Ammonium thiocyanate is classified as a Poison Schedule 5 and is harmful to aquatic organisms. Ammonium thiocyanate, which has started to liquefy should be disposed of by a licenced chemical waste disposal contractor. In the meantime, it should be stored segregated from incompatible chemicals.
We have previously answered related questions which have additional information that you may find helpful:
Ammonium thiocyanate regarding storage suggestions
Chemical disposal regarding disposal of a few chemicals including iron thiocyanate
Chemical Storage Timeframes regarding shelf life of chemicals
Laboratory Chemicals and Waste Management/Setup regarding general information
'Ammonium thiocyanate', Safety Data Sheet, Chem-Supply website, https://www.chemsupply.com.au/documents/AA0101CH17.pdf (February 2014)