The synergistic extraction of lanthanide ions(La3+,Pr3+,Nd3+,Gd3+,Dy3+)by Bis（1′-phenyl-3′-mcthyl-5′-pyrazolonc-4′-yl）Phthaldionc（H2BPMOPP or H2A）with 8-Hydroxyquinolinc（HOx）from nitric acid aolution was studied.The synergistic coefficient for La3+ was 8.1.The composition of the extracted compound was shown to be LaA·HA·HOx.The pH1/2 values for La3+,Pr3+,Nd3+,Gd3+ and Dy3+ were 4.20,3.73,3.49,3.30 and 3.01 respectively.The extraction equilibrium constants,enthalyp change and entropy change of the reaction also were calculated.
