Sorption of yttrium and rare earth elements by amorphous ferric hydroxide: Influence of solution complexation with carbonate

摘要

The influence of solution complexation on the sorption of yttrium and the rare earth elements (YREEs) by amorphous ferric hydroxide was investigated at 25 degrees C over a range of pH (4.0-7. 1) and carbonate concentrations (0 M <= [CO32-] <= 150 mu M). Distribution coefficients, defined as K-i(Fe)T = [MSi](T)/(M-T X [S-i]), where [MSi](T) is the total concentration of sorbed YREE, M-T is the total YREE concentration in solution, and [Si] is the concentration of amorphous ferric hydroxide, initially increased in magnitude with increasing carbonate concentration, and then decreased. The initial increase of iK(Fe)(T) is due to sorption of YREE carbonate complexes (MCO3+) in Fe addition to sorption of free YREE ions (M3+). The subsequent decrease of iK(Fe)(T), which is more extensive for the heavy REEs, is due Fe to the increasing intensity of YREE solution complexation by carbonate ions. The competition for YREEs between solution complexation and surface complexation was modeled via the equation: