Solvent extraction, separation and recovery of lanthanum(III) and cerium(IV) from monazite sand by <i>N</i>-phenylbenzo-18-crown-6 hydroxamic acid

Abstract

A new N-phenylbenzo-18-crown-6-hydroxamic acid is reported for the separation of lanthanum(III) and cerium(IV) from monazite. Lanthanum(III) and cerium(IV) have been ex tracted and separated in presence of thorium, uranium and other associated cations at <i>p</i>H 8.8 and 9.5, respectively, in dichloromethane. Lanthanum(III) gives a colourless complex

with the reagent which is extracted into dichloromethane and has molar absorptivity of 9.0 × 10³ L mol^-1 cm^-1 at 385 nm. Cerium(IV) forms a red colour complex with the reagent extracted in dichloromethane with λ_max 450 nm and molar absorptivity 6.5 × 10³ L mol^-1 cm^-1. For trace determination, the extracts are inserted directly into the plasma for ICP-AES measurements of La(III) and Ce(IV) in the range of 4-80 ng mL^-1 and 8-120 ng mL^-1, respecti vely with the detection limit of 0.5 ng mL^-1. The complexes of lanthanum(III) and cerium(IV) are very stable, (log β₂k<i> </i>20.20 and 20.50, respectively) as compared to those of thorium ( 1.60), uranium (1.80), and other related cations. The proposed method of preconcentration and analysis of La(III) and Ce(IV) is not adversely affected by highly ionic media, rendering the method suitable for their trace determination in sea water.