Immobilisation of Contaminated DEHPA Waste in Portland Cement

The immobilisation of organic liquids in cement products can often be difficult when attempts are made to achieve high waste loading. In this work, diethylhexyl phosphoric acid (DEHPA) contaminated with minor amounts of U (1400 ppm), Th (100 ppm) and rare earth elements (17,900 ppm) arising from solvent extraction technology for rare earth extraction from monazite shows promise of immobilisation in ordinary Portland cement (OPC). Waste loadings of up to 50% (v/v) have been achieved at the laboratory scale. The product was allowed to set overnight and had reasonable resistance to leaching after exposure to deionised water (DIW) at 25°C. Centimetre-sized samples released <0.1% of the rare earth and U inventories after exposure to 100 ml of DIW for 7 days. Releases of Ca, Al and Si were comparable with those from DEHPA free OPC. Samples were examined by SEM to determine elemental distribution and assess the porosity. Compressive strengths and detailed leaching behaviour of sample bodies over the temperature range between 25 °C and 50 °C will be presented. Preliminary attempts with geopolymeric materials were less successful than those using cement. The relative merits of immobilisation in cement compared with other possible means of dealing with the contaminated DEHPA are discussed.