Biomaterial Database

Sorption of selenite and selenate to cement minerals. 2003

Isabel Baur, and C Annette Johnson

Swiss Federal Institute for Environmental Science and Technology (EAWAG), Box 611, Ueberlandstrasse 133, CH-8600 Dübendorf, Switzerland. kellerbaur@freesurf.ch

The sorption of selenite and selenate to ettringite (3CaO x Al2O3 x 3CaSO4 x 32H2O), "monosulfate" (3CaO x Al2O3 x CaSO4 x 12H2O), and calcium silicate hydrate (C-S-H) was investigated in order to understand Se immobilization by cement in hazardous wastes. Sorption kinetics were fast with equilibrium between the minerals and Se species reached within 1 d. Selenite is suggested to sorb by surface reactions, and for ettringite, a sorption maximum of 0.03 mol kg(-1) was determined. Distribution ratios (Rd) for selenite were 0.18, 0.38, and 0.21 m3 kg(-1) for ettringite, monosulfate, and C-S-H, respectively. At high selenite additions, CaSeO3 was precipitated with a solubility product of Kso = 10(-7.27) (I = 0, 25 degrees C). Selenate sorbed only weakly to ettringite (Rd = 0.03), and no significant sorption to C-S-H was found. In contrast, sorption to monosulfate was strong (Rd = 2.06). With increasing selenate addition, XRD analyses revealed changes in the interlayer distance of monosulfate, in parallel with an increase of the ettringite fraction. Substitution of sulfate is suggested to be the relevant process. This indicates that selenate is sorbed more efficiently by monosulfate-rich cement, while the cement composition is of minor importance for selenite sorption.

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D003252	Construction Materials	Supplies used in building.	Building Materials,Building Material,Construction Material,Material, Building,Material, Construction,Materials, Building,Materials, Construction
D000327	Adsorption	The adhesion of gases, liquids, or dissolved solids onto a surface. It includes adsorptive phenomena of bacteria and viruses onto surfaces as well. ABSORPTION into the substance may follow but not necessarily.	Adsorptions
D014961	X-Ray Diffraction	The scattering of x-rays by matter, especially crystals, with accompanying variation in intensity due to interference effects. Analysis of the crystal structure of materials is performed by passing x-rays through them and registering the diffraction image of the rays (CRYSTALLOGRAPHY, X-RAY). (From McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)	Xray Diffraction,Diffraction, X-Ray,Diffraction, Xray,Diffractions, X-Ray,Diffractions, Xray,X Ray Diffraction,X-Ray Diffractions,Xray Diffractions
D018036	Selenium Compounds	Inorganic compounds that contain selenium as an integral part of the molecule.	Compounds, Selenium
D018038	Sodium Selenite	The disodium salt of selenious acid. It is used therapeutically to supply the trace element selenium and is prepared by the reaction of SELENIUM DIOXIDE with SODIUM HYDROXIDE.	Disodium Selenite,Monosodium Selenite,Selenous Acid Disodium Salt,Selenous Acid, Disodium Salt,Sodium Biselenite,Sodium Selenite Pentahydrate,Biselenite, Sodium,Pentahydrate, Sodium Selenite,Selenite Pentahydrate, Sodium,Selenite, Disodium,Selenite, Monosodium,Selenite, Sodium
D064586	Selenic Acid	A strong dibasic acid with the molecular formula H2SeO4. Included under this heading is the acid form, and inorganic salts of dihydrogen selenium tetraoxide.	Ammonium Selenate,Calcium Selenate,Disodium Selenate,Magnesium Selenate,Monosodium Selenate,Potassium Selenate,Selenate,Selenic Acid, Ammonium Salt,Selenic Acid, Calcium Salt,Selenic Acid, Diammonium Salt,Selenic Acid, Disodium Salt, 75Se-Labeled,Selenic Acid, Disodium Salt, Decahydrate,Selenic Acid, Magnesium Salt,Selenic Acid, Monosodium Salt,Selenic Acid, Potassium Salt,Sodium Selenate,Acid, Selenic,Selenate, Ammonium,Selenate, Calcium,Selenate, Disodium,Selenate, Magnesium,Selenate, Monosodium,Selenate, Potassium,Selenate, Sodium