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This article in SSSAJ

  1. Vol. 20 No. 4, p. 466-471
     
    Received: Nov 7, 1955


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doi:10.2136/sssaj1956.03615995002000040006x

Thermodynamics of Zinc Adsorption on Calcite, Dolomite and Magnesite-Type Minerals1

  1. J. J. Jurinak and
  2. Norman Bauer2

Abstract

Abstract

The adsorption of zinc chloride on calcite, dolomite and Casubstituted magnesite crystals from aqueous solution is treated theoretically; and a standard adsorption process is thereby rigorously defined. The thermodynamic characteristics Δ F0θ, Δ H0θ and Δ S0θ are determined for this process by means of adsorption isotherm data at various temperatures with crystals of measured surface area.

It is found that about 10% of the adsorption sites probably available on calcite are occupied by zinc when the equilibrium Zn++aq concentration is 0.90 × 10-6 M at 25.1° C. The Ca-magnesite shows a somewhat greater affinity for zinc ion than calcite, while dolomite is intermediate. The temperature coefficients of Δ F0θ are opposite in sign for calcite and the other two minerals. The resulting endothermic heats of adsorption of Zn++aq on the dolomite and the Ca-magnesite (Δ H0θ = 8.21 ± 2.4 and 22.7 ± 5.9 kcal/mole at about 27° C, respectively), as well as the corresponding very large positive entropies of adsorption (Δ S0θ = 56 ± 8 and 106 ± 20 cal/deg × mole at about 27° C, respectively) indicate that Zn++aq is dehydrated when adsorbed by these two minerals. The known compatability of Zn++ with the MgCO3 crystal lattice is suggested as the reason for the strong interaction of this ion with the dolomite and Ca-magnesite, relative to calcite.

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