Reactio of Plutonium(VI) with Orthosilicic Acid Si(OH)_4

摘要

Reaction of Pu(VI) with Si(OH)_4 (at concentration 0.004-0.025 mol l~(-1)) in a 02 M NaClO_4 solution at pH 3-8 is studied by spectrophotometric method. In the range of pH 4.5-5.5, PuO_2(H_2O)_4OSi(OH)_3~+ complex is formed, while at pH>6, PuO_2(H_2O)_3O_2Si(OH)_2 or hydroxosilicate complex PuO_2(H_2O)_3(OH)OSi(OH)_3 is recorded. The equilibrium constants are calculated for the reactions of formation of PuO_2(H_2O)OSi(OH)_3~+ and PuO_2(H_2O)O_2Si(OH) and their concentration stability constants: logK_1=-3.91(+-)0.17 and logK_2 approx = -10.5; logbeta_1=5.90(+-)0.17 and logbeta_2 approx = 12.6. The PuO_2(H_2O)_4OSi(OH)_3~+ complex is significantly less stable than analogous complex of U(VI). Calculations of the forms of Pu(VI) occurrence at the Si(OH)_4 concentration equal to 0.002 mol l~(-1) showed that the maxmum fraction of the PuO_2(H_2O)_4OSi(OH)_3~+ complex is approx 10& (pH 6.5), while the fraction of PuO_2(H_2O)_3O_2Si(OH)_2 is almost 40% (pH 8).