Concentration des éléments de transition divalents par les gels silicatés. Interprétation thermodynamique de quelques données expérimentales

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Abstract
Distribution equilibria of two divalent transition elements (A,B) between silicate gels p(SiO₂) — (A,B)O — nH₂ and aqueous solutions A²⁺, B²⁺ (А, В = Mg, Mn, Ni, Co, Cu,Zn) were investigated. It was found that the standard molar free enthalpy of exchange reactions is given by the simplified relation ΔG°(experimental) = K(p) ΔG°(calculated) where K(p) is a coefficient which depends only on the silica content of the gel, and ΔG°(calculated) = (G° A(OH)2 — G°B(OH)2)hydrox — (G°A²⁺ — G°B²⁺)sol. This law indicates that the selectivity of the exchange reactions decreases when the silica content of the gels (p) increases. The behaviour of any divalent element can be predicted for any p value. These ion exchange mechanisms can play an important role in the genesis of residual silicate deposits, especially nickel and copper.

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