Sorption of thorium(IV) ions on gibbsite: Effects of contact time, pH, ionic strength, concentration, phosphate and fulvic acid

The sorption of Th(IV) on gibbsite was determined at differing experimental conditions by using the batch technique. The effects of contact time between the solid phase and aqueous solution, pH, ionic strength (background electrolyte, KNO3), concentration of tetravalent thorium, phosphate and fulvic acid (FA) were investigated. The sorption was rapidly increased in the first 20 h, and then remained constant in the period 20–78 h. It was found that the Th(IV) is strongly sorbed onto gibbsite, when the surface charge is positive; that the sorption is abruptly increased with increasing pH in the range 3–4; that the sorption is insensitive to the increase in ionic strength from 0.001 to 0.1 mol/L KNO3 and that the sorption remains constant at pH 3.90–4.15 and in the concentration range of Th4+ 2.0–6.0 × 10−5 mol/L and the saturated solid phase concentration is about 4 × 10−6 mol/g. In addition, the sorption of phosphate on gibbsite as a function of contact time, pH and concentration and the effects of phosphate and FA on Th(IV) sorption onto gibbsite were investigated too. The significantly positive effects of phosphate and FA and the mutual positive effect of thorium(IV) and phosphate were demonstrated. These positive effects are interpreted in terms of formation of surface ternary complexes and precipitate.