Process for the preparation of sodium cyanide

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

• i) an absorption step in the form of an absorption of hydrogen cyanide from a synthesis gas containing hydrogen cyanide in an aqueous alkali metal hydroxide solution having a content of free alkali of approximately 2 to 10 wt. %, in an absorber at a temperature of approximately 35° C. to 75° C. directly after the feed point of the synthesis gas, and a pressure of approximately 1120 to 1600 mbar (a) to produce an aqueous alkali metal cyanide solution;
• ii) a crystallization step in the form of the introduction of the alkali metal cyanide solution into an evaporative crystallizer, which is heated by steam heating so that at the contact surface of the heating element with alkali metal cyanide solution, a temperature of approximately 60-100° C. is provided, and in which a pressure of approximately 30-100 mbar (a) is provided;
• iii) a separation step in the form of the separation of the alkali metal cyanide crystals formed from the mother liquor by centrifuging;
• iv) a recirculation step in the form of the recirculation of approximately X vol. % of the mother liquor separated in step iii) into the absorption and the recirculation of approximately (100-X) vol. % of the mother liquor separated in step iii) into the crystallization according to step ii);
• v) a drying step in the form of the drying of the alkali metal cyanide crystals separated in step iii).