THE IMMOBILISATION OF As_2O_3-RICH WASTES FROM ORE SMELTING USING LOW TEMPERATURE CERAMICS

摘要

Historically, Ordinary Portland cement has been the preferred medium to immobilise arsenic. However, arsenic in cement gives rise to calcium-arsenic phases and their known decomposition to calcium carbonate and arsenic trioxide via atmospheric carbonation raises serious questions about the long-term suitability of cement for arsenic immobilisation. Alternative matrices such as low-temperature ceramics (LTCs) potentially offer superior resistance towards carbonation owing to the absence of calcium. Consequently, the potential for arsenic immobilisation using LTCs has been investigated. Both As~Ⅲ and As~Ⅴ have been incorporated and samples assessed according to a standard leaching protocol. As~Ⅲ persists in the porewater of alkali-bonded LTCs as sodium arsenite rendering them unsuitable for immobilisation. Thermal treatment of these LTCs to consolidate the microstructure and reduce open porosity resulted in sodium-rich cryptocrystalline matrices that leached arsenic and sodium readily. The omission of sodium in acid-bonded LTC formulations resulted in leach data that were close to the target value of 5μg/ml in Toxicity Characterisation Leaching Protocol tests.