Adsorption of lanthanum to goethite in the presence of gluconate

Conference · Sun May 01 00:00:00 EDT 2005

OSTI ID:911742

Hull, Laurence C; Pepper, Sarah; Clark, Sue

Adsorption of Lanthanum to Goethite in the Presence of Gluconic Acid L. C. HULL,1 S. E. PEPPER2 AND S. B. CLARK2 1Idaho National Engineering and Environmental Laboratory, Idaho Falls, ID ([e-mail]) 2Washington State University, Pullman, WA ([e-mail]), ([e-mail]) Lanthanide and trivalent-actinide elements in radioactive waste can pose risks to humans and ecological systems for many years. Organic complexing agents, from natural organic matter or the degradation of waste package components, can alter the mobility of these elements. We studied the effect of gluconic acid, as an analogue for cellulose degradation products, on the adsorption of lanthanum, representing lanthanide and trivalent-actinide elments, to goethite, representing natural iron minearals and degradation products of waste packages. Batch pH adsorption edge experiments were conducted with lanthanum alone, and with lanthanum and gluconate at a 1:1 mole ratio. Lanthanum concentrations studied were 0.1, 1, and 10 mM, covering a range from 10% to 1000% of the calculated available adsorption sites on goethite. In the absence of gluconate, lanthanum was primarily present in solution as free lanthanum ion. With gluconate present, free lanthanum concentration in solution decreased with increasing pH as step-wise deprotonation of the gluconate molecule increased the fraction lanthanum complexed with gluconate. Adsorption to the goethite surface was represented with the diffuse double-layer model. The number of adsorption sites and the intrinsic binding constants for the surface complexes were estimated from the pH adsorption edge data using the computer code FITEQL 4.0. Two surface reactions were used to fit the adsorption data in the absence of gluconate. A strong binding site with no proton release and a much higher concentration of weak binding sites with release of two protons per lanthanum adsorbed. The adsorption of lanthanum was not measurably affected by the presence of gluconate below pH 7. At pH values above 7, however, gluconate doubled the maximum amount of lanthanum adsorbed. This was modeled by including a ternary complex with a lanthanum-gluconate complex binding to a lanthanum bound on the surface. No spectroscopic data were obtained to verify the identify of the surface complexes. The presence of gluconate did not appear to affect the formation of solid lanthanum hydroxide at elevated pH and millimolar lanthanum concentrations. The effect of organic molecules on the mobility of lanthanides and trivalent-actinides cannot be simply described with equilibrium thermodynamic models based on currently available data.

• Research Organization: Idaho National Laboratory (INL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC07-99ID13727
• OSTI ID: 911742
• Report Number(s): INEEL/CON-05-02594
• Conference Information: Goldschmidt Conference,Moscow, ID,05/20/2005,05/25/2005
• Country of Publication: United States
• Language: English

Related Subjects

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
adsorption
CELLULOSE
CHELATING AGENTS
COMPUTER CODES
GLUCONIC ACID
GOETHITE
IRON
lanthanum
LANTHANUM HYDROXIDES
LANTHANUM IONS
ORGANIC MATTER
PH VALUE
PROTONS
radioactive waste
RADIOACTIVE WASTES
RARE EARTHS
surface complexation
THERMODYNAMIC MODEL
WASTES