SOLIDIFICATION OF HAZARDOUS WASTES CONTAINING CYANIDE

Industrial sludges and residues are often solidified by cement-based solidification systems employing OPC. Metal plating wastes are considered compatible with OPC and have been processed using this binder for about 25 years. Recent research has shown that these wastes are capable of compromising OPC hydration reactions which are claimed to be responsible for effective solidification. Plating residues often contain significant levels of cyanide and when present in large quantities an oxidation process is employed to remove it. However, the potential exists for cyanide-containing wastes to be solidified and therefore the effect on the hydration of an OPC binder system is of importance. In a study to evaluate these effects, sodium cyanide has been added to OPC and has been found to retard hydration significantly. The retardation reaction was monitored by calorimetry, and XRD of the product showed that this was as a result of a complexation reaction involving iron.