JPH05309375

PURPOSE:To develop excellent effect in the lowering of the concn. of cyan by repeating operation such that a treated waste solution is discharged at every one batch of thermal hydrolysis treatment and batch treatment is performed a specific number of times during a period when the concn. of cyan is kept within a control limit value to discharge sludge. CONSTITUTION:In the thermal hydrolysis treatment of a cyan waste solution, the cyan waste solution W to be treated containing a cyan complex ion is adjusted to its pH at 10 or more, if necessary to be introduced into a pressure container 1 and heated to 140-250 deg.C under predetermined gauge pressure according to a batchwise system to be held to said temp. to decompose the cyan complex ion into ammonia and formate and the heavy metal bonded to cyan is removed as heavy metal oxide sludge. The treated waste solution is discharged out of the pressure container 1 at every one batch of thermal hydrolysis treatment and this thermal hydrolysis treatment is batchwise performed 1-5 times during a period when the concn. of cyan is kept within a predetermined control limit value and, thereafter, sludge is discharged out of the system from the bottom part of the pressure container 1.