title: Hydroxy- and fluorapatite as sorbents in Cd(II)-Zn(II) multi-component solutions in the absence/presence of EDTA.
abstract: Apatites are suitable sorbent materials for contaminated soil and water remediation because of their low solubility and ability to bind toxic metals into their structure. Whereas in soil/water systems different complexing ligands are present, it is important to examine how these ligands affect apatite metal sorption process. The removal of cadmium (Cd) and zinc (Zn) ions from aqueous solutions by hydroxyapatite (HAP) and fluorapatite (FAP) was investigated by batch experiments with and without EDTA being present in the pH range 4-11. The surface composition of the solid phases was analyzed by X-ray photoelectron spectroscopy (XPS). The surface layer of apatites (AP), according to the (Ca+Cd+Zn):P atomic ratio, remained constant (1.4 ± 0.1) through an ion exchange. The amount of Cd(2+) and Zn(2+) removed increased with increasing pH. The removed amount of Zn(2+) was higher than Cd(2+). In the Cd-Zn binary system, competitive sorption reduced the individual removed amounts but the total maximum sorption was approximately constant. In the presence of EDTA, Cd(2+) and Zn(2+) removal was reduced because of the formation of [CdEDTA](2-) and [ZnEDTA](2-) in solution. XPS revealed an enrichment of AP surface by Cd(2+) and Zn(2+) and formation of new surface solid-solution phase with the general composition Ca8.4-xMex(HPO4)1.6(PO4)4.4(OH)0.4.
authors.affiliation: Laboratory of Inorganic Materials, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia. karin.viipsi@ttu.ee
authors.forename: Karin
authors.initials: K
authors.lastname: Viipsi
authors.forename: Staffan
authors.initials: S
authors.lastname: Sjöberg
authors.forename: Kaia
authors.initials: K
authors.lastname: Tõnsuaadu
authors.forename: Andrey
authors.initials: A
authors.lastname: Shchukarev
mesh_terms: D000327:Adsorption; D001031:Apatites / Q000737:chemistry*; D002104:Cadmium / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry; D002614:Chelating Agents / Q000737:chemistry; D017886:Durapatite / Q000737:chemistry*; D004492:Edetic Acid / Q000737:chemistry; D052918:Environmental Restoration and Remediation / Q000379:methods; D010758:Phosphorus / Q000737:chemistry; D056951:Photoelectron Spectroscopy; D012989:Soil Pollutants / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry*
chemical_list: D001031:Apatites; D002614:Chelating Agents; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical; D002104:Cadmium; D010758:Phosphorus; D017886:Durapatite; D004492:Edetic Acid; D015032:Zinc; C025105:fluorapatite; D002118:Calcium