Complexes of Thorium with Phosphoric Acid

Abstract

The behaviour of 227 Th in the two-phase system HDEHP-C 6 H 6 / H3PO4 -HCIO4 -LÍCIO4 (μ = 0.2), has been investigated as a function of the independent equilibrium parameters which define the system. The data have been interpreted in terms of the formation of phosphoric complexes in the aqueous phase of order I with respect to H3PO4 and charge z. The values obtained were 1 < / < 5 and ζ = -3,0,1,2. Stability constants were determined. The composition of the complexes is proposed on the basis of partial atomic charges. Several complexes were formulated as hydroxophosphoric species resulting from competition between hydroxyl and dihydrogen phosphate anions. In concentrated phosphoric acid (CH3I>O4 -4 M), Th(H 2 P0 4 ) 4 is the predominant species.

Thorium sorption onto magnetite and ferrihydrite in acidic conditions

“…According to Bäes and Mesmer [31], thorium(IV) hydrolysis becomes detectable between pH 2 and 3. Moreover, Elyahyaoui et al [32] observed that at trace levels, thorium hydrolysis seems to start at even lower pH (pH 1.2). Since the slope in the log-log plot is determined within the pH range 1.65-3.60, the possibility of p = 0 cannot be excluded.…”

Th(IV) adsorption on alumina: Effects of contact time, pH, ionic strength and phosphate

“…However, it was found that in the initial period ( 24 h), phosphate ions complex onto the oxide surface in a 1:1 stoichiometry at a fairly rapid rate, and then, in an extended period ( 25 h), the alumina phase transforms into an aluminum phosphate precipitate at a very slow rate [14]. Additionally, it was found that in the pH range 1.7-2, 80% of the Th(IV) appears as Th(H 2 PO 4 ) 4 , at pH 3, and the anionic complex is predominant and incorporates 90% of the thorium at solution conditions C H 3 PO 4 7 × 10 −2 mol/L and C Th ≈ 3 × 10 −4 mol/L [10]. Therefore, a strong effect of phosphate on the extent of adsorption of Th(IV) onto alumina may be expected.…”

“…Elyahyaoui et al [10] observed thorium hydrolysis starting at pH 1.2 at trace levels. In general, several monodentate surface complexation reactions,…”

Preparation of U(VI) and Th(IV) α-sources from calcium nitrate solutions by combining solvent extraction and electrodeposition procedures

“…The organic phases were composed of diethyl ether solutions 0.34 M in acetic acid. 233 U and 228 Th tracers, available in 3 M nitric acid stock solutions, were purified from the daughter activities prior to use with a procedure described previously [19]. Aliquots with activity of 3 Bq were taken from these stock solutions for the extraction and electrodeposition experiments.…”