Investigation of neodymium(3) interaction with ethylenediaminetetraacetic acid by chemical relaxation method

Relaxation times in neodymium(3)-ethylene diaminetetraacetic acid (EDTA) have been studied at pH 2.8-4.0, t=23+-1 deg C and ionic strength 0.1. The indicator temperature jump method was used. The relaxation times and the rate constants of complex formation reactions Nd3+ +Hsub(n)Ysup(n-4) → [NdHsub(n)Ysup(n-1) → [NdY-]+nH+ were calculated by a computer with the use of special ''Relax'' programme allowing for the participation of all the ligands present in the solution. The most feasible mechanism involves the formation of the [NdH3Y]2+ complex at a comparatively slow stage with the direct reaction constant k1=(1.16+-0.05)x107 and the inverse reaction constant k2 = (1.25+-0.20)x104 1xm-1xs-1. The stability constant of the [NdYsup(-)] complex as inferred from the kinetic data is equal to βsub(kin) = 4.3x1015