The influence of pH on the stability constants of lanthanum and europium complexes with humic acids

Jiménez-Reyes, M.; Solache-Ríos, M.
July 2012
Journal of Radioanalytical & Nuclear Chemistry;Jul2012, Vol. 293 Issue 1, p273
Academic Journal
Complex formation of humic acids (HA) with La and Eu was studied. Commercial (HA) was purified and characterized. The stability constants were determined at several pH values and 0.2 M NaClO ionic strength by the Shubert's method of radiochemical ionic exchange. The slopes of the lines $$ \log ((\lambda_{0} /\lambda ) - 1) = \log \beta_{\text{M,j(HA)n}}^{\exp } + {\text{j}} * \log \left[ { ( {\text{HA)}}_{\text{n}} } \right] $$ were dependent on the [(HA)]. The values of log $$ \beta_{\text{M,j(HA)n}}^{\exp } $$ for j = 1 were the following: 6.29 ± 0.04 (pH 4.9 ± 0.4) and 7.61 ± 0.03 (pH 5.9 ± 0.1) for lanthanum and 7.31 ± 0.01 (pH 5.9 ± 0.2) for europium. Log $$ \beta_{\text{M,j(HA)n}}^{\exp } $$ was determined as well for higher values of the j parameter and these values were: 12.2 ± 0.1 (j = 2, pH 7.7 ± 0.2), 15.6 ± 0.2 (j = 3, pH 4.9 ± 0.4) and 16.05 ± 0.07 (j = 3, pH 5.9 ± 0.1), for lanthanum and 13.18 ± 0.03 (j = 2, pH 5.9 ± 0.1) for europium. A discussion is presented about the complex formation regarding pH and [(HA)].


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