains virtually no organic impurities. The waste gas is also chlorine-free.

Abstract: The invention deals with the reduction of the mercury content of industrial waste waters, especially those from a chlorine-alkali electrolysis using the amalgam process.According to the invention all mercury present in the waste water is converted to the form of Hg.sup.++ ions by adding chlorine. Subsequently Fe.sup.++ ions are added. The pH of the solution is raised until a redox potential of from - 0.1 to - 0.8 volts, relative to the normal hydrogen electrode, is obtained. The mercury precipitated and the iron oxide hydrate formed may be filtered from the waste water. Residual mercury contents in the filtrate of about 50 mg/m.sup.3 may be obtained.