The sorption of lead, cadmium and strontium from aqueous solutions on sepiolite

Abstract

The results of the characterization and the sorption properties of sepiolite from the locality Slovići are presented in this paper. X-Ray diffraction analysis, infrared spectroscopy and differential thermal analysis revealed sepiolite as the main phase and small amounts of magnesite as an impurity. The specific surface area of sepiolite, determined by nitrogen adsorption and by applying the BET equation was found to be 339 m2/g. The point of zero charge was determined by the batch equilibration method, under different conditions, and the shift in the point of zero charge, in the presence of Pb2+, Cd2+ and Sr2+ ions, was investigated. It was determined that the point of zero charge changed with modification of the solid/liquid ratio and by washing the powder, which indicated that under the investigated conditions some dissolution of the sepiolite and impurities took place also influencing the position of the point of zero charge. In the presence of Pb2+, Cd2+ and Sr2"1" ions, the point of zero charge was shifted toward lower pH values denoting specific ion sorption. The greatest shift and, therefore the largest specific sorption, appeared in the case of Pb2+ ions, somewhat less with Cd2+, and the least with Sr2"1" ions. The adsorption isotherms were determined for the Pb2+, Cd2+ and Sr2+ ions, as well as the amounts of these ions that were removed from aqueous media by the ion exchange of Mg2+ ions from the sepiolite structure, depending on the equilibrium ion concentrations. In the case of ion exchange, as in the case of specific sorption, the affinity of sepiolite for the investigated ions can be presented in the following order Pb2+ gt Cd2+ gt Sr2"1". For the removal of Sr2"1" ions from aqueous media by sepiolite, a third mechanism is important probably, the ion exchange of exchangeable ions from the sepiolite structure channels. As the result of the action of all the sorption mechanisms sepiolite is removes mostly Pb2+ ions, then Cd2+ and least of all Sr2"1" ions from the aqueous media.

U radu su prikazani rezultati karakterizacije i određivanja sorpcionih svojstava sepiolita sa lokaliteta Slovići. Određena je tačka nultog naelektrisanja sepiolita pri različitim uslovima i ispitano pomeranje tačke nultog naelektrisanja u prisustvu jona Pb2+, CcF+ I Sr2+. Utvrđeno je da se tačka nultog naelektrisanja menja sa promenom odnosa čvrsto/tečno i ispiranjem praha. U prisustvu jona Pb2+, Cd2+ i Sr2+, tačka nultog naelektrisanja se pomera ka nižim pH vrednostima, što ukazuje na specifičnu sorpciju jona. Određene su adsorpcione izoterme za jone Pb2+, Cd2+ i Sr2+ i količine ovih jona koji se jonski izmenjuju sa Mg2+ jonima iz strukture sepiolita u zavisnosti od ravnotežne koncentracije jona. Najveći afinitet sepiolit ima prema jonima Pb2+, nešto manji prema jonima Cd i najmanji za Sr2+ jone, kako u slučaju specifične sorpcije tako i u slučaju jonske izmene Mg2+ jona iz strukture sepiolita.