Adsorption of heavy metals on soil clays
This study examined the relative affinity of the metals Cd, Ni, and Zn for the clay minerals kaolinite and montmorillonite. The influence which different mineral adsorbents and different complexing ligands in solution have on the adsorption of metal ions was assessed using the Hard-Soft Acid-Base Principle as a theoretical framework for predicting the maximum extent of adsorption and rate of adsorption. The HSAB principle is that hard bases prefer to complex hard acids and soft bases prefer to complex soft acids. The hypothesis that initiated these investigations was that the had-soft character of mineral surfaces is due to their surface functional groups and can be measured using metal cation adsorption selectivity experiments where pH and complex ion formation are controlled. When complex ion formation in aqueous solution was minimized (i.e., in Ca(ClO/sub 4/)/sub 2/), adsorption decreased in the order of decreasing softness, Cd > Zn > Ni for both clay minerals. Montmorillonite behaved as a slightly harder Lewis base than kaolinite, sorbing the harder Ni and Zn ions to a greater extent that Cd, although both minerals behaved as soft Lewis bases. In the presence of chloride and sulfate ligands, adsorption sequencies changed reflected results from typical soil solution studies. Adsorption over time and calculated adsorption rate constants were generally consistent with equilibrium selectivity data. Adsorption rates decreased in the order Cd < Zn < Ni in Ca(ClO/sub 4/)/sub 2/ for both clay minerals. The adsorption curves reflect a two-step adsorption process involving a rapid exchange-type reaction followed by a much slower adsorption involving diffusion into the crystal or alteration of the surface through the formation of a new solid phase involving the adsorbed ions.
- Research Organization:
- Arizona Univ., Tucson (USA)
- OSTI ID:
- 6861191
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CADMIUM
ADSORPTION
KAOLINITE
SORPTIVE PROPERTIES
MONTMORILLONITE
NICKEL
ZINC
CHLORIDES
CLAYS
DIFFUSION
ION EXCHANGE
REACTION KINETICS
SULFATES
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
CHLORINE COMPOUNDS
ELEMENTS
HALIDES
HALOGEN COMPOUNDS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
KINETICS
MATERIALS
METALS
MINERALS
OXYGEN COMPOUNDS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SORPTION
SULFUR COMPOUNDS
SURFACE PROPERTIES
TRANSITION ELEMENTS
510100* - Environment
Terrestrial- Basic Studies- (-1989)