Efficient method for decontaminating waste gases and waste water containing cyanide in a method for producing alkali metal cyanides

A method for producing alkali metal cyanides as solids, comprising at least the following steps:

• i) an absorption step, in which hydrogen cyanide from a synthesis gas containing hydrogen cyanide is absorbed in an aqueous alkali metal hydroxide solution to produce an aqueous alkali metal cyanide solution;
• iii) a crystallization step, in which the alkali metal cyanide solution is introduced into an evaporative crystallizer, which is heated by heating and in which a pressure below 1013 mbar is provided;
• iv) a step of condensation of cyanide-containing vapors arising in step iii) to form a cyanide-containing vapor condensate;
• wherein the step of the condensation iv) is performed using a multistage steam jet compressor, which suctions the exhaust vapors out of the crystallizer;
• characterized in that after step iii), a further step iiib) is performed with separating the alkali metal cyanide crystals formed from the mother liquor by centrifuging.