EDTA impact on Cd2+ migration in apatite-water system.

The impact factors on Cd sorption and desorption in aqueous solution on apatite were studied. Batch experiments were carried out using synthetic hydroxyapatite with Ca/P 1.44, 1.66 and 1.94 in Cd(NO3)2 and Cd(NO3)2-EDTA equimolar complex solutions in the pH range from 4 to 7. It was established that Cd sorption on apatite depends not only on apatite specific surface area but also on Ca/P mole ratio in apatite as well as on the presence of chelating compounds. Presence of EDTA in the solution decreases the amount of Cd bound. [CdEDTA]2- prevents chemical sorption of Cd2+ ions on apatite. EDTA considerably decreases the sorption capacity of apatite with Ca excess. Impact of EDTA is smaller for the stoichiometric apatite and for the apatite with calcium deficiency. Cd bound due to adsorption is more easily removed from apatite. Ca2+ ions increase and presence of EDTA in a solution cause total Cd desorption from apatite.