Sorption of divalent metals on calcite

Journal Article · Sat Jun 01 00:00:00 EDT 1991 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(91)90127-Q· OSTI ID:5890969

Zachara, J M; Cowan, C E; Resch, C T ^[1]

---

1. Pacific Northwest Lab., Richland, WA (United States)

The sorption of seven divalent metals (Ba, Sr, Cd, Mn, Zn, Co, and Ni) was measured on calcite over a large initial metal (Me) concentration range in constant ionic strength (I = 0.1), equilibrium CaCO{sub 3}(s)-CaCO{sub 3}(aq) suspensions that varied in pH. At higher initial Me concentrations (10{sup {minus}5} to 10{sup {minus}4} mol/L) geochemical calculations indicated that the equilibrium solutions were saturated with discrete solid phases of the sorbates: CdCO{sub 3}(s), MnCO{sub 3}(s),Zn{sub 5}(OH){sub 6}(CO{sub 3}){sub 2}(s), Co(OH){sub 2}(s), and Ni(OH){sub 2}(s), implying that aqueous concentrations were governed by solubility. However, significant sorption of all the metals except for Ba and Sr was observed at aqueous concentrations below saturation with Me-solid phases. Divalent metaal ion sorption was dependent on aqueous Ca concentration, and the following selectivity sequence was observed: Cd > Zn {ge} Mn > CO > Ni {much gt} Ba = Sr. The metals varied in their sorption reversibility, which was correlated with the single-ion hydration energies of the metal sorbates. The strongly hydrated metals (Zn, Co, and Ni) were most desorbable. A sorption model that included aqueous speciation and Me{sup 2+} -Ca{sup 2+} exchange on cation-specific surface sites was developed that described most of the data well. The chemical nature of the surface complex used in this model was unspecified and could represent either a hydrated or dehydrated surface complex, or a surface precipitate. The authors' data suggested that (1) Cd and Mn dehydrate soon after their adsorption to calcite and form a phase that behaves like a surface precipitate, and (2) Zn, Co, and Ni form surface complexes that remain hydrated until the ions are incorporated into the structure by recrystallization.

• DOE Contract Number: AC06-76RL01830
• OSTI ID: 5890969
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 55:6; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ADSORPTION
ALKALINE EARTH METALS
BARIUM
CADMIUM
CALCITE
CARBONATE MINERALS
CHEMICAL REACTIONS
CHEMISTRY
COBALT
COMPLEXES
DECOMPOSITION
DEHYDRATION
DESORPTION
DISPERSIONS
ELEMENTS
GEOCHEMISTRY
HYDRATION
HYDROLYSIS
ION EXCHANGE
IONIC COMPOSITION
LYSIS
MANGANESE
MATHEMATICAL MODELS
METALS
MINERALS
MIXTURES
MOLECULAR MODELS
NICKEL
PH VALUE
RECRYSTALLIZATION
SATURATION
SOLUBILITY
SOLUTIONS
SOLVATION
SOLVOLYSIS
SORPTION
SORPTIVE PROPERTIES
STRONTIUM
SURFACE PROPERTIES
TRANSITION ELEMENTS
ZINC