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.

Chromatographie à contre courant et micelles inverses pour la séparation et l'extraction de cations métalliques

Countercurrent chromatography (CCC) is a separation technique in which the stationary phase is a liquid. Diethylhexyl phosphoric acid (DEHPA) forms reverse micelles in heptane. Metallic ions, located in an aqueous phase, can be extracted into the aqueous core of the reverse micelles in the heptane phase. A CCC apparatus can be considered as a powerful mixing and extracting machine with efficiency above several hundreds of theoretical plates. La3+, Ce3+, Pr3+, and Nd3+ lanthanide cations were separated using CCC with a DEHPA-containing heptane stationary phase. Studying the retention variations with aqueous mobile phase pH, it was possible to determine the lanthanide extraction constants and separation coefficients. Overloading conditions are described. Frontal chromatography was performed using a Co2+ and Ni2+ solution. The Co2+ ions were concentrated in the heptane + DEHPA stationary phase, a part of the solution was deionized, and another part was enriched in only Ni2+ ions. This method also produced the extraction constants and separation coefficients. The use of CCC with a complexing stationary phase can be applied to any cation for ion filtering and concentration, or for deionization of aqueous phases. Key words: countercurrent chromatography, CCC; ion extraction, ion filtering, deionization, lanthanides, transition metals.