Spectrophotometric study of Solvent extraction of Pb (II) and Cd (II) by aminooctyldiphosphonic acid

This study has investigated the solvent extraction of cadmium and lead ions from an aqueous solution in nitrate medium using aminooctyldiphosphonic acid (AODPA) as extractant in chloroform. In order to establish spectrophotometrically the concentration of metal ion in the aqueous phase before and after extraction, the Arsenazo III method was used. The effects of several extraction parameters on the extraction of these metals ions including volume ratio between the aqueous and organic phases (1–5), extraction kinetic time (0–30 min), molar ratio Q (1–5), addition of HNO 3 (pH =2–6), addition of KNO 3 (0.01 – 1M), temperature (10–40°C) and the synergetic effect by adding TOPO (solvating agent) were evaluated. Thermodynamic parameters including the Gibbs free energy (ΔG 0 ),enthalpy (ΔH 0 ), and entropy (ΔS 0 ) were calculated. Performed experiments showed that Pb (II) can be extracted till 73% when Cd (II) can be recovered completely after two cycles. The extraction of both metallic ions was spontaneous, endothermic and with a slight randomness. Positive synergetic effect was observed at a chelating agent/TOPO ratio of 3. It is a very encouraging result which can lead us to recover cadmium and lower the concentration of lead from wastewater.