Study on the Extraction Mechanism and Thermodynamics of Pb(II) with a o-phenylendiamine Tetraacetic Acid¹

Abstract—The extraction mechanism and thermodynamics of Pb(II) with a novel o-phenylendiamine tetraacetic acid (H₄PDTA) were studied by high performance liquid chromatography with UV detector. The effects of extraction time, reciprocating oscillation frequency, Pb(II) concentration, H₄PDTA concentration and Pb(II) solution acidity on Pb(II) extraction were investigated. The results showed that the extraction ratio of Pb(II) increased with an increase of pH and H₄PEDTA concentration with a reciprocating oscillation frequency of 120 CPM (cycles per minute). The composition of the extraction complex was determined by slope methods and UV spectral analysis. The extraction mechanism of Pb(II) was proved to be a chelate extraction reaction and the values of thermodynamic function at 25°C were determined: $\overline {{{K}_{{{\text{ex}}}}}} $ = 2.18 × 10³, ΔG_r = –19.05 kJ mol^–1, ΔH_r = –9.965 kJ mol^–1 and ΔS_r = 30.47 J mol^–1 K^–1.