A CALORIMETRIC AND MICROSTRUCTURAL STUDY OF SOLIDIFIED TOXIC WASTES .2. A MODEL FOR POISONING OF OPC HYDRATION

During cement-based processing of certain hazardous wastes the hydrati on reactions thought to be responsible for solidification can be poiso ned and appear to be retarded indefinitely. A number of wastes known t o be capable of poisoning hydration were added to ordinary Portland ce ment (OPC) and classified on the basis of interference effects observe d. This paper reports the results from a characterisation of these was tes and the subsequent addition to OPC of waste components identified as significant in single and combined additions. The effects of these additions were examined by conduction calorimetry and microstructural techniques. A comparison of results showed that it was possible to rep roduce the poisoning effects observed previously with real wastes by a n addition of combined metal hydroxides only. These results suggest th at poisoning results from the synergistic effects of compounds contain ed in the waste. A model, representing the early hydration of OPC, has been modified and is presented and its application in explaining pois oning of hydration is discussed.