Specific cadmium sorption in relation to the crystal chemistry of clay minerals

Journal Article · · Soil Sci. Soc. Am. J.; (United States)

DOI:https://doi.org/10.2136/sssaj1988.03615995005200010009x· OSTI ID:7165773

Ziper, C; Komarneni, S; Baker, D E

Three possible locations on clay minerals exist where Cd can be sorbed by ion exchange. These are the external planar, interlayer, and edge surfaces. In this study, montmorillonite, kaolinite, vermiculite, and biotite minerals were used to separate these sorption sites. The vermiculite and biotite were fractionated into five size fractions ranging from <2 to 1000 ..mu..m. The relative effect of one surface type on the others was enhanced by further structural manipulations by K/sup +/ or Li/sup +/ treatments on the vermiculite and montmorillonite. Equilibrium adsorption and desorption of Cd was measured using /sup 109/Cd at 0.02 ..mu..Ci/mL for isotopic dilution to a concentration range of 10/sup -9/ to 10/sup -5/ M in a 0.005 M CaCl/sub 2/ background. The mineral concentrations were defined for a constant cation exchange capacity (CEC) or constant external surface area. The results suggest that the edge and high charge density planar sites (as in biotite) contribute the greatest influence. Generally an increase in the edge to planar surface area ratio with decreasing particle size, or the increase in edge to interlayer surface area ratio by either K/sup +/ or Li/sup +/ treatments, resulted in an enhanced sorption of Cd. These results suggest that CEC alone is not an accurate measurement to predict CD sorption behavior for layer silicates. Equilibrium desorption was used to infer the specific or nonspecific Cd-clay interaction type. The structural manipulations such as K and Li fixation in vermiculite and montmorillonite, respectively, showed that edge sites retained CD specifically. The high charge density edge and planar sites of biotite also desorbed Cd the least, suggesting the role of high charge density in specific Cd retention.

• Research Organization: Pennsylvania State Univ., University Park (USA)
• OSTI ID: 7165773
• Journal Information: Soil Sci. Soc. Am. J.; (United States), Journal Name: Soil Sci. Soc. Am. J.; (United States) Vol. 52:1; ISSN SSSJD
• Country of Publication: United States
• Language: English

Related Subjects

510100* -- Environment
Terrestrial-- Basic Studies-- (-1989)
54 ENVIRONMENTAL SCIENCES
ALKALI METAL COMPOUNDS
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
BIOTITE
CADMIUM
CATIONS
CHARGED PARTICLES
CHEMICAL REACTIONS
CHEMISORPTION
CLAYS
ELEMENTS
INORGANIC ION EXCHANGERS
ION EXCHANGE
ION EXCHANGE MATERIALS
IONS
IRON COMPOUNDS
IRON SILICATES
KAOLINITE
LITHIUM COMPOUNDS
MAGNESIUM COMPOUNDS
MAGNESIUM SILICATES
MATERIALS
METALS
MICA
MINERALS
MONTMORILLONITE
OXYGEN COMPOUNDS
PARTICLE SIZE
POTASSIUM COMPOUNDS
SEPARATION PROCESSES
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SIZE
SORPTION
SURFACE PROPERTIES
TRANSITION ELEMENT COMPOUNDS
VERMICULITE